JP3798604B2 - Broadcast system discrimination device and broadcast system discrimination method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a broadcast system determination apparatus and a broadcast system determination method for automatically determining the broadcast system of a received broadcast when there is an analog broadcast and a digital broadcast that are simultaneously broadcast at nearby frequencies.
[0002]
[Prior art]
Recently, a broadcasting system for simultaneously broadcasting analog broadcasting and digital broadcasting from the same broadcasting location has been proposed. For example, a broadcasting system called an IBOC (In Band On Channel) system proposed by the FCC in the United States corresponds to this.
In such an analog broadcast / digital broadcast receiving apparatus capable of receiving digital broadcasting and analog broadcasting, or in a digital broadcast receiving apparatus, an operation called so-called search is first performed in the receiving apparatus. The search operation is to detect one digital broadcast that can be received at the start of reception. There is a problem that the time required for the search operation is particularly long in a radio wave environment where digital broadcasting and analog broadcasting are mixed.
[0003]
Hereinafter, a search at the time of reception will be described using a specific example of digital audio broadcasting. For digital audio broadcasting, for example, a DAB system compliant with the European standard (Eureka 147) has been put into practical use in Europe and the like.
FIG. 5 is a diagram showing the configuration of the DAB Audio frame in the DAB system. A DAB signal in a DAB system is transmitted as an OFDM signal modulated by an orthogonal frequency division multiplex modulation scheme, that is, OFDM (Orthogonal Frequency Division Multiplex), and a transmission frame is transmitted from a demodulated OFDM signal obtained by demodulating the OFDM signal. can get.
[0004]
As shown in FIG. 5, the transmission frame in the demodulated OFDM signal includes blocks of a synchronization channel (Synchronization Channel), FIC (Fast Information Channel), and MSC (Main Service Channel). The FIC transmits information necessary for the receiving device to select a program, auxiliary information for the program, and the like, and the MSC transmits a subchannel of audio and data.
The FIC for one frame is made up of three data blocks called FIB (Fast Information Block), and the MSC is made up of 1 to 4 data blocks called Common Interleaved Frame (CIF) depending on the transmission mode.
[0005]
A synchronization channel block is provided at the head of the transmission frame. In this synchronization channel block, a null symbol for coarse synchronization is arranged at the head, and subsequently, a phase reference symbol (hereinafter also referred to as PRS) that bears a reference phase for OFDM demodulation (for example, differential QPSK demodulation) is arranged. ing. Channel selection in the DAB receiver is performed in units of ensembles, and when other ensembles are received, the reception frequency is changed. When this reception frequency is changed, a receivable ensemble is searched and received by a search operation (search operation) also called ensemble up / down. Also, when the user starts to receive digital audio broadcast, the ensemble that can be received is searched and received by a search operation (search operation).
[0006]
The search operation ends when the NULL symbol is detected. In the detection of the NULL symbol, in order to prevent erroneous detection, when the NULL symbol is detected three or more times consecutively, the search is terminated assuming that the NULL symbol is detected. If it is not possible to detect three or more times in succession, it is considered that a NULL symbol has not been detected.
In the ETS300401 DAB standard, the time length of each CIF is 24 ms, but MPEG audio data in DAB is arranged in the MSC and time interleaved over 16 CIFs.
[0007]
The time interleaving needs to be canceled before the NULL symbol is detected. Since the frame length of 1 CIF is 24 ms, in order to detect the NULL symbol, a stable period of 16 to 32 times (384 ms to 768 ms) of CIF is required at the minimum.
[0008]
Furthermore, since many broadcasts can be arranged at fine frequency intervals in the digital broadcast, the search for checking whether there is a broadcast for each frequency at which the broadcast can be set takes a long time, for example, 10 seconds. May take a degree. However, if it can be determined in a short time that the received frequency broadcast is an analog broadcast, it is determined in a short time that there is no digital broadcast for that frequency, the search operation for that frequency is interrupted, Since the search operation can be performed for the next reception frequency, the time required for the search can be shortened.
[0009]
In the following, a conventional broadcast method discriminating apparatus in a dual-purpose receiving apparatus will be described with reference to FIG. FIG. 4 is a block diagram of a dual-purpose receiving apparatus for explaining an example of a conventional broadcasting system discriminating apparatus.
In FIG. 4, reference numeral 50 denotes an analog and digital television (TV) broadcast receiver. A specific broadcast is selected by the channel selection circuit 49 from the signal input from the antenna 47. The channel selection circuit 49 inputs the selected broadcast intermediate frequency signal p to the broadcast system switch 51. The broadcast system switch 51 applies the signal p as a signal q to the video detection circuit 53 in the case of analog television broadcasting in response to the broadcast system selection signal h. Digi In the case of tall broadcasting, the signal p is given to the I / Q detection circuit 56 as the signal r.
[0010]
In the case of analog broadcast with amplitude modulation, the video detection circuit 53 outputs the signal sa subjected to AM detection to the video processing circuit 54. The video processing circuit 54 outputs the video signal va to the next stage and also outputs it to the video discrimination circuit 59.
Multiple PSK modulated Digi In the case of tall broadcasting, the I / Q detection circuit 56 receives the I / Q detected signal sd. Digi This is output to the total demodulation circuit 57. The Digi The demodulator 57 has a digital / analog converter, outputs an analog demodulated video signal vd to the next stage, Discrimination Also output to the circuit 59.
[0011]
In the dual-use TV receiving apparatus 50, first, the broadcast system switch 51 is switched to the analog broadcast side at the time of reception. Then, the video signal determination circuit 59 determines whether the video signal va is a correct video signal based on, for example, whether there is a synchronization pulse of the video signal. If it is correct, it is considered that an analog television broadcast has been received. If it is not correct, it is assumed that the analog television broadcast has not been received, and the broadcast system switch 51 is switched to the digital broadcast side.
Next, the video signal determination circuit 59 determines whether or not the demodulated signal vd is a correct video signal. If it is correct, it is assumed that the digital broadcast is received. If it is not correct, it is assumed that the digital broadcast cannot be received.
In this way, is the broadcast selected by the channel selection circuit 49 an analog broadcast? Digi The video discrimination circuit 59 determines whether the broadcast is a tall broadcast, and the broadcast system switch 51 can be switched to a direction where a correct video signal can be obtained via the broadcast system selection signal h.
[0012]
[Problems to be solved by the invention]
However, in the above-described conventional apparatus, at a certain frequency, Digi The synchronization processing in the tall demodulator circuit Digi Until the digital demodulated signal is obtained, it cannot be determined whether the digital broadcast has been received. Therefore, whether the received broadcast is an analog broadcast, Digi There is a problem in that it is impossible to determine whether the broadcast is a tall broadcast in a short time, and the search takes a long time.
The broadcast system discrimination device of the present invention has been made in view of the above problems, and its purpose is to provide a broadcast system discrimination device and a broadcast system discrimination method that can discriminate between analog broadcasting and digital broadcasting in a short time It is to be.
[0013]
[Means for solving the title]
The present invention has been made with the following configuration in order to achieve the above object.
The first aspect of the present invention relates to a reception signal selected by a channel selection circuit of a receiving device, and its intermediate frequency. Wave number First measuring means for measuring the amplitude of the signal; Wave number A second measuring means for measuring the voltage of the signal; and a comparing means for comparing the output of the first measuring means with the output of the second measuring means, wherein the selected broadcast is an analog broadcast. Or a digital broadcasting, wherein the comparison means calculates a ratio between the output of the first measurement means and the output of the second measurement means, and the calculation The broadcast system discrimination device compares a result value with a predetermined value and discriminates a broadcast system of a broadcast selected by the channel selection circuit according to the comparison result.
[0014]
According to the first invention, when it is determined whether a broadcast received at a certain frequency is an analog broadcast or a digital broadcast, the value obtained by measuring the intermediate frequency signal with the first measuring means is It is almost determined only by analog broadcast signals, and hardly fluctuates depending on the presence or absence of digital broadcasting. On the other hand, the voltage value obtained by the measurement by the second measuring means becomes larger than that in the case of only analog broadcasting due to the large number of carriers in digital audio broadcasting.
When analog broadcast and digital broadcast are transmitted simultaneously near the received frequency, it is considered that the amplitude of the analog broadcast signal and the amplitude of the digital broadcast signal have a predetermined ratio in the intermediate frequency signal. Therefore, the ratio of the value obtained by measuring with the first measuring means and the value obtained by measuring with the second measuring means is compared with a predetermined value to compare the received broadcast It is possible to determine the broadcasting system.
[0015]
According to a second aspect of the present invention, there is provided the broadcast system identification device according to the first aspect, wherein the first measuring means measures the maximum amplitude of the intermediate frequency signal.
[0016]
Since the amplitude of the analog broadcast signal is larger than the amplitude of the digital broadcast signal, according to the second aspect of the present invention, the maximum amplitude of the intermediate frequency signal is measured by the first measuring means, so that it is affected by the digital broadcast signal. Therefore, it is possible to accurately measure the amplitude of the analog broadcast signal, thereby making it possible to more accurately determine the broadcast system.
[0017]
The third aspect of the present invention relates to the intermediate frequency of the received signal selected by the channel selection circuit of the receiving device. Wave number A first measuring means for measuring the voltage or amplitude of the signal through a first band-pass filter whose pass band is a frequency range in which the spectrum of one analog broadcast signal is distributed; Wave number A second measuring means for measuring the voltage of the signal; and a comparing means for comparing the output of the first measuring means and the output of the second measuring means, wherein the selected broadcast is an analog broadcast. Or a digital broadcasting, wherein the comparison means calculates a ratio between the output of the first measurement means and the output of the second measurement means, and the calculation The broadcast system discrimination device compares a result value with a predetermined value and discriminates the broadcast system of the broadcast selected by the channel selection circuit according to the comparison result.
[0018]
According to a third aspect of the present invention, a digital broadcast signal is measured by the first measuring means through the first band pass filter having a frequency range in which a spectrum of one analog broadcast signal is distributed as a pass band. Therefore, it is possible to accurately measure the amplitude of the analog broadcast signal without being influenced by the above, and thus it is possible to more accurately determine the broadcasting system.
[0019]
According to a fourth aspect of the present invention, there is provided the broadcasting system discriminating apparatus according to any one of the first to third aspects, wherein the second measuring means defines a frequency range in which a spectrum of one digital broadcast signal is distributed as a passband Through the second bandpass filter Wave number This is a broadcasting system discrimination device that measures the voltage of a signal.
[0020]
According to the fourth aspect of the present invention, the second measuring means performs measurement through the second bandpass filter having a frequency range in which the spectrum of one digital broadcast signal is distributed as a passband. Even when broadcasting is performed in a frequency band adjacent to the frequency, it is possible to accurately measure the voltage of the intermediate frequency signal without being affected by the adjacent broadcast signal. The determination can be made more accurately.
[0021]
According to a fifth aspect of the present invention, a first measurement value is obtained by measuring the amplitude of an intermediate frequency signal frequency-converted from the selected RF signal, and the intermediate frequency Wave number A signal voltage is measured to obtain a second measured value, a ratio between the first measured value and the second measured value is obtained, and a magnitude relationship between the ratio value and a predetermined value is determined. Accordingly, it is a broadcast method discrimination method for discriminating whether the selected broadcast is an analog broadcast or a digital broadcast.
[0022]
A sixth aspect of the invention is the broadcast system identification method according to the fifth aspect of the invention, wherein when obtaining the first measurement value, the maximum amplitude of the intermediate frequency signal is measured.
[0023]
According to a seventh aspect of the present invention, the first measurement value is obtained by measuring the voltage or amplitude of the intermediate frequency signal frequency-converted from the selected RF signal in a frequency range in which the spectrum of one analog broadcast signal is distributed. The intermediate circumference Wave number A signal voltage is measured to obtain a second measured value, a ratio between the first measured value and the second measured value is obtained, and a magnitude relationship between the ratio value and a predetermined value is determined. Accordingly, it is a broadcast method discrimination method for discriminating whether the selected broadcast is an analog broadcast or a digital broadcast.
[0024]
According to an eighth aspect of the present invention, in the broadcast method identification method according to any one of the fifth to seventh aspects, the second measurement value is measured in a frequency range in which a spectrum of one digital broadcast signal is distributed. This is a broadcasting method discrimination method.
[0025]
DETAILED DESCRIPTION OF THE INVENTION
The broadcast system identification device of the present invention is provided in a receiver having a channel selection circuit that performs amplification, channel selection, and generation of an intermediate frequency signal of an RF signal, and outputs an intermediate frequency signal output from the channel selection circuit. The first measurement value is obtained by measurement with one measurement means, the second measurement value is obtained by measurement with the second measurement means, the ratio of the two measurement values is calculated, and the value of the ratio is calculated in advance. The size is compared with a predetermined value, and according to the comparison result, it can be determined in a short time whether the received broadcast is an analog broadcast or a digital broadcast. The first measurement means substantially measures the amplitude of an analog broadcast signal, and the second measurement means measures the voltage of a signal in which the analog broadcast signal and the digital broadcast signal are substantially mixed.
[0026]
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
First, as an example in which analog broadcasting and digital broadcasting are simultaneously broadcast from the same antenna, an IBOC system currently proposed to the US FCC (Federal Communications Committee) will be described with reference to FIG.
FIG. 3 is a diagram showing a power spectrum distribution at the time of transmission in the IBOC system broadcasting system. In FIG. 3, the horizontal axis represents frequency, and the deviation from the center frequency is shown with the center frequency of FM audio broadcast, which is analog broadcast, being 0. The vertical axis shows the intensity of the power spectrum in the broadcast wave, and the dotted line shows the FM audio broadcast. thing The solid line shows the digital audio broadcast broadcast using the gap between FM audio broadcasts. thing It is. The center frequency of the digital audio broadcast is the same as that of the analog broadcast.
[0027]
The FM audio broadcasts are arranged at intervals of 400 kHz. That is, adjacent FM audio broadcasts are arranged with a center frequency of 400 kHz apart. The center frequency of the digital audio broadcast is the same as the center frequency of the FM audio broadcast, and the power spectrum of the digital audio broadcast wave is distributed outside the power spectrum of the FM audio broadcast wave.
For example, the power spectrum intensity of the FM audio broadcast wave indicated by a dotted line has a slope of about 0.35 db / kHz, and the power spectrum is distributed within a range of approximately ± 129 kHz.
[0028]
On the other hand, the power spectrum of the digital audio broadcast wave indicated by the solid line is distributed in ± (129 kHz to 199 kHz).
When analog broadcasting and digital broadcasting are simultaneously performed as in the IBOC system broadcasting system, they are transmitted from the same antenna and received by the same antenna. Therefore, the power spectrum intensity as shown in FIG. 3 is broadcast at a predetermined ratio in analog broadcasting and digital broadcasting, and the electric field intensity at the time of reception has a certain ratio according to the predetermined ratio.
[0029]
As described above, the IBOC system tries to enable simultaneous broadcasting by preventing FM power broadcasting and digital audio broadcasting from being simultaneously broadcast at the same center frequency so that the power spectra of both do not overlap each other. To do.
In addition to the case where analog broadcasting and digital broadcasting are performed at the same time as in the IBOC system described above, the radio wave environment may be only analog broadcasting or only digital broadcasting. The receiving circuit is switched depending on whether it is of the system.
[0030]
FIG. 1 is a block diagram of a dual-purpose receiving apparatus for explaining an example of the broadcasting system discriminating apparatus of the present invention.
Here, it is assumed that the analog broadcast is FM audio broadcast and OFDM (Orthogonal Frequency Division Multiplex) is adopted as a modulation method of digital audio broadcast.
In FIG. 1, an instruction for starting reception and an instruction for starting search in the dual-purpose receiving apparatus 10 are given from a user to a microprocessor (MPU) 35 via an operation panel (not shown). At the time of search or the like, frequency information of the received digital audio broadcast is sent from the MPU 35 to the PLL of the channel selection circuit 13 as a reception frequency setting signal k.
The channel selection circuit 13 here is generally called an RF amplification unit or a front end, and its configuration is not shown, but the RF signal supplied from the antenna 11 is not shown. amplification An RF amplifier circuit, a local oscillator that has a PLL circuit and oscillates at a frequency corresponding to the reception frequency setting signal k, and an RF signal sent from the RF amplifier circuit and the output of the local oscillator are mixed to give a predetermined It comprises a mixer that outputs an intermediate frequency signal, an intermediate frequency filter that removes signals other than the intermediate frequency signal from the signal output from the mixer, and the like. The intermediate frequency signal is output from the channel selection circuit 13 via the intermediate frequency filter constituted by, for example, a SAW filter.
[0031]
In the channel selection circuit 13, the RF signal input from the antenna 11 is amplified, and a digital audio broadcast carrier wave of a specific frequency is received, signal-processed, converted into a predetermined intermediate frequency signal (IF signal), and intermediate It is given to the broadcast system switch 15 and the broadcast system discriminating apparatus 20 through the frequency filter.
The broadcast system switch 15 is provided with a broadcast system selection signal d from the MPU 35 according to the broadcast system, and in the case of FM audio broadcasting, the FM audio broadcast signal f is provided to the FM demodulator 17 and demodulated from the FM demodulator 17. FM audio signal i is output. On the other hand, in the case of digital audio broadcasting, a digital audio signal g is given from the broadcast system switch 15 to the OFDM demodulator 19.
[0032]
The OFDM demodulator 19 includes an analog / digital converter (A / D converter), an I / Q detector, an FFT, a DSP, and the like. In the OFDM demodulator 19, an analog signal is converted into a digital signal, and the I / Q detector divides the signal into an I signal and a Q signal so that the OFDM signal can be processed in a subsequent stage, and is supplied to the FFT. Further, fast Fourier transform is performed by FFT and DSP (digital arithmetic unit), and the result is supplied to the channel decoder 21. The channel decoder 21 performs frequency de-interleaving (QPSK) de-interleaving, QPSK symbol demapping, time de-interleaving, error code detection and correction, and the like for returning the signal order to the original order.
[0033]
A digital audio frame is supplied from the channel decoder 21 to the compression decoder 23. The audio information given to the compression decoder 23 is audio information compressed using an MPEG audio compression method or the like. In the compression decoder 23, the compressed audio information is decoded, decompressed, and decoded. Audio data j is supplied to the D / A converter at the next stage.
[0034]
The broadcast system discrimination device 20 includes a first band pass filter (first BPF) 25, a second band pass filter (second BPF) 27, a first measuring unit 29, a second measuring unit 31, a comparing unit 33, and an MPU 35. .
The first BPF 25 is a narrow-band bandpass filter, the center frequency of which is the same as the center frequency of the intermediate frequency signal, and the pass bandwidth is limited to pass only the frequency range in which the spectrum of FM audio broadcasting is distributed. The bandwidth is set to 258 kHz, for example. The second BPF 27 is a wide and narrow band-pass filter, the center frequency of which is the same as the center frequency of the intermediate frequency signal, and the pass bandwidth is set to at least a frequency range in which the spectrum of digital audio broadcasting is distributed, for example, 398 kHz.
[0035]
The channel selection circuit 13 applies the intermediate frequency signal e to the broadcast system switch 15, the first BPF 25, and the second BPF 27. The first measuring means 29 measures the amplitude of the signal supplied from the first BPF 25 for a predetermined time. This measurement is, for example, the measurement of the maximum value of the amplitude or the measurement of the voltage, and the average value “a” at the predetermined time is output to the comparison means 33. Further, the measurement by the first measuring means 29 is performed by extracting a portion of the intermediate frequency signal e having an amplitude greater than a predetermined value and substantially excluding the digital audio broadcast signal, and then measuring the voltage of the signal. May be. The second measuring means 31 measures the voltage of the signal supplied from the second BPF 27 for a predetermined time and outputs the average value b to the comparing means 33. The comparison means 33 calculates the ratio of a and b, that is, b / a, and supplies the calculation result c to the MPU 35.
[0036]
The comparison means 33 may be constituted by the MPU 35. The first BPF 25 is for accurately measuring a signal only for FM audio broadcasting, and can be omitted when the maximum amplitude is measured by the first measuring means 29, but is measured as a voltage value. Cannot be omitted. Note that when the amplitude is measured by the first measuring means 29 by envelope detection using a diode or the like, it is possible to prevent detection of a digital audio broadcast signal having an amplitude smaller than a predetermined value. One BPF 25 can be omitted.
[0037]
The measurement by the first measuring means 29 is a more accurate measurement that does not include the components of the digital audio broadcast by using a band pass filter whose pass band is the frequency range in which the spectrum of one FM audio broadcast signal is distributed. The measurement can be performed with either maximum amplitude or voltage.
In the measurement by the second measuring means 31, the second BPF 27 can be omitted, but by using a band-pass filter whose pass band is a frequency range in which the spectrum of one digital audio broadcast signal is distributed, Even when there is a broadcast in the adjacent frequency band of the medium frequency, it is possible to perform accurate measurement without being affected by it.
[0038]
The MPU 35 checks the magnitude relationship between the value c, that is, b / a, and a predetermined value m. If c is smaller than m, it is determined that the received broadcast is only FM audio broadcast, and 0 is supplied to the broadcast system switch 15 as a signal d (broadcast system selection signal d) of the determination result. . When c is larger than m, it is determined that the broadcast is a mixture of FM audio broadcast and digital audio broadcast, and 1 is supplied to the broadcast system switch 15 as a signal d (broadcast system selection signal d) of the determination result.
When the broadcast system switch 15 is switched, the intermediate frequency signal e is supplied to the FM demodulator 17 as the signal f when the d is 0, and is supplied to the OFDM demodulator 19 as the signal g when the d is 1. Is done.
[0039]
The predetermined value m is different depending on how the amplitude is measured by the first measuring means 29. For example, the predetermined value m is different when measuring the maximum amplitude and when measuring the voltage. If the value of a is smaller than a predetermined value set in advance, the MPU 35 sets the reception frequency for setting the next reception frequency, assuming that there is no FM audio broadcast at the frequency being received and that reception is impossible. The signal k is supplied to the channel selection circuit 13.
[0040]
Hereinafter, a search process and a broadcasting method discrimination method according to the present invention will be described with reference to FIG. FIG. 2 is a flowchart for explaining the search processing in the present invention.
In FIG. 2, when a search is started by a user instruction, the MPU 35 first sends a reception frequency setting signal k to the channel selection circuit 13 (step S11). Next, in step S13, the channel selection circuit 13 generates an IF signal (intermediate frequency signal) having a predetermined frequency, and the process proceeds to step S15. In step S15, the maximum amplitude (or voltage) is measured for a predetermined time via the narrow band BPF (first BPF 25), and the average value a is obtained, and the process proceeds to step S17.
[0041]
In step S17, is the value of a greater than a predetermined value? If Yes, the process proceeds to step S19 assuming that the FM audio broadcast could be received, and if No, the process returns to step S11 assuming that the FM audio broadcast could not be received. In step S19, the voltage is measured for a predetermined time via the broadband BPF (second BPF 27), and the average value b is obtained, and the process proceeds to step S21.
In step S21, b / a is calculated, and the process proceeds to step S23. In step S23, is b / a larger than a predetermined value? If yes, the process proceeds to step S27, and if no, the process proceeds to step S29.
[0042]
In step S27, it is determined that both the FM audio broadcast (analog broadcast) and the digital audio broadcast (digital broadcast) exist in the received frequency, and the MPU 35 gives 1 to the broadcast system switch 15 as the value of the broadcast system selection signal d.
In step S29, it is determined that only the FM audio broadcast (analog broadcast) exists in the received frequency, and the MPU 35 gives 0 to the broadcast system switch 15 as the value of the broadcast system selection signal d, and the process proceeds to step S31. In step S31, is there an instruction to end the search? If yes, the search is terminated, and if no, the process returns to step S11, and the MPU 35 sets the next reception frequency and gives it to the channel selection circuit 13.
[0043]
When d = 1 is output in step S27, the search is terminated and digital audio broadcast is received. If d is never 1 even after searching for the entire frequency range to be searched, the MPU 35 determines that there is no digital broadcast that can be received and instructs the end of the search. In order to receive the FM audio broadcast, 0 is given to the broadcast system switch 15 as the broadcast system selection signal d.
[0044]
The FM audio broadcast and the digital audio broadcast transmitted from the same antenna have power spectrum intensities as shown in FIG. 3, and the FM audio broadcast carrier amplitude is higher than the digital audio broadcast carrier amplitude at the time of reception. Much bigger.
The value a obtained by measuring the intermediate frequency signal e by the first measuring means 29 is determined only by the FM audio broadcast and hardly fluctuates depending on the presence or absence of the digital audio broadcast.
[0045]
On the other hand, when FM audio broadcast and digital audio broadcast are transmitted simultaneously in the vicinity of the received frequency, the maximum amplitude of the intermediate frequency signal e does not vary much depending on the presence or absence of the digital audio broadcast, but the second measuring means 31. The voltage value b measured in (1) becomes larger than that in the case of only FM audio broadcasting due to a large number of carriers of digital audio broadcasting.
Accordingly, by checking the magnitude relationship between the value of b / a and a predetermined value, it is possible to determine whether the broadcast being received is only an analog broadcast or a mixture of digital broadcasts. .
In addition, since this determination can be performed before the digital broadcast signal is demodulated, it can be performed in a very short time.
[0046]
As described above in detail, according to the broadcasting system discriminating apparatus and the broadcasting system discriminating method of the present invention, when the analog broadcasting / digital broadcasting receiving apparatus is used in a radio wave environment where analog broadcasting and digital broadcasting are mixed, Since the broadcasting system being received can be determined in a short time, if the present invention is applied to a search when receiving a digital broadcast, it is possible to immediately switch to the next frequency when it is determined that there is no digital broadcast at the reception frequency. The time required for the search can be shortened.
[Brief description of the drawings]
FIG. 1 is a block diagram of a dual-purpose receiving apparatus for explaining an example of a broadcasting system discriminating apparatus of the present invention.
FIG. 2 is a flowchart for explaining search processing in the present invention;
FIG. 3 is a diagram showing a power spectrum distribution at the time of transmission in the IBOC system broadcasting system.
FIG. 4 is a block diagram of a dual-purpose receiving apparatus for explaining an example of a conventional broadcasting system discriminating apparatus.
FIG. 5 is a diagram showing a configuration of a DAB Audio frame in the DAB system.
[Explanation of symbols]
13 Tuning circuit
15 Broadcast system switch
17 FM demodulator
19 OFDM demodulator
20 Broadcast system identification device
21 channel decoder
23 Compression decoder
25 First band pass filter (first BPF)
27 Second bandpass filter (second BPF)
29 First measuring means
31 Second measuring means
33 Comparison means
35 Microprocessor (MPU)

Claims (6)

For receiving apparatus receives signals by channel selection circuit was tuned in, first as its intermediate frequency signal of the voltage, a first frequency range passband of a frequency range in which the spectrum of one of the analog broadcast signals are distributed First measuring means for measuring through a one-band pass filter;
The second frequency band pass filter having a second frequency range including a first frequency range and a frequency range in which a spectrum of a digital broadcast signal having a center frequency identical to that of the analog broadcast is distributed. A second measuring means for measuring the voltage of the intermediate frequency signal;
Wherein when the ratio of the output of said second measuring means to the output of the first measuring means is larger than a predetermined value, the received signal in the channel selection is set to include a digital broadcast, if the smaller than a predetermined value, A discriminating means for discriminating that the received signal during channel selection does not include digital broadcasting;
A broadcasting system discriminating apparatus comprising:   When the ratio of the output of the second measurement means to the output of the first measurement means is greater than a predetermined value, the determination means is assumed that the received signal being selected includes both analog broadcast and digital broadcast. 2. The broadcast method discriminating apparatus according to claim 1, wherein if it is smaller than the predetermined value, it is determined that the received signal during channel selection does not include digital broadcasting but includes analog broadcasting.   3. The broadcast system discrimination device according to claim 1, wherein the received signal is related to IBOC. For the received signal selected by the channel selection circuit of the receiving device, the first frequency range as the frequency range in which the spectrum of one analog broadcast signal is distributed is used as the passband of the voltage of the intermediate frequency signal. Measuring as a first measurement value through a band-pass filter;
Intermediate through a second band-pass filter having a second frequency range including a frequency range in which the spectrum of a digital broadcast signal having the same center frequency as that of the analog broadcast is distributed and the first frequency range. Measuring the voltage of the frequency signal as a second measured value;
When the ratio of the second measurement value to the first measurement value is greater than a predetermined value, the received signal being selected includes digital broadcasting, and when the ratio is smaller than the predetermined value, Determining that the received signal does not include a digital broadcast;
A broadcasting method discrimination method comprising:   In the step of determining based on the ratio of the second measurement value to the first measurement value, if the ratio is larger than a predetermined value, the received signal being selected includes both analog broadcast and digital broadcast 5. The broadcast method determining method according to claim 4, wherein if the received signal is smaller than the predetermined value, the received signal being selected is determined not to include digital broadcasting but to include analog broadcasting.   6. The broadcast system discrimination method according to claim 4, wherein the received signal is related to IBOC.

Images