246
14 Pseudo-Ranging Radio Navigation Systems
satellite, performs its shift, and the whole procedure is repeated. This process can
take several minutes.
When a signal from at least one satellite is received, the process goes faster. The
pseudo-range d(t) is determined by the value by which the sequences had to be shifted
so that they coincide. Then a navigation message is received, containing the almanac
of the system (orbits parameters of all NSV and other service information). Based
on these parameters, the receiver can already estimate which NSVs are now within
sight, and begins to purposefully “search” for their signals. After signal receiving
from four NSV, it is possible to determine the spatial position of the user and other
necessary parameters.
The received almanac is stored in the receiver’s memory; therefore, when the
receiver is turned on the next time, it will immediately calculate which NSV can be
in the field of view and will first of all try to receive signals from them, and in a
few seconds the navigation information will be received. If the receiver has not been
turned on for a long time and the almanac is outdated, or if the receiver has been
moved far to another location in the off-state, then the process will take longer.
It should be noted that the power of the signal received from the NSV is negligible
and is on the order of 10
–14 W. The signals are so weak that they are simply lost against
the background of the earth’s natural radio emission, atmospheric interference and
thermal noise from the receiver itself. However, all these noises are random variations
of electronic pulsations, and the received pseudo-random code—is a strictly defined
sequence of video pulses. Since the pseudo-random code sequence is periodically
repeated, then by using algorithms based on methods of optimal reception, it is
possible to perform multiple comparison of the received signals and select the pseudorandom code against the background of the natural radio noise of the Earth.
Figure 14.2 schematically depicts a received radio signal, which possibly also
contains a code sequence. The detection of the NSV signal is carried out using
correlation reception. The correlation receiver is based on calculating the crosscorrelation of the received signal from the NSV s(t) and the signal generated in the
receiver s 0 (t), which is a copy of the useful signal from the satellite:
q =
T
0
s(t)s 0 (t)dt,
(14.5)
Fig. 14.2 Received signal and reference sequence
14 Pseudo-Ranging Radio Navigation Systems
satellite, performs its shift, and the whole procedure is repeated. This process can
take several minutes.
When a signal from at least one satellite is received, the process goes faster. The
pseudo-range d(t) is determined by the value by which the sequences had to be shifted
so that they coincide. Then a navigation message is received, containing the almanac
of the system (orbits parameters of all NSV and other service information). Based
on these parameters, the receiver can already estimate which NSVs are now within
sight, and begins to purposefully “search” for their signals. After signal receiving
from four NSV, it is possible to determine the spatial position of the user and other
necessary parameters.
The received almanac is stored in the receiver’s memory; therefore, when the
receiver is turned on the next time, it will immediately calculate which NSV can be
in the field of view and will first of all try to receive signals from them, and in a
few seconds the navigation information will be received. If the receiver has not been
turned on for a long time and the almanac is outdated, or if the receiver has been
moved far to another location in the off-state, then the process will take longer.
It should be noted that the power of the signal received from the NSV is negligible
and is on the order of 10
–14 W. The signals are so weak that they are simply lost against
the background of the earth’s natural radio emission, atmospheric interference and
thermal noise from the receiver itself. However, all these noises are random variations
of electronic pulsations, and the received pseudo-random code—is a strictly defined
sequence of video pulses. Since the pseudo-random code sequence is periodically
repeated, then by using algorithms based on methods of optimal reception, it is
possible to perform multiple comparison of the received signals and select the pseudorandom code against the background of the natural radio noise of the Earth.
Figure 14.2 schematically depicts a received radio signal, which possibly also
contains a code sequence. The detection of the NSV signal is carried out using
correlation reception. The correlation receiver is based on calculating the crosscorrelation of the received signal from the NSV s(t) and the signal generated in the
receiver s 0 (t), which is a copy of the useful signal from the satellite:
q =
T
0
s(t)s 0 (t)dt,
(14.5)
Fig. 14.2 Received signal and reference sequence