Service Differentiation in IEEE 802.11ah WLAN under Restricted Access Window based MAC protocol

Abstract

The restricted access window (RAW) based channel access scheme proposed for IEEE 802.11ah wireless LAN (WLAN) divides the stations (STAs) in the network into groups and allocates RAW slots for each group of STAs. In this way, the STAs belonging to each group can attempt to access the medium during their designated RAW slot by invoking the enhanced distributed channel access (EDCA) protocol. This paper describes an analytical model to evaluate the saturation throughput of IEEE 802.11ah WLAN under the RAW based scheme, when STAs carry traffic of distinct access categories (ACs) and use the EDCA protocol for medium sharing. However, when groups are formed by randomly selecting the STAs, i.e., if random grouping (RG) scheme is employed, each group will contain STAs carrying traffic of distinct ACs. This will lead to starvation and degraded throughput performance for the low priority class STAs, since they have to contend with high priority class STAs within the same group during the RAW slot assigned. To resolve this issue, we propose an algorithm to realize priority class based grouping (PCG), in which the STAs belonging to the same ACs are grouped together. We also describe an analytical model to evaluate the saturation throughput of the network under the proposed PCG scheme. We establish that saturation throughput of the network and the relative service differentiation ratio of the lower priority class STAs can be significantly improved under the proposed PCG scheme compared to the conventional RG scheme.