车载自组织网络MAC层协议的研究

摘要车载自组织网络以车辆为基本信息单元，可以使车辆实时监测到其附近道路上其他车辆的相关信息，通过车与车、车与路边单元的实时信息交互来保证车辆行驶安全、规避道路拥塞和提高出行舒适度。

作为一种特殊的移动自组织网络，其高速移动、频繁的拓扑变化、多跳路由以及不存在能量和存储空间约束的特征导致了车载自组织网络设计将面临新的问题和挑战。

其中车载自组织网络的MAC 层有着与传统网络不同的特点：无线信道质量受道路环境、交通状况等影响严重，网络拓扑受道路约束及车辆移动速度的影响，链路不稳定等。

目前，不少研究是针对MAC 层多信道协调问题，希望在保证安全应用实时性的同时，提高服务信道中非安全应用网络吞吐量。

本文旨在深入研究IEEE 802.11p协议MAC层的多信道协调机制。

在总结和分析802.11n帧聚合技术的基础上，在IEEE 802.11p协议服务信道上采用帧聚合技术以提高服务信道中非安全应用网络的吞吐量，本文的主要内容包括以下几个方面：1、对IEEE 802.11p协议MAC层多信道机制进行了研究，设计了帧聚合技术在服务信道上的应用方案，建立了非安全应用网络吞吐量的计算模型并进行了性能分析，重点研究了信道误帧率对数据帧长度的影响。

2、通过城市交通场景仿真软件VanetMobiSim生成了仿真场景，在NS-2上进行了IEEE 802.11p协议仿真。

关键词：车载自组织网；IEEE 802.11p协议；帧聚合；MAC层；吞吐量；IAbstractVehicle ad-hoc network consider vehicle as the basic information unit, it can make real-time monitoring of vehicle-related information to other vehicles on the road near by cars to cars, cars and road side units, which can get real-time information exchange to ensure traffic safety, road congestion avoidance and improve travel comfort. As a special mobile ad-hoc network, its fast-moving, frequent topology changes, multi-hop routing, and there is no storage space constraints and energy characteristics of the vehicle resulted in self-organizing network design will face new problems and challenges. Vehicle ad-hoc network MAC layer has different characteristics with traditional network: radio channel quality by serious road environment, traffic conditions and other factors, affected road network topology constraints and vehicle movement speed, link instability. Currently, many studies against MAC layer multi-channel coordination problems, and want to ensure the safety of real-time applications, while improving service channel non-security applications network throughput.This paper aims to in-depth study multichannel coordination mechanism IEEE 802.11p MAC layer protocol. In summary and analysis of 802.11n frame aggregation technology, I apply frame aggregation techniques to improve the service channel network throughput on non-security applications at IEEE 802.11p protocol service channel. The main contents of this paper include the following aspects:A. Research on multi-channel MAC layer protocol IEEE 802.11p mechanism, and designed the application solutions of a frame aggregation technology in service channel, then establish the calculation model of network throughput in the non-secure applications and take network throughput performance analysis, focusing on the channel error impact on the bit rate data frame length.B. Through urban traffic scenario simulation software VanetMobiSim generated simulation scenario, and make IEEE 802.11p protocol simulation in the NS-2.Key Words: Vehicular Ad-hoc Network; IEEE 802.11p Protocol; MAC Layer; Frame Aggregation; Throughput;II目录摘要 (I)Abstract (II)目录 (III)1 绪论 (1)1.1 研究背景和意义 (1)1.2 国内外研究现状 (1)1.3 论文的研究内容 (3)1.4 论文结构安排 (3)2 IEEE 802.11p协议 (4)2.1 车载自组织网络简介 (4)2.2 IEEE 802.11p协议物理层 (5)2.3 IEEE 802.11p协议MAC层 (7)2.3.1 分布式协调功能（DCF） (7)2.3.2 IEEE 802.11e EDCA机制 (10)2.3.3 IEEE 802.11p MAC层的关联和验证机制 (12)2.4 帧聚合技术 (13)2.4.1 A-MSDU聚合 (14)2.4.2 A-MPDU聚合 (15)2.4.3 二级聚合机制 (16)2.5 本章小结 (16)3 IEEE 802.11p协议MAC层多信道机制研究 (17)3.1 IEEE 802.11p协议MAC层多信道机制 (17)3.1.1 CCH信道和SCH信道 (17)3.1.2 多信道协调机制 (18)3.2 帧聚合技术的应用研究 (21)3.2.1 马尔可夫链理论分析模型 (22)3.2.2 帧聚合技术的应用 (25)3.2.3 吞吐量的计算与性能分析 (28)3.2.4 信道误帧率对数据帧长度的影响 (35)3.2.5 吞吐量的计算结果分析 (37)3.3 本章小结 (41)4 车载自组织网络仿真 (42)4.1 NS-2仿真软件 (42)4.1.1 NS-2仿真软件简介 (42)4.1.2 NS-2仿真过程 (42)4.1.3 NS-2移动节点属性配置 (43)4.1.4 IEEE 802.11p协议仿真 (44)4.2 城市交通场景仿真软件VanetMobiSim (46)4.2.1 VanetMobiSim的移动特征 (46)III4.2.2 VanetMobiSim的微移动模型 (47)4.2.3 VanetMobiSim软件的XML配置文件的使用 (48)4.2.4 车辆移动拓扑文件的生成 (49)4.3 IEEE 802.11p协议性能仿真 (50)4.3.1 仿真场景的搭建 (50)4.3.2 网络仿真参数的设定 (51)4.3.3 实验结果分析 (53)4.4 本章小结 (54)总结与展望 (55)参考文献 (56)攻读硕士学位期间发表论文及科研成果 (60)致谢 (61)IV1 绪论1.1 研究背景和意义进入21世纪之后信息化技术蓬勃发展，同时，人们的生活也随之发生了巨大的变革。

I.J. Information Technology and Computer Science, 2012, 2, 11-18Published Online March 2012 in MECS (/)DOI: 10.5815/ijitcs.2012.02.02Survey of MAC Layer Protocols for vehicular AdHoc NetworkVimal BibhuResearch Scholar, Department of IT, B.R.A Bihar University, Mujaffarpur, Bihar, IndiaEmail: vimalbibhu@Dr. Dhirendra Kumar Singh,University Department of Mathematics, B.R.A Bihar University, Mujaffarpur, Bihar, IndiaAbstract -Vehicular Ad Hoc Network is currently challenge for the wireless networking and its researchers. In this paper we have proposed the survey of the different MAC Layer protocols of the wireless medium those can be implemented in the Vehicular Ad Hoc Networking. The survey is based upon the study of the different protocol on their MAC level and its performance factors is evaluated. The performance factor is extracted from the studied materials and current working conditions of the protocols. These all factors are mobility, accuracy, privacy and confidentiality, safety critical message priority, delay control and suitability on vehicle and roadside. According to analyzed performance factor the IEEE 802.11p Wave is most suitable protocol for the Vehicular Ad Hoc Network but it does not cover up all conditional requirements.Index Terms- Intelligent Transportation service, Inter-Vehicular Communication, Medium Access Control, Distributed Coordination Function.1. IntroductionThe improvement of the network technologies and infrastructure have given the opportunity to use it in several different fields. One of the most emergent field of applications of ad hoc network technology is the development of the Vehicular Ad-hoc Networks (VANETs). There are two different kinds of communications such as Vehicle to Vehicle(V2V) and Vehicle to Roadside(V2R) under the Vehicular Ad Hoc Networking. VANETs are developed for a set of communicating vehicles with sensors and roadside wireless devices to provide interconnection among each other without any pre-existing infrastructure (ad-hoc mode). The most important network technology available nowadays for establishing VANETs is the IEEE 802.11b (Wi-Fi) standard, nevertheless new standards as IEEE 802.11p or IEEE 802.16 (WiMax) are promising.The communications of information among the vehicles to vehicles and vehicles to roadside provide a great opportunity for the development of new driver assistance systems. These systems will be able to disseminate and to gather real time information about other vehicles, road traffic with environmental conditions. Such data will be processed and analyzed to facilitate the driving by providing the user with useful information.Intelligent Transportation Systems (ITS) includes the safety, security and efficiency of the transportation systems. It also enables new mobile applications and services for the travelling people. The field of inter-vehicular communications (IVC), including both vehicle-to-vehicle communications and vehicle-to12Survey of MAC Layer Protocols for vehicular Ad Hoc Networkroadside communications are recognized as an important component of Intelligent Transportation System in various national plans. Equipping vehicles with different types of on-board sensors, and V2V and V2R communication capabilities will allow large-scale sensing and decision / control actions in support of VANET objectives. Communication-based active safety is viewed as the next logical step towards proactive safety systems. These systems provide an extended information horizon to warn the driver or the vehicle of potentially dangerous situations at an early stage. In spite of the ongoing academic and industrial research efforts on VANETs, many research challenges remain. One of the interesting areas in VANET is Design and modification of Secure MAC layer for priority based and secured real time scalable access system. From the network perspective, security is one of the most significant challenges. Vehicle safety applications are among the major drivers for VANETs where people’s lives are at stake, it is of course essential to secure VANETs against abuse. On the other hand, like all the other wireless networks, a MAC protocol should play a crucial role in scheduling application packet transmissions fairly and efficiently in VANETs, according to the quality of service (QoS) requirements of the applications with different message priorities for different types of applications to access DSRC (Dedicated Short Range [1][3].Communications channels. The secure communication protocol is designed using time-stamp, digital signature, and trust certificate to guarantee the freshness of the message, message authentication and integrity, message non-repudiation, and privacy and anonymity of the senders. Vehicular Ad-Hoc Network (VANET) is an emerging new type of wireless networks in which vehicles constitute the mobile nodes in the network. This kind of networks supports vehicle-to-vehicle and vehicle-to-gateway communications by providing a self-organized and multi-hop network. The MAC Layer of IEEE 802.11 is simply based upon the carrier sense multiple access and collision avoidance access mechanism. There are many variations of MAC layers in 802.11 but, all are roughly same in functionalities. wireless medium is a lot different from the wired medium used in for example 802.3 (Ethernet), a new MAC layer needs to be defined to successfully mitigate problems such as interference, collisions and the increased security vulnerability. Carrier Sense Multiple Access Collision Avoidance (CSMA/CA) encounters problems such as interference, high collisions on overload and security vulnerability. Distributed coordination is another major problem in the access mechanism of the Vehicular ad hoc network. The basic rule for access under distributed coordination function (DCF) is ‘if a station has to send a frame then first it senses the channel to see if somebody’. If the medium is busy, the station defers from sending and waits until the medium becomes available again. After the medium has become available, it waits for a predefined period of time, the DIFS or Distributed Inter-Frame Space. After this DIFS time the station enters a so-called contention window or backoff window. This is a time window divided in slots. The window size (in number of slots) depends on previous transmissions, but has a minimum and maximum defined by the standard. In 802.11 the contention window size is between 15 and 1023 slots and always increments in powers of 2. The station then randomly chooses a number of slots (within the contention window), that is the number of time slots it will wait before it actually starts trying to transmit. This means that if two stations were both waiting for a transmission to end, they will not both start transmitting directly after the DIFS (and generate a collision). After picking a random number of slots a backoff timer starts counting down to zero, when it reaches zero the station can transmit. If, while waiting a random number of slots, the station senses another transmission, because another station was also waiting and picked a random number smaller than its own, it freezes the backoff timer [1].After that the transmission and a DIFS of idle time on the medium, it restarts the backo ff timer but does not pick a random number.IEEE Std. 802.11 edition for information technology-telecommunication and information exchange between systems (Local and Metropolitan area network” under specific part -11 discussed the ad-hoc networking and its requirements. In this document technical and operational feasibility along with different technical standards for mobile ad-hoc networking are mentioned.A Nasipuri, S.Ye, J. You, and R.E. Heromoto in their paper “A MAC Protocol for Mobile Ad-hoc Networks Using Directional Antennas” proposed a medium access control (MAC) protocol for an ad-hoc network of mobile and wireless terminals that are equipped with directional antennas. The use of directional antennas reduces the radio interference and inhances the packet throughput. The MAC protocol presented in this paper proposes a solution without help of any hardware.J R. Yim, J. Guo, P. Orlik, and J. Zhang in their paper “Received Power-Based Prioritized Rebroadcasting for V2V Safety Message Dissemination” proposed Rapidly and robustly disseminating safety messages. This is an important goal for vehicle-to-vehicle communications. They proposed receive power-based prioritized rebroadcast scheme that minimizes the probability of packet collision during rebroadcast and maximizes the probability that a vehicle that is farthest away from the source rebroadcast an alert message first.R. Jurdak, C. Videria Lopes, and P. Baldi, in their paper “A Survey, Classification and Comparative Analysis of Medium Access Control Protocols for Ad hoc Networks” proposed the Recent technological advances in wireless communications. This offer new opportunities and challenges for wireless ad-hoc networking. In the absence of the fixed infrastructurethat characterizes traditional wireless networks, control and management of wireless ad-hoc networks must be distributed across the nodes, thus requiring carefully designed Medium Access Control (MAC) layer protocols. In this paper they survey, classify, and analyze 34 MAC layer protocols for wireless ad hoc networks, ranging from industry standards to research proposals. Through this analysis, 6 key features emerge: (1) channel separation and access; (2) topology; (3) power; (4) transmission initiation; (5) traffic load and scalability; and (6) range. These features allow them to characterize and classify the protocols, to analyze the tradeoffs produced by different design decisions, and to assess the suitability of various design combinations for ad hoc network applications. The classification and the tradeoff analysis yield design guidelines for future wireless ad hoc network MAC layer protocols.R. K. Lam and P. R. Kumar, in their paper “Dynamic channel reservation to enhance channel access by exploiting structure of vehicular networks”, proposed VANET protocols need to exploit the special structure of vehicular networks. This structure includes the one-dimensional nature of roads, the structure of lanes, thegroup mobility of vehicles, and the communication patterns of the envisaged applications. It is therefore of interest to examine how to specifically tailor VANET protocols to exploit all the above properties. In this paper, motivated by the goal of providing significantly better application level QoS, we study the MAC problem, and examine to what extent one can improve the performance of the mechanism employed in the IEEE 802.11p protocol. We design a dynamic channel reservation (DCR) protocol which leverages the special structure of VANET, and provides greater predictability in channel access, simplifying QoS provision. The key idea, in light of the periodic communication pattern of VANET applications, is to transform the per-packet channel contention mechanism of 802.11p into a per-vehicle one in DCR. We implement the protocol on NS-2 for a comparative evaluation against 802.11p under realistic VANET scenarios. DCR demonstrates lower packet loss probability and higher throughput over 802.11p, and the simulation results appear promising enough to develop a complete protocol specifically for vehicular networks.Ajay Chandra V. Gummalla and John O. Limb, in their paper “Wireless Medium Access Control Protocols”, proposed Technological advances, coupled with the flexibility and mobility of wireless systems, are the driving force behind the Anyone, Anywhere, Anytime paradigm of networking. At the same time, we see a convergence of the telephone, cable and data networks into a unified network that supports multimedia and real-time applications like voice and video in addition to data. Medium access control protocols define rules for orderly access to the shared medium and play a crucial role in the efficient and fair sharing of scarce wireless bandwidth. The nature of the wireless channel brings new issues like location-dependent carrier sensing, time varying channel and burst errors. Low power requirements and half duplex operation of the wireless systems add to the challenge. Wireless MAC protocols have been heavily researched and a plethora of protocols have been proposed. Protocols have been devised for different types of architectures, different applications and different media. This survey discusses the challenges in the design of wireless MAC protocols, classifies them based on architecture and mode of operation, and describes their relative performance and application domains in which they are best deployedIn this paper first we introduce the general terms related to VANET and Ad-hoc networking having technological requirements and feasibility. After that we discuss the issues related to different MAC layers such as IEEE 802.11, IEEE 802.11p (WAVE), Ad-hoc MAC and Directional Antenna Based MAC protocols functionalities. Finally, survey is taken on behalf of different performance factors. The result of survey on the basis of percentage scores for different performance factors are summarized in table 1 and in table 2.2.MAC IssuesMedium access control sub layer design is a measure issue related for the vehicular ad hoc network. Basically, MAC layer in local area network either in wired medium or wireless is broadcast in nature. In a broadcast network that can access the channel is governed by the access mechanism and protocols. For general applications of wireless network the Carrier Sense Multiple Access is suitable and working very well but in case of VANET this CSMA is not suitable due to many reasons. The reasons are mobility and switching, more collision on load increase, Critical and life saving safety information dissemination, quickness, accuracy, privacy and confidentiality. These requirements are the basic need in the Vehicular ad hoc network. The critical information like one hop safety message requires quick and efficient dissemination to the vehicles those are near to vehicle. If this is not performed then vehicle crash may occur. Aloha and S-Aloha are not suitable because low frame success rate. Frequency division multiple access has a problem on the time of switching from one cell to other cell on roadside. Time division multiple access is also not efficient for the VANET MAC layer due to dynamic mobility of vehicles on roadside. On combining two different multiple channel access protocol produces delay in processing that is not allowed in the vehicle to vehicle communication. If this is allowed then active safety message will reach to the vehicle which are one hop distant from the originator vehicle later or after crash. Due to mentioned facts the MAC layers such as IEEE 802.11, IEEE 802.11p (WAVE), Ad-hoc MAC and Directional Antenna based MAC are not suitable VANET application scenarios. Probable Scenario of Vehicle to Vehicle and Vehicle to Roadside Communication is given in figure 1.2.2 IEEE 802.11p WAVEWAVE (Wireless Access in Vehicular Enviournment) is an amendment to all IEEE 802.11 protocols and adapted for the IEEE 802.11 standard for inter-vehicular communications to provide low latency and high reliability. It was published in November 2010 according to the official IEEE 802.11 working group project timelines. 802.11p (WAVE in detail) will be used as the groundwork for Dedicated Short Range Communications (DSRC), it is architecture standard looking at vehicle-based communication networks, particularly for applications such as toll collection, vehicle safety services, and electronic commerce transactions via vehicles. The ultimate vision is a nationwide network in United States(US) that enables communications between vehicles and roadside access points or vehicles to other vehicles.[7][8]. Working diagram for IEEE 802.11p is given in figure 3.Figure 1: V2V and V2R scenariosFigure 1 shows there are many vehicles on the roadside. The roadside unit disseminates and gathers the information in V2R communications and in V2V communications the vehicles disseminates and gathers the information from the vehicles. The MAC layer plays important roles in this type of ad hoc networks. The MAC layer in V2V and V2R should have to be compatible with each other to flexible communication between vehicles to vehicles and vehicles to roadside communications.2.1 IEEE 802.11 MACIn this MAC the Inter Frame Space(IFS) is very important and Sort Inter frame Space(SIFS) should be greater than Distributed Inter Frame Space(DIFS). [4][5][6]. The design of MAC is given in picture 2.Figure: 3 IEEE 802.p WAVE Working diagramFigure 2: Working of IEEE 802.11 MAC Laye r2.3 Adhoc MACThis Ad-hoc MAC is based upon the circuit switching method. The sender vehicle has to establish the circuit first and then frame is being transmitted either to the vehicles or to roadside station.[9][10]. Here the Reliable Reservation Aloha (RR- ALOHA) protocol is used. The medium is divided into several repeated time frames and each frame again divided into n numbers of time slots. The functional diagram of this Ad-hoc MAC is given in figure 4.Figure: 4 Functional behavior of Ad-hoc MAC.2.4 Directional Antenna Based MACDirectional antenna based MAC increase the area of coverage and hence it has greater channel capacity. It is good solution for vehicular network because a vehicle can only run on the road.[2][3]. The working scenario of directional antenna based MAC is given in figure 5.Figure 5: Directional Antenna based communication in VANETDirectional MAC is protocol used at MAC Layer and it uses 4 way handshaking method of IEEE 802.11. Each vehicle is equipped with GPS system which can determine its geographical position [11][12]. The handshaking scenario is illustrated in figure 6.Figure 6: 4 Way Handshaking3.Performance Evaluation for Different MAC of VANETPerformance evaluation of different MAC protocols is based upon the many parameters. The different parameters for performance evaluation are mobility, accuracy, privacy and confidentiality, safety control priority and delay control. The mobility factor is one of the major factors in VANET application. This includes switching of vehicle device one cell to other cell andcontinuation of information exchanges between vehiclesto vehicles and vehicles to roadside units. Accuracy determines how much accurate the information received. Privacy and confidentiality is maintained for the different electronic commerce applications. The VANET is public network hence privacy should have to be provided to individual user. The priority for safety control critical message is very important for the prevention of the crash and accident. This performance factor should be considered as the main factor in the vehicular network scenario. Finally, suitability of different manufacturer hardware such as antenna, GPS systems, computing platform and software such as networking components on different layers at protocol suit should be interoperable These all parameters are categorized under low, medium and high with given condition. The condition makes it more specific in nature for a specified MAC layer protocol in VANET application area. Table 1. shows the different performance for MAC protocols. Each performance factor has 100% Score with Least, low, medium and high includes 5%, 10%, 15% and 20% respectively. These performance factors are analyzed on behalf of the current usability and with conditional suitability for the VANET. The percentage score of different performance factors are obtained by the analysis of the individual performance factor in ad-hoc enviournment. These all performance factors with different protocols are summarized under Table 1.Table 1. Performance of different MAC Layer Protocols forVANETParametersFactorsIEEE802.11IEEE802.11pWAVEAd-hocMACDirectionalAntennabasedMAC Mobility Least Medium Medium Least Accuracy Low Medium Least HighPrivacy &ConfidentialityLeast Low Low HighSafety criticalmessagepriorityLeast Low Least Least Delay control Least Medium Low Medium Suitability Least Medium Least LeastThe given information of performance parameters are survey based for the MAC Layers of different protocols. The final performance of MAC Layer protocols are summarized in table 2. which is based upon the table 1.Table 2. Performance Factor in % for MAC Layers of studiedProtocolsMAC Layer ProtocolPerformance Factor (%) ofMAC Layer of VANETIEEE 802.11 5 + 10 +5 +5 +5 +5 = 35%IEEE 802.11p WAVE 15 +15 +10 +10 +15 +15 =80%Ad-hoc MAC 15 +5 +10 +5 +10 +5 =45% Directional AntennaBased MAC5 +20 +20 +5 +15 +5 =70%Table 2 shows that IEEE 802.11 MAC layer is least suitable MAC layer for VANET and Directional Antenna based MAC layer is highly suitable in case of VANET.4.ConclusionIn this paper we have proposed the survey of MAC layer of different protocols. The feasibility of VANET on current existing MAC layers of different protocols under wireless medium are studied. According to study of the MAC layers of different protocols in which IEEE 802.11p (WAVE) is the most suitable protocol and IEEE 802.11 is the least suitable protocol for the VANET. The requirement at the level of MAC layer in VANET is not fulfilled by the score of 80%. To cover up the requirement for crash and other scenarios of VANET a MAC layer performance factor should be 95% and above. Hence, none of the studied protocols is suitable according to the requirement of the Vehicular Ad-hoc Network. So, it is required to discover the MAC layer protocol that would have 95% and above performance factor by table 1. and table 2.References[1] “IEEE Std 802.11 Edition, “Information Technology – Telecommunication and information exchange between systems – Local and metropolitan area network” – Specific requirement part – 11: Wireless Lan Medium Access Control (MAC) and Physical Layer (PHY Specifications).[2] A. Nasipuri et al., _A MAC Protocol for Mobile Ad Hoc Networks Using Directional Antennas,_ Proceedings of IEEE WCNC 2000, vol. 1, pp. 1214-1219, September 2000.[3] Z. Huang et al., _A Busy Tone-Based Directional MAC Protocol for Ad Hoc Networks,_ Proceedings of IEEE MILCOM 2002, October 2002.[4] Ajay Chandra V. Gummalla and John O. Limb,_Wireless Medium Access Control Protocols,_ IEEE Commun. Surv., 2000.[5] T. Korakis, G. Jakllari and L. Tassiulas, _A MAC protocol for full exploitation of Directional Antennas in Ad-hoc Wireless Networks,_ Proceedings of 4th ACM Int. Symp. on Mobile Ad Hoc Networking and computing, Annapolis, Maryland, June 2003.[6] R. Jurdak, C. Videria Lopes, and P. Baldi, _A Survey, Classification and Comparative Analysis of Medium Access Control Protocols for Ad hoc Networks, _ IEEE Commun. Surv., 2004.[7] “IEEE 1609 - Family of Standards for Wireless Access in Vehicular Environments (WAVE),” U.S. Department of Transportation, January 9, 2006. [8] Fei Ye, Raymond Yim, Jianlin Guo, Jinyun Zhang and Sumit Roy, “Prioritized Broadcast Contention Control in VANET”, Mitsubishi Elect. Research Labs, Cambridge, MA 02139 and University of Washington, Seattle, WA 98195.[9] V. S. Communications, “Vehicle safety communications project-final report,” tech. rep., April 2006.[10] IEEE, IEEE 1609.4-Standard for Wireless Access in Vehicular Environments (WAVE) - Multi-channel Operation.[11] R. Yim, J. Guo, P. Orlik, and J. Zhang, “Received Power-Based Prioritized Rebroadcasting for V2V Safety Message Dissemination,” in Proc. of Int. Transport. Sys. World Congr., Sep. 2009.[12] R. K. Lam and P. R. Kumar. Dynamic channel reservation to enhance channel access by exploiting structure of vehicular networks. In VTC 2010-Spring: Proceedings of the IEEE 71st Vehicular Technology Conference, Taipei, Taiwan, 2010.Vimal Bibhu : Master in Technology in Computer Science and Engineering and pursuing Doctor of Philosophy in Computer Science from BRA Bihar University, Mujaffarpur, Bihar, India. He has published many research papers in different international journals. He is also member of SERC, ISCSIT, IEANG.Dr. Dhirendra Kumar Singh : Doctor of Philosopphy in Mathematics and currently working on the post of Professor under University Department of Mathematics, BRA Bihar University, Mujaffarpur, Bihar, India.。

第15期2023年8月无线互联科技Wireless Internet TechnologyNo.15August,2023基金项目:西安职业技术学院2022年度科研项目;项目名称:基于TDMA +CSMA 的无线自组网中MAC 层协议的研究;项目编号:2022YB05㊂作者简介:张富琴(1981 ),陕西延长人,高级工程师,硕士;研究方向:移动自组网㊂移动自组网中MAC 层协议研究张富琴(西安职业技术学院,陕西西安710077)摘要:移动自组网是由一组相互协作的通信节点组成的无中心控制节点㊁不依赖于任何固定网络设备的特殊网络㊂在该网络中,媒体接入控制(MAC )协议是网络实现最关键的技术之一,主要解决的是多个用户如何高效㊁合理地共享有限的信道资源问题㊂文章主要研究常用的几种MAC 接入协议㊂关键词:MAC ;CSMA ;TDMA中图分类号:TN91㊀㊀文献标志码:A0㊀引言㊀㊀目前,移动通信技术发展迅猛,但是大多数移动通信都需要有线的基础设施(如基站)的支持才能实现㊂为了实现在某些特殊应用场所不需要固定的设施支持就可以进行通信,一种有别于传统的网络技术 移动自组织网络技术应运而生㊂移动自组织网络(Mobile Ad Hoc Networks)是指一种不需要基础设施的移动网络,也常被称为多跳无线网(Multi -hop Wireless Networks)㊂该网络是一个临时构建的多跳无中心网络,网络中的成员是一组具有无线通信功能的移动节点㊂这些移动节点可以在任何地方任意时刻快速地构建起一个移动通信网络,并且不需要基础设施(如基站)的支撑㊂网络中的每个节点都可以自由移动,且相互之间地位平等㊂移动自组网的出现加快了人们实现随时随地进行自由通信的进程,同时移动自组网也为临时通信㊁军事通信和灾难救助等应用提供了有效可行的解决方案㊂移动自组织网络是一种网络拓扑动态可能随时发生变化的无线网络㊂该网络体系㊁同步机制和实际应用等问题都比较复杂[1]㊂传统的固定网络和常见的蜂窝移动通信网中使用的协议和技术很难直接应用到移动自组织网络中,因此需要为移动自组织网络设计专门的协议和技术㊂目前,移动自组织网络研究中面临的主要难点和重点问题为MAC 协议㊁同步机制㊁路由协议㊁功率控制㊁Qos㊁网络资源管理㊁网络互联和安全问题等㊂本文将重点讨论几种常见的MAC 协议㊂1㊀MAC 协议基本概念㊀㊀MAC 协议是数据在无线信道上发送和接收的主要控制者,是移动自组织网络协议的重要组成部分㊂MAC 协议对网络的时延㊁吞吐量㊁数据包传输成功率等性能指标都有着重要的影响㊂传统网络中多点共享的广播信道,蜂窝移动通信系统中由基站管理控制的无线信道以及点对点无线信道都是一跳共享信道,而移动自组织网络的信道则是一个由多个节点共享的多跳信道㊂当一个无线通信节点发送数据时,只有在它通信覆盖范围内的节点才能收到,这种共享的多跳信道会导致移动自组织网络存在隐藏终端㊁暴露终端等问题[2-3]㊂如图1所示,当通信节点1向节点3发送数据时,节点2并不在节点1的通信覆盖范围内,它无法检测节点1正在发送分组,如果此时节点2也向节点3发送数据,就会引起数据碰撞,节点2便称作隐藏终端㊂这种因某些节点不能侦听到其他节点发送数据而引起的数据碰撞就是隐藏终端问题㊂另外,还存在一种情况,如图2所示,当节点3向节点1发送数据时,节点2就会检测到节点3正在发送分组,节点2为了避免引起数据碰撞会推迟向节点4发送数据㊂但实际上这种推迟是不必要的,因为节点2向节点4发送数据并不影响节点3向节点1发送数据,这种情况下节点2就是节点3的暴露终端㊂这种因某些节点在其他正在通信节点的传输范围内而进行不必要的发送推迟便是暴露终端问题㊂为了保证数据传输的及时性以及正确性,移动自组织网络的MAC 协议需要解决隐藏终端及暴露终端问题㊂2㊀移动自组网中常见的MAC 协议的分析㊀㊀目前,在移动自组网实际的应用中,MAC 层主要图1㊀隐藏终端问题示例图2㊀暴露终端问题示例采用的协议有CSMA 协议㊁TDMA 协议以及二者的结合㊂2.1㊀CSMA 协议㊀㊀CSMA 是Carrier Sense Multiple Access 的缩写,是一种允许多个节点在同一个信道发送数据的协议㊂当一个节点发送数据时,需要侦听信道上是否有其他节点在发送数据㊂如果信道此时有其他节点在发送数据,则发送节点需要等待一个时间段后再次侦听,只有侦听到信道空闲后才会发送数据㊂信道中的其他节点接收到来自信道的数据,需要判断该数据是不是发送给自己㊂如果是,则进行下一步处理;如果不是,则将数据抛弃㊂如果在某一信道空闲时刻,两个在彼此通信覆盖范围内的节点同时要给对方发送数据时,且它们都侦听到信道处于空闲状态,这时它们会将自己的数据发送出去,从而引起了数据的碰撞㊂这是因为节点可以侦听信道上是否有数据传输,但是节点无法预判下一时刻信道上是否有数据要传输㊂为了避免出现这种问题,在实际应用中,往往会让节点在发送数据前,先侦听信道上是否有数据正在传输㊂如果此时信道上有数据正在传输,则等待一段时间后继续侦听;如果侦听到信道是空闲的,则需要让节点随机退避一段时间P 后再继续侦听;如果信道仍然空闲,则发送数据;如果这时信道上有数据在传输,则退回到最初的侦听信道状态,具体流程如图3所示㊂在上述的过程中,加入随机退避因子是为了避免两个在彼此通信范围内的节点同时发送数据时引起数据碰撞㊂图3㊀CSMA 处理流程CAMA 协议的主要优点:(1)算法简单㊁易于实现㊂(2)信道空闲情况下会快速发送数据,数据时延小㊂CAMA 协议的主要缺点:(1)在通信中易于引入隐藏终端和暴露终端的问题㊂(2)当系统中节点数量较多时,数据碰撞不可控,且数据时延不可控㊂2.2㊀TDMA 协议㊀㊀TDMA 即Time division multiple access,其协议的核心思想是将时间分为若干个时间片段,称之为时隙,每个发送数据的节点占据一个或多个时隙进行数据发送㊂如图4所示,节点A㊁B㊁C㊁D 分别占用时隙1㊁2㊁3㊁4发送数据,这时由于每个节点在不同的时间段发送数据,所以不会引起数据的碰撞㊂时隙的分配目前有静态预制与动态分配两种㊂图4㊀时隙分配时隙示例TDMA 协议的主要优点:(1)发送数据的节点在不同时隙进行数据发送,不会发生数据碰撞㊂(2)数据传送的时延可控㊂TDMA 协议的主要缺点:(1)对同步要求高,需要精准的时间同步㊂(2)固定分配时隙的TDMA 会引起不必要的数据传输时延,动态分配时隙的TDMA 算法较为复杂,且会引入预约时隙等开销,降低系统的吞吐量㊂2.3㊀TDMA +CSMA 协议㊀㊀TDMA +CSMA 协议就是将整个时间片分为若干个时隙,一部分时隙固定分配给节点发送公共广播㊁同步及路由公告等消息,一部分时隙用来进行CSMA 载波侦听使用,剩余部分时隙留作节点作为固定分配时隙㊂基于这一MAC 接入思想的时隙分配示例如图5所示㊂其中,SS 时隙是各个节点轮流发送同步和拓扑消息,用于网内节点同步与路由的更新与迟入节点的引导;BS 时隙是广播时隙,用于各节点发送广播话音;RS 是动态时隙,用于各节点利用CSMA 机制临时占用发送数据,该时隙用于发送用户短报文等小型业务;DS 时隙是TDMA 时隙,可根据开机前用户根据实际用户数进行配置,也可由节点根据业务需求动态预约占用㊂此时隙适合传输文件㊁视频等大业务量数据㊂图5㊀时隙分配示例㊀㊀如果配置用户数为网内最大节点数64个,则设定71个时隙为一个时帧㊁每64个时帧为1个超帧㊂当然,以上时隙配置只是在某一种应用场合的一种配置示例,在实际应用中可根据实际需要进行配置㊂3　结语㊀㊀研究表明,在众多移动自组网的关键技术中,MAC 协议运行在网络层之下㊁物理层之上,对数据的发送和接收起着直接控制和管理的作用,其性能的好坏会直接影响整个网络的性能和效率㊂因此,对于每一种具体的应用场景来说,选取合适的MAC 协议至关重要㊂参考文献[1]邵玮璐.移动自组网中混合接入协议的研究[D ].上海:上海师范大学,2020.[2]王常虎.基于协同通信的移动自组网关键技术研究[D ].成都:电子科技大学,2022.[3]刘庆刚,李大双,朱家成.多跳TDMA 组网同步的分布式控制方法[J ].通信技术,2012(5):26-28,32.(编辑㊀王永超)Research on MAC protocol of Ad Hoc NetworkZhang FuqinXi an Vocational and Technical College Xi an 710077 ChinaAbstract Mobile Ad Hoc Network is a special network and made up of some communication nodes.There is no central control node and fixed infrastructure in the network.The MAC protocol is the one of the most critical technologies.It mainly solves how the communication nodes in the network share the wireless channel efficiently and reasonably.This article mainly studies the MAC protocol which are frequently -used.Key words MAC CSMA TDMA。

《车联网中MAC协议的退避算法和速率控制研究》篇一一、引言随着车联网（Vehicular Networking）的快速发展，车与车之间、车与基础设施之间的通信变得至关重要。

MAC（Media Access Control）协议作为网络通信的核心部分，负责在共享介质中分配通信资源，对退避算法和速率控制的研究显得尤为重要。

本文旨在研究车联网中MAC协议的退避算法和速率控制技术，为车联网的高效通信提供理论基础和实践指导。

二、车联网概述车联网通过无线通信技术实现车辆之间的信息共享和交互，从而提升道路安全、交通效率及驾驶体验。

在车联网中，MAC协议作为通信协议的关键部分，负责在共享的无线信道中分配通信资源。

因此，退避算法和速率控制技术是MAC协议中重要的研究内容。

三、退避算法研究（一）退避算法概述退避算法是MAC协议中用于解决冲突和防止过载的重要机制。

在车联网中，由于节点众多且通信环境复杂，当多个节点同时发送数据时会产生冲突。

退避算法通过暂时放弃信道使用权来避免冲突，待一定时间后再次尝试发送。

（二）常见的退避算法1. 二进制指数退避算法：当发生冲突时，节点以一定的时间间隔进行退避，退避时间呈指数级增长。

该算法简单有效，但可能导致信道利用率不高。

2. 动态退避算法：根据信道负载和冲突情况动态调整退避时间。

该算法能根据实际情况进行优化，提高信道利用率。

（三）车联网中的退避算法研究针对车联网的特点，研究适合的退避算法是关键。

考虑到车辆移动性和实时性要求，可引入动态预测机制，根据车辆的位置和速度信息预测未来的通信需求，以调整退避策略，从而提高信道利用率和减少通信延迟。

四、速率控制研究（一）速率控制概述速率控制是MAC协议中另一个关键技术。

通过控制数据传输速率，可以在保证数据传输质量的同时降低信道冲突的概率。

在车联网中，由于车辆的高速移动和无线环境的复杂性，速率控制尤为重要。

（二）速率控制的策略1. 静态速率控制：根据信道条件和设备能力设定固定的传输速率。

《车联网中MAC协议的退避算法和速率控制研究》篇一一、引言随着车联网（Vehicular Networking）的快速发展，车辆与车辆之间的通信和车辆与基础设施之间的通信成为了研究的重要方向。

MAC（Media Access Control）协议作为网络通信的重要一环，在车联网中起到了决定数据传输优先级、调度信道和分配时间片的作用。

为了实现高效率和低时延的通信，车联网中的MAC协议退避算法和速率控制成为了关键研究内容。

本文旨在深入探讨车联网中MAC协议的退避算法和速率控制，以推动其技术进步和应用。

二、车联网概述车联网，是指通过无线通信技术将车辆、道路基础设施以及交通参与者等连接起来，形成一个庞大的网络系统。

在这个系统中，车辆之间以及车辆与基础设施之间的信息交换是关键。

为了实现这一目标，MAC协议起着至关重要的作用。

三、MAC协议中的退避算法退避算法是MAC协议中重要的组成部分，它用于解决在数据传输过程中可能出现的冲突问题。

在车联网中，由于节点数量多且移动速度快，冲突的发生是不可避免的。

因此，合理的退避算法对于提高网络性能和减少冲突具有重要意义。

目前，车联网中常用的退避算法包括指数退避和二进制退避等。

指数退避算法根据冲突情况动态调整退避时间，使得在冲突较频繁时能够增大退避时间以降低冲突概率；而在冲突较少时则缩短退避时间以提高传输效率。

二进制退避算法则通过预先设定不同的退避阶段和相应的退避时间，在每个阶段根据冲突情况选择合适的退避策略。

四、速率控制策略速率控制是MAC协议中另一个关键技术。

在车联网中，由于节点移动速度快且网络环境复杂，需要合理的速率控制策略来保证数据的稳定传输和低时延。

速率控制策略主要包括自适应速率控制和固定速率控制两种。

自适应速率控制根据网络状况动态调整数据传输速率，以适应不同的网络环境和节点状态。

固定速率控制则采用固定的数据传输速率，这种方式在稳定的网络环境中可以保证较高的传输效率。

《车载无线自组织网MAC层协议分析》篇一一、引言随着智能交通系统的快速发展，车载无线自组织网络（Vehicular Ad-hoc Networks，简称VANETs）在提高道路安全、交通效率以及信息共享等方面发挥着越来越重要的作用。

作为无线通信网络的关键组成部分，MAC（Media Access Control）层协议在VANETs中扮演着至关重要的角色。

本文将对车载无线自组织网MAC层协议进行深入分析，探讨其工作原理、关键特性及其对VANETs性能的影响。

二、车载无线自组织网络概述VANETs是一种特殊类型的移动自组织网络，由装备有无线通信设备的车辆组成。

这些车辆通过相互之间的通信，实现信息共享和协同驾驶。

VANETs的主要目标是提高道路安全性、减少交通拥堵和提升驾驶体验。

三、MAC层协议在VANETs中的作用MAC层协议是无线通信网络中的关键部分，它负责管理无线信道的使用，控制无线信号的传输和接收。

在VANETs中，MAC 层协议不仅要处理车辆间的通信，还要考虑车辆的高速移动性、信道的不稳定性和节点的高动态性等特点。

因此，一个高效的MAC层协议对于VANETs的性能至关重要。

四、车载无线自组织网MAC层协议分析4.1 协议工作原理车载无线自组织网的MAC层协议通常采用基于竞争的访问方式和无竞争的分配方式相结合的混合模式。

在竞争模式下，车辆通过竞争信道使用权来发送数据。

而在无竞争模式下，节点被分配到固定的信道使用权。

这种混合模式可以在保障实时性需求的同时，有效地避免信道资源的浪费。

4.2 关键特性分析（1）时隙划分：在VANETs的MAC层协议中，时隙划分是一种常用的资源分配策略。

通过将时间划分为多个时隙，可以有效地管理信道资源，减少碰撞并提高信道利用率。

（2）支持QoS：MAC层协议应能够提供对不同类型数据的QoS支持，以满足VANETs中不同应用的需求。

例如，紧急消息的传输需要更高的优先级和可靠性。

《车联网中MAC协议的退避算法和速率控制研究》篇一一、引言随着车联网技术的飞速发展，车辆与车辆之间的通信（V2V）和车辆与基础设施之间的通信（V2I）成为了实现智能交通系统（ITS）的核心。

为了保障数据传输的稳定性和高效性，媒体访问控制（MAC）协议在其中起到了至关重要的作用。

而车联网环境中的退避算法和速率控制策略则是影响数据传输质量的重要因素。

本文旨在深入探讨车联网中MAC协议的退避算法和速率控制策略的研究现状与未来发展。

二、车联网中MAC协议的退避算法在车联网中，由于车辆的高动态性和无线信道的不稳定性，常常出现数据冲突和碰撞问题。

为了解决这些问题，MAC协议中的退避算法被广泛采用。

（一）退避算法的基本原理退避算法通过在检测到冲突后，使节点在一段时间内随机延迟发送数据，以减少再次发生冲突的可能性。

常见的退避算法包括二进制指数退避和递归二分退避等。

在车联网中，需要设计适应不同环境和不同应用需求的退避算法。

（二）退避算法的优化策略针对车联网的特点，研究者们提出了一系列优化策略。

例如，通过动态调整退避时间窗口的大小，以适应不同的网络负载和信道条件。

此外，还可以结合车辆的移动性预测信息，提前调整节点的发送时机，以减少冲突的发生。

三、车联网中速率控制策略速率控制是MAC协议中另一个重要的组成部分，它决定了节点的发送速率和数据传输的效率。

在车联网中，由于车辆的高速移动性和信道的不稳定性，速率控制策略的制定尤为重要。

（一）速率控制的基本原理速率控制策略通过调整节点的发送速率，以适应不同的网络环境和应用需求。

常见的速率控制策略包括固定速率、自适应速率等。

在车联网中，需要设计一种能够根据网络状态和车辆移动性动态调整发送速率的控制策略。

（二）速率控制的优化方法为了优化速率控制策略的性能，研究者们提出了多种方法。

例如，通过引入机器学习算法，根据历史数据和实时信息预测未来的网络状态，从而动态调整节点的发送速率。

此外，还可以结合信道质量信息和车辆的移动性预测信息，制定更加精细的速率控制策略。

《车载无线自组织网MAC层协议分析》篇一一、引言随着汽车智能化和网联化技术的不断发展，车载无线自组织网络（Vehicular Ad-hoc Networks，VANETs）成为了研究热点。

作为无线通信网络的重要组成部分，MAC（Media Access Control）层协议对于网络的性能和效率具有重要影响。

本文将对车载无线自组织网中的MAC层协议进行深入分析，以探究其工作原理、性能特点及优化方向。

二、车载无线自组织网概述车载无线自组织网络是一种基于无线通信技术的车辆间通信网络，旨在提高道路交通安全、缓解交通拥堵以及提供多样化的信息服务。

网络中的车辆通过车载设备进行信息交互，实现车辆间的实时通信和协同驾驶。

三、MAC层协议的工作原理MAC层协议是车载无线自组织网络的关键部分，负责在共享无线信道上进行有效的数据传输和资源分配。

其主要工作原理包括以下几个方面：1. 信道接入：MAC层协议负责管理无线信道的接入，通过一定的信道接入机制，如CSMA/CA（载波侦听多路访问/冲突避免）等，实现车辆间的信道共享。

2. 资源分配：MAC层协议根据网络中的车辆数量、通信需求等因素，动态分配无线资源，如时隙、频段等，以提高信道利用率和系统吞吐量。

3. 数据传输：MAC层协议负责将上层的数据封装成帧，并按照一定的传输机制进行发送和接收。

在数据传输过程中，需要考虑到数据的安全性、实时性和可靠性等因素。

四、MAC层协议的分类及特点根据不同的应用场景和需求，车载无线自组织网的MAC层协议可以分为多种类型。

常见的MAC层协议包括基于竞争的协议、基于调度的协议和混合协议等。

1. 基于竞争的协议：这类协议通过竞争方式获取信道资源，如CSMA/CA等。

其优点是灵活性强、适用于动态变化的网络环境，但可能存在信道冲突和资源浪费的问题。

2. 基于调度的协议：这类协议通过预先分配信道资源的方式，如时分多路复用（TDM）等，实现有序的数据传输。

《车载无线自组织网MAC层协议分析》篇一一、引言随着汽车智能化和网联化技术的快速发展，车载无线自组织网络（Vehicular Ad-hoc Networks，VANETs）在智能交通系统中的应用越来越广泛。

作为无线通信网络的重要组成部分，媒体访问控制（Media Access Control，MAC）层协议对于网络的性能和效率起着至关重要的作用。

本文将对车载无线自组织网的MAC 层协议进行深入分析，探讨其工作原理、性能特点及潜在问题。

二、车载无线自组织网概述车载无线自组织网络是一种特殊的移动自组织网络，由装备了无线通信设备的车辆组成。

这些车辆通过车载单元（OBU）进行相互通信，实现车与车（V2V）、车与基础设施（V2I）以及车与行人（V2P）之间的信息交互。

VANETs能够提供实时交通信息、紧急情况下的安全预警等重要功能，从而提高道路安全和交通效率。

三、MAC层协议分析1. 工作原理MAC层协议是无线通信网络的关键组成部分，负责在共享无线信道上的通信资源管理、多址接入控制和媒体访问控制。

在车载无线自组织网中，MAC层协议主要负责解决高动态环境下的通信需求。

具体来说，MAC层协议需要在多辆车之间公平有效地分配无线资源，以确保信号传输的稳定性和可靠性。

2. 性能特点车载无线自组织网的MAC层协议需要具备以下特点：（1）高效性：能够在高动态环境下实现高效的数据传输。

（2）实时性：能够支持实时交通信息的传输和安全预警的快速响应。

（3）可扩展性：能够适应不同规模的车辆网络和不断增长的数据流量。

（4）安全性：提供数据加密和身份验证等安全机制，确保通信的安全性。

3. 常见协议分析（1）IEEE 802.11p协议：该协议是专为车载通信设计的MAC层协议，具有低延迟和高可靠性的特点。

它采用载波监听多路访问/冲突避免（CSMA/CA）机制，以减少信号冲突并提高信道利用率。

（2）分布式调度协议：该协议通过分布式算法实现信道资源的动态分配，适用于车辆高动态和拓扑结构变化频繁的场景。

机载网络MAC协议研究综述卓琨;张衡阳;郑博;戚云军;贾航川【摘要】随着航空通信应用的不断深化、无线自组织网络研究的迅猛发展，机载网络介质访问控制( MAC)协议的研究已成为新的研究热点。

首先总结和分析了机载网络MAC协议设计的应用需求，进而重点从信道接入方式角度综述了机载网络的基于竞争类MAC协议、基于调度类MAC协议、混合类MAC协议和跨层协议设计等四类MAC协议的研究进展，最后对比分析了各类典型协议的特点、性能和适用范围，并给出了需要进一步重点研究的问题，以期为从事该方面研究的人员提供参考。

%With the constantly deepen application of aeronautical communications and the development in ad hoc network research development,airborne network medium access( MAC) protocol has become a new research hotspot. In this papaer,the main application characteristics and the design requirements of the air-borne network are summarized firstly. Then a more detailed description of four important research topics of MAC protocols is given in view of channel access type,including contention-based MAC protocol,schedu-ling-based MAC protocol,hybrid MAC protocol and cross-layer protocol design. Finally,the characteris-tics,performance and application of various representative MAC protocols for airborne network are com-pared and analyzed,and the open research issues on MAC layer design are given in hope of providing refer-ence for those engaged in this field.【期刊名称】《电讯技术》【年(卷),期】2015(000)009【总页数】11页(P1058-1068)【关键词】航空通信;自组织网;机载网络;MAC协议;竞争类MAC协议;调度类MAC协议;研究进展【作者】卓琨;张衡阳;郑博;戚云军;贾航川【作者单位】空军工程大学信息与导航学院，西安710077;空军工程大学信息与导航学院，西安710077;空军工程大学信息与导航学院，西安710077; 解放军94188部队，西安710077;解放军94188部队，西安710077;解放军94162部队，西安710614【正文语种】中文【中图分类】TN9251 引言近年来，随着科技的不断进步和发展，将地面ad hoc 网络应用于航空通信中就产生了新的研究领域——机载网络(Airborne Network，AN)［1］，也称航空自组网(Aeronautical ad hoc Network)或机载自组网(Airborne ad hoc Network)。

《车载无线自组织网MAC层协议分析》篇一一、引言随着车载网络技术的发展，车载无线自组织网络（VANET，Vehicle Ad-hoc Networks）逐渐成为智能交通系统的重要组成部分。

MAC（Media Access Control）层协议作为无线通信网络的关键技术之一，在VANET中发挥着举足轻重的作用。

本文旨在深入分析车载无线自组织网中MAC层协议的设计、特性和关键技术。

二、车载无线自组织网概述车载无线自组织网络是一种基于无线通信技术的车辆间通信网络，具有动态性、高实时性和高移动性的特点。

通过该网络，车辆能够实时共享道路交通信息，实现协同驾驶和交通安全应用。

三、MAC层协议在VANET中的作用MAC层协议是无线通信网络中负责管理无线信道和帧传输的底层协议。

在VANET中，MAC层协议需要处理诸如多信道接入、动态拓扑变化以及信息同步等问题。

良好的MAC层协议设计能够有效提升网络的吞吐量、传输效率和数据安全性。

四、车载无线自组织网MAC层协议分析（一）协议设计VANET中的MAC层协议设计需要考虑多个因素，如节点密度、传输速率和安全要求等。

典型的车载MAC层协议设计采用了信道接入控制和动态时隙分配的机制，以保证在车辆移动性和动态网络环境中仍能维持较高的传输效率。

（二）协议特性1. 信道接入控制：采用分布式信道接入机制，通过合理的时间和频带分配来提高系统的稳定性，避免不必要的碰撞。

2. 时隙分配策略：针对VANET中高动态拓扑的特点，采用动态时隙分配算法，能够根据网络实时状况进行快速调整，保证信息的可靠传输。

3. 安全性：考虑到VANET中的数据安全性和隐私保护需求，部分MAC层协议采用了加密技术和认证机制来保障信息传输的安全性。

（三）关键技术分析1. 多信道协调：为应对不同类型数据传输的需求，多信道协调技术能够在多个信道之间进行高效切换和协调，减少干扰和碰撞。

2. 实时数据传输：为满足紧急情况下的实时数据传输需求，MAC层协议需要支持高优先级的数据传输机制，确保关键信息的及时传递。

《车载无线自组织网MAC层协议分析》篇一一、引言车载无线自组织网络（Vehicular Ad-hoc Networks，VANETs）是一种特殊类型的移动自组织网络，主要用于在车辆间进行无线通信。

MAC（Media Access Control）层协议是VANETs中重要的组成部分，它负责处理数据传输的底层细节，包括数据的发送、接收和传输等。

本文将对车载无线自组织网MAC层协议进行详细分析，以了解其工作原理、性能特点及优化方向。

二、车载无线自组织网概述车载无线自组织网络是一种以车辆为节点的无线通信网络。

它具有高动态性、复杂性和安全性等特点，可应用于智能交通系统、紧急救援和自动驾驶等领域。

在VANETs中，车辆通过车载设备（如车载单元、GPS等）进行相互通信，实现信息共享和协同驾驶。

三、MAC层协议工作原理MAC层协议是VANETs中数据传输的关键部分，它负责管理无线信道的使用，控制数据的发送和接收。

车载无线自组织网的MAC层协议主要包括信道接入、数据传输和错误控制等部分。

1. 信道接入：MAC层协议通过信道接入机制控制车辆节点的通信。

常见的信道接入方式包括基于竞争的接入方式和基于调度的接入方式。

在VANETs中，由于车辆的高速移动性和动态变化，基于竞争的接入方式更具优势。

2. 数据传输：MAC层协议负责将上层传输的数据进行封装和转发。

在数据传输过程中，MAC层协议需要考虑如何高效地利用无线信道资源，减少数据传输的延迟和丢包率。

3. 错误控制：在数据传输过程中，由于无线信道的干扰和衰落等因素，可能会导致数据传输错误。

MAC层协议通过错误控制机制检测和纠正数据传输中的错误，确保数据的可靠传输。

四、MAC层协议性能特点车载无线自组织网的MAC层协议具有以下性能特点：1. 高动态性：由于车辆的高速移动和频繁的加入与退出网络，导致网络拓扑结构不断变化。

因此，MAC层协议需要具备快速适应网络变化的能力。

2. 低延迟：在VANETs中，数据传输的延迟对系统的性能至关重要。