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No CDMA and sim are two different things

The Major Carrier Technologies

By now, you’ve probably heard all of the acronyms in the alphabet soup of carrier technologies. The two major terms that pertain to cellular phone communication that you’re likely to run into are GSM and CDMA, the two major technologies service providers use to carry voice signals across the network. But what are they and why do they matter? Well, for starters, let’s define the terms.

GSM (Global System for Mobile Communications). GSM is the “branded” term referring to a particular use of TDMA (Time-Division Multiple Access) technology. GSM is the dominant technology used around the globe and is available in more than 100 countries. It is the standard for communication for most of Asia and Europe. GSM operates on four separate frequencies: You’ll find the 900MHz and 1,800MHz bands in Europe and Asia and the 850MHz and 1,900MHz (sometimes referred to as 1.9GHz) bands in North America and Latin America. GSM allows for eight simultaneous calls on the same radio frequency and uses “narrowband” TDMA, the technology that enables digital transmissions between a mobile phone and a base station. With TDMA the frequency band is divided into multiple channels which are then stacked together into a single stream, hence the term narrowband. This technology allows several callers to share the same channel at the same time.

CDMA (Code Division Multiple Access). CDMA takes an entirely different approach from GSM/TDMA. CDMA spreads data out over the channel after the channel is digitized. Multiple calls can then be overlaid on top of one another across the entire channel, with each assigned its own “sequence code” to keep the signal distinct. CDMA offers more efficient use of an analog transmission because it allows greater frequency reuse, as well as increasing battery life, improving the rate of dropped calls, and offering far greater security than GSM/TDMA. For this reason CDMA has strong support from experts who favor widespread development of CDMA networks across the globe. Currently, you will find CDMA mostly in the United States, Canada, and North and South Korea. (As an interesting aside, CDMA was actually invented for the military during World War II for field communications.)

Domestic Travel

The cellular showdown: CDMA (Code Division Multiple Access) vs. GSM (Global System for Mobile Communications).

Because you can find GSM and CDMA in use all across the United States, it might seem at first that it really doesn’t matter which technology you choose. This is not so. When you travel abroad, the likelihood that you will reach areas that do not have digital service is quite high. Anytime you travel between offices via car, train, or bus you will pass through rural and suburban areas that only offer analog access. Most CDMA cell phones include analog capability (also known as roaming), so a user can make calls when he is not in a digital cellular service area. GSM phones usually don’t offer this capability unless you purchase and use a specialty (read: expensive) handset. Of course in most of Asia and in Europe, this is not a problem because digital service is available almost everywhere you turn. This does become an issue for users in North America, however, because digital service is rarely available there.

Another difference between GSM and CDMA is in the data transfer methods. GSM’s high-speed wireless data technology, GPRS (General Packet Radio Service), usually offers a slower data bandwidth for wireless data connection than CDMA’s high-speed technology (1xRTT, short for single carrier radio transmission technology), which has the capability of providing ISDN (Integrated Services Digital Network)-like speeds of as much as 144Kbps (kilobits per second). However, 1xRTT requires a dedicated connection to the network for use, whereas GPRS sends in packets, which means that data calls made on a GSM handset don’t block out voice calls like they do on CDMA phones.