The presence of multiple users in a wireless network offers an opportunity for their cooperation leading to improved overall performance. Cooperative strategies beyond multi-hop routing are expected to bring gains in terms of rate, coverage, reliability and energy-efficiency. This tutorial will present fundamental cooperative strategies for relay channels with and without fading. Several scenarios in which cooperation leads to optimal performance will be shown. The tutorial will also present cooperative strategies for networks with multiple source-destination pairs. Several methods for managing interference, ranging from coherent cancellation to interference amplification, will be discussed. Implications of these approaches on the design of cognitive radio networks will be presented. The impact of cooperation to scaling laws in large networks will be shown. Finally, the network architectures required for cooperative communications, and challenges to their practical realization will be discussed.
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