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Modern Geomatics Technologies and Applications

After code generation, the codes are combined with the navigation data through Gold polynomial 2 adders. The exclusive OR
operation is used on binary sequences represented by 0’s and 1’s, and its properties are shown in Table 1. If the binary sequences
were represented by the polar non-return-to-zero representation, i.e., 1’s and −1’s, ordinary multiplication could be used instead.
The corresponding properties of the multiplication with two binary non-return-to-zero sequences are shown in Table 1.
Table 1. Output of the exclusive OR operation and ordinary multiplication.

This entire sequence of 1,023 chips is repeated 1,000 times each second, resulting in a “Chip-Rate” of 1.023 MHz or
one phase switch (chip) every one-millionth of a second. Each satellite carries its own unique code string. The C/A code is the
code used for the Standard Positioning Service (SPS).

The C/A code generator contains two shift registers known as G and G . These shift registers each have 10 cells
generating sequences of length 1023. The G register always has a feedback configuration with the polynomial as Equation 6:

G : F(X) = 1 + X + X (6)
This meaning that state 3 and state 10 are fed back to the input. Figure 5 show Gold polynomial (G1) shift register
generator configuration.

Figure 5. Gold polynomial (G1) shift register generator configuration [14]

Therefore, only the delay between the polynomials matters in this case, because the sequence repeats itself. The delay
is set by choosing specific tap outputs and combining them with exclusive OR operation, as shown in Table 1. In the same way,
the G register has the polynomial as Equation 7:

G : F(X) = 1 + X + X + X + X + X + X (7)

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