Installation guide

Wi-Fi Location-Based Services—Design and Deployment Considerations

OL-11612-01

Location Tracking Approaches

Pure RSS-based lateration techniques that do not take additional steps to account for attenuation and

multipath in the environment rarely produce acceptable results except in very controlled situations. This

includes those controlled situations where there is always established clear line-of-sight between the

mobile device and the receiving sensors, with little attenuation with which to be concerned other than

free-space path loss (FPL) and little to no concern of multipath.

Angle-Based (Angulation) Techniques

Angle of Arrival (AoA)

The Angle of Arrival (AoA) technique, sometimes referred to as Direction of Arrival (DoA), locates the

mobile station by determining the angle of incidence at which signals arrive at the receiving sensor.

Geometric relationships can then be used to estimate location from the intersection of two lines of

bearing (LoBs) formed by a radial line to each receiving sensor, as illustrated in Figure 5. In a

two-dimensional plane, at least two receiving sensors are required for location estimation with improved

accuracy coming from at least three or more receiving sensors (triangulation).

Figure 5 Angle of Arrival (AoA)

In its purest form (that is, where clear line-of-sight is evident between the mobile device X and receiving

sensors A and B), mechanically-agile directional antennas deployed at the receiving sensors are adjusted

to the point of highest signal strength. The positioning of the directional antennas can be directly used

to determine the LoBs and measure the angles of incidence θ

and θ

In practical commercial and military implementations of AoA, multiple element antenna arrays are used

to sample the receiving signal eliminating the need for more complex and maintenance-intensive

mechanically-agile antenna systems. Electronic switching can be performed between arrays or portions

of each array, and mathematical computations handled by a computing system are used to extract the

angles of incidence. This technique actually involves calculating TDoA between elements of the array

by measuring the difference in received phase at each element. In a properly constructed array, there is

a small but discernible per element arrival time and a difference in phase. Sometimes referred to as

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