Differentially Coherent Detection Technique for Direct-Sequence Code Acquisition in a Rayleigh Fading Mobile Channel
Journal
IEEE Transactions on Communications
Journal Volume
43
Journal Issue
2-4
Pages
1116-1126
Date Issued
1995
Author(s)
Abstract
A novel differentially coherent (DC) detection scheme for rapid code acquisition is proposed for a direct sequence (DS) spread-spectrum system being used to communicate over a fast Rayleigh fading mobile radio channel. The scheme processes the received signal at baseband using a complex differential detector with one-chip time delay and then performs a coherent partial correlation of the detector output with the product of a local DS code and its one-chip delayed phase to form a test sample. While still preserving the pseudo-noise attribute at its output, the differential detector is able to effectively suppress slowly fluctuating phase components due to fading and carrier frequency offset, thereby enhancing the in-sync correlation at the following correlator. The performance of this detection scheme is analysed based on a central-limit-theorem argument, and verified by simulation. Both serial and parallel acquisition systems employing the proposed DC detector are compared with the conventional parallel I-Q system by mean acquisition time performance. It is shown that the serial DC acquisition system significantly outperforms the parallel I-Q system in very fast Rayleigh fading environments.>
Type
journal article