Tuesday, May 18, 2010

Cisco Location Accuracy Tips

To improve the Cisco location system accuracy, follow a few guidelines. Ideally, administrators need to carefully plan and design the wireless network to support location services prior to implementation. However, many times existing networks initially deployed to only serve data clients need to be retrofitted to add voice and/or location services.

If retrofitting an existing network, consider planning for both voice and location services with the upgrade. Many design guidelines for voice and location services overlap, but there will be some differences which need to be considered.

Tips for improving location accuracy:

  1. Proper AP Placement
    It cannot be stressed enough, proper network design is crucial! There are several things to keep in mind when planning access point locations:
    1. Include perimiter APs. Data and voice networks don't need APs at the perimiter of a coverage area, interior APs work fine. However, location accuracy along the edges of the coverage area depend on having APs at the perimiter.
    2. AP density. Location accuracy is best when APs are placed every 50-75 ft. covering 2,500 to 5,000 sq. ft. each. This will vary based on each environment, but plan on a more dense deployment than a data network, 2.4 GHz voice network, and about equivalent density to a 5GHz voice network.
    3. Staggered placement. When covering hallways and long spaces, stagger APs rather than using a linear straight line.
    4. AP height under 20 ft. Ideally around 10 ft.
    5. Not all APs need to serve clients. Use monitor-mode APs if the density required is too great and causes excessive co-channel interference, especially on the 2.4 GHz band. Monitor mode APs don't serve clients or transmit frames, but can track client locations by listening to them.
    6. Ensure a minimum of 3 APs can hear each client at -75 dBm. This is not a hard requirement for location to be determined, but will greatly improve accuracy.
  2. RF Calibration
    Use a CCX v2 or later client to perform a calibration of the environment. A Cisco Aironet CB21AG card is recommended.
  3. Smoothing Algorithm
    In WCS, configure the location server smoothing algorithm. This in effect reduces "jitter" of the location algorithm and weights prior client locations into the calculation of the current client location.
  4. CCX Location Measurement
    If clients in the network are CCX v2 capable, enable CCX Location Measurements in each radio band. The APs will issue broadcast CCX radio measurement requests to clients prompting them to transmit probe requests. The APs in the area can then receive signal strength information immediately for all clients, even if idle.
  5. Install Chokepoints
    Install chokepoints in areas of the network requiring more granular location accuracy or to trigger event notifications.

Following these tips should allow the network to locate devices within 10 meters around 90% of the time.

For more information, see the following document:

Cisco Wi-Fi Location Based Services 4.1 Design Guide



  1. Hi Andrew,
    after a software upgrade of my cisco location solution (controller wlc 2100 ,
    Location server 2710 v.s., WCS I can't start the calibration and I always receive this messages "Calibration is supported only for CCxV2 and above client. Your clinet seems to be either CCXV1 or non-CCX"
    I'm sure that the client i'm using is CCX (it's a Cisco wi-fi card). It's possible that I need to upgrade the software of the Aironet 1130 AP ?
    Thank you very much!

  2. Hi Pius,
    You can look at the client details in the WLC to see if it is recognized as a CCX client. If not, I recommend using a Cisco CB21AG card for location calibration. You can also find a list of compatible clients on the Cisco CCX webpage.

    The software versions you listed seem to be okay based on the Cisco Wireless Software Compatibility Matrix.

    Also, you may want to read the Cisco Location-Based Services 4.1 Design Guide to help you through the process.