In order to analyze the problem of packet collision in the asynchronous mode of persistent carrier sense multiple access (p-CSMA), in which there is no time slot different from synchronous mode and propagation delay have a heavy effect on the probability of packet collision, a preemptive asynchronous p-CSMA probability model is established for the first time in the chapter. From sub-cycle conditional probability, the model gives the expectations of an idle and busy period. On the basis, performance targets, e.g., throughput/delay/success rate and channel efficiency, are gotten. For illustration, VDL2 (a typical asynchronous p-CSMA network) simulation model is set up on OPNET platform and experiments are also carried out to verify the correctness of this model in diverse scenarios. Through simulation, the results of fixed position distribution have the good consistency with the preemptive probability model. Finally, the conclusion is achieved that packet collisions will aggravate with the stations distribution becoming more uneven.
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