Link Selection Strategies for Buffer-Aided Relaying and Overlay Cognitive Radio Systems with Adaptive Discrete Rates

In this paper, aiming at maximizing the system throughput link selection strategies for buffer-aided two-hop relaying and overlay cognitive radio systems which employ discrete-rate adaptive modulation and coding (AMC), have been proposed. At first, a simple tree-node relaying scenario is considered in which the intermediate node (relay) equipped with a buffer and AMC, facilitates data communication between a source (also equipped with AMC) and a destination node in a two-hop communications system. For this scenario we formulate the optimal link selection problem as an integer programming problem and subsequently propose a genetic-based approximate solution using relaxation techniques. We then extend the simple buffer-aided relaying model to an overlay cognitive radio scenario comprising a pair of primary source-destination nodes and a pair of secondary (cognitive) source-destination nodes. In this model, the cognitive source node equipped with a buffer, acts as a relay to facilitate data transmission in the primary system and by this way it finds some opportunities to transmit its data to the cognitive destination node. Hence we optimize the cognitive link throughput by proposing a genetic-based link selection strategy which satisfies a target predefined average rate for the primary system. Numerical and simulation results are provided to evaluate the performance of the proposed link selection strategies.