Which LTE band to operate on

Some might remember the beginning of mobile phones, where you could not continue using your phone when switching from one operator to another. I’m not talking about SIM locks here, which is just a software restriction, but about a physical restriction: your phone only supported one GSM band, and the new operator had only licenses for the other band. Soon phones were “dual-band”, supporting both GSM bands used in your country. But then you had the same issue again when crossing the ocean because the other continent uses yet two other GSM bands, until tri-band or quad-band phones were the norm.

number of GSM bands supported by phone models over time1

Why are there so many bands?

Because air is a shared medium, only one subscriber can use a radio channel at a time. And since there are a lot of mobile subscribers, and multiple operators, you need a lot of radio channels. But because there were no large continuous frequency bands, the channels are distributed over multiple bands, depending on what was available at the time in the current country. For the sake of simplicity we will split the world in 3 ITU regions:

  • Region 1 (yellow): Europe, Middle East, Africa and Russia
  • Region 2 (blue): the Americas, and some Pacific Islands
  • Region 3 (purlple): Asia and Oceania

ITU regions2

Region 1 and 3 use GSM bands E-GSM (at 900 MHz) and DCS (at 1800 MHz), while Region 2 uses GSM-850 (at 850 MHz) and PCS (at 1900 MHz). With quad-band phones you can be confident to be able to roam over the world, provided there is still a GSM network. But there are not only 4 GSM frequency bands. There are actually 14 of them (some overlapping), as defined by 3GPP TS 45.005 (one of the numerous documents specifying GSM3), but only these 4 are used by public operators (and supported by regular phones).

With the next generation mobile network UMTS things did not become easier. New bands have been added to not interfere with the existing ones. Region 1 and 3 mainly use band I (IMT, at 2100 MHz) and sometimes band VIII (reusing E-GSM spectrum, at 900 MHz), while Region 2 uses band IV (AWS, at 1700 MHz) and reuses band II (PCS, at 1900 MHz) and band V (CLR, at 850 MHz). But there are 25 UMTS frequency bands as specified by 3GPP TS 25.101 (some are only reserved).

number of UMTS bands supported by phone models over time4

And with the current generation mobile network LTE there are a whopping 63 LTE frequency bands as defined by 3GPP TS 36.101 (this includes FDD and TDD, and some are overlapping), and this number keeps increasing with releases5.

number of LTE bands specified in 3GPP TS 36.101 over releases

Phones have to cope with this diversity. Some are even able to do carrier aggregation across bands.

number of LTE (FDD) bands supported by phone models over time6

Why am I looking at this?

I want to operate my own LTE network, and while buying commercial bases stations (eNodeB and the corresponding radio unit) I still needed to choose one which operates on a band supported by most phones, so I can actually test it. To find which band this is I decided to make some statistics, based on the data available on phone databases such as PDAdb7. So I scraped the site, did some parsing, and plotted the result8:

LTE (FDD) band supported by phone models over time9

  • Band 3 is the most supported. This is reusing the GSM DCS band at 1800 MHz, and since operators already have licences for this band originally for GSM, switching to LTE is a convenient thing to do. This band is used in region 1 and 3 as before, but now also in part of region 2 (Latin America).
  • Band 1 is reusing the UMTS IMT band already used in region 1 and 3 (but not in all Africa).
  • Band 4 reuses the UMTS AWS band at 1700 MHz, while band 5 reuses the GSM CLR band at 850 MHz. These bands are used in region 2, as expected.
  • Band 8 reuses the GSM E-GSM band at 900 MHz used in Europe and Asia.
  • Band 7 at 2600 MHz and Band 20 at 800 MHz are new bands. Band 7 is used most over the world except in the USA and part of Africa, while band 20 is used in Europe, Africa, and part of Asia

Note that often phone models have variants for different regions, specifically to support the bands used in these areas. But the hardware is mostly the same. There is one RF chip handling the support for all these bands, and it is sometimes possible to unlock additional bands. These are only software unlocks though, and there might be hardware limitations. Plus, the phone won’t be calibrated for these unlocked bands. For experimenting it might be okay, but for something more stable and reliable prefer getting the proper hardware version10. This is even more important when you are setting up an LTE network and you want to avoid unnecessary complications.

The best choice would be to operate on band 7, the most supported one. Instead I acquired a large base station (80W) and a small band station (a femtocell) which both operate on band 4. No wonder since they come from USA, and while I’m located it Europe I still decided to go with it because enough phones support it, and more importantly this was available and not very expensive.

While band 4 is at 1700 MHz, which is not currently used in Europe, I won’t be able to get a license for it because this is just for the uplink (from phone to base station). The downlink (from base station to phone) is at 2100 MHz, right where UMTS operates at, and where all frequencies are already taken (if downlink and uplink would be switched, that would be ideal). But an important benefit of all these frequency bands is that new operators can get licenses for yet unused bands, and the same applies for researchers like myself who want to play with LTE. I still will have to use cables instead of operating over the air (or use a Faraday cage), but for experimenting this is good enough. And once this is working I can still get a new radio unit supporting another band I can get licenses for.


Footnotes:

  1. based on 12247 devices retrieved from PDAdb.net on 2017-10-01, including 9614 released devices supporting GSM
  2. ITU regions representation from Wikipedia
  3. to download the specifications as PDF documents instead of DOC files I recommend using the equivalent standard provided by the ETSI (just add a "1" in front of the number to get the corresponding specification)
  4. based on 12247 devices retrieved from PDAdb.net on 2017-10-01, including 8395 released devices supporting UMTS
  5. Niviuk has a very nice collection of tools to work with all these frequencies
  6. based on 12247 devices retrieved from PDAdb.net on 2017-10-01, including 5468 released devices supporting LTE (FDD)
  7. GSM Arena and Phone Arena are two alternatives I also looked at, but the way they list variants/versions of phone models is hard to parse (but easy to understand for viewers), and they have less devices (except for older GSM phones)
  8. archive including plotted data, plots, and scripts to scrape PDAdb, generate statistics, and plot data (only the scraped database is not included)
  9. based on 12247 devices retrieved from PDAdb.net on 2017-10-01, including 5468 released devices supporting LTE (FDD)
  10. You can verify the supported bands in the detailed specification on PDAdb, or use this conviniency checker