Development of Ultra-Wideband Precision Indoor Positioning, 16-9438Printer Friendly Version
Inclusive Dates: 10/01/03 04/01/05
Background - A highly accurate and rapidly deployable positioning system for use inside buildings would be extremely valuable for numerous applications. Such a system could be used to track fire fighting, law enforcement, and military personnel in dangerous situations. Other applications for this capability include instrumentation for tactical training systems and tracking of valuable cargo. This IR&D project addressed the development of algorithms and RF architectures for precision indoor positioning.
The principal challenge of using radio frequency (RF) signals for accurate positioning in an indoor environment is multipath propagation. Multipath propagation occurs when the RF signal generated by a transmitter reflects from objects in the environment as it propagates to the receiver. The received signal is significantly distorted by the combination of these signals arriving by many different paths. The characteristics of the RF signal that are typically measured in order to compute location are also distorted due to the fact that the multiple arriving signals come from many different angles and arrive at many different times.
Approach - This internal research project investigated two important technologies that assist in overcoming the problems of multipath propagation in the indoor environment. The first of these is the ultra-wideband (UWB) waveform. Pulsed UWB signals consist of extremely short (less than 1 nsec.) pulses of energy. The extremely short duration of this waveform facilitates the isolation of different multipath components of the arriving signals. The second technology studied was a new family of location algorithms that actively exploit multipath propagation. Unlike traditional location algorithms that assume a clear line of sight between the transmitter and the receiver, these algorithms explicitly assume that there are signal components that have been reflected from objects in the environment. The new algorithms use this information to improve the accuracy of location estimates and to permit the computation of location estimates in environments where traditional approaches fail completely.
Accomplishments - The project team characterized the multipath propagation of UWB signals using commercial UWB evaluation hardware. These investigations addressed both the realistic environment of a typical office building and the controlled environment of an RF anechoic chamber. In the anechoic chamber, the desired multipath propagation was induced by introducing various numbers and sizes of radar test targets.
The development of the positioning algorithms addressed the problem of determining the location of a transmitter and the locations of a number of discrete reflecting structures in two or three dimensions using only the arrival times of the pulses of the multipath-propagated UWB signal. A number of effective techniques were developed to solve this problem, the most powerful of which is a highly modified particle swarm optimizer (PSO). PSOs use the biological analogy of foraging insects to solve difficult nonlinear optimization problems. Enhancements made during this program include an active feedback control mechanism and a unique method of decomposing the positioning problem into a number of similar, low-dimensional optimizations. These enhancements permit the solution of the positioning problem with dramatically reduced computational resources. In addition to addressing the location problem of this IR&D program, these algorithms have broad applicability to other challenging non-linear optimization problems.