Performance analysis and optimal resource allocation in non line Of sight OFDM-based cognitive networks

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. 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 these “rich” nodes as helpers to relay the other secondary user´s traffic with their unused spectrum, we can improve the performance of the system. 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 should be optimized such that the interference induced to the primary system is minimized and maximum throughput is achieved. We propose an algorithm that allocates jointly the different resources with less complexity. The performance of the system, by using the rich nodes as relays, over the OFDM channel after allocating the resources is discussed through the simulation.