Optimal Transmission Time of Secondary User in an Overlay Cognitive Radio System

Optimal Opportunistic channel access of the unlicensed users has been a major problem in a cognitive radio system. In this paper, we consider an overlay cognitive radio system, where the secondary user senses the channel for an empty slot and transmits a constant power for a time period without sensing the channel again. We obtain the optimal transmission time of the secondary user to achieve the maximum data rate while keeping the interference on the primary user under a given threshold. We derive closed-form expressions for the interference at the primary receiver side and the achievable data rate of the secondary user. Our analysis is based on a Markov model for the primary user statuses and we consider the probability of error in sensing by the secondary user. Computer simulation results of the system show the validity of our analysis.