Abstract:
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 code division multipleaddress (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 p1 times, where p is code weight, and the correlation is improved, outofphase autocorrelation is λa=1 and crosscorrelation isλc=2. QCC/OOC with better correlation and larger capacity are obtained. Its outofphase auto-correlation is λa=0. All the code words can be divided into p1 groups according to a certain law, crosscorrelation 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 timespread codes in OCDMA systems.