Terahertz (THz) technology has great potential in the next generation of wireless communications due to its abundant spectrum resources. Electronic device-based systems have very limited device bandwidth when used to generate THz waves, which restricts the growth of system throughput, while photonics-aided THz systems are expensive and complex in structure. To solve this problem, a terahertz system using Delta-Sigma modulation (DSM) is proposed. In the study, a set of 0.15 THz 1024-QAM signals is generated and a 2-meter free-space wireless THz wave transmission system is successfully demonstrated. In addition, inspired by the rapid error propagation in DSM demodulation, a method combining digital signal processing (DSP) with complex-valued neural network (CVNN) is proposed to improve the bit error rate (BER) performance of 1024-QAM signals. When the BER soft-decision is 2×10^-2, the sensitivity of the receiver is improved by 0.5 dB. The method proposed in this paper can effectively solve the problems caused by noise in traditional quadrature amplitude modulation (QAM) to improve the spectrum efficiency of electronic devices with insufficient bandwidth.