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Aleix edited this page Oct 23, 2023 · 15 revisions

Concept

OSNMAlib is not a GNSS receiver, hence it piggybacks on a full-featured GNSS receiver to work. From this receiver, OSNMAlib needs the navigation bits transmitted by the satellites, the ID of the satellite that transmitted the data and the GNSS time.

The reception of the GNSS time is key because is the only way OSNMAlib can track time. OSNMAlib receives the navigation bits in nominal pages (also called double pages) and expects these to come timestamped.

The time indicated in each epoch shall never go back, it must always be equal to or greater than the time indicated in the previous epoch.

Implementation

DataFormat object

OSNMAlib gets the navigation bits and complementary data encapsulated in a DataFormat object. This object accepts as mandatory parameters the satellite ID, the GNSS time and the navigation data.

  • svid [int] - ID of the satellite transmitting the navigation data. Valid values: [1,36]
  • wn [int] - Week number of when the navigation data was transmitted with respect to Galileo start time.
  • tow [int] - Time of Week in seconds of when the navigation data was transmitted.
  • nav_bits [BitArray] - The 240 navigation data bits concerning a nominal page. Some of these bits are of no use by OSNMAlib so they can be filled with 0, but the software expects the full page. The parameter shall be a BitArray object.
  • band [str] - Optional parameter to specify the band form which the navigation bits come from. Currently, OSNMAlib only supports I/NAV data, but in the future F/NAV may be of interest. Possible values are GAL_L1BC for I/NAV and GAL_E5b for F/NAV. Defaults to GAL_L1BC.
  • crc [bool] - Optional parameter to specify if the page passed the CRC verification. Defaults to True.

The code implementing this class can be found here.

Iterator

The data reception of OSNMAlib is abstracted behind an iterator. The software receiving loop expects at each iteration a DataFormat object and an index.

In Python, an iterator is an object which implements the iterator protocol, which consists of the methods __iter__() and __next__(). The __iter__() method allows to do some initializing, but must always return the iterator object itself. The __next__() method also allows to do operations and must return the next item in the sequence.

Therefore, any data input class must implement the iterator interface and do the internal operations to provide a DataFormat object for every nominal page with a GNSS time that never goes backwards.

Already Implemented Inputs

SFB from file

TBC

SBF live

TBC

gallon Network

TBC

Official Test Vectors

TBC

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