像机载应用这样的安全关键(safety-critical)系统通常具有非常高的可靠性和实时性需求,而无线连接通常被认为是易错的.因此,在考虑设计或者分析一个安全关键的无线网络时,需要新的QoS参数来衡量系统的实时性.一个合适的参数是在给定信道条件下消息的丢包率,即消息不能在时限之前可靠传输的概率.一种应用于实时系统的概率实时可调度的分析方法被引入来分析无线网络中的消息丢包率.使用错误重传的消息被建模为具有可变长度执行时间的任务,消息的调度过程被建模为一个状态转移的马尔可夫过程.通过这一方法,不仅可以得到关于网络中所有消息的平均丢包率,而且可以得到单个消息的丢包率.实验结果表明:1)通过将该方法的分析结果与仿真结果比较,验证了该方法的有效性;2)通过该方法与假设每个消息都将至少传输某一个固定次数的分析方法的比较,说明了后者的分析结果是过于保守的.%The safety-critical systems like avionics generally have both very high reliability and real-time requirements, while wireless connection is known to be error prone. To design or analyze a wireless safety-critical network, new real-time Quality of Service (QoS) metrics are needed. A proper metric is the loss probability that messages cannot be reliably transmitted before deadlines in a given channel condition. The probabilisfic schedulability analysis method was introduced to calculate the message loss probability in wireless network. A message that would be retransmitted until it had been successfully received before deadline was considered as a task with stochastic execution time and the message scheduling process was modeled as a Markov process with state transition. Through this method, both the average loss probability of all messages and the loss probability of every message in the network can be acquired. The first experiment validates the effectiveness of the method by comparing its analysis results with its simulation results. The second experimental result shows that the usual method, which uses the traditional schedulability analysis method to analyze whether the system design requirements are satisfied by assuming every message is transmitted for a fixed number, is too conservative compared with the proposed method.
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