Making Sense of Global Mobile Phone Networks

The mobile phone network landscape is incredible confusing. I pulled together the following overview to help myself make sense of it, and I thought it might benefit my readers, too.

Overview: 2G, 3G, 4G, and more-G!

Today’s worldwide mobile phone network consists of many different technologies operating at many different frequencies. Setting aside the frequency issue (we’ll get to that in a moment), let’s talk standards.

Generally speaking, the world’s mobile phone networks use one of two “branches” of technology:

• “GSM” is “the European standard”, defining 2G (true GSM and GPRS as well as “2.5G” EDGE), 3G (properly called UMTS, HSPA, etc.), and faux-4G (HSPA+). All GSM phones use a SIM card for subscriber information.
• “CDMA” is popular in the United States, Japan, and some other countries. More properly called IS-95 in 2G guise and CDMA-2000 for 3G, CDMA technology includes 1xRTT and EV-DO data protocols.

This is a vast oversimplification, and the true technology and terminology is much more complex. For example, 3G GSM networks use the W-CDMA channel access method, though are incompatible with the networks commonly referred to as “CDMA”. But these are the popular terms for the two networks.

GSM and UMTS is said to have 80 to 85% of the global mobile phone market, with most of the rest relying on some evolution of IS-95. The SIM card has become ubiquitous in popular culture worldwide, and is as much of an emblem of mobile phones as the floppy disk was of computers a decade ago.

Global roaming is impractical or impossible without a SIM-equipped GSM phone, though some CDMA phones and devices are unlocked and can thus be used on a variety of networks. The SIM card makes it much more practical to self-provision local service, however, as does the ubiquitous presence of GSM networks.

GSM Frequencies: the Blessed and Cursed

Not all GSM phones are capable of roaming even if they are unlocked and equipped with a local SIM card, however. The phone hardware must also be compatible with the local GSM network, and this is a major stumbling block in countries like the United States and Japan which use a variety of frequencies for GSM signals.

There are five frequencies that stand out for worldwide coverage and usability. One could consider these the “blessed” frequencies, since an unlocked device that supports 2G GSM or 3G UMTS here could be used nearly everywhere in the world:

• Globally, the most popular frequencies for GSM access are 900 MHz (Band VIII “GSM”), 1800 MHz (Band III “DCS”), and 2100 MHz (Band I “IMT”). This trio is used in all of Europe and much of the rest of the world for both 2G and 3G service. Note that the DCS Band is only used for 2G communication, while the IMT Band is predominantly a 3G UMTS range. Most countries outside the Americas and Europe are strictly 2100 MHz for 3G service.
• The second most popular frequency pair for GSM access is 850 MHz (Band V “CLR”) and 1900 MHz (Band II “PCS”). Sometimes called the American standard, thanks to the massive AT&T network, this pair is also used in many other Western Hemisphere countries, and 850 MHz is popular in Southeast Asia and the Pacific countries as well.

Alas, not all networks are configured in this “standard” way, and not all devices support the same technologies on all bands. This is particularly thorny in United States, where AT&T (by far the dominant GSM carrier) and T-Mobile operate incompatible 2G and 3G networks. Since AT&T has more than 3 times as many customers as T-Mobile, equipment vendors have been reluctant to support the smaller rival’s 1700/2100 MHz network.

Worldwide, companies operating networks outside the “blessed” bands find it hard to offer the latest devices and attract revenue from tourists and travelers. The iPhone and iPad, for example, support only the four popular 2G and 3G frequencies, dramatically reducing the attractiveness of providers outside this range. In United States, T-Mobile is currently realigning their entire network to the AT&T standards for this reason, a costly and time-consuming process. Examples of non-standard frequencies include 450 MHz, 800 MHz, and 1700 MHz.

Stephen’s Stance

Although frequency mismatches are frustrating to travelers, this is not an easy issue to fix. Allocating spectrum is a massive challenge globally, and realignment and reuse takes decades. It is heartening to see the world: as around “just” 4 frequency bands for GSM and UMTS, but the same battle is starting again with LTE. We haven’t seen the last of hassles and headaches!