In recent years, numerous, relatively inexpensive hardware platforms for conducting scientific research using the software defined radio SDR paradigm have become commercially available.
The Manufacturers section near the end of this article lists examples of several of these. In turn, this has spurred universities and research groups around the world to adopt this technology for advanced GNSS signals-based research and development.
Realtime processing capability is generally not required at this stage of development. However, to achieve maximum productivity researchers find it highly desirable to have flexibility in algorithm development by way of high-level programming languages and robust user-friendly development environments with extensive built-in math library support and data visualization capabilities. Many of the afore-mentioned research topics can involve sampled signal data collection at wide bandwidths, high dynamic range, and multiple coherently sampled streams.
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For example, consider a wideband GNSS data collection campaign for investigating phased array based interference mitigation techniques using a seven-element, controlled reception pattern antenna CRPA. In this case, bandwidth, dynamic range, and multiple channels are all in play. Even with lesser requirements, it is not uncommon to return from a collection campaign with multiple hundreds of gigabytes if not terabytes of data. Thus, a solution is needed to process such large datasets in a reasonable amount of time.
This is made possible with multiple processor cores — each clocking at multiple gigahertz and supporting wide single-instruction-multiple-data SIMD instructions. Hence, these machines are good candidates for crunching through large amounts of SDR data. Unfortunately, the layers of software abstraction built into high-level development environments to facilitate user-friendly coding is one of the main reasons why, in general, these tools cannot take full advantage of the computation capabilities of the platforms they run on.
Thankfully, all such tools support extensions to allow users to integrate their own custom libraries written in low-level code. The goal of the work reported in this article is to develop a truly universal GNSS SDR processing toolbox for education and research that could be distributed in the form of a plug-in for high-level algorithm development platforms — specifically MATLAB. The following high-level features were envisioned for the toolbox:.
The work described in this article achieves, to a large extent, all of these objectives and, more importantly, builds the framework for the baseband signal-processing layer of a truly universal GNSS SDR architecture. The software is currently distributed as a MATLAB toolbox and can be downloaded free of charge for education and research use.
One important note: this toolbox is not a complete GNSS receiver in the sense that it does not output position, navigation, and time PNT solutions. However, the processed-signal outputs available at a one-kilohertz rate contain all the information needed for subsequent processing of PNT solutions. For uninterrupted collections over prolonged intervals, data are sometimes written to multiple small files because such a strategy allows files to be managed more effectively than one file written to a large-capacity volume.
For systems that collect SDR data continuously for the purpose of recording rare anomalous signal events, this multi-file collection strategy allows older files to be deleted to make space for new ones, thus extending the availability of past history to the size of the storage array in contrast to the capacity of a memory-based buffer.First use of the RTL-SDR in MATLAB and Simulink
In some systems, the GNSS samples may be interlaced with binary data from other sensors such as IMUs, laser scanners or cameras to achieve inherent time synchronization between these sensors. In this case, additional metadata information is needed to extract GNSS samples from the file and, optionally, decode the sensor data. This means that the user is forced to set data decoding parameters in an ad hoc manner. When files from a different system are sourced, these parameters and the decoder must be changed manually — a process that is prone to human error.
Part of the effort described in this article aims to address this issue so that files from any data collection system can be seamlessly integrated into any GNSS SDR processing platform.
The proposed solution is to pair a metadata file with each binary data file. The metadata file includes all the information needed to integrate the SDR file into the processor and decode its contents.
All operating systems and application development suites support XML, which is a low-overhead human-readable format, thus providing a straightforward process to integrate it into any data collection system. It contains all of the necessary information to decode the multi-stream samples correctly as well as other information pertaining to the data collection campaign. For multiple files, the user specifies the name of the first file along with the maximum number of one-millisecond blocks to be processed.Since the publication time of book there were several iterations of the front-end versions.
The front-end does not come with the book, but instead can be bought on an online electronics store Sparkfun. Please visit the homepage of the front-end for more details and the original USB drivers at ccar. There are also front-ends from other manufactures, which will work with our SDR, but in some cases the SDR code must by modified. Note this section is here for support of legacy code and hardware.
This driver was designed and tested to work with the first version of the front-end! The driver was tested only on Windows XP and only using the first version of the front-end.
The longer the signal records are the higher is chance that the PC might not be able to keep up writing data to the hard disk. Recording stopped. It means that the PC could not keep up with the incoming data from the front-end. Usually the processor speed is not the crucial factor here. The most important is the speed of the hard disk. Also note that the disk speed is reduced when the disk is nearly full. Here are instructions how to import the recording application source code into Microsoft Visual Studio What kind of the antenna I can use for this front end, active antenna or passive antenna.
I read the datasheet of SEL. It supported bother active antenna and passive antenna. However, when I connect it to an active antenna, it could not work? Does the LNA in the front end is disabled or not? It is the best to ask this question the front-end designers. My quick answer would be that this front-end should be able to support both types of antennas, but the passive antenna may give a very low SNR in the sampled signal. This may require more sensitive acquisition and tracking algorithms.
In the case of the active antenna please make sure that the antenna phantom power voltage is the same as the voltage provided by the front-end. For some active antennas this may be a too low voltage.The role of an Observables block is to collect the synchronization data coming from all the processing Channels, and to compute from them the GNSS basic measurements: pseudorangecarrier phase or its phase-range version and Doppler shift or its pseudorange rate version.
It follows the description of mathematical models for the obtained measurements, with a physical interpretation. Those models will be used in the computation of the Position-Velocity-Time solution. The pseudorange measurement is defined as the difference of the time of reception expressed in the time frame of the receiver and the time of transmission expressed in the time frame of the satellite of a distinct satellite signal.
This corresponds to the distance from the receiver antenna to the satellite antenna, including receiver and satellite clock offsets and other biases, such as atmospheric delays. For a signal from satellite in the i -th band, the pseudorange can be expressed by using the signal reception time s measured by the receiver clock and the signal transmission time s measured by the satellite clock as:.
The equation can be written by using the geometric range between satellite and receiver antennas, the receiver and satellite clock biases andthe ionospheric and tropospheric delays and and the measurement error as:. The result of this approach is not an absolute pseudorange, but a relative pseudorange with respect to the value of pseudorange allocated for a reference satellite. The first step performed by the common reception time algorithm is the selection of a reference satellite: it is the satellite with the most recent TOW which is the nearest satellitedenoted aswhose associated is taken as the common reception time for all channels.
An initial travel time ms is assigned to this satellite, but in general it is a value between and milliseconds according to the user altitude that can be easily converted in meters considering the speed of light. Then, the pseudoranges for all other satellites are derived by adding the relative-arrival times.
Each travel time can be computed as:. Note that, in the case of a multi-system receiver, all pseudorange observations must be referred to one receiver clock only.
The carrier phase measurement is actually a measurement on the beat frequency between the received carrier of the satellite signal and a receiver-generated reference frequency. It can be modeled as:. In order to generate usable phase measurements, the receiver phase observations must maintain a constant integer number of cycles offset from the true carrier phase. That is, if the range increases by one cycle i. Phase measurements are sometimes given in meters. This is referred to as phase-range measurementand it is defined as the carrier phase multiplied by the carrier wavelength.
It can be expressed as:. The term admits a more detailed model including antenna phase center offsets and variations, station displacement by earth tides, phase windup effect and relativity correction on the satellite clock that will be useful for precise point positioning algorithms. The phase-range measurement can then be modeled as:. The relationship between observed frequency and emitted frequency is given by:.
Since the speeds of the receiver and the satellite are small compared to the speed of the wave, the difference between the observed frequency and emitted frequency can be approximated by:. The term is the radial velocity from the receiver relative to the satellite, and and are the receiver and satellite clocks drift, respectively.
The Doppler shift measurement is given in Hz. This is referred to as pseudorange rate measurementand it is defined as the Doppler shift multiplied by the negative of carrier wavelength. Its model can be written as:. The noisy but unambiguous code pseudorange measurements can be smoothed with the precise but ambiguous carrier phase measurements. A simple algorithm, known as the Hatch filter, is given as follows 6 :. Let and be the code and carrier measurements of a given satellitein the bandat the time.
Thence, the smoothed code can be computed as:. This implementation computes observables by collecting the outputs of channels for all kind of allowed GNSS signals.You seem to have CSS turned off. Please don't fill out this field. Calibre has the ability to view, convert, edit, and catalog e-books of almost any e-book format. Join with us! Scientific and industrial applications of GNSS signals and data usually require non-standard features of the receiver.
Access to intermediate signals is not possible in mass-market receivers, and professional equipment is costly and often a 'black box' that does not offer exact information about how signals are being processed. Since all the processing is done in ASICs, one cannot change the implementation of a certain functional block and assess the impact in the whole receiver performance.
We propose the implementation of an open-source GNSS software receiver freely available to the research community. This project provides a common platform for GNSS signal processing and data gathering for scientific applications, testing of algorithms, receiver design, and educational purposes.
This tool is intended to foster collaboration, increase awareness, and reduce development costs in the field of GNSS receiver design and customized use of GNSS signals.
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No, thanks. Mac Linux. Project Samples. Project Activity. Categories AlgorithmsResearchTest and Measurement. Calibre is a cross-platform open-source suite of e-book software. Calibre supports organizing existing e-books into virtual libraries, displaying, editing, creating and converting e-books, as well as syncing e-books with a variety of e-readers.
Learn More. User Ratings 5. User Reviews Filter Reviews: All. Report inappropriate content.GitHub is home to over 40 million developers working together to host and review code, manage projects, and build software together. If nothing happens, download GitHub Desktop and try again. If nothing happens, download Xcode and try again.
If nothing happens, download the GitHub extension for Visual Studio and try again. In addition, some of the scripts for creating the figures in the text are also on included. The copyright holder retains title to and ownership of the package. This makes the software flexible and most of the software properties are controlled at one place. There are three ways to change settings. The default values are defined in function initSettings. The default settings are applied by the init script or by a button click at the settings GUI.
The second way to change settings is to use a dedicated GUI. The GUI is launched by the setSettings script. The GUI has three buttons at the bottom of the dialog window. Button "Default" loads default values defined in the function initSettings. The third way to change settings is to change values in the settings structure using the MATLAB command prompt or variable editor. Examine the file initSettings. The software is made such that three main modules - acquisition, tracking, and positioning can be executed separately.
The scenario depends on the debugged module. The acquisition step is controlled by the field skipAcquisition in the settings for field and allowed values description see comments in function initSettings. The tracking part can be skipped too in case the positioning module is debugged and there are no changes in tracking part.
A correct settings structure and the tracking results must be present structure trackResults. The tracking results and settings are automatically saved after each completion of tracking stage in the MATLAB data file trackingResults. To run the positioning part without running tracking part complete the following steps:.
Examine files init. Skip to content. Dismiss Join GitHub today GitHub is home to over 40 million developers working together to host and review code, manage projects, and build software together. Sign up. Branch: master. Find file. Sign in Sign up. Go back. Launching Xcode If nothing happens, download Xcode and try again. Latest commit. Latest commit e5 Feb 7, Please use a file browser to browse the contents of the DVD.
Press 0 and then press Enter if you want to select a different data file signal record or if the default path is incorrect.These functions are part of the Matlab mapping toolbox which requires a dedicated toolbox license. Here you can download two functions that substitute these functions from the toolbox: deg2dms. These functions are inside of the files Scurve. Here are the download links for the two missing functions: R.
A variable is misspelled at line in the file setSettings. The text settings. The problem occurs in one of the functions for coordinate transformations — the cart2geo. The function fails to approximate the height precise enough.
The quick fix is to modify the function cart2geo. Currently trying to get satellite clock bias, position and velocity using the code, it seems that there is a bias…. Sorry to bother you. I have this book. However, it can run and get some result. Does the software need these files? Thanks a lot! I also have a question for the SiGe front end, what kind of data format does this front end output to the computer? Thank you very much.
The two functions should be in that folder. I have the book of Chinese published inwhich provides the former version of SDR. Now I am working on the vector trackingand I wonder where I can get the update software or the program of vector tracking? I am sorry, but I did not had a chance to try that VLL code. And at the moment I do not have time to look into this problem.
I changed it to numel activeChnList which is appropriate for both column and row vectors. Before in postNavigation. Thank you very much,I have spend more time solve this problem before,now I can run correctly, thanks again! My friend told me to check the code of matlab. And it also has a Chinese version! But it does not work in Matlab This section is under development. We and our readers over time have found some mistakes in the book and the Matlab code which we have collected in a separate webpage with fixes.
More information about this book can be found at the publisher page. The software Matlab code comes on a DVD that is included with the book. Galileo signals were in test mode when the record was made. Just one issue though …. Thanks Nick. All working now! Thank you for your comments. Right now I do not work so much with Matlab, so I did not had a chance to detect this issue. I am not surprised that the code will need some changes to support new versions of Matlab.
The code was written about year ago! Thank you for sharing your fix! Is there any way I can get the files in that DVD? We are unsatisfied with such outcome, but unfortunately at the moment due to several factors we do not have the possibility to change this situation. I understand the situation, but I am studying GPS and Matlab implementations currently and I would like to know if it would be possible for you to send by email or any other way the Simulink code of the PRN simulator.
I am a bit confused what exactly you are looking for so I will give two answers. First — if you are talking about GPS signal simulator — that code is not included in the DVD and it is not for publishing. The second answer — if you are specifically looking for the PRN generator code — then the answer is that this code is not complicated and there are a lot of such generator code examples on the Internet even at the MATLAB Central File Exchange.
All versions are similar as the algorithm is simple. Hi, can you plz tell from where can the simulink model of GPS signal simulator be downloaded? Does it come in DVD with the paper version of the book? I have a question for the collection of data. Could I use the passive antenna and the SiGe version 1 front end to collect data? Because I can collect data use the active antenna. Thanks a lot.
I really appreciated for your help. It depends. I expect that the hardware should work without problems. But the signal to noise ratio will be bad, so the standard GPS signal acquisition and tracking algorithms most likely will not be able to detect and track the GPS signals.
I read the datasheet. However I am wondering what kind of the oscillator is used in the front end since the SEL has a built-in oscillator and also support external TCXO. So I do not know the hardware structure of the front end around the SEL. Does the hardware of the GN3S sampler version 1 is open-source? These questions you should address to the designer of the front-end Dennis Akos.