Achievable Data Rate in Spectrum-Sharing Channels with Variable-Rate Variable-Power Primary Users

In this work, we propose a transmission strategy for secondary users (SUs) within a cognitive radio network where primary users (PUs) exploit variable-rate variable-power modulation. By monitoring the PU´s transmissions, the SU adjusts its transmit power based on the gap between the PU´s received effective signal-to-noise power ratio (SNR) and the lower SNR boundary for the modulation mode that is being used in the primary link. Thus, at the SU´s presence, the PU´s quality of service (QoS) is guaranteed without increasing its processing complexity thanks to no interference cancellation required in the PU´s operation. To demonstrate the advantage of our proposed transmission strategy, we analyze the secondary user´s achievable data rate by taking into account different transmission capabilities for the secondary transmitter. The corresponding numerical results not only prove the validity of our derivations but also provide a convenient tool for the network design with the proposed transmission strategy.