Synchronization of Code-Spread CDMA Systems

Delay estimation of a code-spread code-division multiple-access (CS-CDMA) system using low-rate maximum free distance (MFD) convolutional codes for bandwidth expansion is studied. The MFD codes used, have a repetitive structure, which is utilized for non-data-aided synchronization. The repetition pattern of the code is optimized for good delay estimation properties, using an optimization criterion based on the Cramér-Rao bound for the delay estimation problem. An approximate maximum-likelihood estimator that jointly estimates the channel gain, the codewords and the delay is proposed. A corresponding estimator for direct-sequence CDMA (DS-CDMA) is also derived. The performance, in terms of estimation error, outlier rate and bit-error rate, for both the systems are compared.