CDMA vs GSM vs LTE – What is the differences

Xybernetics Inc : Celluar NetworksA cellular network is a mobile network that provides services by using a large number of base stations with limited power, each covering only a limited area; and each area is called a cell. The limited power makes it possible to re-use the same frequency a few cells away from the base station without causing interference. In this way, a geographic large area can be covered with only a limited set of frequencies which makes cellular network very efficient way of utilizing scarce frequency resources.

The size of a cell can vary according to the number of users that have to be served in a certain area and the amount of traffic per user. If there is too much traffic in an area, the cell size will be smaller than in rural areas. This is done to up keep the integrity of Quality of Service (QOS).

The figure below explains the theory of frequency re-usage.

Xybernetics Inc : Celluar Network Frequency usage

In the example image above, the total amount of frequencies is divided into 7 sets of frequencies. The cluster of 7 cells is repeated to cover the complete geographic area.
When the user moves from one cell to another, the call must be transferred from one base station to another; this is called a handover.

The network has to keep track of the location of the mobile user to direct an incoming call to the right cell, therefore a cellular network is equipped with a location register.


Definition

CDMA
CDMA (Code Division Multiple Access) is a “spread spectrum” for cellular networks enabling many more wireless users to share airwaves than alternative technologies.
The users are separated by the use of different codes and the codes have to be distributed over the cells (instead of the frequencies) in such a way that the interference remains beneath a certain threshold.

GSM 
GSM (Global System for Mobile Communications) is a wireless technology to describe protocols for cellular networks used by mobile phones with over 80% market share globally.

LTE
LTE (Long Term Evolution) is a wireless broadband technology for communication of high speed data for mobile phones.

Differences between LTE and CDMA/GSM
The main difference between the technologies is that both CDMA & GSM can support cellular and data, whereas LTE can only support data.

Differences between CDMA and GSM
However, CDMA/LTE and GSM/LTE are not compatiable for the following reasons.

  • The analog phone (voice) runs on the 2G & 3G spectrum. CDMA and GSM run on different 2G/3G frequencies, thus voice is not compatible between the two.
  • LTE (data) the common denominator, runs on the 4G spectrum. CDMA currently runs on Class 13 and GSM Class 17 LTE, thus data is not compatible between the two.
  • International roaming for CDMA is less accessible than GSM.
  • For a CDMA network, network service is device specific, however for GSM it is SIM card specific or device specific (if the user chooses to use device)
  • There is only one frequency band for CDMA (850MHz). On the other hand, GSM has multiple frequency bands (850/900/1800/1900 MHz). The table below shows CDMA and GSM frequency bands.
    Band Technology UHF Frequency Range
    700 3G, 4G, MediaFLO (defunct), DVB-H 698 – 806
    800 SMR iDEN, ESMR CDMA, ESMR LTE 806-824 and 851-869
    850 GSM, IS-95 (CDMA), 3G 824-849 and 869-894
    PCS GSM, IS-95 (CDMA), 3G, 4G 1850-1910 and 1930-1990
    AWS 3G, 4G 1710-1755 and 2110-2155
    BRS/EBS 4G 2496-2690


International Frequency Band

You can find all the frequency band in the International Frequency Bands


Conclusion

First, neither GSM or CDMA is technically better, they ultimately provide the same service and quality (depending on the carrier) and not the cellular technology (GSM or CDMA).

Second, GSM phones can be unlocked and switched to a new carriers, whereas CDMA phones are locked to a carrier.

Thirdly, if you travel a lot, you have to choose your frequency band carefully as both standards offer multiple frequencies that differ across the globe.

Finally, LTE is being rolled out as a potential global standard, but it falls victim to even more frequency division than GSM and CDMA. The technology also suffers from limited adoption because it’s relatively new.

Reference