Optical Spatial Modulation For Atmosphere Laser Communication

In recent years,with the rapid increase in data transmission traffic,higher requirements have been put forward for the quality of communication services.Traditional wireless optical communication(WOC)technology has been unable to meet the high data rate requirements of users.Optical multiple-input multiple-output(MIMO)technology provides an effective means to solve the above problems.However,there are still many problems in the traditional optical MIMO technology,such as strong inter-channel interference caused by multi-beam transmission,high complexity of receiver interference cancellation algorithm and signal detection algorithm,and high requirement of inter-antenna synchronization.As a special MIMO technology,spatial modulation(SM)uses traditional digital modulation constellation(i.e.signal domain)and active antenna position(i.e.space domain)to convey information.Therefore,higher spectral efficiency can be obtained than the classical systems.Meanwhile,since only one link is responsible for transmitting signals in each time slot,the SM avoids the problem of inter-channel interference.So,there has been a research boom in the field of wireless communications.Current WOC systems mostly adopt intensity modulation/direct detection(IM/DD)method,which makes the SM technology in radio communication can not be directly applied.Therefore,based on the characteristics of wireless laser communication systems,combined with L-PPM modulation,this paper studies the optical spatial modulation technology suitable for atmospheric laser communication system,and proposes improved algorithms for the detection of high complexity in the system.Specifically as follows:(1)For the problem of high complexity of maximum likelihood decoding algorithm(ML),a transmitting signal with sparse characteristics is constructed by mapping the optical spatial modulation laser vector and the pulse position modulation pulse vector together.Based on the constructed transmitting signal with sparse characteristics and employing orthogonal matching pursuit algorithm,a compressed sensing based optical spatial modulation signal detection method is proposed.Simulation results show that the method can greatly reduce the computational complexity at the cost of a small amount of error performance loss.Moreover,due to the introduction of sparsity,the proposed method is more suitable for wireless optical communication systems with large-scale lasers.(2)Generalized optical space modulation(GOSM)combines the advantages of OSM and spatial multiplexing,effectively improves the spectral efficiency of OSM system,and overcomes the limitation of OSM on the number of transmitting antennas,but it increases the complexity of signal detection.Therefore,according to GOSM technology,an OB-MMSE based signal detection algorithm suitable for GOSM is proposed.This algorithm uses OB-MMSE signal detection method and its parameters are modified according to the characteristics of GOSM scheme,which has less complexity compared with maximum likelihood(ML)decoding algorithm.Furthermore,the equation for threshold selection in lognormal turbulence channel is derived.Simulation results show that the proposed OB-MMSE algorithm can effectively reduce the computational complexity at the expense of a small system error performance reduction compared with ML algorithm.Compared with MMSE algorithm,it can effectively reduce the system bit error rate and is also applicable to systems with less receivers than transmitters at the cost of a slight increase in algorithm complexity.