Enhancing QoS parameters using an IEEE 802.11 multi-interface based wireless distribution system (MI-WDS)

Wireless distributed systems (WDS) are used to interconnect a set of access points to form a wireless extended service set (ESS). In this paper, we investigate the performance enhancements accomplished by using multiple interface cards per AP within the WDS system. Detailed simulations are conducted to bring out the enhancements accomplished by just using a few interfaces per access point in terms of a much greater throughput and a much lower end-to-end delay and end-to-end jitter. We propose two different scheduling policies: the sequencing enforced policy (SEP) and the sequencing relaxed policy (SRP) which depend on whether packet sequencing is maintained within the WDS or rather re-established at its edge. For each policy, we discuss two different, yet very simple scheduling algorithms, the round robin (RR) and the random uniform (RU) algorithms, to dictate the selection of the interfaces. We show that both policies provide tangible improvements of QoS parameters. Conducted simulations show, in particular, that the SRP results in almost doubling the network throughput, reducing end-to-end delay and end-to-end jitter when using just two interfaces per access point. The SRP policy along with the RR algorithm outperforms the SEP policy though it requires a re-sequencing action at the edge of the WDS. We finally evaluate the impact of drop out on the end-to-end jitter within the SRP policy and ascertain the needed re-sequencing buffer size.