A novel scheme for relay cooperation in interweave cognitive radio systems

In this paper, we investigate the benefits of using cooperative relays in interweave (opportunistic) cognitive radio systems. A novel distributed space frequency (DSF) code for relay cooperation is presented. The code is designed to be a multi-user multi-OFDM channels code. It achieves a cooperative diversity gain of order NL for all users, where N is the number of relays and L is the number of paths in the multi-path fading channel. Simulation results show that using this DSF code by relays in the proposed system significantly increases system throughput. This code depends on transmitting the signal of each secondary user on a number of channels. Hence, each source will be less sensitive to spatial and temporal variations in channels availability which is one of the main problems in interweave cognitive radio systems.