| 摘要 |
A transmitter device ( 1 ), operable to perform distance measurements by using time-of-flight measurements, has a sampling frequency different to the frequency of a time-of-flight signal sent from the transmitter device to a receiver device ( 12 ) in order for the distance between the transmitter device ( 1 ) and the receiver device ( 12 ) to the determined. The signal, from which the time-of-flight signal is derived, is modulated with a PRN sequence derived from the output signal of a Numerically Controlled Oscillator ( 17 ). A new chip is generated by the NCO ( 17 ) each time a register ( 24 ) in the NCO overflows, but the beginning of the chip according to the desired frequency of the PRN code does not necessarily coincide with a sampling point in the transmitter device ( 1 ). The invention enables time stamps to be generated even when the reference point ( 30 ) to be timed does not coincide exactly with a sampling point ( 31, 32 ) in the transmitter and consequently the time-of-transmission of the time-of-flight signal can be determined accurately. The time-stamp for a reference point ( 30 ) is constituted by the residual phase code ( 34 ) in the register ( 24 ) of the NCO ( 17 ) immediately following the reference point. The difference between the fixed value added to the register ( 24 ) at each sampling point and the recorded residual phase code ( 34 ) at the sampling point ( 32 ) immediately following the reference point ( 30 ) is proportional to the time passed between the sampling point ( 31 ) prior to the reference point ( 30 ) and the reference point ( 30 ).
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