Aug 7, 2017
Qualcomm products mentioned within this post are offered by Qualcomm Technologies, Inc. and/or its subsidiaries.
It’s been an exciting few days in the Gigabit LTE world, with the news that Verizon, along with Ericsson and Qualcomm Technologies, achieved 953 Mbps in a real world environment deployment.
Let’s break down the relationship between advertised network peak speeds, the technologies used to achieve those speeds, and how the LTE capabilities inside the smartphone determine whether you can take advantage of them. This is about to get nerdy — but it’s important. Get ready.
First, let’s review the factors that determine the peak theoretical speed of a network:
- The width of each LTE connection that the network is sending data over (e.g., 15 MHz, 20 MHz…), and the frequency, or band, of the LTE connection (e.g. Band 2, Band 4, etc.)
- The number of those LTE connections, and whether they can be “aggregated” together to form a wider connection. We refer to this technique as carrier aggregation.
- The number of antennas used to send data over each LTE connection to the mobile device. We refer to this as MIMO (multiple input, multiple output).
- The maximum number of 1s and 0s that the network can send in each LTE signal, or modulation (e.g., 64 QAM – 6 bits, 256 QAM – 8 bits).
- Whether the network uses separate connections for downloading and uploading (this is called FDD), or whether the same LTE connection is used for download and upload (this is called TDD).
If you combine those factors, you can arrive at the peak theoretical speed that the network can deliver. We like to think of the LTE network as a highway for trucks, and your data as packages inside those trucks: the width of each lane, the number of lanes present, the number of decks that trucks can travel on, and the number of packages loaded per truck all determine how quickly your data travels.
Here are some hypothetical examples of different LTE networks, and how implementing the above technologies in different combinations affects the peak theoretical speed of each:
For a country as large as the US the reality is that the width and number of LTE connections available on a given network could vary widely, from state to state or even county to county. That means an operator’s network could support 700 Mbps peak speed in one region, and 400 Mbps in another. For example, Networks 1, 2, 4, and 5 could represent different configurations, by geography, in the same operator network.
Now let’s move along to the common pitfalls that even savvy consumers can fall into when comparing network speed and the advertised capabilities of a smartphone they’re considering.
In fact, if you remember only one thing from this post, let it be this:
Many users will see a phone advertised as supporting, say, 600 Mbps peak speed. They look at the peak speed of Network 1 — at 400 Mbps — and conclude, “Aha! My phone’s LTE speed is more than enough to get the fastest speeds on that network.” Unfortunately, they could be completely wrong.
The underlying features that make smartphones or networks fast are vastly more important than the peak advertised speed. The answer to the below questions directly impacts the peak speed that a phone can achieve on a given network:
- Can the phone support receiving data on four antennas?
- Is the modem inside the phone capable of decoding 8 bits of data in every LTE signal?
- Does the phone support receiving LTE data over 5GHz unlicensed spectrum?
Let’s refer back to our table of networks, and see how different phones fare on each of them.
The results are very revealing, if not astonishing in some cases. On each of these hypothetical networks, Snapdragon Gigabit LTE devices would be able to achieve significantly faster LTE speeds than an older Cat 12 or Cat 9 phone. In some cases, it’s double the peak speed. Surprisingly, even a phone advertised as capable of 600 Mbps peak speeds can only achieve 200 Mbps on Network 1. And in Network 5, where the bulk of the LTE signals are transmitted over the 5GHz unlicensed band—the difference is nearly 7x between Snapdragon Gigabit LTE devices and a Cat 9 smartphone.
Why is this the case? Because the only way to get the fastest speeds is for your phone to mimic the capabilities of the network. In every scenario, Snapdragon Gigabit LTE devices are capable of achieving the fastest LTE peak speeds because they have a superset of the required features being deployed in networks this year, and over the course of the next few years, including support for:
- Many LTE bands, but most significantly, Bands 252, 255, and 46 — the new LTE bands in 5GHz unlicensed spectrum (LTE-U and LAA)
- Combining four LTE connections via 4x carrier aggregation.
- 4x4 MIMO (This has a dual benefit — more on that later.)
- 256-QAM modulation (i.e., it can decode up to 8 bits from an LTE signal.)
So far we’ve been speaking about the peak theoretical speeds. But what about expected performance in the real world? Many users often dismiss the peak theoretical numbers outright, thinking that they have no bearing on their actual experience. But nothing could be further from the truth.
It turns out that real world speeds scale roughly in line with the peak theoretical speeds. Qualcomm Technologies has conducted a massive, sophisticated network simulation that allows us to predict real-world download speeds for LTE devices of varying capabilities in the same network.
The simulated network matched the technologies described for “Network 4” above. And as you see from the chart, the median Cat 16 (Gigabit LTE) device in one sector in the network achieved download speeds that are roughly double those of the median Cat 9 device in that same sector. That’s in line with the relationship between their peak speeds - 1 Gbps vs. 450 Mbps.
It’s clear that to take advantage of the fastest speeds on newly upgraded networks, you’ll need a Gigabit LTE device.
But what about if the network in your area has not been upgraded? The answer, perhaps surprisingly, is that you still need a Gigabit LTE device to get the fastest speeds. Here’s why.
A Gigabit LTE phone that supports 4x4 MIMO has a hidden but critical edge over typical LTE devices. Whereas older LTE devices have two antennas, Snapdragon Gigabit LTE devices have four. As we described above, that’ll ensure you can take advantage of faster speeds in areas where the network has been upgraded to 4x4 MIMO.
Here’s the great thing. The two extra antennas take on a whole new role outside of 4x4 MIMO coverage. When you’re far away from the cell tower (even one that hasn’t been upgraded to 4x4 MIMO), or you’re deep inside a building and have just one or two bars of signal, the two extra antennas act as additional “ears” that help Snapdragon Gigabit LTE devices lock on to a stronger, cleaner signal from the tower — a technology called “4-way receive diversity” — and boost download speeds.
Can this be true? We put it to the test, pitting a device with the Snapdragon X16 LTE modem and 4x4 MIMO support, against a device with a competing modem that supports 2x2 MIMO. We even restricted the Snapdragon device to 4-way receive diversity (not full 4x4 MIMO), and turned off support for 256-QAM, to make sure that we only measured the benefits of the 4-way receive diversity feature. The results are astounding.
This chart shows that from the weakest signal (-6dB, where the noise is four times as strong as the signal) to moderate signal (16dB, where the signal is 40 times as strong as the noise), having a 4x4 MIMO device that supports 4-way receive diversity can give you download speeds that are 58-83% faster than with a device with 2x2 MIMO.
That means where you need it most, 4-way receive diversity is there to give you a speed boost to keep downloading, streaming, and checking up on your friends and family — even in weak signal conditions. And again, this feature is completely independent of the network. You do not have to be near a cell tower that has been upgraded in any way. This benefit applies almost everywhere. Why? Because most of the time, you’ll be in weak to moderate signal conditions. It is only occasionally that you’ll be in good to great signal (20dB to 30dB in the above chart).
This is the kind of performance that the Sony XZ Premium, the HTC U11, the Samsung Galaxy S8 and S8+, and the just announced Moto Z2 Force Edition are designed to give you, thanks to Snapdragon Gigabit LTE. This is why you need it to get the fastest speeds possible, whether you’re in a part of the network that has already been upgraded, or will be upgraded over the course of your ownership of the phone.