Galileo OS SIS ICD.indd - GSA - Europa

4.2. F/NAV Message Description
4.2.1. General Description of the F/NAV Message
The F/NAV message structure is presented in Figure 14, where the duration of each
entity is indicated.
4.2.2. F/NAV Page Layout
Figure 14. F/NAV Message Structure
The page layout for the F/NAV message type is according to Table 29 where the symbols
allocation and bits allocation are shown separately. The different fi elds composing this
layout are defi ned in the sections below.
Sync. F/NAV Symbols Total (symb)
12 488 500
4.2.2.1. Synchronisation Pattern
F/NAV Word Tail Total (bits)
Page type Navigation Data CRC
6 208 24 6 244
Table 29. F/NAV Page Layout
The synchronization pattern allows the receiver to achieve synchronisation to the page
boundary. Note the synchronisation pattern is not encoded. The F/NAV synchronisation
pattern is 101101110000
4.2.2.2. Tail Bits
The tail bits fi eld consists of 6 zero-value bits enabling completion of the FEC decoding
of each page’s information content in the user receiver.
4.2.2.3. F/NAV Word
The useful data are contained in the F/NAV word composed of
● A page type fi eld (6 bits) enabling to identify the page content as defi ned in paragraph
4.2.4
● A navigation data fi eld (208 bits) whose structure is presented in paragraph 4.2.4
● A CRC (24 bits) to detect potential bit errors, according to paragraph 5.1.9.4. The
CRC is computed on the Page Type and Navigation Data fi elds.
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OD SIS ICD, Issue 1, February 2010