How Does A TDMA or GSM Cell Phone Work?

Cell phones are cool, we all know that; they’re also absolutely indispensable to many of us nowadays. But is that great cell phone a TDMA or GSM cell phone or not?

Does it matter - perhaps so, perhaps not. It certainly does for some who buy an awesome new cell phone with a full-color display, integrated digital camera and the latest multimedia messaging technology in GSM cell phones and then can’t use it without switching cellular carriers if their cell phone provider uses CDMA cell phone technology instead.

For your ease of reference, here are five popular cell phone service providers stateside and the cellular systems that they use: AT&T Wireless, T-Mobile and Cingular all use GSM for their cell phones, whilst a cellular phone for Sprint and Verizon Wireless is CDMA.

The World Talks GSM

So what’s this TDMA cell phone business then, if the cellular choice is either GSM or CDMA. Well TDMA (Time Division Multiple Access) and GSM (Global System for Mobile communication) are related, and GSM is a more advanced version of the TDMA that has been familiar to most in North America. The US cellular phone carriers who use TDMA have switched, or are switching to GSM, which is the dominant cellular standard from Europe which is used all over the world, with more than one billion GSM cellular subscribers worldwide at the start of 2004.

So how does this work then? Right, have you got all day? Nope didn’t think so. So let’s take a simple look at how these cell phones work on this cellular system, and if you want to know about cellular alternatives, see - What Is CDMA Cell Phone Technology? And the article FDMA, CDMA, TDMA/GSM Cell Phone Technology - A Simple Explanation Of The Differences, may be of help as well.

TDMA as already said (the simpler sibling of GSM) stands for Time Division Multiple Access and this gives a clue as to how it works.

By reading the article: What Is FDMA Cell Phone Technology? You will understand that cell phones use a hexagonal grid of geographic cells in which radio frequencies are used to transmit and receive both voice and data phone calls. Digital cell phone systems are much more efficient than analog FDMA because they compress all the information sent between cell phones by converting it into streams of binary code (trillions of 1s and 0s).

A digital cell phone does not take up so much bandwidth as analog, so it is more efficient. Indeed a TDMA cellular phone system can have three times as much cell capacity as FDMA with the same number of available channels, and GSM can have up to eight times more.

This works by allocating the frequency range of the channel into what are known as `time slots’ where three cell phone voice or data calls simultaneously use the same frequency as others, but at different times measured as thousandths of a second apart, with each cell phone user taking turns to have the time slot available to them. This is called multiplexing and utilizes natural pauses and delays in conversation where only silence or background noise would otherwise be transmitted.

TDMA is the access base for GSM cell phones which have their famous SIM (Subscriber Identification Modules) so that you can easily swap this to a different cell phone (another GSM model) and still keep all your cell phone user and subscription information the same.

Users with GSM cell phones (for users in Europe, Asia and almost everywhere else) can also use their phones internationally but when it comes to North America things are different. The GSM used in the United States is on a different frequency and uses a different `language’ so if you want to use your cell phone abroad you will have to get a tri-band or tri-mode cell phone, which will allow you to switch to the global GSM system used elsewhere.

Also see; cell phone FAQ.

Author Notes:

Matt Jacks contributes and publishes news editorial to http://www.cell-phones-n-plans.com. A cell phone industry resource that features service plan comparisons, cellular phone reviews and articles.