Quadruplex Independent Vector Microwave Signal Transmission Over 100 km Using DSM and Optical Polarization Multiplexing

In this study, we present a novel multi-vector microwave signal generation and detection scheme designed to cater to long-distance multi-user amplifier-less access systems with different service requirements, which provides a promising solution for realizing efficient multi-user access. Utilizing band-pass delta-sigma modulation (BP-DSM) and homodyne detection, we enable simultaneous generation, transmission, and detection of flexible quadruplex independent vector microwave signals, where the carrier frequency and modulation format can be selected arbitrarily and the quadruplex independent vector microwave signals transmitted simultaneously are completely independent of each other without any interference. We validate the flexibility and stability of the scheme through simulations and experiments and successfully achieve non-discriminatory transmission over distances of up to 110 km without the need for optical amplifier and chromatic dispersion (CD) compensation. Using our scheme, a single-polarized optical scenario experimentally verifies the simultaneous generation and detection of a 128 QAM vector microwave signal at a carrier frequency of 10 GHz and 64 QAM at 15 GHz. We use optical polarization multiplexing to experimentally verify the simultaneous generation and detection of quadruplex independent vector microwave signals (a 128 QAM signal at a carrier frequency of 7 GHz, 64 QAM at 10 GHz, 32 QAM at 13 GHz, and 16 QAM at 16 GHz). Since DSM converts high-order QAM signals into digital sequences containing only +1 and -1, the noise tolerance is enhanced, meaning that the transmission performance is consistent over distances of up to 110 km while eliminating the need for optical amplifier. In a dual-polarization scenario, the bit error ratios (BERs) for 16 QAM, 32 QAM, 64 QAM, and 128 QAM vector microwave signals show that error-free transmission is achieved when the received optical power (ROP) is higher than -32, -29, -28, and -28 dBm, respectively. All quadruplex independent vector microwave signals achieve error-free transmission simultaneously when the ROP is higher than -28 dBm. This paper provides an effective solution for flexible access systems in mobile and fixed access networks with different service requirements.