Experimental evaluation of opportunistic access in shared contention-based channels

In this paper, we experimentally evaluate the gains of applying the concept of opportunistic channel access to the traditional contention-based access widely used in unlicensed channels. We consider the scenario in which multiple IEEE 802.11 networks coexist in a given channel and pose the following question: should all networks fairly compete for channel access or should they be prioritized in terms of channel access rights, and use opportunistic access to regulate their transmission? We implement a simple modification to the IEEE 802.11 medium access module of the wireless interface driver to allow opportunistic access of the shared channel. Then, we configure a secondary IEEE 802.11 network to opportunistically access the channel only when a primary network is not using it. Our empirical results show that such opportunistic channel access achieves high channel utilization (up to 188 % utilization gain) while respecting the prioritized access rights of the primary network with primary network outages below 7 %. In contrast, legacy contention-based access achieves higher channel utilization. However, it does not provide prioritized access and causes half the primary network packets to be denied transmission, which is not suitable for the targeted application scenarios.