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raghuinc
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Joined: Mon Oct 18, 2010 8:55 am

Hotspot: outdoor to indoor R52N link with omni ant - issues

Thu Oct 21, 2010 8:52 am

This is my first attempt at using MT and any help will be gratefully welcome.

I am building a hotspot for three buildings and have the following star topology setup of RB411s connected to a central RB433.

RB433 <-> many RB411 (with level 4 license) <-> Clients (laptops)

Before buying all the hardware, I wanted to run some tests. The scenario I tested was RB411 in AP-bridge, R52n in b/g mode, two 7dbi omni antennas, with both chains ON. All other settings are default. AP is placed outdoors (on ground) and client laptop is 20m away (Indoors on 2nd floor) with 1 wall obstruction.

The readings from winbox wireless settings were:
Signal Strength = -77 dBm
SNR = 34 dBm
Tx/Rx CCQ = 36%
P. Throughput = 7.7 Mbps
Tx/Rx rate = 11/36Mbps

Using Inssider, the signal strength on the laptop was -80dBm.

I also ran an FTP test: a 10MB file transfer from laptop to AP. Average throughput of ~4000 Kbps. But, the throughput remains the same even when the laptop is kept close to the AP.

In general, over any distance with LoS, I am not getting lower than 70dB readings, although links are formed upto 100m. My main goal is to push the RSSI levels to below 70 (on laptop) and below 75 (on AP) in order to have a safe margin for a 54Mbps link.

My issues are:

* Even if signal strength values are not a good indicator (as discussed in many threads), the CCQ values are pathetic. They also keep fluctuating (30-60%).

* The laptop is seeing poor signal strength values. Will r52hn help in increasing signal strength at the laptop?

* Do I need a higher gain antenna? My main worry is that a high gain antenna will reduce the omni-direction capability and I need all round connectivity (that is, good elevation).

* Is there any tutorial on how to compute link budget for MIMO case and in such mixed outdoor-indoor scenarios?


Some links here that were useful while I started:
http://forum.mikrotik.com/viewtopic.php ... na#p172669
http://forum.mikrotik.com/viewtopic.php?f=7&t=45273
http://forum.mikrotik.com/viewtopic.php?f=7&t=45750

Thanks.
 
ctech4285
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Re: Hotspot: outdoor to indoor R52N link with omni ant - iss

Thu Oct 21, 2010 5:45 pm

first
I am not getting lower than 70dB readings, although links are formed upto 100m. My main goal is to push the RSSI levels to below 70 (on laptop) and below 75 (on AP)
i think you want to push them above -70dbm they are negative numbers, unless you some special RB Card that i don't know about

you can tolerate lower S/N if you use diversity antenna, because fading won't be to much of a problem
but something does not look right, did you run a spectral history tool?
oh i did you say
with both chains ON.
, i am not sure but they correspond to the two antenna ports you have on your card. if thats the case it could be your problem....oh never ever run a radio without an antenna, since there is no terminating resistor all the power get reflected right back to the send/receive chain 30dbm is a little more then -99dbm, the sensitivity of the card.

so do a spectral scan
check if "both chains on" is what you really want....
good luck
 
raghuinc
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Re: Hotspot: outdoor to indoor R52N link with omni ant - iss

Thu Oct 21, 2010 8:41 pm

Thanks for your reply.
i think you want to push them above -70dbm they are negative numbers, unless you some special RB Card that i don't know about
I guess that is what I meant :-)
but something does not look right, did you run a spectral history tool?
Do you mean Wi-Spy like spectrum analyzer? I just used inssider to scan. Are you suggesting that there might be a fault with the .11n card?
i am not sure but they correspond to the two antenna ports you have on your card. if thats the case it could be your problem...
I have two antennas attached to the R52n on the RB411 box.
check if "both chains on" is what you really want....
I do need them. When I ran tests with the single chain, even though signal strength readings were the same, my CCQ was even lower.

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