DSM-enabled hybrid transmission of SC 32-512QAM signal and OFDM 32-512QAM signal over a single-input single-output wireless link in the 220 GHz terahertz band

Terahertz (THz)-band communication systems have demonstrated significant application potential in sixth-generation (6G) mobile communications, owing to their ultra-wideband transmission capabilities and flexible deployment characteristics. Continuous advancements in high-order modulation, long-distance transmission, and efficient signal processing have further accelerated the development of these systems. Bandpass delta-sigma modulation (BP-DSM) technology enables high data rates and superior spectral efficiency across various wireless transmission bands, thereby offering robust support for the effective transmission of high-order quadrature amplitude modulation (QAM) signals in the THz band. The simultaneous transmission of high-order single carrier quadrature amplitude modulation (SC-QAM) and orthogonal frequency division multiplexing quadrature amplitude modulation (OFDM-QAM) signals based on DSM technology not only significantly enhances the spectral efficiency of communication systems but also dramatically improves their flexibility, making them more adaptable and competitive in multi-user scenarios in the THz band. In this paper, we report the successful demonstration of simultaneous wireless transmission of SC-QAM and OFDM-QAM signals based on 1-bit BP-DSM technology in the 220 GHz THz band. Furthermore, we systematically investigate eight possible combinations of the SC-QAM and OFDM-QAM signals. At the transmitter, one high-order SC-QAM signal and one OFDM-QAM signal are converted into a single SC-QPSK signal through two parallel BP-DSM modulators, leveraging digital signal processing techniques. The SC-QAM and OFDM-QAM signals are mutually independent. Subsequently, the SC-QPSK signal is up-converted to the THz band via a two-stage cascaded digital-analog hybrid up-conversion architecture, enabling wireless transmission of the SC-QPSK signal over a single-input single-output wireless link in the 220 GHz THz band. At the receiver, a two-stage cascaded analog-digital hybrid down-conversion structure is employed, integrated with SC-QPSK digital coherent demodulation and digital bandpass filtering, to reliably recover the original high-order SC-QAM and OFDM-QAM signals from the received THz-band SC-QPSK signal. The experimental results demonstrate that the bit error rate (BER) of the received THz-band SC-QPSK signal remains unaffected by variations in the modulation orders of the SC-QAM and OFDM-QAM signals, and that the SC-QAM and OFDM-QAM signals maintain mutual independence during transmission with no observable crosstalk. In addition, compared to the SC-QPSK signal, the higher-order SC-QAM and OFDM-QAM signals exhibit a slower rate of BER degradation as the wireless transmission distance increases.