Hi Alisthu ,I have attached some papers here which i have read and found these very intersting from the study as well as application point of view
Gurpreet visit these links for better understanding of my statement i have given above
http://www.sciencedirect.com/science/article/pii/S1068520013000254
http://www.researchgate.net/publication/258688471_Isolated_user_security_enhancement_in_optical_code_division_multiple_access_network_against_eavesdropping
http://www.mijst.mju.ac.th/vol6/238-248.pdf