Hierarchic Method for CDMA Synchronization

CDMA (Code Division Multiple Access) is a multiple access technique based on spread spectrum methods. To estimate the delay parameters appearing in the data model, several authors have proposed subspace-based solutions. Unfortunately, these methods, for example the eigenvector-based MUSIC method yields poor results at low signal-to-noise ratios. On the other hand, theoretically optimal maximum likelihood method is com-putationally too demanding in practice. In addition, when the number of users or propagation paths is unknown , the model order should be estimated accurately. To this end, one can use relatively simple Minimum Description Length (MDL) criterion, but it fails when the signal-to-noise ratio (SNR) is not suuciently high. In this paper, we introduce a hierarchic algorithm for delay estimation, called ACM-MUSIC, which has earlier been developed in context with sinusoidal frequency estimation. We also use ACM-MUSIC type algorithm for estimating the model order using a new criterion. Simulations show that the new methods outperform standard MUSIC.