Multibits/Sequence Optical Code Division Multiple Access system applying bit erasure correction by differential encoding

In this paper, we propose a Multibits/Sequence Period Optical Code-Division Multiple-Access (MS-OC-DMA) system applying bit erasure correction by differential encoding. In the proposed system, the present transmitted shifted code pattern is determined on the basis of the previous and the present transmitted bits. In the receiver, threshold detection is applied to the avalanche photodiode (APD) output in each shifted code pattern. When the number of APD outputs exceeding the threshold level is either more than two or zero, the present received bit is judged to be an erasure. Then, the present received bit is estimated by the information about the shifted code patterns for which the APD outputs exceed the threshold and the nonerasure bits before or after the present erasure bit, and the erasure bit is corrected. In addition, the proposed system can correct a received bit sequence as an erasure bit instead of an error bit. We analyze the bit error rate (BER) of the proposed system and show that the proposed system has a better BER than the MS-OCDMA system with Reed-Solomon (RS) codes at the same bit rate and with the same number of subscribers.