Method and apparatus for adjusting a power control setpoint threshold in a wireless communication system

A method of adjusting a power control setpoint threshold (216) in a wireless communication system is provided. The method includes the steps of receiving at a receiver, a communication signal from a mobile communication unit to form a received communication signal, generating a first signal quality indicator (193) based on the received communication signal, generating a second signal quality indicator (194) based on the received communication signal, and generating an estimated signal-to-noise ratio (98). The method further includes setting a predetermined reference region (605) centered around a second signal quality indicator reference (206) where the second signal quality indicator reference (206) is related to the first signal quality indicator (193), and adjusting the power control setpoint threshold (216) based on a comparison between the second quality indicator (194) and the predetermined reference region (605).

FIELD OF THE INVENTION 
The present invention relates generally to wireless communication systems 
and, more particularly, to a method and apparatus for adjusting a power 
control setpoint threshold in a wireless communication system. 
BACKGROUND OF THE INVENTION 
Communication systems that utilize coded communication signals are known in 
the art. One such system is a direct sequence code division multiple 
access (DS-CDMA) cellular communication system, such as set forth in the 
Telecommunications Industry Association Interim Standard 95A (TIA/EIA 
IS-95A) herein after referred to as IS-95A. In accordance with IS-95A, the 
coded communication signals used in the DS-CDMA system comprise signals 
that are transmitted in a common 1.25 MHz bandwidth, hence, 
spread-spectrum, to base sites of the system from communication units, 
such as mobile or portable radiotelephones, that are communicating in the 
coverage areas of the base sites. 
Communication systems that utilize coded communication signals are known to 
employ channel power control methods which control transmission energy of 
mobile communication units. Reverse-link (mobile communication unit to 
base site), power control varies the power transmitted by the mobile 
communication unit to ensure that the power from each mobile communication 
unit arrives at the base site at the minimum possible power level. If the 
mobile communication units' transmit power is too low, voice quality will 
be degraded. If the mobile communication units' power is too high, the 
mobile communication unit may have high quality voice, but because each 
mobile communication unit's signal in a spread-spectrum system is 
typically transmitted on the same frequency, the resulting excess 
interference will degrade the overall system capacity. The magnitude of 
noise, which is inversely proportional to bit energy per noise density 
i.e., Eb/No which is defined as the ratio of energy per information-bit to 
noise-spectral density, is directly related to the received signal power 
of each of the other mobile communication units' transmissions. Thus it is 
beneficial for a mobile communication unit to transmit at the lowest power 
level possible while maintaining the integrity of the signal, the 
integrity characterized by its frame erasure rate (FER). 
It is also desirable to dynamically adjust the power of all mobile 
communication units in such a way that their transmissions are received by 
the base station with substantially the same power level. To accomplish 
this, it is necessary for the closest transmitters to reduce their power 
by as much as 80 dB when compared to the power of the furthest 
transmitters. 
The current method of controlling reverse channel power in a CDMA 
communication system is described in Cellular System Remote Unit Base 
Station Compatibility Standard of the Electronic Industry Association 
Interim Standard 95A (TIA/IS-95A). As described in TIA/IS-95A, a 
power-control group is transmitted from the mobile communication unit and 
received by the base station. The base station compares the energy of the 
power-control group to a setpoint threshold and instructs the mobile 
communication unit to power up or down accordingly via transmitting a 
power adjustment command to the mobile communication unit. Under nominal 
conditions, utilizing such a closed loop power control method will result 
in a setpoint threshold which maintains the Eb/No of the received signal 
at a substantially fixed level. However, under varying conditions, for 
example, when a mobile station is moving at varying speeds, different 
Eb/No are required for a given FER. Thus maintaining a fixed Eb/No may 
result in different FERs for mobile stations under different conditions. 
Therefore, a need exists for a method and apparatus for adjusting a power 
control setpoint threshold in a wireless communication system which 
adjusts the power level needs of the mobile communication system while 
decreasing the period of time over which the threshold adjustments occurs.

SUMMARY 
A method of adjusting a power control setpoint threshold in a wireless 
communication system is provided. The method includes the steps of 
receiving at a receiver, a communication signal from a mobile 
communication unit to form a received communication signal, generating a 
first signal quality indicator based on the received communication signal, 
generating a second signal quality indicator based on the received 
communication signal, and generating an estimated signal-to-noise ratio. 
The method further includes setting a predetermined reference region 
centered around a second signal quality indicator reference where the 
second signal quality indicator reference is related to the first signal 
quality indicator, and adjusting the power control setpoint threshold 
based on a comparison between the second quality indicator and the 
predetermined reference region. 
A controller responsive to a decoder is provided. Stated generally, the 
controller includes means for receiving a first signal quality indicator 
based on a decoded received communication signal, and means for receiving 
a second signal quality indicator based on the decoded received 
communication signal. The controller further includes means for generating 
a second signal quality indicator reference where the second signal 
quality indicator reference is related to the first signal quality 
indicator, means for setting a predetermined reference region centered 
around the second signal quality indicator reference, and means for 
adjusting a power control setpoint threshold based on a comparison between 
the second signal quality indicator and the predetermined reference 
region. 
DETAILED DESCRIPTION OF PREFERRED EMBODIMENT 
Turning now to the drawings, wherein like numerals designate like 
components, FIG. 1 illustrates a wireless communication system 100, such 
as a code division multiple access (CDMA) digital radiotelephone system. 
Base stations 810, 812 and 814 communicate with a mobile station 816 
operating within an area 820 served by base station 812. Areas 822 and 824 
are served by base stations 814 and 810, respectively. Base stations 810, 
812 and 814 are coupled to a centralized controller such as base station 
controller 850, which includes, among other things, a processor 862 and a 
memory 864, and which is in turn coupled to a mobile switching center 860, 
also including a processor 862 and a memory 864. 
Multiple access wireless communication between base stations 810, 812 and 
814 and mobile station 816 occurs via radio frequency (RF) channels which 
provide physical paths over which digital communication signals such as 
voice, data and video are transmitted. Base-to-mobile station 
communications are said to occur on a forward-link channel, while 
mobile-to-base station communications are referred to as being on a 
reverse-link channel. Additionally, mobile communication unit channel 
power control is accomplished on the reverse-link. A communication system 
using CDMA channelization is described in detail in TIA Interim Standard 
IS-95A, Mobile Station-Base Station Compatibility Standards for Dual-Mode 
Wideband Spread Spectrum Cellular Systems, Telecommunications Industry 
Association, Washington, D.C. July 1993 [IS-95A], and "TIA 
Telecommunications Systems Bulletin: Support for 14.4 kbps Data Rate and 
PCS Interaction for Wideband Spread Spectrum Cellular Systems", February 
1996 [the Bulletin], both IS-95A and the Bulletin incorporated herein by 
reference. 
As shown in FIG. 1, forward communication signal 813 has been transmitted 
on an IS-95 forward-link channel such as a Paging Channel or a Traffic 
Channel by base station 812 to mobile station 816. A reverse communication 
signal 815 has been transmitted via an IS-95 reverse-link channel such as 
an Access Channel or a Traffic Channel by mobile station 816 to base 
station 812. 
In addition to data and voice, forward communication signal 813 carries a 
power control bit (PCB) which alters the transmission power of mobile 
station 816, via a feedback algorithm (discussed below), in response to 
Rayleigh/Rician fading, interference level variations (e.g. voice activity 
or loading), differences in transmit and receive antenna gains, and other 
associated losses. Transmit power of mobile station 816 is altered upon 
receipt of a transmitted PCB, multiplexed onto forward communication 
signal 813 at a source base station such as base station 812. 
FIG. 2 is a block diagram of a transmitter 10, for use in a mobile station 
such as mobile station 816, for generating reverse communication signal 
815. A data bit stream 17, which may be voice, video or another type of 
information, enters a variable-rate coder 19, which produces a signal 21 
comprised of a series of transmit channel frames having varying transmit 
data rates. The transmit data rate of each frame depends on the 
characteristics of data bit stream 17. 
Encoder block 28 includes a convolutional encoder 30 and an interleaver 32. 
At convolutional encoder 30, transmit channel frame may be encoded by a 
rate 1/3 encoder using well-known algorithms such as convolutional 
encoding algorithms which facilitate subsequent decoding of the frames. 
Interleaver 32 operates to shuffle the contents of the frames using 
commonly-known techniques such as block interleaving techniques. 
As shown in FIG. 3, each frame 34 of digitally coded and interleaved bits 
includes ninety-six groups of six coded bits, for a total of 576 bits. 
Each group of six coded bits represents an index 35 to one of sixty-four 
symbols such as Walsh codes. A Walsh code corresponds to a single row or 
column of a sixty-four-by-sixty-four Hadamard matrix, a square matrix of 
bits with a dimension that is a power of two. Typically, the bits 
comprising a Walsh code are referred to as Walsh chips. 
Referring again to FIG. 2, each of the ninety-six Walsh code indices 35 in 
frame 34 are input to an M-ary orthogonal modulator 36, which is 
preferably a sixty-four-ary orthogonal modulator. For each input Walsh 
code index 35, M-ary orthogonal modulator 36 generates at output 38 a 
corresponding sixty-four-bit Walsh code W 39. Thus, a series of ninety-six 
Walsh codes W 39 is generated for each frame 34 input to M-ary orthogonal 
modulator 36. 
Scrambler/spreader block 40, among other things, applies a pseudorandom 
noise (PN) sequence to the series of Walsh codes W 39 using well-known 
scrambling techniques. At block 42, the scrambled series of Walsh codes W 
39 is phase modulated using an offset quaternary phase-shift keying 
(OQPSK) modulation process or another modulation process, up-converted and 
transmitted as communication signal S(T) 12 from antenna 46. 
FIG. 4 is a partial block diagram of a receiver 60 within a base station 
such as base station 812 (shown in FIG. 1), for receiving a communication 
signal R(T) 18, originally transmitted by mobile station 816 as 
communication signal S(T) 12 (shown in FIG. 2). Communication signal S(T) 
12 may be subject to multipath fading, path loss and shadowing thus, 
resulting in received communication signal R(T) 18. Receiver 60 is 
preferably a RAKE receiver having a number of fingers, although only a 
single finger is shown. Receiver 60 may be coherent, non-coherent or 
quasi-coherent. 
Antenna 62 receives communication signal R(T) 18, which comprises a number 
of received frames. Front-end processing such as filtering, frequency 
down-converting and phase demodulation of communication signal R(T) 18 is 
performed by well-known methods and circuits at block 64. 
A processed signal 65 from block 64 enters a de-scrambler/de-spreader block 
66. De-scrambler/de-spreader block 66, among other things, removes the PN 
code applied by scrambler block 44 (shown in FIG. 2) to the series of 
Walsh codes W 39 (also shown in FIG. 2). In the IS-95 reverse-link 
channel, a received frame of received signal 18 includes ninety-six 
received symbols, or Walsh codes, which are each sixty-four bits long. The 
received Walsh codes have been altered during transmission by various 
channel parameters, however, and simply appear to receiver 60 to be 
received signal samples. Nevertheless, the received Walsh codes are 
referred to herein as received Walsh codes RW 68. 
Referring again to FIG. 4, each received Walsh code RW 68, after leaving 
de-scrambler/de-spreader 66, is input to an orthogonal demodulator 70, 
such as a Fast Hadamard Transform (FHT). FHT 70 may be implemented using 
commercially available hardware as an array of adders or as a multiplexed 
adder, depending on its size. Alternatively, FHT 70 may be implemented 
utilizing a conventional digital signal processor (DSP) such as a Motorola 
DSP, part no. 56166 or an application specific integrated circuit (ASIC). 
Upon receiving a received Walsh code RW 68, FHT 70 generates a number of 
output signals 72. Sixty-four output signals 72 are generated by FHT 70 
per Walsh code RW 68. Each output signal 72 has an index which references 
one of the sixty-four possible Walsh codes W 39 generated by M-ary 
orthogonal modulator 36 (shown in FIG. 2). Thus, in the IS-95 reverse link 
channel, when a received Walsh code group RW 68 is input to FHT 70, 
sixty-four output signals 72 which correlate to sixty-four possible 
transmitted Walsh codes 39 are produced. It should be understood that in 
addition to having an index, each output signal 72 also has an associated 
complex number, C (not shown). Seven bits are preferably allocated to the 
real and imaginary portions, respectively, of the complex number, although 
fewer or more bits are possible. For simplicity, the index and the complex 
number will be referred to collectively as output signal 72. 
Each output signal 72 further has an associated energy value, C2 (not 
shown) which may be referred to as a Walsh symbol energy value commonly 
calculated by magnitude-squaring the complex number C associated with 
output signal 72. Walsh symbol energy value C2 generally corresponds to a 
measure of confidence, or a likelihood, that output signal 72 indexes a 
Walsh code W 39 which corresponds to a group of received Walsh codes RW 68 
input to FHT 70. The index of output signal 72 with the largest Walsh 
symbol energy value may be referred to as a winning Walsh index with an 
associated energy value referred to as a winning Walsh symbol energy value 
74. Winning Walsh symbol energy value 74 may have any suitable bit width, 
and may be, for example, fourteen bits wide. 
Acting on output signal 72, a decoder 76, which may include a 
de-interleaver 78 and a convolutional decoder 80, further demodulates 
received signal R(T) 18, estimating transmitted communication signal S(T) 
12. Elements of decoder 76 are well known in the art and may be 
implemented in a variety of ways. After the demodulation process, a 
re-encoder (not shown), which may be substantially similar to encoder 28 
shown in FIG. 2, may re-create the transmitted digitally coded and 
interleaved bits, depicted in FIG. 3. and forward them to BSC 850 for 
further processing according to methods well known in the art. 
Referring again to FIG. 1, IS-95A specifies a servo-loop which detects 
signal energy variations and compensates for those variations by adjusting 
the transmission power of mobile station 816 using well known open loop 
power control algorithms as well as closed loop power control algorithms. 
Open loop power control, which is performed at mobile station 816 attempts 
to account for common or symmetrical losses experienced by reverse 
communication signal 815 and forward communication signal 813, due to path 
loss and shadowing. Closed loop power control, consisting of an inner loop 
and outer loop, is designed to compensate for fast (Rayleigh/Rician) 
fading experienced by the reverse communication signal 815 and for 
asymmetrical losses between the forward communication signal 813 and 
reverse communication signal 815. The inner loop is distributed between 
mobile station 816 and base station 812 and provides a feedback mechanism 
via sending power control bits (discussed below). The power control bits 
are sent by puncturing symbols on forward communication signal 813. The 
power control bits vary the transmission power of mobile station 816 to 
achieve the optimal signal to noise level at base station 820. 
Determination of whether a power control bit should take a value of one or 
zero is based on output from an inner loop comparator (discussed below). 
Returning to FIG. 4, six winning Walsh symbol energy value's represent one 
power control group every 1.25 ms. Accumulation of six winning Walsh 
symbols is accomplished at accumulator 75, yielding a power control group 
metric 98 representative of an estimated Eb/No. 
Power control group metric 98 is compared by an inner loop comparator 95 to 
output 93 from an outer loop set point controller 300. Outer loop set 
point controller 300 receives frame quality information 92, for example, 
frame erasure (FE) output, commonly referred to as hard frame quality 
information, from decoder 76, utilizing current methods. An outerloop 
setpoint threshold 93 (discussed below), output from outer loop set point 
controller 300, is updated every 20 ms to prevent significant variation in 
frame quality in an attempt to maintain consistent call quality of mobile 
station 816. 
FIG. 5 shows a prior art sawtooth pattern 500 created by adjusting 
outerloop setpoint threshold 93 over time implemented in outer loop set 
point controller 300 as follows. An initial setpoint threshold is selected 
based on an expected nominal operating point corresponding to sensitivity 
of receiver 60 and changes with time, characterized by a fast attack-slow 
decay period. The decaying speed is determined by a required value for 
FER. Outer loop set point controller 300 reduces outerloop setpoint 
threshold 93 by a substantially small predetermined amount for each good 
full rate frame received until a frame erasure(s) occurs. When a frame 
erasure(s) occurs, the outerloop setpoint threshold 93 is increased up by 
some step size. The step size is predetermined and depends on whether the 
erasure is considered full rate frame or sub-rate frame. Over time, the 
resulting outerloop setpoint threshold 93 dynamically varies in the form 
of a large increase followed by many small decreases, consequently taking 
on the appearance of sawtooth pattern 500 depicted in FIG. 5. 
In FIG. 4, outerloop setpoint threshold 93 is compared with power control 
group metric 98 at inner loop comparator 95, comparators being well known 
in the art. If the resulting value of an inner loop comparator output 94 
is negative, then inner loop comparator 95 sends a power control bit of 1 
to multiplexer 105, which when received by mobile station 816, lowers the 
transmission power of mobile station 816 by 1 dB. If the resulting value 
of comparator output 94 is positive, inner loop comparator 95 sends a 
power control bit of 0 to multiplexer 105, which when received by mobile 
station 816, raises the transmission power of mobile station 816 by 1 dB. 
Thus, the response of mobile station 816 to the PCB generated by receiver 
60 in response to the power control group metric 98 composed of the 
winning Walsh symbol energy measured over a PCG and the FER of received 
communication signal R(T) 18, provides the feedback mechanism to adjust 
subsequent transmission power of mobile station 816. 
While this prior art algorithm strives to insure that the threshold level 
does not contribute to long runs of frame errors, e.g. where mobile 
station 816 is not transmitting at a high enough power level, or is 
transmitting while undergoing fast changing conditions, the transmission 
power level of mobile station 816 may remain higher than necessary for 
lengthy periods of time, needlessly contributing to system noise. 
In a preferred embodiment of the present invention, FIG. 6 shows block 
diagram of an outerloop setpoint controller 300 as shown in FIG. 4., in 
accordance with the present invention. Decoder block 76 receives a 
communication signal such as received signal 72, from demodulator 70. In 
addition to generating a first signal quality indicator 193 such as frame 
erasure FE (discussed in connection with FIG. 4), decoder block 76 
generates a second signal quality indicator 194, q, for example a symbol 
error rate, SER, commonly referred to as a soft frame quality indicator, 
for each frame. 
Referring to FIG. 6, the output associated with first signal quality 
indicator 193, FE, is used to calculate an average frame erasure rate 
(FER) over a predetermined number of frames at filter block f.sub.3 (FE) 
202, yielding an average (FER) 204. Average FER 204 is used to adjust a 
second signal quality indicator reference 206, q.sub.r. The adjustment is 
based on the difference between average FER 204, which is measured via 
filter block f.sub.3 (FE) 202, and a target FER 207 which is 
predetermined, for example, 0.01. 
The variable .delta. represents the difference between the estimated 
average time between erasures and the targeted time between erasures and 
may be represented by .delta.=FER.sup.-1 -0.01.sup.-1. 
If .delta.&lt;0, q.sub.r is decreased by .alpha..sub.1 .vertline.FER.sup.-1 
-0.01.sup.-1 .vertline..sup..beta.1. 
If .delta.&gt;0, q.sub.r is increased by .alpha..sub.2 .vertline.FER.sup.-1 
-0.01.sup.-1 .vertline..sup..beta.2, where .alpha.s and .beta.s (where 
s=1, 2) are predetermined constants. Consequently, the value of the second 
signal quality indicator reference 206, q.sub.r, increases and decreases 
over time, depending on the FER estimated from first signal quality 
indicator 193 output from decoder 76. 
Substantially concurrent to generating first signal quality indicator 193, 
decoder block 76 generates a second quality indicator 194, q. Second 
signal quality indicator 194 is input into filter function block 196, 
f.sub.1 (q). An output f.sub.1 (q) 198 representing a value based on 
averaged second signal quality indicators 194, averaged over the current 
and previous frames, is output from filter function block 196 and is input 
to comparator 200. 
Comparator 200 compares the value of output f.sub.1 (q) 198 with the value 
of q.sub.r at output 208, yielding comparator output .DELTA., 210. 
Comparator output 210 may be represented by the equation, 
EQU .DELTA.=f.sub.1 (q)-q.sub.r. 
Comparator output .DELTA. 210 is input to setpoint controller f.sub.2 
(.DELTA.) 212, yielding a setpoint controller f.sub.2 (.DELTA.) output 
214. If comparator output .DELTA. 210 is smaller than a predetermined 
value 604 (discussed in connection with FIG. 7), .sigma., i.e., 
.vertline..DELTA..vertline.&lt;.sigma., then setpoint controller f.sub.2 
(.DELTA.) output 214=0, thus not varying a power control setpoint 
threshold 216. If comparator output 210 is higher than predetermined value 
604, .sigma., i.e. .DELTA.&gt;.sigma., then setpoint controller f.sub.2 
(.DELTA.) output 214 causes a power control setpoint threshold 216 to be 
increased by f.sub.2 (.DELTA.)=.kappa..sub.1 .DELTA., where .kappa..sub.1 
is a predetermined constant, thus increasing power control setpoint 
threshold 216. If comparator output 210 is lower than predetermined value 
604, .sigma., i.e., .DELTA.&lt;-.sigma., then setpoint controller f.sub.2 
(.DELTA.) output 214 causes power control setpoint threshold 216 to be 
decreased by f.sub.2 (.DELTA.)=.kappa..sub.2 .DELTA., where .kappa..sub.2 
is a predetermined constant, thus decreasing power control setpoint 
threshold 216. 
In FIG. 7, predetermined value 604, a is shown equidistant, above and below 
second signal quality indicator reference 206, forming a predetermined 
reference region 605, 2.sigma.. As discussed in connection with FIG. 6, 
the value of second signal quality indicator reference 206, q.sub.r, is 
variable over time, depending on the FER estimated by filter block f.sub.3 
(FE) 202, thereby adjusting second signal quality indicator reference 206, 
q.sub.r, up or down. Output f.sub.1 (q) 198 representing a value based on 
averaged second signal quality indicators 194, is also shown. 
Thus, setpoint controller f.sub.2 (.DELTA.) output 214 yields power control 
setpoint threshold 216 which is substantially smooth when compared to 
sawtooth pattern 500. FIG. 8 shows a comparison between an example of a 
pattern created generated by power control setpoint threshold 218, 
according to a preferred embodiment of the present invention, and a 
sawtooth pattern 500 generated according to prior art methods. 
Filter block f.sub.3 (FE) 202, filter function block f.sub.1 (q) 196, and 
setpoint controller f.sub.2 (.DELTA.) 212 may be implemented using a 
digital signal processor (DSP) or may be included as an application 
specific integrated circuit (ASIC) operation. 
Returning to FIG. 6, power control setpoint threshold output 218 and power 
control group metric 98, which represents an estimated signal-to-noise 
ratio of a least one received winning walsh symbol or winning Walsh symbol 
energy measured over a PCG, are used to generate a power control command 
219 which subsequently determines whether or not the value of PCB 230 is 1 
or 0. Power control setpoint threshold 216 and power control group metric 
98 are compared at inner loop comparator 95, resulting in power control 
command 219. If the resulting value of power control command 219 is 
negative, then inner loop comparator 95 sends a power control bit 230 
value of 1 to multiplexer 105, which when received by mobile station 816 
(FIG. 1), lowers the transmission power of mobile station 816 by 1 dB. If 
the resulting value of power control command 219 is positive, then inner 
loop comparator 95 sends a power control bit 230 value of 0 to multiplexer 
105, which when received by mobile station 816, raises the transmission 
power of mobile station 816 by 1 dB. Thus, the response of mobile station 
816 to the PCB generated by receiver 60 in response to the power control 
group metric 98 composed of the winning Walsh symbol energy measured over 
a PCG and first signal quality indicator 193, and second signal quality 
indicator 194 of received communication signal R(T) 18, provides the 
feedback mechanism to adjust subsequent transmission power of mobile 
station 816. 
In an alternate embodiment, second signal quality indicator 194 may be 
selected to be a total metric (TM) or other soft quality indicators. In 
addition to generating a first signal quality indicator 193 such as frame 
erasure FE (discussed in connection with FIG. 4), decoder block 76 
generates a second signal quality indicator 194, q, for example a total 
metric, TM, also referred to as a soft frame quality indicator, for each 
frame. 
Referring again to FIG. 6, the output associated with first signal quality 
indicator 193, FE, is used to calculate an average FER over a 
predetermined number of frames at filter block f.sub.3 (FE) 202, yielding 
an average frame erasure rate (FER) 204. Average FER 204 is used to adjust 
a second signal quality indicator reference 206, q.sub.r. The adjustment 
is based on the difference between average FER 204, which is measured, and 
a target FER 207 which is predetermined, for example, 0.01. 
The variable .delta. represents the difference between the estimated 
average time between erasures and the targeted time between erasures and 
may be represented as .delta.=FER.sup.-1 -0.01.sup.-1. 
If .delta.&lt;0, q.sub.r is increased by .alpha..sub.1 .vertline.FER.sup.-1 
-0.01.sup.-1. 
If .delta.&gt;0, q.sub.r is decreased by .alpha..sub.2 .vertline.FER.sup.-1 
-0.01.sup.-1 .vertline..sup..beta.2, where .alpha.s and .beta.s (where 
s=1, 2) are predetermined constants. Consequently, the value of the second 
signal quality indicator reference 206, q.sub.r, increases and decreases 
over time, depending on the FER estimated first signal quality indicator 
193 output from decoder 76. 
Substantially concurrent to generating first signal quality indicator 193, 
decoder block 76 generates a second quality indicator 194, q. Second 
signal quality indicator 194 is input into filter function block 196, 
f.sub.1 (q). An output f.sub.1 (q) 198 representing a value based on 
averaged second signal quality indicators 194, averaged over the current 
and previous frames, is output from filter function block 196 and is input 
to comparator 200. 
Comparator 200 compares the value of output f.sub.1 (q) 198 with the value 
of q.sub.r at output 208, yielding comparator output .DELTA., 210. 
Comparator output 210 may be represented by the equation, 
EQU .DELTA.=f.sub.1 (q)-q.sub.r. 
Comparator output .DELTA. 210 is input to setpoint controller f.sub.2 
(.DELTA.) 212, yielding a setpoint controller f.sub.2 (.DELTA.) output 
214. If comparator output .DELTA. 210 is smaller than a predetermined 
value 604 (discussed in connection with FIG. 7), .sigma., i.e., 
.vertline..DELTA..vertline.&lt;.sigma., then setpoint controller f.sub.2 
(.DELTA.) output 214=0, thus not varying a power control setpoint 
threshold 216. If comparator output 210 is higher than predetermined value 
604, .sigma., i.e. .DELTA.&gt;.sigma., then setpoint controller f.sub.2 
(.DELTA.) output 214 causes a power control setpoint threshold 216 to be 
decreased by f.sub.2 (.DELTA.)=.kappa..sub.1 .DELTA., where .kappa..sub.1 
is a predetermined constant, thus decreasing power control setpoint 
threshold 216. If comparator output 210 is lower than predetermined value 
604, .sigma., i.e., .DELTA.&lt;-.sigma., then setpoint controller f.sub.2 
(.DELTA.) output 214 causes power control setpoint threshold 216 to be 
increased by f.sub.2 (.DELTA.)=.kappa..sub.2 .DELTA., where .kappa..sub.2 
is a predetermined constant, thus increasing power control setpoint 
threshold 216. 
It is contemplated that, although outerloop setpoint controller 300 is 
shown to be collocated with receiver 60 (FIG. 4), located at base station 
812, outerloop setpoint controller 300 may also reside in a centralized 
controller, for example BSC 850. Consequently, first signal indicator 193 
and second signal indicator 194 output from decoder 76 may be transferred 
to outerloop setpoint controller 300 at BSC 850, and processed to yield 
power control command 219. 
In addition, decoder 76 may reside in a centralized controller such as BSC 
850. Consequently, power control setpoint threshold 216 calculated using 
first signal indicator 193 and second signal indicator 194, may be 
transferred to base station 812. Subsequent to transferring power control 
setpoint threshold 216 to base station 812, power control command 219 may 
be generated according to methods described in connection with FIG. 6. 
In any of the above cases, a plurality of received communication signals 
R(T) 18 associated with mobile station 816 will result in a plurality of 
demodulated, decoded signals due to multiple decoders such as decoder 76, 
and subsequently a plurality of first signal quality indicators and second 
quality indicators. Outerloop setpoint controller 300 will select from the 
plurality of signal quality indicators, a first signal quality indicators 
193 and second quality indicators 194 having the highest weighted and 
summed quality values. 
The IS-95A reverse link channel has been specifically referred to herein, 
but the present invention is applicable to any digital channel, including 
but not limited to the forward link IS-95A channel and to all forward- and 
reverse-link TDMA channels, in all TDMA systems such as Groupe Special 
Mobile (GSM), a European TDMA system, Pacific Digital Cellular (PDC), a 
Japanese TDMA system, and Interim Standard 54 (IS-54), a U.S. TDMA system. 
The principles of the present invention which apply to a cellular-based 
digital communication systems, including but not limited to personal 
communicating systems, trunked systems, satellite systems and data 
networks. Likewise, the principles of the present invention which apply to 
all types of digital radio frequency channels also apply to other types of 
communication channels, such as radio frequency signaling channels, 
electronic data buses, wireline channels, optical fiber links and 
satellite links. 
It will furthermore be apparent that other forms of the invention, and 
embodiments other than the specific embodiments described above, may be 
devised without departing from the spirit and scope of the appended claims 
and their equivalents. For example, two methods utilizing so called soft 
frame quality indicators are described herein.