1. HDR 802.11a solution using MIMO-OFDM
May 2002
HDR a solution using MIMO-OFDM
Heejung Yu
ETRI
Wireless LAN Research Team
Heejung Yu, ETRI

2. Contents System and signal model Optimal detection
May 2002
Contents
System and signal model
Optimal detection
ZF and MMSE receiver
Layered architecture using ZF and MMSE
Simulation results
Conclusion
Heejung Yu, ETRI

3. System model May 2002 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

4. Signal model Received Signal for one subcarrier
May 2002
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. Optimal receiver Detect signal maximizing likelihood function
May 2002
Optimal receiver
Detect signal maximizing likelihood function
Exhaustive search : AN candidates (A : # of constellation)
Advantage
Diversity order = # of receiver antennas
Can be applied in case of N>M
The best performance
Disadvantage
Implementation complexity increases exponentially
Heejung Yu, ETRI

6. ZF receiver Only need channel matrix
May 2002
ZF receiver
Only need channel matrix
Exit the noise enhancement problem
Diversity order : M-N+1
( )+ : Pseudo-inverse
Heejung Yu, ETRI

7. May 2002
MMSE receiver
Consider noise power : achieve better performance than ZF
In High SNR, MMSE receiver  ZF receiver
Diversity order : M-N+1
Heejung Yu, ETRI

8. May 2002
Layered receiver(1)
1. Find signal with minimum noise enhancement(using H)
2. Make a decision statistic
3. Decision
Heejung Yu, ETRI

9. Layered receiver(2) 4. Reconstruct signal and cancel it
May 2002
Layered receiver(2)
4. Reconstruct signal and cancel it
5. Update H (zero-forcing the kth column of current H)
6. Return to step 1. until deciding all symbols.
Heejung Yu, ETRI

10. Example of Layered Arch.
May 2002
Example of Layered Arch.
N = M = 3 (BPSK) 1. 2.
Heejung Yu, ETRI

11. Example of Layered Arch.
May 2002
Example of Layered Arch.
3. Hard decision[0.8333] 4. 5.
Heejung Yu, ETRI

12. Example of Layered Arch.
May 2002
Example of Layered Arch. 6. 7.
8. Hard decision[0.4000]
Heejung Yu, ETRI

13. Example of Layered Arch.
May 2002
Example of Layered Arch. 9.
10.
11.
Heejung Yu, ETRI

14. Example of Layered Arch.
May 2002
Example of Layered Arch.
12.
13. Hard decision[-1.633]
14.
Heejung Yu, ETRI

15. Simulation Environment
May 2002
Simulation Environment
Modulation : OFDM (the same as a)
Mapping : BPSK, QPSK, 16-QAM, 64-QAM
Coding : No coding
Channel : Exponentially decaying Rayleigh fading channel with 100nsec RMS delay spread
# of Tx and Rx antennas : 4 x 4
BW = 20MHz
Heejung Yu, ETRI

16. Simulation results (BPSK)
May 2002
Simulation results (BPSK)
48Mbps
12Mbps
Heejung Yu, ETRI

17. Simulation results (QPSK)
May 2002
Simulation results (QPSK)
96Mbps
24Mbps
Heejung Yu, ETRI

18. Simulation results (16-QAM)
May 2002
Simulation results (16-QAM)
192Mbps
48Mbps
Heejung Yu, ETRI

19. Simulation results (64-QAM)
May 2002
Simulation results (64-QAM)
288Mbps
72Mbps
Heejung Yu, ETRI

20. May 2002
Conclusions
We can achieve more than 100Mbps using MIMO-OFDM with a small performance degradation.
In BPSK and QPSK modulation, we can achieve better performance than SISO case
In 16 and 64-QAM, performance degradations due to MIMO are about 0.5 and 2dB, respectively.
We can get the high spectral efficiency by using MIMO-OFDM
MIMO-OFDM is a good solution for HDR a
Heejung Yu, ETRI