Site Surveys and Spectrum Analyzers and their place in Wireless Network Design and Maintenance

Version 2

    Though there are variables in all wireless network designs that make one completely unique from another including size, environment, and use-case, one fact remains true: Spectrum Analyzers and site surveys can improve wireless network design, maintenance, and overall performance. This document discusses site surveys and when to use one as well as using a Spectrum Analyzer to troubleshoot wireless interference.


    Sections Included in this Document


    Site Surveys and When to use one

    Steps Included in a Successful On-Site Survey

    Spectrum Analyzers

    Useful Links


    Site Surveys and When to use one


    A thorough, professional site survey should be done, if possible, before provisioning any wireless network. There are many types of site surveys. One of the most common pre-installation surveys is a predictive site survey. A predictive site survey is a great tool for getting a good start on where APs should be placed, how many are needed, and potential RF complications. This type of survey can be done remotely using site-specific information such as the floor plan, desired client density and throughput requirements. ADTRAN provides predictive survey offerings.

     

    A predictive site survey is just a prediction. It should be noted that this type of survey cannot take into account site-specific environments that affect RF signal propagation or RF interference. For very small deployments that are simple in nature, a predictive site survey may be enough to get APs placed, mounted, and configured and adjustments may possibly be made without a spectrum analyzer on site. However, in larger deployments, opting for a full on-site survey will be the better choice as there will be more outside factors that can affect the deployment.

     

    After completing a wireless installation, an on-site post-installation survey should be performed by a professional company specializing in wireless surveys. This type of survey is needed to verify the network design and make proper adjustments based on the site's unique environment. In smaller installations, a site survey may not be needed if the layout is simple and a predictive site survey was done remotely with accurate floor plans. If an on-site survey is not performed before a wireless installment, the site may be susceptible to a wide range of RF-related complications. Most current wireless network management software can detect improper channel and power settings. In cases where it is determined that problems exist because of inadequate channel and power plans, an on-site site survey should be done to help address these issues. An installation site survey is always the best way to protect again RF interference.

     

    Although many websites and applications advertise that site surveys can be done by an administrator, it is not an easy task to complete properly and any missteps in the survey can lead to a poor user experience and large amounts of time spent troubleshooting wireless issues. To ensure proper functionality, a professional on-site survey is especially critical for outdoor locations (pavilions, stadiums, etc.), high-client-density deployments (arenas, dorms/apartments, etc.), and large wireless deployments (50+ APs in one building/area). These situations generally provide uncontrollable obstacles that must be addressed beforehand for network success.


    Aside from after the initial deployment, a site survey can be very beneficial in many other scenarios. For the best network health, having a site survey performed (professionally is always better but verification is much easier done with wireless analyzers than initial deployment) every 2-3 years is recommended to identify new problem areas and concerns as well as adjust for changes in business services on wireless and client density changes. A site survey is always recommended before any major changes such as additions to an infrastructure, addition of a large number of wireless users, or major changes to the priority of the wireless network and the data on it.

     

    A site survey can also be an extremely helpful step to help eliminate consistent wireless client issues. In many cases, a site survey and proper adjustment will completely resolve these issues. While vWLAN provides many useful tools for solving wireless issues, a site survey with spectrum analysis is second to none.


    Steps Included in a Successful On-Site Survey


    This section will discuss the necessary steps that should be taken before and during an on-site professional survey. In general, it is recommended that this be performed by a professional company specializing in wireless surveys, especially upon initial deployment. Though many websites and applications advertise that it can be done by an administrator, it is not an easy task to complete properly and any missteps in the survey can lead to poor user experience and large amounts of time spent troubleshooting wireless issues.. Outdoor (pavilions, stadiums, etc.), high client density deployments, (arenas, dorms/apartments, etc.) and large wireless deployments (50+ APs in one building/area) should require a professional Site Survey before and during deployment of a wireless network to ensure proper functionality. These situations generally provide uncontrollable obstacles that must be addressed beforehand for network success.

     

    • Steps to Planning a Site Survey
      • Document the wireless requirements clearly

        • How many users at given times will be using the network?

        • What applications will be in use and what bandwidth is required for those applications?
        • What types of client devices will be used?
        • Which radios will be used and what is the client distribution between them?
        • What areas in the infrastructure need wireless coverage?
          • What client density will exist in each area?

      • Obtain Facility Diagrams
        • Wireless site surveys will be planned and executed using exact measurements. Blueprints of the area being provided wireless coverage helps to provide reference for measurements as well as being essential to a proper network diagram/wireless heat-map.

      • Locate Wired Network Locations for AP Network Access
        • All APs will need to be wired to a switch with the proper network access for the clients using the access point. This information will be needed when planning physical AP placement during the site survey.

        • The second part of this is to assess where APs are located in terms of network bandwidth. If a set of APs serving 50 clients is plugged into a switch, does it have the available bandwidth through the network to support it?

     

    In many cases, professional Site Surveys companies will give you forms or questionnaires to fill out detailing and providing this information.

     

    • Steps Included in a Site Survey
      • Visual and Spectral Analysis of the facility

        • This will be done to identify possible problem areas beforehand, inspect availability of proper mounting areas for APs, and how many APs and what types will be needed.

        • The Spectrum Analysis will provide information about possible rouge APs, non-802.11 interference sources, and other areas of concern like metal/concrete walls, or other signal obstruction.
      • Determine Preliminary Access Point Locations
        • This will be a mapped plan using the building blueprints of suggested spots for the APs based on client density, bandwidth requirements, and coverage information provided.

      • Create a Channel Plan based on AP Locations
        • Generally a professional site survey will include a suggested channel plan

      • Deploy APs and Verify Coverage
        • This will include another walk through with the spectrum analyzer and other Wi-Fi devices to identify coverage concerns and usability.

      • Adjust AP Location, Power Settings, and Channel Plan
        • This step will make needed adjustments based on the walk through after initial deployment. It may include more walk-throughs to verify changes.

      • Documentation
        • The documentation of a site survey is key to long-term longevity of a wireless network as it provides initial data on how Aps were configured and placed as well as the reasoning behind it. It also identifies initial problem areas and coverage changes that can provide useful in troubleshooting later.

     


    Spectrum Analyzers

     

    The best and only fully reliable way to capture wireless signals in an area and properly analyze them is with a full-functioned spectrum analyzer. Spectrum Analyzers sense and read the spectra of electronic signals on different frequencies to analyze transmissions on them. Each Spectrum Analyzer has a frequency spectrum/range that it can sense signals on. From here, analyzers will normally be able to read signal strength, bandwidth, distortion, noise and more and create customized output to give the user valuable information about the frequency spectrum in that area, including wireless network signals.


    Many times, devices like phones or PCs with wireless NICs are mistaken for proper spectrum analysis devices because the output shows all wireless signals, channel selections, SSIDs, and other wireless information. However, the important distinction is that these devices are generally based on reading 802.11 signals, not the frequency spectrum in general. As mentioned, many non-wireless devices can and commonly do transmit in spaces that are provisioned for wireless transmissions. The only way to see these non-802.11 signals is with a spectrum analyzer. In many cases, a poor user experience may be occurring but all Wi-Fi analyzers on phones or PCs seem to show no interfering networks or AP misconfigurations in that area. In those cases, the problems could very well be related to non-802.11 transmissions interfering in the same frequency space. Without a proper Spectrum Analyzer, an administrator is blind to these signals and must make changes without that information and rely upon user complaints to see if the problem is resolved. On top of this, Spectrum Analyzers have many more options, are much more granular, and can sense signals at much lower and detailed levels meaning that the most accurate and detailed data will be available for decision making.


    With a spectrum analyzer, security issues such as Rouge APs and normal wireless health issues like gaps in coverage can be seen and addressed. Rouge APs or non-802.11 devices can be traced and tracked down. Wireless areas can be analyzed so coverage can be better adjusted for users. Although many are somewhat expensive, the cost is easily made up in the improved ability to service and maintain a wireless network. This can incredibly benefit a network administrator using vWLAN to troubleshoot interference, covered in the document Using vWLAN to Troubleshoot RF Interference and Maintain a Healthy RF Environment

     

    • Types of Spectrum Analyzers

     

    The two most common types of spectrum analyzers are "bench-top" and portable/mobile analyzers. Generally bench-top analyzers are larger pieces of equipment with large screens and many options to map and display data. Portable/mobile analyzers can range from bench-top analyzer-sized models that have AC batteries to USB dongles that can be plugged into a PC and used to analyze spectrum data. Generally, bench-top models are more verbose and exact, but portable spectrum analyzers are very useful when monitoring large wireless networks as they can be used to quickly find the sources of interference without the extra options that aren't needed. Researching and making a decision about the best model(s) should be done prior to provisioning a wireless network if possible.

     

    • Recommended Spectrum Analyzers
      • Wi-Spy made by MetaGeek. Wi-Spy is a USB dongle with attachable antennas that can analyze the 2.4 GHz and 5 GHz frequency spectrum. It has many report tools available and is as mobile as the device it is connected to. It is also specifically designed with features to help troubleshoot wireless including channel and power setting suggestions based on analyzed data.

      • AirMagnet Spectrum XT by Fluke Networks is another similar USB dongle solution that provides excellent spectrum analysis. The XT focuses more on interference concerns with wireless networks as well as security from Wi-Fi jammers and Wi-Fi attacks.
      • OmniPeek Wireless Network Analyzer by WildPackets. The OmniPeek analyzer supports capturing on more than one channel at a time, roaming analysis of clients, and helps track wireless events. It also has support for options with wired clients as well as 802.11ac analysis.

     

    Useful Links