Systems and methods for de-noising GNSS signals
Certain implementations of the disclosed technology may include systems and methods for reducing noise in dual-frequency GNSS signal observation. The method can include: receiving, at a GNSS receiver, a first signal and a second signal. At least the second signal includes noise. The first signal is characterized by a first carrier frequency, and the second signal is characterized by a second carrier frequency. The method includes: down converting, sampling, cross-correlating, accumulating, determining ambiguous instantaneous phases, determining non-ambiguous instantaneous phases, producing normalized non-ambiguous instantaneous first phase samples, constructing a normalized first counter rotation phasor, generating a counter-rotated second observable, applying a low pass filter to remove noise; and outputting the filtered second observable.
1. A method for reducing noise in dual-frequency GNSS signal observation, the method comprising:
receiving, at a GNSS receiver, a first signal and a second signal, wherein at least the second signal includes noise, and wherein the first signal is characterized by a first carrier frequency, and wherein the second signal is characterized by a second carrier frequency;
down converting the first and second signals to respective first baseband and second baseband signals;
sampling the first baseband and second baseband signals to produce complex first samples and complex second samples;
cross-correlating and accumulating the complex first samples and the complex second samples to obtain a result;
determining ambiguous instantaneous first phase of the result;
determining non-ambiguous instantaneous first phase samples of the result;
producing normalized non-ambiguous instantaneous first phase samples by multiplying the non-ambiguous instantaneous first phase samples by the second carrier frequency divided the first carrier frequency;
constructing a normalized first counter rotation phasor by taking a complex exponential of a negated version of the normalized non-ambiguous instantaneous first phase samples;
generating a counter-rotated second observable by multiplying the complex second samples by the normalized first counter-rotation phasor;
applying a low pass filter to the counter-rotated second observable to remove noise; and
outputting the filtered second observable.
2. The method of claim 1 , wherein sampling the first baseband and second baseband signals generates first and second digital sequences.
3. The method of claim 1 , where accumulating the first and second complex digital sequences comprises accumulating over an interval selected from a range of 1 ms to 100 ms.
4. The method of claim 1 , wherein the first signal and a second signal are in coherence.
5. The method of claim 1 , wherein the first carrier frequency is 1.227 GHz and wherein the second carrier frequency is 1.57 GHz.
6. The method of claim 1 , wherein the first carrier frequency is 1.57 GHz and wherein the second carrier frequency is 1.227 GHz.
7. The method of claim 1 , wherein the ambiguous instantaneous phase of one or more of the complex first samples and complex second samples are 2π ambiguous.
8. The method of claim 1 , wherein the first signal includes more noise than the second signal.
9. The method of claim 1 , wherein the second signal includes more noise than the first signal.
10. A GNSS receiver comprising:
an antenna;
a front end;
an RF to baseband converter;
one or more analog to digital (A/D) converters;
a digital signal processing (DSP) processor; and
memory in communication with the DSP processor;
wherein the GNSS receiver is configured to:
receive, at the antenna, a first signal and a second signal, wherein at least the second signal includes noise, and wherein the first signal is characterized by a first carrier frequency, and wherein the second signal is characterized by a second carrier frequency;
filter, by the front end, at least a portion of the received first and second signals;
down convert, with the RF to baseband converter, the filtered first and second signals to respective first baseband and second baseband signals;
sample, with the one or more A/D converters, the first baseband and second baseband signals to produce complex first samples and complex second samples;
cross-correlating and accumulate the complex first samples and the complex second samples to obtain a result;
determine, with the DSP processor, non-ambiguous instantaneous first phase samples of the result;
produce normalized non-ambiguous instantaneous first phase samples by multiplying the non-ambiguous instantaneous first phase samples of the result by the second carrier frequency divided the first carrier frequency;
construct a normalized first counter rotation phasor by taking a complex exponential of a negated version of the normalized non-ambiguous instantaneous first phase samples;
generate a counter-rotated second observable by multiplying the complex second samples by the normalized first counter-rotation phasor;
apply a low pass filter to the counter-rotated second observable to remove noise; and
output the filtered second observable.
11. The system of claim 10 , wherein the first and second complex digital sequences are accumulated over an interval selected from a range between 1 ms and 100 ms.
12. The system of claim 10 , wherein the first carrier frequency is 1.227 GHz and wherein the second carrier frequency is 1.57 GHz.
13. The system of claim 10 , wherein the first carrier frequency is 1.57 GHz and wherein the second carrier frequency is 1.227 GHz.
14. The system of claim 10 , wherein the second signal includes more noise than the first signal.
15. The system of claim 10 , wherein the first signal includes more noise than the second signal.
16. A non-transitory computer readable storage medium storing instructions for use with one or more processors in communication with a memory, and wherein the instructions are configured to cause the one or more processors to perform a method comprising:
receiving, at a GNSS receiver, a first signal and a second signal, wherein at least the second signal includes noise, and wherein the first signal is characterized by a first carrier frequency, and wherein the second signal is characterized by a second carrier frequency;
down converting the first and second signals to respective first baseband and second baseband signals;
sampling the first baseband and second baseband signals to produce complex first samples and complex second samples;
cross-correlating and accumulating the complex first samples and the complex second samples to obtain a result;
determining ambiguous instantaneous first phase of the result;
determining non-ambiguous instantaneous first phase samples of the result;
producing normalized non-ambiguous instantaneous first phase samples by multiplying the non-ambiguous instantaneous first phase samples by the second carrier frequency divided the first carrier frequency;
constructing a normalized first counter rotation phasor by taking a complex exponential of a negated version of the normalized non-ambiguous instantaneous first phase samples;
generating a counter-rotated second observable by multiplying the complex second samples by the normalized first counter-rotation phasor;
applying a low pass filter to the counter-rotated second observable to remove noise; and
outputting the filtered second observable.
17. The computer readable storage medium of claim 16 , wherein sampling the first baseband and second baseband signals generates first and second digital sequences.
18. The computer readable storage medium of claim 16 , where accumulating the first and second complex digital sequences comprises accumulation over an interval selected from a range of 1 ms to 100 ms.
19. The computer readable storage medium of claim 16 , wherein the first carrier frequency is 1.227 GHz and wherein the second carrier frequency is 1.57 GHz.
20. The computer readable storage medium of claim 16 , wherein the first carrier frequency is 1.57 GHz and wherein the second carrier frequency is 1.227 GHz.