Paul McCartney penned "The Long and Winding Road" a decade before the Advanced Mobile Phone System (AMPS) cellular service was launched, but this lyric perfectly embodies the complex history behind today's 3G wireless. In Part 1 of this tip, we sort out the cellular alphabet soup to understand where 3G came from. In Part 2, we will discuss how to select a 3G wireless service.
In the beginning: 1G
First-generation cellular took off in 1982 with the deployment of commercial AMPS service. AMPS used Frequency Division Multiplexing Access (FDMA) to carry analog voice over several hundred channels within the 800 MHz frequency band. Other incompatible 1G services emerged around the world (e.g., TACS, NMT), and the total number of cellular subscribers grew. But each carrier delivered service to a limited serving area, there were no standards to enable roaming, and channel capacity was rapidly being exhausted.
Going global: 2G
By the early 1990s, carriers began to work together to overcome 1G limitations by defining mobile telephony standards. Two major second-generation technologies emerged: GSM and CDMA. Both increased system capacity by digitizing voice, but each used a different approach to spread digital signals across the available spectrum.
- Global System for Mobile (GSM) standards used Time Division Multiple Access (TDMA) to multiplex up to eight calls on each 200 KHz channel.
- After the first GSM service was launched in 1992, many European and Asian countries quickly adopted GSM as a common mobile telephony platform, using channels allocated primarily from the 900 and 1800 MHz bands.
- Around the same time, the IS-95 standard emerged in the U.S., using Code Division Multiple Access (CDMA) to spread signals across a much wider portion of the 800 MHz band with a coding scheme that transmits up to 64 calls simultaneously over the same channel without interference. Commercial service based on IS-95 was first offered in 1996 under the tradename cdmaOne.
These standards helped bring order to the cellular market -- the same GSM phone could be used in several countries and (later) roam between GSM carrier networks. But there were still other competing services, such as D-AMPS (a North American digital version of AMPS), iDEN (a Motorola/Nextel TDMA-based service), and carriers in the U.S. and elsewhere that deployed GSM on different bands. To bridge this gap, dual and tri-band phones emerged – for example, using PCS 1900 (a North American GSM service) inside the U.S. or GSM at 1800 MHz internationally.
A gradual evolution: 2.5G
In addition to voice, 2G services could also carry digital data. For example, GSM networks could use spare bandwidth to support circuit-switched data sessions at 9.6 to 14.4 Kbps. That proved sufficient for short message delivery but far too slow for most Internet applications and multimedia content delivery. To achieve much higher rates and native support for TCP/IP applications, those old 2G networks had to be replaced with new packet-switched networks that employ broadband radio technologies.
While brand-new third-generation standards were being defined to meet those needs, carriers became impatient. As a result, several near-term improvements were made to existing 2G networks, boosting wireless data rates to achieve v.90-like throughput:
- In 2000, carriers using GSM began to roll out General Packet Radio Service (GPRS), delivering packets at rates up to 114 Kbps. In 2003, GSM was further extended by Enhanced Data Rates for Global Evolution (EDGE), with a top rate of 384 Kbps. But these max. rates are only theoretical. In practice, a GPRS user may see 30-60 Kbps, while an EDGE user may see 75-150 Kbps, depending on how busy the network is.
- Starting in 2002, carriers with CDMA networks started to offer CDMA2000 1x (also known as 1xRTT, for One Times Radio Transmission Technology). Some argue that CDMA2000 1x is 3G because it uses the new IS-2000 signaling standard, but we classify it as 2.5G because of its data rate (144 Kbps in theory, 30-70 Kbps in practice).
Getting there: 3G
Today, many carriers have deployed "true 3G" services in major cities across the world. Those old 2G networks based on GSM and cdmaOne are now being replaced by new 3G networks that employ their descendants: UMTS and CDMA2000.
- The Universal Mobile Telecommunications System (UMTS) is composed of a core network (architecturally similar to GSM/GPRS) and a radio access network based on Wideband CDMA (WCDMA). UMTS is theoretically capable of downlink speeds up to 1.92 Mbps (in practice, users see about 384 Kbps). UMTS was first deployed in 2001, but many carriers have moved to a refinement called High Speed Downlink Packet Access (HSDPA), which boosts theoretical downlink speed to 10 Mbps (in practice, users see 400-700 Kbps, with bursts up to 1 Mbps).
- CDMA2000 is the tradename applied to networks that use the new IS-2000M standard. CDMA2000 1x was the first step in this direction. Today, CDMA2000 1xEV-DO (Evolution – Data Optimized) can deliver packet data at downlink speeds up to 2.4 Mbps. A proposed follow-on, CDMA2000 1xEV-DV (Evolution – Data Voice) promised to deliver both data and voice at downlink speeds up to 3 Mbps. EV-DV plans have been largely pre-empted, however, by an EV-DO upgrade (1xEV-DO Rev. A) that will not only boost downlink speed but will greatly increase uplink speed and reduce latency. In practice, today's EV-DO users may experience 400-700 Kbps, with megabit bursts.
This evolution is likely to continue with even newer radio network technologies such as High-Speed Uplink Packet Access (HSUPA). Internally, carrier network architectures are expanding the use of IP, guided by IP Multimedia Subsystem (IMS) standards. Eventually, even mobile voice calls will be carried over all-IP carrier networks.
Jumping on the 3G bandwagon
Many consumers find this flood of similar-but-different acronyms terribly confusing, but it really all boils down to a choice between two major technology families, where you join the evolutionary chain, and which products and services you'll choose to support the applications that you intend to use. In Part 2 of this tip (Going 3G: Can you hear me now?, we explore which carriers offer these 2.5 and 3G services and where, and factors to consider when making your selection.
This was first published in June 2006