Research On Indoor Visbile Light Communication System Based On MIMO Technology

The visible light communication(VLC)uses visible light as the signal transmission carrier,which can achieve the illumination and communication without extra hardware cost.VLC technology offers a new solution to wireless high-seed communication due to its electromagnetic radiation-free,wide usage frequency band and the popularity of LED lighting devices.In the actual visible light communication,the indoor visible light communication system with MIMO technology can provider higher transmission rate,at the same time,it introduces the multipath effect of the optical path and lends to inter-symbol interference.And the bit error tare performance is reduced.To improving error tare performance,the equalization and proper signal detection algorithms at the receiver can be used.At present,there are few researches on the equalization technology under the condition that the visible light channel changes slowly in the real indoor environment.At the same time,there are few researches on the multiuser signal detection technology in visible light communication.Based on the above problems,the research contents of this paper are divided into the following three aspects.Firstly,the basic principle of non-imaging MIMO visible light communication system is introduced,the channel model is established,and the channel impulse response is analyzed.Based on the analysis,the performance indicators,including illumination distribution,received power distribution,and signal to noise ratio distribution under the direct reflection and the reflection are analyzed.The influence of the distribution of four different LED arrays in the elevator on the light intensity distribution of the system is studied.And then the relationship between the angle of view(FOV)and the factor Q,which measures the uniformity of signal to noise ratio,is studied.When the FOV is 65°,the signal-to-noise ratio is most evenly distributed on the receiving plane,with the least difference in communication performance at each location.Secondly,the equalization techniques of MIMO indoor visible light communication system are studied,including pre-equalization and channel equalization.The pre-equalization includes zero-forcing(ZF)equalization and minimum mean square error(MMSE)equalization.The adaptive equalization algorithms in channel equalization mainly include LMS equalization algorithm,RLS equalization algorithm and blind equalization algorithm.In the case of channel equallization,in view of the fact that the channel of indoor visible light communication changes slowly in general,this paper proposes an improved ISLMS algorithm for the case of slow channel change.The improved algorithm can achieve the same bit error rate with smaller iterations rate performance;For the blind equalization algorithm,the constant modulus algorithm(CMA)is mainly analyzed.Finally,the signal detection algorithms of indoor visible light communication MIMO system are studied,the linear detection including zero forcing(ZF)detection algorithm and minimum mean square error(MMSE)detection algoritlhm;the nonlinear detection algorithm including maximum likelihood(ML)algorithm,ordered successive interference cancellation detection algorithm and lattice reduction aid(LR)detection algorithm.The detection performance of these algorithms is simulated.Based on the analysis above,in the multiuser environment,the LLL in the LR detection algorithm is introduced to the ML-OSIC algorithm and an improved M-ML-LLL-OSIC algorithm is proposed,and the improvement of the algorithm is simulated.The performance of the improved algorithm is close to that of ML.When the SNR is 30dB,the BER performance of the improved algorithm is lower about 3 orders of magnitude than ZF detection.