CoopMAC: A Cooperative MAC for Wireless LANs

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 transmission. 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.

Relay selection for energy-efficient cooperative media access control

“…Remarks: In contrast to the solution of [7], our proposed single relay selection acts in a unilateral fashion, where the relay or the source does not have to exchange detailed information with the other relay nodes, since each node executes the decision autonomously. Additionally, instead of incorporating the priority information into the data or control frame, which inevitably leads to a frame-length extension and to a potential transmission energy wastage, different back-off periods are used to reflect the specific priorities of relays.…”

“…Multiple relay selection is capable of offering considerable throughput improvements and outage probability reduction, albeit at the cost of eroding the energy efficiency [3]- [5], unless sophisticated crosslayer-operation aided physical layer processing, such as advanced beamforming, is employed [6]. On the other hand, single relay selection aided cooperation is capable of providing beneficial energy savings [7], [8], although they tend to complicate the protocol design. More explicitly, Liu et al [7] proposed a single relay selection aided MAC protocol, where each low data rate node has to maintain a cooperative parameter table in order to record all the required information of the potential candidate relays.…”

“…On the other hand, single relay selection aided cooperation is capable of providing beneficial energy savings [7], [8], although they tend to complicate the protocol design. More explicitly, Liu et al [7] proposed a single relay selection aided MAC protocol, where each low data rate node has to maintain a cooperative parameter table in order to record all the required information of the potential candidate relays. As a result, a large amount of extra control messages are required in order to collect the associated information.…”

Cross-Layer Solutions for Cooperative Medium Access Control Protocols

“…In this paper we intrinsically amalgamate physical-layer cooperative techniques with the CoopMAC [6]. We contrive a joint detection scheme for the direct and relayed signals combined with…”

“…Furthermore, references [2], [3], [4], [5] rely on the simplifying assumption of having a perfect physical layer. A CrossLayer (CL) approach designed for the CoopMAC protocol of [6] was presented in [3], although the effect of channel coding was not investigated and the adaptive transmission rate selection algorithm did not exploit the additional information provided by the joint decoding of the signals gleaned from the source (S) and the relay (R) at the destination (D).…”