A Software Defined GPS and Galileo Receiver

The concepts of a signal and a system are crucial to the topic. We will consider time as well as frequency domain models of the signals. We focus on signals and system components that are important to study software-defined GPS and Galileo receiver design. Characterization of Signals In satellite positioning systems, we encounter two classes […]

Signals and Systems (GPS and Galileo Receiver) Part 2

Rectangular Pulse Let us now consider a single rectangular pulse f (t) with amplitude 1 and pulse width equal to T .In Figure 1.1 we have shifted the pulse —T/2 to place it sym-metrically around t = 0. FIGURE 1.2. Top: Magnitude spectrumof rectangular pulse. Notice thathas zeros atBottom: Phase spectrum argof rectangular pulse. Notice […]

Signals and Systems (GPS and Galileo Receiver) Part 3

Sampling A crucial signal processing operation in a GPS or Galileo software-defined receiver is sampling. In the following we briefly review the sampling process. Consider the signal x (t). Suppose that we sample this signal at a uniform rate— say once everyseconds. Then we obtain an infinite sequence of samples, and we denote this sequence […]

Signals and Systems (GPS and Galileo Receiver) Part 4

Representation of Bandpass Signals Signals can also be classified into lowpass, bandpass, and highpass categories depending on their spectra. We define a bandpass signal as a signal with frequency content concentrated in a band of frequencies above zero frequency. Bandpass signals arise in the GPS and Galileo systems where the information-bearing signals are transmitted over […]

GPS Signal (GPS and Galileo Receiver) Part 1

In order to design a software-defined single frequency GPS receiver it is necessary to know the characteristics of the signal and data transmitted from the GPS satellites and received by the GPS receiver antenna. In this topic an overview of the GPS signal generation scheme and the most important properties of the various signals and […]

GPS Signal (GPS and Galileo Receiver) Part 2

C/A Code In this section, the spreading sequences used in GPS are described. We restrict ourselves to the C/A code sequences, as we deal only with L1 signals in this topic. The spreading sequences used as C/A codes in GPS belong to a unique family of sequences. They are often referred to as Gold codes, […]

GPS Signal (GPS and Galileo Receiver) Part 3

Correlation Properties The Gold codes are selected as spreading sequences for the GPS signals because of their characteristics. The most important characteristics of the C/A codes are their correlation properties. These properties are described now. The two important correlation properties of the C/A codes can be stated as follows: Nearly no cross correlation All the […]

Galileo Signal (GPS and Galileo Receiver) Part 1

The Galileo system offers several services, a few are free of charge and the rest are commercial. In this topic we deal only with the L1 OS signal (OS for open service). The L1 OS signal alone is expected to guarantee a horizontal accuracy better than 15 m, a vertical accuracy better than 35 m, […]

Galileo Signal (GPS and Galileo Receiver) Part 2

Binary Offset Carrier Modulation The Galileo signals and the planned modernized GPS signals inherit improved performance compared to the existing GPS signals. One of the improvements is the introduction of the binary offset carrier (BOC) modulation. BOC modulations offer two independent design parameters   FIGURE 3.3. Spreading code, subcarrier, carrier, and signal as result of […]

Galileo Signal (GPS and Galileo Receiver) Part 3

Message Structure This section outlines the Galileo message structure. Frames and Pages The message is composed of frames, see Figure 3.8. The frame is composed of several subframes, and each subframe again is composed of several pages. The page is the basic structure for the navigation message and contains the following fields: – a synchronization […]