CA1218114A - Deterministic multi-access method for a decentralized mobile radio system - Google Patents
Deterministic multi-access method for a decentralized mobile radio systemInfo
- Publication number
- CA1218114A CA1218114A CA000461644A CA461644A CA1218114A CA 1218114 A CA1218114 A CA 1218114A CA 000461644 A CA000461644 A CA 000461644A CA 461644 A CA461644 A CA 461644A CA 1218114 A CA1218114 A CA 1218114A
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- Canada
- Prior art keywords
- station
- channel
- calling
- control
- control channel
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W74/00—Wireless channel access, e.g. scheduled or random access
- H04W74/08—Non-scheduled or contention based access, e.g. random access, ALOHA, CSMA [Carrier Sense Multiple Access]
- H04W74/0808—Non-scheduled or contention based access, e.g. random access, ALOHA, CSMA [Carrier Sense Multiple Access] using carrier sensing, e.g. as in CSMA
- H04W74/0816—Non-scheduled or contention based access, e.g. random access, ALOHA, CSMA [Carrier Sense Multiple Access] using carrier sensing, e.g. as in CSMA carrier sensing with collision avoidance
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W74/00—Wireless channel access, e.g. scheduled or random access
- H04W74/08—Non-scheduled or contention based access, e.g. random access, ALOHA, CSMA [Carrier Sense Multiple Access]
- H04W74/0866—Non-scheduled or contention based access, e.g. random access, ALOHA, CSMA [Carrier Sense Multiple Access] using a dedicated channel for access
- H04W74/0875—Non-scheduled or contention based access, e.g. random access, ALOHA, CSMA [Carrier Sense Multiple Access] using a dedicated channel for access with assigned priorities based access
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- Engineering & Computer Science (AREA)
- Computer Networks & Wireless Communication (AREA)
- Signal Processing (AREA)
- Mobile Radio Communication Systems (AREA)
- Small-Scale Networks (AREA)
Abstract
DETERMINISTIC MULTI-ACCESS METHOD FOR A
DECENTRALIZED MOBILE RADIO SYSTEM
Abstract of the Disclosure A mobile radio system uses a predetermined number of control channels over which a hand-shake routine is per-formed to determine called station availability, before one of a limited number of talk channels (local and repeater) is assigned for communication between a calling and the called station. After locating an idle talk channel (local channels are searched first), the control channel to which the called station is predeterminedly assigned is attempted to be accessed.
Transmission times on the control channel are a function of the called station's identification code, thus creating a logical ring. Provision is made for message based priorities, emergency numbers and high priority for stations having exper-ienced a previous unsuccessful attempt to access a control channel.
DECENTRALIZED MOBILE RADIO SYSTEM
Abstract of the Disclosure A mobile radio system uses a predetermined number of control channels over which a hand-shake routine is per-formed to determine called station availability, before one of a limited number of talk channels (local and repeater) is assigned for communication between a calling and the called station. After locating an idle talk channel (local channels are searched first), the control channel to which the called station is predeterminedly assigned is attempted to be accessed.
Transmission times on the control channel are a function of the called station's identification code, thus creating a logical ring. Provision is made for message based priorities, emergency numbers and high priority for stations having exper-ienced a previous unsuccessful attempt to access a control channel.
Description
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RD-14,728 DETERMINISTIC MUL~I-ACCESS METHOD FOR A
Decentralized MOBILE RADIO SYSTEM
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~dckground of the invention This invention relates to date transmission systems and more p3rtlcularly to a deterministic (i.e.
delays to access d channel are limited or bounded) multi-access method for accessing d 'control channel of a decentralized mule radio system before a voice channel us permitted tug be accessed, herein the system includes a base radio station, d repeater station and one or more mobile or portable radios among which data may be transferred. Each base Stalin, repeater station and rudely comprises a eransmleter and d receiver or a trays-clever. Several known multl-access methods are described in "Mult~access Protocols in Packet Communication Systems"
- foe. Tobago, IEEE Transactions on Communications, Yolk COMMA, No. 4, p. 468 (1980) thereinafter Tob~gi].
In some communication systems, such as TALENT
network of Talent Corporation and others using the X.25 protocol of Internatlondl Consultative Committee or Tote-graph and Telephony tCCITT), a galling station and d called station perform d handshake routine ( i ye. tr~nsm~sslon of a call request and d` call accept packet, respectively to de~ermlne If the called station Is free to accept an incoming call before a virtual c1rcult can be sex up for data trays-m~sslon between the culling and called station. It is to be understood that the terms data channel, tat k channel, .
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ROD 14,728 and voice channel as used herein are interchangeable and indicate that either voice (encoded voice) and/or data may be transmitted over the channel.
In mobile radio systems random multi-access protocols, such as described in Tobago, swooper, about p. 471, have been used. However, only about 18 percent of maximum channel utilization is possible in such a system. A variation allows only about 36 percent of maximum channel utilization and requires synchronization of all transmitters. If the load, i.e. number of stations attempting to access a control channel, exceeds the allowable utilization, the control channel throughput decreases and may drop to zero, even if a voice channel is idle.
Another possible protocol is a token passing scheme (for one type see Tobago, p. 483), i.e. permitting a station to transmit only during the interval it controls the -token. However, a token passing scheme is very difficult to implement for a decentralized system. Among the problems of using a token passing scheme in a mobile radio environment are the following: 1) Only a portion of all stations, i.e. mobile and base, assigned to I a logical ring may be active (i.e., -turned on) and polling to determine active stations takes too long (a logical ring comprises physical units, such as stations, having a logical number assigned to each unit. The units are operated in a ring I configuration (which may not be the same as physical arrangement or interconnection of -the units) based on their assigned logical number in order to provide a modular type of oppression; 2) there is no centralized control or monitor to administer the z _ -RD-14,728 system, i.e. find lost tokens, determine which stations dye dative, provide an up-to-date directory, e.g. in which cell a mobile station is presently located. (A
cell is a geographical area within which a logical ring 5 exists and stations physically located therein can hear each other's transmission via a repeater, i.e., the area over which reception from a repeater us possible); 3) it us not possible for all active stations to receive all I` packet transmissions due to propagation distance limitations;
4) a specific predetermined control channel frequency is typically assigned to each mobile and base receiver to monitor whereas each mobile and base transmitter can typically transmit at all control channel frequencies, and thus it is not possible to predict the level of usage lo of each control channel at any instant; 5) if a called station is not activity so that a call accept or call reject (busy) packet is not received by the calling station, then the calling station typically assumes that a coll~ston with its call request packet has occurred and thy calling station subsequently attempts to regain access to the control channel, resulting in undesirable increased control channel load.
Consider a hypothetical mobile radio commune-ovation system employing a carrier sense multiple access COMA (see Tub, swooper, page 471) protocol over a control channel, before access to a voice channel is per-muted Assume that a an instant during a perk hour all I' voice channels are busy and there are N stations, which P are not transmuting but desire to transmit a control I packet, wafting in a control packet queue. Also assume I, that the voice channel queue stations desiring access ::
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RD-14,728 Jo to a voice channel) is growing at the rate of m stations I` per second. of T seconds idler a voice channel becomes !; aVdlldble, there will be M N m x T stations contending for d control channel in order to gain access to the free voice channel, either immediately or seconds later, where t is d fixed number used by all busied out stations.
Thus all M packets will collide with each other. Moreover, if q retransmission are permitted after being unsuccessful 'I in securing a voice channel then the number of control IO packets in the control packet queue may eventually reach 'I q x M packets, while the voice channel queue is still growing at the rate of m stations per second. The system would block, i.e. free control channels could not be accessed, for an indeterminate period of time despite one or more voice channels being free.
One method for avoiding some of the problems experienced by the system described in the previous paragraph is to use d p - Persistent Carrier Sense ~`~ Multiple Access protocol (see Tobago, swooper, p. 472). In Jo 20 accordance with this protocol, when a voice channel becomes available, M stations transmit with a probability of p dud do not transmit Whitehall a probability of (l - p).
in order to have one successful transmission, i.e. one station gain access to a control channel, the men of the binomial probability distribution must be equal to one, lye. p l/M. However, is very d~fflcult to accurately estimate the value of M on a comply en decentrdl i Ted t communication system since there is by definition no I centralized authority to determine who was involved in a collision and which stations of all possible stations are included in M at any instant, eye. wish stations are trying to transmit.
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RD-1~,728 Jo 'I A more advanced protocol, carrier sense multiple access with collision detection (CSMA/CD) ;` tree Tobdsi, , p. 473), requires that a station I` back-off, i.e. wait a predetermined interval after S experiencing an unsuccessful attempt (e.g. collision Wylie another packet, failure to receive a call accept or call reject packet) to access a control channel, before again trying to gain access to the control channel. This back of procedure penalizes the It unsuccessful station since stations newly desiring to gain access to the control channel Jay be successful during the back-off interval of the unsuccessful station. It would be desirable to provide priority status to an unsuccessful station such that all, IS unsuccessful stations are permitted access to the control channel before any station not having expert fenced an unsuccessful attempt is permitted to try to gain access to the control channel.
, Accordingly, it is an object of the present, 20 invention to provide a determln~stic control channel dccess~ng scheme for a mob radio environment allowing up to about a percent control channel utilization.
~,~ Another object is to provide priority access to a control channel for emergency numbers such as police, fire department, ambulance, etc.
5~111 another object us to provide priority , access to a control channel for stations having had an unsuccessful attempt to gain access to the control channel.
I, Yet another object is to minimize the number ~.~
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RD-14,72a Jo of collisions which result from inability to detect all transmissions by all stations.
grief Descrle~ion of the Invention The method of the present invention provides access to one of a plurality of data channels of a decent trellised Rudy system comprising d plurality of station wherein each station is assigned to monitor one of a plurality of control channels in order to perform d hand-I, shake routine between d galling station and a called . lo station of the system o'er the control channel assigned to the called station, before es~ab7ishing a communication fink between the calling and called station over the one of the plurality of data channels.
A walling station searches for and reserves an idle data channel. There are two types of deed channels, local and repeater. Local data channels are searched first for an idle channel and if none is found I' repeater data channels are searched. After locating an idle data channel, the calling station busies out or 20 reserves the idle channel by transmitting a tone and then monitors the control channel assigned to the called station.
Transmissions received by the calling station over the control channel being monitored are decoded in order to determine which station on the logical rung had just had control of the token so that the galling station's time I! to start transmission can be d~term1ned in order to fit the galling station unto its assigned position in the l og1cal rung .
If a no s pro n so i s fee e f v Ed f rum the c at l Ed I station ~ndfcating the called station is ready and able to accept a call, then a communtca~ion link is established I: over the data channel previously reserved. If no response I" 6 -I , .
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RD-14,728 Jo is received or of the response indicates the called station is busy, another attempt is made to try to establish d communication link.
Provision is made to provide high priority I 5 to stations calling emergency numbers and to stations having previously experienced an unsuccessful attempt, `` i.e. busy indicdt~on or no response received, to establish a communication link.
The features of the invention believed to be .
novel are set forth with particularity in the appended claims. The invention itself however, both do to I` organization and method of operation, together with Jo further objects and advantages thereof, may best be I understood by reference to the detailed description I` 15 taken in connection with the accompanying drawing.
Yo-yo Brief Description of_the_Drawin~
I! Fig. 1 is a schematic representation of a data transmission system of the general type with which the present invention may be used.
Fig. 2 is d schematic representation of channel frequency allocations useful with the accessing scheme of the present invention.
Fig. 3 is a table of control channel assign-mints useful with the accessing scheme of the present lnvent~on.
Fix. 4 is a b10ck diagram of a transceiver ;` useful with the accessing scheme of the present invention.
'j Figs. 5-g are flow diagrams of a program Jo 30 useful with a microprocessor employed in the present in~entlon.
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Detailed description Referring to Fig. 1, d typical radio data c~mmunicdtion system in which the present invention may be employed is shown. The data communication system S includes a base station 30. The base station directly communicates with one or more mobile or portable stations 10l - lo over local talk radio channels and indirectly communicates through repeater 50 over repeater talk radio channels. Similarly, any of mobile StdtjOnS 101 - 10N may directly communicate with any other of mobile stations 101 - JON over local talk radio channels and indirectly communicate through repeater 50 over repeater talk radio channels Further, base station 30 Jay be connected to d telephone 40, so that telephone calls may be automatically made on the public switched telephone network through base station 30 from mobile stations 10 without user intervention do base stall on 30.
Typically direct mobile to mobile commun~cat10n Noah of sight (LOST range is bout 2-3 miles, which range is limited predominately by antenna height, generally about 10 feet maximum. Direct mobile to base commune-cation LOS range it about 3-5 miles since generally a higher antenna, say about 26 feet, is available at the base station. It is anticipated that repeaters would be located on high ground, such as a hill, or atop a tall building, such that maximum direct mobile to repeater communication L05 range is about 15 wiles, shown as a boundary 60 of cell 70 served by repeater 50. Further there are 9enerdlly a limited number of channels within a frequency band which mu be allocated between direct talk channels, repeater talk channels : 8 ~Z~8~
RD-l4,728 and control channels, ire. channels over which d handshake routine is performed in order Jo assign available idle or free talk channels to mobile 101 - JON and base 30 stations requesting a talk channel.
S Because LOS range limitations of the system permit channel reuse within a cell served by repeater 50, all requests for an idle channel are first attempted to be satisfied by assignment of d local talk channel (LTC~, thus conserving use of the llm1ted number of repeater talk channels. Ass19nments of local talk channels are based on a detem1nat10n at each respective calling stat10n of whether there is an idle local talk channel. An idle channel is busted out or reserved, i.e. d tone on the idle channel is transmitted by the galling station, by the culling station before the control channel access procedure (hand-shake routine) is 1nitlated.
As an example of channel reuse, consider the situat10n where there are two pairs of mobile stations Al, A, and By, By, respectively, with station Al disarraying to call station AZ and station 81 desiring to call By.
further assure that members of a pair are within direct communication LOS range of equal other, that neither member of pair A is within direct communication LOS
range of either member of pair B and that both pairs are located within the same cell, eye. within LOS range of the same repeater. (These location requirements may be satisfied due to the Sue of LOS range limitations dls-cussed above). If station Al first establishes a radio 1 ink with station A over direct talk channel Z, and then station 31 attempts to contact station By, dlrec~ talk channel Z may at so ye assigned to the station By to ~2~L8~
RD-1~,728 station By radio link since as far as stations By and By can determine channel Z is idle. Thus, depending on the location of the calling and called stations within the cell, and the direct LOS range limitations of the respective stations, it is possible to have multiple assignments of the same drake talk channel within d cell without radio frequency interference occurring between the commonly assigned parties.
- A calling station first tries to locate a local talk channel and if a local talk channel is not ava11able (eye. none are idle), then the galling station automatically tries to access an idle repeater talk channel (RTC) to complete the communication link to the called station. Once an idle LTC or RTC us lo found, the calling station busies out the idle channel by transmitting d tone over the idle channel and then initiates the control channel access (handshake) routine to try to access the control channel of the called stat10n. If no idle local or repeater elk channel us found after d predetermined number of attempts, then the calling station must re1n1tldte the call process.
Callers who have had a previous unsuccessful attempt to gain access to a control channel or to receive a response from the called station over the control channel are given pretreat for control channel access.
Prison it also mode for callers who are trying to reach emergency numbers and other preident~fied high prowar numbers to have mud access to the system without waiting for previously unsuccessful RD-14,7Z8 callers to ter~indte their ~ry-agdin routines.
Shown in Fig. 2 is a predetermined assignment of 150 channels in the 900 MHz band with each channel Hoyle d bandwidth of 30 kHz. The assignment permits use of separate transmit and receive frequencies with a 45 MHz spacing between frequency pairs to provide full duplex operation in the direct talk mode. The repeater talk mode is two frequency simplex. The single party lone channel is operator selectable and permits the in station to perform in a CB-like mode of operation. There is no repeater mode for the party 1 no channel.
Although spec~f1c frequencies and number of channels have been provided by way of example, it is to be understood that the accessing scheme of the present invention us applicable for assigning idle talk channels and for providing control channel access to any decent trellised system regardless of the transmit and receive frequencies, channel bandwidths, number of channels, simplex or duplex operation, mobile or stationary stations and direct or repeater operation.
Shown in Fig. 3 is d possible arrangement of control channels to which the transceiver at d station is tuned when no involved in a communication link. A
control chinless predeterminedly designed to each station. Typically, the assignment of a control channel may be determined by the three least significant digits of the Titan identlficat~on number in order Jo avoid having assignments concentrated on a few of the available control channels. The std~lon~s identification number I or code is predeterminedly assigned (analogous to assign-mint of telephone number) and must be used for all calls I. I
RD-14,728 to the station, except for calls over the party line channel. Of course, other pre-identified group or groups of numbers within d station's identification number my be used to determine which control channel 5 d destination station is monitoring.
Idle local or repeater talk channel selection is accomplished through exchange of digitally encoded command messages or data packets between the source killing) and destination Cody) stations over d control on channel. During talk channel selection, the source station acts as a "master" and the destination station as a "slave". When seeking to complete d communication link over a direct talk channel, the source station transmits a command message on the control channel in the high band which the destination station is monitoring and the destination channel responds on the corresponding control channel in the low band. when attempting to complete a communication link over d repenter talk channel, the source station transmits d command message to the repeater on the control channel in the low band which the destination channel is monitoring and the repenter transmits the command message to the destination station on the corresponding high bond control channel.
Referring to Fix. 4, a block diagram of apparatus usual with the present invention us shown.
The apparatus illustrated in Fig. 4 is situated do etch respective base and mobile station of the system.
Microprocessor 35 has an output connected Jo an input of transceiver 33 and a first input connected to an output of transceiver 33. A second input of micro-processor 35 is connected to an output of input/output (I/0) control circuitry 37.
RD-14,728 Microprocessor 35 may be a type 8051 into-grated circuit manufactured by Intel, Inc., Santa Clad, California, or eke like. A type 8051 integrated circuit includes d read only memory PROM) wherein programs, such do those represented by the flow diagrams of figs. 5-9, may be stored. If the microprocessor selected does not include d ROM, then one may be provided do is known in the art. 1/0 control circuitry 37, comprises controls (not shown), such as switches, for operator selectable functions, e.g. call initiate;
party line select, repenter assignment and called (destination) station identification.
Microprocessor 35 provides digitally encoded signals to transceiver 33 for assigning appropriate frequencies thereto and transceiver 33 provides micro-processor 35 with digitally encoded signals indicating the status of a called station, i.e. whether a response has been received over a control channel during the hand-shaking routine and if so, the type ox response, e.g. station idle, station busy.
Referring to Fig. 5, a start-up routine of the main program useful for the present invention is shown. Step 100 is executed to reset all counters end timers of the calling station each time the main pro-US gram of the calling station is accessed. Proceeding to step 101 the busy out counter is set to zero.
Execution of step 102 initiates a search for an idle local talk channel LO If no idle LTC is detected, the calling station at step aye calls the calling stoutness assigned repeater which commences a search I
-RD-14,72B
for dun idle repeater talk channel (RTC). If no idle RTC
is detected, step 112 increments the busy out counter by l. Execution of step 114 determines whether the busy out counter hods reached a count of 4. If the busy out counter has retched d Colette of 4, at step 116 a time owe timer To is set to predetermined value. The value to which time out timer To Is set, typically 3-5 seconds, is determined by the time interval it is desired to wait before permitting the program to repeat step 101 in order to attempt to detect an idle LTC or RTC after having had the number of unsuccessful attempts used as the test by test 114, to find an idle LTC or RTC. Execution of step 118 causes the program to welt by looping through step 118 until time out timer To has run out, at which moment the routine repeats step 101. Of course, tome out timer To may by set arbitrarily small, such do zero, so that no appreciable delay exits between execution of step 116 and the return to step 101 from step 118 of the routine.
Also, a greater or lesser number than four may be tested for by step 114 should it be desired that more or fewer, respectively, chances be given to detect an idle LTC
or RTC. If the busy out counter To has not reached the test number when step 11~ is executed, the wait time Two is computed at step 120 before execution of step 102 can be repented. Wait time Two is determined by the q n Two a + NO x Ten, wherein a is d constant to ensure an inlt1al adequate back off time for low Lungs, NO is the LUNG (logical unit number), i.e. the lust three digits of the addressee's or called station's Identification number, and Ten is the back off time, on milliseconds.
Back off time non generally increases aster each unsuccessful attempt to find an idle LTC or RTC. For example, back off :
I
RD-14,728 lime Ten, wherein n represents the number of unsuccessful attempts, eye. number In the busy out counter, may assume values of lo 20, 40, and 80 milliseconds, respectively, for each successive unsuccessful attempt to detect an idle S LTC or RTC. Execution of step 122 sets the writ time timer to the value T determined in step 120. The program then waits by looping through step 124 until the wait time timer runs out at which time the program repeats step 102 to reinitiate the search for an idle LTC or RTC.
If either an idle LTC or RTC is detected do step 104 or step 110, respectively, then step 106 Is performed to busy out or reserve the detected idle channel by trays-milting (TYING) d tone on the channel and the program proceeds to step 150 of the control channel access routine shown on Figure 6. Execution of step lS0 accesses d control channel whose condition (i.e., on use or not in use) is sensed by performing step 152. There are a plurality of control channels and the particular control channel accessed is the one assigned to the addressee station. A typical assignment scheme for a system come prosing five control channels may apportion control channels based on the last three digits (LUNG) of the addressee's identification number (Fig. 3). That is, control channel 1 is assigned to Lung 000 to 199, control channel 2 is assigned to Lung 200 to 399, etc. The program welts by looping through step l54 unwept the accessed control channel is determined to be idle at which lime step 156 is performed to start the cycle lime timer To. Execution ox Steps 158 and 160 involves sensing the control channel and determining if the control channel is idle, respect~lfely. If the control channel I
R0-14,728 is determined to be idle then at step 162 whether cycle timer To has run out is determined. If the cycle time timer has net run out, step l60 is repeated. The program continues to perform steps 160 and 162 until either the control channel is determined to be not idle or the cycle time timer has run out.
If the cycle time timer has run out, the program proceeds to execute step 166. Since the cycle time timer has run out and no packet has been detected, as indicated by the control channel remaining idle during cycle time To interval, at step I66 an assumption is made that d phantom second or lower level priority packet with NO
equal to 000 and d repeater number of the calling station Weds sensed. NO is the LUNG of any packet received from lo a sending station in the system other than the calling station. These assumptions are necessary since there is no central authority in the system to start tokens or to find lost tokens. If the control channel is not idle when step l60 is performed step I64 is executed by decoding and recording the priority, repeater number and S of the packet which was sensed by execution of step 160. Step 168 is then performed to determine of the received packet is a second prowler packet. If it is not a second prorate packet, then step 170 is executed to determine of the packet the calling station is attempt else to send is a retransmiss10n. If the calling station packet is not a retransmission, step 150 is repeated, and it it is a retransmission, step 172 is executed to determine whether the repeater number of the packet sensed prom the sending station us the same as the repeater number of the last transmission prom the calling .
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R0-14,72 station. If these repeater numbers are not the same indicating the sending station is not d member of the some logicd1 ring as the calling station, step 150 is repeated.
S After perfor~lng step 166, determln~ng that the received packet it a second priority packet (step 168) or determining that the repeater number of eke packet sensed us the same as the repeater number of the last packet the calling station transmitted (step It I72), the program proceeds to step 200 (Fig. 7).
There are two levels of control packet pro-rlty in the system. The priority is encoded into a control packet using one bit at a predetermined toga-lion. Should more than two priorities be desired then more than one bit is required. rho first or higher priority includes control packets trying to gain access to an emergency number, such do pot ice station, hospital, fire department, etc., and retransmlss~on packets, i.e. pockets from a galling stdtlon which previously transmitted a control or retransmission packet but did not receive a response from the called station. Information identifying a retransmission packet us also encoded into toe packet using one Kit at a predeter~lned locution. All other packets have second prorate All packets, including any which have been sensed by execut10n of step 160, tow virtual tokens at a distance (token time interval) which is a function of the walk tire (defined below) between the station or~glnatlng the pocket swindling station) and the calling station. Furthermore, the priority ox the token is 3LZ~ 4 RD-14,72 the seine as the priority of the packet which tows it.
A station is allowed to transmit d control packet only while it controls a token. There dye two rules associated with gaining control of a token. The first rule is that for- d station to be able to use d first priority token it must have a first priority packet to transmit (steps 160, 164, 168, 170). The second rule, which applies to all priorities, is that in order for a station to receive a token, the time (token time interval) between the end of the packet and the token must not be invaded by another packet, lye. no packet from a sending station sensed in the token time interval (steps 160, 162).
Rerolling to Fig. 7, the control packet transmit routine is shown. Execution of step 200 determines whether the LUNG of the calling station (NT) is less than or equal to the LUNG of the sensed packet (No) from the sending station or phantom packet, lye. on. If NT is not less than or equal on to No, then at step 204 transmit timer TX is set equal to tot NO 1) x To which is the token wait time or interval, wherein To is the decode time, i.e. the time it takes for a station to start trays-milting a packet after receiving the end of a token towing packet. Decode tire To is also the walk tome between two adjacent stations on the logical ring. It NT is less than or equal to No, the transmit timer TX at step 202 is set to a token wait time or interval equal to tam NO NT I x rod wherein NM represents the number of stations on the logical ring. If Lung are the last Roy digits :`
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lo RD-14,728 of addressee's unique identification code then NM is equal to 1000, i.e. It .
In a retransmission, the retransmission control packet us always identified do a first priority pocket.
As a result, at least one sweep around a logical ring is reserved for all first priority packets if a retransmission control packet is sent. In this manner, it is possible to eliminate from the control packet queue all stations which previously experienced a collusion or did not receive a response to a control packet, before permitting new stations to try to gain access to the control channel (unless, of course, a new station is trying to call an emergency number, i.e. first priority). To permit flushing out to occur without further collisions, decode time To, used in retransmission, is mode a random variable with a typical mean lTdn) as follows:
Tdl 2 1 msec.
do 2 msec.
Td3 4 msec.
do msec.
wherein n is the number of attempts for retr~nsmissions of the same control packet, for use by steps 202 and 20~. Establishing a random variable having d predator-mined mean is known in the art and my be performed by a local communications controller 82536~ manufactured by Intel, or the like.
After establ wishing the token wait eye, step 206 is performed to sense whether the control channel is idle. It the control channel us idle, step 210 is executed to determine If transmit titer To has run out. If transmit timer lo has not run out step 208 lug - - -RD-14,728 is repented and the program continues to loop through steps 208 and 210 until transmit timer TX runs out, at which time step 212 is performed to determine if the number or unique ident1ficdtion code of the called station is an emergency number. If the number being called is not an emergency number, step 214 us executed to stop transmitting the busy tone which was generated by execution of step 106 fig. 5) on the Arc or RTC
determined to be idle by step 104 or 110 (Fig. 5), It respectively. Step 216 is performed to transmit the control packet of the calling station and, if it is a retransmission, to set the priority by e of the control packet. The program then waits by looping through step 218 until the transmission of the control packet is completed at which tome step 220 us executed to set a receive timer TRY for receiving a response packet from the called station and step 222 is executed to sense the return control channel. Receive timer TRY is generally set to the maximum time anticipated for receiving a response packet on the return channel from a called stdt1On.
If the control channel is not idle when step 208 is performed, the program proceeds to step 164 (Fig. 6) which it executes in accordance with the procedure herein before described, in order to try to obtain the token towed by the packet received from d sending station. If the number being calved us an emergency number, then the execution of step 212 causes the program to proceed to step 300 (Fog. 9) to begun execution of the routine for emergency numbers which is described on more Dwight below.
Jo RD-l4,728 Referring to Figure I, the control packet receive routine is shown. After executing step 222 (Fig. 7), the program performs step 250 to determine of d response hods arrived on the return channel from S the called station. If a response is sensed and it indicates that the called station is free to accept a call, then a communication link is established between the Cal 11ng and called station over the LTC or RTC
previously determined to be idle by step 104 or step It 110 (Fig. 5), respectively. The response may alter-natively indicate that the called station is busy, i.e.
has established or is trying to establish a communication link. After r~ce1v1ng any response, step 252 is executed eon reset all program counters. IF a response has not arrived on the return channel when step 250 is performed, step 254 us executed to determine if receive timer TRY
has run out. If receive timer TRY has not run out, the program repeats step 250 and continues to loop through steps 250 and 254 until the receive timer runs out, at which lime step 256 is executed to incre~enk the retrains-mission counter. Step 258 us then performed to determine if the retransmission counter has reached a count of 4.
If the retransmission counter has reached 4 (a greater or lesser number may be used as desired) step 260 is performed to set the time out timer To to a value which equals the time the program must wait before the star up routine of Figure 5 is repeated. After setting the time out timer To the program welts by looping through step 262 until the time out timer runs I out, at which tome step 101 1 s repeated (fix. 5) to reinitiate the start up routine.
Jo -ROY
Lack of d response from d called station to a control packet my indicate: two or more stations on d liquidly channel had the same LUNG i.e. they all attempted to reach stations having the same lust three digits of identification code; the called stations transceiver weds not turned on; two or more stoutness were unable to hear each others' transmissions -- they obtained and used the same token from the same packet -- a collision (i.e., trays-missions from two or more stations within the same time interval and within receive range of a receiving station such that the integrity of the detected transmission do the receiving station cannot be assured) between control packets occurred; a station obtained tokens from two or more logical rings at different times.
A logical rirlg us formed in a cell wherein all stations can hear transmissions from the same repeater.
There may be stations situated near the reception fringes of a cell. These stations can generally hear transmissions from two or more repeaters. The encoding of a repeater identification number into control pockets and determining whether the repenter number of the received packet (which is also the repeater number of the token) from a sending station is the same do the repeater number of a calling station (Fig. 6, step l72~ before allowing the calling station to obtain the packet minimizes the number of got-lesions due to obtaining tokens from Gore than one logical ring) by forcing a station to remain within one logical ring.
In the case of a Molly station moving from one cell to another, an operator must change the assigned repeater ~dentificatton at It control 37 fig. 4) of the mobile station.
If the retransmission counter has not reached 4 when step 258 is performed, step 264 is performed to determine if the LTC or RTC do determined by step 104 or I10 (Fig. 5), respectively, is still idle. If the I
. .
~8~3~4 RD-14,728 LTC or RTC is not still idle, step 10l fig. 5) is repeated to reinitiate the start up routine. If the LTC or RTC is determined at step 264 to still be idle, step 266 busies out the LTC or RTC by transmitting a tone and step lS0 (Fig 6) us repeated to reinitiate the control channel access routine.
Referring to Figure 9, the routine for galling emergency numbers it shown. If at step 212 (Fig. 7) it is determined that the calling station is calling an emergency number, the program proceeds to step 300 to set the priority bit in the control jacket of thy I no station. Step 302 is performed to set the emergency packet top) counter To to Nero and execution of step 304 increments the emergency packet counter To. Execution of step 306 determines if the emergency packet counter has reached 6 Ed greater or lesser number may be used as desired). If it has reached 6, then execution of step 260 (Fig. 8) sets the time out timer To and the program waits by looping on through step 262 unwept the tome out timer To runs out.
After the time out timer runs out, step 10l (Fig. 5) is repeated to reinitiate the start up routine.
If the emergency jacket counter has not reached 6 when step 306 is performer, execution of step 312 causes the program to stop transmitting the busy out tone that was generated by execution of step 10~
Fog 5), on the LTC or RTC determined at step 104 or 110 (F19. 5), respectively to be idle. Execution of step 314 causes the emergency packet to be transmitted and execution of step 316 sots the receive timer TRY
for receiving a response packet as herein before ..Z~8~
RD-I~,728 described. Execution of step 318 senses the return channel and execution of step 320 determines whether d response has arrived on the return channel from the emergency station. If execution of step 320 results in sensing a response on the return channel and the response indicates that the emergency station is free to accept a call, then a communication link is established between the calling and emergency station, over the idle LTC determined at step 104 or idle RTC determined at step II0 (Fog. 5). The response may alternately indicate that the emergency stat10n is busy, i.e.
has established or us trying to establish a communication fink. Aster receiving any response, step 322 is per-formed to reset all counters. If a response has not been resoled from the emergency station when step 320 is performed, step 324 is performed to de~ermlne lo resolve timer TRY has run out. If the receive timer has not run out, step 320 is repeated and the program continues to loop through steps 320 and 324 unwept the receive timer runs out. When the receive timer runs out, step 326 is executed to determine it the LTC or RTC determined in step 104 or step 110 (Fig. 5), respectively, is sly idle. If the LTC
or RTC is not Steele idle the program repeats step 101 (Fig. 5) to reliantly thy start up routine. If the TO or TO d~term1ned to be idle at step lo or step II0 (Fig. 5), respectively, us stilt idle when step 326 is executed the program repeats step 304 and incoherency the emergency packet counter. The program c~ntlnues to loop through step 304 to step 326 until execution of step 306 d~term1nes chat the emergency packet counter has reached 6,-exec~lon ox step 320 ~e~ermlnes that RD-14,728 a response has been received from the emergency station or execution of step 326 determines that the LTC or RTC
is still idle. As indicated do step 306, six attempts are permitted to try to secure d local or repeater talk channel when an emergency number is being culled. Of course, the program may be modified to provide for d greater or lessor number then six attempts.
Thus has been illustrated and described d method for providing deterministic control channel access for a mobile radio environment allowing up to about 80 percent control channel utilization. Further, priority control channel access is provided for emergency numbers and for stations having had an unsuccessful attempt to gain access to the control channel. Add-tonally, the number of collusions resulting from inability to detect all transmissions by all stations has been minimized.
While only certain preferred features of the invention have been shown by way of illustration, many modifications and changes will occur to chose skilled in thy art. It is to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit and scope of the invention.
,
RD-14,728 DETERMINISTIC MUL~I-ACCESS METHOD FOR A
Decentralized MOBILE RADIO SYSTEM
.. .. _ . .
~dckground of the invention This invention relates to date transmission systems and more p3rtlcularly to a deterministic (i.e.
delays to access d channel are limited or bounded) multi-access method for accessing d 'control channel of a decentralized mule radio system before a voice channel us permitted tug be accessed, herein the system includes a base radio station, d repeater station and one or more mobile or portable radios among which data may be transferred. Each base Stalin, repeater station and rudely comprises a eransmleter and d receiver or a trays-clever. Several known multl-access methods are described in "Mult~access Protocols in Packet Communication Systems"
- foe. Tobago, IEEE Transactions on Communications, Yolk COMMA, No. 4, p. 468 (1980) thereinafter Tob~gi].
In some communication systems, such as TALENT
network of Talent Corporation and others using the X.25 protocol of Internatlondl Consultative Committee or Tote-graph and Telephony tCCITT), a galling station and d called station perform d handshake routine ( i ye. tr~nsm~sslon of a call request and d` call accept packet, respectively to de~ermlne If the called station Is free to accept an incoming call before a virtual c1rcult can be sex up for data trays-m~sslon between the culling and called station. It is to be understood that the terms data channel, tat k channel, .
I
ROD 14,728 and voice channel as used herein are interchangeable and indicate that either voice (encoded voice) and/or data may be transmitted over the channel.
In mobile radio systems random multi-access protocols, such as described in Tobago, swooper, about p. 471, have been used. However, only about 18 percent of maximum channel utilization is possible in such a system. A variation allows only about 36 percent of maximum channel utilization and requires synchronization of all transmitters. If the load, i.e. number of stations attempting to access a control channel, exceeds the allowable utilization, the control channel throughput decreases and may drop to zero, even if a voice channel is idle.
Another possible protocol is a token passing scheme (for one type see Tobago, p. 483), i.e. permitting a station to transmit only during the interval it controls the -token. However, a token passing scheme is very difficult to implement for a decentralized system. Among the problems of using a token passing scheme in a mobile radio environment are the following: 1) Only a portion of all stations, i.e. mobile and base, assigned to I a logical ring may be active (i.e., -turned on) and polling to determine active stations takes too long (a logical ring comprises physical units, such as stations, having a logical number assigned to each unit. The units are operated in a ring I configuration (which may not be the same as physical arrangement or interconnection of -the units) based on their assigned logical number in order to provide a modular type of oppression; 2) there is no centralized control or monitor to administer the z _ -RD-14,728 system, i.e. find lost tokens, determine which stations dye dative, provide an up-to-date directory, e.g. in which cell a mobile station is presently located. (A
cell is a geographical area within which a logical ring 5 exists and stations physically located therein can hear each other's transmission via a repeater, i.e., the area over which reception from a repeater us possible); 3) it us not possible for all active stations to receive all I` packet transmissions due to propagation distance limitations;
4) a specific predetermined control channel frequency is typically assigned to each mobile and base receiver to monitor whereas each mobile and base transmitter can typically transmit at all control channel frequencies, and thus it is not possible to predict the level of usage lo of each control channel at any instant; 5) if a called station is not activity so that a call accept or call reject (busy) packet is not received by the calling station, then the calling station typically assumes that a coll~ston with its call request packet has occurred and thy calling station subsequently attempts to regain access to the control channel, resulting in undesirable increased control channel load.
Consider a hypothetical mobile radio commune-ovation system employing a carrier sense multiple access COMA (see Tub, swooper, page 471) protocol over a control channel, before access to a voice channel is per-muted Assume that a an instant during a perk hour all I' voice channels are busy and there are N stations, which P are not transmuting but desire to transmit a control I packet, wafting in a control packet queue. Also assume I, that the voice channel queue stations desiring access ::
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RD-14,728 Jo to a voice channel) is growing at the rate of m stations I` per second. of T seconds idler a voice channel becomes !; aVdlldble, there will be M N m x T stations contending for d control channel in order to gain access to the free voice channel, either immediately or seconds later, where t is d fixed number used by all busied out stations.
Thus all M packets will collide with each other. Moreover, if q retransmission are permitted after being unsuccessful 'I in securing a voice channel then the number of control IO packets in the control packet queue may eventually reach 'I q x M packets, while the voice channel queue is still growing at the rate of m stations per second. The system would block, i.e. free control channels could not be accessed, for an indeterminate period of time despite one or more voice channels being free.
One method for avoiding some of the problems experienced by the system described in the previous paragraph is to use d p - Persistent Carrier Sense ~`~ Multiple Access protocol (see Tobago, swooper, p. 472). In Jo 20 accordance with this protocol, when a voice channel becomes available, M stations transmit with a probability of p dud do not transmit Whitehall a probability of (l - p).
in order to have one successful transmission, i.e. one station gain access to a control channel, the men of the binomial probability distribution must be equal to one, lye. p l/M. However, is very d~fflcult to accurately estimate the value of M on a comply en decentrdl i Ted t communication system since there is by definition no I centralized authority to determine who was involved in a collision and which stations of all possible stations are included in M at any instant, eye. wish stations are trying to transmit.
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RD-1~,728 Jo 'I A more advanced protocol, carrier sense multiple access with collision detection (CSMA/CD) ;` tree Tobdsi, , p. 473), requires that a station I` back-off, i.e. wait a predetermined interval after S experiencing an unsuccessful attempt (e.g. collision Wylie another packet, failure to receive a call accept or call reject packet) to access a control channel, before again trying to gain access to the control channel. This back of procedure penalizes the It unsuccessful station since stations newly desiring to gain access to the control channel Jay be successful during the back-off interval of the unsuccessful station. It would be desirable to provide priority status to an unsuccessful station such that all, IS unsuccessful stations are permitted access to the control channel before any station not having expert fenced an unsuccessful attempt is permitted to try to gain access to the control channel.
, Accordingly, it is an object of the present, 20 invention to provide a determln~stic control channel dccess~ng scheme for a mob radio environment allowing up to about a percent control channel utilization.
~,~ Another object is to provide priority access to a control channel for emergency numbers such as police, fire department, ambulance, etc.
5~111 another object us to provide priority , access to a control channel for stations having had an unsuccessful attempt to gain access to the control channel.
I, Yet another object is to minimize the number ~.~
.
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RD-14,72a Jo of collisions which result from inability to detect all transmissions by all stations.
grief Descrle~ion of the Invention The method of the present invention provides access to one of a plurality of data channels of a decent trellised Rudy system comprising d plurality of station wherein each station is assigned to monitor one of a plurality of control channels in order to perform d hand-I, shake routine between d galling station and a called . lo station of the system o'er the control channel assigned to the called station, before es~ab7ishing a communication fink between the calling and called station over the one of the plurality of data channels.
A walling station searches for and reserves an idle data channel. There are two types of deed channels, local and repeater. Local data channels are searched first for an idle channel and if none is found I' repeater data channels are searched. After locating an idle data channel, the calling station busies out or 20 reserves the idle channel by transmitting a tone and then monitors the control channel assigned to the called station.
Transmissions received by the calling station over the control channel being monitored are decoded in order to determine which station on the logical rung had just had control of the token so that the galling station's time I! to start transmission can be d~term1ned in order to fit the galling station unto its assigned position in the l og1cal rung .
If a no s pro n so i s fee e f v Ed f rum the c at l Ed I station ~ndfcating the called station is ready and able to accept a call, then a communtca~ion link is established I: over the data channel previously reserved. If no response I" 6 -I , .
., .
RD-14,728 Jo is received or of the response indicates the called station is busy, another attempt is made to try to establish d communication link.
Provision is made to provide high priority I 5 to stations calling emergency numbers and to stations having previously experienced an unsuccessful attempt, `` i.e. busy indicdt~on or no response received, to establish a communication link.
The features of the invention believed to be .
novel are set forth with particularity in the appended claims. The invention itself however, both do to I` organization and method of operation, together with Jo further objects and advantages thereof, may best be I understood by reference to the detailed description I` 15 taken in connection with the accompanying drawing.
Yo-yo Brief Description of_the_Drawin~
I! Fig. 1 is a schematic representation of a data transmission system of the general type with which the present invention may be used.
Fig. 2 is d schematic representation of channel frequency allocations useful with the accessing scheme of the present invention.
Fig. 3 is a table of control channel assign-mints useful with the accessing scheme of the present lnvent~on.
Fix. 4 is a b10ck diagram of a transceiver ;` useful with the accessing scheme of the present invention.
'j Figs. 5-g are flow diagrams of a program Jo 30 useful with a microprocessor employed in the present in~entlon.
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Detailed description Referring to Fig. 1, d typical radio data c~mmunicdtion system in which the present invention may be employed is shown. The data communication system S includes a base station 30. The base station directly communicates with one or more mobile or portable stations 10l - lo over local talk radio channels and indirectly communicates through repeater 50 over repeater talk radio channels. Similarly, any of mobile StdtjOnS 101 - 10N may directly communicate with any other of mobile stations 101 - JON over local talk radio channels and indirectly communicate through repeater 50 over repeater talk radio channels Further, base station 30 Jay be connected to d telephone 40, so that telephone calls may be automatically made on the public switched telephone network through base station 30 from mobile stations 10 without user intervention do base stall on 30.
Typically direct mobile to mobile commun~cat10n Noah of sight (LOST range is bout 2-3 miles, which range is limited predominately by antenna height, generally about 10 feet maximum. Direct mobile to base commune-cation LOS range it about 3-5 miles since generally a higher antenna, say about 26 feet, is available at the base station. It is anticipated that repeaters would be located on high ground, such as a hill, or atop a tall building, such that maximum direct mobile to repeater communication L05 range is about 15 wiles, shown as a boundary 60 of cell 70 served by repeater 50. Further there are 9enerdlly a limited number of channels within a frequency band which mu be allocated between direct talk channels, repeater talk channels : 8 ~Z~8~
RD-l4,728 and control channels, ire. channels over which d handshake routine is performed in order Jo assign available idle or free talk channels to mobile 101 - JON and base 30 stations requesting a talk channel.
S Because LOS range limitations of the system permit channel reuse within a cell served by repeater 50, all requests for an idle channel are first attempted to be satisfied by assignment of d local talk channel (LTC~, thus conserving use of the llm1ted number of repeater talk channels. Ass19nments of local talk channels are based on a detem1nat10n at each respective calling stat10n of whether there is an idle local talk channel. An idle channel is busted out or reserved, i.e. d tone on the idle channel is transmitted by the galling station, by the culling station before the control channel access procedure (hand-shake routine) is 1nitlated.
As an example of channel reuse, consider the situat10n where there are two pairs of mobile stations Al, A, and By, By, respectively, with station Al disarraying to call station AZ and station 81 desiring to call By.
further assure that members of a pair are within direct communication LOS range of equal other, that neither member of pair A is within direct communication LOS
range of either member of pair B and that both pairs are located within the same cell, eye. within LOS range of the same repeater. (These location requirements may be satisfied due to the Sue of LOS range limitations dls-cussed above). If station Al first establishes a radio 1 ink with station A over direct talk channel Z, and then station 31 attempts to contact station By, dlrec~ talk channel Z may at so ye assigned to the station By to ~2~L8~
RD-1~,728 station By radio link since as far as stations By and By can determine channel Z is idle. Thus, depending on the location of the calling and called stations within the cell, and the direct LOS range limitations of the respective stations, it is possible to have multiple assignments of the same drake talk channel within d cell without radio frequency interference occurring between the commonly assigned parties.
- A calling station first tries to locate a local talk channel and if a local talk channel is not ava11able (eye. none are idle), then the galling station automatically tries to access an idle repeater talk channel (RTC) to complete the communication link to the called station. Once an idle LTC or RTC us lo found, the calling station busies out the idle channel by transmitting d tone over the idle channel and then initiates the control channel access (handshake) routine to try to access the control channel of the called stat10n. If no idle local or repeater elk channel us found after d predetermined number of attempts, then the calling station must re1n1tldte the call process.
Callers who have had a previous unsuccessful attempt to gain access to a control channel or to receive a response from the called station over the control channel are given pretreat for control channel access.
Prison it also mode for callers who are trying to reach emergency numbers and other preident~fied high prowar numbers to have mud access to the system without waiting for previously unsuccessful RD-14,7Z8 callers to ter~indte their ~ry-agdin routines.
Shown in Fig. 2 is a predetermined assignment of 150 channels in the 900 MHz band with each channel Hoyle d bandwidth of 30 kHz. The assignment permits use of separate transmit and receive frequencies with a 45 MHz spacing between frequency pairs to provide full duplex operation in the direct talk mode. The repeater talk mode is two frequency simplex. The single party lone channel is operator selectable and permits the in station to perform in a CB-like mode of operation. There is no repeater mode for the party 1 no channel.
Although spec~f1c frequencies and number of channels have been provided by way of example, it is to be understood that the accessing scheme of the present invention us applicable for assigning idle talk channels and for providing control channel access to any decent trellised system regardless of the transmit and receive frequencies, channel bandwidths, number of channels, simplex or duplex operation, mobile or stationary stations and direct or repeater operation.
Shown in Fig. 3 is d possible arrangement of control channels to which the transceiver at d station is tuned when no involved in a communication link. A
control chinless predeterminedly designed to each station. Typically, the assignment of a control channel may be determined by the three least significant digits of the Titan identlficat~on number in order Jo avoid having assignments concentrated on a few of the available control channels. The std~lon~s identification number I or code is predeterminedly assigned (analogous to assign-mint of telephone number) and must be used for all calls I. I
RD-14,728 to the station, except for calls over the party line channel. Of course, other pre-identified group or groups of numbers within d station's identification number my be used to determine which control channel 5 d destination station is monitoring.
Idle local or repeater talk channel selection is accomplished through exchange of digitally encoded command messages or data packets between the source killing) and destination Cody) stations over d control on channel. During talk channel selection, the source station acts as a "master" and the destination station as a "slave". When seeking to complete d communication link over a direct talk channel, the source station transmits a command message on the control channel in the high band which the destination station is monitoring and the destination channel responds on the corresponding control channel in the low band. when attempting to complete a communication link over d repenter talk channel, the source station transmits d command message to the repeater on the control channel in the low band which the destination channel is monitoring and the repenter transmits the command message to the destination station on the corresponding high bond control channel.
Referring to Fix. 4, a block diagram of apparatus usual with the present invention us shown.
The apparatus illustrated in Fig. 4 is situated do etch respective base and mobile station of the system.
Microprocessor 35 has an output connected Jo an input of transceiver 33 and a first input connected to an output of transceiver 33. A second input of micro-processor 35 is connected to an output of input/output (I/0) control circuitry 37.
RD-14,728 Microprocessor 35 may be a type 8051 into-grated circuit manufactured by Intel, Inc., Santa Clad, California, or eke like. A type 8051 integrated circuit includes d read only memory PROM) wherein programs, such do those represented by the flow diagrams of figs. 5-9, may be stored. If the microprocessor selected does not include d ROM, then one may be provided do is known in the art. 1/0 control circuitry 37, comprises controls (not shown), such as switches, for operator selectable functions, e.g. call initiate;
party line select, repenter assignment and called (destination) station identification.
Microprocessor 35 provides digitally encoded signals to transceiver 33 for assigning appropriate frequencies thereto and transceiver 33 provides micro-processor 35 with digitally encoded signals indicating the status of a called station, i.e. whether a response has been received over a control channel during the hand-shaking routine and if so, the type ox response, e.g. station idle, station busy.
Referring to Fig. 5, a start-up routine of the main program useful for the present invention is shown. Step 100 is executed to reset all counters end timers of the calling station each time the main pro-US gram of the calling station is accessed. Proceeding to step 101 the busy out counter is set to zero.
Execution of step 102 initiates a search for an idle local talk channel LO If no idle LTC is detected, the calling station at step aye calls the calling stoutness assigned repeater which commences a search I
-RD-14,72B
for dun idle repeater talk channel (RTC). If no idle RTC
is detected, step 112 increments the busy out counter by l. Execution of step 114 determines whether the busy out counter hods reached a count of 4. If the busy out counter has retched d Colette of 4, at step 116 a time owe timer To is set to predetermined value. The value to which time out timer To Is set, typically 3-5 seconds, is determined by the time interval it is desired to wait before permitting the program to repeat step 101 in order to attempt to detect an idle LTC or RTC after having had the number of unsuccessful attempts used as the test by test 114, to find an idle LTC or RTC. Execution of step 118 causes the program to welt by looping through step 118 until time out timer To has run out, at which moment the routine repeats step 101. Of course, tome out timer To may by set arbitrarily small, such do zero, so that no appreciable delay exits between execution of step 116 and the return to step 101 from step 118 of the routine.
Also, a greater or lesser number than four may be tested for by step 114 should it be desired that more or fewer, respectively, chances be given to detect an idle LTC
or RTC. If the busy out counter To has not reached the test number when step 11~ is executed, the wait time Two is computed at step 120 before execution of step 102 can be repented. Wait time Two is determined by the q n Two a + NO x Ten, wherein a is d constant to ensure an inlt1al adequate back off time for low Lungs, NO is the LUNG (logical unit number), i.e. the lust three digits of the addressee's or called station's Identification number, and Ten is the back off time, on milliseconds.
Back off time non generally increases aster each unsuccessful attempt to find an idle LTC or RTC. For example, back off :
I
RD-14,728 lime Ten, wherein n represents the number of unsuccessful attempts, eye. number In the busy out counter, may assume values of lo 20, 40, and 80 milliseconds, respectively, for each successive unsuccessful attempt to detect an idle S LTC or RTC. Execution of step 122 sets the writ time timer to the value T determined in step 120. The program then waits by looping through step 124 until the wait time timer runs out at which time the program repeats step 102 to reinitiate the search for an idle LTC or RTC.
If either an idle LTC or RTC is detected do step 104 or step 110, respectively, then step 106 Is performed to busy out or reserve the detected idle channel by trays-milting (TYING) d tone on the channel and the program proceeds to step 150 of the control channel access routine shown on Figure 6. Execution of step lS0 accesses d control channel whose condition (i.e., on use or not in use) is sensed by performing step 152. There are a plurality of control channels and the particular control channel accessed is the one assigned to the addressee station. A typical assignment scheme for a system come prosing five control channels may apportion control channels based on the last three digits (LUNG) of the addressee's identification number (Fig. 3). That is, control channel 1 is assigned to Lung 000 to 199, control channel 2 is assigned to Lung 200 to 399, etc. The program welts by looping through step l54 unwept the accessed control channel is determined to be idle at which lime step 156 is performed to start the cycle lime timer To. Execution ox Steps 158 and 160 involves sensing the control channel and determining if the control channel is idle, respect~lfely. If the control channel I
R0-14,728 is determined to be idle then at step 162 whether cycle timer To has run out is determined. If the cycle time timer has net run out, step l60 is repeated. The program continues to perform steps 160 and 162 until either the control channel is determined to be not idle or the cycle time timer has run out.
If the cycle time timer has run out, the program proceeds to execute step 166. Since the cycle time timer has run out and no packet has been detected, as indicated by the control channel remaining idle during cycle time To interval, at step I66 an assumption is made that d phantom second or lower level priority packet with NO
equal to 000 and d repeater number of the calling station Weds sensed. NO is the LUNG of any packet received from lo a sending station in the system other than the calling station. These assumptions are necessary since there is no central authority in the system to start tokens or to find lost tokens. If the control channel is not idle when step l60 is performed step I64 is executed by decoding and recording the priority, repeater number and S of the packet which was sensed by execution of step 160. Step 168 is then performed to determine of the received packet is a second prowler packet. If it is not a second prorate packet, then step 170 is executed to determine of the packet the calling station is attempt else to send is a retransmiss10n. If the calling station packet is not a retransmission, step 150 is repeated, and it it is a retransmission, step 172 is executed to determine whether the repeater number of the packet sensed prom the sending station us the same as the repeater number of the last transmission prom the calling .
~2~8~
R0-14,72 station. If these repeater numbers are not the same indicating the sending station is not d member of the some logicd1 ring as the calling station, step 150 is repeated.
S After perfor~lng step 166, determln~ng that the received packet it a second priority packet (step 168) or determining that the repeater number of eke packet sensed us the same as the repeater number of the last packet the calling station transmitted (step It I72), the program proceeds to step 200 (Fig. 7).
There are two levels of control packet pro-rlty in the system. The priority is encoded into a control packet using one bit at a predetermined toga-lion. Should more than two priorities be desired then more than one bit is required. rho first or higher priority includes control packets trying to gain access to an emergency number, such do pot ice station, hospital, fire department, etc., and retransmlss~on packets, i.e. pockets from a galling stdtlon which previously transmitted a control or retransmission packet but did not receive a response from the called station. Information identifying a retransmission packet us also encoded into toe packet using one Kit at a predeter~lned locution. All other packets have second prorate All packets, including any which have been sensed by execut10n of step 160, tow virtual tokens at a distance (token time interval) which is a function of the walk tire (defined below) between the station or~glnatlng the pocket swindling station) and the calling station. Furthermore, the priority ox the token is 3LZ~ 4 RD-14,72 the seine as the priority of the packet which tows it.
A station is allowed to transmit d control packet only while it controls a token. There dye two rules associated with gaining control of a token. The first rule is that for- d station to be able to use d first priority token it must have a first priority packet to transmit (steps 160, 164, 168, 170). The second rule, which applies to all priorities, is that in order for a station to receive a token, the time (token time interval) between the end of the packet and the token must not be invaded by another packet, lye. no packet from a sending station sensed in the token time interval (steps 160, 162).
Rerolling to Fig. 7, the control packet transmit routine is shown. Execution of step 200 determines whether the LUNG of the calling station (NT) is less than or equal to the LUNG of the sensed packet (No) from the sending station or phantom packet, lye. on. If NT is not less than or equal on to No, then at step 204 transmit timer TX is set equal to tot NO 1) x To which is the token wait time or interval, wherein To is the decode time, i.e. the time it takes for a station to start trays-milting a packet after receiving the end of a token towing packet. Decode tire To is also the walk tome between two adjacent stations on the logical ring. It NT is less than or equal to No, the transmit timer TX at step 202 is set to a token wait time or interval equal to tam NO NT I x rod wherein NM represents the number of stations on the logical ring. If Lung are the last Roy digits :`
I
,, ..
lo RD-14,728 of addressee's unique identification code then NM is equal to 1000, i.e. It .
In a retransmission, the retransmission control packet us always identified do a first priority pocket.
As a result, at least one sweep around a logical ring is reserved for all first priority packets if a retransmission control packet is sent. In this manner, it is possible to eliminate from the control packet queue all stations which previously experienced a collusion or did not receive a response to a control packet, before permitting new stations to try to gain access to the control channel (unless, of course, a new station is trying to call an emergency number, i.e. first priority). To permit flushing out to occur without further collisions, decode time To, used in retransmission, is mode a random variable with a typical mean lTdn) as follows:
Tdl 2 1 msec.
do 2 msec.
Td3 4 msec.
do msec.
wherein n is the number of attempts for retr~nsmissions of the same control packet, for use by steps 202 and 20~. Establishing a random variable having d predator-mined mean is known in the art and my be performed by a local communications controller 82536~ manufactured by Intel, or the like.
After establ wishing the token wait eye, step 206 is performed to sense whether the control channel is idle. It the control channel us idle, step 210 is executed to determine If transmit titer To has run out. If transmit timer lo has not run out step 208 lug - - -RD-14,728 is repented and the program continues to loop through steps 208 and 210 until transmit timer TX runs out, at which time step 212 is performed to determine if the number or unique ident1ficdtion code of the called station is an emergency number. If the number being called is not an emergency number, step 214 us executed to stop transmitting the busy tone which was generated by execution of step 106 fig. 5) on the Arc or RTC
determined to be idle by step 104 or 110 (Fig. 5), It respectively. Step 216 is performed to transmit the control packet of the calling station and, if it is a retransmission, to set the priority by e of the control packet. The program then waits by looping through step 218 until the transmission of the control packet is completed at which tome step 220 us executed to set a receive timer TRY for receiving a response packet from the called station and step 222 is executed to sense the return control channel. Receive timer TRY is generally set to the maximum time anticipated for receiving a response packet on the return channel from a called stdt1On.
If the control channel is not idle when step 208 is performed, the program proceeds to step 164 (Fig. 6) which it executes in accordance with the procedure herein before described, in order to try to obtain the token towed by the packet received from d sending station. If the number being calved us an emergency number, then the execution of step 212 causes the program to proceed to step 300 (Fog. 9) to begun execution of the routine for emergency numbers which is described on more Dwight below.
Jo RD-l4,728 Referring to Figure I, the control packet receive routine is shown. After executing step 222 (Fig. 7), the program performs step 250 to determine of d response hods arrived on the return channel from S the called station. If a response is sensed and it indicates that the called station is free to accept a call, then a communication link is established between the Cal 11ng and called station over the LTC or RTC
previously determined to be idle by step 104 or step It 110 (Fig. 5), respectively. The response may alter-natively indicate that the called station is busy, i.e.
has established or is trying to establish a communication link. After r~ce1v1ng any response, step 252 is executed eon reset all program counters. IF a response has not arrived on the return channel when step 250 is performed, step 254 us executed to determine if receive timer TRY
has run out. If receive timer TRY has not run out, the program repeats step 250 and continues to loop through steps 250 and 254 until the receive timer runs out, at which lime step 256 is executed to incre~enk the retrains-mission counter. Step 258 us then performed to determine if the retransmission counter has reached a count of 4.
If the retransmission counter has reached 4 (a greater or lesser number may be used as desired) step 260 is performed to set the time out timer To to a value which equals the time the program must wait before the star up routine of Figure 5 is repeated. After setting the time out timer To the program welts by looping through step 262 until the time out timer runs I out, at which tome step 101 1 s repeated (fix. 5) to reinitiate the start up routine.
Jo -ROY
Lack of d response from d called station to a control packet my indicate: two or more stations on d liquidly channel had the same LUNG i.e. they all attempted to reach stations having the same lust three digits of identification code; the called stations transceiver weds not turned on; two or more stoutness were unable to hear each others' transmissions -- they obtained and used the same token from the same packet -- a collision (i.e., trays-missions from two or more stations within the same time interval and within receive range of a receiving station such that the integrity of the detected transmission do the receiving station cannot be assured) between control packets occurred; a station obtained tokens from two or more logical rings at different times.
A logical rirlg us formed in a cell wherein all stations can hear transmissions from the same repeater.
There may be stations situated near the reception fringes of a cell. These stations can generally hear transmissions from two or more repeaters. The encoding of a repeater identification number into control pockets and determining whether the repenter number of the received packet (which is also the repeater number of the token) from a sending station is the same do the repeater number of a calling station (Fig. 6, step l72~ before allowing the calling station to obtain the packet minimizes the number of got-lesions due to obtaining tokens from Gore than one logical ring) by forcing a station to remain within one logical ring.
In the case of a Molly station moving from one cell to another, an operator must change the assigned repeater ~dentificatton at It control 37 fig. 4) of the mobile station.
If the retransmission counter has not reached 4 when step 258 is performed, step 264 is performed to determine if the LTC or RTC do determined by step 104 or I10 (Fig. 5), respectively, is still idle. If the I
. .
~8~3~4 RD-14,728 LTC or RTC is not still idle, step 10l fig. 5) is repeated to reinitiate the start up routine. If the LTC or RTC is determined at step 264 to still be idle, step 266 busies out the LTC or RTC by transmitting a tone and step lS0 (Fig 6) us repeated to reinitiate the control channel access routine.
Referring to Figure 9, the routine for galling emergency numbers it shown. If at step 212 (Fig. 7) it is determined that the calling station is calling an emergency number, the program proceeds to step 300 to set the priority bit in the control jacket of thy I no station. Step 302 is performed to set the emergency packet top) counter To to Nero and execution of step 304 increments the emergency packet counter To. Execution of step 306 determines if the emergency packet counter has reached 6 Ed greater or lesser number may be used as desired). If it has reached 6, then execution of step 260 (Fig. 8) sets the time out timer To and the program waits by looping on through step 262 unwept the tome out timer To runs out.
After the time out timer runs out, step 10l (Fig. 5) is repeated to reinitiate the start up routine.
If the emergency jacket counter has not reached 6 when step 306 is performer, execution of step 312 causes the program to stop transmitting the busy out tone that was generated by execution of step 10~
Fog 5), on the LTC or RTC determined at step 104 or 110 (F19. 5), respectively to be idle. Execution of step 314 causes the emergency packet to be transmitted and execution of step 316 sots the receive timer TRY
for receiving a response packet as herein before ..Z~8~
RD-I~,728 described. Execution of step 318 senses the return channel and execution of step 320 determines whether d response has arrived on the return channel from the emergency station. If execution of step 320 results in sensing a response on the return channel and the response indicates that the emergency station is free to accept a call, then a communication link is established between the calling and emergency station, over the idle LTC determined at step 104 or idle RTC determined at step II0 (Fog. 5). The response may alternately indicate that the emergency stat10n is busy, i.e.
has established or us trying to establish a communication fink. Aster receiving any response, step 322 is per-formed to reset all counters. If a response has not been resoled from the emergency station when step 320 is performed, step 324 is performed to de~ermlne lo resolve timer TRY has run out. If the receive timer has not run out, step 320 is repeated and the program continues to loop through steps 320 and 324 unwept the receive timer runs out. When the receive timer runs out, step 326 is executed to determine it the LTC or RTC determined in step 104 or step 110 (Fig. 5), respectively, is sly idle. If the LTC
or RTC is not Steele idle the program repeats step 101 (Fig. 5) to reliantly thy start up routine. If the TO or TO d~term1ned to be idle at step lo or step II0 (Fig. 5), respectively, us stilt idle when step 326 is executed the program repeats step 304 and incoherency the emergency packet counter. The program c~ntlnues to loop through step 304 to step 326 until execution of step 306 d~term1nes chat the emergency packet counter has reached 6,-exec~lon ox step 320 ~e~ermlnes that RD-14,728 a response has been received from the emergency station or execution of step 326 determines that the LTC or RTC
is still idle. As indicated do step 306, six attempts are permitted to try to secure d local or repeater talk channel when an emergency number is being culled. Of course, the program may be modified to provide for d greater or lessor number then six attempts.
Thus has been illustrated and described d method for providing deterministic control channel access for a mobile radio environment allowing up to about 80 percent control channel utilization. Further, priority control channel access is provided for emergency numbers and for stations having had an unsuccessful attempt to gain access to the control channel. Add-tonally, the number of collusions resulting from inability to detect all transmissions by all stations has been minimized.
While only certain preferred features of the invention have been shown by way of illustration, many modifications and changes will occur to chose skilled in thy art. It is to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit and scope of the invention.
,
Claims (12)
1. method for accessing one of a first plurality of data channels of a decentralized radio system comprising a plurality of stations, wherein each station is predeterminately assigned to monitor one of a plurality of control channels and assigned to a unique identification code, in order to perform a hand-shake routine over the control channel assigned to a called station, before establishing a communication link between a calling and said called station over said one of said plurality of data channels, comprising:
(a) searching said data channels at said calling station until an idle one of said data channels is obtained;
(b) reserving said idle data channel;
(c) monitoring at said calling station the control channel assigned to said called station, after reserving said idle data channel;
(d) transmitting a control packet on the control channel being monitored by said calling station after the control channel has been determined to be idle for a predetermined interval; and (e) monitoring the control channel after transmitting a control packet to determine if a response packet from the called station is received.
(a) searching said data channels at said calling station until an idle one of said data channels is obtained;
(b) reserving said idle data channel;
(c) monitoring at said calling station the control channel assigned to said called station, after reserving said idle data channel;
(d) transmitting a control packet on the control channel being monitored by said calling station after the control channel has been determined to be idle for a predetermined interval; and (e) monitoring the control channel after transmitting a control packet to determine if a response packet from the called station is received.
2. The method as in claim 1, wherein said system further comprises a repeater station having a second plurality of data channels, said method further comprising searching at said repeater station for an idle data channel selected from said second plurality of data channels in response to a command by said calling station.
3. The method as in claim 2 wherein said first plurality of data channels is searched before said second plurality of data channels is searched.
4. The method as recited in claim 3 wherein said unique identification code comprises a logic unit number.
5. The method as in claim 4 wherein said predetermined interval comprises a transmit time equal to (NM - NS + NT - 1) X Td when the logical unit number (LUN) of the calling station is less than or equal to the LUN of a sending station and equal to (NT - NS - 1) X Td when the LUN of the calling station is greater than the LUN of the sending station, wherein:
NT = LUN of calling station, NS = LUN of sending station, NM = number of stations on logical ring and Td = decode time, and the LUN of the sending station (NS) is decoded from a control packet sensed while monitoring at said calling station the control channel assigned to said called station and NS is equal to zero when no control packet is sensed while monitoring at said calling station the control channel assigned to said called station.
NT = LUN of calling station, NS = LUN of sending station, NM = number of stations on logical ring and Td = decode time, and the LUN of the sending station (NS) is decoded from a control packet sensed while monitoring at said calling station the control channel assigned to said called station and NS is equal to zero when no control packet is sensed while monitoring at said calling station the control channel assigned to said called station.
6. The method as in claim 5 further comprising retransmitting a control packet on the control channel being monitored by said calling station if no response packet is received from the called station, wherein Td is a random variable having a predetermined mean value.
7. The method as in claim 6 further comprising repeating retransmission of a control packet a predetermined number of times wherein Td is a random variable having a different mean value during each retransmission.
8. The method as in claim 6 further comprising assigning the highest priority to said control packet being retransmitted on the control channel.
9. The method as in claim 1 further comprising communicating between said calling and said called station over the data channel determined to be idle when a response packet received from the called station indicates the called station is free to complete the communication link between said calling and said called station.
10. The method as in claim 1 further comprising assigning priority to said control packet wherein said priority is encoded into said control packet.
11. The method as in claim 10 further comprising assigning the highest priority to said control packet addressed to an emergency station.
12. In a decentralized ratio system including a plurality of stations wherein a plurality of data channels are provided for communication between said stations, a method for establishing a communication link between a calling station and a celled station comprising the steps of:
providing a plurality of control channels for performing a handshake routine between said calling station and said called station before establishing communication over one of said plurality of data channels;
monitoring at each station a predetermined one of said control channels;
monitoring at said calling station the particular control channel being monitored by said called station until this channel is determined to be idle for a first predetermined time interval;
transmitting a control packet from said calling station to said called station on said particular channel after said particular channel has been determined to be idle for said first time interval; and monitoring said particular control channel at said calling station after transmitting said control packet to determine if a response packet is received
12. In a decentralized ratio system including a plurality of stations wherein a plurality of data channels are provided for communication between said stations, a method for establishing a communication link between a calling station and a celled station comprising the steps of:
providing a plurality of control channels for performing a handshake routine between said calling station and said called station before establishing communication over one of said plurality of data channels;
monitoring at each station a predetermined one of said control channels;
monitoring at said calling station the particular control channel being monitored by said called station until this channel is determined to be idle for a first predetermined time interval;
transmitting a control packet from said calling station to said called station on said particular channel after said particular channel has been determined to be idle for said first time interval; and monitoring said particular control channel at said calling station after transmitting said control packet to determine if a response packet is received
Claim 12 continued:
from said called station and, if so, establishing communication between said calling station and said called station over one of said plurality of data channels.
from said called station and, if so, establishing communication between said calling station and said called station over one of said plurality of data channels.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US529,197 | 1983-09-06 | ||
| US06/529,197 US4534061A (en) | 1983-09-06 | 1983-09-06 | Deterministic multi-access method for a decentralized mobile radio system |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1218114A true CA1218114A (en) | 1987-02-17 |
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ID=24108920
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000461644A Expired CA1218114A (en) | 1983-09-06 | 1984-08-23 | Deterministic multi-access method for a decentralized mobile radio system |
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| US (1) | US4534061A (en) |
| EP (1) | EP0136517A3 (en) |
| JP (1) | JPS6094550A (en) |
| CA (1) | CA1218114A (en) |
| DK (1) | DK419484A (en) |
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| JP4361902B2 (en) * | 2003-12-15 | 2009-11-11 | 株式会社日立製作所 | In-vehicle control device information update method, update information communication system, vehicle-mounted control device, and information management base station device |
| US7483392B1 (en) * | 2004-03-19 | 2009-01-27 | Bbn Technologies Corp. | Multinode arrangement |
| US7607070B2 (en) * | 2004-09-13 | 2009-10-20 | National Instruments Corporation | System and method for in-line consistency checking of packetized data |
| WO2006065771A2 (en) * | 2004-12-15 | 2006-06-22 | Fry Terry L | Multi-user non-blocking duplex wireless voice communication system and method |
| US9014696B1 (en) * | 2006-01-24 | 2015-04-21 | Nextel Communications Inc. | System and method for priority wireless access |
| US7570927B2 (en) * | 2006-06-16 | 2009-08-04 | Motorola, Inc. | Decentralized wireless communication network and method having a plurality of devices |
| CN101690018B (en) * | 2008-04-25 | 2013-09-25 | 松下电器产业株式会社 | Communication apparatus and communication method |
| US11166222B2 (en) * | 2019-08-02 | 2021-11-02 | AR & NS Investment, LLC | Communication by a repeater system including a network of radio frequency (RF) repeater devices |
Family Cites Families (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| AT338877B (en) * | 1969-07-23 | 1977-09-26 | Sits Soc It Telecom Siemens | REMOTE INDICATION SYSTEM WITH A NUMBER OF TWO-DIRECTIONAL CHANNELS, EACH OF WHICH ONE IS ONLY USED DURING THE DURATION OF THE CONNECTION BETWEEN AT LEAST TWO TRANSCEIVER-RECEIVING DEVICES |
| US4409687A (en) * | 1978-10-30 | 1983-10-11 | General Electric Company | Arrangement and method for establishing radio communication in a system |
| US4360927A (en) * | 1979-03-12 | 1982-11-23 | General Electric Company | Repeater trunking system |
| US4400585A (en) * | 1979-11-30 | 1983-08-23 | Motorola, Inc. | Method and apparatus for automatically attempting to seize a radio channel in a multichannel communication system |
| US4281413A (en) * | 1979-12-03 | 1981-07-28 | General Electric Company | Multichannel radio telephone system |
| US4347625A (en) * | 1980-06-16 | 1982-08-31 | General Electric Company | Arrangement for cellular operation of a repeater trunking system |
| US4395594A (en) * | 1981-08-24 | 1983-07-26 | Bell Telephone Laboratories, Incorporated | Method and apparatus for forcing randomization of idle channel seizures |
-
1983
- 1983-09-06 US US06/529,197 patent/US4534061A/en not_active Expired - Lifetime
-
1984
- 1984-08-23 EP EP84110041A patent/EP0136517A3/en not_active Withdrawn
- 1984-08-23 CA CA000461644A patent/CA1218114A/en not_active Expired
- 1984-08-31 DK DK419484A patent/DK419484A/en not_active Application Discontinuation
- 1984-09-05 JP JP59184728A patent/JPS6094550A/en active Pending
Also Published As
| Publication number | Publication date |
|---|---|
| DK419484D0 (en) | 1984-08-31 |
| EP0136517A2 (en) | 1985-04-10 |
| EP0136517A3 (en) | 1987-07-22 |
| JPS6094550A (en) | 1985-05-27 |
| DK419484A (en) | 1985-03-07 |
| US4534061A (en) | 1985-08-06 |
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