Lakshmi V. Thanayankizil

Effects of time slot reservation in cooperative ADHOC MAC for vehicular networks

Cooperative medium access control (MAC) protocols have been proposed for improving communication reliability and throughput in wireless networks. In a recent study, a cooperative MAC scheme called Cooperative ADHOC MAC (CAH-MAC) has been proposed to increase the network throughput by reducing the wastage of time slots under a static network scenario. Particularly, neighbor nodes cooperate to increase the transmission reliability by utilizing unreserved time slots for retransmission of failed packets. In this paper, we focus on a mobile networking scenario and study the effects of time slot reservation on the performance of CAH-MAC under highly dynamic vehicular environments. We find out that the introduction of time slot reservation results in cooperation collisions, degrading the system performance. To tackle this challenge, we present an enhanced CAH-MAC (eCAH-MAC) that is able to avoid cooperation collisions and thus efficiently utilize a time slot. In eCAH-MAC, the cooperative relay transmission phase is delayed, so that cooperation collisions can be avoided and time slots can be efficiently reserved. Through extensive simulations, we demonstrate that eCAH-MAC uses time slot more efficiently than CAH-MAC in direct and/or cooperative transmissions and in reserving time slots in the presence of relative mobility among nearby nodes.

Link-Layer Cooperation Based on Distributed TDMA MAC for Vehicular Networks

Cooperative medium access control (MAC) protocols have been proposed for improving communication reliability and throughput in wireless networks. In our previous work, a cooperative MAC scheme called Cooperative ADHOC MAC (CAH-MAC) has been proposed to increase the network throughput under a static networking scenario for vehicular communications. In this paper, we study the effects of relative mobility among nodes and channel fading on the performance of CAH-MAC. In a dynamic networking environment, system performance degrades due to cooperation collisions. To tackle this challenge, we present an enhanced CAH-MAC (eCAH-MAC) scheme, which avoids cooperation collisions and efficiently utilizes cooperation opportunities without disrupting the time-slot reservation operations. Through mathematical analysis and computer simulations, we show that eCAH-MAC increases the effectiveness of node cooperation by increasing utilization of an unreserved time slot. Furthermore, we perform extensive simulations for realistic networking scenarios to investigate the probability of successful cooperative relay transmission and usage of unreserved time slots in eCAH-MAC, in comparison with existing approaches.