PRN Code Correlation in GPS Receiver

Abstract

Satellite based positioning systems like GPS (Global Positioning System) exist in every moment of our lives. GPS signal is broadcasted by Link1 (L1) and Link2 (L2) frequencies, separately. L1 is assigned to civil users, while L2 is especially for military users. GPS signal consists of navigation message and PRN codes (C/A for civil and P-code for military) which is an identity for satellite. PRN codes are also used to determine the range between the satellite and the receiver. The navigation message added on PRN code, must be known to find the position of GPS receiver on Earth. Identification of PRN code is the most important process to calculate the receiver's position. A correlation process in receiver is implemented to find PRN code changing for each satellite. Three common methods are available for the correlation process. These methods are Serial Search, Parallel Frequency Space Search and Parallel Code Phase Search Acquisition. Parallel Code Phase Search is faster and ended in less steps compared to other two methods. The aim of this study is to present the correlation technics used for the acquisition of satellite signal in GPS receivers. For this purpose, a correlation example is simulated in MATLAB environment to demonstrate how the correlation process in GPS receiver is performed.