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04/17/2015
Radio Shootout Pt 1 - AC Lite vs. Brand M
Description

Mim-AC.JPG

I was initially going to compare the AF5X with the Brand M radio (in the picture above) so that everyone could see how the two really compare.   But once I did some baseline throughput testing on the bench, it became obvious that Brand M wasn't really in the same league as the AF5X, and was really more like the AC radios (which is actually what it is - it even says "a/n/ac" in one of it's wireless mode selections).   Below is a quick look at the max speeds of a RocketM, and AC Lite, an AF5X (actually on early firmware, so the ones people are getting now are actually faster) and Brand M.   This is a quick and dirty baseline test - the tests farther below were much more thorough and better set up, but all the radios were treated equally for this first one.

BaselineShootout.png

What became immediately obvious was that except with an 80MHz channel the Brand M radio, comparing apples-to-apples (with just one of it's 2x2 radio channels operating) is significantly slower than the AF5X, and still slower than the RocketAC Lite.   

So at this point I abandoned the idea of head-to-head testing (at least for throughput) with the AF5X, which really outclasses the Brand M, and instead stick with the ACs.

 

One thing that should be finally put to bed here - if anyone out there still thinks there's some magic going on inside the Brand M radio for it's "160MHz channel" other  than effectively two AC radios in one box, here's the proof - an AirView of the radios actually running:  

B5cDualRadio.png

If you look at the areas directly adjacent to the two 40MHz channels, you can see how much IM junk is generated in the PA - this is on the bench, so there's no interference from outside radios.

 

Anyway, after this I just concentrated on comparing it to an AC Lite.   Following is a series of automated tests comparing the AC Lite and the Brand M radios.   These are all using iperf in tcp mode, with 10 streams each, and with a complete tests running in each direction at once, so this is testing actual throughput both directions simultaneously for each radio.   Note that the PHY rate (dotted line) is the actual theoretical hardware encoding rate possible at that MCS and channel width, and the actual throughput of the radios is always lower than that - often much lower.

Throughput_bidir_R5AC-LITE,MIMO-B5C,['1x20']1429223748.pngThroughput_bidir_R5AC-LITE,MIMO-B5C,['1x40']1429223942.png

Throughput_bidir_R5AC-LITE,MIMO-B5C,['1x80']1429223960.png

You can see that in 2x2 mode at 80MHz the Brand M is faster than the AC Lite - at that channel width, the AC Lite is at the edge of it's chipset's capabilities, plus it was designed to do more narrow channels.   And who has clear 80MHz chunks of spectrum anyway?

 

Since the Brand M radio has the capability (as seen in the AirView above) to run as two 2x2 MIMO radios on two different channels, and combine the data streams together, the analogous setup for an AC radio is to use two discrete radios, each on it's own channel.   So this was done also (the setup actually used an EdgeRouter in load balancing mode to create the two streams for the two radios, and then another one to recombine them on the other end):

Throughput_bidir_R5AC-LITE,MIMO-B5C,['2x20']1429223709.png

You will note in the above test that the Brand M radio shifted speed part way through the test.   I saw this kind of behavior in other areas too - changing power output to see what effect that had on throughput, I found I could never quite get back to the performance level I initially saw.   And some times the performance would drop off after the radio heated up - this may be indicative of some thermal management issues in their power amplifiers - the actual quality of the PA , or maybe they just need a bigger heatsink...

Throughput_bidir_R5AC-LITE,MIMO-B5C,['2x40']1429223662.pngThroughput_bidir_R5AC-LITE,MIMO-B5C,['2x80']1429223987.png

Note that in the dual 80MHz case the AC Lites are faster than Brand M, unlike in the single 2x2 test before.  My guess is the PA is reaching the limits of it's IM cababilities trying to linearly amplify the two separate frequencies, and therefore the modulation rates go down.

 

Since the test was already set up, here are the AC Lite's results for all the other channel widths it can do:

Throughput_bidir_R5AC-LITE_1429224656.png

And here it is with dual radios:

Throughput_bidir_R5AC-LITE_1429224655.png

Now it's legitimate to ask if using two complete AC radios and an EdgeRouter Lite on each end is a fair comparison in the real world.   Well, economically, a pair of Brand M radios costs $1678, vs $740 for 4 AC Lites plus two EdgeRouters, a less than half the price of the Brand M radios alone.   And yes, to make this work you'd need 2 more antennas for the ACs, but this is a pretty corner case solution anyway - where but in the middle of nowhere or over a very short link are you going to be able to do this (especially at 80MHz channels) and in those cases you can probably do better with AF5s or AF24s anyway.

 

So what's the upshot of all this?   Well, things don't look so good for the Brand M radios so far in this shootout...

 

Part two will look at some other radios (plus these two again) and how they fare in interference situations. 

Jim

Comments
by
on ‎04-17-2015 05:31 PM

Can someone explain what 'M' mean when they say 4x4:4 mimo?

by
on ‎04-17-2015 06:33 PM

Thanks Jim!  I'm seeing similar results in the field and trying to get a handle on it.   Nice to see this extensive lab work to make sense of it all.  

by
‎04-17-2015 08:45 PM - edited ‎04-17-2015 08:50 PM

What their 4x4 MIMO is?   Briefly, MIMO is a way to create multiple streams of data in an RF signal, where the payload data is spread across more than one stream.   In 2x2 MIMO there are two streams or "chains" and each one is encoded in a separate RF carrier.   In most radio systems (like UBNT) the two radio channels are transmitted in the same direction by the antenna, but in orthagonal polarities (90 degrees apart) so they can be kept separate, since the two streams are using the same radio frequency.   If there are more than 2 streams, that just means there have to be additional ways to keep them separate.   In Ms radio, they actually use a 4x4 MIMO chipset, but separate it into 2 2x2 streams by putting them on 2 different frequencies.   You can theoretically create as many streams as you want - the practical limit is around 8 or so - but 3x3 is used in higher-end WiFi systems.

Jim

by
on ‎04-18-2015 01:16 AM

Thanks Jim, I guess I should have been a bit more specific - I'm familiar with 2x2, 3x3 etc, but they write it as 4x4:4 - Whats the last 4??

by
on ‎04-18-2015 01:24 AM

@eejimm Great writeup! Very good work, you're the man!

by
on ‎04-18-2015 02:45 AM

@eejimm Great and detailed writeup.

 

Alot of time spent on this... Kudos

 

/Paetur

by Ubiquiti Employee
on ‎04-18-2015 07:58 AM

Awesome writeup Jim! Thank you for sharing your results

by
on ‎04-18-2015 08:31 AM

can someone please tell me how to power my PTZ 24 volt camera and Ubiquiti NanoStation M5 NSM5 with a 12 o2 24 volt car battery

by
‎04-18-2015 08:36 AM - edited ‎04-18-2015 09:36 AM

by 2m ago

can someone please tell me how to power my PTZ 24 volt camera and Ubiquiti NanoStation M5 NSM5 with a 12 o2 24 volt car battery 


Post that question here:  

http://community.ubnt.com/t5/Installation-Troubleshooting/bd-p/airMAX_Troubleshooting

 

And, you will get some good help.  You intrupted a thread with your oftopic question.

by
‎04-18-2015 09:03 AM - edited ‎04-18-2015 09:03 AM
by 8 hours ago

Thanks Jim, I guess I should have been a bit more specific - I'm familiar with 2x2, 3x3 etc, but they write it as 4x4:4 - Whats the last 4??

 

OK, the nomenclature is kind of repetative, but it goes like this:

 

TxR : S   Where T is the number of transmit chains, R the number of Receive chains, and S the number of Spatial streams.   Not sure who came up with that, but there it is.

Jim