`Reed et al.
`
`54 METHOD AND APPARATUS FOR
`CONTROLLING A POWER LEVEL OFA
`BASE STATION OF A WIRELESS
`COMMUNICATION SYSTEM
`
`(75
`
`(73
`
`r
`Inventors: John D. Reed, Arlington; Walter J.
`Rozanski, Jr., Hurst, both of Tex.
`Assignee: Motorola, Inc., Shaumburg, Ill.
`
`21 Appl. No.: 354,297
`22 Filed:
`Dec. 13, 1994
`
`Related U.S. Application Data
`(63) continuation in part of set No. 16446, Feb. 11, 1993,
`abandoned.
`6
`(51) Int. Cl. .................................................... H04B 7/00
`(52) U.S. Cl. .......................... 455/69; 455/52.1; 455/56.1;
`455/63; 455/67.1
`58) Field of Search ............................... 455/69, 70, 52.1,
`455/52.3, 65, 54.1, 54.2, 67.1, 89, 83, 67.6,
`67.4, 63, 127, 226.1, 226.2, 226.3
`
`(56)
`
`References Cited
`U.S. PATENT DOCUMENTS
`3,940,695 2/1976 Sickles, II.
`4,228,538 10/1980 Scharla-Nielsen et al. .
`4,580,262 4/1986 Naylor et al..
`4,777,653 10/1988 Bonnerot et al..
`4,901,307 2/1990 Gilhousen et al. .
`
`I|||||III
`USOO5574984A
`5,574,984
`11
`Patent Number:
`45 Date of Patent:
`Nov. 12, 1996
`
`5,003,619 3/1991 Morris et al. ............................. 455/69
`5,239,667 8/1993 Kanai.
`5.245,629 9/1993 Hall.
`5,386,589
`1/1995 Kanai ........................................ 455/69
`
`OTHER PUBLICATIONS
`Microwave Mobile Communications, Edited by William C.
`Jakes, Jr., A Wiley-Interscience Publication, 1974.
`Primary Examiner-Andrew Faile
`Assistant Examiner Doris To
`Attorney, Agent, or Firm-Richard A. Sonnentag
`
`ABSTRACT
`(57)
`After setting a base station to a transmit power level (12)
`which Provides signal at a subscribernithaving a target
`quality level, a fading characteristic of a communication
`channel between the subscriber unit and a base site is
`measured (13). The fading characteristic is then compared
`with a threshold value (14). The measuring (13) and com
`paring (14) are repeated until the fading characteristic
`crosses a threshold (15). Once the fading characteristic
`crosses the threshold for a receive Eb/No level that is
`representative of a e.g. static fading condition, the base
`transmit power that is transmitted to the subscriber is
`increased by a predetermined amount in anticipation of the
`need for an increased Eb/No for the case of a faded signal
`(61). The determination of the fading characteristic and
`threshold comparison may be performed at either the sub
`scriber unit or the base station.
`
`7 Claims, 4 Drawing Sheets
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`OPARE FDING CHARACTERISC
`WITF
`OS
`RESOL
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`15
`ES
`EASURE)
`CHARACTERISTIC CROSS
`TRESLD
`16
`NO
`
`SET SBSCRIBER NIT
`TONEHTARGET OUALITYLEVEL
`
`60
`
`OES
`EASREB
`CHARACERISTIC CROSS
`RESD N-1
`
`SET SESCRIBER UNIT TON-TH
`TARGET GUALITY EVEL
`
`DES
`EASRE
`CHARACTERISC CROSS
`TRESOLD
`
`SET SBSCRIBER NIT TO
`IST TARGET CALITY EVEL
`
`SEND INFORATIONSIGNA
`
`ERICSSON v. UNILOC
`Ex. 1011 / Page 1 of 9
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`
`
`U.S. Patent
`
`Nov. 12, 1996
`
`Sheet 1 of 4
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`5,574,984
`
`A/C 7
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`SET SUBSCRIBER UNIT TO A
`TARGET QUALITY EVEL
`
`MEASURE FADING CHARACTERISTIC
`
`COMPARE FADING CHARACTERISTIC
`WITH THRESHODS
`
`DOES
`WEASURED
`CHARACTERISTIC CROSS
`TRESOLD N
`
`
`
`SET SUBSCRIBER UNIT
`TO N TH TARGET QUALITY EVEL
`
`DOES
`EASURED
`CHARACTERISTIC CROSS
`RES D N
`
`
`
`SET SUBSCRIBER UNIT TO N-1 TH
`TARGET QUALITY LEVEL
`
`DOES
`WEASURED
`CHARACTERISTIC CROSS
`TRESOLD
`
`SET SUBSCRIBER UNIT TO
`1ST TARGET QUALITY LEVEL
`
`SEND INFORMATION SIGNAL
`
`CALL
`TERADIED
`YES
`
`17
`
`18
`
`ERICSSON v. UNILOC
`Ex. 1011 / Page 2 of 9
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`
`
`U.S. Patent
`
`Nov. 12, 1996
`
`Sheet 2 of 4
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`5,574,984
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`Eb/No
`a
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`N-1
`3
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`2
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`Eb/No
`5
`4
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`22
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`20
`1.
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`23
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`A/C.2
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`- PRIOR ART -
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`24
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`- I - I - I - KPH
`40
`30
`20
`10
`O
`
`A776.3
`100
`? - PROR ART -
`
`98
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`3
`2
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`99
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`
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`TIME
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`ERICSSON v. UNILOC
`Ex. 1011 / Page 3 of 9
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`U.S. Patent
`
`Nov. 12, 1996
`
`Sheet 3 of 4
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`5,574,984
`
`
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`30
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`- PROR ART -
`
`AVC. 6
`
`SIGNAL
`STRENGTH
`
`91.5
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`NR(Hz)
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`25.6
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`12.8
`8.5
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`AVC. 6
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`H PRIOR ART as
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`40
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`10 15
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`50
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`100
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`V (KPH)
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`- PRIOR ART -
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`OO
`-40 -30 -20 -10
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`0
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`10
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`O
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`ERICSSON v. UNILOC
`Ex. 1011 / Page 4 of 9
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`U.S. Patent
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`Nov. 12, 1996
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`Sheet 4 of 4
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`5,574,984
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`7 7
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`76
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`T
`RANSMITTER
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`f
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`AAC. S.
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`SIGNAL
`OUTPUT 73
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`VOICE
`SIGNAL
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`
`
`
`
`RECEIVER
`
`MEASURING
`DEVICE
`
`COMPARING
`DEVICE
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`ADJUSTING
`MEANS
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`CONTROLLER
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`92
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`93
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`94
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`95
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`96
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`ERICSSON v. UNILOC
`Ex. 1011 / Page 5 of 9
`
`
`
`1
`METHOD AND APPARATUS FOR
`CONTROLLING A POWER LEVEL OFA
`BASE STATION OF A WIRELESS
`COMMUNICATION SYSTEM
`
`The present application is a continuation-in-part of appli
`cation Ser. No. 08/016,446, filed Feb. 11, 1993 now aban
`doned. It is also related to the following applications, all
`owned by the assignee of the present application:
`A Method for Compensating for Capacity Overload in a
`Spread Spectrum Communication System, Ser, No. 07/783,
`751, filed on Oct. 28, 1991.
`
`FIELD OF THE INVENTION
`The present invention relates, in general, to wireless
`communication systems and, more particularly, to a method
`and apparatus for controlling a power level of a base station
`of a wireless communication system.
`
`BACKGROUND OF THE INVENTION
`In wireless communication systems such as Code Divi
`sion Multiple Access (CDMA) environments, it is desirable
`to maintain the energy used per bit as compared to the noise
`in a given bandwidth (E/N) at a level where the signal is
`received sufficiently well (e.g. has sufficient quality) at the
`subscriber unit. However, while raising the E/N level
`would provide a high quality call (e.g. by causing the base
`station to increase its transmit power allocated to a sub
`scriber), it would also reduce the system capacity since the
`signal (E) of one call within the bandwidth is, in general,
`interference (N) to other calls. The CDMA base transmis
`sion uses orthogonal codes assigned to each user to reduce
`the interference on the forward link by partially separating
`the signals of the different users to allow operation on the
`same frequency with a minimum of interference within the
`same cell, but interference from other cells does not benefit
`from this coding method and is added directly as noise
`power (N) Therefore, due to the interference concern, it is
`also desirable to keep the E/N level as low as possible
`while still providing a suitable quality signal. A more
`detailed description of the power level/capacity trade-off is
`made in related application Ser. No. 07/783,751, which is
`incorporated herein by reference. Since a CDMA base
`station uses a single bandwidth for transmitting to multiple
`subscriber units, codes are used to separate the signals that
`are sent simultaneously to each subscriber unit. For this
`reason, the power that is sent to each subscriber can be
`allocated from a maximum base transmit power, to supply
`the needs of each subscriber. This allows a more efficient use
`of the power available at the base to support the power needs
`of all the subscribers in the cell. As subscribers need more
`or less power, the allocation to each subscriber can change
`within limits, such that there will be a minimum and
`maximum that can be supplied to each subscriber. This
`allocation process is well known in the art, and can be
`considered the same as having a fixed power control range
`with a minimum and maximum.
`In order to accomplish the objective of giving each user
`the minimum amount of signal to satisfy the required quality
`level, present proposals use a power control loop to set the
`E/N, to a desired level based on the Word Error Rate
`(WER). When the subscriber is stopped, the E/N at the
`subscribers receiver, is gradually reduced to a level that is
`lower by several decibel (dB) than when the subscriber is
`moving. A higher E/N is necessary for a moving vehicle to
`
`10
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`15
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`20
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`25
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`30
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`40
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`5,574,984
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`2
`maintain the WER in a propagation environment which is
`more hostile, i.e. is subject to Rayleigh fading of the signal
`due to the movement of the user through a large number of
`standing waves and reflections which produce large varia
`tions in the envelope and phase of the received signal. The
`WER is measured to determine power adjustments to be
`transmitted to the base station. These adjustments serve to
`maintain a nominal E/N level. In practice, the base trans
`mit power that is transmitted to a user is gradually reduced
`which results in a reduced E/N and increased WER. Once
`the WER exceeds a certain limit, the subscriber sends a
`message to the base causing the base transmit power to be
`raised to a level where the WER at the subscriber unit is
`acceptable. The process then repeats. This process is referred
`to as a power control loop.
`However, as the subscriber unit begins moving the WER
`will increase at a rate beyond which the low level E/N can
`be maintained. Once the WER increases past a preset point
`(threshold), or accelerates at a given rate, the system will
`gradually increase the E/N level (i.e. by increasing the
`base transmit power) to a higher level required at higher
`speeds.
`There are many power control circuits and algorithms that
`are well known in the art. Almost all of these use an average
`signal value to determine the amount of power to send, this
`average being an estimate of the local mean of the signal at
`the receiver. The reason that the average is used rather than
`the instantaneous signal strength is that the bandwidth
`required to track the instantaneous signal would be prohibi
`tive. Therefore, only slowly changing variations are tracked
`by the power control circuits, which require the receivers to
`be able to tolerate the fast variations of the Rayleigh fading,
`sometimes called fast fading. In the case of a static channel
`when there is no motion, the receiver operates at the lowest
`level of signal since it does not have to tolerate fast varia
`tions in the envelope. The power control tracks the slow
`changing variations, called shadow fading or Log Normal
`fading, by averaging out the fast fading variations to get a
`local mean estimate of the average signal at the receiver. The
`local mean estimate is generally obtained from averaging
`over at least 20 to 40 wavelengths of the signal so that a
`sufficient number of samples of the fading envelope are
`included in the average; alternatively a median of the
`samples can be used rather than an average, but the result is
`still a local mean estimate. Normally at least 20 samples are
`averaged to get a single local mean estimate which from the
`statistics of a Rayleigh fading envelope with uncorrelated
`samples would give an RMS error for the estimate of 1.0 dB
`compared to the true local mean.
`With the Rayleigh fading averaged out, a sample of the
`average power can be used to set the power control. This is
`done now at a slow rate which is compatible with a limited
`bandwidth signal. The slow fading that is corrected for by
`the power control takes seconds to change significantly, and
`this is the type of fading that is compensated for by the prior
`art power control circuits.
`A problem with the present situation as it applies to the
`CDMA radio system is the delay in shifting from one E/N
`level to another as the modem requirements change caused
`by differing channel conditions. This type of delay can result
`in one of two related and undesirable events which occur
`when the subscriber changes speed or stops. A change in
`speed results in a change in the required E/N, which effects
`the quality of the channel due to the delays in the power
`control loop. The first event is that, from a signal perspec
`tive, the E/N is now less than what is considered good for
`the system. This causes a poorer acceptable signal quality in
`
`ERICSSON v. UNILOC
`Ex. 1011 / Page 6 of 9
`
`
`
`5,574,984
`
`10
`
`15
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`20
`
`3
`the channel which directly effects the user signal. The other
`event is that, from a system perspective, the E/N is now
`greater than what is required causing increased noise in the
`bandwidth for other subscribers. The former case in which
`the users signal is degraded is of concern since many bad
`frames will be received by the subscriber before the standard
`power control loop can adjust the signal level.
`Therefore, it would be desirable to reduce the transition
`time for the user who is receiving bad frames due to power
`control loop delay to as short a time period as possible to
`avoid these signal outages and thus improve the overall
`quality of the users service.
`SUMMARY OF THE INVENTION
`A method of controlling a power level of a base unit of a
`wireless communication system having a target quality level
`is provided. The method may include, after first setting a
`target quality level for a subscriber unit, adjusting the power
`level of the base unit to generate a signal providing the target
`quality level when received at a subscriber unit. A fading
`characteristic of the communication channel between the
`Subscriber unit and the base site is then measured and
`compared with a threshold value. The measuring and com
`paring are repeated until the fading characteristic crosses the
`25
`threshold. When the Eb/No received at the subscriber unit is
`below a threshold value, indicative of a static environment,
`and once the fading characteristic crosses the threshold,
`additional power is requested from the base in anticipation
`to the need for a higher Eb/No in a fading environment.
`An apparatus to accomplish the above method is provided
`by a subscriber unit having a receiver to receive an RF
`signal. The received signal is averaged in an averaging
`device and the average is compared with the original RF
`signal in a comparing device. The output data of the com
`35
`parison is provided to a first control unit which uses the
`comparison information to provide an indication of the
`fading environment to determine if the user is in a static
`environment or is experiencing the occurrence of fades.
`BRIEF DESCRIPTION OF THE DRAWINGS
`FIG. 1 is a block diagram of a flow chart illustrating a
`process embodying the present invention;
`FIG. 2 is a graph illustrating the effect of vehicle speeds
`on the required E/N, to obtain a target quality level of
`approximately 1% WER.
`FIG. 3 is a power control graph illustrating the operation
`of a prior art method;
`FIG. 4 is another power control graph providing a com
`50
`parison of the present invention with the prior art;
`FIG. 5 is a prior art graph representing a multipath fading
`characteristic and variation by speeds;
`FIG. 6 is a prior art graph representing fading character
`istic probabilities as a function of speed;
`FIG. 7 is a prior art graph showing normalized level
`crossing rates; and
`FIG. 8 is a block diagram of a power control portion of a
`subscriber unit designed to operate with the method of FIG.
`1.
`FIG. 9 is a block diagram of a power control portion of a
`base station designed to operate with the method of FIG. 1. .
`DETAILED DESCRIPTION OF THE DRAWINGS
`Referring initially to FIG. 1, a block diagram of a flow
`chart illustrating a process, generally designated 10,
`
`4
`embodying the present invention is shown. Process starts at
`block 11 when a call is established. Once established, 12, the
`base transmit power is directed to transmit a power level
`suitable to obtain a predetermined WER at the subscriber,
`representing a given quality level. This quality level repre
`sents a certain Eb/No for the channel conditions that exist at
`this time. A fading characteristic is then measured, 13. This
`information is compared in block 14 to a threshold value. If
`the fading value measured in block 13 is greater than the
`threshold, the level of the E/N is tested in block 60.
`Otherwise, a test for call termination is made in block 17. If
`block 60 found that the Eb/No was above a minimum level,
`then an increase in the Eb/No is requested by directing the
`base to transmit more power (block 61). After the test in
`block 17, the loop repeats.
`As shown in FIG. 2, a prior art graph, generally desig
`nated as 20, the speed of the subscriber can be seen to
`require different levels of Eb/No to maintain a given low
`WER or high quality level. Line 21 represents the Eb/No
`requirement for Rayleigh fading, and line 22 represents the
`Eb/No requirement for Multi-path fading which has delayed
`rays suitable for reception by the type of receiver used in a
`CDMA radio system. It is important to note that for speeds
`near zero, the required Eb/No is reduced dramatically. Also,
`for speeds approaching 5 to 15 KPH (depending on the
`fading), the required E/N increases rapidly. At higher
`speeds, beyond the peak requirement, the needed Eb/No
`gradually decreases due to the effect of interleaving which
`improves the modem performance at higher speeds.
`In FIG. 3, a prior art graph, generally designated 100, is
`depicted representing actual E/N levels over time. As a
`vehicle's speed changes, assume that the WER rate
`improves permitting the transmit power to be reduced,
`resulting in a lower E/N. The E/N level is gradually
`reduced (using a power control loop), line 98, over poten
`tially several seconds until an unacceptable threshold word
`error rate (WER) is exceeded. The base is then given a
`command to raise its power level. The remote units reaction
`is represented by line 99. The level of the step increase can
`be set by the system operator as desired, and may typically
`be near 1 dB. These steps are repeated continuously as
`shown.
`In FIG.4, a composite graph, generally designated 110, is
`illustrated showing E/N adjustments using the prior art and
`the present invention. When the speed of the remote unit,
`represented by line 111, changes, the prior art method results
`in the changes to E/N received at the subscriber unit
`represented by line 25. As an example, a subscriber unit is
`shown to be traveling near 20 KPH at the beginning of the
`graph, and gradually slows down to zero KPH after about 4
`seconds. During this time, the required Eb/No increases to
`maintain the desired quality level, and thus the power
`control loop causes the Eb/No to be increased as seen by line
`25. Once the subscriber is stopped, the required Eb/No is
`reduced, and it falls to a minimum value near 4 dB until the
`subscriber again begins to move. At this time, the required
`Eb/No increases quickly, but before the power control can
`react to this need, it must detect a sufficient number of frame
`errors to indicate that the WER has increased, and then it
`must begin to increase the base station transmit power. This
`represents a time delay in which numerous frame errors are
`occurring, and which will be heard as a degradation in the
`audio of the subscriber unit. In the present invention, this
`delay time is reduced as indicated by 73, from the detection
`of the fading signal which indicates the need for increased
`Eb/No for the case when the Eb/No is low. This invention
`anticipates the need for the increased Eb/No and initiates the
`
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`ERICSSON v. UNILOC
`Ex. 1011 / Page 7 of 9
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`5,574,984
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`5
`base to increase the power level causing the Eb/No to
`increase sooner 74, and thus reduce the effect of the time
`required to detect the frame errors and begin the adjustments
`as in the prior art.
`A Rayleigh multipath fading characteristic is illustrated in 5
`FIG. 5, a prior art graph, generally designated 30. The
`dashed line 32 represents a stationary subscriber unit. As
`shown, even while stationary, the fading characteristics
`would seem to indicate some movement. From a practical
`implementation, a stationary subscriber can encounter nulls 10
`at a rate indicating movement on the order of 10 KPH in
`some traffic conditions, (e.g. from passing vehicles) but in
`other cases may see no fading nulls at all.
`When the subscriber increases speed, the nulls will appear
`more frequently, as represented by solid line 31, or dashed
`line 33, FIG. 5. Therefore, the number of fades in a given
`period is generally representative of the speed of the sub
`scriber. It is only the case in which there are little or no
`fading nulls on the channel that is representative of a static
`channel, which will operate at a very low Eb/No. It is this
`case in which the change in fading characteristics will be
`most easily detected, and also the case in which needs the
`rapid increase in Eb/No when the subscriber starts to see
`fading. It should be noted that a change in the fading
`characteristic could be caused by motion near the subscriber,
`without requiring the subscriber to move. This case would
`still work well with the invention since the detection of the
`fading envelope would still be possible, and the change in
`signal requirement by the subscriber could be detected as in
`the case when the subscriber begins to move.
`Returning now to FIG. 1, once the fading characteristic is
`measured, it is compared to a threshold value. This is
`illustrated in the prior art graph of FIG. 6, generally desig
`nated 40, which shows a graph of the frequency (N) of
`fades as a function of velocity (V). The fades are measured
`in the number of level crossings per second (Hertz or Hz)
`and the velocity in KPH. The graph of FIG. 6 is derived
`using equation (1):
`NRF(f)(x)
`where:
`f is the Doppler shift in Hz; and
`x is a constant which can be obtained from the graph of
`FG. 7.
`r
`The graph of FIG. 7 is a prior art graph representing
`normalized level crossing rates. This graph is described in
`detail in Jakes, "Microwave Mobile Communications”, pg
`35 (1974). If it is assumed that, for p=1, any fade which
`crosses the average value will be counted as a fade then,
`using the graph of FIG. 7, the value of Nelf is 0.915. In
`order to determine N., f must first be determined using
`equation (2):
`f=(1.5)(V)(0.62)(F)
`where:
`V is the velocity in KPH;
`F is the frequency in GigaHertz (GHz);
`the constant 0.62 is used to convert velocity (V) in -
`equation (2) from MPH to KPH; and
`the constant 1.5 represents several combined constants
`and scale factors. Using equation (2), the Doppler shift
`at 10 KPH for a 1 GHz signal is 9.3 Hz. Substituting 65
`this into equation (1) provides a crossing rate, NR, of
`8.5 level crossings per second. At 15 KPH, the crossing
`
`(1) 40
`
`6
`rate is 12.8. At 30 KPH, the crossing rate is 25.6, thus
`a detection of the transition from a stationary user to a
`user that is moving could be made by testing this
`parameter. If the user was stationary, the level crossing
`rate would be at a small number if these were traffic
`nearby, and it would be zero if there were no traffic.
`If the fading characteristic crosses threshold level (deci
`sion step 15) for the case when the Eb/No level is presently
`below a threshold value (decision step 60) then the sub
`scriber will request from the base an increase in the signal
`to raise the Eb/No level in anticipation of the effects of the
`fading on the WER or quality level. Process 10 proceeds to
`determine if the call has been terminated, decision step 17.
`If the call has been terminated, process 10 ends, step 18. If
`the call is not terminated, then process 10 loops back to step
`3.
`In the prior art, the system would have continued to
`measure the WER while the base slowly decreased its
`transmit power. The E/N of the subscriber unit, would be
`allowed to continue to decrease until a poor WER was
`detected. The power of the base unit is then increased until
`an acceptable WER was reached. Only after a sufficient
`number of Word Errors have been detected, such that the
`subscriber unit can determine that the WER has increased
`above a 1% WER or other predetermined WER quality level,
`can it make a request from the base for additional power
`which would raise its Eb/No value. During this delay time,
`the numerous frame errors will degrade the quality of the
`audio of the subscriber unit.
`A block diagram of one embodiment of a power control
`portion of a subscriber unit, generally designated 70, is
`provided in FIG. 8. In FIG. 8, a signal is received from a
`base site 79 by antenna 71 and carried to receiver 72.
`Receiver 72 processes the signal and extracts the envelope
`of the signal which represents the instantaneous received
`power of the signal and supplies this to circuit block 78 to
`detect the threshold crossings of the received signal strength
`with an average signal strength.
`Circuit 78 is comprised of a filter 73 for averaging the
`signal strength from receiver 72 (e.g. by determining a
`moving average over a time period, typically a few seconds);
`and a differential amplifier 74 to compare the averaged
`signal with the instantaneous value of the received signal.
`The output data from circuit 78 represents the zero crossings
`of the instantaneous received signal strength of the received
`signal to a short term average of the received signal power.
`This will then indicate the fading rate and this information
`is provided to a controller 75. The fading information is
`compared in controller 75 with a threshold level. When a
`threshold is crossed, and other decision criteria is met
`(decision 60) then controller 75 signals the base site by
`transmitter 75 through antenna 77. Alternatively, this fading
`information could be forwarded to the base site continuously
`as a part of the standard overhead message. The decision on
`whether a threshold has been exceeded could then be made
`the base site; or at the subscriber unit as before. It should be
`noted here that antenna 71 and 77 may be the same antenna
`if a duplexer is used in subscriber unit 70.
`As an alternative to having the remote unit taking all of
`the measurements and making the various decisions, it
`should be understood that some of the measurements (e.g.
`Rayleigh fading) could be made at the base station based on
`the uplink channel (which should provide an approximation
`of the downlink channel fading characteristic). The base
`station would then direct adjustments to its transmit power
`when it detects a fading signal representative of a change in
`subscriber speed or environment. Information relating the
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`ERICSSON v. UNILOC
`Ex. 1011 / Page 8 of 9
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`subscriber's nominal Eb/No level could be used in this
`decision process. Conversely, actions currently performed
`by the base site could be made at the subscriber unit.
`In particular, FIG. 9 depicts a block diagram of a power
`control portion of a base station designed to operate with the
`method of FIG. 1. In FIG. 9, the apparatus receives a signal
`at antenna 91 and directs said signal to the receiver 92. The
`receiver 92 filters out a useful signal envelope which is
`directed to a measuring device 93 which measures and
`calculates a fading characteristic for said signal. The mea
`suring device 93 directs its output to a comparing device 94
`which compares the fading characteristic against a threshold
`level. Based on the result of the comparison, the adjusting
`device 95 directs the controller 96 to adjust the output power
`of the transmitter 97 in an attempt to improve system
`performance.
`Thus, it will be apparent to one skilled in the art that there
`has been provided in accordance with the invention, an
`improved method and apparatus for controlling a power
`level of a wireless communication system.
`While the invention has been described in conjunction
`with specific embodiments thereof, one skilled in the art will
`appreciate that many alterations, modifications, and varia
`tions are possible and evident in light of the foregoing
`description. Accordingly, the invention is not limited
`thereby, but embraces all such alterations, modifications,
`and variations encompassed by the following claims.
`We claim:
`1. An apparatus for controlling a base station of a wireless
`communication system, the apparatus comprising:
`receiving means for receiving a first radio frequency (RF)
`signal from the base station and determining a received
`signal strength of the first RF signal;
`comparing means for comparing the averaged received
`35
`signal strength with the received signal strength to
`determine a fading characteristic, and for further com
`paring the fading characteristic with a threshold value
`to determine when the fading characteristic crosses the
`threshold value; and
`control means for sending a power level adjustment signal
`to the base station when the fading characteristic
`crosses the threshold value.
`2. A method of controlling a base station of a wireless
`communication system, the wireless communication system
`having an initial target quality level for a signal communi
`cated between a subscriber unit and the base station, the
`method comprising the steps of:
`(a) setting a power level at the base station to obtain the
`initial target quality level at the subscriber unit;
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`(b) measuring a frequency of fades at which a signal
`strength of the signal crosses an average of the signal
`strength;
`(c) comparing the frequency of fades with a preset fre
`quency of fades representing a threshold level;
`(d) controlling the base station to reduce the power level
`when the frequency of fades crosses the preset fre
`quency of fades representing the threshold level.
`3. The method of claim 2 further comprising the step of
`reducing the power level of the base station if a word error
`rate (WER) does not exceed a threshold WER.
`4. The method of claim 2 wherein the wireless commu
`nication system is a Code Division Multiple Access
`(CDMA) system.
`5. An apparatus for controlling a base station of a wireless
`communication system, the apparatus comprising:
`adjusting means for adjusting a power level of the base
`station to obtain a target quality level at a subscriber
`unit;
`receiving means for receiving a first radio frequency (RF)
`signal via the communication channel and determining
`a received signal strength of the received RF signal;
`averaging means for averaging a period of time of the
`received signal strength and providing an averaged
`received signal strength;
`comparing means for comparing the averaged received
`signal strength with the received signal strength to
`determine a fading characteristic, and for further com
`paring the fading characteristic with a threshold value
`to determine when the fading characteristic crosses the
`threshold value; and
`control means for further adjusting the power level of the
`base station when a fading characteristic of a commu
`nication channel between the subscriber unit and the
`base station crosses the threshold value.
`6. The apparatus of claim 5 further comprising receiver
`means for receiving a power adjustment signal from the
`subscriber unit when the fading characteristic crosses the
`threshold value, wherein the control means is operable for
`further adjusting the base station power level based on the
`power adjustment signal.
`7. The apparatus of claim 5, wherein the receiving, the
`averaging and the comparing means reside in either the base
`station or the subscriber unit.
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`ERICSSON v. UNILOC
`Ex. 1011 / Page 9 of 9
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