本文選題：可見光通信 + 隨機接入��； 參考：《吉林大學》2017年碩士論文

【摘要】：隨著無線通信業(yè)務種類的與日俱增,有限的射頻(RF)頻譜資源已經(jīng)無法滿足人們的需求。可見光通信(VLC)以其頻譜自由、無電磁干擾的特點成為無線射頻通信互補技術(shù),被期望能夠克服射頻通信的缺點,提供更高的數(shù)據(jù)速率。近年來,VLC研究方興未艾,但多集中于調(diào)制編碼等物理層(PHY)技術(shù),媒體接入層(MAC)的算法及協(xié)議研究相對較少。IEEE 802.15 TG7提出IEEE 802.15.7作為短距離VLC的標準,提供了四種隨機接入方式,其中最常用的是時隙基于沖突避免的載波偵聽多路接入機制(CSMA/CA)。CSMA/CA在一定程度上緩解上行隨機接入過程中的碰撞,提高系統(tǒng)性能。但由于VLC光波束較窄且具定向性,采用載波偵聽的隨機接入方式仍不能避免隱藏終端的存在,因此隱藏終端問題和通信鏈路被遮擋現(xiàn)象成為不可忽視的問題。目前,已有數(shù)種緩解隱藏終端的方法,例如提高發(fā)射功率、調(diào)整載波偵聽閾值等。本文引入多包接收(MPR)技術(shù)解決隱藏終端問題。因此在多包接收VLC系統(tǒng)中,同時考慮隱藏終端及光遮擋信道情況下,如何提出合理的分析模型研究VLC系統(tǒng),對進一步研究VLC有著舉重若輕的意義。本文基于IEEE 802.15.7時隙CSMA/CA提出新的隨機接入算法,并建模分析、優(yōu)化VLC系統(tǒng)性能。首先,IEEE 802.15.7時隙CSMA/CA機制中,終端在競爭接入階段(CAP)采用偵聽、退避的方式競爭信道資源。由于標準中的CSMA/CA機制未考慮隱藏終端及遮擋,且不適用于接收端具有MPR能力的情況,因而本文首先致力于解決在多包接收VLC系統(tǒng)中,考慮光遮擋信道及欠載波偵聽的情況下,如何提出適合理的接入算法及分析模型,研究系統(tǒng)性能指標。本文針對不飽和終端,采用On/Off馬爾科夫源建模其數(shù)據(jù)生成過程;基于時隙CSMA/CA提出能夠合理利用接收端MPR能力的接入算法,并利用馬爾科夫鏈理論(Markov Chain)建模不飽和終端的數(shù)據(jù)到達過程和接入狀態(tài)轉(zhuǎn)移過程,將到達、遮擋以及隱藏終端的影響映射到Markov Chain轉(zhuǎn)移概率中。基于此模型,推導系統(tǒng)性能指標,包括丟包率、吞吐量和接收功率效率,并分析到達、MPR能力、遮擋及隱藏終端對系統(tǒng)性能指標的影響。其次,MPR技術(shù)的引入增加接收端能量消耗,且在不飽和系統(tǒng)的流量到達先驗不可知情況下,使用固定MPR能力會造成接收端資源利用不完全,增加能量浪費且網(wǎng)絡失去靈活性。因此,如何隨著活躍終端數(shù)的動態(tài)變化調(diào)整系統(tǒng)參數(shù),在保證系統(tǒng)吞吐量的同時提高能量利用率,優(yōu)化系統(tǒng)性能是本文擬解決的第二個問題。由于終端數(shù)據(jù)到達隨機,活躍終端數(shù)時刻發(fā)生變化,接收端無法先驗得知系統(tǒng)內(nèi)活躍終端數(shù),因此優(yōu)化性能的第一步提出估計算法,為協(xié)調(diào)器動態(tài)提供系統(tǒng)中活躍終端數(shù)。第二步,提出MPR能力調(diào)整算法,令接收端根據(jù)活躍終端數(shù)調(diào)整MPR能力,周期性實現(xiàn)接收功率效率最大。在此基礎上,提出退避窗口調(diào)整算法,終端以最大化系統(tǒng)吞吐量為目標,調(diào)整退避窗口;第三步,提出權(quán)衡算法聯(lián)合調(diào)整最優(yōu)MPR能力與最優(yōu)退避窗口,權(quán)衡吞吐量與接收功率效率,最大程度上實現(xiàn)系統(tǒng)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.

【學位授予單位】：吉林大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：TN929.1

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