Exploiting New Forms of Multiuser Diversity for Spectrum Sharing in Cognitive Radio Networks

Multiuser diversity, as a fundamental property for fading wireless networks, has been widely applied in today’s wireless communication systems. Conventionally, due to the multiuser diversity, the long-term throughput of a wireless system consisting of multiple independently fading communication links can be enhanced by selecting one link with the best instantaneous channel quality to transmit at one time. In this paper, we consider the emerging cognitive radio (CR) wireless network that communicates by sharing the spectrum with an existing primary radio (PR) network. Under the assumption that the CR transmit terminal protects the PR link by applying the interference-power constraint at the PR receiver, we demonstrate several new forms of multiuser diversity in the CR network, named as multiuser interference diversity (MID), which are not present in the traditional wireless systems. Three CR multiuser channel models are considered, including the multiple-access channel (MAC), broadcast channel (BC), and parallel access channel (PAC), for which we characterize the transmit MID (TMID), the receive MID (R-MID), and the combined T-MID and R-MID, respectively. It is shown that the new discovered MID can achieve substantial performance gains for the CR network in addition to the conventional multiuser diversity.