Receiver for secure time-of-arrival calculation
Some embodiments include an apparatus, method, and computer program product for secure time-of-arrivals calculations in an ultra-wideband (UWB) system. Some embodiments include a UWB receiver that can inspect a channel impulse response (CIR) between a first and second electronic device and identify one or more first path candidates (FPCs). For a candidate path, the UWB receiver can identify subsequent paths that create inter-pulse interference (IPI) on the candidate path. Using estimates for the interfering path strengths (e.g., channel coefficients from the CIR) and the known cryptographically sequence of pulse polarities (SPP), the UWB receiver can reduce the IPI from these interfering paths on the FPCs, and then make decisions based at least on the remaining pulse polarities, whether the one or more FPCs comprise a legitimate transmission signal.
1. An electronic device, comprising:
a transceiver configured to receive wireless transmissions from a second electronic device;
a processor, coupled to the transceiver, configured to:
receive discrete-time samples that correspond to a received wireless transmission;
estimate a channel impulse response (CIR) comprising estimates of one or more propagation path coefficients based at least on the discrete-time samples and a sequence of pulse polarities (SPP);
based on the CIR, estimate a First-Path Candidate (FPC) corresponding to the SPP;
reduce inter-pulse interference (IPI) on one or more samples that correspond to the FPC; and
after the reduction, determine based at least on the SPP, whether the one or more samples represents a legitimate transmission of the SPP.
2. The electronic device of claim 1 , wherein to reduce the IPI, the processor is configured to:
estimate interference on the one or more samples from preceding pulses in the SPP, wherein the estimate is based at least on the SPP and the CIR; and
subtract the estimated interference from the one or more samples.
3. The electronic device of claim 1 , wherein to determine based at least on the SPP whether the one or more samples represent a legitimate transmission of the SPP, the processor is configured to:
estimate a polarity sequence of the one or more samples;
compare the estimated polarity sequence with the SPP;
determine whether the comparison satisfies a configurable threshold; and
based on the determination, initiate a security operation.
4. The electronic device of claim 3 , wherein to estimate the polarity sequence, the processor is configured to:
equalize the one or more samples based on the one or more propagation path coefficients of the FPC; and
estimate polarities of the equalized one or more samples.
5. The electronic device of claim 1 , wherein the SPP is a cryptographically secure pulse sequence (CSPS) or a training sequence of a physical layer protocol data unit (PPDU).
6. The electronic device of claim 1 , wherein to determine based at least on the SPP whether the one or more samples represents a legitimate transmission of the SPP, the processor is configured to:
compute a correlation between the one or more samples and the SPP;
compute a sample norm of the one or more samples;
compute a ratio between a magnitude of the correlation and the sample norm; and
determine whether the ratio exceeds a configurable threshold.
7. The electronic device of claim 6 , wherein the sample norm comprises a square-root of a sum of squared magnitudes of the one or more samples.
8. A method, comprising:
receiving discrete-time samples that correspond to a received wireless transmission;
estimating a channel impulse response (CIR) comprising estimates of one or more propagation path coefficients based at least on the discrete-time samples;
estimating, based at least on the CIR, a First-Path Candidate (FPC) corresponding to a sequence of pulse polarities (SPP);
generating one or more inter-pulse interference (IPI) reduced samples (IRSs) based at least on the SPP and the CIR that correspond to the FPC; and
after the reducing, determining whether the one or more IRSs represent a legitimate transmission of the SPP.
9. The method of claim 8 , wherein the generating the one or more IRSs comprises:
based on the SPP and the CIR, estimating a subset of the discrete-time samples;
estimating interference on the subset of the discrete-time samples from preceding pulses in the SPP; and
cancelling the estimated interference from the subset of the discrete-time samples.
10. The method of claim 8 , wherein the determining whether the one or more IRSs represent a legitimate transmission of the SPP comprises:
estimating a polarity sequence of the one or more IRSs;
comparing the estimated polarity sequence with the SPP; and
determining whether the comparison satisfies a configurable threshold.
11. The method of claim 10 , wherein the estimating the polarity sequence comprises:
equalizing the one or more IRSs based on the one or more propagation path coefficients of the FPC; and
estimating polarities of the equalized one or more IRSs.
12. The method of claim 8 , wherein the SPP is a cryptographically secure pulse sequence (CSPS) or a training sequence of a physical layer protocol data unit (PPDU).
13. The method of claim 8 , wherein the determining whether the one or more IRS s represents a legitimate transmission of the SPP comprises:
computing a correlation between the one or more IRSs and the SPP;
computing a sample norm of the one or more IRSs;
computing a ratio between a magnitude of the correlation and the sample norm; and
determining whether the ratio exceeds a configurable threshold.
14. The method of claim 13 , wherein the sample norm comprises a square-root of a sum of squared magnitudes of the one or more IRSs.
15. A non-transitory computer-readable medium storing instructions that, when executed by a processor of a first electronic device, cause the processor to perform operations, the operations comprising:
receiving discrete-time samples that correspond to a received wireless transmission;
estimating a channel impulse response (CIR) comprising estimates of one or more propagation path coefficients based at least on the discrete-time samples;
estimating, based at least on the CIR, a First-Path Candidate (FPC);
based at least on the SPP and the CIR, generating one or more inter-pulse interference (IPI) reduced samples (IRSs) that correspond to the FPC;
determining, whether the one or more IRSs represent a legitimate transmission of the SPP; and
based on the determination that the one or more IRSs represent a legitimate transmission of the SPP, performing a security operation.
16. The non-transitory computer-readable medium of claim 15 , wherein the generating the one or more IRSs operation comprises:
based at least on the SPP and the CIR, estimating a subset of the discrete-time samples;
estimating interference on the subset of the discrete-time samples from preceding pulses in the SPP; and
subtracting the estimated interference from the subset of the discrete-time samples.
17. The non-transitory computer-readable medium of claim 15 , wherein the determining whether the one or more IRSs represent a legitimate transmission of the SPP operation comprises:
estimating a polarity sequence of the one or more IRSs;
comparing the estimated polarity sequence with the SPP; and
determining whether the comparison satisfies a configurable threshold.
18. The non-transitory computer-readable medium of claim 17 , wherein the estimating the polarity sequence operation comprises:
equalizing the one or more IRSs based on the one or more propagation path coefficients of the FPC; and
estimating polarities of the equalized one or more IRSs.
19. The non-transitory computer-readable medium of claim 15 , wherein the determining whether the one or more IRSs represent a legitimate transmission of the SPP operation comprises:
computing a correlation between the one or more IRSs and the SPP;
computing a sample norm of the one or more IRSs;
computing a ratio between a magnitude of the correlation and the sample norm; and
determining whether the ratio exceeds a configurable threshold.
20. The non-transitory computer-readable medium of claim 19 , wherein the sample norm comprises a square-root of a sum of squared magnitudes of the one or more IRSs.