Optical Correlation Apparatus and Method
AssigneeInstro Precision Limited
InventorChristopher John Morcom
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Abstract
Optical correlators are discussed, suitable for in-vehicle distance measurement. The correlators use modulation sequences based on maximal length sequences. A number of different modulation sequences are obtained by generator (32) from a single maximal length sequence, either by adding a variable number of cycles to the end of the maximal length sequence or by starting the maximal length sequence at different points in the sequence.
Claims19
A method of operating a correlation system, comprising:
- providing a transmission modulation signal having an integration cycle period;
- modulating a signal with the transmission modulation 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 the time of flight of the signal;
- wherein the step of providing a transmission modulation signal 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:
- adding a variable number of items to the digital sequence and determining the integration cycle period based on the sequence length plus the variable number;
- and/or changing the digital sequence by, at intervals, restarting the digital sequence at a variable one of the items in the digital sequence.
A method according to any preceding claim wherein the digital sequence is a maximal length sequence.
A method according to any preceding claim wherein the transmitted signal is an optical signal.
A method according to any preceding claim wherein the correlation system is mounted in a vehicle, the method further comprising determining distances from the vehicle to nearby objects from the identified correlation peaks.
An correlator, comprising
- a digital signal source providing a modulation signal based on a cyclical maximum length sequence;
- a modulator for modulating a signal with the modulation signal;
- a transmitter and a receiver for transmitting the modulated signal and for receiving a received signal which is a reflected and delayed version of the transmitted signal;
- an integrator adapted to identify correlation peaks of the received signal with the modulation signal;
- wherein the digital signal source includes at least one digital sequence having a sequence length k;
- and the digital signal source is adapted to generate one of a plurality of transmission modulation sequences of different effective phase from the digital sequence by:
- adding a variable number of items to the digital sequence and determining the integration cycle period based on the sequence length plus the variable number;
- and/or changing the digital sequence at intervals by restarting the digital sequence at a variable one of the items in the digital sequence.
Dependencies are inferred from the claim text.