"The difference was especially noticeable in weak signal conditions, the results indicated. "
That is NOT what the results indicate.
The interesting (and non-obvious, to non-engineers) result is that the 4x4 antennas give substantially better throughput when communicating with a 2x2 tower. Why should this be? The naive understanding is that only two data streams can be transported, and both phones support that.
The answer is that there are multiple different problems that can degrade the quality of a cellular signal. One that's especially important, but not obvious, is called fast fading. This is caused by a signal bouncing off multiple flat surfaces (think walls) and interfering. The result of this is that the overall signal amplitude varies dramatically over very short distances (~cm). This is not *exactly* a weak signal; it's not caused by being far from the tower. Rather it's a signal that's very strong in some places, and very weak just a cm over from that strong signal.
Now how do you deal with this? The standard way is called antenna diversity, where you have multiple antennas (which, by definition, are a few cm apart) and you cleverly fuse the signals from each of them. BUT if you are using two antennae for diversity, you can't also use those two antennae for two different MIMO signals! It's one or the other, and one of the secret sauce elements that makes some cellular chipsets better than others is how they decide when to switch antennae between being used for diversity and being used for MIMO.
Obviously if you have 4 antennae and 2x2 MIMO, this is a much easier calculation! Because you can just devote a pair to each MIMO stream and still get the benefit of two streams.
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I just don't see much of a need for 4x4 MIMO in the U.S. right now. The few speed tests I've read about didn't seem all that compelling. The 4x4 handsets basically provided close to the same throughput that LTE networks used to have back when the early adopters were the only people using LTE and everyone else was still using 3G handsets. I have yet to see a single speed test in the U.S. that comes anywhere close to the theoretical 'gigabit class' marketing Apple is claiming.
id love to meet someone who finds the 4x4mimi in this xm to be an improvement. Its no better than my 7 was at getting a signal
So the article gives a reference that EXPLAINS why the 4x4 MIMO is better, along with a whole lot of graphs demonstrating this, but no, your gut feelings are a better indication of reality?
O...K...
The issue is not "do you get your theoretical max possible PHY throughput", it is "do you do better than the pre-existing alternative"? I explained in my earlier comment exactly why there is VASTLY more going on here than might appear to the naive internet commenter who knows nothing of real-world cellular issues.
