Adaptive Turbo Trellis Coded Modulation aided cooperative Cognitive Radio

Abstract

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.