Localization of high speed vehicles using continuous transmit waves
View Patent ↗The selection of multiple, suitably designed, demodulation reference signals can enable the measurement of a vehicle's speed using continuously transmitted frequency modulated (CTFM) signals. The unique solution of vehicle speed can be used to resolve the range Doppler ambiguity found in conventional CTFM sonar and radar systems. This can enable continuous range and speed estimates of high-speed vehicles with an attendant reduction in transmit power relative to pulse-echo systems with similar measures of performance due to the 100% duty cycle.
1. A method of localizing a target comprising:
transmitting a continuous waveform signal;
receiving an echo signal from said target;
demodulating said echo signal to a baseband to obtain a demodulated echo signal;
estimating a rangewise Mach number, M r , based on combining energy in cells along hypothesized tracks of a frequency-time diagram for said demodulated echo signal; and
determining a first range of said target based on said rangewise Mach number.
2. The method of claim 1 , wherein estimating a rangewise Mach number comprises choosing a frequency detection binwidth, δf min , for said cells from a ratio between a minimum bandwidth of said continuous waveform signal, and a number of said cells in a cycle time, T.
3. The method of claim 1 , wherein estimating a rangewise Mach number comprises using matched filters having a minimum baseband frequency resolution, δf min , based on a ratio of an initial frequency of said continuous waveform signal, and a number of said cells in a cycle time, T.
4. The method of claim 1 , wherein demodulating comprises mixing said echo signal with said continuous waveform signal using at least one of dual extended duration interlaced demodulation signals, and dual frequency band demodulation signals.
5. The method of claim 1 , wherein demodulating comprises:
mixing said echo signal with said continuous waveform signal using dual frequency band demodulation reference signals to demodulate said echo signal to a pass band to obtain a demodulated echo signal; and
demodulating said demodulated echo signal to bring said demodulated echo signal down to said baseband.
6. The method of claim 5 further comprising band passing said demodulated echo signal.
7. The method of claim 1 , wherein transmitting said continuous waveform signal further comprises:
determining a frequency separation;
transmitting a continuous waveform upsweep signal; and
transmitting a concurrent continuous waveform downsweep signal, said upsweep signal and said downsweep signal having said frequency separation.
8. The method of claim 7 , wherein demodulating said echo signal further comprises:
demodulating an upsweep echo signal to baseband to obtain an upsweep baseband frequency for said upsweep echo signal; and
demodulating a downsweep echo signal to baseband to obtain a downsweep baseband frequency for said downsweep echo signal.
9. The method of claim 8 , wherein determining a range further comprises combining said upsweep baseband frequency and said downsweep baseband frequency to determine a range rate and a second range of said target.
10. The method of claim 9 , wherein combining said upsweep baseband frequency and said downsweep baseband frequency comprises:
determining a sum and a difference of said upsweep baseband frequency and said downsweep baseband frequency to determine said range rate and said second range, respectively, of said target; and
combining said first range and said second range to localize said target.
11. The method of claim 1 , wherein determining said first range comprises:
estimating a frequency difference, Δf, between said transmit signal and said echo signal; and
solving for said range using the relationship:
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where
f 0 is an initial frequency of said continuous waveform signal, and
T 0 is and observation time less than a cycle time T.
12. A system for localizing a target comprising:
a transmitter to transmit a continuous waveform signal;
a receiver to receive an echo signal from said target; and
a signal processor to demodulate said echo signal to baseband, estimate a rangewise Mach number, M r , based on combining energy in cells along hypothesized tracks of a frequency-time diagram for said demodulated echo signal, and determine a range of said target based on said rangewise Mach number.
13. A system for localizing a target comprising:
means for transmitting a continuous waveform signal;
means for receiving an echo signal from said target;
means for demodulating said echo signal to baseband;
means for estimating a rangewise Mach number, M r , based on combining energy in cells along hypothesized tracks of a frequency-time diagram for said demodulated echo signal;
means for determining a range of said target based on said rangewise Mach number.
14. A computer-readable medium containing instructions for controlling a computer system to localize a target by controlling said computer system to:
transmit a continuous waveform signal;
receive an echo signal from said target;
demodulate said echo signal to baseband;
estimate a rangewise Mach number, M r , based on combining energy in cells along hypothesized tracks of a frequency-time diagram for said demodulated echo signal; and
determine a range of said target based on said rangewise Mach number.
15. The computer-readable medium of claim 14 , wherein said instructions to estimate a rangewise Mach number comprise instructions to choose a frequency detection binwidth, δf min , for said cells from a ratio of a minimum bandwidth of said continuous waveform signal, and a number of said cells in a cycle time, T.
16. The computer-readable medium of claim 14 , wherein said instructions to estimate a rangewise Mach number comprise instructions to use matched filters having a minimum baseband frequency resolution, δf min , based on a ratio of an initial frequency of said continuous waveform signal, and a number of said cells in a cycle time, T.
17. The computer-readable medium of claim 14 , wherein said instructions to demodulate comprise instructions to mix said echo signal with said continuous waveform signal using at least one of dual extended duration interlaced demodulation signals, and dual frequency band demodulation signals.
18. The computer-readable medium of claim 14 , wherein said instructions to demodulate comprise instructions to:
mix said echo signal with said continuous waveform signal using dual frequency band demodulation reference signals to demodulate said echo signal to a pass band to obtain a demodulated echo signal; and
demodulate said demodulated echo signal to bring said demodulated echo signal down to said baseband.
19. The computer-readable medium of claim 18 further comprising instructions to band pass said demodulated echo signal.
20. The computer-readable medium of claim 14 , wherein said instructions to transmit said continuous waveform signal further comprise instructions to:
determine a frequency separation;
transmit a continuous waveform upsweep signal; and
transmit a concurrent continuous waveform downsweep signal, said upsweep signal and said downsweep signal having said frequency separation.
21. The computer-readable medium of claim 20 , wherein said instructions to demodulate said echo signal further comprise instructions to:
demodulate an upsweep echo signal to baseband to obtain an upsweep baseband frequency for said upsweep echo signal; and
demodulate a downsweep echo signal to baseband to obtain a downsweep baseband frequency for said downsweep echo signal.
22. The computer-readable medium of claim 21 , wherein said instructions to determine a range further comprise instructions to combine said upsweep baseband frequency and said downsweep baseband frequency to determine a range rate and a second range of said target.
23. The computer-readable medium of claim 22 , wherein said instructions to combine said upsweep baseband frequency and said downsweep baseband frequency comprise instructions to:
determine a sum and a difference of said upsweep baseband frequency and said downsweep baseband frequency to determine said range rate and said second range, respectively, of said target; and
combine said first range and said second range to localize said target.
24. The computer-readable medium of claim 14 , wherein said instructions to determine said first range comprise instructions to:
estimate a frequency difference, Δf, between said transmit signal and said echo signal; and
solve for said range using the relationship:
r
=
-
c
2
f
.
o
(
1
-
2
M
r
)
[
Δ
f
(
1
-
M
r
)
+
2
M
r
f
o
+
4
M
r
(
1
-
M
r
)
f
.
o
T
0
]
,
where
f 0 is an initial frequency of said continuous waveform signal, and
T 0 is and observation time less than a cycle time T.