MIMO-OFDM with antenna selection July 2003 MIMO-OFDM with antenna selection Heejung Yu, Taehyun Jeon, and Sok-kyu Lee ETRI Wireless LAN Modem Research Team heejung@etri.re.kr Heejung Yu, ETRI

Contents System and signal model MIMO channel model and capacity July 2003 Contents System and signal model MIMO channel model and capacity General MIMO systems MIMO systems with antenna selection Simulation results Conclusion Heejung Yu, ETRI

System model July 2003 S/P IFFT Add CP Mapping Rayleigh Fading Channel Remove FFT Det. P/S Demap Tx ant 1 Tx ant 2 Tx ant N Rx ant 1 Rx ant 2 Rx ant M Heejung Yu, ETRI

Signal model Received Signal for one subcarrier July 2003 Signal model Received Signal for one subcarrier H : Frequency domain channel matrix (hi,j : channel from j-th Tx antenna to i-th Rx antenna) P : Total Tx power N : Total # of Tx antenna x : Tx signal vector (1 x N) y : Rx signal vector (1 x M) n : AWGN noise vector (1 x M) Heejung Yu, ETRI

July 2003 MIMO channel model From IEEE 802.11-03/161r0-Indoor MIMO WLAN channel models Rtx and Rrx are the receive and transmit correlation matrices Hiid is a matrix of independent zero mean, unit variance, complex Gaussian random variables Heejung Yu, ETRI

Channel capacity MIMO channel capacity H : (M  N) MIMO channel matrix July 2003 Channel capacity MIMO channel capacity H : (M  N) MIMO channel matrix M : # of rx antennas, N : # of tx antenna I : identity matrix Heejung Yu, ETRI

General MIMO-OFDM Channel correlation induces performance loss July 2003 General MIMO-OFDM Channel correlation induces performance loss Geometrical characteristics Antenna spacing In PC-card, implement at most 4(?) antennas Can achieve 4 x data rate Cannot guarantee BER performance Induce more retransmission Loss in the throughput of WLAN Heejung Yu, ETRI

July 2003 Solution We use only some antennas out of all antennas in transmitter part. Rx terminal : channel estimation and determine antenna selection method Selection information transfer Tx terminal : data transmission using selected antennas Heejung Yu, ETRI

Selection methods Each sub-carrier base selection July 2003 Selection methods Each sub-carrier base selection We select antennas in terms of sub-carrier Selection pattern depends on a sub-carrier Get high performance gain, but need more feedback information and hard to implement Total sub-carrier base selection(Here, don’t consider) We select antennas in terms of sum of all capacity corresponding to total sub-carriers Get small gain, but need small feedback information and easy to implement Heejung Yu, ETRI

Selection procudure Consider all combinations of Tx antennas July 2003 Selection procudure Consider all combinations of Tx antennas Make a MIMO channel submatrix for each combination Calculate Channel Capacity Decide the antenna selection that maximize the capacity Heejung Yu, ETRI

Simulation environments July 2003 Simulation environments Channel : Complex Gaussian flat fading channel (corresponding to one sub-carrier) with correlation Capacity is calculated with more than 1000 channel generation Same number of Tx and Rx antennas Total Tx power(sum of all used antennas) is the same Heejung Yu, ETRI

Simulation results (I) July 2003 Simulation results (I) Correlation Heejung Yu, ETRI

Simulation results (II) July 2003 Simulation results (II) Correlation Heejung Yu, ETRI

Conclusions Why use selection? July 2003 Conclusions Why use selection? Small capacity gap Detection complexity : matrix inversion( O(M^3) ) MIMO systems with antenna selection can achieve relatively high capacity with small detection complexity Heejung Yu, ETRI

Further Work Initial channel estimation to decide antenna selection July 2003 Further Work Initial channel estimation to decide antenna selection Antenna selection information transfer Simplify antenna selection method Heejung Yu, ETRI