Chapter 4 B-Chase Detector of MIMO-OFDM Systems
4.3 B-Chase Detector in MIMO-OFDM Systems
We will employ MIMO-OFDM systems to extend the B-Chase detector in the MIMO systems. Due to OFDM systems can turns frequency-selective fading channel into several flat-fading subchannels and get high spectral efficiency. When the channel state is multipath
and the cyclic prefix length is longer than the path delay, we can use flat fading MIMO case to handle it in each subcarrier which do not interfere other subcarriers. That is robust for the frequency-selective fading channel when we detect the receiveed signal in the B-Chase detector. We can say that the frequency-selective fading channel can get time delay diversity when we can handle the frequency-selective fading channel as the flat fading channel. For that we can employ OFDM to get that. The subsequent MIMO signal processing takes place on each subcarrier identically. In order to describe the flat fading MIMO systems observed at each subcarrier in the frequency domain. We let [ ,1 ]
t
i i i T
a aN
=
a " denote the Nt × 1 transmit
signal vector of subcarrier i, then the corresponding Nr ×1 receive signal vector
[ ,1 ]
w " represents independent white Gaussian noise of variance ( )σni 2 observed at the Nr receive antennas while the average transmit Gaussian fading gains with unit variance. We assume that the channel matrix Hi is constant over a frame and changes independently between frames (block fading channel).That in the following the algorithms are given on the base of subcarrier i assuming an outer loop over all subcarrier i=1,…, NFFT. The index i is therefore omitted to simplify matters giving r = ri, the received signal on subcarrier i, H =Hi , the channel matrix, a = ai, the transmit symbols on
subcarrier i and w = wi , the noise vector respectively. From that we detect the transmitted signals on each subcarrier of MIMO-OFDM systems by B-Chase detector.
Table 4-1 System parameters
FFT length 16
Symbol period 16 samples
Cyclic prefix 4 samples
Modulation 16-QAM
Transmit antenna 4
Receive antenna 4
Channel is updated in T symbol periods 8
Rayleigh-fading Mean=0,Varance=1
Channel order 3
List length l 1 , 2, and 16
5 10 15 20 25 10-5
10-4 10-3 10-2 10-1 100
SNR dB
BER
B-CHASE*(1) B-CHASE*(2) B-CHASE*(16)
Figure 4-8 Bit error rate versus SNR in the B-Chase detector* ( l ) with l =1,2,16 for MIMO-OFDM Systems
Table 4-2 System parameters
FFT length 16
Symbol period 16 samples
Cyclic prefix 4 samples
Modulation BPSK
Transmit antenna 4
Receive antenna 4
Channel is updated in T symbol periods 8
Rayleigh-fading Mean=0,Varance=1
Channel order 3
List length l 1 , 2
0 2 4 6 8 10 12 10-5
10-4 10-3 10-2 10-1
SNR dB
BER
B-CHASE*(1) B-CHASE*(2) ML
Figure 4-9 Bit error rate versus SNR in the B-Chase detector* ( l ) with l =1,2 for MIMO-OFDM Systems
Chapter 5 Conclusion
The B-Chase of detection algorithm is a combination of a list detector and a parallel bank of subdetectors. The B-Chase detector that can trade performance for reduced complexity by modifying the list length. When applying the B-Chase of detection algorithm in the MIMO-OFDM, we can improve performance in the frequency-selective fading channel.
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自 傳
方自民, 西元 1981 年生於台南市。 西元 2004 畢業於台灣國立台北科技大 學電子系，之後進入交通大學電子研究所攻讀碩士學位，於 2008 年取得碩 士學位。研究方向為無線通訊訊號處理。