GSM vs. CDMA

This debate has been raging on for years. Allow me to give you some background on the two technologies so you can make an informed decision. CDMA stands for "Code-Division Multiple Access". CDMA is a "channel access method". A channel access method allows multiple terminals (in this case, cellphones) to connect over the same multi-point physical medium. In essence, a channel access method allows multiple cellphones to connect over the network using the same radio frequency by divvying up the radio channel in different ways.

There are four major channel access methods. They are:

• FDMA (Frequency-Division Multiple Access) provides different frequency bands to different datastreams, which basically gives each cellphone its own radio frequency. This method was used in AMPS and requires the most available radio frequencies.
• TDMA (Time-Division Multiple Access) gives each cellphone using a radio channel a time slot in which they access the cell tower. For example, during milliseconds 1-2, handset 1 transmits data. Then, from milliseconds 2-3, handset 2 transmits its data. Then, on milliseconds 3-4, handset 1 transmits more data, and so on. This makes it appear as though both handsets are transmitting simultaneously. TDMA has a tendency to cause dropped calls, however.
• CDMA (Code-Division Multiple Access) modulates the signal sent by the cellphone using a specific code given to it by the cell tower. Each handset has its own specific code, assigned by the tower. The data sent by the phone is modulated using the code, and the tower differentiates between each cellphone's data by seeing how the signal is modulated and comparing that to the code assigned to each phone. This allows multiple handsets to transmit over the same channel.
• SDMA (Space-Division Multiple Access) is also called MIMO (Multiple-In Multiple-Out) which means that one handset sends out multiple signals to multiple cell towers. This frees up a lot of bandwidth by effectively dividing the bandwidth of the handset's transmission by the number of towers it's transmitting to.

In this context, CDMA means cdmaOne or CDMA2000, which is not a channel access method but a cellphone technology, although cdmaOne and CDMA2000 use the CDMA channel access method. CDMA transmits on the 1900MHz band, while GSM transmits on the 800MHz band, using TDMA technology. As such, GSM penetrates better into the ground and through walls, but CDMA has better range. Basically, CDMA2000/cdmaOne and GSM are the same, except for two major details: data support and dropped calls. Statistically, CDMA has less dropped calls than GSM, and its current revision supports higher data speeds and better bandwidth. CDMA uses UMB and EVDO technology which allows for 275Mbit/s for data, while GSM uses EDGE and GPRS, which allows for a maximum of 1Mbit/s.