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GSM vs CDMA – Differences between CDMA and GSM

What is GSM?

GSM stands for Global System for Mobile Communication. It is an open, digital communication technology. It is used for communication using voice and data. GSM uses narrowband Time Division Multiple Access (TDMA) technique. The data that is to be transmitted is first digitized and compressed. This data is then sent to a transmission channel with two other data streams. Each in its own time slot. GSM operates in the frequency bands of 850Mhz and 1900MHz.

The architecture of a GSM system is shown below. IT consists of a Mobile Station, the Base Station (BSS), Network Switching subsystem (NSS), and Operation Support subsystem (OSS).


What are the advantages of GSM?

  • GSM provides a higher quality of communication with crisp audio.
  • International roaming is available on GSM at no additional charge.
  • GSM is the most widespread in comparison to CDMA, thus it provides extensive coverage.

What are the disadvantages of GSM?

  • The sharing of bandwidth in GSM leads to communication lag and interference when a high number of users are active.
  • You know how annoying it is when you’re on a flight and have to turn off your cellphones? That’s mostly due to the possibility that someone has a device onboard the aircraft that uses GSM. Since GSM uses a pulse signal technology, it can cause electromagnetic interference with other electronic devices. Including crucial devices like pacemakers. This is the reason that you are asked to switch off your phones on flights and in hospitals.
  • Repeaters are needed to increase its coverage in localities.

We have covered the GSM communication standard in detail here.

What is CDMA?

CDMA stands for Code Division Multiple Access. It is a multiple access technique. Technically, in CDMA a narrow bandwidth message signal is multiplied by a large bandwidth signal. This large bandwidth signal is known as a spreading signal. This multiplication helps reduce the narrowband interference. CDMA possesses high-security features. Thus, it first found application in the military sector. However, with growing processor power and reducing prices it found its way into civil communication around the year 1963.

Each channel (Ki) uses its own frequency at the same time for transmission. Guard spaces provide a layer of separation between the channels to reduce interference. Each channel has its own code. And these codes are orthogonal to all other codes. Since each channel corresponds to a unique code, this results in a lot of codes. However, that’s not an issue as the available space here is huge comparative to the frequency space.

For the detection of a message, the receiver needs to know the codeword used by the transmitter. The receiver performs a time correlation operation to detect only the specific codeword. All the other codewords appear as noise due to decorrelation.


What are the advantages of CDMA?

  • Users of CDMA share the same frequency space.
  • Multipath fading reduces because the signal is spread over a large spectrum.
  • CDMA uses co-channel cells. Thus, it can provide a soft handoff wherever a cellphone is simultaneously connected to two or more stations during a call.

What are the disadvantages of CDMA?

  • Unlike TDMA/FDMA, increasing the number of users in CDMA will raise the noise floor.
  • Self-jamming is an issue with CDMA. When the s[reading sequences of different users are not exactly orthogonal.
  • An undesired user getting a high power signal and the desired user getting a low power signal is called the near-far problem. This is undesirable.


GSM is more widespread. Hence it is very easy to use the phone regardless of location. CDMA networks are less common and don’t generally support GSM phones.
One of the reasons for GSM’s popularity is that it was created jointly by a cohort of organizations. CDMA is mostly owned by Qualcomm which makes it a bit expensive for third parties.
To register on a GSM network, all you need is a SIM card. Carriers have to allow you onto their networks. It’s a bit harder to just connect to the network here.
3G GSM networks can transmit data and voice simultaneously. Comparatively, 3G CDMA networks can’t make voice calls and transmit data simultaneously.
GSM is a time division system. Voice converts to digital data which is given a channel and a time slot here. CDMA is a code division system. Here, we encode voice with unique keys and then transmit them at once.
It requires much lower processing power to process a GSM signal. CDMA signals require higher processing powers.
The subsequent version of GSM released by 3GPP is the HSPA with speeds up to 42MB/s. CDMA works at 3.6MB/s and faster technologies like 4G LTE are being incorporated.
Interference can creep in via other electronic devices in GSM systems. CDMA will not have any interference.
However, it has a hard handoff. CDMA has a soft handoff.
GSM devices emit way more radiation than CDMA devices. CDMA devices barely have any radiations.
GSM signals are less secure. By the nature of their technology, CDMA signals are more secure.
GSM does not provide any built-in encryption. CDMA comes with built-in encryption.
GSM signals operate in the frequency range of 850MHz – 1900MHz. CDMA signals operate in the frequency range of 850MHz – 1900MHz.
GSM is based on wedge spectrum technology. CDMA is based on spread spectrum technology.

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