多包接收VLC系统的随机接入算法研究与性能优化

发布时间：2018-05-12 11:27

本文选题：可见光通信 + 随机接入　；参考：《吉林大学》2017年硕士论文

【摘要】：随着无线通信业务种类的与日俱增,有限的射频(RF)频谱资源已经无法满足人们的需求。可见光通信(VLC)以其频谱自由、无电磁干扰的特点成为无线射频通信互补技术,被期望能够克服射频通信的缺点,提供更高的数据速率。近年来,VLC研究方兴未艾,但多集中于调制编码等物理层(PHY)技术,媒体接入层(MAC)的算法及协议研究相对较少。IEEE 802.15 TG7提出IEEE 802.15.7作为短距离VLC的标准,提供了四种随机接入方式,其中最常用的是时隙基于冲突避免的载波侦听多路接入机制(CSMA/CA)。CSMA/CA在一定程度上缓解上行随机接入过程中的碰撞,提高系统性能。但由于VLC光波束较窄且具定向性,采用载波侦听的随机接入方式仍不能避免隐藏终端的存在,因此隐藏终端问题和通信链路被遮挡现象成为不可忽视的问题。目前,已有数种缓解隐藏终端的方法,例如提高发射功率、调整载波侦听阈值等。本文引入多包接收(MPR)技术解决隐藏终端问题。因此在多包接收VLC系统中,同时考虑隐藏终端及光遮挡信道情况下,如何提出合理的分析模型研究VLC系统,对进一步研究VLC有着举重若轻的意义。本文基于IEEE 802.15.7时隙CSMA/CA提出新的随机接入算法,并建模分析、优化VLC系统性能。首先,IEEE 802.15.7时隙CSMA/CA机制中,终端在竞争接入阶段(CAP)采用侦听、退避的方式竞争信道资源。由于标准中的CSMA/CA机制未考虑隐藏终端及遮挡,且不适用于接收端具有MPR能力的情况,因而本文首先致力于解决在多包接收VLC系统中,考虑光遮挡信道及欠载波侦听的情况下,如何提出适合理的接入算法及分析模型,研究系统性能指标。本文针对不饱和终端,采用On/Off马尔科夫源建模其数据生成过程;基于时隙CSMA/CA提出能够合理利用接收端MPR能力的接入算法,并利用马尔科夫链理论(Markov Chain)建模不饱和终端的数据到达过程和接入状态转移过程,将到达、遮挡以及隐藏终端的影响映射到Markov Chain转移概率中。基于此模型,推导系统性能指标,包括丢包率、吞吐量和接收功率效率,并分析到达、MPR能力、遮挡及隐藏终端对系统性能指标的影响。其次,MPR技术的引入增加接收端能量消耗,且在不饱和系统的流量到达先验不可知情况下,使用固定MPR能力会造成接收端资源利用不完全,增加能量浪费且网络失去灵活性。因此,如何随着活跃终端数的动态变化调整系统参数,在保证系统吞吐量的同时提高能量利用率,优化系统性能是本文拟解决的第二个问题。由于终端数据到达随机,活跃终端数时刻发生变化,接收端无法先验得知系统内活跃终端数,因此优化性能的第一步提出估计算法,为协调器动态提供系统中活跃终端数。第二步,提出MPR能力调整算法,令接收端根据活跃终端数调整MPR能力,周期性实现接收功率效率最大。在此基础上,提出退避窗口调整算法,终端以最大化系统吞吐量为目标,调整退避窗口;第三步,提出权衡算法联合调整最优MPR能力与最优退避窗口,权衡吞吐量与接收功率效率,最大程度上实现系统性能最大化。
[Abstract]:With the increasing number of wireless communication services, the limited radio frequency (RF) spectrum resources have been unable to meet the needs of people. Visible optical communication (VLC) has become a complementary technology for radio frequency communication with its free spectrum and no electromagnetic interference. It is expected to overcome the shortcomings of radio frequency communication and provide higher data rate. In recent years, VLC research The study is in the ascendant, but most of them focus on the physical layer (PHY) technology such as modulation and coding, and the research on the algorithm and protocol of the media access layer (MAC) is relatively less.IEEE 802.15 TG7. It provides the standard of IEEE 802.15.7 as a short distance VLC, and provides four kinds of random access methods, the most commonly used is the carrier interception multichannel access mechanism based on the collision avoidance in time slot. CSMA/CA).CSMA/CA alleviates the collision in the uplink random access process to a certain extent and improves the performance of the system. However, because of the narrower and directionality of the VLC light beam, the random access mode using carrier detection can not avoid the existence of the hidden terminal. Therefore, the hidden terminal problem and the blocking phenomenon of the communication link are a problem that can not be ignored. At present, there are several methods to mitigate the hidden terminal, such as improving the transmission power and adjusting the carrier detection threshold. In this paper, the multi packet reception (MPR) technology is introduced to solve the hidden terminal problem. Therefore, in the multi packet receiving VLC system, a reasonable analytical model is proposed to study the VLC system under the condition of the hidden terminal and optical occlusion channel. Further research on VLC is of great importance. In this paper, a new random access algorithm based on IEEE 802.15.7 time slot CSMA/CA is proposed, and the performance of VLC system is optimized. Firstly, in the IEEE 802.15.7 slot CSMA/CA mechanism, the terminal is competing in the competitive access phase (CAP) to compete for channel resources in the way of detection and backoff. Due to CSMA/C in the standard CSMA/C. The A mechanism does not consider the hidden terminal and occlusion, and does not apply to the MPR capability of the receiver. Therefore, this paper first aims to solve the problem of how to put forward the appropriate access algorithm and analysis model and study the system performance index in the case of multi packet receiving VLC system, considering the optical blocking channel and the under carrier interception. The terminal, using the On/Off Marco f source to model the data generation process; based on the time slot CSMA/CA, an access algorithm which can reasonably utilize the MPR capability of the receiver is proposed, and the Markov chain theory (Markov Chain) is used to model the data arrival process of the unsaturated terminal and the transfer process of the access state, and the impact of the arrival, occlusion and hidden terminals is reflected. The Markov Chain transfer probability is launched. Based on this model, the system performance index is derived, including the packet loss rate, throughput and receiving power efficiency, and the impact of the arrival, the MPR capability, the occlusion and hidden terminal on the system performance. Secondly, the introduction of MPR technology increases the energy consumption of the receiver, and the flow of the unsaturated system does not reach a priori. It can be seen that the use of fixed MPR capability will cause incomplete utilization of the receiver resources, increase energy waste and lose flexibility in the network. Therefore, how to adjust the system parameters with dynamic changes in the number of active terminals, improve the efficiency of the system while ensuring the throughput of the system, and optimize the performance of the system are the second problems to be solved in this paper. As the terminal data arrives at random, the number of active terminals is changed at all times, the receiver can not know the number of active terminals in the system priori, so the first step of the performance optimization is to provide the algorithm for the coordinator to dynamically provide active terminals in the system. The second step is to put forward the MPR capability tuning algorithm, so that the receiver adjusts the MPR energy according to the number of active terminals. The maximum efficiency of receiving power is achieved periodically. On this basis, a backoff window adjustment algorithm is proposed. The terminal adjusts the backoff window by maximizing the system throughput. The third step proposes a tradeoff algorithm to adjust the optimal MPR capability and the optimal backoff window, weighing the throughput and receiving power efficiency, and maximizing the systematicness. It can be maximized.

【学位授予单位】：吉林大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TN929.1

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