基于Ad hoc网络的新EDCA参数调整方案

EDCA parameter adjustment scheme in Ad hoc networks

IEEE802.11e标准中业务优先级不同的AC(access category)是通过设置不同的竞争窗口最大、最小值CWmax,CWmin和仲裁帧间隔值来体现的,如高优先级AC设置小的CWmin,CWmax和AIFS值。研究表明,EDCA对每个AC指定的默认参数值只适用于中等负载、节点数目少的网络场景,并不适用于负载较重、节点数目较多且链路动态变化的Ad hoc网络环境。提出了一种根据网络状况动态调整IEEE 802.11e EDCA的QoS参数的新方案I-EDCA,该方案根据网络状态调整竞争窗口CW,并通过修改退避计数器值调整AIFS参数,使I-EDCA适合动态变化的Ad hoc网络环境,采用NS2仿真软件对EDCA改进协议I-EDCA进行仿真。仿真结果表明,随着网络中负载的增加,I-EDCA的吞吐量表现平稳,而EDCA吞吐量是下降的。另外,在业务公平性方面,对优先级不同的业务I-EDCA比EDCA的表现更公平。

EDCA is enhanced distributed channel access mechanism of competition in IEEE802.11 e standard. Depending on IEEES02.11 e standard QoS parameters, the AC （access category, AC） with different priorities reflects different conten- tion window by setting different maximum and minimum CW min, CWmaX and arbitration frame interval AIFS values. Research shows that the default EDCA parameters specified for each AC value is only suitable for medium loads in the small number of nodes network scenarios, which does not apply to heavy load in more number of nodes and links more dynamic Ad hoc network environment. This paper proposes a new program I-EDCA dynamically adjusted IEEE802.11 e EDCA QoS parame- ters based on network status. The program adjusts the contention window value CW according to the network state and adjusts the AIFS value of the parameter by modifying the backoff counter. So I-EDCA is very suitable for dynamically changing ad hoc network environment. We use NS2 simulation software simulation I-EDCA protocol. Simulation results show that with the increase of network load, throughput performance of I-EDCA is steady, but EDCA protocol is decreased; on the other hand, fairness performance of I-EDCA is better than EDCA for different business priorities.