This paper investigates space and polarization multiplexing for multichannel transmission in a 120-GHz band wireless link system. The 120-GHz-band wireless equipment employs Cassegrain antennas with a gain of about 49dBi and cross-polar discrimination of 23dB. When each of two 120-GHz wireless links transmits a 10-Gbit/s data signal in the same direction over a distance of 800m, a bit error rate (BER) of below 10-12 is obtained when the receivers are set 30m apart. When forward error correction and polarization multiplexing are used for each wireless link, we can set two wireless links within 1m of each other and obtain a BER below 10-12. Moreover, we have experimentally shown that the rain attenuation of V- and H-polarization 120-GHz-band signal is almost the same.

We propose a coherent optical and radio seamless network concept that allows broadband access without deployment of additional optical fibers within an optical fiber dead zone while enhancing network resilience to disasters. Recently developed radio-over-fiber (RoF) and digital coherent detection technologies can seamlessly convert between optical and radio signals. A millimeter-wave radio with a capacity greater than 10 Gb/s and high-speed digital signal processing is feasible for this purpose. We provide a preliminary demonstration of a high-speed, W-band (75–110 GHz) radio that is seamlessly connected to an optical RoF transmitter using a highly accurate optical modulation technique to stabilize the center frequencies of radio signals. Using a W-band digital receiver with a sensitivity of -37 dBm, we successfully transmitted an 18.6 Gb/s quadrature-phase-shift-keying signal through both air and an optical fiber.