Listen before you talk, but on the frequency domain

Abstract

WiFi networks adopt a random backoff mechanism to mediate channel contention. Although effective, backing off has been shown to reduce channel utilization. This is because backing off occurs in the time domain, forcing the channel to remain idle for multiple time slots. This poster proposes to break away from convention, and recreate the time domain operations in the frequency domain. Our basic idea is to pretend that OFDM subcarriers are integer numbers, and hence, counting down from a random backoff value may be equivalent to transmitting on a randomly chosen subcarrier. By looking at all active subcarriers and comparing with one's own chosen subcarrier, it is possible to select the winner of the contention. In fact, a logical ordering among nodes is feasible, enabling a train of scheduled transmissions from only one round of contention. We develop these ideas into a T2F protocol and prototype it on a small testbed of 5 USRPs. Early experimental results confirm its feasibility, along with promising throughput gains of up to 50%.