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IJSTR >> Volume 4 - Issue 6, June 2015 Edition

International Journal of Scientific & Technology Research  
International Journal of Scientific & Technology Research

Website: http://www.ijstr.org

ISSN 2277-8616

Implementation Of Code And Carrier Tracking Loops For Software GPS Receivers

[Full Text]



Win Kay Khaing, Zaw Min Naing, Su Su Yi Mon, Aung Soe Khaing, Hla Myo Tun, Sao Hone Pha



Keywords: code tracking, carrier tracking, discriminator function, software GPS receiver, N-FUELS simulator



Abstract: GPS is playing in very important role in our modern mobile societies. Software approach is very flexible rather than the traditional hardware receivers. The soft-GPS receiver includes two portions: hardware and software. In hardware portion, an antenna, filter, down-converter from RF (Radio Frequency) to IF (Intermediate Frequency), and an ADC (Analog to Digital Converter) are included. In software portion, signal processing such as acquisition, tracking and navigation that runs on general purpose processor is included. The GPS signal is taken from N-FUELS (Full Educational Library of Signals for Navigation) signal simulator. The heart of soft-GPS receiver is the synchronization processes such as acquisition and tracking. In tracking, there are two main loops for code and carrier tracking. The objective of this paper is to analyse and find the optimum discriminator function for the code tracking loop in soft-GPS receivers. The delay lock loop (DLL) is a well-known technique to track the codes for GNSS spread spectrum systems. This paper also presents non-coherent square law DLLs and the impacts of some parameters on DLL discriminators such as number of samples per chip, early-late spacing, different C/ No values where C denotes the signal power and No is the noise spectral density, and the impact of with or without front-end device. The results of discriminator outputs are illustrated by using S-curves. Testing results with the real GPS signal are also described. This optimized discriminator functions can be implemented in any soft-GPS receivers.



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