Ultra-wideband radar system using sub-band coded pulses

• US 6,989,782 B2
• Filed: 05/21/2004
• Issued: 01/24/2006
• Est. Priority Date: 05/22/2003
• Status: Active Grant

• Current Assignee: General Atomics, Inc.
• Original Assignee: General Atomics, Inc.
• Inventors: Walker, Michael L., Askar, Naiel K., Rogerson, Gerald D., Furuno, David S.
• Primary Examiner(s): Gregory, Bernarr E.
• Application Number:
  US10/851,635
• Publication Number:
  US 20050179585A1
• Time in Patent Office: 613 Days
• Field of Search: 342/21, 342 70- 72, 342 82-103, 342/118, 342128-146, 342/175, 342188-197, 342200-205
• US Class Current: 342/134
• CPC Class Codes: G01S 13/0209 Systems with very large relative bandwidth, i.e. larger than 10 %, e.g. baseband, pulse, carrier-free, ultrawideband
• CPC Class Codes: G01S 13/282 using a frequency modulated carrier wave G01S13/286 takes precedence
• CPC Class Codes: G01S 13/284 using coded pulses

Abstract

Methods and apparatus are provided for radar systems using multiple pulses that are shorter than the expected range delay extent of the target to be imaged. In one implementation, a method for performing radar includes the steps of: transmitting a plurality of pulses, each pulse having a different center frequency and a time duration shorter than an expected range delay extent of a target, wherein a total bandwidth is defined by a bandwidth occupied by the plurality of pulses; receiving reflections of the plurality of pulses; and performing pulse compression on the received pulse reflections to generate a detection signal having a radar resolution approximately equivalent to the transmission and reception of a single pulse having the total bandwidth. In preferred form, the pulses comprise ultrawideband (UWB) pulses each occupying a sub-band of the overall system bandwidth.

Claims

1. A method for performing radar comprising:

transmitting a plurality of pulses, each pulse having a different center frequency and a time duration shorter than an expected range delay extent of a target, wherein a total bandwidth is defined by a bandwidth occupied by the plurality of pulses;

receiving reflections of the plurality of pulses; and

performing pulse compression on the received pulse reflections to generate a detection signal having a radar resolution approximately equivalent to the transmission and reception of a single pulse having the total bandwidth.

2. The method of claim 1 wherein a bandwidth of at least one pulse is at least twenty percent of a center frequency of the pulse.

3. The method of claim 1 wherein a bandwidth of at least one pulse is at least 500 MHz.

4. The method of claim 1 wherein the transmitting step comprises:

transmitting the plurality of pulses such that at least two of the plurality of pulses overlap in time.

5. The method of claim 1 wherein the transmitting step comprises:

transmitting the plurality of pulses such that each pulse occupies a different one of a plurality of time slots.

6. The method of claim 1 wherein the total bandwidth is divided into frequency sub-bands, each pulse occupying a respective frequency sub-band.

7. The method of claim 1 wherein the receiving step comprises:

receiving the reflections of the plurality of pulses using a matched filter receiver based on a frequency and time sequence of the transmitted plurality of pulses.

8. The method of claim 1 further comprising:

aligning the received reflections in time prior to performing the pulse compression.

9. The method of claim 1 wherein the receiving step comprises:

generating I and Q data corresponding to the received reflections.

10. The method of claim 9 further comprising:

sampling the I and Q data for at least one range.

11. The method of claim 10 wherein the sampling step comprises:

sampling the I and Q data using an analog to digital converter for said at least one range.

12. The method of claim 10 wherein the sampling step further comprises:

sampling the I and Q data using the analog to digital converter two or more times per received pulse reflection for said at least one range.

13. The method of claim 10 wherein the sampling step comprises:

sampling the I and Q data using a track and hold circuit for said at least one range.

14. The method of claim 10 wherein the performing step comprises:

performing a discrete Fourier transform on the sampled I and Q data for said at least one range to produce a real output and an imaginary output;

squaring the real output;

squaring the imaginary output; and

summing the squared real output and the squared imaginary output to produce the detection signal.

15. The method of claim 1 wherein the receiving step comprises:

generating I and Q data corresponding to the received reflections;

the method further comprising;

generating a real component of an intermediate quantity for each received reflection;

generating an imaginary component of the intermediate quantity for each received reflection, the intermediate quantity defined as;

e<sup>−

j2π

ƒ

kt</sup>(I_k(t)+jQ_k(t)),

where I_k(t) is the I data as a function of time, where Q_k(t) is the Q data as a function of time, and where ƒ

_k is a center frequency of the k^th received reflection.

16. The method of claim 15 further comprising:

aligning the real components in time for the received reflections;

aligning the imaginary components in time for the received reflections; and

wherein the performing step comprises;

summing the real components to produce a first sum;

summing the imaginary components to produce a second sum;

squaring the first sum to produce a first squared sum;

squaring the second sum to produce a second squared sum; and

summing the first squared sum and the second squared sum to produce the detection signal.

17. The method of claim 15 further comprising:

using a track and hold circuit to align a sum of the real components and a sum of the imaginary components in time for the received reflections;

wherein the performing step comprises;

squaring the sum of the real components to produce a first squared sum;

squaring the sum of the imaginary components to produce a second squared sum; and

summing the first squared sum and the second squared sum to produce the detection signal.

18. The method of claim 1 wherein the transmitting step comprises:

transmitting the plurality of pulses according to a defined frequency and time sequence from a first radar transmitting device;

the method further comprising;

using a matched filter based on the defined frequency and time sequence on the received reflections in order to improve the signal to noise and interference ratio of the received reflections in the presence of a second radar transmitting device.

19. The method of claim 1 wherein the transmitting step comprises:

transmitting the plurality of pulses according to a defined frequency and time sequence; and

varying the defined frequency and time sequence based on channel conditions.

20. The method of claim 1 wherein the transmitting step comprises:

transmitting multiple sets of the plurality of pulses varying a defined frequency and time sequence for the transmission of each set;

the method further comprising;

constructing a combined profile signal based on the detection signal generated from the received reflections of the plurality of pulses for each of the multiple sets, wherein aliasing of ranges is reduced.

21. The method of claim 20 wherein the transmitting the multiple sets comprises:

transmitting the multiple sets of the plurality of pulses randomly varying the defined frequency and time sequence for the transmission of each set.

22. The method of claim 20 wherein the constructing comprises:

integrating the detection signals from the received reflections of the plurality of pulses for each of the multiple sets.

23. The method of claim 20 wherein the constructing comprises:

averaging the detection signals from the received reflections of the plurality of pulses for each of the multiple sets.

24. The method of claim 1 wherein the transmitting step comprises:

transmitting the plurality of pulses according to a defined frequency and time sequence from a first radar transmitting device;

wherein the defined frequency and time sequence is selected to be different than frequency and time sequences of other collocated radar transmitting devices.

25. The method of claim 24 wherein the frequency and time sequence is selected to be substantially orthogonal to the frequency and time sequences of the other collocated radar transmitting devices.

26. The method of claim 24 further comprising:

varying the defined frequency and time sequence over time based on channel conditions in use.

27. The method of claim 1 wherein the detection signal is approximately |D(t)|²,

where $D$

(t)=∑

k=0N-1⁢

⁢

ⅇ

-jω

k⁢

t⁢

Zk⁡

(t),

where Z_k(t)=I_k(t)+jQ_k(t)

where I_k(t) is I data and Q_k(t) is Q data generated from the received reflection of the k^th frequency pulse; and

where N is a total number of the pulses.

28. An apparatus for performing radar comprising:

means for transmitting a plurality of pulses, each pulse having a different center frequency and a time duration shorter than an expected range delay extent of a target, wherein a total bandwidth is defined by a bandwidth occupied by the plurality of pulses;

means for receiving reflections of the plurality of pulses; and

means for performing pulse compression on the received pulse reflections to generate a detection signal having a radar resolution approximately equivalent to the transmission and reception of a single pulse having the total bandwidth.

29. An apparatus for performing radar comprising:

an antenna;

a switch coupled to the antenna that switches between transmitting and receiving;

a transmitter coupled to the switch, the transmitter configured to transmit a plurality of pulses, each pulse having a different center frequency and a time duration shorter than an expected range delay extent of a target, wherein a total bandwidth is defined by a bandwidth occupied by the plurality of pulses; and

a receiver coupled to the switch, the receiver comprising;

a pulse compression module configured to perform pulse compression on received pulse reflections of the plurality of pulses to generate a detection signal having a radar resolution approximately equivalent to the transmission and reception of a single pulse having the total bandwidth.

30. The apparatus of claim 29 wherein the transmitter is configured to transmit the plurality of pulses such that a bandwidth of at least one pulse is at least twenty percent of a center frequency of the pulse.

31. The apparatus of claim 29 wherein the transmitter is configured to transmit the plurality of pulses such that a bandwidth of at least one pulse is at least 500 MHz.

32. The apparatus of claim 29 wherein the transmitter is configured to transmit the plurality of pulses such that at least two of the plurality of pulses overlap in time.

33. The apparatus of claim 32 wherein the receiver comprises a matched filter receiver based on a frequency and time sequence of the transmitted plurality of pulses.

34. The apparatus of claim 29 wherein the transmitter is configured to transmit the plurality of pulses such that each pulse occupies a different one of a plurality of time slots.

35. The apparatus of claim 29 wherein the transmitter is configured to transmit the plurality of pulses such that the total bandwidth is divided into frequency sub-bands, each pulse occupying a respective frequency sub-band.

36. The apparatus of claim 29 wherein the receiver further comprises:

a pulse detector coupled to the switch and configured to receive the received reflections; and

a decoder coupled to the pulse detector and configured to align the received reflections in time prior to being input to the pulse compression module.

37. The apparatus of claim 29 wherein the pulse detector comprises:

an IQ downconverter configured to convert the received reflections of the plurality of pulses into corresponding I and Q data.

38. The apparatus of claim 37 wherein the decoder comprises:

a sampler configured to sample the I and Q data for at least one range.

39. The apparatus of claim 38 wherein the sampler comprises an analog to digital converter.

40. The apparatus of claim 39 wherein the pulse compression module comprises:

a discrete Fourier transform module coupled to the sampler, the discrete Fourier transform module configured to perform a discrete Fourier transform on the sampled I and Q data for said at least one range and output a real output and an imaginary output;

a squarer coupled to the discrete Fourier transform module, the squarer configured to square the real output and square the imaginary output for each of said at least one range; and

a summer coupled to the output of the squarer and configured to sum squared real output and the squared imaginary output to produce the detection signal.

41. The apparatus of claim 29 wherein the pulse detector comprises:

an IQ downconverter configured to convert the received reflections of the plurality of pulses into corresponding I and Q data;

wherein the receiver further comprises;

a combiner circuit coupled to an output of the IQ downconverter and configured to generate a real component and an imaginary component of an intermediate quantity for each received reflection, the intermediate quantity defined as;

e <sup>−

j2π

ƒ

kt</sup>(I_k(t)+jQ_k(t)),

where I_k(t) is the I data as a function of time, where Q_k(t) is the Q data as a function of time, and where ƒ

_k is a center frequency of the k^th received reflection.

42. The apparatus of claim 41 further comprising:

a delay circuit coupled to an output of the combiner circuit and configured to align the real components in time for the received reflections and align the imaginary components in time for the received reflections;

wherein the pulse compression module comprises;

a first summer coupled to an output of the delay circuit to sum the real components to produce a first sum;

a second summer coupled to the output of the delay circuit to sum the imaginary components to produce a second sum;

a first squarer coupled to an output of the first summer and configured to square the first sum to produce a first squared sum;

a second squarer coupled to an output of the second summer and configured to square the second sum to produce a second squared sum;

a third summer coupled to an output of the first squarer and an output of the second squarer and configured to sum the first squared sum and the second squared sum to produce the detection signal.

43. The apparatus of claim 41 further comprising:

a first track and hold circuit coupled to an output of the combiner circuit and configured to align a sum of the real components in time for the received reflections;

a second track and hold circuit coupled to an output of the combiner circuit and configured to align a sum of the imaginary components in time for the received reflections;

wherein the pulse compression module comprises;

a first squarer coupled to an output of the first track and hold circuit and configured to square the sum of the real components to produce a first squared sum;

a second squarer coupled to an output of the second track and hold circuit and configured to square the sum of the imaginary components to produce a second squared sum;

a summer coupled to an output of the first squarer and an output of the second squarer and configured to sum the first squared sum and the second squared sum to produce the detection signal.

44. The apparatus of claim 29 wherein the transmitter comprises:

a pulse generator coupled to the switch; and

an encoder coupled to the pulse generator, the encoder configured to cause the pulse generator to transmit the plurality of pulses according to a defined frequency and time sequence;

wherein the receiver further comprises;

a matched filter based on the defined frequency and time sequence on the received reflections in order to improve the signal to noise and interference ratio of the received reflections in the presence of another radar transmitting device.

45. The apparatus of claim 29 wherein the transmitter comprises:

a pulse generator coupled to the switch; and

an encoder coupled to the pulse generator, the encoder configured to cause the pulse generator to transmit the plurality of pulses according to a defined frequency and time sequence;

wherein the receiver further comprises;

a channel estimator configured to take a measurement relating to the received reflections,

wherein the encoder is further coupled to the channel estimator and is configured to cause the pulse generator to vary the defined frequency and time sequence based on the measurement.

46. The apparatus of claim 29 wherein the transmitter comprises:

a pulse generator coupled to the switch; and

an encoder coupled to the pulse generator, the encoder configured to cause the pulse generator to transmit multiple sets of the plurality of pulses varying a defined frequency and time sequence for the transmission of each set;

wherein the receiver further comprises;

a range profile combiner coupled to the pulse compression module and adapted to construct a range profile based on the detection signal generated from the received reflections of the plurality of pulses for each of the multiple sets, wherein aliasing of ranges is reduced.

47. The apparatus of claim 29 wherein the transmitter comprises:

a pulse generator coupled to the switch; and

an encoder coupled to the pulse generator, the encoder configured to cause the pulse generator to transmit the plurality of pulses according to a defined frequency and time sequence, wherein the defined frequency and time sequence is selected to be different than frequency and time sequences of other collocated radar transmitting devices.

48. The apparatus of claim 47 wherein the encoder is configured to select the frequency and time sequence to be substantially orthogonal to the frequency and time sequences of the other collocated radar transmitting devices.

49. The apparatus of claim 47 wherein the encoder is configured to vary the defined frequency and time sequence over time based on channel conditions in use.

50. The apparatus of claim 29 wherein the detection signal output from the pulse compression module is approximately |D(t)|²,

where $D$

(t)=∑

k=0N-1⁢

⁢

ⅇ

-jω

k⁢

t⁢

Zk⁡

(t),

where Z_k(t)=I_k(t)+jQ_k(t)

where I_k(t) is I data and Q_k(t) is Q data generated from the received reflection of the k^th frequency pulse; and

where N is a total number of the pulses.