The 802.11 MAC protocol leads to inefficient equilibria

TL;DR

This paper demonstrates that the standard 802.11 MAC protocol often results in inefficient equilibria in non-cooperative settings, and proposes a new approach to improve overall throughput by decoupling resource allocation from individual strategies.

Contribution

The paper provides a game-theoretic analysis of 802.11 MAC, showing its inefficiencies and proposing a novel protocol design to achieve better equilibria.

Findings

802.11 DCF leads to undesirable Nash equilibria.

Decoupling resource allocation improves throughput.

Simulations confirm the theoretical analysis.

Abstract

Wireless local area networks (WLANs) based on the family of 802.11 technologies are becoming ubiquitous. These technologies support multiple data transmission rates. Transmitting at a lower data rate (by using a more resilient modulation scheme) increases the frame transmission time but reduces the bit error rate. In non-cooperative environments such as public hot-spots or WLANs operated by different enterprises that are physically close to each other, individual nodes attempt to maximize their achieved throughput by adjusting the data rate or frame size used, irrespective of the impact of this on overall system performance. In this paper, we show both analytically using a game theoretic model and through simulation that the existing 802.11 distributed MAC protocol, DCF (for Distributed Coordination Function), as well as its enhanced version, which is being standardized as part of 802.11e, can lead non-cooperative nodes to undesirable Nash equilibriums in which the wireless channel is inefficiently used. We show that by establishing independence between the allocation of the shared channel resource and the transmission strategies used by individual nodes, an ideal MAC protocol can lead rational nodes to arrive at equilibriums in which all competing nodes achieve higher throughputs than with DCF.