QoS 区分的自适应p-Persistent MAC 算法对信道利用率的动态优化

在无线局域网中提供服务质量(QoS)保证的MAC 算法应该满足业务区分服务的要求和系统性能的整体最优.以往的此类自适应MAC 算法依赖于对不同级别的竞争业务数目进行估计,计算过于复杂.提出一种基于QoS区分的自适应p-persistent MAC 算法,QDA-MAC(QoS differentiation based adaptive MAC scheme).该算法引入了新的参数-坚持因子(persistent factor),其优化值能够实时反映网络负载的变化情况,结合近似优化的自适应方法,每次发送尝试后,该算法不需要估计每类竞争业务的数目,利用坚持因子的优化值实时更新各类优先级业务的发送概率,调整相应的协议参数,系统的性能也能接近最优.仿真结果验证了该算法不仅能够根据竞争业务数目的变化对系统的性能进行整体优化,而且能够提供业务区分服务,在QoS区分的基础上可以为实时业务提供严格的QoS保证,尤其在信道利用率和时延等方面明显优于标准的IEEE 802.11 DCF 和IEEE 802.11e EDCA 机制.

QoS Differentiation Based Adaptive p-Persistent MAC Scheme for Dynamic Optimization ofthe Channel Utilization

This paper proposes an adaptive p-persistent MAC scheme, named QDA-MAC (QoS differentiationbased adaptive MAC scheme), for WLAN to maximize the channel utilization and provide the servicedifferentiation among different traffic stations. Specifically, different from the previous work, the proposed schemedoes not need to estimate the number of active stations for each priority class but still achieves the channelutilization close to its optimal value by exploiting a new parameter, persistent factor, whose optimal value candynamically follow the change of the load based on a simple estimation of the network status. At the same time, thetransmission probability of each priority class can be updated by the optimal persistent factor. Simulation andnumerical results show that QDA-MAC can achieve much higher channel utilization and have shorter delay thanstandard IEEE 802.11 DCF and IEEE 802.11e EDCA in all different WLAN environments.