Patent ID: 7525050

Claim:
A method for determining the location of a pointing device in the vicinity of a set of receivers able to receive one or more locating signals transmitted through air near a surface, the method comprising: (a) transmitting one or more ultrasound pulses and one or more electromagnetic signal pulses to or from the pointing device when the pointing device is near the surface, and as a result: (a1) receiving at one or more ultrasound receivers a respective ultrasound signal as a result of a transmitted ultrasound pulse propagating through air between the respective ultrasound receiver and the pointing device, or (a2) receiving at an electromagnetic signal receiver a respective electromagnetic signal as a result of a transmitted electromagnetic pulse signal, or (a1a2) both receiving at one or more ultrasound receivers the respective ultrasound signal and receiving at the electromagnetic signal receiver the electromagnetic signal, wherein at least one of the received signals includes a respective interfering signal; (b) for at least one of the received signals that may include a respective interfering signal, determining a respective estimated interference signal indicative of the respective interfering signal included in the at least one signal received in step (a); (c) for at least one of the received signals that includes a respective interfering signal, determining a signal indicative of the difference between the respective signal received in step (a) and the respective estimated interference signal determined in step (b); and (d) using the signal determined in step (c) to compute the location of the pointing device on or near the surface.