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If you want to put your iPhone in the fast lane, you'll need to buy one of the more expensive models. The iPhone XS and XS Max performed significantly better than the iPhone XR in our tests, and that advantage held for all signal conditions: strong or weak, advanced networks or not.

Both the XS/Max and the XR use the same modem, the new Intel XMM7560. But the XR is missing two of the XS/Max's antenna branches, making it a 2x2 MIMO phone versus the XS/Max's 4x4 MIMO. All flagship Android phones right now are 4x4 MIMO, as well, including XR-priced phones like the LG G7 and the OnePlus 6T.

Curious about previous test results? See:

For the best performance with 4x4 MIMO phones, the network also has to support the capability. But our results show that the XS/Max performs significantly better than the XR even when the cellular base station is only running at 2x2 MIMO, demonstrating that the XS/Max is a better choice in all circumstances. The iPhone XR performed a lot like last year's iPhone X, in fact.

As always, we worked with Cellular Insights and Rohde & Schwarz for these results. Cellular Insights has been producing test reports on the RF performance of leading smartphones using Rohde & Schwarz equipment since the iPhone 7 generation.

R&S provided Cellular Insights with the cutting-edge CMWFlexx solution consisting of two CMW500 Wideband Communication Tester boxes, a CMWC Controller, and a R&S TS7124 RF shielded box equipped with four Vivaldi antennas for up to 4×4 MIMO, ensuring high reproducibility of near-field OTA MIMO measurements.

We saw R&S's solution recently at Mobile World Congress Americas and we were blown away by its power and flexibility. The CMWFlexx can simulate pretty much any signal condition you can think of, including arcane band combinations, signal handoffs, and even 5G. It's used by both handset makers and wireless carriers to test and verify their phones.

We tested using LTE Band 4, the most common LTE frequency band used in the US. Yes, we use many bands in the US, and performance may vary per band. But this testing alone took Cellular Insights a week to complete for us, and that's all of its time that we had.

Our test checked to see what a phone can do with a single 20MHz carrier of Band 4 spectrum. A 2x2 MIMO phone can turn that into two data streams of about 100Mbps each, for a theoretical 200Mbps. A 4x4 MIMO phone can get four data streams for a maximum of 400Mbps. Comparing 2x2 MIMO and 4x4 MIMO phones in a 4x4 MIMO network environment, therefore, leads to some pretty stunning differences in speed.

You'll notice from the chart below that the iPhone XS and XS Max have just about the same network performance—the differences aren't big enough to matter. The iPhone XR, on the other hand, looks a lot more like our results from last year's test of the iPhone X, which is also a 2x2 MIMO phone.

Those lab-tested maximum speeds don't always reflect real-world speeds, because there are a lot of other things that control the maximum speed of your LTE connection: interference, path loss, cell saturation, and available backhaul (the cell's connection to the internet). But look at the speeds down at the right side of the chart. Signal strengths beyond -120Mbps are considered very weak conditions, one bar of signal or less. In those conditions, 4x4 MIMO really matters.

When we zoom in on weak signal conditions, we see the significant difference between the iPhone XS/Max and the XR/X. While there were two models of the iPhone X, with Qualcomm X16 and Intel XMM7480 modems, we're showing the better-performing Qualcomm one here. Don't get too worked up over the Qualcomm model of the iPhone X squeezing a tiny bit of speed out of -2dBm of super-weak signal that the new Intel models can't make use of, although we're happy to let Qualcomm have bragging rights over it (you'll hear more about that in our next story, where we compare the new iPhones with the latest Android phones.)

This comparison feels a little unfair, though. How about where the cellular networks can't handle 4x4 MIMO? Some cell sites around the country still run on 2x2 MIMO, and you'd think that in those conditions, the phones would perform equally well. You'd be wrong. It turns out that the iPhone XS/Max get stronger performance than the XR, even when the network itself is 2x2 MIMO.

The iPhone X was split between two models, one with an Intel 7480 modem and one with a Qualcomm X16 one. The Qualcomm modem performed better, as we established last year. The iPhone XS and XR both have Intel 7560 modems, but as you can see on this chart, the XS performs much, much better than the XR does. That goes for weak signal conditions, too.

In short, if you want to squeeze the best performance out of weak LTE networks, you're going to want an iPhone XS, not an XR. Next, we'll compare the new iPhones with the hottest Android phones on the market.