Galileo Signal - A Software-Defined GPS and Galileo Receiver: A Single-Frequency Approach - page 32

code, leaving the data and the residual Doppler to be removed/measured by a
processor. With the BOC(1,1) codes, the BOC component should have been con-
sidered part of the spreading code for tracking and positioning; but it is equally
viable to consider it part of the carrier during the acquisition phase, and remove it
prior to the empirical correlation of acquisition.
The ACF of a BOC(1,1) code has three peaks, not just one, so care must be
taken to ensure that the correct one has been found.

3.2 Galileo L1 OS Signal

In the following we describe and combine all elements necessary to generate the
Galileo L1 OS signal.
The transmitted bandwidth is 40

× 1 . 023 MHz = 40 . 92 MHz. The minimum

received power for the L1 OS signal is 157 dBW for elevation angles between

10 ◦ and 90 ◦ . The chip length of the ranging code is

−

T c , L1-B = T c , L1-C = 1 / 1 . 023 Mchip/s = 977 . 5ns . (3.1)

The actual chips for the individual satellites are likely to be generated as a trun-
cated Gold code. Higher chipping rates provide better accuracy. Longer codes
reduce cross correlation to more acceptable levels, although acquisition time is
longer.
The corresponding ranging code rates are

R c , L1-A = 2 . 5 × 1 . 023 Mchip/s ,

R c , L1-B = 1 / T c , L1-B = 1 . 023 Mchip/s ,

R c , L1-C = 1 / T c , L1-C = 1 . 023 Mchip/s ,

and subcarrier rates

R sc , L1-B = R sc , L1-C = 1 . 023 MHz .

Channel C uses both a primary and a secondary code of length N P = 4092 chips

and N S = 25 chips, respectively. The primary code is a truncated Gold sequence,

so when the number of 4092 chips is reached, the register is reset to its initial state.
We remember a Gold sequence is obtained as modulo-2 addition of the output
from two shift registers. The initial state for the first register consists of mere ones
while the second register depends on the specific subcarrier and satellite.
The secondary code modulates 25 specific repetitions of the primary code. For
each subcarrier all satellites transmit the same secondary code: the octal sequence
34,012,662. The resulting code length is 4092 × 25. In Galileo lingo the final code

is called a tiered code .
Let the primary code generator work with chip rate R P . The secondary code
generator has chip rate R S N P ,where N P is the length in chips of the

primary code. In all signal modulations the logical levels 1 and 0 are defined as
signal levels

= R P /

− 1 and 1 (polar non-return-to-zero representation).