Cellular networks are complex technologies that have been made easy enough for everyone to use. In this video, you’ll learn about GSM, CDMA and LTE cellular technologies.
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We rely on cellular networks to provide most of our mobile communications, these days. We use our mobile phones and mobile devices to communicate over these separate cells of communication. We have antennas that can converge the data within these cells so that you can move from cell to cell and still maintain communication wherever you happen to be. In the early days of cellular networking there were two primary standards that you would see. One is GSM– which is the Global System for Mobile communications– and the other was CDMA– or Code Division Multiple Access. These were really designed for voice communication. There is limited data functionality. It used circuit switching to be able to set up a call, send data, and it had to emulate that same circuit switching to be able to send data. To be able to perform some type of data or packet switching we needed newer standards that would support these newer ways to communicate.
Let’s start by looking at GSM– the Global System for Mobile communications. This had about a 90% coverage in the market. And that’s because it was a standard almost everywhere in the world. In the United States, AT&T and T-Mobile were big providers of the GSM standard. This also allowed you to take a SIM card out of one phone and move it to another phone. So anytime you needed to change telephones you could simply move your SIM card from phone to phone. This original GSM standard uses a multiplexing called TDMA to be able to communicate where everyone on a particular frequency gets a little slice of time to be able to complete that communication.
Here’s how Time Division Multiple Access– or TDMA– multiplexing works. You would have multiple streams. You can see each of these phones on the left side communicating over a blue, a red, and a purple communication. The multiplexer blends those together and gives everybody a certain timestamp that’s available to them. On the other side that signal is demultiplexed and you would break out the blue, the red, and the purple stream so that they can be sent to their normal destinations.
The other standard of the time was CDMA. This is the Code Division Multiple Access which uses a different method of multiplexing this data. With CDMA everyone’s communicating over the same frequencies but each call is using a different code and the phone on the other end is filtering out all of the information that it doesn’t need to hear. This was a standard commonly used by Verizon and Sprint and all of those handsets were controlled by that network provider. In the United States there wasn’t much adoption outside of Verizon and Sprint for CDMA.
These days, most mobile phone providers have moved towards what they call 4G– or the Fourth Generation– of Long Term Evolution communication– or LTE. This is a converged standard so we no longer have to worry about a provider giving us a GSM or a CDMA phone. This is based on the GSM and EDGE– which is Enhanced Data Rates for GSM Evolution– and it finally allows us to completely and seamlessly communicate with voice and data simultaneously over the same network. The original LTE standard supported download data rates up to 150 megabits per second and the latest version of LTE– LTE Advanced– has doubled that to support download speeds of up to 300 megabits per second.