A team of Japanese scientists have developed a TeraHertz (THz) transmitter that is capable of transmitting digital data at a rate of 105Gbps (Gigabits per second) over a single channel using the 300GHz band, which they claim could power a future generation of Mobile Broadband and Satellite links.
At present most WiFi and 4G Mobile networks prefer to use spectrum in the lower frequency bands of between around 800MHz and 4GHz, while future 5G services will also be able to make use of the higher frequencies up to around 100GHz (note: various 5G solutions have been tested with everything from 800MHz to 73GHz).
Higher frequencies offer a lot of spectrum for carrying more data but related signals also struggle to travel very far and can easily be disrupted, which means that operators need to build a much more complicated / expensive network with lots of distribution points in order to overcome the limitations. Even then there are big question marks over how viable 5G’s predicted speeds (up to 20Gbps – provisional specification) will become outside of the big cities.
Over the past 2-3 years we’ve also seen a growing investment in the development of wireless communications using the even higher frequency TeraHertz (THz) band, such as this one where a team demonstrated a 160Gbps wireless transmission by using one THz emitter and modulating 25GHz spaced 8 channels (20 Gbps per channel) in the 300-500GHz band. At the end of last year another team also achieved something similar (here).
Now a team of scientists working at Hiroshima University and Panasonic claim to have developed a THz transmitter that can push data speeds of 105Gbps over just a single channel in the 300GHz band (using the frequency range from 290GHz to 315GHz), which is a major step forward (here).
Prof. Minoru Fujishima, Hiroshima University, said:
“This year, we developed a transmitter with 10 times higher transmission power than the previous version’s. This made the per-channel data rate above 100 Gbit/s at 300 GHz possible. We usually talk about wireless data rates in megabits per second or gigabits per second. But we are now approaching terabits per second using a plain simple single communication channel.
Fibre optics realized ultrahigh-speed wired links, and wireless links have been left far behind. Terahertz could offer ultrahigh-speed links to satellites as well, which can only be wireless. That could, in turn, significantly boost in-flight network connection speeds, for example.
Another, completely new possibility offered by terahertz wireless is high-data-rate minimum-latency communications. Optical fibers are made of glass and the speed of light slows down in fibers. That makes fiber optics inadequate for applications requiring real-time responses. Today, you must make a choice between ‘high data rate’ (fiber optics) and ‘minimum latency’ (microwave links). You can’t have them both. But with terahertz wireless, we could have light-speed minimum-latency links supporting fiber-optic data rates.”
All of this sounds wonderful, but as usual there are some fairly sizeable catches to the promised performance improvement and as usual the press release doesn’t really touch on any of them. The biggest caveat is distance and indeed many such lab tests have measured the distance of their THz transmissions in centimetres, which is somewhat limiting.
A few teams are now starting to talk in terms of metres, but right now anything up to 10 metres can be a real stretch to achieve and even a big improvement over that still won’t cut it for Mobile communications. The idea of using THz for Satellite links is another highly contentious one because light cloud and rain could easily cause havoc.
Granted a point-to-point Satellite link could conceivably boost its power much more than would be viable for a traditional Mobile network and this might overcome some of the extreme signal attenuation, but even so it’s a daunting task to tackle the very significant physics challenges involved. Not to mention that shrinking all of this down into a portable piece of kit (e.g. Smartphone) is unlikely to be feasible anytime soon.
On the other hand if you would have asked somebody 20 years ago, back when 56kbps dialup modems were cutting edge, whether it would have been possible to send 300Mbps down 200-300 metres of thin copper wire then they would have laughed you out of the room. Today G.fast can do that and so perhaps in the future solutions will be found to make THz based Mobile Broadband and Satellite a reality.
The Japanese team has taken us a big step forward, but they’re still near the bottom of a rather tall staircase. But at least they’re on the staircase rather than just looking at it.
NOTE: At this point somebody usually cries “Radiation.. health danger! Waaaaa!” or something to that affect. However THz are non-ionizing, which means that its photons are not usually energetic enough to knock electrons off atoms and molecules in human tissue (i.e. it shouldn’t be harmful to human health and that’s another reason why using THz is attractive).