a2, United States Patent
`US 6,600,772 B1
`(10) Patent No.:
`Zeira et al.
`Jul. 29, 2003
`(45) Date of Patent:
`
`US006600772B1
`
`COMBINED CLOSED LOOP/OPEN LOOP
`POWER CONTROLIN A TIME DIVISION
`DUPLEX COMMUNICATION SYSTEM
`
`EP
`WO
`WO
`
`0682419
`9749197
`9845962
`
`11/1995
`12/1997
`10/1998
`
`OTHER PUBLICATIONS
`
`Inventors: Ariela Zeira, Trumball, CT
`Fiath
`(US);
`M. Ozluturk, Port Washington, NY
`(US); Sung-Hyuk Shin, Fort Lee, NJ
`(US)
`InterDigital Communications
`Corporation, Wilmington, DE
`(US)
`to any disclaimer, the term of this
`Subject
`patent is extended or
`adjusted under 35
`US.C.
`154(b) by 0 days.
`
`Assignee:
`
`Notice:
`
`Appl. No.: 09/531,359
`Filed:
`Mar. 21, 2000
`occ
`
`Int. C17
`
`US. Che
`
`eee
`
`Field of Search
`
`References Cited
`
`HO4B 1/69; HO4B 1/707;
`HO4B 1/713
`375/130; 375/295; 455/522;
`370/342
`2.0.0.0...es
`375/130, 140,
`375/295; 455/522, 69; 370/342, 252
`
`(54)
`
`(75)
`
`(73)
`
`(*)
`
`(21)
`
`(22)
`
`61)
`
`(52)
`
`(58)
`
`(56)
`
`“Specification of Air—Interface for the 3G Mobile System”,
`Version 1.0, ARIB, Jan. 14, 1999.
`“Combined Closed—Loop/Open—Loop Power Control Pro-
`cess for Time Division Duplexing”, Ariela Zeira, Sun-
`g—Hyuk Shin and Fiath Ozluturk, Apr. 1999.
`“Performance of Weighted Open Loop Scheme for Uplink
`Power Control in TDD Mode”, Aniela Zeira and Sung—Hyuk
`Shin, May 1999.
`“Text Proposal for $1.24”, Ariela Zeira, Sung—Hyuk Shin
`and Stephen Dick, May 1999.
`*
`cited by examiner
`Primary Examiner—TYemesghen Ghebretinsae
`or
`Firm—Volpe & Koenig, P.C.
`(74) Attorney, Agent,
`ABSTRACT
`
`(57)
`Combined closed loop/open loop power control controls
`transmission powerlevels in a
`spread spectrum timedivision
`duplex communication station. The first station transmits
`a
`power commandsbased onin part
`reception quality of the
`received communications. The first station transmits a first
`communication having transmission power commands
`a
`based on in part
`reception quality of the received com-
`munications. The first station transmits a first communica-
`a transmission powerlevel in a first time slot.
`tion having
`The secondstation received the first communication and the
`power commands. A powerlevel of the first communication
`as received is measured. A path loss estimate is determined
`based on in part the measured received first communication
`powerlevel and the first communication transmission power
`level. The second station transmits a first communication to
`the first station in
`first time slot. The second communica-
`tion transmission powerlevel is set based on in part the path
`a factor and power commands.
`loss estimate weighted by
`The factor is a function of a time separation of the first and
`second timeslots.
`
`375/370
`
`370/342
`
`375/130
`455/522
`
`370/252
`
`U.S. PATENT DOCUMENTS
`4,868,795 A
`5,056,109 A
`5,542,111 A
`5,839,056 A
`5,859,838 A
`6,101,179 A
`6,108,561 A
`6,175,586 BL
`6,175,745 Bl
`6,188,678 B1
`6,373,823 Bl
`6,449,462 Bl
`FOREIGN PATENT DOCUMENTS
`
`*
`
`*
`
`*
`
`teens
`
`we.
`
`......
`
`..
`
`9/1989 McDavidetal.
`10/1991 Gilhousen etal.
`7/1996 Ivanovetal.
`11/1998 Hakkinen
`1/1999 Soliman
`.........
`8/2000 Soliman
`8/2000. Mallinckrodt
`....... eee
`teens
`1/2001 Lomp
`.........
`wee
`1/2001 Bringbyetal.
`2/2001 Prescott
`4/2002 Chenetal...
`9/2002 Gunnersonetal.
`
`EP
`
`0462952
`0610030
`
`12/1991
`8/1994
`
`42
`
`
`GENERATE A POWER CONTROL COMMAND.
`BASED ON A SIGNAL TO INTERFERENCE
`RATIO OF A COMMUNICATION SENT
`FROM THE TRANSMITTING STATION
`
`a
`
`40
`TRANSHIT A COMMUNICATION ANO THE POWER
`COMMAND FROM THE RECEIVING STATION
`
`
`DETERMINE THE RECEIVED POWER LEVEL
`OF THE COMMUNICATION FROM THE.
`RECEIVING STATION AT THE
`TRANSMITTING STATION
`
`DETERMINE AN ESTIMATED PATH LOSS BETWEEN
`THE RECEIVING AND TRANSMITTING STATION BY
`SUBTRACTING THE RECEIVED CONNUNICATION'S
`POWER LEVEL iN d8 FROM
`IM THE COMMUNICATION'S
`TRANSMISSION POWER LEVEL IN d8
`
`46 ~
`DETERMINE THE QUALITY OF THE
`
`Van
`
`SETTING THE TRANSMITTING STATION'S POWER
`LEVEL SASED ON IN PART THE POWER
`COMMAND AND WEIGHTING THE ESTIMATED
`PATH LOSS BASED ON THE ESTIMATE'S QUALITY
`
`ESTIMATED PATH LOSS
`
`
`
`23 Claims, 7 Drawing Sheets
`
`DELL 1008
`
`DELL 1008
`
`1
`
`

`

`U.S. Patent
`
`Jul. 29, 2003
`
`Sheet 1 of 7
`
`US 6,600,772 B1
`
`<3
`
`—
`
`<s
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`— ©L
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`<S
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`2
`
`

`

`U.S. Patent
`
`Jul. 29, 2003
`
`Sheet 2 of 7
`
`US 6,600,772 B1
`
`TIME
`
`FIG,
`
`2
`
`3
`
`

`

`U.S. Patent
`
`Jul. 29, 2003
`
`Sheet 3 of 7
`
`US 6,600,772 B1
`
`FIG. 3
`
`
`
`
`GENERATE A POWER CONTROL COMMAND
`BASED ON A SIGNAL TO INTERFERENCE
`RATIO OF A COMMUNICATION SENT
`FROM THE TRANSMITTING STATION
`
`
`
`
`TRANSMIT A COMMUNICATION ANO THE POWER
`COMMAND FROM THE RECEIVING STATION
`
`DETERMINE THE RECEIVED POWER LEVEL
`OF THE COMMUNICATION FROM THE
`RECEIVING STATION AT THE
`
`TRANSMITTING STATION
`
`DETERMINE AN ESTIMATED PATH LOSS BETWEEN
`
`
`THE RECEIVING AND TRANSMITTING STATION BY
`
`
`SUBTRACTING THE RECEIVED COMMUNICATION'S
`POWER LEVEL IN dB FROM THE COMMUNICATION'S
`
`
`TRANSMISSION POWER LEVELIN dB
`
`
`
`DETERMINE THE QUALITY OF THE
`ESTIMATED PATH LOSS
`
`SETTING THE TRANSMITTING STATION'S POWER
`LEVEL BASEO ON IN PART THE POWER
`COMMAND AND WEIGHTING THE ESTIMATED
`PATH LOSS BASED ON THE ESTIMATE'S QUALITY
`
`38
`
`40
`
`42
`
`44
`
`46
`
`48
`
`4
`
`

`

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`
`Jul. 29, 2003
`
`JONSYSSUSLNI
`
`U.S. Patent
`
`Sheet 4 of 7
`
`y'O!470L901
`
`US 6,600,772 B1
`
`NOLLV
`
`YOLYINGON<|
`CNV
`JOINS
`JONSNOSS
`ONINIVEL
`NOLLYSSNI
`ONIGV3udS
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`

`

`U.S. Patent
`
`Jul. 29, 2003
`
`Sheet 5 of 7
`
`US 6,600,772 B1
`
`FIG. 5
`
`SNR(dB)
`STDOFESTIMATED
`
`7
`
`—*—
`
`CLOSED ONLY
`
`T
`
`~—4—
`SCHEME -|
`
`~@—
`SCHEME -11
`
`
`T
`T
`T
`T
`
`
` DELAY
`FIG. 6
`
`1.0E+00
`
`(SLOT)
`
`SNR
`BIASOFESTIMATED
`NORMALIZED
`
`= g
`
`1.0E-02
`
`Soe ee eR ee eee ee ee ee LL LLL LLL
`Tate te oe OK ow ey ee ee ee ee ee ee ee ee ee eee ee ee LLL
`
`
`
`a a
`
`eeae
`
`
`—+—
`
`—=*—
`
`ARIB
`
`CLOSED ONLY
`
`
`—4—
`SCHEME -|
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`~
`@—
`SCHEME -11
`
`
`
`DELAY
`
`(SLOT)
`
`6
`
`

`

`U.S. Patent
`
`Jul. 29, 2003
`
`Sheet 6 of 7
`
`US 6,600,772 Bl
`
`FIG. 7
`
`SNR(dB)
`STDOFESTIMATED
`SNR
`BIASOFESTIMATED
`NORMALIZED
`
`—+—
`
`~a—
`
`~~~
`
`ARIB
`
`CLOSED ONLY
`
`SCHEME -I
`
`SCHEME -1|
`
`
`~~
`
`DELAY (SLOT)
`
`
`
`
`
`1.0E-02 DELAY (SLOT)
`
`11
`SCHEME
`
`
`~«~
`
`—4—
`
`—e—
`
`CLOSED ONLY
`
`SCHEME -|
`-
`
`7
`
`

`

`U.S. Patent
`
`Jul. 29, 2003
`
`Sheet 7 of 7
`
`US 6,600,772 B1
`
`FIG. 9
`
`8
`
`7
`
`6
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`SCHEME-|
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`
`SCHEME -I|
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`T
`T
`T
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`T
`T
`T
`T
`T
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`3
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`
`DELAY
`
`(SLOT)
`
`
`
`6
`
`7
`
`oo
`
`
`
`SNR
`BIASOFESTIMATED
`NORMALIZED
`
`FIG. 10
`
`1.0E+00
`
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`—4&~
`
`CLOSED ONLY
`
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`
`DELAY (SLOT)
`
`8
`
`

`

`US 6,600,772 B1
`
`1
`COMBINED CLOSED LOOP/OPEN LOOP
`POWER CONTROLIN A TIME DIVISION
`DUPLEX COMMUNICATION SYSTEM
`
`BACKGROUND
`This invention generally relates to
`spread spectrum time
`communication systems. More
`division duplex (TDD)
`particularly, the present invention relates to a
`system and
`method for controlling transmission power within TDD
`communication systems.
`a wireless spread spectrum time division
`FIG. 1 depicts
`communication system. The system has a
`duplex (TDD)
`plurality of base stations 30,-30,. Each base station 30,
`communicates with user
`equipments (UEs) 32,-32, in its
`area. Communications transmitted from a base
`operating
`are referred to as downlink com-
`to a UE 32,
`station 30,
`munications and communications transmitted from a
`UE32,
`to a base station 30,
`are referred to as
`uplink communica-
`tions.
`over different frequency
`In addition to
`communicating
`spectrums, spread spectrum TDD systems carry multiple
`communications over the same
`spectrum. The multiple
`are
`distinguished by their respective chip code
`signals
`use the spread
`sequences (codes). Also, to more
`efficiently
`as illustrated in FIG. 2 use
`spectrum, TDDsystems
`repeating
`frames 34 divided into a numberoftime slots
`such
`36,—36,,,
`as fifteen time slots. In such systems,
`a communication is
`sent in selected time slots 36,-36,, using selected codes.
`one frame 34 is capable of carrying multiple
`Accordingly,
`communications distinguished by both time slot 36,-36,
`and code. The combination of a
`single code in a
`single time
`slot is referred to as a resource unit. Based on the bandwidth
`one or
`a
`to support
`communication,
`required
`multiple
`resource units are
`to that communication.
`assigned
`Most TDD systems adaptively control
`transmission
`powerlevels. In a TDD system, many communications may
`share the same time slot and spectrum. When a UE 32, or
`a
`base station 30, is receiving
`specific communication,all
`the other communications using the same time slot and
`cause interference to the specific communication.
`spectrum
`Increasing the transmission power level of one communi-
`cation degrades the signal quality of all other communica-
`tions within that time slot and spectrum. However, reducing
`the transmission powerlevel too far results in undesirable
`and bit error rates
`to noise ratios
`at the
`signal
`(SNRs)
`(BERs)
`receivers. To maintain both the signal quality of communi-
`transmission
`cations and low transmission power levels,
`power control is used.
`to control transmission power levels is
`One approach
`In open loop power control,
`open loop power control.
`a basestation 30, transmits to a UE
`a reference
`typically
`32,
`downlink communication and the transmission powerlevel
`of that communication. The UE 32, receives the reference
`communication and measures its recetved powerlevel. By
`subtracting the received power level from the transmission
`a
`pathloss for the reference communication is
`powerlevel,
`determined. To determine a transmission powerlevel for the
`uplink, the downlink pathloss is added to a desired received
`powerlevel at the base station 30,. The UE’s transmission
`powerlevel is set to the determined uplink transmission
`powerlevel.
`to control transmission powerlevel is
`Another approach
`closed loop power control. In closed loop power control,
`to
`typically the base station 30, determines the signal
`of a communication received from
`interference ratio
`(SIR)
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`2
`the UE 32,. The determined SIR is comparedto a
`target SIR
`Based on the comparison, the base station 30,
`(SIRaircrr).
`transmits a power command, b;p.. After receiving the
`increases or decreases its
`the UE 32,
`power command,
`transmission power level based on the received power
`command.
`Both closed loop and open loop power control have
`disadvantages. Undercertain conditions, the performance of
`closed loop systems degrades. For instance, if communica-
`tions sent between a UEand a basestation are in a
`highly
`dynamic environment, such as due to the UE moving, such
`systems may notbe able to
`to compensate
`adapt fast enough
`rate of closed loop power
`for the changes. The update
`in TDD is 100 cycles per second which is not
`control
`sufficient for fast fading channels. Open loop powercontrol
`is sensitive to uncertainties in the uplink and downlink gain
`chains and interference levels.
`to
`One approach
`combining closed loop and open loop
`power control was
`proposed by the Association of Radio
`and uses
`Industries and Business
`Equations 1, 2, and
`(ARIB)
`3.
`
`Tug=Pps(n)+h
`
`Pas()=Pas-1)+brpcArpc
`
`=
`
`brpc
`
`1: if SIRes ( SIRrarcer
`1: if SIRgs
`SIRparcer
`
`)
`
`Equation 1
`Equation 2
`
`Equation 3
`
`Tug is the determined transmission power level of the UE
`32,. L is the estimated downlink pathloss. P,.(n)
`is the
`as
`desired received power level of the base station 30,
`adjusted by Equation 2. For each received power command,
`is increased or
`the desired received power level
`brpc,
`one decibel
`decreased by A;pe. Arpc is typically
`The
`(dB).
`power command, b;p., 1s one, when the SIR of the UE’s
`uplink communication as measured at the base station 30,
`SIRgs, is less than a
`target SIR, SIRarGer. Conversely, the
`power commandis minus one, when SIR,, is larger than
`SIRgarcer-:
`Under certain conditions, the performance of these sys-
`tems
`if communications sent
`degrades. For
`instance,
`between a UE 32 and a basestation 30 are in a
`highly
`dynamic environment, such as due to the UE 32 moving,the
`path loss estimate for open loop severely degrades the
`overall system’s performance. Accordingly, there is a need
`to maintain signal quality and low
`for alternate approaches
`transmission power levels for all environments and sce-
`narios.
`
`SUMMARY
`Combined closed loop/open loop powercontrol controls
`transmission powerlevels in a
`spread spectrum timedivision
`duplex communication station. The first station transmits
`a
`power commandsbased onin part
`reception quality of the
`received communications. The first station transmits a first
`communication having transmission power commands
`a
`based on in part
`reception quality of the received com-
`munications. The first station transmits a first communica-
`a transmission powerlevel in a first time slot.
`tion having
`The secondstation received the second communication and
`the power commands. A powerlevel of the first communi-
`cation as received is measured. A path loss estimate is
`determined based on in part the measured received first
`communication power level and the first communication
`first
`transmission powerlevel. The first station transmits
`
`9
`
`

`

`US 6,600,772 B1
`
`3
`communicationto thefirst station in a second timeslot. The
`second communication transmission powerlevel is set based
`a factor and
`on in part the path loss estimate weighted by
`power commands. Thefactor is a function of a time sepa-
`ration of the first and second timeslots.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`FIG. 1 illustrates a
`art TDD system.
`prior
`FIG. 2 illustrates time slots in repeating frames of a TDD
`system.
`FIG. 3 is a flow chart of combined closed loop/open loop
`power control.
`FIG. 4 is a
`diagram of components of two communication
`stations using combined closed loop/open loop power con-
`trol.
`FIGS. 5-10 depict graphs of the performance of a closed
`loop, ARIB’s proposal and two
`schemes of combined
`(2)
`closed loop/open loop powercontrol.
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENTS
`The preferred embodiments will be described with refer-
`ence to the drawing figures where like numerals represent
`like elements throughout. Combined closed loop/open loop
`powercontrol will be explained using the flow chart of FIG.
`3 and the components of two
`simplified communication
`stations 50, 52 as shown in FIG. 4. For the following
`discussion, the communication station having its transmit-
`ter’s power controlled is referred to as the transmitting
`station 52 and the communication station receiving power
`controlled communications is referred to as the receiving
`station 50. Since combined closed loop/open loop power
`control may be used for uplink, downlink or both types of
`communications, the transmitter having its power controlled
`or both.
`may be located at a base station 30,, UE 32,
`Accordingly,if both uplink and downlink powercontrol are
`used, the receiving and transmitting station’s components
`are located at both the base station 30, and UE
`32,.
`The receiving station 50 receives various radio frequency
`signals including communications from the transmitting
`or
`an antenna
`an antenna 56,
`station 52 using
`alternately,
`are
`an isolator 60
`array. The received signals
`passed through
`to a demodulator 68 to
`a baseband signal. The
`produce
`basebandsignal is processed, such as
`a channel estima-
`by
`tion device 96 and a data estimation device 98, in the time
`to the trans-
`slots and with the appropriate codes assigned
`mitting station’s communication. The channel estimation
`usesthe training sequence component
`device 96 commonly
`to
`in the baseband signal
`provide channel information, such
`as channel impulse responses. The channel information is
`the interference
`used by the data estimation device 98,
`measurement device 90,
`the signal power measurement
`device 92 and the transmit powercalculation device 94. The
`data estimation device 98 recovers data from the channel by
`information.
`estimating soft symbols using the channel
`Using the soft symbols and channel information, the trans-
`mit power calculation device 94 controls the receiving
`station’s transmission powerlevel by controlling the gain of
`an
`amplifier 76.
`The signal power measurement device 92 uses either the
`or the channel information,
`or
`both, to deter-
`soft symbols
`mine the received signal power of the communication in
`The interference measurement device 90
`decibels
`(dB).
`determines the interference level
`in dB, I,;, within the
`or the soft
`channel, based on either the channel information,
`or both.
`symbols generated by the data estimation device 98,
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`4
`The closed loop power command generator 88 uses the
`measured communication’s received power level and the
`to Interfer-
`to determine the Signal
`interference level, Is,
`ence Ratio
`of the received communication. Based on
`(SIR)
`a
`comparison of the determined SIR with a
`target SIR
`a closed loop power commandis generated,
`(SIRmarcrr),
`brpc, Such as a power command bit, byp., step 38.
`the power command may be based on any
`Alternately,
`measurementof the received signal.
`quality
`For use in estimating the path loss between the receiving
`the
`and transmitting stations 50, 52 and sending data,
`receiving station 50 sends a communication to the transmit-
`ting station 58, step 40. The communication may be sent on
`any one of various channels. Typically, in a TDD system,the
`channels used for estimating path loss are referred to as
`reference channels, although other channels may be used. If
`the receiving station 50 is a base station 30,, the commu-
`sent over a downlink common channel
`nication is preferably
`or a commoncontrol physical channel
`Data to be
`(CCPCH).
`communicated to the transmitting station 52 over the refer-
`ence channel is referred to as reference channel data. The
`as shown,the interference level,
`reference data may include,
`Ips multiplexed with other reference data, such as the
`transmission powerlevel of the reference channel, T,.. The
`interference level, I,;, and reference channel powerlevel,
`Trs, may be sent in other channels, such as a
`signaling
`channel. The closed loop power control command,b7p¢,is
`sent in a dedicated channel. The dedicated channel
`typically
`is dedicated to the communication between the receiving
`station 50 and transmitting station 52, step 40.
`a reference
`The reference channel data is generated by
`channel data generator 86. The reference data is assigned
`one or
`resource units based on the communication’s
`multiple
`bandwidth requirements. A spreading and training sequence
`insertion device 82 spreads the reference channel data and
`makes the spread reference data time-multiplexed with a
`training sequence in the appropriate time slots and codes of
`resource units. The resulting sequence is
`the assigned
`referred to as a communication burst. The communication
`an
`burst is subsequently amplified by
`amplifier 78. The
`a sum
`amplified communication burst may be summed by
`device 72 with any other communication burst created
`through devices, such as a data generator 84, spreading and
`training sequence insertion device 80 and amplifier 76.
`a
`The summed communication bursts are modulated by
`an
`modulator 64. The modulated signal is passed through
`an antenna 56 as shown or,
`isolator 60 and radiated by
`an antenna array. The radiated signal is
`alternately, through
`a wireless radio channel 54 to an antenna 58
`passed through
`of the transmitting station 52. The type of modulation used
`for the transmitted communication can be any of the those
`knownto those skilled in the art, such as direct phase shift
`or
`quadrature phase shift keying (QPSK).
`keying (DPSK)
`antenna array of the
`The antenna 58 or, alternately,
`transmitting station 52 receives various radio frequency
`are
`an isolator
`signals. The received signals
`passed through
`62 to a demodulator 66 to
`a baseband signal. The
`produce
`baseband signal is processed, such as
`a channel estima-
`by
`tion device 100 and a data estimation device 102, in the time
`to the com-
`slots and with the appropriate codes assigned
`munication burst of the receiving station 50. The channel
`estimation device 100 commonlyusesthe training sequence
`to
`in the baseband signal
`provide channel
`component
`information, such as channel impulse responses. The chan-
`a
`nel information is used by the data estimation device 102,
`power measurement device 110 and a
`measurement
`quality
`device 114.
`
`10
`
`10
`
`

`

`US 6,600,772 B1
`
`5
`The powerlevel of the processed communication corre-
`to the reference channel, R;., is measured by the
`sponding
`to a
`power measurement device 110 and sent
`pathloss
`estimation device 112, step 42. Both the channel estimation
`device 100 and the data estimation device 102 are
`capable of
`separating the reference channel from all other channels. If
`an automatic gain control device or
`amplifier is used for
`processing the received signals, the measured powerlevel is
`to correct for the gain of these devices at either the
`adjusted
`power measurement device 110 or the pathloss estimation
`device 112. The power measurement device 110 is a com-
`ponent of the combined closed loop/open loop controller
`108. As illustrated in FIG. 4, the combined closed loop/open
`loop power controller 108 comprises the power measure-
`ment device 110, pathloss estimation device 112, quality
`measurement device 114, and transmit power calculation
`device 116.
`To determine the path loss, L, the transmitting station 52
`also requires the communication’s transmitted powerlevel,
`Trs. The transmitted power level, T,., may be sent
`along
`with the communication’s data or in a
`signaling channel. If
`the powerlevel, Tz, is sent
`along with the communication’s
`data, the data estimation device 102 interprets the power
`level and sends the interpreted power level to the pathloss
`estimation device 112. If the receiving station 50 is a base
`station 30,, preferably the transmitted powerlevel, T,,., is
`sent via the broadcast channel
`from the basestation
`(BCH)
`30,. By subtracting the received communication’s power
`level, R;., in dB, from the sent communication’s transmitted
`powerlevel, T,,, in dB, the pathloss estimation device 112
`estimates the path loss, L, between the twostations 50, 52,
`step 44. In certain situations, instead of transmitting the
`transmitted powerlevel, T,, the receiving station 50 may
`transmit a reference for the transmitted power level. In that
`case, the pathloss estimation device 112 provides reference
`levels for the path loss, L.
`If a time delay exists between the estimated path loss and
`the transmitted communication, the path loss experienced by
`the transmitted communication may differ from the calcu-
`lated loss. In TDD systems where communicationsare sent
`in differing time slots 36,—36,,, the time slot delay between
`received and transmitted communications may degrade the
`performance of an open loop powercontrol system. Com-
`bined closed loop/open loop power control utilizes both
`closed loop and open loop power control aspects. If the
`quality of the path loss measurement is high, the system
`acts as an open loop system. If the quality of the
`primarily
`acts as
`path loss measurementis low, the system primarily
`a closed loop system. To combine the two powercontrol
`aspects, the system weights the open loop aspect based on
`the quality of the path loss measurement.
`measurement device 114 in a
`A quality
`weighted open
`loop power controller 108 determines the quality of the
`estimated path loss, step 46. The quality may be determined
`using the channel information generated by the channel
`estimation device 100, the soft symbols generated by the
`data estimation device 102 or other quality
`measurement
`techniques. The estimated path loss quality is used to
`weight
`the path loss estimate by the transmit power calculation
`was sent in the
`device 116. If the power command, b;p.,
`communication’s data, the data estimation device 102 inter-
`prets the closed loop power command, b;p.. Using the
`closed loop power command, b;,,, and the weighted path
`the transmit power calculation device 116 sets the
`loss,
`transmit powerlevel of the receiving station 50, step 48.
`The following is one of the preferred combined closed
`loop/open loop power control algorithms. The transmitting
`
`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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`35
`
`40
`
`45
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`50
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`55
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`60
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`65
`
`6
`station’s power level in decibels, P;., is determined using
`Equations 4 and 6.
`Equation 4
`Pys=Pot+G(n)+aL
`P, is the powerlevel that the receiving station 50 desires
`to receive the transmitting station’s communication in dB.
`P, is determined by the desired SIR at the receiving station
`at the receiv-
`50, SIRparGe7 and the interference level, I,,,
`ing station 50 using Equation 5.
`Equation 5
`Po=SIRmaercertles
`or broadcasted from the receiving
`Ips 1S either signaled
`station 50 to the transmitting station 52. For downlink power
`control, SIRz,rG"7 1s known at the transmitting station 52.
`For uplink power control, SIRj.p6er 1S signaled from the
`receiving station 50 to the transmitting station 52.
`is the
`G(n)
`closed loop power control factor. Equation 6 is one
`equation
`for determining G(n).
`Equation 6
`GQH)=G(a-1)+bypcArpc
`is the previous closed loop power control factor.
`G(n-1)
`The power command, b;p,, for use in Equation 6 is either
`+1 or -1. One technique for determining the power
`command, b;p,, is Equation 3. The power command,b;p.,
`at a rate of 100 ms in a TDD system,
`is typically updated
`rates may be used. A;p¢ is the change
`although other update
`in powerlevel. The change in powerlevel is typically 1 dB
`although other values may be used. As
`result, the closed
`loop factor increases by 1 dB if bp. is +1 and decreases by
`1 dB if byp¢ is -1.
`The weighting value, a, is determined by the quality
`measurementdevice 114. a is a measure of the quality of the
`estimated path loss and is, preferably, based on the number
`of time slots, D, between the time slot of the last path loss
`estimate and the first time slot of the communication trans-
`mitted by the transmitting station 52. The value of « is from
`zero to one.
`Generally,if the time difference, D, between the
`timeslots is small, the recent
`path loss estimate will be fairly
`accurate and @ is set at a value close to one.
`By contrast, if
`the time difference is large, the path loss estimate may not
`more
`be accurate and the closed loop aspect is most
`likely
`@ is set at a value closer to zero.
`accurate.
`Accordingly,
`Equations 7 and 8 are two
`equations for determining a,
`although others may be used.
`a=1-(D-1)(Dax-1)
`
`Equation 7
`Equation 8
`a=max{1-(D-1)/(Dnax-allowed-1),0}
`D,,,ax 18 the maximum possible delay. A typical value for a
`frame havingfifteen time slots is seven. If the delay is D,,,,,,..
`a is zero.
`D,,..allowed 1S the maximum allowed time slot
`delay for using open loop power control. If the delay
`exceeds D,,allowed? Open loop powercontrol is effectively
`turned off by setting a=0. Using the calculated transmit
`a transmit power calcula-
`powerlevel, P;., determined by
`tion device 116, the combined closed loop/open loop power
`controller 108 sets the transmit power of the transmitted
`communication.
`Data to be transmitted in a communication from the
`a data generator 106.
`transmitting station 52 is produced by
`The communication data is spread and time-multiplexed
`with a
`training sequence by the spreading and training
`sequence insertion device 104 in the appropriate time slots
`a com-
`resource units producing
`and codes of the assigned
`munication burst. The spread signal
`is amplified by the
`amplifier 74 and modulated by the modulator 70 to radio
`frequency.
`
`11
`
`11
`
`

`

`US 6,600,772 B1
`
`7
`The combined closed loop/open loop power controller
`108 controls the gain of the amplifier 74 to achieve the
`determined transmit powerlevel, P;<, for the communica-
`tion. The power controlled communication is passed through
`the isolator 62 and radiated by the antenna 58.
`Equations 9 and 10 are another preferred combined closed
`loop/open loop power control algorithm.
`Equation 9
`Prs=PotK(n)
`Equation 10
`K()=K(n-1)t+bppc Appctob
`is the combined closed loop/open loop factor. As
`K(n)
`shown,this factor includes both the closed loop and open
`loop powercontrol aspects. Equations 4 and 5 segregate the
`two aspects.
`Although the two above algorithms only weighted the
`to the closed
`open loop factor, the weighting may be applied
`loop factor or both the open and closed loop factors. Under
`certain conditions, the network operator may desire to use
`or
`solely closed loop power control. For
`solely open loop
`example, the operator may use
`solely closed loop power
`a to zero.
`control by setting
`FIGS. 5-10 depict graphs 118-128 illustrating the per-
`formance of a combined closed-loop/open-loop power con-
`trol system. These graphs 118-128 depict the results of
`simulations comparing the performance of the ARIB pro-
`a closed loop,
`a combined open loop/closed
`posed system,
`and a
`loop system using Equations 4 and 6
`(scheme I)
`combined system using Equations 9 and 10
`The
`(schemeII).
`simulations were
`at the symbol
`rate. A spreading
`performed
`factor of sixteen was used for both the uplink and downlink
`channels. The uplink and downlink channels are Interna-
`tional Telecommunication Union
`Channel model
`(ITU)
`[ITU-R M.1225, vehicular, type B]. Additive noises were
`simulated as
`being independent of white Gaussian noises
`with unity variance. The path loss is estimated at
`the
`transmitting station 52 which is a UE 32, and in particular
`a mobile station. The BCH channel was used for the path
`loss estimate. The path loss was estimated two times per
`frame at a rate of 200 cycles per second. The receiving
`station 50, which was a base station 30,,
`sent the BCH
`transmission power level over the BCH. RAKE combining
`was used for both the UE 32, and basestation 30,. Antenna
`was usedat the base station 30,.
`diversity combining
`Graphs 118, 122, 126 depict the standard deviation of the
`to noise ratio
`at the base station 30,
`received signal
`(SNR)
`of the UE’s power controlled communication as a function
`of the time slot delay, D. Graphs 120, 124, 128 depict the
`normalized bias of the received SNR as a function of the
`delay, D. The normalization was
`performed with respect to
`the desired SNR. Each point in the graphs 118-128 repre-
`sents the average of 3000 Monte-Carlo runs.
`Graphs 118, 120 depict the results for an a set at one. For
`scheme I and II outperform
`low time slot delays (D<4),
`closed loop powercontrol. For larger delays (D24), closed
`loop outperforms both scheme I and II which demonstrates
`the importance of weighting the open loop and closed loop
`aspects.
`Graphs 122, 124 depict the results for an a set at 0.5. As
`shown, for all delays excluding the maximum, schemesI
`and II outperform closed loop power control. The ARIB
`proposal only outperforms the others at the lowest delay
`(D=1).
`Graphs 126, 128 depict the results for an @ set
`using
`to seven. As shown, schemesI
`Equation 7 with D,,,,.. equal
`and II outperform both closed loop and the ARIB proposal
`at all delays, D.
`
`5
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`15
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`20
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`25
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`30
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`35
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`40
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`50
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`55
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`60
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`65
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`8
`
`Whatis claimedis:
`1. A method for controlling transmission powerlevels in
`a
`spread spectrum time division duplex communication
`system having frames with time slots for communication,
`the method comprising:
`at a first communication station communica-
`receiving
`tions from a second communication station and trans-
`mitting from thefirst station power commandsbased on
`a
`in part
`reception quality of the received communica-
`tions;
`transmitting from the first communication station a first
`a transmission powerlevel in a
`communication having
`first time slot;
`at the second communication station the first
`receiving
`communication and the power commands;
`a powerlevel of the first communication as
`measuring
`received;
`pathloss estimate based on in part
`a
`the
`determining
`measured received first communication power level
`and the first communication transmission powerlevel;
`a transmission powerlevel for a second commu-
`setting
`nication in a second time slot from the secondstation
`to the first station based on in part the pathloss estimate
`a
`quality factor and the power commands,
`weighted by
`wherein the quality factor is a function of a time
`separation of the first and second time slots; and
`a
`quality, a, of the pathloss estimate based on
`determining
`a numberof time slots, D, between the first and
`in part
`the second time slot; and
`wherein the quality factor is a.
`2. The method of claim 1 wherein a maximum timeslot
`delay is D,,,, and the determined quality, a, is determined
`by
`
`a=1-(D-1)/(Dax-1)-
`3. The method of