Inside GNSS Media & Research

NOV-DEC 2017

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Page 50 of 67 N O V E M B E R / D E C E M B E R 2 0 1 7 Inside GNSS 51 • It identifies and brings the inter- nationa l GNSS SDR communit y together as a working group. This collaboration is critical in order to get broad acceptance and usage. • Standardization will help to avoid technolog y segmentation issues while promoting the pace of innova- tion by standard practices and com- pliant tools. • T he for ma l sta nda rd, i f w idely adopted, will help ensure compat- ibility and interoperability of future GNSS SDRs. Specifically, front-end agnostic "plug-and-play" SDRs are envisioned. ese have the potential for revolutionizing positioning, navi- gation, and timing (PNT) systems of the future. Most authors of significant GNSS SDR publications and contributions over the past two decades are ION members and frequent meeting attendees. Hence, we decided to pursue this standard through ION sponsorship. During the January 2014 Council Meeting in San Diego, ION approved the process for establishing a formal standard. e ION GNSS SDR Metadata Working Group (WG) was formed in April 2014. Mem- bership represents academia, industry (including GNSS SDR product vendors as well as traditional GNSS equipment manufacturers), non-profit research entities, and government agencies span- ning countries in America, Europe, Asia and Australia. Justification for GNSS Metadata Standardization Figure 1 shows the metadata transfer scheme mainly used in today's GNSS SDR systems. e top row depicts data collection system (DCS) A, producing an SDR file of format A, consumed by SDR processor A. is may represent an end-to-end solution provided by a vendor or a system that was initially developed around a specific hardware platform. In any case, assume that the metadata for decoding Format A is hard-coded into the processor. Conse- quently, supporting other file formats involves extensive software revisions on a case-by-case basis. One group may want to share SDR files from DCS A with other groups using SDRs X and Y for research collaboration. is involves conveying the file format and other rel- evant information accurately to these ot her groups. Today, t his metadata transfer occurs in an ad-hoc way that is prone to interpretation errors. e second row depicts multi-stream DCS B that produces files with a more complicated format. SDR processors X and Y represents more flexible SDRs that are able to support multiple file formats. However, the data/metadata association requires manual intervention. DCS C multiplexes other data (such as sensor data) along with multiple GNSS sample streams in the same file. This type of multiplexed collection has the potential to become more common with emerging SDR-related data stream- ing standards such as VITA-49 (See T. Cooklev et alia, Additional Resources). In this case, custom-designed processor C represents an SDR that fully supports multi-sensor integration capabilities. Because DCS C's GNSS stream param- eters are open, SDR Y is also able to support GNSS-only processing using an ad-hoc metadata transfer scheme. e sensor data parameters in Format C may or may not be open. As clear from Figure 1, today's ad- hoc methods of metadata exchange do not encourage interoperability and instead cultivates potential for technol- ogy segmentation (i.e., various groups developing their own stove-piped solu- tions and technologies). Figure 2 shows the same systems of Figure 1 that have adopted a metadata standard. As shown, each DCS pro- duces a compliant metadata file along with the SDR file. e metadata file is read-in by the compliant SDR proces- sor to correctly decode and process files seamlessly. Adoption of a metadata standard benefits DCS developers because their systems become applicable to a much wider group of users. Similarly, an SDR processor's utility is extended when it is capable of supporting many file formats from multiple sources seamlessly. us, metadata standardization promotes interoperability of GNSS SDR systems and greatly simplifies the exchange of files between groups. Metadata standardization also bene- fits other use cases beyond post-process- ing GNSS SDRs. For example, consider the use of the metadata specification to synthesize compliant SDR files for use in RF playback systems. Addition- ally, libraries of compliant SDR file sets containing various real-world scenarios could be used interchangeably in com- pliant RF playback simulators for repeat- able and consistent testing of GNSS receivers. SDR Data Collection Topologies e ION Executive Committee stipu- lated that this standardization activity shall not create an unfair advantage or disadvantage to any entity. Specifi- cally, the standard shall not require any existing system to undergo data format changes to achieve compliance. This "do no harm" stipulation implies that the standard be designed such that it FIGURE 1 Ad-hoc Metadata Exchange Collection System (A) Format (A) SDR File GNSS SDR Processor (A) Format (A) Metadata Collection System (B) Format (B) SDR File GNSS SDR Processor (X) Format (B) Metadata GNSS SDR Processor (Y) Collection System (C) Format (C) SDR File GNSS SDR Processor (C) Format (C) Metadata Sensor Collection Systems Data Files SDR Processors Metadata

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