Synchronous optical code-division multiple access systems with constant multi-user interference

A synchronous optical code-division multiple access system with balanced encoder instead of on-off-keying (OOK) encoder is proposed. In the system, the multi-user interference is maintained constant during a frame, and the receiver estimates the interference frame by frame instead of bit by bit. The data rate of the proposed system is no longer severely limited by the electronic processing time in estimating the interference, and the structure of the proposed receiver is simpler than those in OOK systems. In the receiver, both linear and non-linear threshold estimators are introduced. Numerical results show that the proposed system has smaller bit error rate than OOK systems, especially when the number of training bits is increased.