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 to the near-instantaneous channel conditions. The ATTCM switching thresholds specifically adjusted for ensuring that the Bit Error Ratio (BER) is below 10 in order to minimize the potential error propagation from the RN to the DN. It was found that the joint design of coding, modulation, user-cooperation and Cognitive Radio (CR) techniques may lead to significant mutual benefits for both the PUs and the CUs. More specifically, we propose an ATTCM aided two-way relaying cooperative CR scheme that maximizes 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 bandwidth. Index Terms Cognitive Radio Network, Cooperative Communication, Relay selection, two-way relay, ATTCM