Lock step: an algorithm to reduce wi-fi jitter

The exponential backoff algorithm used in IEEE 802.11 does not guarantee short term fairness between flows. We propose an algorithm based on IdleSense where each of N flows tries to transmit every W = 8 N slots; i.e. 8 slots per flow with 7 idle. Each flow adaptively adjusts its contention window W based on the observed proportion of empty slots. One key aspect of Lock Step is setting a deterministic backoff after a successful transmission so that, for persistent flows, eventually all users are in lock step and transmit every 8 N slots. Another key aspect is forcing a second collision between colliding users so all users can better estimate the proportion of idle slots per transmission thus allowing users to estimate N and hence the optimal backoff. This second collision can also be engineered to assist the ZigZag algorithm to decode the colliding packets. Even with transient flows Lock Step reduces jitter and can substantially increase the number of flows carrying Voice over IP traffic through a single access point.