Monday, February 12, 2018
Conventionally, base stations have been connected by optical fiber. One issue with this approach, however, is that it has been difficult to expand service in areas where it is difficult to install a network of optical fiber cables, such as in densely built urban areas or between areas surrounded by rivers or mountains. Demand for connecting base stations wirelessly instead of with optical fiber is increasing for prompt and flexible installation of wireless networks at large-scale stadiums and event venues with transient crowds numbering in the tens of thousands or during disaster recovery.
High-capacity wireless transmissions need to use a broad range of frequencies. To facilitate this, use of the millimeter-waveband (30 to 300 GHz) is a suitable option, as few competing wireless applications use it. But because the millimeter-waveband uses such high frequencies, designing CMOS integrated circuits for that purpose has been a challenge, as the circuits need to be designed to operate near their limits. It has also been difficult to develop transceiver circuits that modulate and demodulate broadband signals into and out of the millimeter-waveband at high quality and interface circuits that connect the circuit board to the antenna, both at low loss. This research group led by Kenichi Okada of Tokyo Tech had achieved wireless transmission at 56 Gbps in 2016, however, an issue was that the band could not be widened any more due to the higher harmonic signals contained in the carrier wave.
Overview of Research Achievement
The newly developed CMOS wireless transceiver chip (Figure 1) uses technology which broadens the band of transceiver circuits by splitting data signals in two, converting them to different frequency ranges, and then recombining them. Each signal is modulated into a band 17.5-GHz wide and demodulated, with the low-band signal occupying the 70.0-87.5 GHz range and the high-band signal occupying the 87.5-105.0 GHz range. This technology enables high-quality signal transmission over an ultra-wideband signal 35 GHz wide. The newly developed CMOS wireless transceiver chip has carrier generation circuits built in for the 70-GHz and 105-GHz carrier signals required to use this technology. Conventionally, the signal quality was degraded by higher harmonics contained by the carrier generation circuit, however, the newly developed harmonic suppression technology resolved this problem. The signal quality required for multi-level modulation of 16-QAM has been achieved by using a lower-order multiplication technique and combining many stages of amplifier circuits and the built-in higher-harmonic-suppressing filter. Tokyo Tech developed technologies for improving transceiver performance and broadening the band, while Fujitsu Laboratories was responsible for module technology.
This outcome makes it possible to increase the capacity of wireless equipment that can be installed outdoors. High-capacity wireless base station networks will become easy to deploy, even in places where new fiber-optic networks are difficult to install, such as urban areas and places surrounded by mountains or rivers, or for temporary base stations such as for the Olympics. This technology will thereby contribute to providing a pleasant communication environment.
Korkut K. Tokgoz1, Shotaro Maki1, Jian Pang1, Noriaki Nagashima1, Ibrahim Abdo1, Seitaro Kawai1, Takuya Fujimura1, Yoichi Kawano2, Toshihide Suzuki2, Taisuke Iwai2, Kenichi Okada1,*, Akira Matsuzawa1, A 120Gb/s 16QAM CMOS Millimeter-Wave Wireless Transceiver, Session 9, WIRELESS TRANSCEIVERS AND TECHNIQUES, 2018 IEEE International Solid-State Circuits Conference (ISSCC)