【作者】 张旭；

【导师】 赵春明；

【作者基本信息】 东南大学 ， 通信与信息系统， 2018， 硕士

【摘要】 近年来,随着移动通信技术的高速发展,人们对于数据流量的需求更加多样化,对传输速率和质量提出了新的要求,由无线射频技术支撑的传统无线通信由于频谱资源日益短缺渐渐不能满足人们对于数据流量的多元需求,而且随着环保观念的普及,人们对于通信技术的成本和节能性都有了新的标准,这些现状迫使人们寻找可以替代传统无线射频的通信技术。可见光通信正是在这样的背景下诞生。可见光通信因其频谱资源丰富、节能环保、绿色安全等特点,很快吸引众多学者和研究机构进行研究。本论文针对室内可见光通信的遮挡场景进行了研究,对遮挡判定、遮挡调度以及MAC层协议实现进行了论述。首先,本文概述了室内可见光通信系统的组成和基本原理。论文介绍了室内光通信系统的典型模型,以该模型为基准分别介绍了系统组成、信道模型和噪声模型,并对遮挡场景进行了概述。最后介绍了可见光通信MAC层协议,分别列举了 IEEE 802.15.7和ICT-213311 OMEGA两种现有的可见光通信MAC层协议。其次,本文对室内遮挡场景进行了分析。由于光波波长较短,无法穿透墙体等障碍物,可见光通信系统中的遮挡通常会造成通信环境急剧恶化,甚至引起通信中断。论文根据遮挡灯组情况不同,将遮挡物分为竖直型遮挡与水平型遮挡。通过对室内典型位置的用户遭受不同特性的遮挡进行仿真,分析了不同类型的遮挡对被遮挡用户的接收信噪比和系统整体吞吐量的影响。接着论文设计了基于上述遮挡分类办法的遮挡判定算法,并比较了不同灯组布局方式对判定准确度的影响,最终获得了较优的灯组布局方式。接着,本文进一步研究遮挡场景下的调度方法。由于遮挡造成了信道条件的急剧恶化,亟需改善,因此论文针对遮挡场景设计了相应的遮挡调度算法。论文对现有的适用于可见光通信的增量式灯组调度算法进行优化,基于遮挡判定的结果,对不同的遮挡情况实行不同的调度策略。对于竖直型遮挡,利用距离较近的未被遮挡灯组进行时隙补偿,对于水平型遮挡,利用相邻灯组进行时隙补偿。仿真结果验证了该遮挡调度算法可以有效降低遮挡造成的衰落影响。最后,本文介绍了可见光通信MAC层协议的模块实现。论文介绍了已有的改进版可见光MAC层协议的整体框架和模块划分,该改进版协议基于IEEE802.15.7标准修改而成。之后在改进版协议的基础上介绍了解关联模块和切换模块的帧结构和原语设计,针对切换过程中出现的乒乓效应和通信延时,论文设置了迟滞电平和驻留帧,并优化原有的切换流程,简化相关原语和帧交互的过程,通过提前为待切换的设备预留资源,将通信延时控制在可以接受的范围内。论文还在Linux主机和树莓派上,对两个模块进行了功能验证。更多还原

【Abstract】 In recent years,as the mobile communication technology develops rapidly,better quality and higher speed are required.However,traditional wireless communication using radio frequency(RF)as the medium gradually fails to meet people’s need due to the scarcity of spectrum resources.In addition,with the concept of green technology and environmental protection propagates,the cost and energy efficiency of communication technology are under consideration.Situations mentioned above urge new communication methods as replacement.Visible light communication(VLC)attracts a great attention for the advantages in rich spectrum resources,green and safe use,high energy conversion rate.This paper focuses on the analysis of obstacle environment of the VLC system and design of effective algorithm which can relieve obstacle’s effect,the design and implementation of MAC layer protocol are also included.Firstly,the paper gives an overview of the components of VLC system and its basic principles.The paper introduces a typical model of VLC system,based on which the detailed components,channel model and noise model are analyzed,and obstacle environment is also introduced.The paper also introduces the VLC MAC layer protocol,listing two popular MAC protocols,among which IEEE 802.15.7 standard is stressed.Additionally,the paper analyzes indoor VLC environment with obstacles.The paper divide the blocking situations into two categories,vertical obstacle and horizontal obstacle,according to the number of links being blocked.Simulations are made to show the effect of different obstacles on the receiving signal to noise ratio(SNR)and overall throughput.Then,based on the obstacle categorization mentioned above,obstacle decision algorithm is proposed and different patterns of light layout are applied to this algorithm so that the most suitable layout is selected.Furthermore,the paper studied the scheduling algorithm under obstacle effect.The paper proposed an improved method based on the incremental light scheduling algorithm suitable for the indoor VLC system.The proposed algorithm deploy different strategies to the blocked user based on the obstacle types.For vertical obstacles,time slots of non-blocked lights nearby are dedicated to the blocked user as compensation.For horizontal obstacles,time slots of adjacent non-blocked lights are shifted to the blocked user.Simulation results show the proposed algorithm can effectively relieve the attenuation caused by obstacles.Finally,the paper introduces the design and implementation of functionality modules in VLC MAC layer protocol.The paper introduces the overall framework and module division of an improved VLC MAC protocol based on the IEEE 802.15.7 standard.Then the frame structure and primitive design of disassociation module and handoff module are proposed.Strategies including hysteresis and dwell timer are introduced to the handoff process to eliminate the Ping Pong effect,and the handoff process is simplified to shorten the delay.In the simulation,we run the program representing coordinator on PC and run the program representing the device on the Raspberry,and the effectiveness of each function module was verified.更多还原