212 Chapter 8
GPS Modulation (Option 409)
Real Time GPS
Data Modes and Subframe Structures
You can select one of the three following data modes for use with the C/A or C/A+P ranging code:
• Raw - The Raw data mode enables the continuous transmission of 300 bits of data per subframe without
incorporating parity bits. Use this mode for BER and low-level demodulation testing.
• Enc - The encoded (Enc) data mode enables the continuous transmission of 10 words per subframe, with
each word containing 24 bits of raw data and 6 trailing parity bits (computed from the selected data by
the PSG).
• TLM - The telemetry (TLM) mode enables the continuous transmission of a formatted TLM word, a
handover word (HOW), and default navigation data as outlined in the Global Positioning System
Standard Positioning Service Signal Specification, 2nd Edition, June 2, 1995. Use this mode for receiver
testing.
Figure 8-4 shows the subframe structures for each data mode.
Figure 8-4 Subframe Structures
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