车辆自组网物理层性能改进

发布时间：2018-04-20 05:38

  本文选题：车辆自组网 + 物理层　； 参考：《东南大学》2016年博士论文

【摘要】：随着无线通信技术的日益普及和对其它技术领域的广泛渗透,汽车制造业正在积极寻求利用无线通信技术提升市场竞争优势的方案。本文中,车辆自组网(VANET)已有诸多应用,例如安全、救援、勘探、军事、人口稀疏地的冗余通信、以及作为智能交通系统(ITS)重要组成部分的传统城市及高速公路通信。不过,这一技术的渗透尚显不足,仍有大量问题亟待解决,以建造弹性、可靠、高效的车辆自组网。通信服务质量(QoC)主要取决于物理层(PHY)的可靠性,其中包含了VANET中各类颇有挑战性的问题。车辆的高速运动会导致VANET中的大量碎片化和拓扑不定性。PHY的性能是提升通信质量的一个关键因素。物理层需要解决有限带宽、应用需求以及不稳定和碎片化的网络拓扑。本文主要研究物理层,包括与VANET应用相关的问题、挑战及研究机遇。主要贡献和创新如下：1.提出了通过理论途径显著提升车辆网络通信性能的方法,即在不改变带宽、费用及系统复杂度的前提下,提升物理层OFDM系统的性能。本文提出了一种通用模型来描述车辆通信场景的物理层传输技术,能够解决车辆通信中一些具有挑战性的问题,并从理论上探究不同传输场景下的通信效果。物理层的传输过程包含了诸多复杂步骤,本文模型对其均有涉及。该模型对应着IEEE 802.11p的物理层结构,也描述了车辆网络中的无线信道特征,并发展了用参数化形式描述信道最重要特征的简化信道模型。该模型随后将用于评估系统性能并研究物理层的挑战,以提升车辆网的总体通信效率。2.应用代数lattice理论及其它数学工具改进OFDM系统,从而直接提升了整个VANET物理层的性能。为了改进通信的可靠性,采用order理论和Hamming距离,提出了一种适用于车辆网络的高阶OFDM分集方案,其频域分集通过在传输符号中规定特定的相关性来实现。由于子信道历经独立衰落,至少有一个符号拥有可靠的信噪比,接收机可利用该符号来检测其它符号。3.研究了利用最小二乘(LS)和最小均方误差(MMSE)的信道估计器,发展了一种提高VANET物理层通信性能的新方法。该方法通过将DFT和SVD与LS和MMSE相结合,提升了系统性能,并降低了系统复杂度。4.针对车辆网络提出了一种新型的符号同步技术,即利用不同OFDM子载波之间的功率差异和定时误差导致的相移。该方案采用3种方法最小化由于符号时间偏移导致的子载波干扰(ICI)和码间干扰(ISI)。第一种方法通过第一个OFDM接收符号来检测由定时误差而导致的子载波相移,以此来估计时移,即利用了时移导致的相移来估计定时误差,故本文称其为相移估计器(PSME);第二种方案最小化相邻子载波在同一OFDM符号内的功率差异,假设了这些子载波的信道响应近似相同。因其仅在频域利用子信道,故称为频域累计功率差异估计器(FD-APDE);第三种方案通过测量相邻OFDM符号的等下标的子载波功率差异,假设了信道在两个相邻OFDM符号之间是缓变的,故叫做时域累计功率误差估计器(TD-APDE)。这3种估计器均为全盲估计,因为接收端没有任何关于发送数据或者信道状态(CSI)的信息,但这些信息能够极大地提高估计器的性能。为了在不同的VANET场景提供定时同步,这些估计器能够组合与互补应用。5.利用物理层的内在随机性来提高车辆网络的安全性。探索了利用通常被视作不利因素的噪声和干扰作为提高安全性的随机因子的可能,提出了一种针对车辆网络的密钥生成方法,其利用了无线信道本身的随机特性。把由于车辆移动、噪声、多径衰落而导致的接收信号场强(RSS)变化量化后用来生成密钥。仿真结果显示该算法尤其适合VANET,因为VANET的多种工作环境比其它通信系统的随机性更强。本文算法能够提取高熵率的高速或低速密钥,且合法车辆间的信息交换量更少。该密钥能够用于诸多安全系统以支持VANET服务的安全性。
[Abstract]:With the increasing popularity of wireless communication technology and the widespread penetration of other technology fields, the automobile manufacturing industry is actively seeking a scheme to improve the competitive advantage of the market by using wireless communication technology. In this paper, the vehicle ad hoc network (VANET) has many applications, such as security, rescue, exploration, military, sparse population of redundant communications, and as The important components of the intelligent transportation system (ITS) are the traditional city and the expressway communication. However, the penetration of this technology is still insufficient. There are still a lot of problems to be solved to build an elastic, reliable and efficient vehicle ad hoc network. The quality of communication (QoC) depends mainly on the reliability of the physical layer (PHY), which includes the various types of VANET. Challenging problems. High speed movement of vehicles will lead to a large number of fragmentation in VANET and the performance of topology uncertainty.PHY is a key factor in improving communication quality. The physical layer needs to solve the limited bandwidth, application requirements, and the unstable and fragmented network topology. This paper mainly studies the physical layer, including the questions related to the VANET application. Problems, challenges and research opportunities. Main contributions and innovations are as follows: 1. a method of improving vehicle network communication performance by means of theoretical approaches is proposed, that is, to improve the performance of the physical layer OFDM system without changing the bandwidth, cost and system complexity. A general model is proposed to describe the physical layer of vehicle communication scenes. Transmission technology can solve some challenging problems in vehicle communication, and explore the communication effect in different transmission scenarios. The transmission process of the physical layer contains many complex steps. This model is involved in the model. The model corresponds to the physical layer structure of IEEE 802.11p and the wireless network in the vehicle network. A simplified channel model is developed to describe the most important characteristics of the channel by parameterized form. This model will be used to evaluate the performance of the system and study the challenges of the physical layer to improve the overall communication efficiency of the vehicle network.2. application algebra lattice theory and other mathematical tools to improve the OFDM system, thus improving the whole VANET directly. In order to improve the reliability of communication, in order to improve the reliability of communication, a high order OFDM diversity scheme suitable for vehicle networks is proposed by using order theory and Hamming distance. The frequency diversity is realized by specific correlation in the transmission symbols. At least one symbol has a reliable SNR because of the subchannel failure. The receiver can use this symbol to detect other symbols.3. to study the channel estimator using the least square (LS) and least mean square error (MMSE), and develops a new method to improve the communication performance of the VANET physical layer. By combining DFT and SVD with LS and MMSE, the system performance is enhanced and the system complexity.4. is reduced to the vehicle. The network proposes a new symbol synchronization technique, which uses the power difference and the timing error between different OFDM subcarriers. The scheme uses 3 methods to minimize the subcarrier interference (ICI) and Intercode interference (ISI) due to the symbol time offset. The first method is to detect by the first OFDM receiving symbol. The subcarrier phase shift caused by the timing error is used to estimate the time shift, that is, the phase shift caused by the time shift is used to estimate the timing error, so this paper is called the phase shift estimator (PSME); the second scheme minimizes the power difference between the adjacent subcarriers in the same OFDM symbol, assuming that the channel responses of these subcarriers are approximately the same because they are only in the same way. Using subchannels in frequency domain, it is known as the frequency domain cumulative power difference estimator (FD-APDE); the third scheme is called the time domain cumulative power error error estimator (TD-APDE) by measuring the subcarrier power difference between the adjacent OFDM symbols, which is called the time domain cumulative power error error estimator (TD-APDE). All of the 3 estimators are all blind. Because the receiver does not have any information about sending data or channel state (CSI), these information can greatly improve the performance of the estimator. In order to provide timing synchronization in different VANET scenarios, these estimators can combine and complementary application.5. to improve the security of the vehicle network using the intrinsic randomness of the physical layer. By using the noise and interference usually considered as adverse factors as a possibility to improve the random factors of security, a key generation method for vehicle networks is proposed, which takes advantage of the random characteristics of the wireless channel itself. It is used to quantify the change of the received signal field intensity (RSS) due to vehicle movement, noise and multipath fading. The simulation results show that the algorithm is especially suitable for VANET, because the multiple working environment of VANET is more random than other communication systems. This algorithm can extract high entropy high speed or low speed key and less information exchange between legitimate vehicles. This key can be used in many security systems to support VANET services. Full.

【学位授予单位】：东南大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TN929.5
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本文编号：1776485