Figure 2. The mean value of localization error μ∆r as a
function of acquisition time tA for different path lengths S.
Analyzing the above results, we can see that the
lowest mean localization error μ∆r is obtained in the
case when the acquisition time tA is about 65% of all
seconds needed to cover the entire route tAmax.
However, this value is difficult to achieve, especially in
the case of scenarios where there are more than 1300 of
them. The measurement time to the first localization
would reach more than 10 minutes. It can also be seen
that with the increase in the length of the measurement
path S, the difference between the localization errors
for individual acquisition times tA increases. However,
the trend itself is identical. In ideal simulation
conditions, we can see, however, that the selection of
the acquisition time tA does not have a critical
significance in the localization error.
3.3 The influence of the range of Doppler frequency
changes
As mentioned in Section 3.2, the accuracy of
localization is influenced by the acquisition time tA of
the signal, i.e. the number of fD values taken to calculate
the emitter coordinates (x,y). In general, the lowest
localization error was obtained when the acquisition
time tA was about 60% of the entire Doppler curve. In
real conditions, we do not always have the possibility
to collect data that will allow for the analysis of the full
Doppler curve and localization procedures must be
performed on its part. In such a case, a decision must
be made when to start determining the coordinates so
as not to burden the result with too large a localization
error ∆r. For this purpose, another simulation study
was conducted, in which it was decided to analyze the
influence of the range of Doppler frequency changes
BfD on the localization error ∆r. For assume that this
parameter has a constant value, the acquisition time tA
is changed dynamically by appropriately adding and
subtracting values from the fD vector, to maintain
a constant, previously determined the range of
Doppler frequency changes BfD.
3.3.1 Scenarios assumptions
The study was conducted taking the assumptions
from Section 3.1 into account. Additionally, the
following assumptions were made:
− x0,y0,z0={(10,10,-0.1),(10,5,-0.1),(10,2,-0.1),
(10,1,-0.1),(1.2,1.2,-0.1),(1.2,0.6,-0.1)
(1.2,0.2,-0.1),(1.2,0.1,-0.1)} km,
− f0={300,600,900,1200,1500,1800,2100,2400,2700,
3000} MHz,
− v={15,20,30} m/s,
− the range of Doppler frequency changes was
selected so that each scenario could meet the
requirements for its value, it was therefore decided
to test all possible BfD values in the range from 0.5
to 20 Hz with a step of 0.5 Hz,
− the acquisition time tA is selected taking the range of
Doppler frequency changes BfD into account,
− for each value of the range of Doppler frequency
changes BfD, the mean value μ∆r and deviation σ∆r
of the localization error ∆r is determined according
to formula (7) and (8).
3.3.2 Results
Figure 3 presents courses of the mean value μ∆r and
standard deviation σ∆r of the localization error as a
function of the range of Doppler frequency changes
BfD.
Figure 3. The mean value μ∆r and standard deviation σ∆r of
localization error as a function of the range of Doppler
frequency changes BfD.
Analyzing the obtained results, it can be noticed
that with small values of the range of Doppler
frequency changes BfD, the mean localization error μ∆r
can reach almost 3 meters. By increasing the value of
the tested parameter, localization error begins to
decrease quickly. Assuming that the localization
procedure is to be carried out as quickly as possible and
the error cannot exceed 0.5 meters, localization can be
done on data for which the range of Doppler frequency
changes BfD equals 5 Hz. Further reduction of the value
of this parameter obviously causes a decrease in the
localization error and for BfD=20 Hz, the mean
localization error value μ∆r=0.278 m. However, the
parameter study was performed for ideal conditions