一种跳频扩时码的构造及性能分析

以一维二次同余码(QCC)作为扩时模式，以光正交码(OOC)和QCC码作为频域跳频模式，通过时域和频域的组合，构造了适用于光码分多址(OCDMA)系统的QCC/QCC和QCC/OOC 2种跳频扩时码，并对码的容量及其相关性进行了分析。与一维QCC码相比，QCC/QCC跳频扩时码的容量扩大了p 1倍（p为码重），相关性得到改善，并且码字异相自相关限λa=1，互相关限λc=2；QCC/OOC跳频扩时码具有更大的码容量和更好的相关性，码字异相自相关限λa=0，所有码字按一定规律可分成p 1组（p为码重），每组内码字的互相关限λa=1，不同组间码字的互相关限λa=2。所得结果为光码分多址系统中跳频扩时码的构造提供了一种新的方法。

Construction and characteristic analysis of a frequency-hop time-spread code

Taking one-dimensional quadratic congruence code (QCC) as time-spread mode,optical orthogonal code (OOC) and QCC as frequency-hop mode,two types of frequency-hop time-spread codes of QCC/QCC and QCC/OOC applicable to two-dimensional optical codedivision multiple-address (OCDMA) systems were constructed by combining time domain and frequency domain. The correlation and capacity of the codes were analyzed. In comparison with one-dimensional QCC,the capacity of QCC/QCC is enlarged р-1 times,where р is code weight,and the correlation is improved,out-of-phase autocorrelation is λa=1 and cross-correlation is λi=2.QCC/OOC with better correlation and larger capacity are obtained. Its out-of-phase autocorrelation is λa=O. All the code words can be divided into р-1 groups according to a certain law,cross-correlation of code words in the same group is λa=1 and in different groups is λa=2.The study provides a new method for constructing frequency-hop time-spread codes in OCDMA systems.