LTE 5-Carrier Aggregation

I just had a look in my archive when I first started to see carrier aggregation in LTE networks. It turned out that, from my point of view, first networks and devices started to support the aggregation of 2 carriers with a maximum bandwidth of 2x 20 MHz in 2014. A few years later in 2016, high end devices began to support the aggregation of up to 3 carriers. Since then, network operators have have continued to increase the amount of spectrum they use in dense urban deployments, and mobile device hardware has further improved as well. Hence, I recently had another look at the state of the art.

Obviously, the best way to add capacity in dense urban areas is to use band n78 with 5G in addition to LTE, so let’s take a little detour first: Band n78 offers up to 100 MHz per carrier, and in many countries, operators have been able to get 80 to 100 MHz for their networks. That’s more on a single carrier than most of them can aggregate in lower bands with LTE.

Let’s come back to LTE: High end devices today in 2022 can aggregate up to 5 LTE bands, and, in addition, a 5G n78 carrier with up to 100 MHz. In total, that’s up to 200 MHz of bandwidth that can be used in the downlink direction. That’s a long way from the 10 to 20 MHz first LTE networks were launched with a decade ago. And it’s direly needed, as in dense urban areas, even 4-CA LTE networks without 5G n78 are highly loaded in many places, especially in the evening hours.

A quick note on the ‘up to 100 MHz’ aggregation statement. Aggregating 100 MHz with 5CA would mean that every carrier would have a bandwidth of 20 MHz. Most network operators, however, do not have 20 MHz in all bands. Here’s a typical 5CA combination found in Europe today:

  • 10 MHz in band 20 (800 MHz)
  • 20 MHz in band 3 (1800 MHz)
  • 10 MHz in band 3 (1800 MHz)
  • 20 MHz in band 1 (2100 MHz)
  • 20 MHz in band 7 (2600MHz)

That’s 80 MHz in total. Quite a bit compared to the 10 to 20 MHz used when first networks started, and massive compared to the 5 MHz used by early 3G UMTS networks, but still less than the 100 MHz offered by a single 5G NR carrier in band n78. Nevertheless, in load situations, every MHz counts!