技术领域technical field
本发明涉及车载自组织网络中的信道接入方法，属于网络通讯技术领域。The invention relates to a channel access method in a vehicle self-organizing network, and belongs to the technical field of network communication.
背景技术Background technique
车载自组网技术(Vehicular Ad-hoc Network,简称VANET)。VANET是专门用于汽车通信的自组织网络，是智能交通系统组成的重要部分。联邦通信委员会把5.850～5.925GHz的75Mhz的频段专门用于智能交通系统。通过专用短程通信(DSRC)，这75Mhz被专门的用于车与车(Vehicle-to-Vehicle,V2V)以及车与设施(Vehicle-to-Infrastructure,V2I)之间的通信，因此这75Mhz也被叫做DSRC信道。IEEE工作组专门成立了IEEE 802.11p小组进行DSRC的研究，提出了WAVE模式。Vehicular Ad-hoc Network (VANET for short). VANET is an ad hoc network dedicated to vehicle communication and is an important part of the intelligent transportation system. The Federal Communications Commission uses the 75Mhz frequency band of 5.850-5.925GHz exclusively for intelligent transportation systems. Through dedicated short-range communication (DSRC), this 75Mhz is specially used for communication between vehicles (Vehicle-to-Vehicle, V2V) and vehicles (Vehicle-to-Infrastructure, V2I), so this 75Mhz is also used It is called a DSRC channel. The IEEE working group specially established the IEEE 802.11p group to conduct research on DSRC and proposed the WAVE mode.
DSRC信道7个10MHz的信道组成。此外5.850GHz到5.855GHz共5MHz频谱被作为保留频谱，用于潜在的可扩展应用。信道178被称为控制信道(Control Channel,CCH)，主要用于公共安全通信，主要用于传播和安全相关的消息(如WAVE短消息，WAVE服务广播)。Ch 172、174、176、180、182、184被称为业务信道(Service Channel.SCH)，主要用来传输WAVE短消息和个人业务的数据包。Ch 172和Ch 184被专门的应用于涉及财产和生命的公共安全应用。Ch 172主要用于V2V之间安全应用的通信，旨在避免交通事故发生，保障人们的行车安全。Ch 184主要应用于基于公共设施的安全应用，常用于避免十字交叉口发生碰撞事故。The DSRC channel consists of seven 10MHz channels. In addition, a total of 5MHz spectrum from 5.850GHz to 5.855GHz is reserved as spectrum for potential scalable applications. The channel 178 is called a control channel (Control Channel, CCH), and is mainly used for public safety communication, and is mainly used for broadcasting safety-related messages (such as WAVE short message, WAVE service broadcast). Ch 172, 174, 176, 180, 182, and 184 are called service channels (Service Channel. SCH), which are mainly used to transmit WAVE short messages and data packets of personal services. Ch 172 and Ch 184 are specially used in public safety applications involving property and life. Ch 172 is mainly used for communication between V2V safety applications, aiming to avoid traffic accidents and ensure people's driving safety. Ch 184 is mainly used in safety applications based on public facilities, and is often used to avoid collision accidents at intersections.
现有的分布式协作功能(Distributed Coordination Function，DFC)为802.11标准的MAC接入技术。它其他接入方式的基础。它主要采用CSMA/CA算法进行进到接入，一旦发生碰撞后就使用二进制指数退避。为了让节点访问信 道，DCF定义了两种信道访问方式：一种是基本访问接入机制也被叫做二次握手机制；另一种是基于四次握手的请求发送/清除发送机制，通过载波监听来尽量避免碰撞的发生，一旦发生碰撞就是用退避算法来退避。然而802.11DCF协议在竞争节点个数增多时，吞吐量和时延性能会迅速下降，自协议提出以来，人们已经提出了许多的改进方案：(1)改变竞争窗口调节机制，如DIDD(DoubleIncrease Double Decrease)协议，逐步增减竞争窗口。(2)设置最优化参数，如OCB(Optimal Constant Window)协议，根据竞争节点个数调节参数，使网络饱和吞吐量达到最优。这两种改进都存在一些问题：(1)最然改变竞争窗口调节机制不需要估测网络中节点个数，但是因为参数固定性能往往达不到最优。(2)设置最有参数的方法虽能达到最优，但是需要在线估计竞争节点个数，因而估计误差对网络性能影响较大。The existing Distributed Coordination Function (Distributed Coordination Function, DFC) is a MAC access technology of the 802.11 standard. It is the basis for other access methods. It mainly uses the CSMA/CA algorithm for incoming access, and uses binary exponential backoff once a collision occurs. In order for nodes to access the channel, DCF defines two channel access methods: one is the basic access access mechanism, also known as the two-way handshake mechanism; the other is the request-to-send/clear-to-send mechanism based on the four-way handshake, through carrier sense To avoid collisions as much as possible, once a collision occurs, the backoff algorithm is used to back off. However, when the number of competing nodes increases in the 802.11DCF protocol, the throughput and delay performance will drop rapidly. Since the protocol was proposed, many improvement schemes have been proposed: (1) Change the contention window adjustment mechanism, such as DIDD (DoubleIncrease Double Decrease) agreement to gradually increase or decrease the contention window. (2) Set optimization parameters, such as OCB (Optimal Constant Window) protocol, adjust parameters according to the number of competing nodes, so as to achieve optimal network saturation throughput. There are some problems in these two improvements: (1) Most of all, changing the competition window adjustment mechanism does not need to estimate the number of nodes in the network, but because of the fixed parameters, the performance is often not optimal. (2) Although the method of setting the most parameters can achieve the optimum, it needs to estimate the number of competing nodes online, so the estimation error has a great influence on the network performance.
IEEE 802.11p基本的MAC协议是IEEE 802.11DCF机制，IEEE 802.11p MAC扩展层是基于IEEE 802.11e的，采用EDCA(Enhanced Distributed Channel Access，增强分布式信道接入机制)机制接入媒体。通过EDCA机制，IEEE 802.11p可以将不同的数据流按优先级分成不同的接入类别，这样可以保证车载应用的服务质量。它定义了四种基于IEEE 802.1D的访问类型(AccessCategory，AC)即：语音、视频、尽力而为和背景流，使用8种用户优先级来接入无线信道，为不同的业务类型提供不同的业务等级，使得那些实时业务有较高的优先级优先接入信道。8种优先级(UP)和四种访问类型(AC)的映射规则为：一个UP对应一个AC；每个AC包括两个UP；在同一个AC中优先级高的UP优先进入信道。但是由于网络状况的复杂性，EDCA中的静态参数设置并不能使系统性能实现最优，很多研究表明，在高负载的状况下由于网络中有较高的冲突率，EDCA的性能表现并不如人意，而在低负载情况下又会造成空闲时隙的浪费。而本发明能够很好地解决上面的问题。The basic MAC protocol of IEEE 802.11p is the IEEE 802.11DCF mechanism. The IEEE 802.11p MAC extension layer is based on IEEE 802.11e, and uses the EDCA (Enhanced Distributed Channel Access) mechanism to access the media. Through the EDCA mechanism, IEEE 802.11p can divide different data streams into different access categories according to priority, which can guarantee the service quality of vehicle applications. It defines four types of access (AccessCategory, AC) based on IEEE 802.1D: voice, video, best effort and background flow, and uses 8 user priorities to access wireless channels, providing different service types for different Service level, so that those real-time services have higher priority to access the channel first. The mapping rules of 8 kinds of priorities (UP) and four types of access (AC) are as follows: one UP corresponds to one AC; each AC includes two UPs; the UP with higher priority in the same AC enters the channel first. However, due to the complexity of the network conditions, the static parameter settings in EDCA cannot optimize the system performance. Many studies have shown that the performance of EDCA is not satisfactory due to the high collision rate in the network under high load conditions. , and in the case of low load, it will cause waste of idle time slots. And the present invention can well solve the above problems.
发明内容Contents of the invention
本发明目的在于提供了一种基于IEEE 802.11p的车辆接入网络的方法，该 方法为一种全新的车辆接入决策(简称：VeDA)，能够适应车载自组网安全应用对时延和接收率的要求。VeDA是基于802.11p/DSRC的，允许车辆在无竞争期接入到共享的信道中。VeDA方案支持两种不同优先级的安全服务(即：紧急安全消息和路由安全消息)并提供了严格的时延界限。车辆接入决策够很好的胜过基于退避算法的接入方案，尤其是在高通信负载的情况下，可以有效的降低时延和提高接收率。The purpose of the present invention is to provide a method for a vehicle access network based on IEEE 802.11p, which is a brand-new vehicle access decision (VeDA for short), which can adapt to the time delay and reception of security applications in VANETs. rate requirements. VeDA is based on 802.11p/DSRC, allowing vehicles to access shared channels during contention-free periods. The VeDA scheme supports two security services with different priorities (namely: emergency security message and routed security message) and provides a strict delay limit. The vehicle access decision is good enough to outperform the access scheme based on the back-off algorithm, especially in the case of high communication load, which can effectively reduce the delay and improve the reception rate.
方法流程：Method flow:
步骤1：DTIM(即：传输业务指示消息)的信标帧以32μs被分割成多个时隙，VDAOPs(即：VeDA Opportunitys)为接入媒介进入信道时提前预定的接入时隙。VDAOP为无竞争期(CFP)所预定的多个时隙，节点通过预定好的时隙有序的接入信道。Step 1: The beacon frame of DTIM (ie: transmission service indication message) is divided into multiple time slots in 32 μs, and VDAOPs (ie: VeDA Opportunities) are the access time slots scheduled in advance when the access medium enters the channel. VDAOP is a plurality of time slots reserved by the contention-free period (CFP), and nodes access channels in an orderly manner through the predetermined time slots.
步骤2：每当有新的接入需求时，需要进行VDAOP请求单元(即：InformationElement，IE)的转发来建立起新的VDAOP。使网络中的节点共同的更新VDAOP，防止碰撞的发生。Step 2: Whenever there is a new access requirement, it is necessary to forward a VDAOP request element (ie: InformationElement, IE) to establish a new VDAOP. Make the nodes in the network jointly update VDAOP to prevent collisions.
本发明上述步骤1包括：DTIM信标帧以32μs被分割成了多个时隙。在开始时，节点通过VDAOP进行信道接入的预定，VDAOP就是在无竞争期(CFP)所预定的多个时隙，CFP以最大接入系数(MAF＝αT)被定义为CFP＝αT，其中T为DTIM的长度。DTIM剩下的部分为竞争期(CP)主要针对的是那些对吞吐量比较敏感而对时延不敏感的应用。The above step 1 of the present invention includes: the DTIM beacon frame is divided into multiple time slots at 32 μs. At the beginning, the node performs channel access reservation through VDAOP. VDAOP is a plurality of time slots reserved in the contention-free period (CFP). CFP is defined as CFP=αT with the maximum access factor (MAF=αT), where T is the length of DTIM. The remaining part of DTIM is the contention period (CP), which is mainly aimed at those applications that are sensitive to throughput but not sensitive to delay.
本发明上述步骤2包括：VDAOP为两种安全消息建立了优先级，Me的优先级要高于Mr同样VDAOP优先级的方案也适用于CP期间的私人消息，因为这类消息对时延不敏感，所以优先级较低。收到VDAOP建立请求消息的网络节点首先会检查IE。当该节点接收到的这个VDAOP不与接收的其他的VDAOP冲突 时且不与临近的网络节点的VDAOP有冲突，则该网络节点就会接受这个VDAOP的建立请求。此后，VDAOP接收者和发起者都会通过广播或者单播的形式通知相邻节点关于VDAOP的建立。Above-mentioned step 2 of the present invention comprises: VDAOP has established priority for two kinds of security messages, and the priority of Me will be higher than the scheme of Mr the same VDAOP priority is also applicable to the private message during CP, because this kind of message is to time delay Insensitive, so lower priority. A network node that receives a VDAOP Setup Request message first checks the IE. When the VDAOP received by the node does not conflict with other received VDAOPs and does not conflict with the VDAOP of the adjacent network node, the network node will accept the establishment request of the VDAOP. Thereafter, both the VDAOP receiver and the initiator will notify the adjacent nodes about the establishment of the VDAOP through broadcast or unicast.
本发明将消息进行优先级划分，紧急安全消息具有最高的优先级，路由安全消息的优先级次之，最低的就是一些非安全应用的业务消息。The invention divides the priority of the messages, the emergency safety message has the highest priority, the routing safety message has the second priority, and the lowest is some non-safety application business messages.
有益效果：Beneficial effect:
1、本发明通过预定信道接入时隙减少了信道竞争程度1. The present invention reduces the degree of channel competition by presetting channel access time slots
2、本发明合理地为竞争节点分配信道2. The present invention reasonably allocates channels for competing nodes
附图说明Description of drawings
图1为DTIM帧结构。Figure 1 shows the DTIM frame structure.
图2为VeDA中Mr和Me消息预定方案。Fig. 2 shows the Mr and Me message reservation scheme in VeDA.
图3为VDAOP在相邻节点的传播方案。Figure 3 is the propagation scheme of VDAOP in adjacent nodes.
图4为车辆的运动分布模型Figure 4 is the motion distribution model of the vehicle
图5为VeDA与DCF在不同大小的通信密度和消息包的情况下的时延Figure 5 shows the delay between VeDA and DCF in the case of different communication densities and message packets
图6为VeDA方案在不同消息下的时延Figure 6 shows the delay of the VeDA scheme under different messages
图7为VeDA方案的紧急消息与路有消息的时延与DCF方案的对比Figure 7 shows the comparison of the time delay between the emergency message and the road message of the VeDA scheme and the DCF scheme
图8为VeDA机制与DCF机制接收率的对比(消息频率为500包/s，消息大小为500B)Figure 8 is a comparison of the receiving rate between the VeDA mechanism and the DCF mechanism (the message frequency is 500 packets/s, and the message size is 500B)
图9为VeDA机制与DCF机制接收率的对比(消息频率为1250包/s，消息大小为200B)Figure 9 is a comparison of the receiving rate between the VeDA mechanism and the DCF mechanism (the message frequency is 1250 packets/s, and the message size is 200B)
图10为本发明的方法流程图。Fig. 10 is a flow chart of the method of the present invention.
具体实施方式Detailed ways
下面结合说明书附图对本发明创造作进一步的详细说明。The invention will be described in further detail below in conjunction with the accompanying drawings.
1.VeDA帧间结构1. VeDA inter-frame structure
VeDA的帧结构如图1所示，VeDA将DTIM(Delivery Traffic Indication Message，传输业务指示消息)信标帧以32μs被分割成多个时隙，VDAOPs(VeDA Opportunitys)是接入媒介进入信道时提前预定的接入时隙。媒介接入点通过发送VDAOP请求信息单元(Information Element，IE)来建立起VDAOP。请求IE包含如下：The frame structure of VeDA is shown in Figure 1. VeDA divides the DTIM (Delivery Traffic Indication Message) beacon frame into multiple time slots in 32 μs. VDAOPs (VeDA Opportunities) are the advance scheduled access slots. The media access point establishes the VDAOP by sending a VDAOP request information element (Information Element, IE). The request IE contains as follows:
VDAOP长度(1B长度)VDAOP length (1B length)
VDAOP周期(1B长度)VDAOP cycle (1B length)
VDAOP偏移量(2B长度)VDAOP offset (2B length)
因此，VDAOP的最大帧长为4096μs。所谓的VDAOP周期实际就是在一个DTIM区间中，存在的VDAOP子区间的个数。VDAOP的周期为0指的是只预定一次，不会重复预定。VDAOP偏移量为VDAOP起始点与DTIM区间起始点的距离。Therefore, the maximum frame length of VDAOP is 4096μs. The so-called VDAOP period is actually the number of VDAOP sub-intervals in a DTIM interval. The period of VDAOP is 0, which means that the reservation is only made once, and the reservation will not be repeated. The VDAOP offset is the distance between the VDAOP start point and the DTIM interval start point.
2.VeDA中Mr和Me的预定2. Reservation of Mr and Me in VeDA
在802.11p中车辆的安全信息分为了2个类型：紧急安全信息(Me)和周期新标信息即路由安全信息(Mr)。紧急信息发生比较突然，并且它需要很好的可靠性、低碰撞、低时延；路由信息即信标消息主要用于广播，广播频率一般为每秒10～20次。路由信息一般是用于广播车辆的一些基本信息如位置和方向等，所以它相比于紧急信号需要较低的可靠性和延时要求。In 802.11p, vehicle security information is divided into two types: emergency security information (Me ) and periodic new standard information, namely routing security information (Mr ). Emergency information occurs suddenly, and it requires good reliability, low collision, and low delay; routing information, that is, beacon messages, are mainly used for broadcasting, and the broadcasting frequency is generally 10 to 20 times per second. Routing information is generally used to broadcast some basic information of vehicles such as location and direction, so it requires lower reliability and delay requirements than emergency signals.
在开始时，节点通过MDAOP进行信道接入的预定，MDAOP就是在无竞争期(CFP)所预定的多个时隙，CFP以最大接入系数(MAF＝αT)被定义为CFP＝αT，其中T为DTIM的长度，其中DTIM剩下的部分为竞争期(CP)主要针对的是那些对吞吐量比较敏感而对时延不敏感的应用(如VANET中的私人服务信息Mp)。At the beginning, the node performs channel access reservation through MDAOP. MDAOP is a plurality of time slots reserved in the contention-free period (CFP). CFP is defined as CFP=αT with the maximum access factor (MAF=αT), where T is the length of the DTIM, and the remaining part of the DTIM is the contention period (CP). It is mainly aimed at applications that are sensitive to throughput but not to delay (such as private service information Mp in VANET).
图2展示了VeDA中Me和Mr在CFP中的详细细节，VeDA为两种安全消息建立了优先级，Me的优先级要高于Mr同样VeDA优先级的方案也适用于CP期间的私人消息，因为这类消息对时延不敏感，所以优先级较低。值得注意的是，即 使CCH和SCH区间结构不同，WAVE的信道切换标准仍然允许CCH和SCH进行切换，只要他们俩的DTIM区间长度相同就可以切换。因此，本发明定义驻留时间比例为CCH和SCH的百分比(如75％的CCH驻留比例和25％的SCH的驻留比例)。Figure 2 shows the details ofMe and Mr in VeDA in CFP. VeDA establishes priorities for two security messages. The priority ofMe is higher than that of Mr . The same VeDA priority scheme is also applicable during CP private messages, because such messages are not sensitive to delay, so the priority is low. It is worth noting that even if the interval structures of CCH and SCH are different, the channel switching standard of WAVE still allows CCH and SCH to switch, as long as the DTIM interval lengths of both of them are the same. Therefore, the present invention defines the dwell time ratio as the percentage of CCH and SCH (such as 75% of CCH dwell ratio and 25% of SCH dwell ratio).
3.VDAOP的建立3. Establishment of VDAOP
收到VDAOP建立请求消息的网络节点首先会检查IE。当该节点接收到的这个VDAOP不与接收的其他的VDAOP冲突时且不与临近的网络节点的VDAOP有冲突，则该网络节点就会接受这个VDAOP的建立请求。此后，VDAOP接收者和发起者都会通过广播或者单播的形式通知相邻节点关于VDAOP的建立。在TX-RX时间报告指出了MP发送的消息主要包含：有发送者和接收者的VDAOP、它自己或者所期望的临近节点的信标发送、其他不可用的时隙。此外该接收节点还会发送一个干扰时间报告。此报告是接收节点邻点的TX-RX时间报告的备份。VDAOP的预定信息在直接和间接的邻点之间传播开。VDAOP的建立如图3所示，其中坐标x和y分别表示长度和偏移量。A network node that receives a VDAOP Setup Request message first checks the IE. When the VDAOP received by the node does not conflict with other received VDAOPs and does not conflict with the VDAOP of the adjacent network node, the network node will accept the establishment request of the VDAOP. Thereafter, both the VDAOP receiver and the initiator will notify the adjacent nodes about the establishment of the VDAOP through broadcast or unicast. The TX-RX time report indicates that the messages sent by the MP mainly include: VDAOP with sender and receiver, beacon transmission by itself or expected neighboring nodes, and other unavailable time slots. In addition, the receiving node sends an interference time report. This report is a backup of the TX-RX time reports of the neighbors of the receiving node. VDAOP subscription information is propagated between direct and indirect neighbors. The establishment of VDAOP is shown in Figure 3, where the coordinates x and y represent the length and offset, respectively.
本发明把每个VDAOP为消息k建立的预定请求表示为其中ok为VDAOP距离DTIM起始点的偏移量，φk为VDAOP的周期即在DTIM中出现的次数，为VDAOP时隙的长度。实际上每个在通信范围内的车辆都会作为VDAOP的请求节点或转发节点进行VeDA消息的广播，从而让每个车辆都知道信道的预定方案。VDAOP实际就是由VDAOP持有者和目的车辆建立的在每个DTIM区间内一个周期时隙。The present invention expresses the reservation request established by each VDAOP for message k as Among them, ok is the offset of VDAOP from the starting point of DTIM, φk is the period of VDAOP, that is, the number of occurrences in DTIM, is the length of the VDAOP time slot. In fact, each vehicle within the communication range will broadcast VeDA messages as a VDAOP request node or forwarding node, so that each vehicle knows the channel's predetermined scheme. VDAOP is actually a periodic time slot in each DTIM interval established by the VDAOP holder and the destination vehicle.
在VeDA预定方案中，为x类安全消息的预定时隙的长度(等式3.1)，在每一个的子时隙都要遵从严格的时隙限定即m跳的最大时延(等式3.2)。同时本发明假设Mx∈{Me,Mr}即Mx表示的是x类型的安全信息，x为e时表示的是紧急消息，r则路由消息或者信标消息。本发明把让安全消息Mx的 传输发生在之后。为了防止单跳的延时过高，周期必须满足这里本发明处于简单的考虑，把统一计算，当然这里也可以根据不同的负载情况进行分配。如下，等式3.1为VDAOP的长度；等式3.2为它的周期：In the VeDA scheduled scheme, is the length of the scheduled slot for safety messages of type x (Equation 3.1), in each The sub-slots of all must comply with strict slot restrictions That is, the maximum delay of m hops (Equation 3.2). At the same time, the present invention assumes that Mx ∈ {Me , Mr }, that is, Mx represents security information of type x, when x is e, it represents emergency messages, and r represents routing messages or beacon messages. In the present invention, the transmission of the safety message Mx takes place at after. In order to prevent the single-hop delay from being too high, the period must meet Here the present invention is in simple consideration, put Unified computing, of course, it can also be distributed according to different load conditions. As follows, Equation 3.1 is the length of VDAOP; Equation 3.2 is its period:
其中τ是指时隙长度，是指包的大小，指的是IEEE 802.11p的传输速率，指的是x类型消息的数量，指的是x类型消息的最大时延，它的计算公式如等式3.3所示。where τ is the slot length, is the packet size, Refers to the transmission rate of IEEE 802.11p, refers to the number of messages of type x, Refers to the maximum delay of messages of type x, and its calculation formula is shown in Equation 3.3.
表示的就是最大时延，它指的就是在最大跳数m跳的路径上最大时延的严格界限。其中就是安全消息Mx要求的时延限定。 Indicates the maximum delay, which refers to the strict limit of the maximum delay on the path with the maximum number of m hops. in is the time delay limit required by the safety messageMx .
本发明定义VeDA的延时为服务时延和排队时延的总和。服务时延为VeDA的预定时延、数据包发送时延的的总和。本发明认为VeDA的预定时延就是等待下一个包发送的时间，这是为了防止被预定的VDAOP发送时不产生竞争。本发明认为VDAOP的发送时的退避时延是可以忽略不计的，因为在已经预定好的VDAOP发送时，很少发生碰撞。最后，本发明认为排队时延就是数据包在发送队列里等待的时间。The present invention defines VeDA delay as the sum of service delay and queuing delay. The service delay is the predetermined delay of VeDA, The sum of packet sending delays. The present invention considers that the scheduled time delay of VeDA is the time to wait for the next packet to be sent, which is to prevent no contention when the scheduled VDAOP is sent. The present invention considers that the back-off time delay during VDAOP transmission is negligible, because collisions seldom occur during scheduled VDAOP transmission. Finally, the present invention considers that the queuing delay is the waiting time of the data packet in the sending queue.
对于紧急消息，本发明都以一跳的广播型式进行传输，在每个DTIM区间内有π1个包需要传输。因此对于一跳的服务率定义为rrate＝π1/DTIM，在多跳的情况 下表示为rrate＝πm/DTIM。For emergency messages, the present invention transmits in a one-hop broadcast mode, and there are π1 packets to be transmitted in each DTIM interval. Therefore, the service rate for one hop is defined as rrate =π1 /DTIM, and in the case of multiple hops, it is expressed as rrate =πm /DTIM.
4.仿真场景与参数4. Simulation scenarios and parameters
本发明使用NS2进行仿真，评估和对比本发明提出的协议即VeDA与现有的802.11p下的DCF协议。本发明采用由6个可循环的高速车道(即：每个方向各3个车道)的拓步网络。发射节点的射频发射范围r的值在以下数值中取值：150m、200m、250m。设定每个车辆节点发送时产生干扰范围R可达到550m。虽然在802.11p中DSRC通信范围理论上可以打到1000m，但是在文献中主要采用的范围是150m、200m和250m。这主要是考虑到具体的在安全应用中所期望的通信范围并不太远，而且当通信范围过大时，信道就会容易拥塞，而且会被远处的车辆间的毫无意义的通信所干扰。此外，本发明主要考虑了8种高优先权的协作车辆安全应用。这8种协作车辆安全应用是由美国的国家公路交通安全局以及2006年的防碰撞项目提出来的，而且这些安全应用对延时的要求都非常的高，需要提前定义好严格的时延界限，例如，在南京南亿迪纳数字科技有限公司这些应用(交通信号破坏、前向碰撞预警、变道预警、停车迹象协助、左转协助等)的时延一般被限定为不的超过100ms，并且它们传输的范围分别对应为250m、150m、150m、300m、300m。下表展示了剩下的一些参数。The present invention uses NS2 to simulate, evaluate and compare the protocol proposed by the present invention, that is, VeDA and the existing DCF protocol under 802.11p. The present invention adopts the step-by-step network of 6 recyclable high-speed lanes (that is, 3 lanes in each direction). The value of the radio frequency transmission range r of the transmitting node is selected from the following values: 150m, 200m, 250m. When each vehicle node is set to transmit, the interference range R can reach 550m. Although the DSRC communication range in 802.11p can reach 1000m theoretically, the ranges mainly adopted in the literature are 150m, 200m and 250m. This is mainly because the expected communication range in safety applications is not too far away, and when the communication range is too large, the channel will be easily congested and will be overwhelmed by meaningless communication between distant vehicles. interference. In addition, the present invention mainly considers 8 high-priority cooperative vehicle safety applications. These 8 collaborative vehicle safety applications were proposed by the National Highway Traffic Safety Administration of the United States and the 2006 Anti-Collision Project, and these safety applications have very high requirements for delay, and strict delay boundaries need to be defined in advance For example, in Nanjing Nanyi Dina Digital Technology Co., Ltd., the delay of these applications (traffic signal destruction, forward collision warning, lane change warning, parking sign assistance, left turn assistance, etc.) is generally limited to no more than 100ms, And their transmission ranges correspond to 250m, 150m, 150m, 300m, and 300m respectively. The table below shows some of the remaining parameters.
仿真参数表Simulation parameter table
SINR：信噪比；DTIM传递业务指示消息；CCH：控制信道；MAC：媒体接入控制层；DSRC：专用短程通信技术；CBR：恒定比特率；UDP：用户数据报协议。SINR: Signal-to-Noise Ratio; DTIM Transfer Service Indication Message; CCH: Control Channel; MAC: Media Access Control Layer; DSRC: Dedicated Short Range Communication Technology; CBR: Constant Bit Rate; UDP: User Datagram Protocol.
本发明定义接收率为数据包被成功接收的比率。接收率可以被看成在发送车辆的传输范围内的所有汽车成功接收到广播的安全消息的概率。本发明把接收率记作PRR。The present invention defines the reception rate as the rate at which data packets are successfully received. The reception rate can be viewed as the probability that all cars within the transmission range of the sending vehicle will successfully receive the broadcasted safety message. In the present invention, the reception rate is recorded as PRR .
如图4所示，本发明假设汽车都在同一车道上，符合泊松分布，其网络密度为β(车辆数/米)。本发明可以表示在R的传输范围内的v辆车的接收率如下：As shown in Fig. 4, the present invention assumes that cars are all on the same lane, conforming to Poisson distribution, and its network density is β (number of vehicles/meter). The present invention can represent the reception rate of v vehicles within the transmission range of R as follows:
本发明表示在C(为载波监听范围R'减去传输范围R即R'-R)的传输范围内的NC辆车的接收率如下：The present invention shows that the receiving rate of the NC vehicle in the transmission range of C (for the carrier monitoring range R' minus the transmission range R, i.e. R'-R) is as follows:
其中的NC就是在发送汽车的传输范围Rs内可能与它竞争同一个时隙的车辆数。where NC is the number of vehicles that may compete with the sending vehicle for the same time slot within its transmission range Rs .
本发明把在传输范围Rs内的传输率PRR表示如下：The present invention expresses the transmission rate PRR in the transmission range Rs as follows:
在发送者S的传输范围Rs内的任意一辆汽车X的接收率等于汽车S的接收 率乘以在RX内的汽车X'不与RX内的车X发生碰撞的概率。值得一提的是X'不会用到和OX，因为这是关于那是分配给同时位于Rs和RX内的车辆X的。The reception rate of any car X within the transmission range Rs of the sender S is equal to the reception rate of car S multiplied by the probability that a car X' within RX does not collide with a car X within RX . It is worth mentioning that X' will not use and OX , as this is about that is assigned to vehicle X that is within both Rs and RX .
因此，为了更好的描述PRR(S,RS)，本发明设计了一下两个方案：Therefore, in order to better describe PRR (S, RS ), the present invention designs two schemes:
方案一：在Rs当没有车辆与发送者竞争同一个信道时隙时即(NC＝0)。Scheme 1: at Rs when no vehicle competes with the sender for the same channel time slot (NC =0).
这里的因为发送者是在Rs内唯一的拥有和OS的车辆。既然本发明引进决策接入的VeDA，本发明就希望有较少的碰撞发生，所以本发明假设在R范围内，所有的汽车的平均数为2πR，而在范围C内，发生干扰的车辆为NC＝2πC。here Because the sender is the only one within Rs that has and OS vehicles. Since the present invention introduces VeDA for decision-making access, the present invention expects fewer collisions to occur, so the present invention assumes that within the range of R, the average number of all cars is 2πR, and within the range C, the vehicles that interfere areNC = 2πC.
方案二：有NC辆车在发送者的传输范围内可以与其发生竞争即(NC≠0)。Scheme 2: There are NC vehicles that can compete with the sender within the transmission range (NC ≠ 0).
其中就是指当发送车辆S在其传输范围Rs内进行传输时，在CS内没有一辆汽车S'与发送者在CFP时期进行竞争的概率。in It is the probability that when the sending vehicle S transmits in its transmission range Rs , there is no car S' in CS that competes with the sender in the CFP period.
本发明定义P0就是有一辆汽车发生了紧急事件或者需要发送路由信息的概率。为了实现发送车辆S的决策接入，本发明需要计算即在CS范围内不存在一个车辆以和OS进行传输的概率。The present invention defines that P0 is the probability that a car has an emergency or needs to send routing information. In order to realize the decision-making access of the sending vehicle S, the present invention needs to calculate That is, there is no vehicle within the range of CS The probability of transmitting withOS .
因此要想计算出等式4.3和4.6就必须要计算出为了证明出本发明先计算出当CEP有2个时隙并且NC≥2(等式4.6)以及CEP有3个时隙和NC≥3(等式4.7)这两种情况下的值。并且归纳出的一般表达式。Therefore to calculate Equations 4.3 and 4.6 one must calculate to prove The present invention first calculates the values in two cases when the CEP has 2 time slots and NC ≥ 2 (Equation 4.6) and the CEP has 3 time slots and NC ≥ 3 (Equation 4.7). and concludes general expression of .
CFP＝2个时隙；NC≥2CFP = 2 time slots; NC ≥ 2
CFP＝3个时隙；NC≥3CFP = 3 time slots; NC ≥ 3
推理归纳出如下：The reasoning is summarized as follows:
CFP＝K个时隙；NC≥K，本发明推出：CFP=K time slots; NC ≥ K, the present invention releases:
对于NC≤K；for NC ≤ K;
5.本发明的NS2仿真结果5. NS2 simulation result of the present invention
图5展示了在不同的消息包的大小以及不同的通信密度下，VeDA和DCF方案在时延方面的表现。从图中本发明可以看出，随着消息包大小的增加，紧急消息的时延就会增加，但是与DCF方案的时延相比，VeDA方案的时延仍然很低。此外，当通信密度较高的时候，VeDA方案的时延表现一般情况下比DCF方案的时延要低97％。使用决策接入可以为安全信息提供时延界限的保证，从而以可以接受的低时延来发送紧急消息。Figure 5 shows the performance of VeDA and DCF schemes in terms of delay under different message packet sizes and different communication densities. It can be seen from the figure that the present invention, with the increase of the size of the message packet, the time delay of the emergency message will increase, but compared with the time delay of the DCF scheme, the time delay of the VeDA scheme is still very low. In addition, when the communication density is high, the delay performance of the VeDA scheme is generally 97% lower than that of the DCF scheme. The use of decision-making access can provide a guarantee of delay bounds for safety information, so that emergency messages can be sent with an acceptable low delay.
图6展示了VeDA方案中，紧急消息相比于路有消息具有更高的优先级，即使是在通信密度较大的时候，VeDA依然能够保证紧急安全消息具有较高的优先级。在VANET网络中，紧急消息相比于路有消息具有更高的时延要求，在图中本发明可以看到，本发明提出的VeDA方案可以很好的保证紧急消息的低时延，同时也为路有消息的时延设置了界限，同样也能够很好的适应路有消息的时延要求。Figure 6 shows that in the VeDA scheme, emergency messages have a higher priority than Luyou messages. Even when the communication density is high, VeDA can still ensure that emergency safety messages have a higher priority. In the VANET network, emergency messages have higher delay requirements than Luyou messages. As can be seen from the figure, the present invention can ensure the low delay of emergency messages, and at the same time The limit is set for the delay of the message on the road, and it can also be well adapted to the delay requirement of the message on the road.
在图7中展示了随着通信传输范围的不同，VeDA方案与DCF方案在紧急消息与路有消息上的时延表现。本发明的目的是为了检测在信道场景较为密集的情况下即通信密度较大，适当的改变传输范围能否加强DCF的表现，使DCF方 案打到VeDA方案的表现或者接近它的表现。消息频率、车辆密度、数据速率和消息大小这些数据已经在仿真参数表中给了出来。从图中本发明可以看出，在VeDA方案下，紧急消息的时延在所有的通信范围内都是最低的，平均时延大约为9.0003504s，这个时延相比于VANET网络对时延的要求，要低很多。但是在DCF方案下消息的平均时延为0.0219s，是VeDA方案下紧急消息时延的62倍之多。同时，如图7所示，在使用VeDA方案的情况下，一般的路有消息的时延也是完全可以接受的，即使是在通信范围为200m时，时延最高也只是达到了0.0173s。这也正是本发明期望见到的，因为从图2中本发明已经能看出，紧急消息的优先级要优于路有消息的，而且路有消息的时延也是可以接受的。Figure 7 shows the delay performance of the VeDA scheme and the DCF scheme on emergency messages and on-the-road messages with different communication transmission ranges. The purpose of the present invention is to detect whether the performance of DCF can be enhanced by appropriately changing the transmission range in the case of relatively dense channel scenes, that is, the communication density is relatively high, so that the DCF scheme can achieve the performance of the VeDA scheme or approach its performance. The data of message frequency, vehicle density, data rate and message size are given in the simulation parameter table. As can be seen from the present invention in the figure, under the VeDA scheme, the time delay of the emergency message is the lowest in all communication ranges, and the average time delay is about 9.0003504s, which is compared to the time delay of the VANET network The requirements are much lower. However, the average message delay under the DCF scheme is 0.0219s, which is as much as 62 times of the emergency message delay under the VeDA scheme. At the same time, as shown in Figure 7, in the case of using the VeDA scheme, the time delay of general road messages is completely acceptable. Even when the communication range is 200m, the time delay is only up to 0.0173s. This is exactly what the present invention expects to see, because it can be seen from the present invention in Fig. 2 that the priority of urgent messages is better than that of messages on the road, and the time delay of messages on the road is also acceptable.
对于消息而言，本发明也要考虑到它的接收率问题，因此本发明需要考虑随着距离的变化，两种方案关于接收率方面有如何的表现。图8展示了在消息大小为500B，传输范围为200m，消息频率为500pkt/s以及数据速率为6Mbps的情况下，DCF机制和VeDA机制关于接收率的表现。VeDA机制的接收率平均要优于DCF机制大约25％。此外，从图中还可以看出，当通信较为密集时(如距离为50m)，VeDA方案的接受率达到了99％；而对于相同的情况下的DCF机制，接收率只是达到了73％。For the message, the present invention also needs to consider its reception rate, so the present invention needs to consider the performance of the two schemes with respect to the reception rate as the distance changes. Figure 8 shows the performance of the DCF mechanism and VeDA mechanism on the reception rate when the message size is 500B, the transmission range is 200m, the message frequency is 500pkt/s, and the data rate is 6Mbps. The reception rate of the VeDA mechanism is about 25% better than that of the DCF mechanism on average. In addition, it can also be seen from the figure that when the communication is relatively intensive (such as the distance is 50m), the acceptance rate of the VeDA scheme reaches 99%; while for the DCF mechanism in the same situation, the acceptance rate only reaches 73%.
当本发明增加信道负载的等级时(如消息频率为1250pkt/s，消息包大小为200B)，DCF方案和VeDA方案的图形展示如图9。在通信距离为50m时，VeDA方案的接收率为89％，而DCF方案的接收率为52％。从图中也可以清晰的看出来，随着通信距离的变化，VeDA方案在接收率上，始终优于DCF方案。DCF的平均接收率为46％，而VeDA方案的平均接受率达到了90％。When the present invention increases the level of channel load (for example, the message frequency is 1250pkt/s, and the message packet size is 200B), the graphic display of the DCF scheme and the VeDA scheme is shown in FIG. 9 . When the communication distance is 50m, the acceptance rate of VeDA scheme is 89%, while that of DCF scheme is 52%. It can also be clearly seen from the figure that as the communication distance changes, the VeDA scheme is always better than the DCF scheme in terms of receiving rate. The average acceptance rate of DCF is 46%, while the average acceptance rate of VeDA program reaches 90%.
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN201510293661.2ACN104967670B (en) | 2015-06-01 | 2015-06-01 | A kind of method of the vehicle access network based on IEEE 802.11p |
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN201510293661.2ACN104967670B (en) | 2015-06-01 | 2015-06-01 | A kind of method of the vehicle access network based on IEEE 802.11p |
| Publication Number | Publication Date |
|---|---|
| CN104967670A CN104967670A (en) | 2015-10-07 |
| CN104967670Btrue CN104967670B (en) | 2018-07-06 |
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CN201510293661.2AActiveCN104967670B (en) | 2015-06-01 | 2015-06-01 | A kind of method of the vehicle access network based on IEEE 802.11p |
| Country | Link |
|---|---|
| CN (1) | CN104967670B (en) |
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN106713243A (en)* | 2015-11-17 | 2017-05-24 | 中国移动通信集团公司 | Application program business strategy processing method and device and controller |
| CN106817675B (en)* | 2015-12-01 | 2020-02-21 | 中国移动通信集团公司 | A channel access method and device applied to an inter-vehicle communication system |
| JP6162278B1 (en)* | 2016-02-26 | 2017-07-12 | 日本電信電話株式会社 | Wireless environment determination method and wireless communication system |
| CN106102099B (en)* | 2016-06-08 | 2020-11-24 | 华南理工大学 | A Dwell Time Based Switching Method for Heterogeneous Vehicle Networking |
| CN107094321B (en)* | 2017-03-31 | 2020-04-28 | 南京邮电大学 | A multi-agent Q-learning-based channel access method for in-vehicle communication MAC layer |
| CN107396453B (en)* | 2017-08-30 | 2019-12-10 | 福建师范大学 | A VANET Channel Access Method Based on SD-TDMA |
| CN110087214B (en)* | 2019-04-16 | 2022-04-08 | 常熟理工学院 | DSRC/WAVE-based cooperative transmission method for safety messages in vehicle networking |
| CN110224888B (en)* | 2019-06-10 | 2023-03-07 | 公安部交通管理科学研究所 | Test method, device and system for vehicle-mounted V2X communication equipment |
| CN111313989B (en)* | 2019-12-04 | 2021-07-16 | 大连理工大学 | A Reliability Analysis Method of In-vehicle Network Based on Signal-to-Noise and Interference Ratio |
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN101378343A (en)* | 2008-03-07 | 2009-03-04 | 华中科技大学 | System and method for implementing speedway vehicle wideband communication |
| CN101779419A (en)* | 2007-07-30 | 2010-07-14 | 马维尔国际贸易有限公司 | Simultaneously maintaining bluetooth and 802.11 connections to increase data throughput |
| CN103475580A (en)* | 2013-09-26 | 2013-12-25 | 中国科学技术大学苏州研究院 | Optimal relay selecting method based on power control technology in internet of vehicles |
| CN103763682A (en)* | 2013-12-31 | 2014-04-30 | 同济大学 | Method for broadcasting safety information in heterogeneous network environment for safe travel |
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN101779419A (en)* | 2007-07-30 | 2010-07-14 | 马维尔国际贸易有限公司 | Simultaneously maintaining bluetooth and 802.11 connections to increase data throughput |
| CN101378343A (en)* | 2008-03-07 | 2009-03-04 | 华中科技大学 | System and method for implementing speedway vehicle wideband communication |
| CN103475580A (en)* | 2013-09-26 | 2013-12-25 | 中国科学技术大学苏州研究院 | Optimal relay selecting method based on power control technology in internet of vehicles |
| CN103763682A (en)* | 2013-12-31 | 2014-04-30 | 同济大学 | Method for broadcasting safety information in heterogeneous network environment for safe travel |
| Publication number | Publication date |
|---|---|
| CN104967670A (en) | 2015-10-07 |
| Publication | Publication Date | Title |
|---|---|---|
| CN104967670B (en) | A kind of method of the vehicle access network based on IEEE 802.11p | |
| Qureshi et al. | A dynamic congestion control scheme for safety applications in vehicular ad hoc networks | |
| Djahel et al. | A robust congestion control scheme for fast and reliable dissemination of safety messages in VANETs | |
| Chung et al. | Time coordinated V2I communications and handover for WAVE networks | |
| Gupta et al. | Adaptive beaconing in mobility aware clustering based MAC protocol for safety message dissemination in VANET | |
| Bazzi et al. | Beaconing from connected vehicles: IEEE 802.11 p vs. LTE-V2V | |
| CN107277855B (en) | A vehicle network media access method for guaranteeing security services | |
| Kakarla et al. | A survey and qualitative analysis of multi-channel MAC protocols for VANET | |
| Kolte et al. | Adaptive congestion control for transmission of safety messages in VANET | |
| Tomar et al. | Enhanced SDMA for VANET communication | |
| Deng et al. | Implementing distributed TDMA using relative distance in vehicular networks | |
| Böhm et al. | Context-aware retransmission scheme for increased reliability in platooning applications | |
| Shen et al. | Self-sorting-based MAC protocol for high-density vehicular ad hoc networks | |
| Ahizoune et al. | A contention-free broadcast protocol for periodic safety messages in vehicular ad-hoc networks | |
| CN110691349B (en) | Adaptive control method for safe application-oriented combined power and competition window in Internet of vehicles | |
| Bi et al. | Safety message broadcast in vehicular networks | |
| Kim et al. | CMMP: clustering-based multi-channel MAC protocol in VANET | |
| Wei et al. | Power-control-based broadcast scheme for emergency messages in VANETs | |
| Kolte et al. | A design approach of congestion control for safety critical message transmission in VANET | |
| Li et al. | ASTSMAC: Application suitable time-slot sharing MAC protocol for vehicular ad hoc networks | |
| CN113225712B (en) | Reference model adaptive rate control system and method in cooperative vehicle safety system | |
| Huang et al. | A scheme to reduce merging collisions in TDMA-based VANETs | |
| Ouladdjedid et al. | CSSA MAC: Carrier sense with slotted-Aloha multiple access MAC in vehicular network | |
| KR101560486B1 (en) | Method for managing TXOP(Transmission Opportunity) limit in Vehicular communication network and vehicular communication network system using thereof | |
| Rico Garcia et al. | Performance of MAC protocols in beaconing Mobile Ad-hoc Multibroadcast Networks |
| Date | Code | Title | Description |
|---|---|---|---|
| C06 | Publication | ||
| PB01 | Publication | ||
| C10 | Entry into substantive examination | ||
| SE01 | Entry into force of request for substantive examination | ||
| GR01 | Patent grant | ||
| GR01 | Patent grant |