Imagine downloading a two-gigabyte high-definition movie onto your phone within seconds? Or conducting 24 end-to-end video conferences at the same time?

This sort of magic is out of reach of consumers now, but the advent of next-generation mobile communications technologies, 4G, will make it possible.

Engineers and network equipment vendors have started to explore and test 4G.

In China, where 3G is not yet available, the government and firms have begun to prepare for 4G.

What is 4G?

The technology of 4G is envisaged to handle a wide range of supported data rates according to economic and service demands in multi-user environments with peak data rates, as targets for research, of up to about 100 Mbps (megabits per second) for high mobility applications such as mobile access.

It also supports up to approximately one Gbps (one gigabit equals 1,000 Mbps) for low mobility applications such as local wireless access.

That means, under 4G mobile networks, people can download a 2G video file, or the equivalent of 500 songs, on a mobile phone within 20 seconds.

At the latest industry show, firms demonstrated the 4G network - its data transfer speed has surpassed 150 Mbps.

The application of 4G is widely expected to be in high-definition video transfer and high-speed exchange among users.

Global telecommunications regulator ITU hasn't decided the 4G's framework or technological standards but most industry officials define 4G according to speed requirements.

LTE (Long Term Evolution), UMB (Ultra Mobile Broadband) and updated WiMAX all fulfil these requirements and they are the primary 4G technology contenders.

While some analysts, such as Gartner's Sandy Shen, didn't put WiMAX in either 3G or 4G categories, Shen admitted 4G will take some WiMAX technologies such as OFDMA (Orthogonal Frequency-Division Multiple Access) for multi-user functions.