Tech Briefs

New linear solutions are significantly simpler than the previous complex nonlinear solutions.

The wireless radio positioning or radiolocation problem is of great importance in society today. Existing radiolocation systems such as the Global Positioning System (GPS), Radio-Frequency Identification (RFID) systems, and Ultra Wide-Band (UWB) systems use propagating EM waves and show reduced accuracy in non-line-of-sight (NLoS) environments due to propagation losses, delays, or multi-path effects. These significantly limit their use in radiolocation applications where the line of sight to the device is blocked. Examples of these are many, and include radiolocation for a device inside a cave or building, embedded underground or in a tunnel or mine, and for underwater applications, which covers a multitude of space, military, and civilian applications. In addition to these severe limitations, existing radiolocation systems using propagating EM waves enable ranging and positioning, but cannot provide precision two-dimensional (2D) or three-dimensional (3D) orientation sensing, which is critical in many applications where the sensor's attitude is important.

In contrast, magnetostatic fields are not significantly disturbed and can offer accurate radiolocation in NLoS environments. In the past, magnetostatic systems using frequencies of up to a few kilohertz were developed for above-ground positioning. These techniques did not account for induced eddy-currents in the ground, which limited the range of operation to a few meters above the ground, typically as low as 1.5 m of maximum range. However, this simplification of neglecting nearby induced eddy-currents, and using a very low frequency for short-range applications, did permit a decoupled solution for position and orientation. This decoupling was critical to enable a linear solution to position and orientation for what is otherwise a nonlinear coupling problem.

To enable long-range positioning, the magnetostatic technique must use higher frequencies and benefit from increased signal-to-noise from Faraday's law. This class of systems falls into the magnetoquasistatic or MQS region. Long-range MQS positioning above ground was recently demonstrated using frequencies of a few hundred kilohertz and by accounting for the induced eddy-currents in the ground. However, the strong ground effects did not permit a decoupled solution for range and orientation of the device to be radiolocated, and instead required solution of nonlinear coupling equations. Due to use of the nonlinear field coupling equations, previous attempts to extend the long-range MQS technique to 2D and 3D have resulted in solutions that exhibit large error, which are strongly varying as a function of the orientation and position of the transmitter and receivers. Furthermore, the complexity in the nonlinear solution space impedes the ability to converge to a correct solution, or to solve in real time. Attempts to use orthogonal fields to aid the nonlinear convergence have resulted in slight improvements in accuracies at the expense of significantly more complicated algorithms with high computational complexity.

By using multi-axis transmit and receive sensor concepts, the innovator recently showed that the coupling equations in long-range MQS systems could indeed be derived in a manner that enables decoupling. The decoupled theory and algorithms enable linear long-range position and orientation sensing using MQS fields for the first time. In addition, the linear solutions were significantly simpler than the previous complex nonlinear solutions, and thus permitted low-latency (fast) position and orientation solutions that were previously not possible in long-range MQSs.

This work was done by Darmindra D. Arumugam of Caltech for NASA's Jet Propulsion Laboratory. NASA is seeking partners to further develop this technology through joint cooperative research and development. For more information about this technology and to explore opportunities, please contact Dan Broderick at This email address is being protected from spambots. You need JavaScript enabled to view it. . NPO-49719

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