Anti-interference pulsed laser ranging system

Andrey Sadchenko; Oleg Kushnirenko; Yevgen Koshelev

doi:10.15222/TKEA2020.1-2.08

Andrey Sadchenko Odessa National Polytechnic University https://orcid.org/0000-0002-2517-6892
Oleg Kushnirenko Odessa National Polytechnic University https://orcid.org/0000-0002-7045-5620
Yevgen Koshelev Odessa National Polytechnic University

DOI: https://doi.org/10.15222/TKEA2020.1-2.08

Keywords: laser ranging, logical convolution, Walsh functions, binary sequences, logical matched filter

Abstract

Pulsed laser rangefinders prove to be cost-effective and practical devices when used at distances of several tens of kilometers due to their compactness, portability and energy efficiency. However, the measurement accuracy is significantly reduced by the presence of pulsed interference affecting the input of the optical receiver both during the sensing period and when the reflected signal is being received. Using the algorithms with the accumulation and subsequent processing of the results of several successive measurements reduces the speed of decision-making and does not guarantee the convergence of the results to the real value of the distance.
The paper proposes a structural diagram of a laser rangefinder with the ability to detect pulsed interference in the range interval and correct errors that occur in the structure of the signal reflected from the target. The basis of the rangefinder circuit is a logical consistent filter, the structure of which contains multipliers (multiplication operations).
The following requirements were formulated for the structure of the probe signal:
— the first element should always be set to +1 to synchronize the receiver decider;
— the weight of the coding sequence is equal to half its length;
— the length of the coding sequence is even.
Based on the requirements for coding sequences, the optimal structures of binary probing signals of length 8 were found, providing the best corrective ability.
Comparison of the correlation properties of the found sequences and the sequences that are constructed using the Walsh functions showed the advantage of the optimal sequences by the criterion of the minimum level of the ACF side lobes.
The simulation of the rangefinder under pulsed noise conditions has shown that the logical filter is advisable to use for those cases when the duration of the obstacle does not exceed 1/3 of the duration of the probing signal.

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