AP Placement - Location Grade Wi-Fi Tracking

Here we review how the typical AP layout for location grade WLAN is laid out - but also take a look at the Cisco Hyperlocation module and how that might help you achieve the highest levels of location accuracy.

Wi-Fi has an increasing array of use cases, with the days of a single use Wi-Fi network behind us.

Many customers are looking to use their network for multiple purposes and one of these is to location track tags and devices.

AP Placement

 

What is a Wi-Fi Location Tag? Tags are small Wi-Fi transmitters, which can be attached to objects to allow them to be tracked.

If you're interested in a bit of a background read on how to make Wi-Fi work, take a look at the Top 8 Secrets to Great Wi-Fi.

 

Wi-Fi Tracking

Traditional wireless location tracking is based solely on RSSI (Received Signal Strength Indication).

CenTrak Asset Tag

This is how loud the AP can hear the clients, and is used to work out the client position.

APs use the RSSI to estimate distance from itself to a client.

Since each AP only knows the distance to the client but not the direction, one AP is not enough to identify the location of the client; a minimum of 3 APs with good signal strength is recommended in order to tri-laterate the location. 

For a good Location Grade design, sub 5m accuracy is pretty achievable, although this can drift in wide open areas. Typically quoted figures are 5 - 10m of accuracy with a good Location Grade design.

 

Location Grade Predictive Wi-Fi Survey

AP Placement Feature Image

 

Predictive Surveys are the starting point for any RF design and that includes Location Grade Wi-Fi.

The recommended AP design/layout is to place the APs in a staggered manner (rather than a grid or just down the centre of corridors) and also around the perimeter of the building. 

 

In reality, the RF environment is affected by many factors, especially wall position and wall type and this affects the AP positioning as well.

 

Recommended AP Locations

It is recommended to position APs around the perimeter of a building, so that all tracked clients are on the inside of that perimeter. It stands to reason that if you only position a single AP in a location, you will be able to get location accuracy of 'nearest AP', but that's going to give quite a wide expanse over which the client could be located.

Location grade designs typically have the highest density of the various types of RF survey designs that we undertake.

As with all RF designs, a pre-install survey should be conducted to confirm the AP placement in the predictive survey is correct.

 

Cisco Hyperlocation

Cisco AP 3700 hyperlocation module

Cisco Hyperlocation is a technique used to augment the capability of base Wi-Fi Location tracking alone.
 
The module is shown on the left (cover removed), to show the antenna array. 
 
The array features an additional set of 32 antennas surrounding the access point and these are used to listen to inbound Wi-Fi transmissions to determine the angle of arrival. 
 
Based on the AoA, the location of the client can be determined with much greater precision - typically between 1 -  3m of the actual location.
 
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