The Detecton Algorthms Performance n BLAST Enhanced IEEE 802.11a WLAN Standard on Measured Channels Unversty of Brstol Robert Pechoc, Paul Fletcher, Andy Nx, Nshan Canagarajah and Joe McGeehan The Thrd IEEE Worshop on Wreless Local Area Networs, Sep. 27-28 The Boston Marrott otel, Newton, Massachusetts Unversty of Brstol Centre for Communcatons Research
Outlne Motvatons MIMO-OFDM MIMO ndoor channel soundng BLAST-OFDM Numercal Results Unversty of Brstol Centre for Communcatons Research
Motvatons Capacty of MIMO lns (Telatar,, 1995; Foschn & Gans 1998) Capacty of the multplexed channels sums up: C = N 1 ence log + λ 2 1 P Nσ 2 C P log 2 1 + σ = N 2 Capacty ncreases lnearly wth N! e.g. 40 db for 80 b/s/z!!! Unversty of Brstol Centre for Communcatons Research
MIMO Measurements Setup Wdeband ndoor MIMO measurements Customsed Medav RUSK BRI vector channel sounder 5.2 Gz operatng frequency 120 Mz bandwdth up to 8 Tx elements by 8 Rx elements complete MIMO snapshot of the channel: 102.4 µs (well wthn coherence tme of the channel) Measurements were taen n large open plan offce wth approxmate dmensons 30L x 20W x 4 (m). Unversty of Brstol Centre for Communcatons Research
MIMO Measurements Access Pont Crcular array of prnted dpoles used for the Access Pont Unversty of Brstol Centre for Communcatons Research
MIMO Measurements Moble Termnal Laptop-szed four double polarzed element antenna array used for the Moble Termnal Unversty of Brstol Centre for Communcatons Research
MIMO OFDM: A General Schematc Space-tme transmsson n MIMO OFDM CSI V-BLAST Encoder IFFT RF RF FFT V-BLAST Decoder IFFT RF RF FFT System wth sequental MIMO tranng CSI Transmtted from Antenna No 1 Payload CP Payload CP C Preamble CP Payload CP Payload CP C Preamble Transmtted from Antenna No 2 CP Payload CP Payload CP C Preamble CP Transmtted from Antenna No N Payload Data MIMO Tranng Unversty of Brstol Centre for Communcatons Research
MIMO OFDM: Approaches I. Space Tme Codng (Frequency-Space n OFDM) PROS Channel codng (error correcton) Transmt dversty Modulaton mappng Receve dversty All of the above optmsed jontly (Taroh, Seshadr & Calderban 1998) CONS No data throughput mprovement Complexty senstve to modulaton format Improves manly ln relablty Unversty of Brstol Centre for Communcatons Research
MIMO OFDM: Approaches II. Spatal Multplexng (BLAST) (Foschn 1996, Paulraj & Kalath 1994) PROS Drectly explots MIMO channel capacty to mprove the data throughput CONS poor ln relablty - requres channel codng Improves manly data throughput Unversty of Brstol Centre for Communcatons Research
Spatal Multplexng BLAST OFDM Cyclc prefx OFDM sgnal model (CP-OFDM ) SIMO case revsted: th transmtted bloc of data T cp - CP nserton matrx (P x K ) u = T cp F 1 u F - Fourer transform matrx (K x K) receved sgnal bloc pertanng to u x + = 0u + 1u 1 0, 1 - Toepltz channel matrces - the ubqutous addtve nose vector nput output relatonshp 1 x = F T T F u + R 0 cp F T R CP remove Unversty of Brstol Centre for Communcatons Research
Spatal Multplexng BLAST OFDM TR 0 T cp s crculant, and thus s dagonalsed by F F T R T 0 cp F 1 = = 0 ( ω ) h 0 0 # 0 0 h 0 # 0 1 ( ω ) 0 0 h # 0 2 ( ω ) " " " % " 0 0 0 # ( ) K 1 h ω Fnally, the CP-OFDM SIMO case s gven x = u + Unversty of Brstol Centre for Communcatons Research
Spatal Multplexng BLAST OFDM Extenson to MIMO CP-OFDM confguraton wth N transmt and M receved antennas Defne: [ ] () T ( ) T ( N ) T ( N ) u 1 u 2 u 1 u T T = " [ ] () 1 T ( ) T ( M ) T ( M ) x 2 x 1 x x T T $ = " N staced u vectors (K*N x 1) transmtted sgnal (Frequency - Space) staced vector of the receved data (K*M x 1) = # 1,1 2,1 M,1 # 1,2 2,2 M,2 " " % " # 1, N 2, N M, N the overall channel matrx Fundamental model: $ = + / Unversty of Brstol Centre for Communcatons Research
Spatal Multplexng BLAST OFDM The Maxmum Lelhood (ML) detector of V-Blast CP-OFDM = arg mn $ 2 Snce s bult up of dagonal matrces, t s possble to separate the above problem nto K ndependent but lower dmensonal lnear problems (.e. each subcarrer s treated separately) Defne: ( M ) T $ x = C Fnally ML V-BLAST:, = arg mn. x and,, 2 = C ( M ) T ( N ) C C compacton matrces (subcarrer separaton) Unversty of Brstol Centre for Communcatons Research
Spatal Multplexng BLAST OFDM Lnear Detecton Zero Forcng (ZF) G, = x, G Where: ( ) = 1 Represents Least Squares soluton Ordered Successve Interference Cancellaton (OSIC) (G. Golden et al 1999) Unversty of Brstol Centre for Communcatons Research
Spatal Multplexng BLAST OFDM Maxmum Lelhood Zero Forcng ybrd - ZFML (X. L et al, 2000) Step 1: Step 2: Perform ZF and dentfy shortlsts for each antenna Perform ML search on shortlsts Antenna 1 Antenna 2 Shortlst 1 ZF soluton 16 QAM Shortlst 2 ZF soluton Unversty of Brstol Centre for Communcatons Research
Numercal Results (1/4) 96 Mb/s, 2 Tx by 2 & 4 Rx, 16 QAM, MIMO channel estmated va sequental preamble Unversty of Brstol Centre for Communcatons Research
Numercal Results (2/4) 96 Mb/s, 2 Tx by 4 Rx, 16 QAM, meas measured channel smul ETSI, /2 Channel A, (energy normalsed) Unversty of Brstol Centre for Communcatons Research
Numercal Results (3/4) 96 Mb/s, 4 Tx by 6 Rx, QPSK, Measured channel deal deal MIMO CSI avaable estm MIMO CSI estmated va sequental preamble Unversty of Brstol Centre for Communcatons Research
Numercal Results (4/4) 192 Mb/s, 4 Tx by 6 Rx, 16-QAM, Measured channel deal deal MIMO CSI avaable estm MIMO CSI estmated va sequental preamble Unversty of Brstol Centre for Communcatons Research
Conclusons Possblty of 192 Mb/s (uncoded n IEEE 802.11A band) n a real settng has been demonstrated Dfference between an deal settng and our measured channel s 12 db (@ BER 10-2, 2x4, 16-QAM) Dfference n the performance between the detecton algorthms tghtens as the number of receve antennas ncreases Future research nto MIMO-OFDM: Flexble blend of spatal multplexng/frequency space codng Advanced detecton algorthms (Reduced complexty) Antenna confguratons/strateges studes Authors gratefully acnowledge sponsorshp provded by QnetQ Ltd Unversty of Brstol Centre for Communcatons Research
References G. Golden, G. Foschn, R. Valenzuela and W.Wolnansy Detecton algorthm and ntal laboratory results usng the V-BLAST space-tme communcaton archtecture, IEE Electroncs Letters, vol.35, no.1, pp.14-15, Jan 1999. V. Taroh, N. Seshadr, and A. Calderban, Space-tme codes for hgh data rate wreless communcaton - performance crteron and code constructon IEEE Trans on Informaton Theory, Vol. 44, No. 2, March 1998, pp. 744 765. X. L,. uang, A. Lozano, G. Foschn, Reduced complexty detecton algorthms for systems usng mult-element arrays, IEEE Globecom 2000, San Francsco, G.J. Foschn, M.J. Gans, On Lmts of Wreless Communcatons n a Fadng Envronment when Usng Multple Antennas Wreless Personal Communcatons, 1998, 6, (3), pp.311-335. G. Foschn, Layered space-tme archtecture for wreless communcaton n fadng envronment when usng mult element antennas, BLTJ, Autumn, 1996. I.E. Telatar Capacty of mult-antenna Gaussan channels, tech. Rep. AT&T Bell Labs nternal memo. 1995. A. Paulraj and T. Kalath Increasng capacty n wreless systems usng dstrbuted transmsson/drectonal recepton (DTDR), Sep 1994. Unversty of Brstol Centre for Communcatons Research