Japan tests 2.5Gbit wireless net

A prototype wireless network capable of delivering 2.5Gbits/sec to users travelling at 20Km per hour is being tested in Japan, according to a US report.

The NTT Docomo system uses a combination of Multiple In Multiple Out (Mimo) technology and a tweaked version of quadrature amplitude modulation (QAM), says a report in MIT's Technology Review .

Mimo, which is used in a the draft 802.11n Wifi standard and turbo versions of existing Wifi products, uses a combination of several antennas and clever processing to boost data rates.

Most current Wifi implementations use up to three antennas on both the base station and client device. The Docomo system uses six on each, says the Technology Review.

This might be viable when transmitting to larger client devices, such as Origami ultra-mobiles. But it is unclear whether Docomo can or will implement Mimo on small mobile phones, something already judged impracticable within the industry.

A cut-down version of 802.11n is being adopted for next-generation Wifi-enabled phones because the devices are thought to be too small to have more than one aerial.

Rather than Mimo, 11n phones will use Multiple In Single Out (Miso): that is several base station aerials transmitting to a single client aerial, which still offers greater bit rates than a one-to-one system.