SPC11-2: Blind Multiuser Detection in Multirate CDMA Transmissions Using Fluctuations of Correlation Estimators

This paper deals with the problem of blind multiuser detection in multirate direct-sequence code division multiple access (DS-CDMA). Direct-sequence spread spectrum (DSSS) signals are well-known for their low probability of interception: their statistics are similar to those of a noise; furthermore, they are usually transmitted below the noise level. Here, the method based on the fluctuations of autocorrelation estimators, previously described in a single user context, is extended to multiusers. From the variable spreading length technique, we will evidence an increase of these periodical fluctuations and, on average, a relationship between their peak amplitudes and sequence lengths. A theoretical analysis will show that detection is possible, even with a very low signal-to-noise ratio (SNR) at the detector input. This approach will be illustrated with experimental results. The assessment of symbol periods allows one to start the synchronization process proposed recently, which also permits the determination of the number of interfering users in each group of users transmitting at the same symbol period, thus, conversely at the same data rate.