Receiver in a position-finding system and method for position-finding with increased sensitivity
View Patent ↗The invention relates to a receiver in a position-finding system, having a calculation unit for calculating a statistical value from a received signal, and a detector unit for comparing the statistical value with a threshold value and for determining whether the signal is a synchronized position-finding signal. The system also includes an estimation unit for estimating the quotient of the signal-carrier power and the noise-power spectral density of the signal, and a determination unit for threshold-value determination from the estimated quotient.
1. A receiver in a position-finding system which is configured to ascertain a position based on an evaluation of different propagation times for position-finding signals, the position-finding signals being emitted by a plurality of transmitters at known positions and being received by the receiver, comprising:
a calculation unit configured to calculate a statistical value from a signal received by the receiver; and
a detector unit configured to compare the statistical value with a threshold value and use the comparison to determine whether the received signal is a position-finding signal or whether the received signal is used for finding the position of the receiver;
an estimation unit configured to estimate a ratio of the signal-carrier power to the noise-power spectral density of the received signal; and
a determination unit configured to determine the threshold value from the estimated ratio of the signal-carrier power to the noise-power spectral density.
2. The receiver of claim 1 , wherein the determination unit is configured to calculate a probability density of the received signal from the estimated ratio of the signal-carrier power to the noise-power spectral density and calculate the threshold value from the probability density.
3. The receiver of claim 1 , wherein the determination unit is further configured to calculate a probability density of the received signal from the estimated ratio of the signal-carrier power to the noise-power spectral density, and determine the threshold value from the probability density using a table associated therewith.
4. The receiver of claim 1 , wherein the determination unit is configured to determine the threshold value from the estimated ratio of the signal-carrier power to the noise-power spectral density using a table associated therewith.
5. The receiver of claim 1 , wherein the determination unit is configured to calculate the threshold value from a prescribed fixed misdetection probability, wherein the misdetection probability comprises the probability that the received signal is not a synchronized position-finding signal, but is incorrectly considered to be a position-finding signal by the detector unit.
6. The receiver of claim 1 , wherein the calculation unit is configured to sample the received signal and feed the samples to a series circuit which comprises a first integrator for coherent integration, an absolute-value squaring unit or absolute-value formation unit, and a second integrator for non-coherent integration, wherein the series circuit is operable to generate the statistical value based on the samples.
7. The receiver of claim 1 , wherein the position-finding signals emitted by the transmitters are spread-coded, and wherein the calculation unit comprises a despreading unit for despreading the received signal.
8. The receiver of claim 7 , wherein the estimation unit is fed with the statistical value by the calculation unit or with despread samples of the received signal by the despreading unit.
9. The receiver of claim 1 , further comprising a further estimation unit configured to estimate a Rice factor of the radio link which was used to transmit the received signal, and wherein the determination unit is configured to use the estimated Rice factor to determine the threshold value.
10. The receiver of claim 9 , wherein the Rice factor is estimated by the estimation unit in accordance with
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11. The receiver of claim 1 , wherein the ratio of the signal-carrier power to the noise-power spectral density of the received signal is estimated by the estimation unit in accordance with
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12. The receiver of claim 1 , wherein the transmitters in the position-finding system are arranged on satellites or terrestrially.
13. A method for finding a position of a receiver in a position-finding system which is based on the evaluation of different propagation times for position-finding signals, the position-finding signals being emitted by a plurality of transmitters at known positions and being received by the receiver, comprising:
(a) calculating a statistical value from a signal received by the receiver;
(b) estimating a ratio of the signal-carrier power to the noise-power spectral density of the received signal;
(c) determining a threshold value from the estimated ratio of the signal-carrier power to the noise-power spectral density of the received signal;
(d) comparing the statistical value with the threshold value; and
(e) using the comparison result to determine whether the received signal is a position-finding signal or whether the received signal is used for finding the position of the receiver.
14. The method of claim 13 , wherein act (c) further comprises calculating a probability density of the received signal from the estimated ratio of the signal-carrier power to the noise-power spectral density of the received signal, and wherein in act (d) the threshold value is determined from the probability density.
15. The method of claim 13 , wherein act (c) further comprises calculating a probability density of the received signal from the estimated ratio of the signal-carrier power to the noise-power spectral density of the received signal, and wherein in act (d) the threshold value is determined from the probability density using a table.
16. The method of claim 13 , wherein act (c) further comprises determining the threshold value from the estimated ratio of the signal-carrier power to the noise-power spectral density of the received signal using a table.
17. The method of claim 13 , wherein determining the threshold value comprises calculating the threshold value from a prescribed fixed misdetection probability, wherein the misdetection probability comprises the probability that the received signal is not a synchronized position-finding signal but is incorrectly considered to be a position-finding signal in step (e).
18. The method of claim 13 , wherein the received signal is a spread-coded signal, and wherein act (a) further comprises:
sampling and dispreading the received spread-coded signal;
integrating coherently the despread samples;
absolute-value squaring the results of the coherent integration; and
integrating non-coherently the absolute-value squares to calculate the statistical value.
19. The method of claim 18 , wherein estimating the ratio of the signal-carrier power to the noise-power spectral density of the received signal in act (b) comprises estimating the ratio from the statistical value or from despread samples of the received signal, or from coherently integrated despread samples of the received signal, or from the absolute value of coherently integrated despread samples of the received signal.
20. The method of claim 13 , further comprising estimating a Rice factor of the radio link which was used to transmit the received signal, and using the estimated Rice factor to determine the threshold value in act (c).
21. The method of claim 20 , wherein the Rice factor is estimated in accordance with
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22. The method of claim 13 , wherein the ratio of the signal-carrier power to the noise-power spectral density of the received signal is estimated in accordance with
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23. The method of claim 13 , wherein the transmitters in the position-finding system are arranged on satellites or terrestrially.