CoopMAC: A Cooperative MAC for Wireless LANs

TLDR

Wireless broadcasts can be overheard by neighboring stations, and recent cooperative communication research seeks to exploit this by having those stations retransmit overheard data to improve spatial diversity. The paper shows that cooperative MAC in WLANs can increase throughput, reduce interference, and improve signal‑to‑interference ratios in dense deployments. CoopMAC lets high‑rate stations forward traffic for low‑rate stations, with each low‑rate node maintaining a CoopTable of helpers and selecting the fastest path, yielding a simple, backward‑compatible protocol. Analysis, simulation, and testbed experiments demonstrate that CoopMAC raises network throughput, cuts delay, and enhances signal‑to‑interference ratios.

Abstract

Due to the broadcast nature of wireless signals, a wireless transmission intended for a particular destination station can be overheard by other neighboring stations. A focus of recent research activities in cooperative communications is to achieve spatial diversity gains by requiring these neighboring stations to retransmit the overheard information to the final destination. In this paper we demonstrate that such cooperation among stations in a wireless LAN (WLAN) can achieve both higher throughput and lower interference. We present the design for a medium access control protocol called CoopMAC, in which high data rate stations assist low data rate stations in their transmission by forwarding their traffic. In our proposed protocol, using the overheard transmissions, each low data rate node maintains a table, called a CoopTable, of potential helper nodes that can assist in its transmissions. During transmission, each low data rate node selects either direct transmission or transmission through a helper node in order to minimize the total transmission time. Using analysis, simulation and testbed experimentation, we quantify the increase in the total network throughput, and the reduction in delay, if such cooperative transmissions are utilized. The CoopMAC protocol is simple and backward compatible with the legacy 802.11 system. In this paper, we also demonstrate a reduction in the signal-to-interference ratio in a dense deployment of 802.11 access points, which in some cases is a more important consequence of cooperation