Resource allocation for cooperative transmission in wireless networks with orthogonal users

This paper investigates the problem of efficient power allocation in a wireless communication system with two cooperating sources and one destination. The sources in the system each transmit information to a single destination at a fixed SNR target and cooperate via an orthogonal amplify-and-forward protocol with two timeslots. We develop a framework for power allocation in this scenario around the concept of "cooperation ratios" and derive expressions for the transmit power required by each source to achieve their SNR targets as a function of these cooperation ratios. Numerical examples are presented for time-invariant channels as well as Rayleigh fading channels. Our results show that cooperation does not reduce required transmit powers when both sources have symmetric time-invariant channels to the destination. When sources have asymmetric time-invariant channels to the destination, total power is minimized when only the source with the stronger channel cooperates. In the case of Rayleigh fading channels, we demonstrate that mutual cooperation can minimize the average total required transmit power and can also lead to a reduction in average required transmit power for both sources.