Closed-Form expressions for the capacity of spectrum-sharing constrained relaying systems

Capacity of relay-based systems under spectrumsharing constraints is studied in this paper. We consider that a secondary user (SU) is allowed to use the spectrum band allocated to a primary user (PU) as long as the former meets the interference-power requirements of the latter so that it does not disrupt the PU´s communication process. We assume that the direct link between the SU´s sender and destination is in deep fade and that data is transmitted through the help of a dedicated relaying device. Closed-form expressions for the ergodic and outage capacities are derived for different fading and shadowing environments. Numerical results corroborating the analysis are also provided.