Influence of the channel model in the optimum switching points in a cognitive radio network combined with adaptive modulation

The combination of cognitive radios with adaptive modulation has been studied in order to improve the performance of wireless networks. The key issue when defining the performance of an adaptive modulation system is finding the switching point between neighboring modulations. In this paper, we investigated the performance of a Cognitive Radio Network, emphasizing the secondary user's performance, and we analyzed the influence of a Nakagami-m fading channel model in the optimum switching points. Users are modeled by a priority M/G/1 queue, where the primary user has priority. The switching points are computed by a performance metric called Power Metric, defined by the ratio between the throughput and the delay in the system. Two cases are analyzed: An unlimited retransmission scenario, where all packets are transmitted correctly; and a second one where the number of retransmissions is limited.