GPS Software Receivers - Fundamentals of Global Positioning System Receivers: A Software Approach - page 195

are different, a data set cutover has occurred and these data cannot be used
and new data should be collected.
9. idot: The rate of inclination angle has 14 bits from 279 - 292 in two's
complementary form. These data are converted into decimal form. The unit
is in semicircles, thus, the data are multiplied by π to change to radians.

It should be noted that the TOWs from subframes 2 and 3 are not decoded
because the TOW from subframe 1 will provide the necessary information. All
the data from subframes 1, 2, and 3 are decoded and converted to decimal form
and have the desired units. The following steps are to calculate the satellite
positions and user position.
Three computer program ( p9 3 ), ( p9 4 ), and ( p9 5 ) are listed at the end of
this chapter and they are used to obtain the navigation data from subframes 1, 2,
and 3.

9.8 TYPICAL VALUES OF EPHEMERIS DATA

Some of the ephemeris data are user located dependent. Others are somewhat
user location independent, such as the inclination angle. Some of the ephemeris
data that are user location independent are listed in Table 9.1 as a reference.
These data are from three different satellites and most of the values have about
the same order of magnitude.

9.9 FINDING PSEUDORANGE

In collecting the digitized data there is no absolute time reference and the only
time reference is the sampling frequency. As a result, the pseudorange can be

TABLE 9.1 Typical Ephemeris Data

n 5 . 117713173295686e − 009 5 . 055924885279763e − 009 4 . 529831542808932e − 009

√ a s

5 . 153714639663696e + 003 5 . 153681760787964e + 003 5 . 153659612655640e + 003

i 0 9 . 560779626333219e − 001 9 . 478276108359106e − 001 9 . 581404971861649e − 001

˙

− 8 . 277844805462636e − 009 − 8 . 656432003710486e − 009 − 7 . 999618930523888e − 009

idot − 6 . 393123442109902e − 011 7 . 857470152313846e − 011 − 6 . 468126566291079e − 010

e s 4 . 112668684683740e − 003 1 . 435045502148569e − 003 9 . 771452634595335e − 003

crs − 1 . 375000000000000e + 000 1 . 093750000000000e + 001 − 1 . 453125000000000e + 001

cuc − 1 . 583248376846314e − 007 5 . 904585123062134e − 007 − 7 . 711350917816162e − 007

cus 4 . 576519131660461e − 006 1 . 367181539535523e − 006 1 . 043826341629028e − 005

cic 2 . 048909664154053e − 008 2 . 793967723846436e − 008 − 1 . 471489667892456e − 007

cis − 8 . 940696716308594e − 008 3 . 725290298461914e − 009 1 . 862645149230957e − 007

crc 2 . 872500000000000e + 002 3 . 436875000000000e + 002 1 . 749375000000000e + 002

a f 0 6 . 267381832003593e − 005 5 . 940999835729599e − 005 3 . 222310915589333e − 004

a f 1 1 . 136868377216160e − 012 3 . 410605131648481e − 012 6 . 662048690486699e − 011

a f 2 0 0 0

t oc 4 . 032000000000000e + 005 4 . 031840000000000e + 005 4 . 032000000000000e + 005

t gd 4 . 656612873077393e − 010 1 . 396983861923218e − 009 1 . 396983861923218e − 009