Power Allocation for Cognitive Radio Systems Based on Nonregenerative OFDM Relay Transmission

Cognitive radio (CR) is a promising concept for improving the utilization of scarce radio spectrum resources. Orthogonal frequency division multiplexing (OFDM) is regarded as a potential transmission technology for CR systems. This paper applies relay technology to such OFDM-based CR system and investigates the power allocation over the frequency subchannels at the source and relay to maximize the total rate for the cognitive system while keeping the instantaneous interference introduced into the primary user below a certain threshold. An alternate, separate optimization of source and relay power allocation algorithm is presented. Based on simulation results, relay technology greatly improves the reliability of the cognitive system with an interference level doing no harm to the primary user and our proposed power allocation algorithm achieves a better capacity and BER performance than the uniform one.