As set forth by the International Telecommunications Union's (ITU's) IMT2000 broad set of guidelines for third-generation (3G) Personal Communication Services (PCS) and cell phones, current standards and systems must either evolve, or change completely, to satisfy the new 3G objectives. After nearly 15 years of experience, cell-phone manufacturers and telephony infrastructure companies all have ideas about what the next generation should be like. As we all know, though, more than one path will take us there. That makes the challenges for design engineers particularly exciting or excruciatingly difficult depending upon their point of view.
Just what exactly is a 3G phone? Lest we forget, cell phones have undergone a natural evolutionary process which so far has produced two generations of increasingly capable and complex systems. Today's second-generation (2G) digital phones are already being upgraded to a mid-generational phase known as 2.5G phones (Fig. 1). These new phones implement many features which are objectives for 3G phones. So while we aren't yet at the third generation, we're getting closer through an evolutionary process
Market research studies predict as many as 500 million cellular subscribers by the end of 2001. At that point, the total number of cellular subscribers will actually exceed the total number of hard-line-based subscribers. Many forecast a growth to over one billion subscribers by 2003 or 2005 at the latest. This means steady growth of the cellular business and lots of opportunities for continued product design.
The table summarizes the features and technical specifications of all cell phones to date, from the original Advanced Mobile Telephone Service (AMPS) analog phones to the latest iteration 2.5G phones. Although all of these phones support a common standard, 3G phones could potentially have a common standard. But, that's a real long shot. While efforts are under way to resolve the various conflicts among the different parties, it's expected that 3G phones will support multiple new standards as well as continue supporting those from previous generations, including analog standards.
The ITU didn't define specific interfaces or technical details for 3G phones. Instead, the union put forward a broad set of guidelines stating desirable features and capabilities that virtually everyone agrees with. Where the disagreement lies is in how to achieve them. As usual, the devil is in the details when it comes to addressing the design objectives. But isn't that what engineers are for?
Global Roaming
One design issue is global roaming. This is a good objective as it would permit any new 3G phone to work essentially anywhere in the world. As you deplane from your New York to London flight, you can flip open your phone and make calls immediately.
Neat. Yet while this seems to be a great objective, it probably isn't the most important in the whole scheme of things. Recent surveys of cell-phone users have shown that over 80% couldn't care less about global roaming. It's probably more important for Europeans than for U.S. citizens who really only need U.S. roaming.
The IMT2000 guidelines set the objectives of 144 kbits/s as the minimal data rate achievable from a fast-moving vehicle. A data rate of 384 kbits/s should be possible with pedestrian speed. Furthermore, a 2-Mbit/s rate should be possible from a fixed location. Such high data rates make it possible to achieve all of the desired data and multimedia features suggested by the guidelines.
According to Scott A. Schmok, strategic marketing manager of Motorola's Wireless Infrastructure Systems Division, one really exciting outcome of such high data rates is that 3G phones will have capabilities far greater than fixed hard-line phones, which use the Public Switched Telephone Network (PSTN) and current access methods. These include the Integrated Services Digital Network (ISDN), cable modems, and xDSL lines. It's anyone's guess just what the full implications of this will be.
Already, 2.5G cellular systems are addressing the e-mail and Internet access issues. Results are mediocre at best because of the data-rate limitations of current 2G systems that provide data transfer rates of 9.6 or 14.4 kbits/s. Third-generation systems will provide much higher data rates, making the performance in e-mail and Internet access far more acceptable.
In the meantime, 2.5G enhancements, such as Enhanced Data Rates for GSM Evolution (EDGE), the General Packet Radio Service (GPRS) system, and the High-Speed Circuit Switched Data systems, are expected to provide 3G high-speed data access for the GSM and IS-136 TDMA systems during the late 2.5G period. I might check my e-mail by cell phone, but utilizing it to access the web on a tiny monochromatic screen seems ridiculous. Still, I can picture myself using a laptop computer that's plugged into an Internet-enabled 3G phone. Multimedia applications will be easier and more acceptable when the operating systems and better (larger/color) screens become available at a reasonable cost.
Once high data rates are achieved, many additional multimedia applications become practical. Navigation and location services are an example. The U.S. Federal Communications Commission's (FCC's) mandate for installing an emergency 911 number on telephones is expected to be implemented before the third generation is reached. Known as Enhanced 911 service (E911), the FCC expects 60% of the new cell phones to have E911 capability by Oct. 1, 2001. With the expected higher data rates, even more sophisticated navigation and location services can be employed.
Video is another potential 3G cell-phone application. Along with the higher data rates and new compression algorithms, such as MPEG-4, two-way video becomes a possibility.