Demodulating modulated signals

Patent metadata

Field	Value
Publication number	US-12081377-B2
Application number	US-202118010432-A
Country	US
Kind code	B2
Filing date	Jun 16, 2021
Priority date	Jun 16, 2020
Publication date	Sep 3, 2024
Grant date	Sep 3, 2024

Abstract

An apparatus for demodulating a frequency-modulated signal comprises a joint frequency-offset & modulation-index estimator, and a signal demodulator. The joint estimator receives data representative of a preamble portion of the signal, modulated with predetermined preamble data. It jointly determines a frequency-offset estimate and a modulation-index estimate by using an optimization process that minimizes a cost function that is a function of the received data and that is parameterised by a frequency-offset parameter and by a modulation-index parameter. The signal demodulator receives data representative of a message portion of the signal, modulated with message data, and uses the frequency-offset estimate to demodulate the message.

First claim

The invention claimed is:

1. An apparatus for demodulating a frequency-modulated signal, the apparatus comprising:
a joint frequency-offset and modulation-index estimator; and
a signal demodulator,
wherein the joint frequency-offset and modulation-index estimator is configured to:
receive data representative of a preamble portion of the frequency-modulated signal, wherein the preamble portion is modulated with predetermined preamble data; and
jointly determining a frequency-offset estimate and a modulation-index estimate by using the received data to perform an optimization process, wherein the optimization process minimizes a cost function that is a function of the received data and that is parameterised by a frequency-offset parameter and by a modulation-index parameter,
and wherein the signal demodulator is configured to:
receive data representative of a message portion of the frequency-modulated signal, wherein the message portion is modulated with message data; and
use the frequency-offset estimate to demodulate the message.

2. The apparatus of claim 1 , wherein the signal demodulator is configured to use the modulation-index estimate, as well as the frequency-offset estimate, when demodulating the message portion.

3. The apparatus of claim 1 , wherein the data representative of the preamble portion comprise a sequence of complex sample values, and wherein the joint frequency-offset and modulation-index estimator is configured to calculate a phase angle for each of the complex sample values, for performing the optimization process in a phase domain.

4. The apparatus of claim 1 , wherein the cost function is a least-squares cost function.

5. The apparatus of claim 1 , configured to store or access stored data relating to the predetermined preamble data, wherein the cost function is a function of both the stored data and the received data, and wherein the joint frequency-offset and modulation-index estimator is configured to use the stored data when performing the optimization process.

6. The apparatus of claim 5 , wherein the stored data represents a sequence, or a function of a sequence, of accumulated phase offsets for a signal modulated with the predetermined preamble data.

7. The apparatus of claim 5 , wherein the stored data encodes a matrix that is a function of one or more matrices, wherein at least one of the matrices has a row or column containing a series of accumulated phase-offset values that are dependent on the predetermined preamble data.

8. The apparatus of claim 1 , wherein the cost function is further parameterised by a phase-unwrapping parameter and wherein the joint frequency-offset and modulation-index estimator is configured to minimize the cost function over the phase-unwrapping parameter.

9. The apparatus of claim 8 , wherein the joint frequency-offset and modulation-index estimator is configured to keep the frequency-offset parameter constant when performing the optimization process, and is further configured to determine the frequency-offset estimate by back-substitution after determining an optimal value for the phase-unwrapping parameter using the optimization process.

10. The apparatus of claim 9 , wherein the joint frequency-offset and modulation-index estimator comprises a frequency estimator configured to determine a first estimate of the frequency offset; and is configured to perform the optimization process with the frequency-offset parameter set to the first estimate, or is configured to use the first estimate to apply frequency-offset compensation to the data representative of the preamble portion and to perform the optimization process with the frequency-offset parameter set to zero.

11. The apparatus of claim 8 , wherein the joint frequency-offset and modulation-index estimator is configured to keep the modulation-index parameter constant during the optimization process, and is further configured to determine the modulation-index estimate by back-substitution after determining an optimal value for the phase-unwrapping parameter.

12. The apparatus of claim 1 , wherein the joint frequency-offset and modulation-index estimator is configured to determine the frequency-offset estimate and the modulation-index estimate by performing the optimization process a plurality of times, with the frequency-offset parameter and the modulation-index parameter set to a different pair of constant values each time, and to determine a pair of the pairs of constant values that resulted in a lowest minimum cost for the cost function.

13. The apparatus of claim 1 , wherein the joint frequency-offset and modulation-index estimator is configured to minimize the cost function by performing a closest-lattice-point search to identify a closest point in a lattice.

14. The apparatus of claim 13 , wherein the joint frequency-offset and modulation-index estimator is configured to search for a closest point over the lattice A n *, for an integer n, using an algorithm having O(N) complexity.

15. The apparatus of claim 1 , wherein the frequency-modulated signal is a radio signal and wherein the apparatus comprises a radio receiver for receiving the modulated radio signal and for generating the data representative of the preamble and message portions.

16. The apparatus of claim 1 , wherein the frequency-modulated signal is a Gaussian frequency-shift-key (GFSK) modulated signal.

17. The apparatus of claim 1 , wherein the frequency-modulated signal is modulated with constant amplitude.

18. A method of demodulating a frequency-modulated signal, the method comprising:
receiving data representative of a preamble portion of the frequency-modulated signal, wherein the preamble portion is modulated with predetermined preamble data;
jointly determining a frequency-offset estimate and a modulation-index estimate by using the received data to perform an optimization process, wherein the optimization process minimizes a cost function that is a function of the received data and that is parameterised by a frequency-offset parameter and by a modulation-index parameter;
receiving data representative of a message portion of the frequency-modulated signal, wherein the message portion is modulated with message data; and
using the frequency-offset estimate when demodulating the message portion.

19. The method of claim 18 , wherein the frequency-modulated signal is a Gaussian frequency-shift-key (GFSK) modulated signal.

20. The method of claim 18 , wherein the frequency-modulated signal is modulated with constant amplitude.

Assignees

• Nordic Semiconductor Asa

Inventors

• Ryan Daniel

Classifications

• H04L27/2017

  in which the phase changes are non-linear, e.g. generalized and Gaussian minimum shift keying, tamed frequency modulation (H04L27/201 takes precedence) · CPC title

• H04L27/144 Primary

  with demodulation using spectral properties of the received signal, e.g. by using frequency selective- or frequency sensitive elements · CPC title

• H04L2027/0089

  In-band signals · CPC title

• H04L2027/0095

  in a preamble or similar structure · CPC title

• H04L27/0014 Primary

  Carrier regulation (of chaotic carriers H04L27/001; for multicarrier receivers H04L27/2657) · CPC title