It is expected that unused terahertz waves can be applied to high-speed wireless transmission since a wide frequency band can be secured. In this research, we implemented a mixer circuit that applied a unique proprietary high isolation design technology with an Indium phosphide high electron mobility transistor (InP-HEMT). This enlarged the transmission bandwidth, which is a problem in the conventional 300 GHz band wireless front end. It also improved the signal-to-noise ratio (SNR). In addition, using this we realized a 300 GHz band wireless front-end module, and we achieved wireless transmission of 100 Gbps (gigabits per second).
In this research, we realized 100 Gbps wireless transmission with one wave (one carrier), so in the future, we can extend to multiple carriers by making use of the wide frequency band of 300 GHz band, and use spatial multiplexing technology such as MIMO and OAM. It is expected to be an ultra high-speed IC technology that enables high-capacity wireless transmission of 400 gigabits per second. This is about 400 times the current LTE and Wi-Fi, and 40 times 5G, the next-generation mobile communication technology. It is also expected to be a technology that opens up utilization of the unused terahertz wave frequency band in the communications field and non-communication fields.
The details of this technology will be presented at the 2018 IEEE MTT-S International Microwave Symposium which will be held in Philadelphia in the United States from June 10 to 15.
In the carrier frequencies from 28 GHz to 110 GHz that are currently being researched and developed, the transmission bandwidth is limited. So, researchers are studying the use of frequencies which make it easier to expand the transmission band area, from the 300 GHz band to the terahertz wave*2 frequency band. The 300 GHz band has a frequency that is 10 or more times higher than the 28 GHz band which is being studied for 5G, which will be the next generation mobile communication technology. With the 300 GHz band, it will be easier to secure a wide transmission bandwidth. On the other hand, with a high frequency, leakage of unnecessary signals between the ports inside the IC and mounting tends to occur, and so far, it has been impossible to obtain a sufficiently high signal-to-noise ratio (SNR)*3. For this reason, even if a 300 GHz band is used, it is impossible to obtain both a wide transmission bandwidth and a high modulation multi-level value at the same time, and so wireless transmission up to now has remained at the rate of several-tens Gbps.*4
By adding a quarter-wave line and series capacitance, we were able to create a unique design that dramatically improved isolation between ports. The high isolation characteristics realized in this way can suppress unnecessary signals, contributing not only to improvement of SNR, but also to prevention of deterioration of frequency characteristics when the mixer IC is mounted on a module. As a result, we achieved both broadband characteristics and high SNR characteristics for a wireless front-end module.
This work was supported in part by the research and development program on multi-tens gigabit wireless communication technology at subterahertz frequencies of Ministry of Internal Affairs and Communications, Japan.
- *1Speeding up adoption of 5G! Wireless transmission speeds of 120 Gbps achieved February 13, 2018 Tokyo Tech News
- *2Terahertz wave: Just as we use the phrase ‘kilo’ to mean 103 , so we use the term ‘giga’ to mean 109 and the term ‘tera’ to mean 1012 . “Hertz (Hz)” is a unit of a physical quantity called frequency. It indicates how many times alternating electric signals and electromagnetic waves change polarity (plus and minus) per second. That is, one terahertz (1 THz = 1,000 GHz) is the frequency of the electromagnetic wave changing the polarity by 1 × 1012 times per second. In general, a terahertz wave often indicates an electromagnetic wave of 0.3 THz to 3 THz.
- *3Signal-to-noise ratio (SNR) characteristics: Represents the ratio of the power of the signal to the noise
- *4“The world’s-first compact transceiver for terahertz wireless communication using the 300-GHz band—with transmission rate of several-dozen gigabits per second—was developed and experimentally demonstrated high-speed data transmission.” May 26, 2016 NTT press release
- *5InP-HEMT: High Electron Mobility Transistor (HEMT) using an Indium Phosphide (InP) compound semiconductor
- *6“World first: NTT successfully demonstrates 100 Gbps wireless transmission using the new principle of OAM multiplexing NTT” May 15, 2018 NTT press release
- *7Opening of “Ultra-high-speed IC Technology Using an Advanced Compound Semiconductor Process,” February 7, 2017 NTT press release.