Distributed sensing of signals linked by sparse filtering

• US 8,787,501 B2
• Filed: 01/12/2010
• Issued: 07/22/2014
• Est. Priority Date: 01/14/2009
• Status: Expired due to Fees

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Vetterli, Martin, Hormati, Ali, Roy, Olivier, Lu, Yue M.
• Primary Examiner(s): Ahn, Sam K
• Assistant Examiner(s): Ali, Shawkat M
• Application Number:
  US12/686,183
• Publication Number:
  US 20100177906A1
• Time in Patent Office: 1,652 Days
• Field of Search: 375/130, 375/136, 375/219, 375/316, 375/340, 375/343, 375/260, 375/285, 381/71.8, 381/71.11, 381/74, 600/300, 702/8, 702/189, 708/290, 708/313, 708/404, 708/405, 714/794, 370/241
• US Class Current: 375/316
• CPC Class Codes: A61B 5/121 evaluating hearing capacity
• CPC Class Codes: A61B 5/318 Heart-related electrical modalities, e.g. electrocardiography [ECG]
• CPC Class Codes: A61B 5/7257 using Fourier transforms
• CPC Class Codes: G06F 2218/12 Classification; Matching
• CPC Class Codes: H04R 25/407 Circuits for combining signals of a plurality of transducers
• CPC Class Codes: H04R 25/552 Binaural

Abstract

Certain aspects of the present disclosure provide methods for distributed sensing and centralized reconstruction of two correlated signals, modeled as the input and output of an unknown sparse filtering operation.

Claims

1. A method of reconstructing a pair of signals, comprising:

observing with a first sensor first samples of a first signal;

observing with a second sensor second samples of a second signal, wherein the first signal is linked to the second signal by an unknown filter;

exploiting the knowledge that the first and the second signal are linked by the unknown filter for reconstructing said first signal and said second signal from said first samples and said second samples, wherein each of a number of the first samples and a number of the second samples observed is below a minimal number of samples given by a Nyquist relation;

receiving discrete Fourier transform (DFT) coefficients of said first signal and said second signal, the DFT coefficients including K+1 coefficients for each of the first signal and the second signal and complementary subsets of remaining DFT coefficients for each of the first signal and the second signal, wherein K is a number of non-zero elements of an impulse response of the unknown filter;

computing 2K consecutive DFT coefficients of the unknown filter and building a matrix using the received DFT coefficients of the first and second signals and an annihilating filter technique, wherein said matrix is a Toeplitz matrix and has rank-K;

obtaining the impulse response of the unknown filter using the computed 2K DFT coefficients;

reconstructing the first signal using the impulse response of the unknown filter and the received DFT coefficients of the second signal; and

reconstructing the second signal using the impulse response of the unknown filter and the received DFT coefficients of the first signal.

2. An apparatus for reconstructing a pair of signals, comprising:

a receiver configured to observe first samples of a first signal;

wherein the receiver is further configured to receive second samples of a second signal and wherein the first signal is linked to the second signal by an unknown filter;

a reconstructing circuit configured to reconstruct said first signal and said second signal from said first and second samples, wherein said reconstructing circuit exploits the knowledge that the first and the second signal are linked by the unknown filter and wherein each of a number of the first samples and a number of the second samples observed is below a minimal number of samples given by a Nyquist relation, wherein the receiver is further configured to receive discrete Fourier transform (DFT) coefficients of said first and second signals, the DFT coefficients including K+1 coefficients for each of the first and second signals and complementary subsets of remaining DFT coefficients for each of the first and second signals, wherein K is a number of non-zero elements of an impulse response of the unknown filter;

a calculator configured to compute 2K consecutive DFT coefficients of the unknown filter and build a matrix using the received DFT coefficients of the first and second signals and an annihilating filter technique, wherein said matrix is a Toeplitz matrix and has rank-K;

a circuit configured to obtain the impulse response of the unknown filter using the computed 2K DFT coefficients;

a circuit configured to reconstruct the first signal using the impulse response of the unknown filter and the received DFT coefficients of the second signal; and

a circuit configured to reconstruct the second signal using the impulse response of the unknown filter and the received DFT coefficients of the first signal.

3. A method for signal processing, comprising:

receiving discrete Fourier transform (DFT) coefficients of a first signal and a second signal, the DFT coefficients including K+1 coefficients for each of the first and second signals and complementary subsets of remaining DFT coefficients for each of the first and second signals, wherein K is a number of non-zero elements of an impulse response of an unknown filter and wherein the first signal is linked to the second signal by the unknown filter;

computing 2K consecutive DFT coefficients of a filter matrix using the received DFT coefficients of the first and second signals, wherein said matrix has rank-K and is a Toeplitz matrix;

obtaining the impulse response of the unknown filter using the computed 2K DFT coefficients;

reconstructing the first signal using the impulse response of the unknown filter and the received DFT coefficients of the second signal; and

reconstructing the second signal using the impulse response of the unknown filter and the received DFT coefficients of the first signal, wherein the unknown filter comprises a piecewise bandlimited filter.

4. The method of claim 3, wherein the unknown filter comprises a piecewise polynomial filter.

5. An apparatus for signal processing, comprising:

a receiver configured to receive discrete Fourier transform (DFT) coefficients of a first signal and a second signal, the DFT coefficients including K+1 coefficients for each of the first and second signals and complementary subsets of remaining DFT coefficients for each of the first and second signals, wherein K is a number of non-zero elements of an impulse response of an unknown filter and wherein the first signal is linked to the second signal by the unknown filter;

a computer configured to compute 2K consecutive DFT coefficients of a filter matrix using the received DFT coefficients of the first and second signals, wherein said matrix has rank-K and is a Toeplitz matrix;

a calculator configured to obtain the impulse response of the unknown filter using the computed 2K DFT coefficients;

a first reconstructing circuit configured to reconstruct the first signal using the impulse response of the unknown filter and the received DFT coefficients of the second signal; and

a second reconstructing circuit configured to reconstruct the second signal using the impulse response of the unknown filter and the received DFT coefficients of the first signal, wherein the unknown filter comprises a piecewise bandlimited filter.

6. The apparatus of claim 5, wherein said apparatus is a headset.

7. The apparatus of claim 5, wherein said apparatus is a monitor for monitoring patient vital signs.

8. The apparatus of claim 5, wherein the unknown filter comprises a piecewise polynomial filter.

9. An apparatus for signal processing, comprising:

means for receiving discrete Fourier transform (DFT) coefficients of a first signal and a second signal, the DFT coefficients including K+1 coefficients for each of the first and second signals and complementary subsets of remaining DFT coefficients for each of the first and second signals, wherein K is a number of non-zero elements of an impulse response of an unknown filter and wherein the first signal is linked to the second signal by the unknown filter;

means for computing 2K consecutive DFT coefficients of the unknown filter using the received DFT coefficients of the first and second signals, wherein said matrix has rank-K and is a Toeplitz matrix;

means for obtaining the impulse response of the unknown filter using the computed 2K DFT coefficients;

means for reconstructing the first signal using the impulse response of the unknown filter and the received DFT coefficients of the second signal; and

means for reconstructing the second signal using the impulse response of the unknown filter and the received DFT coefficients of the first signal, wherein the unknown filter comprises a piecewise bandlimited filter.

10. The apparatus of claim 9, wherein the unknown filter comprises a piecewise polynomial filter.

11. A computer-program product for signal processing, comprising a non-transitory computer readable medium comprising instructions executable to:

receive discrete Fourier transform (DFT) coefficients of first and second signals, the DFT coefficients including K+1 coefficients for each of the first and second signals and complementary subsets of remaining DFT coefficients for each of the first and second signals, wherein K is a number of non-zero elements of an impulse response of an unknown filter and wherein the first signal is linked to the second signal by the unknown filter;

compute 2K consecutive DFT coefficients of the unknown filter using the received DFT coefficients of the first and second signals, wherein to compute the 2K consecutive DFT coefficients the instructions are executable to compute a Toeplitz rank-K filter matrix;

obtain an impulse response of the unknown filter using the computed 2K DFT coefficients;

reconstruct the first signal using the impulse response of the unknown filter and the received DFT coefficients of the second signal; and

reconstruct the second signal using the impulse response of the unknown filter and the received DFT coefficients of the first signal, wherein the unknown filter comprises a piecewise bandlimited filter.

12. A headset, comprising:

a receiver configured to receive discrete Fourier transform (DFT) coefficients of a first signal and a second signal, the DFT coefficients including K+1 coefficients for each of the first and second signals and complementary subsets of remaining DFT coefficients for each of the first and second signals, wherein the first signal is linked to the second signal by an unknown filter and wherein K is a number of non-zero elements of an impulse response of the unknown filter;

a computer configured to compute 2K consecutive DFT coefficients of the unknown filter using the received DFT coefficients of the first and second signals, wherein to compute the 2K consecutive DFT coefficients, the computer is configured to compute a Toeplitz rank-K filter matrix;

a calculator configured to obtain an impulse response of the unknown filter using the computed 2K DFT coefficients;

a first reconstructing circuit configured to reconstruct the first signal using the impulse response of the unknown filter and the received DFT coefficients of the second signal;

a second reconstructing circuit configured to reconstruct the second signal using the impulse response of the unknown filter and the received DFT coefficients of the first signal; and

a transducer configured to provide an audio output based on the reconstructed first and second signals, wherein the unknown filter comprises a piecewise bandlimited filter.

13. A monitor for monitoring patient vital signs, comprising:

a receiver configured to receive discrete Fourier transform (DFT) coefficients of a first signal and a second signal, the DFT coefficients including K+1 coefficients for each of the first and second signals and complementary subsets of remaining DFT coefficients for each of the first and second signals, wherein the first signal is linked to the second signal by an unknown filter and wherein K is a number of non-zero elements of an impulse response of the unknown filter;

a computer configured to compute 2K consecutive DFT coefficients of the unknown filter using the received DFT coefficients of the first and second signals, wherein to compute the 2K consecutive DFT coefficients, the computer is configured to compute a Toeplitz rank-K filter matrix;

a calculator configured to obtain an impulse response of the unknown filter using the computed 2K DFT coefficients;

a first reconstructing circuit configured to reconstruct the first signal using the impulse response of the unknown filter and the received DFT coefficients of the second signal;

a second reconstructing circuit configured to reconstruct the second signal using the impulse response of the unknown filter and the received DFT coefficients of the first signal; and

a user interface for displaying parameters related to the patient vital signs derived from the reconstructed first and second signals, wherein the unknown filter comprises a piecewise bandlimited filter.

14. A method of signal processing, comprising:

sampling of first and second signals to obtain samples of the first and second signals;

performing a discrete Fourier transform (DFT) on the samples of the first and second signals to obtain DFT coefficients of the first and second signals;

sending first L+1 DFT coefficients for each of the first and second signals and complementary subsets of remaining DFT coefficients for each of the first and second signals;

wherein the first signal is an input of a sparse unknown filter, the second signal is an output of the sparse unknown filter, L≧

K, wherein K is a number of non-zero elements of an impulse response of the sparse unknown filter, wherein L is a number of samplings performed to obtain said samples wherein a number of first samples and a number of second samples sampled is below a minimal number of samples given by a Nyquist relation, wherein the number of samples of the first signal M₁ and the number of samples of the second signal M₂ satisfy a following condition;

M₁≧

min{K+1,N}, M₂≧

min{K+1,N} and M₁+M₂≧

min{N+K+1,2N}, where N is a number of samples of the first and second signals after performing a windowing operation and a min{ } function retrieves a smaller number of two numbers; and

reconstructing the first and second signals using the sent first coefficients is performed based on a zero probability that the two reconstructed signals are different if the same samples of the first and second signals are used.

15. The method of claim 14, wherein sampling of the first and second signals comprises sampling of one or more frames of the first and second signals.

16. An apparatus for signal processing, comprising:

a sampler configured to sample first and second signals to obtain samples of the first and second signals;

a circuit configured to perform a discrete Fourier transform (DFT) on the samples of the first and second signals to obtain DFT coefficients of the first and second signals;

a transmitter configured to send first L+1 DFT coefficients for each of the first and second signals and complementary subsets of remaining DFT coefficients for each of the first and second signals, wherein the first signal is an input of a sparse unknown filter, the second signal is an output of the sparse unknown filter, L≧

K, wherein K is a number of non-zero elements of an impulse response of the sparse unknown filter, wherein L is a number of samplings performed to obtain said samples, wherein a number of first samples and a number of second sampled observed is below a minimal number of samples given by a Nyquist relation, and wherein a number of samples of the first signal M₁ and a number of samples of the second signal M₂ satisfy the following condition;

M₁≧

N, and M₂≧

N, where N is a number of samples of the first and second signals after performing a windowing operation; and

a universal reconstruction configured to reconstruct the first and second signals using the sent first coefficients is performed based on the two reconstructed signals being the same if the same samples of the first and second signals are used.

17. The apparatus of claim 16, wherein the sampler configured to sample the first and second signals comprises a circuit configured to sample one or more frames of the first and second signals.

18. An apparatus for signal processing, comprising:

means for sampling first and second signals to obtain samples of the first and second signals;

means for performing a discrete Fourier transform (DFT) on the samples of the first and second signals to obtain DFT coefficients of the first and second signals;

means for sending first L+1 DFT coefficients for each of the first and second signals and complementary subsets of remaining DFT coefficients for each of the first and second signals, wherein the first signal is an input of a sparse unknown filter, the second signal is an output of the sparse unknown filter, L≧

K, wherein L is a number of samplings performed to obtain said samples, wherein K is a number of non-zero elements of an impulse response of the sparse unknown filter, wherein a number of first samples and a number of second samples sampled is below a minimal number of samples given by a Nyquist relation and wherein a number of samples of the first signal M₁ and a number of samples of the second signal M₂ satisfy a following condition;

M₁≧

N, and M₂≧

N, where N is a number of samples of the first and second signals after performing a windowing operation; and

means for reconstructing the first and second signals using the first coefficients sent by the sending means is performed based on the two reconstructed signals being the same if the same samples of the first and second signals are used.

19. The apparatus of claim 18, wherein the means for sampling the first and second signals comprises means for sampling one or more frames of the first and second signals.

20. A computer-program product for signal processing, comprising a non-transitory computer readable medium comprising instructions executable to:

sample first and second signals to obtain samples of the first and second signals;

perform a discrete Fourier transform (DFT) on the samples of the first and second signals to obtain DFT coefficients of the first and second signals;

send first L+1 DFT coefficients for each of the first and second signals and complementary subsets of remaining DFT coefficients for each of the first and second signals, wherein the first signal is an input of a sparse unknown filter, the second signal is an output of the sparse unknown filter, L≧

K, wherein L is a number of samplings performed to obtain said samples, wherein K is a number of non-zero elements of an impulse response of the sparse unknown filter, wherein a number of first samples and a number of second samples sampled is below a minimal number of samples given by a Nyquist relation and wherein a number of samples of the first signal M₁ and a number of samples of the second signal M₂ satisfy a following condition;

M₁≧

N, and M₂≧

N, where N is a number of samples of the first and second signals after performing a windowing operation; and

reconstructing the first and second signals using the sent first coefficients is performed based on the two reconstructed signals being the same if the same samples of the first and second signals are used.

21. A sensing device, comprising:

a sampler configured to sample first and second signals to obtain samples of the first and second signals;

a circuit configured to perform a discrete Fourier transform (DFT) on the samples of the first and second signals to obtain DFT coefficients of the first and second signals;

a transmitter configured to transmit first L+1 DFT coefficients for each of the first and second signals and complementary subsets of remaining DFT coefficients for each of the first and second signals;

a sensor configured to provide data to be transmitted via the transmitter, wherein the first signal is an input of a sparse unknown filter, the second signal is an output of the sparse unknown filter, L≧

K, wherein L is a number of samplings performed to obtain said samples and K is a number of non-zero elements of an impulse response of the sparse unknown filter, wherein a number of first samples and a number of second samples sampled is below a minimal number of samples given by a Nyquist relation and wherein a number of samples of the first signal M₁ and a number of samples of the second signal M₂ satisfy a following condition;

M₁≧

N, and M₂≧

N where N is a number of samples of the first and second signals after performing a windowing operation; and

configured to reconstruct the first and second signals using the transmit first coefficients is performed based on a the two reconstructed signals being the same if the same samples of the first and second signals are used.

22. A method for signal processing, comprising:

receiving first L+1 discrete Fourier transform (DFT) coefficients for each of first and second signals, wherein the first signal is linked to the second signal by an unknown filter;

generating a filter matrix of dimension L×

(L+1) using the received DFT coefficients of the first and second signals;

generating a rank-K filter matrix by setting L−

(K+1) smallest singular values of the filter matrix to zero, if a ratio of (K+1)^th singular value of the filter matrix to K^th singular value of the filter matrix is not smaller than a defined threshold value, wherein L is a number of samplings performed to obtain samples, K is a number of non-zero elements of an impulse response of the unknown filter, and L≧

K;

generating a Toeplitz rank-K filter matrix by averaging coefficients along diagonals of the rank-K filter matrix;

obtaining DFT coefficients of the unknown filter based on elements of the first row and the first column of the Toeplitz rank-K filter matrix, if a ratio of (K+1)^th singular value of the Toeplitz rank-K filter matrix to K^th singular value of the Toeplitz rank-K filter matrix is smaller than the defined threshold value;

computing the impulse response of the unknown filter using the obtained DFT coefficients of the unknown filter;

reconstructing the first signal using the impulse response of the unknown filter and the received DFT coefficients of the second signal; and

reconstructing the second signal using the impulse response of the unknown filter and the received DFT coefficients of the first signal, wherein the unknown filter comprises a piecewise bandlimited filter.

23. The method of claim 22, wherein the unknown filter further comprises a piecewise polynomial filter.

24. An apparatus for signal processing, comprising:

a receiver configured to receive first L+1 discrete Fourier transform (DFT) coefficients for each of first and second signals, wherein the first signal is linked to the second signal by an unknown filter;

a first generator configured to generate a filter matrix of dimension L×

(L+1) using the received DFT coefficients of the first and second signals;

a second generator configured to generate a rank-K filter matrix by setting L−

(K+1) smallest singular values of the filter matrix to zero, if a ratio of (K+1)^th singular value of the filter matrix to K^th singular value of the filter matrix is not smaller than a defined threshold value, wherein L is a number of samplings performed to obtain samples, K is a number of non-zero elements of an impulse response of the unknown filter, and L≧

K;

a third generator configured to generate a Toeplitz rank-K filter matrix by averaging coefficients along diagonals of the rank-K filter matrix;

a calculator configured to obtain DFT coefficients of the unknown filter based on elements of the first row and the first column of the Toeplitz rank-K filter matrix, if a ratio of (K+1)^th singular value of the Toeplitz rank-K filter matrix to K^th singular value of the Toeplitz rank-K filter matrix is smaller than the defined threshold value;

a computer configured to compute the impulse response of the unknown filter using the obtained DFT coefficients of the filter;

a first reconstructing circuit configured to reconstruct the first signal using the impulse response of the unknown filter and the received DFT coefficients of the second signal; and

a second reconstructing circuit configured to reconstruct the second signal using the impulse response of the unknown filter and the received DFT coefficients of the first signal, wherein the unknown filter comprises a piecewise bandlimited filter.

25. The apparatus of claim 24, wherein the unknown filter further comprises a piecewise polynomial filter.

26. An apparatus for signal processing, comprising:

means for receiving first L+1 discrete Fourier transform (DFT) coefficients for each of first and second signals, wherein the first signal is linked to the second signal by an unknown filter;

means for generating a filter matrix of dimension L×

(L+1) using the received DFT coefficients of the first and second signals;

means for generating a rank-K filter matrix by setting L−

(K+1) smallest singular values of the filter matrix to zero, if a ratio of (K+1)^th singular value of the filter matrix to K^th singular value of the filter matrix is not smaller than a defined threshold value, wherein L is a number of samplings performed to obtain samples, K is a number of non-zero elements of an impulse response of the unknown filter, and L≧

K;

means for generating a Toeplitz rank-K filter matrix by averaging coefficients along diagonals of the rank-K filter matrix;

means for obtaining DFT coefficients of the unknown filter based on elements of the first row and the first column of the Toeplitz rank-K filter matrix, if a ratio of (K+1)^th singular value of the Toeplitz rank-K filter matrix to K^th singular value of the Toeplitz rank-K filter matrix is smaller than the defined threshold value;

means for computing the impulse response of the unknown filter using the obtained DFT coefficients of the filter;

means for reconstructing the first signal using the impulse response of the unknown filter and the received DFT coefficients of the second signal; and

means for reconstructing the second signal using the impulse response of the unknown filter and the received DFT coefficients of the first signal, wherein the unknown filter comprises a piecewise bandlimited filter.

27. The apparatus of claim 26, wherein the unknown filter further comprises a piecewise polynomial filter.

28. A computer-program product for signal processing, comprising a non-transitory computer readable medium comprising instructions executable to:

receive first L+1 discrete Fourier transform (DFT) coefficients for each of first and second signals, wherein the first signal is linked to the second signal by an unknown filter;

generate a filter matrix of dimension L×

(L+1) using the received DFT coefficients of the first and second signals;

generate a rank-K filter matrix by setting L−

(K+1) smallest singular values of the filter matrix to zero, if a ratio of (K+1)^th singular value of the filter matrix to K^th singular value of the filter matrix is not smaller than a defined threshold value, wherein L is a number of samplings performed to obtain samples, K is a number of non-zero elements of an impulse response of the unknown filter, and L≧

K;

generate a Toeplitz rank-K filter matrix by averaging coefficients along diagonals of the rank-K filter matrix;

obtain DFT coefficients of the unknown filter based on elements of the first row and the first column of the Toeplitz rank-K filter matrix, if a ratio of (K+1)^th singular value of the Toeplitz rank-K filter matrix to K^th singular value of the Toeplitz rank-K filter matrix is smaller than the defined threshold value;

compute the impulse response of the unknown filter using the obtained DFT coefficients of the filter;

reconstruct the first signal using the impulse response of the unknown filter and the received DFT coefficients of the second signal; and

reconstruct the second signal using the impulse response of the unknown filter and the received DFT coefficients of the first signal, wherein the unknown filter comprises a piecewise bandlimited filter.

29. A headset, comprising:

a receiver configured to receive first L+1 discrete Fourier transform (DFT) coefficients for each of first and second signals, wherein the first signal is linked to the second signal by an unknown filter;

a first generator configured to generate a filter matrix of dimension L×

(L+1) using the received DFT coefficients of the first and second signals;

a second generator configured to generate a rank-K filter matrix by setting L−

(K+1) smallest singular values of the filter matrix to zero, if a ratio of (K+1)^th singular value of the filter matrix to K^th singular value of the filter matrix is not smaller than a defined threshold value, wherein L is a number of samplings performed to obtain samples, K is a number of non-zero elements of an impulse response of the unknown filter, and L≧

K;

a third generator configured to generate a Toeplitz rank-K filter matrix by averaging coefficients along diagonals of the rank-K filter matrix;

a calculator configured to obtain DFT coefficients of the unknown filter based on elements of the first row and the first column of the Toeplitz rank-K filter matrix, if a ratio of (K+1)^th singular value of the Toeplitz rank-K filter matrix to K^th singular value of the Toeplitz rank-K filter matrix is smaller than the defined threshold value;

a computer configured to compute the impulse response of the unknown filter using the obtained DFT coefficients of the unknown filter;

a first reconstructing circuit configured to reconstruct the first signal using the impulse response of the unknown filter and the received DFT coefficients of the second signal;

a second reconstructing circuit configured to reconstruct the second signal using the impulse response of the unknown filter and the received DFT coefficients of the first signal; and

a transducer configured to provide an audio output based on the reconstructed first and second signals, wherein the unknown filter comprises a piecewise bandlimited filter.

30. A monitor for monitoring patient vital signs, comprising:

a receiver configured to receive first L+1 discrete Fourier transform (DFT) coefficients for each of first and second signals, wherein the first signal is linked to the second signal by an unknown filter;

a first generator configured to generate a filter matrix of dimension L×

(L+1) using the received DFT coefficients of the first and second signals;

a second generator configured to generate a rank-K filter matrix by setting L−

(K+1) smallest singular values of the filter matrix to zero, if a ratio of (K+1)^th singular value of the filter matrix to K^th singular value of the filter matrix is not smaller than a defined threshold value, wherein L is a number of samplings performed to obtain samples, K is a number of non-zero elements of an impulse response of the unknown filter, and L≧

K;

a third generator configured to generate a Toeplitz rank-K filter matrix by averaging coefficients along diagonals of the rank-K filter matrix;

a calculator configured to obtain DFT coefficients of the unknown filter based on elements of the first row and the first column of the Toeplitz rank-K filter matrix, if a ratio of (K+1)^th singular value of the Toeplitz rank-K filter matrix to K^th singular value of the Toeplitz rank-K filter matrix is smaller than the defined threshold value;

a computer configured to compute the impulse response of the unknown filter using the obtained DFT coefficients of the unknown filter;

a first reconstructing circuit configured to reconstruct the first signal using the impulse response of the unknown filter and the received DFT coefficients of the second signal;

a second reconstructing circuit configured to reconstruct the second signal using the impulse response of the unknown filter and the received DFT coefficients of the first signal; and

a user interface for displaying parameters related to the patient vital signs derived from the reconstructed first and second signals, wherein the unknown filter comprises a piecewise bandlimited filter.