A Software Defined GPS and Galileo Receiver

Galileo Signal (GPS and Galileo Receiver) Part 4

Time and Clock Correction Parameters As for GPS, Galileo has its own system time, called Galileo System Time (GST). Its starting epoch still has to be determined. GST consists of two parts: week number, WN, and time of week, TOW. The WN covers 4096 weeks and is then reset to zero. A week has 604,800 […]

GNSS Antennas and Front Ends (GPS and Galileo Receiver) Part 1

Background Although the focus of this text is on the algorithms for software signal processing of the Global Navigation Satellite System (GNSS) signals, it is important to consider the source of that data stream to be processed. Since "software" signal processing is stated, it implies an input digital data stream. Thus, the purpose of this […]

GNSS Antennas and Front Ends (GPS and Galileo Receiver) Part 2

Amplifier Amplification is the process that increases the signal magnitude. Thus, an amplifier is a component that does just that. Unlike most filters, an amplifier is an active component and requires power to accomplish its function. Note that the ideal amplifier would only increase the amplitude of the signal. However, any commercial amplifier will not […]

GNSS Receiver Operation Overview (GPS and Galileo Receiver)

Receiver Channels The signal processing for satellite navigation systems is based on a channelized structure. This is true for both GPS and Galileo. This topic provides an overview of the concept of a receiver channel and the processing that occurs. In later topics the specifics of the signal and data processing are outlined. Figure 5.1 […]

Acquisition (GPS and Galileo Receiver) Part 1

The present and the following topics are based on signals recorded according to parameters described in Section 4.3. The theory can be applied similarly to records with a different selection of parameters. Motivation The purpose of acquisition is to determine visible satellites and coarse values of carrier frequency and code phase of the satellite signals. […]

Acquisition (GPS and Galileo Receiver) Part 2

Parallel Code Phase Search Acquisition As seen from Equation (6.1), the amount of search steps in the code phase dimension is significantly larger than that of the frequency dimension (1023 compared to 41). The previous method parallelized the frequency space search eliminating the necessity of searching through the 41 possible frequencies. If the acquisition could […]

Carrier and Code Tracking (GPS and Galileo Receiver) Part 1

Motivation The acquisition provides only rough estimates of the frequency and code phase parameters. The main purpose of tracking is to refine these values, keep track, and demodulate the navigation data from the specific satellite (and provide an estimate of the pseudorange). A basic demodulation scheme is shown in Figure 7.1. The figure shows the […]

Carrier and Code Tracking (GPS and Galileo Receiver) Part 2

Damping Ratio The damping ratio controls how fast the filter reaches its settle point. The damping ratio also controls how much overshoot the filter can have. A smaller settling time results in a larger overshoot. This can be seen in Figure 7.4. Noise Bandwidth The second parameter in the PLL filter is the noise bandwidth […]

Carrier and Code Tracking (GPS and Galileo Receiver) Part 3

Code Tracking The goal for a code tracking loop is to keep track of the code phase of a specific code in the signal. The output of such a code tracking loop is a perfectly aligned replica of the code. The code tracking loop in the GPS receiver is a delay lock loop (DLL) called […]

Carrier and Code Tracking (GPS and Galileo Receiver) Part 4

Multipath Of the multiple error sources associated with GNSS signal processing, multipath directly impacts the code tracking performance. With the prior description of how code tracking is implemented, it makes sense to investigate how multipath impacts the code tracking loop. The signal observed at the receiver is a distorted version of the one transmitted. One […]