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Throughput Analysis of Cooperative HARQ Protocols for Cognitive Radio Networks Using Multihop Multibranch Relaying in the Presence of Primary and Secondary Interferences
Nadhir Ben Halima and Hatem Boujemâa

In this paper, we derive the throughput of cooperative Hybrid Automatic Repeat reQuest protocols for underlay cognitive radio networks. We have considered mutlihop and multibranch relaying, with ARQ, HARQ I and HARQ II being examined. Different relaying techniques are investigated when there are many branches. The first technique consisted of selecting the available branch with the highest SNR (Signal to Noise Ratio). A branch is said to be available if all relays satisfy interference constraint. Another solution was to combine the packets received from all available branches using MRC (Maximum Ratio Combining). Amplify and Forward (AF) relaying was used on all relays. We analyze both interference from secondary nodes to the primary receiver and interference from the primary transmitter to secondary nodes. In this paper, we show that multihop relaying offers higher throughput than dual hop relaying. We also suggest the use of relay nodes with adaptive transmit power to increase the throughput. Relays with adaptive transmit power are regularly active and therefore an improved cooperative diversity can be achieved when compared to nodes with fixed transmit power.

Keywords: Cognitive radio networks, cooperative communications, HARQ protocols, Multihop and multibranch relaying.

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