Patent ID: 8098712

Claim:
A method of operating a correlation system, comprising: providing a transmission modulation sequence having an integration cycle period; modulating a signal with the transmission modulation sequence to generate a modulated signal; transmitting the modulated signal; receiving a received signal which is a reflected and delayed version of the transmitted signal; and integrating the received signal cyclically over a plurality of integration cycle periods to identify correlation peaks between the transmitted and received signal to determine a time of flight of the signal; wherein the step of providing a transmission modulation sequence includes: providing a digital sequence having a sequence length k; and generating one of a plurality of transmission modulation sequences of different effective phase from the digital sequence by: changing the effective phase of the digital sequence by, at intervals, restarting the digital sequence at a variable one of the items in the digital sequence; wherein the effective phase is varied by restarting the digital sequence at the j-th clock cycle, where j is an integer 1≦j≦k, in which j is changed at intervals to vary the phase, including determining the intervals using a pseudorandom number generator.