多用户干扰对可见光通信直流偏置光正交频分复用码分多址系统性能的影响

Influence of Multiuser Interference on Performances of Direct-CurrentBiased Optical Orthogonal Frequency Division Multiplexing Code Division Multiple Access System for Visible Light Communication

结合直流偏置光正交频分复用(DCO-OFDM)和码分多址(CDMA),建立了DCO-MC-CDMA系统。受系统结构限制,选用Gold码和m序列作为扩频地址码时,互相关性比正交码差,进而导致更大的多用户间干扰(MUI)。采用最大比合并、等增益合并和正交恢复合并(ORC),推导了受加性高斯白噪声、MUI和限幅噪声影响时信噪比的表达式,并基于Matlab建立了蒙特卡罗误码率(BER)仿真模型。研究结果表明:随着用户数的增大,MUI会使系统BER性能变差;ORC消除了子信道增益不同导致的MUI,因而BER性能最好;Gold码的互相关性比m序列好,采用Gold码的DCO-MC-CDMA系统BER性能更好。

Based on the direct-current-biased optical orthogonal frequency division multiplexing(DCO-OFDM)combined with code division multiple access(CDMA),a DCO-MC-CDMA system is built.When the Gold code and m-sequence are selected as spread spectrum address codes in the proposed system,their cross-correlation is worse than that of orthogonal codes owing to the limitation of the system structure,leading to a greater multi-user interference(MUI).The maximum ratio combining,equal gain combining,and orthogonal recovery combining(ORC)are used to derive the signal-to-noise ratio expression under the influences of additive white Gaussian noise,MUI,and limiting noise.The simulation model of the Monte Carlo bit error rate(BER)in MATLAB is established.The research results show that with the increase of the number of users,the MUI makes the system BER performance worse.In contrast,the ORC eliminates the MUI induced by the difference between subchannel gains,and thus the BER performance is the best.The BER performance of the DCO-MC-CDMA system with the Gold code is better,because the cross-correlation of the Gold code is better than that of the m-sequence in.