Design of Multiple Access Techniques for Multihop Wireless Networks\\from a Physical Layer Point of View

This thesis collects the key research results on wireless networking developed during the three years of the PhD. The approach that underlies all work has been the analysis and design of wireless network protocols together with their physical layer. The former have been created keeping in mind the features of the adopted physical layer techniques and, conversely, the physical layer has been chosen according to the employed MAC/routing and its necessities. The results focus on three main areas. In the first branch, MIMO signal processing is applied in order to optimize broadcast in a wireless MIMO network, to improve the robustness of Network Coding to the vagaries of the wireless environment and finally to design cooperative protocols that reward nodes which help each other. In all these cases, great emphasis has been placed on signal processing and on its actual algorithmic implementation. In the second part, Carrier Sense optimization for radio networks is studied. First a special type of carrier sense system for MIMO ad hoc networks is described. Then, attention is focused on single antenna terminals, and an analytical model for carrier sense optimization in static networks (i.e., topology is known) is developed so as to find the carrier sense threshold that maximizes aggregate throughput. Moreover, specific algorithms have been created also for dynamic networks (i.e., nodes are mobile or the topology is not known beforehand). In addition, the analytical model for static networks is applied also to design a low-complexity, high-performance scheduler for mesh networks. In any case, interference analysis and the characteristics of the propagation environment play a key role to study this problem. In the last portion of this thesis, a more theoretical approach is undertaken: the performance of an Aloha multihop wireless network in terms of throughput and delay is analyzed, under saturation conditions or not. The impact of a variety of physical layer parameters (like rate, path-loss exponent or SNR decoding threshold) on network performance is analyzed, and we establish how certain parameters (e.g., transmission probability, rate, route length, admission control) must be tuned in order to optimize performance.