CA2195984A1 - Remote transmitter power control in a cdma communications system - Google Patents
Remote transmitter power control in a cdma communications systemInfo
- Publication number
- CA2195984A1 CA2195984A1 CA002195984A CA2195984A CA2195984A1 CA 2195984 A1 CA2195984 A1 CA 2195984A1 CA 002195984 A CA002195984 A CA 002195984A CA 2195984 A CA2195984 A CA 2195984A CA 2195984 A1 CA2195984 A1 CA 2195984A1
- Authority
- CA
- Canada
- Prior art keywords
- reverse channel
- spectral density
- energy per
- per bit
- total interference
- 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.)
- Abandoned
Links
Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B7/00—Radio transmission systems, i.e. using radiation field
- H04B7/005—Control of transmission; Equalising
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W52/00—Power management, e.g. TPC [Transmission Power Control], power saving or power classes
- H04W52/04—TPC
- H04W52/30—TPC using constraints in the total amount of available transmission power
- H04W52/34—TPC management, i.e. sharing limited amount of power among users or channels or data types, e.g. cell loading
- H04W52/343—TPC management, i.e. sharing limited amount of power among users or channels or data types, e.g. cell loading taking into account loading or congestion level
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W52/00—Power management, e.g. TPC [Transmission Power Control], power saving or power classes
- H04W52/04—TPC
- H04W52/06—TPC algorithms
- H04W52/14—Separate analysis of uplink or downlink
- H04W52/146—Uplink power control
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W52/00—Power management, e.g. TPC [Transmission Power Control], power saving or power classes
- H04W52/04—TPC
- H04W52/18—TPC being performed according to specific parameters
- H04W52/24—TPC being performed according to specific parameters using SIR [Signal to Interference Ratio] or other wireless path parameters
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W52/00—Power management, e.g. TPC [Transmission Power Control], power saving or power classes
- H04W52/04—TPC
- H04W52/18—TPC being performed according to specific parameters
- H04W52/24—TPC being performed according to specific parameters using SIR [Signal to Interference Ratio] or other wireless path parameters
- H04W52/241—TPC being performed according to specific parameters using SIR [Signal to Interference Ratio] or other wireless path parameters taking into account channel quality metrics, e.g. SIR, SNR, CIR, Eb/lo
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W52/00—Power management, e.g. TPC [Transmission Power Control], power saving or power classes
- H04W52/04—TPC
- H04W52/30—TPC using constraints in the total amount of available transmission power
- H04W52/34—TPC management, i.e. sharing limited amount of power among users or channels or data types, e.g. cell loading
- H04W52/346—TPC management, i.e. sharing limited amount of power among users or channels or data types, e.g. cell loading distributing total power among users or channels
Abstract
The power control process of the present invention enables a base station communicating over a forward packet channel to a mobile radio to control the power of the mobile radio transmitting over a reverse packet channel to the base station. The base station maintains a maximum energy per bit to total interference spectral density ratio threshold for the reverse channel as well as a desired threshold that results in a low frame error rate. By comparing each radiotelephone's estimated energy per bit to total interference spectral density ratio to the desired and maximum thresholds, power control commands to increase or decrease the radiotelephone's transmit power are generated depending on the outcome of the comparison.
Description
~WO96/03813 Z1959~k ~ .,S/~76 , Remote Transmitter Power Contro7 in a CDMA Commun1cat~ons System R~ ~ouND OF TslE INVENTION
I. FIELD OF TEIE INV~ON
The present invention relates to wireless rommnnirsltinnc More particularly, the present invention relates to power control in a CDMA
10 communication system.
II. DESCRIPTION OF T~E RELATED ART
A packet is one method of pslrkslging user data. Typically, the l~ packet is divided up into various fields, with each field comprising one or more bits. Each field is used for a pr-~-7-~t-~rmin-~d function such as user data, addresses, error detection, etc. Data packets can be formed according to pre-existing protocols such as X.25 and TCP/IP that are well known in the art.
Packets may be used with a true packet service in which the stpr1irsltif)n~ transport, or other layer generates the packet. Packets can also be generated by a network's lower protocol layer that breaks a stream of data bits into data packets of ~ler1 l ~ ~ . l . i . .-~d length.
Data packets can be trslncmit~~d over a radio channel using many 25 methods. A first method uses a dedicated channel to carry packets between a pair of radio Ls~.eiv~ . A second method rnr.,~ c~rc a single, central radio transceiver that transmits over a common channel to one or more other radio l~;s~scv;vvl~ that are monitoring for packets rnntstining data in the address field signifying that radio transceiver's 30 particular address. A third method uses a random access or rnntpnti,.n based protocol in which the packets are Ll,--.h..-DIed from one or more radio Lsclsss~vivvl~ to either a central termina or each other.
In a typical CDMA cellular communication system that follows the Tr~ ir~sltinnc Industries Accnrisltion/Electronic _ndustries 35 Acenrisltinn Interim Standard 95 (TsTA/EsTA/IS-95), the dedicated channel corresponds to a traffic channel. This channel transmits voice and data signals between the mobile radio and the base station. The common channel approach cul~e~pu~ds to trs~1n.emit~ing on the paging channel that is used to broadcast pages in a CDMA system when each page carries an 40 address. The random access approach corresponds to the access channel.
SU8STITUTE SHEET (RULE 26) ~ ?~
wo 96/03813 2 1 9 ~ 9 ~4 ~_I/,J~. 1 176 ~
A typical CDMA-type n nmmnnirAti~m system is described in E~reater detail in U.S. Patent No. 5,103,459 to ('Ti1hm1cPn et al. and assigned to Qualcomm, Inc.
When one or more packets are to be trAncmittod between a base 5 station and mobile radio or vice versa, a traffic channel can be allocated between the two. Once a packet is trAncmitte-l the time to the next packet is often unknown. Instead of having the traffic channel allocated and unused, the channel is rlPA11noAtPr1 after a period of idleness. This period can be fixed with the period determined by analyzing typical traffic l0 patterns. Alternatively, this period can also be variable with the period set by analyzing the trAncmitted packet stream.
The allocation of traffic channels presents at least two problems.
First, the traffic channel takes time to set up, thus delaying the packet trAncmi-~ nn In some in~tqnrr~c, setting up a traffic channel could 15 require more than a second. Second, the resources to set up and use a traffic channel may be too expensive to justify the trAn.cmiccinn of ~-r~ u~cu~ packets, short packets, or short se~lu~ . of packets.
Power control in a CDMA system is very ~r,.~u ~;.r~ since a large number of mobile radios are trAncmitting on the same ~r~ ut~u~ If one 20 mobile is trAncmittine at a power output that is too large, it can degrade the received E~o from other mobile radios to the point that the base station cannot correctly riPmn-ln1AtP trAncmiccinnc If the mobile radio transmits at too low of an output power, the received E~o from the mobile radio at the base station will be too low to properly rlPmnr~ AtP the E~Oreceived 2~ signal. The mobile radio's transmit power, therefore, has an affect on system capacity.
The correlation between E~o and system capacity can be shown as follows. When there are no mobile radios in other cells, the maximum number of cimll1tAnPous trAncmiccinn.c, N, is approximately:
N /1~ /~)d~s( ~P-) ( ~/o)des where:
W = spreading bandwidth, 35R = data rate, ~STITUTE SHEET (RULE 26) ~wo 96/03813 2 1 ~ S ~ 8 ~ Sl~ ~ 76 (E~o)d = desired quality metric subsequently explained in greater detail, No = thermal noise spectral density of the base station receiver, and Pr = received power per trrnqmicci~n The second term in the numerator is typically very small compared to W~g~ therefore, Ns (E~/R) . Thus, a system using a higher desired El~o lowers capacity.
For the ith mobile radio, the received EyO~ denoted by (EyO) ~ at the 10 base station is approximately (E~o)i ~ ~. The probability that the j~i trAncmiccinn can be surcPccfillly rlPmn~ ted is high if (EYo)i exceeds (EYo)d as is described above. If Pri is large, however, the El~o is degraded for other mobile radios. If the received E~o falls below (El~/o)d~ ~
the probability that the tr~nqmir~;nn will not be surcPccfillly rlpmodlllrtpd 15 is high~
The mobile radio dynamically adjusts its transmit power using closed and open loop power control in order to maintain the proper received E~o at the base station as channel cnn~iti~lnc change or the range to be base station changes. Open loop power control adjusts the 20 mobile radio's transmit power flnt-n-~m~-usly by measuring the received power on the forward channel. Closed loop power control adjusts the mobile radio's transmit power by a feedback bit stream from the base station. 'rhe base station measures the received El~o to ~lPtPrminP the feedback bit stream. Closed loop and open loop power control together 25 dPtprminp the mobile radio's transmit power, as disclosed in U.S. Patent No. 5,056,109 to Gilhousen et al. and assigned to Qualcomm, Incorporated.
Closed loop power control cu~pculs~l~es for the dirr~ .es in fading between the forward and reverse links, such as occurs when they are 30 different L,-4~ ..ripc A~rlitinnrlly, it serves to compensate for the di~t,1~..ce., in transmit and receive path gains in the mobile radio and base station.
Closed loop power control is possible in a typical communication ,cystem since there is one traffic channel per mobile radio. This one-to-one SUe,STlTUTE SHEET (RULE 26) 3 2 1 9 ~ 9 8 ~ 76 ~
channel pairing permits the base station to measure the mobile radio's reverse channel power and for the mobile radio to utilize the power control ~ bit stream from the base station on the forward channel.
A multi-access channel, however, does not have a one-to-one 5 channel pairing, as multiple mobile radios can transmit simultaneously.
The identity of the mobile radio, therefore, is not necessarily known to the base station. Also, the mobile radios do not know the number of mobile radios ~ F, thus the ~ ;.,., of the power control bit stream is not clear to the mobile radio.
Since the mobile radio aligns its transmit timing with the timing of the signals that it receives from the base station and all base station signals are time aligned, when two simultaneous trAncmicqinnc occur on the reverse channel and there is no mn1tirAth the trAncmiCcinnc arrive at the base station separated by times equal to the difference of twice the 15 distances between each mobile radio and the base station. If this time exceeds one pseùdo noise chip, the two trAncmiccinns can be distinguished by the base station. The inability to distinguish these m111tipAth iL~ llllc~innc is a collision.
When there is mn1tirAth there is no collision if the base station can 20 identify and properly combine the mn1tir~th ~ If three or more access channel trAncmiCcinnc occur in the same slot, then some trAncmiccinnA may collide while others do not. In a typical multi-access channel, such as is found in a TDMA or an FDMA system, when two cim11ltAnPo11c trAncmiccinnc occur there is a collision and neither 26 lL~IICl~ m is sn~cP~efillly ~Pmn~ t~d by the base station.
Base stations may further reduce il~tt:~rel~ e with each other by trAncmitf;nF with the minimum power necessary for their signals to be received by the base station. A mobile radio transmits its first ~L..I~ .. or probe at a power level somewhat less than it estimates to 30 be necessary to reach the base station. This CU1LS~1 v~iv~ estimate may be a ,ule~dt k~ i- ed value or it may be ~Alr7llAted in response to the measured power level of a signal that the mobile radio has or is receiving from the base station.
A preferred ~mho~imf~nt is for the mobile radio to measure the 35 received power from the base station. This received power is the ~L~ d power of the base station times the path loss. The mobile radio then uses this estimate, plus a constant correction, plus adjustment factors to set the initial transmit power. These adjustment factors may be sent to the mobile radio from the base station. Some of these factors S~IBSTITUTE SHEET (RULE 26) ~ i ~wos6/038l3 219~98~ v~ S.of 176 correspond to radiated power of the base station. Since the path loss from the mobile station to the base station is essentially the same as from the base station to the mobile station, the signal received at the base station should be at the correct level, assuming that the base station has supplied 6 the n~UI~lU,U~ e Cu~ iuu factors and that the mobile radio and base station gains are error free.
After trAncmitt;nF the first access probe at this Illhli~ulll power level, the mobile station increases the power of successive probes within each access probe sequence by a predetermined step amount. A thorough 10 discussion of access probes is evident in IS-95, section 6.6.3.1 and in co-pending patent, Apporatus and Method for Reducing Collisions Between Mobile Stations Si~7atnrle~ s7r Accessing a Base Station in a CDMA
Cellular Con7~7u~2i((7t~ s System, S~N 08/219,867 to TiotlomAnn et al. and assif~ned to Qualcomm7 Inc.
In addition7 between successive trAncmiCci-n~ of an access probe7 the mobile radio can randomize its trAncmiqcion time and choose another access channel so as to avoid a potential collision. IS-957 section 6.6.3.1 describes this in greater detail.
It can be seen, therefore7 that power control is very il.~,uu~ l for 20 proper operation of a CDMA r~-iiotolophr~no system. There is a resulting need for a power control process in a multiple access system to increase system capacity.
SUMMAE~Y OF TEIE INVENTION
The power control process of the present invention uses a comparison threshold to determine whether the base station should instruct the mobile radios to increase or decrease their transmit power.
The total received EyO for all the mobile radios rr~mmllnicAting with a 30 particular base station is compared to a mA~imnm threshold for the reverse channel. A~lflit;~-nAIly, a minimnm comparison threshold for the mobile radio being controlled is determined. If the total received E~o is greater than or equal to the msl~imllm threshold or the minimum received EyO for any mobile radio is greater than the reverse channel 36 minimum, the base station instructs the mobile radio to decrease its output power. If the total received EyO is less than the mA~imnm reverse channel threshold and the minimllm received EyO for any mobile radio is S~BSTlTuTE SHEET (RULE 26) WO g6/03813 2 1 9 5 9 ~ ,,5 ~ 176 ~
less than or equal to the reverse channel minimum, the base station instructs the mobile radio~ to increase power.
BRIEF D~ )N OF T~E DRAWINGS
FIG. 1 shows a flowchart of the process of the present invention.
FIG. 2 shows a graph of the frame error rate versus E~o FIGs. 3a and 3b show a typical forward packet channel structure in accordance with the present invention.
FIG. 4 shows the power control bit positions in accordance with the present invention.
FIG. 5 shows a block diagram of a typical mobile radio in accordance with the present invention.
FIG. 6 shows a block diagram of a typical base station in accordance 15 with the present invention.
FIG. 7 shows the format of a forward CDMA channel in accordance with the present invention.
FIG. 8 shows the format of a reverse CDMA channel in accordance with the present invention.
FIG. 9 shows a plot of the transmit power of two radios and their reaction to power control crlmmAn~ie in ac.o~ ce with the present invention.
n~TA~r.F.n L~ OF TEE r~K~;U r-The present invention ~n~rmnpAcR~g a pair of channels, sub-sequently referred to as the forward and reverse packet channels. The base station cnnnm-1ni~ At~c with the mobile radios over the forward chan-nel and the mobile radios communicate with the base station over the 30 reverse channel. A base station uses the power control process of the present invention, over the forward packet channel, to dynamically adjust the transmit power of one or more mobile radios trAnemi~ing on the reverse packet channel.
The following ~1iccnecinn refers to mobile radios and base stations 35 as the preferred ~mho~im~nt Mobile radios include rA~ t~ ph~m~c used - in both a terrestrially based cr~mmllni~Ati(m system and a satellite based rf~mmlJni~Ati~ln system. Similarly, the base stations can be located on the earth or as orbiting satellites.
SU8STITUTE SHEET (RUI F 26) - P~ 76 ~wo 96103813 2 1 ~ ~ 5 8 ~
The reverse packet channel, in the preferred PmhoflimPnt is a variable rate channel that transmits data packets that have been broken up into a sequence of one or more frames. In an alternate embodiment, the reverse packet channel handles data at a fixed rate.
Each tr~ncmiccinn includes a preamble, to aid in spread spectrum acquisition, followed by the datagram. The preamble of the reverse packet channel is the same as the preamble used in the access channel; a sequence of one or more nnmorllllAted frames of Walsh function 0. The access channel preamble is discussed in greater detail in TIA/EIA IS-95.
10 Alternate PmhoflimPntc use other preambles than the Walsh function 0.
Another alternate Pmho~lim.ont. includes frames mndlll~tPd by known fic:4uem~;es~ However, this increases receiver complexity.
In the preferred Pmho~imPnt the forward CDMA channel consists of a pilot channel, a ~y~.h~u~ .Lion channel, one or more paging 15 channels, one or more forward packet channels and forward traffic channels. FIG. 7 illustrates the format of the preferred PmhoAimPnt of the forward CDMA channel including the traffic channels (705) and packet channels (710) with power control sllhrh~nnPlc (715). The forward packet channel is a spread spectrum channel similar in operation to the forward 20 traffic channel as disclosed in IS-95 as is illustrated in FIGs. 3a and 3b. A more complete (li~ . of this channel can be found in IS-95.
FIG. 8 illustrates the format of the reverse CDMA channel. A set of one or more access channels (805) are ~cRori~tDd with each paging channel. An overhead message defines the number of access channels 26 (805) that are ~A~or: l~cl with a particular paging channel. Similarly, one or more reverse packet channels are RcRori~ted with a forward packet channel and an overhead message defines the number of reverse packet channels ~Rcori~ted with a particular forward packet channel. Different reverse packet channels (810) ~ o ,.l~d with the same forward packet 30 channel are dirr~ tiated by each reverse packet channel having a unique spreading code.
In the preferred ~mhor1imPnt., assignment of a reverse packet channel to a forward packet channel is static in that a mobile radio con-tinually monitors the same forward packet channel while in the same 35 cell. The channel may be assigned by using information from overhead pcu~lue~l s, by S~qRi~nmPnt on a per mobile radio basis, or via some static procedure.
The reverse packet channels enable multiple mobile radios to trans_it cimlllt~npously~ In the preferred PmhoflimPnt of a CDMA
Sl.lBSTlTUTE SHEET (FIULE 26) Wo96/03813 21~.9~598.~ 76 ~
system, the multiple trAnqmiCcinnc from multiple mobile radios only collide if their multipath rnmpnnPntc overlap as was described previously.
In the preferred PmhorlimPnt, a mobile radio randomly chooses, for its trAncmiceinn.c, one of the reverse packet channels Ac.coriAtPd with a 5 forward packet channel. Alternate Pmho~1imPntc use other methods for choosing channels. AfltiitinnAlly, the trAn.cmiccinn time of a radio using a reverse packet charmel can be rAnrlnmi7Pd as is done for the access chan-nel. These Le~ uès lower the probability of a collision by distributing the mobile radios over channels or time. This also serves to increase system lO capacity. When the mobile radio retransmits a packet, it may randomize trAn.cmiccinn time and choice of reverse packet channel so as to avoid collisions as previously described for the access channel.
A flowchart of the power control process of the present invention is illustrated in FIG. 1. In the preferred Pmho~imPnt, this process uses the 15 (1imPncinn1P.cc ratio E~/o to ~ipt~rminp whether to adjust the radio's transmit power and, if so, whether to increase or decrease the power.
Alternate Pmho~im~ntc use other si~,nal quality metrics for threshold cnmrAricnn such as P~/NO~ Pr~ or some scaled equivalent Of E~; Pr being the received power.
The E~o ratio is a standard quality mea:~u~elue~lt for digital com-mnnioAti~nc system performance. The ratio expresses the energy per bit to the totl hlLelf~ e spectral density of the channel. El~/o can be considered a metric that ch~lL.. .el;~.~.., the performance of one rommllninAtinn system over another; the smaller the required E~o the 25 more efficient is the system mnrln1Atinn and detection process for a given probability of error. ~ more detailed ~ ;.... of this concept can be seen in B. Sklar, Digital Con~ n;cations, Fundamentals and App~ications, Chapter 3 (1988).
The process of the present invention, in the preferred embodiment, 30 is used in a typical CDMA cellular radiotelephone system as disclosed in the '459 patent described above. The radiotelephone system is comprised of numerous rA~intPlprhnnpc that transmit to a base station over a reverse channel and receive from the base station over a forward channel.
The ~ x;~ . total E~/o is subsé~luelltly referred to as the allocated 35 E~/o (step 100). The allocated E~o may vary with the traffic channel load.
The allocated El~o is used by the base station as the maximum threshold for all mobile radios trAncmit~;ng to that base station. If a par-ticular mobile radio trAncmitt;ng to the base station requires a transmit SUBSTlTuTE SHEET (RULE 26) ~WO 96/03813 2 ~: 9 ~ ~ ~ 4 P~ 76 power increase, the base station will not instruct the mobile radio to in-crease its transmit power beyond the allocated E~/o.
In the preferred Pmho~liment, the reverse link has a desired E~/o assigned to it by the base station (step 105). The desired ratio is the value ~ 5 that gives a high probability that a data packet will be received without error from the base station and yet ms~int~inR a high capacity as explained above. As an e~ample, a packet cnnqiQting of 10 frames with a 3 dB E~/o has an appro~imate error rate of 10%, as seen in FIG. 2.
Choosing a larger Eb/o causes the packet error probability of the 10 tr~ncmi.q.qion to decrease. This is illustrated in the graph of FIG. 2. This plot shows the effect to the frame error rate of increasingE~O. For e~ample, referring to FIG. 2, if the E~b/o is 4 dB, the resulting error rate for the 10 frame packet is 4 ~ 10-3. If E~/o is chosen too large, however, the tr~n.qmitf~ l signal may cause hlLe~lrt~ to other mobile radios 15 rommnnirFt.ing with the base station.
The received E~fo of each mobile radio is estimated by the base station (step 115). Since the base station acquires the mobile radios during the trAncmiFQinn of the packet preamble, it can determine the number of mobile radios that are tr~n.cmitting to the base station. These individual 20 E~o's for the base station are summed (step 120) and, as will be rliRcllqqed later, the sum is used in ~ e the proper power control command to be sent to the mobile radios.
In the preferred Pmho~limPnt, all mobile radios that are listening to the same forward packet channel are also receiving the same power con-25 trol bit stream. Thus each power control bit stream controls all the mobileradios that are Lr~ g on any of the reverse packet channels that are ~lcRori~tpd with the forward packet channel.
The base station controls the mobile radio's transmit power using closed loop power control. In other words, if the base station ~lPtPrminP5 30 that the transmit power of the received signal is too high, the base station sends a command to the mobile radio to decrease its transmit power. The base station sends a cnmm:~ntl instructing an increase if the transmit power is too low. This power control cnmm~n~l~ in the preferred embodi-ment, is two modulation symbols. The preferred embodiment format of 35 such a word is illustrated in FIG. 4.
In the preferred PmhorlimPnt, the power control bit of the present invention is set by the base station according to the following r.nnrlitinnR.
SlJBSTlTUTE SHEET (F~ULE 26) wo 96/03813 219 5 9 8 4 ~ 176 ~
The power control bit is set to a l, instructing the mobile radio to decrease its power output if the following condition is true:
(~(E~/) 2all0CatedE~/O)OR((miin ( I~/o)j) ~o) where i = the ith mobile radio.
The power control bit is set to a 0, instructing the mobile radio to increase its power output if the following condition is true:
(~,(E~) <allocatedE~/o)AND((nliin ( ~o)c) where i = the ith mobile radio.
In other words, the first condition (step 12'i) is true when the total or sum of the E~o's of all the mobile radios communicating with the base 15 station is greater than or equal to the maximum E~/o or when the minimnm El~ of any one of the mobile radios is greater than the desired Ely/o. In this case, the total amount of E~/o that has been allocated to the reverse packet channel has been exceeded as might be the case when too many mobile radios are tr~ncnnit+in~ A particular mobile radio's ~/No 20 could also have been bigher than needed and the received signal may perturb the remaining reverse packet channel users so the mobile radio's power output needs to be decreased (step 130).
The second condition (step 135) is true when the sum of +Ihe E~/o's of all the mobile radios rnmmnnir~tinF with the base station is less than the 25 m~imllm E~o and when the minimum E~o of any one of the mobile radios is less than or equal to the desired E7/o. In both cases, the mobile radio's E~o is too low and the received signal may not be (irmn~ tpd correctly so the mobile radio's power output needs to be increased (step 140).
Alternate embodiments of the power control process of the present invention uses other cr~n~litinnC yielding similar results. Also, the other C~ thresholds mrntinnPd above could be snhc+it11t~ in the above cnn~itinnC to yield similar results.
In an alternate ~mhorlim~nt~ of the power control process of the pre-35 sent invention, the base station dtl~l~.,les if the command to increase power will cause the mobile radio's power output to exceed the allocated S~BSTITUTE SHEET (RULE 26) ~ WO 96/03813 2 1 9 5 ~I g-4 . P~ 76 El~/o. If this is true, the base station ~nmm~nrlq the mobile radio to de-crease its transmit power instead of increasing.
If there is a single tr~ncmi.qqinn on the reverse packet channel of the present invention, power control is performed on the traffic channel as 5 discussed in U.S. Patent No. 5,056,109 to Gilhousen et al. and assigned to Qualcomm, Inc. When there are multiple tr~ncmigqinnc~ the base station tries to keep the mobile radio with the poorer El7~o at the allocated El~/o, subject to the cullQLlaill~ that the total received El~o is not too great.
An example of the above described power control process is 10 illustrated in FIG. 9. FIG. 9 shows a plot of the transmit power of two users, A and B. The desired E~/o is the lower threshûld while the upper threshold is the allocated El~/o. The upper curve shows ~: El~o that, in this case, is A + B. The power control cnmm~m1.q trAncmit+od by the base station are illustrated at the bottom of the plot.
The initial portiûns of the user A and user B w~v~ru-.--s are both above the desired E~o and the ~ E~b/o is above the allocated E~/o. Using the prûcess of the present inventiûn~ the base station sends out power control cnmm~n~lq instructing the mobiles to turn down their transmit pûwer. As required by IS-95 7.1.3.1.7, a twû pûwer control group delay issued before a 20 power control cnmm~nrl is impl~mPntPfl Therefore, the plot shows that the power does not decrease until the slot i+2. This is illustrated in FIG.
I. FIELD OF TEIE INV~ON
The present invention relates to wireless rommnnirsltinnc More particularly, the present invention relates to power control in a CDMA
10 communication system.
II. DESCRIPTION OF T~E RELATED ART
A packet is one method of pslrkslging user data. Typically, the l~ packet is divided up into various fields, with each field comprising one or more bits. Each field is used for a pr-~-7-~t-~rmin-~d function such as user data, addresses, error detection, etc. Data packets can be formed according to pre-existing protocols such as X.25 and TCP/IP that are well known in the art.
Packets may be used with a true packet service in which the stpr1irsltif)n~ transport, or other layer generates the packet. Packets can also be generated by a network's lower protocol layer that breaks a stream of data bits into data packets of ~ler1 l ~ ~ . l . i . .-~d length.
Data packets can be trslncmit~~d over a radio channel using many 25 methods. A first method uses a dedicated channel to carry packets between a pair of radio Ls~.eiv~ . A second method rnr.,~ c~rc a single, central radio transceiver that transmits over a common channel to one or more other radio l~;s~scv;vvl~ that are monitoring for packets rnntstining data in the address field signifying that radio transceiver's 30 particular address. A third method uses a random access or rnntpnti,.n based protocol in which the packets are Ll,--.h..-DIed from one or more radio Lsclsss~vivvl~ to either a central termina or each other.
In a typical CDMA cellular communication system that follows the Tr~ ir~sltinnc Industries Accnrisltion/Electronic _ndustries 35 Acenrisltinn Interim Standard 95 (TsTA/EsTA/IS-95), the dedicated channel corresponds to a traffic channel. This channel transmits voice and data signals between the mobile radio and the base station. The common channel approach cul~e~pu~ds to trs~1n.emit~ing on the paging channel that is used to broadcast pages in a CDMA system when each page carries an 40 address. The random access approach corresponds to the access channel.
SU8STITUTE SHEET (RULE 26) ~ ?~
wo 96/03813 2 1 9 ~ 9 ~4 ~_I/,J~. 1 176 ~
A typical CDMA-type n nmmnnirAti~m system is described in E~reater detail in U.S. Patent No. 5,103,459 to ('Ti1hm1cPn et al. and assigned to Qualcomm, Inc.
When one or more packets are to be trAncmittod between a base 5 station and mobile radio or vice versa, a traffic channel can be allocated between the two. Once a packet is trAncmitte-l the time to the next packet is often unknown. Instead of having the traffic channel allocated and unused, the channel is rlPA11noAtPr1 after a period of idleness. This period can be fixed with the period determined by analyzing typical traffic l0 patterns. Alternatively, this period can also be variable with the period set by analyzing the trAncmitted packet stream.
The allocation of traffic channels presents at least two problems.
First, the traffic channel takes time to set up, thus delaying the packet trAncmi-~ nn In some in~tqnrr~c, setting up a traffic channel could 15 require more than a second. Second, the resources to set up and use a traffic channel may be too expensive to justify the trAn.cmiccinn of ~-r~ u~cu~ packets, short packets, or short se~lu~ . of packets.
Power control in a CDMA system is very ~r,.~u ~;.r~ since a large number of mobile radios are trAncmitting on the same ~r~ ut~u~ If one 20 mobile is trAncmittine at a power output that is too large, it can degrade the received E~o from other mobile radios to the point that the base station cannot correctly riPmn-ln1AtP trAncmiccinnc If the mobile radio transmits at too low of an output power, the received E~o from the mobile radio at the base station will be too low to properly rlPmnr~ AtP the E~Oreceived 2~ signal. The mobile radio's transmit power, therefore, has an affect on system capacity.
The correlation between E~o and system capacity can be shown as follows. When there are no mobile radios in other cells, the maximum number of cimll1tAnPous trAncmiccinn.c, N, is approximately:
N /1~ /~)d~s( ~P-) ( ~/o)des where:
W = spreading bandwidth, 35R = data rate, ~STITUTE SHEET (RULE 26) ~wo 96/03813 2 1 ~ S ~ 8 ~ Sl~ ~ 76 (E~o)d = desired quality metric subsequently explained in greater detail, No = thermal noise spectral density of the base station receiver, and Pr = received power per trrnqmicci~n The second term in the numerator is typically very small compared to W~g~ therefore, Ns (E~/R) . Thus, a system using a higher desired El~o lowers capacity.
For the ith mobile radio, the received EyO~ denoted by (EyO) ~ at the 10 base station is approximately (E~o)i ~ ~. The probability that the j~i trAncmiccinn can be surcPccfillly rlPmn~ ted is high if (EYo)i exceeds (EYo)d as is described above. If Pri is large, however, the El~o is degraded for other mobile radios. If the received E~o falls below (El~/o)d~ ~
the probability that the tr~nqmir~;nn will not be surcPccfillly rlpmodlllrtpd 15 is high~
The mobile radio dynamically adjusts its transmit power using closed and open loop power control in order to maintain the proper received E~o at the base station as channel cnn~iti~lnc change or the range to be base station changes. Open loop power control adjusts the 20 mobile radio's transmit power flnt-n-~m~-usly by measuring the received power on the forward channel. Closed loop power control adjusts the mobile radio's transmit power by a feedback bit stream from the base station. 'rhe base station measures the received El~o to ~lPtPrminP the feedback bit stream. Closed loop and open loop power control together 25 dPtprminp the mobile radio's transmit power, as disclosed in U.S. Patent No. 5,056,109 to Gilhousen et al. and assigned to Qualcomm, Incorporated.
Closed loop power control cu~pculs~l~es for the dirr~ .es in fading between the forward and reverse links, such as occurs when they are 30 different L,-4~ ..ripc A~rlitinnrlly, it serves to compensate for the di~t,1~..ce., in transmit and receive path gains in the mobile radio and base station.
Closed loop power control is possible in a typical communication ,cystem since there is one traffic channel per mobile radio. This one-to-one SUe,STlTUTE SHEET (RULE 26) 3 2 1 9 ~ 9 8 ~ 76 ~
channel pairing permits the base station to measure the mobile radio's reverse channel power and for the mobile radio to utilize the power control ~ bit stream from the base station on the forward channel.
A multi-access channel, however, does not have a one-to-one 5 channel pairing, as multiple mobile radios can transmit simultaneously.
The identity of the mobile radio, therefore, is not necessarily known to the base station. Also, the mobile radios do not know the number of mobile radios ~ F, thus the ~ ;.,., of the power control bit stream is not clear to the mobile radio.
Since the mobile radio aligns its transmit timing with the timing of the signals that it receives from the base station and all base station signals are time aligned, when two simultaneous trAncmicqinnc occur on the reverse channel and there is no mn1tirAth the trAncmiCcinnc arrive at the base station separated by times equal to the difference of twice the 15 distances between each mobile radio and the base station. If this time exceeds one pseùdo noise chip, the two trAncmiccinns can be distinguished by the base station. The inability to distinguish these m111tipAth iL~ llllc~innc is a collision.
When there is mn1tirAth there is no collision if the base station can 20 identify and properly combine the mn1tir~th ~ If three or more access channel trAncmiCcinnc occur in the same slot, then some trAncmiccinnA may collide while others do not. In a typical multi-access channel, such as is found in a TDMA or an FDMA system, when two cim11ltAnPo11c trAncmiccinnc occur there is a collision and neither 26 lL~IICl~ m is sn~cP~efillly ~Pmn~ t~d by the base station.
Base stations may further reduce il~tt:~rel~ e with each other by trAncmitf;nF with the minimum power necessary for their signals to be received by the base station. A mobile radio transmits its first ~L..I~ .. or probe at a power level somewhat less than it estimates to 30 be necessary to reach the base station. This CU1LS~1 v~iv~ estimate may be a ,ule~dt k~ i- ed value or it may be ~Alr7llAted in response to the measured power level of a signal that the mobile radio has or is receiving from the base station.
A preferred ~mho~imf~nt is for the mobile radio to measure the 35 received power from the base station. This received power is the ~L~ d power of the base station times the path loss. The mobile radio then uses this estimate, plus a constant correction, plus adjustment factors to set the initial transmit power. These adjustment factors may be sent to the mobile radio from the base station. Some of these factors S~IBSTITUTE SHEET (RULE 26) ~ i ~wos6/038l3 219~98~ v~ S.of 176 correspond to radiated power of the base station. Since the path loss from the mobile station to the base station is essentially the same as from the base station to the mobile station, the signal received at the base station should be at the correct level, assuming that the base station has supplied 6 the n~UI~lU,U~ e Cu~ iuu factors and that the mobile radio and base station gains are error free.
After trAncmitt;nF the first access probe at this Illhli~ulll power level, the mobile station increases the power of successive probes within each access probe sequence by a predetermined step amount. A thorough 10 discussion of access probes is evident in IS-95, section 6.6.3.1 and in co-pending patent, Apporatus and Method for Reducing Collisions Between Mobile Stations Si~7atnrle~ s7r Accessing a Base Station in a CDMA
Cellular Con7~7u~2i((7t~ s System, S~N 08/219,867 to TiotlomAnn et al. and assif~ned to Qualcomm7 Inc.
In addition7 between successive trAncmiCci-n~ of an access probe7 the mobile radio can randomize its trAncmiqcion time and choose another access channel so as to avoid a potential collision. IS-957 section 6.6.3.1 describes this in greater detail.
It can be seen, therefore7 that power control is very il.~,uu~ l for 20 proper operation of a CDMA r~-iiotolophr~no system. There is a resulting need for a power control process in a multiple access system to increase system capacity.
SUMMAE~Y OF TEIE INVENTION
The power control process of the present invention uses a comparison threshold to determine whether the base station should instruct the mobile radios to increase or decrease their transmit power.
The total received EyO for all the mobile radios rr~mmllnicAting with a 30 particular base station is compared to a mA~imnm threshold for the reverse channel. A~lflit;~-nAIly, a minimnm comparison threshold for the mobile radio being controlled is determined. If the total received E~o is greater than or equal to the msl~imllm threshold or the minimum received EyO for any mobile radio is greater than the reverse channel 36 minimum, the base station instructs the mobile radio to decrease its output power. If the total received EyO is less than the mA~imnm reverse channel threshold and the minimllm received EyO for any mobile radio is S~BSTlTuTE SHEET (RULE 26) WO g6/03813 2 1 9 5 9 ~ ,,5 ~ 176 ~
less than or equal to the reverse channel minimum, the base station instructs the mobile radio~ to increase power.
BRIEF D~ )N OF T~E DRAWINGS
FIG. 1 shows a flowchart of the process of the present invention.
FIG. 2 shows a graph of the frame error rate versus E~o FIGs. 3a and 3b show a typical forward packet channel structure in accordance with the present invention.
FIG. 4 shows the power control bit positions in accordance with the present invention.
FIG. 5 shows a block diagram of a typical mobile radio in accordance with the present invention.
FIG. 6 shows a block diagram of a typical base station in accordance 15 with the present invention.
FIG. 7 shows the format of a forward CDMA channel in accordance with the present invention.
FIG. 8 shows the format of a reverse CDMA channel in accordance with the present invention.
FIG. 9 shows a plot of the transmit power of two radios and their reaction to power control crlmmAn~ie in ac.o~ ce with the present invention.
n~TA~r.F.n L~ OF TEE r~K~;U r-The present invention ~n~rmnpAcR~g a pair of channels, sub-sequently referred to as the forward and reverse packet channels. The base station cnnnm-1ni~ At~c with the mobile radios over the forward chan-nel and the mobile radios communicate with the base station over the 30 reverse channel. A base station uses the power control process of the present invention, over the forward packet channel, to dynamically adjust the transmit power of one or more mobile radios trAnemi~ing on the reverse packet channel.
The following ~1iccnecinn refers to mobile radios and base stations 35 as the preferred ~mho~im~nt Mobile radios include rA~ t~ ph~m~c used - in both a terrestrially based cr~mmllni~Ati(m system and a satellite based rf~mmlJni~Ati~ln system. Similarly, the base stations can be located on the earth or as orbiting satellites.
SU8STITUTE SHEET (RUI F 26) - P~ 76 ~wo 96103813 2 1 ~ ~ 5 8 ~
The reverse packet channel, in the preferred PmhoflimPnt is a variable rate channel that transmits data packets that have been broken up into a sequence of one or more frames. In an alternate embodiment, the reverse packet channel handles data at a fixed rate.
Each tr~ncmiccinn includes a preamble, to aid in spread spectrum acquisition, followed by the datagram. The preamble of the reverse packet channel is the same as the preamble used in the access channel; a sequence of one or more nnmorllllAted frames of Walsh function 0. The access channel preamble is discussed in greater detail in TIA/EIA IS-95.
10 Alternate PmhoflimPntc use other preambles than the Walsh function 0.
Another alternate Pmho~lim.ont. includes frames mndlll~tPd by known fic:4uem~;es~ However, this increases receiver complexity.
In the preferred Pmho~imPnt the forward CDMA channel consists of a pilot channel, a ~y~.h~u~ .Lion channel, one or more paging 15 channels, one or more forward packet channels and forward traffic channels. FIG. 7 illustrates the format of the preferred PmhoAimPnt of the forward CDMA channel including the traffic channels (705) and packet channels (710) with power control sllhrh~nnPlc (715). The forward packet channel is a spread spectrum channel similar in operation to the forward 20 traffic channel as disclosed in IS-95 as is illustrated in FIGs. 3a and 3b. A more complete (li~ . of this channel can be found in IS-95.
FIG. 8 illustrates the format of the reverse CDMA channel. A set of one or more access channels (805) are ~cRori~tDd with each paging channel. An overhead message defines the number of access channels 26 (805) that are ~A~or: l~cl with a particular paging channel. Similarly, one or more reverse packet channels are RcRori~ted with a forward packet channel and an overhead message defines the number of reverse packet channels ~Rcori~ted with a particular forward packet channel. Different reverse packet channels (810) ~ o ,.l~d with the same forward packet 30 channel are dirr~ tiated by each reverse packet channel having a unique spreading code.
In the preferred ~mhor1imPnt., assignment of a reverse packet channel to a forward packet channel is static in that a mobile radio con-tinually monitors the same forward packet channel while in the same 35 cell. The channel may be assigned by using information from overhead pcu~lue~l s, by S~qRi~nmPnt on a per mobile radio basis, or via some static procedure.
The reverse packet channels enable multiple mobile radios to trans_it cimlllt~npously~ In the preferred PmhoflimPnt of a CDMA
Sl.lBSTlTUTE SHEET (FIULE 26) Wo96/03813 21~.9~598.~ 76 ~
system, the multiple trAnqmiCcinnc from multiple mobile radios only collide if their multipath rnmpnnPntc overlap as was described previously.
In the preferred PmhorlimPnt, a mobile radio randomly chooses, for its trAncmiceinn.c, one of the reverse packet channels Ac.coriAtPd with a 5 forward packet channel. Alternate Pmho~1imPntc use other methods for choosing channels. AfltiitinnAlly, the trAn.cmiccinn time of a radio using a reverse packet charmel can be rAnrlnmi7Pd as is done for the access chan-nel. These Le~ uès lower the probability of a collision by distributing the mobile radios over channels or time. This also serves to increase system lO capacity. When the mobile radio retransmits a packet, it may randomize trAn.cmiccinn time and choice of reverse packet channel so as to avoid collisions as previously described for the access channel.
A flowchart of the power control process of the present invention is illustrated in FIG. 1. In the preferred Pmho~imPnt, this process uses the 15 (1imPncinn1P.cc ratio E~/o to ~ipt~rminp whether to adjust the radio's transmit power and, if so, whether to increase or decrease the power.
Alternate Pmho~im~ntc use other si~,nal quality metrics for threshold cnmrAricnn such as P~/NO~ Pr~ or some scaled equivalent Of E~; Pr being the received power.
The E~o ratio is a standard quality mea:~u~elue~lt for digital com-mnnioAti~nc system performance. The ratio expresses the energy per bit to the totl hlLelf~ e spectral density of the channel. El~/o can be considered a metric that ch~lL.. .el;~.~.., the performance of one rommllninAtinn system over another; the smaller the required E~o the 25 more efficient is the system mnrln1Atinn and detection process for a given probability of error. ~ more detailed ~ ;.... of this concept can be seen in B. Sklar, Digital Con~ n;cations, Fundamentals and App~ications, Chapter 3 (1988).
The process of the present invention, in the preferred embodiment, 30 is used in a typical CDMA cellular radiotelephone system as disclosed in the '459 patent described above. The radiotelephone system is comprised of numerous rA~intPlprhnnpc that transmit to a base station over a reverse channel and receive from the base station over a forward channel.
The ~ x;~ . total E~/o is subsé~luelltly referred to as the allocated 35 E~/o (step 100). The allocated E~o may vary with the traffic channel load.
The allocated El~o is used by the base station as the maximum threshold for all mobile radios trAncmit~;ng to that base station. If a par-ticular mobile radio trAncmitt;ng to the base station requires a transmit SUBSTlTuTE SHEET (RULE 26) ~WO 96/03813 2 ~: 9 ~ ~ ~ 4 P~ 76 power increase, the base station will not instruct the mobile radio to in-crease its transmit power beyond the allocated E~/o.
In the preferred Pmho~liment, the reverse link has a desired E~/o assigned to it by the base station (step 105). The desired ratio is the value ~ 5 that gives a high probability that a data packet will be received without error from the base station and yet ms~int~inR a high capacity as explained above. As an e~ample, a packet cnnqiQting of 10 frames with a 3 dB E~/o has an appro~imate error rate of 10%, as seen in FIG. 2.
Choosing a larger Eb/o causes the packet error probability of the 10 tr~ncmi.q.qion to decrease. This is illustrated in the graph of FIG. 2. This plot shows the effect to the frame error rate of increasingE~O. For e~ample, referring to FIG. 2, if the E~b/o is 4 dB, the resulting error rate for the 10 frame packet is 4 ~ 10-3. If E~/o is chosen too large, however, the tr~n.qmitf~ l signal may cause hlLe~lrt~ to other mobile radios 15 rommnnirFt.ing with the base station.
The received E~fo of each mobile radio is estimated by the base station (step 115). Since the base station acquires the mobile radios during the trAncmiFQinn of the packet preamble, it can determine the number of mobile radios that are tr~n.cmitting to the base station. These individual 20 E~o's for the base station are summed (step 120) and, as will be rliRcllqqed later, the sum is used in ~ e the proper power control command to be sent to the mobile radios.
In the preferred Pmho~limPnt, all mobile radios that are listening to the same forward packet channel are also receiving the same power con-25 trol bit stream. Thus each power control bit stream controls all the mobileradios that are Lr~ g on any of the reverse packet channels that are ~lcRori~tpd with the forward packet channel.
The base station controls the mobile radio's transmit power using closed loop power control. In other words, if the base station ~lPtPrminP5 30 that the transmit power of the received signal is too high, the base station sends a command to the mobile radio to decrease its transmit power. The base station sends a cnmm:~ntl instructing an increase if the transmit power is too low. This power control cnmm~n~l~ in the preferred embodi-ment, is two modulation symbols. The preferred embodiment format of 35 such a word is illustrated in FIG. 4.
In the preferred PmhorlimPnt, the power control bit of the present invention is set by the base station according to the following r.nnrlitinnR.
SlJBSTlTUTE SHEET (F~ULE 26) wo 96/03813 219 5 9 8 4 ~ 176 ~
The power control bit is set to a l, instructing the mobile radio to decrease its power output if the following condition is true:
(~(E~/) 2all0CatedE~/O)OR((miin ( I~/o)j) ~o) where i = the ith mobile radio.
The power control bit is set to a 0, instructing the mobile radio to increase its power output if the following condition is true:
(~,(E~) <allocatedE~/o)AND((nliin ( ~o)c) where i = the ith mobile radio.
In other words, the first condition (step 12'i) is true when the total or sum of the E~o's of all the mobile radios communicating with the base 15 station is greater than or equal to the maximum E~/o or when the minimnm El~ of any one of the mobile radios is greater than the desired Ely/o. In this case, the total amount of E~/o that has been allocated to the reverse packet channel has been exceeded as might be the case when too many mobile radios are tr~ncnnit+in~ A particular mobile radio's ~/No 20 could also have been bigher than needed and the received signal may perturb the remaining reverse packet channel users so the mobile radio's power output needs to be decreased (step 130).
The second condition (step 135) is true when the sum of +Ihe E~/o's of all the mobile radios rnmmnnir~tinF with the base station is less than the 25 m~imllm E~o and when the minimum E~o of any one of the mobile radios is less than or equal to the desired E7/o. In both cases, the mobile radio's E~o is too low and the received signal may not be (irmn~ tpd correctly so the mobile radio's power output needs to be increased (step 140).
Alternate embodiments of the power control process of the present invention uses other cr~n~litinnC yielding similar results. Also, the other C~ thresholds mrntinnPd above could be snhc+it11t~ in the above cnn~itinnC to yield similar results.
In an alternate ~mhorlim~nt~ of the power control process of the pre-35 sent invention, the base station dtl~l~.,les if the command to increase power will cause the mobile radio's power output to exceed the allocated S~BSTITUTE SHEET (RULE 26) ~ WO 96/03813 2 1 9 5 ~I g-4 . P~ 76 El~/o. If this is true, the base station ~nmm~nrlq the mobile radio to de-crease its transmit power instead of increasing.
If there is a single tr~ncmi.qqinn on the reverse packet channel of the present invention, power control is performed on the traffic channel as 5 discussed in U.S. Patent No. 5,056,109 to Gilhousen et al. and assigned to Qualcomm, Inc. When there are multiple tr~ncmigqinnc~ the base station tries to keep the mobile radio with the poorer El7~o at the allocated El~/o, subject to the cullQLlaill~ that the total received El~o is not too great.
An example of the above described power control process is 10 illustrated in FIG. 9. FIG. 9 shows a plot of the transmit power of two users, A and B. The desired E~/o is the lower threshûld while the upper threshold is the allocated El~/o. The upper curve shows ~: El~o that, in this case, is A + B. The power control cnmm~m1.q trAncmit+od by the base station are illustrated at the bottom of the plot.
The initial portiûns of the user A and user B w~v~ru-.--s are both above the desired E~o and the ~ E~b/o is above the allocated E~/o. Using the prûcess of the present inventiûn~ the base station sends out power control cnmm~n~lq instructing the mobiles to turn down their transmit pûwer. As required by IS-95 7.1.3.1.7, a twû pûwer control group delay issued before a 20 power control cnmm~nrl is impl~mPntPfl Therefore, the plot shows that the power does not decrease until the slot i+2. This is illustrated in FIG.
4.
After four decrease power control cnmm~n~lq, the user B transmit power is below the desired E~/o. The base station then sends three turn up 25 cnmm:~n~lc After the two power control group delay, the ûutput power of user B is above the dosired El~o and the ~ E/~D is above the allocated El~o.
This process continues in a similar manner.
If a large number of tr~ncmiQQ;nnq are received on a busy channel, the power control process of the present invention limits the power output 30 at the allocated E~o. This will likely force a higher error rate in some packet i~ ;nnc In this case, the base station can make the decision to power control only a few streams by making the minimum E~o in the above conditions over a subset of the received tr~nqmiccinnc This will likely limit the rmpact on other mobile radios.
In the preferred embodiment, the desired El~/o can be adjusted for different channel onn~itinnq so as to maintain a desired packet error rate.
If the packet error rate is too high for a desired E~/o, the base station can S~IBSTITUTE SHEET (R~JLE 26) _ _ _ _ _ _ _ , . . . .
219.~
WO96/03813 ~ g!4 F~ q76 increase the desired EyO, thus lowering the packet error rate Alternatively, if the packet error rate is lower than needed, the base station can decrease the desired E~o, thus increasing the packet error rate.
This latter adjustment serves to increase the overall system capacity. The adjustments mPntionP-1 above may need to be done for different channel rrmrlitinnc For e~ample, if there are many mnltirAth rnmpnnPntc, the base station may not be able to combine energy as effectively. In the art, this is called rr,mhining loss. On the other extreme, 10 fading may cause a higher packet error rate if there is only one mnltir?th rrmpnnpnt To maintain a low packet error rate in both these cases, the base station may increase the desired E~o In the preferred PmhorlimPnt, the desired EyO is the same for all mobile radios. Alternatively, the desired E~/o could be different for each 15 mobile radio. The previous equations can then be written as:
(~(E~/) 2all~CatedE~o)OR(~di(( ~b/o)l ( ~/~))i) where i = the ith mobile radio and ~il sigmfies that for all i, such that if theabove is true, the mobile radio is told to decrease its power; and (~,(Ey ) < allocatedEyO) AND (3il( Yo)i ( Yo)i) where i = the ith mobile radio and 3i I sig~nifies that there exists an i such that if the above is true, the mobile radio is told to increase its power.
After l.rn~ lg the first access probe at a minimum power level, 25 the mobile radio increases the power of successive probes within each access probe sequence by a ~ l ,..;rl~d step amount. This step amount is different for different Pmhor~im~ntq and is set to optimize the system performance.
A cimplifiP~ block diagram of a typical mobile radio is illustrated in 30 FIG. 5. Signals received from the base station are received with the antenna (501). The duple~er (502) splits the signal to the low noise amplifier (503) that amplifies the signal. This amplified signal is then input to a variable gain amplifier (504), the gain of which is controlled by a receive ,~,.l~"" .1 :~ gain control circuit (505). The output of the variable gain 35 amplifier (504) is input to a llPmor~nlAtnr and decoder (506). The rlPmnr~lllAtnr portion removes the signal mnrlnlAti~-n so that the p~ d SUBSTlTUTE SHEET (RULE 26) ~WO 96103813 2 ~ 9 5 9 8~ . s ~76 information can be broken up by the packet receiver (507) into a digital form that is usable by a computer or other electronic device.
A digital signal to be tr~ncm;ttel from a computer or other elec-tronic device is first packetized (520). The packets of data are then mod-~ 5 ulated by the encoder and mnclnl~tnr (525). The mor~ tPd signal is input to a variable gain amplifier (530) that amplifies the signal prior to the fixed gain power amplifier (535). The output of the power amplifier (535) is input to the duplexer (502) that couples the signal to the antenna (501) to be radiated.
The gain of the variable gain amplifier is controlled by the power control bit of the present invention that is tr~ncmit~rd by the base station.
When the mobile radio receives the power control bit, it is input to the closed loop power control circuitry (540). This circuitry (540) simply de-termines whether the power control bit is a logic 1 or a logic 0 and gener-15 ates the proper control voltage to increase or decrease the gain of the variable gain power amplifier (530).
In the preferred Pmho~imPnt., the gain is increased or decreased in 1 dB increments. The power control circuitry (540) outputs a digital value indicative of each 1 dB increase or decrease. This digital value is input to a 20 digital to analog converter (DAC) (545). The DAC converts the digital value to an analog signal that controls the gain of the variable gain power amplifier. In this way, the process of the present invention enables the base station to dynamically adjust the transmit power of the mobile radio as cnnrlitinnc change.
Alternatively, the increase and decrease in gain does not have to be by the same amount. In addition, the increase and decrease in power control gain may adapt based upon the sequence of up or down commands that have been received by the mobile radio.
FIG. 6 shows a block diagram of a typical CDMA base station 30 system incul~ Li-,g the power control process of the present invention.
This diagram shows the antennas of a base station (601 and 602) that receive the signals Lln~ Pd from the mobile radio. The received signals are ~iio+rihutp(l to various receivers (605 - 620) ~iPpPnrling on which one is being used. The receivers (605 - 620) generate the 11Pmn~n1sltPd bits 35 for use by other devices such as external colu~uL~
The receivers (605 - 620) also generate the signal to interference ratios, E~o, that are used by the power control process of the present invention (625) to generate the power control bits. These bits are inserted into the power control stream by puncturing (630) the forward channel S~BSTITUTE SHEET (RULE 26) wo 96/03813 21~ ~ ~ 8;~ 76 ~, signal that has been generated by the mnrlnlAtflr (635). This signal is then eventually trAn.crnitf~d by the transmit antenna (603) to the mobile radio.
In the preferred embodiment, the power control is p~.ru-,..ed by a single bit. Alternate embodiments, however, use multiple bits to form a 5 power control command word. Such a word can not only control the direction of the transmit power but the rate of power change. For example, one bit of the command instructs the radio to increase power while another bit of the command instructs the increase to be in 2 dB increments instead of 1 dB.
In summary, the power control process of the present invention uses a single power control bit stream from the base station to control the transmit power of multiple radios. The signal quality metric, E~o, is used to ~1. 1....,;"~ whether to increase or decrease the power and what amount of power change is needed.
I claim:
S~STITUTE SHEET (RULE 26)
After four decrease power control cnmm~n~lq, the user B transmit power is below the desired E~/o. The base station then sends three turn up 25 cnmm:~n~lc After the two power control group delay, the ûutput power of user B is above the dosired El~o and the ~ E/~D is above the allocated El~o.
This process continues in a similar manner.
If a large number of tr~ncmiQQ;nnq are received on a busy channel, the power control process of the present invention limits the power output 30 at the allocated E~o. This will likely force a higher error rate in some packet i~ ;nnc In this case, the base station can make the decision to power control only a few streams by making the minimum E~o in the above conditions over a subset of the received tr~nqmiccinnc This will likely limit the rmpact on other mobile radios.
In the preferred embodiment, the desired El~/o can be adjusted for different channel onn~itinnq so as to maintain a desired packet error rate.
If the packet error rate is too high for a desired E~/o, the base station can S~IBSTITUTE SHEET (R~JLE 26) _ _ _ _ _ _ _ , . . . .
219.~
WO96/03813 ~ g!4 F~ q76 increase the desired EyO, thus lowering the packet error rate Alternatively, if the packet error rate is lower than needed, the base station can decrease the desired E~o, thus increasing the packet error rate.
This latter adjustment serves to increase the overall system capacity. The adjustments mPntionP-1 above may need to be done for different channel rrmrlitinnc For e~ample, if there are many mnltirAth rnmpnnPntc, the base station may not be able to combine energy as effectively. In the art, this is called rr,mhining loss. On the other extreme, 10 fading may cause a higher packet error rate if there is only one mnltir?th rrmpnnpnt To maintain a low packet error rate in both these cases, the base station may increase the desired E~o In the preferred PmhorlimPnt, the desired EyO is the same for all mobile radios. Alternatively, the desired E~/o could be different for each 15 mobile radio. The previous equations can then be written as:
(~(E~/) 2all~CatedE~o)OR(~di(( ~b/o)l ( ~/~))i) where i = the ith mobile radio and ~il sigmfies that for all i, such that if theabove is true, the mobile radio is told to decrease its power; and (~,(Ey ) < allocatedEyO) AND (3il( Yo)i ( Yo)i) where i = the ith mobile radio and 3i I sig~nifies that there exists an i such that if the above is true, the mobile radio is told to increase its power.
After l.rn~ lg the first access probe at a minimum power level, 25 the mobile radio increases the power of successive probes within each access probe sequence by a ~ l ,..;rl~d step amount. This step amount is different for different Pmhor~im~ntq and is set to optimize the system performance.
A cimplifiP~ block diagram of a typical mobile radio is illustrated in 30 FIG. 5. Signals received from the base station are received with the antenna (501). The duple~er (502) splits the signal to the low noise amplifier (503) that amplifies the signal. This amplified signal is then input to a variable gain amplifier (504), the gain of which is controlled by a receive ,~,.l~"" .1 :~ gain control circuit (505). The output of the variable gain 35 amplifier (504) is input to a llPmor~nlAtnr and decoder (506). The rlPmnr~lllAtnr portion removes the signal mnrlnlAti~-n so that the p~ d SUBSTlTUTE SHEET (RULE 26) ~WO 96103813 2 ~ 9 5 9 8~ . s ~76 information can be broken up by the packet receiver (507) into a digital form that is usable by a computer or other electronic device.
A digital signal to be tr~ncm;ttel from a computer or other elec-tronic device is first packetized (520). The packets of data are then mod-~ 5 ulated by the encoder and mnclnl~tnr (525). The mor~ tPd signal is input to a variable gain amplifier (530) that amplifies the signal prior to the fixed gain power amplifier (535). The output of the power amplifier (535) is input to the duplexer (502) that couples the signal to the antenna (501) to be radiated.
The gain of the variable gain amplifier is controlled by the power control bit of the present invention that is tr~ncmit~rd by the base station.
When the mobile radio receives the power control bit, it is input to the closed loop power control circuitry (540). This circuitry (540) simply de-termines whether the power control bit is a logic 1 or a logic 0 and gener-15 ates the proper control voltage to increase or decrease the gain of the variable gain power amplifier (530).
In the preferred Pmho~imPnt., the gain is increased or decreased in 1 dB increments. The power control circuitry (540) outputs a digital value indicative of each 1 dB increase or decrease. This digital value is input to a 20 digital to analog converter (DAC) (545). The DAC converts the digital value to an analog signal that controls the gain of the variable gain power amplifier. In this way, the process of the present invention enables the base station to dynamically adjust the transmit power of the mobile radio as cnnrlitinnc change.
Alternatively, the increase and decrease in gain does not have to be by the same amount. In addition, the increase and decrease in power control gain may adapt based upon the sequence of up or down commands that have been received by the mobile radio.
FIG. 6 shows a block diagram of a typical CDMA base station 30 system incul~ Li-,g the power control process of the present invention.
This diagram shows the antennas of a base station (601 and 602) that receive the signals Lln~ Pd from the mobile radio. The received signals are ~iio+rihutp(l to various receivers (605 - 620) ~iPpPnrling on which one is being used. The receivers (605 - 620) generate the 11Pmn~n1sltPd bits 35 for use by other devices such as external colu~uL~
The receivers (605 - 620) also generate the signal to interference ratios, E~o, that are used by the power control process of the present invention (625) to generate the power control bits. These bits are inserted into the power control stream by puncturing (630) the forward channel S~BSTITUTE SHEET (RULE 26) wo 96/03813 21~ ~ ~ 8;~ 76 ~, signal that has been generated by the mnrlnlAtflr (635). This signal is then eventually trAn.crnitf~d by the transmit antenna (603) to the mobile radio.
In the preferred embodiment, the power control is p~.ru-,..ed by a single bit. Alternate embodiments, however, use multiple bits to form a 5 power control command word. Such a word can not only control the direction of the transmit power but the rate of power change. For example, one bit of the command instructs the radio to increase power while another bit of the command instructs the increase to be in 2 dB increments instead of 1 dB.
In summary, the power control process of the present invention uses a single power control bit stream from the base station to control the transmit power of multiple radios. The signal quality metric, E~o, is used to ~1. 1....,;"~ whether to increase or decrease the power and what amount of power change is needed.
I claim:
S~STITUTE SHEET (RULE 26)
Claims (22)
1. A method for controlling transmit power of a plurality of radios, the plurality of radios communicating with a base station, the method comprising the steps of:
the base station determining the transmit power required from each radio of the plurality of radios; and the base station transmitting a single power control bit stream to the plurality of radios to instruct each radio to alter its transmit power in response to the required transmit power.
the base station determining the transmit power required from each radio of the plurality of radios; and the base station transmitting a single power control bit stream to the plurality of radios to instruct each radio to alter its transmit power in response to the required transmit power.
2. The method of claim 1 wherein the step of determining the transmit power comprises the steps of:
determining a first signal quality threshold;
determining a second signal quality threshold;
determining a signal quality metric for each radio of the plurality of radios; and comparing the signal quality metrics for the plurality of radios to the first and second signal quality thresholds.
determining a first signal quality threshold;
determining a second signal quality threshold;
determining a signal quality metric for each radio of the plurality of radios; and comparing the signal quality metrics for the plurality of radios to the first and second signal quality thresholds.
3. The method of claim 2 wherein the signal quality metric is an energy per bit to total interference spectral density ratio.
4. The method of claim 2 and further including the steps of:
increasing the transmit power of a radio having a signal quality metric that is less than the first signal quality threshold; and decreasing the transmit power of a radio having a signal quality metric that is greater than the second signal quality threshold.
increasing the transmit power of a radio having a signal quality metric that is less than the first signal quality threshold; and decreasing the transmit power of a radio having a signal quality metric that is greater than the second signal quality threshold.
5. The method of claim 2 wherein the first signal quality threshold is a minimum signal quality threshold and the second signal quality threshold is a maximum signal quality threshold.
6. A method for controlling a power output of a remote transmitter in a first mobile radio of a plurality of mobile radios, the first mobile radio receiving signals from a base station over a forward channel, the base station receiving signals from the first mobile radio over a reverse channel, the method comprising the steps of:
determining a maximum reverse channel signal quality metric;
determining a desired reverse channel signal quality metric;
determining a reverse channel signal quality metric for each of the plurality of mobile radios, thus creating a plurality of reverse channel signal quality metrics;
determining a minimum reverse channel signal quality metric of the plurality of mobile radios;
summing the plurality of reverse channel signal quality metrics;
and the base station instructing the remote transmitter to decrease the power output if the sum of the reverse channel signal quality metrics is greater than or equal to the maximum reverse channel signal to noise ratio or the minimum reverse channel signal quality metrics is greater than the desired reverse channel signal quality metric.
determining a maximum reverse channel signal quality metric;
determining a desired reverse channel signal quality metric;
determining a reverse channel signal quality metric for each of the plurality of mobile radios, thus creating a plurality of reverse channel signal quality metrics;
determining a minimum reverse channel signal quality metric of the plurality of mobile radios;
summing the plurality of reverse channel signal quality metrics;
and the base station instructing the remote transmitter to decrease the power output if the sum of the reverse channel signal quality metrics is greater than or equal to the maximum reverse channel signal to noise ratio or the minimum reverse channel signal quality metrics is greater than the desired reverse channel signal quality metric.
7. The method of claim 6 and further including the step of the base station adjusting a minimum reverse channel energy per bit to total interference spectral density ratio depending on reverse channel conditions.
8. The method of claim 6 and further including the step of adjusting a maximum reverse channel energy per bit to total interference spectral density ratio in response to an increase or decrease in the quantity of the plurality of radiotelephones.
9. The method of claim 6 wherein the mobile radio is a code division multiple access radiotelephone and the base station is a code division multiple access base station.
10. The method of claim 6 wherein the signal quality metric is an energy per bit to total interference spectral density ratio.
11. The method of claim 10 wherein the energy per bit to total interference spectral density ratio is Eb/Io.
12. A method for controlling a power output of a remote transmitter in a first mobile radio of a plurality of mobile radios, the first mobile radio receiving signals from a base station over a forward channel, the base station receiving signals from the first mobile radio over a reverse channel, the method comprising the steps of:
determining a maximum reverse channel signal quality metric;
determining a desired reverse channel signal quality metric;
determining a reverse channel signal quality metric for each of the plurality of mobile radios, thus creating a plurality of reverse channel signal quality metrics;
determining a minimum reverse channel signal quality metric of the plurality of mobile radios;
summing the plurality of reverse channel signal quality metrics;
and the base station instructing the remote transmitter to increase the power output if the sum of the reverse signal quality metrics is less than the maximum reverse channel signal quality metric.
determining a maximum reverse channel signal quality metric;
determining a desired reverse channel signal quality metric;
determining a reverse channel signal quality metric for each of the plurality of mobile radios, thus creating a plurality of reverse channel signal quality metrics;
determining a minimum reverse channel signal quality metric of the plurality of mobile radios;
summing the plurality of reverse channel signal quality metrics;
and the base station instructing the remote transmitter to increase the power output if the sum of the reverse signal quality metrics is less than the maximum reverse channel signal quality metric.
13. The method of claim 12 and further including the step of the base station adjusting a minimum reverse channel energy per bit to total interference spectral density ratio depending on reverse channel conditions.
14. The method of claim 12 and further including the step of adjusting a maximum reverse channel energy per bit to total interference spectral density ratio in response to an increase or decrease in the quantity of the plurality of radiotelephones.
15. A method for controlling a power output of a remote transmitter in a first mobile radio of a plurality of mobile radios, the first mobile radio receiving signals from a base station over a forward channel, the base station receiving signals from the first mobile radio over a reverse channel, the method comprising the steps of:
determining a maximum reverse channel energy per bit to total interference spectral density ratio;
determining a desired reverse channel energy per bit to total interference spectral density ratio;
determining a reverse channel energy per bit to total interference spectral density ratio for each of the plurality of mobile radios, thus creating a plurality of reverse channel energy per bit to total interference spectral density ratios;
determining a minimum reverse channel energy per bit to total interference spectral density ratio of the plurality of mobile radios;
summing the plurality of reverse channel energy per bit to total interference spectral density ratios; and the base station instructing the remote transmitter to increase the power output if the minimum reverse energy per bit to total interference spectral density ratio is less than or equal to the desired reverse channel energy per bit to total interference spectral density ratio.
determining a maximum reverse channel energy per bit to total interference spectral density ratio;
determining a desired reverse channel energy per bit to total interference spectral density ratio;
determining a reverse channel energy per bit to total interference spectral density ratio for each of the plurality of mobile radios, thus creating a plurality of reverse channel energy per bit to total interference spectral density ratios;
determining a minimum reverse channel energy per bit to total interference spectral density ratio of the plurality of mobile radios;
summing the plurality of reverse channel energy per bit to total interference spectral density ratios; and the base station instructing the remote transmitter to increase the power output if the minimum reverse energy per bit to total interference spectral density ratio is less than or equal to the desired reverse channel energy per bit to total interference spectral density ratio.
16. A method for controlling power output of a first remote transmitter of a plurality of remote transmitters, each remote transmitter being part of a mobile radiotelephone, the plurality of mobile radiotelephones receiving data packets from a cellular base station over a forward channel, the cellular base station receiving data packets from the plurality of mobile radiotelephones over a reverse channel, the reverse channel having a maximum energy per bit to total interference spectral density ratio, the data packets being comprised of frames, the method comprising the steps of:
determining a desired reverse channel energy per bit to total interference spectral density ratio;
determining a energy per bit to total interference spectral density ratio on the reverse channel for each of the remote transmitters, thereby creating a plurality of energy per bit to total interference spectral density ratios;
summing the plurality of energy per bit to total interference spectral density ratios to produce a summation value;
determining a minimum reverse channel energy per bit to total interference spectral density ratio for the plurality of mobile radiotelephones;
comparing the maximum reverse channel energy per bit to total interference spectral density ratio to the summation value;
comparing the minimum reverse channel energy per bit to total interference e spectral density ratio to the desired energy per bit to total interference spectral density ratio; and the base station instructing the first remote transmitter to decrease power if the summation value is greater than or equal to the maximum reverse channel energy per bit to total interference spectral density ratio or the minimum reverse channel energy per bit to total interference spectral density ratio is greater than the desired reverse channel energy per bit to total interference spectral density ratio.
determining a desired reverse channel energy per bit to total interference spectral density ratio;
determining a energy per bit to total interference spectral density ratio on the reverse channel for each of the remote transmitters, thereby creating a plurality of energy per bit to total interference spectral density ratios;
summing the plurality of energy per bit to total interference spectral density ratios to produce a summation value;
determining a minimum reverse channel energy per bit to total interference spectral density ratio for the plurality of mobile radiotelephones;
comparing the maximum reverse channel energy per bit to total interference spectral density ratio to the summation value;
comparing the minimum reverse channel energy per bit to total interference e spectral density ratio to the desired energy per bit to total interference spectral density ratio; and the base station instructing the first remote transmitter to decrease power if the summation value is greater than or equal to the maximum reverse channel energy per bit to total interference spectral density ratio or the minimum reverse channel energy per bit to total interference spectral density ratio is greater than the desired reverse channel energy per bit to total interference spectral density ratio.
17. The method of claim 16 wherein each of the energy per bit to total interference spectral density ratios is determined by an Eb/Io of the reverse channel.
18. The method of claim 16 wherein each of the energy per bit to total interference spectral density ratios is determined by a Pr/No of the reverse channel.
19. The method of claim 16 wherein each of the energy per bit to total interference spectral density ratios is determined by a scaled version of an Eb/Io of the reverse channel.
20. A method for controlling power output of a first remote transmitter of a plurality of remote transmitters, each remote transmitter being part of a mobile radiotelephone, the plurality of mobile radiotelephones receiving data packets from a cellular base station over a forward channel, the cellular base station receiving data packets from the plurality of mobile radiotelephones over a reverse channel, the reverse channel having a maximum energy per bit to total interference spectral density ratio, the data packets being comprised of frames, the method comprising the steps of:
determining a desired reverse channel energy per bit to total interference spectral density ratio;
determining a energy per bit to total interference spectral density ratio on the reverse channel for each of the remote transmitters, thereby creating a plurality of energy per bit to total interference spectral density ratios;
summing the plurality of energy per bit to total interference spectral density ratios to produce a summation value;
determining a minimum reverse channel energy per bit to total interference spectral density ratio for the plurality of mobile radiotelephones;
comparing the maximum reverse channel energy per bit to total interference spectral density ratio to the summation value;
comparing the minimum reverse channel energy per bit to total interference spectral density ratio to the desired energy per bit to total interference spectral density ratio; and the base station instructing the first remote transmitter to increase power if the summation value is less than the maximum reverse channel energy per bit to total interference spectral density ratio and the minimum reverse channel energy per bit to total interference spectral density ratio is less than or equal to the desired reverse channel energy per bit to total interference spectral density ratio.
determining a desired reverse channel energy per bit to total interference spectral density ratio;
determining a energy per bit to total interference spectral density ratio on the reverse channel for each of the remote transmitters, thereby creating a plurality of energy per bit to total interference spectral density ratios;
summing the plurality of energy per bit to total interference spectral density ratios to produce a summation value;
determining a minimum reverse channel energy per bit to total interference spectral density ratio for the plurality of mobile radiotelephones;
comparing the maximum reverse channel energy per bit to total interference spectral density ratio to the summation value;
comparing the minimum reverse channel energy per bit to total interference spectral density ratio to the desired energy per bit to total interference spectral density ratio; and the base station instructing the first remote transmitter to increase power if the summation value is less than the maximum reverse channel energy per bit to total interference spectral density ratio and the minimum reverse channel energy per bit to total interference spectral density ratio is less than or equal to the desired reverse channel energy per bit to total interference spectral density ratio.
21. The method of claim 20 and further including the step of the base station adjusting the minimum reverse channel energy per bit to total interference spectral density ratio depending on reverse channel conditions.
22. The method of claim 20 and further including the step of adjusting the maximum reverse channel energy per bit to total interference spectral density ratio in response to an increase or decrease in the quantity of the plurality of radiotelephones.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US08/280,095 US5604730A (en) | 1994-07-25 | 1994-07-25 | Remote transmitter power control in a contention based multiple access system |
| US08/280,095 | 1994-07-25 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2195984A1 true CA2195984A1 (en) | 1996-02-08 |
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002195984A Abandoned CA2195984A1 (en) | 1994-07-25 | 1995-07-05 | Remote transmitter power control in a cdma communications system |
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| EP (2) | EP0774179B1 (en) |
| JP (1) | JP3078330B2 (en) |
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| CA (1) | CA2195984A1 (en) |
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| TW (1) | TW281836B (en) |
| WO (1) | WO1996003813A1 (en) |
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