System and method for determining a position of a mobile device within a surveillance volume in the presence of multipath interference

A system of determining a position of a mobile device within a surveillance volume in the presence of multipath radio interference, comprising:

• a spatially diverse phase difference array of N sensors for detecting radio frequency (RF) signals from the mobile device, wherein N is greater than 4, and acquiring phase difference data from the RF signals with respect to frequency at a plurality of frequencies between any selected pair of sensors, wherein spatial diversity of the array comprises at least one of the following;
• (1) separations between sensors in any selected sensor pair are different, (2) azimuth angles between sensor pairs are different, (3) distribution of azimuth angles of sensor pairs is uniform;
• (4) placement of three sensors along any given line between sensors is avoided, (5) any parallel orientations of sensor pairs are avoided, whereby as a result of the spatial diversity of the array, multipath phase difference errors in the measured phase difference measurements summed across the phase difference array is approximately zero;
• and
• a processor for determining the position of the mobile device from the phase difference data, the processor configured to determine phase difference with respect to frequency between any pair of sensors at a plurality of frequencies without use of a time reference, the processor configured to solve a system of at least N-1 independent nonlinear equations of the form 2dij(Di+Dj)−2(xj−xi)X−2(yi−yi)Y+(xj2−xi2)+(yi2−yi2)=0, where dij is the phase difference acquired between i-th and j-th sensors, Di is the distance between the mobile device and the i-th sensor, the position of the i-th sensor is (xi, yi, zi), and the position of the mobile device is (X, Y, Z), whereby the position is iteratively determined using the system of equations to reduce effects of multipath interference.