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:
- 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:
- 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.
- 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.
- Staggered placement. When covering hallways and long spaces, stagger APs rather than using a linear straight line.
- AP height under 20 ft. Ideally around 10 ft.
- 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.
- 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.
- RF Calibration
Use a CCX v2 or later client to perform a calibration of the environment. A Cisco Aironet CB21AG card is recommended.
- 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.
- 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.
- 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