Differences Between cellular networks – GSM, CDMA, TDMA, EVDO, UMTS, And HSPA+

In a matter of roughly 40 years, different wireless networks were developed all around the world, giving people the opportunity for never-before-seen connection speed and include billions of subscribers. But how do they differ? What is the difference between CDMA and GSM? Us, mere users, rarely realize these networks are not the same and why it’s important to know about them. So without further ado, let’s discuss each network separately. 

GSM – Global System for Mobile communications

Global System for Mobile communications or GSM was created in the late ’80s and first used in Finland in 1991 to facilitate the 2G digital cellular networks. It is still the most popular network in the US today, and it’s also used around the world in 193 countries. In order to be connected to the GSM network in a certain area, the user has to have a sim card put in their phone, so the network can identify the device. 

CDMA Network – Code-Division Multiple Access

What is CDMA network? Code-Division Multiple Access or CDMA is a network that uses a channel access method to transmit data, meaning there can be multiple simultaneous transfers through the same channel, and a code identifies each one. Thus there’s no need for each call or data transfer to occupy a frequency. The code-division technology was known and used even before WW2, and became a widely used technology in the modern world, with a lot of potential. It does not require a sim card, as the phone is connected to the network directly. 

TDMA Network

Time-division Multiple Acess or TDMA Network tries to solve the problem of limited frequency potential by dividing each data transmission into time slots. This way, multiple users can share, by occupying only a part of the same frequency channel, instead of occupying it to full capacity. This principle was first used for satellite communications in the late ‘70s. 


Evolution-Data Optimized or EVDO is typically used for broadband internet access and is an optimization over CDMA and TDMA networks, thus using both code-encrypting and time division as it’s base principles. 


Universal Mobile Telecommunications System or UMTS is built for the GSM network standard by also using CDMA technology, as it’s more advanced. UMTS is a third-generation (3G) mobile technology system, and it can compare with the EVDO system, which is used for the CDMA network, as mentioned above. 


Evolved High-Speed Packet Acess or HSPA+ is a standard used for wireless communications and is basically an enhanced 3G protocol that combines two systems in one: the HSDPA (High-Speed Downlink Packet Access)  and the HSUPA (High-Speed Uplink Packet Access). 

How do GSM, CDMA, and TDMA transmit data?

We all know that our phones transmit data to other devices through electromagnetic waves, or radiofrequency, in other words. Then, this wave is picked up by the nearest cell tower, which passes it along to a switching center, which then passes it to the user you intended to call. But what is a GSM network, and how does it manage data transmission?


Now the principle behind GSM networks is the following: each operator is given a range of frequencies for a certain area to manage all the data traveling within that area. Practically, this means that each call ‘occupies’ a certain frequency or rather a fraction of that frequency. This poses quite a challenge when the number of potential users grows within this system. Of course, there are ways to optimize the process, but the principle remains the same. Each data transmission will occupy a fraction of a frequency at a time, so GSM uses time and frequency markers to identify callers within the network. 


CDMA uses a different principle to function. It practically encodes each data transfer with a special key, which is then transferred to the recipient to unlock the message. CDMA can transfer multiple codes simultaneously, eliminating the necessity for users to stay on a certain frequency, which makes it a more optimized network, compared to the GSM. 


TDMA transfers data through a certain frequency, each one of which is divided into time slots. This optimization method allows multiple devices to use the same frequency. 


But what does this have to do with us? That’s a valid question. How do users feel the difference between networks used by their phones and carriers? Mainly through the authentication process. If your carrier uses GSM Network, you are a proud owner of a phone with a sim card. This means that as a user, you are identified through your sim card, and that sim card is linking you to the network. Switching sim cards means changing authentication, and you can do that without notifying your carrier. Furthermore, changing phones is also not a problem. Just pop your sim card into the new device, and you’re good to go.


CDMA is a different story. As we mentioned already, your call or data transmission within this Network is identified with a code, which is held by the carrier. So it works like this: your carrier provides you with a phone that is already linked to their network, so it doesn’t require a sim card, and you cannot switch carriers and use the same phone. If you wish to purchase another phone or switch carriers, you can only deal with the carrier itself. 


Is my phone CDMA or GSM– How to check?

This is the short answer to this question: you can check according to the carrier. If you are a Sprint or Verizon subscriber, then your phone is probably a CDMA phone. And which carriers are GSM? If you use AT&T or T-mobile, you can be almost sure your phone uses the GSM network. But naturally, there’s a more sophisticated way to find out which it is. 


  • If you have an iPhone – Settings–General–About–(look for MEID, ESN, or IMEI number)
  • If you have an Android phone – Settings–System–About Phone–(look for MEID, ESN, or IMEI number)

If what you find is an ESN or a MEID number, than your phone uses a CDMA network. If you see only the IMEI number, your phone uses GSM. If you are lucky enough to see both, then the device you have can support both networks. 

Basically, this information will give you the opportunity to choose your options wiser and select carriers and services you will be most content with. 

GSM – Pros and Cons

There’s a lot of speculation within the GSM vs CDMA fight. But the facts are clear. Let’s see what they are, in Pros and Cons.



  • GSM is able to give the user more freedom of choice when it comes to devices and carrier switching opportunities. 
  • Opportunity to use the same phone in other countries, in case you travel a lot



  • CDMA is a more advanced technology that allows more optimization possibilities in the future.
  • GSM has more interference than CDMA networks. 


  • Is Verizon using GSM or CDMA? 

Verizon generally uses CDMA Network. Thus you get a phone directly from the carrier, and it won’t have a sim card. 


  • Is US Cellular using GSM or CDMA?


US Cellular also uses CDMA, so you cannot change your phone and keep the number without the carrier’s permission. It has to be done directly through them. 


  • Is Sprint Using GSM or CDMA?


Sprint is a CDMA Network that works similarly to the two described above. 


  • Is T-mobile using GSM or CDMA?


T-mobile uses a GSM network, so you do have a sim card, and you can purchase a new device and still use the same number as the number is attached to the sim card only. 


  • Is AT&T using GSM or CDMA?


AT&T is also a GSM carrier, one of the biggest in the US. 


Hopefully, now you don’t feel lost in the terminology anymore and can clearly differentiate between main networks. Keep yourself informed and make the right decision. 

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