JP5814649B2 - Reception device and signal processing method - Google Patents

Description

  The present invention relates to signal processing of broadcast waves.

  Conventionally, processing for determining a reception state of a broadcasting station corresponding to a specific frequency such as radio or TV has been performed. Such a determination process is sequentially performed on specific frequencies having a predetermined frequency interval, for example. Specifically, a local signal having a frequency corresponding to one specific frequency is generated by the local oscillation unit of the receiving device. Then, the local signal and the reception signal obtained by receiving the broadcast wave are mixed. The received signal is converted into an intermediate frequency signal by mixing the local signal and the received signal. That is, an IF (Intermediate Frequency) signal that is a conversion signal of an intermediate frequency is generated.

  Then, when the signal level of the IF signal satisfies a predetermined condition, the control unit of the receiving apparatus determines that the reception state of the broadcasting station corresponding to one specific frequency is good. As a result, for example, acoustic information is output from the receiving device.

  Here, the frequency of the local signal to be mixed with the received signal is set in advance to be one of the high frequency side (Upper-Local) and the low frequency side (Lower-Local) with respect to one specific frequency. Has been. The frequency of the local signal corresponding to one specific frequency is also set in advance. For example, when one specific frequency is 83.0 MHz, the local signal on the high frequency side with respect to the one specific frequency is set to 93.7 MHz, for example. Then, the reception signal and the local signal are mixed to obtain an IF signal having a frequency of 10.7 MHz.

  And according to the sequential selection of one specific frequency, the frequency of the local signal mixed with the received signal is also changed sequentially. For example, when a local signal is set on the higher frequency side than the specific frequency and the specific frequency is sequentially selected from 83.0 MHz to 83.2 MHz, the frequency of the local signal is changed from 93.7 MHz according to the change of the specific frequency. Sequentially changed to 93.9MHz. In this way, the same frequency as the specific frequency 200 KHz has been changed in the local signal.

  Here, there is a demand for cost reduction by reducing the size and weight of each component in the receiving apparatus. One countermeasure for satisfying such a requirement is to lower the frequency of the IF signal. Specifically, for example, by reducing the frequency of the IF signal generated as a result of mixing a specific frequency and a local signal from 10.7 MHz to 300 KHz, the number of filters that remove noise superimposed on the IF signal can be reduced. it can. That is, by reducing the frequency of the IF signal processed in the receiving apparatus, the number of parts in the receiving apparatus can be reduced, and the size and weight can be reduced.

  Note that there is Patent Document 1 as a material for explaining the technology related to the present invention.

JP 2010-154501 A

  However, the frequency of the IF signal may be lowered to be affected by the image frequency described below within the frequency band targeted for signal processing (for example, the frequency band of FM broadcast waves). In other words, by setting the IF signal frequency to a relatively low frequency, the frequency of the local signal in the frequency band subject to signal processing is somewhat symmetric with respect to one specific frequency with the frequency of the local signal as the central axis. There may be another broadcast station signal having a signal level of. When such another broadcasting station exists in the frequency band targeted for signal processing, a signal (image frequency) that does not originally exist at the position of one specific frequency sometimes appears. As a result, the control unit may erroneously determine that the reception state is good even though the reception state of the broadcast station corresponding to one specific frequency is not good.

  The object of the present embodiment is to provide a technique for accurately determining the reception state of a broadcast wave.

In order to solve the above-mentioned problem, the invention of claim 1 is a receiving device for receiving a broadcast wave, an oscillation means for oscillating a local signal, a received signal obtained by receiving the broadcast wave, and the local signal. Mixing means for obtaining an intermediate frequency conversion signal, and the conversion signal obtained by mixing the local signal having a predetermined frequency difference from a specific frequency to the high frequency side and the reception signal. Derivation for deriving the signal level of the signal and the signal level of the second signal that is the converted signal obtained by mixing the local signal having a predetermined frequency difference from the specific frequency to the low frequency side and the received signal means and, based on the signal level of the acquired first signal signal level and said second signal of the transmission of the request signal to the deriving means, to correspond to the specific frequency to the received signal Determination means for determining whether or not a broadcast station signal is included, and change control means for performing control related to a change from the specific frequency to a different frequency, wherein the determination means includes a signal level of the first signal. There is judged whether or not the signal level of the observed pre-Symbol second signal is greater than the first threshold value is larger than the first threshold value, the change control means, wherein the signal level of the first signal first If two signals of the signal level is greater than the first threshold value, without performing the determination by said first signal and other signals other than the second signal, the control is not changed the specific frequency to a different frequency Do.

Further, the invention of claim 2, in the receiving apparatus according to claim 1, wherein the change control means, said first signal contact and said second signal noise deviation or the signal level of one signal of the first If the frequency is smaller than the threshold value, the control is performed to change the frequency from the specific frequency to a frequency different from the previous frequency immediately before the specific frequency is changed without executing a plurality of determinations based on the signal level of any one of the signals. I do.

According to a third aspect of the present invention, in the receiving apparatus according to the first or second aspect, the derivation means is located at a position symmetrical to the position of the specific frequency with the position of the frequency of the local signal as a central axis. Deriving a signal level of the unique signal existing in the frequency, the determining means determines whether the signal level of the unique signal is smaller than a second threshold, and the change control means is the signal level of the unique signal Is smaller than the second threshold value, the control is performed so as not to change the specific frequency to a different frequency without performing determination based on signals other than the first signal, the second signal, and the specific signal. Do.

The invention according to claim 4 is the receiving device according to claim 2, further comprising sound output means for outputting sound information, wherein the sound output means is controlled not to change the specific frequency to a different frequency. In such a case, the acoustic information corresponding to the specific frequency is output without outputting the acoustic information corresponding to the immediately preceding frequency, and control is performed to change the specific frequency to a frequency different from the immediately preceding frequency. If so, the acoustic information corresponding to the immediately preceding frequency and the acoustic information corresponding to the specific frequency are not output.
Further, the invention of claim 5 is a signal processing method for processing a received broadcast wave signal, (a) a step of oscillating a local signal, and (b) a received signal obtained by receiving the broadcast wave. Obtained by mixing the local signal and the local signal to obtain a conversion signal of an intermediate frequency, and (c) obtained by mixing the local signal having a predetermined frequency difference from the specific frequency to the high frequency side and the received signal The signal level of the first signal that is the converted signal and the second signal that is the converted signal obtained by mixing the local signal having a predetermined frequency difference from the specific frequency to the low frequency side and the received signal. a step of deriving a signal level, based in (d) of the signal level of the first signal obtained by the transmission of the request signal to the deriving means and the second signal of the signal level, the specific to the received signal Zhou And performing the step of determining whether included signal of a broadcast station corresponding to the number, the control of changes to a different frequency from the (e) the specific frequency,
Comprising a pre Symbol step (d) determines whether the signal level of the observed pre-Symbol second signal when the signal level of the first signal is greater than the first threshold value is greater than the first threshold value and, wherein step (e), the case where the signal level of the first signal the signal level and the second signal is greater than the first threshold value, the first signal and other signals other than the second signal The control without changing the specific frequency to a different frequency is performed without executing the determination according to .

  According to the first aspect of the present invention, the first signal which is a conversion signal obtained by mixing the local signal having a predetermined frequency difference from the specific frequency to the high frequency side and the received signal, and the predetermined frequency from the specific frequency to the low frequency side. Based on both the second signal, which is a converted signal obtained by mixing the local signal having a frequency difference and the received signal, it is determined whether or not the received signal includes a broadcast station signal corresponding to the specific frequency. By determining, the reception state of the signal of the broadcasting station corresponding to the specific frequency can be accurately determined.

  According to the second aspect of the present invention, it is possible to accurately determine the reception state for each specific frequency by further including selection control means for sequentially selecting the specific frequency.

  According to the invention of claim 3, the determination means includes a broadcast station signal corresponding to a specific frequency in the received signal based on one of the first signal and the second signal. If it is determined, the reception state based on one and the other converted signal is determined for each specific frequency by determining whether the received signal includes a broadcast station signal corresponding to the specific frequency based on the other signal. Can be judged accurately.

  According to the fourth aspect of the present invention, when the determination means determines that the received signal includes a broadcast station signal corresponding to the specific frequency based on the first signal and the second signal, the selection control means By stopping the selection at the specific frequency, it is possible to accurately determine whether or not the received signal includes the broadcast station signal of the selected specific frequency, and the selection can be stopped at the frequency at which the broadcast station signal exists.

  According to the invention of claim 5, the determination means determines that the received signal does not include the signal of the broadcasting station corresponding to the specific frequency based on one of the first signal and the second signal. In such a case, the selection control means can determine whether or not the received signal of the selected broadcast station is included in the received signal by continuing the sequential selection of the specific frequency, and there is no broadcast station signal. However, it is possible to determine whether or not another broadcast station signal exists.

  In addition, according to the invention of claim 6, by changing the sensitivity for detecting the noise based on the bandwidth and the degree of the influence of the multipath, the sound quality provided to the user is relatively affected. Noise can be removed.

  According to the invention of claim 7, the influence of noise on the audio signal is reduced by enabling one of the switching means and the removing means and invalidating the other based on the bandwidth, thereby reducing the user's influence. You can ensure the quality of the sound you provide.

  In addition, according to the invention of claim 8, by changing the sensitivity for detecting noise based on the bandwidth and the degree of the influence of multipath, the sound quality provided to the user is relatively affected. Noise can be removed.

  According to the ninth aspect of the present invention, when the signal level of the received signal is lower than the predetermined threshold, the filter means uses the bandwidth as the first width, and when the signal level of the received signal exceeds the threshold, By setting the bandwidth to a second width wider than the first width, the bandwidth can be adjusted according to the signal level of the specific frequency.

  According to the invention of claim 10, the sensitivity changing means sets the sensitivity when the bandwidth is the first width to be higher than the sensitivity when the bandwidth is the second width. Noise that degrades quality can be reliably detected and removed.

  According to the eleventh aspect of the present invention, the sensitivity changing means may change the sensitivity when the bandwidth is the second width and the degree of the multipath influence is relatively small, to the influence of the multipath influence. By making it higher than the sensitivity when the degree is relatively large, the sensitivity of noise can be set according to the degree of the influence of multipath, and the quality of sound provided to the user can be ensured.

  According to the twelfth aspect of the present invention, it is possible to reduce the influence of noise on the audio signal by enabling one of the switching means and the removing means and invalidating the other based on the bandwidth. You can ensure the quality of the sound you provide.

  According to a thirteenth aspect of the present invention, when the interfering wave exists near the frequency of the received signal, the filter means sets the bandwidth to the first width, and when no interfering wave exists near the frequency of the received signal. By setting the bandwidth to a second width wider than the first width, signal noise can be reduced, and the quality of sound provided to the user can be ensured.

  According to the invention of claim 14, the control means enables the removal means when the bandwidth is the first width, and disables the switching means, so that the antenna is affected by an interference wave. It can be prevented that the quality of the sound provided to the user is deteriorated due to frequent switching.

  Further, according to the invention of claim 15, the control means activates the switching means when the bandwidth is the second width, and invalidates the removal means, so that the received signal from the antenna having a good receiving station state is obtained. And the quality of the sound provided to the user can be ensured.

FIG. 1 is a block diagram of a receiving apparatus. FIG. 2 is a diagram illustrating mixing by a high frequency side signal. FIG. 3 is a diagram illustrating mixing by a low frequency side signal. FIG. 4 is a flowchart illustrating the tuner processing. FIG. 5 is a flowchart illustrating processing performed by the DSP and the reception control unit. FIG. 6 is a block diagram showing the configuration of the DSP and the configuration of the reception control unit. FIG. 7 is a diagram illustrating the bandwidth of the variable band filter. FIG. 8 is a graph showing noise sensitivity. FIG. 9 is a diagram illustrating a process for complementing noise included in an audio signal. FIG. 10 is a process flowchart of the reception control unit. FIG. 11 is a process flowchart of the reception control unit. FIG. 12 is a block diagram of the receiving apparatus. FIG. 13 is a diagram illustrating a vehicle including a plurality of antennas. FIG. 14 is a block diagram showing the configuration of the DSP and the configuration of the reception control unit. FIG. 15 is a graph showing a selection state of the switching unit and the adaptive filter. FIG. 16 is a graph showing the S / N ratio when the adaptive filter is disabled and when the adaptive filter is enabled. FIG. 17 is a process flowchart of the reception control unit. FIG. 18 is a process flowchart of the reception control unit.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

<First Embodiment>
<1. Configuration>
<1-1. Block diagram>
FIG. 1 is a block diagram of the receiving device 1. The receiving device 1 receives a broadcast wave via the antenna 101. Then, the received broadcast wave received signal is subjected to signal processing to output sound, images, and the like. In addition, the receiving device 1 is a navigation device having a display for displaying navigation guidance, an audio device having a display for displaying music title information, TV video, and acoustic information, etc., and is carried by a user and used in a vehicle. Possible smartphones. Hereinafter, in the present embodiment, a radio apparatus that receives FM (Frequency Modulation) broadcast waves and outputs an audio signal will be described as an example.

  The receiving apparatus 1 mainly includes an antenna 101, a tuner 31, a DSP (Digital Signal Processor) 41, a reception control unit 51, an amplification unit 61, an operation unit 71, and a speaker 201.

  The antenna 101 is provided in the vehicle and receives broadcast waves. The antenna 101 is, for example, one of a feeder antenna provided near the A pillar of the vehicle, a pole antenna provided on the roof of the vehicle, and a film antenna provided on the glass surface of the vehicle.

  The tuner 31 selects a broadcast station corresponding to a specific frequency and performs a process of converting a received signal corresponding to the specific frequency into an intermediate frequency. The tuner 31 mainly includes functions of a BPF (Band Pass Filter) 301, a tuning unit 302, a local oscillation unit 303, and a mixing unit 304.

  The BPF 301 passes a signal in a frequency band (for example, 88.0 MHz to 108 MHz, 76.0 MHz to 90.0 MHz, etc.) corresponding to the FM broadcast wave among a plurality of frequencies included in the broadcast wave reception signal.

  The tuning unit 302 is a signal of a broadcasting station corresponding to a specific frequency (hereinafter, based on an instruction signal of a tuner control unit 501 of the reception control unit 51 described later, among reception signals in a frequency band corresponding to an FM broadcast wave that has passed through the BPF 301. , Also referred to as “specific frequency signal”). For example, a broadcast station signal corresponding to a specific frequency having a center frequency of 98.1 MHz is derived from frequencies of 88.0 MHz to 108 MHz.

  Note that the tuning unit 302 sequentially selects a specific frequency from one specific frequency to another specific frequency by an instruction signal from the tuner control unit 501. For example, when the frequency interval between a broadcast station corresponding to one specific frequency and a broadcast station corresponding to another specific frequency is 200 KHz, if one specific frequency is 98.1 MHz, then another specific frequency 98.3 MHz is set. select. As a result, it is possible to change the specific frequency for accurately determining the reception state for each specific frequency.

  The local oscillator 303 oscillates a local signal mixed with the specific frequency signal. Specifically, a local signal (hereinafter, also referred to as “high frequency side signal”) having a difference of a predetermined frequency (for example, 300 KHz) from the specific frequency to the high frequency side is oscillated. Further, a local signal (hereinafter also referred to as “low frequency side signal”) having a difference of a predetermined frequency (for example, 300 KHz) from the specific frequency to the low frequency side is oscillated.

  Note that the local oscillator 303 changes the frequency of the local signal as the tuner controller 501 sequentially selects specific frequencies. For example, when the specific frequency is 98.1 MHz, the frequency of the local signal is 98.4 MHz having a difference of 300 KHz on the high frequency side. When the specific frequency derived by the tuning unit 302 is changed from 98.1 MHz to 98.3 MHz by the sequential selection of specific frequencies by the tuner control unit 501, the local signal is changed from 98.4 MHz to 98.6 MHz. Similarly, the local signal on the low frequency side is also changed to a signal having a frequency having a predetermined frequency difference from the specific frequency. Note that the frequency difference between the specific frequency and the frequency of the local signal is associated with an intermediate frequency (for example, 300 KHz) processed by the DSP 41 in advance.

  The mixing unit 304 mixes the specific frequency signal output from the tuning unit 302 and the local signal oscillated from the local oscillation unit 303. Specifically, the high frequency side signal and the specific frequency signal are mixed. Then, the low frequency side signal and the specific frequency signal are mixed at a timing different from the timing at which the high frequency side signal and the specific frequency signal are mixed. The mixed signal is output to the DSP 41 as an intermediate frequency conversion signal.

  The DSP 41 performs processing for deriving an audio signal from the converted signal converted to the intermediate frequency. Further, a signal level of an intermediate frequency conversion signal (hereinafter also referred to as “high frequency side conversion signal”) in which the high frequency side signal and the specific frequency signal are mixed is derived and transmitted to the reception control unit 51. Further, a signal level of an intermediate frequency conversion signal (hereinafter, also referred to as “low frequency side conversion signal”) obtained by mixing the low frequency side signal and the specific frequency signal is derived and transmitted to the reception control unit 51.

  The reception control unit 51 is a computer including a CPU, a RAM, a ROM, and the like, and various functions including signal processing of the reception device 1 are realized by the CPU performing arithmetic processing according to a predetermined program. The reception control unit 51 transmits and receives signals to and from the tuner 31 and the DSP 41. The reception control unit 51 mainly includes functions of a tuner control unit 501, a DSP control unit 502, and a determination unit 503.

  The tuner control unit 501 outputs an instruction signal for selecting a specific frequency selected by a user operation from the operation unit 71 or the like to the tuner 31. Specifically, the tuner control unit 501 instructs to stop selection at one specific frequency in response to the determination by the determination unit 503, which will be described later, whether or not the received signal includes a broadcast station signal corresponding to the specific frequency. One of the signal and the instruction signal that continues the sequential selection of the specific frequency is output to the tuner 31. The tuner 31 receives these instruction signals, thereby stopping selection at one specific frequency or continuing sequential selection of specific frequencies.

  The DSP control unit 502 outputs a request signal requesting the DSP 41 for information on at least one of the high-frequency side converted signal and the low-frequency side converted signal. When the determination unit 503 determines that the received signal includes a broadcast station signal corresponding to the specific frequency from the information of one signal, the signal requesting the information of the other converted signal is output to the DSP 41.

  The determination unit 503 determines whether or not the signal level of the converted signal exceeds a predetermined threshold value. And when the signal level of both the high frequency side conversion signal and the low frequency side conversion signal exceeds a predetermined threshold value, it is determined that the signal of the broadcasting station corresponding to the specific frequency is included in the received signal. Thereby, the reception state of the signal of the broadcasting station corresponding to a specific frequency can be determined correctly.

  The amplifying unit 61 amplifies the signal level of the audio signal output from the DSP 41 based on a predetermined amplification factor, and outputs the amplified audio signal to the speaker 201.

  The operation unit 71 is operated by the user in order to realize various functions of the receiving device 1, and is, for example, a hard switch provided in the receiving device 1. Further, when the receiving device 1 includes a display, the operation unit 71 is a touch panel that is operated by bringing a user's finger into contact with the display.

The speaker 201 outputs the audio signal whose signal level is amplified by the amplification unit 61 to the user as acoustic information.
<1-2. Mixing treatment of high frequency side and low frequency side>
FIG. 2 is a diagram illustrating mixing by a high frequency side signal. In the graph shown in FIG. 2, the vertical axis represents the signal level, the horizontal axis represents the signal frequency, and the signal level of the broadcast wave is shown for each frequency.

  First, based on an instruction signal from the tuner control unit 501 to the tuner 31, the tuning unit 302 derives a specific frequency signal that is a broadcast wave signal corresponding to a specific frequency (for example, 98.1 MHz).

  Then, as shown in the upper diagram of FIG. 2, a local signal LH having a frequency f2 (for example, 98.4 MHz) having a predetermined frequency difference (for example, 300 KHz) from the specific frequency f1 (98.1 MHz) to the high frequency side is generated by the local oscillation unit 303. It is oscillated from. Next, the signal of the specific frequency f1 and the local signal LH are mixed by the mixing unit 304. As a result, a conversion signal (high frequency side conversion signal) having an intermediate frequency (300 KHz) that is the difference between the frequency (98.1 MHz) of the specific frequency f1 and the frequency f2 (98.4 MHz) of the local signal LH is output to the DSP 41.

  Note that, by changing the frequency of the local signal corresponding to the specific frequency f1, the frequency of the IF signal processed in the receiving apparatus 1 can be set to a frequency different from 300 KHz. For example, the frequency of the local signal corresponding to the specific frequency is set so that the frequency of the IF signal generated by mixing the specific frequency and the local signal is 10.7 MHz, which is higher than 300 KHz. However, the IF signal is more susceptible to noise as the frequency becomes higher. As a result, it is necessary to provide a filter for removing the influence of noise on the IF signal, and the increase in the number of parts hinders the reduction in size and weight of the receiving apparatus 1 and increases the manufacturing cost. Therefore, by setting the IF signal to a relatively low frequency (for example, a frequency of 300 KHz with respect to a frequency of 10.7 MHz), the IF signal is hardly affected by noise. Thereby, size reduction and weight reduction of the receiver 1 can be achieved, and manufacturing cost can also be reduced.

  However, if the frequency of the IF signal is relatively low (300 KHz), the frequency of another broadcast station that exists at the position of the specific frequency and the target frequency with the local signal as the central axis is the frequency band ( For example, it may be included in the frequency band of FM broadcast waves. Such a phenomenon occurs more frequently when the frequency of the IF signal is relatively low (300 KHz) than when the frequency of the IF signal is relatively high (10.7 MHz). In other words, when the frequency interval between the specific frequency and the local signal is narrower than when the frequency interval between the specific frequency and the local signal is wide (when the frequency of the IF signal is set relatively high), the frequency of the IF signal is reduced. When set relatively low), it is often affected by the image frequency described below.

  Returning to the upper diagram of FIG. 2, since the signal of the broadcasting station corresponding to the specific frequency f1 is not included in the received signal, the signal level is zero. Therefore, originally, even if the mixing unit 304 mixes the signal of the specific frequency f1 and the local signal LH, a signal that is the difference between the two is not output to the DSP 41. Therefore, the received signal of the broadcast station corresponding to the specific frequency f1 is not output. The determination unit 503 of the reception control unit 51 determines that no signal is included.

  However, a broadcast station signal SA (hereinafter also referred to as “specific signal SA”) corresponding to a frequency f3 (for example, 98.7 MHz) having a frequency interval of 300 KHz with the local signal LH is included in the frequency band of the FM broadcast wave. May exist. As described above, when the specific signal SA having a certain signal level exists at the position of the frequency symmetrical to the specific frequency f1 with the local signal LH as the central axis, a signal that does not originally exist at the position of the specific frequency appears (image). frequency).

  That is, the image frequency appears as a frequency signal SIa that does not originally exist at the position of the specific frequency f1 as shown in the lower diagram of FIG. The frequency at which the frequency signal SIa appears is at the same frequency as the specific frequency f1. Then, the mixing unit 304 mixes the frequency signal SIa and the local signal LH.

  As a result, a converted signal obtained by mixing the frequency signal SIa and the local signal LH based on the request signal of the DSP control unit 502 is output from the DSP 41 to the reception control unit 51. If the high-frequency conversion signal exceeds a predetermined threshold in the determination performed by the determination unit 503, the determination unit 503 erroneously determines that the received signal includes a broadcast station signal corresponding to the specific frequency. There is a time.

  Therefore, when the determination unit 503 determines that the received signal includes a broadcast station signal corresponding to the specific frequency based on the high frequency side converted signal, the low frequency side converted signal causes the broadcast corresponding to the specific frequency to the received signal. The determination unit 503 determines whether a station signal is included.

  FIG. 3 is a diagram illustrating mixing by a low frequency side signal. In the graph shown in FIG. 3, the vertical axis represents the signal level, the horizontal axis represents the signal frequency, and the signal level of the broadcast wave is shown for each frequency. Based on an instruction signal from the tuner control unit 501 to the tuner 31, the tuning unit 302 derives a signal having a specific frequency f1.

  Then, as shown in the upper diagram of FIG. 3, a local signal LL having a frequency f4 (97.8 MHz) having a predetermined frequency difference (300 KHz) from the specific frequency f1 to the low frequency side is oscillated from the local oscillator 303. As a result, the signal of the specific frequency f1 and the local signal LL are mixed by the mixing unit 304, and the conversion signal (low frequency side conversion) of the intermediate frequency (300 KHz) of the difference between the specific frequency f1 and the frequency f4 of the local signal LL Signal) is output to the DSP 41.

  In this case, since the signal of the broadcasting station corresponding to the specific frequency f1 is not included in the received signal, the signal level is zero. Therefore, even if the mixing unit 304 mixes the signal of the specific frequency f1 and the local signal LL, a signal that is the difference between the two is not output to the DSP 41. As a result, the determination unit 503 determines that the received signal does not include a broadcast station signal corresponding to the specific frequency f1.

  As shown in the upper diagram of FIG. 3, the specific signal SA exists at the position of the frequency (98.7 KHz) on the high frequency side from the local signal, but the position of the frequency symmetrical to the specific signal SA with the local signal LL as the central axis. Is a frequency f5 (96.9 MHz). Then, the frequency signal SIb of the image frequency appears at the position of the frequency f5. In this case, even if the mixing unit 304 mixes the signal of the specific frequency f1 and the local signal LL, a signal that is the difference between the specific frequency f1 and the frequency f5 of the frequency signal SIb is present in the DSP 41. Not output. As a result, the determination unit 503 determines that the received signal does not include a broadcast station signal corresponding to the specific frequency f1.

  In this way, the high-frequency side converted signal that is a converted signal obtained by mixing the high-frequency side signal and the received signal, and the low-frequency side converted signal that is a converted signal obtained by mixing the low-frequency side signal and the received signal. Based on both of the above, the determination unit 503 determines whether or not the received signal includes a broadcast station signal corresponding to the specific frequency. Thereby, the reception state of the signal of the broadcasting station corresponding to a specific frequency can be determined correctly.

<1-3. Processing flowchart>
FIG. 4 is a flowchart for explaining the processing of the tuner 31. In step S101, when the tuner 31 receives an instruction signal from the tuner control unit 501 of the reception control unit 51 (Yes in step S101), the tuning unit 302 derives a specific frequency signal based on the instruction signal. (Step S102), the process proceeds to Step S103. If the tuner 31 has not received the instruction signal from the tuner control unit 501 (No in step S101), the process is terminated.

  In step S103, the local oscillation unit 303 oscillates either the high frequency side signal or the low frequency side signal (step S103), and proceeds to the process of step S104. In addition, when the conversion signal obtained by mixing one specific frequency and one of the high frequency side signal and the low frequency side signal satisfies the determination condition of the determination unit 503, the other local signal is It oscillates. Specifically, based on the instruction signal from the tuner control unit 501, the other local signal of the high frequency signal and the low frequency signal is oscillated at a timing different from that of the one local signal.

  In step S104, the specific frequency signal output from the tuning unit 302 and the local signal oscillated from the local oscillation unit 303 are mixed (step S104), and the process proceeds to step S105.

  In step S105, the intermediate frequency conversion signal generated by mixing the specific frequency signal and the local signal is output to the DSP 41 (step S105).

  FIG. 5 is a flowchart showing processing of the DSP 41 and the reception control unit 51.

  In step S201, the DSP control unit 502 of the reception control unit 51 transmits a request signal for conversion signal information (for example, the signal level of the high frequency side conversion signal) to the DSP 41, and the process proceeds to step S301.

  In step S301, the DSP 41 that has received the request signal from the DSP control unit 502 transmits the signal level of the high frequency side converted signal to the reception control unit 51 (step S301), and proceeds to the process of step S202.

  In step S202, the reception control unit 51 receives the signal level of the high frequency side converted signal (step S202), and the process proceeds to step S203.

  In step S203, when the signal level of the high-frequency side converted signal exceeds a predetermined threshold (step S203 is Yes), the process proceeds to step S204. If the signal level of the high frequency side converted signal is below the predetermined threshold (No at Step S203), the process proceeds to Step S208 described below.

  In step S204, the DSP control unit 502 transmits a request signal for conversion signal information (for example, the signal level of the low frequency side conversion signal) to the DSP 41 (step S204), and the process proceeds to step S205. In addition, the information of the conversion signal requested | required with respect to DSP41 requests | requires the signal level of the low frequency side conversion signal, when the signal level of the high frequency side conversion signal is requested | required in step S201. If the signal level of the low frequency side converted signal is requested in step S201, the signal level of the high frequency side converted signal is requested in step S204.

  In step 205, the reception control unit 51 receives the signal level of the low frequency side converted signal (step S205), and the process proceeds to step S206.

  In step S206, when the signal level of the low frequency side converted signal exceeds the predetermined threshold (step S206 is Yes), the process proceeds to step S207. If the signal level of the low frequency side converted signal is below the predetermined threshold (No in step S206), the process proceeds to step S208.

  As described above, when the determination unit 503 determines that the received signal includes a broadcast station signal corresponding to the specific frequency based on one of the high-frequency side converted signal and the low-frequency side converted signal, the other side Based on this signal, the determination unit 503 determines whether the received signal includes a broadcast station signal corresponding to the specific frequency. Thereby, the receiving state based on one and the other converted signals can be accurately determined for each specific frequency.

  Returning to step S207, the tuner control unit 501 outputs to the tuner 31 an instruction signal for stopping the selection of the specific frequency of the tuner 31, and the process is terminated. Thereby, it is possible to accurately determine whether or not the signal of the selected broadcasting station of the specific frequency is included in the received signal, and the selection can be stopped at the frequency where the signal of the broadcasting station exists. Note that the sound information of the broadcasting station corresponding to the specific frequency is output from the speaker 201 by stopping the selection of the specific frequency.

In step S208, the tuner control unit 501 outputs an instruction signal for changing to a specific frequency different from one specific frequency to the tuner 31 (step S208), and the process is terminated. That is, the tuner control unit 501 continues to sequentially select specific frequencies. Thereby, it is possible to accurately determine whether or not the signal of the selected broadcasting station is included in the received signal, and it is possible to determine whether or not the signal of another broadcasting station exists even when the signal of the broadcasting station does not exist. It becomes possible.
<Second Embodiment>
Next, a second embodiment will be described. In the first embodiment, the tuner 31 mainly mixes the received signal and the local signal on the high frequency side and the low frequency side to acquire the conversion signal of the intermediate frequency, and includes the broadcast station signal of the specific frequency. The process of determining whether or not has been described. In contrast, in the second embodiment, the processing of the DSP 41 for the converted signal (IF signal) converted to the intermediate frequency will be described.

  In the second embodiment, the sensitivity for detecting the noise included (superposed) in the audio signal detected by the DSP 41 is adjusted. Specifically, the bandwidth information of the band-variable filter 402 shown in FIG. 6 to be described later, the signal level information of the IF signal of the adaptive filter 404, and the information of the amplitude fluctuation value of the IF signal (hereinafter, these three pieces of information will be described). The detection sensitivity of noise is adjusted based on “sensor information”.

  In the second embodiment described below, a part of the configuration and processing is the same as that of the first embodiment. Therefore, the description of the same part is omitted, and the different configuration and processing are described in detail. explain.

  Conventionally, noise included in an audio signal after detecting a converted signal at an intermediate frequency (for example, pulse noise generated due to an operation related to a vehicle such as an opening / closing operation of an electric door mirror of a vehicle) is a quality of sound provided to a user. It becomes a big factor to decrease. Therefore, it is necessary to detect and remove such noise with high accuracy. Specifically, for example, noise detection is performed on a signal exceeding the frequency band of the audio signal (for example, exceeding the frequency band of 20 Hz to 15 KHz) based on a predetermined threshold, and there is a signal exceeding the predetermined threshold. When doing so, the complementary process which removes the signal of the noise contained in an audio | voice signal was performed.

  In order to improve the accuracy of noise detection that is a target of the complement processing, the detection threshold value is lowered. In addition, among the noises included in the audio signal, for example, there is multipath noise in addition to the pulse noise which is a major factor that degrades the quality of the sound provided to the user as described above. Here, compared with pulse noise, multipath noise often has a relatively small influence on the deterioration of sound quality provided to the user. When such multipath noise is detected as the noise to be complemented and the complement process is performed, the quality of the sound provided to the user may be lower than when the complement process is not performed.

  However, if the threshold value for detecting the noise to be complemented as described above is lowered, there is no need to detect it as a target for the complement processing when the degree of influence of the quality of the sound provided to the user is taken into consideration. In some cases, multipath noise is also detected and complementary processing is performed on an audio signal including (superimposing) multipath noise. Thus, the quality of the sound provided to the user may be deteriorated by detecting the multipath noise as a target of the complement processing.

  The object of the present embodiment is to adjust the noise detection sensitivity in accordance with the degree of the influence of the sound quality degradation provided to the user.

<2-1. Block diagram>
FIG. 6 is a block diagram showing the configuration of the DSP 41a and the configuration of the reception control unit 51a. The DSP 41a performs a process of deriving an audio signal from the intermediate frequency conversion signal. The DSP 41 a mainly includes an A / D conversion unit 401, a variable band filter 402, a detection unit 403, an adaptive filter 404, a detection unit 405, a noise detection unit 406, and a complement unit 407.

  The A / D converter 401 samples and quantizes the analog data IF signal output from the tuner 31 and converts it into digital data.

  The band variable filter 402 passes and outputs some IF signals in a frequency band among IF signals including a plurality of frequency signals. For example, an IF signal included in a bandwidth of ± 100 KHz is passed symmetrically about a frequency of 300 KHz. Further, the variable band filter 402 changes a symmetrical bandwidth with respect to the central axis. For example, the bandwidth of ± 100 KHz is changed symmetrically to the bandwidth of ± 200 KHz with the frequency being 300 KHz as the central axis. The bandwidth changing condition will be described in detail later.

  The detection unit 403 detects the signal level and amplitude fluctuation value of the IF signal that has passed through the band-variable filter 402. Here, the FM broadcast wave is frequency-modulated by superimposing an audio signal on the carrier wave. For this reason, the amplitude fluctuation value of the FM broadcast wave is essentially substantially zero. An intermediate frequency IF signal obtained by receiving a broadcast wave and down-converting the received signal is also a frequency-modulated signal, and the amplitude variation value is a substantially zero signal.

  Therefore, when the detection unit 403 detects an amplitude fluctuation value exceeding a predetermined threshold value from the IF signal that has passed through the band-variable filter 402, it is possible that the IF signal is affected by other signals. For example, there is a case where a broadcast wave reception signal is affected by a multipath effect that a direct wave of a broadcast wave is reflected by an object and becomes a reflected wave, and an amplitude variation occurs in an IF signal obtained by frequency conversion of the reception signal. Note that the amplitude fluctuation value of the IF signal and the value of the signal level of the IF signal detected by the detection unit 403 are output to the reception control unit 51.

  The adaptive filter 404 performs processing for setting the amplitude fluctuation value to substantially zero based on the instruction signal from the reception control unit 51 based on the amplitude fluctuation value. That is, the amplitude variation of the IF signal caused by the multipath effect is removed.

  The detection unit 405 detects the IF signal and derives an audio signal. Detection in the case of FM broadcast waves is performed by, for example, a PTL (Phase Tracking Loop) method, a PLL (Phase locked loop) method, or the like.

  The noise detection unit 406 detects noise included in the audio signal detected by the detection unit 405. That is, noise detection is performed based on the threshold value for a signal exceeding the frequency band of the audio signal (for example, exceeding the frequency band of 20 Hz to 15 KHz). Note that the sensitivity change corresponding to the noise detection threshold is determined by the bandwidth of the variable bandwidth filter 402 and the degree of multipath influence on the IF signal detected by the detection unit 403 (specifically, the amplitude of the IF signal). (Variable value).

  Specifically, information on the bandwidth of the variable bandwidth filter 402 and the degree of multipath influence on the IF signal detected by the detection unit 403 is transmitted from the detection unit 403 to the reception control unit 51a. Then, noise detection sensitivity information derived by the deriving unit 504 based on the bandwidth and the degree of multipath influence is transmitted from the reception control unit 51a to the DSP 41a. As a result, the sensitivity of the noise detection unit 406 is changed.

  The complement unit 407 removes the noise signal superimposed on the audio signal by the complement process, and outputs the signal as an audio frequency band (AF) signal. The supplement processing will be described in detail later.

  The reception control unit 51 transmits / receives a signal to / from the DSP 41a and mainly includes a derivation unit 504. The reception control unit 51 mainly receives sensor information from the DSP 41a and performs various processes.

  The deriving unit 504 derives the sensitivity of noise detected by the noise detecting unit 406 (hereinafter also referred to as “noise sensitivity”) based on the bandwidth and amplitude fluctuation value information received from the DSP 41a. The derived noise sensitivity is transmitted from the reception control unit 51a to the DSP 41a, and the sensitivity of the noise detection unit 406 is changed to be the noise sensitivity received from the reception control unit 51a.

<2-2. Changing bandwidth of variable bandwidth filter>
FIG. 7 is a diagram illustrating the bandwidth of the variable band filter 402. FIG. 7 is a graph in which the vertical axis represents the signal level and the horizontal axis represents the frequency. Further, the upper diagram of FIG. 7 shows a signal passing region FT1 having a bandwidth having a symmetric frequency (± 200 KHz) with a frequency fc (for example, 300 KHz) set as a frequency for performing signal processing by the DSP 41a as a central axis. Yes.

  That is, the frequency fh (500 KHz) obtained by adding the frequency fw11 (200 KHz) to the high frequency side with respect to the frequency fc (300 KHz) serving as the central axis is one end of the bandwidth. Further, the band variable filter 402 converts the IF signal included in the signal passing region FT1 of the bandwidth fwa (100 KHz to 500 KHz) whose frequency fs (100 KHz) obtained by subtracting the frequency fw11 (200 KHz) to the low frequency side is the other end of the bandwidth. Pass through. Note that signals outside the range of the signal passing region FT1 are not allowed to pass through the band variable filter 402.

  Next, a lower part of FIG. 7 shows a signal passing region FT2 having a bandwidth that is symmetric with respect to a frequency fc (for example, 300 kHz) as a central axis.

  That is, the frequency fha (400 KHz) obtained by adding the frequency fw21 (100 KHz) to the high frequency side with respect to the frequency fc (300 KHz) serving as the central axis is one end of the bandwidth. Further, the band variable filter 402 converts the IF signal included in the signal passing region FT2 of the bandwidth fwb (200 KHz to 400 KHz) whose frequency fsa (200 KHz) is the other end of the bandwidth by subtracting fw21 (100 KHz) to the low frequency side. Let it pass. Note that signals outside the range of the signal passing region FT2 are not allowed to pass through the band variable filter 402.

  Here, the difference between the upper diagram and the lower diagram in FIG. 7 is the bandwidth. That is, when the bandwidth fwb shown in the lower diagram is the first width and the bandwidth fwa shown in the upper diagram is the second width, the first width is narrower than the second width. Further, such a change in bandwidth is performed based on the signal level of the IF signal detected by the detection unit 403.

  Specifically, when the signal level of the IF signal detected by the detection unit 403 is lower than a predetermined threshold, the bandwidth of the band variable filter 402 becomes the first width (bandwidth fwb). When the signal level of the IF signal detected by the detection unit 403 exceeds a predetermined threshold, the bandwidth of the band variable filter 402 becomes the second width (bandwidth fwa). Thereby, the bandwidth of the variable band filter 402 can be adjusted according to the signal level of the IF signal.

<2-3. Noise sensitivity value>
FIG. 8 is a graph showing noise sensitivity. The vertical axis of the graph is sensitivity, and the horizontal axis is signal level. The signal level is the signal level of the IF signal detected by the detection unit 403. The horizontal axis threshold 1 is, for example, 5 dB, and the threshold 2 is, for example, 1 dB. In addition, the signal level that is a condition for changing the bandwidth of the above-described variable band filter 402 to the first width and the second width is the signal of the IF signal detected by the detection unit 403 as with the signal level on the horizontal axis. Is a level. The predetermined threshold of the signal level under the condition for changing the bandwidth is a value different from the threshold 1 and threshold 2 of the signal level on the horizontal axis in FIG. 8, for example, a value of 20 dB.

  As shown in FIG. 8, when the signal level is lower than the threshold value 2, the sensitivity of the noise detection unit 406 is the sensitivity Fe1. Sensitivity Fe1 is the lowest sensitivity. That is, the threshold value for detecting the noise of the noise detection unit 406 is set to be the highest.

  Next, when the signal level of the IF signal exceeds the threshold value 1, the sensitivity of the noise detection unit 406 becomes the sensitivity Fe2. When the signal level of the IF signal exceeds the threshold 2 and falls below the threshold 1, the signal level of the IF signal has a sensitivity of Fe2, Fe3, or Fe4. Which of these sensitivities is set is determined by the bandwidth of the variable band filter 402.

  Specifically, when the bandwidth of the variable band filter 402 is the second width, the sensitivity is one of the sensitivity Fe2 and the sensitivity Fe3. Further, when the bandwidth of the variable band filter 402 is the first width, the sensitivity is the sensitivity Fe4. That is, the sensitivity when the bandwidth of the variable bandwidth filter 402 is the first bandwidth is set higher than the sensitivity when the bandwidth is the second bandwidth. Thereby, the noise which degrades the quality of the sound provided to the user can be reliably detected and removed.

  In addition, when the bandwidth of the noise detection unit 406 is the second bandwidth, which of the sensitivity Fe2 and the sensitivity Fe3 is determined is determined according to the degree of multipath influence detected by the detection unit 403. Is done. Specifically, when the bandwidth of the noise detection unit 406 is the second bandwidth, the sensitivity when the degree of multipath influence is relatively small is higher than the sensitivity when the multipath influence is relatively large. Also make it high.

  More specifically, when the amplitude fluctuation value of the IF signal detected by the detection unit 403 is below a predetermined threshold (when the degree of multipath influence on the IF signal is relatively small), the sensitivity of the noise detection unit 406 is set as sensitivity. Fe3. When the amplitude fluctuation value of the IF signal detected by the detection unit 403 exceeds a predetermined threshold (when the influence of multipath is relatively large), the sensitivity of the noise detection unit 406 is set as sensitivity Fe2. Thereby, the sensitivity of noise can be set according to the degree of multipath influence, and the quality of sound provided to the user can be ensured.

  When the sensitivity of the noise detection unit 406 is any one of the sensitivity Fe2, sensitivity Fe3, and sensitivity Fe4, and the signal level falls below the threshold value 2, the sensitivity of the noise detection unit 406 is set to the sensitivity Fe1. Is done.

<2-4. Complementary processing>
FIG. 9 is a diagram illustrating a process for complementing noise included in an audio signal. In the upper and lower diagrams of FIG. 9, the vertical axis represents amplitude and the horizontal axis represents time. The upper diagram of FIG. 9 shows a state where the pulse noise SN is superimposed on the audio signal S1. When the pulse noise SN exceeds the noise sensitivity that is a threshold for detecting noise of the noise detection unit 406, the complementing unit 407 removes the pulse noise signal included in the audio signal by the complementing process as shown in the lower diagram of FIG. To do. That is, a complement section GW is set from the time (time t1) at which complement processing is started to the time (time t2) at which complement processing is ended, and the pulse noise SN to be complemented from the audio signal S1 is supplemented by the complement unit 407. Removed.

<2-5. Processing flowchart>
10 and 11 are processing flowcharts of the reception control unit 51a. In step S401, the reception control unit 51a receives the sensor information from the DSP 41a (step S401), and the process proceeds to step S402.

  In step S402, when the signal level of the IF signal included in the sensor information is lower than the threshold 2 when compared with the threshold 2 (No in step S402), the reception control unit 51a transmits information on the sensitivity Fe1 to the DSP 41a (step S402). S403). The DSP 41a that has received the information on the sensitivity Fe1 sets the noise sensitivity of the noise detection unit 406 to the sensitivity Fe1. Thereby, it is possible to detect only noise having a large influence on the quality of the sound provided to the user.

  Returning to step S402, if the signal level of the IF signal exceeds the threshold 2 (Yes in step S402), the process proceeds to step S404.

  In step S404, if the signal level of the IF signal exceeds the threshold 1 that is higher than the threshold 2 (Yes in step S404), the process proceeds to step S405, and information on the sensitivity Fe2 is transmitted to the DSP 41a (step S405). . The DSP 41a that has received the information on the sensitivity Fe2 sets the noise sensitivity of the noise detection unit 406 to the sensitivity Fe2.

  Returning to step S404, if the signal level of the IF signal is lower than the threshold 1 (No in step S404), the process proceeds to step S406 shown in FIG.

  In step S406, when the bandwidth of the variable band filter 402 included in the sensor information is the first width narrower than the second width (step S406 is Yes), the process proceeds to step S407.

  In step S407, the reception control unit 51a transmits information on sensitivity Fe4 to the DSP 41a (step S407). The DSP 41a that has received the information on the sensitivity Fe4 sets the noise sensitivity of the noise detection unit 406 to the sensitivity Fe4. Thereby, the noise (for example, pulse noise) which reduces the quality of the sound provided to the user can be reliably detected.

  Returning to step S406, if the bandwidth of the band-variable filter 402 is not the first width, that is, if the bandwidth is a second width wider than the first width (step S406 is No), the process proceeds to step S408.

  In step S408, when the amplitude variation value of the IF signal included in the sensor information exceeds a predetermined threshold (step S408 is Yes), the process proceeds to step S409. That is, when the influence of multipath is relatively large, the process proceeds to step S409.

  In step S409, the reception control unit 51 transmits information on sensitivity Fe2 to the DSP 41a (step S409). The DSP 41a that has received the information on the sensitivity Fe2 sets the noise sensitivity of the noise detection unit 406 to the sensitivity Fe2. Thus, when the degree of multipath influence is relatively large, the noise sensitivity of the noise detection unit 406 can be set relatively low.

  Returning to step S408, if the amplitude fluctuation value of the IF signal included in the sensor information is below the predetermined threshold (No in step S408), the process proceeds to step S410. That is, when the influence of multipath is relatively small, the process proceeds to step S410.

  In step S410, the reception control unit 51a transmits information on sensitivity Fe3 to the DSP 41a (step S410). The DSP 41a that has received the information on the sensitivity Fe3 sets the noise sensitivity of the noise detection unit 406 to the sensitivity Fe3. Thereby, when the degree of multipath influence is relatively small, the sensitivity of noise can be set relatively high.

<Third Embodiment>
Next, a third embodiment will be described. In the second embodiment, the noise detection sensitivity of the noise detection unit 406 is changed based mainly on the bandwidth of the variable bandwidth filter 402 and the fluctuation value of the amplitude of the IF signal detected by the detection unit 403. explained. On the other hand, in the third embodiment, one of the two functions is validated and the other function is invalidated based on the bandwidth of the band-variable filter 402. Specifically, the function of switching to an antenna having a good broadcast wave reception state among a plurality of antennas (for example, the antennas 101 and 101a illustrated in FIG. 13) provided in the vehicle (for example, the vehicle 9 illustrated in FIG. 13). Then, one of the functions of the adaptive filter 404 that removes amplitude fluctuations due to multipath is enabled, and the other is disabled. Thereby, the influence of noise on the audio signal can be reduced, and the quality of the sound provided to the user can be ensured.

  In the third embodiment described below, a part of the configuration and processing is the same as that of the second embodiment. Therefore, description of the same part is omitted, and a different configuration and processing will be described. .

  Conventionally, an antenna of a receiving device provided in a vehicle has received a reflected wave in which a direct wave is reflected on an object together with the direct wave. That is, there are radio waves that are directly received by the antenna among broadcast waves and radio waves that are received by the antenna after being reflected by the reflector, and the arrival times of the two radio waves are slightly different (multipath). For this reason, the direct wave and the reflected wave interfere with each other, resulting in a received signal that is affected by multipath (amplitude fluctuation and phase shift occur in the signal) compared to the received signal of the direct wave. For this reason, noise (hereinafter also referred to as “multipath noise”) may be superimposed on an audio signal or the like provided to the user. As a countermeasure for this, for example, a technique (diversity) is provided in which a vehicle is provided with a plurality of antennas, broadcast waves are received by the respective antennas, and a broadcast wave of an antenna having the best reception state is selected.

  However, when the antenna is switched in order to select an antenna having a good reception state, a sharp amplitude variation sometimes occurs in the IF signal. If the receiver has an adaptive filter that adjusts amplitude fluctuations due to the effects of multipath, if the amplitude fluctuation occurs in the IF signal while the adaptive filter is operating, the adaptive filter immediately changes the amplitude. In some cases, noise may be superimposed on the audio signal after the IF signal is detected by performing the adjustment to restore the IF. In particular, when another broadcast station (hereinafter also referred to as “jamming wave”) exists in the vicinity of the broadcast station corresponding to the selected specific frequency, antenna switching frequently occurs. As a result, the adjustment of the amplitude by the adaptive filter is frequently performed, and there is a case where a lot of noise is superimposed on the audio signal, resulting in a decrease in the quality of the sound provided to the user.

  An object of the present embodiment is to provide a receiving apparatus that ensures the quality of sound to be provided to a user.

<3-1. Block diagram>
FIG. 12 is a block diagram of the receiving device 1b. FIG. 13 is a diagram illustrating a vehicle including the antenna 101 and the antenna 101a. The receiving apparatus 1b in FIG. 12 includes an antenna 101 and a plurality of antennas 101a. The receiving device 1b mainly includes a switching unit 21, a DSP 41b, and a reception control unit 51b. Other configurations are the same as those of the receiving apparatus 1 described in FIG.

  The antenna 101 and the antenna 101a are arranged at different positions on the vehicle 9 as shown in FIG. For example, the antenna 101 is arranged in the vicinity of the A pillar of the vehicle 9 as a feeder antenna. The antenna 101 a is a pole antenna provided on the roof of the vehicle 9. Thus, the antenna 101 and the antenna 101a are disposed at different positions on the vehicle 9 and receive broadcast waves.

  The switching unit 21 illustrated in FIG. 12 selects a reception signal to be processed by the reception device 1b from broadcast wave reception signals received by the antenna 101 and the antenna 101a. That is, switching is performed so that one of the signal lines outputting the reception signals of the two antennas is connected to the subsequent tuner 31 and the other signal line is not connected to the subsequent tuner 31.

  The antenna switching is performed as follows. A received signal of one selected antenna (for example, the antenna 101) is input to the DSP 41b via the tuner 31. Then, when the reception state of the broadcast wave received by the selected antenna 101 is poor, the switching unit 21 switches to the other antenna (for example, the antenna 101a). That is, when the degree of the noise influence of the audio signal corresponding to the reception signal of the antenna 101 detected by the noise detection unit 406 of the DSP 41b exceeds a predetermined threshold, one antenna is connected to the other antenna (for example, the antenna 101). To the antenna 101a).

  When the reception state of the broadcast wave received by the antenna 101a is good, that is, when the degree of the influence of noise based on the reception signal of the broadcast wave received by the antenna 101a is below a predetermined threshold, the broadcast wave by the antenna 101a Will continue to be received. In addition, when the reception state of the broadcast wave by the antenna 101a is deteriorated, the switching unit 21 performs switching from the antenna 101a to the antenna 101.

  The DSP 41b includes a band variable filter 402b. The band variable filter 402b is partially different from the band variable filter 402 described in FIG. The configuration and processing of the other DSP 41b are the same as the configuration of the DSP 41a described in FIG.

  The reception control unit 51b mainly includes a selection unit 505. The processing of the selection unit 505 will be described in detail later.

  FIG. 14 is a block diagram showing the configuration of the DSP 41b and the configuration of the reception control unit 51b. The band-variable filter 402b passes a part of the IF signal that is a received signal, and changes the bandwidth of the frequency to be passed depending on the presence or absence of an interference wave near the frequency of the IF signal corresponding to the specific frequency.

  That is, when there is an interference wave in the frequency (for example, 500 KHz) in the vicinity of the frequency (for example, 300 KHz) of the IF signal corresponding to the specific frequency (for example, 98.1 MHz), the band variable filter 402b passes the IF signal. The width is the first width (for example, the bandwidth fwb shown in FIG. 7). Further, when there is no interference wave in the vicinity of the frequency of the IF signal corresponding to the specific frequency, the bandwidth of the band-variable filter 402b is set to a second width wider than the first width (for example, the bandwidth fwa shown in FIG. 7). ). Thereby, the noise of a signal can be reduced and the quality of the sound provided to a user can be ensured.

  The presence / absence of an interfering wave is determined as follows. When noise exceeding the threshold is detected by the noise detection unit 406, the bandwidth of the band variable filter 402b is alternately switched between the second width and the first width, and the noise detected by the noise detection unit 406 varies. When this occurs, an interference wave exists in the vicinity of the frequency of the IF signal.

  In addition, when noise exceeding the threshold is detected by the noise detection unit 406, the noise detected by the noise detection unit 406 is switched by alternately switching the bandwidth of the band-variable filter 402b between the second width and the first width. If no fluctuation occurs in the signal, no interfering wave exists in the vicinity of the frequency of the IF signal.

  The reception control unit 51b mainly includes a selection unit 505. The selection unit 505 enables one of the switching of the antenna that receives the broadcast wave by the switching unit 21 and the elimination of the multipath effect of the adaptive filter 404 based on the bandwidth of the variable band filter 402b, and the other Is output to the DSP 41b.

<3-2. Selection graph>
FIG. 15 is a graph showing a selection state of the switching unit 21 and the adaptive filter 404. Two functions of the switching unit 21 and the adaptive filter 404 are shown on the vertical axis of the graph. Then, one of these two functions is enabled and the other is disabled. In addition, the horizontal axis indicates the signal level. The signal level is the signal level of the IF signal detected by the detection unit 403. The threshold value 1 on the horizontal axis is, for example, 5 dB, and the threshold value 2 is, for example, 1 dB.

  As shown in FIG. 15, when the signal level is lower than the threshold value 2, the removal of the influence of multipath included in the IF signal by the adaptive filter 404 is validated (hereinafter also referred to as “filter validation”), and switching is performed. The antenna switching by the unit 21 is invalidated (hereinafter also referred to as “switch invalidation”). That is, the switching unit 21 does not switch the antenna, but the received signal of the broadcast wave received by one of the plurality of antennas is processed, and the adaptive filter 404 removes the influence of the multipath of the IF signal. Is done.

  Next, when the signal level of the IF signal exceeds the threshold value 1, the switching of the antenna by the switching unit 21 is validated (hereinafter also referred to as “switching validation”), and is included in the IF signal by the adaptive filter 404. The removal of the effect of multipath is invalidated (hereinafter also referred to as “filter invalidation”). That is, the switching unit 21 switches to an antenna having a good reception state, and the adaptive filter 404 does not remove the influence of the IF signal multipath. This is because when the signal level of the IF signal is at a high level exceeding the threshold 1, the influence of noise on the audio signal is reduced.

  Next, when the signal level of the IF signal exceeds the threshold 2 and falls below the threshold 1, either the switching of the antenna by the switching unit 21 or the removal of the influence of the multipath included in the IF signal by the adaptive filter 404 is performed. Is enabled and which is disabled is determined by the bandwidth of the variable band filter 402.

  Specifically, when the bandwidth of the variable band filter 402 is the first width, the filter is enabled and the switching is disabled. Thereby, it is possible to prevent the quality of the sound provided to the user from being deteriorated due to frequent switching of the antenna due to the influence of the interference wave.

  When the bandwidth of the variable bandwidth filter 402 is a second width that is wider than the first width, switching is enabled and filter is disabled. Thereby, the reception signal from the antenna having a good reception state can be acquired, and the quality of the sound provided to the user can be ensured.

<3-3. Effect of Adaptive Filter on Interference>
FIG. 16 is a graph showing the S / N ratio when the adaptive filter 404 is disabled and when it is enabled. In FIG. 16, the vertical axis represents the signal level, and the horizontal axis represents the input level of the interference wave. In the upper diagram of FIG. 16 showing the case of filter invalidation, the noise signal level increases from the vicinity of the input level of the interference wave of 75 dBμV. On the other hand, in the case of the filter validation in the lower diagram of FIG. 16, the noise signal level rises from the vicinity of 85 dBμV where the input level of the disturbing wave has risen from 75 dBμV. Further, the slope of the noise signal level is gentler in the lower diagram than in the upper diagram. By operating the adaptive filter 404 in this way, it is possible to reduce the influence of interference waves on the IF signal.

<3-4. Processing flowchart>
17 and 18 are processing flowcharts of the reception control unit 51b. In step S501, the bandwidth information of the variable bandwidth filter 402b and sensor information including the signal level of the IF signal are received from the DSP 41b (step S501), and the process proceeds to step S502.

  In step S502, the signal level of the IF signal included in the sensor information is compared with the threshold value 2. If the signal level is lower than the threshold value 2 (No in step S502), the process proceeds to step S503.

  In step S503, the reception control unit 51b transmits to the DSP 41b an instruction signal for enabling the filter and disabling the switching (step S503).

  Returning to step S502, if the signal level of the IF signal exceeds the threshold value 2 (step S502 is Yes), the process proceeds to step S504.

  In step S504, if the signal level of the IF signal exceeds the threshold 1 that is higher than the threshold 2 (Yes in step S504), the process proceeds to the process of step S505, the switching is validated, and the instruction signal that the filter is invalidated. Is transmitted to the DSP 41b by the reception control unit 51b (step S505).

  Returning to step S504, if the signal level of the IF signal is below the threshold value 1 (No in step S504), the process proceeds to step S506 shown in FIG.

  In step S506, when the bandwidth of the band-variable filter 402b included in the sensor information is the first width that is narrower than the second width (step S506: Yes), the instruction signal to enable the filter and disable the switch Is transmitted to the DSP 41b by the reception control unit 51b. Thereby, it is possible to prevent the quality of the sound provided to the user from being deteriorated due to frequent switching of the antenna due to the influence of the interference wave.

  Returning to step S506, when the bandwidth of the band-variable filter 402b is not the first width, that is, when the bandwidth is a second width wider than the first width (step S506: No), the switching is enabled and the filter is disabled. The reception control unit 51b transmits an instruction signal for conversion to the DSP 41b. Thereby, the reception signal from the antenna having a good reception state can be acquired, and the quality of the sound provided to the user can be ensured.

<Modification>
Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications are possible. Below, such a modification is demonstrated. In addition, all the forms including the form demonstrated in the said embodiment and the form demonstrated below are combinable suitably.

  In the above embodiment, the DSP and the reception control unit are configured separately, but may be configured as an integrated unit.

  In the above embodiment, the target of the broadcast wave has been described by taking the FM broadcast wave as an example. However, in the first embodiment, the broadcast wave for frequency modulation other than the FM broadcast wave, and the AM broadcast wave The present invention can also be applied to broadcast waves that undergo amplitude modulation. In the second and third embodiments, the present invention can also be applied to other frequency-modulated broadcast waves other than FM broadcast waves.

  In the first embodiment, whether or not the received signal includes a broadcast station signal corresponding to the specific frequency is determined by whether or not the signal level of the converted signal by the determination unit 503 exceeds a predetermined threshold value. It went by. On the other hand, you may determine by the determination conditions different from a signal level. Specifically, the determination is made by using any one of the determination conditions such as the frequency shift of the converted signal and the signal level of the interference wave whose frequency is adjacent to the specific frequency, or by combining a plurality of conditions. Also good.

  Here, the frequency shift of the converted signal is a difference between the reference frequency (for example, 300 KHz) of the intermediate frequency converted signal obtained by mixing the local signal and the specific frequency signal, and the difference value is predetermined. Is exceeded, it is determined that the received signal does not contain a broadcast station signal corresponding to the specific frequency. If the difference value is below a predetermined threshold value, it is determined that the received signal includes a broadcast station signal corresponding to the specific frequency.

  Further, the determination of the signal level of the interference wave having a frequency adjacent to the specific frequency is made when the signal of the broadcasting station corresponding to the specific frequency is included in the received signal when the signal level of the adjacent interference wave exceeds a predetermined threshold. It is determined that it is not included. If the signal level of the adjacent interfering wave is below a predetermined threshold, it is determined that the received signal contains a broadcast station signal corresponding to the specific frequency.

  Further, in the second embodiment, it has been described that the sensitivity for detecting noise is changed based on the bandwidth of the variable bandwidth filter 402 and the degree of multipath influence detected by the detection unit 403. In addition to this, the width of the complementary section GW in which the complementing unit 407 performs the complementing process based on the bandwidth of the band-variable filter 402 and the degree of multipath influence detected by the detection unit 403 (the complementing unit 407 performs the complementing process). The time from the start to the end (for example, 120 μsec) may be changed.

  In the second embodiment, when the signal level of the IF signal changed by the band variable filter 402 is lower than a predetermined threshold, the bandwidth is set to the first width, and the signal level of the IF signal exceeds the predetermined threshold. In this case, the second width is described. In addition, the bandwidth may be changed to a width other than the first width and the second width according to the signal level of the IF signal.

1. Receiving device 31 ... Tuner 41 ... DSP
51... Reception control unit 61... Amplification unit 71.

Claims (5)

A receiving device for receiving broadcast waves,
An oscillation means for oscillating a local signal;
Mixing means for mixing the reception signal obtained by receiving the broadcast wave and the local signal to obtain a conversion signal of an intermediate frequency;
The signal level of the first signal, which is the converted signal obtained by mixing the local signal having a predetermined frequency difference from the specific frequency to the high frequency side and the received signal, and the predetermined frequency from the specific frequency to the low frequency side. Derivation means for deriving a signal level of the second signal which is the converted signal obtained by mixing the local signal having a difference and the received signal;
Based on the signal level of the signal level and the second signal of the first signal obtained by the transmission of the request signal to the deriving means, whether the signal of the broadcasting station corresponding to the specific frequency to the received signal is included Determining means for determining whether or not;
Change control means for controlling the change from the specific frequency to a different frequency;
With
The determination means determines whether or not the signal level of the observed pre-Symbol second signal when the signal level of the first signal is greater than the first threshold value is greater than the first threshold value,
The change control means, the determination by the case where the signal level of the first signal the signal level and the second signal is greater than the first threshold value, the first signal and other signals other than the second signal Without performing the control without changing the specific frequency to a different frequency,
A receiving device.
The receiving device according to claim 1,
The change control means, wherein when the first signal contact and the signal level of the second signal noise deviation or the other signal is less than the first threshold value, a plurality of times by the signal level of the one of the signal Performing control to change to a frequency different from the immediately preceding frequency immediately before the specific frequency is changed from the specific frequency without performing the determination of
A receiving device.
The receiving apparatus according to claim 1 or 2,
The derivation means derives a signal level of the specific signal existing at a frequency at a position symmetrical to the position of the specific frequency with the position of the frequency of the local signal as a central axis,
The determination means determines whether the signal level of the specific signal is lower than a second threshold;
When the signal level of the specific signal is smaller than the second threshold, the change control means does not execute the determination based on the first signal, the second signal, and other signals other than the specific signal. Performing control without changing the specific frequency to a different frequency;
A receiving device.
The receiving device according to claim 2,
It further comprises sound output means for outputting sound information,
The sound output means outputs the sound information corresponding to the specific frequency without outputting the sound information corresponding to the immediately preceding frequency when control is performed without changing the specific frequency to a different frequency. When the control to change from the specific frequency to a frequency different from the immediately preceding frequency is performed, the acoustic information corresponding to the immediately preceding frequency and the acoustic information corresponding to the specific frequency are not output,
A receiving device.
A signal processing method for processing a received broadcast wave signal,
(A) oscillating a local signal;
(B) mixing a reception signal obtained by receiving the broadcast wave and the local signal to obtain an intermediate frequency conversion signal;
(C) The signal level of the first signal, which is the converted signal obtained by mixing the local signal having a predetermined frequency difference from the specific frequency to the high frequency side and the received signal, and from the specific frequency to the low frequency side Deriving a signal level of the second signal that is the converted signal obtained by mixing the local signal having a predetermined frequency difference and the received signal;
And (d) based on the signal level of the signal level of the first signal obtained by the transmission of the request signal to the deriving means and the second signal, the signal of the broadcasting station corresponding to the specific frequency to the received signal Determining whether it is included;
(E) performing control related to the change from the specific frequency to a different frequency;
Equipped with a,
Previous Stories step (d) it determines whether or not the signal level of the observed pre-Symbol second signal when the signal level of the first signal is greater than the first threshold value is greater than the first threshold value,
Wherein step (e), determined by the case where the signal level of the first signal the signal level and the second signal is greater than the first threshold value, the first signal and other signals other than the second signal Without performing the control without changing the specific frequency to a different frequency,
A signal processing method characterized by the above.

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