Galileo OS SIS ICD.indd - GSA - Europa

4.3.2.2. 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.
4.3.2.3. I/NAV Page Part
The structure of the nominal I/NAV even and odd page parts on E5b-I and E1-B are
defi ned in Table 39. A nominal page is composed by the two page parts (even and odd)
transmitted sequentially over the same frequency (“vertical page”).
Even/odd=0
Page Type
E5b-I E1-B
Data i (1/2) Tail
34 © European Union 2010
Document subject to terms of use and disclaimers p. ii-iii
OD SIS ICD, Issue 1, February 2010
Total (bits)
Even/odd=1
Page Type
Data j
(2/2)
1 1 112 6 120 1 1 16 40 22 2 24 8 6 120
Even/odd=1
Page Type
Data i
(2/2)
Reserved 1
CRC i
Reserved 2
Tail
Total (bits)
Even/odd=0
Page Type
Reserved 1
SAR
Spare
CRC j
Reserved 2
Tail
Data k (1/2) Tail
1 1 16 64 24 8 6 120 1 1 112 6 120
Table 39. I/NAV Nominal Page with Bits Allocation
The parameters for the nominal page have the following meaning and related values:
● Even/Odd fi eld (1 bit) to indicate the part of the page (0=even/1=odd) that is
broadcast
● Page Type (1 bit) equal to 0 to indicate the nominal page type
● Data fi eld composed of a nominal word (described in 4.3.5) of 128 bits (112 bits +
16 bits)
● The reserved fi elds will be published in a future update of this ICD
● SAR data (22 bits) composed of SAR RLM data on E1-B only as defi ned in 4.3.7
● CRC (24 bits) computed on the Even/Odd fi elds, Page Type fi elds, Data fi elds (1/2
and 2/2), Spare fi eld, SAR (on E1-B only) and reserved fi elds (Reserved 1 for E5b-I
and Reserved 1 for E1-B). In nominal mode the CRC is computed for the Even
and Odd parts of a page of the same frequency (“vertical CRC”) and is always
broadcast on the second part of the “vertical page”. Note the Reserved 2 fi eld on
E5b-I and the Reserved 2 fi eld on E1-B are not protected by the CRC.
● Tail bits (2*6 bits) as defi ned in 4.3.2.2. These fi elds are not protected by the CRC
The structure of the alert I/NAV even and odd page parts on E5b-I and E1-B are defi ned
in Table 40. An alert page is composed by the two page parts (even and odd) transmitted
at the same epoch over E5b-I and E1-B (“horizontal page”).
Total (bits)
Total (bits)