基于802.11的多信道MAC协议性能分析

Performance Analysis of Multi-Channel MAC Schemes Based on 802.11

为了改善无线网络中信道带宽的利用率,提高网络的吞吐量性能,已有研究提出了采用多信道MAC协议的方法,将单个信道分割成控制子信道和数据子信道进行联合使用.针对基于802.11DCF的该类型MAC协议,采用离散Markov链对DCF的退避机制进行建模分析,研究了多信道下两种MAC机制的饱和吞吐量性能与信道带宽分配比例的关系,分析了网络节点数、数据分组大小和DCF竞争窗口等对优化多信道带宽分配的影响,并将多信道MAC机制下的网络性能与单信道MAC机制进行了对比.分析和仿真结果表明,采用优化的信道带宽分配,多信道的MAC机制可以一定程度上提高网络的吞吐量性能.但是,当允许控制帧以最大信道速率传输时,多信道MAC机制吞吐量性能并不比单信道MAC机制好.

In order to improve the throughput performance of medium access control （MAC） schemes in wireless communication networks, some researchers proposed to split the single shared channel into two sub-channels： a control sub-channel and a data sub-channel. The control sub-channel is used for access reservation to the data sub-channel over which the data packets are transmitted. In this paper, an analytical framework is presented to evaluate the maximum achievable throughput of a class of generic multi-channel MAC schemes that are based on the RTS/CTS （ready-to-send/clear-to-send） dialogue and on the backoff contention resolution mechanism proposed in 802. 11 DCF（distributed coordination }unction）. By making use of a discrete Markov chain model for the backoff mechanism, the interval time of successfully transmitted RTS/CTS on the control sub-channel is obtained, and then it is applied to derive the saturation throughput of the multi-channel MAC schemes, which is closely related to the bandwidth allocation ratio between the control sub-channel and the data sub- channel. Moreover. the influence of the number of stations, the packet size, and the minimum contention window on the optimal bandwidth allocation ratio is investigated. Compared with the performance of the corresponding single channel MAC scheme that sends RTS/CTS packets and DATA packets on a single shared channel, the experiment results show that the multi-channel MAC schemes can only bring some performance enhancement. But under the condition that RTS/CTS are transmitted in full channel rate, the single channel MAC scheme can out-perform the multi-channel MAC schemes.