Wi-Fi Scanning, Power Consumption and Bandwidth for LPWAN


The ability to accurately and efficiently locate IoT devices is a key data element in an integrated IoT solution. With its power, bandwidth and cost constraints, LPWAN presents unique location challenges. GNSS-based positioning is challenging for IoT because (a) acquiring GNSS location consumes battery life; (b) GNSS receiver adds cost to device; and (c) poor urban/indoor coverage.
Wi-Fi positioning allows for extended battery life and may rely on low cost Wi-Fi chipsets. It also provides excellent coverage in an urban or indoor environment. This white paper will discuss options for how to reduce and optimize bandwidth and power consumption for LPWAN networks during Wi-Fi positioning. 
At a high level, Wi-Fi based positioning requires a scan to be performed and then for all scanned access points (APs) to be sent to the server. Scanning can be over multiple RF channels and bands. In an urban environment, it is common to see a very large number of APs (tens to hundreds). Sending all observed APs can be optimal for positioning accuracy, however it may require sending on the uplink packets of >500 bytes. While this is not a problem for LTE networks, it can be a challenge in LPWAN networks and can negatively impact battery consumption.
In this white paper, we provide several techniques that reduce bandwidth (uplink packets size) with limited impact on accuracy and yield. In general, there is a delicate trade-off between the number of APs sent to server and yield. Some scanned APs can’t be used for positioning (example mobile APs from tethered device). Other APs may be unknown at the server (example newly deployed). 
Overall energy consumption optimization for Wi-Fi localization can be achieved primarily by:
  1.  Reducing payload (scanned APs) that need to be sent to the server to complete positioning. Wi-Fi scan payload can be reduced to single packet (even Sigfox or LoRa packet at highest spreading factor of 12).
  2. Reducing scan time – There are several techniques used to reduce scan time by an order of magnitude (from 3-4 seconds to hundreds of milliseconds).
Download the full white paper to learn more about the techniques. 
DOWNLOAD THE white paper

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