光MIMO-OFDM预编码矩阵优化

由于水下非成像光多输入多输出正交频分复用(multiple input multiple output-orthogonal frequency division multiplexing，MIMO-OFDM)通信系统采用强度调制-直接检测的通信方式，缺失频率和相位分量，不同光源的光束在接收端相互叠加，因此其信道相关性强，误码率(bit error rate，BER)高。针对这一问题，提出一种基于非成像光MIMO-OFDM接收信号欧氏距离的预编码算法。假设发送端预知信道状态信息，在满足光信号非负性和总功率受限的约束下求解最优预编码矩阵，通过对不同光源分配不同的功率实现最大化接收信号的最小欧氏距离。系统发送端通过预编码矩阵对信号进行预编码，接收端通过最大似然方法对最大化欧氏距离的接收信号进行解码。仿真结果表明，与基于奇异值分解的光MIMO预编码算法相比，提出的算法在总功率不变的前提下，进一步降低了非成像光MIMO-OFDM系统误码率。

Optimization of optical MIMO-OFDM precoding matrix

The underwater non-imaging optical Multiple Input Multiple Output-Orthogonal Frequency Division Multiplexing (MIMO-OFDM) communication system adopts intensity modulation-direct detection method without the frequency and phase components. The beams of different light sources superimpose each other at the receiving end, so the channel correlation is strong and the bit error rate (BER) is high. In order to solve this problem, a precoding algorithm based on MIMO-OFDM received signal Euclidean distance is proposed.Assuming that the transmitter anticipates the channel state information,the optimal precoding matrix is solved under the constraints of non-negative optical signal and limited total power,and the minimum Euclidean distance of the received signal is maximized by allocating different power to different light sources. The transmitting end of the system precodes the signal through the precoding matrix, and the receiving end decodes the received signal which maximizes the Euclidean distance by the maximum likelihood method. The simulation results show that compared with the optical MIMO precoding algorithm based on singular value decomposition (SVD), the proposed algorithm can reduce the BER of the non-imaging optical MIMO-OFDM system under the premise of constant total power.