NTT DoCoMo, Japan's biggest mobile telco, has successfully tested 1Gbps transmission speeds using 4G technology in outdoor experiments, taking 4G a step nearer to use in mobile phones, the company said Friday.

In experiments conducted in May, the technology worked at up to 400 metres, according to Miki Nakajima, a DoCoMo spokeswoman.

While the company demonstrated 1Gbps transmission speeds with an earlier version of the same technology last August, that was in the lab, so the latest experiments show the technology is a step nearer to practical usage, she said.

The company's current 3G (third-generation) network offers download and upload speeds up to 384Kbps, and DoCoMo won't build a 4G network until around 2010, she said.

Before 2010, however, the company will be increasing the speed of its 3G network.

From April, it will introduce a technology called HSDPA (High Speed Downlink Packet Access) to its 3G network, which will boost speeds to up to 14M bps, although the faster network will only be available in major cities initially, the company said.

By the end of 2007, DoCoMo will also have decided the technical specifications for an even faster technology called Super 3G, Nakajima said. This will offer up to 100M bps downlink and 50M bps uplink speeds, and the network should be operational between 2008 and 2010, the company said.