Hardware, Technology

How-to: Understand GSM and CDMA (phones)

Vector - Smartphone collection - iconshock.com CC 3.0You would think, by now, we’d have one global standard for mobile telecoms. But no. Depending on your country of residence, you may have a bewildering choice of cellphone standards. You want to buy a piece of technology to make your life better and easier: instead you end up in acronym hell.

In the UAE, for example, you can buy a phone to run on any network on the planet, using any protocol available. In the United States, AT&T and T-Mobile are GSM networks; Sprint and Verizon are CDMA and don’t use SIM cards. So what should you get? And what’s the difference anyway?

The current dominant player is the Global System for Mobile CommunicationsGSM. It hasn’t quite got total domination, however. The alternative cellular standard is the wonderfully named Code Division Multiple Access – CDMA. Used by many carriers around the world, it is most popular in the United States and Russia, and as a technical alternative set-up by foreign companies in new markets, is found in some Asian and African countries, often alongside competing GSM services.

Both GSM and CDMA have protocols for use with Third Generation or 3G phones – Universal Mobile Telecommunications System (UMTS) and CDMA2000. Aside from the different ways in which the carrier connects to the phone and turns voice data into radio waves, other differences include coverage, data transfer speeds, and the type of hardware supported.

If your country has only one type of network available, you better get a phone that runs on it. This is why the smart Americans travelling abroad bring dual network phones. CDMA is most commonly found in North America and some (not all) parts of Asia. GSM dominates most everywhere else. If you’re not travelling outside your home network, don’t worry about it, get the single-protocol phone. If you’re roaming Internationally or have thin coverage across your territory using both network types, you may benefit from both.

Data Transfer Speed
3G is the smartphone standard for fast Internet, but not all 3G is equally fast. 3G on GSM can be faster than 3G on CDMA, which can make a big difference if you’re phone is also your computer, social networking hub and personal organiser through the Cloud. The fastest 3G on CDMA2000 is the catchy EV-DO Rev B, which has a theoretical maximum downstream data rate of 15.67 Megabits (not megabytes!) per second (Mbit/s). The fastest on UMTS is HSPA+, with a theoretical maximum downstream data rate of 28 Mbit/s.

GSM phones and CDMA phones use different types of removable cards known as Universal Integrated Circuit Cards (UICC) – the small removable plastic and gold foil cards used to store contact lists connect and upgrade phones without carrier intervention as long as the phone is unlocked. Everyone uses the common term SIM card, although strictly, those that only work with GSM phones are Subscriber Identity Module (SIM) cards and those that only work with CDMA phones are CDMA2000 Subscriber Identity Module (CSIM) cards. To add to the confusion, a few types of UICCs are able to work as GSM, UMTS, CDMA, and CDMA2000, CSIM/USIM cards and Removable User Identity Module (R-UIM) cards.

Most importantly before buying any new equipment, check that the phone, the ‘SIM’ and the target networks are compatible.

Population density in major towns and cities generally ensures good coverage wherever there’s a substantial GSM or CDMA network, and this often extends along major highways. Do not confuse coverage with capacity – just because you get a signal in urban areas, don’t assume you will get decent data rates or voice connections. Network antennas and relays have a finite number of concurrent connections and limited throughput. Even today, stray too far off the highway or into hilly countryside and you may lose connectivity altogether.

The GSM carriers commonly have roaming contracts with other GSM carriers in shared territories, allowing wider coverage of rural areas, either with or without roaming charges to the customer. CDMA networks traditionally haven’t covered rural areas well, and cross-connection to GSM networks for roaming can be expensive.

International Roaming
Almost all GSM and CDMA carriers offer International roaming via a plethora of roaming agreements. To roam Internationally, the phone handset has to be a quad-band phone, operating on frequencies of 850, 900, 1800, and 1900 MHz to inter-operate across networks. Fewer countries have CDMA networks, which is why it is important to check ahead roaming agreements exist in the countries you are visiting. Note that romaing tariffs can vary wildly from slightly above normal to utterly extortionate! The European Union implemented caps on roaming charges in 2014 on the justification that they were an abuse of monopoly power. No such caps exist anywhere else in the world that I know of.

It is possible to buy a SIM card with talk-minutes, data allowance and a local number specific to the country visited to avoid paying international rates.

Always keep tabs on the minutes and data used while roaming, as the tariff within your allowance may be reasonable, but rise to eye-wateringly expensive once you exceed the allowance.

Next: 4G, LTE and into the future. AJS

Image credit: Smartphone Collection, http://www.iconshock.com, Creative Commons Attribution 3.0

About Allan J. Smithie

Allan J. Smithie is a journalist and commentator based in Dubai.



  1. Pingback: How-to: Understand GSM and CDMA (phones) II | Everything Express - Feb 3, 2015

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

Twitter Updates

Follow us on Twitter @EverythingExpre

Find Us on Facebook

Enter your email address to follow this blog and receive notifications of new posts by email.



BBC World News

BBC World News
Opens the BBC World News page.
%d bloggers like this: