Demodulating frequency-modulated signals

Patent metadata

Field	Value
Publication number	US-12047210-B2
Application number	US-202118010413-A
Country	US
Kind code	B2
Filing date	Jun 16, 2021
Priority date	Jun 16, 2020
Publication date	Jul 23, 2024
Grant date	Jul 23, 2024

Abstract

A method of, and apparatus for, demodulating a frequency-modulated signal. The method comprises: for each of a plurality of templates, performing a respective cross-correlation operation between the template and data representative of the frequency-modulated signal, each template comprising data representative of a signal that is frequency-modulated with predetermined preamble data using a different respective modulation index; generating frequency-offset data from one or more of the cross-correlation operations, the frequency-offset data being representative of a difference between a reference frequency and a carrier frequency of the frequency-modulated signal; determining a respective peak correlation-coefficient value from each of the cross-correlation operations; identifying a highest peak correlation-coefficient value in the determined peak correlation-coefficient values; determining a modulation index estimate in dependence on which template produced the highest peak correlation-coefficient value; and using the frequency-offset data and the modulation index estimate to demodulate at least a portion of the frequency-modulated signal.

First claim

The invention claimed is:

1. A method of demodulating a frequency-modulated signal, the method comprising:
for each of a plurality of templates, performing a respective cross-correlation operation between the template and data representative of the frequency-modulated signal, wherein each template comprises data representative of a signal that is frequency-modulated with predetermined preamble data using a different respective modulation index;
generating frequency-offset data from one or more of the cross-correlation operations, the frequency-offset data being representative of a difference between a reference frequency and a carrier frequency of the frequency-modulated signal;
determining a respective peak correlation-coefficient value from each of the cross-correlation operations;
identifying a highest peak correlation-coefficient value in the determined peak correlation-coefficient values;
determining a modulation index estimate in dependence on which template produced the highest peak correlation-coefficient value; and
using the frequency-offset data and the modulation index estimate to demodulate at least a portion of the frequency-modulated signal.

2. The method of claim 1 , further comprising generating timing information from one or more of the cross-correlation operations, the timing information comprising symbol-synchronization or frame-synchronization information, and additionally using the timing information when demodulating at least a portion of the frequency-modulated signal.

3. The method of claim 1 , comprising:
performing a first cross-correlation operation between a first template and data representative of the frequency-modulated signal by determining a respective correlation-coefficient value for each of a plurality of different time offsets between the first template and the data representative of the frequency-modulated signal;
determining timing information from the first cross-correlation operation; and
performing a second cross-correlation operation between a second template and the data representative of the frequency-modulated signal by determining a correlation-coefficient value for a time offset between the second template and the data representative of the frequency-modulated signal, wherein the time offset depends on the timing information determined from the first cross-correlation operation.

4. The method of claim 3 , wherein the frequency-modulated signal contains the predetermined preamble data, and wherein the timing information used by the second cross-correlation operation identifies a position of the predetermined preamble data within the signal.

5. The method of claim 1 , wherein the data representative of the frequency-modulated signal comprises a sequence of complex, baseband sample values.

6. The method of claim 1 , comprising receiving the frequency-modulated signal, wherein the frequency-modulated signal is a radio signal.

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

8. The method of claim 1 , wherein, for at least one of the templates, performing the respective cross-correlation operation comprises generating one or more correlation-coefficient values that each depend on a respective dot product between the template and a sequence of values derived from the data representative of the frequency-modulated signal, wherein each value depends on the product of a respective first sample from the data representative of the frequency-modulated signal and the complex conjugate of a respective second sample from the data representative of the frequency-modulated signal, wherein each second sample is offset from the respective first sample by an offset period.

9. The method of claim 1 , wherein the modulation index estimate is different from the modulation index of the template that produced the highest peak correlation-coefficient value.

10. An apparatus for demodulating a frequency-modulated signal, the apparatus comprising:
a preamble correlator; and
a signal demodulator,
wherein the preamble correlator is configured to:
perform, for each of a plurality of templates, a respective cross-correlation operation between the template and data representative of the frequency-modulated signal, wherein each template comprises data representative of a signal that is frequency-modulated with predetermined preamble data using a different respective modulation index;
generate frequency-offset data from one or more of the cross-correlation operations, the frequency-offset data being representative of a difference between a reference frequency and a carrier frequency of the frequency-modulated signal;
determine a respective peak correlation-coefficient value from each of the cross-correlation operations;
identify a highest peak correlation-coefficient value in the determined peak correlation-coefficient values; and
determine a modulation index estimate in dependence on which template produced the highest peak correlation-coefficient value,
and wherein the signal demodulator is configured to:
use the frequency-offset data and the modulation index estimate to demodulate at least a portion of the frequency-modulated signal.

11. The apparatus of claim 10 , wherein the preamble correlator is further configured to generate timing information from one or more of the cross-correlation operations, the timing information comprising symbol-synchronization or frame-synchronization information, wherein the signal demodulator is configured to use the timing information when demodulating at least a portion of the frequency-modulated signal.

12. The apparatus of claim 10 , wherein the preamble correlator is configured to:
perform a first cross-correlation operation between a first template and data representative of the frequency-modulated signal by determining a respective correlation-coefficient value for each of a plurality of different time offsets between the first template and the data representative of the frequency-modulated signal;
determine timing information from the first cross-correlation operation; and
perform a second cross-correlation operation between a second template and the data representative of the frequency-modulated signal by determining a correlation-coefficient value for a time offset between the second template and the data representative of the frequency-modulated signal, wherein the time offset depends on the timing information determined from the first cross-correlation operation.

13. The apparatus of claim 12 , wherein the timing information using by the second cross-correlation operation identifies a position of the predetermined preamble data within the frequency-modulated signal.

14. The apparatus of claim 10 , wherein the preamble correlator is configured to perform the respective cross-correlation operations serially.

15. The apparatus of claim 10 , comprising an analogue or digital mixer and a digital-to-analogue converter for sampling the frequency-modulated to generate the data representative of the frequency-modulated signal, wherein the data comprises a sequence of complex, baseband sample values.

16. The apparatus of claim 10 , comprising a radio receiver and an antenna for receiving the frequency-modulated signal, wherein the frequency-modulated signal is a radio signal.

17. The apparatus of claim 10 , wherein the preamble correlator is configured, for at least one of the templates, to perform the respective cross-correlation operation by generating one or more correlation-coefficient values that each depend on a dot product betw

Assignees

• Nordic Semiconductor Asa

Inventors

• Ryan Daniel

Classifications

• H04W4/80

  Services using short range communication, e.g. near-field communication [NFC], radio-frequency identification [RFID] or low energy communication · CPC title

• H04L27/14

  Demodulator circuits; Receiver circuits · CPC title

• H04L27/156 Primary

  with demodulation using temporal properties of the received signal, e.g. detecting pulse width · CPC title