The paper presents a cooperative MAC based on opportunistic relaying for ad hoc networks. In the proposed MAC, the cooperative scheme will be activated on the condition that the source contended the channel successful, but the destination receives the inaccurate packets because of the channel noise. Based on opportunistic relaying, the neighbor which has the best channel condition to the destination will be selected as the relay to help the source transmitting packets. An innovative analytical model which considers both of the cooperative scheme and the opportunistic relaying is presented to evaluate the performance of the proposed MAC. Simulations are also performed to validate the analytical model. The comparison with the DCF shows the cooperative scheme can achieve substantial throughput performance improvement when the direct link is poor. Furthermore, the paper compares the proposed MAC with the cooperative MAC based on proactive relay selection. The proposed MAC not only has the benefits that required less cooperative overhead and more suitable for distributed networks, but also has the close performance to the cooperative MAC based on proactive relay selection which is shown from the analytical results.
Keywords-cooperative MAC, opportunistic relaying, ad hoc networks
Ⅰ INTRODUCTIONCooperative communication can take full advantage of the broadcast nature of the wireless channel and creates spatial diversity, thereby achieving tremendous improvement in system performance. It is becoming a promising technology for wireless networks. Cooperative communication has been widely explored for physical layer cooperation[1][2][3] [4]. However, to maximize its benefits, it is fundamentally important to design good media access control (MAC) protocols.Recently, there have been active research works in developing cooperative MAC schemes. Two similar MAC protocols CoopMAC[5] and rDCF [6], are proposed by taking the advantage of the multi-rate capability of IEEE802.11, each of their terminals maintains a cooperative table. When the channel is poor, the source selects a best relay from cooperative table before transmitting, instead of sending its packets at a low rate to a destination directly, uses a relay that is located between the source and the destination, and is able to transmit at a higher rate in a two-hop manner. These schemes can significantly improve the system performance when the direct link quality is poor.[7] proposes a cooperative diversity MAC called C-MAC. In C-MAC, in order to transmit data packet using cooperative diversity, four control packets (RS, RA, RB, TS) are defined in addition to conventional handshake (RTS, CTS, ACK). This results in unreliable delivery of control packets, which may limit the applicability of this protocol. CD-MMAC[8] and CAM-MAC[9] utilize multiple channels and incorporates opportunistic cooperative diversity dynamically to improve their performance. CD-MAC[10] is proposed to enhance the link reliability. Both the source and a proactively chosen relay will jointly retransmi...
