Optimized Design Of User Scheduling Scheme Based On Indoor Visible Light Communication System

Visible light communication is a new type of wireless communication technique. Since it can fulfill the functions of illumination and high speed wireless communication simultaneously, and it has the advantage of no electromagnetic radiation, natural confidentiality, VLC is considered a promising communication method.In the development of VLC technology, there also exist many problems. In the studies of indoor VLC system, most of them focused on point-to-point VLC technologies. In such scenarios, inter-user interference is not involved. So for multi-user VLC scenarios in which multiple optical access points transmitting data to multiple receivers, as each AP can only serve at most one single user in a time slot, when an AP is in two or more than two users’ receiving range, there is interference between users. And the inter-user interference constitutes the major factor limiting the performance of VLC system.Therefore, we built a multi-user indoor VLC system firstly, and designed three different kinds of AP layout: ring layout, cellular layout and grid layout. In the process of communication, multiple APs transmit signals to multiple users at the same time. Then we studied a scheduling scheme based on graph theory, greedy algorithm and the concept of virtual cell, and we compared our improved schedule scheme with the original scheme.In our improved scheme, we used conflict graph of graph theory to model the inter-user interference firstly, then improved the calculation of user’s priority and weight. This way, the scheduling problem can be transformed into a Maximum weighted independent set(MWIS) problem. For a MWIS problem, the greedy algorithm is undoubtedly the most applicable method. When we found the MWIS of the conflict graph, the active users of the current time slot are decided. For each active user, all APs within its receiving range will form a virtual cell and broadcast identical signals simultaneously to enhance transmitting diversity. This is our schedule algorithm. Then we compared our improved scheme with the original scheme of users’ sum capacity under three different kinds of LED layouts, and we found the best field of view of each LED layout through simulation.Simulation results shows that our schedule scheme improved users’ sum capacity compared to the original scheme. And our improved scheme reduced the hardware complexity and calculation. At the same time, our schedule scheme can avoid inter-user interference, optimize the performance of the system, ensure a certain degree of user fairness. Finally, improve the communication quality of indoor VLC system effectively.