可见光通信系统MAC层协议研究

发布时间：2018-10-12 07:40

【摘要】：可见光通信因为具有提供照明、频谱免许可、绿色环保、安全性高等优点,成为近年来无线通信领域的研究热点之一。本文主要研究室内可见光通信场景下的媒体接入控制(MAC)层协议,主要工作如下:一、针对下行链路为多LED覆盖方案,上行链路为传统无线或红外光方案的室内可见光通信系统,提出了将无线通信场景下的接入协议应用于此室内可见光通信场景下的调整方案,并改进了接入方案中的退避算法。由于在多LED场景下,用户终端不能相互侦听,为了能够使协调器掌握用户终端的相对位置,因此在传统无线的RTS/CTS模式基础上,增加了一次RTS/CTS过程。推导了用户接入碰撞概率和系统归一化吞吐量的数学表达式。此外还针对接入方案中的退避算法,结合缓慢减小竞争窗口方案和快速解决碰撞方案的优点,提出了改善用户接入公平性的改进方案。二、提出了一种改进的自适应保障时隙分配方案。结合不均匀的保障时隙分配方案和共享的保障时隙分配方案的优点,提出了改进的自适应保障时隙分配方案。改进方案融合了前两种方案,且用户周期性的反馈到达速率,从而使得协调器能够尽快调整保障时隙分配,避免由于用户到达速率的迅速下降引起的保障时隙带宽利用率的骤降。三、提出了可见光通信场景下的用户接入和保障时隙分配优先级实现方案。用户接入优先级方案的基本思路:高优先级用户设置较小的初始竞争窗口和较小的最大退避阶数,而低优先级用户设置较大的初始竞争窗口和较大的最大退避阶数。与低优先级用户相比,高优先级用户更容易接入系统。此外还推导了优先级接入的用户接入碰撞概率和系统归一化吞吐量的数学表达式。保障时隙分配的优先级实现方案的思路:各个优先级用户可使用的保障时隙数目不定,与用户申请保障时隙的到达速率有关;高优先级用户可使用的保障时隙数目较多,相应的保障时隙申请阻塞率较低;低优先级用户可使用的保障时隙数目较少,相应的保障时隙申请阻塞率较高。四、对比分析了可见光通信场景下硬切换和软切换性能差异。在介绍硬切换和软切换方案的区别的基础上,运用排队论方法,推导了两种切换方案的新呼叫阻塞率和切换呼叫丢弃率这两个性能指标的数学表达式。
[Abstract]:The visible light communication has become one of the research hotspots in wireless communication field in recent years because of its advantages of providing lighting, spectrum exemption, environmental protection, high security and so on. This paper mainly studies the (MAC) layer protocol of media access control in indoor visible light communication scene. The main work is as follows: first, for indoor visible light communication system with multiple LED coverage scheme in downlink and traditional wireless or infrared light scheme in uplink, In this paper, the access protocol in wireless communication scenario is applied to the adjustment scheme of the indoor visible light communication scenario, and the Backoff algorithm in the access scheme is improved. Because the user terminal can not listen to each other in the multi-LED scenario, in order to enable the coordinator to grasp the relative position of the user terminal, a RTS/CTS process is added based on the traditional wireless RTS/CTS mode. The mathematical expressions of user access collision probability and system normalized throughput are derived. In addition, aiming at the Backoff algorithm in the access scheme, combining the advantages of the slow reduction of competitive window scheme and the fast collision resolution scheme, an improved scheme to improve the fairness of user access is proposed. Secondly, an improved adaptive guaranteed slot allocation scheme is proposed. An improved adaptive guaranteed slot allocation scheme is proposed by combining the advantages of uneven guaranteed slot allocation scheme and shared guaranteed slot allocation scheme. The improved scheme combines the first two schemes and the periodic feedback arrival rate of the user, which enables the coordinator to adjust the guaranteed slot allocation as soon as possible. To avoid the sudden drop of bandwidth utilization of guaranteed slot caused by the rapid decline of user arrival rate. Thirdly, the scheme of user access and time slot allocation priority in visible light communication is proposed. The basic idea of user access priority scheme is that high priority users set smaller initial contention window and smaller maximum Backoff order, while lower priority users set larger initial competition window and larger maximum Backoff order. High priority users have easier access to the system than low priority users. In addition, the mathematical expressions of user access collision probability and system normalized throughput for priority access are derived. The idea of the priority implementation scheme for guaranteeing slot allocation: the number of guaranteed slots available for each priority user is variable, which is related to the rate of arrival of the guaranteed slot, and the number of guaranteed slots that can be used by high-priority users is higher. The corresponding guaranteed slot request blocking rate is lower, and the low priority user can use less secure time slot number, and the corresponding guaranteed slot request blocking rate is higher. Fourthly, the performance differences between hard handoff and soft handoff in visible light communication scene are compared and analyzed. On the basis of introducing the differences between hard handoff and soft handoff schemes, the mathematical expressions of the new call blocking rate and the handoff call dropping rate of the two handoff schemes are derived by using the queuing theory method.
【学位授予单位】：东南大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TN929.1

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