Photonics-Assisted mmWave Wireless Transmission System With Sampling Frequency Offset-Based Channel Estimation

Photonics-assisted millimeter-wave (mmWave) technologies, capable of supporting large signal bandwidths, hold great promise for future ultrahigh-speed wireless communication systems. Optical device-based intensity modulation, photodetector-enabled mmWave generation, and envelope detector (ED)-aided systems offer broadband signal transmission with reduced cost, system complexity, and carrier frequency drift. In this work, we propose a novel method to analyze the characteristics of sampling frequency offset (SFO) and leverage these properties to estimate the time-domain impulse response of a 145-GHz D-band mmWave intensity-modulation envelope-detection system. The proposed estimation method facilitates arbitrary sampling rate and timing estimation of the system’s time-domain impulse response. The validity and accuracy of the method are demonstrated through three key aspects: the frequency-domain shape of the estimated impulse response, the equalization performance, and the spectral characteristics of the constructed equalizer. The signal equalizer based on this method outperforms traditional adaptive blind equalization algorithms and training-sequence-based equalizers. In addition, the proposed estimation method is shown to be minimally influenced by the modulation format of the transmitted signal. Using this method, we successfully achieve reliable transmission of a 30-GBaud four-level pulse amplitude modulation (PAM-4) signal over a 50-m free-space photonics-assisted D-band 145-GHz mmWave system with intensity-modulation envelope detection. Finally, we illustrate how SFO, traditionally viewed as a source of signal degradation, can be harnessed as a resource to enhance system performance.