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淘豆网网友近日为您收集整理了关于Combined Beamforming and Space-Time Block Coding for High Speed Wireless municati的文档，希望对您的工作和学习有所帮助。以下是文档介绍：Combined Beamforming and Space-Time Block Coding for High Speed Wireless municati Combined Beamforming and Space-Time Block Coding for High SpeedWireless municationsRobert H. Morelos-Zaragoza, Mohammad GhavamiAdvanced munication puter Science Laboratories, Inc.Takanawa Muse Bldg., 3-14-13 Higashi GotandaShinagawa-ku, Tokyo 141-0022, JAPAN(morelos,ghavami)@csl.sony.co.bination of a digital beamforming technique withspace-time block coding in an indoor wireless environment isthe purpose of this pa(来源：淘豆网[/p-.html])per. Uplink transmission is achieved byan omnidirectional mobile antenna, with signals arriving at thebase station having relatively wide angular spread. The spa-tial channel response, an estimate of the channel angular gainpattern, is obtained by using an array antenna at the base sta-tion. The array creates scanned multiple beams in azimuth andprovides the effective angular spread of the ing signals.These signals are assumed to be propagated in a(来源：淘豆网[/p-.html]) microcell radiochannel with a large number of single bounce -ponents. A simple algorithm estimates the number of beams fordownlink transmission, and the transmitter -work in the base station provides the required beams. Based onthe number of beams, different signals are transmitted simul-taneously. In particular, space-time block coding is applied tothe beams. The performance of the proposed method is studiedwith respect to the number of transmite(来源：淘豆网[/p-.html])d beams and of multi-ponents.KeywordsBeamforming, Transmit Diversity, Space-Time Block Coding.1. IntroductionMultipath fading is a phenomenon that makes reliable wirelesstransmission difcult [1]. bining -bine the signals from multipath antennas in a way that mitigatesfading. In most scattering environments, antenna diversity isa practical, effective and hence widely applied technique. Theclassical approach is to use multiple antennas at the receive(来源：淘豆网[/p-.html])rand bining or selection and switching in order toimprove the quality of the received signal. Transmit diversity,and most recently space-time block (STB) coding, using multi-ple transmit antennas, have been studied in many recent studies(see, e.g., [2]-[8] and references therein), and shown to providean improvement in wireless system performance equivalent tothat of maximum bining diversity schemes.Adaptive beamforming using antenna arrays is widel(来源：淘豆网[/p-.html])y usedto reduce interference and mitigate multipath fading, hence im-prove capacity. Adaptive arrays cancel ponentsof the desired signal and remove interfering signals that havedifferent directions of arrival from the desired signal [6]-[8].Beamforming in conjunction with space-time block coding isbriey considered in ref. [9], where the authors show that or-thogonal transmit diversity can also be applied to beams. Anextension of the space-time tran(来源：淘豆网[/p-.html])smit diversity approach, to thecase of beamforming using two distinct beams, was proposedin ref. [10]. It is shown that two space-time coded beams im-prove downlink performance, compared to the conventional sin-gle beam and two antenna transmitting scheme. Also, ref. [11]shows that beamforming can bined with space-time cod-ing to achive full diversity.In this paper, we propose the introduction of a controllednumber of beams in STB coding. This appr(来源：淘豆网[/p-.html])oach is refered toas beam STB (BSTB) coding. The basic steps in the proposedmethod are as follows: Very fast¤§beam scanning with 3 sets of linear arrayelements. Processing the output power of the -works for estimating the channel spatial gain pattern(CSGP). Estimating the number of beams and their correspondingangles. BSTB coding of the signals and distribution of the mes-sages onto time slots for downlink transmission frombase station (B(来源：淘豆网[/p-.html])S). BSTB decoding of the received signals at the mobile sta-tion (MS).It will be shown that, by applying ¨ -PSK modulations (inparticular, QPSK and 8-PSK are considered herein), the errorperformance of the system is improved by increasing the num-ber of beams, according to spatial channel conditions, and pro-vided that the number of ponents (or scatteringelements) is sufciently large in order to have diversity gain.The remainder of this paper (来源：淘豆网[/p-.html])anized as follows. Insection 2, a beamforming method to produce scanned beamsat¤ is described. Section 3 details the CSGP estimation anda method to decide the number of beams. In section 4, BSTBcoding is explained and, in section 5, simulation results are pre-sented. Finally, section 6 concludes the paper.2. Narrowband BeamformingFigure 1 shows a simplied diagram of a¤ narrowbandbeamformer employed at the BS for estimation of the arrivala(来源：淘豆网[/p-.html])ngles. Each antenna element is connected to plex weight ,
denotes the number of elementsin each of these sectors. During reception, the weighted signalsare summed together making an output signal as follows [12]:Figure 1: Conguration of the BS array antenna system.&!$#&%(')0§132 !
%@ACBEDGFIHP (1)where 4 !$#&% is the received signal at the rst element, @ is the dis-tance between elements,Ais the propagation speed and H is theangle of arrival (AOA) for the main sector, 8 ¤
HRQ ¤ .We note that other two array sectors, operating for 8 TS¤ HUQV8 ¤and¤ HUQ TS¤§, are essentially the same as therst one and hence, attention is paid only to the main sector.In the frequency domain, equation (1) can be written as fol-lows: W!YXa`&H§%(')0§132 5b !YXc%edgfghpieqr§sf2utTvw3x$y a(2)or !YXa`EH%'W!YXa`&H§%b !YXc%')0§132
d fghpieq§rsf2utvw3x$y a(3)For narrowband beamforming, X is a constant and H is vari-able. For the beam to be directed toward the desired directionH , we have'd hpieq§rsf2utTvw x$y aEg(4)In other words, for H'H
, equation (3) reduces to!YXa`&H%'
(5)which is the maximum attainable amplitude by beamforming.Figure 2 shows the normalized !YXa`&H%
' ¤ ,
'¤,A' ¤m/s, X'V GHz and @'ATdX' ¤mm. Thesharpness of the beams reduces considerably for
H e¤§,reason why H
is limited to
g¤ .80 60 40 20 0 20 40 60 80 10 010Angle, degreesNormalizedpower,dBFigure 2: Direction pattern of the simple narrowband beam-former.3. Estimation of the CSGPTo include beamforming and the estimation of angular spreadin the system under consideration, we have to employ achannel model which creates not only plex gain, but alsothe AOA for each path. This channel model is used for thepurpose of simulation and for producing ing signals atthe BS receiver array antenna. An appropriate candidate isthe method of geometrically based single bounced (GBSB)model [13]. This model is useful for microcell indoor systemswith low transmitter and receiver antenna heights, and also forcode division multiple access (CDMA) cellular radio systemsapplying adaptive antennas and switched beams systems atthe BS. Main parameters in the GBSB modeling include theseparation between transmitter and receiver, the pass lossexponent, the reference power, the reection loss and thenumber of ponents. Figure 3 demonstrates atypical power-angle prole generated using the GBSB model.The estimation of CSGP is done using a set of switchedbeams in three d ¤ sectors. There are totally f beams witha separation angle of¤
f . The output powers of each
fbeamformers are used for determination of the number of beamsrequired for downlink beamforming and their respective angles.Figure 4 shows the estimated CSGP of the channel indicated ingure 3 with
f ' . The gure is normalized for a maximumgain of 0 dB. As indicated in gure 4, the result of switchedbeamforming is a piecewise linear function of angle,hg!iH§% for8 TS¤§ HjQ S¤§. The next step is to distinguish the peakpoints of this function. This is done by monitoring the signchanges in a discrete differentiation of5g!iH§% , for values whichare larger than a selected threshold levelth, below the maxi-mum gain. The case ofth'k8 ¤dB in gure 5 shows thebeampattern of the BS transmitter work. Fivebeams, with angles of departure (AOD) of -85, -25, 5, 25 and85 degrees are required for transmission. The spatial channelis characterized by the number of beams and the correspond-ing beam angles, as obtained in the method described above.It remains a task of the BS transmitter to perform BSTB cod-ing, according to the number of beams selected by the adaptivealgorithm. This is the topic of the next section.Figure 3: A typical power-angle prole of the GBSB modelingalgorithm.4. BSTB CodingVarious transmit diversity schemes have been proposed inthe past (notably, the pioneering work reported in [14]-[16].See also [5] and references cited therein.) Space-time bines coding techniques at the multiple-antenna transmitterwith signal processing at the receiver. Space-time blockcoding was introduced in [2] in order to reduce the plexity.The BSTB coding method proposed in this paper is basedon both Alamouti’s scheme [2] (for two beams) and Tarokh etal. [5] (for three and four beams). In the notation of [5], we useli ,hmandhn, with code rate 1, 3/4 and 3/4 (in symbols/timeslot), for two, three and four transmitted beams, respectively.Extensions to higher number of beams is relatively straight for-ward, although a coding rate loss will be present if full diversityis to be achieved. The main idea in space-time block coding isthat the transmission matricesli ,hmandhnhave orthogonalcolumns. This in turn means that, at the receiver, the signals ar-riving from different beams can be decoupled with simple linearprocessing.4.1. Alamouti’s scheme for two beamsIn this section, we illustrate BSTB coding and decoding. Con-sider two transmitted beams. Alamouti’s scheme uses the trans-mission matrixli'porqs 2 qsi&t` where qs 2 'uo 4v2 8 4cwi tyx ,qsi'zo 4i4 w2 t x , and 4v2 , 4i are plex symbols car-rying the information. The physical interpretation of transmis-sion vectors qsh , { '
`d, is that symbols 4v2 and 8 4cwi are sentwith the rst beam, while 4i and 4cw2 are transmitted through thesecond beam, at times # and #}|~ , respectively, where ~ is thesymbol duration. At the mobile station, the superpositions ofthe signals from the two beams, received at times # and #e|j~ ,are !$#
%'2 '
2&4v2 |i4i|
|~% 'i' 8I}2 4 wi|i4 w2 |
i`150 100 50 0 50 100 150 8 64 20AOA, degreesNormalizedpower,dBFigure 4: Normalized estimate,hg!iH% , of the CSGP of thechannel of gure 3. The threshold of -10 dB is also indicatedby a horizontal line.respectively, where } ,
`d, are samples of an AWGN pro-cess.The BSTB bines the received symbols, usingestimates of plex channel gains, and produces the fol-lowing metrics which are used to obtained the estimates, 4 2 and4i , of the transmitted symbols 2 '
2 w2 | iwi`i' iw28 2wiBecause !&qsw2 %xqsi' ¤holds,li is said to be plex gene-ralized orthogonal design that provides unitary coding rate,with a diversity equivalent to maximum bining withtwo receive antennas.4.2. General BSTB coding schemesAlamouti’s scheme can be generalized to any number of trans-mit beams,
, to achieve full diversity, at the expense of redu-cing the coding rate [5]. In general, a rate-BSTB code has,for C , a
transmission matrix with entries equalto a symbol 4
, or its conjugate 4 w , or binations of 4 and 4w .The fundamental difference between the methods of [2] and[5] and BSTB coding here is that coding is done for beams of anadaptive antenna array, as opposed to diversity antenna systems,with xed elements. Since in the proposed method the numberof beams determines the coding scheme and diversity, basedon channel characteristics, this method may be considered anadaptive BSTB coding technique.5. Simulation ResultsFor the purpose of simulations in this section, the number oftransmitted beams is limited to a maximum of four. For eachresult reported, ¤ntransmissions were simulated. The asssign-ment of one or two transmitted beams (coding rate equal to one)applies QPSK modulation (a bandwidth efciency of 2 bps/Hz),while for three and four transmitted beams (coding rate equal to3/4), 8-PSK modulation is employed (2.25 bps/Hz). The para-meters of the GBSB model were set as shown in Table 1.150 100 50 0 50 100 150 5 05 10AOD, degreesNormalizedpower,dBFigure 5: Five beams at -85, -25, 5, 25 and 85 degrees are se-lected based on the data obtained from gure 4 from the channelresponse of gure 3.Table 1: Main parameters in the GBSB model.Parameter Symbol ValueCarrier frequency X
¤Max. normalized delay2Path loss exponent
4Dist. Tx to Rx @ 1-100 5.1. Distribution of number of beamsIn this section, we study the empirical distribution of the num-ber of beams transmitted, as a function of the number of multi-ponents
and the gain thresholdU. Computer sim-ulations of ¤nchannel transmissions were performed using theGBSB model[13]. Figure 6 shows the relative frequency of thenumber of beams for values of thresholdth' ¤ `
` (dB)and increasing number of ponents
. Comparedto two-beam only transmission [10], as the threshold value isincreased, more beams are used for transmission, resulting inincreased diversity. The middle plot in gure 6 shows that ponents uniformly distributed between 11 and 25,and threshold value increased from 10 dB to 13 dB, the distri-bution of the number of beams es more uniform. With athreshold value of 16 dB, in 50% of the cases four beams are se-lected. Consequently, error performance is improved, becausemore spatial diversity is achieved.These results conrm that greater diversity is achieved inrich multipath environments. As evidenced by gure 6 (bottomplot), with uniformly distributed ponents in therange od
`& ¤t andth' dB, about 70% of the blocks utilizefour beams. As a result, more spatial diversity is obtained. Thisobservation is substantiated by the simulated error performanceresults reported in the next section.5.2. Error performanceIn this section, error rate performance of the proposed schemeis studied. Perfect channel estimation at the mobile is assumed.1 2 3 4 00.2 0.4 0.6 0.8L ∈[4,10]Rel.frequency10 dB13 dB16 dB1 2 3 4 00.2 0.4 0.6 0.8L ∈[11,25]Rel.frequency10 dB13 dB16 dB1 2 3 4 00.2 0.4 0.6 0.8L ∈[26,40]Rel.frequencyNo. of beams10 dB13 dB16 dBFigure 6: Histogram of the number of beams obtained puter simulations using the GBSB model, as a function ofthe gain threshold value (in dB) and number of -ponents,
o ` ¤t , middle:
`dt , bottom: od
`& ¤t .As mentioned before, in puter simulations, the GBSBmodel[13] is used in the uplink for the BS to determine the re-quired number of beams. Based on puted number ofbeams,
, space-time block coding is applied. For the purposeof simulations,
was limited to a maximum value of 4. In thedownlink, it is assumed that the
beams have uncorrelatedfrequency non-selective Rayleigh distributed fading amplitudesfrom block to block (a block has length
'd`e and
de-pending on the number of beams transmitted
'd` and , respectively.) In other words, the channel coherence timeis assumed to be larger than the length of a block. Also, wenote that line-of-sight (LOS) is used in the GBSB model. Thetransmitted power is evenly distributed among the beams, as inconventional multiple transmit antennas.Figure 7 shows a plot of the bit (BER) error rates for theproposed method with the GBSB model parameters as in Ta-ble 1 and d
`& ¤§. The thresholdth was set to 10and 16 dB. Larger diversity translates into better error perfor-mance, as the parameterth increases. As indicated previously,the bandwidth efciency increases with the number of transmit-ted beams, from 2 bps/Hz with
`d, to 2.25 bps/Hz with
`E . In the simulations reported in gure 7, the aver-age efciency was 2.101577 bps/Hz and 2.205340 bps/Hz, forth' ¤dB andth' dB, respectively. The effect ofthe difference in bandwidth efciency has been taken into ac-count in the average g
. From gure 7, we conclude thatan improvement of 2 to 3 dB in average signal-to-noise ratio isachieved, at a BER of ¤ fm, with a thresholdth set at pared to ¤dB.6 8 10 12 14 16 18 103 102 101Eb/N0(dB)BER10 dB16 dBFigure 7: BER performance of BSTB coding with5$equal to10 dB and 16 dB.6. ConclusionsAn adaptive scheme for assignment of the number of employedbeams was proposed for downlink transmission in an munication channel. Data for determination of thisnumber are obtained by a triangular sectored switched beam ar-ray at the base station providing an estimate of the indoor chan-nel condition. The number of peak points of this estimationand a prescribed gain threshold level, give the required beamsthrough the whole azimuth angles. The resulting adaptive beam(or angle) diversity is employed for space-time block coding ofthe downlink signal transmission.It has been shown that an increase in the gain threshold,which is used pute the number of transmission beams,results in a larger diversity factor and therefore in better per-formance, compared with a xed assignment of the number ofbeams. Because plexity of BSTB coding is low, con-catenation with powerful error correcting coding schemes canbe applied, in a similar way as in conventional multiple trans-mit antenna diversity systems [17]-[20]. Also, the average datarate of a BSTB coding system can be increased by assigningmore beams in the munication and using modula-tion sets of higher density. The proposed method constitutes anadvantageous approach in wireless munication sys-tems with a large angular spread.7. References[1] W.C.Y. Lee, Mobile munications, McGrawHill Publications, 1995.[2] S.M. Alamouti, “A Simple Transmit Diversity Techniquefor munications,” IEEE JSAC, vol. 16, no.8, pp. , Oct. 1998.[3] V. Tarokh, N. Seshadri and A.R. Calderbank, “Space-Time Codes for High Data Rate muni-cation: Performance Criterion and Code Construction,”IEEE Trans. Info. Theory, vol. 44, no. 2, pp. 744-764, Mar.1998.[4] A. M. Tehrani, R. Negi and J.M. Ciof, “Space-Time Cod-ing and Transmission Optimization for Wireless Chan-nels,” Proc. 32nd Asilomar Conf. on Signal, System puters, vol. 2, pp. , 1998.[5] V. Tarokh, H. Jafarkhani and A.R. Calderbank, “Space-Time Block Coding for munications: Per-formance Results,” IEEE JSAC, vol. 17, no. 3, pp. 451-460, March 1999.[6] J.C. Liberti and T.S. Rappaport, Smart Antenna for Wire-munications: IS-95 and Third Generation CDMAApplications, Prentice Hall, 1999.[7] P. van Rooyen, M. Loetter and D. van Wyk, Space-TimeProcessing for CDMA munications, KluwerAcademic Publishers, 2000.[8] R. Kohno, “Spatial and munication TheoryUsing Adaptive Array Antenna,” IEEE m.Mag., pp. 28-38, February 1998.[9] T. Lo and V. Tarokh, “Space-Time Block Coding – From aPhysical Perspective,” Proc. 1999 IEEE m.working Conf. (WCNC’99), vol. 1, pp. 150-153,1999.[10] M. Katz and J. Ylitalo, “Extension of Space-Time Codingto Beamforming WCDMA Base Stations,” in Proc. IEEEVTC’2000-Spring, pp. , May 2000.[11] R. Negi, A.M. Tehrani and J. Ciof, “Adaptive Antennasfor Space-Time Coding Over Block-Time Invariant Multi-Path Fading Channels,” Proc. IEEE VTC 1999, pp. 70-74,1999.[12] B. D. Van Veen and K. M. Buckley, “Beamforming:A Versatile Approach to Spatial Filtering,” IEEE ASSPMag., pp. 4-24, April 1988.[13] J.C. Liberti and T.S. Rappaport, “A Geometrically BasedModel for Line-of-Sight Multipath Radio Channels,”Proc. IEEE ICUPC’96, pp. 844-848, 1996.[14] A. Wittneben, “Base Station Modulation Diversity forDigital Simulcast,” Proc. IEEE VTC’91, pp. 848-853,May 1991.[15] N. Seshadri and J. Winters, “Two Signalling Schemesfor Improving Error Performance of FDD TransmissionSystems Using Transmit Antenna Diversity,” Proc. IEEEVTC’93, pp. 508-511, May 1993.[16] V.M. DaSilva and E.S. Sousa, “Fading-Resistant Modu-lation Using Several Transmitter Antennas,” IEEE m., vol. 45, no. 10, pp. , Oct. 1997.[17] S.M. Alamouti, V. Tarokh and P. Poon, “Trellis-CodedModulation and Transmit Diversity: Design Criteria andPerformance Evaluation,” Proc. ICUPC’98, pp. 703-707,1998.[18] G. Bauch, “Concatenation of Space-Time Block Codesand ‘turbo’-TCM,” Proc. ICC’99, pp. , June1999.[19] T.H. Liew, J. Pliquett, B.L. Yeap, L. Yang and L. Hanzo,“Concatenated Space Time Block Codes and TCM, TurboTCM, Convolutional as well as Turbo Codes,” Proc. 2000, pp. , San Francisco, Nov.2000.[20] Y. Liu, M.P. Fitz and O.Y. Takeshita, “Full Rate Space-Time Turbo Codes,” IEEE JSAC, vol. 19, no. 5, pp. 969-980, May 2001.播放器加载中，请稍候...
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Combined Beamforming and Space-Time Block Coding for High Speed Wireless municati Combined Beamforming and Space-Time Block Coding for High SpeedWireless municationsRobert H. Morelos-Zaragoza, Mohammad GhavamiAdvanced munication puter Science Laboratories, Inc.Takanawa Muse Bldg., 3-14-13 Higashi Go...
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