JP2009260877A - Fm multiplex broadcast receiver and method of demodulating fm multiplex broadcast signal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an FM multiplex broadcast receiver capable of optimally setting a filtering characteristics suitable for a broadcast station under receiving. <P>SOLUTION: A controller 3 of an FM multiplex broadcast receiver 1 determines whether a subcarrier of which the frequency is 57 kHz is included for a received and demodulated FM multiplex broadcast signal and if the subcarrier is included, a filtering algorithm is changed corresponding to a minimum degree of multiplexing of the received signal but if the subcarrier is not included, the filtering algorithm is changed to be corresponding to a greater degree of multiplexing of the received signal. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an FM multiplex broadcast receiver that receives an FM multiplex broadcast signal by RDS (Radio Data System), and an FM multiplex broadcast signal demodulation method.

  One of the factors that determine the reception performance of the FM multiplex broadcast receiver is the filtering characteristics of various filters used in the intermediate frequency (IF) band. On the other hand, even if it is a premise that the RDS system is used as the actual situation on the broadcasting station side that performs transmission, the multiplicity that greatly affects the quality of communication may differ depending on the country. For example, in the EBU (European Broadcasting Union), the multiplicity of data communication is set to be ± 2 kHz, but there are EU (European Union) countries that ignore this recommended value.

  In Europe, there are countries where ARI (Auto-fahrer Rundfunk Information), which is a broadcasting service providing traffic information, remains. Since the communication band used by the ARI has a portion overlapping with the RDS, the multiplicity of data communication is a standard that changes depending on whether the ARI exists or not. In the conventional FM multiplex broadcast receiver, the filtering characteristic is fixedly set, and this characteristic may cause a mismatch with respect to the multiplicity of the broadcast that is actually performed. There was a problem that decreased.

For example, Patent Document 1 does not correspond to FM multiplex broadcasting, but includes a filter coefficient table for correcting the frequency characteristics of a communication line, and dynamically changes and sets the characteristics of a bandpass filter (BPF). Is disclosed.
JP 2007-195204 A

  However, assuming that the method of Patent Document 1 is applied to an FM multiplex broadcast receiver, a circuit and a memory device for providing a filter coefficient table inside the receiver are required. In addition, there is a problem that there is no reference for selecting a filter coefficient suitable for the broadcasting station that is currently receiving a signal from the filter coefficient table.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an FM multiplex broadcast receiver capable of optimally setting a filtering characteristic suitable for a receiving broadcast station, and an FM multiplex broadcast signal. It is to provide a demodulation method.

According to the FM multiplex broadcast receiver of the first aspect, when the demodulated FM multiplex broadcast signal includes a subcarrier that is not detected by the RDS, the control means includes a number of FM multiplex broadcast signals received by the RDS. When the filtering algorithm is changed so as to correspond to a signal whose severity is a predetermined value, and the subcarrier is not included, the multiplicity of the FM multiplex broadcast signal by the received RDS is equal to or greater than the predetermined value Change the filtering algorithm to
That is, RDS employs a balanced modulation system that suppresses subcarriers that modulate multiplexed data. However, if another broadcast is being performed in parallel with the RDS, the broadcast wave may include a subcarrier that is not detected by the RDS. Therefore, it is possible to easily determine whether another broadcast is being performed in parallel depending on whether the subcarrier is detected.

  When other broadcasts are also performed, the RDS multiplicity is defined to be lower in order to avoid interference with the broadcasts. Therefore, when the subcarrier is detected, the filtering algorithm corresponding to the received signal having a predetermined multiplicity is changed, and when the subcarrier is not included, the multiplicity is equal to or higher than the predetermined value. By changing the filtering algorithm so as to correspond to the above, it is possible to appropriately set the characteristics of the filter and improve the reception performance.

  According to the FM multiplex broadcast receiver of claim 2, the subcarrier is included in the ARI broadcast signal. That is, since the frequency component of the subcarrier that modulates multiplexed data in RDS is included in the ARI broadcast wave, the filtering algorithm can be changed to correspond to the ARI when the subcarrier is detected. .

  According to the FM multiplex broadcast receiver of claim 3, the frequency of the subcarrier is set to 57 kHz. That is, since the frequency of the subcarrier that modulates multiplexed data in the current RDS is set to 57 kHz, it is possible to clearly determine whether or not broadcast other than RDS is performed by specifying the frequency.

  According to the FM multiplex broadcast receiver of claim 4, since the predetermined value is set to a value lower than the multiplicity specified for the broadcast signal of the ARI, the RDS is received when the ARI is broadcast. It is possible to optimally set a filtering algorithm for the purpose.

  According to the FM multiplex broadcast receiver of claim 5, when the subcarrier is not included, the control means performs in the country indicated by the country code included in the PI (Programme Identification) code of the multiplexed data. Since the filtering algorithm is changed to the one corresponding to the FM multiplex broadcasting, a specific country name can be specified and changed to the optimum filtering algorithm.

  An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a functional block diagram showing the configuration of the FM multiplex broadcast receiver according to the subject matter of the present invention. When the front end 2 of the FM multiplex broadcast receiver 1 selects and receives an FM multiplex broadcast signal of about several tens to several hundreds of MHz received by an antenna (not shown), the received signal is received at an intermediate frequency (IF) of about 10 MHz. Convert to obi. The channel selection control is performed by a controller 3 (control means) constituted by a microcomputer.

  When the signal converted into the intermediate frequency band by the front end 2 is sampled (A / D conversion) by the A / D converter 4 at a sufficiently high sampling frequency of about 48 MHz, for example, the next-stage decimation filter ( DFI) 5. The decimation filter 5 performs a thinning process on the A / D converted data, drops the data frequency band to a lower band (for example, 512 kHz), and outputs the data to the FM demodulation unit 6 (demodulation means). The FM demodulator 6 performs detection processing using a Costas loop method or the like by software processing, and outputs the demodulated composite signal (see FIG. 2) to the FM multiplex demodulator 7 (multiplex demodulation means) at the next stage. The composite signal is also output to a sound signal processing unit (not shown) (including a stereo matrix) for outputting stereo sound.

  In the RDS system, as described above and shown in FIG. 2, the multiplexed data is modulated with a 57 kHz subcarrier. The FM multiplex demodulator 7 performs a filtering process by digital calculation in order to demodulate the multiplex data. The filtering characteristics are variably controlled by the controller 3, and the filtering characteristics are changed by branching to a program (filtering algorithm) in which a set of filter coefficients corresponding to each characteristic is incorporated in advance. Is called.

  Further, the FM multiplex demodulator 7 has a function of detecting a 57 kHz subcarrier contained in the ARI broadcast wave, although it is not detected because it is suppressed by the RDS. Given. The data decoding unit 8 (decoding unit) decodes the baseband multiplexed data demodulated by the FM multiplex demodulation unit 7 and outputs the decoded data to a data processing unit (display unit or the like) not shown. Further, the data decoding unit 8 extracts a country code indicating the name of the country where FM multiplex broadcasting is performed, which is included in the decoded data, and outputs the extracted country code to the controller 3.

  Next, the operation of this embodiment will be described with reference to FIGS. FIG. 3 is a flowchart showing the contents of processing performed with the controller 3 as the center, with respect to the part according to the gist of the present invention. First, the controller 3 determines whether or not a broadcast service by ARI is being performed based on whether or not the FM multiplex demodulator 7 has detected a subcarrier having a frequency of 57 kHz (step S1), and the service is performed. If yes (YES), the filtering algorithm D is changed (step S7).

Here, the filter in the FM multiplex demodulator 7 is constituted by, for example, an FIR (Finite Impulse Response) filter as shown in FIG. In FIG. 4, for the sake of illustration, a 6th order configuration is used, but in actuality, a 10th order configuration is used, as shown by the following equation, and its filtering characteristics are determined by coefficients h0 to h10.
H (z) = h0 + h1 · z ⁻¹ + h2 · z ⁻² +... + H10 · z ⁻¹⁰ (1)
The FIR filter is realized by calculating the equation (1), but the filtering algorithm D in step S7 has characteristics corresponding to the one that minimizes the multiplicity of received signals (related to FIG. 5 described later). A set of coefficients h0 to h10 is set. In each of the algorithms including other algorithms A to C described later, a set of coefficients h0 to h9 corresponding to each characteristic is described in advance in the program, and each filtering algorithm is implemented by branching to each program. .

  The filtering algorithm D in step S7 is set to a characteristic corresponding to, for example, an RDS multiplicity of ± 1.2 kHz (a predetermined value, a value lower than the ARI multiplicity of ± 3.5 kHz). This is because when the ARI is broadcast according to the EBU regulations, the RDS multiplicity is defined as ± 1.2 kHz, and a filtering characteristic corresponding to the multiplicity is set. If step S7 is performed, it will transfer to the following step S8 and the multiple demodulation process by the FM multiple demodulation part 7 will be performed using the changed filtering algorithm.

  On the other hand, if the subcarrier component having the frequency of 57 kHz is not detected in step S1 and it is determined that the broadcasting service by ARI is not performed (NO), the controller 3 acquires the country code from the data decoding unit 8 (step S2). ). At this stage, the filtering algorithm in the FM multiplex demodulator 7 may not be optimized, but the multiplexed data cannot be demodulated at all, so the country code is acquired in the default setting state for the filter. Here, the default setting state may be set to a filter characteristic corresponding to the multiplicity not corresponding to any of the filtering algorithms A to D, or set to any state of the filtering algorithms A to D. May be.

  FIG. 6 shows a data format (structure) of a PI (Programme Identification) code included in the RDS data. The PI code is 16-bit data arranged at the beginning of the RDS data block, and 4 bits (b15 to b12) on the MSB side are country codes. The country code is a code for identifying the country where the RDS broadcast is performed, and the remaining 12 bits (b11 to b0) indicate a broadcast cover area and a reference number, and are defined and used in each country. .

  And the controller 3 determines the country which is broadcasting based on the country code acquired by step S2 (step S3), and changes to filtering algorithm AC according to a country (step S4-S6). For example, change to algorithm A (step S4) for countries A to H or other countries, algorithm B (step S5) for countries I and J, and algorithm C (step S6) for country K. To do. For example, algorithm A has characteristics corresponding to RDS multiplicity of ± 1.5 kHz or more and less than ± 4.0 kHz, and algorithm B has characteristics corresponding to multiplicity of ± 4.0 kHz or more and less than ± 7.5 kHz. Algorithm C is set so that the multiplicity has characteristics corresponding to ± 7.5 kHz or more. Then, the process proceeds to step S8.

  Here, FIG. 5 shows an example in which the filtering characteristics are changed by changing the settings of the filter coefficients h1 to h10 (h0 is omitted) (Set1, Set2). The vertical axis represents the filter attenuation factor. As described above, Set2 is changed so that the cutoff frequency is lower and the passband attenuation rate is higher than Set1. That is, when the RDS multiplicity is large, the power of the received signal is relatively large, and when the multiplicity is low, the power of the received signal is relatively small. Therefore, when the multiplicity is high, the passband attenuation factor is relatively large as in Set2, and when the multiplicity is low, the multiplicity is increased by reducing the passband attenuation factor as in Set1. Even when they are different, the received signal power can be adjusted to be substantially equal.

  As described above, according to the present embodiment, the controller 3 of the FM multiplex broadcast receiver 1 has a multiplicity of received signals when the received and demodulated FM multiplex broadcast signal includes a subcarrier with a frequency of 57 kHz. Change to a filtering algorithm corresponding to the minimum one, specifically, the ARI multiplicity lower than ± 3.5 kHz, and if the subcarrier is not included, the received signal multiplicity is larger Change the filtering algorithm corresponding to the thing. Therefore, it is possible to change the filtering algorithm according to whether the ARI is broadcast or not, to set the filter characteristics appropriately, and to improve the reception performance of multiplexed data.

  If the subcarrier is not detected, the controller 3 refers to the country code included in the PI code of the multiplexed data demodulated by the FM multiplex demodulator 7 and decoded by the data decoder 8. Since the filtering algorithm is changed to be compatible with FM multiplex broadcasting performed in the country indicated by the country code, a specific country name can be specified and the optimal filtering algorithm can be changed.

The present invention is not limited to the embodiments described above and shown in the drawings, and the following modifications or expansions are possible.
The filtering algorithm may be changed in two types corresponding to the case where the ARI is broadcasted and the case where the ARI is not broadcasted (in this case, it is not necessary to acquire a country code). Five or more types may be changed.
In addition, the multiplicity setting range in each filtering algorithm may be changed as appropriate.
An IIR (Infinite Impulse Response) filter may be employed as the filtering algorithm. Further, the order of the filter may be appropriately changed according to the individual design.

The frequency of the subcarrier is not limited to 57 kHz, and is not limited to the frequency corresponding to the frequency included in the ARI broadcast wave.
The multiplicity when the ARI is not broadcast may be set to the same value as the multiplicity when the ARI is broadcast.

1 is a functional block diagram showing a configuration of an FM multiplex broadcast receiver according to an embodiment of the present invention per part according to the gist of the present invention. The figure which shows the frequency spectrum of the composite signal by RDS The flowchart which shows the processing content which concerns on the summary of this invention The figure which shows the structure of a FIR filter The figure which shows an example in the case of changing a filtering characteristic Diagram showing PI code data format

Explanation of symbols

  In the drawings, 1 is an FM multiplex broadcast receiver, 3 is a controller (control means), 6 is an FM demodulator (demodulator), 7 is an FM multiplex demodulator (multiplex demodulator), and 8 is a data decoder (decoder). Indicates.

Claims (10)

Demodulation means for A / D converting and demodulating the received FM multiplex broadcast signal by RDS (Radio Data System);
Multiplex demodulating means for demodulating multiplexed data by filtering the demodulated FM multiplex broadcast signal;
Control means for changing a filtering algorithm for the filtering process according to the demodulated FM multiplex broadcast signal;
When the demodulated FM multiplex broadcast signal includes a subcarrier that is not detected by the RDS, the control means corresponds to the multiplicity of the FM multiplex broadcast signal received by the RDS having a predetermined value. If the subcarrier is not included, the filtering algorithm is changed so that the multiplicity of the FM multiplex broadcast signal by the received RDS is greater than or equal to the predetermined value. An FM multiplex broadcast receiver.   2. The FM multiplex broadcast receiver according to claim 1, wherein the subcarrier is included in a broadcast signal of ARI (Auto-fahrer Rundfunk Information).   3. The FM multiplex broadcast receiver according to claim 1, wherein a frequency of the subcarrier is 57 kHz.   The FM multiplex broadcast according to any one of claims 1 to 3, wherein the predetermined value is set to a value lower than a multiplicity defined for a broadcast signal of ARI (Auto-fahrer Rundfunk Information). Receiving machine.   When the sub-carrier is not included, the control means refers to a country code included in a PI (Programme Identification) code of the multiplexed data, and performs FM multiplexing performed in the country indicated by the country code 5. The FM multiplex broadcasting receiver according to claim 1, wherein the filtering algorithm is changed to one corresponding to broadcasting. Received RDS (Radio Data System) FM multiplex broadcast signal is A / D converted and demodulated,
In an FM multiplex broadcast signal demodulation method for demodulating multiplexed data by filtering a demodulated FM multiplex broadcast signal,
When the demodulated FM multiplex broadcast signal includes a subcarrier that is not detected by RDS, the filtering algorithm is set so as to correspond to the multiplicity of the FM multiplex broadcast signal received by RDS having a predetermined value. If the subcarrier is not included, the filtering algorithm is changed so that the multiplicity of the FM multiplex broadcast signal by the received RDS is greater than or equal to the predetermined value. Demodulation method of FM multiplex broadcast signal.   7. The method of demodulating an FM multiplex broadcast signal according to claim 6, wherein the subcarrier is included in a broadcast signal of ARI (Auto-fahrer Rundfunk Information).   The method of demodulating an FM multiplex broadcast signal according to claim 6 or 7, wherein the frequency of the subcarrier is 57 kHz.   9. The FM multiplex broadcast signal according to claim 6, wherein the predetermined value is set to a value lower than a multiplicity defined for a broadcast signal of ARI (Auto-fahrer Rundfunk Information). Demodulation method.   If the subcarrier is not included, the country code included in the PI (Programme Identification) code of the multiplexed data is referred to, and it corresponds to the FM multiplex broadcasting performed in the country indicated by the country code The method of demodulating an FM multiplex broadcast signal according to any one of claims 6 to 9, wherein the filtering algorithm is changed.

Images