Optimal power allocation for fading channels in cognitive radio networks: Ergodic capacity and outage capacity

Abstract

A cognitive radio network (CRN) is formed by either allowing the secondary\nusers (SUs) in a secondary communication network (SCN) to opportunistically\noperate in the frequency bands originally allocated to a primary communication\nnetwork (PCN) or by allowing SCN to coexist with the primary users (PUs) in PCN\nas long as the interference caused by SCN to each PU is properly regulated. In\nthis paper, we consider the latter case, known as spectrum sharing, and study\nthe optimal power allocation strategies to achieve the ergodic capacity and the\noutage capacity of the SU fading channel under different types of power\nconstraints and fading channel models. In particular, besides the interference\npower constraint at PU, the transmit power constraint of SU is also considered.\nSince the transmit power and the interference power can be limited either by a\npeak or an average constraint, various combinations of power constraints are\nstudied. It is shown that there is a capacity gain for SU under the average\nover the peak transmit/interference power constraint. It is also shown that\nfading for the channel between SU transmitter and PU receiver is usually a\nbeneficial factor for enhancing the SU channel capacities.\n