Future mobile and terrestrial communication systems B5G/6G are strongly expected to heterogeneously realize typically diversified performances, i.e. high-data-rate, high-mobility, low-latency, high-capacity, massive-connectivity and low-energy in order to satisfy the highly diversified application requirements. To achieve those goals the operation band of B5G/6G should be primarily in the millimeter-wave (mmW) range. Generation and distribution of mmW with traditional methods is limited by electronic bottleneck and associated complexity. Consequently broad bandwidth, simple, efficient, and cost-effective photonic mmW-over-fiber (mmWoF) transmission systems are solutions for B5G/6G. The spectral purity of mmW carriers is necessary. Numerous approaches have been proposed to generate pure mmW signals. Compared with other technologies, quantum dash or dot (QD) coherent comb lasers (QD CCLs) have great advantages for mmW generation because QD-CCLs with low power consumption and chip-scale integration capacity with silicon can provide multiple highly correlated and low noise optical channels. In this paper we will present our developed InAs/InP QD-CCLs around 1550 nm with the channel spacing from 10 GHz to 1000 GHz and the output power up to 50 mW. By using a C-band QD CCL and based on the single- and dual-optical carrier modulation schemes, an up to 16-Gb/s mmWoF optical heterodyne wireless signal at 28 GHz through a 25-km single mode fiber before the mmW carrier is optically synthesized remotely for detection over a 2-m free space. The data capacity and performance of the proposed mmWoF link can be significantly increased by utilizing a duplex mmWoF link with MIMO and WDM technique, which provides a cost-efficient and promising solution for Terabit/s capacity mmWoF fronthaul systems of B5G/6G networks.
A photonic-assisted multi-functional system that can implement simultaneous distance, velocity and frequency measurement is proposed and experimentally demonstrated. The distance and the radial velocity of a moving target are measured by transmitting a complementarily (V-shaped) linear-frequency-modulated microwave waveform, and by mixing the reflected microwave waveform with the transmitted microwave waveform, two de-chirped waveforms with different carrier frequencies are generated. The distance and the radial velocity are measured by analyzing the de-chirped microwave waveforms. Frequency measurement can also be performed by the system which is done by modulating a received unknown signal on an optical carrier which is mixed with a frequency-sweeping light. By passing the mixed signal through an electrical bandpass filter, short electrical pulses are generated. By measuring the time delay difference between adjacent pulses, the frequency of the unknown signal is measured. The operation of the proposed system is evaluated experimentally. The results show that the distance and velocity can be measured with mean absolute errors of 2.95 cm and 6.09 cm/s, respectively, with a range resolution better than 5.5 cm. The frequency measurement function with the capability of implementing single-tone, multi-tone and broadband signals is verified for an input signal with a frequency ranging from 1 to 20 GHz. The mean absolute error of the frequency measurement is 34.22 MHz.
We propose a novel image-like channelization method that utilizes a convolutional recurrent neural network (CRNN) for channel synthesis to reduce the bandwidth requirements of the electrical hardware. In this study, the spectrum of a 30-GBaud QPSK signal is spectrally sliced and received by four low-speed coherent receivers based on a conventional coherent optical communication system. After the recovery of the trained CRNN, the average error vector magnitude (EVM) of the 30-GBaud baseband signal is improved from over 60% by uncorrected channel synthesis to around 15%.
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