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An adaptive Turbo Trellis Coded Modulation (ATTCM) aided Cognitive Radio (CR) scheme is proposed for cooperative communication among Primary Users (PUs) and Cognitive Users (CUs). The new 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). More specifically, an active cooperation between the PU and the CU would lead to a reduction of the transmission power and/or to an increased transmission rate for the PU. These benefits may be translated into a reduced transmission bandwidth and the freed bandwidth may be leased to a group of CUs for their secondary communications. Furthermore, our ATTCM scheme appropriately adjusts the code rate and the modulation mode according to the near-instantaneous channel conditions. The ATTCM switching thresholds are chosen to ensure that the Bit Error Ratio (BER) is below 10-6 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 CR techniques may lead to significant mutual benefits for both the PUs and the CUs.
Date of Conference: 1-4 April 2012