Experimental Analysis of MIMO-OFDM Eigenmode Transmission with MMSE Interference Canceller Yuichi KAKISIMA Le ai Doan Ting See o Kei Sakaguchi Kiyomichi Araki Graduate School of Science and Engineering Tokyo Institute of Technology
Background Contents MIMO-OFDM Eigenmode Transmission System (EMTS) Performance degradation of EMTS due to channel variation Performance improvement by using MMSE canceller Experimental analysis System of 4x4 MIMO-OFDM transceivers Experimental setup for channel variation BER measurement with different time-correlation (Transmission experiment) Conclusions and future works PIMRC'06 elsinki 2
MIMO-OFDM EMTS MIMO-OFDM eigenmode transmission system (MIMO-OFDM EMTS) U Rx Weight UΣV y y ~ y = x + n = U Vs = Σs + n ~ = + U n Tx Weight Σ = diag[ λ1 m = min( M t, M r λ ] ) m Gain of an each eigenmode Perfect orthogonalization of the channel s : Transmit signal y : Receive signal : Channel matrix n :Noise : Eigen value No inter-eigenmode interference PIMRC'06 elsinki 3
Channel Variation Channel variation t = ρ + 2 1 ρ var : Correlation coefficient : Channel used for making Tx/Rx weight t : Transmission channel var : Variation of the channel Inter-eigenmode Interference ~ y = U y = U = [ ρu Vs + U t n 2 V + 1 ρ U 2 = [ ρσ + 1 ρ N ] s + n ~ var V ] s + U n U V =Σ = t < 1 : Decrease of the gain > 0 : Inter-eigenmode interference Imperfect orthogonalization of the channel Performance degradation due to the channel variation PIMRC'06 elsinki 4
MMSE Canceller W W MMSE MMSE ~ y = W = ( Σ * MMSE U mt I Σ + γ Vs + W 0 m r t ) 1 Σ * MMSE U n Removes inter-eigenmode interference Simply, yet efficient y improves performance PIMRC'06 elsinki 5
Effect of MMSE Canceller w/o MMSE canceller with MMSE canceller Experimental analysis of MIMO-OFDM EMTS with MMSE interference canceller PIMRC'06 elsinki 6
Experiment System of MIMO-OFDM EMTS Compact PCI 6U Rubidium DSP Board AD Board DA Board LO Board RF Board CPU No. of antenna 4 x 4 MIMO-OFDM EMTS Most of the calculation is conducted in CPU Tx weight feedback with LAN Feedback delay is about 3 seconds Antenna specification Center frequency Bandwidth FFT point /2 spacing ULA 5.06 Gz 20 Mz 64 points PIMRC'06 elsinki 7
Transmission Result PIMRC'06 elsinki 8
Measurement Environment Tx antenna array NLOS office environment with furniture All doors are closed Static condition Transceivers PIMRC'06 elsinki 9
Measurement Setup Channel variation Time-varying channel Time correlation Static channel Spatial correlation t t+ t d d + d Feedback delay of 3 seconds Difficult to regenerate the environment Measurement of the spatial correlation Channel measurement Same area with the BER measurement WSS is assumed in the area Average received SNR for the measurement is about 25 db Measurement area Measurement step Training signal 40 40 cm 5 mm IEEE802.11a base (64OFDM symbols) PIMRC'06 elsinki 10
Spatial Correlation 0 5 9 ρ = abs[ position subcarrier mt i= 1 j= 1 k = 1 l= 1 position subcarrier mt i= 1 j= 1 k = 1 l= 1 mr h ijkl 1 h mr h ijkl 1 h ijkl* 2 position subcarrier mt mr ijkl* 1 i= 1 j= 1 k = 1 l= 1 h ijkl 2 h ijkl* 2 ] Correlation Distance 1 0 mm 0.95 5 mm 0.90 9 mm PIMRC'06 elsinki 11
Transmission Experiment Training signal IEEE802.11a base (8OFDM symbols) Initialization X-Y Position Control Modulation FEC Antenna moving distance Measurement area Measurement step QPSK None 0, 5, 9 mm 40 x 40 cm 2 cm Pre Transmission Position Avg. SNR Setting Pre Transmission Channel Estimation SVD Transmission Position Transmission Measurement points 441 Points Error Count Move Rx antenna to generate channel variation 441 points of measurement to average out the effect of the fading Range of the SNR is controlled from 0dB to 30dB NO SNR Loop END? YES Position Loop END? YES NO PIMRC'06 elsinki 12
Experimental Result (d = 0 mm) ρ = 0.99 Performance w/wo canceller are almost the same Measurement results well agree with simulation PIMRC'06 elsinki 13
Experimental Result (d = 5mm) ρ = 0.95 Degradation of BER performance w/o canceller PIMRC'06 elsinki 14
Experimental Result (d = 9mm) ρ = 0.89 Improvement in BER performance with MMSE canceller PIMRC'06 elsinki 15
Conclusions & Future Works Conclusions Implementation of measurement system of EMTS with channel variation Measurement of BER performance for MIMO-OFDM EMTS Effect of MMSE interference canceller in the presence of feedback delay Future works Establishment of a theoretical channel model for channel variation Comparative analysis with other interference cancellers Thank you for your attention PIMRC'06 elsinki 16