Encoding scheme for 2-D time/frequency domain optical CDMA system

Abstract

Applying CDMA techniques to optical communications and combining CDMA techniques with optical communication has its advantages, which not only keeps the characteristics of CDMA techniques in wireless communication, such as interference immunity, secrecy, soft capacity and simple network protocol, but also make use of the huge bandwidth of fiber. Therefore, optical CDMA communication system has the virtue of asynchronism, broad band and reliable. In this paper, we have done tasks as below: first we thoroughly study the development and recent progress in 2-D time / frequency domain optical CDMA encoding schemes. Then we put forward an implement encoding/ decoding scheme based on optical time spreading/ frequency hopping to solve the problem in current schemes. The scheme adopts 2-D time / frequency domain combination codes as address codes, by assigning two orthogonal address codes to each user and encoding "1" and "0" to these address codes respectively, in sink side differential detection technique is adopted. The scheme has the advantage of increasing power efficiency and improving system performance. While under the condition that two branches are balance, the best judge threshold of system is not variety with the environment, so the scheme also has the merit of lower systemic complexity.