Rate adaptation in cognitive radio links with time-varying channels

In this work we address the optimal rate adaptation problem of a cognitive radio (CR) link in time-variant channels. A secondary user (SU) link detects an idle channel and starts the transmission with the goal of transmitting a given amount of data packets. During the transmission the transmitter dynamically adapts the frames rate, from a finite number of available rates, according to the channel state. If a frame is decoded with error, the corresponding data must be retransmitted in further frames. If a primary user (PU) access the channel during the process, the CR link immediately stops the transmission. The rate adaptation problem is formulated as an infinite-horizon Markov decision process (MDP). We split the problem in a finite number of much simpler MDP problems that can be efficiently solved by conventional MDP solving algorithms. So, the optimal policy and the corresponding maximum probability of successful transmission can be easily obtained.