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.
Best of Luck.