FSO中分层空时编码的误码性能

分层空时编码(BLAST)虽然具有极高的频谱效率,能成倍提高光通信系统的信息传输速率,但BLAST系统的误码率较大,严重影响了光通信系统的可靠性。在描述了湍流信道中多输入多输出(MIMO)系统的信道模型后,针对多进制脉冲位置调制(Q-PPM)技术,推导出了采用线性译码算法时分层空时码的极大似然判决准则及其误码率公式,并比较了最大似然译码算法、线性译码算法、串行干扰消除译码算法的误码性能。最后,利用仿真实验进行了验证。结果表明:在自由空间光通信(FSO)中,串行干扰消除译码算法的误码性能更接近最大似然译码算法的性能,明显优于线性译码算法。在4×4系统中,当误比特率为2×10-2时,相对于最小均方误差(MMSE)译码算法,最大似然译码算法和MMSE-SIC译码算法的信噪比分别改善了约14.5 dB和7 dB。理论分析与实验结果相一致。

BER performance of layered spacetime code in FSO

The spectrum effectiveness of layered space-time code(BLAST) is very high,which enables it to improve the information transmittance speed in free space optical communication systems.But it improves BER contemporarily,which affects the system reliability.After the model of the MIMO systems was proposed in turbulence channel,the decoding of BLAST was advised using serial interference cancellation(SIC).Besides,its nonmaximum likelihood decision rule and BER performance were analyzed,and its BER was compared with linear decode algorithms and maximum likelihood(ML) decoding algorithm based on Q-ray pulse position modulation(Q-PPM).At last,the feasibility of the technique was proved by simulation analysis.The results indicate that the error performance of SIC decoding algorithm is inferior to the ML decoding algorithm′s,but it is superior to the linear decoding algorithm.In a 4×4 MIMO system,the ML and MMSE-SIC decode algorithm has improved by 14.5 dB and 7 dB respectively compared with MMSE algorithm when BER is 2×10-2.The experimental results accord with theoretical analysis.