多信道车载网中基于时分多址的MAC改进算法

An Improved TDMA-based MAC Algorithm for Multichannel VANETs

车载网(VANETs)需提供时延敏感的安全应用和非安全应用的通信服务。这就使得媒体接入控制(MAC)协议既要满足安全消息的时延和可靠率,又要保证非安全消息的服务信道利用率,给MAC的设计提出了挑战。为此,提出基于时分多址的MAC改进算法(I-TDMA-MAC)。I-TDMA-MAC算法在每个同步帧内给每辆车分配两个子时隙,旨在提高无碰撞信道接入率和安全消息的传递率。同时,对空闲时隙采取重分配策略,并基于最短作业优先准则(SJF)给空闲时隙设置优先级,旨在提高服务信道利用率。仿真结果表明,提出的I-TDMA-MAC算法的安全消息传递率高达99%,当车流密度到达100 vehicle/km时,服务信道利用率接近于90%。

The Vehicular Ad-Hoc Networks （ VANETs） provide communication services for time-critical road safety applications and non-safety applications. The challenges of multichannel VANETs Medium Ac-cess Control （MAC） protocol include successful delivery of time-critical safety messages and high reliabili-ty, and high channel utilization for non-safety messages. Therefore, an improved time division multiple ac-cess-based MAC （I-TDMA-MAC） is proposed in this paper. In I-TDMA-MAC, the two mini-slots in synchronous frame interval are allocated to each vehicle to increase the collision-free channel access ratio and reliable time-critical safety message deliveries. At the same time, empty slots are reallocated to en-hance bandwidth utilization of service channels, and the Shortest Job First （SJF） algorithm is used to give the prioritization to allocate the empty slots. The simulation results show that the packet delivery ratio of safety messages is enhanced as high as 9 9 % , and the bandwidth utilization of service channels is up to 90% when traffic density is more than 100 vehicle/km.