PCT
`INTERNATIONAL APPLICATION PUBLISHED UNDER THE PATENT COOPERATION TREATY (PCT)
`
`WORLD INTELLECTUAL PROPERTY ORGANIZATION
`International Bureau
`
`(51) International Patent Classification 7 :
`HO4B 7/005
`
`Al
`
`(11) International Publication Number:
`
`WO 00/57574
`
`(43) International Publication Date:
`
`28 September 2000 (28.09.00)
`
`(81) Designated States: AE, AL, AM, AT, AU, AZ, BA, BB, BG,
`BR, BY, CA, CH, CN, CR, CU, CZ, DE, DK, DM, EE,
`ES, FI, GB, GD, GE, GH, GM, HR, HU, ID, IL, IN, IS, JP,
`KE, KG, KP, KR, KZ, LC, LK, LR, LS, LT, LU, LV, MA,
`MD, MG, MK, MN, MW, MX, NO, NZ, PL, PT, RO, RU,
`SD, SE, SG, SI, SK, SL, TJ, TM, TR, TT, TZ, UA, UG,
`US, UZ, VN, YU, ZA, ZW, ARIPO patent (GH, GM, KE,
`LS, MW, SD, SL, SZ, TZ, UG, ZW), Eurasian patent (AM,
`AZ, BY, KG, KZ, MD, RU, TJ, TM), European patent (AT,
`BE, CH, CY, DE, DK, ES, FI, FR, GB, GR, IE, IT, LU,
`MC, NL, PT, SE), OAPI patent (BF, BJ, CF, CG, CI, CM,
`GA, GN, GW, ML, MR, NE, SN, TD, TG).
`
`Published
`With international search report.
`
`(21) International Application Number:
`
`PCT/US00/07476
`
`(22) International Filing Date:
`
`22 March 2000 (22.03.00)
`
`(30) Priority Data:
`60/125,417
`60/136,556
`60/136,557
`
`22 March 1999 (22.03.99)
`28 May 1999 (28.05.99)
`28 May 1999 (28.05.99)
`
`US
`US
`US
`
`(71) Applicant (for all designated States except US): INTERDIG-
`ITAL TECHNOLOGY CORPORATION [US/US]; Suite
`527, 300 Delaware Avenue, Wilmington, DE 19801 (US).
`
`(72) Inventors; and
`(75) Inventors/Applicants (for US only): ZEIRA, Ariela [US/US];
`8 Old Oak Road, Trumball, CT 06611 (US). OZLUTURK,
`Fatih, M. [TR/US]; 70 Willowdale Avenue, Port Washing-
`ton, NY 11050 (US). SHIN, Sung—Hyuk [KR/US]; 1531 8th
`Street, Fort Lee, NJ 07024 (US).
`
`(74) Agents: VOLPE, Anthony, S. et al.; Volpe and Koenig,
`P.C., One Penn Center, Suite 400, 1617 John F. Kennedy
`Boulevard, Philadelphia, PA 19103 (US).
`
`(54) Title: COMBINED CLOSED LOOP/OPEN LOOP POWER CONTROL IN A TIME DIVISION DUPLEX COMMUNICATION
`SYSTEM
`
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`
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`SPREADING AND
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`(57) Abstract
`
`Combined closed loop/open loop power control controls transmission power levels in a spread spectrum time division duplex
`communication station. A first communication station (50) receives communications from a second communication station (52). The
`first station transmits power commands based on in part a reception quality of the received communications. The first station transmits a
`second communication having a transmission power level in a first time slot. The second station receives the second communication and
`the power commands. A power level of the second communication as received is measured. A path loss estimate is determined based on in
`part the measured received second communication power level and the first communication transmission power level. The second station
`transmits a second communication to the first station in a second time slot. The second communication transmission power level is set
`based on in part the path loss estimate weighted by a factor and the power commands. The factor is a function of a time separation of the
`first and second time slots.
`
`Ericsson Exhibit 1011
`Page 1
`
`

`

`FOR THE PURPOSES OF INFORMATION ONLY
`
`Codes used to identify States party to the PCT on the front pages of pamphlets publishing international applications under the PCT.
`
`AL
`AM
`AT
`AU
`AZ
`BA
`BB
`BE
`BF
`BG
`BJ
`BR
`BY
`CA
`CF
`CG
`CH
`CI
`CM
`CN
`CU
`CZ
`DE
`DK
`EE
`
`Albania
`Armenia
`Austria
`Australia
`Azerbaijan
`Bosnia and Herzegovina
`Barbados
`Belgium
`Burkina Faso
`Bulgaria
`Benin
`Brazil
`Belarus
`Canada
`Central African Republic
`Congo
`Switzerland
`Cote d'Ivoire
`Cameroon
`China
`Cuba
`Czech Republic
`Germany
`Denmark
`Estonia
`
`ES
`FI
`FR
`GA
`GB
`GE
`GH
`GN
`GR
`HU
`1E
`IL
`IS
`IT
`JP
`KE
`KG
`KP
`
`KR
`KZ
`LC
`LI
`LK
`LR
`
`Spain
`Finland
`France
`Gabon
`United Kingdom
`Georgia
`Ghana
`Guinea
`Greece
`Hungary
`Ireland
`Israel
`Iceland
`Italy
`Japan
`Kenya
`Kyrgyzstan
`Democratic People's
`Republic of Korea
`Republic of Korea
`Kazakstan
`Saint Lucia
`Liechtenstein
`Sri Lanka
`Liberia
`
`LS
`LT
`LU
`LV
`MC
`MD
`MG
`MK
`
`ML
`MN
`MR
`MW
`MX
`NE
`NL
`NO
`NZ
`PL
`PT
`RO
`RU
`SD
`SE
`SG
`
`Lesotho
`Lithuania
`Luxembourg
`Latvia
`Monaco
`Republic of Moldova
`Madagascar
`The former Yugoslav
`Republic of Macedonia
`Mali
`Mongolia
`Mauritania
`Malawi
`Mexico
`Niger
`Netherlands
`Norway
`New Zealand
`Poland
`Portugal
`Romania
`Russian Federation
`Sudan
`Sweden
`Singapore
`
`SI
`SK
`SN
`SZ
`TD
`TG
`TJ
`TM
`TR
`TT
`UA
`UG
`US
`UZ
`VN
`YU
`ZW
`
`Slovenia
`Slovakia
`Senegal
`Swaziland
`Chad
`Togo
`Tajikistan
`Turkmenistan
`Turkey
`Trinidad and Tobago
`Ukraine
`Uganda
`United States of America
`Uzbekistan
`Viet Nam
`Yugoslavia
`Zimbabwe
`
`Ericsson Exhibit 1011
`Page 2
`
`

`

`WO 00/57574
`
`PCT/US00/07476
`
`COMBINED CLOSED LOOP/OPEN LOOP POWER CONTROL IN A
`TIME DIVISION DUPLEX COMMUNICATION SYSTEM
`
`BACKGROUND
`
`This invention generally relates to spread spectrum time division duplex
`
`(TDD) communication systems. More particularly, the present invention relates to
`
`a system and method for controlling transmission power within TDD communication
`
`5
`
`systems.
`
`Figure 1 depicts a wireless spread spectrum time division duplex (TDD)
`
`communication system. The system has a plurality of base stations 301-307. Each
`
`base station 301 communicates with user equipments (UEs) 321-323 in its operating
`
`area. Communications transmitted from a base station 301 to a UE 321 are referred
`
`10
`
`to as downlink communications and communications transmitted from a UE 321 to
`
`a base station 301 are referred to as uplink communications.
`
`In addition to communicating over different frequency spectrums, spread
`
`spectrum TDD systems carry multiple communications over the same spectrum. The
`
`multiple signals are distinguished by their respective chip code sequences (codes).
`
`15
`
`Also, to more efficiently use the spread spectrum, TDD systems as illustrated in
`
`Figure 2 use repeating frames 34 divided into a number of time slots 361-36.,, such
`
`as fifteen time slots. In such systems, a communication is sent in selected time slots
`
`361-36n using selected codes. Accordingly, one frame 34 is capable of carrying
`
`multiple communications distinguished by both time slot 361-36n and code. The
`
`-1-
`
`Ericsson Exhibit 1011
`Page 3
`
`

`

`WO 00/57574
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`PCT/US00/07476
`
`combination of a single code in a single time slot is referred to as a resource unit.
`
`Based on the bandwidth required to support a communication, one or multiple
`
`resource units are assigned to that communication.
`
`Most TDD systems adaptively control transmission power levels. In a TDD
`
`5
`
`system, many communications may share the same time slot and spectrum. When
`
`a UE 321 or base station 301 is receiving a specific communication, all the other
`
`communications using the same time slot and spectrum cause interference to the
`
`specific communication.
`
`Increasing the transmission power level of one
`
`communication degrades the signal quality of all other communications within that
`
`10
`
`time slot and spectrum. However, reducing the transmission power level too far
`
`results in undesirable signal to noise ratios (SNRs) and bit error rates (BERs) at the
`
`receivers. To maintain both the signal quality of communications and low
`
`transmission power levels, transmission power control is used.
`
`One approach to control transmission power levels is open loop power
`
`15
`
`control. In open loop power control, typically a base station 301 transmits to a UE
`
`321 a reference downlink communication and the transmission power level of that
`
`communication. The UE 321 receives the reference communication and measures
`
`its received power level. By subtracting the received power level from the
`
`transmission power level, a pathloss for the reference communication is determined.
`
`20
`
`To determine a transmission power level for the uplink, the downlink pathloss is
`
`added to a desired received power level at the base station 301. The UE's
`
`transmission power level is set to the determined uplink transmission power level.
`
`-2-
`
`Ericsson Exhibit 1011
`Page 4
`
`

`

`WO 00/57574
`
`PCT/US00/07476
`
`Another approach to control transmission power level is closed loop power
`
`control. In closed loop power control, typically the base station 301 determines the
`
`signal to interference ratio (SIR) of a communication received from the UE 321. The
`
`determined SIR is compared to a target SIR (SIRTARGET)• Based on the comparison,
`
`5
`
`the base station 301 transmits a power command, bTpc. After receiving the power
`
`command, the UE 321 increases or decreases its transmission power level based on
`
`the received power command.
`
`Both closed loop and open loop power control have disadvantages. Under
`
`certain conditions, the performance of closed loop systems degrades. For instance,
`
`10
`
`if communications sent between a UE and a base station are in a highly dynamic
`
`environment, such as due to the UE moving, such systems may not be able to adapt
`
`fast enough to compensate for the changes. The update rate of closed loop power
`
`control in TDD is 100 cycles per second which is not sufficient for fast fading
`
`channels. Open loop power control is sensitive to uncertainties in the uplink and
`
`15
`
`downlink gain chains and interference levels.
`
`One approach to combining closed loop and open loop power control was
`
`proposed by the Association of Radio Industries and Business (ARIB) and uses
`
`Equations 1, 2, and 3.
`
`TUE = PBS(11) + L
`
`20
`
`PBS (n) = PBS (n-1) + bTpc ATPC
`
`bTPC =
`
`1: if SIRES ( SIRTARGET
`- 1: if SIRES ) SIRTARGET
`
`-3-
`
`Equation 1
`
`Equation 2
`
`Equation 3
`
`Ericsson Exhibit 1011
`Page 5
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`

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`WO 00/57574
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`PCT/US00/07476
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`TUE is the determined transmission power level of the UE 321. L is the estimated
`
`downlink pathloss. PBS(n) is the desired received power level of the base station 301
`
`as adjusted by Equation 2. For each received power command, bTpc, the desired
`
`received power level is increased or decreased by ATpc . OTPc is typically one decibel
`
`5
`
`(dB). The power command, bTpc, is one, when the SIR of the UE's uplink
`
`communication as measured at the base station 30, SIRBS, is less than a target SIR,
`
`Conversely, the power command is minus one, when SIRBS is larger than
`
`S IRTARGET •
`
`S IRTARGET •
`
`Under certain conditions, the performance of these systems degrades. For
`
`10
`
`instance, if communications sent between a UE 32 and a base station 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 for alternate approaches to maintain signal quality and
`
`low transmission power levels for all environments and scenarios.
`
`15
`
`SUMMARY
`
`Combined closed loop/open loop power control controls transmission power
`
`levels in a spread spectrum time division duplex communication station. A first
`
`communication station receives communications from a second communication
`
`20
`
`station. The first station transmits power commands based on in part a reception
`
`quality of the received communications. The first station transmits a second
`
`communication having a transmission power level in a first time slot. The second
`
`-4-
`
`Ericsson Exhibit 1011
`Page 6
`
`

`

`WO 00/57574
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`PCT/US00/07476
`
`station receives the second communication and the power commands. A power level
`
`of the second communication as received is measured. A path loss estimate is
`
`determined based on in part the measured received second communication power
`
`level and the first communication transmission power level. The second station
`
`5
`
`transmits a second communication to the first station in a second time slot. The
`
`second communication transmission power level is set based on in part the path loss
`
`estimate weighted by a factor and the power commands. The factor is a function of
`
`a time separation of the first and second time slots.
`
`10
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`Figure 1 illustrates a prior art TDD system.
`
`Figure 2 illustrates time slots in repeating frames of a TDD system.
`
`Figure 3 is a flow chart of combine closed loop/open loop power control.
`
`Figure 4 is a diagram of components of two communication stations using
`
`15
`
`combined closed loop/open loop power control.
`
`Figures 5-10 depict graphs of the performance of a closed loop, ARIB's
`
`proposal and two (2) schemes of combined closed loop/open loop power control.
`
`DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
`
`20
`
`The preferred embodiments will be described with reference to the drawing
`
`figures where like numerals represent like elements throughout. Combined closed
`
`loop/open loop power control will be explained using the flow chart of Figure 3 and
`
`-5-
`
`Ericsson Exhibit 1011
`Page 7
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`

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`WO 00/57574
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`PCT/US00/07476
`
`the components of two simplified communication stations 50, 52 as shown in Figure
`
`4. For the following discussion, the communication station having its transmitter'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
`
`5
`
`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 may be located at a base station 301, UE 321 or both. Accordingly, if both
`
`uplink and downlink power control are used, the receiving and transmitting station's
`
`components are located at both the base station 301 and UE 321.
`
`10
`
`The receiving station 50 receives various radio frequency signals including
`
`communications from the transmitting station 52 using an antenna 56, or alternately,
`
`an antenna array. The received signals are passed through an isolator 60 to a
`
`demodulator 68 to produce a baseband signal. The baseband signal is processed,
`
`such as by a channel estimation device 96 and a data estimation device 98, in the
`
`15
`
`time slots and with the appropriate codes assigned to the transmitting station's
`
`communication. The channel estimation device 96 commonly uses the training
`
`sequence component in the baseband signal to provide channel information, such as
`
`channel impulse responses. The channel information is used by the data estimation
`
`device 98, the interference measurement device 90, the signal power measurement
`
`20
`
`device 92 and the transmit power calculation device 94. The data estimation device
`
`98 recovers data from the channel by estimating soft symbols using the channel
`
`infoi illation. Using the soft symbols and channel information, the transmit power
`
`-6-
`
`Ericsson Exhibit 1011
`Page 8
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`

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`WO 00/57574
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`PCT/US00/07476
`
`calculation device 94 controls the receiving station's transmission power level by
`
`controlling the gain of an amplifier 76.
`
`The signal power measurement device 92 uses either the soft symbols or the
`
`channel information, or both, to determine the received signal power of the
`
`5
`
`communication in decibels (dB). The interference measurement device 90
`
`determines the interference level in dB, IRS, within the channel, based on either the
`
`channel information, or the soft symbols generated by the data estimation device
`
`102, or both.
`
`The closed loop power command generator 88 uses the measured
`
`10
`
`communication's received power level and the interference level, IRS, to determine
`
`the Signal to Interference Ratio (SIR) of the received communication. Based on a
`
`comparison of the determined SIR with a target SIR (SIRTARGET), a closed loop power
`
`command is generated, bTpc, such as a power command bit, bTpc, step 38.
`
`Alternately, the power command may be based on any quality measurement of the
`
`15
`
`received signal.
`
`For use in estimating the path loss between the receiving and transmitting
`
`stations 50, 52 and sending data, the receiving station 50 sends a communication to
`
`the transmitting 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
`
`20
`
`loss are referred to as reference channels, although other channels may be used. If
`
`the receiving station 50 is a base station 301, the communication is preferably sent
`
`over a downlink common channel or a common control physical channel (CCPCH).
`
`-7-
`
`Ericsson Exhibit 1011
`Page 9
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`

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`WO 00/57574
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`PCT/US00/07476
`
`Data to be communicated to the transmitting station 52 over the reference channel
`
`is referred to as reference channel data. The reference data may include, as shown,
`
`the interference level, IRS, multiplexed with other reference data, such as the
`
`transmission power level of the reference channel, TRS. The interference level, IRS,
`
`5
`
`and reference channel power level, TRS, may be sent in other channels, such as a
`
`signaling channel, step 40. The closed loop power control command, larpc, is
`
`typically sent in a dedicated channel, dedicated to the communication between the
`
`receiving station 50 and transmitting station 52.
`
`The reference channel data is generated by a reference channel data generator
`
`10
`
`86. The reference data is assigned one or multiple resource units based on the
`
`communication's 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 the assigned resource units. The resulting sequence is referred to as a
`
`15
`
`communication burst. The communication burst is subsequently amplified by an
`
`amplifier 78. The amplified communication burst may be summed by a sum 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.
`
`The summed communication bursts are modulated by a modulator 64. The
`
`20
`
`modulated signal is passed through an isolator 60 and radiated by an antenna 56 as
`
`shown or, alternately, through an antenna array. The radiated signal is passed
`
`through a wireless radio channel 54 to an antenna 58 of the transmitting station 52.
`
`-8-
`
`Ericsson Exhibit 1011
`Page 10
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`

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`WO 00/57574
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`PCT/US00/07476
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`The type of modulation used for the transmitted communication can be any of the
`
`those known to those skilled in the art, such as direct phase shift keying (DPSK) or
`
`quadrature phase shift keying (QPSK).
`
`The antenna 58 or, alternately, antenna array of the transmitting station 52
`
`5
`
`receives various radio frequency signals. The received signals are passed through
`
`an isolator 62 to a demodulator 66 to produce a baseband signal. The baseband
`
`signal is processed, such as by a channel estimation device 100 and a data estimation
`
`device 102, in the time slots and with the appropriate codes assigned to the
`
`communication burst of the receiving station 50. The channel estimation device 100
`
`10
`
`commonly uses the training sequence component in the baseband signal to provide
`
`channel information, such as channel impulse responses. The channel information
`
`is used by the data estimation device 102 and a power measurement device 110.
`
`The power level of the processed communication corresponding to the
`
`reference channel, RTS, is measured by the power measurement device 110 and sent
`
`15
`
`to a 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 power level is adjusted to correct for
`
`the gain of these devices at either the power measurement device 110 or the pathloss
`
`20
`
`estimation device 112. The power measurement device 110 is a component of the
`
`combined closed loop/open loop controller 108. As illustrated in Figure 4, the
`
`combined closed loop/open loop power controller 108 consists of the power
`
`-9-
`
`Ericsson Exhibit 1011
`Page 11
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`WO 00/57574
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`measurement 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 power level, T Rs. The transmitted power level, T Rs,
`
`5
`
`may be sent along with the communication's data or in a signaling channel. If the
`
`power level, T Rs, 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 301,
`
`preferably the transmitted power level, T Rs, is sent via the broadcast channel (BCH)
`
`10
`
`from the base station 301. By subtracting the received communication's power level,
`
`R Ts in dB, from the sent communication's transmitted power level, T Rs in dB, the
`
`pathloss estimation device 112 estimates the path loss, L, between the two stations
`
`50, 52, step 42. In certain situations, instead of transmitting the transmitted power
`
`level, TRs, the receiving station 50 may transmit a reference for the transmitted power
`
`15
`
`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 calculated loss. In TDD systems where communications are sent in
`
`20
`
`differing time slots 361-36n, the time slot delay between received and transmitted
`
`communications may degrade the performance of an open loop power control
`
`system. Combined closed loop/open loop power control utilizes both closed loop
`
`-10-
`
`Ericsson Exhibit 1011
`Page 12
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`WO 00/57574
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`PCT/US00/07476
`
`and open loop power control aspects. If the quality of the path loss measurement is
`
`high, the system primarily acts as an open loop system. If the quality of the path loss
`
`measurement is low, the system primarily acts as a closed loop system. To combine
`
`the two power control aspects, the system weights the open loop aspect based on the
`
`5
`
`quality of the path loss measurement.
`
`A quality measurement device 114 in a 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
`
`10
`
`measurement techniques. The estimated path loss quality is used to weight the path
`
`loss estimate by the transmit power calculation device 116. If the power command,
`
`bTpc, was sent in the communication's data, the data estimation device 102 interprets
`
`the closed loop power command, bTpc. Using the closed loop power command, bTpc,
`
`and the weighted path loss, the transmit power calculation device 116 sets the
`
`15
`
`transmit power level of the receiving station 50, step 48.
`
`The following is one of the preferred combined closed loop/open loop power
`
`control algorithms. The transmitting station's power level in decibels, PTS, is
`
`determined using Equations 4 and 6.
`
`PTS = Po G(n) + aL
`
`Equation 4
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`20
`
`Po is the power level that the receiving station 50 desires to receive the
`
`transmitting station's communication in dB. Po is determined by the desired SIR at
`
`the receiving station 50, SIRTARGET, and the interference level, IRS, at the receiving
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`station 50 using Equation 5.
`
`PO = SIRTARGET+IRS
`
`Equation 5
`
`IRS is either signaled or broadcasted from the receiving station 50 to the
`
`transmitting station 52. For downlink power control, SIRTARGET is known at the
`
`5
`
`transmitting station 52. For uplink power control, SIRTARGET is signaled from the
`
`receiving station 50 to the transmitting station 52. G(n) is the closed loop power
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`control factor. Equation 6 is one equation for determining G(n).
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`G(n) = G(n-1) + bTpc A —TPC
`
`Equation 6
`
`G(n-1) is the previous closed loop power control factor. The power
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`10
`
`command, bTpc, for use in Equation 6 is either +1 or -1. One technique for
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`determining the power command, bTpc, is Equation 3. The power command, bTpc,
`
`is typically updated at a rate of 100 ms in a TDD system, although other update rates
`
`may be used. ATpc is the change in power level. The change in power level is
`
`typically 1 dB although other values may be used. As a result, the closed loop factor
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`15
`
`increases by 1 dB if bTpc is +1 and decreases by 1 dB if bTpc is -1.
`
`The weighting value, a, is determined by the quality measurement device 114.
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`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 transmitted by the transmitting station 52.
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`20
`
`The value of a is from zero to one. Generally, if the time difference, D, between the
`
`time slots is small, the recent path loss estimate will be fairly accurate and a is set at
`
`a value close to one. By contrast, if the time difference is large, the path loss
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`estimate may not be accurate and the closed loop aspect is most likely more accurate.
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`Accordingly, a is set at a value closer to zero.
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`Equation 7 is one equation for determining a, although others may be used.
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`a = 1 - (D - 1)/D.
`
`Equation 7
`
`5
`
`D. is the maximum possible delay. A typical value for a frame having fifteen time
`
`slots is six. If the delay is D. or greater, a approaches zero. Using the calculated
`
`transmit power level, PTs, determined by a transmit power calculation device 116, the
`
`combined closed loop/open loop power controller 108 sets the transmit power of the
`
`transmitted communication.
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`10
`
`Data to be transmitted in a communication from the transmitting station 52 is
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`produced by a data generator 106. 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 and codes of the assigned resource
`
`units producing a communication burst. The spread signal is amplified by the
`
`15
`
`amplifier 74 and modulated by the modulator 70 to radio frequency.
`
`The combined closed loop/open loop power controller 108 controls the gain
`
`of the amplifier 74 to achieve the determined transmit power level, Pis, for the
`
`communication. The power controlled communication is passed through the isolator
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`62 and radiated by the antenna 58.
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`20
`
`Equations 8 and 9 are another preferred combined closed loop/open loop
`
`power control algorithm.
`
`PTS = PO + K(n)
`
`Equation 8
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`K(n) = K(n-1) + bTpc A + aL
`- TPC
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`PCT/US00/07476
`
`Equation 9
`
`K(n) is the combined closed loop/open loop factor. As shown, this factor includes
`
`both the closed loop and open loop power control aspects. Equations 4 and 5
`
`segregate the two aspects.
`
`5
`
`Although the two above algorithms only weighted the open loop factor, the
`
`weighting may be applied to the closed loop factor or both the open and closed loop
`
`factors. Under certain conditions, the network operator may desire to use solely open
`
`loop or solely closed loop power control. For example, the operator may use solely
`
`closed loop power control by setting a to zero.
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`10
`
`Figures 5-10 depict graphs 118-128 illustrating the performance of a
`
`combined closed-loop/open-loop power control system. These graphs 118-128
`
`depict the results of simulations comparing the performance of the ARM proposed
`
`system, a closed loop, a combined open loop/closed loop system using Equations
`
`4 and 6 (scheme I) and a combined system using Equations 8 and 9 (scheme
`
`15
`
`The simulations were performed at the symbol rate. A spreading factor of sixteen
`
`was used for both the uplink and downlink channels. The uplink and downlink
`
`channels are International Telecommunication Union (ITU) Channel model [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
`
`20
`
`transmitting station 52 which is a UE 321 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
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`was a base station 301, sent the BCH transmission power level over the BCH. RAKE
`
`combining was used for both the UE 321 and base station 301. Antenna diversity
`
`combining was used at the base station 301.
`
`Graphs 118, 122, 126 depict the standard deviation of the received signal to
`
`5
`
`noise ratio (SNR) at the base station 301 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 represents the average of 3000 Monte-Carlo runs.
`
`10
`
`Graphs 118, 120 depict the results for an a set at one. For low time slot
`
`delays (D<4), scheme I and II outperform closed loop power control. For larger
`
`delays (D_4), 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
`
`15
`
`excluding the maximum, schemes I 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 a set using Equation 7 with Dr.
`
`equal to six. As shown, schemes I and II outperform both closed loop and the ARIB
`
`proposal at all delays, D.
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`20
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`CLAIMS
`
`1.
`
`A method for controlling transmission power levels in a spread
`
`spectrum time division duplex communication system having frames with time slots
`
`for communication, the method comprising:
`
`receiving at a first communication station communications from a second
`
`5
`
`communication station and transmitting from the first station power commands based
`
`on in part a reception quality of the received communications;
`
`transmitting from the first communication station a first communication
`
`having a transmission power level in a first time slot;
`
`receiving at the second communication station the first communication and
`
`10
`
`the power commands;
`
`measuring a power level of the first communication as received;
`
`determining a pathloss estimate based on in part the measured received first
`
`communication power level and the first communication transmission power level;
`
`and
`
`15
`
`setting a transmission power level for a second communication in a second
`
`time slot from the second station to the first station based on in part the pathloss
`
`estimate weighted by a quality factor and the power commands, wherein the quality
`
`factor is a function of a time separation of the first and second time slots.
`
`2.
`
`The method of claim 1 further comprising:
`
`determining a quality, a, of the pathloss estimate based on in part a number
`
`-16-
`
`Er