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Wireless networks in non-ergodic multipath fading : capacity and relaying performance analysis


Wireless channels experience random multipath fading. Reliable and efficient communication in slow-varying channel fading conditions may be challenging due to limited time diversity. This problem may be alleviated by leveraging network path diversity, which is a form of distributed spatial diversity. Utilization of relays and node cooperation in wireless communication have been proposed in recent years to achieve a certain level of spatial diversity. Cooperative diversity is mostly needed when other sources of diversity, namely frequency diversity, time diversity and conventional spatial diversity, are limited. Under such conditions, the coherence time of the channel is likely to be sufficiently large to allow local channel state information to be obtained. In the first part of this dissertation, we consider the problem of two-hop path selection, namely relay selection. We show that with limited channel gain information at the source a relay can be selected such that improved outage performance and dramatic energy savings are obtained while utilizing a simple packet forwarding scheme that resembles store-and-forward routing in wired networks. Performance is evaluated at practical SNR levels, using mutual information outage for both limited relay diversity, and in the limit of large relay diversity. Compared to this simple scheme, under relay selection, the advantage of more sophisticated relaying schemes is shown to be rather limited. In the second part, we consider a large wireless network. The problem is to find a way to systematically utilize network path diversity to overcome the added uncertainty due to random multipath fading, and assure each node in the network a certain throughput. Also, by upper bounding the achievable throughput, we prove the efficiency of the construction. We find the exact per-node capacity scaling in an extended, distributed wireless network where the node locations are random, the channel attenuation between pairs of nodes exhibits independent random multipath fading, and data forwarding is restricted to multihop delivery. The lower bound is mainly motivated by a bond-percolation-based protocol construction that was recently introduced. The key to the upper bound is to bound the total network transport capacity

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