Satellite Signal Acquisition, Tracking, and Data Demodulation - Understanding GPS: Principles and Applications - page 215

30 seconds = 1,500 bits

Frame Subframe 5

Subframe 1 Subframe 2 Subframe 3 Subframe 4

6 seconds = 4 Z-counts

4 Z-counts

Z-count n Z-countn+3

6 seconds = 10 words = 300 bits

Subframe

TLM HOW Word 3 Word 4 Word 5 Word 6 Word 7 Word 8 Word 9 Word 10

600 milliseconds = 30 bits

Word ... ...

bit 1 bit 2 bit i bit 30

20 milliseconds=1bit

Data bit C/A code

period 1

C/A code
period 2

C/A code
period j

C/A code
period 20

... ...

1 millisecond = 1023 C/A code chips

C/A code
chip 1

C/A code
chip 2

C/A code
chip k

C/A code
chip 1,023

C/A code
period

... ...

977.5 nanoseconds = 10 X1 counts

10 X1 counts
10 P chips

X1
count m

X1
count m+1

X1
count m+2

X1
count m+3

X1
count m+4

X1
count m+5

X1
count m+6

X1
count m+7

X1
count m+8

X1
count m+9

P code
chip 10

P code
chip 1

Figure 5.33 GPS C/A code timing relationships.

gitude computations are also unrealistic, but there is usually no boundary condition
for comparison. However, the velocity and elevation computations can be

compared to acceptable boundary conditions.
The bit synchronization process is a statistical process that is dependent on
C / N 0 . It will occasionally be incorrect. It will be incorrect almost every time the