Cooperative communication between cognitive and primary users

The active cooperation between a primary user (PU) and a cognitive user (CU) has the potential of leading to a transmission power reduction and transmission rate increase for both the PU and the CU. Alternatively, the required bandwidth may be reduced and the freed bandwidth may be leased to a group of CUs for their secondary communications. More explicitly, our cooperative protocol allows a CU to serve as a relay node (RN) for relaying the signal of the first PU, which is a source node (SN), to the second PU, which is a destination node (DN). Furthermore, we conceived adaptive turbo trellis coded modulation (ATTCM) for appropriately adjusting both the code rate and the modulation mode according I to the near-instantaneous channel conditions. More specifically, we propose an ATTCM aided two-way relaying cooperative CR scheme that maximises the CU´s own data rate and improves the exploitation of the bandwidth released by the PUs. Our numerical and simulation results show that the bandwidth reduction attained by the proposed two-way relay based CR scheme is more than 80% of the PU´s band.width.