CA2156707A1

CA2156707A1 - Method and system for the dynamic modification of control parameters in a transmitter power control system

Info

Publication number: CA2156707A1
Application number: CA002156707A
Authority: CA
Inventors: Roberto Padovani; Noam Ziv
Original assignee: Individual
Current assignee: Qualcomm Inc
Priority date: 1993-02-22
Filing date: 1994-02-02
Publication date: 1994-09-01
Also published as: FI953938A; AU666811B2; AU6099994A; IL108445A0; DE69409368T2; DK0685129T3; FI953938A0; FI112744B; HU9403846D0; RU2114508C1; HU216370B; ATE164712T1; BR9405695A; KR0153354B1; EP0685129B1; DE69409368D1; JP3051176B2; CN1284344C; MY138518A; SG52679A1

Abstract

In a communication system in which direct sequence spread spectrum modulation techniques are used, interference is generated in communication by remote stations since the communication share the same frequency spectrum. In order to increase system capacity the power level of the remote station transmitters are controlled by the local station. A setpoint in generated at the local station by a power control processor (118) and compared by a comparator (120) with the remote station signal strength measured at the local station by a power averager (114). The result of this comparison is used to generate power level adjustment commands by a command generator (122) which are transmitted to the remote station. The remote station is responsive to the power level adjustment commands for increasing or decreasing remote station transmitter power. In a spread spectrum communication system in which data is encoded at variable data rates, the local station determines via a rate determination processor (116) the rate at which received data was encoded by the transmitting remote station. The data is decoded by decoder (112) at each possible rate with error metrics generated that are representative of the quality of the data decoded at each rate. A rate decision algorithm is used by processor (116;) to evaluate the error metrics and make a decision on the rate at which the data was transmitted. A pattern match of rate decisions is used by processor (118) to modify a setpoint so as to closely control the transmitting power of the remote station as a function of the quality of the received data.

Description

~ 21567~7 ~ wo 94/19876 - PCT/US94/011~0 METHOD AND SYSTEM FOR THE DYNAMIC
MODIFICATION OF CONTROL PARA~ S IN A
TRANS~l l l ~ POWER CONTROL SYSTEM

BACKGROUND OF THE INVENI ION

I. Field of the Invention The present invention relates generally to digital communication 10 systellls and, more specifically, to a method and apparatus for adjusting transmitter power in such systems both to minimize inter~rence among transmitters operating simultaneously and to m~imi7.e the quality of individual comrnllnications.

15 II. Description of the R~?late~ Art In a cellular telephone or personal communication system (PCS), a large number of "mobile stations" communicate through cell sites or "base stations." The transmitted signal experiences multipath fading as the 20 mobile station moves in relation to features in the e~lvirolul~ent that reflect the signal. Controlling mobile station transmitter power to overcome multipath fading is described in U.S. Patent No. 5,056,109, titled "METHOD
AND APPARATUS FOR CONTROLLING TRANSMISSION POWER IN A
CDMA MOBILE CELLULAR TELEPHONE SYSTEM," issued on October 8, 25 1991 to the assignee of the present illvenLion and incorporated herein by reference.
If the mobile station transmits an excessively powerful signal, it will inlelrere with the transmitted si~n~lC of other mobile stations. If the mobile station transmits an ins-lffi~iPntly powerful signal, the base station will be 30 unable to recover the transmitted information from the received signal. In the above-referenced patent, the base station measures the power of the signal received from a mobile station and transmits power adjustment comm~n-1s to the mobile station over a separate rh~nnel. The commands instruct the mobile station to increase or decrease tr~ncmicsion power to 35 maintain the average received signal power at a predetermined level. The base station must periodically adjust the trarcrnicsion power of the mobile station to m~int~ an acceptable balance between inlelference and signal quality as the mobile station moves.

[QCPA48PA3B 'tl ' 2 1~ 6 7 0 7 P~ S 9 4 ~ 01 1 5 0 ~E~U6 10 APR 1995 The base station processor may monitor error rates in the received signal to select an optimal power level at which to mAintAin the average received signal. The base station processor detects errors as disclosed in copending U.S. patent application Serial No. 08~079,196, titled "METHOD

TRANS~lll l I~L~ VARIABLE RATE DATA IN A COMMUNICATIONS
RECEIVER," and A~si~ne~1 to the A~si~nee of the present invention. In the exemplary CDMA cellular telephone ~y~Lell~ described in the above-referenced U.S. patent and cop~ in~ application, the mobile station 10 trAn~mit~ "frames" comprising "symbols," which represent ~ligiti7eri voice or other data. Further details on the exemplary CDMA celllllAr telephone ~yst~lll are described in U.S. Patent No. 5,103,459, titled "SYSTEM AND
METHOD FOR GENERATING SIGNAL WAVEFORMS IN A CD~MA
CELLULAR TELEPHONE SYSTEM," issued April 17,1992 to the assignee of 15 the present i~lvenlion and incol~oldted herein by ~eferellce.
The mobile station encodes frames at one of four rates; the rate is s~lecte-l according to the needs of the user. The m~ um rate, which is generally pfe~red for high quality voice trAn~mi~sions or rapid data trAn~mi~sions, is called "full rate." Rates of one half, one fourth, and 20 one eighth of the full rate are called "half rate," "quarter~ rate," and "eighth rate," respe~;~ively. Each symbol of a frame to be encoded at half rate, quarterrate, and eighth rate is r~ealed two, four, and eight times, respectively, to ~ill the frame. The frame is then trar cmit~ to the base station at a constant rate, regardless of the rate at which the symbols are ~n~o-l~
The base station has no advance notice of the data rate at which a received frame is encoded and the rate may be diLl~rent from that of the pf~:ViOUS ,~e,-,~i frame. The base st~t~Qn decodes each received frame at each of the four rates and pro~llces a set of error me~i. c co,~ onding to eàch rate. The error metrics provide an in~licAtion of the quality of the 30~;-ve~ frame and may in~ e a cyclic rè~ltlndAncy check (CRC) result, a ~yAmAmoto Quality MetriG, and a re-~co~le~l symbol comparison result. The generation and use of these error ntetrics are well known in the art with details on the YAmAmoto Quality Metric provided in the article "Viterbi Decoding Algorithm for Convolutional Codes with Repeat Request", 35 Hirosuke YAmAmoto et al., IEEE Transactions on Inforrnation Theory, Vol.
IT-26t No. 5, Sept~mh~r 1980. The set of error metrics for the decoding of each frame at each rate thus inl~ltl~lps one or more of the CRC result~ the YAmAmoto Quality Metric, and the re encoded symbol comparison result.
The base station ~rocessor analyzes the sets of error nletri~ using a novel ~ME~DED ~HEEt ~ WO 94tl9876 PCT/US94/01150 7 ~ 7 3 decision algorithm and determines the most probable rate at which the received frame was encoded. The base station then uses the rate decision to select the colles~onding decoded data from the multiple data rate decodings to recover the transmitted frame information.
5 The base station processor also produces an "erasure" indication if the ~uality of the frame data is too poor for the processor to determine the rate.
Similarly, the processor produces a "full rate likely" indication if bit errors exist in the data but the rate is probably full rate. If an erasure occurs, the base station may simply discard the frame or may replace it with 10 interpolated data.
It would be desirable to mor~itor the error rate of the received frames and to periodically adjust the tra~cmission power level to m~in~in the error rate at an accephble value. These problems and ~1~fi~iPrlcies are clearly felt in the art and are solved by the present invention in the manner 15 ~lpcrrihed below.

SUMMARY OF THE INVENTION
The present invention comprises a method and apparatus for 20 adjusting the power level of a remote tr~nsmitte~ to provide a subst~nti~lly constant error rate in the received data. The yrese~lt invention may be used in the base station of a cellular telephone sy~lelll to m~imi7e the number of mobile stations that may transmit simultaneously with minim~l inLelference by enhancing control over the power of the signal that each 25 mobile station tr~n~mit~.
In the CDMA cellular telephone :jyslelll described in the above-referenced U.S. patent, the mobile station transmits a signal comprising frames of digitized voice or other information to the base station at an initial power level or setpoint. As described in the above-referenced 30 copending application, the information is encoded into either full rate, half rate, quarter rate, or eighth rate data frames. The base station receives the signal and decodes each frame at each of these rates. A col~esponding set of error metrics is produced for each rate that provides an indication of the quality of the received inform~tion if the frame is decoded at that rate.
35 The base station processor then analyzes the sets of error metrics using a decision algorithm and either provides an indication of the most probable rate at which the information was encoded or provides an "erasure"
indication, i.e., an indication that the rate could not be determined with the desired prob~hility of co..ecl~ess.

WO 94/19876 21~ ~ 7 ~ 7 PCT/US94tO1150 ~

In the present invention, the base station processor counts the number of consecutive frames encoded at a rate such as full rate and the number of frames that are erasures. A count of a predetermined number of consecutive full rate indications, i.e., without an inle~ ning less than full 5 rate indication, erasure indication or full rate likely ir~lir~tion, is indicative of a high quality full rate trarlcmicsion and is called a "full rate run." If the processor detects a full rate run and then detects an additional full rate frame, it should decrease the signal power to a level at which a small but acceptable number of erasure or full rate likely indications occur between 10 the full rate frames. For example, one error inrlic~tion in 100 full rate frames, where each frame consists of 576 symbols and is l.a-~smitted at a rate of 28,800 symbols per second, is inaudible in a tra~cmi~sion consisting of ordinary speech A count of a predetermined number of consecutive erasure 15 indications, i.e., without an intervening other rate indication, is indicative of a poor quality trarlcmicsion and is called an "erasure run." If the processor detects an erasure run, it should increase the signal power. The increased signal power may o.~e~co-.le mtlltipath f~ing, thereby reflllring the erasure rate.
A predetermined consecutive number of half rate, quarter rate, or eighth rate indications is called a "variable rate run." As a further enhancement in controlling tr~ncmitt~r power the processor may, while in a variable rate run, also reduce the signal power if it detects a half rate, quarter rate, or eighth rate indication. In addition while in the variable rate run, the processor may increase the signal power if it detects an erasure indication.
Although the present invention may be used to adjust the power level of tr~ncmicsions consisting of any ty-pe of data, it is optimi7e~l for tr~ncmicsions consisting of voice information. In communications ~y~lems 30 such as the cellular telephone ~y:~le~l~ described in the above-refere..ced copending application and U.S. patent, voice tra~mi~sions are encoded at a variable rate; the complexity uf the speech deterxnines the rate. However, continuous speech is generally encoded at full rate. Speech occurring after a period of relative inactivity may be encoded at lower rates, transitioning to 35 full rate as the speech increases in complexity. The algoAthm thus expects to detect variable rate runs alternating with full rate runs as the speaker pauses between words or syllables. Therefore, the processor may also increase the signal power if it detects an erasure indication or a full rate likely indication following a full rate run. The increment by which the ~ wo 94/19876 2I 56 70 ~ PCT/US94/01150 processor increases the power upon detecting an erasure or full rate likely indication following a full rate run need not be the same as the increment by which the processor increases the power upon detecting an erasure run.
The foregoing, together with other features and advantages of the 5 present invention, will become more apparent when referring to the following specification, claims, and accompanying drawings.

BRIEF DESCRIPTION OF THE DR~WINGS
The features, objects, and advantages of the present invention will become more apparent from the detailed description set forth below when taken in conj~lrlc~ion with the drawings in which like re~ere~lce characters identify co~re~onrlingly throughout and wherein:
Figure 1 is a block diagram showing the present invention in the base 15 station receiver of a c~ r telephone ~ysLe~
Figure 2 is a generalized flow diagram of an exemplary power control setpoint algorithm; and Pigures 3a -3c illustrate a detailed flow diagram of an exemplary power control seL~oillt algorithm for a det~rminPd rate le~i-cion pattern.
DETA~ n DESCRIPTION OP THE PREFERRED
EMBODIMENTS

In a CDMA cellular communication system where system user 25 capacity is a function of the total system power, any reduction of mobile station power facilitates an increase in system capacity. The present invention provides a method and system for closely and dynamically controlling the mobile station tr~ncmitter power as a function of the communication link. Through dynamic control over mobile station 30 tr~n~mitt~r power greater system capacity may be achieved.
In Fig. 1, the present invention is used in a base station receiver of a CDMA cellular telephone system. This receiver is described in the above-referellced U.S. Patent and is now described only briefly. A mobile station (not shown) transmits a commllnic~tion signal, typically a CDMA signal of 35 a spreading bandwidth for example of 1.25 MHz at one frequency band, to the base station radio receiver (not shown).
In order to aid in underst~llAing of the present invention, a brief discussion of the mobile station data encoding for tr~ncmicsion is provided.
In the exempl~ry embodiment user data provided at various data rates is A48PA31322] ' 7 P~rlus 9 4 / 01 1 5 0 - 6. ~ J~ 10 APR 1995 encoded and formatted for tr~n~mi~sion in data frames typically 20 mill;~e-onds in length. The user data along with frame overhead data are preferab~y forward error correction encoded. the effective data rates for this example are 9.6 kbps (full rate), 4.8 kbps (half rate), 2.4 kbps (quarter rate) and 5 1.2 kbps (half rate). It should be noted that a constant symbol rate for the frames is yrerel.~d but is not nec~cs~ry.
In this example rate 1/3 convolutional encoding is used to produce three symbols for each user data or frame ov~-he~-l bits. For a full rate frame, col.esyonding to a 9.6 kbps dah rate, a tohl of 192 user data and 10 frame ov~rheA~l bits are encoded to produce 576 symbols for the frame. For a half rate data frame, col.esyollding to a 4.8 kbps data rate, a total of 96 user data and frame ovPr~le~ bits are P-~co~e~l to produce 288 symbols for the frame. Si ~milarly for quarter rate and eighth rate data fr~m~c, respectively - co~ yol~ding to 2.4 and 1.2 kbps dita rates, a total of 48 and 24 user data and 15 frame ovprheal1 bits are encoded to produce 144 and 72 symbols for the -respective rate frame. It should be noted that groups of symbols are conve.led into a respective orthogonal flmction sequence or code of a set of orthogonal function codes according to the value of the symbol set. In the exemplary embollim~t six symbols for a binary value that is used to select 20 one of sixty-four Walsh function sequences each sixty-four chips in length.
Further details on this modulation s~heme is disclosed in the above mPnhonefl U.S. Patent No. 5,103,459. -At thé base stati:on the signal is receiv~l at ~ A 100 and providedto receiver 102 for frequency downcollvel~on and filtering. Analog-to-25 digital (A/D) co~,vc~t~ 104 r~:e.ves the analog spread spe~l,~n signal fromreceiver 102 and COllV~ it to a digital signal. A pse~ldor~ onl noise (PN) corn~!ator 106 ~eives~the digital signal and a PN code provided by a PN
gen~rator 108. PN correlator 106 perfofms a correlation yr~ess and p~es an output to a Fast H~ m~rd ~ s~O~ l processor or 30 " ~10. - . . . ., --In a ~re~ired embo~ pnt of a multipath dive~sil~ receiver PN
generator 108 generates a pIurality of a same-PN codes with timing offsets dependent upon the particular path of the signAl PN correlator 106 correlates each of the PN codes with a respective path signal to produce a 35 respective orthogonal function symbol data. Filter 110 converts the orthogonal fl1nction symbol data into soft decision symbol data for each multipath sign~l The multipath symbol data is then combined and provided as soft 1P~;Q;OI1 symbol data for .1 ?co~inf~ by user dah ~eCo~lpr 112.

.

.

~ WO 94119876 ~? 1 S~ ~0 7 PCT/US94101150 Pilter 110 as part of the conversion process determines from each orthogonal function symbol from each multipath signal an energy value.
Keeping in mind that each orthogonal function symbol is converted into a group of data symbols, the energy values from the different paths are 5 combined to produce a corresponding symbol energy value. Filter 110 in addition to providing soft decision data to decoder 112, also provides the symbol energy value to power averager circuit 114.
Decoder 112, which typically in~ s a Viterbi decoder, receives the filter soft decision symbol data output and produces user data and decoder 10 error metrics which are provided to rate determination processor 116.
Processor 116 may send the user data to a digital-to-analog converter or other output circuitry (not shown). Decoder 112 is described in further detail in the above-rerere~ced copending U.S. Patent application and is only briefly described herein.
Upon reception at the base station, decoder 112 leco~c each frame at each possible rate and provides a collesl,onding set of error metrics representative of the quality of the symbols as decoded at each rate. Error metric~ for decodings at each rate include, for ~y~mple~ a symbol error result based upon a re-encoding of the ~co~ed bits to produce re-encoded symbols 20 that are and then compared with the received symbols and a Y~m~moto Quality metric. In addition, for full rate and half rate frames a CRC check result is ~e~ .ed on CRC bits in the frame overhead bits.
After decoder 112 has decoded each frame, prGcessor 116 executes the rate determination algorithm described in the above-referenced copending 25 U.S. Patent application to determine the most likely rate at which the frame was encoded. The algorithm uses the error metriCc provided by decoder 112 to estimate or decide the rate at which the frame of data was tr~ncmitte~l-Once processor 116 determines the rate for the frame of data, the data is il~te~reled by control bits included in the frame as either control or user 30 data with the user data output for further use. From the error metrics processor 116 determinec whether the received data frame cont~ined data that was transmitted at either full rate, half rate, quarter rate or eighth rateand generates a corresponding rate indication. This rate indication is provided to outer loop power control processor 118, whose function is 35 described in further detail later herein.
In the case where the error metrics provided by decoder 112 indicate to processor 116 that the received frame was corrupted beyond that which the error correction techniques employed by decoder 112 may correct, processor 116 does not decide the rate of the data for the frame.

WO 94/19876 PCT/US94/01150 ~
~5~7~7 8 Processor 116 in this case does not use or provide an output of the data for that frame, with the frame being considered an erasure frame. Processor 116 for the erasure frame, generates and provides an erasure indication to processor 118 indicative that could not determine the rate at which the 5 frame was encoded.
In the case where the error metrics provided by decoder 112 indicate to processor 116 that the received frame is a corrupted full rate frame that was coLlecled by decoder 112. Typically in this case the metrics indicate only that an error exists in the CRC. From this information processor 116 10 determinPs that the most likely the rate of the data for the frame is that offull rate, and identifies the frame as a full rate likely frame. Processor 116 uses or outputs the data as if it were full rate data with a conditional understanding that it may contain errors. Processor 116 for the full rate likely frame generates and provides a full rate likely indication to 15 processor 118.
The rate decisions and detected frame errors may be used as an indication of the power level at which the mobile station need tr~n~mit ~ign~l~ at to m~int~in a quality cornmllnic~tion link. In those cases where a nurnber of frames are received at a rate or rates in which the occurrence of 20 frames in error is low, the tT~obil~ station trancmitt~r power may be re~ cerl.
This tr~ncmitt~- power reduction may continue until the error rate begins to rise to a level which may adversely affect the quality of the commt-nic~tion link. Similarly the power may be increased where the errors adversely affect the ~uality of the communication link.
Upon receiving the rate indications from processor 116, processor 118 exec~ltes a novel algorithm to control a power level setpoint. This setpoint is used as discussed with rererellce to Fig. 1 in generating power comm~nCls which control the power of the mobile station transmitter power.
As mPntionerl previously filter 110 provides the scaled symbol energy value to power averager 114. Power averager 114 sums or averages the scaled symbol energy values over a 1.25 rnillisecond interval, i.e.
corr~s~onding to a group of six Walsh symbols or thirty-six data symbols, and provides a received power level signal to cornp~rator 120.
Processor 118, which i~rlt~ s a~io~,;ate internal counters, program 35 mernQry and data rnemory, computes under program control a power level setpoint signal as described below and provides it to comparator 120.
Processor 118 may be either located at the base station through which the mobile station is in commllnic~tion with or at a remote location such as the mobile telephone switching office (not shown). In the situation where the ~ WO94/19876 ~6~ PCT/US94/01150 . ~

mobile station is communicating through multiple base stations, with power control provided through the multiple base stations, from a control standpoint the location of processor 118 at the MTSO is more convenient.
In those situations where processors 116 and 118 are located together the 5 function of these two processors may be combined into a single processor.
Comparator 120 compares the received power level signal and the power level setpoint signal, and provides a deviation signal representative of the deviation of the received power from the power level setpoint set by processor 118. Power up/down co~nm~nd generator 122 receives the 10 deviation signal and generates either a power up command or a power down comm~nd, which the base station transmits to the mobile station (not shown). Should the signal from power averagr circuit 114 fall below the threshold established by the power level setpoint signal, the deviation signal generated by comparator results in the generation of power 15 up comm~nfl- Simil~rly, should the power averager circuit signal exceed the power level setpoint signal, a power down command is generated.
These power cc-mm~nds are provided to trPr~ itle~ 124 where inserted into the data being transmitted to the mobile station. Transmitter spread spectrum modulates and transmits the modulated data via 20 antenna 100 to the mobile stAtion Tr~n~mitter 124 typically transmits the CDMA signal in a different frequency band than the mobile station tra~cmicsiQn but of the same spreading bandwidth, e.g. 1.25 MHz.
Fig. 2 illustrates a generalized flow diagram of this algorithm used to dynamically adjust the power level setpoint, and thus indirectly modify the 25 mobile station transmitter power. The implementation of the algorithm seeks to effect a reduction or increase in the mobile station transmitter power as a function of the link quality with respect to various frame rate data. In this implementation a pattern of rate decisions is used to modify the power level sel~oint. Although the exemplary embodiment is ~esrrihed 30 with referellce to using the rate ~iecicion as an indicator of patterns, other parameters may be used.
In Fig. 2, a group of one or more of frame rate ~1eri~ions is provided for inspection, step 150. This group may be compAsed of a collection of sequential frame rate decisions, or according to some other order, and/or 35 which may be dependent upon the frame rate. The group of rate decicionc are inspected to determine if their pattem is matched to predetermined rate decision pattern P1, step 152. If there is a pattern match, a moAifi~tion in the power level setpoint is made, step 154. This mo~lific~tion may be in the form of an increase or decrease in the power level setpoint by an [QCPA48PA.3E3221 21 5 6 7 ~ 7 PC~IUS , 4 / 01 ~ 5q - 10 IPE4US 10 APR l9g5 incrP~nPntAl value. This increase or decrease in the power level setpoint llltimAtPly results in a corresponding increase or decrease in the mobile station transmitter power. In those cases where a rate decision pattem match indicates a good communication link, the power level setpoint is 5 increased to result in the generation of power down commAn~c and ultimately a decrease in mobile station trAncmitt~r power. Similarly, in those cases where a rate decision pallelll match indicates a low quality communication link, the power level setpoint is increased to result in the generation of power up commAn~l~ and llltimAtPly an increase in mobile 10 station trAncmitPr power.
Should a pattem match occur with a molii*rAtion of the setpoint, steps 152 and 154, a rate ~e~icion is updated, step 156, and the process repeated. Further details on the update aspect of the invention are ~ic~lcse~ later.
In the event that pattem ietPrminAti~n step 152 results in no pattem - mAt~hing, the process may proceed under several options. In one option the power level setpoint may be mo~iifie~l~ step 158, the rate decision updated~ step 156, and the process ~ealed. The mo~1ifi~Ati-)n in step 158 is plererdbly a different modification from that of step 154 ~increase vs.
20 decrease or vise versaj where a pAtt~m match was ietecte~l It should also benoted that any setpoint mo~lifi~ Atinn as ~ cserl herein may also be set to provide no change in the selp~int.
In a prere.led impl~m~nt~Atit)n should pai~f~ eterminAtion step 152 result in no palle... mAt~hin~, at least orie A~ itional patt~rn ~iet~rminAtiQn 25 step is pel~o~ ed. For example, the group of rate ~ icions are inspected to dePrmine if their pattern is matched to another predetermined rate ~le~i~ion ~alle~ P2, step 160. If there is a ~ . " mat~ h, a mo-li*- ~tion in lhç power level setpoint is made, step 162. This mo~li*t ~tion may be in the form of an increase or dec~eas~ in the ~ower leve~ setpoint by an 30 ~4~^~t~1 value, or the setpoint is left ~lnrh~nged. This increase or deerease in the power le~el se~point llltim~t~ly results in a corres~onding increase or decrease in the mobile station t~ r power. As was fo~ r the case of step 152 where no p~ match oc~ d, sho~ i there be no pAttem match in step 160 the setpoint may be modified or left lm~ h~n~e-l, step 164.
In the case where no pattem match occurs in step 160 ~ ition~l pattern match determinations and setpoint modifications may be pe~rl~.ed. Should there be no pattern match in each of these pattem match deterrnin~tion~ a final or Nth p~ match ~eterrnin~tion is made.
The group of rate decisions are inspected to determin~ if their pattern is ~MEN~D ~HEET

~ WO 94119876 2 1~ ~ 7 7 PCTIUS94/UIISO

matched to yet another predetermined rate decision pattern PN~ step 166. If there is a pattern match, a modification in the power level setpoint is made, step 168. This modification may be in the form of an increase or decrease in the power level setpoint by an incremental value, or the setpoint is left 5 unchanged. This increase or decrease in the power level setpoint ultimately results in a corresponding increase or decrease in the mobile station transmitter power. As was for the case of steps 152 and 160 where no yalLelll match occurred, should there be no pattern match in step 166 the setpoint may be modified or left unchanged, step 170.
The process steps of Pig. 2 are repeated generally with an updated group of rate decisions with the updating accomplished in step 156. This updated group may be comprised of the previous group with the addition of a new frame rate decision and the deletion of the oldest frame rate decision using well known memory techniques. In the alternative, the group may be 15 comprised of any collection of rate decisions as may be desired.
It should be noted that the selected pattern typically defines whether an increase or decrease in the power level setpoint is necessary. Increase and decrease increm~nts of the power level setpoint may be of dirreLent incrPm~nt~l quantities for the various ~alle~ll m~t~hes~ but they may also be 20 of the same incr~ment~l quantity. Furt~rmore pattern Pl, as may ~atleins P2 through PN, may each ~ncompass a set of patterns to facilitate a modification associated with the pattern. Further a modification of the setpoint, such as in step 154, may be dirr~lent depending upon the pattern of the set of patterns that is matched in the pattern determination step. It 25 should also be noted that the setpoint may be modified by a zero increnlellt~l quantity such that the setpoint is effectively unchanged.
The use of different pattern match deterrnin~tions permits greater flexibility in adjusting the mobile station tr~r~cmitter power level according to the quality of the comm~ ication link. For those cases where link quality 30 is above that which is necessary to support reliable communications, tr~ncmicsion power may be reduced to the minimum necess~-y to maintain a reliable communication link. Simil~rly in those cases where link quality is below that which is necessary to support reliable communications, trancmission power may be increased to a level necessary to m~ t~in a 35 reliable communication link.
Figures 3a - 3c illustrates a detailed example of the use of rate rie~icion pattern in controlling adjustment of the mobile station transmitter power.
In Pigure 3a, if the frame is the first frame of a l~a~c~icsion~ processor 118 (Figure 1) initi~li7es variables at step 200. Processor 118 sets "Setpoint,"

2CPA48PA 3B7~l 2 1 ~ ~ 7 0 7 P~r/~ ~ 4 / 0 1 1 5 0 12 ~E~US 10 AP~ 1995 which represents the power level setpoint signal, to an initial value "Initial setpoint." Processor 118 changes the power level setpoint signal, and ultimate~y the mobile station power level when it changes the variable "Setpoint."
Processor 118 has counters "Pull Rate Count" and "Erasure Count,"
which represent the number of consecutive full rate indications and the number of erasure indications, respectiveIy. These counters are inihAli~e~l to zero at step 200. A full rate run consists of three consecutive full rate in~ir~Ations; an erasure run cor~ t~ of one erasure indication; and a variable 10 rate run consists of one half rate in~1ic~Atioll~ one quarter rate in~i~Ation~ or one eighth rate in~ Ation. Processor 118 sets boolean variables "Full Rate Run," "Erasure Run," and "Variable Rate Run," which in~ Ate a state of the process, to a value of FALSE at step 200. The setting of these varia~les to FALSE is indicative of an initial p~ess state.
Processor 118 waits at step 202 until processor 116 has produced a rate lle~ i~ion. At step 204, processor 118 brAnrhes to step 206 if "Full Rate Run" is true and to step 208 ~Figllre,3b) if false.
At step 206, processor 118 brAn~hes to step 210 if the rate ~ ion is a full rate in~licAhon and to step 212 if it is not a full rate in~i~Ation. At step 210, processor 118 decreases "Setpoint" by an amount eqtlal to a value "Delta Down Full Rate." At step 21.2, yl~cessol 118 brAn~ h~c to step 214 if the rate le~i!siQn is a half rate in~licAtion, a quarter rate in~ At~oI~ or an eighth rate n~i~Ation and to step 216 if the rate ierisio~ is an elasure or full rate likely indication.
At step 214, processor 118 sets'"Full Rate Run" to a value of FALSE, "Variable 3~ate Run'r to a value of TRU~, and both "Full Rate Count" and "Erasure Count" to a value of zero. At step 216, processor 118 increases "Setpoint" by an amount equal to a value "Dêlta Up Full Rate."
r~c*J~r 118 ~Lu~ns to step 202 to wait for the next rate fle~io~ after *
~ ~ step 21Q, 214, or 216.
-At step 208, proces_or 118 brAnlh~c to step 218 i-f "Variable Rate Run"
is true and to step 220 if false. The trAnCition to step 220 from step 208 is bydehult an irulirAtion of the "Era~ure Run" variable is true. At step 218, processor 118 brAn~hes to step 2_2 if the rate ~ cion is a full rate indi~Ahon and to step 228 if it is not a full rate irulirAtiQn At step 22~, processor 118 increments "Full Rate Count" and proceeds to step 224. At step 224, processor 118 brAnrhes to step 226 if "Full Rate Count" is grealer than three and to step 202 to wait for the next rate ~ c-ion if "Full gate Count" is less than or equal to three. At step 226, processor 118 sets "Pull Rate Run" to a ,~MEN~

.

wo 94/l9876 ~ ~ 5 6 7 0 ~ PCT/US9410115û

value of TRUE and "Variable Rate Run" to a value of FALSE and then proceeds to step 202 to wait for the next rate decision.
At step 228, processor 118 branches to step 230 if the rate decision is a half rate indication, a quarter rate indication, an eighth rate indication, or a5 full rate likely indication, and to step 232 if the rate decision is an erasure indication. At step 230, processor 118 sets "Full Rate Count" and "Erasure Count" to zero and proceeds to step 202 to wait for the next rate decision. In step 230, the "Setpoint" may also be decreased by an amount equal to a value "Delta Down Variable Rate" to achieve greater power level setpoint control.
10 At step 232, processor 118 increments "Erasure Count," sets "Erasure Run"
to a value of TRUE, and "Variable Rate Run" to a value of false, and then proceeds to step 202 to wait for the next rate decision. Furthermore, in order to achieve greater power level setpoint control, the "Setpoint" may be increased by an amount equal to a value "Delta Setpoint Up Variable Rate"
15 in step 232. Processor 118 then proceeds to step 202 to wait for the next rate decision.
The transition to step 220 from step 208 results from "Variable Rate Run" being set false and "Erasure Run" being set true in step 232. Although the "Erasure Run" state is not directly used in a decision step for entering 20 step 212, which it could be, it is used in this example as identifying the shte in which the ~locess is in. At step 212 processor 118 branches to step 234 if the rate decision is a full rate ir~ t;on and to step 236 if it is not a full-rate indication. At step 234, processor 118 increments "Full Rate Count," sets "Variable Rate Run" to a value of TRUE, "Erasure Run" to a value of 25 FALSE, and "Erasure Count" to a value of zero, then proceeds to step 202 to wait for the next rate lericion. At step 236, ~r~cessor 118 branches to step 238 if the rate decision is a half rate indication, a quarter rate indication, an eighth rate indication, or a full rate likely indication, and to step 240 if therate decision is an erasure indication.
At step 238, processor 118 sets "Variable Rate Run" to a value of TRUE, "Erasure Run" to a value of FALSE, and both "Full Rate Count" and "Erasure Count" to a value of zero, then proceeds to step 202 to wait for the next rate decision. At step 240, processor 118 increments "Erasure Count"
and proceeds to step 242.
At step 242, processor 118 branches to step 244 if "Erasure Count" is less than five. In step 244 the "Setpoint" is increased by an amount equal to a value "Delta Up Variable Date" and returns to step 202 to wait for the next rate decision. The adjustment of the "Setpoint" in step 244 provides for WO 94119876 PCT/US94/0115û
~15~;~707 14 enhanced control over the power level setpoint upon the occurrence of several erasure frames.
However should additional consecutive erasure frames occur it is desirable to increase the setpoint by a greater value in an attempt to 5 eliminate the occurrence of more erasure frames. At step 242, processor 118 branches to step 246 if "Erasure Count" is greater or e~ual to five. At step 246, processor 118 increases "Setpoint" by an amount equal to a value "Delta Up Erasure" and returns to step 202 to wait for the next rate decision. In the exemplary embo~ ent the value "Delta Up Erasure" is greater than the 10 value "Delta Up Variable Date".
In a modification of the present invention the adjustment of the "Setpoint" in step 244 may be omitted. When the "Erasure Count" is less than the count value in step 242, then no adjustment is made to "Setpoint"
Since less control is provided over the power level setpoint for the run of 15 erasure frames, it is desirable that the count value be reduced to enàble the adjustment in step 246 to occur sooner. For example the value may be re~tlce-l to a value of two or three.
In an exemplary execution of the power control algorithm, processor 118 init~ i7.eS variables at step 200 and waits at step 202. The base 20 station receives the first frame of a tranclnicsion and generates error metri~. Power averager 114 measures the power of the symbols over a 1.25 millicecond interval and updates its output ever 1.25 milliseconds while ~leco~er 112 rleco~lPs the frame. Processor 116 produces a rate rleri~ion in response to the error metrics. When processor 116 has produced the rate 25 flericion, processor 118 branches via steps 204 and 208 to step 218 bècause the al~o~ ... initially begins in a variable rate run.
Frames in a voice trAncmicsion generally fluctuate between full rate and other rates, with continuous speech being encorle~ at full rate. If, for example, processor 116 produces an eighth rate indication in response to the first frame, processor 118 branches from step 218 to step 228 and proceeds to step 230. Because the frame was neither an erasure nor a full rate frame, processor 118 sets both "Full Rate Count" and "Erasure Count" to zero.
Processor 118 returns to step 202 to wait for the rate lecision coi~esyonding to the second frame.
If, for example, processor 116 produces a quarter rate indication in res~onse to the second frame, processor 118 branches in the same manner as in response to the previous frame. SimilArly~ if processor 116 produces a half rate indication in response to the third frame, processor 118 again br~nr~es in the same mar~ner. While processor 116 produces eighth rate, pA48pA~3B77l 2 1 5 6 7 0 7 ~ 9 4 / O 1 ¦ 5 0 - 15 ~ E~JS 10 APR 1995 quarter rate, or half rate indications in response to the received &ames, processor 118 does not change the power level.
If processor 116 produces a full rate indication in response to the fourth frame, processor 118 branches via steps 208 and 218 to step 222 5 because the full rate indication follows a variable rate run. At step 222, processor 118 increments "Full Rate Count," which would then be equal to one, and proceeds to step 224. At step 224, processor 118 returns to step 202 because three full rate in~1ic~Ations have not been counted.
If processor 116 produces a full rate in~licAtiorl in response to the fifth 10 frame, processor 118 would increment i'Full Rate Count" as was described for the fourth frame. Should the sixth frame also be a full rate frame, again via steps 204, 208! 218 and 222 processor 118 would increment "Pull Rate Count". Since three full rate in~licAtions havé now been counted~ in step 224 processor 118 brAnt-h~s to step 226 and sets "Full Rate Run" to a 15 value of TRUE and '~ariable Rate Run" to a value of FALSE. Processor ~18 then returns to step 202.
If processor 116 produces a full rate in~licAtion in res~o,-se to the seventh frame, processor 118 br~n~h~P~ via steps 204 and 206 to step 210 because the full rate indi~Ation follows a full rate run. At step 210, ~f~cessor .
20 118 decreases the value "Selpoi~.t". Processor 118 returns to step 202 to wait for the next rate decision.
Comparator 120 compares the received power level signal, which is updated çvery 1.25 milliceconds, with the power level setpoint signal generated according to the modified value "Setpoint" and produces a 25 deviation signal. In the case wherè the læeivell power level signal is n~hAnged or r~m~in~ above the power level setpoint signal, comparator 120 generates a deviation signal to whi~h the comm~n~l generator 122 re~t,onds by pro~l~cin~ a power down r~mm~ The base station ~rAn~mit~
this comm?n~1 to the mobile station, which decreases the power of the 30 ~i~ t~at it t~ ..i~, so as to reduce the deviation signal.
-If processor 116 pr~duces an efdS~e or full raté likely in~lirAtiQn in response to the eig~th frame, processor 118 brAl~ches to step 216, via steps 204, 206, 212, because the erasure follows- a full rate run. At step 216, processor 118 increases the value "Setpoint". Processor 118 returns to step 35 202 to wait for the next rate ~
Comparator 120 again compares the received power level signal with the power level setpoint signal generated according to the value "Setpoint"
and produces a deviation signal. In the case where the receive.i power level signal is llnch~nged~ or is below the power level setpoint signal, ~M~DED ~
, -~CPA48PA.3B221 2 15 6 7 0 7 P~¦US 9 4 / 01 1 5 0 16 ~I~US 10 APR 1995 comparator 120 generates a deviation signal to which the comm~n~i generator 122 responds by producing a power up command. The base station again trAn~mits this command to the mobile station, which adjusts the power of the signal that it l~ , so as to reduce the deviation signal.
While processor 118 is in a full rate run state, i.e., "Full Rate Run" is TRUE, and processor 116 produces full rate indications, erasure in~ Ations, or full rate likely indications, processor 118 r~mAin~ in a full rate run state and adjusts the power level as described above to optimize the power of the signal that the mobile station trAn~mit~.
If processor 116 produces a half rate int1i--Ation in the ninth frame, processor 118 branches via steps 204, 206, and 212 to step 214 where "Variable Rate Run" is set to a value of TRUE ànd "Full Rate Run" set to a value of FALSE. Processor 118 then returns to step 202 to wait for the next~rate decision. If pl~cessor i16 then produced an erasure indication in r~p~nse 15 to the tenth frame, processor 1I8 branches through steps 204, 208, 218 and 228 to step 232. Processor 118 in step 232 incrPmentc "Erasure Count,"
which would then be equal to one, and sets "Erasure Run" to a value of TRUE," sets "Variable Rate Run" to a value of FALSE, and optionally increases the value "Setpoint". Processor 118 then returns to step 202 to 20 wait for the next rate cie~icion.
If processor 116 produces an erasure indication in response to the elevent~ frame, processof 118 would branch via steps 204, 208, 220, and 236 to; step 240. At step 240, the "Erasure Count" is incrPmente~ and then proceeds to step 242. In step 242, since "Erasure Count" is less than 5, 25 processor 118 br~n~hes to step 244. In step~244, processor 118 increases the value "Set~o~lt'l. Processor 118 returns to step 202 to wait for the next rate decision.
If processor 116 produces erasure indit~Ations for the twelfth and tl~te~..th frames, the steps discllcse~l with re~rence to the eleventh frame 30 ar~ epeated. Howe.~er in the fourteenth frame should processor 116 , produce an erasure in~lit Ation~ processor 118 then br~nt l~s via steps 204, 208, 220, and 236 to step 242. ~ step 242, sin~"Erasure Count" is equal to 5, processor 118 br~n- h~ to step 246. In step 246, the value "Setpoint" is increased. P~ocessor 1~8 then returns to step 202 to wait for the next rate 35 decision.
Although the above discussed processin~ example does not specifically ~li~lss each step in the pror~si~g of Figures 3a - 3c it is readilyetermine~i from these figures other processing examples. Pl~cessor 118 ~.ME~D ~EET

PA48PA.3B221 PCf - ~ ~ 2 ~ ~ ~ 7 0 7 ~ tPEVUS 1 0 APP<-1~95 continll~s to execute t~e power control algo,ill~ as illustrated in Figures 3a - 3c until it is reset, at which time it returns to step 200.
In~ sum, the algo-iLlull initially begins in a variable rate run state. The al~o,itl~-l need not adjust the power level setpoint during the variable rate 5 run state. However, in order to achieve greater control over the power level setpoint, an adj-l~tment is made. The algorithm uses the variable rate run state to enter either a full rate run state if it detects three full rate in~ Ations or an erasure run state if it ~iPtect~ one erasure in~ Ation.
After ~ g a full rate run state, the algo-ill~l?~ increases the power 10 level setpoint if it detects an erasure indication or a full rate likely indication so as to result in a gPnerAtion of a power up command which is trAn~mitte~l to the mobile stAtion The algoliLl~ , when in the full rate run state, decreases the power level setpoint if it ~lPtectc a full rate in~ Ahon~. If, while in the full rate run state, the aigorithm lete~tC a half rate in~ Atiorl, a 15 quarter rate in~ Ation, or an eighth rate in~ Ation, the variable rate run state is entered.
After el.te~ g an erasure run state from the variable rate run state, the algo~ increases the power level selpoml if it detects an erasure. ~
while in the erasure run state the algori~hm ~ietect~ a half rate in~i~Afiorl, a .
20 quarter rate indication, or an eighth rate inrlitA*o~, a transition to the variable rate run state is made.
In the exemplary invention, the relative size in values of the incrP~nPntAl changes in the value ''Setpoint" are as follows. With respect to the increasing se~int mo lificA*on values, the value "Delta Up Full Rate"
25 is the largest relative value followed by the "Delta Up Erasure" value, and then the "Delta Up Variable Rate" valué. - With res~t,e~t to the dec~easing s~tpoi~t mo~lifi~ion va~ues, the largest relative value is the "Delta Down Full R~ate" followed by the "Delta DoYvn Variable Rate." In ge~ l the de~ g set~il-t values are ~mAller than the in~fea~ set~oil-t values.
3~ Et~ should be ~1m~ lood tha~t~ various m~if~- A*ons to the exemplary ,dia~lall. of Figures 3a - 3c may be made and remain within the scope of the illv~ ;on. For example, since in an embo~iiment where both the full and half rate frames iT~ a CRC, the diàgrams of Pigure 3a - 3c need not change. On the other hand, since both full and half rate frAmes have a CRC, 35 half rate frames may be considered as full rate frames for purposes of modifying the value "Set~oil.t".
Although the present invention is ~iesrrihed in the context of a CDMA cellular comm~mi~tion ~y:~te.ll, the present invention is equally applicable to other tr~n~mi~sion s~hemes and env~o.~ Pnts where digital .
~MENDED ~ÆEr wo 94/19876 PcT/usg4/01l5n ~

2~ ~7~ 18 data is transmitted in a frame format. Thus the present invention is not limited by the transmission scheme or environment of a cellular communication system. For example the present invention is applicable to ~y~lems such as cellular telephone, personal communications service (PCS) 5 wireless local loop and private branch exchange (PBX). The use in a receiver of pattern detection of the various frame rates and detection of frames in errors for the various patterns provides a flexible scheme for adjusting the tra~mission power to ensure a quality link for data frames transmitted at the various frame rates. Furthermore, although the present invention is 10 discussed with reference to the absence of transmitted frame rate information, the invention is applicable to those systems in which rate information is transmitted. In the rate ~ ittec~ cases the quality of the signal may be used to assist in determining rate data for certain conditions such as erasure and full rate likely frames.
The previous description of the ~lefe~ed embo~limPnts is provided to enable any person slcille~ in the art to make or use the ~resel.t invention.
The various modifications to these embo~iimentc will be readily apparent to those skille~l in the art, and the generic principles riefine~l herein may be applied to other embo~iiments without the use of the inventive faculty.
20 Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

WE CLAIM:

Claims

1. In a communications system having a first station and a remotely located second station, said second station transmitting at a predetermined power level a communication signal comprised of frames of data each encoded at a predetermined one of a plurality of data rates, said second station receiving power level information from said first station and responsive thereto for adjusting said power level, a method for controlling said power level, comprising the steps of:
receiving said communication signal at said first station;
measuring a power level of said received communication signal;
producing a rate decision for each frame of data in said received communication signal;
producing power level information in response to said rate decision and said measured power level; and transmitting said power level information to said second station.

2. The method of Claim 1, wherein said step of producing said rate decision comprises the steps of decoding each frame of data at each data rate of said plurality of data rates;
producing at least one error metric for each decoding of each frame at each data rate; and determining from said error metrics for each frame an estimate of one of said data rates at which said data was encoded in each respective frame.

3. The method of Claim 2 wherein said step of producing said rate decision further comprises the step of determining from said error metrics an erasure frame in which data is corrupted beyond which a determination can be made as to one of said data rates at which said data was encoded in the respective frame.

4. The method of Claim 3 wherein said step of producing said rate decision further comprises the step of determining from said error metrics a full rate likely frame in which data is of a highest data rate with corrupted data.

5. The method of Claim 2 wherein:
said rate decision is provided as a full rate indication when said rate at which said data is encoded is of a predetermined highest data rate;
said rate decision is provided as a half rate indication when said rate at which said data is encoded is about one half said predetermined highest data rate;
said rate decision is provided as a quarter rate indication when said rate at which said data is encoded is about one fourth said predetermined highest data rate; and said rate decision is provided as an eighth rate indication when said rate at which said data is encoded is about one eighth said predetermined highest data rate.

6. The method of Claim 4 wherein:
said rate decision is provided as a full rate indication when said rate at which said data is encoded is of a predetermined highest data rate;
said rate decision is provided as a half rate indication when said rate at which said data is encoded is about one half said predetermined highest data rate;
said rate decision is provided as a quarter rate indication when said rate at which said data is encoded is about one fourth said predetermined highest data rate;
said rate decision is provided as an eighth rate indication when said rate at which said data is encoded is about one eighth said predetermined full rate;
said rate decision is provided as an erasure indication when said rate at which said data is encoded is corrupted beyond which a determination can be made as to one of said data rates at which said dah was encoded; and said rate decision provides an full rate likely indication when said rate at which said data is encoded is of said predetermined highest data rate and said data contains bit errors.

7. The method of Claim 1 wherein said step of producing power level information in response to said rate decision and said measured power level comprises the steps of:
adjusting a power level setpoint according to each rate decision;
comparing said power level setpoint with said measured power level;
and generating power adjustment commands from each result of said step of comparing.

8. The method of Claim 4 wherein said step of producing power level information in response to said rate decision and said measured power level comprises the steps of:
adjusting a power level setpoint according to each rate decision;
comparing said power level setpoint with said measured power level;
generating a power increase adjustment command when said measured power level is less than said power level setpoint; and generating a power decrease adjustment command when said measured power level is greater than said power level setpoint.

9. The method of Claim 8 wherein said step of adjusting said power level setpoint comprises the step of decreasing said power level setpoint by an incremental value when a current frame rate decision is indicative of a frame of data of a highest data rate as following a predetermined number of previous frame rate decisions each indicative of a frame of data at said highest data rate.

10. The method of Claim 8 wherein said step of adjusting said power level setpoint comprises the step of increasing said power level setpoint by an incremental value when a current frame rate decision is indicative of a frame of data of one of said erasure frame and said full rate likely frame as following said predetermined number of previous frame rate decisions each indicative of a frame of data at said highest data rate.

11. The method of Claim 8 wherein said step of adjusting said power level setpoint further comprises the step of increasing said power level setpoint by an incremental value when a current frame rate decision is indicative of an erasure frame as following a predetermined number of previous frame rate decisions each indicative of an erasure frame.

12. The method of Claim 8 wherein said step of adjusting said power level setpoint comprises the steps of:
decreasing said power level setpoint by a first incremental value when a current frame rate decision is indicative of a frame of data of a highest data rate as following a predetermined number of previous frame rate decisions each indicative of a frame of data at said highest data rate; and increasing said power level setpoint by a second incremental value when a current frame rate decision is indicative of a frame of data of one of said erasure frame and said full rate likely frame as following said predetermined number of previous frame rate decisions each indicative of a frame of data at said highest data rate.

13. The method of Claim 12 wherein said step of adjusting said power level setpoint further comprises the step of increasing said power level setpoint by a third incremental value when a current frame rate decision is indicative of an erasure frame as following a predetermined number of previous frame rate decisions each indicative of an erasure frame.

14. In a communication system in which a first transceiver controls transmission signal power of a second transceiver transmitted communication signal comprised of frames of variable rate data by measuring and comparing a level of signal power of said communication signal with a setpoint power level to generate and communicate power adjustment commands to said second transceiver which is responsive thereto for adjusting signal power in said communication signal, said first transceiver estimating a data rate for each frame of data in said communication signal and providing a corresponding rate decision, a method for adjusting said setpoint power level comprising the steps of:
determining from a set of rate decisions a matching to a predermined rate decision pattern; and modifying said setpoint power level according to a modification parameter when the matching to said predetermined rate decision pattern is determined.

15. The method of Claim 14 further comprising the step of modifying said setpoint power level according to another modification parameter at times-other than the matching of said set of rate decisions to said predetermined rate decision pattern.

16. The method of Claim 14 further comprising the steps of:determining from said set of rate ~le~i~ions a m~t-hing to at least one additional predetermined rate decision pattern; and modifying said setpoint power level according to a corresponding additional modification parameter when the matching to a respective one of said predetermined rate decision patterns is determined.

17. The method of Claim 16 further comprising the step of modifying said setpoint power level according to a respective one of other additional modification parameter at times other than the matching of said set of rate decisions to said predetermined rate decision pattern and each additional predetermined rate decision pattern.

18. In a communications system having a first station and a remotely located second station, said second station transmitting at a predetermined power level a communication signal comprised of frames of data each encoded at a predetermined one of a plurality of data rates, said second station receiving power level information from said first station and responsive thereto for adjusting said power level, the system for controlling said power level comprising:
means for determining a power level of said communication signal as received at said first station;
means for producing a rate decision for each frame of data in said received communication signal;
means for producing power level information in response to said rate decision and said determined power level; and means for transmitting said power level information to said second station.

19. The system of Claim 18 wherein said means for producing the rate decision decodes each frame of data at each data rate of said plurality of data rates, produces at least one error metrics for each decoding of each frame at each data rate and determines from said error metrics for each frame an estimate of one of said data rates at which said data was encoded in each respective frame.

20. The system of Claim 19 wherein said means for producing the rate decision further determines from said error metrics an erasure frame in which data is corrupted beyond which a determination can be made as to one of said data rates at which said data was encoded in the respective frame.

21. The system of Claim 20 wherein said means for producing the rate decision further determines from said error metrics a full rate likely frame in which data is of a highest data rate with corrupted data.

22. The system of Claim 18 wherein said means for producing power revel information comprises:
means for adjusting a power level setpoint according to each rate decision;
means for comparing said power level setpoint with said determined power level; and means for generating power adjustment commands from each power level setpoint and said determined power level comparison result.