The company announced earlier this week that it has managed to achieve a maximum connection rate of 300 megabits per second, and an average rate of 130Mbps, using cutting-edge wireless technologies.
DoCoMo's conducted the test at its research centre in Yokosuka. It involved a receiving unit that was transported in a car moving at 30 kilometers per hour, which connected wirelessly to a number of 4G base stations that were up to one kilometer away.
Two wireless technologies were used by DoCoMo in its testing. Variable Spreading Factor Orthogonal Frequency and Code Division Multiplexing (VSF-OFCDM) provides the downlink from the network, and Variable Spreading Factor Code Division Multiple Access (VSF-CDMA) is used for the uplink.
DoCoMo has been testing these technologies since last year, when it first announced it was exploring 4G. The company's approach uses spread spectrum modulation, in which a packet of data is split up and broadcast across a patch of bandwidth, to allow faster and more robust transmission than is possible otherwise.
DoCoMo had previously said that it would use 4G to give download speeds of 100Mbps, so this week's news suggests that the company is on track to delivering this. However, it isn't expected to launch a commercial service until 2010.
There is also disagreement and uncertainly about exactly what 4G will turn out to be, as a number of vendors are preparing rival technologies in a bid to dominate the future markets.
Supporters of 802.16e, the mobile flavor of WiMax, say it could support mobile connections of 10Mbps or more and provide a viable alternative to the 4G networks of the future.
IPWireless is pushing a rival technology that uses 3G spectrum to offer similar speeds to WiMax. Flarion is behind Flash-Orthogonal Frequency Division Multiplexing, which is being tested by Vodafone in Japan as a faster way of sending data to mobile handsets.