For people in the telecom industry, concepts like FDMA, TDMA and CDMA are fairly well-understood as these are the techniques used by telecom networks for enabling multiple access. Multiple access is the capability that allows multiple people to access the mobile network simultaneously. Therefore, the whole CDMA vs GSM discussion is misleading because the comparison is not between two multiple-access techniques but between two mobile network evolution tracks for 2G and 3G: GSM & UMTS and IS-95 (cdmaOne) & CDMA2000. However, for people who live in countries where mobile operators have both GSM and CDMA-based mobile networks, e.g. the US, this topic is more than just a telecom theory discussion. Therefore, this post aims to answer some of the confusing questions that pop up due to the special relationship that GSM and CDMA networks have.
GSM is a 2G cellular technology that follows a mobile network evolution track that uses UMTS technology for 3G migration; CDMA2000 is the 3G technology for the CDMA-led evolution track that uses cdmaOne (IS-95) for 2G and CDMA2000 for 3G. Both GSM and CDMA evolution tracks use LTE for 4G migration.
2G and 3G network evolution for GSM
GSM or Global System for Mobile Communications started as a European 2G solution for providing digital cellular communication using a combination of TDMA and FDMA. In the US, at the same as GSM, a technology called Digital Advanced Mobile Phone System (D-AMPS) was launched, which was a digital version of the earlier 1G standard Advanced Mobile Phone System (AMPS). GSM later saw some enhancements in the form of General Packet Radio Service (GPRS) and Enhanced Data for Global Evolution (EDGE) for introducing packet-switching, which was not part of the original solution. GSM, GPRS and EDGE are second-generation (2G) cellular technologies. The technology that allowed GSM networks to migrate to 3G is called Universal Mobile Telecommunication System (UMTS), which is based on Wideband Code Division Multiple Access (WCDMA).
The original frequency band for GSM networks was from 890 MHz to 915 MHz for the uplink and 935 MHz to 960 MHz for the downlink. This frequency band is known as the Primary GSM band or P-GSM. The primary GSM band was later extended to add 10 MHz to both the uplink and the downlink. The extended band is known as Extended GSM or E-GSM, and it ranges from 880 MHz to 915 MHz for the uplink and 925 MHz to 960 MHz for the downlink.
2G and 3G network evolution for CDMA
When GSM and D-AMPS were introduced in the early 1990s, there was no CDMA based technology available in mobile communications. In the mid-1990s, a CDMA-based cellular standard, IS-95 (Interim Standard 1995), was introduced, which is commercially known as cdmaOne. cdmaOne is a second-generation (2G) cellular standard just like GSM and D-AMPS. The standard IS-95 has two variants; IS-95A and IS-95B. The 3G network evolution for IS-95 is based on the CDMA2000 technology. The frequency band used by the IS-95 network has similarities with that of GSM. IS-95A can either use 824 to 894 MHz or 1850 to 1990 MHz with separate frequency bands for the uplink and the downlink. The carrier frequencies used in IS-95 have a bandwidth of 1.25 MHz. The peak data rates of up to 14.4 kbps can be achieved by IS-95A, while the technology enhancements in IS-95B can increase the data rates to up to 115 kbps.
2G GSM, 2G cdmaOne(IS-95) and 3G CDMA2000
While D-AMPS was a crucial part of second-generation (2G) mobile networks, it wasn’t part of the 3G network evolution. From 3G onwards, the only technologies that continued their journey were standards based on the GSM and IS-95 technologies. So, GSM and CDMA technologies represent two tracks for the launch and evolution of digital mobile-cellular networks that we see today. The evolution track on the GSM side consists of GSM itself for 2G and UMTS for 3G, whereas the CDMA track consists of IS-95 (cdmaOne) for 2G and CDMA2000 for 3G. For the 3G migration, GSM and IS-95 continued on separate yet aligned paths under 3GPP and 3GPP2. However, the fourth-generation (4G) migration streamlines the cellular technologies to create a single evolution track. Therefore, LTE or Long Term Evolution technology provides a 4G migration path to both GSM/UMTS and IS-95/CDMA2000 networks. Have a look at the table below that summarises the network evolution for CDMA and GSM.
|2G||2G was enabled by GSM (GSM-900, GSM-1800)||2G was enabled by cdmaOne (IS-95)|
|3G||3G was enabled by UMTS, which is based on WCDMA||3G was enabled by CDMA2000 based on CDMA|
|4G||4G introduced by LTE||4G introduced by LTE|
|5G||5G introduced by New Radio – NR||5G introduced by New Radio – NR|
Is 4G LTE CDMA or GSM?
4G LTE networks are neither CDMA nor GSM. GSM is a 2G technology, and cdmaOne (IS-95) is also a 2G technology. These technologies follow two separate tracks for their 3G evolution. GSM migrated to 3G using the UMTS technology, and cdmaOne migrated to 3G using the CDMA2000 technology. LTE is a 4G technology that allows both 3G CDMA2000 and 3G UMTS to migrate to 4G. It means that no matter which mobile operator you are with, they use LTE technology for 4G; however, depending on which technology they use for 3G, your requirements may differ. If your mobile operator is a GSM-based operator, they use UMTS for 3G and LTE for 4G, in which case your 4G SIM would also connect you to the 3G and 2G networks. However, if your operator is CDMA-based, they use CDMA2000 for 3G, which means 4G SIM will only connect you to 4G and not the 3G and 2G networks. For 3G and 2G connectivity, you would need the CSIM capability within your phone on a CDMA-based network.
Can phones be both CDMA and GSM?
Yes. All new 4G and 5G mobile phones are backwards compatible, which means they support the 3G and 2G technologies. Since LTE is the global 4G standard that provided the 4G migration path to networks on GSM and CDMA tracks, the 4G phones support GSM and CDMA.
Does CDMA use SIM cards?
CDMA mobile networks, including CDMA2000 and IS-95, do not use separate or detachable SIM cards. The SIM capability, called CDMA Subscriber Identity Module (CSIM), is built into the user device. Since 4G LTE networks provide a 4G migration path to CDMA2000 also, the 4G phones can take in the SIM card; however that is only to enable the 4G LTE capability and if the user goes into a 3G area (3G-CDMA2000), then the CSIM capability is required to enable the connection. 4G connectivity does not rely on the CSIM.
Which one is better GSM or CDMA?
GSM and CDMA are the two separate mobile communications tracks that continued their separate journeys in the 2G and 3G era and eventually got streamlined when 4G LTE networks were launched. IS-95, also known as cdmaOne, was the first CDMA-based second-generation technology that later evolved to CDMA2000 in the 3G era. On the other hand, GSM is the most widely deployed 2G technology, which evolved to UMTS for 3G. Both these technologies use LTE for the fourth generation (4G) services. From a technology viewpoint, GSM can offer greater flexibility to you as a customer because you can choose your SIM from any operator (on an unlocked phone) and also because it is more widely available globally. But depending on where you live, it may be that your operator has better CDMA2000 coverage than UMTS, in which case you may be better off on CDMA2000. Either way, since they both use the same LTE technology for 4G, given the maturity of 4G LTE and the introduction of 5G NR, your dependency on 3G and 2G networks will diminish gradually.
GSM (Global System for Mobile Communications) is a 2G cellular technology that evolved to 3G using UMTS (Universal Mobile Telecommunication System) technology. CDMA2000 is another 3G cellular technology just like UMTS, and it evolved from a 2G technology, IS-95 (Interim Standard 1995). Both GSM/UMTS and IS-95/CDMA2000 tracks still exist today however, they both use the LTE technology (Long Term Evolution) for 4G migration.
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, 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 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.