This week, researchers at the Fraunhofer Institute and Karlsruhe Institute of Technology in Germany have successfully transmitted 40 gigabits per second over a one kilometre (0.62 miles) wireless link – a new world record.
The technology, dubbed Millilink, is the same speed as the fastest commercial fibre optic links, and could represent a major breakthrough for carrier backbones, broadband Internet access in rural areas, and ultra-fast last mile access for customers who haven’t had fibre rolled out in their area.
So you have some idea of the scale of this accomplishment, the most advanced Wi-Fi technology, 802.11ad (WiGig) manages around 7Gbps over a distance of a few metres. 802.11ac can theoretically be used over longer ranges, but even with 8-antennae MIMO it maxes out at around 7Gbps.
To achieve 40Gbps (a transfer speed of around 5GB/sec, or a Blu-ray disc in five seconds), the German researchers use a massive, 80GHz block of wireless spectrum between 200 and 280GHz. In comparison, your Wi-Fi router at home probably uses just 20MHz in the 2.4GHz or 5GHz range.
As you can imagine, you can squeeze a lot more data into 80GHz of bandwidth than 20MHz. In fact, with such a vast amount of bandwidth, link speeds well beyond 40Gbps should be obtainable – but for now, it sounds like the researchers are using a fairly rudimentary transmission protocol. With some multiplexing, it shouldn’t be hard to reach 100Gbps or more.
At this point, you might be wondering why Wi-Fi, 3G, and LTE use tiny blocks of low frequencies, when massive amounts of bandwidth are available in the 30-300GHz (EHF, millimetre wave) range. The short answer is: The higher the frequency, the shorter the wave, the more the signal is attenuated (blocked) by obstacles. Longer waves can pass through walls, or bounce around corners – shorter waves can’t.
This means that the Fraunhofer system is really only useful for point-to-point links that are less than a few miles long. Fortunately, that’s more than enough for backhaul between cell towers and ultra-fast last mile Internet access. If the German researchers can commercialise their system, there would be a bevy of telecom giants who would love to roll out 40Gbps+ wireless links, instead of the very expensive task of laying cables in an urban environment.
There’s also another interesting corollary benefit of using such a high frequency: Higher frequencies have a shorter wavelength – and the shorter the wavelength, the smaller the antenna needs to be. In the case of Millilink, the transceiver chip measures just 4 x 1.5mm (it’s pictured above). To generate such high frequencies, Fraunhofer uses its own III-V CMOS process to create transistors that are capable of operating at 300GHz.
Finally, it’s worth noting that faster wireless transfer speeds have been achieved in the lab – “infinite capacity” wireless vortex beams have managed 2.5 terabits per second (64 times faster) over one metre – but this is the first time that such speeds have been obtained in a real-world setting.