`
`i11111 11111111 III 11111 Hill JIJI J1911i1121t121,1111111111111111111111111
`
`
`
`
`
`(12) United States Patent
`Anderson
`
`(10) Patent No.:
`(45) Date of Patent:
`
`US 8,897,828 B2
`*Nov. 25, 2014
`
`(54)
`
`POWER CONTROL IN A WIRELESS
`COMMUNICATION SYSTEM
`
`(75)
`
`Inventor: Nicholas William Anderson, Bristol
`(GB)
`
`(73) Assignee: Intellectual Ventures Holding 81 LLC,
`Las Vegas, NV (US)
`
`( * ) Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 891 days.
`
`This patent is subject to a terminal dis-
`claimer.
`
`(21)
`
`Appl. No.: 10/917,968
`
`(22)
`
`Filed:
`
`Aug. 12, 2004
`
`(65)
`
`Prior Publication Data
`
`US 2006/0035660 Al
`
`Feb. 16, 2006
`
`(51) Int. Cl.
`H04B 7/00
`H04W 72/04
`HO4W 52/06
`HO4W 52/24
`H04W 52/08
`H04W 52/10
`H04W 52/12
`H04W 52/22
`(52) U.S. Cl.
`CPC
`
`(2006.01)
`(2009.01)
`(2009.01)
`(2009.01)
`(2009.01)
`(2009.01)
`(2009.01)
`(2009.01)
`
`HO4W 72/0473 (2013.01); H04W 52/06
`(2013.01); H04W 52/24 (2013.01); H04W
`52/08 (2013.01); H04W 52/10 (2013.01); HO4W
`52/12 (2013.01); H04W 52/221 (2013.01);
`H04W 52/242 (2013.01); H04W 52/243
`(2013.01)
` 455/522; 455/68; 455/69
`USPC
`(58) Field of Classification Search
`CPC
`HO4W 72/0473; HO4W 52/24; HO4W
`52/242; HO4W 52/08; HO4W 52/10; HO4W
`52/12; HO4W 52/221; HO4W 52/248
`
`USPC
`
` 455/522, 68, 69, 296, 135, 226.3,
`455/277 2, 115.3, 126, 127.1, 127.2, 67.11,
`455/434, 436; 370/331, 320, 335, 342, 318,
`370/392, 252, 276, 280; 375/147, 130
`See application file for complete search history.
`
`(56)
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`5,719,583 A
`5,887,245 A
`
`2/1998 Kanai
`3/1999 Lindroth et al.
`(Continued)
`
`FOREIGN PATENT DOCUMENTS
`
`EP
`EP
`
`1/2001
`1 071 227 A2
`1/2002
`1176739 Al
`(Continued)
`
`OTHER PUBLICATIONS
`
`"Recommendation ITU-R M.1225: Guidelines for Evaluation of
`Radio Transmission Technologies for IMT-2000," International Tele-
`communication Union/ITU Radiocommunication Sector, Jan. 1,
`1997, Rec. ITU-R M.1225, pp. 1-61.
`
`(Continued)
`
`Primary Examiner — Dominic E Rego
`(74) Attorney, Agent, or Firm — Volpe and Koenig, P.C.
`
`ABSTRACT
`(57)
`Power control in a wireless network is disclosed. Transmit
`power control (TPC) commands may be accumulated by a
`user equipment (UE). If accumulation is enabled, the UE may
`receive on a single physical channel an allocation of a sched-
`uled uplink resource and a TPC command. The TPC com-
`mand may be accumulated with other received TPC com-
`mands. A transmit power for an uplink communication based
`on both the path loss and the accumulated TPC commands
`may then be calculated by the UE. If accumulation is not
`enabled, the UE may receive an allocation of a scheduled
`uplink resource to transmit data at a calculated power level.
`
`42 Claims, 4 Drawing Sheets
`
`Controller
`(RNC)
`110
`
`Network 100
`
`Base station
`(Node-B)
`120
`
`Base station
`(Node-B)
`130
`
`Channel
`160
`
`User #1
`(UE)
`140
`
`User #2
`(UE)
`150
`
`Ericsson Exhibit 1001
`Page 1
`
`

`

`US 8,897,828 B2
`Page 2
`
`(56)
`
`References Cited
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`U.S. PATENT DOCUMENTS
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`7/2000 Sendonaris et al.
`6,085,106 A
`10/2000 Almgren et al.
`6,137,993 A
`8/2002 Padovani et al.
`6,442,398 B1
`1/2003 Park et al.
`6,512,931 B1
`7/2003 Zeira et al.
`6,597,723 B1
`9/2003 Bark et al.
`6,628,956 B2
`11/2004 Haim
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`1/2006 Shiu et al.
`6,983,166 B2 *
`7,190,688 B1 * 3/2007 Kamel et al.
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`3/2012 Liu et al.
`2001/0036823 Al * 11/2001 Van Lieshout et al.
`2003/0032411 Al *
`2/2003 Kim et al.
`2003/0103530 Al
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`2003/0134655 Al * 7/2003 Chen et al.
`2004/0137860 Al * 7/2004 Oh et al.
`2004/0141483 Al * 7/2004 Zeira et al.
`2004/0162093 Al *
`8/2004 Bevan et al.
`2004/0171387 Al * 9/2004 Miyoshi et al.
`2004/0190485 Al
`9/2004 Khan
`2004/0203987 Al * 10/2004 Butala
`2005/0003846 Al
`1/2005 Anderson
`2005/0025056 Al *
`2/2005 Chen et al.
`2005/0041673 Al *
`2/2005 Jiang et al.
`2005/0073973 Al
`4/2005 LaRoia et al.
`2005/0130690 Al *
`6/2005 Shinozaki
`2005/0136961 Al *
`6/2005 Simonsson et al.
`2005/0176455 Al *
`8/2005 Krishnan et al.
`2005/0207359 Al * 9/2005 Hwang et al.
`2007/0081492 Al *
`4/2007 Petrovic et al.
`2009/0028111 Al *
`1/2009 Chao et al.
`
`FOREIGN PATENT DOCUMENTS
`
`GB
`JP
`WO
`WO
`WO
`WO
`WO
`WO
`WO
`WO
`
`2350522 A
`2004-040187
`WO-96/31009 Al
`WO-99/07105 A2
`WO -00/57574
`WO-00/57574 A2
`WO-01/08322 Al
`WO 01/84740 A2
`03010903
`WO-03/036816 Al
`
`11/2000
`2/2004
`10/1996
`2/1999
`* 9/2000
`9/2000
`2/2001
`11/2001
`2/2003
`5/2003
`
`
`
` HO4B 7/005
`
` 455/522
` 370/342
`
` 455/418
` 455/414
`
` 455/522
` 455/127.1
` 370/335
` 455/502
` 455/452.2
`
` 455/522
`
` 370/235
` 370/401
`
` 455/522
` 455/522
` 455/522
` 370/278
` 370/331
` 370/331
`
`OTHER PUBLICATIONS
`
`Great Britain Search Report mailed May 14, 2002, for Great Britain
`Application No. 0125504.1 filed Oct. 24, 2001, 1 page.
`International Search Report mailed Dec. 22, 2005, for PCT Applica-
`tion No. PCT/EP2005/053931 filed Aug. 10, 2005, 4 pages.
`International Search Report mailed Jan. 21, 2003, for PCT Applica-
`tion No. PCT/GB02/04811 filed Oct. 24, 2002, 3 pages.
`European Search Report Dated Dec. 2, 2010 from European Appli-
`cation No. 10185576.5-1246.
`Communication pursuant to Article 94(3) EPC from European Patent
`Application No. 05 801 370.7-1246 dated Dec. 30, 2009.
`Office Action for Japanese Application No. 2007-525302, issued
`Mar. 13, 2012.
`Third Generation Partnership Project, Technical Specification Group
`Radio Access Network; Feasibility Study on Uplink Enhancements
`for UTRA TDD; (Release 6); 3GPP TR 25.804 V6.0.0 (Mar. 2005).
`Non-Final Rejection, U.S. Appl. No. 13/726,976, dated May 22,
`2014.
`Non-Final Rejection, U.S. Appl. No. 13/727,153, dated May 22,
`2014.
`Office Action, Japanese Patent Application No. 2011-234218, dated
`Dec. 6, 2012.
`
`EP
`EP
`
`1 367 740 Al
`1 367 740 Al
`
`12/2003
`12/2003
`
`* cited by examiner
`
`Ericsson Exhibit 1001
`Page 2
`
`

`

`U.S. Patent
`
`Nov. 25, 2014
`
`Sheet 1 of 4
`
`US 8,897,828 B2
`
`Controller
`(RNC)
`110
`
`Network 100
`
`Base station
`(Node-B)
`120
`
`Base station
`(Node-B)
`130
`
`Channel
`160
`
`User #1
`(UE)
`1411
`
`User #2
`(UE)
`150
`
`FIGURE 1
`
`Measure uplink
`interference level
`207
`
`Network
`Determine error
`metric of uplink
`signal
`206
`
`Radio link
`
`Uplink 202
`User data
`204
`
`Update Interference
`measurements table
`208
`
`outer
`loop
`
`Update
`SNIR Target
`210
`
`i
`
`Transmit
`SNIR Target
`212
`
`UE
`
`Transmit
`User data
`200
`
`4
`
`Transmit
`power
`level
`
`Downlink 214
`SNIR Target
`216
`
`Save
`SNIR Target
`220
`
`Broadcast beacon (including Power level
`and Interference measurements)
`222
`
`Set
`Transmit power level
`234
`
`Measure
`received
`power level
`230
`
`Save
`Interference
`measurements
`212,
`
`inner
`loop
`
`open
`loop
`
`Downlink 224
`Power level
`226
`Interference
`measurements
`228
`
`FIGURE 2
`
`Ericsson Exhibit 1001
`Page 3
`
`

`

`U.S. Patent
`
`Nov. 25, 2014
`
`Sheet 2 of 4
`
`US 8,897,828 B2
`
`Network
`
`Radio link
`
`UE
`
`Determine error
`metric of uplink
`signal
`306
`
`Measure
`received SNIR
`310
`
`Uplink 302
`
`User data
`403
`
`Update
`SNIR Target
`308
`
`titer
`loop
`
`inner
`loop
`
`compare received SNIR
`with SNIR Target
`
`Transmit user data
`300
`
`Transmit
`power
`level
`
`closed
`loop
`
`Set
`Transmit power level
`322
`
`Generate and transmit TPC command
`314
`
`Downlink 316
`
`TPC command
`318
`
`Accumulate
`TPC commands
`320
`
`FIGURE 3
`
`Ericsson Exhibit 1001
`Page 4
`
`

`

`U.S. Patent
`
`Nov. 25, 2014
`
`Sheet 3 of 4
`
`US 8,897,828 B2
`
`Network
`
`Radio link
`
`UE
`
`r
`Update
`i
`Interference
`i
`1 measurements
`table
`422
`r
`
`i
`
`+
`
`Determine
`error metric of
`uplink signal
`406
`
`Measure
`received
`SNIR
`410
`
`Uplink 402
`
`User data
`404
`
`outer
`loop
`
`Update
`SNIR Target
`408
`
`compare received SNIR with
`SNIR Target
`412
`
`i
`
`Generate and transmit TPC
`command
`414
`
`V
`
`Broadcast beacon
`(including transmit power level and
`Interference measurements)
`424
`
`inner
`loop
`
`Downlink 416
`
`TPC command
`4111
`
`open
`..._loop...A
`
`Downlink 426
`
`power level
`428
`
`Interference
`measurements
`430
`
`FIGURE 4
`
`Transmit
`user data
`400
`
`Transmit
`power
`level
`
`Set
`Transmit power level
`436
`
`A
`
`Accumulate
`mil
` TPC commands
`420
`
`Ir
`
`Save signalled
`power level
`and measure
`received
`power level
`432
`
`Save
`Interference
`measure-
`ments
`434
`
`Ericsson Exhibit 1001
`Page 5
`
`

`

`U.S. Patent
`
`Nov. 25, 2014
`
`Sheet 4 of 4
`
`US 8,897,828 B2
`
`Distribution of received SNIR
`Open loop scheme
`
`-10
`
`-5
`
`0
`dB
`Closed loop scheme
`
`5
`
`10
`
`15
`
`FIGURE
`5A
`
`FIGURE
`56
`
`600
`
`500
`
`0 400
`6'
`E 300
`5
`0200
`
`1000
`
`800
`
`600
`
`400
`
`200
`
`8 0
`
`0
`-15
`
`-10
`
`-5
`
`0
`dB
`Combined scheme
`
`5
`
`10
`
`15
`
`FIGURE
`5C
`
`20
`I
`69
`
`-10
`
`-5
`
`0
`dB
`
`5
`
`10
`
`15
`
`Ericsson Exhibit 1001
`Page 6
`
`

`

`1
`POWER CONTROL IN A WIRELESS
`COMMUNICATION SYSTEM
`
`US 8,897,828 B2
`
`CROSS-REFERENCE TO RELATED
`APPLICATIONS
`
`Not applicable.
`
`BACKGROUND OF THE INVENTION
`
`1. Field of the Invention
`This invention relates to power control in a mobile radio
`system or wireless communication system, and more particu-
`larly, to controlling received power levels in a code division
`multiple access (CDMA) radio system.
`2. Description of the Prior Art
`Typically, radio signals transmitted with increased power
`result in fewer errors when received than signals transmitted
`with decreased power. Unfortunately, signals transmitted
`with excessive power may interfere with the reception of
`other signals sharing the radio link. Wireless communication
`systems employ power control schemes to maintain a target
`error rate of a signal received on a radio link.
`If a received signal includes a rate of errors far above a
`target error rate, the received signal may result in an undesir-
`able effect on a delivered service. For example, excessive
`errors may lead to broken voice during voice calls, low
`throughput over data links, and glitches in displayed video
`signals. On the other hand, if the received signal includes a
`rate of errors well below the target error rate, the mobile radio
`system is not efficiently using its radio resources. A very low
`error rate may mean that a signal is transmitted with an
`excessive level of power and that user could be provided a
`higher data rate. Alternatively, if the power level of a signal is
`sufficiently reduced, additional users may be serviced. If data
`rates are increased, a user may receive a higher level of
`service. Therefore, if a target error rate for each user is met
`within a tolerance threshold, a radio resource may be more
`optimally used.
`A wireless communication system often employ one of
`either an open loop scheme or a closed loop scheme to control
`uplink transmit power of a mobile radio. Uplink typically
`refers to the radio link from a mobile radio to a base station,
`where as the downlink typically refers to the link from the
`base station to the mobile radio. A mobile radio is not neces-
`sarily mobile and may also be referred to as a mobile, a user,
`user equipment (UE), a terminal or terminal equipment. A
`base station may also be referred to as a Node-B.
`The error rate is related to a received signal to noise-plus-
`interference ratio (SNIR); a higher SNIR generally results in
`a lower error rate; and conversely, a lower SNIR generally
`results in a higher error rate. The exact relationship between
`SNIR and error rate, however, is often a function of several
`factors including radio channel type and the speed at which a
`mobile is travelling.
`A target error rate is often reached using a two stage pro-
`cess, which includes an outer loop and an inner loop. A first
`process may operate as an outer loop and may be tasked to
`adjust a target received SNIR (SNIR Target). This first pro-
`cess tracks changes in the relationship between SNIR and
`error rate. The outer loop sets an SNIR Target that is generally
`used several times by the inner loop. Periodically, the outer
`loop may adjust or update this SNIR Target used by the inner
`loop. For example, if an actual error rate exceeds a desired
`error rate, the outer loop may increase the value of the SNIR
`Target.
`
`5
`
`2
`A second process operates as an inner loop and tries to
`force the link to exhibit the SNIR Target determined by the
`outer loop. The inner loop may operate by closed loop or by
`open loop means.
`In the open loop method of the inner loop process, a UE
`uses an SNIR Target value that is derived by the network and
`signalled to the UE. The inner loop running in the UE
`attempts to maintain the SNIR Target. The UE uses the infor-
`mation signalled to it and monitors the received strength of
`10 signals it receives to determine a power level at which it will
`transmit. Advantageously, this open loop method compen-
`sates for fast channel fading by determining the path loss on
`a per frame bases and by adjusting the transmit power accord-
`ingly. Unfortunately, this open loop method is relatively slow
`15 at compensating for changes due to interfering signals from
`other transmitters.
`In the closed loop method of the inner loop process, a
`closed loop scheme operates to match an SNIR Target. A
`received SNIR measurement is made by the network on an
`20 uplink signal. The SNIR measurement is compared within the
`network to the SNIR Target value. The inner loop drives the
`system to match the SNIR Target by issuing transmit power
`control commands from the network to a UE. The commands
`instruct the UE to increase or decrease its transmitted power
`25 by a predetermined step dB amount. Unfortunately, such
`closed loop methods demand a very high command update
`rate to adequately compensate for fast channel fading because
`of the single-dB-step commands used. At slower update rates,
`fast channel fading is not tracked adequately since a large
`30 number of iterations and long delays are needed to compen-
`sate for a change in power that is substantially larger than the
`dB-step value.
`Both the closed loop scheme and the open loop scheme
`have their disadvantages. Therefore, an improved method and
`35 system are needed that better balances the conflicting goals of
`reducing errors in a received signal while also reducing inter-
`ference imposed on signals received at other receivers. An
`improved method and system are also needed to better reduce
`the overall residual SNIR fluctuations experienced by each
`40 users signal at a receiver.
`
`BRIEF SUMMARY OF THE INVENTION
`
`Some embodiments provide a method of power control in
`45 a radio communications system, the method comprising:
`determining a path loss of a radio channel between a base
`station and a remote transceiver; receiving a transmit power
`control (TPC) command transmitted to the remote transceiver
`from the base station; and calculating a transmit power level
`so for the remote transceiver based on the path loss and the TPC
`command
`Some embodiments provide a method of power control in
`a radio communications system, the method comprising:
`receiving a signal at a second transceiver transmitted from a
`55 first transceiver; measuring a power level of the received
`signal; receiving a transmit power control (TPC) command at
`the second transceiver transmitted from the first transceiver;
`and calculating a transmit power level for the second trans-
`ceiver based on the power level of the received signal and the
`60 TPC command
`Some embodiments provide a method of uplink power
`control in a CDMA radio communications system, the
`method comprising: receiving an uplink signal; determining
`an error metric of the uplink signal; updating an SNIR target
`65 based on the error metric ;measuring a received SNTIR of the
`uplink signal; comparing the measured received SNIR with
`the SNIR target; assigning a first value to a step indicator if the
`
`Ericsson Exhibit 1001
`Page 7
`
`

`

`US 8,897,828 B2
`
`3
`measured received SNIR is greater than the SNIR target, and
`assigning a second value to a step indicator if the measured
`received SNIR is less than the SNIR target; transmitting a
`transmit power control (TPC) command instructing a trans-
`mitter to adjust an uplink transmit power level based on the
`step indicator; receiving the TPC command including the step
`indicator; accumulating the step indicator value; broadcast-
`ing a downlink signal including an indication of a downlink
`power level, wherein the signal is transmitted at the downlink
`power level; measuring the received power of the downlink
`signal; and setting a transmit power level base on the received
`power level, the indication of the downlink power level, and
`the accumulated step indicator value.
`Some embodiments provide a method comprising: mea-
`suring a power level of a received signal; receiving a transmit
`power control (TPC) command; and calculating a transmit
`power level based on the power level of the received signal
`and the TPC command
`Some embodiments provide a radio comprising: a receiver
`including an output to provide a measured received power
`level; an accumulator having an input for accepting step
`increase and decrease instructions and an output providing a
`sum of past step instructions; a power level setting circuit
`coupled to the accumulator output and coupled to the receiver
`output, wherein the power level setting circuit sets a transmit
`power bases on the accumulator output and the measured
`received power level; and a transmitter, wherein the transmit-
`ter transmits a signal at the set transmit power.
`Other features and aspects of the invention will become
`apparent from the following detailed description, taken in
`conjunction with the accompanying drawings which illus-
`trate, by way of example, the features in accordance with
`embodiments of the invention. The summary is not intended
`to limit the scope of the invention, which is defined solely by
`the claims attached hereto.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 shows a block diagram of a wireless communication
`system.
`FIG. 2 illustrates a wireless communication system using
`an open loop scheme.
`FIG. 3 illustrates a wireless communication system using a
`closed loop scheme.
`FIG. 4 illustrates a wireless communication system using
`elements of both open loop and closed loop schemes, in
`accordance with the present invention.
`FIGS. 5A, 5B and 5C each illustrate a simulated probabil-
`ity density function of the received SNIR in the network.
`
`DETAILED DESCRIPTION OF THE INVENTION
`
`In the following description, reference is made to the
`accompanying drawings which illustrate several embodi-
`ments of the present invention. It is understood that other
`embodiments may be utilized and mechanical, composi-
`tional, structural, electrical and operational changes may be
`made without departing from the spirit and scope of the
`present disclosure. The following detailed description is not
`to be taken in a limiting sense, and the scope of the embodi-
`ments of the present invention is defined by the claims of the
`issued patent.
`Some portions of the detailed description which follows
`are presented in terms of procedures, steps, logic blocks,
`processing, and other symbolic representations of operations
`on data bits that can be performed on computer memory. A
`procedure, computer executed step, logic block, process etc.,
`
`4
`are here conceived to be a self-consistent sequence of steps or
`instructions leading to a desired result. The steps are those
`utilizing physical manipulations of physical quantities. These
`quantities can take the form of electrical, magnetic, or radio
`5 signals capable of being stored, transferred, combined, com-
`pared, and otherwise manipulated in a computer system.
`These signals may be referred to at times as bits, values,
`elements, symbols, characters, terms, numbers, or the like.
`Each step may be performed by hardware, software, firm-
`10 ware, or combinations thereof.
`FIG. 1 shows a block diagram of a wireless communication
`system. A network 100 may include one or more base station
`controllers 110, such as a radio network controller (RNC),
`and one or more base stations 120, 130 such as a Node-B,
`15 wherein each Node-B is connected to an RNC. The network
`100 communicates with one or more users 140, 150 through
`a channe1160, also referred to as a radio link, created between
`a base station and a user.
`Two mechanisms are primarily responsible for changes in
`20 the SNIR of a signal travelling through a radio link.
`First, changes in the channel affect the SNIR. The instan-
`taneous path loss between a base station and a user may vary
`as the user changes position or the user's environment
`changes. Rapid changes may occur as a result of a transmitted
`25 signal combining constructively and destructively as the sig-
`nal travels along multiple paths from a base station and to the
`user. Additionally, slower changes may occur due to attenu-
`ation of the radio waves with increased distance between the
`base station and the user. Slower changes may also occur due
`30 to signal obstruction by buildings, vehicles and hills.
`Second, signals from other transmitters affect the SNIR.
`For example, signals intended for other mobile radios or other
`base stations may increase interference in the radio link and
`thus reduce a received signal's SNIR.
`In Time Division Duplex (TDD) systems, both uplink and
`downlink share the same carrier frequency. Due to this reci-
`procity in the links, path loss measurements made on the
`downlink by a mobile radio may be used estimate the path
`loss on the uplink. That is, a measured downlink path loss may
`40 be used to estimate the uplink path loss. The estimated uplink
`path loss will be less reliable with the passing of time but may
`be adequate within a frame period. Therefore, a mobile radio
`may determine a transmit power level for an uplink transition
`that compensates for an estimated uplink path loss, thereby
`45 providing a received signal to a base station at an expected
`input power level.
`Downlink path loss measurements may be facilitated by a
`beacon channel, which is transmitted from a base station at a
`reference power level. A mobile radio is informed of the
`so actual transmit power level being used by the base station for
`the beacon channel. In addition to knowing the actual trans-
`mit power level of a beacon channel, the mobile radio may
`measure a received signal power level. By measuring the
`received signal power level, the mobile radio can compute a
`55 downlink path loss as the difference between the actual trans-
`mit power level and the received signal power level. Thus, the
`mobile radio is able to estimate the uplink path loss in a
`channel between the base station and the mobile radio and
`properly set its uplink transmit power level.
`The path loss calculation may be updated as often as a
`beacon signal is transmitted and received. In a UTRA TDD
`system in compliance with the third generation partnership
`project (3GPP) specifications, a beacon signal is transmitted
`either once or twice every 10 milliseconds (ms). If an uplink
`65 transmission follows a beacon transmission within a rela-
`tively short period of time, a mobile radio can compensate for
`the fast fluctuations (fast-fading) in a radio channel. Such is
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`the case for mobiles travelling at slow to moderate speeds if a
`beacon signal is transmitted either once or twice every 10 ms
`and the uplink transmissions occur in the intervening period.
`Additionally, a radio channel may be adversely affected by
`changes in interference levels over time. These temporal
`interference changes may be accommodated by a base station
`measuring and communicating interference levels seen in
`each uplink timeslot. In a UTRA TDD system, a table having
`values of the measured interference for each timeslot may be
`broadcast to all users via a Broadcast Channel (BCH). The
`broadcasted information may be updated approximately
`every 16 frames (160 ms) depending upon the system con-
`figuration. In other embodiments, a mobile radio may receive
`this interference table as a signalled message directed to the
`individual mobile radio.
`The 3GPP specifications describe two separate schemes
`for power control of uplink channels: an open loop scheme
`and a closed loop scheme. For example, in 3GPP 3.84 Mega-
`chips per second (Mcps) TDD systems, open loop power
`control is specified for all uplink channels. In 3GPP 1.28
`Mcps TDD systems, open loop power control is specified
`only for physical random access channels (PRACH). Also
`defined by 3GPP is an implementation of a closed loop power
`control scheme. For example, see 3GPP recommendations
`for UTRA TDD systems operating at 1.28 Mcps for non-
`PRACH uplink channels.
`In a wireless communication system using an open loop
`scheme, a network and UE use an outer loop to update and
`signal to the UE an SNIR Target value, thereby influencing
`the UE's transmit power. The network updates the SNIR
`Target value to be signalled based upon an observed error rate
`on the uplink. Once received, the mobile radio takes into
`account the signalled SNIR Target value when deriving a
`transmit power level that it will apply to the next uplink signal
`transmitted.
`In a 3GPP 3.84 Mcps system incorporating an open loop
`scheme, a network instructs the UE with an SNIR Target
`value. The network also signals its beacon transmit power
`level and may also provide a measure of uplink interference
`for each timeslot as measured by the network. The UE
`receives an input signal that is typically a combination of
`attenuated versions of the network signal, which passed
`through a radio channel, along with interfering signals from
`other transmitters. The UE measures the received power level
`of the attenuated network signal and determines a path loss of
`the radio channel. The UE also decodes the signalled SNIR
`Target value from the network signal. The UE computes a
`transmit power level based on the SNIR Target value, the
`determined path loss and, if available, the uplink interference
`measurements.
`FIG. 2 illustrates a wireless communication system using
`an open loop scheme. A UE transmits 200 user data at a
`determined transmit power level. An uplink signal 202, which
`includes user data 204, propagates through the radio link. The
`network receives an attenuated version of the transmitted
`signal. The network measures 207 an uplink interference
`value and determines 206 an error metric of the uplink signal.
`The network may use the measured uplink interference value
`to update 208 an interference measurement table. The inter-
`ference measurement table may include average measured
`interference levels for each uplink timeslot.
`The network also uses the error metric to update 210 an
`SNIR Target value. The network transmits 212 SNIR Target
`in a signalling message on the downlink 214, which includes
`the SNIR Target 216. The UE receives and saves 220 the
`SNIR Target. The network also broadcasts 222 a beacon
`signal on the downlink 224. The downlink 224 propagates the
`
`20
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`6
`signal, which includes an indication of the beacon power level
`226, over the radio link. The network may also broadcast the
`interference measurements 228. The UE measures 230 the
`received power level and saves 232 the interference measure-
`5 ments for later processing.
`With the measured power level and the signalled beacon
`power level, the UE may determine a path loss. The UE may
`use the saved received SNIR Target 216, the saved received
`interference measurements 228 and the computed path loss to
`10 set 234 a transmit power level. This transmit power level may
`be used by transmitter 200 to set the power level of transmit-
`ted user data 204 on the uplink 202.
`The 3GPP specifications also define a closed loop scheme.
`For example, a 3GPP 1.28 Mcps system employs a closed
`15 loop scheme using an outer loop and an inner loop. The closed
`loop TPC scheme is the primary power control mechanism
`used for all non-PRACH channels in a 1.28 Mcps TDD sys-
`tem. The closed loop TPC scheme is not currently employed
`for the uplink of 3.84 Mcps TDD systems.
`The outer loop determines an SNIR Target value and the
`inner loop uses the SNIR Target value. The outer loop
`includes network components that determine an error metric,
`such as a bit error rate, a block error rate or a CRC error count,
`on uplink traffic from UEs. This error metric is used to set and
`25 update an SNIR Target value. An inner loop includes network
`components that use the SNIR Target value computed and set
`by the outer loop. The network measures a received SNIR
`value of the uplink signal.
`Next, a comparator determines whether the measured
`30 SNIR value is greater than or less than the SNIR Target value.
`If the measured SNIR value is greater than the SNIR Target
`value, the network signals a transmit power control (TPC)
`command on the downlink instructing the UE to reduce its
`current transmitter power by a step value (e.g., 1 dB). On the
`35 other hand, if the measured SNIR value is less than the SNIR
`Target value, the network signals a TPC command instructing
`the UE to increase its current transmitter power by the step dB
`value.
`In a system employing only a closed loop power control
`40 scheme, several TPC commands may be necessary to prop-
`erly bring the UE's transmitted power in line with the SNIR
`Target value. For example, if a path loss increases from one
`frame to the next by 15 dB, the system will take 15 TPC
`commands to compensate for the 15 dB fade. A UE accumu-
`45 lates the increase and decrease TPC commands to determine
`a proper uplink transmit power level. By increasing and
`decrease uplink power levels of each UE, a network attempts
`to control the power level of each UE such that the ratio of the
`received uplink energy level per transmitted bit to the spectral
`so density of the noise and interference signals is a constant
`value. This TPC command adjustment process is performed
`for each UE in a cell. The constant value, however, may be
`non-uniform among the UEs depending upon the configura-
`tion of the system.
`In a closed loop TPC scheme, the inner loop SNIR is
`maintained via a closed loop method using binary feedback.
`The feedback indicates either power up or power down. Every
`time a TPC command is received an integrator in the UE is
`used within the inner loop to update the UE transmit power by
`60 a step amount +/-4 dB. The TPC commands themselves are
`derived by the network and are signalled to the UE via a
`downlink channel. When calculating the proper TPC com-
`mand to send, the network measures the received SNIR and
`compares this measured value to an SNIR Target value. If the
`65 SNIR is too low, an up command is sent. If the SNIR is too
`high, a down command is sent. The target SNIR value is
`updated by the outer loop based upon the observed error
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`US 8,897,828 B2
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`7
`performance of the link. In this way, both the inner and outer
`feedback loops are closed by the TPC signalling.
`FIG. 3 illustrates a wireless communication system using a
`closed loop scheme. The closed loop scheme includes an
`outer loop in which a UE transmits 300 user data over the
`radio link in an uplink signal 302 that contain the user data
`304. The network determines 306 an error metric of the
`received uplink signal. Using the error metric, the network
`computes and updates 308 an SNIR Target value.
`The closed loop scheme also includes an inner loop in
`which the network measures 310 the received SNIR of the
`uplink signal 302. The network compares 312 the measured
`SNIR with the SNIR Target determined in the outer loop. The
`inner loop generates and transmits 314 a TPC command
`based on the comparison 312. A downlink signal 316 carries
`the TPC command 318 over the radio link. The UE accumu-
`lates 320 the TPC commands and uses the accumulated TPC
`commands to set 322 a transmit power for future uplink
`transmissions 300.
`A mobile radio system employing either an open loop
`scheme or a closed loop scheme has its advantages and dis-
`advantages.
`The open loop scheme advantageously adapts quickly to
`path loss changes. If the path loss is observed to have wors-
`ened, for example by 15 dB in one 10 ms interval, the transmit
`power may be adjusted accordingly. A further advantage is
`that the open loop may continue to be partially updated in the
`absence of user-specific feedback signalling. For example,
`when a UE does not receive updated SNIR Target values, the
`outer loop pauses but changes in the path loss may continue to
`be tracked.
`Disadvantageously, the timeslot interference level