Cooperation in ADHOC MAC

Abstract

This chapter presents a node cooperation scheme, referred to as (CAH-MAC), mainly focusing on the MAC layer in VANETs (Bharati and Zhuang, Performance analysis of cooperative ADHOC MAC for vehicular networks, in Proceedings of IEEE Global Communications Conference (GLOBECOM), 2012; Bharati and Zhuang, IEEE J Sel Areas Commun. 31(9):470–479, 2013). Existing works on link-layer cooperation are not suitable for VANETs scenarios and cannot be applied directly. Different from the existing works, here we consider a VANET using a distributed TDMA based MAC. In the system, nodes reserve their time slots and nearby nodes form a cluster to share a time frame. For cooperation at the link layer, a helper node utilizes an idle time slot to relay a packet that a source node failed to deliver to the target destination node in a direct transmission due to a poor channel condition. Furthermore, cooperative relay transmissions in the proposed node cooperation scheme do not affect normal (non-cooperation) transmissions. Using idle time slots for the cooperative relay transmissions, the proposed CAH-MAC protocol improves system throughput and transmission reliability of the D-TDMA MAC for VANETs. We derive a close-form expressions for the throughput and packet dropping rate of the newly proposed CAH-MAC protocol, which is verified using simulations. Our analysis shows that the CAH-MAC protocol achieves a higher throughput and a lower packet dropping rate than that of the ADHOC MAC under a similar networking condition.