A multi-band microwave vector signal generation and transmission scheme is proposed for mobile fronthaul networks based on dense wavelength division multiplexing (DWDM) and optical tandem single-sideband (OTSSB) modulation. At the distributed cell, two adjacent DWDM channels are divided into a group and both the frequency spacing of the adjacent optical carriers and the adjacent DWDM channels are 50 GHz in the system. A pre-distortion circuit is used for mitigating the modulation non-linearity. At an active antenna unit, when both two DWDM channels in a group are selected, six vector signals centered at different frequencies from 3.5 to 60 GHz are generated. When only one of the DWDM channels is selected, two vector signals centered at 16.5 and 33 GHz or two vector signals centered at 3.5 and 10 GHz can be generated. A simulation is performed to verify the proposed system and its performance by employing 16 quadrature amplitude modulation signals. In the simulation, the error vector magnitudes (EVMs) for different frequency vector signals are around 1% in the back-to-back case. When a section of 25-km single-mode fiber is inserted, the EVMs are still better than 5%.
KEYWORDS: Polarization, Modulators, Silicon carbide, Signal detection, Radio over Fiber, Radio optics, Single mode fibers, Phase shifts, Modulation, Dispersion
A photonic approach for radio-frequency (RF) self-interference cancellation (SIC) incorporated into an in-band full-duplex radio-over-fiber system is proposed. A dual-polarization binary phase-shift keying modulator is used for polarization multiplexing at the central office (CO). A local oscillator signal and an intermediate-frequency signal carrying the downlink data are single-sideband modulated on the two polarization directions of the modulator, respectively. The optical signal is then transmitted to the remote unit, where the optical signals in the two polarization directions are split into two parts. One part is detected to generate the up-converted downlink RF signal, and the other part is re-modulated by the uplink RF signal and the self-interference, which is then transmitted back to the CO for the signal down-conversion and SIC via the optical domain signal adjustment and balanced detection. The functions of SIC, frequency up-conversion, down-conversion, and fiber transmission with dispersion immunity are all incorporated into the system. An experiment is performed. Cancellation depths of more than 39 dB for the single-tone signal and more than 20 dB for the 20-Mbaud 16 quadrature amplitude modulation signal are achieved in the back-to-back case. The performance of the system does not have a significant decline when a section of 4.1-km optical fiber is incorporated.
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