Signal detection and sequential estimation techniques for DS/CDMA code acquisition systems

Abstract

In this dissertation, we propose new techniques for two practical and important topics in code acquisition. The first one is the acquisition of codes in general and realistic communication environments, in which we assume chip-asynchronous models and non-Gaussian noise channels. The second is the code acquisition for pseudo noise (PN) codes when the period is very long. First, we consider the residual code phase offset problem in chip-asynchronous models, in which a mismatch between the chip boundaries of two PN codes exists. The residual code phase offset causes the signal component in the matched filter output of an acquisition system to be divided into two components having smaller energy than that in the original signal component. Thus, the performance of the conventional systems based on the assumption that only one signal component exists deteriorates by the residual code phase offset. We propose new acquisition techniques using an efficient combination of the two divided components based on the locally optimum (LO) criterion. We derive LO detectors in the known and random signal cases. Numerical results show that the proposed schemes have better performance than the conventional schemes. Second, we consider the acquisition problem in non-Gaussian noise. The real-life noise such as atmospheric and man-made noise arising in indoor/outdoor mobile communication systems is known through experimental measurements to be decidedly non-Gaussian due to the impulsive nature. It is clear that acquisition systems using squared-sum (SS) detector (designed under the Gaussian noise assumption) are no longer appropriate in many such non-Gaussian environments. We propose an LO detector system for code acquisition in non-Gaussian noise channel. Numerical results show that the proposed detector dramatically outperforms the conventional detector for various parameter values in a non-Gaussian noise model. Finally, we consider the acquisition scheme of long period PN codes whi...