hi all

we r facing problems with channal interferance with all channals in 2.4 cuz we have like 50 wifi ommni in the same regien so..
how can i reduce the interferance? is the signal filter good for this problem or enything else??

thnak u all

You can't do nothing with interference. Just change the channel or band.

M.

Signal filters are for out-of-band interference. You can change to HPOL or switch to channel hopping hardware.

use 5Ghz, you can't do anything else. Changing polarisation will not help.

hi all

we r facing problems with channal interferance with all channals in 2.4 cuz we have like 50 wifi ommni in the same regien so..
how can i reduce the interferance? is the signal filter good for this problem or enything else??

thnak u all

What are you using for an antenna at your AP? We can pick up a lot more than 50 aps at some sites.

Inox why are you giving bad advice?

Changing to HPOL will certainly help. I would also drop the channel size if the bandwidth isn't needed.

changing polarisation didn't help me in an area with ~15 ap's with omni atenna. Using 5Mhz could help...worked for one more month until I change to 5Ghz. I had a lot of reassociation.

plz what is the HPOL and i dont need a larg bandwidth pre clint??? so what i should do??

thanks

Well to start we really don't have enough information to help you.

Explain your setup. What are you using for CPE devices? Are users connecting with laptops? What country are you in?

if the customers are laptop users than changing pol will not help because you need vpol in this case.

If your cpes are fixed than change to hpol than it will certanily help. (Also you should change your cpes polarization too)

Dont do channel hoping cos im sure it wont select the best channel.

Once again inaccurate information.

FHSS works wonders in high-noise environments. It broadcasts the same information on multiple smaller channels. This means the CPE will have a better chance of receiving that information on a low-noise channel. Alvarion FHSS uses 2mhz channels. Keep in mind that 802.11 devices do not TX/RX all the time. If you are sending/receiving on say 12 channels (I believe FHSS in 2.4ghz allows for over 70 channels) you have a much better chance of RX/TX on a clean channel at the time.

I believe the above poster is confusing frequency hopping with DFS.

The Alvarion fhss 2.4 uses 1mhz channels, and has about 23 unique hopping sequences (meaning you can have 23 different radios that avoid most self-interference via their hopping algorithms.) We've had more than a dozen radios at a site without interference. The 1 mhz gets 3mbit of wireless rate (about 2mbps data), so it's a very efficient technology compared to 802.11b. Too bad it's no upgradable. I'd still buy it if it did more than 2mbps. It wreaks havoc on dss gear at the same site if you've got a couple busy alvarion AUs.

The fhss 900mhz gear uses 2 mhz channels. It works great. I'd still buy it if it did better speed.

We use MicroHard FHSS 900 radios. Works stunningly well when nothing else will. Including true NLOS paths. And also doesnt bother any of the 'normal' 900 radios at all, they don't even see the MicroHards.

Bad news is that they are both slow and very expensive.

George

George,

I'm not familiar with that brand at all. Can you define expensive and slow? I'm intrigued.

About $1500 per end. Speed is switchable between 300Kb and 1.1Mb. 30dB output variable in 1dB steps, hopping pattern can be tightly controlled as well. True industrial quality.
http://www.microhardcorp.com/IP921.htm

Very, very nice gear for tough shots where it just *has* to work. We use a few where nothing else will work, typically for SCADA sites and we typically install with them set to the lowest speed range to gain the best reliability. Integrates with our MikroTik network without issues.

They just came out with a new, faster model that we haven't tried yet.
http://www.microhardcorp.com/IP922.htm

George

Dear all
thanks for all ur post.

can i use 2.4ghz but with 5 mhz or 10mhz to reduce the interfeance cuz i cant use other band

and how can i do that??

thanks

to use 5mhz or 10mhz bandwith channel, need Atheros chipset on AP (like mikrotik R52 cars or ubiquitis XRs, etc) and on client.. no realtek, ralink etc, use CPE mikrotik or Nanostation or laptop with atheros chipset on it.

and select 5mhz or 10mhz on the wireless menu

to use 5mhz or 10mhz bandwith channel, need Atheros chipset on AP (like mikrotik R52 cars or ubiquitis XRs, etc) and on client.. no realtek, ralink etc, use CPE mikrotik or Nanostation or laptop with atheros chipset on it.

and select 5mhz or 10mhz on the wireless menu

Dear marceloru

if i use 5mhz or 10mhz is the interferance reduced?????


thanks

Using 5mhz or 10mhz reduces the width of your wireless signal. This in effect creates more usable channels and more room to move around the interference or between it.

Interference. This could be a large chapter in a book to explain what can be done about it. I operate a small ISP in the southern Oregon area. In approximately 200 square miles we have over 115 ISM band transmitters. Many operating above FCC limits. I cant go into detail however here is a run down of what I use to eliminate interference or at the very least reduce it.

The easy things you can do about interference.

1. Change the frequency used. The simplest way to reduce interference is to move away from it. One of the easiest ways to do this is to simply move to an alternate frequency away from the interference. I have found that running several scans of the area with whatever gear I have at my disposal (scope, wispy, or at the very least scans within the MT OS on every band) and create a frequency map of what the antenna at the site can see. Knowing most 802.11 based communications use a 20Mhz band I can derive any "holes" where I can possibly set my center frequency.
2. Change the band entirely. The most commonly used band seems to be 2.4ghz not only due to the age of the band but the limited 85.5Mhz range typically only allows 3 non overlapping channels leaving the band rather crowded. Moving to 5.8Ghz band you step to a full 125mhz of available frequency's at the same 20mhz channel width the possibilities are much much higher in finding an interference free (relatively) channel. 900Mhz is also a possibility and due to the low frequency permeation LOS issues can be eliminated to an extent with 900Mhz. Currently 900Mhz is highly utilized by many paging transmitters, these are an older analog style and many are swapping them for digital transmitters or removing them entirely due to the decline in the paging market. The problem with 900Mhz is the cost of CPE and the adjacent 800Mhz and 1Ghz bands that are high powered licensed spectrum's. In many cases you will run into a site nearby transmitting on these bands with a dirty transmitter leaking into your 900Mhz. There is also the newly available 700mhz and 3.5Ghz bands as well. As we head into the new year and the 700mhz band is vacated by the television industry the possibilities of 700Mhz are high. 3.5Ghz has been great in my experience since many mainstream component manufacturers have not yet mass produced components in this band to be sucked up by wireless electronic devices either so the relative performance and band availability is also good. One last point of note with a band change. If you are using any Umbiquity products that utilize "frequency freedom" please note they are based on a 2.4 or a 5.8 card then "convert" to there model frequency. This means you can still get interference within the card itself at times on the popular 2.4 and 5.8 bands. Pay attention to the Atheros chipset used to know what the "base frequency" is within the XR card.

Not so easy things to try.

1. The fact that interference exists may not be able to be avoided. However you may be able to do something about how (or if) you are listening to it. If the interference is coming from an out of band frequency (something other than the frequency you are operating on) you can install a pole / canister etc filter to eliminate the "out of band" interference. If you cant find a manufacturer with a "canned" filter for the frequency you are using there are many out there that will tune or manufacture one for you at inexpensive cost.
2. Use your antenna. The other thing you can possibly due is use the gain of your antenna to your advantage. For example if the interference is coming from a mountain site across the valley from yours, you could install a good antenna with a very small vertical beam with (like 4 degrees) then use a down tilt calculator to "focus" the antenna beam on your service area. This virtually eliminates the noise from being "amplified" my the gain of your antenna. This is difficult to do so if you are not experienced with RF design consult someone who is. You will be amazed what an antenna can do if you design it right. You can also consider a strong front to back ratio if your interference is coming from behind your antenna and so on. Basically keeping the interferences outside of the gain of the antenna by any means possible. In some cases i used the mounting location of the antenna on the tower to place other antennas or the structure itself between the antenna and the interference source to reduce it. We also use what we call a "float" we link up several customers and experiment with alternate tower locations to see how the signals are affected from different regions of our service area and find the "Sweet spot" to permanently mount our antennas.
3. Drop your signal. Lastly you can attenuate your receive signal. Now I know that seems crazy but lets say for example your signal levels from your customers are a good -50db. With a noise floor of 90 you have a good 40db of SNR to work with (roughly). Now if you are receiving weak interference causing the CCQ to be affected and reducing the performance of the link you can attenuate the signal to reduce the noise from every reaching the receive threshold of the transmit card. This can be complicated however it does work very well if you are dealing with a week interference signal and have enough margin in your legitimate signals to pull it off. Remember the noise floor setting in MT OS does not work, its only there for backwards compatibility with some older cards that will actually pay attention to that setting. Your modern mPCI card will likely ignore anything you set there, so you have to physically create the attenuation using a longer cable run, filter or attenuator.
4. Increase or reduce the frequency channel width. Now reducing the channel width to say 10mhz or 5mhz mode makes sense the less you are listening to the less interference you may receive. In addition the noise floor seems to be reduced in this mode and the overall SNR increases to combat the interference as well. Now widening the channel width? Thats right. In many cases if you are not working at 10mhz I have seen links take off and perform very well by increasing the channel width. How can this be? Simple, not all interference is fixed. In other words there are many transmitters out there that use some form of frequency hopping or modulation where the interference will move around to some degree. If you are using only 10mhz the offending signal may wipe out the entire 10mhz leaving your redundant transmit rate mute. Let me step back for a sec. With MT OS like many 802.11 based devices the transmit rate is used to "duplicate" a packet when a higher rate packet does not reach the other end. Unfortunately 802.11 devices don't get much feedback to indicate what is going on with the link outside of success of receiving a packet. This acknowledgment is what sets the CCQ and transmit rate. When less acknowledgments are received the transmitter reduces the transmit rate. In reducing the transmit rate it literally sends a smaller packet (hence the smaller throughput) and duplicates it on both sides of the band. That way one will get through or so the transmitter hopes. If that rate still does not yeld an acknowledgments the transmit rate is reduced again and the packet is sent four times (reducing the throughput again) and so on. If your offending signal occupies the entire 10mhz of your channel then a reduction in transmit rate does nothing, however if you increase the channel to the standard 20mhz then the offending 10mhz will land on one side of your transmit packet or the other (one on each side of the center channel at a 24mb transmit rate in G for example) then the transmit is a success and the data gets through. In this case increasing the channel width gives the transmitter more flexibility to move around the interference and get more data trough the link.

I hope some of that helps guys... and one last thing. All of this is in a license free band so it can change on you!

Best to you all..