The Multi-user Access And Interference Management For Indoor Visible Light Communication Networks

Light emitting diodes(LEDs),a type of solid-state lighting device,is revolution-izing the indoor illumination.Apart from extremely high energy efficiency,LEDs have the ability of switching to different lighting intensity at a very fast rate,which prepares LED to serve as a communication transfer resulting in visible light communi-cations(VLC).While the radio frequency communication is suffering from the rapidly dwindling spectrum,VLC have received tremendous interest due to unregulated con-siderable spectrum,natural confidentiality,electromagnetic compatibility,convenient deployment,etc.As VLC have been proposed as a promising candidate for 5th genera-tion wireless networks,the research is upgraded from link analysis to network applica-tions.In VLC networks,the cell coverage is limited to small area for the light propaga-tion characteristics and user field-of-view,and thus cells should be densely distributed which poses high requirement to the multi-user access scheme.Furthermore,the user in the overlapping areas of adjacent cells receives line-of-sight signals from multiple access points.As a result,interference management strategy is urgently needed.In this thesis,the multi-user access and interference management scheme are carefully studied for the indoor VLC networks.Firstly,the characteristics of the transceiver are summarized and the indoor multi-path optical channel is studied by Monte-Carlo simulation.Besides,some signal mod-ulation and multi-user access techniques are listed and analyzed.Secondly,the optical interference alignment technique is proposed.The precoding method is specially de-signed for the 2×2 VLC network with which the communication algorithm can adjust the coefficients to fit the user need of bit-of-error rate(BER).The simulation results reveal the BER performance is lowered by interference alignment compared to random precoding.Thirdly,the framework of non-orthogonal multiple access(NOMA)VLC networks is researched.The multi-user access scheme based on user locations is pro-posed and the inter-cell interference is avoided by proper user grouping.The power allo-cation within each cell is optimized to improve the sum user rate or the max-min user rate under quality of service constraint.For the formulated non-convex optimization prob-lem,the gradient-projection method is adopted and some approximate transformation is performed to eliminate the non-differentiability of the minimum objective function.As the channel estimation error may exist,the residual interference during the process of successive interference cancellation in NOMA is taken into account.The simulation results demonstrate the effectiveness of the proposed multi-user access scheme in avoid-ing inter-cell interference.The NOMA technique significantly improves the user rate compared to orthogonal multiple access although the residual interference can degrade the system performance.