The launch of third-generation cellphone systems nearly five years ago promised to transform the speech-and-message handset into an exciting multimedia tool. It is a promise largely unfulfilled, mainly because bandwidths have been limited to between 384 kilobits per second and 2 megabits per second at best. But network operators are looking ahead—admittedly rather far ahead—to get things right with next-generation (4G) technology: it will be an all-packet service that integrates voice and data transmitted at high speeds and capacities [see photo, " "].
With an eye to 4G, Japan’s largest mobile phone company, NTT DoCoMo Inc., announced in February that it had successfully transmitted 2.5 Gb/s of packet data in a downlink to a vehicle moving at 20 kilometers per hour. The field test more than doubled the transmission rates of a similar test performed the previous summer.
DoCoMo, based in Tokyo, owed its success partly to using bandwidth more efficiently and partly to bumping up two key technologies: multiple-input, multiple-output (MIMO) and quadrature amplitude modulation (QAM). MIMO is a data transmission scheme in which different data streams can be sent over the same radio frequency using multiple transmitter and receiver antennas. QAM is a modulation technique that uses variations in signal amplitude to transmit data.
”In terms of our research progress in [4G] wireless technology, we are satisfied,” says Seizo Onoe, vice president and managing director of the radio systems development and IP radio departments in DoCoMo’s R&D Center, in Yokusuka Research Park, 50 km south of Tokyo. ”I believe we are at the top level, globally. But we will probably face many difficult challenges in the development phase and in commercializing the system.”
One immediate challenge is the sheer size of the equipment being used to carry out the recent tests. With no specific large-scale integration chip sets available yet for 4G, the surrogate phones are currently ”as big as a fridge,” says Onoe.
Such obstacles lead some analysts to ask what all the fuss is about. ”When I see these benchmarks for a technology that is so far away, I don’t really pay too much attention,” says Kirk Boodry, global wireless analyst for securities firm Dresdner Kleinwort Wasserstein (Japan) Ltd., Tokyo Branch. ”This is a technology that is probably not going to [be widely implemented] until 2013.”
The 4G system will also require a new infrastructure to support it, though given the high costs, DoCoMo says it may decide to deploy the service, at least initially, only in the most user-dense parts of major cities, where there is going to be a demand for such high data rates.
Still, if the technology pans out, the wait could be worth it. 4G has the potential to provide a rich multimedia experience, including realistic videoconferencing, interactive online gaming, and high-definition video. This is why development of 4G standards is a high priority at the International Telecommunication Union, which already has recommended targets of 100 Mb/s point-to-point download transmission speed when riding in a vehicle and 1 Gb/s when walking.
Those numbers cannot be set in concrete, however, until such fundamental specifications as spectrum allocation and capacity have been agreed on.