Researchers
at the Tokyo Institute of Technology, in association with Japan’s
largest mobile operator, NTT Docomo, have successfully transmitted data
at 10 gigabits per second from a mobile device to a base station, in a
real-world outdoor environment. This is about 2000 times faster than the
5-megabits-per-second upload speed that you can expect to get on an LTE
network in the US. 10Gbps is fast enough to upload a five-minute video
to YouTube in under a second — or a 25GB Blu-ray disc in under three
minutes.
The experiment, carried out in December 2012, utilized
400MHz of bandwidth in the 11GHz band. To achieve a transmission data
rate of 10Gbps, the mobile device was outfitted with eight transmitting
MIMO (multiple-input-multiple-output) antennae, with the data encoded in
QAM64 (quadrature amplitude modulation — the same scheme used by TV
signals, LTE, CDMA, and WiFi). Exact details of this specific experiment
are hard to come by, but a previous similar experiment carried out by
the Tokyo Institute also used OFDM to boost data throughput — again,
OFDM is used by LTE, digital TV, WiFi, ADSL, and just about every modern
networking technology under the sun.
At
this point it’s worth noting that the “mobile device” in question was
actually an NTT Docomo minivan filled to the brim with technology and
topped with a huge array of antennae (pictured below). The minivan
transmitted data at 10Gbps while moving at 9 kmh (5.5 mph). There’s no
mention of how much power the demonstration required, but it was
probably a lot more than a smartphone battery can provide — and, yes, it
might be hard to squeeze those huge, high-gain antennae into the next
iPhone. The engineers say that the same technology could be used to
receive data at 10Gbps, too.
In
the US, the 11GHz band is reserved for wireless, microwave backhaul
between cell towers, but presumably in Japan it is unlicensed. The 11GHz
band is desirable for ultra-fast wireless communications because
there’s so much spare bandwidth up there (400MHz, vs. the puny 20MHz
blocks used by LTE); more bandwidth, put simply, equates to higher
possible throughput. The problem with higher frequencies, though, is
that they are seriously attenuated (weakened) by obstacles and
atmospheric conditions. This is why most long-range transmissions, such
as TV (~100 miles) and cellular (up to 20 miles), use UHF frequencies
between 300MHz and 3GHz. UHF frequencies can bend around hills, aren’t
too bothered by rain, and can penetrate the walls of buildings — but due
to the lack of bandwidth (20MHz, in LTE’s case), there are fairly
restrictive limitations on just how much data you can squeeze into these
lower frequencies.
Presumably, if NTT Docomo is experimenting
with the 11GHz band, their engineers have found a way of using 11GHz
over longer ranges. Alternatively, especially in Tokoyo, NTT might
already have a network of closely-spaced base stations that could be
upgraded to work in the 11GHz band — in urban environments, where there
are lots of obstacles and millions of users clamoring for bandwidth, it
is already standard operating procedure to use lots of smaller cells,
rather than a few big ones.
Either
way, a real-world demonstration of 10Gbps in an urban environment is
impressive, and an exciting glimpse of what we can expect from wireless
networks in the future. For the time being, though, citizens of Tokyo
will have to make do with Docomo’s 100Mbps LTE service, while we in the
US and Europe can simply look on wistfully at the LTE-Advanced spec and pray.
