4G LTE networks have now been around for over a decade in most countries, but the increasing number of existing cellular technologies can make it a bit hard to distinguish LTE from technologies like GSM and CDMA.
4G LTE is neither CDMA nor GSM but a separate cellular technology that provides the 4G migration path to 3G networks on CDMA and GSM tracks. CDMA2000 is the 3G technology on the CDMA track, and UMTS is the 3G technology on the GSM track. Both UMTS and CDMA2000 use the LTE technology for 4G services.
For people who live in European countries or any other country where GSM has been the primary 2G cellular technology, the concept of LTE is quite straightforward. LTE allows 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 (IS-95) and CDMA2000 were deployed, LTE can be a bit difficult to fully comprehend. In this post, we will look at LTE from both of these angles to clarify what it means for GSM and CDMA.
Does LTE use GSM technology or CDMA?
LTE is a cellular technology just like GSM, UMTS, IS-95 and CDMA2000. It allows mobile networks following the GSM and CDMA network evolution tracks to offer 4G cellular services in addition to the 2G and 3G services they already provide.
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 it employed technologies like D-AMPS (Digital Advanced Mobile Phone System) and IS-95 (Interim Standard 1995) for 2G cellular services. GSM and IS-95 networks still exist today, and they have also replaced D-AMPS networks.
After GSM, the next step is 3G UMTS (Universal Mobile Telecommunication System), and the next step after IS-95 is CDMA2000. LTE technology is compatible with UMTS and CDMA2000, allowing both these 3G technologies to use LTE for 4G cellular services.
Where does LTE fit in the overall GSM and CDMA picture?
There have been two key technology tracks for the evolution of mobile-cellular networks: GSM and CDMA. GSM originated in Europe and is now the most widely deployed cellular technology worldwide.
CDMA cellular technologies started in the US in the mid-1990s with the launch of IS-95 (Interim Standard 1995), which is commercially known as cdmaOne. But it is important to note that even though these two technology tracks still exist today (2022), they are limited to 2G and 3G only. Both tracks use the LTE technology (Long Term Evolution) for 4G and NR technology (New Radio) for 5G.
| Network Generations | GSM Track | CDMA Track |
|---|---|---|
| 2G | GSM | IS-95 (commercial name: cdmaOne) |
| 3G | UMTS | CDMA2000 |
| 4G | LTE | LTE |
| 5G | NR | NR |
What is LTE in plain English?
LTE stands for Long Term Evolution, and it is a cellular technology that allows mobile networks to offer high-speed mobile internet services in addition to voice calls and text messages (SMS). It was introduced in 2009 as part of the fourth generation of mobile networks referred to as 4G.
LTE is an all IP (internet) technology which means all services, including voice calls, text messages and mobile data, are delivered over the data network.
Therefore, you can think of it as delivering all services over the internet but keep in mind that the Quality of Service and security standards are very high in mobile communications. The earlier mobile networks, 2G and 3G, used a combination of conventional methods (circuit-switching) for voice calls and SMS and data network (packet switching) for mobile internet.
Since moving all services to data is a huge step, LTE networks also have a 2G/3G backup for voice calls (and SMS). This backup is called circuit-switched fallback (CSFB), and it ensures that there is a fallback system in place if the data-based calls and SMS cannot be facilitated for any reason. CSFB uses the existing 2G and 3G networks.
I have written a detailed post on Voice over LTE, the technology in LTE that enables IP based voice calls and SMS. Also, since the initial launch of LTE in 2009, there have been multiple enhancements, including LTE-Advanced and LTE-Advanced Pro, which can offer average download speeds of 60-100 Mbps.
How is LTE related to GSM?
The GSM-based 2G networks migrated to 3G through the UMTS technology. Universal Mobile Telecommunication System or UMTS is a Wideband CDMA network introduced in the early 2000s. 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.
How is 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 technology is relevant for the US: GSM or CDMA?
Both GSM and CDMA networks are relevant for the US market because 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 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. When a user of a GSM-based network is served by 2G or 3G, they are likely to see a “G” or “E” symbol instead of 4G or LTE.
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. The same mobile phone will need to access CDMA through the CSIM and LTE through a detachable SIM for a mobile user.
Conclusion
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 extra support, especially when preparing for a new job, studying a new topic, or 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 you 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 the product overview and product roadmap.
