Abstract:
Cognitive radio is a wireless system that exploits side information about the channel for more efficient communications. Side information can contain knowledge about channel conditions, the activity, codebooks or messages of the other nodes. The approach of utilizing this extra knowledge is naturally expected to lead to better use of spectrum and improved network performance. We consider a building block of a network with cognitive users - a two-sender, two-receiver channel in which one encoder has extra side information. We present different regimes in which this network can operate depending on channel conditions. We show that a variety of encoding techniques - rate-splitting, Gel'fand-Pinsker coding and superposition coding becomes relevant and improves the rates. We observe gains from cooperation at the cognitive user. The obtained rates are evaluated for Gaussian channels. We discuss the impact of the causal knowledge of the side information at the cognitive encoder on these techniques. We contrast this approach to the the interweave approach in which the cognitive radio transmits in unused frequency bands. Our results bring insights into operating networks in licensed bands with primary and secondary users. They also apply to heterogeneous networks operating in unlicensed bands. Our results encourage the view of a network in which cognition is a means to enable cooperation, where all users are cognitive and use the learned side information for relaying. This will lead to more efficient cognitive systems that fully benefit from cooperative communications.
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