High duty cycle radar with near/far pulse compression interference mitigation

• US 8,259,003 B2
• Filed: 05/14/2010
• Issued: 09/04/2012
• Est. Priority Date: 05/14/2010
• Status: Active Grant

• Current Assignee: Massachusetts Institute of Technology
• Original Assignee: Massachusetts Institute of Technology
• Inventors: Song, William S.
• Primary Examiner(s): Sotomayor, John B
• Application Number:
  US12/780,221
• Publication Number:
  US 20110279307A1
• Time in Patent Office: 844 Days
• Field of Search: 342/132, 342/134, 342/145, 342/195
• US Class Current: 342/132
• CPC Class Codes: G01S 13/282 using a frequency modulated carrier wave G01S13/286 takes precedence
• CPC Class Codes: G01S 7/023 Interference mitigation, e.g. reducing or avoiding non-intentional interference with other HF-transmitters, base station transmitters for mobile communication or other radar systems, e.g. using electro-magnetic interference [EMI] reduction techniques auxiliary means for detecting or identifying radar signals or the like G01S7/021; means for anti-jamming G01S7/36
• CPC Class Codes: G01S 7/0232 Avoidance by frequency multiplex
• CPC Class Codes: G01S 7/292 Extracting wanted echo-signals

Abstract

In conventional pulse compression processing, sidelobes from strong return signals may hide correlation peaks associated with weaker return signals. Example embodiments include methods of mitigating this near/far interference by weighting a received return signal or corresponding reference signal based the return signal'"'"'s time of arrival, then performing pulse compression using the weighted signal to produce a correlation peak that is not hidden by sidelobes from another return. Multi-frequency processing can also be used to reduce the pulse width of the transmitted pulses and received return signals, thereby mitigating near/far interference by decreasing the overlap between signals from nearby targets. Weighting can be combined with multi-frequency pulse transmission and reception to further enhance the fidelity of the processed correlation peak. Weighting and multi-frequency processing also enable higher duty cycles than are possible with conventional pulse compression radars.

Claims

1. A method of determining range information associated with a target, the method comprising:

receiving a near return signal reflected from a near target;

receiving a far return signal reflected from a far target, at least a portion of the far return signal overlapping in time with the near return signal;

generating a reference signal that corresponds to the far return signal;

weighting at least part of either the far return signal or the reference signal to produce a weighted far return signal or a weighted reference signal, respectively; and

performing pulse compression using the weighted far return signal or the weighted reference signal to determine range information associated with the far target that is at least partially free of interference from the near return signal.

2. The method of claim 1 wherein weighting the at least part of the far return signal or the reference signal includes applying a weighting function whose shape varies as a function of time delay associated with the far return signal.

3. The method of claim 2 wherein the width of the weighting function varies linearly with the time delay associated with the far return signal.

4. The method of claim 1 wherein weighting the at least part of the far return signal or the reference signal includes dividing the far return signal or the reference signal into sub-pulses based on a range to the far target.

5. The method of claim 1 further comprising:

determining an amount of overlap between the near and far return signals.

6. The method of claim 1 wherein performing pulse compression includes:

performing a Fourier transform of the weighted far return signal or the weighted reference signal to produce a frequency-domain weighted signal;

performing a Fourier transform of the reference signal or the far return signal to produce a frequency-domain unweighted signal;

multiplying the frequency-domain weighted signal with the frequency-domain unweighted signal to produce a frequency-domain product; and

performing an inverse Fourier transform of the frequency-domain product to produce the range information.

7. The method of claim 1 further comprising:

transmitting a pulse towards the near and far targets, the transmitted pulse reflecting off the near and far targets to produce the near and far return signals, respectively.

8. The method of claim 7 wherein the transmitted pulse is a coded pulse or an up-down chirp pulse.

9. The method of claim 7 wherein at least a portion of the transmitted pulse has a bandwidth that is substantially the same as the bandwidth of the entire transmitted pulse.

10. The method of claim 7 wherein performing pulse compression further includes applying a windowing function to the far return signal or the reference signal.

11. The method of claim 7 wherein the pulse is at a first carrier frequency and further comprising:

transmitting another pulse at a second carrier frequency;

receiving another near return signal reflected from the near target;

receiving another far return signal reflected from the far target, at least a portion of the other far return overlapping in time with the other near return signal;

generating another reference signal corresponding to the other far return signal;

weighting at least part of the other far return signal or the other reference signal to produce another weighted far return signal or another weighted reference signal, respectively;

performing pulse compression using the other weighted far return signal or the other weighted reference signal to determine additional range information associated with the far target; and

combining the additional range information with the range information to produce an enhanced estimate of a location of the far target.

12. An apparatus for determining range information associated with a target, the apparatus comprising:

an antenna configured to receive near and far return signals from near and far targets, respectively, at least a portion of the far return signal overlapping with the near return signal;

a weighting block operably coupled to the antenna and configured to weight at least part of far return signal or a reference signal corresponding to the far return signal to produce a weighted far return signal or a weighted reference signal, respectively; and

a pulse compression processor operably coupled to the weighting block and configured to determine range information associated with the far target by performing pulse compression processing on the weighted far return signal or the weighted reference signal.

13. The apparatus of claim 12 further comprising:

an analog-to-digital converter operably coupled to the antenna and the weighting block and configured to produce a digital representation of the far return signal, and wherein the weighting block is configured to weight the part of the portion of the far return signal by operating on the digital representation of the far return signal.

14. The apparatus of claim 12 further comprising:

a controller operably coupled to the weighting block and configured to control the weighting of the far return signal.

15. The apparatus of claim 12 further comprising:

a transmitter configured to transmit a pulse towards the near and far targets via the antenna, the transmitted pulse reflected by the near and far targets to form the near and far return signals, respectively.

16. The apparatus of claim 15 wherein the transmitter is further configured to modulate the transmitted pulse such that at least a portion of the transmitted pulse has a bandwidth that is substantially the same as the bandwidth of the entire transmitted pulse.

17. The apparatus of claim 15 wherein the transmitter is further configured to transmit pulses at different center frequencies towards the near and far targets, wherein the antenna is further configured to receive return signals at the different center frequencies.

18. The apparatus of claim 17 further comprising:

a filter operably coupled to the antenna and configured to discriminate between returns at the different center frequencies, and wherein the pulse compression processor is further configured to determine range information associated with at least one target using the return signals at the different center frequencies.

19. A method of processing a radar signal, the method comprising:

receiving a first return signal that overlaps in time with a second return signal;

sampling the first return signal to produce a first return vector;

weighting samples in the first return vector based on an amount of overlap between the first and second return signals to produce a weighted first return vector; and

processing the weighted first return vector to obtain range information.

20. The method of claim 19 further comprising:

receiving the second return signal and wherein receiving the first return signal begins after receiving the second return signal.

21. The method of claim 19 wherein sampling the first return signal includes zero-padding the first return vector.

22. The method of claim 19 wherein weighting samples in the first return vector includes adjusting an amplitude of samples in portions of the first return vector that include information associated with the second return signal.

23. The method of claim 19 wherein weighting samples in the first return vector includes setting samples to zero to mitigate interference from the second return signal.

24. The method of claim 19 wherein the amount of overlap is known a priori or estimated based on a priori knowledge.

25. The method of claim 19 further comprising:

determining the amount of overlap between the first and second return signals.

26. The method of claim 19 further comprising:

receiving a third return signal that overlaps in time with a fourth return signal;

sampling the third return signal to produce a second return vector;

weighting samples in the second return vector to produce a weighted second return vector that is at least partially free of interference from the fourth return signal;

processing the weighted second return vector to obtain range information that is substantially free of interference from the fourth return signal; and

combining the range information that is substantially free of interference from the fourth return signal with the range information that is substantially free of interference from the second return signal.

27. An apparatus for determining range information associated with a target, the apparatus comprising:

means for receiving a near return signal reflected from a near target and for receiving a far return signal reflected from a far target, at least a portion of the far return signal overlapping in time with the near return signal;

means for weighting at least part of the portion of the far return signal that overlaps with the near return signal to produce a weighted far return signal that is at least partially free of interference from the near return signal; and

means for performing pulse compression on the weighted far return signal to determine range information associated with the far target.

28. A method of determining range information associated with a target that is farther from a receiver than at least one other target, the method comprising:

receiving a plurality of return signals reflected from the target, each return signal being at a different carrier frequency;

generating a plurality of reference signals, each reference signal corresponding to a respective return signal;

weighting at least two of either the plurality of return signals or the plurality of reference signals to produce at least two weighted return signals or at least two weighted reference signals, respectively; and

performing pulse compression on the weighted return signals or the weighted reference signals to determine range information associated with the target that is at least partially free of interference from the at least one other target.