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Aggregation or Aggravation

Is Carrier Aggregation just more techno-babel aggravation?

A long time ago, in a galaxy far, far away, understanding radio broadcasts was pretty simple- just get the strongest possible signal and soon you’ll be able to listen to radio broadcasts from all over the country! Television added some complexity to this and taught us about things like “ghosts” but, still, increasing signal strength remained the primary objective.

Even when cellular service began some ~30 years ago, it was an analog transmission with “stronger is better” still being a key principle. However, in the mid-90’s cellular service transitioned to digital and this maxim was no longer operative.

With digital signals, “strong enough” became the underlying principle. If a signal is “strong enough,” further increases in strength usually didn’t buy much of an improvement. This is true not just for cellular signals, but also for HDTV, RV park WiFi, satellite TV, etc.

But this doesn’t mean that there’s no way to improve a signal, and that’s where today’s digital technology has brought us some exciting new options. Understanding this new technology isn’t nearly as easy as understanding that stronger signals are better than weaker ones.

Understanding Carrier Aggregation

In a previous blog we talked about how MIMO antenna technology makes it possible for a smart phone or hotspot to create multiple connections to a cell tower. It’s pretty easy to understand that multiple physical connections to a tower using multiple antennas are better than a single one. As we explained in that earlier blog, having more than one “pipe” makes it easier for more “stuff” to flow through them. But even though MIMO can result in significantly improved download speeds, the bandwidth of each of these multiple connections is the same as each of them would have been individually. Therefore, if each MIMO channel is 20 MHz wide, that’s the bandwidth you have matter how many “pipes” you connect.

Carrier aggregation (CA) is like taking MIMO to the next level. Instead of multiple independent pipes, with carrier aggregation it’s as if all the stuff flowing through those pipes is all part of a much larger pipe. With respect to radio frequency signals, this means that the effective bandwidth of the aggregated signals is the sum of the bandwidth of each of the “pipes!” So, if each channel has a 20 MHz bandwidth, with 5-level carrier aggregation, the effective bandwidth of the resulting connection is 100 MHz.

Think of CA as if, in addition to the parallel pipes created by the MIMO antennas, there are now “virtual pipes” created by your phone or hotspot connecting to the tower on multiple frequencies. Essentially, what you end up with is a matrix of “pipes.” In one direction there are the multiple connections created using the MIMO antennas and in the other direction there are the multiple connections created by using multiple communications channels.

Visualize Carrier Aggregation

Carrier aggregation can be implemented using channels in the same cellular band (intra-band) or in multiple bands (inter-band). Within a band, aggregated channels can either be adjacent (contiguous) or not. Figure 1 provides examples of the various ways in which carrier aggregation can be implemented with channel widths ranging from 5 to 20 MHz:

Figure 1: Carrier Aggregation Models

Speeds of Carrier Aggregation and MIMO

MIMO and Carrier Aggregation (CA) work together to improve upload and download speeds. Both create multiple pathways between a cellular device and a cell tower. It’s a bit easier to see multiple antennas than it is to visualize how CA works, but Figure 2 shows how they work together:

Figure 2: Overview of Speeds with Carrier Aggregation & MIMO (Artiza Networks, 2021)

Although this illustration appears rather complex, it’s actually understandable if we examine it piece by piece. Let’s first look at just the section of Figure 3 labeled 2×2 MIMO:

Figure 3: Analyzing Speeds of 20 MHz Channel and 2×2 MIMO (Artiza Networks, 2021)

Without CA, a 2×2 MIMO system with a 20 MHz active channel will provide a theoretical maximum data rate of ~150 Mbps. However, by adding a layer of CA using a second 20 MHz channel, the maximum data rate rises to ~300 Mbps as shown in Figure 4:

Figure 4: Analyzing Speeds of two 20 MHz Channels (CA) and 2×2 MIMO (Artiza Networks, 2021)

As we increase either the complexity of our antenna system (MIMO) or the number of channels employed (CA), we can increase the effective maximum speed of the connection to the cellular tower. As currently defined, up to five 20 MHz CA channels to create an effective 100 MHz channel which would provide a theoretical maximum of 750 Mbps. But if 8×8 MIMO was used instead of 2×2, this maximum increases to 3.0 Gbps! That’s the maximum effective speed of a 4G LTE connection, not a 5G one!

The Takeaways of Carrier Aggregation

So, what does all this mean to you? What it means is that there’s a lot of growth left in the 4G LTE system before we even consider transitioning to 5G. For example, my new Inseego M2000 hotspot has the capability to utilize 5 layer carrier aggregation with built-in 4×4 MIMO which gives it a maximum theoretical speed of ~1.5 Gbps using LTE! Sure, it could go faster if I could access 5G, but those speeds would be more than adequate for anything I would want to do. Similarly, with my Pixel 5 phone, the other day I measured a download speed >140 Mbps on 4G. The phone is capable of using 5G, but I won’t argue about 4G speeds like that!

If all of this stuff is technically baffling, you certainly aren’t alone. These are pretty complicated technologies being used. Fortunately, you don’t need to fully understand it in order to use it as a consumer!

I had set out to explain that the solution to obtaining better cell service is no longer just buying a bigger cellular amplifier. Amplifiers definitely still have their place in locations with very weak cell service; but now there are additional tools you can use to improve your cellular service, even when the signal is strong enough to not need an amplifier.

High on your list of tools ought to be the advanced modems and antennas built into the best of the new phones and hotspots. Unleashing the power of CA and MIMO does require newer hardware, but “newer” doesn’t always mean “very expensive.” Look for the detailed specs of devices you are interested in purchasing. Quite often the usual advertising materials focus on colors, cameras, and other things that don’t impact cellular performance. But if you dig, you can find out info on “the guts” of the device. What category modem does it use? What MIMO antennas are built in? What 5G service does it support? By becoming a knowledgeable consumer, you can identify high performance devices that don’t cost an arm and a leg! Yes, you can pay a thousand dollars for a high quality phone, but you can pay half of that and get one with virtually equal cellular performance.


Artiza Networks (retrieved 01/08/2021). DL Acceleration with CA and MIMO.