On the Multi-User Diversity with Fixed Power Transmission in Cognitive Radio Networks

In this letter, we investigate the multi-user diversity (MUD) in an underlay cognitive radio (CR) network where multiple secondary transmitters and primary receivers exist. Many studies on MUD in the underlay CR network have assumed that the secondary transmitters adaptively control their transmit power in order to achieve the {optimal} MUD gain, maintaining the interference at the primary receivers below a pre-determined level. We, however, prove the optimal MUD gain can be also achieved by the fixed power transmission strategy. In contrast to the adaptive power transmission strategy, the fixed power operation in the secondary transmitters relaxes the coordination constraint between the primary and secondary networks, and significantly reduces the signaling and feedback overhead from the secondary transmitters to the secondary receiver.