中文摘要：

基于双伽玛（Gamma-Gamma）湍流信道,研究了低密度奇偶校验码（LDPC）的自由空间光通信多输入多输出（FSO-MIMO）系统迭代检测解码（IDD）算法。针对最优最大后验概率（MAP）算法复杂度高和BP迭代过程中比特节点后验对数似然比（LLR）震荡现象,结合概率数据辅助（PDA）算法在信号检测中的良好性能,提出了一种基于反馈均值的LDPC＋PDA系统IDD码算法,采用BP解码方法,经迭代处理,求出每次内迭代中比特节点输出的后验信息均值,并将其作为解码器的输出反馈给检测器,从而提高了解码器传递给检测器的消息可靠性。仿真结果表明,当误码率（BER）为10^-5左右时,在弱湍流条件下,改进的IDD算法相对传统的算法具有0.3dB的性能优势;在强湍流条件下,改进的IDD算法比传统的算法提高了0.65dB的性能增益。因而,改进的IDD算法能够进一步抑制湍流特别是强湍流的影响,提高了系统性能。

英文摘要：

Based on the Gamma-Gamma turbulence channel, an iterative detection and decoding algorithm of low-density parity-check （LDPC） coded free-space optical communication multiple-input-multiple-out- put （FSO-MIMO） system is studied. For high complexity of the optimal maximum a posteriori （MAP） algorithm and bit nodes posterior log likelihood ratio （LLR） oscillation in BP iterative process, an improved LDPC＋PDA iterative detection and decoding algorithm based on mean value of a feedback is promoted. After iteration process of BP decoding algorithm,the mean of posteriori information, which is the output of bit nodes within each inner iteration,is taken as a feedback to detector,in order to improve the reliability of the decoder messages passed to the detector. The simulation results show that when the bit error rate is about 10^-5 ,under the condition of weak turbulence,the improved algorithm has 0.3 dB performance advantages compared with traditional algorithm. Under the condition of strong turbulence, the improved algorithm increases the gain of 0.65 dB. The improved algorithm of iterative detection and decoding can further suppress the turbulence effect and improve the performance of the system, especially under strong turbulence conditions without significant increase in computational complexity.