METHOD FOR MULTIPATH ERROR COMPENSATION AND MULTIPATH ERROR-COMPENSATED INDIRECT TIME OF FLIGHT RANGE CALCULATION APPARATUS

A method for multipath error compensation for an indirect time of flight calculation apparatus 100 comprises an unstructured light source 142 illuminating a scene during a plurality of consecutive time frames. A structured light source 144 illuminates the scene concurrently, the illumination by the structured source 144 occurring during predetermined frames of the plurality of consecutive time frames. An array of photodetectors 102 each generate a set of signals in response to irradiation with light reflected from the scene according to an indirect time of flight calculation technique to yield a plurality of sets of signals. An error estimate is derived 130 from the plurality of sets of signals generated during a selected time frame of the plurality of consecutive time frames when structured illumination takes place and another time frame temporally about the selected time frame when both structured and unstructured illumination takes place. The error estimate is applied in a range calculation with respect to the scene. A cathode of a photodiode 104 is coupled to a first input of a photonic mixer 106, and an output of the photonic mixer 106 is coupled to an input of an integrator 108. A timing control unit 118 has a first control output 120 coupled to a control input 114 of a phase signal generator 112, and a synchronisation output 122 operably coupled to a timing input 124 of a phase buffer 110. The plurality, m, of outputs of the phase buffer 110 are respectively coupled to a plurality of parallel inputs of a Digital Fourier Transform (DFT) unit 116. A pair of I/Q outputs 126, relating to the first harmonic of received reflected optical signals, is coupled to a vector input 128 of a range calculation unit 130. The range calculation unit 130 has a multipath calculation control port 132 operably coupled to a second control output 134 of the timing control unit 118. The vector input 128 of the range calculation unit 130 is operably coupled to a vector buffer 140, the vector buffer 140 also being operably coupled to a vector-to-range calculation unit 136. The vector buffer 140 of the range calculation unit 130 is also operably coupled to a multipath calculation unit 138. A multipath calculation activation signal is provided by the timing control unit 118 to the range calculation unit 130 to calculate a compensated vector.