DoCoMo also tweaked a commonly used form of signal modulation called QAM (quadrature amplitude modulation), which increases the number of bits that a single radio wave contains. Data is encoded on radio waves by altering characteristics of the waves themselves: the amplitude of wave peaks, and the phase, or relative position of the peaks compared with waves of the same frequency. DoCoMo used an advanced form of QAM that adjusted the amplitude and phase of each wave to 64 different levels. Traditionally, says Gilmore, the phase and amplitude of the radio wave is adjusted only to four levels. Increasing these levels, as DoCoMo has done, is partially responsible for its fast download rate.
There remain technical challenges to pumping up the capabilities of MIMO and QAM in a real-world setting. It could be difficult to design a consumer-friendly MIMO handset, says Bill Krenik, wireless advanced architectures manager at Texas Instruments. One of the main reasons is that sorting through data that come from different paths can be processor intensive, which can quickly drain a battery – not good news for mobile device users.
Also, Gilmore notes, QAM becomes less effective as engineers try to cram more information onto a single radio wave. He says the signal “starts to become more fragile,” which could mean that in a real-world situation transmissions could be lost.
Aside from the technical challenges of 4G networks, other business and political issues may also keep it shelved for at least a few more years. For one, no 4G standards are currently in force. Moreover, corporations could be unwilling to shell out cash on new, upgraded networks when the old ones still haven’t paid for themselves. In the United States, especially, 3G networks have been slow to catch on, mainly because providers wanted to be sure there was a market for the extra features 3G could provide, such as Internet access.
Yet, the growing demand for smart phones proves that, if you build better networks, consumers will use them. Krenik believes that when the transition to 4G occurs – some analysts estimate it will be after 2013 in the United States – the mobile device will become an even more important part of daily life, providing a combination of services, from e-mail and gaming to voice and video.
“Voice was the killer app for the first and second generations of phones,” says Krenick. “For a while we thought the Internet would be it for the third generation; now I think we’re maturing as an industry and realizing that there really isn’t [another] killer app – with high-speed data, it’s a killer experience.”