Research On Indoor MIMO VLC System Based On Prism Array Receiver

With the rapid increase of the number of mobile devices in the world,the traffic volume of high-speed communication is also experiencing a surge,which poses a great challenge to the traditional RF communication.Visible Light Communication(VLC),which takes into account both lighting and communication functions,has received extensive attention as a new research hotspot and is expected to become a powerful complement to futurc 6G technologies.Multiple Input Multiple Output(MIMO)technology can achieve higher data rates,which is of significance to study indoor MIMO VLC system.In the indoor MIMO VLC system,the receiver needs to have the characteristics of compact structure,small size and large angle of view.Due to the use of intensity modulation/direct detection techniques,ill-conditioned channel matrices may occur,resulting in reduced system performance.The prism array receiver with large field of view Angle can provide a good channel matrix in a compact structure and solve this problem.Therefore,indoor MIMO VLC system based on prism array receiver is studied,which mainly includes the following contents:(1)The principle of the prism array receiver is studied,and its channel is modeled.The performance of the prism array receiver is analyzed from the aspects of the field of view,the directionality of the receiving element and the rank of the channel matrix.An improved prism array receiver is proposed to solve the problem of receiving blind area,which is caused by the limited field of view of the receiver.We simulate and analyze the influence of the prism shape,tilt angle and the number of receiving elements on the prism array receiver.Simulation results show that the improved prism array receiver effectively improves the BER performance of the system.(2)Since traditional Asymmetrically Clipped Optical Orthogonal Frequency Division Multiplexing(ACO-OFDM)technology does not make full use of the spectrum resource,the layered ACO-OFDM technology is applied to improve the system's frequency efficiency.The indoor VLC system based on layered ACO-OFDM is extended from the single-input single-output ideal channel model to the actual MIMO channel model using the improved prism array receiver.The demodulation process of the signal has been divided into two stages.In the first stage,three first-stage receivers are used to eliminate inter-layer interference,and the estimated transmitted signal in each layer is obtained.In the second stage,the four second-level receivers are studied to suppress the additional noise and improve the bit error rate performance of the system.We simulate and analyze the performance of three first-level receivers and four second-level receivers,and discussed the impact of receiver position on BER performance(3)Similar to the radio frequency system,VLC can simultaneously support multiple user equipments,pushing forward multi-cell multi-user MIMO VLC system.By dividing cells and reusing spatial spectrum resources,the transmission rate of the system is improved.Existence of inter-cell interference,intra-cell interference and channel correlation make it harder to research multi-cell multi-user MIMO VLC system.Using the improved prism array receiver can significantly lower the channel correlation.Taking advantage of the strong directivity of each receiving element in the receiver,non-dynamic cell division method is proposed to eliminate inter-cell interference.According to user distribution,We propose a dynamic cell division method to eliminate inter-cell interference and use block diagonalization procoding technology to clear intra-cell interference.On this basis,we use the photodetector selection technology and optimize the parameters of receiver to improve the performance of the system,and analyze its computational complexity.We simulate and compare the performance of the space-separated receiver and the improved prism array receiver,and make discourse upon performances of proposed two cell division methods.