Galileo OS SIS ICD.indd - GSA - Europa

Figure 15. I/NAV Message Structure in the Nominal Mode
The I/NAV message structures for the E5b-I and E1-B signals use the same page
layout since the service provided on these frequencies is a dual frequency service,
using frequency diversity. Only page sequencing is different, with page swapping
between both components in order to allow a fast reception of data by a dual frequency
receiver. Nevertheless, the frame is designed to allow receivers to work also with a
single frequency.
4.3.2. I/NAV Page Layout
Two types of I/NAV pages are defi ned
● Nominal pages having a duration of 2 seconds transmitted sequentially in time in
two parts of duration 1 second each on each of the E5b-I and E1-B components
according to Table 39. The fi rst part of a page is denoted ‘even’ and the second one
is denoted ‘odd’.
● Alert pages having a duration of 1 second transmitted in two parts of duration 1
second each at the same epoch over the E5b-I and E1-B components according
to Table 40. Again, the fi rst part of a page is denoted ‘even’ and the second one is
denoted ‘odd’. This transmission is repeated at the next epoch but switching the two
parts between the components.
The I/NAV page part (even or odd) layout is defi ned in Table 38 for both nominal and
alert page types. This table shows the symbols allocation and bits allocation separately.
The different fi elds composing this layout are defi ned in the sections below.
Sync. I/NAV Page Part (even or odd) Symbols Total (symb)
10 240 250
4.3.2.1. Synchronisation Pattern
I/NAV Page Part (even or odd) Bits Tail Total (bits)
114 6 120
Table 38. I/NAV Page Part Layout
The synchronization pattern allows the receiver to achieve synchronisation to the page
boundary. Note the synchronisation pattern is not encoded. The I/NAV synchronisation
pattern is 0101100000
© European Union 2010
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OD SIS ICD, Issue 1, February 2010
33