无线局域网中一种自适应RTS门限调整算法

媒体访问控制是无线局域网的重要部分,决定了具有受限通信带宽的无线信道的共享效率.IEEE 802.11系列标准基于现有以太网技术,具有良好的操作性和兼容性,已发展成为WLAN的主要标准.IEEE 802.11 DCF中有两种接入方式:基本方式和RTS/CTS方式.RTS/CTS方式是IEEE 802.11无线网络的可选握手过程,用于减小碰撞的可能性.决定使用RTS/CTS握手方式的RTS门限值是研究的重要参数,不同的取值对数据传送会产生不同的性能特点.文章通过分析IEEE 802.11 DCF分组发送成功和碰撞的持续时间,获得了RTS和基本方式下分组传输时间开销与分组长度的关系.给出了以最小化分组传输时间代价为优化目标的最优RTS门限的计算公式.通过对当前信道分组发送的冲突概率的预测实现了最优RTS门限的计算;给出了一个具体的RTS门限自适应调整算法,使终端能自动调整其RTS门限以达到或接近最优值.仿真表明RTS门限自适应调整算法明显减小了分组传送时收发器发送单位比特数据的时间开销.

An Adaptive RTS Threshold Adjustment Algorithm for Wireless LAN

In wireless LANs, the medium access control protocol is the main element that determines the efficiency in sharing the limited communication bandwidth of the wireless channel. IEEE 802.11 set standards based on Ethernet technology, being have favorable handle ability and compatibility, have become the main standards of WLAN. There are two access methods in IEEE 802.11DCF. basic and RTS/CTS. The RTS/CTS method is an optional handshaking procedure used by the IEEE 802.11 wireless networks to reduce the possibility of collision. The RTS threshold value, which determines when the RTS/CTS handshaking mechanism should be used, is an important parameter to investigate, since different values will produce different performance characteristics in data transmission. This paper achieves the relationships between packet transmission time overhead and packet length of RTS and basic methods through analyzing the time overhead of single successful packet transmission and single packet collision of IEEE 802.11 DCF. Formulas to calculate the optimal RTS threshold aimed to minimize time overhead of packets transmission are given out. The optimal RTS threshold is calculated by estimate the packet collision probability. An adaptive RTS threshold adjustment algorithm is presented. It enables the nodes to adjust RTS threshold to the optimal value. Simulations show that the adaptive RTS threshold adjustment algorithm greatly decreased the per-bit time overhead of transceiver.