6.5 本章小结
首先，介绍MIMO-DCO-OFDM和MIMO-ACO-OFDM系统收发端原理；然后，在室内可见光通信多径信道下，采用ZF和MMSE检测算法、理论分析系统的误码率性能；最后，建立了Monte Carlo误码率仿真模型，对系统的性能进行仿真和分析。
为了保证系统性能比较有公平性，分析时假设发射光功率不变，研究误码率性能随着发送电能量 Es与AWGN功率谱密度N0之比之间的关系，这样可以将信道的差异引入性能分析。结果表明，在 Es/N0较小时，MMSE检测算法优于ZF算法，但随着 Es/N0逐渐增大，两者性能趋于相同。
当PD在室内房间中心位置时，接收信号功率大，且反射路径信号小，所以误码率性能最好，越往墙边移动，性能越差。考虑多径效应的影响，要达到相同的 BER性能，就需要更多的发射功率。对于MIMO-DCO-OFDM系统，由于限幅噪声和AWGN共同影响系统性能。当 Es/N0较小时，AWGN主要影响系统性能，直流偏置越大，信号中包含信息的成分越小，则误码率性能越差。随着 Es/N0逐渐增大，N0变小，限幅噪声成了影响系统性能的主要因素，直流偏置越大，限幅噪声越小，误码率性能越好。因此，较小直流偏置时的误码率曲线和较大直流偏置曲线总会相交。
参考文献
[1]LI H,CHEN X,HUANG B,et al.High Bandwidth Visible Light Communications Based on a Post-Equalization Circuit[J].IEEE Photonics Technology Letters,2014,26(2):119–122.
[2]ZENG L,O’BRIEN D C,MINH H L,et al.High data rate multiple input multiple output（MIMO）optical wireless communications using white LED lighting[J].IEEE Journal on Selected Areas in Communications,2009,27(9):1654–1662.
[3]NUWANPRIYA A,HO S W,CHEN C S.Angle diversity receiver for indoor MIMO visible light communications[C].GLOBECOM Workshops.IEEE,2014:444–449.
[4]WANG T Q,SEKERCIOGLU Y A,ARMSTRONG J.Analysis of An Optical Wireless Receiver Using a Hemispherical Lens With Application in MIMO,Visible Light Communications[J].Journal ofLightwave Technology,2013,31（11）:1744–1754.
[5]WANG T Q,ARMSTRONG J.Performance of indoor MIMO optical wireless system using linear receiver with prism array[C].Communications Theory Workshop.IEEE,2014,51–56.
[6]HONG Y,CHEN J,WANG Z,et al.Performance of a Precoding MIMO System for Decentralized Multiuser Indoor Visible Light Communications[J].IEEE Photonics Journal,2013,5（4）:7800211.
[7]FATH T,HAAS H.Performance Comparison of MIMO Techniques for Optical Wireless Communications in Indoor Environments[J].IEEE Transactions on Communications,2013,61（2）:733–742.
[8]WU L,ZHANG Z,LIU H.MIMO-OFDM visible light communications system with low complexity[C].IEEE International Conference on Communications.IEEE,2013,3933–3937.
[9]WANG T Q,GREEN R J,ARMSTRONG J.MIMO Optical Wireless Communications Using ACO-OFDM and a Prism-Array Receiver[J].IEEE Journal on Selected Areas in Communications,2015,33（9）:1959–1971.
[10]A H AZHAR,T A TRAN,D O'BRIEN.Demonstration of high-speed data transmission using MIMO-OFDM visible light communications[C].IEEE Globecom2010Workshop on Optical Wireless Communications,2010,1052–1056.
[11]HONG Y,WU T,CHEN L K.On the Performance of Adaptive MIMO-OFDM Indoor Visible Light Communications[J].IEEE Photonics Technology Letters,2016,28（8）:907–910.
[12]PAULRAJ A J,GORE D A,NABAR R U,et al.An overview of MIMO communications a key to gigabit wireless[J].Proceedings of the IEEE,2004,92（2）:198-218.
[13]ELGALA H,MESLEH R,HAAS H.Practical considerations for indoor wireless optical system implementation using OFDM[C]International Conference on Telecommunications.IEEE,2009,25–29.
[14]AZHAR A H,TRAN T,O’BRIEN D.A Gigabit/s Indoor Wireless Transmission Using MIMO-OFDM Visible-Light Communications[J].IEEE Photonics Technology Letters,2013,25(2):171–174.
[15]YAN F,WANG Y,SHAO Y,et al.Experimental demonstration of subcarrier multiplexing-based MIMO-OFDM system for visible light communication[C].201218th Asia-Pacific Conference on Communica-tions(APCC),2012,924–926.
[16]LU I C,LIU Y L,LAI C H.High-speed2X2MIMO-OFDM visible light communication employing phosphorescent LED[C].Eighth International Conference on Ubiquitous and Future Networks.IEEE,2016,222–224.