Decode-and-Forward Cooperation-Aided Triple-Layer Turbo-Trellis-Coded Hierarchical Modulation

Hierarchical modulation (HM) is widely employed across the telecommunication industry. The potential application of the coded HM scheme in cooperative communications has drawn much interest. In this paper, a twin-relay-aided triple-layer cooperative communication system is proposed. The system amalgamates rate-1/2 TTCM, triple-layer HM-64QAM, and twin-layer SPM-16QAM schemes in the context of cooperative communications. We have optimized the entire system based on the HM ratio pair (R₁, R₂), the superposition modulation (SPM) weighting pair (α, β), and the positions of the two relays. The simulation results show that our optimized system is capable of reliably transmitting a triple-layer HM-64QAM signal with the aid of two time slots at an average signal-to-noise ratio of 6.94 dB per time slot.