Reliability and the accuracy of position-finding methods by estimation of the Rice factor of a radio link
View Patent ↗In order to improve the reliability and the accuracy of a position-finding method such as the GPS method, the quality of a radio link which is used for the position-finding method is determined by estimating a parameter, in particular the Rice factor of the amplitude distribution density, which is characteristic of the ratio of the strength of a signal transmitted via a line-of-sight path, with respect to the strength of the signals transmitted via non-line-of-sight paths.
1. A method for determination of the quality of a radio link, in which the radio signals propagate via two or more propagation paths, comprising:
estimating a parameter that is characteristic of a signal strength of a received signal that is transmitted via a line-of-sight path, with respect to a strength of received signals transmitted via non-line-of-sight paths; and
assuming a Rice distribution as the distribution function for the signal strength amplitude, wherein the estimated parameter comprises a Rice factor (K), and wherein the Rice factor is estimated using:
K
^
E
≈
E
^
{
R
2
}
-
2
·
E
^
{
(
R
-
E
^
{
R
}
)
2
}
2
·
E
^
{
(
R
-
E
^
{
R
}
)
2
}
where R is the amplitude of the sample values of the received signal and Ê{x} is approximated by a running averaging of x.
2. A method for determination of the quality of a radio link, in which the radio signals propagate via two or more propagation paths, comprising:
estimating a parameter that is characteristic of a signal strength of a received signal that is transmitted via a line-of-sight path, with respect to a strength of received signals transmitted via non-line-of-sight paths; and
assuming a Rice distribution as the distribution function for the signal strength amplitude, wherein the estimated parameter comprises a Rice factor (K), and wherein the Rice factor is estimated using:
K
^
2
,
4
=
E
^
{
R
4
}
-
2
·
(
E
^
{
R
2
}
)
2
-
E
^
{
R
2
}
·
2
·
(
E
^
{
R
2
}
)
2
-
E
^
{
R
4
}
(
E
^
{
R
2
}
)
2
-
E
^
{
R
4
}
where R is the amplitude of the sample values of the received signal and Ê{x} is approximated by a running averaging of x.
3. A method for finding the position of a mobile station by means of a radio link between the mobile station and at least one reference station, comprising:
determining a quality of the radio link, wherein the quality determination comprises estimating a parameter that is characteristic of a signal strength of a received signal that is transmitted via a line-of-sight path, with respect to a strength of received signals transmitted via non-line-of-sight paths; and
using the parameter to decide whether the signal received from the reference station is to be used for position finding; or
using the signals associated with the line-of-sight path and non line-of-sight paths for position finding after assigning weights to each of the signals by means of a weighting factor based on the value of the parameter for each of the signals.
4. The method of claim 3 , wherein the signals that are received from the reference station are used for position finding only when the value of the parameter is greater than a first predetermined threshold value.
5. The method of claim 3 , wherein the signals that are received from the reference station are used for position finding only when the value of the parameter is less than a second predetermined threshold value.
6. The method of claim 3 , wherein the signals that are received from the reference station are weighted differently by using the signals to a greater or lesser extent for position finding, in accordance with their associated parameter.
7. The method of claim 3 , wherein the position-finding method comprises a satellite-assisted method, and the reference station comprises a satellite with the position-finding method being carried out in the GPS system, the GLONASS system or in the European Galileo system.
8. The method of claim 3 , further comprising:
assuming a Rice distribution as the distribution function for the signal strength amplitude, wherein the estimated parameter comprises a Rice factor (K), and wherein the Rice factor is estimated using:
K
^
s
≈
E
^
{
R
2
}
-
2
·
E
^
{
(
R
-
E
^
{
R
}
)
2
}
2
·
E
^
{
(
R
-
E
^
{
R
}
)
2
}
where R is the amplitude of the sample values of the received signal and Ê{x} is approximated by a running averaging of x.
9. The method of claim 3 , further comprising: assuming a Rice distribution as the distribution function for the signal strength amplitude, wherein the estimated parameter comprises a Rice factor (K), and wherein the Rice factor is estimated using:
K
^
2
,
4
=
E
^
{
R
4
}
-
2
·
(
E
^
{
R
2
}
)
2
-
E
^
{
R
2
}
·
2
·
(
E
^
{
R
2
}
)
2
-
E
^
{
R
4
}
(
E
^
{
R
2
}
)
2
-
E
^
{
R
4
}
where R is the amplitude of the sample values of the received signal and Ê{x} is approximated by a running averaging of x.
10. The method of claim 3 , wherein the signals employed to determine the quality of the radio link are received from a plurality of reference stations.