Outage Analysis of a Cognitive Radio System With Nakagami-m Fading and Cooperative Decode and Forward Relaying

The advent of the next generation of wireless communication (NextGen) demands substantial investments and collaborative research for the fundamental need of wireless communications. Therefore, cooperative communication plays a vital role in overcoming challenges such as reliability, throughput, and outage trade-offs. We propose a two-transmission phase spectrum-sharing protocol, employing cooperative decode-and-forward relaying to grant spectrum access for both primary and secondary users. The system consists of a primary sender (PS), primary recipient (PR), secondary sender (SS), and secondary recipient (SR), linked as PS-SS, PS-PR, PS-SR, SS-SR, and SS-PR. In the first transmission phase, PS broadcasts the primary signal, received by PR, SS, and SR. SS regenerates the primary signal after successful reception, combining it linearly with the secondary signal, and allocating power fractions $\epsilon $ and ( $1 - \epsilon $ ) to the primary and secondary signals. SS then broadcasts the combined signal in the second transmission phase. Analysis reveals a threshold for optimal performance when SS is within range of PS. Beyond this threshold, the outage performance for the primary user equals or exceeds the case without spectrum sharing. The outage performance for the secondary system is also quantified. The performance of both the primary and secondary users is assessed by deriving a closed-form expression for the outage probability using the Nakagami-m distribution. The effectiveness of the scheme is affirmed through analytical and simulation results.