United States Patent
`US 7,155,231 B2
`(10) Patent No.:
`(12)
`Burkeet al.
`(45) Date of Patent:
`*Dec. 26, 2006
`
`
`US007155231B2
`
`(54) TRANSMIT PRE-CORRECTION IN A
`WIRELESS COMMUNICATION SYSTEM
`
`(75)
`
`Inventors: Joseph P. Burke, Carlsbad, CA (US);
`Michael J. Wengler, Carlsbad, CA
`(US); Bhaskar D. Rao, San Diego, CA
`(US); Harris S. Simon, Poway, CA
`(US)
`
`.
`.
`(73) Assignee: Qualcomm, Incorporated, San Diego,
`CA (US)
`;
`,
`;
`Subject to any disclaimer, the term ofthis
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 390 days.
`
`;
`(*) Notice:
`
`This patent is subject to a terminal dis-
`claimer.
`(21) Appl. No.: 10/271,934
`(22)
`Filed:
`Oct. 15, 2002
`(65)
`Prior Publication Data
`US 2003/0153322 Al
`Aug. 14, 2003
`
`Related U.S. Application Data
`(60) Provisional application No. 60/355,296,filed on Feb.
`8 2002
`°
`
`.
`
`(51)
`Int. Cl.
`(2006.01)
`HO4Q 7/20
`(52) U.S. Ch oes 455/450; 455/67.14; 342/423;
`375/357
`,
`,
`,
`(58) Field of Classification Search ................ 455/450,
`455/67.11, 67.14, 423, 424, 425; 342/111,
`342/129, 423, 430, 432, 444, 463; 375/296,
`oo.
`375/355 356, 357
`See application file for complete search history.
`References Cited
`
`(56)
`
`U.S. PATENT DOCUMENTS
`
`.......... 455/67.14
`1/1996 Mahany et al.
`5,483,676 A *
`........... 370/310
`5,828,658 A * 10/1998 Ottersten et al.
`5,930,288 A *
`7/1999 Eberhardt ........ 375/148
`11/1999 Vook et al. eee 342/380
`5,982,327 A *
`
`3/2000 Sumner .......... ee 455/412.2
`6,041,227 A *
`6,118,983 A *
`9/2000 Egusa et al. oe 455/69
`6,426,960 Bl
`7/2002 Antonio
`......00.... 455/69
`6,434,366 B1*
`8/2002 Harrison et al.
`6,615,024 B1*
`9/2003 Boroset al... 455/67.14
`.......... 455/562.1
`6,665,545 BL* 12/2003 Raleigh et al.
`
`3/2004 Tellado et al. we. 455/506
`6,711,412 B1*
`6,747,594 BL*
`6/2004 Lindskog et al.
`........... 342/174
`
`.
`.
`* cited by examiner
`Primary Examiner—Charles N Appiah
`Assistant Examiner—Nghi H. Ly
`Gockey Agent, orFirm—Philip Wadsworth; Sandra L.
`(57)
`ABSTRACT
`
`Techniques for pre-correction of transmit signals are dis-
`closed. In one aspect, a transmit antenna array configurable
`to generate multiple transmit beamsis deployed. The param-
`eters for configuring the antennalaw. areomer’ m
`response to c anne. estimates and a noise | oor estimate
`made at the receiver. Information is transmitted in accor-
`dance with the multiple transmit beams, delayed as neces-
`.
`vo
`:
`sary, such that the multipaths may arrive time-aligned an
`in-phase at the receiver. In another aspect,
`pre-RAKE pre
`phase
`a depl
`db
`Iculati Wi
`> Pre-'
`hts.
`I P
`correction is deploye
`oy calcu ating Wiener weig,
`ts.
`In yet
`another aspect, space-time diversity is deployed for calcu-
`lating tap values for FIRfilters used in transmission on the
`transmit antenna array. In yet another aspect, space only
`pre-correction is deployed. Various other aspects are also
`disclosed. These aspects have the benefit of reducing the
`interference experiencedat a receiver, resulting in increased
`capacity increased data throughput, and other system ben-
`efits.
`
`4,780,721 A * 10/1988 Dobson .........cceeeeee 342/178
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`44 Claims, 17 Drawing Sheets
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`US 7,155,231 B2
`
`1
`TRANSMIT PRE-CORRECTIONIN A
`WIRELESS COMMUNICATION SYSTEM
`
`CLAIM OF PRIORITY UNDER 35 U.S.C. §119
`
`The present Application for Patent claims priority to
`Provisional Application No. 60/355,296, entitled “TRANS-
`MIT PRE-CORRECTION IN A WIRELESS COMMUNI-
`
`CATION SYSTEM,”filed Feb. 8, 2002, and assigned to the
`assignee hereof and hereby expressly incorporated by ref-
`erence herein.
`
`BACKGROUND
`
`1. Field
`The present invention relates generally to wireless com-
`munication, and more specifically to an improved method
`and apparatus for space-time pre-correction of transmitted
`wireless signals.
`2. Background
`Wireless communication systems are widely deployed to
`provide various types of communication such as voice and
`data. These systems may be based on code division multiple
`access (CDMA), time division multiple access (TDMA), or
`some other modulation techniques. A CDMA system pro-
`vides certain advantages over other types of systems, includ-
`ing increased system capacity.
`ACDMA system maybe designed to support one or more
`CDMA standards such as (1) the “TIA/EIA-95-B Mobile
`Station-Base Station Compatibility Standard for Dual-Mode
`Wideband Spread Spectrum Cellular System” (the IS-95
`standard), (2) the standard offered by a consortium named
`“3rd Generation Partnership Project” (GPP) and embodied
`in a set of documents including Document Nos. 3G TS
`25.211, 3G TS 25.212, 3G TS 25.213, and 3G TS 25.214
`(the W-CDMAstandard), (3) the standard offered by a
`consortium named “3rd Generation Partnership Project 2”
`(3GPP2) and embodied in a set of documents including
`“C.S0002-A Physical Layer Standard for cdma2000 Spread
`Spectrum Systems,” the “C.S0005-A Upper Layer (Layer 3)
`Signaling Standard for cdma2000 Spread Spectrum Sys-
`tems,” and the “C.S0024 cdma2000 High Rate Packet Data
`Air Interface Specification” (the cdma2000 standard), and
`(4) some other standards. Systems may incorporate support
`for delay-sensitive data, such as voice channels or data
`channels supported in the IS-2000 standard, along with
`support for packet data services such as those described in
`the IS-856 standard. One such system is described in a
`proposal submitted by LG Electronics, LSI Logic, Lucent
`Technologies, Nortel Networks, QUALCOMM Incorpo-
`rated, and Samsung to the 3rd Generation Partnership
`Project 2 (3GPP2). The proposal is detailed in documents
`entitled “Updated Joint Physical Layer Proposal for 1xEV-
`DV”, submitted to 3GPP2 as document number C50-
`20010611-009, Jun. 11, 2001; “Results of L3NQS Simula-
`tion Study”, submitted to 3GPP2 as document number
`C50-20010820-011, Aug. 20, 2001; and “System Simulation
`Results for the L3NQS Framework Proposal for cdma2000
`1x-EV-DV”, submitted to 3GPP2 as document number
`C50-20010820-012, Aug. 20, 2001. These are hereinafter
`referred to as 1xXEV-DV. Non-CDMAsystems include the
`AMPSand GSMsystems.
`Multipath is a condition that occurs when a transmitter
`transmits a single signal that is then received at a receiver
`through multiple signal paths, each having a different length.
`The difference in the lengths of the paths may causedifferent
`copies of the signal to arrive at different times, causing
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`inter-channel interference. Various techniques are known in
`the art for combating multipath interference. One example is
`a RAKEreceiver. A RAKE receiver attempts to separate
`interfering multipaths and combine them to improve
`receiver performance.
`Given the limited amount of spectrum available to com-
`munication carriers,
`it
`is desirable to increase the data
`throughput for the given amount of power in a given
`frequency band. Doing so may increase data rates, increase
`capacity, and/or reduce power(and potentially reduce costs
`in communication equipment). For example, due to expected
`asymmetric data rates on the forward link versus the reverse
`link of a CDMA system,there is interest in increasing the
`forward link system capacity and/or data throughput via
`spatial signal processing techniques. For example, transmit
`antenna arrays are being deployed to achieve gains.
`However, it would be desirable if multi-path interference
`could be reduced or eliminated before it occurred,
`thus
`reducing or eliminating the need for multipath mitigating
`processing at the receiver, as well as improving the overall
`capacity and/or throughput of the system. There is, there-
`fore, a need in the art for pre-correction of transmit signals
`to reduce multipath interference.
`
`SUMMARY
`
`Embodiments disclosed herein address need in the art for
`pre-correction of transmit signals to reduce multipath inter-
`ference. In one aspect, a transmit antenna array configurable
`to generate multiple transmit beamsis deployed. The param-
`eters for configuring the antenna array are computed in
`response to channel estimates and a noise floor estimate
`made at the receiver. Information is transmitted in accor-
`
`dance with the multiple transmit beams, delayed as neces-
`sary, such that the multipaths may arrive time-aligned and
`in-phase at the receiver. In another aspect, pre-RAKE pre-
`correction is deployed by calculating Wiener weights. In yet
`another aspect, space-time diversity is deployed for calcu-
`lating tap values for FIR filters used in transmission on the
`transmit antenna array. In yet another aspect, space only
`pre-correction is deployed. Various other aspects are also
`disclosed. These aspects have the benefit of reducing the
`interference experiencedat a receiver, resulting in increased
`capacity, increased data throughput, and other system ben-
`efits.
`
`The invention provides methods and system elements that
`implement various aspects, embodiments, and features of
`the invention, as described in further detail below.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`The features, nature, and advantages of the present inven-
`tion will become more apparent from the detailed descrip-
`tion set forth below when taken in conjunction with the
`drawings in which like reference characters identify corre-
`spondingly throughout and wherein:
`FIG. 1 is a general block diagram of a wireless commu-
`nication system capable of supporting a numberofusers;
`FIG. 2 depicts a portion of a wireless communication
`system for transmitting along multiple paths;
`FIG. 3 depicts one embodiment of a base station;
`FIGS. 4A-4C depict transmit frame formats;
`FIG. 5 depicts a signal conditioner for use with simulta-
`neously transmitted pilot and data;
`FIG. 6 depicts a pre-correction processor;
`FIG. 7 depicts a signal conditioner for use with pre-
`corrected data and pilot bursts;
`
`Exhibit 1006
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`US 7,155,231 B2
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`3
`to a PN
`FIGS. 8A-8C depict alternatives for input
`spreader, depending on the forward link channel structure
`chosen;
`FIG. 9 depicts a signal conditioner for space time pre-
`correction;
`FIG. 10 depicts a signal conditioner for space only
`pre-correction for use with simultaneously transmitted pilot
`and data;
`FIG. 11 depicts a signal conditioner for space only pre-
`correction for use with pre-corrected data and pilot bursts;
`FIG. 12 depicts one embodiment of a mobile station;
`FIGS. 13A and 13B depict portions of demodulators;
`FIG. 14 depicts a flowchart of an embodiment of a method
`of transmission, adaptable for use with any of the embodi-
`ments described herein;
`FIG. 15 depicts a flowchart of an embodiment of a method
`of computing beam forming parameters for use with space
`only pre-correction;
`FIGS. 16A and 16B depict embodiments of methods of
`signal conditioning; and
`FIG. 17 depicts a flowchart of an embodiment of a method
`of receiving, adaptable for use with any of the embodiments
`described herein.
`
`DETAILED DESCRIPTION
`
`FIG.1 is a diagram of a wireless communication system
`100 that may be designed to support one or more COMA
`standards and/or designs (e.g., the W-CDMAstandard, the
`IS-95 standard, the cdma2000 standard, the HDRspecifica-
`tion). For simplicity, system 100 is shown to include three
`base stations 104 in communication with two mobile sta-
`
`tions 106. The base station and its coverage area are often
`collectively referred to as a “cell”. In IS-95 systems, a cell
`mayinclude one or moresectors. In the W-CDMA specifi-
`cation, each sector of a base station and the sector’s cover-
`age area is referred to as a cell. As used herein, the term base
`station may be used interchangeably with the terms access
`point or NodeB. The term mobile station may be used
`interchangeably with the terms user equipment (UE), sub-
`scriber unit, subscriber station, access terminal, remote
`terminal, or other corresponding terms knownin the art. The
`term mobile station encompasses fixed wireless applica-
`tions.
`
`Depending on the CDMA system being implemented,
`each mobile station 106 may communicate with one (or
`possibly more) base stations 104 on the forward link at any
`given moment, and may communicate with one or more base
`stations on the reverse link depending on whetheror not the
`mobile station 106 is in soft handoff. The forward link (1.e.,
`downlink) refers to transmission from the basestation to the
`mobile station, and the reverse link (i.e., uplink) refers to
`transmission from the mobile station to the base station.
`
`For clarity, the examples used in describing this invention
`may assumebasestations as the originator of signals and
`mobile stations as receivers and acquirers of those signals,
`i.e. signals on the forward link. Those skilled in the art will
`understand that mobile stations as well as base stations may
`be equipped to transmit data as described herein and the
`aspects of the present invention apply in those situations as
`well. The word “exemplary” is used exclusively herein to
`mean “serving as an example, instance, orillustration.” Any
`embodimentdescribed herein as “exemplary” is not neces-
`sarily to be construed as preferred or advantageous over
`other embodiments.
`
`Though discussed primarily in the context of a wireless
`communication system, a mobile station (or fixed subscriber
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`station) may also communicate through a wired channel, for
`example using fiber optic or coaxial cables. A mobile station
`mayfurther be any of a numberof types of devices including
`but not limited to a PC card, compact flash, external or
`internal modem, or wireless or wireline phone.
`FIG. 2 depicts a portion of wireless communication
`system 100 in which a basestation 104, having a plurality
`of transmit antennas 110A—110M,sendssignals to a mobile
`station 106, having a receive antenna 112,
`through two
`signal paths 150 and 160. Base station 104 transmits signals
`through the antennas 110 such that transmit beam 130 is
`created for transmitting signals along signal path 150. At the
`same time, base station 104 transmits signals through the
`antennas 110 such that transmit beam 132 is created for
`
`along signal path 160. Though
`transmitting signals
`described in terms of two signal paths (150 and 160), the
`techniques described below extend to any numberofsignal
`paths.
`The formation of transmit beams by adapting signals
`transmitted through multiple antennas, called beam forming,
`is well knownin the art. Antenna beam patternsare typically
`shown radiating from a central point of transmission, with
`the distance of the curve from the central point indicating the
`relative strength of a signal transmitted through the antenna.
`For clarity, the base station 104 and associated antennas 110
`are drawn to the left of the antenna beam patterns 130 and
`132. In actuality, the antennas 110 would be placed in the
`center 140 of the antenna beam patterns 130 and 132, rather
`than in their center 140.
`In the example shown, antenna beam pattern 130 is
`characterized by a primary lobe 130A and twoside lobes
`130B and 130C. Similarly, antenna beam pattern 132 is
`characterized by a primary lobe 132A and twoside lobes
`132B and 132C. Primary lobe 130A extends further from
`center 140 than either side lobe 130B or 130C, indicating
`that a signal transmitted through antenna beam pattern 130
`will be strongest in the direction of the primary lobe 130A.
`As shown, antenna beam pattern 130 is formed such that
`primary lobe 130A points in the direction of signal path 150.
`Sunilarly, antenna beam pattern 132 is formed such that
`primary lobe 132A points in the direction of signal path 160.
`In one embodiment, delays are applied to the signals trans-
`mitted along the different signal paths such that they arrive
`at the antenna 112 ofthe receiving mobile station 106 at the
`same time. In this way, the effects of multipath transmission
`may be mitigated.
`Between the lobes of an antenna beam pattern there exists
`a null, in which the signals transmitted through antennas 104
`destructively interfere with each other. For example, in the
`antenna pattern 130, nulls exist between lobes 130A and
`130B, between lobes 130B and 130C, and between 130C
`and 130A. In an embodiment, antenna beam pattern 130 is
`formed such that its primary lobe 130A is placed within or
`nearly within the null between lobes 132A and 132B of
`antenna beam pattern 132. Similarly, antenna beam pattern
`132 is formed such that its primary lobe 132A is placed
`within or nearly within the null between lobes 130A and
`130C of antenna beam pattern 130. Such careful arrange-
`ment of antenna beam patterns 130 and 132 reduces the
`degree to which the signals transmitted through each of the
`antenna beam patterns will interfere with each other when
`received at mobile station antenna 112.
`FIG. 3 is an embodimentofa base station 104. An array
`of M antennas (110A—110M,described above), are driven by
`M transmitters 350A—350M,respectively. Transmitted sig-
`nals are formatted in transmitters 350 according to one or
`more wireless system standards, such as those listed above,
`
`Exhibit 1006
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`Page 20 of 37
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`US 7,155,231 B2
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`5
`deployed in system 100. Examples of components that may
`be included in transmitters 350 are encoders, interleavers,
`spreaders, modulators of various types, amplifiers, filters,
`digital-to-analog (D/A) converters, radio frequency (RF)
`converters, and the like. One or more pilot signals and one
`or more data signals are delivered to signal conditioner
`block 320, where various processing, examples of which are
`described below,
`is performed to generate M signals for
`delivery to transmitters 350A—350M, respectively. Various
`parameters for use in generating the M signals for transmis-
`sion on the M-antenna array 110 are generated in pre-
`correction processor 310.
`The parameters are generated in response to information
`fed back from the mobile station 106 receiving the signals
`transmitted on antenna array 110. Received signals arrive at
`antenna 360 and are processed in receiver 370, in accor-
`dance with one or more systemsor standards, such as those
`referenced above. Alternative embodiments may deploy an
`array of antennas for antenna 360, or one or more antennas
`110 may be shared for receive and transmit. Examples of
`components that may be deployed in receiver 370 include
`RF downconverters, amplifiers,
`filters, analog-to-digital
`(A/D)converters, demodulators, RAKE receivers, combin-
`ers, deinterleavers, decoders (Viterbi, turbo, block decoders
`such as those implementing Bode-Chaudhury-Hocqueng-
`hem (BCH) codes, etc.), and others. Data from receiver 370
`is delivered to message decoder 380, where various signals
`or messages directed to the base station 104 from a mobile
`station 106 are decoded. In the present embodiment, the
`information sent to base station 104 includes channel infor-
`mation and noise floor information as estimated at
`the
`mobile station 106.
`Someor all of the functions of signal conditioner 320,
`transmitters 350, receiver 370, message decode 380, and
`pre-correction processor 310 maybe carried out in processor
`such as a Digital Signal Processor (DSP) or other general or
`special purpose processor (not shown). These functions may
`also be may also be performed using special purpose hard-
`ware, co-processors, a combination of processors or DSPs,
`or a combination ofall of the above. A processor, including
`pre-correction processor 310, will commonly contain, or be
`connected with, one or more memory elements 350 for
`storing instructions to carry out the various tasks and pro-
`cesses described herein as well as for data storage.
`Throughout this description, base station 104 will be
`described as communicating with a single user, or mobile
`station 106. This is for clarity. Those of skill in the art will
`recognize that the principles of the present invention also
`apply to multi-user systems, and a typical system 100 will be
`a multi-user system. Certain systems, such as the IS-856
`standard, use the entire available spectrum to transmit to one
`user at any given time. Other systems, such as IS-95 and
`cdma2000,
`transmit
`to multiple users
`simultaneously.
`Antennas 110A—110M may be used to transmit signals to
`one user or to multiple users simultaneously.
`The parameters generated by pre-correction processor
`310 may vary according to the particular embodiment
`deployed. Various
`embodiments
`are described below,
`including independent space and independent
`time pre-
`correction (also referred to as pre-RAKEprocessing), space-
`time pre-correction, and space only pre-correction. All of
`these pre-correction techniques fall within the scope of the
`present invention, and one or more of these techniques may
`be deployed in accordance with the type of system deployed.
`In an alternate embodiment, base station 104 may be
`deployed without pre-correction processor 310. The pre-
`correction parameters may be generated in an alternate
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`device, such as mobile station 106, and transmitted for
`application to signal conditioner 320 via antenna 360,
`receiver 370, and message decoder 380, as described above.
`This alternate embodiment is not shown.
`
`FIGS. 4A-4C depict three forward link channel struc-
`tures. In FIG. 4A, a per-antenna pilot burst is transmitted
`periodically through each transmit antenna. The basestation
`104 transmits signals within time slots, or frames, 412 of a
`fixed duration. Each timeslot is divided into two half-slots
`
`410A and 410B. In a cdma2000 system, time slots have a
`fixed length of 2048 symbol chips and a duration of 1.667
`milliseconds. Accordingly, each half-slot has a fixed length
`of 1024 symbol chips. One skilled in the art will recognize
`that alternate embodiments mayuseslots of different lengths
`or lengths that are not fixed in duration.
`In one embodiment, a per-antenna pilot burst 406 is
`transmitted through each transmit antenna at the center of
`each half-slot 410. The pilot bursts 206 are covered with
`antenna-specific codes to enable the mobile station to dis-
`tinguish the pilot received through each antenna. The
`antenna-specific codes are Walsh codes, with a different
`Walsh code being assigned to the pilot for each transmit
`antenna 110.
`In each frame 412,
`the base station 104
`transmits Medium Access Control (MAC) channel signals
`404 immediately before and after each pilot burst 406. The
`remaining portions 402 of each time slot 412 are used to
`carry forward link data.
`The data portions 402 ofthe time slot 412 are transmitted
`along multiple transmit beams 130 and 132, formed to
`transmit signals optimally through multipath signal paths
`150 and 160. Because the transmit paths 150 and 160
`generally have different lengths, signals transmitted through
`them take different amounts of time to reach the mobile
`station 106. In one embodiment, base station 104 advances
`or retards the signals transmitted through transmit beams
`130 and 132 as necessary to ensure that these signals arrive
`at the antenna 112 of the mobile station 106 at substantially
`the same time. Thus, someof the data portions 402 may be
`transmitted with variable delaysrelativeto the pilot portions
`406 and MACportions 404 of the time slot 412.
`Advancingor retarding the data portions 402 of the frame
`may result
`in some overlap of the data with the MAC
`portions 404 or the pilot burst portions 406 of the frame.
`Such overlap may cause substantial surges or spikes in the
`power required to transmit the composite signals. Such
`surges may overload a high power amplifier (HPA) in a
`transmitter or cause increased interference to signals in the
`coverage
`areas of neighboring base
`stations. Many
`approaches may be used for mitigating these surges. For
`example, a guard band may be placed between the data
`portions 402 and MACportions 404 of the frame (or
`alternatively, between the MAC portions 404 and the pilot
`portions 406, if the MAC portions are time shifted in the
`same manneras the data). The guard band would be wide
`enough to accommodate the largest probable difference in
`the lengths of the signal paths 150 and 160 (also referred to
`as “multipath spread”). For example, a guard bandof three
`chips might be enough to accommodate the multipath spread
`of a typical wireless communication system. Another
`approach to mitigating transmit power surges would be to
`truncate or gate the MAC portions 404 as necessary to avoid
`overlap with the data portions 402 of the frame. Alterna-
`tively, the data portions 402 could be truncated or gated in
`order to avoid such overlap. In another example, the over-
`lapping regions of the MAC portions 404 and the data
`
`Exhibit 1006
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`7
`portions 402 could be attenuated so that the power in the
`sum of the signals is approximately the same as in other
`portions of the frame.
`FIG. 4B showsan alternate forward link channel struc-
`ture. A pilot 430 is transmitted simultaneously with a data
`portion 420 during the entire frame. With this structure, the
`data may be coherently demodulated with the pilot signal
`that is simultaneously being transmitted. For clarity, a MAC
`portion is not shown, although one of skill in the art will
`readily adapt this to accommodate MACsignaling, or any
`other type of signaling that is desired. In one embodiment,
`both the pilot and data are time shifted to arrive at essentially
`the sametime at the mobile station 106. This is in contrast
`to the embodimentusing a structure as described in FIG. 4A,
`where the pilot was not time-shifted with the data. In the
`previous structure of FIG. 4A, the pilots from each of the
`various multipaths could be distinguished by their respective
`time offsets. In the structure of FIG. 4B, when the pre-
`correction processor is performing well, the pilots from each
`path will not be readily distinguishable, since they arrive at
`the same time. Therefore,
`in one embodiment using the
`frame structure of FIG. 4B, the pilot signal will be coded
`with a code per antenna, as before, as well as per path. Thus,
`an estimate of each path, with a component corresponding to
`each antenna for that path, may be made. Embodiments
`using each of the frame formats will be described in further
`detail below.
`FIG. 4C showsyet another alternate forward link channel
`structure. The structure includes all of the components of
`FIG. 4A, described above. The pilot portion 406 will be
`coded per antenna, and will not be time shifted. Pilot 406
`may thus be used for estimating the channel, as described
`above. An additional pilot 440 (shown in three sections,
`440A, 440B and 440C)is transmitted simultaneously with
`the data portions 402, and conditioned in the same manner.
`The additional pilot may be used for data demodulation (as
`maypilot 406). However, unless pilot 440 is covered with
`codes per path and per antenna, as described in FIG. 4B, or
`identified with an alternate technique, pilot 440 may not be
`as readily usable for channel estimation as pilot 406.
`The format of FIG.4C is essentially a blend of the formats
`shown in FIG. 4A and FIG.4B. One skilled in the art will
`
`recognize other variations on transmitting per-antenna pilot
`signals