Interference mitigation for positioning systems

1. An interference removal filter comprising:

a first frequency translator operable to produce an altered input signal by altering a carrier frequency of an input signal from an initial value to a first value;

a first filter implemented in hardware and operable to pass the altered input signal over a frequency range of size B with a variation of less than +/−3 dB;

a second filter implemented in hardware and operable to pass the altered input signal over a second frequency range that is less than 25% of the size B;

a delay positioned before the first filter or the second filter to displace a peak value of an impulse response of the first filter and a peak value of an impulse response of the second filter in time from one another by at least 2/B time units

wherein outputs of the first filter and the second filter are combined to produce a filtered signal; and

a second frequency translator operable to produce an altered filtered signal by altering a carrier frequency of the filtered signal to a second value.

2. The interference removal filter of claim 1 , wherein the first filter and the second filter produce a notch in frequency at a frequency value within the frequency range of the size B.

3. The interference removal filter of claim 2 , wherein the first frequency translator is operable to alter the carrier frequency of the input signal to the first value so that the frequency value corresponds to the frequency of an undesired signal.

4. The interference removal filter of claim 2 , wherein the first frequency translator is operable to alter the carrier frequency of the input signal to the first value so that the frequency value is within 20% of a bandwidth of the notch from 0 Hz.

5. The interference removal filter of claim 1 , wherein the initial value and the second value are equal.

6. The interference removal filter of claim 1 , wherein the initial value and the second value are different.

7. The interference removal filter of claim 1 , wherein the interference removal filter further comprises:

a third filter implemented in hardware and operable to pass the altered filter signal;

a fourth filter implemented in hardware and operable to pass the altered filter signal;

another delay positioned before the third filter or the fourth filter to displace a peak value of an impulse response of the third filter and a peak value of an impulse response of the fourth filter in time from one another,

wherein outputs of the third filter and the fourth filter are combined to produce an additional filtered signal; and

a third frequency translator operable to produce an additional altered filtered signal by altering a carrier frequency of the additional filtered signal to a third value.

8. The interference removal filter of claim 7 , wherein the third filter is operable to pass the altered filter signal over the frequency range of the size B with the variation of less than +/−3 dB, wherein the fourth filter is operable to pass the altered filtered signal over the second frequency range that is less than 25% of the size B, wherein the first filter and the second filter produce a first notch in frequency at a first frequency value within the frequency range of the size B, and wherein the third filter and the fourth filter produce a second notch in frequency at a second frequency value within the frequency range of the size B.

9. The interference removal filter of claim 8 , wherein the first frequency value and the second frequency value are the same.

10. The interference removal filter of claim 8 , wherein the first frequency value and the second frequency value are different.

11. A method for removing interference, the computer-implemented method comprising:

producing an altered input signal by altering a carrier frequency of an input signal from an initial value to a first value;

passing, through a first filter, the altered input signal over a frequency range of size B with a variation of less than +/−3 dB;

passing, through a second filter, the altered input signal over a second frequency range that is less than 25% of the size B;

delaying the altered input signal before the altered input signal passes through the first filter or the second filter to displace a peak value of an impulse response of the first filter and a peak value of an impulse response of the second filter in time from one another by at least 2/B time units;

combining outputs of the first filter and the second filter to produce a filtered signal; and

producing an altered filtered signal by altering a carrier frequency of the filtered signal to a second value.

12. The method of claim 11 , wherein the method comprises: using the first filter and the second filter to produce a notch in frequency at a frequency value within the frequency range of the size B.

13. The method of claim 12 , wherein the method comprises: altering the carrier frequency of the input signal to the first value so that the frequency value corresponds to the frequency of an undesired signal.

14. The method of claim 12 , wherein the method comprises: altering the carrier frequency of the input signal to the first value so that the frequency value is within 20% of a bandwidth of the notch from 0 Hz.

15. The method of claim 11 , wherein the initial value and the second value are equal.

16. The method of claim 11 , wherein the initial value and the second value are different.

17. The method of claim 11 , wherein the method further comprises:

passing the altered filter signal through a third filter;

passing the altered filter signal through a fourth filter;

delaying the altered filter signal before the altered filter signal passes through the third filter or the fourth filter to displace a peak value of an impulse response of the third filter and a peak value of an impulse response of the fourth filter in time from one another;

combining outputs of the third filter and the fourth filter to produce an additional filtered signal; and

producing an additional altered filtered signal by altering a carrier frequency of the additional filtered signal to a third value.

18. The method of claim 17 , wherein the method comprises:

using the third filter to pass the altered filter signal over the frequency range of the size B with the variation of less than +/−3 dB;

using the fourth filter to pass the altered filtered signal over the second frequency range that is less than 25% of the size B;

using the first filter and the second filter to produce a first notch in frequency at a first frequency value within the frequency range of the size B; and

using the third filter and the fourth filter to produce a second notch in frequency at a second frequency value within the frequency range of the size B.

19. The method of claim 18 , wherein the first frequency value and the second frequency value are the same.

20. The method of claim 18 , wherein the first frequency value and the second frequency value are different.

21. One or more non-transitory machine-readable media embodying program instructions that, when executed by one or more machines, cause the one or more machines to implement a method for removing interference, the method comprising:

producing an altered input signal by altering a carrier frequency of an input signal from an initial value to a first value;

passing, through a first filter, the altered input signal over a frequency range of size B with a variation of less than +/−3 dB;

passing, through a second filter, the altered input signal over a second frequency range that is less than 25% of the size B;

delaying the altered input signal before the altered input signal passes through the first filter or the second filter to displace a peak value of an impulse response of the first filter and a peak value of an impulse response of the second filter in time from one another by at least 2/B time units;

combining outputs of the first filter and the second filter to produce a filtered signal; and

producing an altered filtered signal by altering a carrier frequency of the filtered signal to a second value.

22. The one or more non-transitory machine-readable media of claim 21 , wherein the method comprises: using the first filter and the second filter to produce a notch in frequency at a frequency value within the frequency range of the size B.

23. The one or more non-transitory machine-readable media of claim 22 , wherein the method comprises: altering the carrier frequency of the input signal to the first value so that the frequency value corresponds to the frequency of an undesired signal.

24. The one or more non-transitory machine-readable media of claim 22 , wherein the method comprises: altering the carrier frequency of the input signal to the first value so that the frequency value is within 20% of a bandwidth of the notch from 0 Hz.

25. The one or more non-transitory machine-readable media of claim 21 , wherein the initial value and the second value are equal.

26. The one or more non-transitory machine-readable media of claim 21 , wherein the initial value and the second value are different.

27. The one or more non-transitory machine-readable media of claim 21 , wherein the method further comprises:

passing the altered filter signal through a third filter;

passing the altered filter signal through a fourth filter;

delaying the altered filter signal before the altered filter signal passes through the third filter or the fourth filter to displace a peak value of an impulse response of the third filter and a peak value of an impulse response of the fourth filter in time from one another;

combining outputs of the third filter and the fourth filter to produce an additional filtered signal; and

producing an additional altered filtered signal by altering a carrier frequency of the additional filtered signal to a third value.

28. The one or more non-transitory machine-readable media of claim 27 , wherein the method comprises:

using the third filter to pass the altered filter signal over the frequency range of the size B with the variation of less than +/−3 dB;

using the fourth filter to pass the altered filtered signal over the second frequency range that is less than 25% of the size B;

using the first filter and the second filter to produce a first notch in frequency at a first frequency value within the frequency range of the size B; and

using the third filter and the fourth filter to produce a second notch in frequency at a second frequency value within the frequency range of the size B.

29. The one or more non-transitory machine-readable media of claim 28 , wherein the first frequency value and the second frequency value are the same.

30. The one or more non-transitory machine-readable media of claim 28 , wherein the first frequency value and the second frequency value are different.