
258 Chapter 10
GPS Modulation
GPS Concepts
Data Modes and Subframe Structures
The GPS personality lets you transmit data three different ways using the C/A or C/A+P
ranging code selection:
• A raw (Raw) data mode which enables the continuous transmission of 300 bits of data per
subframe without incorporating parity bits. This is well suited for BER and low-level
demodulation testing.
• An encoded (Enc) data mode which enables the continuous transmission of 10 words
(30-bits each) per subframe, with each word containing 24 bits of raw data along with 6
trailing parity bits computed from the selected data by the ESG.
• The telemetry (TLM) mode which enables the continuous transmission of a formatted TLM
and handover word (HOW) along with default navigation data as outlined in the GLOBAL
POSITIONING SYSTEM STANDARD POSITIONING SERVICE SIGNAL
SPECIFICATION, 2nd Edition, June 2, 1995. This is a good mode for testing receiver
functionality. For example, the C/No can be determined by testing the sensitivity of the
receiver accepting the data.
Figure 10-2 shows the subframe structures for each data mode.
Figure 10-2 Subframe Structures
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