Research And Implementation On The Key Networking Techniques For Indoor Visible Light Communications

Visible Light Communication (VLC), a new short-range high-speed wireless communications technology, provides a powerful complement to the indoor networks. It is necessary to provide VLC networking supports for meeting various application requirements. However, the networking techniques in Radio Frequency (RF) wireless communication are not suitable to be used in VLC network, owing to the characteristics of the optical link including a strong directivity, a small coverage and a poor diffraction. As a result, data collisions cannot be avoided through carrier sense, the communication requirements of multiple users cannot be satisfied by a small optical cell, and the optical links can be interrupted frequently due to obstacles and terminals’mobility.To solve above problems, this dissertation focuses on the multiple access techniques as foundation of VLC networking, the optimization method for full frequency reuse based cellular networks, RGB-LED based downlink resource allocation algorithm and a fast recovery algorithm for enhancing link robustness. The main work and innovations are summarized as follows:1. A Media Access Control (MAC) protocol with the estimation of the number of active terminals is proposed considering directional hidden terminals. An Extend Kalman Filter (EKF) based algorithm for estimation the number of active terminals is proposed which calculates the network traffic periodically. The estimation of the number of active terminals is achieved by the algorithm of which the Mean Squared Error (MSE) is lower than three. According to estimation results, the access point (AP) schedules the transition of uplink data so that the data collisions would be controlled by receivers. Simulation results show that the system throughput reaches 87% stably for different network traffic.2. Coverage optimization and downlink resource allocation are studied for the co-channel interference (CCI) between adjacent cells. An optimization method for downlink seamless coverage based on full frequency reuse cellular networks is proposed. For minimizing the areas of communication and illumination dead zones, this method analyzes the influences of different light layouts and computes optimal LEDs’semi-angles at half-power and heights with genetic algorithm. The simulation results show that the seamless coverage of the communication and illumination can be approximately achieved after optimization and about 75% communication coverage improvement is achieved when illumination requirement is fulfilled. An RGB-LED based downlink resource allocation algorithm supporting multiple users is proposed. A global allocation algorithm is studied first for improving cell utilization ratio. Then a graph coloring based channel allocation algorithm is proposed after constructing downlink conflict graph model. Simulation results show that the proposed algorithm doubles the mean cellular network throughput and maintains the fairness of users’ communication as well compared with cellular network based on channel fixed allocation.3. A fast recovery algorithm for enhancing link robustness in VLC cellular networks is proposed in view of frequency link interruption. A link interruption is discovered depending on a signal-noise-ratio threshold. And features of different kind of interruptions are deduced. Furthermore, the interruptions are classified by using support vector machines (SVM), with an accuracy of 99.42%. Integrating the delay and signaling costs, a price function of the link interruption is then calculated, and a fast link recovery mechanism is designed based on interruption classification. Simulation results show that while achieving improved link interruption delay and signaling costs, the algorithm also realizes a minimum link interruption price and enhances the link robustness.4. A MAC protocol for VLC based Coal Mine Integrated Information System is designed and implemented considering the special networking environment and application demand in the coal mine. Frame construers and protocol procedure are given. And the solution of software implementation for the protocol is designed. Through system testing the functional requirements of the MAC protocol are verified.