Apparatus for adaptively reducing noise of an FM radio signal

Abstract

An apparatus (10) for reducing noise in a radio signal received in the FM band is proposed, comprising: - a module (11) for demodulating the radio signal, adapted for generating a demodulated radio signal from the received radio signal; - a noise suppression module (12) adapted for replacing a time sequence of the demodulated radio signal with a sequence of noise removed; - a module (13) for controlling the noise suppression module, adapted for controlling the activation of the noise suppression module for reducing noise, characterized in that it further comprises a module (14) for analyzing the spectrum of the received radio signal, and in that the control module is configured for controlling the noise suppression module according to an activation strategy selected among a plurality of predetermined activation strategies depending on the spectral content of the received radio signal.

Description

Technical Field

[0001] This disclosure relates to an apparatus for reducing noise (particularly impulse noise) in received FM radio signals, and particularly for use in an onboard radio receiver integrated into an autonomous vehicle. Background Technology

[0002] Radio receivers typically include devices for noise reduction, which include modules for demodulating the received radio signals and noise suppression modules (known in English as "noise blanker").

[0003] In particular, an example of a noise suppression module configured to replace the noisy part of a signal with a self-signal portion is described in document US6577851.

[0004] In other cases, the noise suppression module can replace the noisy part of the signal with a portion reconstructed from certain components of the noisy part.

[0005] In all cases, a strategy needs to be set regarding the detection of noisy components and the activation of a well-performing noise suppression module. In practice, ineffective detection of noisy components does not allow for sufficiently satisfactory noise elimination. On the other hand, since techniques known as "blanking" or noise suppression can introduce distortion into the reconstructed audio signal, it is appropriate to avoid overly stringent activation of the noise suppression module.

[0006] To ensure satisfactory noise reduction, a method for limiting impulse noise in radio signals has been proposed in patent application FR3049132, wherein the noise suppression module is activated based on the derivation of the magnitude decrease of the ratio between the in-phase and quadrature components of the modulated received radio signal and the detection of high-frequency noise in the demodulated received radio signal.

[0007] In this solution, the thresholds proposed for the two detections are determined by professionals during device adjustments and then set in a defined manner.

[0008] However, this adjustment may not be suitable for all situations and all types of audio content. For example, when the audio content involves "pop" music, listeners are less sensitive to noise compared to when it involves classical music or oral performances.

[0009] Therefore, there is a need to mitigate this drawback. Summary of the Invention

[0010] In view of the above, the purpose of this disclosure is to provide an apparatus for reducing noise in radio signals, which allows for noise cancellation adapted to the content of the signal.

[0011] In this regard, an apparatus for reducing noise in radio signals received in the FM band is proposed, comprising:

[0012] - A module for demodulating radio signals, adapted to generate demodulated radio signals from received radio signals.

[0013] - A noise suppression module, adapted to replace the time series of the demodulated radio signal with a noise-removed sequence.

[0014] - A module for controlling the noise suppression module, adapted to manipulate the activation of the noise suppression module.

[0015] The device for reducing noise is characterized in that it further includes a module for analyzing the spectrum of the received radio signal, and a control module is configured to control the noise suppression module according to an activation strategy selected from a plurality of predetermined activation strategies based on the spectral content of the received radio signal.

[0016] In some embodiments, the predetermined activation strategy includes a first strategy in the case of adjacent channel interference, a second strategy in the case of no adjacent channel interference and a weak dynamic spectrum of the received radio signal, and a third strategy in the case of no adjacent channel interference and a strong dynamic spectrum of the received radio signal.

[0017] In some embodiments, the means for reducing noise further includes:

[0018] - A module for detecting high-frequency noise in demodulated radio signals based on a high-frequency noise detection threshold:

[0019] - A module for detecting a decrease in the modulus of the ratio between the in-phase and quadrature components of a modulated radio signal, based on a modulus decrease detection threshold.

[0020] The control module is adapted to activate the noise suppression module based on the detection of high-frequency noise and the detection of a decrease in the modulus of the ratio between the in-phase and quadrature components.

[0021] Furthermore, the control module is also adapted to set the values ​​of the high-frequency noise detection threshold and the modulus decrease detection threshold according to the selected activation strategy.

[0022] In some embodiments, the values ​​of the high-frequency noise detection threshold and the modulus descent detection threshold corresponding to the first strategy are respectively included between the values ​​of the high-frequency noise detection threshold and the modulus descent detection threshold corresponding to the second activation strategy and the third activation strategy.

[0023] In some embodiments, the apparatus further includes a module for converting the frequency of the received radio signal toward an intermediate frequency, and a module for analyzing the spectrum is adapted to analyze the spectrum of the signal from the frequency conversion module.

[0024] In some embodiments, the module for analyzing the spectrum is adapted to detect adjacent channel interference, and in the event of adjacent channel interference, the control module is configured to implement a first strategy for activating the noise suppression module.

[0025] In some embodiments, in order to detect adjacent channel interference, the module for analyzing the spectrum is configured to:

[0026] - Determine the ratio between the spectral energy at frequencies included in the center band of the spectrum and the spectral energy at frequencies included in bands located at the ends of the spectrum.

[0027] - The ratio is compared with a predetermined threshold, and if the ratio is less than the threshold, adjacent channel interference is detected.

[0028] In some embodiments, in the absence of adjacent channel interference, the module for analyzing the spectrum is further adapted to determine whether the spectrum of the radio signal is weakly dynamic or strongly dynamic, and the control module is configured to implement a second strategy for activating the noise suppression module suitable for weakly dynamic content or a third strategy for activating the noise suppression module suitable for strongly dynamic content, respectively.

[0029] In some embodiments, the module for analyzing the spectrum is configured to determine the time variation of the energy of a signal at a frequency included in the center band of the spectrum, compare the time variation with a predetermined threshold, and determine the sound content of the radio signal as weak dynamic if the time variation is less than the threshold, and determine the sound content of the radio signal as strong dynamic if the time variation is greater than the threshold.

[0030] In some embodiments, the noise suppression module is adapted to replace the time series of the demodulated signal with a sequence obtained by polynomial interpolation between the last noise-free sample and the returned noise-free sample.

[0031] According to another objective, an FM radio receiving apparatus suitable for receiving and demodulating multiplexed FM radio signals is proposed, characterized in that it includes means for reducing noise as described above.

[0032] For another purpose, a method for reducing noise in received FM radio signals is proposed, the method comprising the following steps:

[0033] -Analyze the spectrum of the received radio signals,

[0034] - Based on the analysis performed, a noise suppression strategy is selected from a set of predetermined strategies, and

[0035] - Achieve noise suppression according to the selected strategy.

[0036] In some embodiments, analyzing the spectrum of the received radio signal includes:

[0037] - Determine the ratio between the energy of the spectrum of the radio signal at frequencies included in the center band of the spectrum and the energy of the signal at frequencies included in bands located at the ends of the spectrum, and if the ratio is less than a determined threshold, select the first activation strategy; otherwise...

[0038] - Determine the temporal variation of the spectral energy of a radio signal at frequencies included in the center band of the spectrum, compare the temporal variation with a predetermined threshold, and

[0039] If the time change is less than the threshold, then the second activation strategy is selected.

[0040] Otherwise, choose the third activation strategy.

[0041] The proposed noise reduction device includes a noise suppression module, which can be selectively activated according to different activation strategies based on the frequency content of the received signal. The activation strategies correspond to more or less high noise detection thresholds, and therefore to more or less stringent activation conditions for the noise suppression module.

[0042] In this way, compared to pop music where the noise detection threshold may be higher, the noise detection threshold for audio content (such as classical music) for which the listener will perceive noise more easily can be reduced. Attached Figure Description

[0043] Other features, details, and advantages will become apparent from reading the following detailed description and from analyzing the accompanying drawings, in which:

[0044] [ Figure 1 This illustrates a radio receiving apparatus according to an embodiment, including means for reducing noise.

[0045] [ Figure 2This illustrates a method for selecting an activation strategy for a noise suppression module, implemented by a noise reduction apparatus according to an embodiment. Detailed Implementation

[0046] Now refer to [ Figure 1 The image schematically illustrates a radio receiver in the FM band, which can typically (but not exclusively) be mounted on an autonomous vehicle. The radio receiver 1 includes an antenna (not shown) and noise reduction means 10. The antenna allows the acquisition of radio signals, and the noise reduction means 10 is adapted to demodulate the received radio signals while also suppressing noise, particularly impulse noise or multipath noise.

[0047] In the following text, the different modules of the noise reduction device 10 can be analog modules or digital modules.

[0048] The received FM signal is modulated in a manner known per se using quadrature amplitude modulation (QAM) techniques, so that the received FM signal is modulated and has an in-phase component I and a quadrature component.

[0049] The noise reduction apparatus 10 includes: a module 11 for demodulating a received signal, adapted to generate a demodulated radio signal from the received signal; a noise suppression module 12, adapted to replace the time sequence of the demodulated radio signal with a noise-removed sequence; and a module 13 for controlling the noise suppression module, adapted to manipulate the activation of the noise suppression module 12 according to an activation strategy. The activation strategy corresponds to a noise detection threshold that is more or less high, and the module 13 is controlled to activate or deactivate the noise suppression module according to this threshold.

[0050] In some embodiments, the noise suppression module 12 may be adapted to replace a sequence of radio signals with a self-signal portion. As a variation, the noise suppression module 12 may replace a noisy sequence of signals with a sequence constructed by polynomial interpolation between the last noiseless signal sample and the first returned noiseless sample. Further details will be available in, for example, document FR3049132.

[0051] The control module 13 is configured to control the activation of the noise suppression module according to an activation strategy selected from a plurality of predetermined activation strategies based on the spectral content of the received radio signal.

[0052] Advantageously, at least two, and preferably at least three, predetermined activation strategies are prepared.

[0053] In this embodiment, the control module 13 is configured with two activation strategies, each adapted for the spectrum of a radio signal with correspondingly weak or strong dynamics. The spectrum with weak dynamics may, for example, correspond to classical music or spoken programs. In these cases, the listener is more sensitive to the presence of noise, and the strategy used to activate the noise suppression module must be more stringent, with a lower noise detection threshold. As for the spectrum with strong dynamics, which may involve "pop" music, the presence of noise is less of an obstacle, as it does not significantly interfere with listening. In this case, the strategy used to activate the noise suppression module can be less stringent, with a higher noise detection threshold.

[0054] In an embodiment, where the received signal includes adjacent channel interference—also known as ACI (Adjacent Channel Interference)—the control module 13 employs a third activation strategy. In this case, the noise suppression module needs to be activated frequently to prevent such interference, and therefore a specific activation strategy is employed.

[0055] To enable the control module 13 to determine the activation strategy to be selected from the predetermined strategies, the noise reduction device 10 further includes a module 14 for analyzing the spectrum of the received radio signal. (See [...]) Figure 2 The diagram illustrates an example of performing spectral analysis on a received signal in order to determine an appropriate activation strategy for a noise suppression module.

[0056] Module 14 for analyzing the spectrum is configured to preferably first determine whether the radio signal 100 includes interference from adjacent channels, which in [ Figure 2 The text is marked with the question mark "ACI?".

[0057] The noise reduction apparatus 10 typically includes a module 15 for converting the frequency of a received signal toward an intermediate frequency, located upstream of the demodulation module 11, and a module 14 for analyzing the spectrum, adapted to analyze the spectrum of the signal from the frequency conversion module, in order to compare the energy of the spectrum at frequencies (e.g., the center frequency) within the center frequency band of the signal with the energy of the spectrum at frequencies included in bands at the ends of the spectrum. The determined energy of the spectrum in the frequency bands can be obtained by integrating or summing the power spectral density of the signal with respect to the frequencies included in the bands. The analysis module 14 can, for example, calculate the ratio between the energy in the center frequency band and the energy in the end frequency bands of the spectrum.

[0058] For example, if the frequency band on which the signal is transmitted has a bandwidth L with a center frequency f, then the ends of the spectrum can be considered to include frequencies contained in the intervals [fL / 2; fL / 2+0.2L] and [f+L / 2-0.2L; f+L / 2]. It can also be considered that, for example, the center band of the spectrum corresponds to a frequency band in the intervals [fL / 10; f+L / 10] or [fL / 5; f+L / 5].

[0059] As an example, in the case of the FM band, the width of the band on which the signal is transmitted is on the order of 100 kHz. Frequency bands located at the ends of the spectrum can be outside the 80 kHz range centered on the band's center frequency.

[0060] Once the ratio of the signal energy at the center frequency to the signal energy at frequencies at the ends of the spectrum is calculated, the analysis module 14 compares this ratio with a predetermined threshold. This threshold is, for example, greater than or equal to 1, such as greater than or equal to 1.5.

[0061] If the ratio is less than a threshold, it means that the content of the received signal is significant at the ends of the frequency band allocated to the signal, while the signal should generally be in the center of that frequency band, and therefore this allows the detection of interference from adjacent channels (arrow Y departing from step 100). In this case, the analysis module 14 sends information about the detected interference from adjacent channels to the control module 13, and the control module selects the corresponding strategy for activating the noise suppression module, which in [ Figure 2 The symbol is marked with "STRAT1".

[0062] Conversely, if the ratio is greater than the threshold, no interference from adjacent channels is detected (arrow N departing from step 100).

[0063] Then, the frequency analysis module is configured to determine whether the spectrum of the signal received by 200 is weak or strong dynamic, which is in [ Figure 2 The query "DYN?" is used to indicate this. This analysis is also performed on the signal at the output of the frequency conversion module.

[0064] To perform this analysis, the frequency analysis module calculates the time-varying energy of the signal at frequencies located in the center band of the spectrum and compares this time-varying energy to a predetermined threshold. If the time-varying energy is less than the threshold, then the signal's spectrum is considered weakly dynamic. Figure 2 The arrow "CLA" indicates that the spectrum is considered strongly dynamic if the time variation exceeds a threshold. Figure 2 (The arrow "POP" in the image). The determined result is sent to the control module of the noise suppression module, which then selects the strategy for activating the noise suppression module. [In...] Figure 2Indicated as “STRAT2” and “STRAT3”, “STRAT2” is an activation strategy corresponding to weak dynamic spectrum, and “STRAT3” is an activation strategy corresponding to strong dynamic spectrum.

[0065] In an embodiment, the activation strategy corresponds to the value of a noise detection threshold.

[0066] Therefore, the device 2 for reducing noise may further include a module 16 for detecting a decrease in the modulus of the ratio between the in-phase component and the quadrature component of a modulated radio signal (hereinafter indicated as the I / Q modulus) according to a modulus decrease detection threshold SI / Q. This module may be located downstream of the module for converting the frequency towards an intermediate frequency.

[0067] The device 2 for reducing noise further includes a module 17 for detecting high-frequency noise in a demodulated radio signal, which detects the presence of these spikes by comparing the high-frequency spikes in the demodulated radio signal with a frequency threshold - hereinafter referred to as the high-frequency noise detection threshold SHF.

[0068] The module 16 for detecting a decrease in the I / Q modulus and the module 17 for detecting high-frequency noise are configured to convey to the control module 13 the fact that a decrease in the I / Q modulus or high-frequency noise has been correspondingly detected due to the corresponding threshold being crossed. When the two detection thresholds of modules 16 and 17 have been correspondingly crossed, the control module 13 activates the noise suppression module 12.

[0069] In this embodiment, the different strategies for activating the noise suppression module 12 correspond to the respective values of the modulus decrease detection threshold and the high-frequency noise detection threshold, which are set by the control module 13 at the end of the analysis implemented by the frequency analysis module.

[0070] Therefore, the value of these thresholds in the case of detecting adjacent band interference is indicated by the index “ACI”, the value of these thresholds in the case of no adjacent band interference and in the case of strong dynamic spectrum content is indicated by the index “POP”, and the value of these thresholds in the case of no adjacent band interference and in the case of weak dynamic spectrum content is indicated by the index “CLA”.

[0071] The thresholds are set such that: SI / Q, CLA < SI / Q, ACI < SI / Q, POP and SHF, CLA < SHF, ACI < SHF, POP.

[0072] The thresholds corresponding to weak dynamic spectrum content are the lowest, meaning they correspond to fairly frequent activation of the noise suppression module 12. The thresholds corresponding to strong dynamic spectrum content are the highest, meaning they correspond to less frequent activation of the noise suppression module. Finally, the thresholds used in the case of adjacent channel interference fall between these two, because frequent activation of the noise suppression module 12 is necessary to effectively prevent this type of interference.

Claims

1. An apparatus (10) for reducing noise in radio signals received in the FM band, comprising: - A module (11) for demodulating radio signals, which is adapted to generate demodulated radio signals from received radio signals. - Noise suppression module (12), which is adapted to replace the time series of the demodulated radio signal with the noise-removed sequence. - A module (17) for detecting high-frequency noise in demodulated radio signals based on a high-frequency noise detection threshold. - A module (16) for detecting a decrease in the modulus of the ratio between the in-phase and quadrature components of a demodulated radio signal based on a modulus decrease detection threshold. - A control module (13) for controlling the noise suppression module, which is adapted to manipulate the activation of the noise suppression module, wherein the control module (13) is adapted to activate the noise suppression module (12) based on the detection of high-frequency noise detection and the detection of a decrease in the modulus of the ratio between the in-phase component and the quadrature component. - A spectrum analysis module (14) for analyzing the spectrum of the received radio signal, wherein the control module (13) is configured to control the noise suppression module to achieve: - The first strategy when the spectrum analysis module determines adjacent channel interference. -A second strategy when the spectrum analysis module determines that there is no adjacent channel interference and the received radio signal has a weak dynamic spectrum, and - A third strategy when the spectrum analysis module determines that there is no adjacent channel interference and the received radio signal has a strong dynamic spectrum. The control module (13) is also adapted to set the values ​​of the high-frequency noise detection threshold and the modulus decrease detection threshold according to the selected activation strategy.

2. The device (10) for reducing noise according to claim 1, wherein the values ​​of the high-frequency noise detection threshold and the modulus decrease detection threshold corresponding to the first strategy are respectively included between the values ​​of the high-frequency noise detection threshold and the modulus decrease detection threshold corresponding to the second activation strategy and the third activation strategy.

3. The noise reduction apparatus (10) according to claim 1 further includes a module (15) for converting the frequency of the received radio signal toward an intermediate frequency, and a spectrum analysis module (14) is adapted to analyze the spectrum of the signal from the frequency conversion module.

4. The device (10) for reducing noise according to claim 1, wherein, The spectrum analysis module (14) is adapted to detect adjacent channel interference, and in the event of adjacent channel interference, the control module (13) is configured to implement a first strategy for activating the noise suppression module (12).

5. The noise reduction device (10) according to claim 4, wherein, To detect adjacent channel interference, the spectrum analysis module (14) is configured to: - Determine the ratio between the spectral energy at frequencies included in the center band of the spectrum and the spectral energy at frequencies included in bands located at the ends of the spectrum. - The ratio is compared with a predetermined threshold, and if the ratio is less than the threshold, adjacent channel interference is detected.

6. The noise reduction device (10) according to any one of claims 4 or 5, wherein, In the absence of adjacent channel interference, the spectrum analysis module (14) is also adapted to determine whether the spectrum of the radio signal is weakly dynamic or strongly dynamic, and the control module is configured to implement a second strategy for activating the noise suppression module suitable for weakly dynamic content or a third strategy for activating the noise suppression module suitable for strongly dynamic content, respectively.

7. The noise reduction device (10) according to claim 6, wherein, The spectrum analysis module (14) is configured to determine the time variation of the energy of a signal at a frequency included in the center band of the spectrum, compare the time variation with a predetermined threshold, and determine the sound content of the radio signal as weak dynamic if the time variation is less than the threshold, and determine the sound content of the radio signal as strong dynamic if the time variation is greater than the threshold.

8. The noise reduction device (10) according to any one of claims 1 to 5, wherein, The noise suppression module (12) is adapted to replace the time series of the demodulated signal with a sequence obtained by polynomial interpolation between the last noise-free sample and the returned noise-free sample.

9. An FM radio receiver (1) suitable for receiving and demodulating multiplexed FM radio signals, characterized in that, It includes a noise reduction device (10) according to any one of the preceding claims.

10. A method for reducing noise in a received FM radio signal, the method comprising the steps of: -Analyze the spectrum of the received radio signals, - Demodulate the received radio signals. - Detect the presence of high-frequency noise in the demodulated radio signal based on a high-frequency noise detection threshold. - Detects the decrease in the modulus of the ratio between the in-phase and quadrature components of the demodulated radio signal based on a modulus decrease detection threshold. - Noise suppression is activated based on the detection of the decrease in the modulus of the ratio between the in-phase and quadrature components of the demodulated radio signal and the detection of high-frequency noise. - Determine (100) the ratio between the energy of the spectrum of the radio signal at a frequency included in the center band of the spectrum and the energy of the signal at a frequency included in the bands located at the ends of the spectrum, and if the ratio is less than a determined threshold, select the first activation strategy; otherwise... - Determine (200) the temporal variation of the energy of the radio signal spectrum at frequencies included in the center band of the spectrum, compare the temporal variation with a predetermined threshold, and, - If the time change is less than the threshold, then the second activation strategy is selected. Otherwise, choose the third activation strategy. The values ​​of the high-frequency noise detection threshold and the modulus decrease detection threshold are set according to the selected activation strategy.

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