Processing of signals to provide a delay Doppler map

Patent metadata

Field	Value
Publication number	US-9465115-B2
Application number	US-201313918618-A
Country	US
Kind code	B2
Filing date	Jun 14, 2013
Priority date	Jun 15, 2012
Publication date	Oct 11, 2016
Grant date	Oct 11, 2016

Abstract

An apparatus is disclosed for processing a sequence of samples of a received signal R reflected by a target surface and having a delay and a frequency shift relative to a reference signal D to obtain a delay Doppler map for the reflected signal. A first correlation module can obtain partial correlations z(n′, k) between samples corresponding to the reflected signal R and a samples corresponding to the reference signal D, across a set of delays. An inverse discrete fourier transform (DFT) of a sequence of samples can be derived from at least DFTs of a first reflected signal sequence and second reference signal sequence.

First claim

The invention claimed is:

1. A method of processing a reflected signal R having a delay and a frequency shift relative to a reference signal D to obtain a delay Doppler map, the method comprising:
a signal receiver receiving a sequence of samples x r (n) corresponding to the reflected signal R transmitted from a satellite and reflected to the signal receiver by a target area, and the signal receiver receiving a sequence of samples x d (n) corresponding to said reference signal D;
a signal processor obtaining a plurality of partial correlations z(n′, k) between the sequence of samples x r (n) corresponding to the reflected signal and the sequence of samples x d (n) corresponding to the reference signal received by the signal receiver, across a set of delays, to provide a set of partial correlation samples for each delay, each partial correlation sample of a set corresponding to a different partial correlation for that delay, wherein obtaining a number of partial correlations of said plurality of partial correlations, providing one partial correlation sample for each delay, comprises:
obtaining discrete fourier transforms (DFTs) of at least a first and an associated second sequence of samples, the first sequence including at least one subsequence of the reflected signal and the second sequence comprising at least one associated subsequence of the reference signal, and obtaining an inverse DFT of a sequence of samples derived from at least a product of said DFTs of the first and second sequences;
the signal processor obtaining a DFT for each set of partial correlation samples to determine a correlation between sequences of samples across a plurality of frequency shifts at each delay of the set of delays; and
the signal processor outputting the delay Doppler map representing the energy received from the target area, which reflects the reflected signal R, transmitted from the satellite, to the signal receiver, as a function of delay and Doppler shift, using the determined correlation between the sequences of samples.

2. A method according to claim 1 , wherein each set of partial correlation samples includes a number N′ of partial correlation samples, and wherein obtaining the DFT of each set comprises:
computing an N′-point fast fourier transform FFT.

3. A method according to claim 2 , wherein the set of delays includes K delays and each of the first and second sequences includes 2K samples, and wherein obtaining the DFTs of the first and second sequences comprises:
computing 2K-point FFTs and obtaining the inverse DFT comprises computing a 2K-point inverse DFT.

4. A method according to claim 3 , wherein obtaining a number of partial correlations providing one partial correlation sample for each delay comprises:
multiplying each sample of the DFT of the first sequence with a corresponding sample of the DFT of the second sequence to form a product of the DFTs, wherein obtaining the inverse DFT of a sequence of samples derived from at least a product of said DFTs comprises:
obtaining the inverse DFT directly on said product of the DFTs.

5. A method according to claim 3 , wherein obtaining the number of partial correlations providing one partial correlation sample for each delay comprises:
obtaining DFTs of each of a plurality of first sequences of samples, comprising said first sequence of samples, to provide a plurality of first transformed sequences, each of the plurality of first sequences of samples comprising samples of at least one respective subsequence of the reflected signal; and
obtaining DFTs of each of a plurality of second sequences of samples, comprising said second sequence of samples, to obtain a plurality of second transformed sequences, each of the plurality of second sequences of samples comprising samples of at least one respective associated subsequence of the reference signal;
multiplying each sample of each of the first transformed sequences with a corresponding sample of an associated second transformed sequence to provide a plurality of transformed product sequences; and
summing the transformed product sequences to provide a summed product sequence, wherein obtaining the inverse DFT of a sequence of samples derived from at least a product of said DFTs of the first and second sequences comprises:
obtaining the inverse DFT of the summed product sequence.

6. A method according to claim 1 , wherein the set of delays includes K delays and each of the first and second sequences includes 2K samples, and wherein obtaining the DFTs of the first and second sequences comprises:
computing 2K-point FFTs and obtaining the inverse DFT comprises computing a 2K-point inverse DFT.

7. A method according to claim 1 , wherein obtaining the number of partial correlations providing one partial correlation sample for each delay comprises:
multiplying each sample of the DFT of the first sequence with a corresponding sample of the DFT of the second sequence to form a product of the DFTs, wherein obtaining the inverse DFT of a sequence of samples derived from at least a product of said DFTs comprises:
obtaining the inverse DFT directly on said product of the DFTs.

8. A method according to claim 1 , wherein obtaining the number of partial correlations providing one partial correlation sample for each delay comprises:
obtaining DFTs of each of a plurality of first sequences of samples, comprising said first sequence of samples, to provide a plurality of first transformed sequences, each of the plurality of first sequences of samples comprising samples of at least one respective subsequence of the reflected signal; and
obtaining DFTs of each of a plurality of second sequences of samples, comprising said second sequence of samples, to obtain a plurality of second transformed sequences, each of the plurality of second sequences of samples comprising samples of at least one respective associated subsequence of the reference signal;
multiplying each sample of each of the first transformed sequences with a corresponding sample of an associated second transformed sequence to provide a plurality of transformed product sequences; and
summing the transformed product sequences to provide a summed product sequence, wherein obtaining the inverse DFT of a sequence of samples derived from at least a product of said DFTs of the first and second sequences comprises:
obtaining the inverse DFT of the summed product sequence.

9. A method according to claim 8 , wherein the plurality of first sequences includes at least two first sequences, and the plurality of second sequences includes at least two second sequences.

10. A method according to claim 1 , comprising:
forming said at least one subsequence of the reflected signal and said at least one subsequence of the reference signal form part of a plurality of subsequences of K samples of the reflected signal and the reference signal respectively, wherein each partial correlation for a specific delay corresponds to a contiguous segment of the reflected signal, comprising one or more of the plurality of subsequences, and an associated contiguous segment of the reference signal, comprising one or more associated subsequences of the plurality of subsequences of the reference signal; and
wherein a subsequence of the plurality of subsequences of the sequence of samples corresponding to the reflected signal x r (n) comprises samples x r (n+iK), and a subsequence of the plurality of subsequences of the sequences of samples corresponding to the reference signal x d (n) comprises samples x d (n+iK), where 0≦n<K and i=0, 1, 2 . . . .

11. A method according to claim 10 , comprising:
forming each of the first sequences of samples x r i and each of the second seque

Assignees

• Astrium Ltd
• Airbus Defence & Space Ltd

Inventors

• Wishart Alexander Walker

Classifications

• G01S19/14 Primary

  specially adapted for specific applications · CPC title

• G01S13/955

  mounted on satellite · CPC title

• G01S13/003

  Bistatic radar systems; Multistatic radar systems · CPC title

• G01S19/42 Primary

  Determining position · CPC title

• G01S19/37

  Hardware or software details of the signal processing chain · CPC title