A Free-Space Optical Communication System using Digital Signal Processors

• Main Authors: Yu-Ming Wang, 王裕閔
• Other Authors: Jean-Fu Kiang
• Format: Others
• Language: en_US
• Published: 2006
• Online Access: http://ndltd.ncl.edu.tw/handle/48707730704569658993

碩士 === 國立臺灣大學 === 電信工程學研究所 === 94 === There are several advantages with optical communications in free space such as high data rate, dedicated communication and being difficult to eavesdrop. Free-space optical communications is an alterative to short-distance communcations. In this work, optical transceiver modules are designed to demonstrate an optical communications link. An optical transceiver module consists of a tansmitter and a receiver. The transmitter is composed of a driver circuit and a Thorlabs L850P010 850 nm 10 mW diode laser with a monitor-diode feedback loop and focused by an external collimation tube. The receiver is composed of a TMC-8D41-000 GaAs PIN plus pre-amplifier photodiode and decision circuits. Digital signals from PC are encoded and sent to a digital-to-analog converter (DAC) to modulate the diode laser. At the receiver side, the light is received by the GaAs PIN photodiode, then sent to an analog-todigital converter (ADC) for post processing. We propose a revised protocol to improve the performance in the conventional encoding scheme. The revised protocol has the capability of synchronization and error correction. The preamble code and Hamming encoding scheme are used to improve the accuracy and reliability of the bit stream. The TI TMS320C6416T fixed-point digital signal processor (DSK) with an analog expansion daughterboard (AED-101) are used to provide maximum sampling rate up to 80 Msps. In this work, IrDA data rate of 1.152 Mbps is chosen as a reference for a communications link over one meter.