Inside GNSS Media & Research

NOV-DEC 2017

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54 Inside GNSS N O V E M B E R / D E C E M B E R 2 0 1 7 www.insidegnss.com STANDARDS e soware is written in C++ and managed using CMake. It has been div ided into t wo libraries, "apilib " implementing the Metadata Interpreter and "converterlib" implementing the binary data conversion, and is accom- panied by a selection of utilities, includ- ing a data-converter application and a simple test application. e soware is available on the Institute of Naviga- tion's GitHub account at the following link: < https://github.com/IonMeta- dataWorkingGroup/GNSS-Metadata- Standard>. The Metadata Interpreter library includes a reader functionality that can parse a metadata file and populate a corresponding metadata object that can then be queried through a selection of member-function calls. Similarly, a metadata object can be instantiated and configured through a selection of mem- ber functions and, subsequently, it can be instructed to write a corresponding metadata file. e converter library can be used for parsing binary data files and interpret- ing the data according to a metadata file. e basic converter can be adapted to support processing of the converted data streams, and two such adaptations have been implanted in the reference soft- ware. e first functionality is depicted in Figure 5 , where the data-converter is embedded in a file-converter. e file- converter conf igures the embedded data-converter using a Metadata Inter- preter object, and is capable of parsing a packed binary input file and produc- ing one file per IF data stream in a user- specified data type (int8, int16, f loat, double, etc.). A second functionality has been implemented by embedding the data converter in a "front-end", as depict- ed in Figure 6 . is front-end offers a means of loading short portions of the binary data file and converting them to a user-specified data type (int8, int16, f loat, double, etc.) whi le ha nd li ng details such as sample alignment, when different streams are sampled at differ- ent rates. e soware suite includes a selec- tion of example binary datasets and associated metadata files along with a simple MATLAB/Octave script to test the build against reference datasets. To date five different file formats have been included in the repository including a wide range of front-end configurations and data packing variations. A number of working group mem- bers volunteered to perform " blind testing" of SDR data files against dra specifications. is involves exchanging SDR data files and associated metadata specifications among parties and verify- ing that the files can be fully decoded without additional information. Work- ing group members participating in this activity will comprise the Compliance Verification Subcommittee. SDR Data Repository As with most standards and program- ming projects, they are best understood through good examples. us, the page: http://sdr.ion.org/api-sample-data.html has been created and contains several binary sample files together with meta- data files. All file sets have been tested to follow the standard and to be read- able by the normative reference soft- ware. e binary files typically contain samples over a duration of more than 60 seconds and position fixes have been obtained by at least one soware receiver implementation. Further examples will be added, not only emphasizing new data recording systems but also illustrating different SDR applications such as antenna arrays, reflectometry or ionospheric scintilla- tion analysis. Further, data from GNSS seen only at certain locations of the FIGURE 5 Example of the Normative Reference Software configured as a file converter File‐Converter Interface Binary XML Binary Metadata Interpreter Data Converter IF Samples IF Samples IF Samples Description of packed data Raw binary file(s) Interprets XML file and passes file description to converter Parses binary file and provides dumps IF data to file in native machine type (int8_t, int16_t, float, etc) Basic interface: Open() Convert() Close() FIGURE 6 Example of the Normative Reference Software configured as a software GNSS receiver front-end Front‐End Interface Binary XML Binary Metadata Interpreter Data Converter Baseband Receiver Processor Description of packed data Raw binary file(s) Interprets XML file and passes file description to converter Parses binary file and provides 'streams' of native‐format data to user application Basic interface: Open() Load() GetSource()‐>GetSamples() Close()

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