Relay, power and subchannel allocations for underlay non LOS OFDM-based cognitive networks under interference temperature

In this paper, we consider the case where two communicating cognitive radio users are not near to each other or have no direct line of sight(LOS). Some secondary users don´t need the entire spectrum available to them because of their traffic demand being low. If we are able to use this unused spectrum to relay the data of other secondary users through these rich nodes, the performance of the system can be improved. In cognitive systems, that are based on OFDM channel, the different resources such as subcarrier pairing, relays to be selected for pairing and powers allocated to relays must be optimized in a way to minimize the induced interference to primary users and maximum throughput is achieved. We propose an algorithm that allocates jointly the different resources with less complexity. Performance of the system, by using the rich nodes as relays, over the OFDM channel after allocating the resources is discussed through the simulation.