Joint constrained data detection and channel estimation algorithms for QS-CDMA signals

In this paper, we consider quasi-synchronous CDMA (QS-CDMA) systems, where mobiles synchronize their transmission to a common clock (e.g. pilot signal or GPS.) The key advantage of QS-CDMA exploited is that the need for code acquisition is eliminated. However, residual delay/channel estimation is still an important problem in QS-CDMA systems. For a time-invariant channel, we propose a new joint delay/channel estimation and constrained integer data detection algorithm, based on the Lenstra-Lenstra-Lovasz (LLL) basis reduction algorithm and the ellipsoid approximating technique. By using this constrained data detection algorithm, we can reduce the computational complexity without a significant degradation in the bit-error-rate (BER) performance.