基于RS编码及网格编码调制的光PPM通信纠错技术

分析了RS（Reed-Solomon）纠错码和网格编码调制（Trellis Coded Modulation，TCM）技术在光脉冲位置调制通信中的应用．在此基础上，提出了以RS码作为外码，以网格编码调制技术作为内码，用于光脉冲位置调制通信的新编码方案，能以几乎不减少通信速率的优势，提高传统RS码系统在时变带限光信道中的通信性能．模拟研究了在不同空间光信道条件下，传统RS码的符号正确传输率和误码率，并对网格编码调制的编码增益、RS码与网格编码调制级联时的编码增益进行了仿真研究，证实了本方案的有效性．

Code conversion from signed-digit to complement representation based on look-ahead optical logic operations

We present, for the first time to our knowledge, a generalized lookahead logic algorithm for number conversion from signed-digit to complement representation. By properly encoding the signed-digits, all the operations are performed by binary logic, and unified logical expressions can be obtained for conversion from modified-signed-digit (MSD) to 2's complement, trinary signed-digit (TSD) to 3's complement, and quarternary signed-digit (QSD) to 4's complement. For optical implementation, a parallel logical array module using an electron-trapping device is employed and experimental results are shown. This optical module is suitable for implementing complex logic functions in the form of the sum of the product. The algorithm and architecture are compatible with a general-purpose optoelectronic computing system. (C) 2001 Society of Photo-Optical Instrumentation Engineers.

Chemical environment code and measure of molecular similarity

A new scheme for the code of chemical environments of compounds is described in this paper, and three molecular similarity methods have been used to select nearest neighbors from four different types of probe compounds. One of the methods is based on the C-13 NMR spectra. The second method is based on the code of chemical environments and molecular topological index A(x). The third approach, i.e. the Tanimoto coefficient, is also based on the code of chemical environments, but not to use the topological index. Five nearest neighbors for each probe compound using these three molecular similarity methods were determined and taken from the database of 7309 structures. The results indicate that the scheme of the chemical environment code and the method for similarity measure of intermolecules suggested in this study are reasonable. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.

Code for chemical environment and computation of molecular similarity

A new code for chemical environment and an empirical mathematical pattern Sa(m) on computation of molecular similarity were suggested. Seven molecules which referred to as the probe compounds and the nearest neighbors of each probe structure were determined by the methods of Sa(m) and Tanimoto, The results show an intuitive notion of chemical similarity.