Global Positioning System Reference
In-Depth Information
7. C us : The amplitude of the sine harmonic correction term of the argument
of latitude has 16 bits from 211 - 226 in two's complementary form. These
data are converted into decimal form.
8. a s : The square root of the semi-major axis of the satellite orbit has 32 bits
in binary form. These data are divided into two parts, the 8-bit MSB from
227 - 234 and 24-bit LSB from 241 - 264, and converted into decimal form.
9. t oe : The reference time ephemeris has 16 bits from 271 - 286 in binary form.
These data are converted into decimal form.
9.7 OBTAINING EPHEMERIS DATA FROM SUBFRAME 3
The data from subframe 3 will be obtained in a similar way. Referencing Figure 5.9c,
the following data can be obtained from subframe 3:
1. C ic : The amplitude of the cosine harmonic correction term to the angle of
inclination has 16 bits from 61 - 76 in two's complementary form. These
data are converted into decimal form.
2. 0 : The longitude of the ascending node of orbit plane at weekly epoch has
32 bits in two's complementary form. These data are divided into two parts,
the 8-bit MSB from 77 - 84 and 24-bit LSB from 91 - 114, and converted
into decimal form. The unit is in semicircles, thus, the data are multiplied
by π to change to radians.
3. C is : The amplitude of the sine harmonic correction term to the angle of
inclination has 16 bits from 121 - 126 in two's complementary form. These
data are converted into decimal form.
4. i 0 : The inclination angle at reference time has 32 bits in two's comple-
mentary form. These data are divided into two parts, the 8-bit MSB from
137 - 144 and 24-bit LSB from 151 - 174, and converted into decimal form.
The unit is in semicircles, thus, the data are multiplied by π to change
to radians.
5. C rc : The amplitude of the cosine harmonic correction term to the orbit
radius has 16 bits from 181 - 196 in two's complementary form. These
data are converted into decimal form.
6. ω : The argument of perigee has 32 bits in two's complementary form.
These data are divided into two parts, the 8-bit MSB from 197 - 204 and
24-bit LSB from 211 - 234, and converted into decimal form. The unit is
in semicircles, thus, the data are multiplied by π to change to radians.
7. ˙ : The rate of right ascension has 24 bits from 241 - 264 in two's comple-
mentary form. These data are converted into decimal form. The unit is in
semicircles, thus, the data are multiplied by π to change to radians.
8. IODE: The issue of data, ephemeris has 8 bits from 271 - 278. This bit
pattern is compared with the 8 least significant bits (LSB) of the issue of
data, clock (IODC) in subframe 1, and the IODE in subframe 2. If they
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