Research On Non-ideal Transmission Performance Of Indoor Visible Light Communication Based On OFDM

As an emerging field of optical wireless communication systems,visible light communication has received more and more attention in recent years.Orthogonal frequency division multiplexing(OFDM)has been used in visible light communication systems as an effective technique to improve spectrum efficiency.However,non-ideal transmission problems such as inter-symbol interference caused by multipath effects and limited bandwidth of LEDs in visible light communication systems have seriously affected the development of visible light communication systems,restricted the high-speed data transmission rate,and affected the performance and stability of the entire communication system.In response to the problems raised,this article will use channel estimation and equalization technology to improve the non-ideal transmission performance in the visible light communication system——reduce the BER of data and increase the transmission rate of the system.The main innovations of this article are as follows:First of all,an artificial neural network(ANN)adaptive channel equalization technology based on indoor visible light communication is proposed in this paper,which constructs an ANN equalizer and converts the equalization problem into the classification problem,and uses the fitting and prediction properties of ANN to equalize the received signal sequence.The simulation results show that the mean square error after using the ANN equalizer is reduced by three to four orders of magnitude compared with the traditional equalizer.Besides,under the same transmission conditions,the ANN equalizer can use less training length(TL)to obtain better error performance,reduce system complexity,and improve throughput.When the data transmission rate is 200Mbit/s and SNR=25dB,the ANN linear equalizer only needs to use the training length of 200 bits to achieve the error performance of the traditional linear equalizer using the training length of 1000 bits;when TL=500,the error performance of ANN decision feedback equalizer is similar to that of traditional equalizer when TL=2000.The above results indicate that the higher the information transmission rate,the more obvious the advantages of the ANN equalizer.It proves that ANN equalizers can better meet the needs of high-speed visible light communication systems than general equalizers.Secondly,this paper designs an improved DFT channel estimation algorithm suitable for indoor visible light OFDM systems,which can filter most of the noise in the cyclic prefix.According to the different baseband modulation conditions of visible light communication system based on OFDM,the performance of the system after using LS channel estimation algorithm,DFT channel estimation algorithm and improved DFT algorithm is compared and analyzed.The simulation results show that whether using BPSK,QPSK,16QAM or 32QAM modulation,the system performance after using the improved DFT channel estimation algorithm is the best.And the higher the modulation order is,the more obvious the advantage of the improved DFT algorithm compared to the other two algorithms.