Research On Signal Recovery For VLC System With Incomplete Channel

Visible light communication（VLC）has attracted much attention because of its high data rate and energy efficiency.In general,the system performance of VLC depends heavily on perfect channel state information.However,the incomplete channel due to the link blockages caused by shadowing is one of challenges in VLC system.Therefore,it is necessary to develop an effective approach against shadowing effect.In VLC system,considered that the mobile people or obstacles would be at random positions with any shape and size,the standard channel uncertainty model,such as norm-bounded error and statistical error,cannot be implemented in the shadowing scenario.Considering the shadowing caused by the mobile obstacles,we model the dynamical link blockages as randomly selected zero elements.The corresponding channel is composed by the incomplete channel matrix and the shadowing loss matrix.With the incomplete channel,we strive to recover the transmitted signal by7)₀-norm minimization of the transmitted signal while eliminating the effect of missing elements on system performance.It is further approximated as7)₁-7)₁ minimization with optimum solution iteratively achieved via alternating direction method of multipliers（ADMM）algorithm.In this paper,several signal recovery algorithms are compared from the aspects of convergence speed,mean square error and bit error rate.Simulation results indicate that the effectiveness of the proposed ADMM algorithm on robust signal recovery.Moreover,due to the small emitter separation of the PDs,the indoor VLC channel responses among the users could be highly correlated,handicapping the performance of the aforementioned signal recovery.To further improve the accuracy performance,we design the transmit beamforming to reduce the mutual coherence of the equivalent sensing matrix.However,it is difficult to compute the mutual coherence of the equivalent sensing matrix,especially when the number of transmit/receive antenna is large.Therefore,considering that the recovery accuracy is more related to the average coherence,we introduce the total coherence and develop the beamforming design to reduce the total coherence.Simulation results validate that the minimize total coherence（MTC）algorithm can effectively reduce the transmit coherence,reduce the mean square error and bit error rate,further enhance the accuracy of the signal recovery.