Method for carrier-to-noise ratio estimation in GNSS receivers

1. A method for determining an indicator of an amount of noise comprised within a received signal of a plurality of received satellite signals received by a Global Navigation Satellite System (GNSS) receiver, the method comprising

extracting, by the GNSS receiver, a received modulating signal from the received signal, wherein the received signal has incurred a transmission delay, wherein the received signal is indicative of a carrier signal modulated with a modulating signal, and wherein the modulating signal comprises an in-phase component and a quadrature component;

determining, by the GNSS receiver, an estimate of the transmission delay based on an in-phase component of the received modulating signal;

generating, by the GNSS receiver, a prompt replica of the modulating signal using the estimate of the transmission delay;

determining, by the GNSS receiver, a prompt quadrature correlation of a quadrature component of the received modulating signal and of a quadrature component of the prompt replica;

determining, by the GNSS receiver, the indicator of the amount of noise comprised within the received signal based on the prompt quadrature correlation; and

selecting, by the GNSS receiver, a subset of the plurality of received satellite signals based at least in part on the indicator.

2. The method of claim 1 , further comprising:

determining, by the GNSS receiver, a prompt in-phase correlation of the in-phase component of the received modulating signal and an in-phase component of the prompt replica; and

determining, by the GNSS receiver, the indicator of the amount of noise comprised within the received signal based on a ratio of a value derived from the prompt in-phase correlation and a value derived from the prompt quadrature correlation.

3. The method of claim 2 , wherein:

I P is the prompt in-phase correlation;

Q P is the prompt quadrature correlation;

a first signal-to-noise ratio is determined as

SNR

=

[

1

N

⁢

∑

k

=

1

N

⁢

⁢

2

·

⁢

Q

P

,

k

2

I

P

,

k

2

]

-

1

,

 with k identifying a sample of the prompt in-phase and quadrature correlations and with N being an integer greater than one; and

the indicator of the amount of noise comprised within the received signal is determined based on the first signal-to-noise ratio or a scaled value of the first signal-to-noise ratio.

4. The method of claim 3 , wherein:

the indicator of the amount of noise comprised within the received signal is a carrier-to-noise ratio; and

the carrier-to-noise ratio is determined by multiplying the first signal-to-noise ratio with an equivalent noise bandwidth.

5. The method of claim 2 , wherein determining, by the GNSS receiver, the indicator of the amount of noise comprised within the received signal comprises:

determining a mean value of the prompt in-phase correlation; and

determining the indicator of the amount of noise comprised within the received signal based on a difference of the prompt in-phase correlation and a mean value of the prompt in-phase correlation.

6. The method of claim 5 , further comprising:

determining a third signal-to-noise ratio based on a ratio of a squared difference of the prompt in-phase correlation, the mean value of the prompt in-phase correlation, and a squared prompt in-phase correlation; and

determining the indicator of the amount of noise comprised within the received signal based on the third signal-to-noise ratio.

7. The method of claim 1 , wherein determining, by the GNSS receiver, the indicator of the amount of noise comprised within the received signal comprises:

generating an early replica of the modulating signal using the estimate of the transmission delay and using an early gate time offset;

determining an early in-phase correlation of the in-phase component of the received modulating signal and an in-phase component of the early replica;

generating a late replica of the modulating signal using the estimate of the transmission delay and a late gate time offset;

determining a late in-phase correlation of the in-phase component of the received modulating signal and an in-phase component of the late replica; and

determining the indicator of the amount of noise comprised within the received signal based on a difference of the early in-phase correlation and the late in-phase correlation.

8. The method of claim 7 , further comprising:

determining a mean value of a squared difference of the early in-phase correlation and the late in-phase correlation; and

determining the indicator of the amount of noise comprised within the received signal based on the squared difference of the early in-phase correlation and the late in-phase correlation, normalized by a mean value of the squared difference of the early in-phase correlation and the late in-phase correlation.

9. The method of claim 8 , further comprising:

determining a prompt in-phase correlation of the in-phase component of the received modulating signal and an in-phase component of the prompt replica;

determining the indicator of the amount of noise comprised within the received signal based on a ratio of a value derived from the prompt in-phase correlation and a value derived from the prompt quadrature correlation;

determining a second signal-to-noise ratio based on a ratio of a squared difference of the early in-phase correlation and the late in-phase correlation, normalized by a mean value of a squared difference of the early in-phase correlation and the late in-phase correlation, and of a squared prompt in-phase correlation; and

determining the indicator of the amount of noise comprised within the received signal based on the second signal-to-noise ratio.

10. The method of claim 1 , wherein determining, by the GNSS receiver, the indicator of the amount of noise comprised within the received signal comprises:

generating an offset replica of the modulating signal using the estimate of the transmission delay and using a decorrelating time offset, wherein an autocorrelation value of the modulating signal for a lag corresponding to the decorrelating time offset is below a pre-determined autocorrelation threshold;

determining an offset in-phase correlation of the in-phase component of the received modulating signal and an in-phase component of the offset replica; and

determining the indicator of the amount of noise comprised within the received signal based on the offset in-phase correlation.

11. The method of claim 10 , wherein:

the modulating signal is indicative of a code signal;

the code signal has a pre-determined symbol duration T c ; and

the decorrelating time offset is equal to or greater than the pre-determined symbol duration T c .

12. The method of claim 1 , wherein the modulating signal comprises a BPSK signal or a binary offset carrier signal.

13. The method of claim 1 , wherein extracting, by the GNSS receiver, the received modulating signal from the received signal comprises estimating, by the GNSS receiver, a phase or a frequency of the carrier signal.

14. The method of claim 1 , wherein determining, by the GNSS receiver, a correlation of a component of the received modulating signal and a component of a replica of the modulating signal comprises multiplying, by the GNSS receiver, corresponding samples of the component of the received modulating signal and of the component of the replica.

15. A Global Navigation Satellite System (GNSS) receiver, wherein the receiver is configured to:

receive a plurality of received satellite signals, including a received signal having incurred a transmission delay, wherein the received signal is indicative of a carrier signal modulated with a modulating signal, wherein the modulating signal comprises an in-phase component and a quadrature component;

extract a received modulating signal from the received signal;

determine an estimate of the transmission delay based on an in-phase component of the received modulating signal;

generate a prompt replica of the modulating signal using the estimate of the transmission delay;

determine a prompt quadrature correlation of a quadrature component of the received modulating signal and of a quadrature component of the prompt replica; and

determine an indicator of an amount of noise comprised within the received signal based on the prompt quadrature correlation;

select a subset of the plurality of received satellite signals based at least in part on the indicator.