Patent ID: 8994590
Filing Date: 2015-03-31
Classification: G01S

Abstract:
1. A method of forming an estimate of a two-dimensional position of a radio receiver relative to a plurality of radio transmitters each radio transmitter having an associated position estimate and a position uncertainty expressed as an uncertainty ellipse having major and minor axes, respective lengths and orientations of the major and minor axes defining the uncertainty ellipse, the method comprising: receiving the position estimates and position uncertainties of the plurality of radio transmitters; receiving at the radio receiver respective signals from the plurality of radio transmitters and forming, by a weighting determination unit, in dependence on the received signals respective transmitter weighting values each weighting value being inversely proportional to a measure of distance between a respective radio transmitter of the plurality of radio transmitters and the radio receiver; for each of the plurality of radio transmitters, scaling, by a position calculation unit, an uncertainty vector having an argument describing an orientation of the respective uncertainty ellipse in a predetermined coordinate system, defined relative to the major and minor axes of the uncertainty ellipse, by a scaling value, wherein the scaling value is proportional to the respective transmitter weighting value, and rotating the scaled uncertainty vector by multiplying its argument by a factor of four, wherein the argument of the uncertainty vector represents an angle that the uncertainty vector makes relative to a predetermined direction in the predetermined coordinate system; summing, by the position calculation unit, the scaled and rotated vectors of the plurality of radio transmitters so as to form a total vector; dividing, by the position calculation unit, the argument of the total vector by a factor of four and using the resulting rotated total vector to define a compound coordinate basis comprising first and second coordinate axes; and forming, by a position calculation unit, an estimate of the two-dimensional position of the radio receiver in the compound coordinate basis by: