Multiple Prism 2.5 Cards and Sector Antennas?

[wispy]

If a Linux Box with 6 pci slots and StarOS has 4 Prism 2.5 minipci 200 Mw cards installed, are there software/hardware provisions to use 3 ea. 65 degree patch panel antennas for concentrated coverage and the 4th antenna as a long distance PtP using a 24 dbi parabolic antenna.

If yes, what is the absolute limit on cards+antennas that can be driven from a single Linux box with StarOS?

If not, could it be explained why not?

[georgew]

Yes, you can do this...

However you are defeating your purpose. If you use more than 3 802.11b channels, your sectors will interfere with each other, reducing their effectiveness. You should use no more than three channels at a time, and they need to be chosen not to overlap.

The purpose of using a combination of sectors and directionals, as you have proposed, is to increase the gain and selectivity of your antennas to improve the connection quality. As soon as you use overlapping channels, you start generating local noise that is thousands of times stronger than the distant signals you are trying to receive.

Regardless of how hard you try, it is impossible to shield the radios from each other without putting some distance between them... Distance as in not being in the same box, or even on the same hill... let alone in the same router.

StarOS supports 8 radio cards at this time. You can configure each card independantly of the others, so the answer is simply "yes".

The question you didn't ask, but I offered an answer to anyway was "should use 4 or more cards together in one router?".

Personally I would like to be able to use each channel simultaneously, for up to 11 radios per installation, using really focused sectors. However the FCC didn't give us the bandwidth for 11 channels, they gave us the bandwidth for three channels, then packed 11 channels into that space.

Think of it like lanes of traffic on a highway... We are given 11 lanes in the space required by three vehicles passing each other almost touching. If you try to assign 4 lanes and send vehicles down these lanes in opposite directions, there will be collisions. Collisions equate to packets that are lost. If there is no traffic, you can use all 11 channels... no packets being sent, so no collisions. But as soon as two overlapping channels have traffic at the same time, both of them will loose packets that are being interfered with by other radios.

Using 802.11b with sector antennas and a backhaul point to point link, you should use two 180* sector antennas, rather than 3 120* antennas... that way you have enough useful channels so that your point to point shot does not loose packets because of interference from one or two of your sectors.


George

[wispy]

So, George...........

If I wanted to use 3 ea. 120 degree sector antennas as my PtMP, I would then install 3 Prism 2.5 cards and set them on channels 1, 6 and 11. My PtP could be in the 5.0 Ghz band and that would reduce any interference on the colocated antenna mounted radios.

And, this should all work in one box.

Right?

[lonnie]

Yes it would work - trouble is we have no 5 GHz card support yet.

If you are careful with separation and polarization, you can use 6 radios and 3 channels and have minimal interference


CH 1V, CH 11H

CH 6V CH 6H

CH 11V, CH 1H

Distance, direction, Channel and Polarization can all be used to separate the signals

[dkii]

IMHO a better setup would be:

Chan 1h
Chan 3v
Chan 6h
Chan 9v
Chan 11h

Use channel 6 as the backhaul and keep 1/6/11 in one box and 3/9 in another box, since the cards being so close would undoubtably pick up each other. Use H-pol for chan6 always because this is the default channel for most off-the-shelf wireless equipment, thus will most likely have the most noise. All of this is theoretical of course, I haven't been playing the game long enough to have the experience some of you have though.

[georgew]

You need a lot of isolation on shared channels, as the problem will be the local noise which is bouncing from nearby objects, repolarized because of the reflection, so cross-polar rejection is diminished. It will only hurt when you start to fill both of the shared channels. So really, you should share the two least-used channels to minimize the impact of interference. Put as much distance as possible between the antennas of the shared channels, and use antennas with the highest possible f/b ratio, and finally mounting so as to have fewest possible nearby reflectors. Oh, and stand on your head as you do all of that... ;)


Or, use a 5ghz backhaul based on a frequency shifter, (which is compatable with StarOS) or just buy a pair of 5ghz building to building bridges from someone, and use ethernet.

Adding a 5ghz AP to a StarOS router via ethernet is an easy way to support 5ghz untill you have native support. The advantage is you can use cheaper bridges, and do real routing with the StarOS box, so when you /need/ 5ghz, it is there.

But as far as having the assortment of low-cost high-power 5ghz solutions with freely available driver support, we are still a couple years away from 5ghz being as mature as the 2.4 market is.

George

[Davader]

George,

Do you have any recommendations for a 5.x backhaul solution that can go 3 miles? I'll do ethernet into the StarOS at both ends. :wink:

Any info is appreciated

Davader


Or, use a 5ghz backhaul based on a frequency shifter, (which is compatable with StarOS) or just buy a pair of 5ghz building to building bridges from someone, and use ethernet.

Adding a 5ghz AP to a StarOS router via ethernet is an easy way to support 5ghz untill you have native support. The advantage is you can use cheaper bridges, and do real routing with the StarOS box, so when you /need/ 5ghz, it is there.

[georgew]

I can't give any specific reccomendations. They are all somewhat expensive, and the prices fall weekly, so really any of the "building to building bridges" are good for this.

Tell them you are an ISP and will be buying more of these in the future, and see if you can get a better deal... but really you are probably wanting to shop around on this one since they are so expensive.

Other people using 5ghz can chime in here and tell you what they are using.... c'mon guys...

George

[dkii]

what about a couple of dlink 5ghz access points? I've never used one but I'd think they would go into some sort of ap client mode. To me it looks like the killer at 5ghz is the antennas.