Listen (on the frequency domain) before you talk

Abstract

Conventional WiFi networks perform channel contention in time domain. This is known to be wasteful because the channel is forced to remain idle, while all contending nodes are backing off for multiple time slots. This paper proposes to break away from convention and recreate the backing off operation in the frequency domain. Our basic idea is to pretend that OFDM subcarriers are integer numbers, and thereby, view today's random backoff process as equivalent to transmitting on a randomly chosen subcarrier. By employing a second antenna to listen to all the subcarriers, each node can determine whether its chosen integer (or subcarrier) is the smallest among all others. In fact, each node can even determine the rank of its chosen integer, enabling the feasibility of a TDMA-like schedule from every round of contention. We develop these ideas into a Time to Frequency (T2F) protocol and prototype it on a small testbed of 8 USRPs. Experiments confirm its feasibility, along with promising throughput gains of more than 35% at high bit rates. A fuller design and thorough evaluation of T2F is a topic of ongoing work.