Navigation of unmanned vehicles using Bluetooth
Background
Bluetooth is a well-known wireless technology standard that enables communication between many of our smart devices. However, recent and upcoming additions to the Bluetooth standard enable new use cases; navigation, using range and/or directional information. In version 5.1 of the Bluetooth standard, the constant tone exchange (CTE, a constant sine wave) was added to the end of the Bluetooth package. By measuring the phase of this sine wave using multiple antennas in different positions, the direction to the signal source can be estimated.
The range between the transmitter and the receiver can be found in three different ways. Using signal strength (RSSI) is typically the least accurate, while measuring the time it took for the data to travel (time of flight) improves this somewhat, to an accuracy of 2-4 meters. The third and most accurate method, multi-carrier phase differencing, considers the phase, which also is a function of the distance between the sender and transmitter, enabling accuracies down to 30-50 cm.
While the focus of the industry and the literature seem to be on indoor use of Bluetooth, the underlying technology also has merit in outdoor navigation of unmanned vehicles, like landing of drones and docking of autonomous ships, see the below videos:
| Net landing | Ship docking |
|---|---|
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Both videos represent scenarios where it is critical to know the exact position of the vehicle, so relying on a single position sensor, like GPS, makes the system vulnerable and error-prone.
Scope
There are many possible areas of focus within this project, that can be adapted to the interests and competence of the candidate. This includes, but is not limited to
- experimenting with the use of multi-carrier phase differencing (MCPD) for measuring range, using this library by Nordic Semiconductor. For drone applications, quantities like accuracy, precision, achievable range, and measurement rate are of interest, in different environments.
- How can ranging be combined with directional information from an antenna array? Using both range and directional information it is possible to determine the full 3D position of the transmitter using a single receiving antenna array
- How can Bluetooth range measurements be combined with other measurements to estimate the position, velocity and attitude of a drone? One option could be to use a Kalman filter to fuse the information from inertial sensors (accelerometer and gyroscope) with multiple range measurements and other sensors common in drone payloads (barometer/altimeter, GPS)
Please indicate what aspects of the project that caught your attention.
Regardless of the focus, experimental validation will be important, where flight testing using one of our drones is a natural step on the way.
Proposed tasks
The tasks will vary based on the focus of the project, as decided by the student (you) and the supervisor (me), but the below steps are common:
- Perform a literature study on the state of the art within radio-based navigation
- Familiarize with the capabilities and limitations of relevant, existing development kits and software libraries for Bluetooth range and/or direction measurements
- Extend/adapt solutions from the literature and/or
- Discuss the results with a critical eye, and conclude the work in a written report
The work will continue in a master thesis for the spring semester, and could possibly lead to a job at Nordic Semiconductor.
Prerequisites
The project lies in the intersection of estimation/navigation, embedded computers and signal processing. No candidate is expected to be an expert in all these domains, but the background and interest of the candidate will help determine the focus of the project.
Contact
Contact supervisor Kristoffer Gryte. Other people involved in the project, depending on the chosen focus, are
- Carsten Wulff (Assoc. Prof. NTNU IES/Wireless Group Manager Nordic Semiconductor)
- Kimmo Kansanen (Prof. NTNU IES)
- Torleiv H. Bryne (Assoc. Prof. NTNU ITK)