A distributed MAC scheme to achieve QoS in ad hoc networks

Real-time applications introduce new requirements on wireless networks and impose quality thresholds on parameters like delay, jitter, throughput, and packet loss in order to run smoothly. This paper addresses this issue by presenting a MAC scheme that offers real-time applications the opportunity to reserve transmission time based on their QoS requirements for contention-free medium access. Our scheme, which is called EDCA with Resource Reservation (EDCA/RR), operates in a fully distributed manner, is compatible with IEEE 802.11, and provides both prioritized and parameterized QoS. In this study, we have extended EDCA/RR to handle reservation collisions and, through extensive simulations, we show that our proposal can handle multiple reservations as well as uninformed stations that lie outside the transmission range of both the transmitter and the receiver while providing QoS guarantees. We compare EDCA/RR with EDCA and our results show that, as the traffic in the network increases, EDCA/RR succeeds providing the required service to QoS-demanding applications whereas EDCA fails in this task. In addition, when the medium is lossy we show that, not only does EDCA/RR give better service to real-time traffic, but also to contending non-real-time traffic.