Investigation of Digitalization in Laser Rangefinder Receiver - How to Use Digital Signal Processing and Pulse Detection to Improve Performance in the Laser Rangefinder Receiver

Abstract

Digitization provides many opportunities for a wide range of applications since it can generate more flexible and stable solutions compared to analog solutions. It also allows using other tools than the ones available for analog solutions. The purpose of this master’s thesis was therefore to investigate how the performance of an analog laser rangefinder receiver can be improved by digitalizing the receiver and using digital techniques on the laser rangefinder’s received echo signal. This included investigating the detection sensitivity, as well as, the possibility to separate false alarms and true optical echo pulses in the received signal. Separating the two would provide a possibility for increased bias voltage in the Avalanche Photodiode (APD), used for detection in the laser rangefinder. An increase in bias voltage would also improve the sensitivity of the laser rangefinder. The investigation was done by simulations in MATLAB. The simulations consisted of constructing a laser rangefinder’s received echo signal, applying digital signal processing to it and using digital pulse detection. It was also investigated if some other analog solutions in the laser rangefinder can be replaced by digital techniques in a digital solution. The Central Processing Unit (CPU) time for the investigated digital methods was also measured. The result demonstrated that a digital laser rangefinder receiver would be superior to an analog receiver under the circumstances of the thesis. The detection statistics were much improved and the detection sensitivity of the optical pulse amplitude was increased by 10.57 dB. The digital solution also managed to separate false alarms and true optical pulses to a certain extent. Thereby making it possible to increase the bias voltage in the APD.