What is the difference between GSM, UMTS and LTE?

We live in an era where life without our mobile phones seems very unusual to say the least. According to a report from Ericsson (Ericsson Mobility Report Nov 2019), there were around 8 billion mobile subscriptions in Q3 2019, which could mean that we may already have more mobile subscriptions in this world than people. In the early 1980s when it all started, mobile phones were more of a luxury item for those among us who needed to make important phone calls while being on the move. We still had fixed telephones back then but the demand for mobility consistently grew from voice-only communication in the early 80s to virtually every mode of communication today. The emergence of smartphones has been the real game-changer which transformed our mobile phones into mini-computers where voice calling is just one of the many available options.

While the evolution of mobile devices may have been an obvious part, it is the technological advancements in the overall mobile communications ecosystem that has made all this possible. Mobile networks have seen major improvements in order to overcome the key challenges around capability, quality and security since their inception. They have evolved continuously from the first generation (1G) of mobile networks in the early 1980s to the fifth-generation (5G) that we have today. You can learn more about 5G in another post by clicking on this link.

Were mobile networks always digital?

In today’s world, the word ‘digitisation’ is used quite frequently by mobile operators and other communication service providers. With 5G networks already available that can potentially digitise many industries, it is hard to imagine a time when mobile networks themselves were not digital. The first generation of mobile networks (1G) was analogue and employed Frequency Division Multiple Access (FDMA) for the air interface to enable wireless connectivity. The digital era of mobile networks started in the early 90s with the introduction of second-generation (2G) networks which were more secure. The key technologies that enabled 2G were GSM (Global System for Mobile Communications) and D-AMPS (Digital Advanced Mobile Phone System). You can learn more about digital and analogue networks by checking out this post.

2G

The second-generation (2G) of mobile networks introduced two new access technologies TDMA (Time Division Multiple Access) and CDMA (Code Division Multiple Access) into the mix. For simplicity, access technology is what connects a mobile phone to the mobile network by sending and receiving signals through the air interface wirelessly.

GSM was the most widely deployed standard for the second generation of mobile networks. It used a combination of FDMA and TDMA to offer mobile communication services. In GSM, the available frequency spectrum is first broken down into smaller frequency channels, and then broken down further based on time-slots. 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 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.

GPRS or General Packet Radio Service was an enhancement to the existing GSM network in order to provide mobile data services efficiently. GPRS could offer peak downlink speeds of up to 171.2 kbps. Later, there was another enhancement called EDGE (Enhanced Data for Global Evolution) that increased the peak downlink speeds to 384 kbps. GPRS and EDGE are sometimes referred to as 2.5G and 2.75G respectively. You can learn more about GSM in our dedicated post on GSM by clicking here.

Even today, after almost 30 years to their first introduction, you can still get GSM phones. If you think about GSM from a cellular perspective, you are better off getting any smartphone supporting 2G/3G/4G. But if you think of GSM as an alternative to your fixed phone, you can still get a nice looking GSM phone and use it as your home telephone for voice calls.

D-AMPS or Digital AMPS was the other 2G standard that also used a combination of FDMA and TDMA for the air interface. The timing of D-AMPS was similar to that of GSM i.e. the early 1990s. D-AMPS uses the same frequency band for communication as its 1G counterpart AMPS (Advanced Mobile Phone System), which is 824 MHz to 894MHz. You can learn more about D-AMPS and AMPS in our dedicated post here. During the same period, a third technology called Interim Standard 1995 (IS-95) was introduced which used CDMA (Code Division Multiple Access) for the air interface. Details of IS-95 can be found in our dedicated post on this topic here.

3G

There have been two key tracks for the third-generation of mobile networks (3G) and both of them were based on Code Division Multiple Access (CDMA). The first track was Universal Mobile Telecommunications Systems (UMTS), which was used for migrating GSM networks to 3G. The other track was CDMA2000 which enabled IS-95 (cdmaOne) as well as D-AMPS to migrate to 3G.

UMTS was based on Wideband Code Division Multiple Access (WCDMA) and could offer peak downlink speeds of up to 2 Mbps. Since GSM, GPRS and EDGE used a different radio access technology, the UMTS migration required the radio base stations to be upgraded for supporting WCDMA. UMTS networks used the same packet-switched approach that GPRS and EDGE used and made use of SGSN and GGSN in the core network to support mobile data services. Since UMTS networks were designed to co-exist with the GSM networks, they were well-integrated to make sure that inter-technology handovers (IRAT – Inter Radio Access Technology) could take place. The high-level architecture of the WCDMA based UMTS networks can be seen in the diagram below.

For customers, this meant new 3G/UMTS capable mobile phones that could support the new access technology as well as the new frequencies that UMTS networks employed. Just like the GPRS and EDGE technologies were introduced as enhancements to GSM, HSPA (High-Speed Packet Access) was introduced as an enhancement to UMTS networks. This enhancement focused on increasing data speeds of the 3G networks even further. HSPA is a combination of HSDPA (High-Speed Downlink Packet Access) and HSUPA (High-Speed Uplink Packet Access). It can offer peak downlink and uplink speeds of up to 14.4 Mbps and 5.76 Mbps respectively. With further improvement in the form of HSPA+, these speeds have moved up to 42 Mbps and 11.5 Mbps. If you need more information on HSPA and HSPA+, you can check out our dedicated post on this topic by clicking here.

High-level network diagram for GSM (2G) and UMTS (3G)

If you want to get a quick summary view of UMTS networks, check out this 3-minute video.

The 3G migration for the two other 2G technologies D-AMPS and IS-95 followed a different path and used CDMA2000. CDMA2000, also known as CDMA2000 1xRTT or IS-2000 is a successor of the earlier standard IS-95 (cdmaOne) and offers 3G mobile services as specified in IMT2000 (International Mobile Telecommunication specifications for the year 2000). CDMA2000 is backwards compatible with its predecessor IS-95, which makes the upgrade from IS-95 to CDMA2000 easy and seamless. It uses the same carrier bandwidth of 1.25 MHZ and is both circuit-switched as well as packet-switched. Just like HSPA was introduced to improve the data speeds in the UMTS networks, a technology called EVDO (Evolved Data Optimized) was introduced in CDMA2000 to offer higher data speeds. EVDO can offer peak downlink and uplink speeds of up to 14.7 Mbps and 5.4 Mbps respectively. If you are interested, you can check out our dedicated post on IS-95 and CDMA2000 by clicking here. We also have a post on EVDO which you can find here.

4G

The fourth generation of mobile networks (4G) was enabled by a new technology called LTE which stands for Long Term Evolution (of mobile networks). LTE is the 4G migration path for key 3G technologies including Universal Mobile Telecommunication System (UMTS) and CDMA2000. Another technology WiMax (Worldwide Interoperability for Microwave Access) can also provide a 4G upgrade path but LTE has been the primary technology used worldwide for the deployment of 4G networks.

Unlike GSM and UMTS, LTE uses separate multiple-access technologies for the downlink (base station to mobile) and the uplink (mobile to base station). It employs Orthogonal FDMA (OFDMA) for the downlink and Single-Carrier FDMA (SC-FDMA) for the uplink. LTE is much more efficient than the earlier 3G technologies, and it also reduces the latency in data transfer. The achievable data rates depend on which flavour of LTE we are talking about but the following peak data rates can be achieved:

  • LTE – up to 300 Mbps in the downlink
  • LTE Advanced – up to 1Gbps in the downlink
  • LTE Advanced pro – up to 3 Gbps in the downlink

As you might be thinking, these speeds are almost never achievable in real life because these are peak speeds. Have a look at this post to find out the actual or average speeds you can get with 4G LTE networks. You can learn more about the LTE technology in our dedicated post by clicking here.

High-level network diagram for UMTS (3G) and LTE (4G)

To summarise; GSM, UMTS and LTE represent 2G, 3G and 4G mobile network technologies respectively. GSM stands for Global System for Mobile Communications, UMTS stands for Universal Mobile Telecommunications System, and LTE stands for Long Term Evolution (of Mobile Networks). GSM uses TDMA and FDMA for its air interface, UMTS uses WCDMA, and LTE uses a combination of OFDMA and SC-FDMA.

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