A Reliable Broadcast and Unicast MAC Protocol for Ad Hoc Networks

Current applications and services for ad hoc net works heavily rely in advertisements, which are transmitted using broadcast. In the current Medium Access Control (MAC) schemes, namely in IEEE 802.11, broadcast co-exists with unicast frames. While the transmission scheme used for unicast frames is considered reliable, the IEEE 802.11 does not offer any possibility of retransmission for broadcast frames. This work presents a novel reliable MAC scheme, which is designed to maximize the network throughput. In our scheme all nodes adopt a common optimal contention window, which is based on a common view of the channel. Contrary to IEEE 802.11 we use the same contention window for both unicast and broadcast transmissions. Thus the conditional collision probability is independent of the traffic type. Departing from the optimal throughput for a saturated network, we estimate the number of nodes, which is a prime parameter to regulate the medium access control. We show that each node is suitable to estimate the number of competing nodes by using both its own medium access probability and the idle slot probability observed from the channel. Several simulation results evaluate the reliability and the throughput of our proposal, for different amounts of unicast/broadcast traffic. The results are compared to the well known IEEE 802.11 MAC, indicating that even without retransmitting the broadcast frames, the probability of successful transmission can be doubled. Moreover, the throughput of our approach outperforms IEEE 802.11 MAC and the results show it can be boosted up to 100%.