A Wireless Taxonomy

Global System for Mobile Communications (GSM): A digital cellular phone technology that uses TDMA transmission techniques, it is sometimes referred to as Wideband TDMA. GSM is a circuit-switched system that divides each 200kHz channel into eight 25kHz time-slots. GSM operates in the 900MHz and 1.8GHz bands in Europe and the 1.9GHz PCS band in the US. Unlike CDMA or TDMA, GSM defines the entire cellular system, not just the air interface. GSM also supports short messaging service (SMS), which enables text messages of up to 160 characters in length to be sent to and from compatible phones. SMS is probably the most successful wireless data service in the world at the moment. The GSM Association has said that around 3 billion SMS messages are sent each month. GSM supports data transfer speeds of up to 9.6 kbit/s and has become the de facto standard in Europe and Asia. Over 80 percent of the world’s mobile phone subscribers use GSM-compatible phones.

Code-Division Multiple Access (CDMA): A "spread spectrum," digital, cellular, air interface technology mainly used in the U.S. and parts of Asia, such as South Korea. CDMA sends multiple signals or streams of information at one time as a single signal and then unravels the separate strands at the receiving end. CDMA operates in the 800MHz band and 1.9GHz PCS band and supports data transfer speeds of up to 14.4 kbit/s.

Time Division Multiple Access (TDMA): This air interface technology is used in GSM, as a digital upgrade of the AMPS analog system in the U.S. and as the basis of Personal Handyphone System (PHS) in Japan. TDMA is especially popular in the Americas. The technology divides each cellular channel into three time slots, tripling the data capacity from analog technology. TDMA was first specified as a standard in EIA/TIA Interim Standard 54 (IS-54). IS-136, a version of IS-54, is the U.S. standard for TDMA for the 850MHz and 1.9 GHz spectrums. PHS was first introduced in Japan in 1995; intended as a worldwide standard, it never made it outside of the domestic market. Using the PHS Internet Access Forum Standard (PIAFS), PHS provides up to 64 kbit/s of data transfer.

Integrated Digital Enhanced Network (iDEN): iDEN is a proprietary version of the digital TDMA system developed by Motorola Inc. The technology has proved something of a dead end, even though it can support both packet- and circuit-switched data and offers data transfer rates of up to 10 kbit/s.

Cellular Digital Packet Data (CDPD): A wireless data-only packet overlay for the existing analog AMPS network in the U.S., CDPD shunts data over unused intervals in the voice channels. It has a data transfer rate of 19.2 kbit/s. CDPD networks cover about 90 percent of the U.S..

These are the major 2.5G air interfaces:

General Packet Radio Service (GPRS): A packet-based extension to GSM networks that has an always-on connection to the Internet and offers data transfer rates of up to 114 kbit/s. However, early adopters have found that the real-world data rates are between 20 kbit/s and 40 kbit/s. In GPRS, communication channels are allocated on a shared-use, as-packets-are-needed basis rather than dedicated to one user per call.

CDMA 1xRTT: A packet-based extension to CDMA networks that can theoretically support data rates of 144 kbit/s. Advocates of the technology claim that this means that it actually meets the requirements for the first phase of 3G network technology. However, once again, in the real world users are finding that 1XRTT offers rates of around 50 kbit/s.

Note: Some folks (notably U.S. carriers looking for an edge in some sort of spurious global 3G race) have taken to referring to CDMA 1xRTT as a third-gen standard. However, we here at Unstrung still consider it an intermediate technology. Yes, we know that it can match some of the data transfer rate requirements of 3G – especially if you stand really, really still while testing 1xRTT phones in El Big-O™ Telecom's lab. However, it doesn’t achieve those rates in the real world, and it certainly doesn’t meet the requirements for global roaming and service availability that the International Telecommunication Union (ITU) originally intended as an integral part of 3G. So, 1xRTT is a 2.5G standard. There, we said it. Don’t bother writing in to complain: The editor’s decision, as always, is final. Until next time.

These are the major 3G air interfaces:

Enhanced Data GSM Environment (EDGE): An enhancement to the GSM and TDMA wireless communications systems – using a TDMA air interface – that increases data throughput to 384 kbit/s. EDGE uses the same basic network structure as existing 2G technologies. Some wags refer to EDGE as a 2.75G technology, because it is faster than existing networks but slower than true 3G networks were – at least originally – expected to be.

Universal Mobile Telecommunications Service (UMTS): UMTS is targeted as a 3G upgrade path for GSM operators. Derived from the IMT-2000 framework from the ITU, it has an air interface based on wideband CDMA (W-CDMA) and a core network based on GPRS/GSM.

Wideband-CDMA (W-CDMA): A 3G technology that increases data rates in GSM systems by using the CDMA air interface instead of TDMA. In the ITU's IMT-2000 3G specification, W-CDMA is called the Direct Sequence (DS) mode. W-CDMA is part of the UMTS specification, but it can be used as the air interface (cf. NTT DoCoMo’s FOMA network) on other systems.

Cdma2000 1xEV-DV Based on Qualcomm Inc.’s High Data Rate technology, 1xEV cranks up data transfer rates to 2 Mbit/s. Qualcomm also has a data-only version of this specification, 1xEV-DO.

Key Trends

Operators worldwide are now rolling out 2.5G GPRS and CDMA systems. Third generation is expected to really start taking hold in 2005 and beyond. People are already talking about 4G systems for 2010.

Market Forecasts

The UMTS Forum forecasts that revenues from 3G services worldwide will represent a market worth as much as $1 trillion between now and 2010.

Vendors

Nokia Corp.
Ericsson AB
Motorola Corp.
Qualcomm Inc.
NTT DoCoMo

Organizations

UMTS Forum
CDMA Development Group
GSM Association
3G Americas

Related Unstrung articles:

Nokia Throws Its Cap Into the Ring
Operators Cast Doubts On GPRS
Verizon Is Not the Nation's First
CDMA Handsets Line Up Ahead of GSM at the Start of the Race
Guide to Mobile Wireless Air Interface Technology