The transmission of multimedia data over wireless systems generally require network devices designed with a high communication bandwidth, power, and processing resources. To deal with these bottlenecks commonly associated with multimedia transmission, various diversity coding schemes have been proposed. We have previously shown that wireless OFDM systems based on space-time block-coding with adaptive beamforming (STBC-OFDM-AB) are well suited to multimedia communication. Recent studies have shown further performance gains in systems utilizing space-time-frequency (STF) coding. In this paper, we introduce a transmission system which combines STF coding with adaptive beamforming (STF-OFDM-AB). Simulation results based on the transmission of compressed images showed that the performance improvements introduced by STF-OFDM-AB can be readily observed

Athanasiadis, T

Hussain, Z

Lin, K

RMIT Research Repository

Multimedia Transmission over Wireless Space-Time-Frequency coded OFDM
Systems with Adaptive Beamforming
Tasso Athanasiadis, Kevin H. Lin, and Zahir M. Hussain
School of Electrical and Computer Engineering, RMIT University
124 LaTrobe Street, Melbourne, Victoria 3000, Australia
E-mails: s890299 1 @ student.rmit.edu.au; s95 10490@ student.rmit.edu.au; zmhussain@ieee.org
Abstract high-rate multimedia data over existing wireless systems
- limited communication bandwidth, power, and process-
The transmission of multimedia data over wireless sys- ing capabilities. Also, in a wireless environment, the time-
tems generally require network devices designed with a varying nature of channel conditions and propagation char-
high communication bandwidth, power; and processing re- acteristics such as multipath fading, inherently subject wire-
sources. To deal with these bottlenecks commonly associ- less signals to intersymbol interference (ISI) leading to high
ated with multimedia transmission, various diversity coding bit error rates (BER) [1]. Moreover, the transmission of
schemes have been proposed. We have previously shown wireless data over band-limited multipath fading channels
that wireless OFDM systems based on space-time block- cause a degradation in both communication channel per-
coding with adaptive beamforming (STBC-OFDM-AB) are formance, system latency, and the acceptable or subjective
well suited to multimedia communication. Recent studies quality of data received on wireless terminals/devices.
have shown further performance gains in systems utilizing To support multimedia transmission through noisy wire-
space-time-frequency (STF) coding. In this paper; we in- less radio environments various key technologies have
troduce a transmission system which combines STF cod- emerged: compression systems such as, JPEG2000, MPEG,
ing with adaptive beamforming (STF-OFDM-AB). Simula- H.263/L [2]; 'adaptive' channel coding techniques [5],[6];
tion results based on the transmission ofcompressed images and transmit diversity schemes such as, space-time block
showed that the performance improvements introduced by coding (STBC) [3],[4]. However, any improvements in the
STF-OFDM-AB can be readily observed. error performance and capacity of wireless OFDM systems
can be mainly attributed to the recent developments in adap-
tive transmit diversity coding techniques [7],[8].
1. Introduction In [9] and [10], we have shown that the use of space-
time coded OFDM with an adaptive beamforming scheme
(STBC-OFDM-AB) is well suited to the application of mul-
Recent trends in wireless/mobile networks have shown timedia data, and that a significant performance gain read-
an increased demand for modern communication products ily facilitates the transmission of high-quality/high data-rate
that are capable of the transmission and processing of high- multimedia signals. More recently, however, the authors in
speed multimedia applications (high-quality digital video, [11]-[13] have shown that additional diversity branches in
images, and audio). This suggests a significant paradigm broadband multipath channels can be exploited using space-
shift towards digital communication systems designed to frequency (SF) and space-time-frequency coding (STF).
support wireless multimedia-equipped devices capable of Providing significant improvements over other space-time
high data-rate transmission. As a result, wireless multi- coded OFDM systems. This can be seen in Figure 1, which
media communication has attracted considerable interest shows the resulting error performance curves in bit-error-
by both the research community and industry to address rate (BER) and symbol-error-rate (SER) for OFDM systems
the growing need for high-speed multimedia services over that are STBC and STF coded respectively.
wireless networks such as 3G mobile communication sys- In this paper, we present a transmission system for
tems. the application of compressed images over wireless chan-
In designing communication devices for next-generation nels using a combined source coding and STF-OFDM-AB
(NG) wireless networks, one must however deal with the scheme. This method can be extended to study the trans-
bottlenecks commonly associated with the transmission of mission of other sources of multimedia information such
I1-4244-0574-2/06/$20.OO (0)2006 IEEE
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_____________..........______________________
Com pre ssion Block
-e- Bigen-STEERnputFile Mcimi C W Adaptive CM Entropy Tosiso
10......... .......:.....:(Image, etc) Doe2QoontizerEnc derMoe
: ................. ~~~~~~~~~~~~ Formatting o e
~~ 10 CMTransform.......CoefficientMannic......
..................................................... ~~~ ireles
.............
ms :::: :: ::: :: ::: :: :: :: ::: ::CM OsconCM tTran edo Coefficientnt atrix
lo .............................. ...........(.co.stocte.Dote... MI Doanstu te Co fiierntMa ropiecie
......................m.e..t) nstoctn cod de
~ ~~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ eCopesin lc
n0 SNR,..... dB utuFigu e 2. uloct da ramoehe mutme i
...................transmission.systm.with.STF-OFDM-AB
Figure1. ~~~~Eroperformance curvesrofcSTBC-
relatedfading channels. sou~~~~:::: (ecnsrcedat istconerteD InWT o ae-mantrixzrae M )cn
.The.output...of.the. compression...block. providesssan vec-
norm,Hermitian square root~~SN,adB theuedeterminantaofma-ultiedi
Figue 1.Erroperormace crveso maTriCes h TFdcdr
smlluDerline are veTFOrs. B ytesincr
2.eSytem Modelcanes 2.2.c dataiscompertessinonamti ray( )cn
The trnsmissonsysem proosedithisapertcnsists ReferingtoFintgevaures2shigna comressioncofreimage dtah
of 3 ain bocks:multiediadata ormating, ata cm- tcnsistsnomtoofwavhetrnsomatinadenrpeodn..
prssdion,a andi anadaptiveoSatF-FMaoe.Note,ouethouhauta Theae oftutrnmitn digitalpimages,alc multiresolution
cheannel encudersuhea,trocdn,i notlorequired asre 2D-DWTyodneopoiiorsrpreerformted uisingebiorthogonal
are nly nterstedin te baelin perormace o thesys- waveetsio. oavco fa fbsbn ouae
te.Canlcodjgto,tasoiiong nsHeesrovidea errnsorsoretion,e Int waveolet asnalysis',wesr presifent bthelwrSolTiOnFsub
spcapaivly. ~AndFonly addrdundAnc teothe tentropycoedn badub apoiton=oefcnt(A)adhi-ps
datamt aHeriieean BqaeR close,todtheshannelmit.nA bockma subba.ndsptial-requencypthinomtionwithrs hopraizontal,ver-
diagratmoftessemoeisswnn Figre2.lhi is tial Dand diaonalretai oefiins(Hn V,c
baesedion,adntheaSTBC-OFDM-ABDsimulatio scheme previ- rhecspetiely Forans n-leveldecoalmpoesito,authresoefficint
ousl outlyintedesin [10] Ah daesineption mnof thevaiurcsys- mavltrisMcnit.o h olwngcefcet
tmChneenoingelem tsmar providedithfolwn sro rections. aee nlss erpesn h o-eouinsb
diagam o th sysem odelis hownin igur 2Thi Duringl tansmdission,ldtransorcoefficients (DWTCn,cD)ar
basdaptive eSTF-OFDM M-ABtAnsisinschemtonsce,mmultimedi frmespcaivlar qurantiz leer.Aditionalposslessthcompessiionti
osinls fomtie n[O.Adsrpinoh variousdaasucepwihraesoredson- machieve by fursithe reovhfoingspatialandisttistclrdn
PC)eemntareov rtedito dsintabe formatwhichscainsb.ute ac fth WCuigacmindrnlnt n n
chomendgiable stillsimuaget(ith 8-itpielreotimeiaaon), the codapingscelymeaesriedtafinit[14]. lesuin ui
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[gi,j(), gij-(L-1)] as the L-tap channel impulse re-
Data Space!IFFT _ \ T .Maximum Received c r for . a ethnSpace
~~ ~ ~ ~ od ybosthe( t receive-transmit atnapair.Data Spc/._X1Likelihood Symbols sponse vector for the ,grcletasl nen arS bols Frequen eigy Dete The channel frequency response matrix can be expressed
Block Mapper ) / NT * * /' '\thlck Mapper N T (MLD) as Hk with its (i,) entry hi,j,k g. f where f'EncderIFFT
~ Channel-
tt.
.A, ANt Estimator [1, eJ2(k-l)/N, ... e_2_(k1)TL1/NC ]T is the corre-
Computation of sponding discrete Fourier transform coefficients and T isComputation 4
Adaptive Weights the integer delay of the /th tap. The correlated channel fre-R=VDVH i
quency response can then be given as HkV/R. We assume
that the spatial correlation is the same for all subcarriers.
To facilitate STF codeword transmission in the eigen-
Figure 3. General structure of the adaptive modes of the correlation matrix, eigen-weight mapping is
STF-OFDM model. Bold arrows represent performed across the space dimension of the STF code-
multi-line signals. word, {Ck }IN,,, prior to transmission. Mathematically, it
can be expressed as WHCk, where W = [wl, ,WNtJ
is the eigen-weight mapping matrix and Wj = Vj. Signal
2.3. The Adaptive Space-Time-Frequency transmission on different eigenvectors of, Rt, amounts for
OFDM Model transmitting Nt orthonormal beams in the direction of thedominant multipaths seen by the BS. In the case when Rt
is not the same for all subcarriers, beamforming should be
The general structure of the MJMO-OFDM system em- performed individually for groups of subcarriers with one
ploying the proposed adaptive STF transmission structure coherent bandwidth apart.
can be found in Fig. 3. We assume that the OFDM system At the receiver, discrete Fourier transformation (DFT) is
uses NC frequency tones with Nt transmit and Nr receive applied to the received signals from Nr antennas. The dis-
antennas, and that the channel is frequency-selective. crete time baseband equivalent expression of the received
At the BS, STF encoding is performed by formatting the signal has the form
compressed multimedia data symbols into a codeword ma-
trix C: [C1, , Ck, , CNJ] CNtxPNC where Ck Y = Hk RWHCk + Ek (3)
is a Nt xp sub-matrix (which spans across p OFDM-symbol
intervals and Nt transmit antennas) to be transmitted on the where Ek is the receiver noise matrix and its elements are
kth subcarrier. Because the number of baseband constel- modeled as uncorrelated white Gaussian random variables
lation points is finite, there is a limited number of possi- having A((O, r2 ). At the receiver, channel estimation is per-
ble STF codeword matrices and we denote this finite set as formed by correlating pilot tones embedded in the transmit-
T 3 C. Details of the design criteria and the formatting of ted signal. The result is then fed into the MLD for STF
STF codewords can be found in [11] and [12]. decoding of the multimedia data symbols by evaluating the
Assuming that a uniform linear array (ULA) configura- decision matrix as follows
tion is used for Nt BS antennas with a spacing of d meters, N,
the normalized spatial covariance matrix that specifies the C = arg mi E3 - H RWHCk (4)
spatial correlation between antenna elements is defined as CE 1
[15]
1L 3. Simulation Results
Rt =-,aQI/5)aHQI/5) (2)L =l The performance of the overall transmission system was
evaluated using the application of compressed images. A re-
where L denotes the number of dominant resolvable paths, sized (128x128) version of the standard 512x512 gray scale
a(OX) :=[1, eij ej2 *... ei(Nt-1)]T is the array prop- Lena image, with 8 bits/pixel resolution, is used as the mul-
agation vector for the £th tap with an AoA of , and timedia source data. The Lena image used for processing is
i = [2wr d sin(Oe)]/A with A being the carrier fre- shown in Figure 4. This was compressed using biorthogonal
quency wavelength. In general, Rt is a nonnegative- wavelets and a level 4 decomposition.
definite Hermitian matrix and its eigenvalue-decomposition The STF-OFDM-AB scheme was configured for QPSK
(EVD) can be expressed as Rt=VDVH, where V = baseband modulation and simulated using a maximum
[vl , Nt]is a unitary matrix with columns that are Doppler frequency of 100Hz and a ULA with Nt 4 and
the eigenvectors of Rt and D =diag{uii, ,U2,* ** I'N, } Nr =2 (with a spacing of O.5A employed at the transmit-
contains the corresponding eigenvalues. Define gi ff ter), over a correlated fading channel with a system SNR
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20
;03fll_
100 40
120 L 0l 06080100120
Figure 4. Original Lena source image (8-bit 1o00
gray scale) resized to 128x128. 120
of OdB. Also, the source coder was configured for a com- Figure 5. Reconstructed Lena image from
pression ratio (CR) of 32.2 using a global DWTC threshold the STBC-OFDM system with adaptive beam-
of 5. In order to determine the effectiveness of the STF- forming: SNR=OdB.
OFDM-AB system, this was simulated and compared to the
STBC-OFDM-AB scheme presented in [10]. The resulting
images obtained are shown in the accompanying Figures 5
and 6.
As expected, analysis of the performance curves and vi-
sual inspection (comparison of subjective fidelity measures)
of the images simulated, show quite clearly that significant
improvements in system performance are achieved with an
OFDM system using STF coding and adaptive beamform-
ing.
4. Conclusions 20
In this paper, we have introduced a transmission system 60
for the application of multimedia data over wireless chan-
nels using a combined source coding and STF-OFDM-ABat
scheme. Simulation results based on the application of digi -1
tal still images, show a good match between between perfor-
mance curves obtained through numerical studies and sub- 120
jective fidelity measures (human visual perception). Finally, 20 40 60 80 100 120
this study confirms that wireless communication systems
based on adaptive STF-OFDM are better suited to multime- Figure 6. Reconstructed Lena image from the
dia communication when compared to other diversity-coded STF-OFDM system with adaptive beamform-
OFDM systems. ing: SNR=OdB.
Currently, we are working on an extension of this re-
search study, which aims to further improve the overall per-
formance of diversity-coded OFDM systems by combining
an adaptive wavelet compression and adaptive modulation
scheme for the optimization of various transmission para-
meters towards the system SNRIBER.
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Multimedia transmission over wireless space-time-frequency coded OFDM

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