Demonstration of 200-m Wireless Transmission in Photonics-Aided Terahertz 2 × 2 MIMO System Utilizing MRC Technology for OFDM Signals

The photonics-aided terahertz (THz) signal generation method has the advantages of large available bandwidth and easy integration with fiber optic networks. However, THz wireless transmission has drawbacks, including spreading loss and absorption loss, resulting from its high-frequency characteristics, which considerably restrict the transmission distance. It is essential to use antenna diversity methods, such as multiple-input multiple-output (MIMO) technology, to combat these impacts. Meanwhile, an orthogonal frequency division multiplexing (OFDM) scheme is employed to resist dispersion effects in fiber optic links and multipath fading in wireless links. Discrete Fourier transform-spread (DFT-s) technology reduces the PAPR of OFDM signal and alleviates high-frequency power attenuation. Furthermore, an advanced post-DFT maximum ratio combination (MRC) algorithm combined with a $2\times 2$ MIMO structure is designed for DFT-s OFDM wireless transmission to fully utilize spatial dimension resources to improve signal-to-noise ratio (SNR). Therefore, we experimentally demonstrate photonics-aided THz $2\times 2$ MIMO 200-m wireless transmission at 300 GHz. The 16/64QAM DFT-s OFDM signals are successfully transmitted at the 99-/137-Gbit/s net rate. The SNR gain between $2\times 2$ MIMO and $1\times 1$ SISO can be up to 5.1 dB. It is the first experimental demonstration of antenna diversity technology applied to the photonics-aided THz $2\times 2$ MIMO transmission system, contributing to large-capacity and long-distance THz wireless communication.