The evolution of wireless networks, from simple first-generation analog through 2G, 2.5G, and 3G, involve enormous complexity and rapid change. They also involve convergence, for 3G is the long-sought juncture at which the GSM and CDMA evolutionary paths come together into a single, official, globally roamable system.
As defined by a standards body called the Third Generation Partnership Program (3GPP), a global wireless standard called the Universal Mobile Telephone Standard (UMTS) should be firmly in operation by 2005. UMTS will have circuit-switched voice and packet-switched data. 3G networks must be able to transmit wireless data at 144+ Kbps at mobile user speeds, 384 Kbps at pedestrian user speeds, and an impressive 2+ Mbps in fixed locations (home and office).
This flexibility derives from UMTS' two complementary radio access modes: Frequency-Division Duplex (FDD), which offers full mobility and symmetrical traffic, and Time-Division Duplex (TDD), which offers limited (indoor) mobility and handles asymmetric traffic, such as web browsing.
Ultimately, UMTS itself will evolve into an "all IP" or "end-to-end IP" network, or at least a network in which IP is used as much as possible.
UMTS is Europe's answer to an earlier (and ongoing) project, the ITU-T's International Mobile Telecommunications 2000 (IMT-2000), which stakes out frequencies for future use. Amusingly, the independent-minded allies of the U.S. and Japan refer to 3G as IMT-2000 (not UMTS), despite the fact that the Europeans, to keep the Americans in the loop, established a separate Third Generation Partnership Project Number 2 (3GPP-2) body.
Furthermore, the exact line separating 3G from its predecessors has blurred lately, especially since the highest-end 2.5G technology is called "3G" by both manufacturers and the IMT-2000. The great dream is that all of the high-end technology will interoperate with UMTS under the general term "3G."
A 3G phone is supposed to handle more than simple voice mobility. Cramming streaming color video, multimedia messaging, and broadband Internet surfing into a single device may make some of the first true 3G phones a bit bulky, a throwback to the 1980s.
Indeed, the cell phone should run as many timesaving intelligent agents as possible. When you must use the phone, you should be able to efficiently use voice, data, and touch-sensitive screen simultaneously. In fact, Cisco, Comverse, Intel, Microsoft, Philips, and SpeechWorks recently formed the Speech Application Language Tags (SALT) Forum to develop a device- and network-independent de facto standard to do just that.
Aside from the mobile phone, the wireless broadband-enabled laptop and PDA will also play a role in the wireless future. Some people may prefer making VoIP calls from a laptop in a higher-bandwidth, fixed-wireless scenario (an animal different from a pure mobility play), while others may prefer a more portable, integrated cell phone/PDA.
THE FAMILY TREE
In the 1980s, some of us were using thick-as-a-brick analog phones. In the early 1990s, things began to change. At the moment, we're in a digital 2G wireless world. The Global System for Mobile Communications (GSM) is the world's most popular 2G mobile standard, having conquered Europe, Asia, Australia, and New Zealand, and is spreading through the U.S. thanks to an aggressive marketing campaign by Voice-Stream. GSM operates on the 900 mHz and 1.8 gHz bands worldwide except for the Americas, where it occupies the 1.9 gHz band.
Other 2G systems include the Integrated Digital Enhanced Network (iDEN), which Motorola (Arlington Heights, IL - 847-632-2560, www.mot.com) launched in 1994. iDEN runs in the 800 mHz, 900 mHz, and 1.5 gHz bands. GSM and iDEN use Time Division Multiple Access (TDMA), which involves timesharing a channel somewhat like a T1 does.
Another 2G system, cdmaOne (also called IS-95A, which debuted in 1996), doesn't use timesharing. It uses a unique spread-spectrum technology, Code Division Multiple Access (CDMA), which relies on a special encoding technique to let lots of users share the same pair of 1.25 mHz bands.
Qualcomm owns most of the CDMA-related patents. Major cdmaOne carriers include Verizon and Sprint in the U.S.; Bell Mobility and Telus in Canada.
Unfortunately, typical data transmission rates for 2G networks range between 9.6 and 14.4 Kbps. This isn't great for web browsing and multimedia applications, but okay for SMS - short (160 Latin character) text messages.
BETWEEN TWO G'S
The major improvement 2.5G brings over 2G is the introduction of packet-switched data services that conserve bandwidth even though they're "always on." This means that when you use a data service over 2.5G you only occupy bandwidth when you actually send and receive packets (shades of the Internet!). Voice calls on 2.5G, however, are definitely still circuit-switched, and use a constant bandwidth.
On the GSM path, an effort was made to send packets over GSM circuit-switched voice channels, called High Speed Circuit Switched Data (HSCSD). More powerful, however, is General Packet Radio Service (GPRS), a GSM-based packet data protocol that can be configured to gobble up all eight timeslots that exist in a GSM channel. With some software and hardware upgrades, GPRS can commandeer existing spectrum, servers, and billing engines.
GPRS can support a 115 Kbps data rate, though 50 to 60 Kbps is more likely in practice, especially since the packets must contend for the same bandwidth as GSM circuit-switched voice, and providers will tweak the bandwidth based on the number of subscribers as they try to find a profitable mix of number-of-users versus bandwidth-per-user.
To enjoy both GPRS data and GSM voice, one must have a new Subscriber Terminal or "TE" (mobile phone, PDA, PC or laptop card) that supports packets as well as voice. One also needs to upgrade software at the GSM Base Transceiver Site (BTS) and the Base Station Controller (BSC). The BSC also must have a new piece of hardware called Packet Control Unit (PCU), which helps direct data traffic to the GPRS network. Also, databases such as the Home Location Register (HLR) and the Visitor Location Register (VLR) should be upgraded to register GPRS user profiles.
Existing GSM Mobile Switching Centers (MSCs) don't handle packets, so two new network elements, collectively referred to as GPRS Support Nodes, must be introduced. The Serving GPRS Support Node (SGSN) delivers packets to mobile devices around the service area. SGSNs query HLRs for GPRS subscriber profile data, they detect new GPRS mobile devices entering a service area, and record their location.
The second new element is the Gateway GPRS Support Node (GGSN), which is an interface to external Packet Data Networks (PDNs) that work with Protocol Data Units (PDUs). One or more GGSNs may support multiple SGSNs.
