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The next step in wireless sensing and radio telemetry

 Encounternet System Overview

How Encounternet works

Encounternet tags are microprocessor controlled and have radio transceivers that can detect and log the transmit pulses of other tags. Each tag pulses a unique ID number so logs of received pulses, along with their date and time, can be used to study associations among animals in great detail. Additionally, tags log the received signal strength (RSSI) of ID pulses, allowing researchers to estimate distance between individuals. Tags collect association data continuously as "encounter logs", even when researchers are not present. Tags can store as many as 8000 encounter logs to non-volatile memory.

The second critical component of Encounternet are wireless base stations, which are placed out in the environment where tagged animals roam. Base stations also detect and log tag ID pulses, and will automatically download the encounter logs stored on any tag. With base stations in the field to collect tag logs at all hours, a researcher only needs to periodically visit the field site to wirelessly download tag encounter logs stored on base stations.

A PC-connected hand-held device called the master node is used to downlod logs from base stations, and tags. The master node is also used to configure tag and base station parameters, and for conventional tag tracking.

Encounternet proximity logging tag network

Data flow in an Encounternet system configured for proximity logging: tags monitor and log ID pulses of other tags, base stations collect the logs from tags when they are within radio range, and a master node connected to a PC is used to download logs from base stations (and tags, if required) and store them onto the PC. Once logs are transferred from one device to another, the are deleted from the original device, to free memory.

Low power tag mode

In addition to proximity logging mode, Encounternet tags can operate in a very low power radio mode. The low power mode operates similarly to a conventional radio tag (transmit pulses but do not receive), except that all tags transmit on the same frequency and each tag transmits a unique digital ID code with every radio pulse. These features allow all base stations to continuously detect and log any tag pulses transmitted in range. Tags configured to run in low power mode can use smaller batteries and so can be made smaller and lighter (currently >= 0.7g), and have a longer lifespan. Although the low power tag mode does not allow tag-to-tag proximity logging, base stations can be used instead to monitor tag locations.

Using signal strength to monitor animal locations

Tag coordinates can be calculated if base stations are placed in a grid in the habitat such that at least three base stations can detect and log each tag pulse along with its RSSI value. The differential RSSI values of tag pulses received by different base stations can be used to estimate tag distance to each base station, and tag position can be then determined using triangulation.

The advantage of this system over conventional methods is that tagged animals can be continuously, and autonomously located as long as they are in range of three or more base stations. Furthermore, this system can be used with less accuracy in more sparsely distributed base station placements: the detection of a tag by a single base station places that tag within the radio range of that base station.

Encounternet tag location monitoring network

A grid of six base stations are used to record the position of tag 1 (any number of tags can be monitored in this system). In the figure, the leftmost base stations all detect and log tag 1's pulses. If tag 1 moves, then the differences in pulse signal strength received by base stations can be used to locate it. A typical location deployment will have many more base stations covering a much larger area.