For many people who live in Europe or in a country where GSM has been the key 2G technology, LTE is a relatively straightforward concept as it allows their mobile phones to access 4G services in addition to 3G and 2G. However, if you live in the US or in a country where CDMA-based technologies like cdmaOne and CDMA2000 were deployed, LTE can be a bit difficult to fully comprehend. In this post, we will look at LTE from a view that allows us to understand its relationship with GSM and CDMA.

What is LTE in general?

LTE is a fourth-generation mobile network technology that allows all key third-generation mobile networks i.e. UMTS and CDMA2000 to migrate to 4G. It stands for Long Term Evolution and was introduced initially in 2009. Since then, LTE has experienced multiple updates in the form of LTE-Advanced and LTE-Advanced Pro, which are enhancements that improve the download and upload speeds for 4G users. Have a look at our dedicated post on LTE Advanced and LTE Advanced pro to learn about these enhancements.

Does LTE use GSM or CDMA?

LTE is neither GSM nor CDMA, but it is a separate technology allowing GSM and CDMA networks to access 4G cellular services. GSM or Global System for Mobile Communications is a second-generation mobile network technology introduced in the early 1990s. GSM started its journey in Europe and gradually became the most widely deployed 2G technology standard worldwide. Initially, the US was not a GSM country and instead, it employed technologies like D-AMPS (Digital Advanced Mobile Phone System) and IS-95 (Interim Standard 1995 or cdmaOne) to launch 2G cellular services. GSM and IS-95 are still around, but the D-AMPS networks have mostly been replaced by these two 2G technologies. That brings us to an interesting point that GSM and IS-95 (CDMA) are the two existing 2G network technologies worldwide. Therefore any 3G and 4G technologies today must be compatible with these two technologies to provide uninterrupted cellular service to customers. In case you are wondering, we didn’t mention 5G here, but don’t worry; we will cover that separately in this post.

Is LTE related to GSM?

The GSM-based 2G networks migrated to 3G through the UMTS technology. UMTS or Universal Mobile Telecommunication System is a Wideband CDMA network introduced at the beginning of 2000. Later, the 3G UMTS networks migrated to 4G using the LTE technology. So, the 2G mobile networks on the GSM track used UMTS for 3G and LTE for 4G. LTE is a technology that aims to streamline mobile communications by allowing a single 4G migration to all 3G mobile networks.

Is 4G LTE related to CDMA?

The IS-95 2G networks migrated to 3G through the CDMA2000 technology. As the name suggests, CDMA2000 was also a CDMA-based technology standard; however, it used smaller bandwidth (1.25 MHz) than UMTS and was, therefore, a narrowband CDMA technology. The UMTS networks, in comparison, employed wider bandwidths (5 MHZ and higher). Thus, both IS-95 and CDMA2000 collectively represent the CDMA track, a counterpart or competitor of the GSM track. Furthermore, the 4G migration for CDMA2000 was also based on the LTE technology, which means that the LTE technology is related to both GSM and CDMA tracks.

Which one is relevant for the US: GSM or CDMA?

Both GSM and CDMA networks are relevant in the US because the US mobile network operators employ both technologies. For example, T-Mobile US has a CDMA2000 network but also a GSM/GPRS/UMTS network. AT&T has a UMTS based 3G network, whereas Verizon has a CDMA2000 based 3G network. These mobile operators also have the LTE technology for 4G and the NR (New Radio) technology for 5G. 4G LTE streamlines mobile communication by creating a single path for CDMA and GSM-based networks to evolve to 4G. 5G NR follows the exact same approach and creates a single path for all mobile networks to move to 5G.

When a mobile user is on a GSM network, they always have a SIM card in their mobile phone, and the mobile network can switch between GSM (2G), UMTS (3G), LTE (4G) and NR (5G) depending on the location of the user. The CDMA track, on the other hand, does not use separate or detachable SIM cards. The SIM capability in CDMA networks is called CDMA Subscriber Identity Module (CSIM) and is built directly into the user device. If a mobile operator is CDMA-based, they will also have LTE for 4G. For a mobile user that the same mobile phone will need to access both CDMA through the CSIM and LTE through a detachable SIM.


The LTE standard is a fourth-generation network technology that allows mobile networks on GSM and CDMA tracks to migrate to 4G. LTE is neither GSM nor CDMA but a separate technology that provides the 4G migration path to 3G UMTS and 3G CDMA2000 networks. All 4G LTE networks, including those that use UMTS or CDMA2000 for 3G, employ the New Radio (NR) technology for migrating to the fifth generation (5G).

Here are some helpful downloads

Thank you for reading this post, I hope it helped you in developing a better understanding of cellular networks. Sometimes, we need some extra support especially when preparing for a new job, or studying a new topic, or maybe just buying a new phone. Whatever you are trying to do, here are some downloads that can help you:

Students & fresh graduates: If you are just starting, the complexity of the cellular industry can be a bit overwhelming. But don’t worry, I have created this FREE ebook so you can familiarise yourself with the basics like 3G, 4G etc. As a next step, check out the latest edition of the same ebook with more details on 4G & 5G networks with diagrams. You can then read Mobile Networks Made Easy which explains the network nodes e.g. BTS, MSC, GGSN etc.

Professionals: If you are an experienced professional but new to mobile communications, it may seem hard to compete with someone who has a decade of experience in the cellular industry. But not everyone who works in this industry is always up to date on the bigger picture and the challenges considering how quickly the industry evolves. The bigger picture comes from experience which is why I’ve carefully put together a few slides to get you started in no time. So if work in sales, marketing, product, project or any other area of business where you need a high-level view, Introduction to Mobile Communications can give you a quick start. Also, here are some templates to help you prepare your own slides on product overview and product roadmap.

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