Power allocation in Cognitive Radio: Single and multiple secondary users

Cognitive Radio (CR) improves spectral efficiency by allowing unlicensed (secondary) users to concurrently operate with licensed (primary) users. The side-lobe interference from an OFDM-based secondary user (SU) causes unwanted interference to the primary user (PU) of the spectrum. While interference mitigation to the PU spectral band has received a lot of attention in recent literature, the novelty of our work is in considering sub-bands of the PU, and ensuring that the interference to each of them is below a specified threshold. The approach is realistic and more effective in protecting the PU from the SU interference. We formulate an optimization problem for power allocation for a single SU to maximize its throughput, within a power budget, and an interference constraint on each PU sub-band. After extensively analyzing the solution form, we propose an iterative algorithm to meet the aforementioned objective. A power allocation algorithm is also proposed for a multiple SU scenario, which involves assigning sub-carriers to each user, besides the power and PU interference constraint, to maximize the sum throughput. Simulation results are provided, for both single and multi-user cases, which indicate that the proposed algorithms outperform those which have been previously presented in literature.