Synchronous fiber-optic CDMA systems with interference estimators

Multiple-user interference estimation and cancellation techniques are proposed for synchronous optical code-division multiple-access (CDMA) communication systems. At the receiving end the multiple-user interference is estimated and is used to adapt a threshold level that is placed after an optical correlator. The special properties of the modified prime sequence codes are utilized in the estimation process. Four methods for adapting the threshold are proposed in this paper. The performance of the above system is analyzed and the bit error rates of the four adaptation schemes are compared to each other and to that of the system without cancellation. Our results reveal that the proposed system is very efficient in eliminating the effect of the multiple-user interference. Moreover, it is shown that the error floor which distinguishes the traditional systems is removed under the proposed schemes.