变包长对WLAN MAC协议性能的影响

Impact of variable packet length on the performance of WLAN MAC protocol

为更加准确分析WLAN MAC协议性能,讨论了在数据包长随机分布时的系统吞吐量与RTS门限值及分段门限值的关系.通过二维M arkov链的分析,研究了数据包长度服从均匀分布时的网络吞吐量性能,给出了最佳RTS门限值的计算方法.讨论了分段门限值与系统性能的关系,以及RTS门限值与分段门限值结合对系统性能的影响.计算表明RTS门限值和分段门限值变化时,系统吞吐量性能呈现出复杂变化态势.但存在两者最佳的组合,使得系统吞吐量达到最大值,并给出了近似计算该最佳组合值的方法.最后通过计算机仿真验证了文中的推导结果.

The relationship between the throughput performance of WLAN （wireless local area networks） MAC （media access control） protocol and the RTS （request to send） threshold as well as the fragmentation threshold is discussed when packet lengths are randomly distributed. The throughput performance of network is analyzed based on 2-dimension Markov chain when packet lengths are uniformly distributed, and the optimal RTS threshold is presented. The relationship between the fragmentation threshold and the system performance, as well as the effect of combination of the RTS threshold and the fragmentation threshold on the system performance are discussed. It is shown that the throughput performance varies complicatedly with the variation of the RTS threshold and the fragmentation threshold, and there exists an optimal combination. A simple method to estimate this optimal combination is presented. Finally, the related conclusions under certain conditions are verified by computer simulations.