Multi-user Diversity in Spectrum Sharing Systems over Fading Channels\n with Average Power Constraints

The multi-user diversity in spectrum sharing cognitive radio systems with\naverage power constraints over fading channels is investigated. Average power\nconstraints are imposed for both the transmit power at the secondary\ntransmitter and the interference power received at the primary receiver in\norder to provide optimal power allocation for capacity maximization at the\nsecondary system and protection at the primary system respectively. Multiple\nsecondary and primary receivers are considered and the corresponding fading\ndistributions for the Rayleigh and Nakagami-m fading channels are derived.\nBased on the derived formulation of the fading distributions, the average\nachievable channel capacity and the outage probability experienced at the\nsecondary system are obtained, revealing the impact of the average power\nconstraints on optimal power allocation in multi-user diversity technique in\nfading environments with multiple secondary and primary receivers that share\nthe same channel. The obtained results highlight the advantage of having on one\nhand more secondary receivers and on the other hand fewer primary receivers\nmanifested as an increase in the achievable capacity.\n