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Locating Sources of Noise In Your Wireless Network… NOT!

May 1, 2012

Mitigate your RF noise and interference

OVERVIEW

If you have installed, audited, managed, serviced, or had anything remotely to do with broadband radios operating in the unlicensed ISM band (including WiFi), chances are you share an intimate relationship with noise and interference. Of course, both exist in the licensed world as well, but usually with much less of an impact. Each has a separate meaning but yield the same results: calls from customers complaining about their service. After all, it usually isn’t the radio’s hardware designers and engineers that are stuck with trying to figure out why performance has tanked or find the cause of an outage. It’s the WISP operators, staff or IT consultants who are looking for a practical way to solve an immediate problems.

Unfortunately there is no magic bullet – this is the mysterious and enigmatic world of wireless we’re talking about. However, you should be able to take what you have learned and methodologically apply it to your unique situation in order to lessen the negative effects of wireless noise, improving your customers’ overall performance. Most importantly, you’ll cement your reputation as a miracle worker!

ATTEMPTING TO LOCATE SOURCES OF INTERFERENCE

After numerous failed attempts, we have concluded that trying to locate sources of interference (ie. drive testing), especially when it comes to unlicensed frequency bands, is mostly a waste of time. The amount of effort put into trying to locate an interferer far exceeds any possible favorable outcome, for reasons that are explained below.

  1. Any affected sector(s) (ie. on which you have paying customers) must be disabled during the location process to help reveal and hone in on any potential source of interference that is mostly masked by said sector(s). Whether operating in an advertised maintenance window or an unexpected service outage, you can expect your inbound support call volume to rapidly increase as a result.
  2. The system behind the source of the inference needs to be fairly active in order to be detected and then confirmed. If the effects of the interference on your sector (or sectors) are at their worst during business hours it is probably due to the nature of the traffic propagating from the offending system. This emphasizes the first point above. You won’t be very popular for taking a coverage area offline mid day to scan for noise, regardless of how much the interference is affecting performance. End users usually take ‘slow’ a lot easier than ‘down’.
  3. Once you locate the source of the offending signal, who says the operator of the system needs to cooperate? Although FCC and (to a certain extent) CRTC regulations dictate operators of radios transmitting in the unlicensed bands need to play nice, little if any action is taken, nor do penalties exist to hand out to parties accused of inhibiting one’s wireless services. Note that this can also apply to licensed bands as well. Licensing of non-military designated frequencies is usually nothing more than a public registry to map out who gets to operate what frequency where.
  4. Lastly, the very nature of wireless is dynamic. This not only applies to fluctuating RSSI and SNR levels, but also to the center frequencies any wireless network operator chooses to use at any given time. In the most extreme case, we witnessed an operator who changed the operating frequencies of all the radios across his entire network on a weekly basis in attempts to improve performance or simply navigate around fluctuating noise concerns in his coverage area. Radios with their frequency hopping feature switched on further underscore this point.

In the end, it is best to develop a frequency plan based on solid data (path profiles, coverage plots, site survey measurements, radio and antenna specifications, etc.) and try to stick with it once deployed. Changes to the original design should only be made if they are absolutely necessary; that is, when all efforts to mitigate the noise or interference have been exhausted. Remember that changing the frequency of one sector could ultimately affect all sectors throughout your entire system, resulting in a mind-warping frequency juggling act that may have been best left alone. Be aware that interference is a two-way street. So extend the RF olive branch to your neighbors. Mutual cooperation will help improve one another’s network performance and stability, hence reducing cost and maximizing return on investment.

Finally, if you feel out of your depth, get an IT consulting firm who has wireless experience to help – it’s an investment you won’t regret.

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From → Wireless

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