Investigation on Multiuser Diversity in Spectrum Sharing Based Cognitive Radio Networks

A new form of multiuser diversity, named \emph{multiuser interference diversity}, is investigated for opportunistic communications in cognitive radio (CR) networks by exploiting the mutual interference between the CR and the existing primary radio (PR) links. The multiuser diversity gain and ergodic throughput are analyzed for different types of CR networks and compared against those in the conventional networks without the PR link.

💡 Research Summary

The paper introduces a novel form of multi‑user diversity, termed Multi‑User Interference Diversity (MID), specifically designed for spectrum‑sharing cognitive radio (CR) networks where primary radio (PR) links coexist with secondary CR links. Traditional multi‑user diversity (MUD) exploits the variability of the direct channel gains among users: by scheduling the user with the strongest instantaneous channel, the system throughput scales as log log K for K users. However, in a spectrum‑sharing environment the secondary users are simultaneously constrained by the interference they receive from the PR and the interference they cause to the PR. This dual interference creates a new random dimension that varies from user to user, which the authors propose to harness as an additional source of diversity.

System Model and MID Definition
The authors consider K secondary users, each characterized by a direct channel gain (h_k) to its own receiver and an interference channel gain (g_k) from the primary transmitter. The primary imposes an interference temperature limit (\gamma) that any secondary transmission must respect. The scheduling metric for user k is defined as
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