Proximity Tagging Description
Overview and FAQs
Proximity Tagging allows your activity monitors to record the presence of other nearby devices. This feature is useful when there is a need to evaluate the effect that location (or other subjects) have on a subject's physical activity or sleep efficiency. Devices can be configured as either Receivers, which store a time-stamped serial number or Subject Name of nearby beacons, or Beacons, which constantly broadcast their serial number and Subject Name out for detection by receivers. The image below illustrates one example of a use-case for Proximity Tagging.
Figure 1 - Beacon devices placed in various rooms of a building
Use case example 1 (see Figure 1): Multiple Beacon devices placed in various rooms of a building or house. The Receiver device (worn by the subject) flags whenever the wearer walks near a Beacon device.
Do Beacons or Receivers record physical activity (movement) data like normal?
Both beacons and receivers record physical activity data (accelerometry data in all three planes and ambient light data) while also performing their proximity tagging role.
What is the battery life of Beacons and Receivers?
Beacon devices can be constantly powered using the optional USB charger. Receiver Battery life TBD
What do Receivers and Beacons store?
Both devices record physical activity data in the same fashion as a normal device. However, Receiver devices will log the Received Signal Strength Indication (RSSI) value for Beacon devices that are detected within range. Note that this RSSI value is not directly proportional to Bluetooth signal strength. Read more about RSSI here.
Which ActiGraph devices support Proximity Tagging?
ActiGraph's wGT3X-BT and wActiSleep-BT devices support proximity tagging (serial numbers begin with "MOS")
Do Beacons have to be placed on stationary objects?
Beacons can be placed on stationary or mobile objects.
What software is required?
ActiLife 6.10 and later support the Proximity Tagging feature.
Do I have to initialize all of my Beacons and Receivers at the same time? Can I add more Beacon devices later?
Preparing devices for Proximity Tagging
- Obtain two or more wGT3X-BT or wActiSleep-BT devices and connect them to the PC running ActiLife 6.10 or later.
- Click "Initialize" and choose "Proximity Initialization." Unless dismissed, the "Proximity Tagging Welcome Screen" will appear, giving a brief description of how proximity tagging works.
- Select a start time and date; optionally set a stop time
- The start date/time indicates when 1) Receivers will start collecting Beacon tags and 2) all devices will begin collecting activity data
- The "Device Time" indicates the exact time of day that the device will use as its own timebase. Choose "Atomic Server" to synchronize the minutes/seconds with an atomic server (Internet access required). The hour will always be relative to the local computer.
- Select device roles by clicking on a row and using the left/right arrows to change. Click "identify device..." anytime to flash the LED on the device for identification purposes
- Provide each device with a "Label." The label can be the subject's name for Receivers (e.g., "Subject 001") and the static location for Beacons (e.g., "Living Room," "Bedroom," "Vehicle," etc).
- Regardless of its role, all devices will capture and store actigraphy data. Receiver devices, however, are the only devices that will store Beacon serial number logs.
- Click the "Go to Advanced Settings and Bio" button to enter advanced options for each device or click "Initialize" to begin the initialization process.
- Following initialization, devices will be Grouped and will appear with the Group indicator in the Devices grid (see "What is Group Initialization?" for more details). When downloading, if one of the Beacons or Receivers is not present, ActiLife will indicate that a device which is part of the proximity group is missing.
- IMPORTANT: Not all devices need to be present to download Proximity information. The grouping is for convenience only.
- - Two devices in a Proximity Tagging group in the Devices grid
- Place Receiver and Beacon devices in the appropriate location or on the appropriate subjects at the desired time.
The optimal placement of Beacon devices will depend on the specific study aim. For optimal signal strength, devices should be placed in an elevated location with the top of the device facing outwards. For example, mounting a device on a wall 5ft from the ground with the bottom part of the device against the wall would likely maximize the signal strength of the beacon.
The maximum distance that a beacon can be detected will depend on the environment. Maximum detection distance indoors (beacon-to-receiver) can range from 10 meters to 20 meters. According to the Bluetooth 4.0 specification, outdoor line-of-sight range can extend to 100m under ideal conditions. Our internal testing indicated that devices detected at 10m line-of-site distance exhibited close to a -90dB RSSI. Devices exhibiting RSSI below -90dB were often not detected at all.
High- vs. Low- Resolution Proximity Tagging
Device signal strength is a poor indicator of "distance" as many variables can affect the receiver and beacon signal strength and receive power. For example, a subject facing away from a beacon will log a much lower signal strength than the same subject, the same distance away, facing toward a beacon device. The best option for estimating "proximity" is to examine the study requirements to determine whether or not a high or low resolution of detection is necessary. For instance, a low-resolution study protocol objective might look at total time spent and activity level differences for a subject while in their home, at work or in their vehicle over a week-long time span. In this case, two or three beacons placed throughout the subject's home, one in the subject's car and one near their office desk may be sufficient for detecting those three modes (home, vehicle, work). This data can then be algorithmically smoothed and parsed to provide general information on total time and activity for each mode.
Alternatively, a high-resolution study protocol objective might include investigating total time and difference in activity levels for a subject while in various rooms of a single building (e.g., kitchen, living room near a TV, bathroom and/or bedroom). In this case, a higher resolution of proximity information will probably be necessary and thus, more beacon devices needed (e.g., near the TV, couch, kitchen sink, stove, bedroom night stand, bathroom sink, etc). Placing beacon devices no further than 3m apart will help guarantee that the subject's location within the home can be more precisely determined.
Constant Power for Beacons
Stationary Beacons can be constantly powered (optional) by connecting them directly to a wall outlet. Doing so eliminates the need to recharge beacon stations during data collection. The USB Charger accessory may be purchased from the ActiGraph web store here.
Downloading Data from Beacons and Receivers
Both Beacons and Receivers will contain activity data following a period of data collection. However, only Receivers will contain Proximity Tagging data. To download and view Proximity Tagging data:
- Connect the Receiver (and/or Beacons) to the computer running ActiLife
- Note that other devices that were part of the Proximity Tagging network will appear in the Devices grid even if they are not connected. This is because these devices are "Grouped" together following Proximity Initialization. All devices do not need to be present - only the Receiver the device. The blue shading is only for convenience.
- Click the "Download" button and choose a file name convention for the output file. Be sure to also check "Create AGD File" and choose a desired activity data epoch length. Click "Download All Devices."
- After the download has completed and the AGD has been created, click on the "finished downloading" hyperlink in the Status column of the Devices grid; this will open the AGD viewer
- Click on the "Proximity" export button in the AGD Viewer
- From the dialogue, choose whether or not to include the Subject Name in the exported CSV column headers. Doing so will concatenate the label (entered during initialization) with the device serial number. Click "Export."
- Note the "Create Log Diary..." option. This feature is coming soon. This will allow Log Diaries to be created for all Beacons and Receivers in the network in order to filter out data.
- The resultant CSV file will contain time stamped epoch-level activity data from the Receiver device along with RSSI values (in dB) from all detected Beacons in column format. An example is shown below.
How do I export Proximity data at a later time (not at download)?
Proximity data can be exported from Receiver AGD files at a later time by clicking File -> Import/Export -> Proximity Tagging and using the resulting export form to browse to the appropriate AGD file.
For more information on interpreting the Proximity Tagging RSSI data, refer to the help article "Interpreting Proximity Data".