# Localization in Low Power Wide Area Networks Using Wi-Fi Fingerprints
## 1 Introduction  
The location of an asset at a given time is an important piece of information in supply chain management [1; 2; 3]. [PERSON] and [PERSON] [4] divide tracking and tracing of assets into two categories: discrete and continuous. The discrete category relies on barcodes and Radio Frequency Identification (RFID) approaches to know when a specific asset is at a predefined location. The continuous category relies on a Global Navigation Satellite System (GNSS) such as the Global Positioning System (GPS) to establish the location of the asset and a cellular data connection to communicate this location with the management software. [PERSON] et al. [5] define a subcategory to continuous tracking, called the quasi-continuous tracking. In this subcategory, the management software continuously tracks a vehicle, while the vehicle has knowledge about the assets it carries through discrete tracking. [PERSON] et al. [6] present and discuss a number of recent quasi-continuous tracking solutions. In an Internet of Things scenario, assets would have a permanent connection to the internet themselves, rather than through a hub in the transportation vehicle. This allows the owner of the assets to be independent of the transporter. While this connection can in theory be a cellular data connection, in practice the energy requirements for such connections limit its applicability only to assets that are large enough to carry additional batteries for this connection. Low Power Wide Area Networks (LPWAN) propose to reduce the energy requirement of the mobile data connection, albeit at reduced data rates [7]. Sigfox [8] is one of the major players in the LPWAN market. It uses an ultra narrow band (UNB) channel of 100 Hz with a Differential Binary Phase Shift Keying (BPSK) modulation operating on the 868 MHz telecommunication frequency in Europe. This frequency does not require a license for operating Short Range Devices (SRD), defined as devices with a limited transmission power. To comply with these regulations, a Sigfox device can only transmit 140 messages of 12 B each on a single day at 100 bit/s. This stems from a 1% hourly duty cycle regulation, limiting Sigfox to 36 s of signal transmission or six messages per hour. The transmission of a single Sigfox message takes 6 s, during which the same information is transmitted three times for error prevention. The communication range is around 30 km outside cities and 3 km inside cities [7; 9]. In this article, we present our idea of enabling localization of a device using the 12 B payload limit of Sigfox. Localization based on wireless communication can be split into three categories: proximity; geometry, better known as trilateration or triangulation; and pattern recognition, also referred to as scene analysis or fingerprinting [10]. Proximity localization assumes that a mobile unit is at or near the location of the gateway with which it is connected. The proximity method's accuracy depends on the range of the communication method. Proximity localization is often used in Radio Frequency Identification (RFID) scenarios, which have a limited range [11]. If the range increases, the mobile unit can be in communication with multiple gateways, which allows more sophisticated estimation of the mobile unit's location. These types of estimation quickly approach the trilateration technique. Trilateration, a type of geometric localization, estimates the distance between the mobile unit and multiple gateways. These distance estimates can be based on the time of flight of the signal [12], or based on the attenuation of the signal when received by either the mobile unit or the gateways [13]. Triangulation, as opposed to trilateration, estimates the angle of arrival of the received signal through an antenna array. Pattern recognition, most commonly known in the localization community as fingerprinting, consists of comparing a snapshot of the current environment with a database of such snapshots linked to known locations [14].