An Optimized M-ary Amplitude Phase Shift Keying Scheme for Ultrabroadband Terahertz Communication

Terahertz (THz) band (0.1 THz to 10 THz) communication is envisioned as a key technology to satisfy the demand for Terabit-per-second (Tbps) links in the sixth generation (6G) wireless systems and beyond. Significant progress within different device technologies is finally closing the so-called THz technology gap. However, there are notable limitations relating to the efficiency and reliability of THz devices. In order to overcome the challenges, innovative ways of digital signal processing, as well as waveform design techniques, need to be considered. In this context, to simultaneously overcome the limitations due to peak to average power ratio (PAPR) and reduce the effective symbol error rate (SER), both while using a high-order modulation scheme for ultrabroadband THz communication, the utilization of m-ary amplitude phase shift keying (M-APSK) is proposed. After optimizing the constellation with the number of rings as a constraint, the performance of the scheme is compared with M-ary quadrature amplitude modulation (M-QAM) and M-ary phase-shift keying (M-PSK) in terms of SER and PAPR. As a proof of concept, experimental results are provided to demonstrate the performance of the proposed scheme in the 120-140 GHz band, achieving bit-rates of up to 50 Gbps on a single-carrier, single-channel tens-of-meters-long link. This constellation will serve as a building block for multi-carrier modulations able to reach the 1 Tbps goal.