Idle sense

TLDR

Wireless LANs such as IEEE 802.11 operate in the unlicensed spectrum, yet despite higher nominal bit rates, the MAC layer has remained largely unchanged. The authors aim to design an access method that simultaneously maximizes throughput and fairness, adapts dynamically to physical channel conditions, and provides equal time shares across hosts using different bit rates. Idle Sense achieves this by having each host monitor the average number of idle slots between transmissions to adjust its contention window and estimate frame error rates for appropriate bit‑rate switching. Simulations demonstrate that Idle Sense delivers high throughput, low collision overhead, low delay, fast reactivity, and time‑fair channel allocation.

Abstract

We consider wireless LANs such as IEEE 802.11 operating in the unlicensed radio spectrum. While their nominal bit rates have increased considerably, the MAC layer remains practically unchanged despite much research effort spent on improving its performance. We observe that most proposals for tuning the access method focus on a single aspect and disregard others. Our objective is to define an access method optimized for throughput and fairness, able to dynamically adapt to physical channel conditions, to operate near optimum for a wide range of error rates, and to provide equal time shares when hosts use different bit rates.We propose a novel access method derived from 802.11 DCF [2] (Distributed Coordination Function) in which all hosts use similar values of the contention window CW to benefit from good short-term access fairness. We call our method Idle Sense, because each host observes the mean number of idle slots between transmission attempts to dynamically control its contention window. Unlike other proposals, Idle Sense enables each host to estimate its frame error rate, which can be used for switching to the right bit rate. We present simulations showing how the method leads to high throughput, low collision overhead, and low delay. The method also features fast reactivity and time-fair channel allocation.