Mobile networks have used several cellular technologies worldwide for their evolution from 1G through to 5G. During the 2G and 3G eras, two distinct tracks were created for the future development of mobile networks. These tracks, GSM and CDMA, continued to progress separately until 4G LTE was introduced to streamline the future growth of mobile networks.
GSM is a second-generation (2G) cellular technology and also an evolution path that uses UMTS for 3G migration and LTE for 4G. CDMA is a multiple access technology which enables the CDMA evolution path in mobile networks that uses IS-95 (cdmaOne) for 2G, CDMA2000 for 3G and LTE for 4G migration.
The FDMA, TDMA and CDMA techniques are fundamental in mobile communications as they enable multiple access in mobile networks. Multiple access is the technique that allows multiple people to access the mobile network simultaneously. FDMA, TDMA and CDMA have all been used in mobile networks to create radio access technologies in mobile networks.
The GSM technology is based on FDMA and TDMA, whereas CDMA networks, as the name suggests, are based on CDMA technology. GSM and CDMA laid the foundation of 2G networks, but they continued to develop on separate evolution tracks until 4G LTE was introduced, which is common for both.
GSM and CDMA are two separate mobile network evolution paths
GSM stands for Global System for Mobile Communications, and it is the most widely deployed second-generation (2G) technology standard. The 3G and 4G cellular technologies that follow GSM must meet specific requirements in order to be compatible with GSM.
Compatibility with GSM means the ability to ensure seamless inter-technology handovers between GSM and 3G / 4G cellular technologies. It also means that the 3G and 4G mobile phones can access GSM in geographical locations where 3G and 4G networks have limited coverage. GSM, therefore, provides a complete evolution path to mobile operators.
On the CDMA track, there are two technologies: Interim Standard 1995 (IS-95) and CDMA2000. These technologies create a separate evolution track to develop new techniques and features for meeting customer requirements in the 2G and 3G eras. The fourth generation of mobile networks on the CDMA track, like the GSM track, employs LTE technology.
GSM and IS-95 are 2G cellular technologies
GSM (Global System for Mobile Communications) and IS-95 (Interim Standard 1995) are cellular technologies that enable the second generation of mobile networks. GSM was introduced in 1991/92, whereas IS-95 was launched in 1995. 2G technologies offer voice calls, text messages and essential mobile internet services.
GSM started its journey as a European technology for 2G services to offer digital cellular communication through FDMA and TDMA. In the same era, another technology Digital Advanced Mobile Phone System (D-AMPS), was launched to migrate US-based mobile operators that were using AMPS for 1G.
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. GPRS can facilitate peak data rates of up to 171.2 kbps which is improved to a maximum of 384 kbps with the EDGE enhancement.
GSM, GPRS, and EDGE collectively comprise the second-generation (2G) mobile network evolution. 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 P-GSM (Primary GSM band).
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, which ranges from 880 MHz to 915 MHz for the uplink and 925 MHz to 960 MHz for the downlink.
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. IS-95 A can deliver peak data rates of up to 14.4 kbps, while the technology enhancements in IS-95B can increase the peak data rates to 115.2 kbps.
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.
CDMA2000 and UMTS are 3G cellular technologies
CDMA2000 and UMTS (Universal Mobile Telecommunication System) are cellular technologies that enable the third generation of mobile networks, also known as 3G. CDMA2000 is the 3G migration path for IS-95, whereas UMTS is the 3G migration path for GSM networks.
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.
CDMA2000 follows the same principles as the earlier IS-95 standard and also employs the same frequency bands. UMTS, on the other hand, uses Wideband Code Division Multiple Access (WCDMA) which is different from the FDMA and TDMA combination that GSM employs.
CDMA2000, like IS-95, employs the 850 MHz and 1900 MHz frequency bands with 1.25 MHz channel bandwidths. They are built upon the Direct Sequence Spread Spectrum (DSSS) technique. CDMA2000 has various flavours where multiple channels can be combined (RTT = Radio Transmission Technology) to offer higher data rates.
CDMA2000 with a single radio frequency channel of 1.25 MHz (1 x RTT) can offer peak download data rates of up to 153 kbps. CDMA2000 can also support 3 x RTT, which means three frequency channels combined into one to achieve a bandwidth of 3.75 MHz to offer higher data rates.
WCDMA-based UMTS networks can use flexible bandwidths of 5 MHz, 10 MHz and 20 MHz, but 5 MHz is the most common channel bandwidth. UMTS supports multiple frequency bands, including 850, 900, 1700 and 2100 MHz, and different bands have been used in different parts of the world. UMTS can deliver peak data rates of up to 2 Mbps, but the average is around 384 kbps.
EVDO or EVolution Data Optimized is a series of enhancements in 3G CDMA2000 networks for high-speed data, which offers peak download data rates of up to 14.7 Mbps. Similarly, HSPA or High-Speed Packet Access is a series of improvements in 3G UMTS networks that provides peak download data rates of up to 42 Mbps.
Both GSM and CDMA tracks use LTE for 4G migration
The 3G evolution for the GSM and CDMA tracks continued under two separate projects, 3GPP and 3GPP2. 3GPP stands for Third Generation Partnership Project. 3GPP is a standards organisation that specifies the requirements for cellular technologies that follow the GSM/UMTS network evolution track. 3GPP2, on the other hand, is for the CDMA-based mobile network evolution.
The fourth generation of mobile networks, 4G, streamlines the cellular network evolution by employing the same technology to migrate both GSM and CDMA-based networks to 4G. LTE or Long Term Evolution is the cellular technology that provides the 4G migration path to GSM/UMTS and IS-95/CDMA2000 networks. The table below summarises the network evolution for both CDMA and GSM tracks.
|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|
Phones and SIM cards for GSM and CDMA networks
4G LTE networks are relevant for both CDMA and GSM tracks and are not limited to just CDMA2000 or UMTS. LTE has the capability to allow both UMTS and CDMA2000 mobile networks to offer 4G services. It means that no matter which mobile operator you are with, they use LTE technology for 4G.
All new 4G and 5G mobile phones are backwards compatible, which means they also support earlier cellular network generations, including 2G and 3G. Since LTE is a global 4G standard for GSM and CDMA tracks, 4G LTE phones support cellular technologies on both tracks.
If you are with a GSM-based mobile operator, your 3G service uses UMTS, and your 4G service uses LTE technology. In that case, the 4G SIM card inside your mobile phone will connect you to 4G LTE, 3G UMTS and 2G GSM networks.
CDMA mobile networks, including CDMA2000 and IS-95, do not use separate or detachable SIM cards. Instead, the SIM capability, called CDMA Subscriber Identity Module (CSIM), is built into the user’s device.
Since 4G LTE networks provide a 4G migration path to CDMA2000 also, the 4G phones can take in the SIM card but only to enable the 4G LTE capability in the phone. If a phone user goes into a 3G location (3G CDMA2000), the CSIM capability is required to enable the 3G connectivity. The 4G connectivity does not rely on the CSIM.
In simple terms, if you are with a CDMA-based mobile operator, your 3G service uses CDMA2000, and your 4G service uses LTE technology. So, the 4G SIM inside your cell phone will connect you to the 4G network only. For 3G and 2G connectivity on a CDMA network, your phone needs CSIM capability.
Is GSM a better technology than CDMA?
The choice between GSM and CDMA tracks is not based on which one is a better technology but on which one is available in your region. For example, in Europe, we mostly see GSM-based commercial mobile networks. However, in the US, both CDMA and GSM-based mobile networks are available.
From a technology viewpoint, GSM can offer greater flexibility to a customer because customers can choose their SIM from any mobile operator as long as they have an unlocked cell phone. In addition, GSM networks are also more widely available worldwide, which may make them a safer choice.
But depending on where you live, it may be that mobile operators in your area offer better IS-95 and CDMA2000 coverage than GSM and UMTS, in which case you may be better off on a CDMA network. 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.
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.