Medium distance N speed router to router link

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thenuma
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Joined: 03 Apr 2010
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PostPosted: Fri Apr 16, 2010 12:32    Post subject: Medium distance N speed router to router link Reply with quote
My setup is as follows:
2xWNR-834b version 2
both are running 14205M NEWD Eko
both have externally mounted higher gain directional antennas
Routers are 1200 feet apart with clear line of sight
signal noise and SNR are roughly -40, -90, -50 respectively.
Link shows a stable speed of 135mbps, and it sits at 135 always.
running basically all default settings under advanced wireless settings, though I have tried them all. Transmit power on each one is turned way down, like 15mw. (doesn't seem to make much difference though).

The problem is, I'm AT BEST getting 27mbps (peaks) on transfers between the routers. if they have a 135 link, it 'should' do a bit better than 27mbps? My average throughput is 3megabytes/sec, which generally corresponds to the 27mbps transfer. So, what gives? are my results typical?
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phuzi0n
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Joined: 10 Oct 2006
Posts: 10143

PostPosted: Fri Apr 16, 2010 14:37    Post subject: Reply with quote
First off if you have seen it yet: http://www.dd-wrt.com/wiki/index.php/Wireless-N_Configuration

There isn't much info about how well MIMO works with long distance links, but hopefully you understand that MIMO makes use of multiple antennas so you need to change all your antennas not just 1 like you could with G spec. Have you replaced all the antennas on both routers or just 1 on each?

You could try using 40MHz channel width which doubles the bandwidth, but I've had terrible performance out of 40MHz channels with my Broadcom based models (great on Ralink though).

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thenuma
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Joined: 03 Apr 2010
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PostPosted: Fri Apr 16, 2010 14:45    Post subject: Reply with quote
Yep I swapped to 3 seperate, and have adjusted their polarity to try to minimize interference. So, I have a total of 6 total antennas blasting at each other. This is why I can go long distance at only 15mw (i probably overbought the size of the antenna neccesary, but I'm sorta figuring this out as I go). And yes, this is with a 40mhz bandwidth it reports 135mbps. perhaps someone has some insight on a better ACK timing, I'm currently running 300.
phuzi0n
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Joined: 10 Oct 2006
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PostPosted: Fri Apr 16, 2010 15:07    Post subject: Reply with quote
Well that sucks, 135mbps link rate at 40MHz channel means it's only using 1 spacial stream. Have you compared the 20MHz channel performance to see if your throughput is any better?

http://en.wikipedia.org/wiki/IEEE_802.11n-2009#Data_rates

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Read the forum announcements thoroughly! Be cautious if you're inexperienced.
Available for paid consulting. (Don't PM about complicated setups otherwise)
Looking for bricks and spare routers to expand my collection. (not interested in G spec models)
thenuma
DD-WRT Novice


Joined: 03 Apr 2010
Posts: 15

PostPosted: Fri Apr 16, 2010 15:09    Post subject: Reply with quote
yeah I have, what's odd, is even though it now reports a 65mbps link, which is also fine, my 'real' throughput as measured by the wlan counter, and verified by windows transfer rates is still 27 or so mbps. Which, I think is very weird.

Also, I've read the N data rates document you linked to like a bible, I've been playing with this for a few weeks, with the same results, and am simply out of ideas.
phuzi0n
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Joined: 10 Oct 2006
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PostPosted: Fri Apr 16, 2010 15:45    Post subject: Reply with quote
thenuma wrote:
yeah I have, what's odd, is even though it now reports a 65mbps link, which is also fine, my 'real' throughput as measured by the wlan counter, and verified by windows transfer rates is still 27 or so mbps. Which, I think is very weird.

Also, I've read the N data rates document you linked to like a bible, I've been playing with this for a few weeks, with the same results, and am simply out of ideas.

A 65mbps N spec link can do ~40mbps throughput so that's not weird at all. The fact that Broadcom hardware using 40 MHz channel width gives the same (often worse) performance as 20 MHz is the problem I mentioned at first and on the wiki. I've tried NEWD/NEWD2/k2.6 NEWD2 and it never really changed much. Some people have been able to get better 40MHz throughput so it may be an hardware issue with older chipsets.

You're one of a very limited few who have even tried replacing the antennas to do MIMO long range, so I don't think you're going to find much help in that regard. Sad There was a discussion ~1 year ago where some of us questioned if it's even possible to do MIMO (at least spacial multiplexing) at long range since there would be a clean signal without any of the phase variance from reflecting/refracting that make MIMO work. AFAIK nobody has successfully gotten MIMO working long range, but if you really need more throughput then you could try finding hardware that has better 40MHz channel performance.

_________________
Read the forum announcements thoroughly! Be cautious if you're inexperienced.
Available for paid consulting. (Don't PM about complicated setups otherwise)
Looking for bricks and spare routers to expand my collection. (not interested in G spec models)
thenuma
DD-WRT Novice


Joined: 03 Apr 2010
Posts: 15

PostPosted: Fri Apr 16, 2010 15:56    Post subject: Reply with quote
yeah, that's currently my thought as well. Time to find some more N hardware. <sigh>
Peabody
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Joined: 28 Dec 2009
Posts: 1518

PostPosted: Fri Apr 16, 2010 16:52    Post subject: Reply with quote
phuzi0n wrote:
You're one of a very limited few who have even tried replacing the antennas to do MIMO long range, so I don't think you're going to find much help in that regard. Sad There was a discussion ~1 year ago where some of us questioned if it's even possible to do MIMO (at least spacial multiplexing) at long range since there would be a clean signal without any of the phase variance from reflecting/refracting that make MIMO work. AFAIK nobody has successfully gotten MIMO working long range, but if you really need more throughput then you could try finding hardware that has better 40MHz channel performance.


In my previous research, I believe that I saw that some vendors were selling MIMO Directional Antennas. No idea if they really work, or whether they are more examples of antenna snake oil.

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