Distributed magnetic field positioning system using code division multiple access

An apparatus for determining a state of an object in a reference coordinate frame, wherein said state comprises position and attitude, said apparatus comprising:

• a) a plurality of beacons at known beacon positions and beacon orientations within said reference coordinate frame, each of said beacons generating a magnetic field whose amplitude varies according to a pseudorandom code, wherein said codes are substantially mutually orthogonal;
• b) a magnetic sensor fixed to said object for measuring a total magnetic field generated by said beacons;
• and
• c) a processor in communication with said magnetic sensor for analyzing magnetic field measurements produced by said magnetic sensor to determine said state of said object.

A magnetic sensor position- and attitude-estimation method, comprising the steps of:

• a) using a plurality of beacons, generating a plurality of magnetic fields at known beacon positions and beacon orientations in a reference coordinate frame, wherein the amplitude of each generated magnetic field varies according to a pseudorandom code, wherein said codes are substantially mutually orthogonal;
• b) measuring a sum magnetic field at a sensor position to obtain a series of magnetic field measurements;
• and
• c) analyzing said magnetic field measurements to estimate a position of said sensor in said reference coordinate frame.

A method for determining a state of a magnetic sensor in a coverage area containing at least two beacons at known beacon locations and beacon orientations, wherein said state comprises position and attitude, each beacon generating a magnetic dipole field, said method comprising the steps of:

• a) measuring a magnetic field vector at a position of said sensor;
• b) decomposing said magnetic field vector into component vectors, each component vector representing one of said magnetic dipole fields;
• c) based on a magnetic field magnitude at said position of said sensor, calculating an approximate sensor position;
• and
• d) using said approximate sensor position as an initial position to determine said position of said sensor.