Analysis of the Effects of GPS Receiver Acquisition Parameters

Acquisition is the first step in the signal processing section of a Global Positioning System (GPS) receiver. It detects the presence of a GPS signal in the signals received by the antenna and provides estimates of code phase and Doppler to the tracking loops. The acquisition process depends upon the precorrelation bandwidth, analog-to-digital conversion (ADC), sampling frequency and predetection integration time. A GPS software receiver was developed to perform acquisition and tracking of GPS signals. A GPS front-end data logger was used to collect digitized intermediate frequency (IF) data which provides input to the software receiver which performs acquisition, fine frequency estimation and tracking of GPS signals. Different acquisition schemes were implemented in the software receiver and can be chosen to acquire signals depending on the GPS signal conditions. The aim of this paper is to analyze various parameters of the acquisition process and their effects. Circular convolution and modified circular convolution schemes were considered during the analysis. The various parameters analyzed are the sampling frequency, predetection integration period and false detection probability. A GPS simulator (STR 6560) was used to generate GPS signals and the Signal Tap was used to collect data for various analyses. This allowed for the use of real GPS signals rather than simulating them in software with assumptions. These analyses provide a better understanding of acquisition parameters and allow their proper selection.