Investigation of localization properties of Bluetooth Beacon II

Received Signal Strength (RSS) measurement is the basis for many indoor localization systems due to its ease of implementation and the fact that an RSS parameter is available in most commercially used wireless protocols. In practice, however, these RSS measurements are impaired by various physical propagation effects such as shadowing and multipath propagation, but also by interference with other devices. This results in a less robust and accurate determination of position than it is possible with time-based methods such as Time (Difference) of Arrival (TDoA).

Within this project, the possibilities for reducing the interference with RSS measurement by means of directional antennas were investigated. Directional radio is usually used by applications to increase signal quality and signal strength and to suppress interference outside defined areas. Here, particular focus was placed on the Bluetooth standard.

Since common methods for calculating the distance between transmitter and receiver from the measured field strength are based on an omni-directional and uniform radiation pattern, these algorithms cannot be applied for directional antennas. In simple terms, the mathematical difference is that the field strength of directional antennas depends on two parameters (distance and angle) and not just distance only. Therefore, a novel algorithm has been developed which combines the measured field strengths of several directional antennas and calculates an estimated position of the transmitter.

A simulation framework was developed to verify the designed algorithms, which allows the calculation and graphical representation of real and estimated positions, using simplified dispersion models and parameters (e.g. free-space propagation or log-normal path loss model). The verification was carried out via indoor and outdoor measurements using commercially available Bluetooth (BLE) transceivers and directed 60° antennas. Using Bluetooth specific characteristics such as frequency hopping, it was also possible to reduce fading and multipath influences.

** This project has been funded by the Austrian Research Promotion Agency (FFG) within the programme "Innovationsscheck".