Opt-TDMA/DCR: Optimized TDMA Deterministic Collision Resolution Approach for Hard Real-Time Mobile Ad hoc Networks

A new kind of critical applications, using Mobile Ad hoc networks, has appeared. These applications such as vehicular or robotic ones are called Hard Real Time Applications. Their major requirement is to respect the real time constraints especially the deadlines on the treatment and the communication delay. However, providing real-time communication, with predictable delay, is a challenge because of the Ad Hoc network features, particularly the node’s mobility. In this paper, we propose a new medium access protocol (which we call: Opt-TDMA/DCR) for these hard real time applications. Our approach consists in a distributed protocol considering dynamic network topology with mobile nodes. It is based on the TDMA protocol which we optimize by reducing the TDMA frame size. The reduction of the slot number of the TDMA frame is made with the “modulo” function which is used to select slots for transmission. However, this will probably lead to collisions between nodes selecting the same slots. Hence, a deterministic collision resolution procedure will then be applied to make communication with distinct slots. In order to verify the respect of real time constraints by our protocol, we made a communication delay analysis in the worst case and in the average case. Key-Words: mobile Ad Hoc networks, hard real time, TDMA, deterministic medium access protocol, communication delay