Which two factors influence the location accuracy of a device using scanning APIs? (Choose two)

Location accuracy using scanning APIs, primarily through RSSI-based trilateration, is fundamentally dependent on two main categories of factors: the network infrastructure design and the characteristics of the client device's radio signals. AP placement (A) is the most critical infrastructure design factor. For accurate trilateration, the location engine requires RSSI measurements from multiple, well-positioned APs surrounding the client. Poor geometry, such as APs in a straight line or insufficient AP density, makes accurate location calculation impossible. Client device orientation (C) is a major client-side factor that introduces significant real-time variance. The way a user holds a device can cause signal attenuation (body blocking) of 10-20 dB. This drastic change in signal strength directly corrupts the RSSI data used by the location engine, leading to large errors in the calculated position.

B. Device manufacturer/OS: While this is a valid factor (encompassing antenna design, power levels, and drivers), it is a broad category. Options A and C represent more specific, primary factors that are consistently highlighted as the most impactful.
D. Battery life of the device: This has an indirect and minor influence. A low battery might trigger power-saving modes that reduce Wi-Fi scanning frequency, affecting the freshness of location data, but not the accuracy of a specific calculation.
E. Amount of device antennas: This is a secondary factor. While antenna diversity can improve signal stability, its impact is far less significant than the fundamental network geometry (AP placement) or the massive signal loss caused by device orientation.

1. Cisco CMX Location Accuracy Best Practices

White Paper (2018).

Page 5

Section: "AP Placement": "The single most important factor that influences location accuracy is the number and placement of APs. For trilateration to work well

a client needs to be heard by at least three APs

and ideally four or five." This directly supports option A.

Page 7

Section: "Client Diversity": "Client signal strength can vary significantly depending on the device manufacturer

and even the way the device is held. Cisco has observed that the way a user holds a device can cause a 10- to 20-dB difference in signal strength." This directly supports option C.

2. Enterprise Mobility 8.5 Design Guide

Cisco Validated Design (2019).

Chapter 10

Section: "Location-Based Services Infrastructure"

Subsection: "AP Location and Density": This section details the critical requirements for AP placement

including placing APs on the perimeter of the tracking area and avoiding linear arrangements to ensure proper trilateration geometry. This reinforces the importance of option A.

3. Farid

Z.

Naffaa

M.

& Dasgupta

M. (2013). A survey of wireless indoor localization techniques and systems. IEEE Communications Surveys & Tutorials

15(4)

1568-1586.

Section III.A

"RSSI": This peer-reviewed article discusses the challenges of RSSI-based localization

noting that "The human body's presence and orientation can cause significant RSSI variations

" which validates the impact of client device orientation (Option C). It also discusses how the placement of reference nodes (APs) is fundamental to the accuracy of lateration algorithms

supporting Option A.