This is a low cost, scalable, positioning system. Unlike other Ultrasonic positioning systems, we transmit from the surroundings to devices including wearables. Any number of devices can receive the ultrasonic chirps and determine their position (similar to GPS).

Our systems can be used for many diverse applications ranging from the scientific to the artistic. For example, our positioning and tracking systems have been used for interactive games and displays for tourists which change as they move around. They have also been used by researchers to follow the positions of items used in a household, and in an interactive lab with children’s toys.

Positioning and Tracking

All our systems are based on a set of fixed nodes placed around a room, plus one or more moving nodes which we want to monitor the position of. We separate the systems into two classes:

Positioning systems where each moving node carries equipment to monitor its position, using signals transmitted from the fixed nodes in the room. Because each moving node monitors its own position, any number of moving nodes can be present in the room without interfering with each other’s operation. However, the extra equipment carried by each moving node increases the cost.

A further consideration is that the information about position ends up with each moving node, and not in some central place. This means that positioning systems are better suited to applications where the moving nodes are completely independent of each other. Communication is possible, but comes at the expense of more equipment and limiting the number of moving nodes that can be monitored at once.

The second class is tracking systems, where each moving node regularly transmits a signal which is picked up by the fixed nodes in the room. Because each moving node uses the airspace as it transmits, the number of nodes which can be tracked at once is limited. However, the moving nodes do not need to carry any complicated processing power, so will usually be cheaper than those used in a positioning system. A tracking system is best suited to applications where a small number of moving nodes need to co-ordinate with some central monitoring system.

To choose a system for a particular application, decisions need to be made about the number of objects to be monitored, the update rate required, and the cost in terms of size and perhaps money. In general, the positioning system's advantages are the ability to monitor unlimited objects with privacy, while the tracking system offers small tag size for monitoring relatively few objects.

Auto-Calibration

A problem shared by all of the positioning and tracking systems is the need to know the positions of the fixed nodes in the system. These are used as reference points during the computation of a moving node’s position.

In the past, installing a positioning system required the user (e.g. the curator of a museum, or a psychologist doing a study) to spent a considerable time up ladders measuring the distances between transmitters. We identified this as a major obstacle to installing positioning systems, and have developed algorithms to simplify the calibration process. The intention was to end up with a system that can be installed by a single non-technical person on the ground.

Although more information can be found during auto-calibration (both the fixed node positions and the moving node position) we can apply batch techniques to solve for the unknowns. This is because unlike positioning, auto-calibration does not have to be performed in real-time.

So far we have developed auto-calibration algorithms for the first two positioning systems plus the tracking system. We have also developed a method for aligning an arbitrary auto-calibration solution with a desired real-world co-ordinate system. This makes it easy to have the positioning system (for example) treat the corner of a room as the origin, and its walls as parallel to the X, Y and Z axes.

Ultrasonics Positioned on Ceiling