Delivering DVDs in Seconds

Japan's NTT DoCoMo is testing a network that could send DVDs to handheld devices in about 10 seconds. Here's how they do it.

NTT DoCoMo in Japan, one the world's leading mobile providers, recently announced a prototype wireless network that could send data packets at 2.5 gigabits per second -- fast enough to download a DVD movie in between 7.5 and 10 seconds -- to a mobile device traveling at 20 kilometers per hour.

If their prototype wireless technology can produce even a fraction of that 2.5-gigabit transfer rate in real-world applications, it would vastly enhance mobile functions -- allowing video telephony, robust Internet connectivity, and streaming media services, while at the same time extending the range of traditional voice calls.

These high-speed data networks, along with increasingly powerful mobile handsets, have the potential to supplant the use of desktop computers -- a trend that's already occurring in some Asian countries. This potential market has DoCoMo, along with almost every other major wireless player, including Motorola, Samsung, and Qualcomm, scrambling to develop their own technology for the next generation of wireless networks, often labeled "4G."

DoCoMo's demonstration gives a glimpse into the two types of technology that will most likely be adopted to increase bandwidth and range: MIMO, which is applied to network base stations and mobile devices, and QAM, which loads more data onto radio waves.

MIMO (multiple input, multiple output) uses multiple antennas to send and receive data, as well as specific coding that scrambles and unscrambles the signals produced by those antennas (see "Faster, Farther Wi-Fi"). A base station that uses MIMO technology has multiple antennas that simultaneously receive and send data to and from wireless devices. Unlike base stations with a single antenna, those with MIMO use the multiple antennas to create a number of intertwining channels through which data moves. The jumbled signals are untangled by a "signal processing" that sorts through the bits.

Because MIMO base stations can handle many more data streams than single antenna wireless stations, there's more bandwidth and built-in redundancy, which increases network reliability and range, says Rob Gilmore, senior vice president of engineering at NextWave Wireless. By deploying MIMO routers, a mobile network such as DoCoMo's 4G can increase the amount of data sent and received, as well as increasing the range, he says.

Most MIMO routers have two or three antennas. In DoCoMo's demonstration, the router as well as the receiver used six antennas to produce rates of 2.5 gigabits per second, says Satoru Kawamura, a company representative. Tripling the number of antennas on a MIMO access point and receiver can triple the amount of bandwidth of the network, says Gilmore.