If you install, audit, manage, service, or have anything remotely to do with broadband radios, chances are you share an intimate relationship with noise and interference. Given that there are a large number of wireless networks operating in the unlicensed (ISM) bands (900 MHz, 2.4 and 5.8 GHz), I thought it would be beneficial to put together a series of articles containing tips and tricks for identifying and mitigating noise and interference.
I would like to devote the first article in the series to commenting on the practice of attempting to locate the source(s) of interference (or noise). Usually the amount of effort put into trying to locate an interferer far exceeds any possible favourable outcome, for reasons explained below.
- Any of your affected sectors must be disabled to help reveal and hone in on potential sources of interference that will be predominately masked by these sectors. Obviously this can be scheduled after hours or during periods of low traffic. However, there really is no way to predict how long the planned outage will be, as your search will almost always exceed your allotted timeframe.
- 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’.
- Once you locate the source of the offending signal, who says the operator of the system needs to cooperate with you? 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 when offenses are perpetrated. No penalties are bestowed upon those found to be inhibiting another’s wireless services. Note that this can also apply to licensed bands as well. For example, obtaining a license for your 3.65GHz WiMAX gear amounts to little more than having your company name and coverage area added to a database so that other interested parties know you’re there.
- The very nature of wireless is dynamic. This not only applies to fluctuating RSS (receive signal strength) levels and SNR (signal-to-noise ratios), but also to the center frequencies any wireless network operator chooses to use at any given time. I have witnessed operators who change the operating frequencies of all the radios in their networks on a regular basis in vain attempts to improve performance by trying to navigate around noise fluctuations in their coverage areas. 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 data analysis, radio and antenna specifications, etc.) and try to stick with it once deployed. Changes to the original plan 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 would have been best left alone.
Also be aware that interference is a two-way street. Extend the RF olive branch to your neighbours. Mutual cooperation can only serve to improve your network’s performance and stability, ultimately reducing costs and maximizing your return on investment.
Author Profile: Tim Preston is a Senior Network and Systems Analyst with experience dating back to 1998. He started on the front lines of technical support for a large northern Ontario Internet service provider while earning his diploma in Computer Programming and Network Analysis. After being hired by a major wireless broadband radio manufacturer, Tim moved to Toronto in 2001. In 2009 Tim started Haven IT Consulting. Examples of work he has done for his clients include providing management and troubleshooting services to wireless ISPs, interconnecting retail outlets for an equipment supplier, and providing technical auditing, network design, operations advice, and technical support for various local businesses and network solutions providers.