120-GHz-Band Fully Integrated Wireless Link Using QSPK for Realtime 10-Gbit/s Transmission

This paper describes a 10-Gbit/s fully integrated wireless link for last-one-mile access in optical fiber networks. The wireless equipment employs quadrature phase-shift keying (QPSK) for modulation. The transmitter (TX) head of the link includes a 120-GHz-band QPSK TX module and an encoder board for generating an in-phase and quadrature signal from a 10-Gbit/s optical signal. The receiver (RX) head consists of an RX module using QPSK differentially coherent detection and a decoder board. To obtain sufficient output power for a link distance of over 1 km, we designed a power amplifier (PA) monolithic microwave integrated circuit (MMIC) using a 0.1-mu m-gate indium-phosphide HEMT. The MMIC uses a novel RF pad for high isolation between input and output ports. The measured gain of the amplifier is over 15 dB from 110 to 140 GHz. The saturation output power at 128 GHz is 15 dBm. The TX, RX, and PA modules provide sufficient data-transmission performance: a bit error rate of less than 10 and an error vector magnitude of 10%. The integrated TX head exhibits the 99% power bandwidth of 8.4 GHz and the spectral efficiency is 1.32 bit/s/Hz. We demonstrated real-time 10-Gbit/s building-to-building connection using a new QPSK wireless link over the distance of 170 m.