Quality-of-service differentiation by multilength variable-weight time-and-frequency-hopping optical orthogonal codes in optical code-division multiple-access networks

We consider multilength variable-weight time-and-frequency-hopping (TFH) codes for optical code-division multiple-access (CDMA) networks. To design a TFH code that can support differentiated requirements on transmission rates (TRs) and bit error rates (BERs), we propose a general construction method for two-dimensional optical CDMA code sequences with arbitrary code lengths and variable code weights. The cross-correlation peak and the autocorrelation sidelobe of the proposed code are made to be at most "1" and "0", respectively, for any pair of different-length and different-weight code sequences. We show that the ratio between signal-to-interference ratios (SIRs) of the codes with different weight and length can effectively be approximated by the ratio of the code weights, regardless of the code lengths for the proposed codes. Therefore, independent adjustment of code length and weight can differentiate TR and BER for multiple service classes, and it simplifies code design for the service differentiation. We also demonstrate BER performances under various conditions and corroborate that the proposed codes accomplish accurate and fine-tuned differentiation of TR and BER compared to the fixed-weight or fixed-length codes. (C) 2006 Optical Society of America.