GSM vs. CDMA: What’s the difference between CDMA and GSM?

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 communications systems, GSM and IS-95 (cdmaOne). 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 a lot 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.

What’s the main difference between CDMA and GSM?

GSM and CDMA technologies represent two paths for the launch and evolution of digital mobile-cellular networks. GSM (Global System for Mobile Communications) is a second-generation (2G) network technology that uses a combination of FDMA and TDMA. The CDMA-based mobile networks, as the name suggests, follow the CDMA technology and were introduced through IS-95 (cdmaOne) as second-generation mobile networks. For the 3G migration, GSM and IS-95 continued on separate yet aligned paths under 3GPP and 3GPP2. GSM migrated to 3G through UMTS (Universal Mobile Telecommunication Systems) and IS-95 networks migrated to 3G using CDMA2000. Both technologies use LTE (Long Term Evolution) for the fourth generation (4G) cellular services. Have a look at the table below that summarises the network evolution for CDMA and GSM.

Network GenerationGSM-TrackCDMA-Track
2G2G was enabled by GSM (GSM-900, GSM-1800)2G was enabled by cdmaOne (IS-95)
3G3G was enabled by UMTS which is based on WCDMA3G was enabled by CDMA2000 based on CDMA
4G4G introduced by LTE4G introduced by LTE
5G5G introduced by New Radio – NR5G introduced by New Radio – NR
Table showing the relationship between GSM and CDMA

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 are using 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.

Is CDMA or GSM better?

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. 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 a better CDMA2000 coverage as compared to 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.

Does dual SIM mean CDMA and GSM?

Dual SIM means a mobile phone with two SIM card slots either physical or eSIM. With a dual-SIM phone, you may be able to put two 4G or 5G SIMs in the phone. As such, Dual-SIM does not tell you anything about whether a phone has both GSM and CDMA capability. CDMA networks do not have a separate SIM slot but instead an inbuilt CSIM application that typically is programmed by the mobile operator.

What is a GSM network?

GSM was the most widely deployed 2G standard and it used a combination of TDMA and FDMA to provide voice, SMS and mobile data services. The initial GSM networks provided limited data services using the circuit-switched technology which wasn’t very efficient. Therefore, some enhancements were made to the GSM networks in the later years in the form of GPRS (General Packet Radio Service) and EDGE (Enhanced Data for Global Evolution). These enhancements added the packet-switched part to the existing GSM networks in order to offer data services in an efficient manner. GPRS can offer peak downlink speeds of up to 171.2 kbps while EDGE can offer peak downlink speeds of up to 384 kbps. GPRS and EDGE are often referred to as 2.5G and 2.75G respectively.

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 in order to add 10 MHz to both the uplink as well as 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.

What is a CDMA network?

IS-95 was the first standard in mobile communications that utilised CDMA technology. The standard IS-95 has two variants; IS-95A and IS-95B. The frequency band used by IS-95A can either be 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. IS-95 provided capacity advantages for its ability to accommodate more users per MHz of bandwidth.

The power consumption in these CDMA networks is low which allows mobile users to be able to make phone calls in decent quality even when the signal quality is not at its best. Low power consumption also extends the cell coverage which in turn increases the size of the cell. Due to soft handovers (also known as handoffs), the calls are less likely to be dropped.

GSM vs. CDMA – Conclusion

GSM and CDMA are two key tracks of mobile network evolution. The GSM track started with the launch of second-generation GSM (Global System for Mobile Communications) networks where the CDMA track started with the launch of second-generation IS-95 networks also known as cdmaONE. For its 3G evolution, GSM employed the WCDMA-based UMTS technology (Universal Mobile Telecommunication System). On the other hand, the IS-95 (cdmaONE) networks migrated to 3G through CDMA2000.

Here are some helpful downloads

Thank you for reading this post, I hope it helped you in developing a better understanding of cellular networks. But 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 challenges given 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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