Sub-channels selection schemes with interference management for underlay cognitive networks

Cognitive Radio is a promising concept that offers solution to spectral crowding problem by introducing opportunistic usage of the unoccupied licensed frequency bands. Improving the network capacity and reliability of the communication has been recently studied and this through the introduction of cooperative technology in the CR networks. Furthermore, OFDM system is considered to be a good candidate to enhance the flexibility of the CR network, where individual carriers can be switched off for occupied frequencies by the primary user (PU) or for interfering Sub-channels. In this paper, an underlay cognitive network based on OFDM technique is proposed where secondary users (SUs) coexisting with a PU are adhering to stringent interference threshold constraint. Cooperative technology will help improving the CR network performances under PU limitation. This paper proposes new Sub-channel selection schemes which adapt either the transmission power or the sequential order of selection to enhance the system performances. We first provide the exact probability density function (PDF) of the received SNR at the secondary destination. Then, the PDFs are used to derive closed form expressions of the outage probability, the average BER and the ergodic capacity. Analytic results are validated by simulation for the proposed Sub-channels selection schemes.