Galileo OS SIS ICD.indd - GSA - Europa

3. Galileo Spreading Codes Characteristics
3.1. Code Lengths
The ranging codes are built from so-called primary and secondary codes by using a
tiered codes construction described in paragraph 3.2. The code lengths to be used for
each signal component are stated in Table 13. Note that the E6 ranging codes are not
subject of this SIS ICD.
Signal
Component
3.2. Tiered Codes Generation
Tiered Code
Period (ms)
12 © European Union 2010
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OD SIS ICD, Issue 1, February 2010
Code Length (chips)
Primary Secondary
E5a-I 20 10230 20
E5a-Q 100 10230 100
E5b-I 4 10230 4
E5b-Q 100 10230 100
E1-B 4 4092 N/A
E1-C 100 4092 25
Table 13. Code Lengths
Long spreading codes are generated by a tiered code construction, whereby a
secondary code sequence is used to modify successive repetitions of a primary code
periods, as shown in Figure 9 for a primary code of length N and chip rate f c, and a
secondary code of length N S and chip rate f cs = f c/N. The duration of N chips is also
called a primary code epoch in Figure 9. In logical representation, the secondary code
chips are sequentially exclusive-ored with the primary code, always one chip of the
secondary code per period of the primary code.
Figure 9. Tiered Codes Generation