One of the most important andpractical aspects of digital communication is mobile communication. It is a tremendous accomplishment in and of itself to be able to wirelessly link two mobile devices, and the two technologies that have shown to be essential to this success are GSM (Global System for Mobile Communications) and CDMA (Code Division Multiple Access).
CDMA and GSM are mobile technology standards that enable calls and data transfer over a network. Understanding the key differences betweenCDMA vs GSM will help us understand about the evolution of mobile communication.
What is GSM?
GSM is a globally accepted mobile communication standard. Although initiallyy focused on voice communication between mobile devices, it has since advanced to include ways to facilitate data transfer as well. GSM falls under the category of 2G communication, where ‘G’ stands for generation. This is how the evolution of mobile communication standards has been classified: through generations. Each next generation offers much better data transfer capabilities and can support a larger user base.
Cell phones of the first generation were analog. In the shift to 2G digital networks in the 1990s, only CDMA and GSM survived. The third generation of cellular improved data speeds but both technologies were still incompatible. With the launch of 4G, the difference between CDMA and GSM was theoretically resolved when all operators began implementing LTE in 2010, a single, global standard. Voice calling over 4G was also gradually introduced globally and is now supported by all four carriers.
The time division multiple access (TDMA) and frequency division multiple access (FDMA) techniques are the foundation of the GSM technology. The accessible frequency spectrum or time is divided using this technique into discrete slots. Each user has a specific time slot or a frequency bandwidth allotted to them for their data transmission and reception requirements. Because of this reason, a specific contact number on call can’t connect to any other call simultaneously.
GSM led to the introduction of SIM (Subscriber Identity Module) cards, which act as a mechanism of user authentication within the network and hold crucial subscriber information. Each device has a different SIM card which distinguishes the various subscribers of the GSM technology. A network tower keeps track of all SIM card numbers in its radius and controls their communication, by transmitting signals in varied time slots.
Advantages
- TDMA technology in GSM allows multiple users to access the same frequency band in different time slots, making efficient utilization of the spectrum.
- Being a widely accepted global standard, GSM makes international calls and data transfer over several networks in the world easier and more efficient
- GSM ensures high-quality voice and data signals
- The implementation of technology in the form of SIMs and network towers is cheaper compared to other technologies.
What is CDMA?
CDMA is another mobile technology standard similar to GSM. The spread spectrum technique acts as the foundation of CDMA. It identifies each user’s signal with a unique code and the signal is spread over the entire frequency spectrum. This enables multiple users to transmit simultaneously, and the receiver can separate and decode the signals using their respective codes. The use of the entire frequency spectrum by each user increases the capacity of communication possible.
Utilizing a special coding, each user’s signal is dispersed across the whole frequency range. These codes are orthogonal hence they don’t interfere with each other. This makes it possible for numerous users to transmit at once, with the receiver being able to isolate and decode the signals using their unique codes. Because of this reason, CDMA delivers one of the most secure modes of communication. The use of CDMA is majorly confined to certain countries US, Canada, and Japan.
CDMA has also been involved in CDMA2000 and further EVDO (Evolution-Data Optimized) which are 3G technologies based on CDMA but offer better usage of bandwidth of a higher user base. These technologies can be implemented alongside voice services from a wireless carrier.
Advantages
- The spread spectrum technology utilizes the frequency spectrum in an optimized manner, making communication
more efficient. - CDMA is
highly securebecause the spread spectrum technology doesn’t let different signals easily interfere because of unique codes. - Spread Spectrum allows multiple users to communicate simultaneously. Hence, the
capacity is much improved. - CDMA allows
flexible allocation of resourcesbecause a huge range of frequency bandwidths can be accommodated.
Difference between CDMA and GSM
Having discussed whatCDMA and GSM is, we now focus on the differences between CDMA and GSM. They are as follows:
| Criteria | GSM | CDMA |
|---|---|---|
| Technology Used | GSM uses FDMA and TDMA | CDMA uses spread spectrum technology |
| User Information | GSM distinguishes between its subscribers using the SIM card | CDMA stores its user info in handset or phone rather |
| Availability | Global standard, highly acceptable | Not common, exclusive to some particular countries only |
| Voice and Data | GSM supports simultaneous transfer of voice and data | CDMA can’t transmit both simultaneously |
| Roaming | GSM offers worldwide roaming | CDMAoffers limited roaming only |
| Security | GSM offers comparatively less secure communication | CDMA is one of the most secure communication standards |
| Signal Distinction | The signals for each user are divided into different time slots or frequency bands, no other signal can interfere in that time slot or frequency band | In CDMA, multiple users can transmit signals over the entire frequency spectrum, the spreading codes applied to them are orthogonal and hence don’t interfere |
| Signal Detection | GSM signals can be detected because they are concentrated in a narrow frequency bandwidth | CDMA spread over the entire spectrum, hence difficult to detect |
| Encryption | GSM doesn’t include built-in encryption | CDMA includes built-in encryption |
| Flexibility | Multiple SIMs can be used and one SIM can be replaced in different devices, hence GSM is flexible | CDMA is specific to the device and hence not as flexible as GSM |
| Radiation | GSM devices emit approximately 28 times more radiation than CDMA devices | CDMA technology emits very low radiation as compared to GSM technology |
| Spectrum Type | GSM operates on a wedge spectrum called carrier | CDMA uses spread spectrum |
| Use Case Scenarios | GSM is ideal for international travelers and old device users, due to standardized networks and SIM cards. | CDMA is ideal for many users and high-demanding data requirements since it is optimized for high-capacity networks and data-intensive applications with better security. |
CDMA vs GSM: Detailed Comparison
Let’s do a detailed comparison to understand the differences between CDMA and GSM. These are based on:
- Technology Used:
GSM operates on wedge spectrum technology, also called a carrier. TDMA divides the carrier into various time slots and assigns to each user. No other user can interfere with any other’s time slot. FDMA divides the frequency band to allow multiple users to access the spectrum. On the other hand, spread spectrum technology in CDMA allows full access to the bandwidth by multiple users by using different orthogonal spreading codes. - User Information:
GSM makes use of SIM cards to store user information that helps identify the subscriber and participate in communication. Because these cards can be easily replaced from one phone to another, GSM is flexible. CDMA makes use of ESN (Electronic Serial Number) to store customer information that is specific to the mobile device. Hence, this makes changing mobile phones difficult as a proper process would be required to enable CDMA in the new device. - Spectrum Frequencies:
GSM operates within the frequency range from 850 MHz to 1900 MHz, and while on the same lines CDMA also operates in the frequency range of 850MHz and 1900MHz. - Radiation:
GSM phones transmit ‘continuous’ wave pulses while CDMA phones do not transmit any. This leads to radiation in GSM phones which is approximately 28 times more in GSM than CDMA. - Global Reach:
GSM is a widely accepted mobile communication standard, and d globally used. CDMA isn’t used that commonly, however. GSM is used in approximately 80% of the mobile networks across 210 countries. CDMA-based phones are mostly used in the US, Canada, and Japan. - Security:
Due to its inbuilt encryption as well as the use of spread spectrum for data transmission, CDMA is much more secure than GSM. Signal detection is very difficult in GSM. - Data Transfer Rate:
CDMA offers a higher data transfer rate than CDMA. CDMA makes use of EVDO data transfer technology, providing a maximum download speed of 2 Mbps.
On the other hand, GSM uses EDGE technology providing a maximum download speed of 384 Kbps, much slower than CDMA.
Conclusion
In this article, we discussed in-depth GSM vs. CDMA. To summarize:
- GSM stands for
Global Systemfor Mobile Communication and is a globally accepted standard, which uses TDMA and FDMA technologies, and stores user information in SIM cards. - CDMA stands for Code Division Multiple Access and is a less commonly used standard, using the spread spectrum technology, and storing user info in devices.
- Regarding features of CDMA vs. GSM, CDMA offers a higher data transfer rate and is more secure, but less flexible. It emits very little radiation than GSM.
- GSM offers a comparatively lower data transfer rate and is less secure but very flexible due to the easy replacement of SIM Cards. It emits much higher radiation than CDMA.
