Customer Service Center

• PosApp (SimGEN / SimREPLAYplus / SimREPLAY)
• GLONASS
• Navigation data messages

NOTE: Spirent provide a GLONASS nav data decoder
                - Go to the PosApp directory (C:\Program Files\Spirent Communications\Positioning Application)
                        OR
                - Go to PosApp menu [Tools-->General Utilities]

FILE STRUCTURE

• XML format
• Open with any standard text editor, like Notepad.
• One 'string' of nav data looks like
          <string svid="2" framenum="5" stringnum="8">
                          6A965 96955 665A9 69956 6555A 55996 55555 5556A 567E3 75096 
          </string>
   
• XML header identifies the related SVID, Frame and String.
• There are 50 hex characters
• Each character represents 4 nav data symbols = 200 symbols total
• The 200 symbols contain 170 symbols of nav message + 30 bits (time mark)
• The 170 symbols of nav message is the Modulo-2 addition of
      - The wanted 85 bits of nav data (20ms period)
      - A meander sequence (10ms period)

DECODING THE DATA

• Convert the symbols to bits
• Remove 30 bits for the time mark
      - This is always "111110001101110101000010010110" = "E375096" (in hex)
      - Notice this sequence on the end of each string
• Reverse the Modulo-2 process for the remaining bits
      - The meander is a repeating 10101010 sequence
      - Align the nav message bits with the meander
      - Take 2 bits at a time
      - A "1" in the nav message identifies the meander bit that becomes the output
   
• The following example takes the first 5 hex characters from the above nav data extract
  The first few bit pairs are colour-coded to show how output bits are selected
  
      - 6A965 96955 = 01 10 10 10 10 01 01 10 01 01 10 01 01 10 10 01 01 01 01 01 ... (10ms period)
      - Meander       = 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 ... (10ms period)
      - Output         =  0   1   1   1  1   0   0  1   0   0   1   0  0   1   1   0   0  0   0   0  ... (20ms period)