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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。
Hierarchical space-time coding (BLAST), while having a very high spectral efficiency, can exponentially increase the information transmission rate of an optical communication system. However, the BLAST system has a large bit error rate and seriously affects the reliability of the optical communication system. After describing the channel model of multiple-input multiple-output (MIMO) system in turbulent channel, the paper presents a new scheme of multi-level pulse-space modulation (Q-PPM) Likelihood decision criterion and its bit error rate formula, and compares the BER performance of maximum likelihood decoding algorithm, linear decoding algorithm and serial interference cancellation decoding algorithm. Finally, the simulation experiments were used to verify. The results show that the BER of serial interference cancellation decoding algorithm is much closer to the performance of maximum likelihood decoding algorithm in free space optical communication (FSO), which is obviously better than the linear decoding algorithm. In the 4 × 4 system, when the bit error rate is 2 × 10-2, the signal-to-noise ratio of the maximum likelihood decoding algorithm and the MMSE-SIC decoding algorithm with respect to the minimum mean square error (MMSE) decoding algorithm Improved by about 14.5 dB and 7 dB. The theoretical analysis is consistent with the experimental results.