Experimental investigation on fiber-wireless MIMO system with different LO at W band

We experimentally demonstrate an optical-wireless transmission system at W band, which can support long-distance wireless transmission and tolerate some frequency difference of the local oscillators (LOs) at the receiver. The generation of millimeter-wave signal is based on the photonic technique by heterodyne mixing of an optical polarization division multiplexing quadrature phase shift keying (PDM-QPSK) signal and an optical LO signal. After 20-km fiber transmission, tens of gigabit-per-second millimeter-wave signals are delivered over multiple-input-multiple-output (MIMO) wireless links by different polarization antennas. Then, analog downconversion is performed before the received signal is demodulated by coherent detection and advanced digital signal processing. Using this system, we experimentally demonstrate the transmission of 18.7-, 29.9-, and 37.4-Gb/s PDM-QPSK wireless signals at W band over 80-, 40-, and 20-m wireless links, respectively, with bit error rate less than the forward error correction threshold of 3.8 × 10^-3. In addition, we investigate the effect of different frequency LOs on the MIMO system performance, finding that the system can tolerate about 1.25-GHz frequency difference for a 10-Gbaud signal. The proposed system can be suitable for the building-to-building broadband connection, in-building hybrid fiber-wireless access networks, and some scenarios that bridge natural obstacles and difficult-to-access terrain.