Demonstration of D-band photonic-assisted terahertz IQ-Mixer wireless communication employing LS-MRC technology with over 2 dB gain

As the demand for higher data throughput continues to grow, next-generation wireless communication systems are expected to deliver per-link data rates in the range of tens to hundreds of gigabits per second. Photon-assisted generation of terahertz (THz) signals can support larger modulation bandwidths in future ultrahigh-speed wireless communication systems. Orthogonal frequency-division multiplexing (OFDM) has emerged as a promising candidate for future THz communication systems owing to its capability to combat frequency-selective fading and suppress inter-symbol interference (ISI). The least-squares (LS) method is widely used for channel estimation due to its simplicity and low computational complexity. However, it is highly sensitive to noise and interference, resulting in limited estimation accuracy. In this work, we proposed an LS maximum ratio combining (MRC) scheme that combines the SNRs of I- and Q-branch pilot-based channel estimations using the MRC technique to enhance the accuracy of channel estimation and equalization. We experimentally demonstrate 16-GBaud QPSK wireless transmission over 4.6 km at 137.5 GHz using a photon-assisted terahertz IQ-mixer communication system. By employing LS-MRC, we achieve more than 2 dB gain, significantly improving link performance. To the best of our knowledge, this is the first experimental demonstration of high-gain performance achieved through the use of I/Q mixer and LS-MRC techniques in a D-band terahertz communication system.