GSM vs CDMA

Both GSM and CDMA are standards for digital cellular communication. They define the protocols for how mobile devices communicate over the airwaves and connect to the cellular network. Both GSM and CDMA have been specified in 3GPP series of standards.

Both GSM and CDMA support voice and data transmission, allowing users to make calls, send text messages, and use mobile data services. GSM uses GPRS feature to facilitate data services. Both technologies require a cellular network infrastructure that includes base stations, mobile switching centers, and other components to facilitate communication between mobile devices.

Despite the similarities, there are key differences between GSM and CDMA as follows. GSM (Global System for Mobile Communications) utilizes TDMA (Time Division Multiple Access) which allows multiple users to share the same frequency through different time slots. In contrast, CDMA (Code Division Multiple Access) relies on Code Division Multiple Access, which enables simultaneous communication by assigning unique codes to users on the same frequency. Let us understand features of both before comparing them in tabular form.

What is GSM ?

GSM stands for Global System for Mobile Communications. It is a standard developed to ensure a common platform for mobile devices, facilitating communication across different networks and countries. Originally conceived in the 1980s, GSM has become the predominant mobile communication standard globally.

This technology uses TDMA/FDMA access scheme in order to assign channels to the different subscribers to utilize the service from the service operator's base stations. One frequency and one time slot (f1,t1) is needed for one way communication and a pair for two-way communication( (f1,t1) and (f2,t2) ). Here, different users share same frequency but at distinct time slots for transmission.

GSM also introduced the use of SIM (Subscriber Identity Module) cards, allowing users to easily switch devices by transferring the SIM card. The figure-1 depicts GSM network architecture and its elements. Refer GSM tutorial >> for more information.

What is CDMA ?

CDMA stands for Code Division Multiple Access. It is a digital cellular technology that allows multiple users to share the same frequency band simultaneously. CDMA was developed as an alternative to other multiple access technologies, such as TDMA/FDMA.

This technology uses PN codes for communication between subscribers and NodeBs. As the PN codes are unique to the users, information is extracted by despreading at the receiver using the same PN code which is used at the transmit side. Pls. note that information is not retrieved using (time,frequency) assignment in CDMA. All the different PN codes will utilize the same frequency/time in order to communicate. CDMA uses 1xEV-DO and EV-DV versions in 3rd generation. CDMA has edge over GSM due to its immunity to interference as well as jamming. The figure-2 depicts CDMA network architecture and its elements.

In CDMA, each user's signal is spread over a wide frequency band using a unique code. This spreading of signals enables multiple users to transmit and receive data simultaneously without interfering with each other. Unlike GSM, CDMA doesn't use time slots for different users; instead, it assigns a unique code to each user, and all users can communicate at the same time. Refer CDMA tutorial >>, UMTS tutorial >> and UMTS network architecture >> for more information.

Difference between GSM and CDMA

Following table compares both the cellular technologies and mentions difference between GSM and CDMA.

Some of the comparison between two are as follows.
➨In GSM, as the available transmission BW (Bandwidth) is small and hence leads to compromise in quality of voice transmission. In CDMA entire transmission BW (Bandwidth) is utilized and hence voice quality can be enhanced.
➨ In GSM(i.e. TDMA/FDMA), cell frequency planning is more tedium task as frequency and time planning need to be carried out in CDMA frequency planning is minimal.
➨ GSM (due to TDMA) is a band-limited system. CDMA is a power limited system.

Conclusion : GSM and CDMA have historically represented two distinct technologies in the realm of mobile communication. Both standards have made significant contributions to the global telecommunications landscape, with GSM's widespread international adoption and CDMA's historical prominence in North America.

The convergence towards common technologies, such as LTE and 5G, has diminished the significance of their differences. Today, the choice between GSM and CDMA is less relevant for consumers as modern networks and devices often support both standards. The focus has shifted towards delivering advanced features, higher data speeds and enhanced user experiences, transcending the traditional distinctions between GSM and CDMA.

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