Weak laser communication

• Main Author: Lim, Yong Jin.
• Other Authors: School of Electrical and Electronic Engineering
• Format: Final Year Project
• Language: English
• Published: 2013
• Subjects: DRNTU::Engineering::Electrical and electronic engineering::Wireless communication systems
• Online Access: http://hdl.handle.net/10356/53340
• Institution: Nanyang Technological University

Pulse Position Modulation (PPM) is a modulation technique where messages are encoded into the position of the pulse. This modulation technique is widely used in deep space optical communication system where it is less susceptible to bandwidth limitation and multipath interference problems. Optical Pulse Position Modulation uses Laser Diode and Photo Detector for the transmission and detection of signal. Avalanche Photodiode and Single Photon Avalanche Diode (SPAD) are used in deep space optical communication due to their high sensitivity and capability to detect weak signal. This makes the SPAD an attractive choice due to its capability of detecting signal to the single photon level. However, present projects employed the use of the SPAD in low detection efficiency (less than 40%). In this project, an Optical Pulse Position Modulation project using SPAD at high detection efficiency would be studied. Results shown that under different SPAD dead time condition, the saturation power level for the SPAD would vary. At longer dead time condition, it is possible to find an optimized power level for the system where the detection efficiency is at 99%. Finally, a 32-ary PPM of bit rate 0.35Mbps achieving good Symbol Error Rate (SER) and having stable performance over a range of optical power is developed. It is evident from the findings that it is possible to employ this weak laser communication system at high efficiency and achieving good Bit Error Rate/Symbol Error Rate (BER/SER).