Difference Between GSM and CDMA

Global System for Mobile Communication (simply known as GSM) and Code Division Multiple Access (simply known as CDMA) are the two major standards for Mobile Communication. Before seeing the differences between the GSM and CDMA technologies, let us have very brief understanding of both the systems.
The GSM Mobile Telephone System is developed by the ETSI (European Telecommunications Standard Institute) for digital cellular networks.

Since its deployment in Finland in the year 1991, it became the widely used mobile communication standard across Europe and majority of the World.
In fact, the GSM Technology enjoys a worldwide share of over 90% users using GSM Standard and making it a de-facto standard for telephony.


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Coming to CDMA, it stands for Code Division Multiple Access and is a multiple access method used in various wireless communications technologies. There are other multiple access methods like TDMA (Time Division Multiple Access), FDMA (Frequency Division Multiple Access), SDMA (Space Division Multiple Access), etc.
Using CDMA, multiple users can transmit data in a single channel i.e. all the users transmit data on the same frequency. In order to distinguish the users, the CDMA, as the name suggests, uses unique Code of the user or transmitter.
Based on the CDMA multiple access method, there are several mobile phone standards. IS – 95 or cdmaOne is the first digital mobile technology that is based on CDMA access method. cdmaOne is a 2G mobile communication standard and its 3G evolution is CDMA2000.
Both these standards are based on CDMA and often are just addressed as CDMA. As a result, cdmaOne mobile communication standard is often confused with the CDMA Multiple Access method.
NOTE: Here after, whenever we use the term CDMA, it refers to the mobile communication standard rather than the multiple access method.

Comparison between GSM and CDMA (GMS vs CDMA)

Both the GSM and CDMA are mobile telecommunication standards and work completely differently. Devices like mobile phones built for one standard of communication cannot operate on the other.
The key difference between GSM and CDMA is the multiple access method they use. CDMA mobile communication standard uses, well the obvious CDMA method. Whereas, GSM uses a combination of TDMA and FDMA methods.
In case of CDMA, each device like a mobile phone or a wireless modem is given a unique code that is registered with the carrier. Whenever a CDMA device starts transmitting data, it is distinguished by this code and hence all the CDMA devices can work on the same carrier frequency.
But the case is different in GSM. As GSM uses a combination of TDMA and FDMA for effectively sharing the bandwidth i.e. with FDMA, the bandwidth is divided into number of channels and with TDMA, these channels are provided with different time slots. Let us see some of the differences between GSM and CDMA.

Identification System

GSM uses a special device called SIM Card. SIM stands for Subscriber Identity Module and the information like mobile number, call plan, data plan, SMS plan etc. are all stored in this SIM Card.
In case of CDMA, there is nothing like a SIM Card but all the information is stored in the devices’ i.e. mobile phone or modem’s software. Even though some CDMA devices uses RUIM or Removable User Identity Module, they aren’t really popular.

Transferability

If the user wants to upgrade his mobile phone or if his or her mobile phone is damaged, it is very easy in case of GSM.
As all the information and plan details or stored in the user’s SIM Card, all he needs to do is buy a new mobile phone and swap in the old SIM Card. Also, if we want to change the network i.e. the service provider, all we need to do is buy the new networks SIM Card and replace it with the old one.
This is not the case for CDMA devices. All the information is loaded in to the phone’s software and is generally done by the carrier. If we want to change our device with the same number, we need to request the carrier to unlock the device, get the serial number and other important codes and store them in the new devices.
It is not possible to change a device’s network from the existing network as the device gets “locked” by the carrier. If we want to change the network on the same device, then we need unlock the device with existing carrier’s approval.

Locked Devices

Usually, all GSM devices will be available as unlocked devices i.e. user can put any SIM Card in it and use that particular network. In case of CDMA, the device is usually locked by the carrier and we must buy devices that are approved by the carrier.

Global Reach and Market Share

With over 90% of mobile communications market share, GSM is the World’s largely used mobile telephony standard. GSM Technology is spread over 219 countries. In contrast, the CDMA enjoys its share only in the Unites States, parts of Canada and Japan.

Roaming

GSM standard’s wide coverage and huge global coverage makes it international roaming friendly. Also, many GSM Network provides have agreed to an international roaming agreement with operators from other countries such that the users can easily access their existing mobile phone while roaming internationally.
CDMA is limited to a small market compared to GSM and is dominant only in the United States, Japan and Canada. Hence, international roaming will not be an easy one.

Frequency Band

There is a wide range of carrier frequencies for GSM Networks. The most commonly used carrier frequencies are GSM 850 (850 MHz), GSM 900 (900 MHz), GSM 1800 (1800 MHz) and GSM 1900 (1900 MHz).
GSM 900 and GSM 1800 are predominant in most of the world whereas GSM 850 and GSM 1900 are used in the United States.Coming to CDMA, most networks operate at CDMA 800 (800 MHz) or CDMA 1900 (1900 MHz) carrier frequencies.

Security

As mentioned earlier, each CDMA device has a unique code that is assigned by the carrier. Also, the there is an encryption standard embedded into the device and all the conversation is encrypted by the device and can be decrypted only with appropriate receiver device.
Even though the GSM networks are encrypted, the data being stored in the SIM card makes it vulnerable to hacking or misuse.

Performance with Number of Users

If the number of users increase in GSM, there won’t be any effect on the performance of the GSM system, as it uses both TDMA and FDMA multiple access methods. The additional users are fixed in different time slots.
In case of CDMA, there is no limit to the number of users as all the users use the same carrier frequency are distinguished by their unique code. As the number of users increases in CDMA, the performance degrades equally for all the users.

Data Transfer Rates

The GSM uses GPRS (General Packet Radio Services) and EDGE (Enhanced Data rates for GSM Evolution, or EGPRS) for data services. The original CDMA standard cdmaOne or IS-95 doesn’t support data whereas its 3G equivalent CDMA2000 used EV-DO or Evolution Data Optimized for data transmission.
The maximum transfer rate in GPRS is 114 kbps (download) and 42.8 kbps (upload). In case of EDGE or EGPRS, the maximum download speed is 1Mbps with a typical bit rate of around 400 kbps.
In comparison, the CDMA’s EV-DO technology supports a data transfer rates of up to 3.1 Mbps.

Efficiency

Since the CDMA system uses a single carrier frequency, the cluster size of a CDMA cell becomes 1. This means the same frequency can also be used in the adjacent cells and thus maximizing the reuse of frequency.
In GSM, the efficiency is dependent on the cluster size and number of operators and the efficiency is less than that of CDMA.
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