Constrained adaptive CMA for desired-user synchronization and detection in asynchronous DS-CDMA systems

A technique for estimation of desired-user bits in asynchronous DS-CDMA systems is developed without an explicit bit synchronization between the receiver and the transmitter. A bit value is estimated based on the observation window of size 2N-1, where N is the length of bit period. The window shifts for N in order to estimate a new bit. A constrained adaptive constant modulus algorithm (CMA) is used to estimate bits. The constraint limits the maximum elevation angle a weight vector that multiplies the observations can have with respect to the hyperplane defined by shifted copies of the desired-user spreading sequence. The constraint is parameterized so that monitoring is not needed. The constrained CMA is compared with the unconstrained CMA. In addition to the bit estimation, the constrained CMA can estimate the desired-user signal delay.