Third-generation wireless systems promise mobile voice and wideband data communications, with global roaming anywhere in the world. Because market demand is there, this vision will be realized, but the transition will be more difficult than the hype suggests.
Today's mobile telephony evolved from a variety of incompatible analog cellular telephone and paging systems to an almost as diverse set of digital wireless schemes dubbed the "second generation." Second generation (2G) standards have regional origins.
Europe's global standard for mobile communications (GSM) is now the most pervasive standard with an estimated 330 million users worldwide according to EMC World Cellular Database.
The United States has two of its own standards--IS-95 code division multiple access (CDMA) and IS-136 time division multiple access (TDMA)--plus a variant of GSM. Japan, too, has its own second-generation wireless systems, personal digital cellular (PDC).
Although not as globally pervasive as GSM, the U.S.-based and Japan-based systems have been deployed widely, notably in South America and parts of Asia.
All 2G wireless systems are voice-centric. GSM includes short message service (SMS), enabling text messages of up to 160 characters to be sent, received and viewed on the handset. Most 2G systems also support some data over their voice paths, but at painfully slow speeds usually 9.6 Kb/s or 14.4 Kb/s. So in the world of 2G, voice remains king while data is already dominant in wireline communications. And, fixed or wireless, all are affected by the rapid growth of the Internet.
The wireless community is reacting with generation 2.5 systems that add packet data capability under names like general packet radio service (GPRS) and wireless application protocol (WAP). These schemes can pass subsets of Web pages across limited bandwidth wireless channels to the small screens of WAP-enabled handsets. Meanwhile, developers are focusing on the much-hyped third generation (3G) of wireless systems.
Planning for 3G started in the 1980s. Initial plans focused on multimedia applications such as videoconferencing for mobile phones. When it became clear that the real killer application is the Internet, 3G thinking had to evolve. As personal wireless handsets become more common than fixed telephones, it is clear that personal wireless Internet access will follow. And users will want broadband Internet access wherever they go.
Today's 3G specifications call for 144 Kb/s while the user is on the move in an automobile or train, 384 Kb/s for pedestrians, and ups to 2 Mb/s for stationary users. That is a big step up from 2G bandwidth using 8 to 13 Kb/s per channel to transport speech signals.
The second key issue for 3G wireless is that users will want to roam worldwide and stay connected. Today, GSM leads in global roaming. Because of the pervasiveness of GSM, users can get comprehensive coverage in Europe, parts of Asia and some U.S. coverage. A key goal of 3G is to make this roaming capacity universal.
A third issue for 3G systems is capacity. As wireless usage continues to expand, existing systems are reaching limits. Cells can be made smaller, permitting frequency reuse, but only to a point. The next step is new technology and new bandwidth.
International Mobile Telecommunications-2000 (IMT-2000) is the official International Telecommunication Union name for 3G. Two years ago, people optimistically projected the first IMT-2000 systems would roll out as early as this year. Through 1998 and 1999, the ITU made progress gathering system suggestions from many participants worldwide. Some now expect the launch of 3G trial systems in 2001, but because of the convergence of three regional viewpoints--Europe, Japan and the U.S.--these trials will not be comprised of an ultimate 3G system.
GSM proponents put forward the universal mobile telecommunications system (UMTS), an evolution of GSM, as the road to IMT-2000. Alternate schemes have come from the U.S., Japan and Korea. Each scheme typically involves multiple radio transmission techniques in order to handle evolution from 2G.
Agreeing on frequency bands for IMT-2000 has been more difficult. A broad definition was laid out in 1992, but actual availability of bands varies from country to country.
In May, the ITU Radiocommunication Assembly meeting in Istanbul formalized a grand compromise including five different radio standards and three widely different frequency bands. They are now all part of IMT-2000. To roam anywhere in this "unified" 3G system, users will likely need a quintuple-mode phone able to operate in an 800/900 MHz band, a 1.7 to 1.9 GHz band and a 2.5 to 2.69 GHz band.
This is not completely irrational. While everyone has been fighting over standards, digital signal processor (DSP) technology has been advancing at a great pace. Today's mobile handset is increasingly based on a "soft radio" approach. That is, the radio modulation is computed using software on a DSP so that the computed radio signal is only converted to an actual electrical signal "at the last minute."
It is becoming possible to design quintuple-mode phones to support different protocols and modulation schemes just by changing the active software set. This assumes you have enough memory to hold all five sets of software. With cheaper memory, multi-mode phones are more feasible and are showing up commercially.
Third-generation wireless also requires new infrastructure. There are two mobility infrastructures in wide use. GSM has the mobile access protocol, GSM-MAP. The North American infrastructure uses the IS-41 mobility protocol. These protocol sets define the messages passed between home location registers and visitor location registers when locating a subscriber and the messages needed to deal with hand-offs as a subscriber moves from cell to cell.
3G proponents have agreed on an evolution path so that existing operators, running on either a GSM-MAP or an IS-41 infrastructure, can interoperate. But the rest of the landline infrastructure to support IMT-2000 will be in flux in the near future.
With the advent of mobile Internet access, suddenly the circuit-based backhaul network from the base station and back has to significantly change. 3G systems are IP-centric and will justify an all-IP infrastructure.
Since the hot new application for wireless systems is Internet access, 3G concepts are being glued onto 2G systems. 2.5G protocols include GPRS and WAP. WAP defines how Web pages and similar data can be passed over limited bandwidth wireless channels to small screens being built into new mobile telephones. NTT DoCoMo's "i-mode" provides an equivalent service in Japan. At the next lower layer, GPRS defines how to add IP support to the existing GSM infrastructure. GPRS provides both a means to aggregate radio channels for higher data bandwidth and the additional servers required to off-load packet traffic from existing GSM circuits.
There will be no flip to 3G, but rather an evolution. And, because of the practical need to re-use the existing infrastructure and to take advantage of new frequency bands as they become available, that evolution will look a bit different depending on where you are. The very definition of 3G is now an umbrella, not a single standard.
In the next two years we will hear a lot about 3G rollouts. These "rollouts" will be a mixture of 2.5G and 3G trials with a large dose of hype. However, the industry is moving in the right direction towards a worldwide, converged, network.
Changes in the backhaul infrastructure are being driven hard by the need for Internet access, so 3G will evolve to a pure IP infrastructure eventually. Meanwhile, ever-improving DSPs will allow multi-mode, multi-band telephones that solve the problem of diverse radio interfaces and numerous frequency bands. When one handset provides voice and data anywhere in the world, that will be 3G no matter what is running behind the scenes.
Brough Turner (rbt@nmss.com) is senior vice president, chief technology officer and co-founder of Natural MicroSystems Corp. in Framingham, Massachusetts.