Difference between GSM & CDMA

GSM Vs CDMA:

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.)

The Main points of contention between TDMA and CDMA is as below:-

Data Transfer Speed: With the advent of cellular phones doing double and triple duty as streaming video devices, podcast receivers and email devices, speed is important to those who use the phone for more than making calls. CDMA has been traditionally faster than GSM, though both technologies continue to rapidly leapfrog along this path. Both boast "3G" standards, or 3rd generation technologies.

EVDO, also known as CDMA2000, is CDMA's answer to the need for speed with a downstream rate of about 2 megabits per second, though some reports suggest real world speeds are closer to 300-700 kilobits per second (kbps). This is comparable to basic DSL. EVDO is in the process of being deployed. It is not available everywhere and requires a phone that is CDMA2000 ready.

 
GSM's answer is EDGE (Enhanced Data Rates for GSM Evolution), which boasts data rates of up to 384 kbps with real world speeds reported closer to 70-140 kbps. With added technologies still in the works that include UMTS (Universal Mobile Telephone Standard) and HSDPA (High Speed Downlink Packet Access), speeds reportedly increase to about 275—380 kbps. This technology is also known as W-CDMA, but is incompatible with CDMA networks. An EDGE-ready phone is required.

Subscriber Identity Module (SIM) cards: In most of the countries only GSM phones use SIM cards. The removable SIM card allows phones to be instantly activated, interchanged, swapped out and upgraded, all without carrier intervention. The SIM itself is tied to the network, rather than the actual phone. Phones that are card-enabled can be used with any GSM carrier.

The CDMA equivalent, an R-UIM card, is only available in parts of Asia. CDMA carriers require proprietary handsets that are linked to one carrier only and are not card-enabled. To upgrade a CDMA phone, the carrier must deactivate the old phone then activate the new one. The old phone becomes useless.

Roaming: For the most part, both networks have fairly concentrated coverage in major cities and along major highways. GSM carriers, however, have roaming contracts with other GSM carriers, allowing wider coverage of more rural areas, generally speaking, often without roaming charges to the customer. CDMA networks may not cover rural areas as well as GSM carriers, and though they may contract with GSM cells for roaming in more rural areas, the charge to the customer will generally be significantly higher.

International Roaming: If you need to make calls to other countries, a GSM carrier can offer international roaming, as GSM networks dominate the world market. If you travel to other countries you can even use your GSM cell phone abroad.

Radiation Exposure: GSM phones emit continuous wave pulses, so there is a large need to reduce the exposures to electromagnetic fields focused on cell phones with “continuous wave pulses”. On the other hand CDMA cell phones do not produce these pulses. GSM phones emit about 28 times more radiation on average as compared to CDMA phones. Moreover, GSM phones are more biologically reactive as compared to CDMA.