MAC Rate Adaptation and Cross Layer Behavior for Vehicular WiFi Access: An Experimental Study

Vehicular WiFi is different from conventional WiFi access. Firstly, as the connections arise opportunistically, they are short lived and intermittent. Secondly, at vehicular speeds channel conditions change rapidly. Under these conditions, the MAC bit rate adaptation plays a critical role to ensure that devices can maximize throughput performance. The goal of this work is to gain a deeper understanding of current MAC bit rate adaptation algorithms and their interaction with higher layer protocols under vehicular settings. Towards this end, we evaluate the performance of four MAC bit rate adaptation algorithms; SampleRate, AMRR, Minstrel, and RRAA, and their interactions with transport layer protocols such as TCP in real world vehicular settings. Our experimental study reveals that in general these algorithm perform poorly in vehicular settings, and can have an extremely adverse impact on TCP performance.