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Enhancing Wireless LAN Performance: MIMO-OFDM with Antenna Selection

Explore the benefits of MIMO systems with antenna selection for improved capacity in wireless LAN environments. Understand system models, channel capacity, simulation results, and solution methods.

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Enhancing Wireless LAN Performance: MIMO-OFDM with Antenna Selection

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  1. 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

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

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

  4. 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

  5. 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

  6. 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

  7. 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

  8. 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

  9. 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

  10. 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

  11. 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

  12. Simulation results (I) • Correlation Heejung Yu, ETRI

  13. Simulation results (II) • Correlation Heejung Yu, ETRI

  14. 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

  15. Further Work • Initial channel estimation to decide antenna selection • Antenna selection information transfer • Simplify antenna selection method Heejung Yu, ETRI

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