轨道车辆MVB通信网络的实时特性

多功能车辆总线(MVB)应用于轨道交通车辆的车厢级通信网络已经成为新一代列车通信网的发展趋势。采用MVB必须满足轨道车辆对数据传输提出的实时性要求。MVB网络的端到端传输延迟主要包括报文分组在缓存器内的平均等待延迟、发送报文分组延迟、介质传播延迟等,而影响发送报文分组延迟的主要因素是报文分组的平均等待延迟受介质访问控制方式的约束;主设备消息事件请求帧的到达过程服从泊松分布,多消息事件并发引发的事件仲裁延迟是影响消息数据报文延迟的重要因素。仿真实验结果表明,MVB网络的过程数据具有报文分组传输时间确定、报文分组长度对网络延迟影响小等实时特性,但消息数据的报文延迟受网络负载的影响较大。运用排队理论分析主从轮询方式下过程数据的延迟与MVB的轮询周期、通信速率的关系;分析数据表明,该方法可以取代以往的国外经验值来配置网络,而且配置指标更符合实际运行的要求,并已经成功应用于实际设备的测试分析中。

Real-Time Performance of MVB Communication Network in Rail Vehicles

To apply MVB(Multifunction Vehicle Bus) for the rail vehicles communication network is the trend of train communication network development.The application of MVB must meet the request of real-time data transfer by rail vehicles.The end-to-end delay of data transfer in the MVB network involves the average delay of packets in buffer memory,the sending packet and the medium transmission delay,etc.The main factor influencing packets delay is that the average delay of packets is limited by medium access control.Arrival of the Event-Request-Frame in the Master Device follows Poisson Distribution.Event-Arbitration delay caused by Multiple-Event-Collision is an important factor contributing the message delay of Message Data.Simulation experiments show that the Process Data of MVB network have such real-time characteristics that the transfer time of packets is ensured and the message packet length has little impacts on network delay.But the network workload has great influences on the message delay of Message Data.The queuing theory is applied to analyzing the relation between Process Data delay and the MVB polling cycle time and communication rate under the master-slave polling.The results show that the method can replace the previous foreign experimental value to set network.The configuration is more suitable for real conditions.At present,this method is successfully applied to testing and analyses of real equipment.