An Agile and Efficient MAC for Wireless Access over TV Whitespaces

The FCC mandate of allowing TV Whitespaces for unlicensed access has the potential for dramatic improvements in wireless access data rates. We argue that an ideal MAC should account for diverse user-location and spectrum dependent channel rates to provide fair data rates and efficient utilization. Furthermore, due to limited tunable bandwidth of a radio and fragmented spectrum, the AP should support multiple radios. We make the following contributions by designing a MAC for wireless LAN access over TV Whitespace. (i) We propose an architecture and beaconing mechanism to enable such a MAC. Our MAC is an evolution of 802.11 MAC. (ii) We propose an algorithm that chooses the Whitespaces for the different radios of the AP and assigns clients to the radios. Our algorithm has provable guarantee and is near-optimal in many scenarios. (iii) Extensive simulation over OMNET platform demonstrates the benefit of our design over a frequency and client-location agnostic Wi-Fi-like MAC. The typical throughput gain is 30-76 percent, whereas, the reduction in collisions is up to 80 percent. (iv) We implemented a proof-of-concept prototype (by modifying madWiFi drivers) that demonstrates feasibility of our design, robustness to temporal variation of available spectrum, and system throughput.