Digital Communications 101

When you are trying to compare digital services it can often be complex and confusing, this article will try to break it down to its most basic elements. First of all digital cellular communications occur at two different frequencies 800 MHZ and 1900 MHZ. At the time this article was written 1900 MHZ has far less subscribers and therefore less congested, so this gives it a slight advantage, however over time this will even out and become a non-issue. Within each of these digital services there are four separate subdivisions of communications TDMA, CDMA, GSM, and ESMR.

TDMA or Time Division Multiple Access was the first type of digital cellular service offered to consumers. In a nutshell what's happens is the calls are broken up into distinct time division or slots. These divisions are then sent over the cellular network and mixed with other divisions from other customers. This gave the cellular companies the ability to add additional capacity without the expense of additional network infrastructure. This made the cellular services more efficient and allowed the prices to decrease.

CDMA or Code Division Multiple Access was the next digital service that was offered. It wasn't used by cellular customers until the mid 1990's. CDMA calls instead of being broken up are assigned a unique identifier. This allows multiple callers to use the same service, the calls are separated by the unique ID's. This allows additional features like caller ID and text messaging to be added to the service. The downside is the equipment and personal needed to install and maintain this type of service are much more expensive. However once it is completed and has attained "critical mass" it is much efficient and cost effective compared to a TDMA network.

GSMC or Global Systems Mobile Communications has a much wider usage in countries other than the United States. The technology behind GSMC is very similar to TDMA however the information is broken up into smaller sections with a much higher compression, allowing the cellular network to carry a larger call volume.

ESMR or Enhanced Specialized Mobile Radio is much more similar to a walkie talkie concept. Subscribers inside of the network are allowed to communicate with each other the same way they would as if they were using walkie talkies. While this is a simplex mode of communication (only person can talk at a time), it can be used to communicate over much greater distances. You could be in Maine and communicate with some in Los Angeles via walkie talkie instead of by phone. For business with a dispersed or mobile staff this is an extremely attractive option. The phones also have the ability to act as regular cell phones when needed. Compared to standard cellular service it is a more expensive solution, but can result in cost savings due to more efficient communication.