On the capacity of a cognitive user with subcarrier collisions over rayleigh fading channels

The paper evaluates the capacity of a cognitive user in an orthogonal frequency-division multiplexing-based spectrum sharing communication system that assumes ran- dom subcarrier allocation and absence of spectrum sensing information at the secondary (cognitive) user. In the absence of the primary user's channel occupation information, i.e., no spectrum sensing mechanism is used, the secondary user randomly accesses the subcarriers of the primary network and collides with the primary users' subcarriers. The capacity of a secondary user under such a random access that assumes subcarrier collisions is evaluated herein paper and used as a performance benchmark to investigate the proposed commu- nication scheme over the Rayleigh fading channel.