Further details in
Ortega, A. A., V. A. Bettachini, and J. I. Alvarez-Hamelin. ‘CDMA Time-Hopping Optical Network with Enhanced Security’. Journal of E-Technology 3, no. 4 (November 2012): 196–204.
Ortega, A. A., V. A. Bettachini, J. I. Alvarez-Hamelin, and D. F. Grosz. ‘Hamming-Weight Minimisation Coding for CDMA Optical Access Networks with Enhanced Security’. In Future Generation Communication Technology (FGCT), 2012 International Conference On, 185–189, 2012. https://doi.org/9.1109/FGCT.2012.6476559.