GSM vs CDMA: A Detailed Comparison of Mobile Communication Standards

gsm
cdma
mobile communication
cellular technology
network

GSM and CDMA are both digital cellular communication standards, defining how mobile devices communicate and connect to cellular networks. Both have been specified in the 3GPP series of standards and support voice and data transmission, enabling users to make calls, send texts, and use mobile data services. GSM utilizes GPRS for data, and both require cellular network infrastructure with base stations and mobile switching centers. Despite these similarities, key differences exist between GSM and CDMA.

GSM (Global System for Mobile Communications) uses TDMA (Time Division Multiple Access), allowing multiple users to share the same frequency through different time slots. CDMA (Code Division Multiple Access) relies on code division, enabling simultaneous communication by assigning unique codes to users on the same frequency.

Let’s delve into the features of each technology before comparing them in detail.

What is GSM?

GSM, short for Global System for Mobile Communications, is a standard developed to ensure a common platform for mobile devices, facilitating communication across networks and countries. Conceived in the 1980s, GSM has become the dominant mobile communication standard globally.

This technology employs a TDMA/FDMA access scheme to allocate channels to different subscribers, allowing them to utilize services from the operator’s base stations. One frequency and one time slot (f1, t1) are needed for one-way communication, and a pair ((f1, t1) and (f2, t2)) for two-way communication.

Here, different users share the same frequency but at distinct time slots for transmission.

gsm network architecture

GSM also introduced the use of SIM (Subscriber Identity Module) cards, enabling users to easily switch devices by transferring the SIM. The figure above depicts the GSM network architecture and its elements.

What is CDMA?

CDMA stands for Code Division Multiple Access, 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. It uses PN codes for communication between subscribers and NodeBs. Information is extracted by despreading at the receiver using the same PN code used at the transmitter.

Note that information isn’t retrieved using (time, frequency) assignment in CDMA. All different PN codes utilize the same frequency/time to communicate. CDMA uses 1xEV-DO and EV-DV versions in 3rd generation.

CDMA has an edge over GSM due to its immunity to interference and jamming.

UMTS network architecture

In CDMA, each user’s signal is spread over a wide frequency band using a unique code. This spreading allows multiple users to transmit and receive data simultaneously without interfering with each other. Unlike GSM, CDMA doesn’t use time slots; instead, it assigns a unique code to each user, allowing all users to communicate at the same time.

Difference between GSM and CDMA

The following table compares these cellular technologies, highlighting the differences between GSM and CDMA.

SpecificationsGSMCDMA
Full formGlobal System for Mobile CommunicationCode Division Multiple Access
Frequency Band(MHz)UL: 890-915, DL: 935-960, UL: 1710-1785, DL: 1805-1885UL: 824-849, DL: 869-894, UL: 1850-1910, DL: 1930-1990
Carrier Spacing(KHz)2001230
Physical channels per carrier8Soft capacity
Channel accessFDMA/TDMACDMA
RangeShorterLonger
SecurityRelies on SIM card for security featuresBuilt-in security features including encryption and authentication
Frame Duration(ms)4.620
Modulation MethodGMSKPSK
Channel rate (Kb/s)270.8331228.8
Modulation Efficiency (b/s/Hz)1.351.0
Maximum Terminal Transmitter Power (watt)86.3
Speech codingRPEQCELP
Speech rate, including channel coding(kb/s)22.8Variable
Cellular Efficiency(conversations/cell/MHz)5.0-6.612.1-45.1
Associated Control Channelseparate slots in each framedim-and-burst
Out-of-band ACCH rate(b/s)9504400-7600 (Speech quality reduced when control channel is active)
Standard versionsGSM and GSM Advanced (supports MUROS, VAMOS, MSRD, AMR, SAIC)CDMA-one (as per IS-95), CDMA-2000 (as per CDMA2000), WCDMA (as per UMTS 3G std.)
Network structureMore widespread globallyHistorically more prevalent in North America
Handset compatibilityMore international compatibilityMore region-specific
Tutorial for further study

Some key comparisons include:

  • In GSM, the available transmission bandwidth is smaller, potentially compromising voice transmission quality. In CDMA, the entire transmission bandwidth is utilized, potentially enhancing voice quality.
  • GSM (TDMA/FDMA) requires more tedious cell frequency planning, while CDMA frequency planning is minimal.
  • GSM (due to TDMA) is a band-limited system, while CDMA is a power-limited system.

Conclusion

GSM and CDMA have historically been distinct technologies in mobile communication. Both have significantly contributed to global telecommunications, with GSM’s international adoption and CDMA’s prominence in North America.

The convergence towards technologies like LTE and 5G has diminished the significance of their differences. Today, the choice between GSM and CDMA is less relevant as modern networks and devices often support both standards.

The focus has shifted to delivering advanced features, higher data speeds, and enhanced user experiences, transcending the traditional distinctions between GSM and CDMA.

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