Abstract
Cooperative diversity is a transmission technique, where multiple terminals form a virtual antenna array that realizes spatial diversity gain in a distributed fashion. The concept of cooperation has already been introduced to MAC layer to design MAC protocol. But it does not take advantage of physical layer's cooperation. In this paper, we present a novel MAC protocol based on IEEE 802.11, called CโMAC, which is able to support the basic building block of cooperative system. In other words, in CโMAC, a source would invite a relay node into data transmission if there exits an available one. During data transmission, the source sends the signal to destination in the first time slot. The relay node will retransmit the overheard information to the destination in the second time slot. The destination combines two signals from the source and the helper to create the spatial diversity and robustness against channel fading. The CโMAC is backward compatible to the legacy IEEE 802.11 system. The performance of CโMAC mainly depends on physical layer's performance as it just provides the support for cooperation at the MAC layer. If the physical layer works well, CโMAC would outperform IEEE 802.11 when considering packet error rate (PER). We also perform extensive simulation using nsโ2 with assumptive physical parameters. The results show that CโMAC would outperform 802.11 if PER is over some threshold, e.g. when PER is 0.4, CโMAC can achieve up to 11.5% higher throughput than IEEE 802.11. Copyright ยฉ 2011 John Wiley & Sons, Ltd.