Design and Deployment Considerations

Network design

Some network design considerations are essential for a location-ready network deployment. The detection of a wireless device (client) by a minimum of three access points is required for the computation of the X and Y coordinates of the client. The client’s location is established based on the RSSI (signal strength) detected by access points, using the four strongest RSSI values on the same channel.

In general, having a good density and proper placement of APs that detect the clients increases the likelihood of more precise device location. To learn more about the accuracy, refer to the Accuracy section.

AP placement

​Most non-location-ready deployments are designed such that APs are placed in the inner spaces of the floor plan. APs are generally not placed on the perimeters or corners since their coverage cells would bleed outside the floor, which may not be necessary as the WLAN, in most cases, is not required to serve clients outside the floor boundaries.

In a location-ready network, APs are not only placed in the center spaces but also spread across the perimeters and corners of the floor. This helps in improving location accuracy as it increases the likelihood that a device at any coordinate on the floor is seen by more than three APs for trilateration at better signal strength.

Distance between the access points

Utilize the grid line functionality within Central to optimize the AP layout, ensuring consistent spacing in all directions. Maintaining a recommended 10-15-meter gap between APs is advised, allowing the grid lines to be configured accordingly.

Minimum RSSI and AP separation

The distance between APs can impact the location accuracy of a wireless client. Radio signals are subject to the inverse square law, which for this purpose means that every time the distance between the signal generator (client) and the signal receiver (AP) doubles, the received signal power, sometimes referred to as received signal strength indicator (RSSI), will be quartered. Once the received signal has diminished to a certain point, typically around -65 dBm received at the AP, the ability to determine a specific distance based on the signal has diminished to the point of uselessness. Too much distance between access points means that accurately locating client devices will be difficult or result in incorrect positioning.

For accurate trilateration of a client within an area, the recommendation is for APs to be placed so that at least three APs can hear the client at -65dBm or better. This will usually correlate to the APs being separated by 40-50 feet but placed no more than 60 feet apart.

Air monitors

Air Monitors are APs deployed in a mode specifically dedicated to the purpose of listening to the Wi-Fi environment, allowing for more data to be collected.

An access point should be spending as many cycles as possible to serve WLAN clients, and so the AP may capture data frame RSSI from associated clients, as both the AP and clients exchange data on the same channel. However, for the same AP to capture data frame RSSI from clients associated with other APs, the AP must go off-channel to listen on the same channel where the clients are exchanging data frames. For instance, if AP1 serves client X on channel 1, and AP2 serves client Y on channel 11, the probability of AP1 switching to channel 11 simultaneously while client Y transmits data is statistically low. An Air Monitor scans channels more aggressively than an AP, and has a higher likelihood of picking up data frame RSSI from both channels 1 and 11, contributing more data to location computations.

For a deployment that demands analytics concerning associated devices, the incorporation of a combination of APs and AMs (for example, one AM for every four to five APs) is advised. For additional information on setting an AP to monitor mode, refer to AOS10 documentation for AOS10 APs and Instant AP Radio Mode - Monitor for Instant APs.

Best practice summary

In summary, the best practices for an installation that provides the best location results are:

• Deploy the APs with a sufficient density for trilateration within the entirety of the coverage area.

• Make sure to deploy APs at the edges of the coverage area.

• Deploy access points meant to be used in Air Monitor mode, in the prescribed ratio.

  • Using Air Monitors is especially important for analytics around associated devices that don’t have a high usage pattern.

• When testing Central Location Services, use enough devices to get accurate results.

  • When testing with only three APs, the data collected will almost certainly not show the minimum 3 APs needed for trilateration; insufficient data causes the location algorithm to attempt locations based on the Single AP method.

  • Better test results will be obtained by using seven to eight APs, with one or two of those deployed as an Air Monitor.

Pre-requisites

Before deploying and testing Central Location Services, ensure that the following prerequisites have been met:

1. Central account: An active Central account with online access points; Central serves as the management platform for various network services, including Presence Analytics and Floor Plan Manager. For more details on getting started with Central, visit the Central onboarding and provisioning.

2. Upload a floor plan to Central: A floor plan of the area to be tracked must be uploaded to Central and scaled correctly. For more details, refer to the Central documentation on creating, importing, and modifying floor plans.

3. Place access points on the map: Position the APs on the uploaded floor plan in Central. This step is crucial for the system to calculate the location of connected wireless devices. Refer to the Central documentation for more details on placing APs on the floor plan.

4. Connect clients to the APs from the floor: Connect clients (devices like smartphones, laptops, etc.) to visualize the devices on the Central floor plan. Refer to the Central documentation for more details on creating a WLAN SSID. This allows CLE to track and analyze the client device’s location based on signal strength and other factors.

Correctly following these prerequisites should allow for contextual information for clients including tracking their locations.