| With sharp increase of global mobile data traffic,a new wireless communication technology——visible light communication(VLC)has attracted more and more attention in the market.As a potential enabling technology of 6G,it uses light emitting diode(LED)that can emit light source as the transmitting antenna to realize the communication target expectation of high peak rate,high-precision positioning,low delay jitter,high security and three-dimensional coverage while compatible with lighting.However,in order to meet the increasing mobile data traffic,visible light communication technology based on multiple input multiple output(MIMO)has attracted extensive attention in the academic community.Therefore,it is of great significance to study how to realize high-speed and reliable VLC MIMO system on the premise of compatible lighting.The topic of this paper comes from the project "Research on spatial dimming theory and technology of visible light communication" supported by the National Natural Science Foundation of China(Project No.:61871047).Due to nonlinear characteristics of LEDs,the interference between different data streams and the high correlation of visible channel in VLC MIMO system,this paper studies the spatial dimming algorithm in VLC MIMO system in order to realize VLC MIMO system compatible with lighting and communication.The main contents and innovations of this topic are as follows:1.Adaptive amplitude spatial dimming algorithm based on repeated coding is studied.In order to solve the problem of clipping noise caused by peak to average peak ratio(PAPR)of optical orthogonal frequency division multiplexing(O-OFDM)modulation signal in VLC MIMO system,an amplitude adaptive spatial dimming algorithm based on repeated coding is proposed in this paper,which is,based on adaptive DC optical orthogonal frequency division multiplexing and generalized-spatial dimming control(ADCO-OFDM-GDC)algorithm.The basic idea of algorithm is:under constraint of fixed dimming level,adaptive amplitude O-OFDM modulation signal based on piecewise function is designed,and spatial domain,time domain and signal domain resources in VLC MIMO system are combined to achieve goal of high reliability and high rate communication performance of VLC MIMO system.Then PAPR and clipping noise of algorithm are analyzed.Theoretical and simulation results show that the proposed algorithm can improve dimming control range and communication reliability of system;Compared with the existing traditional spatial dimming algorithm,while bit error rate(BER)of the proposed algorithm is 3.8 × 10-3,signal-to-noise ratio(SNR)gain of 1 dB to 6 dB can be obtained;On the premise of keeping the spectrum efficiency unchanged,dimming control range of the proposed algorithm is wider.2.Adaptive amplitude spatial dimming algorithm based on spatial multiplexing is studied.In order to solve interference between different data streams and decline of system communication caused by high correlation of visible channel in VLC MIMO system,an adaptive amplitude spatial dimming algorithm based on spatial multiplexing,which is,QR decomposition ordered successful interference cancellation(QROSIC)dimming algorithm,is proposed in this paper.The basic idea of the algorithm is:under the given dimming level constraint,construct optimization problem with maximizing the system reachable combining rate as the optimization goal,and then find corresponding optimal value of electric power allocation.Then,interference between different data streams is divided into two parts.The first half of interference uses QR decomposition to obtain the precoding matrix from the channel matrix for pre-elimination of interference at transmitter,the second half of interference uses OSIC detector to eliminate remaining interference step by step in the iterative cycle at receiving end.The algorithm effectively eliminates interference between data streams,reduces the impact of visible channel correlation on the performance of the communication system,and improves the effectiveness,multiplexing gain and system achievable rate of communication system.Then,the complexity of the proposed algorithm and the traditional linear precoding dimming algorithm are analyzed,and main source of algorithm overhead is pointed out.Finally,theoretical and simulation results show that compared with the traditional linear precoding algorithm,there is a performance gain of 10 dB,and system can achieve the highest combining rate. |
