802.11p review
通用范文(正式版)802.11协议精读1学习资料整理
802.11协议精读学习资料整理一、概述802.11是一种无线局域网（WLAN）协议，它定义了在无线通信中如何实现高速数据传输和网络连接。
该协议的发展始于20世纪90年代初，经过多次更新和改进，如今已经成为无线网络通信的重要标准之一。
本文将对802.11协议进行精读，以帮助读者深入了解该协议的细节和工作原理。
二、802.11协议的主要特性1. 网络拓扑结构802.11协议支持两种主要的网络拓扑结构：基础设施模式和自组织（ad-hoc）模式。
基础设施模式下，无线终端通过接入点（Access Point，简称AP）连接到有线网络。
而在自组织模式下，无线终端可以直接与其他终端进行通信，而不需要基础设施的支持。
2. 频段和信道802.11协议操作在多个频段上，包括2.4GHz和5GHz频段。
每个频段又被划分为多个不重叠的信道，通过在不同信道上进行通信，可以减少干扰和提高系统容量。
3. 链路管理802.11协议提供了一套链路管理机制，用于在无线网络中建立和维护通信链路。
这些机制包括身份验证、关联和漫游等。
身份验证验证终端的身份，关联将终端与AP建立关联关系，而漫游则用于在多个A P之间切换。
4. 介质访问控制（MAC）802.11协议使用的MAC层协议是基于载波侦听多路访问/冲突避免（Carrier Sense Multiple Access with CollisionAvoidance，简称CSMA/CA）的。
CSMA/CA机制通过监听信道上的活动，避免数据碰撞并提高传输的可靠性。
5. 系统容量与速率自适应802.11协议支持自适应调制和编码方案，以根据无线信道的质量和干扰程度来选择合适的调制和编码参数。
这样可以提高系统的容量和传输速率。
三、学习资料推荐是一些学习资料，可以帮助读者更深入地学习和理解802.11协议：1. 《802.11 Wireless Networks: The Definitive Guide》这本书由MatthewGast撰写，是对802.11无线网络的全面介绍。
IEEE 802.11p的英文文档
Runtime Optimization of IEEE802.11Wireless LANs PerformanceLuciano Bononi,Marco Conti,and Enrico GregoriAbstract—IEEE802.11is the standard for Wireless Local Area Networks(WLANs)promoted by the Institute of Electrical and Electronics Engineers.Wireless technologies in the LAN environment are becoming increasingly important and the IEEE802.11is the most mature technology to date.Previous works have pointed out that the standard protocol can be very inefficient and that an appropriate tuning of its congestion control mechanism(i.e.,the backoff algorithm)can drive the IEEE802.11protocol close to its optimal behavior.To perform this tuning,a station must have exact knowledge of the network contention level;unfortunately,in a real case,a station cannot have exact knowledge of the network contention level(i.e.,number of active stations and length of the message transmitted on the channel),but it,at most,can estimate it.This paper presents and evaluates a distributed mechanism for contention control in IEEE802.11Wireless LANs.Our mechanism,named Asymptotically Optimal Backoff(AOB),dynamically adapts the backoff window size to the current network contention level and guarantees that an IEEE802.11WLAN asymptotically achieves its optimal channel utilization.The AOB mechanism measures the network contention level by using two simple estimates:the slot utilization and the average size of transmitted frames.These estimates are simple and can be obtained by exploiting information that is already available in the standard protocol.AOB can be used to extend the standard802.11access mechanism without requiring any additional hardware.The performance of the IEEE802.11protocol,with and without the AOB mechanism,is investigated in the paper through simulation.Simulation results indicate that our mechanism is very effective,robust,and has traffic differentiation potentialities.Index Terms—Wireless LAN(WLAN),IEEE802.11,multiple access protocol(MAC),protocol capacity,performance analysis.æ1I NTRODUCTIONF OR decades,Ethernet has been the predominant networktechnology for supporting distributed computing.In recent years,the proliferation of portable and laptop computers has led to the development of the wireless LAN(WLAN)technology([28],[43]).The success of WLANs is connected to the development of networking products that can provide wireless network access at a competitive price.A major factor in achieving this goal is the availability of appropriate networking standards.IEEE Standard802.11defines a Medium Access Control(MAC) and Physical Layer(PHY)specification for a wireless local area network to provide wireless connectivity for fixed, portable,and moving stations within a local area[42].Two different approaches can be followed in the implementation of a WLAN:an infrastructure-based ap-proach or an ad hoc networking one([18],[25],[50]). Infrastructure-based802.11WLANs are currently widely used,while the use of IEEE802.11-based ad hoc networks is an open research issue([3],[21]).Since the wireless links will continue to have signifi-cantly lower capacity than wired links,the WLAN conges-tion is more problematic than in wired networks.In WLANs,the medium access control(MAC)protocol is the main element that manages congestion situations that may occur inside the network.For this reason,in this paper,we focus on the efficiency of the IEEE802.11MAC protocol and we propose a solution for increasing both protocol efficiency and protocol’s ability to react to congestion conditions.The IEEE802.11access scheme incorporates two access methods:Distributed Coordination Function(DCF)for asynchronous,contention-based,distributed access to the channel and Point Coordination Function(PCF)for centra-lized,contention-free access([42],[50]).PCF is intended to support real-time services(by using a centralized polling mechanism),but is not generally supported by current cards. Hereafter,we will concentrate our study on DCF only.The DCF is based on a Carrier Sensing Multiple Access protocol with Collision Avoidance,CSMA/CA,see,for example,([19],[38],[53]).The CSMA/CA protocol is typically adopted in a wireless environment due to its reliability, flexibility,and robustness.However,the performance of a WLAN based on the CSMA/CA protocol may be degraded by the presence of hidden terminals[54].A pair of stations is referred to as being hidden from each other if a station cannot hear the transmission from the other station.This event makes the carrier sensing unreliable as a station wrongly senses that the wireless medium has been idle while the other (hidden)station is transmitting.To avoid the hidden terminal problem,the CSMA/CA protocols are extended with a virtual carrier sensing mechanism,named Request To Send (RTS)/Clear To Send(CTS).This mechanism has been studied extensively;several variations and analyses of the RTS/CTS scheme can be found in the literature,see,for example,([4], [31],[29],[32]).IEEE802.11includes an optional RTS/CTS mechanism.In this work,we do not explicitly consider the RTS/CTS mechanism.The results presented hereafter always refer to the data transmission using the basic access only.A.L.Bononi is with the Department of Computer Science,University ofBologna,Mura Anteo Zamboni,7,40127Bologna,Italy.E-mail:bononi@cs.unibo.it..M.Conti and E.Gregori are with the National Research Council(CNR),IIT Institute,Via G.Moruzzi,1,56124Pisa,Italy.E-mail:{marco.conti,enrico.gregori}@r.it.Manuscript received14Mar.2001;revised5Aug.2002;accepted29May2003.For information on obtaining reprints of this article,please send e-mail to:tpds@,and reference IEEECS Log Number113793.1045-9219/04/$17.00ß2004IEEE Published by the IEEE Computer Societymethodology for analyzing the optimal tuning of the backoff algorithm when a portion of the traffic is transmitted using the RTS/CTS mechanism can be found,for example,in([6], [13]).In addition,recent simulation and experimental results indicate that phenomena occurring at the physical layer make the effectiveness of the RTS/CTS mechanism arguable since the hidden station phenomenon rarely occurs([56],[11],[23]).The relevance of the IEEE802.11standard has generated extensive literature on its MAC protocol.A complete survey of the IEEE802.11literature is out of the scope of this paper.Below,we will show the main research areas together with some related references.Simulation studies of the IEEE802.11protocol performance are presented in([62] [2]).IEEE802.11analytical models are proposed and evaluated in([5],[6],[16],[17],[20],[59],[60]).The use of the PCF access method for supporting real-time applica-tions is investigated in([26],[57]).The optimization of the DCF mechanism from the power-saving standpoint is investigated in([7],[44]).Recently,considerable research activity has concentrated on supporting service differentia-tion on the IEEE802.11DCF access method(e.g.,[49],[58], [1],[47]),and on the use of IEEE802.11for constructing multihop ad hoc networks([63],[64]).In this paper,we propose and evaluate a mechanism, Asymptotically Optimal Backoff(AOB),for improving the efficiency of the IEEE802.11standard protocol.In the literature,it is extensively recognized that the backoff algorithm plays a crucial role in achieving a high aggregated throughput and a fair allocation of the channel to the stations,see[4].To meet this target,the backoff value should reflect the actual level of contention for the media. The IEEE802.11adopts a binary exponential backoff protocol([42],[36],[38])which does not always adequately guarantee the best time-spreading of the users’access for the current congestion level.Each station,to transmit a frame,accesses the channel within a random self-defined amount of time whose average length depends on the number of collisions previously experienced by the station for that frame.When the network is congested,for each transmitted frame,a station must experience several collisions to increase the backoff window size,thus achieving a time spreading of the transmission attempts that is adequate for the current congestion level.No experience from the previous transmitted frame is exploited.On the other hand,our AOB mechanism extends the binary exponential backoff algorithm of IEEE802.11to guarantee that the backoff interval always reflects the current congestion level of the system(in the standard backoff,any new transmission assumes a low congestion level in the system).Our mechanism forces the network stations to adopt a backoff window size that maximizes the channel utilization1for the current network condition. There are two main factors that reduce the channel utilization:collisions and idle periods(introduced by the spreading of accesses).As these two factors are conflicting (i.e.,reducing one causes an increase of the other),the optimal tuning of the backoff algorithm is approximately achieved by equating these two costs([15],[16],[30]).Since these costs change dynamically(depending on the network load),the backoff should adapt to congestion variations in the system.Unfortunately,in a real case,a station does not have an exact knowledge of the network and load configurations,but,at most,can estimate them.The most promising direction for improving backoff protocols is to obtain information of the network status through channel observation([34],[37],[45]).A great amount of work has been done on studying the information that can be obtained by observing the system’s parameters([33],[48],[55]).Our work follows the same direction of feedback-based proto-cols,but provides original contributions as it is based on an analytical characterization of the optimal channel utilization and uses a very simple feedback signal:slot utilization.Several authors have investigated the enhancement of the IEEE802.11backoff protocol to increase its performance. In[61],given the Binary Exponential Backoff scheme adopted by the Standard,heuristic solutions have been proposed for a better time spread of the transmission attempts.In([5],[6],[15],[16],[17]),feedback-based mechanisms have been proposed for adapting the station backoff to the network congestion and maximizing channel utilization.Recently,these mechanisms have been general-ized to achieve both optimal channel utilization and weighted fairness in an IEEE802.11network with traffic streams belonging to different classes[47].All the feedback-based mechanisms cited above are based on analytic models of an IEEE802.11network.These models provide the optimal setting of the backoff parameters for achieving the maximum channel utilization.Unfortunately,these methods require an estimation of the number of users in the system that could prove expensive,difficult to obtain, and subject to significant error,especially in high contention situations[17].The AOB mechanism proposed in this paper goes a step further:1.By exploiting the analytical characterization of theoptimal IEEE802.11channel utilization presented in[16],we show that the optimal value is almostindependent of the network configuration(numberof active stations)and,hence,the maximum channelutilization can be obtained without any knowledgeof the number of active stations.2.The AOB mechanism tunes the backoff parameters tothe network contention level by using two simple andlow-cost load estimates(obtained by the informationprovided by the carrier sensing mechanism):slotutilization and average size of transmitted frames.3.AOB extends the standard802.11access mechanismwithout requiring any additional hardware. Specifically,AOB schedules the frames’transmission accord-ing to the IEEE802.11backoff algorithm,but adds an additional level of control before a transmission is enabled.A transmission already enabled by the standard backoff algorithm is postponed by AOB in a probabilistic way.The probability of postponing a transmission depends on the network congestion level and is equal to one if the channel utilization tends to exceed the optimal value.The postponed transmission is rescheduled as in the case of a collision,i.e., the transmission is delayed by a further backoff interval.In this paper,via simulation,we have extensively evaluated the performance of the IEEE802.11access scheme,with and without the AOB mechanism.The IEEE 802.11performance has been investigated both in steady-state and under transient conditions.Furthermore,we also1.In the literature,the maximum channel utilization is called protocol capacity;see[22].For this reason,hereafter,maximum channel utilization and protocol capacity are used interchangeably.investigate the mechanism robustness to errors and its potential for traffic differentiation.The work is organized as follows:In Section2,we present a brief explanation of the IEEE802.11standard,and we sketch the critical aspects connected to the contention level of the system.In Section3,we present a simple mechanism to extend the IEEE802.11standard and,in Section4,we discuss its tuning.In Sections5,6,and7,the AOB performance is deeply investigated through simula-tion.Section8discusses an AOB potential for traffic differentiation.Conclusions and future research are out-lined in Section9.2IEEE802.11In this section,we only sketch the portions of the IEEE802.11 standard that are relevant for this paper.A detailed description can be found in([42],[13],[27]).The IEEE802.11standard defines a MAC layer and a Physical Layer for WLANs.The basic access method in the IEEE802.11MAC protocol is the Distributed Coordination Function(DCF),which is a Carrier Sense Multiple Access with Collision Avoidance(CSMA/CA)MAC protocol.Besides the DCF,the IEEE802.11also incorporates an alternative access method known as the Point Coordination Function(PCF)—an access method that is similar to a polling system and uses a point coordinator to determine which station has the right to transmit.The DCF requires that every station,before transmitting, perform a carrier sensing activity to determine the state of the channel(idle or busy).If the medium is found to be idle for an interval exceeding the Distributed InterFrame Space(DIFS),the station continues with its transmission.If the medium is busy, the transmission is deferred until the ongoing transmission concludes.When the channel becomes idle,a Collision Avoidance mechanism is adopted.The IEEE802.11Collision Avoidance mechanism is a Binary Exponential Backoff scheme ([42],[36],[38],[39]).According to this mechanism,a station selects a random interval,called a backoff interval,that is used to initialize a backoff counter.When the channel is idle,the length of the time is measured in constant units(Slot_Time) indicated as slots in the following.The backoff interval is an integer number of slots and its value is uniformly chosen in the interval(0,CW_Size-1),where CW_Size,in each station is a local parameter defining the current station Contention Window size.Specifically,the backoff value is defined by the following expression[42]:Backo ff Counter¼INT RndðÞÁCW SizeðÞ; where Rnd()is a function that returns pseudorandom numbers uniformly distributed in[0,1).The backoff counter is decreased as long as the channel is sensed to be idle,stopped when a transmission is detected on the channel,and reactivated when the channel is sensed to be idle again for more than a DIFS.A station transmits when its backoff counter reaches zero.The Binary Exponential Backoff is characterized by the expression giving the dependency of the CW_Size parameter by the number of unsuccessful transmission attempts(N_A)already performed for a given frame.In[42],it is defined that the first transmission attempt for a given frame is performed adopting CW_Size equal to the minimum value CW_Size_min(assuming low contention). After each unsuccessful(re)transmission of the same frame,the station doubles CW_Size until it reaches the maximum value fixed by the standard,i.e.,CW_Size_MAX,as follows: CW SizeðN AÞ¼min CS Size MAX;CW Size minÁ2ðN AÀ1Þ: Positive acknowledgments are employed to ascertain a successful transmission.This is accomplished by the receiver(immediately following the reception of the data frame),which initiates the transmission of an acknowl-edgment frame(ACK)after a time interval Short InterFrame Space(SIFS),which is less than DIFS.If the transmission generates a collision,2the CW_Size parameter is doubled for the new scheduling of the retransmission attempt,thus further reducing contention.The increase of the CW_Size parameter value after a collision is the reaction that the IEEE802.11standard DCF provides to make the access mechanism adaptive to channel conditions.In[8],by analyzing the behavior of the IEEE 802.11DCF mechanism,it was shown that the channel utilization is negatively affected by the increase of the contention level.This occurs because1)the increase in the CW_Size is obtained at the cost of a collision,and2)after a successful transmission,no memory of the actual contention level is maintained.3L OW-C OST D YNAMIC T UNING OF THEB ACKOFF W INDOW S IZEThe drawbacks of the IEEE802.11backoff algorithm, explained in the previous section,indicate a direction for improving the performance of a random access scheme by exploiting the information on the current network conges-tion level that is already available at the MAC level. Specifically,the utilization rate of the slots(Slot Utilization) observed on the channel by each station is used as a simple and effective estimate of the channel congestion level.The estimated Slot Utilization must be frequently updated.For this reason,in[9],it was proposed that an estimate be updated by each station in every Backoff interval,i.e.,the defer phase that precedes a transmission attempt.A simple and intuitive definition of the slot utilization ðS UÞis then given by:S U¼Num Busy SlotsNum Available Slots;where:.Num_Busy_Slots,hereafter referred to as busy slots,is the number of slots in the backoff interval in whichone or more stations start a transmission attempt.Atransmission attempt can be either a successfultransmission or a collision;and.Num_Available_Slots is the total number of slots available for transmission in the backoff interval,i.e.,the sum of idle and busy slots.In the IEEE802.11standard mechanism,every station performs a Carrier Sensing activity and,thus,the proposed S_U estimate is simple to obtain.The information required to estimate S_U is already available to an IEEE802.11 station and no additional hardware is required.The current S_U estimate can be used by each station (before trying a“blind”transmission)to evaluate the2.A collision is assumed whenever the ACK from the receiver is missing.opportunity to either perform or defer the scheduled transmission attempt.In other words,if a station knows that the probability of a successful transmission is low,it should defer its transmission attempt.This can be achieved in an IEEE 802.11network by exploiting the DCC mechan-ism proposed in [9].According to DCC,each IEEE 802.11station performs an additional control (beyond carrier sensing and backoff algorithm)before any transmission attempt.This control is based on a new parameter,named Probability of Transmission P_T(...),whose value depends on the current contention level of the channel,i.e.,S_U .The heuristic formula proposed in [9]for P_T (...)is:P T S U;N A ðÞ¼1ÀS U N A ;where,by definition,S U assumes values in the interval [0,1],and N_A is the number of attempts already performed by the station for the transmission of the current frame.3The N_A parameter is used to partition the set of active stations in such a way that each stations’subset is associated with a different level of privilege to access the channel.Stations that have performed several unsuccessful attempts have the highest transmission privilege [9].The P_T parameter allows filtering the transmission attempts.When,according to the standard protocol,a station is authorized to transmit (backoff counter is equal to zero and channel is idle)in the protocol extended with the Probability of Transmission,a station will perform a real transmission with probability P_T ;otherwise (i.e.,with probability 1-P_T )the transmission is rescheduled as a collision would have occurred,i.e.,a new backoff interval is sampled.To better understand the relationship between the P_T definition and the network congestion level,we can observe Fig.1.In Fig.1,we show the P_T curves (for users with different N_A )with respect to the estimated S_U values.Assuming S_U is close to zero,we can observe that each station,independently of its number of performed attempts,obtains a Probability of Transmission (P_T )close to 1.This means that the proposed mechanism has no effect on the system and each user performs its accesses as in the standard access scheme,without any additional contention control.This point is significant as it implies the absence ofoverhead introduced in low-load conditions.The differ-ences in the users’behavior as a function of their levels of privilege (related to the value of the N_A parameter)appear when the slot utilization grows.For example,assuming a slot utilization close to 1,say 0.8,we observe that the stations with the highest N_A value obtain a Probability of Transmission close to 1,while stations at the first transmis-sion attempt transmit with a probability equal to 0.2.It is worth noting a property of the DCC mechanism:The slot utilization of the channel never reaches the value 1.Assuming S_U is close to or equal to 1,the DCC mechanism reduces the Probabilities of Transmission for all stations close to zero,thus reducing the network contention level.This effect is due to the P_T definition and,in particular,to the explicit presence of the upper bound 1for the slot utilization estimate.The DCC choice to use 1as the asymptotic limit for the S_U is heuristic and does not guarantee the maximum channel utilization.To achieve the maximum channel utilization,we need to know the optimal congestion level,i.e.,the optimal upper bound for the S_U value (opt_S_U).It is worth noting that,if opt_S_U is known,the P_T mechanism can be easily tuned to guarantee that maximum channel utilization is achieved.Intuitively,if the slot-utilization boundary value (i.e.,the value one for DCC)is replaced by the opt_S_U value,we reduce all the probabilities of transmission to zero in correspondence with slot utilization values greater than or equal to the opt_S_U .This can be achieved by generalizing the definition for the Probability of Transmission:P T opt S U;S U;N A ðÞ¼1Àmin 1;S U opt S UNA:ð1ÞSpecifically,by applying this definition of the transmission probability,we obtain the P_T curves shown in Fig.2.These curves were obtained by applying the generalized P_T definition with opt_S_U =0.80.As expected,the curves indicate the effectiveness of the generalized P_T definition to limit S_U to the opt_S_U value.The generalized Probability of Transmission provides an effective tool for controlling the congestion inside an IEEE 802.11WLAN in an optimal way,provided that the opt_S_U value is known.In the following,we will present a simple mechanism to set the opt_S_U value.Our mechanism is named Asymptoti-cally Optimal Backoff as it guarantees that the optimal utilization is asymptotically achieved,i.e.,for large M values.3.Atthe first transmission attempt,N Ais equal to 1.Fig.1.DCC probability of transmission.Fig.2.Generalized probability of transmission.4A SYMPTOTICALLY O PTIMAL B ACKOFF(AOB) M ECHANISMThe aim of the AOB mechanism is to dynamically tune the backoff window size to achieve the theoretical capacity limit of the IEEE802.11protocol.The AOB mechanism is simpler, more robust,and has lower costs and overhead introduced than the contention mechanisms proposed in[16],[17]. Specifically,the AOB mechanism requires no estimate of the number M of active stations.An accurate M estimate may be very difficult to obtain because M may be highly variable in WLANs.In this section,we exploit the results obtained from the analysis of the theoretical capacity limits of the IEEE802.11 protocol to develop the AOB mechanism.For this reason, below,we briefly summarize the results derived in[16].In [16],to study the protocol capacity,a p-persistent IEEE 802.11protocol was defined.This protocol differs from the standard protocol only in the selection of the backoff interval.Instead of the binary exponential backoff used in the standard,the backoff interval of the p-persistent IEEE 802.11protocol is sampled from a geometric distribution with parameter p.Specifically,at the beginning of an empty slot,a station transmits(in that slot)with a probability p, while it defers the transmission with a probability1-p and then repeats the procedure at the next empty slot.4Hence, in this protocol,the average backoff time is completely identified by the p value.By setting p¼1=ðE½B þ1Þ(where E½B is the average backoff time of the standard protocol5), the p-persistent IEEE802.11model provides an accurate approximation(at least from a capacity analysis standpoint) of the IEEE802.11protocol behavior[16].The IEEE802.11p-persistent model is a useful and simple tool for analytically estimating the protocol capacity in a network with a finite number,M,of stations operating in asymptotic conditions.Furthermore,to simplify the discussion,hereafter we assume that stations transmit messages whose lengths are a geometrically distributed (with parameter q)number of slots.By denoting with t slot the length of a slot,the average message length, m,is: m¼t slot=ð1ÀqÞ.By exploiting the p-persistent model,in[16],a closed analytical formula for the channel utilization, ,is derived¼ m=fðM;p;qÞ:ð2ÞBy noting that fðÞis a function of the protocol and traffic parameters,it results that,for a fixed network and traffic configuration(i.e.,constant M and q),the maximum channel utilization corresponds to the p value,p min,that minimizes fðÞ.Due to the correspondence(from the capacity stand-point)between the standard protocol and the p-persistent one,the IEEE802.11maximum channel utilization is closely approximated by adopting,in the standard protocol,a contention window whose average size is identified by the optimal p value,i.e.,E½CW ¼2=p minÀ1.The previous analysis shows that the IEEE802.11 theoretical capacity is identified by p min.Hereafter,we will show the relationship between p min and the opt_S_U value of the AOB mechanism.To this end,we will further elaborate the capacity analysis presented in[16].4.1Theoretical Capacity Limits:An Invariant Figure Results presented in this section(see Table1)point out that the increase in the number of active stations has an almost negligible impact on the theoretical capacity bounds,while the average payload size(indicated as MFS in the following)greatly affects the optimal utilization level.Results presented in Table1are numerically derived by computing the optimal p value,i.e.,p min,according to formulas presented in[16].Specifically,in this table,we report,for various network and traffic configurations (defined by the(M,q)couples),the p min values derived analytically as explained before.In this table,we also report for each configuration the value MÁp min.It is worth noting that,while p min is highly affected by the M value,given a q-value,the product MÁp min is almost constant.Specifically,results indicate that,for a given message length,the product MÁp min has an asymptotic value with respect to M.Furthermore,when M!4,the MÁp min values are very close to the asymptotic value. This is the reason for calling MÁp min an invariant figure, i.e.,for a given MFS,it is almost constant.Hereafter,we will analytically investigate the rationale behind the MÁp min quasi-constant value(for a given MFS). To perform this analysis,instead of the exact p min derivation presented in[16](it is too complex for our purpose),we approximate p min with the p value that satisfies the following relationship:E½Coll ¼E½Idle p Át slot;ð3ÞOptimal pValues4.On the other hand,in the standard protocol,a station transmits in theempty slot selected uniformly inside the current contention window.5.Note that E½B ¼ðE½CW À1Þ=2,where E½CW is the average contention window.。
80211协议标准[1]
![80211协议标准[1]](https://img.taocdn.com/s3/m/f720425db52acfc788ebc940.png)
IEEE 802.11 标准规定的物理层协议可以分为一般物理层管理和物理层汇聚过 程、物理媒体依赖两个子层（图中未示出物理层管理）。
80211协议标准
物理层管理（Physical Layer Management）：物理层管理与
MAC层管理相连，为物理层提供管理功能。
物理层汇聚子层（PLCP）：媒体访问控制（MAC）子层和物理层
80211协议标准
红外线（IR）物理层描述了一种在850到950nM波段 运行的调制类型，用于小型设备和低速率连接的数据 传输应用。这种红外线介质的基本数据速率是利用十 六进制脉冲位置调制（16PPM）的1Mbit/s速率和利用 四进制脉冲位置调制（4PPM）的2Mbit/s增强速率。 基于红外线设备的峰值功率被限定为2W。
直接序列扩频（DSSS，Direct Sequence Spread Spectrum ）系统则将要传输的数据流通过扩展码调 制而人为地扩展带宽，即使在传输波段中存在部分噪 声信号，接收机也可以无错误地接受数据。
80211协议标准
扩频是一种在信号的带宽进行扩展的技术。采用扩频 的好处是： 抗干扰。若使用窄频，容易受到使用相同频率的通信 干扰导致完全无法通信。 对于非特定的目的的接收器，扩展了带宽的信号混在 背景噪声中，让蓄意想侦听窃取数据资料的人不易判 别真正的信号，避免他人的截听。 提供了供多个用户使用同一传输波段的方法，保证了 无线设备在频段上的可用性和可靠的吞吐量，也保证 了使用同一频段的设备不互相影响。
发送器以1Mbit/s的速率发送前同步码和适配头，为接收器的收听 提供特定的通用数据速率。适配头的发送结束后，发送器将数据速率改 到适配头确认的速率。整个发送完成后，PLCP向MAC层发送一条 PHY-TXEND.confirm原语，关闭发送器，并将PMD电路转换到接收模 式。
ieee802.11无线局域网协议分析系统的分析与实现
——一些蔓盔堂堡圭兰堡垒壅ＡｂｓｔｒａｃｔＴｈｅｓｔａｎｄａｒｄｓｏｆＷＬＡＮ（ＷｉｒｅｌｅｓｓＬｏｃａｌＡｒｅａ／Ｎｅｔｗｏｒｋ）ｈａｙｅｄｅｖｅｌｏｐｅｄｍｏｒｅｐｅｒｆｅｃｔｔｈｒｏｕｇｈｅｖｅｒｙｌａｒｇｅｍａｎｕｆａｃｔｕｒｅａｎｄｅｘｐｅｒｔ’ｓｅｆｆｏｒｔｓｉｎｒｅｃｅｎｔｙｅａｒｓ．ＷＬＡＮｈａｓｇｏｔｍｏｒｅａｎｄｍｏｒｅｅｘｔｅｎｓｉｖｅａｐｐｌｉｃａｔｉｏｎｓｉｎｔｈｅｗｈｏｌｅｗｏｒｌｄａｎｄｉｓｐｌａｙｉｎｇａｎｍｏｒｅａｎｄｍｏｒｅｉｍｐｏｒｔａｎｔｒｏｌｅｉｎｍａｎｙｆｉｅｌｄｓ．～ｆｅａｎｗｈｉｌｅ．ｔｈｅｕｓｅｒｓａｎｄａｄｍｉｎｉｓｔｒａｔｏｒｓｏｆｔｈｅＷＬＡＮｓａｌｌｐｕｔｆｏｒｗａｒｄｈｉｇｈｅｒａｎｄｈｉｇｈｅｒｒｅｑｕｅｓｔｔｏｔｈｅｓｅｃｕｒｉｔｙｏｆＷＬＡＮ，ａｎｄｅｘｐｅｃｔｔｏｕｔｉｌｉｚｅｍｏｒｅｐｅｒｆｅｃｔＷＵ州ｐｒｏｔｏｃｏｌｓａｎａｌｙｓｉｓｓｙｓｔｅｍｔｏｃａｒｒｙｏｎｒｅａｌ—ｔｉｍｅｃｏｎｔｒｏｌａｎｄｍａｎａｇｅｍｅｎｔｔｏＷＬＡＮ．Ａｔｐｒｅｓｅｎｔ．ｔｈｅｒｅｉｓｎｏｒｉｐｅＷＬＡＮｐｒｏｔｏｃｏｌｓａｎａｌｙｓｉｓｓｙｓｔｅｍｔｏｐｕｔｏｎｍａｒｋｅｔａｔｈｏｍｅ．Ｓｏ．ｉｔｉｓｇｒｅａｔｌｙｍｅａｎｎｉｇｆｕｌｔｏｒｅｓｅａｒｃｈｔｈｅ孔ＡＮｓｔａｎｄａｒｄｓａｎｄｄｅｖｅｌｏｐＷＬＡＮｐｒｏｔｏｃ０１ｓａｎａｌｙｓｉｓｓｙｓｔｅｍｗｉｔｈｉｎｄｅｐｅｎｄｅｎｔｉｎｔｅｌｌｅｃｔｕａｌｐｒｏｐｅｒｔｙｒｉｇｈｔ．ＴｈｉｓｔｈｅｓｉｓｐｕｔｓｕｐｔｈｅｒｅａｌＷＬＡＮｏｆｉｎｆｒａｓｔｒｕｃｔｕｒｅｍｏｄｅｂａｓｅｄｏｎＩＥＥＥ８０２．１１．ＡｎｄｔｈｒｏｕｇｈｕｓｉｎｇｔｈｅｗｉｒｅｌｅｓｓＬＡＮｆｏｒａｌｏｎｇｔｉｍｅ，ＩｈａｖｅｃａｒｒｉｅｄｏｎｆｕｒｔｈｅｒｊｎｖｅｓｔｊｇａｔｉｏｎｏｎｍａｉｎｒｅｓｐｅｃｔｓｏｆＷＬＡＮ，ａｎｄｕｔｉｌｉｚｅｄｔｅｃｈｎｏｌｏｇｙｓｔｕｄｉｅｄｉｎｄｅｐｅｎｄｅｎｔｌｙｔｏｓｏｌｖｅｓｏｍｅｋｅｙｐｒｏｂｌｅｍｓｏｆａｄｍｉｎｉｓｔｒａｔｉｎｇａｎｄｃｏｎｔｒｏｌＩｉｎｇＷＬＡＮ．ＴｈｉｓｔｈｅｓｉｓｉｎｔｒｏｄｕｃｅｓｔｈｅｄｉｆｆｅｒｅｎｔｓｔａｎｄａｒｄｓａｎｄｔｈｅｃｏｍｐｏｎｅｎｔｓｏｆＷＬＡＮａｔｆｉｒｓｔ，ａｎｄｔｈｅｎｎａｒｒａｔｅｓＩＥＥＥ８０２．１ｌｇｆｆ４Ｃｐｒｏｔｏｃｏｌｓｉｎｓｅｒｖｉｃｅ、姒Ｃａｃｃｅｓｓｍｏｄｅｓ（ＤＣＦａｎｄＰＣＦ）、ｓｃａｎｎｉｎｇｄｅｔａｉｌ．ｉｎｃｌｕｄｉｎｇＭＡＣ＆ｓｖｎｃｈｒｏｎｉｚａｔｉｏｎ、ｓｅｃｕｒｉｔｙ、ｃｏｎｎｅｃｔｉｏｎ、ｐｏｗｅｒｍａｎａｇｅｍｅｎｔ，ａｎｄｅｔｃ．ＩｔａｌｓｏａｎａｌｙｓｅｓｖａｒｉｏｕｓｋｉｎｄｓｏｆＭＡＣｆｒａｍｅｓｔｒｕｃｔｕｒｅｏｆＩＥＥＥ８０２．ｉｉｗｉｒｅｌｅｓｓＬＡＮｉｎｐａｒｔｉｃｕｌａｒ．ＴｈｅｔｈｅｓｉｓｐｒｏｖｉｄｅｓｆｒａｍｅｗｏｒｋｃｈａｒｔｏｆｎｅｔｗｏｒｋｐｒｏｔｏｃｏｌｓａｎａｌｙｓｉｓｒｅｓｅａｒｃｈｏｎｈｏｗｔｏｃａｐｔｕｒｅＩＥＥＥ８０２·ＩＩＷＬＡＮｓｙｓｔｅｍ，ａｎｄｔｈｅｎｍａｋｅｓａｄｅｅｐｆｏｒｄｉｆｆｅｒｅｎｔｋｉｎｄｓｏｆＤａｃｋｅｔｓ．ａｎｄｔｈｅｎｇｉｖｅｓｄｉｆｆｅｒｅｎｔｍｅｔｈｏｄｓａｎｄｇｉｖｅｗｉｒｅｌｅｓｓｅａｒｄｓ．Ｉｒｅｓｅａｒｃｈｔｈｅｍｅｔｈｏｄｓｏｆｆｉｌｔｅｒｉｎｇｐａｃｋｅｔｓ２——一——些查查兰堡圭兰竺丝兰ａｃｔｕａｌｆｌｏｗｃｈａｒｔｏｆｐｒｏｇｒａｍｍｉｎｇ．Ｉｎｔｈｅｄｅｃｏｄｉｎｇｍｏｄｕｌｅ，Ｉｇｉｖｅｔｈｅｆｌｏｗｃｈａｒｔｏｆｔｈｅｔｏｐｍａｎａｇｅｍｅｎｔｆｕｎｃｔｉｏｎｏｆｄｅｃｏｄｉｎｇｍｏｄｕｌｅａｎｄｔｈｅｋｅｙｄａｔａｓｔｒｕｃｔｕｒｅｓ．Ｉｎｔｈｅｅｎｄ，ＩｇｉｖｅｔｈｅｄｅｓｉｇｎｍｅｔｈｏｄｓｏｆＣｈｉｎｅｓｅｓｙｓｔｅｍｉｎｔｅｒｆａｃｅｉｎＬｉｎｕｘ，ａｎｄｐｒｏｖｉｄｅｔｈｅｇｒａｐｈｉｃｉｎｔｅｒｆａｃｅｔｈａｔｔｈｅｓｙｓｔｅｍｏｐｅｒａｔｅｓ．ＴｈｅｓｙｓｔｅｍｓｕｃｃｅｓｓｆｕｌｌｙｃａｐｔｕｒｅｓｖａｒｉｏｕｓｋｉｎｄｓｏｆｆｒａｍｅｓｉｎＷＬＡＮｂａｓｅｄｏｎＩＥＥＥ８０２．１１．ａｎｄｃａｎｄｅｃｏｄｅａｎｄｒｅｐｒｏｄｕｃｅｔｈｅＩＥＥＥ８０２．１１ＭＡＣｐｒｏｔｏｃｏｌｌａｙｅｒ、ｔｈｅｔｈｉｒｄｐｒｏｔｏｃｏｌｌａｙｅｒａｎｄｔｈｅｈｉｇｈｅｒｐｒｏｔｏｃｏｌｌａｙｅｒｏｆａ１１ｐａｃｋｅｔｓ，ａｎｄｃａｎａｌｓｏｆｉｌｔｅｒａｎｄｃｏｕｎｔｖａｒｉｏｕｓｋｉｎｄｓｏｆｆｒａｍｅｓｉｎｒｅａｌｔｉｍｅ．ＴｈｉｓｓｙｓｔｅｍｐｒｏｖｉｄｅｓａｕｓｅｆｕｌｔｏｏｌｆｏｒｍｏｎｉｔｏｒｉｎｇａｎｄａｄｍｉｎｉｓｔｒａｔｉｎｇＷＬＡＮ．Ａｔｔｈｅｓａｍｅｔｉｍｅ，ｉｔｃａｎａｌｓｏｐｒｏｖｉｄｅｔｅｃｈｏｎｏｌｏｇｙｓｔｏｒａｇｅｆｏｒｓｅｃｕｒｉｔｙｔｅｃｈｎｏｌｏｇｙｏｆＷＬＡＮ．ＫｅｙＷｏｒｄｓ：ＷＬＡＮ，ＩＥＥＥ８０２．１ｌ，ｃａｐｔｕｒｉｎｇｐａｃｋｅｔｓ。
Performance Evaluation of the IEEE 802.11p WAVE Communication Standard 中文翻译
C.曼哈顿电网低数据情况下的通信量
在第二次模拟场景中，我们使用的场景 大小 2000 米×2000 米分为 500 个米长度的 一个网格。在内部网格边界道路都位于生成 曼哈顿网格。该节点将在这些道路上，平均 速度 60 公里/秒。仿真时间设定为 15 分钟。 每个节点使用指数到达间隔时间与生成的 消息平均参数标签在二中给出。模拟与运行 不同的节点密度已经进行，其中 100 个节点 相当于平均 1.9 邻居，200 个节点是相当于 3.8 邻居，和 300 个节点相当于 5.9 邻居。
表格-Ⅱ 交通荷载参数
D.曼哈顿电网高数据情况下的通信量 在模拟中使用高数据流量各自的应用
消息生成参数表二。他们仅仅导致比低数据 流量方案两倍多一点的负荷，。
发送和接收的消息的平均数目 每个节点的绘制见图 10。节所描述的影响。 Ⅳ-C 为低数据流量可以在高看到结果负载 的情况下更大。由于高负荷由于模拟控制器 0 和 1 的减少与广播的数量越来越多的节 点。这种下降几乎为 0 指数，而 AC1 是以线 性方式跌幅的，同样的效果，但并在发生模 拟控制器 2 和 3（见图 10（b））中并不严 重。而在模拟控制器 2 降低的消息数 16%比 15000 的平均的发送的消息，消息在 AC3 数 仍下降 9%相比 11250 的平均消息发送。一个 高度的影响饱和信道和为不同的模拟控制 器的后果可以清楚地看到在接收机侧（图 10 （c））。第一接收的数据包数（0 开始在 100 节点）然后接收的数据包数（AC1 200 开始节点）严重下降。高优先级的模拟控制 器不影响严重，然而，为了进一步增加节， 点的吞吐量也将达到一个最大值。
在车载环境下无线接入的 MAC 层相当于 IEEE 802.11e 增 强 的 分 布 式 信 道 接 入 （EDCA）质量服务（QoS）的扩展[ 3 ]。因 此，应用程序消息分为不同的 ACS，其中 AC0 具有最低的优先级和 AC3 的最高优先级。在 MAC 层的数据包中，每个 AC 队列存在的分组 的选择时四个 ACS 内容内部传输。选定分组 然后竞争信道从外部使用其选择的竞争参 数，竞争参数用于 CCH 显示选项卡。我们计 算的 CWmin 和 CWmax 值。CWmin=15，CWmax = 1023 都有使用价值。
802.11介绍
802.11 介绍802.11是IEEE最初制定的一个无线局域网标准，主要用于解决办公室局域网和校园网中，用户与用户终端的无线接入，业务主要限于数据存取，速率最高只能达到2Mbps。
目前，3Com 等公司都有基于该标准的无线网卡。
由于802.11在速率和传输距离上都不能满足人们的需要，因此，IEEE小组又相继推出了802.11b和802.11a两个新标准。
三者之间技术上的主要差别在于MAC子层和物理层。
标准详解802.11协议组是国际电工电子工程学会（IEEE）为无线局域网络制定的标准。
虽然WI-FI使用了802.11的媒体访问控制层（MAC ）和物理层（PHY），但是两者并不完全一致。
802.11a是802.11原始标准的一个修订标准，于1999年获得批准。
802.11a标准采用了与原始标准相同的核心协议，工作频率为5GHz，使用52个正交频分多路复用（OFDM）副载波，最大原始数据传输率为54Mb/s，这达到了现实网络中等吞吐量（20Mb/s ）的要求。
目前正在开发中的版本是802.11ae —2012 。
工作频段802.11采用2.4GHz和5GHz这两个ISM频段。
其中2.4GHz的ISM频段为世界上绝大多数国家采用。
5GHz ISM频段在一些国家和地区的使用情况比较复杂，加上高载波频率所带来了负面效果，使得802.11a的普及受到了限制，虽然它是协议组的第一个版本。
1997年，原始标准（2Mbit/s ，工作在2.4GHz ）。
1999年，物理层补充（54Mbit/s ，工作在5GHz ）。
,1999年，物理层补充（11Mbit/s 工作在2.4GHz ）。
，符合802.1D 的媒体接入控制 层桥接（MAC Layer Bridging ）。
，根据各国 无线电规定做的调整。
对服务等级（Quality of Service,QoS ）的支持。
基站的互连性（IAPP,Inter-Access Point Protocol ），2006 年2月被 IEEE 批准撤2003年，物理层补充（54Mbit/s ，工作在2.4GHz ）。
802.11简介
Key Features
TDLS Discovery TDLS Setup/Teardown TDLS U-APSD TDLS Peer Power Save Mode TDLS Channel Switching
NAS Drive 11n Radio
AP 11gRadio
TDLS
802.11 -2012
802.11n High Throughput (>100 Mbps)
802.11W Management Frame Security
PHY
2
IEEE 802.11 Revisions
MAC
802.11ak GLK 802.11aq PAD Smart Grid High Efficiency WLAN WNG 802.11 ah 802.11af TVWS 802.11ac VHT 5GHz 802.11ai FILS 802.11aa Video Transport
Bandwidth
Maximum 40MHz
MCS
BPSK, QPSK, 64QAM
BPSK, QPSK, 64QAM, 256 QAM (optional)
11.5 times
11
Max Throughput
600 Mbps
6933.3 Mbps
IEEE 802.11ad
Goal
A maximum single link throughput of at least 1Gbps
802.11r Fast Roam 802.11k RRM
802.11Y
802.11 -2003
j JPห้องสมุดไป่ตู้bands
802.11协议帧详解
802协议桢格式802.11和Wi-Fi技术并不是同一个东西。
Wi-Fi标准是802.11标准的一个子集，并且是Wi-Fi联盟负责管理无线网络协议桢的分类类型和字段定义了无线网络的三种类型，分别是：1: Management frames，它的主要作用是维护接入点和无线客户端之间的通信，管理该框架拥有以下子类型：AuthenticationDe-authenticationAssociation RequestAssociation ResponseReassociation RequestReassociation ResponseDisassociationBeaconProbe RequestProbe Response2: Control frames控制帧是负责客户端和接入点的数据交换，类型为：Request to Send (RTS) Clear to Send (CTS) Acknowledgement (ACK）这些数据可以在一些报文请求中看到。
3: Data frames这些不同类别的数据包被统称为"数据包类型"。
WLAN有以下三种网络拓扑结构1) 独立基本服务集(Independent BSS, IBSS)网络(也叫ad-hoc网络)2) 基本服务集(Basic Service Set, BSS)网络3) 扩展服务集(Extent Service Set, ESS)网络1) AD-Hoc网络win7自带的AD-Hoc组建功能，可以让我们很方便的在一个小范围内快速组建"局域网"，联网打游戏啥的很方便2) BSS网络对于个人PC来说，使用最多的所谓"无线Wi-Fi"指的就是BSS网络模式，我们通过AP(Access Point)接入点来接入网络3) ESS网络其中，ESS中的DS(分布式系统)是一个抽象系统，用来连接不同BSS的通信信道(通过路由服务)，这样就可以消除BSS中STA与STA之间直接传输距离受到物理设备的限制。
802.11p
• 基于载波监听多点接入/碰撞避免CSMA/CA协议， 采用四次握手（RTS/CTS/DATA/ACK）或两次握手 （DATA/ACK）机制。核心思想是载波监听，信道 预约（RTS/CTS），数据传输，等待确认。在每个 节点使用CSMA算法，各个站竞争获取信道使用权 。 • 信道预约机制是为了解决无线网络隐藏终端问题 。
802.11p协议
-------基于竞争的CSMA/CA协议
• 当前主要的车载自组织网络MAC协议 • 802.11p协议的优点和缺点
当前主要的车载自组织网络MAC协议
• 1、基于竞争的CSMA/CA协议（如802.11p协议） • 2、基于预约的时分多址技术TDMA协议（如可靠预约 ALOHA协议）
802.11p协议的优点和缺点
• 管理，可以在CFP和CP期间均可 启动一个TXOP。与PCF有如下不同： 1、竞争机制。 2、HCCA可以在CP阶段启动CAP。 3、TXOP概念。获得发送机会节点可以连续发送多个数据 帧。
• 802.11p对802.11的修改 1、PHY 工作频率：802.11p必须工作在多个频率。 参数：802.11p时域参数翻倍，降低码间干扰，信号带宽 和传输速率减半。 2、MAC 主要不同在标志位dot11OCBEnabled。当其为false时，与 802.11相同。当为true时，无需认证和关联；节点无需加 入BSS即可相互通信，从而减少时延；所有的AC将TXOP均 设为0；无需同步，因为节点不属于任一个BSS；同时，节 点发送的管理帧和数据帧的BSSID设为wildcard BSSID。
802.11p协议介绍
802.11p协议又称为WAVE，是车载自组织网络MAC和PHY规 范。其是802.11协议的改进版本。 首先介绍802.11协议： 基于竞争分布的协调功能DCF机制 基于集中管理的点协调功能PCF机制 混合协调功能HCF机制 802.11p对802.11的修改
IEEE 802.11、802.15、802.16、802.20标准简介-文档资料
Wi-Fi与其他无线协议。 802.11v 无线网络管理。V工作组是最新成立的小组，
其任务将基于802.11k所取得的成果。802.11v主要面对 的7
与802.11b不兼容，是其最大的缺点。也许会因此而被 802.11g淘汰。
7
IEEE 802.11b标准
1999年9月被正式批准，又称Wi-Fi标准，目前最流行的 WLAN协议。该标准规定无线局域网工作频段在 2.4GHz~2.4835GHz，数据传输速率达到11 Mbps。该标 准是对IEEE 802.11的一个补充，采用点对点模式和基本 模式两种运作模式，在数据传输速率方面可以根据实际情 况在11 Mbps、5.5 Mbps、2 Mbps、1 Mbps的不同速率 间自动切换，而且在2 Mbps、1 Mbps速率时与802.11兼 容。
802.11j针对日本标准进行的补充，类似于 802.11h是对欧洲标准的补充。
12
IEEE 802.11i标准
IEEE 802.11i标准是结合IEEE 802.1x中的用户 端口身份验证和设备验证，对无线局域网MAC 层进行修改与整合，提出了新的TKIP协议解决 了WEP协议中的漏洞。定义了严格的加密格式 和鉴权机制，以改善无线局域网的安全性。 IEEE 802.11i新修订标准主要包括两项内容： “Wi-Fi保护访问”（WPA）技术和“强健安全 网络”。Wi-Fi联盟计划采用802.11i标准作为 WPA的第二个版本，并于2004年初开始实行。
16
IEEE 802.11o/p/Q/t/u/v标准
802.11o 针对VOWLAN（Voice over WLAN）而制订 ，更 快速的无限跨区切换，以及读取语音（voice）比数据 （Data）有更高的传输优先权。
IEEE 802.11p Towards an International Standard for Wireless Access in Vehicular Environments
IEEE 802.11p: Towards an International Standard for Wireless Access in Vehicular EnvironmentsDaniel Jiang, Luca DelgrossiMercedes-Benz Research & Development North America, Inc.{daniel.jiang, luca.delgrossi}@ABSTRACTVehicular environments impose a set of new requirements on today’s wireless communication systems. Vehicular safety communications applications cannot tolerate long connection establishment delays before being enabled to communicate with other vehicles encountered on the road. Similarly, non-safety applications also demand efficient connection setup with roadside stations providing services (e.g. digital map update) because of the limited time it takes for a car to drive through the coverage area. Additionally, the rapidly moving vehicles and complex roadway environment present challenges at the PHY level.The IEEE 802.11 standard body is currently working on a new amendment, IEEE 802.11p, to address these concerns. This document is named Wireless Access in Vehicular Environment, also known as WAVE. As of writing, the draft document for IEEE 802.11p is making progress and moving closer towards acceptance by the general IEEE 802.11 working group. It is projected to pass letter ballot in the first half of 2008.This paper provides an overview of the latest draft proposed for IEEE 802.11p. It is intended to provide an insight into the reasoning and approaches behind the document.KeywordsIEEE 802.11, DSRC, WAVE1.INTRODUCTIONThe IEEE 802.11p WAVE standardization process originates from the allocation of the Dedicated Short Range Communications (DSRC) spectrum band in the United States and the effort to define the technology for usage in the DSRC band.This section first provides a brief overview of the DSRC spectrum. The context and history of WAVE standardization is then described.1.1DSRC Spectrum AllocationIn 1999, the U.S. Federal Communication Commission allocated 75MHz of Dedicated Short Range Communications (DSRC) spectrum at 5.9 GHz to be used exclusively for vehicle-to-vehicle and infrastructure-to-vehicle communications.The primary goal is to enable public safety applications that can save lives and improve traffic flow. Two such application scenarios are shown in Figure 1. Private services are also permitted in order to spread the deployment costs and to encourage the quick development and adoption of DSRC technologies and applications.Figure 1, Vehicle safety communication examplesAs shown in Figure 2, the DSRC spectrum is structured into seven 10 MHz wide channels. Channel 178 is the control channel (CCH), which is restricted to safety communications only [1]. The two channels at the ends of the spectrum band are reserved for special uses [2]. The rest are service channels (SCH) available for both safety and non-safety usage.Figure 2, DSRC spectrum band and channels in the U.S. The DSRC band is a free but licensed spectrum. It is free because the FCC does not charge a fee for the spectrum usage. Yet it should not be confused with the unlicensed bands in 900 MHz, 2.4 GHz and 5 GHz that are also free in usage. These unlicensed bands, which are increasingly populated with WiFi, Bluetooth and other devices, place no restrictions on the technologies other than some emission and co-existence rules. The DSRC band, on the other hand, is more restricted in terms of the usages and technologies. FCC rulings regulate usage within certain channels and limit all radios to be compliant to a standard. In other words, one cannot develop a different radio technology (e.g. that uses all 75 MHz of spectrum) for usage in the DSRC band even if it is limited in transmission power as related to the unlicensed band. These DSRC usage rules are referred as “license by rule”.Similar efforts are occurring in other parts of the world to set spectrum aside for vehicular usage. Europe, for example, is getting close to allocating 30 MHz of spectrum band in the 5 GHz range for the express purpose of supporting vehicular communications for safety and mobility applications.1.2 WAVE Standardization HistoryIn the U.S., the initial effort at standardizing DSRC radio technology took place in the ASTM 2313 working group [5]. In particular, the FCC rule and order specifically referenced this document for DSRC spectrum usage rules.In 2004, this effort migrated to the IEEE 802.11 standard group as DSRC radio technology is essentially IEEE 802.11a adjusted for low overhead operations in the DSRC spectrum. Within IEEE 802.11, DSRC is known as IEEE 802.11p WAVE, which stands for Wireless Access in Vehicular Environments [4]. IEEE 802.11p is not a standalone standard. It is intended to amend the overall IEEE 802.11 standard [3].One particular implication of moving the DSRC radio technology standard into the IEEE 802.11 space is that now WAVE is fully intended to serve as an international standard applicable in other parts of the world as well as in the U.S. The IEEE 802.11p standard is meant to:•Describe the functions and services required by WAVE-conformant stations to operate in a rapidly varying environment and exchange messages without having to join a Basic Service Set (BSS), as in the traditional IEEE 802.11 use case.•Define the WAVE signaling technique and interface functions that are controlled by the IEEE 802.11MAC.Figure 3, DSRC standards and communication stack As shown in Figure 3, IEEE 802.11p WAVE is only a part of a group of standards related to all layers of protocols for DSRC-based operations. The IEEE 802.11p standard is limited by the scope of IEEE 802.11, which is strictly a MAC and PHY level standard that is meant to work within a single logical channel. All knowledge and complexities related to the DSRC channel plan and operational concept are taken care of by the upper layer IEEE 1609 standards. In particular, the IEEE 1609.3 standard covers the WAVE connection setup and management [6]. The IEEE 1609.4 standard sits right on top of the IEEE 802.11p and enables operation of upper layers across multiple channels, without requiring knowledge of PHY parameters [7].At the time of writing, the IEEE 802.11p draft version 3.0 had already gone through its third letter ballot in the IEEE 802.11 working group. It failed to reach the critical approval rate of 75% by just 2 votes. The task group is currently resolving the comments received through the letter ballot and updating the draft standard document accordingly. This paper provides an overview of the general direction and technical approach in this draft standard but its content should not be viewed as binding or final.2. MAC AMENDMENT DETAILSIn an overly simplified manner, the IEEE 802.11 MAC is about how to arrange for a set of radios in order to establish and maintain a cooperating group. Radios can freely communicate among themselves within the group but all transmissions from outside are filtered out. Such a group is a Basic Service Set (BSS) and there are many protocol mechanisms designed to provide secure and robust communications within a BSS. The key purpose of the IEEE 802.11p amendment at the MAC level is to enable very efficient communication group setup without much of the overhead typically needed in the current IEEE 802.11 MAC. In other words, the focus is on simplifying the BSS operations in a truly ad hoc manner for vehicular usage. In this section, we first provide an overview of the core mechanism in setting up the IEEE 802.11 connectivity. Then the approach introduced by the IEEE 802.11p amendment is described.2.1 IEEE 802.11 Operations Overview2.1.1 Basic Service SetAn Infrastructural Basic Service Set is a group of IEEE 802.11 stations anchored by an Access Point (AP) and configured to communicate with each other over the air-link. It is usually just referred to as a BSS. The BSS mechanism controls access to an AP’s resources and services, and also allows for a radio to filter out the transmissions from other unrelated radios nearby. A radio first listens for beacons from an AP and then joins the BSS through a number of interactive steps, including authenticationand association.Figure 4, Independent and extended service set concepts As shown in Figure 4, the IEEE 802.11 standard further allows administrators to logically combine a set of one or more interconnected BSSs into one ESS (Extended Service Set) using DS (Distribution Service). An ESS appears as a single BSS to the LLC (Logical Link Control) layer at any station associated with one of those BSSs.The ad-hoc operating mode defined for IEEE 802.11 also follows the similar interactive establishment process of a Infrastructure BSS and is called IBSS (Independent BSS). While the name is “ad hoc”, IBSS still carries too much complexity and overhead to be suitable for vehicular communications in the DSRC use cases.A BSS is known to the users through the Service Set Identification (SSID). This corresponds to the names of WiFi hotspots that people can observe and connect to at home orpublic locations. The SSID information field is between 0 and 32 Bytes.2.1.2 BSSID and received frame filteringThe SSID should not be confused with the BSSID, which stands for Basic Service Set Identification. In contrast to SSID, BSSID is the name of a BSS known to the radios at the MAC level and is a 48-bit long field just like a MAC address. Each BSS must have a unique BSSID shared by all members. This is ensured simply by using the MAC address of the AP.For an IBSS, a locally administered IEEE MAC address is used. This is formed by using a random 46-bit number with the individual/group bit set to 0 and the universal/local bit set to 1. BSSID filtering is the key mechanism to restrict, at the MAC level, all incoming frames to only those received from radiosthat are members in the same BSS.Figure 5, IEEE 802.11 data frame formatAs shown in Figure 5, each IEEE 802.11 data frame includes up to 4 address fields. These address fields are used to carry source address (SA), destination address (DA), transmitting STA address (TA), receiving STA address (RA) and BSSID. The use of the four address fields differ according to the “To DS” (Distribution Service) and “From DS” bits in the frame control field, and is illustrated in Figure 6.To DS From DSAddress 1 Address 2 Address 3 Address 4 0 0 RA = DA TA = SA BSSID N/A 0 1 RA = DA TA = BSSID SA N/A 1RA = BSSIDTA = SADAN/A1 1 RA TA DA SAFigure 6, IEEE 802.11 data frame address field contents The MAC level of a station, upon receiving a frame from the PHY, uses the contents of the Address 1 field to perform address matching for receiving decisions. If the Address 1 field contains a group address (e.g., a broadcast address), the BSSID is compared to ensure that the broadcast or multicast originated from a station in the same BSS.A special case of the BSSID is the wildcard BSSID, which is composed of all “1s”. The current IEEE 802.11 standard limits the usage of the wildcard BSSID to only management frames of subtype probe request.2.2 WAVE Approaches2.2.1 WAVE modeIEEE 802.11 MAC operations, as described above, are too time-consuming to be adopted in IEEE 802.11p. Vehicular safety communications use cases demand instantaneous data exchange capabilities and cannot afford scanning channels for the beacon of a BSS and subsequently executing multiple handshakes to establish the communications.Think, for instance, of a scenario where a vehicle encounters another vehicle on the road coming from the opposite direction: depending on the vehicles dynamics, the time available for the communications may be extremely short.Therefore, it is essential for all IEEE 802.11p radios to be, by default, in the same channel and configured with the same BSSID to enable safety communications.A key amendment introduced by the IEEE 802.11p WAVE is the term “WAVE mode”. A station in WAVE mode is allowed to transmit and receive data frames with the wildcard BSSID value and without the need to belong to a BSS of any kind a priori. This means, two vehicles can immediately communicate with each other upon encounter without any additional overhead as long as they operate in the same channel using the wildcard BSSID.2.2.2 WAVE BSSEven for non-safety communications and services, the overhead of traditional BSS setup may be too expensive. A vehicle approaching a road side station that offers, say digital map download service, can hardly afford the many seconds that are typically needed in a conventional WiFi connection setup because the total time this vehicle would be in the coverage is very short.The WAVE standard introduces a new BSS type: WBSS (WAVE BSS). A station forms a WBSS by first transmitting a on demand beacon. A WAVE station uses the demand beacon, which uses the well known beacon frame and needs not to be periodically repeated, to advertise a WAVE BSS. Such an advertisement is created and consumed by upper layer mechanisms above the IEEE 802.11. It contains all the needed information for receiver stations to understand the services offered in the WBSS in order to decide whether to join, as well as the information needed to configure itself into a member of the WBSS. In other words, a station can decide to join and complete the joining process of a WBSS by only receiving a WAVE advertisement with no further interactions.This approach offers extremely low overhead for WBSS setup by discarding all association and authentication processes. It necessitates further mechanisms at upper layers to manage the WBSS group usage as well as providing security. These mechanisms, however, are out of the scope of the IEEE 802.11.2.2.3 Expanding wildcard BSSID usageGiven the focus of safety as the key usage of WAVE, the use of wildcard BSSID is also supported even for a station already belonging to a WBSS (i.e., configured with a particular BSSID). In other words, a station in WBSS is still in WAVE mode and can still transmit frames with the wildcard BSSID in order to reach all neighboring stations in cases of safety concerns. Similarly, a station already in a WBSS and having configured its BSSID filter accordingly, can still receive frames from others outside the WBSS with the wildcard BSSID.The ability to send and receive data frames with wildcard BSSID benefits not only safety communications. It is also able to support signaling of future upper layer protocols in this ad hoc environment.2.2.4 Distribution ServiceThe DS is still available to WAVE devices. Over the air, this simply means that it is possible for data frames to be transmitted with “To DS” and “From DS” bits set to 1. However, the ability for a radio in a WAVE BSS to send and receive data frames with the wildcard BSSID introduces complications. It is likely that a radio will be restricted to send a data frame with thewildcard BSSID only if the “To DS” and “From DS” bits are set to 0. In other words, radios that are communicating within the context of a WAVE BSS need to send data frames using a known BSSID in order to access DS.2.2.5MAC amendment summaryHere is a quick summary of the changes at MAC for WAVE operations:• A station in WAVE mode can send and receive data frames with the wildcard BSSID with “To DS” and “From DS”fields both set to 0, regardless of whether it is a member ofa WAVE BSS.• A WAVE BSS (WBSS) is a type of BSS consisting of a set of cooperating stations in WAVE mode that communicate using a common BSSID. A WBSS is initialized when a radio in WAVE mode sends a WAVE beacon, which includes all necessary information for a receiver to join. • A radio joins a WBSS when it is configured to send and receive data frames with the BSSID defined for that WBSS.Conversely, it ceases to belong to a WBSS when its MAC stops sending and receiving frames that use the BSSID of that WBSS.• A station shall not be a member of more than one WBSS at one time. A station in WAVE mode shall not join an infrastructure BSS or IBSS, and it shall not use active or passive scanning, and lastly it shall not use MAC authentication or association procedures.• A WBSS ceases to exist when it has no members. The initiating radio is no different from any other member after the establishment of a WBSS. Therefore, a WBSS can continue if the initiating radio ceases to be a member.3.PHY AMENDMENT DETAILSAt PHY level, the philosophy of IEEE 802.11p design is to make the minimum necessary changes to IEEE 802.11 PHY so that WAVE devices can communicate effectively among fast moving vehicles in the roadway environment. This approach is feasible because IEEE 802.11a radios already operate at 5 GHz and it is not difficult to configure the radios to operate in the 5.9 GHz band in the U.S. and similar bands internationally. It is also desirable and sensible because of the technical challenges involved in radically amending a wireless PHY design. While MAC level amendments are fundamentally software updates that are relatively easy to make, PHY level amendment necessarily should be limited in order to avoid designing an entirely new wireless air-link technology. Accordingly, three changes are made and are described in the following subsections.3.1.110 MHz channelIEEE 802.11p is essentially based on the OFDM PHY defined for IEEE 802.11a, with a 10 MHz wide channel instead of the 20 MHz one usually used by 802.11a devices.IEEE 802.11 already defines 10 MHz wide channels, and it is straightforward in implementation since it mainly involves doubling of all OFDM timing parameters used in the regular 20 MHz 802.11a transmissions. The key reason for this scaling of 802.11a is to address the increased RMS delay spread in the vehicular environments. A recent study by CMU and General Motors [8] shows that•Guard interval at 20 MHz is not long enough to offset the worst case RMS delay spread (i.e. the guardinterval is not long enough to prevent inter-symbolinterferences within one radio’s own transmissions inthe vehicular environments).•If choice is simply between scaled versions of 802.11a, then 10 MHz is a reasonable choice.3.1.2Improved receiver performance requirements While there are a number of channels available in the US and (expectedly) internationally for IEEE 802.11p deployment and usage, the nature of closely distributed vehicles on the road creates increased concern for cross channel interferences. The measurements presented in [9] demonstrated the potential for immediate neighboring vehicles (i.e., next to each other in adjacent lanes) to interfere each other if they are operating in two adjacent channels. For example, a vehicle A transmitting in channel 176 (see Figure 2) could interfere and prevent a vehicle B in the next lane (i.e. 2.5 m apart) from receiving safety messages sent by vehicle C that is 200 m away in channel 178. Cross channel interference is a well known and natural physical property of wireless communications. The most effective and proper solution to such concerns is through channel management policies that is completely outside of the scope at IEEE 802.11. Nevertheless, IEEE 802.11p introduces some improved receiver performance requirements in adjacent channel rejections. There are two categories of requirements listed in the proposed standard. Category 1 is mandatory and generally understood to be reachable with today’s chip manufacturers. Category 2 is more stringent and optional. It is likely to be more expensive to realize in the next few years.3.1.3Improved transmission maskSpecific to the usage of IEEE 802.11p radios in the U.S. ITS band (i.e., the 5.9 GHz DSRC spectrum), four spectrum masks are defined that are meant for class A to D operations. These constraints are issued in FCC CFR47 Section 90.377 and Section 95.1509.•For Class A operation using 10 MHz channel spacing, the transmitted spectrum shall have a 0 dBr bandwidthnot exceeding 9 MHz, and shall not exceed -10 dBr at5 MHz frequency offset, -20 dBr at 5.5 MHzfrequency offset, -28 dBr at 10 MHz frequency offset,-40 dBr at 15 MHz frequency offset and above.•For Class B operation using 10 MHz channel spacing, the transmitted spectrum shall have a 0 dBr bandwidthnot exceeding 9 MHz, and shall not exceed -16 dBr at5 MHz frequency offset, -20 dBr at 5.5 MHzfrequency offset, -28 dBr at 10 MHz frequency offset,-40 dBr at 15 MHz frequency offset and above.•For Class C operation using 10 MHz channel spacing, the transmitted spectrum shall have a 0 dBr bandwidthnot exceeding 9 MHz, and shall not exceed -26 dBr at5 MHz frequency offset, -32 dBr at 5.5 MHzfrequency offset, -40 dBr at 10 MHz frequency offset,-50 dBr at 15 MHz frequency offset and above.•For Class D operation using 10 MHz channel spacing, the transmitted spectrum shall have a 0 dBr bandwidthnot exceeding 9 MHz, and shall not exceed -35 dBr at5 MHz frequency offset, -45 dBr at 5.5 MHzfrequency offset, -55 dBr at 10 MHz frequency offset,-65 dBr at 15 MHz frequency offset and above.Generally speaking, these spectrum masks are more stringent than the ones demanded of the current IEEE 802.11 radios. There are debates regarding whether and when chip makers would be able to meet such requirements.4.SUMMARYWireless access in vehicular environment imposes a set of new requirements on the communications system that led to the introduction of the WAVE operating mode and of the WAVE BSS in IEEE 802.11p.When operating in WAVE mode, stations do not need to join a BSS as they can exchange data using a wildcard BSSID that is available at all times. This dramatically reduces the connection setup overhead and suits vehicular safety applications well. Private services offered over the DSRC spectrum service channels benefit from a reduced connection setup overhead through mechanisms defined for a WAVE BSS. Joining a WAVE BSS only requires receiving a single WAVE Advertisement message from the initiating station. A station in a WAVE BSS is further enabled to still send and receive data frames with the wildcard BSSID.While the IEEE 802.11p standardization process is moving closer to pass a letter ballot in the general IEEE 802.11 working group, there are also industry efforts in implementing and field testing such radios. Prototype IEEE 802.11p radios have been developed by the Vehicle Infrastructure Integration Consortium (VII-C) in 2007 both for on-board and roadside units. Likewise, interoperable radios are being built by the Crash Avoidance Metric Partnership (CAMP) for collision avoidance and vehicle-to-vehicle safety applications.It should be noted that while IEEE 802.11p describes how the communications take place over each individual channel of the DSRC spectrum, a complete communications system for WAVE needs to include support for multi-channel operations, security, and other upper layer operations. These are addressed by the IEEE 1609 trial-use standards, which are expected to be substantially updated in the near future.5.REFERENCES[1]“FCC Report and Order 03-324: Amendment of theCommission’s Rules Regarding Dedicated Short-RangeCommunication Services in the 5.850-5.925 GHz Band,”December 17, 2003.[2]“FCC Report and Order 06-110: Amendment of theCommission’s Rules Regarding Dedicated Short-RangeCommunication Services in the 5.850-5.925 GHz Band,”July 20, 2006.[3]“IEEE Std. 802.11-2007, Part 11: Wireless LAN MediumAccess Control (MAC) and Physical Layer (PHY)specifications,” IEEE Std. 802.11, 2007.[4] “IEEE P802.11p/D3.0, Draft Amendment for WirelessAccess in Vehicular Environments (WAVE),” July 2007. [5]“Standard Specification for Telecommunications andInformation Exchange Between Roadside and VehicleSystems - 5 GHz Band Dedicated Short RangeCommunications (DSRC) Medium Access Control (MAC)and Physical Layer (PHY) Specifications”, ASTM DSRCSTD E2313-02, 2002[6]“IEEE 1609.3-2007 WAVE Networking Services”, 2007[7]“IEEE 1609.4-2007 WAVE Multi-Channel Operation”,2007[8] D. Stancil, L. Cheng, B. Henty and F. Bai, “Performance of802.11p Waveforms over the Vehicle-to-Vehicle Channelat 5.9 GHz ”, IEEE 802.11 Task Group p report, September 2007[9]V. Rai, F. Bai, J. Kenney and K. Laberteaux, “Cross-Channel Interference Test Results: A report from the VSC-A project”, IEEE 802.11 Task Group p report, July 2007。
ieee.802.11p的工作原理
ieee.802.11p的工作原理IEEE 802.11p是一种无线通信标准，也被称为Wireless Access in Vehicular Environments（WAVE），它主要应用于车辆与车辆之间的通信，也被视为一种短距离的无线接入技术。
以下是对其工作原理的简要介绍：1. 物理层（Physical Layer）：这是IEEE 802.11p协议的最底层，主要负责处理无线信号的发送和接收。
它包括调制、扩频、解扩频、混频等操作，以将数据转化为适合无线传输的信号。
2. 数据链路层（Data Link Layer）：这一层包括逻辑链路控制子层（LLC）和媒体访问控制子层（MAC）。
LLC子层负责处理错误检测和修复，以及数据序列的重排。
MAC子层则负责管理无线信道的访问，包括信道分配、流量控制和多路复用等。
3. 网络层（Network Layer）：这一层主要负责处理数据包的路由选择和转发。
它使用IP协议进行数据包的封装和解析，并通过无线路由器或其他网络设备将数据包从一个网络转发到另一个网络。
4. 传输层（Transport Layer）：这一层主要负责提供端到端的通信服务，包括数据包的分段、重组、错误控制和流量控制等。
通常使用TCP或UDP协议。
5. 应用层（Application Layer）：这是最顶层，它根据应用程序的不同需求，提供各种应用协议。
例如，在车辆间通信中，可能会使用交通安全应用协议、导航应用协议等。
在通信过程中，IEEE 802.11p使用直序扩频（DSSS）或者跳频扩频（FHSS）方式发送数据，接收端则通过对应的方式接收和解码数据。
此外，为了确保通信的可靠性，IEEE 802.11p还支持多种重传机制，例如自动重传请求（ARQ）和前向纠错（FEC）。
IEEE 802.11p是一种非常有效的短距离无线通信技术，尤其适用于车辆间的高速移动通信环境。
然而，由于其工作原理涉及到复杂的编码和解码过程，以及多个层次的协议处理，因此在实际应用中需要针对具体场景进行优化和调整。
802.11标准简述
802.11是IEEE在1997年为无线局域网(Wireless LAN)定义的一个无线网络通信的工业标准。
此后这一标准又不断得到补充和完善，形成802.11x的标准系列。
802.11x标准是现在无限局域网的主流标准，也是Wi-Fi的技术基础。
目前，WLAN领域主要是IEEE 802.11x系列与HiperLAN ／x（欧洲无线局域网）系列两种标准。
在以下标准中，平时应用最多的应该是802.11a/b/g三个标准，均已得到相当广泛的应用；最新讨论中的标准是802.11n，在传输速度上有了一个大的飞跃，但截至2006年5月，该标准尚未被通过。
802.11802.11是IEEE最初制定的一个无线局域网标准，主要用于解决办公室局域网和校园网中用户与用户终端的无线接入，业务主要限于数据存取，速率最高只能达到2Mbps。
由于它在速率和传输距离上都不能满足人们的需要，因此，IEEE小组又相继推出了802.11b和802.11a两个新标准，前者已经成为目前的主流标准，而后者也被很多厂商看好。
802.11a802.11a（Wi-Fi5）标准是得到广泛应用的802.11b标准的后续标准。
它工作在5GHzU-NII频带，物理层速率可达54Mbps，传输层可达25Mbps。
可提供25Mbps的无线ATM接口和10Mbps 的以太网无线帧结构接口，以及TDD/TDMA的空中接口；支持语音、数据、图像业务；一个扇区可接入多个用户，每个用户可带多个用户终端。
802.11b802.11b即Wi-Fi，它利用2.4GHz的频段，2.4GHz的ISM频段为世界上绝大多数国家通用，因此802.11b得到了最为广泛的应用。
它的最大数据传输速率为11Mb/s，无须直线传播。
在动态速率转换时，如果射频情况变差，可将数据传输速率降低为5.5Mb/s、2Mb/s和1Mb/s。
支持的范围是在室外为300米，在办公环境中最长为100米。
802.11b使用与以太网类似的连接协议和数据包确认，来提供可靠的数据传送和网络带宽的有效使用。
信息安全与交通运输：802.11p、DSRC和WAVE标准的安全问题说明书
Hacking the Fast Lane: Security Issues with 802.11p, DSRC, and WAVEA White Paper for Black Hat DC 2011Rob Havelt and Bruno OlivieraJanuary 7, 2011AbstractThe new 802.11p standard aims to provide reliable wireless communication for vehicular environments. The P802.11p specification defines functions and services required by Wireless Access in Vehicular Environments (WAVE) conformant stations to operate in varying environments and exchange messages either without having to join a BSS or within a BSS, and defines the WAVE signaling technique and interface functions that are controlled by the 802.11 MAC.Wireless telecommunications and information exchange between roadside and vehicle systems present some interesting security implications. This talk will present an analysis of the 802.11p 5.9 GHz band Wireless Access in Vehicular Environments (WAVE) / Dedicated Short Range Communications (DSRC), Medium Access Control (MAC), and Physical Layer (PHY) Specifications of this protocol. We will present methods of analyzing network communications, and potential security issues in the implementation of the protocol in practical environments such as in toll road implementations, telematics systems, and other implementations.OverviewVehicle Ad-Hoc networks (VANET) are nothing new. The basic concept of a VANET is also fairly straightforward. Take a widely adopted and relatively low cost wireless technology (WiFi/WLA N) used to connect mobile devices together and to the Internet and add that to vehicles. Of course, if it were truly that straightforward, we would likely already have the self navigating conveyances only seen in sci-fi movies already, fuel conservation would not be an issue, nor would delays in morning or evening commutes due to traffic. If it were truly that straightforward, the nation’s roadways would be among the safest and most effective way to travel. However its not exactly that easy. There are some unique challenges involved in deploying wireless networking in vehicular environments. Those challenges have been addressed in many different ways over the years.The history of the use of radio and infrared communication for vehicle to roadside and vehicle to vehicle communication is long and storied. The concept of roadside automation, i.e. the use of communication technologies to make roadside travel safe, efficient, and friendly for the environment, was exhibited as early as the 1939 World’s Fair. The General Motors exhibit “Futurama” envisioned the state of Intelligent Transportation Systems (ITS) twenty years in the future.Later, since at least the 1960’s actual radio based automation systems were developed and demonstrated. However it wasn’t until the late 1990’s that a total game changer happened when the Federal Communication Commission in the United States allocated a 75MHz band in the 5.9GHz range to Dedicated Short Range Communications (DSRC) technology. In 2000 the ASTM International established a working group to develop requirements for the DSRC standards. The first radio technology adopted for the DSRC range was the 802.11a wireless networking standard. Four years later a working group would be started to work on the 802.11p amendment to the standard, as well as the Wireless Access in Vehicular Environments (WAVE) standards based on the existing ASTM Vehicle Safety Communication (VSC) standard. The standards for 802.11p and multiple components of WAVE were recently ratified, and as a result, we can expect to see a proliferation of these technologies in the near future.Services and ApplicationsThere are many services and applications for VANET’s, and they are generally classified with two categories – safety applications and non-safety/commercial.Typical safety applications would involve:•Assisted collision avoidance•Forward obstacle detection and avoidance•Lane departure warning•Automated variable message signs•Turn accident warningTypical non-safety and commercial applications would involve:•Roadway toll collection•Traffic management•Parking lot payment•Traveller information support•Freight and cargo managementWAVE standards overviewDSRC communications using 802.11p and WAVE are comprised of several standards. The following is an overview of these standards and the portions of the protocols that they govern.Protocols Standards OSI Layer WAVE PHY and MAC IEEE 802.11p PHY and MAC functions for an IEEE 802.11p device to function in a vehicular environment. layer 1 and 2 Multichannel operation IEEE 1601.4 Enhancements to the 802.11p MAC to support multichannel operation layer 2 WAVE Networking Services IEEE 1609.3 addressing and routing layer 2, 3, and 4 WAVE Resource Manager IEEE 1609.1 defines an application that allows communication from remote sites to onboard units (OBU) N/A WAVE Security Services IEEE 1609.2 Secure messaging format and processing N/A Table 1 - WAVE StandardsSecurity ModelThe IEEE 1609.2 standard defines a secure messaging format based on a “defence in depth” strategy. It involves a complicated public key infrastructure (PKI) with the government as the root certificate authority (CA). Due to the overall complexity and comprehensiveness of the security model, its effectiveness will depend heavily upon the implementation.The overall security model aims to provide: Security, Anonymity, and Trust.SecuritySecurity services via PKI aim to provide authentication for messages (signatures), and encryption of confidential data, In order to do this, messages must be short and interactions must be fast. To achieve this for broadcast, high priority, messages a new compact certificate format and public key algorithm with short keys are used. Trust ModelIn vehicle safety applications the operator is consider un-trusted and applications should be isolated from the operator. In public safety applications, the operator is trusted. For e-Commerce applications, conventional trust models are used.AnonymityThings such as IP addresses, MAC Addresses, and Certificates can all be used to track and end node. Measures are put into place to anonymize and in some cases randomize these identifiers.Protocol AnalysisIn a paper published at the 6th Karlsruhe Workshop on Software Radios entitled “IEEE 802.11p Transmission Using GNURadio” Fuxjagaer et al. Show “a method to rapidly prototype a fully standard-compliant OFDM frame encoder using the GNURadio framework and the Universal Software Radio Peripheral (Version 2).”“The encoder generates OFDM frames in digital complexbase-band representation and uses the USRP Version 2 as digital-to-analog front-end to up-convert and transmit them in the 5.9GHz band that has been allocated for dedicated short range communication (DSRC) for vehicular applications.”This is convenient for testing protocol robustness in real world applications, as well as performing security analysis. Our presentation uses the work done here to analyze some non-safety/commercial applications of the protocol.References“VANET: Vehicular Applications and Inter-Networking Technologies” editors Hannes Hartenson and Kenneth Laberteaux – Wiley 2010“Vehicular Networks: From Theory to Practice” Stephan Olariu, Michele C. Weigle - Chapman & Hall/CRC Computer & Information Science SeriesIEEE 802.11p Transmission Using GNURadio - P. Fuxjäger∗, A. Costantini∗†, D. Valerio∗, P. Castiglione∗, G. Zacheo∗, T. Zemen∗, F. Ricciato∗† - http://userver.ftw.at/~valerio/files/wsr10.pdfA SECURE VANET MAC PROTOCOL FOR DSRC APPLICATIONS, Yi Qian, Kejie Lu, and Nader Moayeri - /pubs/Yi-Paper1.pdfStandards: WAVE / DSRC / 802.11p, Dr. Michele Weigle - /~mweigle/courses/cs795-s08/lectures/5c-DSRC.pdfNovel Issues in DSRC Communication Radios, Yasser L. Morgan - /reg/7/canrev/cr63/IEEECanadianReview_no63.pdfSAE International – DSRC Implementation Guide -/standardsdev/dsrc/DSRCImplementationGuide.pdfAbout TrustwaveTrustwave is the leading provider of on-demand and subscription-based information security and payment card industry compliance management solutions to businesses and government entities throughout the world. For organisations faced with today’s challenging data security and compliance environment, Trustwave provides a unique approach with comprehensive solutions that include its flagship TrustKeeper® compliance management software and other proprietary security solutions. Trustwave has helped thousands of organisations—ranging from Fortune 500 businesses and large financial institutions to small and medium-sized retailers—manage compliance and secure their network infrastructure, data communications and critical information assets. Trustwave is headquartered in Chicago with offices throughout North America, South America, Europe, Africa, Asia and Australia. For more information, visit https://.About Trustwave SpiderLabsSpiderLabs is the advanced security team within Trustwave focused on incident response, ethical hacking and application security testing for our premier clients. The team has performed hundreds of forensic investigations, thousands of ethical hacking exercises and hundreds of application security tests globally. In addition, the SpiderLabsrResearch team provides intelligence through bleeding-edge research and proof of concept tool development to enhance Trustwave's products and services. For more information, visithttps:///spiderLabs.php.。
802.11p综述
IEEE 802.11p综述摘要汽车在能够与路上相遇的汽车通信前，不能容忍长时间的建立连接而产生的延时，加上飞速行驶的汽车和复杂的道路状况给物理层带来了很大的挑战。
IEEE802.11P的研究是基于IEEE802.11解决汽车网络的方案。
由于设计的IEEE802.11标准在灵活性上很差，所以IEEE802.l1p标准主要是解决快速连接高频率切换问题和新的安全问题。
以下就802.11p协议的产生，IEEE802.11p协议与与IEEE802.11的不同之处，以及应用做简单的介绍。
引言0 引言近年来汽车网络越来越受到人们的关注，利用无线通信标准DSRC实现路边到汽车和汽车到汽车的公共安全和私人活动通信的短距离的通信服务。
最初的设定是在300 m距离内能有6 Mb/s的传输速度。
拥有304.8 m的传输距离和6 Mb/s的数据速率。
从技术上来看，它对IEEE802.11进行了多项针对汽车这样的特殊环境的改进，如：热点间切换更先进、更支持移动环境、增强了安全性、加强了身份认证等等。
目前的汽车通信市场，很大程度上由手机通信所占据，但客观上说，蜂窝通信覆盖成本比较高昂，提供的带宽也比较有限。
使用IEEE802.11p有望降低成本、提高带宽、实时收集交通信息等。
1、IEEE 802.11p无线局域网标准，用于智能交通ITSIEEE 802.11p（又称WAVE,Wireless Access in the Vehicular Environment）是一个由IEEE 802.11标准扩充的通信协议，主要用于车载电子无线通信。
它本质上是IEEE 802.11的扩充延伸，符合智能交通系统（ITS，Intelligent Transportation Systems）的相关应用。
应用层面包括高速车辆之间以及车辆与ITS路边基础设施（5.9千兆赫频段）之间的数据交换。
IEEE 1609标准则基于IEEE 802.11p通信协议的上层应用标准。
802.11标准详答
802.11标准详答802.11标准详答802.11的标准是什么?下面是由店铺为大家准备的802.11标准详答，喜欢的可以收藏一下!了解更多详情资讯，请关注店铺!802.11标准是什么IEEE 802.11是IEEE最初制定的一个无线局域网标准，主要用于解决办公室局域网和校园网中，用户与用户终端的无线接入，业务主要限于数据存取，速率最高只能达到2Mbps。
由于802.11在速率和传输距离上都不能满足人们的需要，因此，IEEE小组又相继推出了802.11b和802.11a两个新标准。
三者之间技术上的主要差别在于MAC子层和物理层。
虽然有人将Wi-Fi与802.11混为一谈，但两者并不一样。
(见下文IEEE 802.11b)历史自第二次世界大战，无线通讯因在军事上应用的成果而受到重视，无线通讯一直发展，但缺乏广泛的通讯标准。
于是，IEEE在1997年为无线局域网制定了第一个版本标准──IEEE 802.11。
其中定义了媒体访问控制层(MAC层)和物理层。
物理层定义了工作在2.4GHz的ISM 频段上的两种展频作调频方式和一种红外传输的方式，总数据传输速率设计为2Mbit/s。
两个设备之间的.通信可以设备到设备(ad hoc)的方式进行，也可以在基站(Base Station, BS)或者访问点(Access Point，AP)的协调下进行。
为了在不同的通讯环境下取得良好的通讯质量，采用CSMA/CA (Carrier Sense Multi Access/Collision Avoidance)硬件沟通方式。
1999年加上了两个补充版本：802.11a定义了一个在5GHz ISM 频段上的数据传输速率可达54Mbit/s的物理层，802.11b定义了一个在2.4GHz的ISM频段上但数据传输速率高达11Mbit/s的物理层。
2.4GHz的ISM频段为世界上绝大多数国家通用，因此802.11b得到了最为广泛的应用。
802.11p review
5.1.2.10 Multiple Devices Multiple devices each implementing a separate function or
application on a different frequency
– Multi-device configurations have the advantage of being able to listen for safety messages on the Control Channel and simultaneously conduct an application transaction on one of the two Service Channels at the edge of the DSRC band or in the U-NII band.
• Onboard Units initiate a link by sending a PST in Action Frames on the Control Channel
Submission
Broady Cash, ARINC/ASRliIdNeC8ARINCARINCARINCARINCARINCARINCARINCARINC
Submission
Broady Cash, ARINC/ASRlidINe C10ARINCARINCARINCARINCARINCARINCARINCARINC
July 2004
doc.: IEEE 802.11-04/1074r0
Multiple DSRC Devices
Single device One device operating on one channel at a time
802.11总结
802.11总结802.11a协议笔记：1、OFDM PHY包含两个协议功能：phy会聚功能（由plcp⽀持）、能将psdu映射成适合在两个或多个pmd系统的sta间发送和接收数据及管理信息的成帧格式，pmd系统，定义了多个采⽤ofdm系统的sta之间通过⽆线媒体发送和接收数据的特性和⽅法ofdm phy 包含三个功能实体：PMD功能、 PHY会聚功能、层管理功能ofdm phy服务通过phy服务原语提供给MAC层2、ofdm phy功能PLCP ⼦层PLCP ⼦层的作⽤是使MAC 层操作对PMD ⼦层的依赖性最⼩化。
该功能简化了PHY 层到MAC 层的服务接⼝。
PMD ⼦层PMD ⼦层为在两个或多个STA 之间发送和接收数据提供了⼀种⽅法PHY 管理实体(PLME)PLME 与MAC 管理实体共同完成对本地PHY 功能的管理层或⼦层的服务是⼀组能⼒，它提供给下⼀个较⾼层（或⼦层）的⽤户。
通过描述代表每⼀个服务的服务原语和参数来规定抽象的服务3、OFDM PHY 特定服务参数本部分MAC 层的结构设计与PHY 层⽆关。
在特定的PMD 实现中，MLME可能需要作为标准PHY SAP原语的⼀部分与PLME 相互作⽤。
对于每个PMD 层，这些参数列表以及它们的可能取值在特定的PHY规范中都有定义。
TXVECTOR 参数长度(LENGTH) 表⽰MAC 层请求PHY 层发送的MPDU 的⼋位位组数PHY-TXSTART.request(TXVECTOR) 1～4095数据速率(DATARATE)PHY-TXSTART.request(TXVECTOR)6,9,12,18,24,36,48 和54 (单位为Mbit/s；6,12 和24 是必备的)服务(SERVICE)PHY-TXSTART.request(TXVECTOR)对加扰器进⾏初始化；7 个空⽐特+9 个保留的空⽐特发射功率等级(TXPWR_LEVEL)PHY-TXSTART.request(TXVECTOR) 1～8RXVECTOR 参数长度指⽰在PLCP 报头中包含的LENGTH 字段的值(LENGTH) PHY-RXSTART.indicate 1～4095接收信号强度指⽰(RSSI)PHY-RXSTART.indicate(RXVECTOR) 0～RSSI 最⼤值数据速率(DATARATE)PHY-RXSTART.request(RXVECTOR)6，9，12，18，24，36，48和54 （单位为Mbit/s）服务(SERVICE)PHY-RXSTART.request(RXVECTOR)空4、OFDM PLCP ⼦层PSDU 和PPDU 相互转化的会聚过程。
基于IEEE802.11p协议的车载网信标消息性能研究
基于IEEE802.11p协议的车载网信标消息性能研究刘南杰;葛剑飞;赵海涛;刘委婉【期刊名称】《信息通信技术》【年(卷),期】2013(000)005【摘要】This paper discusses the performance of beacons exchanged among vehicles. Firstly, it analyzes the acceptance rate and average delay with the variation of minimum contention window size and vehicle density theoretically by building Markov Model, then studies the theoretical by results using ns-2 network simulator. The simulation results are consistent with the theoretical analysis, it demonstrats that the Markov Model proposed in this paper is suitable to be used to study the beacon performance, and the simulation results will provide some reference for further research of other performance of VANETs.%研究车辆间通信交换信标消息的性能。
首先通过建立马尔科夫链模型在理论上分析随着最小竞争窗口和车辆密度的变化关系信标消息的平均到达时延和广播接收率；然后对理论分析结果进行NS2仿真，仿真结果与理论分析具有一致性，表明文章提出的模型适用于研究车载网中的信标消息，对进一步研究车载网的其他性能也具有一定的参考价值。
802.11帧结构分析报告
802.11帧结构分析1. 802.11介绍1.1 802.11概述802.11协议组是国际电工电子工程学会（IEEE）为无线局域网络制定的标准。
IEEE 最初制定的一个无线局域网标准，主要用于解决办公室局域网和校园网中用户与用户终端的无线接入，业务主要限于数据存取，速率最高只能达到2Mbps。
虽然WI-FI使用了802.11的媒体访问控制层（MAC）和物理层（PHY），但是两者并不完全一致。
在以下标准中，使用最多的应该是802.11n标准，工作在2.4GHz频段，可达600Mbps（理论值）。
IEEE 802.11是一个协议簇，主要包含以下规：a.物理层规：802.11b，802.11a，802.11g；b.增强型MAC层规：802.11i，802.11r，802.11h等；c.高层协议规：802.11f，802.11n，802.11p，802.11s等。
802.11中定义了三种物理层规，分别是：频率跳变扩展频谱(FHSS)PHY规、直接序列扩展频谱(DSSS)PHY规和红外线(IR)PHY规，由于物理层的规与无线信息安全体系关系不大，故本文不对物理层做过多阐述。
802.11同802.3一样，主要定义了OSI模型中物理层和数据链路层的相关规，其中数据链路层又可分为MAC子层和LLC子层，802.11与802.3的LLC子层统一由802.2描述。
1.2 802.11拓扑结构及服务类型WLAN有以下三种网络拓扑结构：a.独立基本服务集(Independent BSS, IBSS)网络(也叫ad-hoc网络)，如图1所示。
b.基本服务集(Basic Service Set, BSS)网络，如图2所示。
c.扩展服务集(Extent Service Set, ESS)网络，如图2所示。
STA1 STA2图1其中，ESS中的DS（分布式系统）是一个抽象系统，用来连接不同BSS的通信信道(通过路由服务)，这样就可以消除BSS中STA与STA之间直接传输距离受到物理设备的限制。
- 1、下载文档前请自行甄别文档内容的完整性，平台不提供额外的编辑、内容补充、找答案等附加服务。
- 2、"仅部分预览"的文档,不可在线预览部分如存在完整性等问题,可反馈申请退款(可完整预览的文档不适用该条件!)。
- 3、如文档侵犯您的权益，请联系客服反馈,我们会尽快为您处理(人工客服工作时间：9:00-18:30)。
September 2004
doc.: IEEE 802.11-04/1074r0
WAVE Mode Performance Requirements
• 5.1.2.2 WAVE Communications • DSRC devices operating in the WAVE Mode are capable of transferring messages to and from vehicles each traveling at speeds up to 140 km/h with a Packet Error Rate (PER) of less than 10% for PSDU lengths of 1000 bytes and to and from vehicles at speeds up to a minimum of 200 km/h with a PER of less than 10 % for PSDU lengths of 64 bytes. For vehicle-to-vehicle communications DSRC devices are capable of transferring messages at closing speeds of up to a minimum of 283 km/h with a PER of less than 10 % for PSDU lengths of 64 bytes.
Submission Slide 10 WKFisher/ARINC
September 2004
doc.: IEEE 802.11-04/1074r0
Multiple DSRC Devices
Single device One device operating on one channel at a time or 5.1.2.10 Multiple Devices Multiple devices each implementing a separate function or application on a different frequency
Submission
Slide 11
WKFisher/ARINC
September 2004
doc.: IEEE 802.11-04/1074r0
RSSI for WAVE
• 17.2.3.2 RXVECTOR RSSI • For the WAVE mode, subsequent to a period of no less than 2 ms after an alert signal, the minimum RSSI resolution should be less than or equal to 0.2 dB and shall be accurate to ± 1 dB across the entire operating temperature range within -60 to -30 dBm of the receiving signal range
Submission
Slide 3
WKFisher/ARINC
September 2004
doc.: IEEE 802.11-04/1074r0
Implementing WAVE Mode
• 5.1.2.6 WAVE Mode
– The WAVE mode is used to allow IEEE 802.11 units in the DSRC band to both broadcast messages and establish almost instantaneous links for data transfer with fast moving vehicles – The WAVE mode provides two basic types of communication services:
September 2004
doc.: IEEE 802.11-04/1074r0
Back-up Info:
Submission
Slide 14
WKFisher/ARINC
September 2004
doc.: IEEE 802.11-04/1074r0
IEEE 802.11e Reference
doc.: IEEE 802.11-04/1074r0
DSRC and WAVE Terminology
• DSRC – Dedicated Short-range Communications is the name of the 5.9 GHz Band allocated for the ITS communications • WAVE – Wireless Access in Vehicular Communications is the mode of operation used by IEEE 802.11 devices to operate in the DSRC band
± 15
Reduction in Power Spectral Density, dBr
• • • •
0 0 0 0
-10 -16 -26 -35
Slide 13
-20 -20 -32 -45
-28 -28 -40 -55
-40 -40 -50 -65
WKFisher/ARINC
Submission
Submission
Slide 5
WKFisher/ARINC
September 2004
doc.: IEEE 802.11-04/1074r0
Implementing WAVE Mode, 3
• Roadside Units (RSUs) meet the FCC Safety Message priority requirement by broadcasting Safety messages in Message Elements in Beacon or Action Frames primarily on the Control Channel • Onboard Units (OBUs) meet the FCC Safety Message priority requirement by broadcasting Safety messages in Message Elements in Action Frames primarily on the Control Channel
Submission
Slide 8
WKFisher/ARINC
September 2004
doc.: IEEE 802.11-04/1074r0
Implementing WAVE Mode, 6
• In establishing the link for data transfer the operating channel is switched from the Control Channel to a Service Channel • Continued WAVE Mode operation may be implemented on this Service Channel or routine BSS or IBSS operations may be implemented
• 7.1.2 General frame format • Insert the following text at the end of subclause 7.1.2: • For WAVE implementation the QoS Control field shall be used as defined in IEEE 802.11e, Clause 7.1.3.5.
– a. Channel scan shall be disabled. – b. The channel shall be set to 178. – c. The data rate shall be set to 6 Mbps. – d. The unit shall be able to receive at any mandatory data rate.
– Multi-device configurations have the advantage of being able to listen for safety messages on the Control Channel and simultaneously conduct an application transaction on one of the two Service Channels at the edge of the DSRC band or in the U-NII band.
Submission Slide 6 WKFisher/ARINC
September 2004
doc.: IEEE 802.11-04/1074r0
Implementing WAVE Mode, 4
• Non-Safety Messages are sent in Message Elements in Action Frames • For RSUs the message duration is limited to 750 us and a minimum interval of 100 ms. For OBUs the message duration shall be limited to 580 us at a minimum interval of 750 ms
September 2004