Distributed MAC protocols for heavily loaded ad hoc networks

This thesis contributes to the domain of medium access control for ad hoc networks. These networks are by definition created for the occasion, or for a specific purpose, and usually have to operate without any existing fixed infrastructure. In this context, the MAC layer appears to be a performance bottleneck, especially at high input loads. It can be demonstrated that the off-the-shelf solutions like the standard IEEE 802.11 present lack of performance related to throughput and fairness in multi-hop networks. A new slotted protocol, called Collision-free Receiver Oriented MAC (CROMA), provides an elegant solution to overcome the above mentioned drawbacks especially in heavily loaded wireless multi-hop ad hoc networks. The receiver oriented nature of CROMA is a determining factor both for the fairness and for an improved throughput (with respect to IEEE 802.11) in multiple targeted environments. Cross-layer mechanisms useful for further capacity increase and enhancement of CROMA exist. This has been demonstrated through theoretical analysis and simulations in the following three cases: (i) A simplified version of CROMA and an associated scheduling policy can take advantage of node mobility for throughput improvement. (ii) Multi-user diversity considerably improves the CROMA reservation scheme based on slotted ALOHA. (iii) Multi-user detection can offer additional improvement for reservation too.