Construction and characteristic analysis ofa 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 code division 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 p1 times, where p is code weight, and the correlation is improved, outofphase autocorrelation is λa=1 and crosscorrelation isλc=2. QCC/OOC with better correlation and larger capacity are obtained. Its outofphase auto-correlation is λa=0. All the code words can be divided into p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.