Difference between CDMA EVDO GSM and EDGE Mobile Phones

There are two major categories of mobile device protocols. One is known as GSM which stands for Global System for Mobile Communications. The other is known as CDMA which stands for Code Division Multiple Access. These are technologies which essentially allow a mobile device to communicate with a mobile communications network. It allows the network to identify the phone, the phone number and to provide wireless network connectivity through access points or mobile phone antennas.

GSM is a name for an implementation of a network protocol known as TDMA or Time Division Multiple Access. This protocol allows up to eight callers to use the same frequency with a technology remarkably similar to communications between a mobile phone handset and base station. Each frequency is divided into "channels" each of which can be used by a different caller but which are combined by the protocol into a "stream" which is transmitted to the network.

While GSM can be thought of as a vertical signal, with calls stacked on top of one another, CDMA constructs a more horizontal signal, with calls occupying the entire width of the frequency, but sequenced so that each call has its own "place in line" so to speak. CDMA has some theoretical advantages with analog transmissions due to the way radio frequencies work.

Since mobile phones have to do a lot more than just transmit and receive phone calls, the speed of network transmissions and the speed of network data access is becoming more and more important as mobile phone technology upgrades continue and new phones become available.

CDMA has been viewed as the faster technology for some time, despite the fact that GSM is available in more countries. The most recent upgrade to CDMA is CDMA2000 or EVDO, an acronym which stands for Evolution Data Optimized. EVDO operates in much the same way as the standard Internet Protocol (IP) or Transmission Control Protocol (TCP) does. Data exchanged between the phone and the network is transmitted in packets which conserves bandwidth and theoretically increases average speeds across the network.

CDMA2000 or EVDO capable network devices have practical average speeds in the 500Kbps range, roughly half that of a T1 wired Internet connection or approximately 1/4 the theoretical upper limit of speed on a cable modem wired Internet connection. Kbps stands for Kilobits per second.

The GSM upgrade is known as the EDGE protocol, which stands for Enhanced Data rates for GSM Evolution. EDGE network devices have speeds roughly 1/4 that of CDMA devices, or network connection speeds in the 120Kbps range.

There is a second level of network technology associated with GSM or CDMA phones and that is data transfer. GSM phones use a protocol known as GPRS or General Packet Radio Service. While it is slower than the CDMA equivalent, known as 1xRTT or Single user Radio Transmission Technology, GPRS does not block incoming voice traffic on the same frequency, since it uses a packet based technology. Data connections on a CDMA phone block simultaeneous voice connections.

GSM and CDMA also have one other important difference, and that is the storage of the unique user information associated with a given phone. In a GSM phone, the user account information and unique user data are stored on a plug-in device known as a "SIM card." SIM is an acronym for Subscriber Identity Module. It is a removable card that can be inserted into any GSM compatible phone, converting it to use that user's account information.

CDMA uses a centralized approach which stores all account information in the CDMA carrier's databases. The differences between the two approaches are the essence of a six/half-dozen argument. They have an equal share of pros and cons, and the competition between the two approaches to user information storage has been in progress since the first mainframe user accounts.

Once the basics of the two competing technologies are well enough understood, a user can use this knowledge to decide on the best phone to use in a given situation. The most versatile devices include technologies such as multi-band and multi-mode capability.

GSM networks are available in roughly 3/4 of the mobile phone enabled regions of the world, including Europe and Asia. For those who wish to use their phones outside of the U.S., a multi-band GSM phone can offer some flexibility. In the U.S. the frequencies for GSM transmissions may differ from other countries, but a multi-band phone will automatically select a compatible and available GSM frequency to connect to.

A multi-mode phone, on the other hand, can change between available carrier network protocols, meaning if no GSM network is available, some phones can switch to the CDMA protocol and make use of the opposite network. Purchasing a multi-band or multi-mode phone can be very confusing without specific information on exactly what will and will not work with a given handset.

In the next part of this series, we'll cover some of the currently available phones and see what features they offer for users of GSM and CDMA mobile phone network.