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.