Simon, you saved my day,
On Thu, Mar 29, 2012 at 9:51 AM, Simon Wunderlich simon.wunderlich@s2003.tu-chemnitz.de wrote:
the problem using one radio is explained further here (from another company, but this applies to any WiFi mesh technology)
http://revolutionwifi.blogspot.com/2012/02/mesh-network-performance-impact.h...
I was fully aware of this problem with single-radio nodes, and that's why I was trying to build cheap two-radio nodes using mr3220 + usb dongles.
Also, if you use two-radio nodes, they may interfere with each other if the antennas are near to each other. There are quite a few ppl who can confirm this, e.g. check this:
Ah! you hit the nail right in the head! I walked around the battlemesh wiki a couple of weeks ago, interested into past events results, but only came across an rsync daemon serving a tree with videos, photos and results, mostly in raw data form, collected during the last (before athens) WBM edition.
I think i was a bit short-sighted, since the Wbm2009v2 link (and the rest of that wbm wiki) was a wonderful read!
I did a couple of tests, and indeed increasing the distance between the dongle and the router makes the whole difference.
I googled more on the subject and found a paper with thorough testing results http://edoc.hu-berlin.de/oa/conferences/reSNAVwf8bA/PDF/28TjAjjEtU7ts.pdf
and even finer-grained testing here http://userver.ftw.at/~valerio/files/wons.pdf
None of them use 802.11n equipment, so i set out to make my own experiment. In my case, i needed about 1.5 meter between omni antennas to achieve full throughput, placing both omni antennas perpendicular to the ground and on the same plane. On the other hand, if i place them one over the other (that is, align their vertical axis, while holding them at different altitudes) a distance as little as 20cm was enough to overcome interference. (Sounds reasonable given the omnis gain spatial pattern)
I was able to get 20mbps from A to C (and viceversa), hopping on B. [A ch=11] -- [ ch=11 B(2 radio) ch=1] -- [ch=1 C] This was done using either BATMAN or static routing, giving almost equal results (~1mbps less using batman)
If i put the two radios in B really close to each other (<5 cm) throughput fell down to 8 mbps. It's a relief it was such a simple issue!
Thanks a lot Simon and Marek for getting me into the right path,
So far we haven't heard of anyone implementing OpenWRT+batman-adv on mr3220+usb to build two-radio-nodes mesh network, which means we're mostly in a "solo adventure" so your help and attention was even more appreciated!
Guido