Wifi protocol, number of antenna and performance

I upgraded(long time ago) my old laptop from an older Intel 2xxx series wifi card to an Intel 7260 AC. I have a Linksys LAPAC1200 AP to serve up the wifi. I noticed today, after YEARS, that it was not moving data as fast as it could. Why am I not getting anywhere close to 1200mpbs? Obviously that's not possible with 2 antennas. Checking the protocol it was using to connect, it identified an AC connection with 150mbps bandwidth. Transferring a large file produces around 10 MB/s transfer rate. So I did some more reading. AC is supposed to be capable of 430 mbps per stream. I have only two streams (antennas), effectively. I figure, WORST case it should be 430 mbps up and down, but I am getting N speeds.


Question:

Is a 430mbps per stream throughput only available there are 3 streams present or should it be defaulting to 430 mbps total with only two streams or does it gimp down to 150mbps?

According to this:https://ark.intel.com/products/78541/Intel-Dual-Band-Wireless-AC-7260-for-Desktop

I should be getting 800, but im not. The laptop is at most 15 feet away from the AP.

The bandwidth is determined to some degrees by having 2-3 antennas, yes (diversity starts with 2 so the hardware can decide which one is getting the better quality signal at any given moment, so 3 or even more offers more potential for more stable signals). But the biggest determinant for bandwidth and speed is the channel bandwidth set by the AP. Some devices, even the high end models, default to 40 MHz channel spacing but to get really high speed speed connections it's going to require 80 MHz.

You'd need to go into the AP and find the settings for the given SSID you're using and make sure it's showing as 80 MHz which should give you a nice boost in performance - of course this is presuming that you don't already have that channel width set for 80 MHz to begin with, and if you do then yep, something's a bit fishy there I'd say.

I have an LG V20 smartphone that gives me roughly 420-450 Mb/s off the 11ac cable modem/AP that I have (gigabit Internet service since mid-November) at 40 MHz bandwidth. If I adjust that to 80 MHz I get 800-825 Mbps easily during a speedtest so, that's what determined the boost in my setup. I'm stuck with this Technicolor POS cable modem/AP which I hate 'cause they have it locked down so much, gotta use Mediacom's shitty web interface to get into it and it just offers so little customization, one of these days I gotta buy my own damned DOCSIS 3.1 device and stop renting this thing.

The Lurker said:

I figure, WORST case it should be 430 mbps up and down, but I am getting N speeds.


Question:

Is a 430mbps per stream throughput only available there are 3 streams present or should it be defaulting to 430 mbps total with only two streams or does it gimp down to 150mbps?

According to this:https://ark.intel.com/products/78541/Intel-Dual-Band-Wireless-AC-7260-for-Desktop

I should be getting 800, but im not. The laptop is at most 15 feet away from the AP.

Click to expand...

Well, you figured wrong.


Wireless is bound by several things, and basically any parameter you talk about has to be at 100% in order to achieve those numbers. A link speed of 430mbps is still only a real world transfer rate of about ~258mbps, in half duplex, assuming perfect conditions. A general rule of thumb is take the link speed and multiple by 60%, as about 40% of the link speed is used in overhead. To answer your specific question though, if you look on the chart at the link you posted you'll see:

Antenna 2x2

That means that 3 spatial streams is never going to be possible in your configuration. So in the following information you'll never want to look at spatial streams above 2 as those won't be possible for you.



So here's a great place to start:

https://en.wikipedia.org/wiki/IEEE_802.11ac

If you look at that table, it's very nicely formatted and gives you all of the info you need. If you only have HT40 (AKA 40mhz channels), then if your device only has 2 antenna chains, the max link speed is 400mbps. So real world link speed is going to be about ~240mbps in one direction assuming no one else is on the channel you are on.

The only 150 on the chart is for single spatial stream, MCS7 @ 40mhz. That would indicate that there is probably an issue between the two devices, and it's not working correctly. (Or in your case you'd probably want to verify that both of the antennas are properly plugged in since you switched out cards. If the device only had 1 antenna plugged in that would certainly cause the issue you're seeing.)

The good thing is that if you're on Windows, there is a way to get some more useful information out of the device.

Open up powershell, and type in:

netsh wlan show interfaces

The most important things here is to look at channel, receive rate, transmit rate, and Signal.

First thing, if the channel is 1-11, then you're not on 5ghz but connected to 2.4ghz. 2.4ghz does not run AC, so you will only be able to run at N speeds, which maxes out at 300mbps link speed for most devices. If the number is higher than that, then you're likely on 5ghz.

receive / transmit rate: These numbers are very useful. Every time you run the command it will tell you the exact speed that the link is connected at. These numbers correspond directly to the table I linked. If you have a 2 antenna device (Which the 7260 is) then you can ignore anything on the table above spatial streams 2. (3 or 4) You should be able to search the table and find what MCS number you're connected at, or at least have a guess between a couple of options. Unfortunately it's possible to hit the same link rates in a couple of ways, so there is a bit of guessing using these numbers. The other part that is useful is going to be the signal percentage.

Signal: This should help you narrow down which option you have. You'll need a signal strength of like 95% + if you want to move into the highest numbers. I'm showing 80% connected right now and I have a connection to my AP with a 468mbps link rate. There are 5 places in the chart of how you can achieve that link rate. But we can quickly narrow it down and find the right one. The 160mhz column is more or less N/A to 99% of devices, as almost nothing can support it. So that knocks out 3 of my choices. The 4th choice has a spatial stream of 4, but I know that my wireless card can only support 2. So we can throw that out. That means that the only choice I could have is 2 spatial streams with an MCS 5. That's definitely plausible, and is very likely the rate I have. (On some APs you could confirm that info, or other programs might just tell you that. There might be a wifi tool that Intel has which will give you real info)

If you want to really hit those MCS7 - 9 numbers, you basically need to get Windows to show that signal % at almost 100%. You'll quickly realize that you basically need to be on top of your AP for that to happen. But the best part is that since that command is real time, you can keep issuing it and you'll get real time data. I just moved my laptop to within 10 feet of the AP, and now I have a signal % of 99, but only a link rate of 351mbps. What gives? Chances are there is some power limiting thing going on in the background, to keep the speed down. With 99% signal strength I would actually guess that I'm using a single spatial stream now, but getting MCS8. It's either that or I'm using 2 spatial streams at MCS4. I could try to reconnect to see if stuff changes, or I could start a transfer and see if it speeds up. I've seen several things occur with laptops when you start moving data. Sometimes they going up in link rate, sometimes they stay the same, sometimes they go down. Now is the best time to actually start a large transfer, then rerun the command and see what happens. In my case, the laptop instantly jumped up to 702mbps, then settled in at 585mbps. So in my case yes, I'd say that it's power limiting itself to 1 spatial stream, then when work comes in it's kicks on the other stream. It tried going directly from MCS8 @ 1 stream to MCS8 @ 2 streams, but found out real quick it couldn't support it. So it dropped down to MCS7 @ 2 and happily moves along at that. I get roughly 45MBps, which is about 360mbps. 585 link rate x 60% = 351mbps, so we're right in that ballpark.

So do the same test I just did, and let us know what happens. That should give you an indication of what's going on with the device. The biggest take away is that wireless numbers are 100% BS, and the MCS8 and MCS9 that was added in AC only happens when you have really good signal strength. 4 "bars" out of 5 probably really only means MCS6, so if you look at the chart the "best case" is really 585, but in reality I'd expect you'd get 800ns GI (Long guard) so MCS6 @ 80mhz 2 streams which delivers about 527mbps link rate for a real world number of ~316mbps in one direction. If you attempt to move traffic in both, expect that number to be worse than half as there will be additional overhead.


EDIT: Snipped out my edit as it wasn't correct.

Thanks to the both of you guys for your very good explanations I was able to determine the problem. The configuration in my AP was correct... for the most part. Specifically, the 5ghz antenna was set for 20/40/80, it was configured to allow AC connections, signal power maximum, etc connection settings were set to default values except for one. Reading what you wrote about the role channel width plays in the throughput and the relationship to the antennas, I started to investigate further. I agreed with you that something is going on either with the antennas or the channel width. I downloaded wifi analyzer on my phone and went to work. After staring at the app a good 10 minutes I noticed by AP's 5ghz network was only operating at 20mhz. Well how could that be if the AP is configured for 20/40/80? At the same time the app is recommending the best channels to use are 42,44,48. I said, OK, no one is using those channel around me so lets give that a shot. NOW... A few days ago, in my experimentation to narrow down a possible interference issue I changed my 5 ghz network channel selection from Auto to 165. After switching it to channel 44, the network reports 80mhz bandwidth in the app. After a bit of googling, I learned that Channel 165 is a 20mhz band only.

Problem solved, thanks to you guys and the education.



In hind sight, I think it was always fast, its just been a while since i had to move a large chunk of data and screwing around with the AP a few days ago just broke what was perfectly working.