Alvin Lim, associate professor of computer science and software engineering, is developing a mobile system that will provide accurate GPS positioning and navigational information for mobile devices in environments that currently disrupt data transfer, such as indoors, urban canyons and under tree canopies.

Other positioning systems require sophisticated hardware that is not cost-effective, or use positions of dedicated infrastructures, such as cellular base stations or wireless access points, which are grossly inaccurate. Another approach uses signal strength which has been found to be inaccurate because of multipath and fading effects. Lim’s positioning system does not require special hardware, and instead relies on commercial, off-the-shelf mobile devices to work with each other.

With Lim’s system, a GPS-denied target node with no position information communicates opportunistically with a number of in-range mobile peer nodes with some positioning capabilities. Data exchanges between the target node and peer nodes are used by the target node to refine its position estimation using three algorithms: enhanced time of arrival, mathematical constraints solver and barycentric algorithms. The mathematical constraints solver determines the raw device position from a set of inequalities while the barycentric algorithm combines the raw positions to generate more accurate positioning.