WO2008027294A2 - Systems and methods for synchronizing communication networks - Google Patents
Systems and methods for synchronizing communication networks Download PDFInfo
- Publication number
- WO2008027294A2 WO2008027294A2 PCT/US2007/018691 US2007018691W WO2008027294A2 WO 2008027294 A2 WO2008027294 A2 WO 2008027294A2 US 2007018691 W US2007018691 W US 2007018691W WO 2008027294 A2 WO2008027294 A2 WO 2008027294A2
- Authority
- WO
- WIPO (PCT)
- Prior art keywords
- node
- time
- time slot
- message
- nodes
- Prior art date
Links
Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W40/00—Communication routing or communication path finding
- H04W40/02—Communication route or path selection, e.g. power-based or shortest path routing
- H04W40/12—Communication route or path selection, e.g. power-based or shortest path routing based on transmission quality or channel quality
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
- G01D21/00—Measuring or testing not otherwise provided for
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
- G01D9/00—Recording measured values
- G01D9/005—Solid-state data loggers
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04J—MULTIPLEX COMMUNICATION
- H04J3/00—Time-division multiplex systems
- H04J3/02—Details
- H04J3/06—Synchronising arrangements
- H04J3/0635—Clock or time synchronisation in a network
- H04J3/0638—Clock or time synchronisation among nodes; Internode synchronisation
- H04J3/0652—Synchronisation among time division multiple access [TDMA] nodes, e.g. time triggered protocol [TTP]
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L45/00—Routing or path finding of packets in data switching networks
- H04L45/22—Alternate routing
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W56/00—Synchronisation arrangements
- H04W56/003—Arrangements to increase tolerance to errors in transmission or reception timing
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W56/00—Synchronisation arrangements
- H04W56/004—Synchronisation arrangements compensating for timing error of reception due to propagation delay
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04J—MULTIPLEX COMMUNICATION
- H04J3/00—Time-division multiplex systems
- H04J3/02—Details
- H04J3/06—Synchronising arrangements
- H04J3/0635—Clock or time synchronisation in a network
- H04J3/0679—Clock or time synchronisation in a network by determining clock distribution path in a network
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W40/00—Communication routing or communication path finding
- H04W40/02—Communication route or path selection, e.g. power-based or shortest path routing
- H04W40/04—Communication route or path selection, e.g. power-based or shortest path routing based on wireless node resources
- H04W40/10—Communication route or path selection, e.g. power-based or shortest path routing based on wireless node resources based on available power or energy
Definitions
- the present invention generally relates to systems and methods for synchronizing devices or nodes in communication networks, particularly slotted ad- hoc communication networks such as wireless sensor networks.
- Wireless sensor networks are widely used in a number of military and civilian applications including battlefield surveillance, environment/habitat monitoring, healthcare applications, home automation and traffic control.
- These WSNs are typically ad-hoc networks that include spatially distributed devices or nodes having transceivers and sensors to cooperatively monitor physical or environmental conditions and to communicate relevant information.
- the nodes are typically powered by an on-board battery supply so that they may be deployed in isolated locations and operate autonomously. To conserve battery energy and thereby permit long-term use, the nodes are typically duty-cycled whereby each node is turned on or off during selected time slots.
- each node may be willing to forward information from one node to a neighboring node thereby establishing one or more communication channels through the network.
- the systems and methods described herein provide for an accurate, energy efficient and fault tolerant synchronization scheme that synchronizes boundaries of time slots in neighboring nodes in slotted wireless communication networks, for example, without the nodes first synchronizing clocks.
- the nodes in slotted communication networks are configured to transmit or receive data during one or more selected time slots. Typically, these time slots are short intervals in time (e.g., 20ms), during which a node transmits or receives packets of data. The beginning and the end of these time slots are referred to as the boundary or boundary region of the time slots, hi certain embodiments, during certain ones of these time slots, one or more nodes transmit a synchronization message that is received by one or more neighboring nodes. The neighboring nodes adjust the boundary of their time slots based on the time of receipt of the synchronization message, thereby synchronizing the neighboring nodes to the transmitting one or more nodes.
- the invention relates to a method for synchronizing a communication network.
- the method includes providing a slotted communication network, such as a mobile ad-hoc network, a wireless sensor network or a wireless mesh network, which includes at least a first node and a second node.
- the first node is configured to operate at least during a first time slot
- the second node is configured to operate at least during a second time slot, which corresponds to the first time slot.
- the first node and/or the second nodes are configured to operate during a plurality of time slots according to pre-determined schedule and/or a dynamically determined schedule.
- the method further includes transmitting, from the first node, a message during the first time slot and receiving the message at the second node at a first receipt time during the second time slot.
- the message may include network topology information and/or a heartbeat signal.
- the method includes the step of aligning a boundary portion of the second time slot with the first receipt time, thereby synchronizing the second time slot with the first time slot.
- the step of aligning the boundary portion of the second time slot may include shifting a start time or an end time of the second time slot based on the first receipt time.
- the boundary portion includes a guard time
- the second time slot includes a data time period in between two guard time periods during which data packets may be transmitted and/or received.
- aligning the boundary portion of the second time slot includes aligning an edge of the guard time period of the second time slot with the first receipt time. The message may be transmitted from the first node, during or at the beginning of a boundary portion of the first time slot.
- the method may include repeating the steps of transmitting the message, receiving the message and, aligning a time slot after a re- sync time period has elapsed.
- At least one of the first time slot and second time slot may include a guard time period having a length based at least in part on the re-sync time period.
- the slotted communication network further includes a third node configured to operate during a third time slot.
- the method may include the steps of transmitting, from the second node, a second message during the second time slot, receiving the second message at the third node, at a second receipt time during the third time slot, and aligning a boundary portion of the third time slot with the second receipt time, thereby synchronizing the third time slot with the second time slot.
- the invention relates to a node in a slotted- communi cation network.
- the node includes a receiver and a processor.
- the receiver is configured to receive a message, such as a heartbeat signal, at a receipt time during a first time slot.
- the message would have been transmitted by a transmitting node.
- the processor may be configured for aligning a boundary portion of the first time slot with the receipt time. In certain embodiments, the processor aligns the boundary portion of the first time slot with the receipt time without synchronizing the clock of the node with the clock of the transmitting node.
- the node may further include a transmitter for transmitting a message during a second time slot based on which a second node synchronizes at least one time slot to at least one time slot of the node.
- the processor aligns the boundary portion of the first time slot by shifting a start time or an end time of the first time slot based on the receipt time.
- the boundary portion includes a guard time
- the first time slot includes a data time period in between two guard time periods during which data packets may be transmitted and/or received.
- the processor aligns the boundary portion of the first time slot by aligning an edge of the guard time period of the first time slot with the receipt time. The message may be transmitted from the first node, during or at the beginning of a boundary portion of the first time slot.
- the receiver may receive a second message and the processor aligns a second time slot to the receipt time of the second message.
- the first time slot may include a guard time period having a length based at least in part on the re-sync time period.
- the invention relates to a method for synchronizing a communication network.
- the method includes providing a network topology for a communication network including a plurality of nodes, and selecting a root node from the plurality of nodes in the network.
- the method further include transmitting from a first node a first message, and aligning a slot boundary of a second node, neighboring the first node along the network topology, based on the receipt time of the first message.
- the method includes transmitting from the second node a second message, and aligning a slot boundary of a third node, neighboring the second node along the network topology, based on the receipt time of the second message.
- the invention in still another aspect, relates to a method for synchronizing communication schedules of nodes in a communication network having a plurality of nodes.
- the method includes transmitting a plurality of messages from the plurality of nodes, receiving at a first node, the plurality of messages, calculating a statistic based, at least in part, on a time of reception of each of the plurality of messages, and synchronizing the first node based on the statistic.
- the statistic is calculated based on a set of slot deltas between neighboring nodes.
- the slot deltas may represent differences between start times of slots of the first node and start times of slots of the plurality of nodes.
- Figure 1 depicts an exemplary slotted ad-hoc communication network.
- Figure 2 depicts a pair of nodes communicating in the communication network of Figure 1, according to an illustrative embodiment of the invention.
- Figure 3 depicts the misalignment of slots in a pair of nodes in a network.
- Figure 4 depicts an exemplary pair of nodes of the communication network of Figure 1.
- Figure 5 A depicts the synchronization of the pair of nodes, according to an illustrative embodiment of the invention.
- Figure 5B is a flow diagram depicting a process for synchronizing of the pair of nodes of Figure 2, according to an illustrative embodiment of the invention.
- Figure 6 A depicts the synchronization of the network of Figure 1, according to an illustrative embodiment of the invention.
- Figure 6B is a flow diagram depicting a process for synchronizing the network of Figure 2, according to an illustrative embodiment of the invention.
- Figure 7 depicts an exemplary slotted ad-hoc communication network.
- Figures 8A and 8B depict node-based processes for synchronizing a network, according to an illustrative embodiment of the invention.
- Figure 8C depicts a filter-based process for synchronizing a network, according to an illustrative embodiment of the invention.
- Figure 9 depicts the synchronization of slots provisioned with exemplary guard times.
- Figure 10 is a flow diagram depicting the synchronization and re- synchronization of nodes in a network, according to an illustrative embodiment of the invention.
- the invention relates to systems and methods for synchronizing a communication network, particularly a slotted communication network, having a plurality of nodes.
- the nodes are configured to transmit or receive data during one or more selected time slots.
- each node may transmit a synchronization message that is received by a neighboring node.
- the neighboring node adjusts its time slot boundary based on the time of receipt of the synchronization message, thereby synchronizing each node with a neighboring node.
- Figure 1 depicts an exemplary communication network 100 having devices or nodes 102a-102e (generally, "nodes 102") that are illustrated as being spatially separated from each other. Each node may be capable of communicating with one or more other nodes in the network 100 along any direction.
- a node 102 communicates with other neighboring nodes 102 in the network, i.e., nodes located within its communication range.
- node 102c may be able to communicate with either one of neighboring nodes 102b or 102d.
- Nodes 102 may also be able to communicate with more distant nodes (i.e., those nodes that are out of communication range) through a hopping process whereby one node 102 communicates with a neighboring node 102, which in turn communicates with another node 102 that is more distant.
- a hopping process common to ad-hoc communication networks, facilitates communication across vast distances whereby nodes transmit or receive data packets from distant nodes by hopping through one or more intermediate nodes. For example, node 102b looking to transmit a data packet to node 102e, first transmits the message to node 102c.
- Node 102c then transmits the received data to node 102d, and node 102d finally transmits the data to the destination node 102e.
- the nodes 102 may be able to move from one location to another and thereby communicate with other nodes 102 in the network that were previously distant nodes. For example, node 102c may move closer to node 102a and be able to directly communicate with node 102a.
- the nodes 102a-102e may include sensors in a wireless sensor network whereby the sensors are capable of measuring at least one of heat, pressure, sound, light, electro-magnetic field and vibration.
- the nodes 102a-102e may also include computer components for processing the sensor data and for communicating the sensor data to other nodes in the network 100.
- the computer components may be used for managing the operation of a node, and transmission and/or reception of data packets to and from a node.
- nodes 102 in a stationary or mobile slotted communication network 100 are configured to operate during one or more selected time slots during which a node transmits or receives packets of data. Different nodes 102 may be scheduled to operate during different such time slots to allow for a communication across a network.
- Figure 2 depicts an exemplary time slot scheduling scheme 200 that allows communication between nodes through a network 100.
- Figure 2 shows time slot schedules 202a, 202b and 202c for nodes 102a, 102b and 102c, respectively.
- the time slot schedules 202a, 202b and 202c identify when the nodes 102a, 102b and 102c are powered-on and when they transmit and/or receive data.
- Schedule 202a includes adjacent time slots 204a, 206a, 208a and 210a.
- schedules 202b and 202c include a corresponding set of time slots. In such protocols, the time slots may be allocated in a periodic fashion such that they repeat after certain intervals of time.
- the time slots may be of fixed or variable length depending on the nature of the application. In certain embodiments, each of the time slots are about 20ms long. Time slots can be longer or shorter than 20ms, without departing from the scope of the invention.
- One class of protocols often used for scheduling in an ad-hoc networking environment is a Time Division Multiple Access (TDMA) Multiplexing MAC layer protocol.
- TDMA Time Division Multiple Access
- a communication device using a periodic TDMA communications protocol remains in one of two states, transmit or receive. In order to remain in either state, the communication device supplies power to a transceiver.
- the node 102a is "on," i.e., its transceiver is operational, during time slot 204a.
- the data packet that is transmitted from node 102a during time slot 204a is received at node 102b during the time slot 204b.
- the node 102b is configured to transmit the same or another data packet during the next time slot 206b.
- the data packet transmitted from node 102b is received at node 102c during the time slot 206c.
- the boundaries of slots in neighboring nodes are aligned with each other, i.e., for example, the beginning of slot 204a is scheduled for the same time as the beginning of slot 204b.
- time slots of communicating nodes are misaligned.
- Such a misalignment of time slots can occur due to various factors including factors that are internal to the node (e.g., clock drifts), and factors that are external to the node (e.g., distance between nodes and propagation delays).
- Figure 3 depicts the misalignment of slots in a pair of nodes 102a and 102b in the network 100 of Figure 1.
- Figure 3 shows a scheduling scheme 300 including a pair of nodes 302a and 302b that are duty-cycled such that their transceivers are either "on” or "off during one or more time slots.
- Each time slot is of duration 312.
- the time slot schedule controlling the operation of node 102a requires the transceiver of node 102a to be powered "on" at least during time slots 306a and 310a and powered "off at least during time slots 304a and 308a.
- the node is capable of transmitting and/or receiving data during a time slot that its transceiver is in the "on” state.
- the time slot schedule controlling the operation of node 102b requires the transceiver of the node to be powered “on” at least during time slots 306b and 310b and powered "off at least during time slots 304b and 308b.
- the nodes 102a and 102b are misaligned such that the time slots are offset by a time period 318.
- the offset time period 318 causes a portion of the "off slot 304b to overlap with a portion of the "on" slot 306a.
- a portion of a message 316 transmitted during time slot 306a is not received by the node 102b because it was "off when the message portion 316 arrived.
- the initial portion of a communication in a time slot is critical for a recipient to receive in order to receive the remainder of the communication. For example, the initial portions often include signaling data to inform the receiving node that additional data is forthcoming directed to that node.
- the initial portions of a commuication include waveforms used for phase alignment.
- node 102b may not receive it.
- the nodes 102a and 102b have to be synchronized such that a message transmitted in a time slot by node 102a arrives in its entirety while node 102b is "on". This means that the beginning and end portions of the message that are transmitted at the beginning and end, respectively, of a time slot in node 102b have to be received during an "on" time slot in node 102b.
- one or more nodes may include circuitry, and/or software as shown in Figure 4, to synchronize (e.g., modifying time slot schedules in response to received data) it with another one of the nodes in the network.
- FIG 4 is a block diagram of nodes 102a and 102b.
- Nodes 102a and 102b include transceivers 404a and 404b ("transceiver 404"), respectively, that are connected to antennas 406a and 406b ("antenna 406").
- the nodes 102a and 102b communicate with each other wirelessly; however, it can be understood that the nodes 102a and 102b can communicate in a wired network, without departing from the scope of the invention.
- the nodes 102a and 102b further include clocks 402a and 402b ("clock 402") for maintaining time.
- the clocks 402a and 402b are connected to processors 410a and 410b ("processor 410").
- the processors 410a and 410b are connected to memory components 412a and 412b ("memory 412").
- Nodes 102a and 102b may be part of a wireless sensor network. If so, the nodes 102a and 102b include one or more sensor components 414a and 414b ("sensors 414").
- the processor 410 establishes a time slot schedule for the node.
- the schedule indicates which time slots in the node 102a should be "on,” and in which of these "on" time slots, the node can transmit data.
- the processor 410 measures time with the aid of the clock 402.
- a node 102a communicates with another node 102b when the transceivers of both the nodes 102a and 102b are in a "on" or “powered” state.
- the time slots during which each of the nodes 102a and 102b are "on,” are synchronized, whereby each time slot begins and ends at substantially the same time.
- the time slots between neighboring nodes become misaligned and, consequently, unsynchronized.
- the nodes need to resynchronize.
- FIGs 5 A and 5B depict the synchronization of node 102b to node 102a of Figures 1-4, according to an illustrative embodiment of the invention.
- node 102a includes a time slot schedule 501a having assigned time slots 502a, 504a, 506a and 508a.
- node 102b includes a time slot schedule 501b having a slotted configuration with time slots 502b, 504b, 506b and 508b.
- the time slot schedules are calculated by the processor 410 ( Figure 4) and the state of the node 102a and 102b are stored in memory 412 ( Figure 4).
- the node 102a transmits a message 512 beginning at the slot boundary 514a of a time slot 502a (step 532, Figure 5B).
- the processor 410a generates the message and sends it to the transceiver 404a, which in turn, transmits the message 512 during the appropriate time interval.
- the message 512 may include, among other things, a message identified as a synchronization message.
- the message 512 may exclusively consist of such a synchronization message.
- the message 512 may also be heartbeat signal.
- a receiving node may use any received message as a basis for resynchronization.
- the node 102b receives the message 512 after a certain delay (typically due to propagation of the signal through the wireless channel) at a receipt time 510 (step 534, Figure 5B). As noted above due to factors such as clock drifts and propagation delay, the receipt time may not coincide with the slot boundary 514b of time slot 502b in node 102b.
- the transmitted message occupies substantially the entire length of the time slot 502.
- the receipt time 510 does not coincide with the slot boundary 514b of time slot 502b, certain portions of the message may be received in time slot 504b.
- the node 102b may be duty-cycled such that the time slot 504b is assigned as an "off state whereby the node 102b is non operational during the time slot 504b. In such cases, any portion or the entirety of the message received during time slot 504b may not be reliably received.
- the node 102b upon receiving the message 512 at the receipt time 510, the node 102b adjusts its time slot schedule 501b to move the slot boundary 514b to substantially coincide with the receipt time 510, resulting in a new time slot schedule 501c (step 536, Figure 5B).
- the message 512 includes a data packet configured to be transmitted in a slotted communication network.
- the message 512 may include particular information relating to a node's location in the network, a node's relationship with one or more other nodes, one or more timestamps and any other flags or information relevant towards synchronization.
- the message 512 includes data that may not be related to synchronization. In such embodiments, the message 512 may still be used for synchronization because the receipt time of the message 512 in a node may be sufficient to align slot boundaries.
- the synchronization message 512 includes a heartbeat signal.
- synchronization messages 512 may be embedded in other communication messages.
- the above described method 530 used to synchronize communication pair 104 of nodes 102a and 102b is applied repeatedly across each of the nodes 102a-102e in the network 100 to synchronize the entire network.
- Figures 6A and 6B depict the synchronization of the network 100 of Figure 1 , according to an illustrative embodiment of the invention.
- FIGs 6 A and 6B depict the synchronization of the network 100 of Figure 1, according to an illustrative embodiment of the invention.
- nodes 102a and 102b are configured with time slot schedules having corresponding time slots 602a, 604a, 606a, and 608a and time slots 602b, 604b, 606b, and 608b, respectively.
- Time slot 602a corresponds to time slot 602b
- time slot 604a corresponds to time slot 604b, and so forth.
- Nodes 102c-102e are also configured with timing protocols having time slots that correspond to the time slots of nodes 102a and 102b, for example, time slots 604c, 606c and 608c; 606d and 608d; and time slots 608e and 61Oe, respectively.
- time slots 604c, 606c and 608c; 606d and 608d; and time slots 608e and 61Oe respectively.
- the time slots in each of the nodes 102a-102e may become misaligned with respect to each other.
- a first time slot for example, time slot 602a of node 102a, may have become misaligned such that it begins after a second corresponding time slot, for example, 602b.
- a first time slot for example, time slot 604b
- time slot 604b may begin before the start time of a corresponding second time slot 604c.
- the network 100 is synchronized such that each node 102a-102e is synchronized to its neighbor from which the node receives messages.
- the synchronization process 630 begins with selecting a starting node (step 631) or root node from which to begin transmitting the synchronization message.
- node 102a is selected as the starting root node since node 102a is not shown as having a neighbor from which it receives data (step 631).
- the node 102a transmits a synchronization message 612a to node 102b during time slot 602 (step 632).
- the node 102b receives message 612a at a time within the time slot 602b.
- Node 102b realigns the boundary of its slot 602b to the receipt time of the message from node 102a (step 634).
- Node 102b transmits a synchronization message 612b to node 102c during time slot 604b, and node 102c re-aligns the boundary of its slot 604c to the receipt time of the message from node 102b.
- the processor 410 in each node determines if it is the last node in the network 100 to be synchronized (step 636). If not, then the processor 410 instructs the node to transmit a synchronization message during the next time slot.
- synchronization of the network 100 is complete when each of the nodes 102a-102e are synchronized to their neighbor (step 638).
- node 102b is synchronized with node 102a
- node 102c is synchronized with node 102b
- node 102d is synchronized with node 102c
- node 102e is synchronized with node 102d.
- network 100 includes nodes 102a-102e that are spatially arranged such that they are each within the range of one or two other nodes. Therefore, depending on the direction of communication, each node typically communicates with one other node in the network 100.
- the nodes in network 100 may communicate and/or be synchronized in any direction as desired without departing from the scope of the invention.
- the nodes may be spatially arranged such that each node is within the range of more than two nodes and therefore capable of communicating with more than one node in the network.
- Figures 7-8C depict such networks and processes for synchronizing them.
- Figure 7 depicts an exemplary slotted ad-hoc communication network 700 having a plurality of nodes 702.
- each node 702 in network 700 is connected to each other either through arrows or lines.
- the arrows indicate possible direction of synchronization from one node 702 to another node 702.
- the arrows are merely for illustrative purposes and do not limit the scope of the invention.
- the nodes in network 700 may communicate and/or be synchronized in any direction and along any path as desired without departing from the scope of the invention.
- the straight lines connecting certain nodes indicate that those nodes 702 are within communication range of each other; however, they may not be configured to communicate with each other.
- synchronization messages are sent along the arrows from one node 702 to another until each node is synchronized to its neighbor. These synchronization messages typically originate from a starting node or root node 704 and propagate along a selected path through the network to reach each of the nodes. In certain embodiments, the synchronization messages originate from one or more nodes in network 700.
- these synchronization messages are transmitted along a communication path that is deemed to be optimal.
- the optimal path is the shortest path to the root or starting node.
- the optimal path is selected as desired based on the application.
- one path might allow for faster synchronization of the network than another path.
- the selection of a root node, calculation of optimal paths or network topology, and the contents of synchronizing messages may play a role in the performance of the synchronization of the network 700.
- Figures 8A-8C depict processes for synchronizing networks such as network 700.
- Figures 8A and 8B depicts processes for synchronizing a network, according to an illustrative embodiment of the invention.
- the process 800 of Figure 8 A begins with determining a suitable synchronization network topology (step 802, Figure 8A).
- a network topology typically describes the interconnectivity of the various nodes in the network.
- the plurality of nodes and their interconnectivity in a network can be modeled as a graph in mathematics having several statistical properties. Using certain statistical properties of these mathematical graphs, one or more interconnections can be identified, thereby providing a network topology that describes the interconnection of nodes in the network.
- the synchronization network topology includes a Minimum Hop Level Spanning Tree or its approximation.
- the synchronization network topology includes a Breadth-First Search (BFS) Spanning Tree.
- BFS Breadth-First Search
- a synchronization network topology is determined by each node from the information gathered from other nodes in the network.
- Each of the nodes sends out periodic heartbeats to neighbors by means of a broadcast.
- Each heartbeat broadcast contains information about the node, its neighbors and the node's relationship with the neighbors.
- Each of the nodes adjusts its location in the synchronization network topology based on the received heartbeat broadcasts.
- a node 704 is elected as a root node or starting node (step 804, Figure 8A).
- the step of electing a root node is performed simultaneously with the determination of a suitable network topology.
- the root node transmits and/or broadcasts a synchronization message (step 806) that is used to synchronize the neighboring nodes.
- a synchronization message (step 806) that is used to synchronize the neighboring nodes.
- one or more synchronization messages are propagated from the root node along the synchronization network topology to each of the other nodes in the network.
- the calculation of a synchronization network topology may be avoided by driving the synchronization process from the root node as depicted in Figure 8B.
- the process 820 depicted in Figure 8B begins with electing a node in the network as a starting node or root node (step 822).
- the root node broadcasts a message through a periodic heartbeat that contains a sequence number (step 824).
- the root node increments the sequence number before sending out the next heartbeat.
- Each node receiving the message, either directly or indirectly, from the root node keeps track of the largest sequence number received so far.
- Each node adjusts its slot boundary to the receipt time of the first message having a particular sequence number (step 828), thereby synchronizing the network.
- Each node may then broadcast another message that includes the largest sequence number received so far in its periodic heartbeat message.
- a node is synchronized with a neighboring node by aligning its slot boundary based on the receipt time of a synchronization message from the neighboring node.
- the slot boundary instead of associating the slot boundary of a node to a particular neighboring node or the closest neighboring node, the slot boundary can be associated with a plurality of neighboring nodes.
- FIG. 8C depicts a process 830 for synchronizing a network, according to an illustrative embodiment of the invention.
- the process 830 begins when the nodes in the network broadcast a message and/or a heartbeat signal (step 832). Each node may, therefore, receive a plurality of messages or heartbeat signals from a plurality of neighboring nodes (step 834).
- the node measures the time difference between its slot boundary and the receipt times of each of the plurality of messages or heartbeat signals (step 836). In certain embodiments, the node measures the time difference between its slot boundary and the slot boundaries of each its neighboring nodes, referred to as slot deltas.
- the node calculates one or more statistics from these slot deltas including at least one of mean, median, mode, maximum, and minimum (step 838). To synchronize the network, the node adjusts its slot boundary based, at least in part, on the calculated statistics (step 840). As an example, the node adjusts its slot boundary by the mean of the slot-deltas.
- the nodes in a network are re-synchronized when the misalignment between communicating nodes are greater than certain thresholds. If such thresholds are not crossed within a pre-determined waiting period, the nodes in the network may be re-synchronized after the expiration of the waiting time period. In certain embodiments, nodes in a network are re-synchronized after periodic intervals of time. In still other embodiments, the nodes in a network are re- synchronized as desired depending on the application. Depending on the direction of communication, the transmitting node may periodically send synchronization messages to synchronize one or more nodes in the network.
- the slots may be provisioned with guard times. These guard times arc portions, typically at the beginning and at the end of each slot, during which data is not transmitted. Guard times are typically calculated based on the parameters described with reference to Figure 3.
- guard times are useful for communication in a direction that is opposite to that of synchronization.
- a node is synchronized with a neighbor when the slot boundary of the node is shifted in time to match the receipt time of a message transmitted from the neighbor.
- the node may need to transmit data back to the neighboring node. This might be made difficult due to the shifting of the slot boundary of the node.
- Figure 9 depicts the provisioning of guard times to ease such a reverse transmission of data in a network.
- Figure 9 depicts the synchronization 900 of slots provisioned with guard times.
- Node 902a has a time slot schedule in which a slot 904a is provisioned with a beginning guard time 908a and an end guard time 910a. Similarly, slot 906a is provisioned with a beginning guard time 912a and an end guard time 914a. Also, node 902b has a timing protocol in which slots 904b and 906b are provisioned with guard times 908b, 910b, 912b and 914b. During operation, node 902a sends a message 916 during slot 904a and after the end of the guard time 908a. On receiving the message 916, the node 902b, aligns its slot boundary such that the end of the guard time 908b is shifted to the receipt time of the message 916 at the node 902b.
- the node 902b transmits a message 918 during slot 906b back to node 902a. Since the slots in node 902b are shifted from the previous synchronization, a portion of the message sent near the end of the slot 906b is received by node 902a during guard time 914a. In certain embodiments, node 902a is capable of receiving messages during the guard times and therefore the message can be reliably communicated. The guard times provide a buffer which is capable of tolerating misalignments in the slots in the period between re-synchronizations.
- the processes 900, 920 and 930 described with reference to Figures 8A-8C may be used to re-synchronize a network either periodically or at selected times.
- FIG 10 is a flow diagram depicting a process 1000 for synchronizing and re-synchronizing nodes in a network, according to an illustrative embodiment of the invention.
- the process 1000 begins with initializing a network to an asynchronous listening mode (step 1002) whereby each of the nodes in the network are turned "on" and kept at low power so that they may be able to listen to synchronization messages or heartbeat signals.
- the processes 800 and 820 described with reference to Figures 8A and 8B are applied to synchronize the network (step 1004).
- the nodes are transitioned into a duty-cycling mode whereby the nodes are either "on” or “off 1 during selected time slots (step 1006).
- the nodes are re-synchronized using the process 830 described with reference to Figure 8C (step 1008).
- the processes described herein may be carried out by software, firmware, or microcode or computing device of any type.
- software implementing the processes may comprise computer executable instructions in any form (e.g., source code, object code, interpreted code, etc.) stored in any computer-readable medium (e.g., ROM, RAM, magnetic media, punched tape or card, compact disc (CD) in any form, DVD, etc.).
- computer-readable medium e.g., ROM, RAM, magnetic media, punched tape or card, compact disc (CD) in any form, DVD, etc.
- such software may also be in the form of a computer data signal embodied in a carrier wave, such as that found within the well-known Web pages transferred among devices connected to the Internet. Accordingly, the present invention is not limited to any particular platform, unless specifically stated otherwise in the present disclosure.
- the processor 410 may include a single microprocessor or a plurality of microprocessors for configuring the node as a multi-processor system.
- the processor may be a shared purpose processor, a DSP, an ASIC or other special purpose processor.
- the memory 412 may include a main memory and a read only memory.
- the memory 412 may also include a mass storage device having, for example, various disk drives, tape drives, etc.
- the memory 412 may further include dynamic random access memory (DRAM) and high-speed cache memory.
- DRAM dynamic random access memory
- the main memory 412 stores at least portions of instructions and data for execution by the processor 410 to carry out the functions described herein.
Landscapes
- Engineering & Computer Science (AREA)
- Computer Networks & Wireless Communication (AREA)
- Signal Processing (AREA)
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Mobile Radio Communication Systems (AREA)
Abstract
In many aspects, the invention relates to systems and methods for synchronizing a communication network, particularly a slotted communication network, having a plurality of nodes. In slotted communication networks, the nodes are configured to transmit or receive data during selected time slots. During a selected time slot, each node transmits a synchronization message that is received by a neighboring node. The neighboring node adjusts its time slot boundary to coincide with the time of receipt of the synchronization message, thereby synchronizing each node with a neighboring node. Such systems and methods are energy efficient, accurate, fast, fault tolerant and easy to implement.
Description
Systems and Methods for Synchronizing Communication
Networks
Cross Reference to Related Applications
This application claims priority from U.S. Provisional Application No. 60/840,417, filed August 25, 2006, the disclosures of which are incorporated herein by reference in their entirety.
Government Contract
The U.S. Government has a paid-up license in this invention and the right in limited circumstances to require the patent owner to license others on reasonable terms as provided for by the terms of Contract No. DAAD 19-01-2-0011 awarded by U.S. Army Research Laboratory (ARL).
Field of Invention
The present invention generally relates to systems and methods for synchronizing devices or nodes in communication networks, particularly slotted ad- hoc communication networks such as wireless sensor networks.
Background
Wireless sensor networks (WSN) are widely used in a number of military and civilian applications including battlefield surveillance, environment/habitat monitoring, healthcare applications, home automation and traffic control. These WSNs are typically ad-hoc networks that include spatially distributed devices or nodes having transceivers and sensors to cooperatively monitor physical or environmental conditions and to communicate relevant information. The nodes are typically powered by an on-board battery supply so that they may be deployed in isolated locations and operate autonomously. To conserve battery energy and thereby permit long-term use, the nodes are typically duty-cycled whereby each node is turned on or off during selected time slots.
In ad-hoc communication networks including WSNs, each node may be willing to forward information from one node to a neighboring node thereby establishing one or more communication channels through the network. However, due to signal propagation delay between nodes and drifting clocks within each node, the time slots in neighboring nodes and across the network are not synchronized. This poses a communication problem because, when one node transmits information, another node that would otherwise be required to be turned on to receive the information might be off and unable to receive information or only receive portions of information.
Current techniques to solve this problem focus on synchronizing time clocks in each of the nodes in the network to a single global time. Most of these techniques involve an elaborate process of exchanging a series of messages between nodes that contain time stamped information generated in higher layers of the network protocol stack. A dominant source of error in such techniques is the variability between nodes in the time spent by the time-stamped messages in these higher layers. Furthermore, these techniques are energy inefficient in that they require numerous exchanges of timing information between nodes to synchronize their respective clocks, as well as the additional step of aligning the boundaries of the time slots based on the now synchronized clocks.
Accordingly there is a need for an alternative technique to synchronize nodes in communication networks such as WSNs.
Summary of the Invention
The systems and methods described herein provide for an accurate, energy efficient and fault tolerant synchronization scheme that synchronizes boundaries of time slots in neighboring nodes in slotted wireless communication networks, for example, without the nodes first synchronizing clocks. The nodes in slotted communication networks are configured to transmit or receive data during one or more selected time slots. Typically, these time slots are short intervals in time (e.g.,
20ms), during which a node transmits or receives packets of data. The beginning and the end of these time slots are referred to as the boundary or boundary region of the time slots, hi certain embodiments, during certain ones of these time slots, one or more nodes transmit a synchronization message that is received by one or more neighboring nodes. The neighboring nodes adjust the boundary of their time slots based on the time of receipt of the synchronization message, thereby synchronizing the neighboring nodes to the transmitting one or more nodes.
According to one aspect, the invention relates to a method for synchronizing a communication network. The method includes providing a slotted communication network, such as a mobile ad-hoc network, a wireless sensor network or a wireless mesh network, which includes at least a first node and a second node. The first node is configured to operate at least during a first time slot, and the second node is configured to operate at least during a second time slot, which corresponds to the first time slot. In certain embodiments, the first node and/or the second nodes are configured to operate during a plurality of time slots according to pre-determined schedule and/or a dynamically determined schedule.
The method further includes transmitting, from the first node, a message during the first time slot and receiving the message at the second node at a first receipt time during the second time slot. The message may include network topology information and/or a heartbeat signal. The method includes the step of aligning a boundary portion of the second time slot with the first receipt time, thereby synchronizing the second time slot with the first time slot.
The step of aligning the boundary portion of the second time slot may include shifting a start time or an end time of the second time slot based on the first receipt time. In certain embodiments, the boundary portion includes a guard time, and the second time slot includes a data time period in between two guard time periods during which data packets may be transmitted and/or received. In such embodiments, aligning the boundary portion of the second time slot includes aligning an edge of the guard time period of the second time slot with the first
receipt time. The message may be transmitted from the first node, during or at the beginning of a boundary portion of the first time slot.
Additionally and optionally, the method may include repeating the steps of transmitting the message, receiving the message and, aligning a time slot after a re- sync time period has elapsed. At least one of the first time slot and second time slot may include a guard time period having a length based at least in part on the re-sync time period.
In certain embodiments, the slotted communication network further includes a third node configured to operate during a third time slot. In such embodiments, the method may include the steps of transmitting, from the second node, a second message during the second time slot, receiving the second message at the third node, at a second receipt time during the third time slot, and aligning a boundary portion of the third time slot with the second receipt time, thereby synchronizing the third time slot with the second time slot.
According to another aspect, the invention relates to a node in a slotted- communi cation network. The node includes a receiver and a processor. The receiver is configured to receive a message, such as a heartbeat signal, at a receipt time during a first time slot. The message would have been transmitted by a transmitting node. The processor may be configured for aligning a boundary portion of the first time slot with the receipt time. In certain embodiments, the processor aligns the boundary portion of the first time slot with the receipt time without synchronizing the clock of the node with the clock of the transmitting node. The node may further include a transmitter for transmitting a message during a second time slot based on which a second node synchronizes at least one time slot to at least one time slot of the node.
In certain embodiments, the processor aligns the boundary portion of the first time slot by shifting a start time or an end time of the first time slot based on the receipt time. In certain embodiments, the boundary portion includes a guard time,
and the first time slot includes a data time period in between two guard time periods during which data packets may be transmitted and/or received. In such embodiments, the processor aligns the boundary portion of the first time slot by aligning an edge of the guard time period of the first time slot with the receipt time. The message may be transmitted from the first node, during or at the beginning of a boundary portion of the first time slot.
Additionally and optionally, after a re-sync time period has elapsed, the receiver may receive a second message and the processor aligns a second time slot to the receipt time of the second message. The first time slot may include a guard time period having a length based at least in part on the re-sync time period.
According to another aspect, the invention relates to a method for synchronizing a communication network. The method includes providing a network topology for a communication network including a plurality of nodes, and selecting a root node from the plurality of nodes in the network. The method further include transmitting from a first node a first message, and aligning a slot boundary of a second node, neighboring the first node along the network topology, based on the receipt time of the first message. In certain embodiments, the method includes transmitting from the second node a second message, and aligning a slot boundary of a third node, neighboring the second node along the network topology, based on the receipt time of the second message.
In still another aspect, the invention relates to a method for synchronizing communication schedules of nodes in a communication network having a plurality of nodes. The method includes transmitting a plurality of messages from the plurality of nodes, receiving at a first node, the plurality of messages, calculating a statistic based, at least in part, on a time of reception of each of the plurality of messages, and synchronizing the first node based on the statistic. In certain embodiments, the statistic is calculated based on a set of slot deltas between neighboring nodes. The slot deltas may represent differences between start times of slots of the first node and start times of slots of the plurality of nodes.
Brief Description of the Drawings
The following figures depict certain illustrative embodiments of the invention in which like reference numerals refer to like elements. These depicted embodiments may not be drawn to scale and are to be understood as illustrative of the invention and not as limiting in any way.
Figure 1 depicts an exemplary slotted ad-hoc communication network.
Figure 2 depicts a pair of nodes communicating in the communication network of Figure 1, according to an illustrative embodiment of the invention.
Figure 3 depicts the misalignment of slots in a pair of nodes in a network.
Figure 4 depicts an exemplary pair of nodes of the communication network of Figure 1.
Figure 5 A depicts the synchronization of the pair of nodes, according to an illustrative embodiment of the invention.
Figure 5B is a flow diagram depicting a process for synchronizing of the pair of nodes of Figure 2, according to an illustrative embodiment of the invention.
Figure 6 A depicts the synchronization of the network of Figure 1, according to an illustrative embodiment of the invention.
Figure 6B is a flow diagram depicting a process for synchronizing the network of Figure 2, according to an illustrative embodiment of the invention.
Figure 7 depicts an exemplary slotted ad-hoc communication network.
Figures 8A and 8B depict node-based processes for synchronizing a network, according to an illustrative embodiment of the invention.
Figure 8C depicts a filter-based process for synchronizing a network, according to an illustrative embodiment of the invention.
Figure 9 depicts the synchronization of slots provisioned with exemplary guard times.
Figure 10 is a flow diagram depicting the synchronization and re- synchronization of nodes in a network, according to an illustrative embodiment of the invention.
Detailed Description of Certain Illustrated Embodiments
To provide an overall understanding of the invention, certain illustrative embodiments will now be described, including the network synchronization scheme and constituent components thereof. However, it will be understood by one of ordinary skill in the art that the methods and systems described herein may be adapted and modified as is appropriate for the application being addressed and that the systems and methods described herein may be employed in other suitable applications, and that such other additions and modifications will not depart from the scope hereof.
As will be seen from the following description, in one aspect, the invention relates to systems and methods for synchronizing a communication network, particularly a slotted communication network, having a plurality of nodes. In slotted communication networks, the nodes are configured to transmit or receive data during one or more selected time slots. During these selected time slots, each node may transmit a synchronization message that is received by a neighboring node. The neighboring node adjusts its time slot boundary based on the time of receipt of
the synchronization message, thereby synchronizing each node with a neighboring node.
Figure 1 depicts an exemplary communication network 100 having devices or nodes 102a-102e (generally, "nodes 102") that are illustrated as being spatially separated from each other. Each node may be capable of communicating with one or more other nodes in the network 100 along any direction. In typical ad-hoc communication networks, a node 102 communicates with other neighboring nodes 102 in the network, i.e., nodes located within its communication range. For example, node 102c may be able to communicate with either one of neighboring nodes 102b or 102d. Nodes 102 may also be able to communicate with more distant nodes (i.e., those nodes that are out of communication range) through a hopping process whereby one node 102 communicates with a neighboring node 102, which in turn communicates with another node 102 that is more distant. Such a hopping process, common to ad-hoc communication networks, facilitates communication across vast distances whereby nodes transmit or receive data packets from distant nodes by hopping through one or more intermediate nodes. For example, node 102b looking to transmit a data packet to node 102e, first transmits the message to node 102c. Node 102c then transmits the received data to node 102d, and node 102d finally transmits the data to the destination node 102e. In certain communication networks (such as mobile sensor networks), the nodes 102 may be able to move from one location to another and thereby communicate with other nodes 102 in the network that were previously distant nodes. For example, node 102c may move closer to node 102a and be able to directly communicate with node 102a.
The nodes 102a-102e may include sensors in a wireless sensor network whereby the sensors are capable of measuring at least one of heat, pressure, sound, light, electro-magnetic field and vibration. The nodes 102a-102e may also include computer components for processing the sensor data and for communicating the sensor data to other nodes in the network 100. The computer components may be used for managing the operation of a node, and transmission and/or reception of data packets to and from a node.
As noted earlier, nodes 102 in a stationary or mobile slotted communication network 100 are configured to operate during one or more selected time slots during which a node transmits or receives packets of data. Different nodes 102 may be scheduled to operate during different such time slots to allow for a communication across a network.
Figure 2 depicts an exemplary time slot scheduling scheme 200 that allows communication between nodes through a network 100. In particular, Figure 2 shows time slot schedules 202a, 202b and 202c for nodes 102a, 102b and 102c, respectively. The time slot schedules 202a, 202b and 202c identify when the nodes 102a, 102b and 102c are powered-on and when they transmit and/or receive data. Schedule 202a includes adjacent time slots 204a, 206a, 208a and 210a. Similarly, schedules 202b and 202c include a corresponding set of time slots. In such protocols, the time slots may be allocated in a periodic fashion such that they repeat after certain intervals of time. The time slots may be of fixed or variable length depending on the nature of the application. In certain embodiments, each of the time slots are about 20ms long. Time slots can be longer or shorter than 20ms, without departing from the scope of the invention. One class of protocols often used for scheduling in an ad-hoc networking environment is a Time Division Multiple Access (TDMA) Multiplexing MAC layer protocol. In practice, a communication device using a periodic TDMA communications protocol remains in one of two states, transmit or receive. In order to remain in either state, the communication device supplies power to a transceiver.
As shown in Figure 2, the node 102a is "on," i.e., its transceiver is operational, during time slot 204a. The data packet that is transmitted from node 102a during time slot 204a is received at node 102b during the time slot 204b. The node 102b is configured to transmit the same or another data packet during the next time slot 206b. The data packet transmitted from node 102b is received at node 102c during the time slot 206c. As shown in Figure 2, the boundaries of slots in neighboring nodes are aligned with each other, i.e., for example, the beginning of slot 204a is scheduled for the same time as the beginning of slot 204b. However, in
practicality, in most slotted communication networks, the time slots of communicating nodes are misaligned. Such a misalignment of time slots can occur due to various factors including factors that are internal to the node (e.g., clock drifts), and factors that are external to the node (e.g., distance between nodes and propagation delays).
Figure 3 depicts the misalignment of slots in a pair of nodes 102a and 102b in the network 100 of Figure 1. In particular, Figure 3 shows a scheduling scheme 300 including a pair of nodes 302a and 302b that are duty-cycled such that their transceivers are either "on" or "off during one or more time slots. Each time slot is of duration 312. In the illustrative scheduling scheme 300 the time slot schedule controlling the operation of node 102a requires the transceiver of node 102a to be powered "on" at least during time slots 306a and 310a and powered "off at least during time slots 304a and 308a. The node is capable of transmitting and/or receiving data during a time slot that its transceiver is in the "on" state. Similarly, the time slot schedule controlling the operation of node 102b requires the transceiver of the node to be powered "on" at least during time slots 306b and 310b and powered "off at least during time slots 304b and 308b.
The nodes 102a and 102b are misaligned such that the time slots are offset by a time period 318. The offset time period 318 causes a portion of the "off slot 304b to overlap with a portion of the "on" slot 306a. During operation, a portion of a message 316 transmitted during time slot 306a is not received by the node 102b because it was "off when the message portion 316 arrived. Tn many slotted communication protocols, the initial portion of a communication in a time slot is critical for a recipient to receive in order to receive the remainder of the communication. For example, the initial portions often include signaling data to inform the receiving node that additional data is forthcoming directed to that node. At the radio layer, the initial portions of a commuication include waveforms used for phase alignment. Thus, even though node 102b is "on" when message portion 320 arrives, node 102b may not receive it.
To reliably communicate data, the nodes 102a and 102b have to be synchronized such that a message transmitted in a time slot by node 102a arrives in its entirety while node 102b is "on". This means that the beginning and end portions of the message that are transmitted at the beginning and end, respectively, of a time slot in node 102b have to be received during an "on" time slot in node 102b. If the time slots in node 102b are not aligned with the time slots in node 102a, then portions of the data packet may be received by node 102b in an adjacent time slot during which the node 102b may be "off" and unable to receive these portions of the transmitted data. To allow for reliable communication between nodes in the network, one or more nodes may include circuitry, and/or software as shown in Figure 4, to synchronize (e.g., modifying time slot schedules in response to received data) it with another one of the nodes in the network.
Figure 4 is a block diagram of nodes 102a and 102b. Nodes 102a and 102b include transceivers 404a and 404b ("transceiver 404"), respectively, that are connected to antennas 406a and 406b ("antenna 406"). The nodes 102a and 102b communicate with each other wirelessly; however, it can be understood that the nodes 102a and 102b can communicate in a wired network, without departing from the scope of the invention. The nodes 102a and 102b further include clocks 402a and 402b ("clock 402") for maintaining time. The clocks 402a and 402b are connected to processors 410a and 410b ("processor 410"). The processors 410a and 410b are connected to memory components 412a and 412b ("memory 412"). Nodes 102a and 102b may be part of a wireless sensor network. If so, the nodes 102a and 102b include one or more sensor components 414a and 414b ("sensors 414").
In a node 102, the processor 410 establishes a time slot schedule for the node. The schedule indicates which time slots in the node 102a should be "on," and in which of these "on" time slots, the node can transmit data. The processor 410 measures time with the aid of the clock 402.
A node 102a communicates with another node 102b when the transceivers of both the nodes 102a and 102b are in a "on" or "powered" state. For reliable and
complete communication, the time slots during which each of the nodes 102a and 102b are "on," are synchronized, whereby each time slot begins and ends at substantially the same time. However, during normal operation, the time slots between neighboring nodes become misaligned and, consequently, unsynchronized. Thus, from time to time the nodes need to resynchronize.
Figures 5 A and 5B depict the synchronization of node 102b to node 102a of Figures 1-4, according to an illustrative embodiment of the invention. In particular, as depicted in Figure 5A, node 102a includes a time slot schedule 501a having assigned time slots 502a, 504a, 506a and 508a. Similarly, node 102b includes a time slot schedule 501b having a slotted configuration with time slots 502b, 504b, 506b and 508b. Typically, the time slot schedules are calculated by the processor 410 (Figure 4) and the state of the node 102a and 102b are stored in memory 412 (Figure 4). During synchronization, the node 102a transmits a message 512 beginning at the slot boundary 514a of a time slot 502a (step 532, Figure 5B). In certain embodiments, the processor 410a generates the message and sends it to the transceiver 404a, which in turn, transmits the message 512 during the appropriate time interval. The message 512 may include, among other things, a message identified as a synchronization message. The message 512 may exclusively consist of such a synchronization message. The message 512 may also be heartbeat signal. Alternatively, a receiving node may use any received message as a basis for resynchronization. The node 102b receives the message 512 after a certain delay (typically due to propagation of the signal through the wireless channel) at a receipt time 510 (step 534, Figure 5B). As noted above due to factors such as clock drifts and propagation delay, the receipt time may not coincide with the slot boundary 514b of time slot 502b in node 102b.
In certain embodiments (not illustrated in Figure 5A), the transmitted message occupies substantially the entire length of the time slot 502. In such embodiments, if the receipt time 510 does not coincide with the slot boundary 514b of time slot 502b, certain portions of the message may be received in time slot 504b. However, the node 102b may be duty-cycled such that the time slot 504b is assigned
as an "off state whereby the node 102b is non operational during the time slot 504b. In such cases, any portion or the entirety of the message received during time slot 504b may not be reliably received. To prevent such occurrences, upon receiving the message 512 at the receipt time 510, the node 102b adjusts its time slot schedule 501b to move the slot boundary 514b to substantially coincide with the receipt time 510, resulting in a new time slot schedule 501c (step 536, Figure 5B).
In certain embodiments, the message 512 includes a data packet configured to be transmitted in a slotted communication network. The message 512 may include particular information relating to a node's location in the network, a node's relationship with one or more other nodes, one or more timestamps and any other flags or information relevant towards synchronization. In certain embodiments, the message 512 includes data that may not be related to synchronization. In such embodiments, the message 512 may still be used for synchronization because the receipt time of the message 512 in a node may be sufficient to align slot boundaries. In other embodiments, the synchronization message 512 includes a heartbeat signal. In still other embodiments, synchronization messages 512 may be embedded in other communication messages.
In certain embodiments, the above described method 530 used to synchronize communication pair 104 of nodes 102a and 102b, is applied repeatedly across each of the nodes 102a-102e in the network 100 to synchronize the entire network. Figures 6A and 6B depict the synchronization of the network 100 of Figure 1 , according to an illustrative embodiment of the invention.
Figures 6 A and 6B depict the synchronization of the network 100 of Figure 1, according to an illustrative embodiment of the invention. As shown in Figure 6 A, nodes 102a and 102b are configured with time slot schedules having corresponding time slots 602a, 604a, 606a, and 608a and time slots 602b, 604b, 606b, and 608b, respectively. Time slot 602a corresponds to time slot 602b, time slot 604a corresponds to time slot 604b, and so forth. Nodes 102c-102e are also configured with timing protocols having time slots that correspond to the time slots of nodes
102a and 102b, for example, time slots 604c, 606c and 608c; 606d and 608d; and time slots 608e and 61Oe, respectively. However, as noted earlier, due to various internal as well as external factors, the time slots in each of the nodes 102a-102e may become misaligned with respect to each other. As illustrated in the Figure, a first time slot, for example, time slot 602a of node 102a, may have become misaligned such that it begins after a second corresponding time slot, for example, 602b. In other cases, a first time slot, for example, time slot 604b, may begin before the start time of a corresponding second time slot 604c. To correct such a misalignment, the network 100 is synchronized such that each node 102a-102e is synchronized to its neighbor from which the node receives messages.
Referring to Figure 6B, the synchronization process 630 begins with selecting a starting node (step 631) or root node from which to begin transmitting the synchronization message. In the illustrated embodiment of network 100, node 102a is selected as the starting root node since node 102a is not shown as having a neighbor from which it receives data (step 631). The node 102a transmits a synchronization message 612a to node 102b during time slot 602 (step 632). The node 102b receives message 612a at a time within the time slot 602b. Node 102b realigns the boundary of its slot 602b to the receipt time of the message from node 102a (step 634). Node 102b transmits a synchronization message 612b to node 102c during time slot 604b, and node 102c re-aligns the boundary of its slot 604c to the receipt time of the message from node 102b. In certain embodiments, the processor 410 in each node determines if it is the last node in the network 100 to be synchronized (step 636). If not, then the processor 410 instructs the node to transmit a synchronization message during the next time slot. In certain embodiments, synchronization of the network 100 is complete when each of the nodes 102a-102e are synchronized to their neighbor (step 638). In such embodiments, node 102b is synchronized with node 102a, node 102c is synchronized with node 102b, node 102d is synchronized with node 102c, and node 102e is synchronized with node 102d.
As noted earlier with reference to Figures 1 -6B, network 100 includes nodes 102a-102e that are spatially arranged such that they are each within the range of one or two other nodes. Therefore, depending on the direction of communication, each node typically communicates with one other node in the network 100. The nodes in network 100 may communicate and/or be synchronized in any direction as desired without departing from the scope of the invention. However, in certain network topologies, the nodes may be spatially arranged such that each node is within the range of more than two nodes and therefore capable of communicating with more than one node in the network. Figures 7-8C depict such networks and processes for synchronizing them.
In particular, Figure 7 depicts an exemplary slotted ad-hoc communication network 700 having a plurality of nodes 702. As shown, each node 702 in network 700 is connected to each other either through arrows or lines. The arrows indicate possible direction of synchronization from one node 702 to another node 702. The arrows are merely for illustrative purposes and do not limit the scope of the invention. The nodes in network 700 may communicate and/or be synchronized in any direction and along any path as desired without departing from the scope of the invention. The straight lines connecting certain nodes indicate that those nodes 702 are within communication range of each other; however, they may not be configured to communicate with each other. In certain embodiments, synchronization messages are sent along the arrows from one node 702 to another until each node is synchronized to its neighbor. These synchronization messages typically originate from a starting node or root node 704 and propagate along a selected path through the network to reach each of the nodes. In certain embodiments, the synchronization messages originate from one or more nodes in network 700.
To achieve network-wide 700 synchronization in an efficient and accurate manner, these synchronization messages are transmitted along a communication path that is deemed to be optimal. In certain embodiments, for a given node, the optimal path is the shortest path to the root or starting node. In other embodiments, the optimal path is selected as desired based on the application. In certain
embodiments, based on the selection of the root or starting node, one path might allow for faster synchronization of the network than another path. In such networks 700, the selection of a root node, calculation of optimal paths or network topology, and the contents of synchronizing messages may play a role in the performance of the synchronization of the network 700. Figures 8A-8C depict processes for synchronizing networks such as network 700.
Figures 8A and 8B depicts processes for synchronizing a network, according to an illustrative embodiment of the invention. The process 800 of Figure 8 A begins with determining a suitable synchronization network topology (step 802, Figure 8A). A network topology typically describes the interconnectivity of the various nodes in the network. In certain embodiments, to determine such a topology, the plurality of nodes and their interconnectivity in a network can be modeled as a graph in mathematics having several statistical properties. Using certain statistical properties of these mathematical graphs, one or more interconnections can be identified, thereby providing a network topology that describes the interconnection of nodes in the network. In certain embodiments, the synchronization network topology includes a Minimum Hop Level Spanning Tree or its approximation. In certain embodiments, the synchronization network topology includes a Breadth-First Search (BFS) Spanning Tree.
In certain embodiments, a synchronization network topology is determined by each node from the information gathered from other nodes in the network. Each of the nodes sends out periodic heartbeats to neighbors by means of a broadcast. Each heartbeat broadcast contains information about the node, its neighbors and the node's relationship with the neighbors. Each of the nodes adjusts its location in the synchronization network topology based on the received heartbeat broadcasts.
Once the synchronization network topology is established whereby each node is connected to a neighbor along a selected path, a node 704 is elected as a root node or starting node (step 804, Figure 8A). In certain embodiments, the step of electing a root node is performed simultaneously with the determination of a suitable
network topology. The root node transmits and/or broadcasts a synchronization message (step 806) that is used to synchronize the neighboring nodes. With the aid of these neighboring nodes, one or more synchronization messages are propagated from the root node along the synchronization network topology to each of the other nodes in the network.
In certain embodiments, the calculation of a synchronization network topology may be avoided by driving the synchronization process from the root node as depicted in Figure 8B. In particular, the process 820 depicted in Figure 8B begins with electing a node in the network as a starting node or root node (step 822). The root node broadcasts a message through a periodic heartbeat that contains a sequence number (step 824). The root node increments the sequence number before sending out the next heartbeat. Each node receiving the message, either directly or indirectly, from the root node keeps track of the largest sequence number received so far. Each node adjusts its slot boundary to the receipt time of the first message having a particular sequence number (step 828), thereby synchronizing the network. Each node may then broadcast another message that includes the largest sequence number received so far in its periodic heartbeat message.
As discussed thus far, a node is synchronized with a neighboring node by aligning its slot boundary based on the receipt time of a synchronization message from the neighboring node. In certain embodiments, instead of associating the slot boundary of a node to a particular neighboring node or the closest neighboring node, the slot boundary can be associated with a plurality of neighboring nodes.
Figure 8C depicts a process 830 for synchronizing a network, according to an illustrative embodiment of the invention. The process 830 begins when the nodes in the network broadcast a message and/or a heartbeat signal (step 832). Each node may, therefore, receive a plurality of messages or heartbeat signals from a plurality of neighboring nodes (step 834). The node measures the time difference between its slot boundary and the receipt times of each of the plurality of messages or heartbeat signals (step 836). In certain embodiments, the node measures the time difference
between its slot boundary and the slot boundaries of each its neighboring nodes, referred to as slot deltas. The node calculates one or more statistics from these slot deltas including at least one of mean, median, mode, maximum, and minimum (step 838). To synchronize the network, the node adjusts its slot boundary based, at least in part, on the calculated statistics (step 840). As an example, the node adjusts its slot boundary by the mean of the slot-deltas.
In certain embodiments, the nodes in a network are re-synchronized when the misalignment between communicating nodes are greater than certain thresholds. If such thresholds are not crossed within a pre-determined waiting period, the nodes in the network may be re-synchronized after the expiration of the waiting time period. In certain embodiments, nodes in a network are re-synchronized after periodic intervals of time. In still other embodiments, the nodes in a network are re- synchronized as desired depending on the application. Depending on the direction of communication, the transmitting node may periodically send synchronization messages to synchronize one or more nodes in the network.
To ensure reliable communication of data between two or more nodes, even if there are misalignments between re-synchronizations, the slots may be provisioned with guard times. These guard times arc portions, typically at the beginning and at the end of each slot, during which data is not transmitted. Guard times are typically calculated based on the parameters described with reference to Figure 3.
In certain embodiments, guard times are useful for communication in a direction that is opposite to that of synchronization. As described earlier, a node is synchronized with a neighbor when the slot boundary of the node is shifted in time to match the receipt time of a message transmitted from the neighbor. However, in certain embodiments, the node may need to transmit data back to the neighboring node. This might be made difficult due to the shifting of the slot boundary of the node. Figure 9 depicts the provisioning of guard times to ease such a reverse transmission of data in a network.
Figure 9 depicts the synchronization 900 of slots provisioned with guard times. Node 902a has a time slot schedule in which a slot 904a is provisioned with a beginning guard time 908a and an end guard time 910a. Similarly, slot 906a is provisioned with a beginning guard time 912a and an end guard time 914a. Also, node 902b has a timing protocol in which slots 904b and 906b are provisioned with guard times 908b, 910b, 912b and 914b. During operation, node 902a sends a message 916 during slot 904a and after the end of the guard time 908a. On receiving the message 916, the node 902b, aligns its slot boundary such that the end of the guard time 908b is shifted to the receipt time of the message 916 at the node 902b.
In certain embodiments, the node 902b transmits a message 918 during slot 906b back to node 902a. Since the slots in node 902b are shifted from the previous synchronization, a portion of the message sent near the end of the slot 906b is received by node 902a during guard time 914a. In certain embodiments, node 902a is capable of receiving messages during the guard times and therefore the message can be reliably communicated. The guard times provide a buffer which is capable of tolerating misalignments in the slots in the period between re-synchronizations. The processes 900, 920 and 930 described with reference to Figures 8A-8C may be used to re-synchronize a network either periodically or at selected times.
In certain embodiments, as illustrated in Figure 10, the processes 800, 820 and 830 may be used in combination for at least one of initial synchronization and re-synchronization. Figure 10 is a flow diagram depicting a process 1000 for synchronizing and re-synchronizing nodes in a network, according to an illustrative embodiment of the invention. The process 1000 begins with initializing a network to an asynchronous listening mode (step 1002) whereby each of the nodes in the network are turned "on" and kept at low power so that they may be able to listen to synchronization messages or heartbeat signals. During initial synchronization, the processes 800 and 820 described with reference to Figures 8A and 8B are applied to synchronize the network (step 1004). Once the network is initialized and
synchronized, the nodes are transitioned into a duty-cycling mode whereby the nodes are either "on" or "off1 during selected time slots (step 1006). During the duty-cycling mode the nodes are re-synchronized using the process 830 described with reference to Figure 8C (step 1008).
The processes described herein may be carried out by software, firmware, or microcode or computing device of any type. Additionally, software implementing the processes may comprise computer executable instructions in any form (e.g., source code, object code, interpreted code, etc.) stored in any computer-readable medium (e.g., ROM, RAM, magnetic media, punched tape or card, compact disc (CD) in any form, DVD, etc.). Furthermore, such software may also be in the form of a computer data signal embodied in a carrier wave, such as that found within the well-known Web pages transferred among devices connected to the Internet. Accordingly, the present invention is not limited to any particular platform, unless specifically stated otherwise in the present disclosure.
The processor 410 may include a single microprocessor or a plurality of microprocessors for configuring the node as a multi-processor system. The processor may be a shared purpose processor, a DSP, an ASIC or other special purpose processor. The memory 412 may include a main memory and a read only memory. The memory 412 may also include a mass storage device having, for example, various disk drives, tape drives, etc. The memory 412 may further include dynamic random access memory (DRAM) and high-speed cache memory. In operation, the main memory 412 stores at least portions of instructions and data for execution by the processor 410 to carry out the functions described herein.
As noted above, the order in which the steps of the present method are performed is purely illustrative in nature. In fact, the steps can be performed in any order or in parallel, unless otherwise indicated by the present disclosure. The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The forgoing embodiments are each therefore to be considered in all respects illustrative, rather than limiting of the invention.
Claims
1. A method for synchronizing a communication network, comprising: providing a slotted communication network, including a first node configured to operate at least during a first time slot, and a second node configured to operate at least during a second time slot, wherein the second time slot corresponds to the first time slot; transmitting, from the first node, a message during the first time slot; receiving, at the second node, the message, at a first receipt time during the second time slot; and aligning a boundary portion of the second time slot with the first receipt time, thereby synchronizing the second time slot with the first time slot.
2. The method of claim 1, wherein aligning a boundary portion of the second time slot includes shifting a start time or an end time of the second time slot based on the first receipt time.
3. The method of claim 1, wherein the boundary portion comprises a guard time period.
4. The method of claim 3, wherein aligning a boundary portion includes aligning an edge of the guard time period of the second time slot with the first receipt time.
5. The method of claim 4, wherein the second time slot includes a data time period in between two guard time periods.
6. The method of claim 1, wherein the message is transmitted during or at the beginning of a boundary portion of the first time slot.
7. The method of claim 1, wherein at least one of the first node and the second node is configured to operate during a plurality of time slots according to pre-determined schedule.
8. The method of claim 1, wherein at least one of the first node and the second node is configured to operate during a plurality of time slots according to dynamically determined schedule.
9. The method of claim 1, further comprising repeating the steps of transmitting the message, receiving the message and aligning the second time slot after a re-sync time period has elapsed.
10. The method of claim 9, wherein at least one of the first time slot and second time slot includes a guard time period having a length based at least in part on the re- sync time period.
11. The method of claim 1 , wherein the slotted communication network further includes a third node configured to operate during a third time slot, the method further comprising: transmitting, from the second node, a second message during the second time slot; receiving, at the third node, the second message, at a second receipt time during the third time slot; and aligning a boundary portion of the third time slot with the second receipt time, thereby synchronizing the third time slot with the second time slot.
12. The method of claim 1, wherein the slotted communication network comprises at least one of a mobile ad-hoc network, a wireless sensor network and a wireless mesh network.
13. The method of claim 1 , wherein the message includes network topology information.
14. The method of claim 1, wherein the message includes a heartbeat signal.
15. A node in a slotted-communication network, comprising: a receiver configured to receive a message at a receipt time during a first time slot, the message having been transmitted by a transmitting node, and a processor configured for aligning a boundary portion of the first time slot with the receipt time.
16. The node of claim 15, wherein the processor aligns the boundary portion of the first time slot with the receipt time without synchronizing the clock of the node with the clock of the transmitting node.
17. The node of claim 15, wherein aligning a boundary portion of the first time slot includes shifting a start time or an end time of the first time slot based on the receipt time.
18. The node of claim 15, wherein the boundary portion comprises a guard time period.
19. The node of claim 18, wherein aligning a boundary portion includes aligning an edge of the guard time period of the first time slot with the receipt time.
20. The node of claim 19, wherein the first time slot includes a data time period in between two guard time periods.
21. The node of claim 15, wherein after a re-sync time period has elapsed, the receiver receives a second message and the processor aligns a second time slot to the receipt time of the second message.
22. The method of claim 21, wherein the first time slot includes a guard time period having a length based at least in part on the re-sync time period.
23. The node of claim 15, wherein the node comprises a transmitter for transmitting a message during a second time slot based on which a second node synchronizes at least one time slot to at least one time slot of the node:
24. The node of claim 15, wherein the message includes a heartbeat signal.
25. A method for synchronizing a communication network, comprising: providing a network topology for a communication network including a plurality of nodes, selecting a root node from the plurality of nodes in the network, transmitting from a first node a first message, aligning a slot boundary of a second node, neighboring the first node along the network topology, based on the receipt time of the first message, and transmitting from the second node a second message, and aligning a slot boundary of a third node, neighboring the second node along the network topology, based on the receipt time of the second message.
26. A method of synchronizing a communication network having a plurality of nodes, comprising: transmitting a plurality of messages from the plurality of nodes, receiving at a first node, the plurality of messages, calculating a statistic based, at least in part, on a time of reception of each of the plurality of messages, and synchronizing the first node based on the statistic.
27. The method of claim 26, wherein the statistic is calculated based on a set of slot deltas between neighboring nodes.
28. The method of claim 27, wherein the slot deltas comprises differences between start times of slots of the first node and start times of slots of the plurality of nodes.
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US84041706P | 2006-08-25 | 2006-08-25 | |
US60/840,417 | 2006-08-25 |
Publications (1)
Publication Number | Publication Date |
---|---|
WO2008027294A2 true WO2008027294A2 (en) | 2008-03-06 |
Family
ID=38941888
Family Applications (2)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
PCT/US2007/018691 WO2008027294A2 (en) | 2006-08-25 | 2007-08-24 | Systems and methods for synchronizing communication networks |
PCT/US2007/018721 WO2008027310A2 (en) | 2006-08-25 | 2007-08-24 | Systems and methods for energy-conscious communication in wireless ad-hoc networks |
Family Applications After (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
PCT/US2007/018721 WO2008027310A2 (en) | 2006-08-25 | 2007-08-24 | Systems and methods for energy-conscious communication in wireless ad-hoc networks |
Country Status (2)
Country | Link |
---|---|
US (2) | US7924728B2 (en) |
WO (2) | WO2008027294A2 (en) |
Cited By (6)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
EP2266259A2 (en) * | 2008-04-11 | 2010-12-29 | Nokia Siemens Networks OY | Network node power conservation apparatus, system, and method |
US7957418B2 (en) | 2007-07-31 | 2011-06-07 | Research In Motion Limited | Data burst communication techniques for use in increasing data throughput to mobile communication devices |
WO2014085142A1 (en) * | 2012-11-30 | 2014-06-05 | Qualcomm Incorporated | Systems and methods for synchronization of wireless devices in an ad-hoc network |
CN103716137B (en) * | 2013-12-30 | 2017-02-01 | 上海交通大学 | Method and system for identifying reasons of ZigBee sensor network packet loss |
WO2021053263A1 (en) * | 2019-09-18 | 2021-03-25 | Wirepas Oy | A decentralized synchronization solution for wireless communication networks |
EP3656071A4 (en) * | 2017-07-20 | 2021-04-21 | Itron Networked Solutions, Inc. | Compensating for oscillator drift in wireless mesh networks |
Families Citing this family (67)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JP3891145B2 (en) | 2003-05-16 | 2007-03-14 | ソニー株式会社 | Wireless communication apparatus, wireless communication method and program |
US8145201B2 (en) * | 2004-12-17 | 2012-03-27 | Raytheon Bbn Technologies Corp. | Methods and apparatus for reduced energy communication in an ad hoc network |
US7924728B2 (en) | 2006-08-25 | 2011-04-12 | Raytheon Bbn Technologies Corp | Systems and methods for energy-conscious communication in wireless ad-hoc networks |
US8189474B2 (en) * | 2006-09-27 | 2012-05-29 | Infosys Limited | Dynamic stack-based networks for resource constrained devices |
US7697488B2 (en) * | 2006-12-28 | 2010-04-13 | Oracle America, Inc. | Organizing communications in a network |
US8306533B2 (en) * | 2007-04-16 | 2012-11-06 | Telefonaktiebolaget L M Ericsson (Publ) | Method for exchanging cell information between networks |
US8149716B2 (en) * | 2007-08-20 | 2012-04-03 | Raytheon Bbn Technologies Corp. | Systems and methods for adaptive routing in mobile ad-hoc networks and disruption tolerant networks |
EP2109339B8 (en) * | 2007-12-12 | 2016-05-25 | Panasonic Intellectual Property Management Co., Ltd. | Data transmitting and receiving system, terminal, relay device, and data transmitting method |
US8130657B2 (en) * | 2008-03-18 | 2012-03-06 | Palo Alto Research Center Incorporated | Network routing using a retransmission-time-based link metric |
US8582491B2 (en) * | 2008-05-02 | 2013-11-12 | Lockheed Martin Corporation | Method and apparatus for routing communications using active and passive end-to-end quality-of-service reservations based on node mobility profiles |
JP4991627B2 (en) * | 2008-05-16 | 2012-08-01 | 株式会社日立製作所 | Plan execution management device and program thereof |
US8539035B2 (en) * | 2008-09-29 | 2013-09-17 | Fujitsu Limited | Message tying processing method and apparatus |
US8358968B2 (en) * | 2008-10-03 | 2013-01-22 | Motorola Solutions, Inc. | Method for selecting a channel to be monitored by subscriber units that are idle in a communication system |
US8279991B2 (en) * | 2008-10-03 | 2012-10-02 | Motorola Solutions, Inc. | Method of efficiently synchronizing to a desired timeslot in a time division multiple access communication system |
US8159944B2 (en) * | 2008-12-24 | 2012-04-17 | At&T Intellectual Property I, L.P. | Time based queuing |
US8665736B2 (en) * | 2009-02-27 | 2014-03-04 | Intel Corporation | MAC slot alignment among multiple wireless stations |
US8824449B2 (en) * | 2009-03-05 | 2014-09-02 | Chess Et International Bv | Synchronization of broadcast-only wireless networks |
US8730938B2 (en) * | 2009-04-08 | 2014-05-20 | Qualcomm Incorporated | Minimizing the impact of self synchronization on wireless communication devices |
US8630229B2 (en) * | 2009-07-06 | 2014-01-14 | Intel Corporation | Base station and method for reducing asynchronous interference in a multi-tier OFDMA overlay network |
US8406245B2 (en) * | 2009-07-09 | 2013-03-26 | Qualcomm Incorporated | System and method of transmitting content from a mobile device to a wireless display |
US7944840B2 (en) * | 2009-08-17 | 2011-05-17 | Edgewater Networks, Inc. | Method for facilitating latency measurements using intermediate network devices between endpoint devices connected by a computer network |
CN101789852B (en) * | 2010-01-12 | 2012-12-26 | 浙江大学 | Method for dynamic control of data packet length in wireless sensor network |
US9178949B2 (en) * | 2010-03-03 | 2015-11-03 | Blackberry Limited | Method, system and apparatus for managing push data transfers |
US8599826B2 (en) * | 2010-04-15 | 2013-12-03 | Motorola Solutions, Inc. | Method for synchronizing direct mode time division multiple access (TDMA) transmissions |
US8503409B2 (en) | 2010-04-15 | 2013-08-06 | Motorola Solutions, Inc. | Method for direct mode channel access |
US8897134B2 (en) * | 2010-06-25 | 2014-11-25 | Telefonaktiebolaget L M Ericsson (Publ) | Notifying a controller of a change to a packet forwarding configuration of a network element over a communication channel |
US8705368B1 (en) * | 2010-12-03 | 2014-04-22 | Google Inc. | Probabilistic distance-based arbitration |
WO2012077259A1 (en) * | 2010-12-10 | 2012-06-14 | Nec Corporation | Communication system, control device, node controlling method and program |
US8462766B2 (en) | 2011-03-07 | 2013-06-11 | Motorola Solutions, Inc. | Methods and apparatus for diffusing channel timing among subscriber units in TDMA direct mode |
JP5716587B2 (en) * | 2011-07-19 | 2015-05-13 | 富士通株式会社 | Route determination device, route determination method, management program, and management device |
US9167463B2 (en) * | 2011-09-02 | 2015-10-20 | Telcordia Technologies, Inc. | Communication node operable to estimate faults in an ad hoc network and method of performing the same |
US8964724B2 (en) * | 2011-10-03 | 2015-02-24 | Texas Instruments Incorporated | Clock synchronization and distributed guard time provisioning |
CN102377525B (en) * | 2011-11-10 | 2014-03-19 | 北京邮电大学 | Self-adaptive adjustment method and self-adaptive adjustment system for transmitters |
US9225614B2 (en) * | 2011-11-17 | 2015-12-29 | Google Inc. | Service and application layer optimization using variable rate optical transmission |
US20130235757A1 (en) * | 2012-03-07 | 2013-09-12 | Samsung Electronics Co. Ltd. | Apparatus and method for a biology inspired topological phase transition for wireless sensor network |
US8902901B2 (en) | 2012-03-23 | 2014-12-02 | Itron, Inc. | Communication packet conversion |
US20130329566A1 (en) * | 2012-06-07 | 2013-12-12 | Alcatel-Lucent Canada Inc. | OAM Power Packet |
DE102012210126A1 (en) * | 2012-06-15 | 2013-12-19 | Siemens Aktiengesellschaft | Method for operating a network arrangement, network device and network arrangement |
US10588173B2 (en) * | 2012-06-22 | 2020-03-10 | Honeywell International Inc. | Wi-Fi mesh fire detection system |
US9312977B1 (en) * | 2012-08-28 | 2016-04-12 | Bae Systems Information And Electronic Systems Integration Inc. | System and method to provide channel access synchronization without time-stamp exchange in time division multiple access (TDMA) multi-hop networks |
US9510286B2 (en) | 2013-03-27 | 2016-11-29 | Qualcomm Incorporated | Systems and methods for synchronization within a neighborhood aware network |
US9172517B2 (en) * | 2013-06-04 | 2015-10-27 | Texas Instruments Incorporated | Network power optimization via white lists |
EP2811796A1 (en) | 2013-06-07 | 2014-12-10 | Stichting Vu-Vumuc | Position-based broadcast protocol and time slot schedule for a wireless mesh network |
US9544162B2 (en) * | 2013-09-30 | 2017-01-10 | Cisco Technology, Inc. | Lightweight multicast acknowledgement technique in communication networks |
TWI516148B (en) | 2013-10-29 | 2016-01-01 | 財團法人工業技術研究院 | A system of dynamic adjusting message generation frequency in vehicular networks and method thereof |
CN103747505B (en) * | 2013-12-09 | 2017-07-25 | 联想(北京)有限公司 | A kind of means of communication and electronic equipment |
US10015812B2 (en) | 2013-12-25 | 2018-07-03 | Intel IP Corporation | Apparatus, system and method of setting transmit slots in a wireless communication network |
CN105101393B (en) * | 2014-05-19 | 2018-08-31 | 中兴通讯股份有限公司 | Wireless synchronization method and wireless synchronization master |
KR102319698B1 (en) * | 2015-05-29 | 2021-11-01 | 삼성전자 주식회사 | A method and apparatus for trasceving in moible communicatoin system |
US10701174B2 (en) * | 2016-01-05 | 2020-06-30 | Micro Focus Llc | Resource requests |
US10028276B2 (en) * | 2016-02-25 | 2018-07-17 | Electronics And Telecommunications Research Institute | Node device and method of allocating resources in wireless sensor networks |
US11076370B2 (en) * | 2016-06-07 | 2021-07-27 | Texas Instruments Incorporated | Node synchronization for networks |
CN108632842B (en) * | 2017-03-17 | 2020-06-16 | 华为技术有限公司 | Out-of-step determining method and device |
CN108809858B (en) * | 2017-04-28 | 2020-11-10 | 华为技术有限公司 | Network congestion control method, equipment and system |
US10353829B2 (en) * | 2017-06-30 | 2019-07-16 | Dell Products, Lp | System and method to account for I/O read latency in processor caching algorithms |
US11864110B2 (en) | 2018-01-16 | 2024-01-02 | Nokia Technologies Oy | Monitoring user equipment energy consumption |
US10813169B2 (en) | 2018-03-22 | 2020-10-20 | GoTenna, Inc. | Mesh network deployment kit |
US11218981B2 (en) * | 2018-09-20 | 2022-01-04 | Kabushiki Kaisha Toshiba | Wireless mesh network and data transmission method |
CN111294146B (en) * | 2019-04-12 | 2021-08-10 | 展讯通信(上海)有限公司 | Retransmission method and device of data frame |
US11265835B1 (en) * | 2019-06-12 | 2022-03-01 | Birket Ip Holdings, Inc. | Low skew synchronization of disparate wireless nodes in a pyrotechnic environment |
CN110601976B (en) * | 2019-08-12 | 2021-07-20 | 浙江工业大学 | Self-adaptive deflection routing control method for electromagnetic nano network |
EP4011045B1 (en) * | 2019-08-13 | 2024-04-24 | Huawei Technologies Co., Ltd. | Control and management for impairment-aware optical network |
EP4017118A4 (en) * | 2019-10-17 | 2022-09-07 | Guangdong Oppo Mobile Telecommunications Corp., Ltd. | Communication method, communication device, and storage medium |
TWI707564B (en) * | 2019-11-01 | 2020-10-11 | 瑞昱半導體股份有限公司 | Wireless communication device and wireless communication method |
US11102698B2 (en) * | 2019-12-30 | 2021-08-24 | Prince Sultan University | Tabu node selection with minimum spanning tree for WSNs |
US11191053B1 (en) * | 2020-08-06 | 2021-11-30 | Facebook, Inc. | Network-based clock for time distribution across a wireless network |
US11388073B1 (en) * | 2021-06-30 | 2022-07-12 | Amazon Technologies, Inc. | Estimating end-to-end loss distributions in computer networks |
Family Cites Families (168)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US5203020A (en) | 1988-06-14 | 1993-04-13 | Kabushiki Kaisha Toshiba | Method and apparatus for reducing power consumption in a radio telecommunication apparatus |
US5128938A (en) | 1989-03-03 | 1992-07-07 | Motorola, Inc. | Energy saving protocol for a communication system |
US6714983B1 (en) | 1989-04-14 | 2004-03-30 | Broadcom Corporation | Modular, portable data processing terminal for use in a communication network |
US4964121A (en) | 1989-08-30 | 1990-10-16 | Motorola, Inc. | Battery saver for a TDM system |
US5119373A (en) * | 1990-02-09 | 1992-06-02 | Luxcom, Inc. | Multiple buffer time division multiplexing ring |
JP3034282B2 (en) | 1990-07-12 | 2000-04-17 | 株式会社東芝 | Asynchronous mobile radio communication system |
US6374311B1 (en) | 1991-10-01 | 2002-04-16 | Intermec Ip Corp. | Communication network having a plurality of bridging nodes which transmit a beacon to terminal nodes in power saving state that it has messages awaiting delivery |
JP2796464B2 (en) | 1991-12-27 | 1998-09-10 | 株式会社日立製作所 | Wireless communication system and wireless communication method |
GB9304638D0 (en) * | 1993-03-06 | 1993-04-21 | Ncr Int Inc | Wireless data communication system having power saving function |
US5790946A (en) | 1993-07-15 | 1998-08-04 | Rotzoll; Robert R. | Wake up device for a communications system |
JP2630561B2 (en) * | 1993-09-13 | 1997-07-16 | 宇宙開発事業団 | Beam compression processing method of antenna pattern in radar |
JP2856050B2 (en) | 1993-11-30 | 1999-02-10 | 日本電気株式会社 | Routing control method |
US6292508B1 (en) | 1994-03-03 | 2001-09-18 | Proxim, Inc. | Method and apparatus for managing power in a frequency hopping medium access control protocol |
US5590396A (en) | 1994-04-20 | 1996-12-31 | Ericsson Inc. | Method and apparatus for a deep-sleep mode in a digital cellular communication system |
US5583866A (en) | 1994-12-05 | 1996-12-10 | Motorola, Inc. | Method for delivering broadcast packets in a frequency hopping local area network |
GB2303988A (en) | 1995-07-31 | 1997-03-05 | Secr Defence | Thermal imaging system with detector array calibration mode |
US6418148B1 (en) | 1995-10-05 | 2002-07-09 | Lucent Technologies Inc. | Burst-level resource allocation in cellular systems |
US5710975A (en) | 1995-12-26 | 1998-01-20 | Motorola, Inc. | Selective call transceiver with system approved power saving state |
GB9604951D0 (en) | 1996-03-08 | 1996-05-08 | Glass Antennas Tech Ltd | Antenna arrangement |
FI103454B1 (en) | 1996-04-01 | 1999-06-30 | Nokia Telecommunications Oy | Control of the operation of a mobile station in a packet radio system |
US5754790A (en) | 1996-05-01 | 1998-05-19 | 3Com Corporation | Apparatus and method for selecting improved routing paths in an autonomous system of computer networks |
US6130602A (en) * | 1996-05-13 | 2000-10-10 | Micron Technology, Inc. | Radio frequency data communications device |
US6697415B1 (en) | 1996-06-03 | 2004-02-24 | Broadcom Corporation | Spread spectrum transceiver module utilizing multiple mode transmission |
SE518132C2 (en) * | 1996-06-07 | 2002-08-27 | Ericsson Telefon Ab L M | Method and apparatus for synchronizing combined receivers and transmitters in a cellular system |
US6236365B1 (en) | 1996-09-09 | 2001-05-22 | Tracbeam, Llc | Location of a mobile station using a plurality of commercial wireless infrastructures |
US6118769A (en) * | 1997-05-01 | 2000-09-12 | Itt Manufacturing Enterprises, Inc. | Method and apparatus for voice intranet repeater and range extension |
US5987024A (en) | 1997-05-09 | 1999-11-16 | Motorola, Inc. | Self synchronizing network protocol |
GB2328046B (en) * | 1997-08-08 | 2002-06-05 | Ibm | Data processing network |
US6590889B1 (en) * | 1997-08-11 | 2003-07-08 | Gte Internetworking Incorporated | Data communications system and hybrid time-code multiplexing method |
US6104708A (en) * | 1997-08-11 | 2000-08-15 | Bbn Corporation | Wireless data communications system |
US6188911B1 (en) | 1997-09-09 | 2001-02-13 | Telefonaktiebolaget Lm Ericsson (Publ) | Efficient message transmission in a mobile communication system |
US6016322A (en) * | 1997-09-22 | 2000-01-18 | Kor Electronics, Inc. | Apparatus and method for self synchronization in a digital data wireless communication system |
GB9721008D0 (en) | 1997-10-03 | 1997-12-03 | Hewlett Packard Co | Power management method foruse in a wireless local area network (LAN) |
US6058106A (en) | 1997-10-20 | 2000-05-02 | Motorola, Inc. | Network protocol method, access point device and peripheral devices for providing for an efficient centrally coordinated peer-to-peer wireless communications network |
US6097957A (en) * | 1997-11-14 | 2000-08-01 | Motorola, Inc. | Radiotelephone service planning system and method for determining a best server for a communication connection |
US6130881A (en) | 1998-04-20 | 2000-10-10 | Sarnoff Corporation | Traffic routing in small wireless data networks |
US6473607B1 (en) | 1998-06-01 | 2002-10-29 | Broadcom Corporation | Communication device with a self-calibrating sleep timer |
US6463307B1 (en) | 1998-08-14 | 2002-10-08 | Telefonaktiebolaget Lm Ericsson | Method and apparatus for power saving in a mobile terminal with established connections |
US6208247B1 (en) | 1998-08-18 | 2001-03-27 | Rockwell Science Center, Llc | Wireless integrated sensor network using multiple relayed communications |
US6359901B1 (en) * | 1998-09-02 | 2002-03-19 | General Dynamics Decision Systems, Inc. | Method and apparatus for asynchronous adaptive protocol layer tuning |
US6400317B2 (en) * | 1998-09-21 | 2002-06-04 | Tantivy Communications, Inc. | Method and apparatus for antenna control in a communications network |
US6100843A (en) | 1998-09-21 | 2000-08-08 | Tantivy Communications Inc. | Adaptive antenna for use in same frequency networks |
US6404386B1 (en) | 1998-09-21 | 2002-06-11 | Tantivy Communications, Inc. | Adaptive antenna for use in same frequency networks |
JP2002534842A (en) * | 1998-12-23 | 2002-10-15 | ノキア・ワイヤレス・ルーターズ・インコーポレーテッド | Unified routing scheme for ad hoc internetworking |
US6646604B2 (en) | 1999-01-08 | 2003-11-11 | Trueposition, Inc. | Automatic synchronous tuning of narrowband receivers of a wireless location system for voice/traffic channel tracking |
KR100287896B1 (en) * | 1999-02-06 | 2001-04-16 | 서평원 | Cell Search Method in Mobile Communication System |
US7184413B2 (en) * | 1999-02-10 | 2007-02-27 | Nokia Inc. | Adaptive communication protocol for wireless networks |
US6414955B1 (en) | 1999-03-23 | 2002-07-02 | Innovative Technology Licensing, Llc | Distributed topology learning method and apparatus for wireless networks |
US7218630B1 (en) * | 1999-04-30 | 2007-05-15 | Lucent Technologies Inc. | Data session setup system for wireless network |
US6721275B1 (en) | 1999-05-03 | 2004-04-13 | Hewlett-Packard Development Company, L.P. | Bridged network stations location revision |
US6127799A (en) | 1999-05-14 | 2000-10-03 | Gte Internetworking Incorporated | Method and apparatus for wireless powering and recharging |
US6338606B1 (en) * | 1999-06-07 | 2002-01-15 | Recot, Inc. | Method and apparatus for stacking tortilla chips |
US6490461B1 (en) | 1999-06-24 | 2002-12-03 | Telefonaktiebolaget Lm Ericsson (Publ) | Power control based on combined quality estimates |
EP1071228B1 (en) | 1999-07-20 | 2009-04-15 | Texas Instruments Inc. | Wireless network with steerable antenna calibration over independent control path |
US6598034B1 (en) * | 1999-09-21 | 2003-07-22 | Infineon Technologies North America Corp. | Rule based IP data processing |
US7020701B1 (en) * | 1999-10-06 | 2006-03-28 | Sensoria Corporation | Method for collecting and processing data using internetworked wireless integrated network sensors (WINS) |
US6735630B1 (en) | 1999-10-06 | 2004-05-11 | Sensoria Corporation | Method for collecting data using compact internetworked wireless integrated network sensors (WINS) |
US7376827B1 (en) * | 1999-11-05 | 2008-05-20 | Cisco Technology, Inc. | Directory-enabled network elements |
US6601093B1 (en) | 1999-12-01 | 2003-07-29 | Ibm Corporation | Address resolution in ad-hoc networking |
US6694149B1 (en) | 1999-12-22 | 2004-02-17 | Motorola, Inc. | Method and apparatus for reducing power consumption in a network device |
US6894975B1 (en) | 2000-01-15 | 2005-05-17 | Andrzej Partyka | Synchronization and access of the nodes in a communications network |
US6505052B1 (en) | 2000-02-01 | 2003-01-07 | Qualcomm, Incorporated | System for transmitting and receiving short message service (SMS) messages |
WO2001058237A2 (en) | 2000-02-12 | 2001-08-16 | Hrl Laboratories, Llc | Scalable unidirectional routing for mobile ad-hoc networks |
US7327683B2 (en) | 2000-03-16 | 2008-02-05 | Sri International | Method and apparatus for disseminating topology information and for discovering new neighboring nodes |
US6512935B1 (en) * | 2000-03-24 | 2003-01-28 | Gte Internetworking Incorporated | Energy conserving network protocol |
US6791949B1 (en) * | 2000-04-28 | 2004-09-14 | Raytheon Company | Network protocol for wireless ad hoc networks |
US6735178B1 (en) * | 2000-05-10 | 2004-05-11 | Ricochet Networks, Inc. | Method for maximizing throughput for multiple links using directional elements |
US6477361B1 (en) | 2000-05-23 | 2002-11-05 | Lucent Technologies Inc. | Remote power-down control of wireless terminal |
US6859135B1 (en) * | 2000-06-05 | 2005-02-22 | Brig Barnum Elliott | System and method for conserving energy in wireless devices |
US7103344B2 (en) * | 2000-06-08 | 2006-09-05 | Menard Raymond J | Device with passive receiver |
JP4431919B2 (en) | 2000-06-12 | 2010-03-17 | ソニー株式会社 | Mobile phone and distance measuring method |
US6757248B1 (en) | 2000-06-14 | 2004-06-29 | Nokia Internet Communications Inc. | Performance enhancement of transmission control protocol (TCP) for wireless network applications |
US7142520B1 (en) | 2000-06-16 | 2006-11-28 | Nokia Mobile Phones Ltd. | Method and apparatus for mobile internet protocol regional paging |
US6381467B1 (en) * | 2000-06-22 | 2002-04-30 | Motorola, Inc. | Method and apparatus for managing an ad hoc wireless network |
US6262684B1 (en) | 2000-06-27 | 2001-07-17 | 3Com Corporation | Stylus antenna |
US6476773B2 (en) | 2000-08-18 | 2002-11-05 | Tantivy Communications, Inc. | Printed or etched, folding, directional antenna |
AU2001296378A1 (en) * | 2000-09-29 | 2002-04-08 | The Regents Of The University Of California | Ad hoc network accessing using distributed election of a shared transmission schedule |
US6888819B1 (en) * | 2000-10-04 | 2005-05-03 | Yitran Communications Ltd. | Media access control utilizing synchronization signaling |
US6735448B1 (en) * | 2000-11-07 | 2004-05-11 | Hrl Laboratories, Llc | Power management for throughput enhancement in wireless ad-hoc networks |
US6574269B1 (en) | 2000-11-21 | 2003-06-03 | Bbnt Solutions Llc | Asymmetric orthogonal codes for wireless system receivers with multiplication-free correlators |
US6894991B2 (en) | 2000-11-30 | 2005-05-17 | Verizon Laboratories Inc. | Integrated method for performing scheduling, routing and access control in a computer network |
US6973039B2 (en) * | 2000-12-08 | 2005-12-06 | Bbnt Solutions Llc | Mechanism for performing energy-based routing in wireless networks |
US6377211B1 (en) | 2000-12-13 | 2002-04-23 | Lockheed Martin Corporation | Apparatus and method for pointing a directional device from a moving vehicle toward a spacecraft |
US7165102B2 (en) | 2000-12-18 | 2007-01-16 | Raza Microelectronics, Inc. | Adaptive link quality management for wireless medium |
US7209771B2 (en) | 2000-12-22 | 2007-04-24 | Terahop Networks, Inc. | Battery powered wireless transceiver having LPRF component and second wake up receiver |
US6745027B2 (en) | 2000-12-22 | 2004-06-01 | Seekernet Incorporated | Class switched networks for tracking articles |
US7363371B2 (en) * | 2000-12-28 | 2008-04-22 | Nortel Networks Limited | Traffic flow management in a communications network |
US20020146985A1 (en) | 2001-01-31 | 2002-10-10 | Axonn Corporation | Battery operated remote transceiver (BORT) system and method |
US7058031B2 (en) * | 2001-01-31 | 2006-06-06 | Qualcomm Incorporated | Method and apparatus for efficient use of communication resources in a data communication system under overload conditions |
US7024482B2 (en) | 2001-02-28 | 2006-04-04 | Sharp Laboratories Of America, Inc. | Pseudo-random dynamic scheduler for scheduling communication periods between electronic devices |
US6583675B2 (en) | 2001-03-20 | 2003-06-24 | Broadcom Corporation | Apparatus and method for phase lock loop gain control using unit current sources |
US20020145978A1 (en) | 2001-04-05 | 2002-10-10 | Batsell Stephen G. | Mrp-based hybrid routing for mobile ad hoc networks |
US6611231B2 (en) | 2001-04-27 | 2003-08-26 | Vivato, Inc. | Wireless packet switched communication systems and networks using adaptively steered antenna arrays |
EP1271896B1 (en) * | 2001-06-18 | 2004-07-28 | Swisscom Mobile AG | Method and system for mobile IP Nodes in heterogeneous networks |
US7027392B2 (en) * | 2001-08-14 | 2006-04-11 | Qualcomm, Incorporated | Method and apparatus for scheduling packet data transmissions in a wireless communication system |
MXPA04001267A (en) * | 2001-08-25 | 2004-05-27 | Nokia Corp | System and method for collision-free transmission scheduling using neighborhood information and advertised transmission times. |
US7088678B1 (en) * | 2001-08-27 | 2006-08-08 | 3Com Corporation | System and method for traffic shaping based on generalized congestion and flow control |
US7720045B2 (en) | 2003-05-02 | 2010-05-18 | Microsoft Corporation | Method to enable simultaneous connections to multiple wireless networks using a single radio |
US7881202B2 (en) | 2002-09-25 | 2011-02-01 | Broadcom Corporation | System and method for dropping lower priority packets that are slated for wireless transmission |
US20030066090A1 (en) * | 2001-09-28 | 2003-04-03 | Brendan Traw | Method and apparatus to provide a personalized channel |
US7020501B1 (en) * | 2001-11-30 | 2006-03-28 | Bbnt Solutions Llc | Energy efficient forwarding in ad-hoc wireless networks |
US6981052B1 (en) | 2001-12-07 | 2005-12-27 | Cisco Technology, Inc. | Dynamic behavioral queue classification and weighting |
US6671525B2 (en) | 2001-12-13 | 2003-12-30 | Motorola, Inc. | Beacon assisted hybrid asynchronous wireless communications protocol |
US7486693B2 (en) * | 2001-12-14 | 2009-02-03 | General Electric Company | Time slot protocol |
US7113505B2 (en) * | 2001-12-17 | 2006-09-26 | Agere Systems Inc. | Mesh architecture for synchronous cross-connects |
US7342876B2 (en) * | 2001-12-20 | 2008-03-11 | Sri International | Interference mitigation and adaptive routing in wireless ad-hoc packet-switched networks |
US6804208B2 (en) | 2002-01-10 | 2004-10-12 | Harris Corporation | Method and device for establishing communication links with parallel scheduling operations in a communication system |
US20030152110A1 (en) | 2002-02-08 | 2003-08-14 | Johan Rune | Synchronization of remote network nodes |
US7133398B2 (en) | 2002-03-27 | 2006-11-07 | Motorola, Inc. | System and method for asynchronous communications employing direct and indirect access protocols |
US7151945B2 (en) | 2002-03-29 | 2006-12-19 | Cisco Systems Wireless Networking (Australia) Pty Limited | Method and apparatus for clock synchronization in a wireless network |
US7110783B2 (en) | 2002-04-17 | 2006-09-19 | Microsoft Corporation | Power efficient channel scheduling in a wireless network |
US8009607B2 (en) | 2002-04-24 | 2011-08-30 | Telefonaktiebolaget Lm Ericsson (Publ) | Method and apparatus for uplink transmission timing in a mobile communications system |
US7764617B2 (en) | 2002-04-29 | 2010-07-27 | Harris Corporation | Mobile ad-hoc network and methods for performing functions therein based upon weighted quality of service metrics |
US7072432B2 (en) * | 2002-07-05 | 2006-07-04 | Meshnetworks, Inc. | System and method for correcting the clock drift and maintaining the synchronization of low quality clocks in wireless networks |
US7346679B2 (en) | 2002-08-30 | 2008-03-18 | Microsoft Corporation | Method and system for identifying lossy links in a computer network |
JP2004204299A (en) * | 2002-12-25 | 2004-07-22 | Ebara Corp | Diamond film-deposition silicon and electrode |
US8159998B2 (en) | 2002-12-27 | 2012-04-17 | Rockstar Bidco Lp | Method and apparatus for improving a transmission signal characteristic of a downlink signal in a time division multiple access wireless communication system |
US7340615B2 (en) * | 2003-01-31 | 2008-03-04 | Microsoft Corporation | Method and apparatus for managing power in network interface modules |
US6816115B1 (en) | 2003-01-31 | 2004-11-09 | Bbnt Solutions Llc | Systems and methods for antenna selection in an ad-hoc wireless network |
US7286844B1 (en) | 2003-01-31 | 2007-10-23 | Bbn Technologies Corp. | Systems and methods for three dimensional antenna selection and power control in an Ad-Hoc wireless network |
KR101188396B1 (en) | 2003-04-23 | 2012-10-08 | 콸콤 인코포레이티드 | Methods and apparatus of enhancing performance in wireless communication systems |
US7356561B2 (en) | 2003-05-01 | 2008-04-08 | Lucent Technologies Inc. | Adaptive sleeping and awakening protocol for an energy-efficient adhoc network |
US7564842B2 (en) | 2003-07-02 | 2009-07-21 | Mitsubishi Electric Research Laboratories, Inc. | Methods and apparatuses for routing data in a personal area network |
US7245946B2 (en) * | 2003-07-07 | 2007-07-17 | Texas Instruments Incorporated | Optimal power saving scheduler for 802.11e APSD |
GB0317372D0 (en) | 2003-07-25 | 2003-08-27 | Royal Holloway University Of L | Routing protocol for ad hoc networks |
US7388847B2 (en) | 2003-08-18 | 2008-06-17 | Nortel Networks Limited | Channel quality indicator for OFDM |
US7406296B2 (en) | 2003-08-22 | 2008-07-29 | Telefonaktiebolaget L M Ericsson (Publ) | Co-located radio operation |
US8166204B2 (en) * | 2003-08-29 | 2012-04-24 | Raytheon Bbn Technologies Corp. | Systems and methods for automatically placing nodes in an ad hoc network |
US7466655B1 (en) | 2003-09-16 | 2008-12-16 | Cisco Technology, Inc. | Ant-based method for discovering a network path that satisfies a quality of service equipment |
US7523220B2 (en) * | 2003-09-17 | 2009-04-21 | Microsoft Corporation | Metaspace: communication middleware for partially connected mobile ad hoc networks |
US7542437B1 (en) * | 2003-10-02 | 2009-06-02 | Bbn Technologies Corp. | Systems and methods for conserving energy in a communications network |
GB0323244D0 (en) * | 2003-10-03 | 2003-11-05 | Fujitsu Ltd | Uplink scheduling |
US7369512B1 (en) | 2003-11-06 | 2008-05-06 | Bbn Technologies Corp. | Systems and methods for efficient packet distribution in an ad hoc network |
US7801065B2 (en) | 2003-11-25 | 2010-09-21 | Motorola Mobility, Inc. | Reception timing method and apparatus |
US7034748B2 (en) | 2003-12-17 | 2006-04-25 | Microsoft Corporation | Low-cost, steerable, phased array antenna with controllable high permittivity phase shifters |
US7408914B2 (en) * | 2004-01-08 | 2008-08-05 | Qualcomm Incorporated | Time-hopping systems and techniques for wireless communications |
US7324817B2 (en) | 2004-02-07 | 2008-01-29 | Interdigital Technology Corporation | Wireless communication method and apparatus for selecting and reselecting cells based on measurements performed using directional beams and an omni-directional beam pattern |
US7376122B2 (en) | 2004-02-23 | 2008-05-20 | Microsoft Corporation | System and method for link quality source routing |
US7333830B2 (en) | 2004-02-26 | 2008-02-19 | Quorum Systems, Inc. | Method and apparatus for synchronizing WLAN in a multi-mode radio system |
US7155263B1 (en) | 2004-02-27 | 2006-12-26 | Bbn Technologies Corp. | Battery-conserving transmission and encoding method for wireless ad hoc networks |
US7466681B2 (en) * | 2004-03-19 | 2008-12-16 | Nortel Networks Limited | Method and apparatus for sensor network routing |
US7907898B2 (en) * | 2004-03-26 | 2011-03-15 | Qualcomm Incorporated | Asynchronous inter-piconet routing |
US7489638B2 (en) * | 2004-04-08 | 2009-02-10 | Alcatel-Lucent Usa Inc. | Scheduling with delayed graphs for communication networks |
US7720382B2 (en) * | 2004-04-16 | 2010-05-18 | Alcatel-Lucent Usa Inc. | Time-domain wavelength interleaved network with communications via hub node |
GB0412847D0 (en) * | 2004-06-09 | 2004-07-14 | Nortel Networks Ltd | Method of applying the radius restricted routing scheme in a communication network |
KR100904003B1 (en) | 2004-06-29 | 2009-06-22 | 노키아 코포레이션 | Control of a short-range wireless terminal |
US7924726B2 (en) * | 2004-07-12 | 2011-04-12 | Cisco Technology, Inc. | Arrangement for preventing count-to-infinity in flooding distance vector routing protocols |
US20060013160A1 (en) * | 2004-07-19 | 2006-01-19 | Haartsen Jacobus C | Peer connectivity in ad-hoc communications systems |
US20060047807A1 (en) * | 2004-08-25 | 2006-03-02 | Fujitsu Limited | Method and system for detecting a network anomaly in a network |
US7413513B2 (en) | 2004-09-10 | 2008-08-19 | Igt | Apparatus and methods for wireless gaming communications |
US7599443B2 (en) * | 2004-09-13 | 2009-10-06 | Nokia Corporation | Method and apparatus to balance maximum information rate with quality of service in a MIMO system |
US7085031B2 (en) * | 2004-09-16 | 2006-08-01 | Canon Kabushiki Kaisha | Optical scanner and image forming apparatus using the same |
US7489635B2 (en) | 2004-09-24 | 2009-02-10 | Lockheed Martin Corporation | Routing cost based network congestion control for quality of service |
KR100703726B1 (en) * | 2004-12-11 | 2007-04-05 | 삼성전자주식회사 | Method for managing neighbor node and determining routing path in mobile ad hoc network, and network apparatus thereof |
US7330736B2 (en) * | 2004-12-17 | 2008-02-12 | Bbn Technologies Corp. | Methods and apparatus for reduced energy communication in an ad hoc network |
US8145201B2 (en) | 2004-12-17 | 2012-03-27 | Raytheon Bbn Technologies Corp. | Methods and apparatus for reduced energy communication in an ad hoc network |
US7525988B2 (en) | 2005-01-17 | 2009-04-28 | Broadcom Corporation | Method and system for rate selection algorithm to maximize throughput in closed loop multiple input multiple output (MIMO) wireless local area network (WLAN) system |
WO2006096097A1 (en) | 2005-03-08 | 2006-09-14 | Telefonaktiebolaget Lm Ericsson (Publ) | Method and arrangement for advanced routing metrics in multihop networks |
US7664055B2 (en) * | 2005-03-21 | 2010-02-16 | Rf Monolithics, Inc. | System and method for synchronizing components in a mesh network |
US8599822B2 (en) | 2005-03-23 | 2013-12-03 | Cisco Technology, Inc. | Slot-based transmission synchronization mechanism in wireless mesh networks |
US7366111B2 (en) | 2005-04-08 | 2008-04-29 | Cisco Technology, Inc. | Arrangement for providing optimized connections between peer routers in a tree-based ad hoc mobile network |
JP2006319934A (en) * | 2005-05-11 | 2006-11-24 | Waimachikku Kk | Wireless network node |
US20070070983A1 (en) * | 2005-09-28 | 2007-03-29 | Bbn Technologies Corp. | Methods and apparatus for improved efficiency communication |
US7583654B2 (en) | 2005-12-28 | 2009-09-01 | Honeywell International Inc. | Sub-frame synchronized multiplexing |
US20070153731A1 (en) * | 2006-01-05 | 2007-07-05 | Nadav Fine | Varying size coefficients in a wireless local area network return channel |
US7742399B2 (en) | 2006-06-22 | 2010-06-22 | Harris Corporation | Mobile ad-hoc network (MANET) and method for implementing multiple paths for fault tolerance |
US7924728B2 (en) | 2006-08-25 | 2011-04-12 | Raytheon Bbn Technologies Corp | Systems and methods for energy-conscious communication in wireless ad-hoc networks |
US8149716B2 (en) | 2007-08-20 | 2012-04-03 | Raytheon Bbn Technologies Corp. | Systems and methods for adaptive routing in mobile ad-hoc networks and disruption tolerant networks |
-
2007
- 2007-08-24 US US11/895,608 patent/US7924728B2/en active Active
- 2007-08-24 WO PCT/US2007/018691 patent/WO2008027294A2/en unknown
- 2007-08-24 US US11/895,527 patent/US8149733B2/en active Active
- 2007-08-24 WO PCT/US2007/018721 patent/WO2008027310A2/en active Application Filing
Cited By (11)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US7957418B2 (en) | 2007-07-31 | 2011-06-07 | Research In Motion Limited | Data burst communication techniques for use in increasing data throughput to mobile communication devices |
EP2266259A2 (en) * | 2008-04-11 | 2010-12-29 | Nokia Siemens Networks OY | Network node power conservation apparatus, system, and method |
EP2266259A4 (en) * | 2008-04-11 | 2012-10-03 | Nokia Siemens Networks Oy | Network node power conservation apparatus, system, and method |
WO2014085142A1 (en) * | 2012-11-30 | 2014-06-05 | Qualcomm Incorporated | Systems and methods for synchronization of wireless devices in an ad-hoc network |
US20140153440A1 (en) * | 2012-11-30 | 2014-06-05 | Qualcomm Incorporated | Systems and methods for syncrhonization of wireless devices in an ad-hoc network |
CN104823495A (en) * | 2012-11-30 | 2015-08-05 | 高通股份有限公司 | Systems and methods for synchronization of wireless devices in ad-hoc network |
US9307507B2 (en) | 2012-11-30 | 2016-04-05 | Qualcomm Incorporated | Systems and methods of selective scanning for ad-hoc networks |
US9386551B2 (en) | 2012-11-30 | 2016-07-05 | Qualcomm Incorporated | Systems and methods for synchronization of wireless devices in an ad-hoc network |
CN103716137B (en) * | 2013-12-30 | 2017-02-01 | 上海交通大学 | Method and system for identifying reasons of ZigBee sensor network packet loss |
EP3656071A4 (en) * | 2017-07-20 | 2021-04-21 | Itron Networked Solutions, Inc. | Compensating for oscillator drift in wireless mesh networks |
WO2021053263A1 (en) * | 2019-09-18 | 2021-03-25 | Wirepas Oy | A decentralized synchronization solution for wireless communication networks |
Also Published As
Publication number | Publication date |
---|---|
WO2008027310A2 (en) | 2008-03-06 |
US20080049620A1 (en) | 2008-02-28 |
US20080232344A1 (en) | 2008-09-25 |
WO2008027310B1 (en) | 2008-08-21 |
WO2008027310A3 (en) | 2008-07-10 |
US7924728B2 (en) | 2011-04-12 |
US8149733B2 (en) | 2012-04-03 |
Similar Documents
Publication | Publication Date | Title |
---|---|---|
WO2008027294A2 (en) | Systems and methods for synchronizing communication networks | |
US7496059B2 (en) | Energy-efficient medium access control protocol and system for sensor networks | |
Rodoplu et al. | An energy-efficient MAC protocol for underwater wireless acoustic networks | |
EP2139166B1 (en) | method and device for time synchronization in a TDMA multi-hop wireless network | |
US8824449B2 (en) | Synchronization of broadcast-only wireless networks | |
CN101002436A (en) | Wireless communication system with channel hopping and redundant connectivity | |
EP2195949B1 (en) | Method, computer program product and system for the tick synchronization of nodes in a wireless multi-hop network | |
JP4919204B2 (en) | Sensor network system and media access control method | |
EP1886415A2 (en) | Communicating over a wireless network | |
Leidenfrost et al. | Firefly clock synchronization in an 802.15. 4 wireless network | |
Casari et al. | A detailed simulation study of the UWAN-MAC protocol for underwater acoustic networks | |
JP4536771B2 (en) | Apparatus for synchronizing a first transmitting or receiving device to a second transmitting or receiving device | |
TWI733177B (en) | Low-power wireless mesh network | |
Magzym et al. | Synchronized ESP-NOW for Improved Energy Efficiency | |
Ruzzelli et al. | MERLIN: A synergetic integration of MAC and routing protocol for distributed sensor networks | |
JP7003384B2 (en) | Multi-hop relay system, communication method, and communication device | |
Brzozowski et al. | Completely distributed low duty cycle communication for long-living sensor networks | |
Lemmens et al. | Network-wide synchronization in wireless sensor networks | |
Sheikh et al. | Fair scheduling algorithm for wireless sensor networks | |
Zhang et al. | A Lightweight Time Synchronisation for Wireless Sensor Networks | |
Chen et al. | Synchronization considerations for real-time wireless sensor and actuator networks | |
Shinde et al. | An energy efficient critical event monitoring routing method for wireless sensor networks | |
US20230292265A1 (en) | Synchronising network nodes | |
US20230239925A1 (en) | Scheduling system and method | |
Mirabella et al. | Improving the dynamic continuous clock synchronization for WSNs |
Legal Events
Date | Code | Title | Description |
---|---|---|---|
121 | Ep: the epo has been informed by wipo that ep was designated in this application |
Ref document number: 07837282 Country of ref document: EP Kind code of ref document: A2 |
|
NENP | Non-entry into the national phase |
Ref country code: DE |
|
NENP | Non-entry into the national phase |
Ref country code: RU |