Interference, Even with MCCA Channel Access Method in IEEE 802.11s Mesh Networks

IEEE 802.11s draft defining mesh networking includes two channel access methods: mandatory EDCA and optional MCCA. It is known that random access with EDCA, designed for ad hoc and infrastructure modes, is weak in multihop case because of the hidden stations effect. In contrast, by means of channel reservation and advertisement of set up reservations MCCA combats against the effect, provides more coordinated channel access and comes as a solution when better QoS is desired. In this paper, we draw readers attention to the hidden stations effect again and show that the interference caused by transmissions of ACK frames by hidden stations is not combated with MCCA. We evaluate the effect with a simulation model and propose a solution which is compatible with IEEE 802.11 and may be implemented in the framework of MCCA. Also, we discuss the issue of the interference coming out of MCCA advertisement horizon and propose a solution which appear to require more flexibility than provided by the current IEEE 802.11s draft.