Mobile-BAT-A Novel Ultra-Low Power Wildlife Tracking System

Abstract

We introduce a novel ultra-low power system for tracking animal movements over long periods with an unprecedented high-temporal-resolution. The localization principle is based on the detection of cellular base stations using a miniaturized software-defined radio, weighing 2.0 g, including the battery, and having a size equivalent to two stacked 1-euro cent coins. Therefore, the system is small and lightweight enough to be deployed on small, wide-ranging, or migrating animals, such as European bats, for movement analysis with an unprecedented spatiotemporal resolution. The position estimation relies on a post-processing probabilistic RF pattern-matching method based on the acquired base stations and power levels. In several field tests, the system has been successfully verified, and a run-time of close to one year has been demonstrated.

Keywords: GSM; bats; low-power electronics; mobile communication; movement ecology; radio propagation; telemetry; wildlife tracking; wireless sensor networks.

Figure 1

The logger receives four exemplary GSM cells with distinct cell IDs at different power levels. First, the spectrum of the GSM 900 band is analyzed, and up to 20 channels are chosen for decoding. The acquired data are then saved in the onboard memory.

Figure 2

Block diagram of the miniaturized software-defined radio. The power supply is shown in red.

Figure 3

Instantaneous frequency $\frac{\mathrm{d}}{\mathrm{d}t}\varphi \left(t\right)$ read-out from CC1200 (measurement) and absolute phase $\varphi \left(t\right)$ calculated by integration. The plot shows a measured frequency and time-synchronized GSM SCH burst with its training sequence highlighted with a gray box.

Figure 4

Mass and energy of commercially available coin cell batteries by technology.

Figure 5

Simulated battery and capacitor voltages and currents [47].

Figure 6

Manufacturing steps of the miniature GSM cell logger: (a) the 1 euro cent coin as a size reference, (b) assembled printed circuit board and CR1616 coin cell, (c) folded around the battery, (d) with fiberglass fabric, (e) molded in epoxy resin. The antenna has a length of 8 cm and is not fully visible [47].

Figure 7

Weight contributions of the logger by components. Total weight: 1.988 g [47].

Figure 8

RF TRX base station for return detection and data upload. (a) The phone module (FONA 808) is directly supplied from the li-ion battery due to high peak currents during TX, whereas all other components are operated at 3.3 V. (b) Solar-powered base station mounted at a tree. The left antenna is for the wireless sensor network in the 868 MHz band, and the right antenna is used for the GSM/GPRS phone connection. On top of the box is a GPS antenna (not visible). The waterproof aluminum box is mounted to a tree with long zip ties [47].

Figure 9

Predicted mean receive power ${\overline{P}}_{\mathrm{RX}}$ of an isotropic receiver at $h_{\mathrm{RX}}=2$ m for GSM cell 262/03/58162/8863 (N49.573859/E11.027138, $h_{\mathrm{RX}}=52$ m, $\theta ={30}^{\circ }$) [47].

Figure 10

Example of the distribution for $P_{\mathrm{RX},1}=-75.5$ dBm and $P_{\mathrm{RX},2}=-74.5$ dBm and density function for a received signal with $P_{\mathrm{RX}}=-75$ dBm in a 1 dB interval [47].

Figure 11

Depiction of the position estimation showing a reference measurement. The true position is in the center (base map: © OpenTopoMap) [47].