United States Patent (19)
`Gilhousen et al.
`
`11)
`(45)
`
`Patent Number:
`Date of Patent:
`
`5,056,109
`Oct. 8, 1991
`
`(54)
`
`(75)
`
`(73)
`(21)
`22
`(51)
`(52)
`(58)
`(56)
`
`METHOD AND APPARATUS FOR
`CONTROLLING TRANSMISSION POWER
`IN A CDMA CELLULAR MOBILE
`TELEPHONE SYSTEM
`Inventors: Klein S. Gilhousen; Roberto
`Padovani, both of San Diego; Charles
`E. Wheatley, III, Del Mar, all of
`Calif.
`Assignee: Qualcomm, Inc., San Diego, Calif.
`Appl. No.: 433,031
`Filed:
`Nov. 7, 1989
`Int. Cl. ...................... H04L 27/30; H04J 13/00;
`H04B 7/204
`U.S. C. .......................................... 375/1; 370/18;
`379/59; 455/33; 455/54; 455/69
`Field of Search ....................... 455/33, 54, 59, 69;
`370/18, 50; 379/58, 59
`References Cited
`U.S. PATENT DOCUMENTS
`Frost ..................................... 379/60
`9/1978
`4,112,257
`Lampert et al. ........................ 375/1
`4,123,718
`10/1978
`Cooper et al. .....
`375/1
`4,222,115
`9/1980
`Osborne et al.
`... 455/226
`4,225,976
`9/1980
`Giger .................
`... 445/73
`4,495,648
`1/1985
`Naylor et al. ..
`... 371/5.5
`4/1986
`4,580,262
`Hasegawa .............................. 375/1
`2/1987
`4,641,322
`Kavehrad et al. .
`... 379/63
`4,672,658
`6/1987
`Schmidt ................................ 379/60
`4,765,753
`8/1988
`
`4,811,421 3/1989 Havel et al. ........................... 455/69
`Primary Examiner-Bernarr E. Gregory
`Attorney, Agent, or Firm-Russell B. Miller
`57
`ABSTRACT
`A power control system for a cellular mobile telephone
`system in which system users communicate information
`signals between one another via at least one cell site
`using code division multiple access spread spectrum
`communication signals. The power control system con
`trols transmission signal power for each cellular mobile
`telephone in the cellular mobile telephone system
`wherein each cellular mobile telephone has an antenna,
`transmitter and receiver and each cell-site also has an
`antenna, transmitter and receiver. Cell-site transmitted
`signal power is measured as received at the mobile unit.
`Transmitter power is adjusted at the mobile unit in an
`opposite manner with respect to increases and decreases
`in received signal power. A power control feedback
`scheme may also be utilized. At the cell-site communi
`cating with the mobile unit, the mobile unit transmitted
`power is measured as received at the cell-site. A com
`mand.signal is generated at the cell-site and transmitted
`to the mobile unit for further adjusting mobile unit
`transmitter power corresponding to deviations in the
`cell site received signal power. The feedback scheme is
`used to further adjust the mobile unit transmitter power
`so as to arrive at the cell-site at a desired power level.
`
`27 Claims, 5 Drawing Sheets
`
`FROM
`ANALOG
`RECEIVER
`
`A/D
`CONVERTER
`
`O
`
`
`
`
`
`
`
`
`
`
`
`
`
`FAST
`HADAMARD
`TRANSFORM
`FLTER
`
`USER
`DATA -
`DECODER
`
`USER
`
`8
`
`PN
`GENERATOR
`
`
`
`POWER
`AVERAGER
`
`TO TRANSMT
`MODULATOR
`
`
`
`POWER
`UP/DOWN
`COMMAND
`GENERATOR
`
`COMPARATOR
`
`
`
`POWER LEVEL
`SET FROM
`PROCESSOR
`
`IPR2018-01473
`Apple v. INVT
`INVT Exhibit 2004 - Page 1
`
`

`

`U.S. Patent
`
`Oct. 8, 1991
`
`Sheet 1 of 5
`
`5,056,109
`
`TO FROM
`PSTN
`
`
`
`
`
`O
`
`TO FROM OTHER
`CELL-STES
`
`SYSTEM
`CONTROLLER
`8 SWTCH
`
`24 O
`
`6
`
`FG.
`
`IPR2018-01473
`Apple v. INVT
`INVT Exhibit 2004 - Page 2
`
`

`

`U.S. Patent
`
`Oct. 8, 1991
`
`Sheet 2 of 5
`
`5,056,109
`
`MOBILE
`UNT
`RECEIVED
`St GNAL
`POWER
`
`
`
`MOBLE
`UNIT
`TRANSMT
`POWER
`
`
`
`D STANCE
`
`FG, 2A
`
`D STANCE
`
`FG. 2B
`
`IPR2018-01473
`Apple v. INVT
`INVT Exhibit 2004 - Page 3
`
`

`

`U.S. Patent
`
`Oct. 8, 1991
`
`Sheet 3 of 5
`
`5,056,109
`
`
`
`MOBILE
`UNT
`TRANSMIT
`POWER
`
`
`
`CELL-STE
`RECEIVED
`SIGNA
`POWER
`
`DSTANCE
`
`DISTANCE
`
`FIG. 2D
`
`IPR2018-01473
`Apple v. INVT
`INVT Exhibit 2004 - Page 4
`
`

`

`U.S. Patent
`
`Oct. 8, 1991
`
`Sheet 4 of 5
`
`5,056,109
`
`54
`
`50s
`
`Moelle Unit N
`
`A NALOG
`RECEIVER
`
`
`
`
`
`
`
`
`
`
`
`
`52
`
`D G TAL
`DATA
`RECEIVER
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`
`
`
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`
`
`ANT ENNA
`
`
`
`
`
`
`
`
`
`
`
`P LOT
`S. GNAL
`GENERATOR
`
`RECEIVED,
`POWER
`MEASUREMENT
`
`TO OTHER DIGITAL
`DATA RECEIVERS
`
`FIG.3
`
`FROM OTHER
`TRANSMIT MODULATORS
`
`
`
`USER
`D G T A L
`BASEBAND
`
`
`
`. 62
`
`TRANSMT
`MODULATOR
`--
`PROCESSOR
`
`72
`
`74
`
`-82
`
`
`
`
`
`
`
`AN ALOG
`
`
`
`RECEIVER
`
`
`
`
`
`ANT ENNA
`
`DIGITAL
`DATA
`RECEIVER
`
`
`
`USER
`DIGITAL
`BASEBAND
`
`CONTROL
`PROCESSOR
`
`
`
`
`
`
`
`
`
`TRANSMT
`POWER
`CONTROL
`
`
`
`TRANSMT
`POWER
`CONTROL
`
`
`
`TRANSMT
`MODULATOR
`
`FIG.4
`
`IPR2018-01473
`Apple v. INVT
`INVT Exhibit 2004 - Page 5
`
`

`

`U.S. Patent
`
`Oct. 8, 1991
`
`Sheet 5 of 5
`
`5,056,109
`
`FROM
`ANTENNA
`
`9 O
`
`DOWN-
`CONVERTER
`
`92
`BPF
`
`Y
`94
`
`TO A/D
`CONVERTER
`
`96
`
`A GC
`DETECTOR
`
`POWER LEVEL
`SET FROM
`PROCESS OR
`
`FROM TRANST
`MODULATOR
`
`POWER LEVEL
`CONTROL FROM
`PROCESSOR
`
`OO
`
`NON- LINEAR
`F LTER
`
`98
`
`O
`ANTENNA
`
`IO2
`
`O4
`
`F.G. 5
`
`FROM
`ANALOG
`RECEIVER
`
`A/D
`CONVERTER
`
`
`
`2
`
`PN
`CORRELATOR
`
`
`
`
`
`
`
`
`
`PN
`GENERATOR
`
`FAST
`HADAMARD
`TRANSFORM
`FLER
`
`USER
`
`user
`DATA .
`DECODER
`
`8
`
`POWER
`AVERAGER
`
`TO TRANSMT POWER
`MODULATOR
`UPyDOWN
`COMMAND
`GENERATOR
`
`
`
`
`
`
`
`
`
`COMPARATOR
`
`F.G. 6
`
`POWER LEVEL
`SET FROM
`PROCESSOR
`
`IPR2018-01473
`Apple v. INVT
`INVT Exhibit 2004 - Page 6
`
`

`

`1.
`
`METHOD AND APPARATUS FOR CONTROLLING
`TRANSMISSION POWER IN A CDMA CELLULAR
`MOBILE TELEPHONE SYSTEM
`
`10
`
`5,056, 109
`2
`level necessary to maintain quality communications so
`as to result in a reduction in system interference.
`The Hub then transmits a power control command
`signal to each mobile user so as to adjust or "fine tune"
`the transmit power of the mobile unit. This command
`signal is used by the mobile unit to change the transmit
`power level closer to a minimum level required to main
`tain the desired communications. As channel conditions
`change, typically due to motion of the mobile unit, both
`the mobile unit receiver power measurement and the
`power control feedback from the Hub continually read
`just the transmit power level so as to maintain a proper
`power level. The power control feedback from the Hub
`is generally quite slow due to round trip delays through
`the satellite requiring approximately of a second of
`propagation time.
`One important difference between satellite or terres
`trial base stations systems are the relative distances
`separating the mobile units and the satellite or cell-site.
`Another important different in the satellite versus the
`terrestrial system is the type of fading that occurs in
`these channels. Thus, these differences require various
`refinements in the approach to system power control
`for the terrestrial system.
`In the satellite/mobile unit channel, i.e. the satellite
`channel, the satellite repeaters are normally located in a
`geosynchronous earth orbit. As such, the mobile units
`are all at approximately the same distance from the
`satellite repeaters and therefore experience nearly the
`same propagation loss. Furthermore, the satellite chan
`nel has a propagation loss characteristic that follows
`approximately the inverse square law, i.e. the propaga
`tion loss is inversely proportional to the square of the
`distance between the mobile unit and the satellite re
`peater in use. Accordingly, in the satellite channel the
`variation in path loss due to distance variation is typi
`cally on the order of only 1-2 dB.
`In contrast to the satellite channel, the terrestrial/mo
`bile unit channel, i.e. the terrestrial channel, the distance
`between the mobile units and the cell sites can vary
`considerably. For example, one mobile unit may be
`located at a distance of five miles from the cell site while
`another mobile unit may be located only a few feet
`away. The variation in distance may exceed a factor of
`one hundred to one. The terrestrial channel experiences
`a propagation loss characteristic as did the satellite
`channel. However, in the terrestrial channel the propa
`gation loss characteristic corresponds to an inverse
`fourth-power law, i.e. the path loss is proportional to
`the inverse of the path distance raised to the fourth
`power. Accordingly, path loss variations may be en
`countered which are on the order of over 80 dB in a cell
`having a radius of five miles.
`The satellite channel typically experiences fading that
`is characterized as Rician. Accordingly the received
`signal consists of a direct component summed with a
`multiply reflected component having Rayleigh fading
`statistics. The power ratio between the direct and re
`flected component is typically on the order of 6-10 dB,
`depending upon the characteristics of the mobile unit
`antenna and the environment about the mobile unit.
`Contrasting the satellite channel with the terrestrial
`channel, the terrestrial channel experiences signal fad
`ing that typically consists of the Rayleigh faded compo
`nent without a direct component. Thus, the terrestrial.
`channel presents a more severe fading environment
`
`BACKGROUND OF THE INVENTION
`I. Field of the Invention
`The present invention relates to cellular mobile tele
`phone systems. More specifically, the present invention
`relates to a novel and improved method and apparatus
`for controlling transmitter power in a code division
`multiple access (CDMA) cellular mobile telephone
`System.
`II. Description of the Related Art
`15
`The use of code division multiple access (CDMA)
`modulation techniques is one of several techniques for
`facilitating communications in which a large number of
`system users are present. Although other techniques
`such as time division multiple access (TDMA), fre
`quency division multiple access (FDMA) and AM mod
`ulation schemes such as amplitude companded single
`sideband (ACSSB) are known, CDMA has significant
`advantages over these other techniques. The use of
`CDMA techniques in a multiple access communication
`system is disclosed in U.S. Pat. application Ser. No.
`25
`O6/921,261, filed Oct. 17, 1986, entitled “SPREAD
`SPECTRUM MULTIPLE ACCESS COMMUNICA.
`TION SYSTEM USING SATELLITE OR TERRES
`TRIAL REPEATERS", now U.S. Pat. No. 4,901,307
`assigned to the assignee of the present invention, the
`disclosure thereof incorporated by reference.
`In the just mentioned patent, a multiple access tech
`nique is disclosed where a large number of mobile tele
`phone system users each having a transceiver communi
`cate through satellite repeaters or terrestrial base sta
`35
`tions (also known as cell-sites stations, or for short cell
`sites) using code division multiple access (CDMA)
`spread spectrum communication signals. In using
`CDMA communications, the frequency spectrum can
`be reused multiple times thus permitting an increase in
`system user capacity. The use of CDMA results in a
`much higher spectral efficiency than can be achieved
`using other multiple access techniques. In a CDMA
`system, increases in system capacity may be realized by
`controlling the transmitter power of each mobile user so
`45
`as to reduce interference to other system users.
`In the satellite application of the CDMA communica
`tion techniques, the mobile unit transceiver measures
`the power level of a signal received via a satellite re
`peater. Using this power measurement, along with
`50
`knowledge of the satellite transponder downlink trans
`mit power level and the sensitivity of the mobile unit
`receiver, the mobile unit transceiver can estimate the
`path loss of the channel between the mobile unit and the
`satellite. The mobile unit transceiver then determines
`the appropriate transmitter power to be used for signal
`transmissions between the mobile unit and the satellite,
`taking into account the path loss measurement, the
`transmitted data rate and the satellite receiver sensitiv
`1ty.
`The signals transmitted by the mobile unit to the
`satellite are relayed by the satellite to a Hub control
`system earth station. The Hub measures the received
`signal power from signals transmitted by each active
`mobile unit transceiver. The Hub then determines the
`deviation in the received power level from that which is
`necessary to maintain the desired communications.
`Preferably the desired power level is a minimum power
`
`30
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`55
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`65
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`IPR2018-01473
`Apple v. INVT
`INVT Exhibit 2004 - Page 7
`
`

`

`5,056, 109
`4
`3
`power of the mobile unit transmitted signal multiplied
`than the satellite channel where Rician fading is the
`by the number of mobile units transmitting within the
`dominant fading characteristic.
`cell. To this is added the noise power received at the
`The Rayleigh fading characteristics in the terrestrial
`channel signal is caused by the signal being reflected
`cell-site from mobile units in adjacent cells.
`The CDMA receivers of the cell-site respectively
`from many different features of the physical environ- 5
`operate by converting a wideband CDMA signal from
`ment. As a result, a signal arrives almost simultaneously
`a corresponding one of the mobile unit transmitters into
`at a mobile unit receiver from many directions with
`a narrow band digital information carrying signal. At
`different transmission delays. At the UHF frequency
`the same time, other received CDMA signals that are
`bands usually employed for mobile radio communica
`tions, including those of cellular mobile telephone sys- . 10
`not selected remain as wide band noise signals. The
`tems, significant phase differences in signals traveling
`bit-error-rate performance of the cell-site receiver is
`thus determined by the ratio of the power of the desired
`on different paths may occur. The possibility for de
`signal to that of the undesired signals received at the
`structive summation of the signals may result, with on
`occasion deep fades occurring.
`cell-site, i.e., the received signal power in the desired
`Terrestrial channel fading is a very strong function of 15
`signal transmitted by the selected mobile unit transmit
`the physical position of the mobile unit. A small change
`ter to that of the received signal power in undesired
`in position of the mobile unit changes the physical de
`signals transmitted by the other mobile unit transmit
`lays of all the signal propagation paths, which further
`ters. The bandwidth reduction processing, a correlation
`process which results in what is commonly called "pro
`results in a different phase for each path. Thus, the
`cessing gain", increases the signal to noise interference
`motion of the mobile unit through the environment can 20
`result in a quite rapid fading process. For example, in
`ratio from a negative value to a positive value thus
`allowing operation within an acceptable bit-error-rate.
`the 850 MHz cellular radio frequency band, this fading
`can typically be as fast as one fade per second per mile
`In a terrestrial CDMA cellular mobile telephone
`system it is extremely desirable to maximize the capac
`per hour of vehicle speed. Fading on this order can be
`extremely disruptive to signals in the terrestrial channel 25
`ity in terms of the number of simultaneous telephone
`calls that may be handled in a given system bandwidth.
`resulting in poor communication quality. However,
`System capacity can be maximized if the transmitter
`additional transmitter power can be used to overcome
`the problem of fading.
`power of each mobile unit is controlled such that the
`The terrestrial cellular mobile telephone system typi
`transmitted signal arrives at the cell-site receiver at the
`cally requires a full-duplex channel to be provided in 30
`minimal signal to noise interference ratio which allows
`acceptable data recovery. If a signal transmitted by a
`order to allow both directions of the telephone conver
`sation to be simultaneously active such as provided by
`mobile unit arrives at the cell-site receiver at a power
`the conventional wired telephone system. This full
`level that is too low, the bit-error-rate may be too high
`duplex radio channel is normally provided by using one
`to permit high quality communications. On the other
`hand if the mobile unit transmitted signal is at a power
`frequency band for the outbound link, i.e. transmissions 35
`level that is too high when received at the cell site
`from the cell-site transmitter to the mobile unit receiv
`receiver, communication with this particular mobile
`ers. A different frequency band is utilized for the in
`unit will be acceptable. However, this high power sig
`bound link, i.e. transmissions from the mobile unit trans
`mitters to the cell-site receivers. According, this fre
`nal acts as interference to other mobile unit transmitted
`signals that are sharing the same channel, i.e. band
`quency band separation allows a mobile unit transmitter 40
`width. This interference may adversely affect commu
`and receiver to be active simultaneously without feed
`back or interference from the transmitter into the re
`nications with other mobile units unless the total num
`ber of communicating mobile units is reduced.
`ceiver.
`The path loss of signals in the UHF frequency band
`The use of different frequency bands has significant
`implications in the power control of the cell-site and 45
`of the cellular mobile telephone channel can be charac
`terized by two separate phenomena, average path loss
`mobile unit transmitters. Use of different frequency
`and fading. The average path loss can be described
`bands causes the multipath fading to be independent
`statistically by a log-normal distribution whose mean is
`processes for the inbound and outbound channels. A
`proportional to the inverse fourth-power of the path
`mobile unit cannot simply measure the outbound chan
`nel path loss and assume that the same path loss is pres- 50
`distance, and whose standard deviation is approxi
`mately equal to 8 dB. The second phenomena is a fading
`ent on the inbound channel.
`process caused by multipath propagation of the signals
`It is therefore, an object of the present invention to
`provide a novel and improved method and apparatus
`which is characterized by a Rayleigh distribution. The
`average path loss, which is a log-normal distribution,
`for controlling in the terrestrial channel transmitter
`power so as to overcome deleterious fading without 55
`can be considered to be the same for both the inbound
`causing unnecessary system interference which can
`and outbound frequency bands, as is for the conven
`adversely affect overall system capacity.
`tional cellular mobile telephone systems. However, as
`mentioned previously Rayleigh fading is an indepen
`SUMMARY OF THE INVENTION
`dent phenomena for the inbound and outbound link
`frequency bands. The log-normal distribution of the
`In a terrestrial CDMA cellular mobile telephone 60
`average path loss is a relatively slow varying function of
`system, it is desirable that the transmitter power of the
`position. In contrast, the Rayleigh distribution varies
`mobile units be controlled so as to produce at the cell
`relatively fast as a function of position.
`site receiver a nominal received signal power from each
`In the present invention, a CDMA approach to multi
`and every mobile unit transmitter operating within the
`ple user access in a cellular mobile telephone system is
`cell. Should all of the mobile unit transmitters within an 65
`implemented. In such a system all the cell-sites in a
`area of coverage of the cell-site have transmitter power
`region transmit, a "pilot' signal of the same frequency
`controlled accordingly the total signal power received
`and code. The use of a pilot signal in CDMA systems is
`at the cell-site would be equal to the nominal receiver
`
`IPR2018-01473
`Apple v. INVT
`INVT Exhibit 2004 - Page 8
`
`

`

`O
`
`20
`
`35
`
`5,056, 109
`6
`5
`the sudden decrease in signal power in signals received
`well known. In this particular application, the pilot
`signal is used by the mobile units for initial synchroniza
`at the mobile unit. The rate of increase of the mobile
`unit transmitter transmit power must generally be lim
`tion of the mobile unit receiver. The pilot signal is also
`ited to the rate of a closed loop power adjustment com
`used as a phase and frequency reference and a time
`reference for demodulation of the digital speech signals
`mand transmitted from the cell-site, as described below,
`can reduce the mobile unit transmitter transmit power.
`transmitted by the cell-site.
`Using the cell-site generated power adjustment con
`In the present invention, each mobile unit estimates
`mands, the mobile unit transmitter power will be pre
`the path loss in signals transmitted from the cell-site to
`vented from being increased to a level significantly
`the mobile unit. In order to make this signal path loss
`higher than the level required for communications,
`estimate, the power level of the cell-site transmitted
`particularly when a sudden channel degradation occurs
`signals, as received at the mobile unit, are measured.
`in only the outbound link path and not in the inbound
`The mobile unit thus measures the pilot signal power as
`link path.
`received from the cell-site to which the mobile unit is
`It should be noted that it is undesirable to simply use
`communicating. The mobile unit also measures the
`a slow response on the mobile unit transmitter power
`power level sum of all cell-site transmitted signals as
`15
`control in an attempt to separate the fast Rayleigh fad
`received at the mobile unit. The power level sum mea
`ing from the slow fading due to distance and terrain. A
`surement as described in further detail later herein, is
`slow response in the mobile unit transmitter power
`necessary to handle cases in which the mobile unit
`control is undesirable because the possibility of sudden
`might temporarily obtain a better path to a more distant
`improvements and fades that affect the inbound and
`cell-site than to a normally preferred closest cell-site.
`outbound channels equally. If the response to a sudden
`The outbound link path loss estimate is filtered using
`improvement were to be slowed down by a filter, then
`a non-linear filter. The purpose of the non-linearity in
`there would be frequent occasions when the mobile unit
`the estimation process is to permit a rapid response to a
`transmitter power would be quite excessive and cause
`sudden improvement in the channel while only allow
`interference to all other mobile users. Thus the present
`ing a much slower response to a sudden degradation in
`25
`invention uses a two time constant, non-linear approach
`the channel. The mobile unit in response to a sudden
`in estimating the path loss.
`improvement in the channel thus suddenly reduces
`In addition to measuring the received signal strength
`mobile unit transmitter transmit power.
`in the mobile unit, it is also desirable for the processor in
`Should the channel for one mobile unit suddenly
`the mobile unit to know the cell-site transmitter power
`improve, then the signal as received at the cell-site from
`and antenna gain (EIRP), the cell-site G/T (receive
`this mobile unit will suddenly increase in power. This
`antenna gain G divided by receiver noise level T), the
`sudden increase in power causes additional interference
`to all signals sharing the same wide band channel. A
`mobile unit antenna gain, and the number of calls active
`rapid response to the sudden improvement will thus
`at this cell-site. This information allows the mobile unit
`processor to properly compute the reference power
`reduce system interference.
`level for the local power setting function. This compu
`A typical example of a sudden improvement in the
`tation is done by calculating the cell-site to mobile link
`channel occurs when a mobile unit is moving through
`power budget, solving for the path loss. This path loss
`an area that is shadowed by a large building or other
`estimate is then used in the mobile cell-site link budget
`obstruction and then drives out of the shadow. The
`equation, solving for the mobile unit transmit power
`channel improvement, as a result of the vehicle move
`required to produce a desired signal level. This capabil
`ment, can take place on the order of a few tens of milli
`ity allows the system to have cell-sites with differing
`seconds. As the mobile unit drives out of the shadow,
`EIRP levels to correspond to the size of the cells. For
`the outbound link signal as received by the mobile unit
`will suddenly increase in strength.
`example, a small radius cell need not transmit with as
`high a power level as a large radius cell. However,
`The outbound link path loss estimate at the mobile
`unit is used by the mobile unit to adjust the mobile unit
`when the mobile unit is a certain distance from a low
`power cell, it would receive a weaker signal than from
`transmitter power. Thus, the stronger the received sig
`a high power cell. The mobile unit would respond with
`nal, the lower the mobile unit transmitter power will be.
`a higher transmit power than would be necessary for
`Reception of a strong signal from the cell-site indicates
`the short range. Hence, the desirability of having each
`that the mobile unit is either close to the cell-site or else
`an unusually good path to the cell-site exists. Reception
`cell-site transmit information as to its characteristics for
`of a strong signal means that a relatively smaller mobile
`power control.
`unit transmitter power level is required in order to pro
`The cell-site transmits information such as cell-site
`duce a nominal received power at the cell-site in trans
`EIRP, G/T and number of active calls on a cell-site
`setup channel. The mobile unit receives this information
`missions by the mobile unit.
`when first obtaining system synchronization and contin
`In the case where there is a temporary but yet sudden
`ues to monitor this channel when idle for pages for calls
`degradation in the channel it is desirable that a much
`originated within the public telephone switching net
`slower increase in mobile unit transmitter power be
`permitted. This slow increase in mobile unit transmitter
`work intended for the mobile unit. The mobile unit
`power is desired so as to prohibit an unnecessarily rapid
`antenna gain is stored in a memory in the mobile unit at
`increase in mobile unit transmit power which increases
`the time the mobile unit is installed in the vehicle.
`As mentioned previously, mobile unit transmitter
`the interference to all other mobile units. Thus a tempo
`power is also controlled by a signal from the cell-site.
`rary degradation in one mobile unit channel will be
`Each cell-site receiver measures the strength of the
`tolerated in order to prevent a degradation of all mobile
`signal, as received at the cell-site, from each mobile unit
`unit channels.
`In the case of a sudden degradation in the channel,
`to which the cell-site is in communication with. The
`measured signal strength is compared to a desired signal
`the non-linear filter prevents the mobile transmitter
`strength level for that particular mobile unit. A power
`power from being increased at a high rate in response to
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`IPR2018-01473
`Apple v. INVT
`INVT Exhibit 2004 - Page 9
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`interference can be compensated for by allowing the
`adjustment command is generated and sent to the mo
`neighbor cells a small increase in inbound link power.
`bile unit in the outbound link data, or voice channel,
`Such an increase in inbound power in neighboring cells
`addressed to that mobile unit. In response to the cell-site
`power adjustment command, the mobile unit increases
`would be smaller than that of the increase given to the
`mobile users communicating in the high noise environ
`or decreases the mobile unit transmitter power by a
`predetermined amount, nominally 1 dB.
`ment cell. It is further understood that the cell-site pro
`The power adjustment command is transmitted by
`cessor may monitor the average bit-error-rate. This data
`the cell-site transmitter at a relatively high rate, typi
`may be used by the system controller to command the
`cell-site processor to set an appropriate inbound link
`cally on the order of about one command every milli
`power level to assure acceptable quality communica
`second. The rate of transmission of the power adjust
`10
`ment command must be high enough to permit Ray
`tions.
`It is also desirable to provide a means for controlling
`leigh fading on the inbound link path to be tracked. It is
`further desirable for the outbound link path Rayleigh
`the relative power used in each data signal transmitted
`fading impressed on the inbound link path signal to be
`by the cell-site in response to control information trans
`mitted by each mobile unit. The primary reason for
`tracked. One command per millisecond is adequate to
`track the fading processes for vehicle speeds in the
`providing such control is to accommodate the fact that
`range of 25-50 miles per hour for 850 MHz band mobile
`in certain locations, the outbound channel link from the
`communications. It is important that the latency in de
`cell-site to the mobile unit may be unusually disadvan
`termining the power adjustment command and the
`taged. Unless the power being transmitted to this mo
`bile is increased, the quality may become unacceptable.
`transmission thereof be minimized so that channel con
`ditions will not change significantly before the mobile
`An example of such a location is a point where the path
`unit receives and responds to the signal.
`loss to one or two neighboring cells is nearly the same
`To account for the independence of the two Rayleigh
`as the path loss to the cell-site communicating with the
`fading paths, the mobile unit transmitter power is also
`mobile unit. In such a location, the total interference
`controlled by the power adjustment command from the
`would be increased by three times over the interference
`seen by the mobile unit at a point relatively close to its
`cell-site. Each cell-site receiver measures the received
`signal strength from each mobile unit. The measured
`cell-site. In addition, the interference coming from these
`signal strength is compared to the desired signal
`neighboring cell-sites will not fade in unison with the
`strength for that mobile unit and a power adjustment
`desired signal as would be the case for interference
`command is generated. The power adjustment com
`coming from the desired cell-site. This situation may
`30
`required 3-4 dB additional signal power to achieve
`mand is sent to the mobile unit in the outbound data or
`adequate performance.
`voice channel addressed to that mobile unit. This power
`adjustment command is combined with the mobile unit
`In another situation, the mobile unit may be located
`where several strong multi-path signals arrive, resulting
`one way estimate to obtain the final value of the mobile
`unit transmitter power.
`in larger than normal interference. In such a situation,
`The power adjustment command signal is transmit
`increasing the power of the desired signal relative to the
`ted, in an exemplary embodiment, by overwriting one
`interference may allow acceptable performance. At
`or more user data bits every millisecond. The modula
`other times, the mobile unit may be located where the
`tion system employed in CDMA systems is capable of
`signal-to-interference ratio is unusually good. In such a
`providing error detection and correction coding for
`case, the cell-site could transmit the desired signal using
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`user data bits. The overwrite by the power adjustment
`a lower than normal transmitter power, reducing inter
`ference to other signals being transmitted by the system.
`command is treated as a channel bit error or erasure and
`To achieve the above objectives, the preferred em
`corrected by the error correction as decoded in the
`bodiment includes a signal-to-interference measurement
`mobile unit receiver. Error correction coding on the
`power adjustment command bits in many cases may not
`capability within the mobile unit receiver. This mea
`45
`surement is performed by comparing the power of the
`be desirable because of the resulting increased latency in
`reception and response to the power command. It is also
`desired signal to the total interference and noise power.
`envisioned that time division multiplexing for transmis
`If the measured ratio is less than a predetermined value
`sion of the power adjustment command bits may be
`the mobile transmits a request to the cell-site for addi
`used without overwriting user data channel symbols.
`tional power in cell-site transmissions. If the ratio ex
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`The cell-site controller or processor can be used to
`ceeds the predetermined value, the mobile unit trans
`determine the desired signal strength, as received at the
`mits a request for a reduction in power.
`The cel