RECEIVER DESIGN AND PERFORMANCE ANALYSIS FOR FREE-SPACE OPTICAL COMMUNICATIONS

Abstract

To detect intensity-modulated signals, two photodetection schemes are commonly used, namely, direct detection and photon counting. For both of them, the channel state information (CSI) and the strength of the background radiation are required for reliable signal detection. In this thesis, for each combination of photon detection method and background radiation condition, we develop an optimum sequence receiver and a simplified symbol-by-symbol receiver, both of which can automatically estimate the CSI and/or the background radiation, and detect the data accordingly. Since very few pilot symbols are used, these receivers are efficient. The error performance of each receiver can approach that of detection with perfect channel knowledge, as the length of the observation window increases. Besides robust signal detection algorithms, choosing appropriate value for adjustable parameters can also improve the system performance. In this thesis, we give an example for properly adapting the laser beam waist dynamically at the transmitter and show that with our proposed method, the system performance is improved significantly.