Cooperative ARQ protocols for underlay cognitive radio networks

In this paper, we derive the throughput of cooperative Automatic Repeat reQuest protocols for underlay cognitive radio networks. Three relay selection techniques are investigated: Opportunistic Amplify and Forward (O-AF), Partial Relay Selection AF (PRS-AF) and Opportunistic Decode and Forward (O-DF). In O-AF, the selected relay should offer the highest SNR of the relaying link (S-R-D) and verify some interference constraint. In PRS-AF, the selected relay offers the highest SNR of the first hop (S-R) and verify the interference constraint. In O-DF, the selected relay should have correctly decoded the packet, verify the interference constraint and offer the highest SNR of the second hop. Theoretical curves are validated using simulation results for different number of relays and interference threshold.