Hangers On

2G? 3G? 4G? Why some older wireless technologies will be sticking around awhile.

Mobile Network Operators’ (MNO) most valuable asset is doubtlessly their spectrum. It forms the backbone of their ability to support the exponential data traffic growth that we’re seeing today. Adding new spectrum is a typical way of increasing capacity in a wireless network — but new spectrum is not always available, and can be an expensive option to license when auctioned off by regulators.

To this end, MNOs need to make the best use of the spectrum they already have, striving to offer better spectral efficiency. It’s well known that of the wireless air-interface technologies, 4G has better efficiency than 3G — enjoying increases of up to 500%.* This is due to using more advanced techniques to improve the number of bits transmitted per single hertz of the spectrum. This includes higher modulation schemes (such as 64 QAM) which results in each transmitted symbol holding 6 bits of information, or radio techniques such as Multiple-Input Multiple-Output (MIMO).

So if 4G networks are vastly superior, why don’t all MNOs discontinue their 2G and 3G networks, and rely exclusively on 4G?

The answer is because they must support legacy services, or systems which were designed well before the introduction of 4G. It’s funny to think that voice calls are a legacy service, considering that this is the reason mobile networks were invented, but it takes only a quick glance at how most people, especially youth, use mobile phones today to believe this. Most 4G networks currently do not support voice call functionality, and require either switching to 3G for the duration of the call (called Circuit Switch Feedback) or the MNO to implement a network function called Voice over LTE (VoLTE).

Every MNO is currently working towards a date within the next 2-3 years when 3G will be completely replaced by 4G, with systems such as VoLTE likely to become ubiquitous in the industry. However, this still leaves the often forgotten but widely used 2G services. This is surprisingly challenging to replace because there are many services which totally rely on the 2G spectrum. For example, many machines use 2G for inter-machine connectivity and communication. This includes credit card readers, vending machines, and the consoles receiving instruction from them. It’s due to these vital and easily forgotten machines that 2G networks will be more slowly phased out.

So in the near future, and likely longer, most MNOs will still need to support multiple technologies in their networks. While 4G will continue to provide the fastest possible data service and replace 3G, 2G networks will likely stay around longer. While users will continue to check email and watch TV on the 4G networks, machines will still be communicating on the 2G network, leaving MNOs with the need to create solutions for adding and managing these multiple technologies — both indoors and out.

Endnotes
*OfCom "4G: Long-term Capacity Gains Report", http://www.realwireless.biz/4g-long-term-capacity-gains-report/.
Spectral efficiency, Wikipedia, https://en.wikipedia.org/wiki/Spectral_efficiency.

Voice over LTE – VoLTE Tutorial, Radio-Electronics.com, http://www.radio-electronics.com/info/cellulartelecomms/lte-long-term-evolution/voice-over-lte-volte.php

"Wireless spectrum: What it is, and why you should care", by Marguerite Reardon, CNET, Mobile, August 13, 2012. http://www.cnet.com/news/wireless-spectrum-what-it-is-and-why-you-should-care/