JP4076912B2 - IBOC broadcast receiver - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a radio broadcast receiver adapted to receive digital audio broadcast (DAB), and more particularly, to an IBOC (In Band On Channel) performed using an analog radio frequency band such as an existing FM broadcast. The present invention relates to a technique useful for optimally performing a station search (hereinafter also referred to as “seek”) operation in an IBOC broadcast receiver having a function of receiving broadcast waves transmitted in a modulation format.
[0002]
[Prior art]
With the recent digitalization of broadcasting, digitalization of radio broadcasting is also progressing. In digital radio broadcasting using satellites, in September 2001, XM Satellite Co., Ltd. and in February 2002 Sirius Satellite ( The service of Sirius Satellite) has been started. Furthermore, in addition to the digital radio broadcasting by these satellites, “HD (High Definition) radio” has been proposed by iBiquity Digital Corporation as terrestrial digital radio broadcasting. This HD radio is a free service, although it is not commercial free, for the paid satellite digital radio broadcast, so the market is expected to expand in the future.
[0003]
A major feature of this HD radio is that it can receive the same content broadcast with a conventional analog radio receiver by adopting the IBOC system that adds a digital signal to the analog radio wave of the existing FM broadcast, and also for digital reception A compatible HD radio receiver can also listen to digital broadcasts. As a result, in the case of digital reception, sound quality similar to that of FM broadcasting can be obtained in AM broadcasting, and sound quality equivalent to CD can be obtained in FM broadcasting.
[0004]
A typical HD radio (IBOC broadcast receiver), as its basic function, outputs a digitally received signal in an area where digital reception is possible, and prevents sound interruptions in areas where digital reception is not possible. Automatically outputs analog received signals. Specifically, at the time of station search (seek), the frequency is first tuned to a frequency at which an analog broadcast wave can be received. At first, the analog broadcast wave is demodulated, but whether the analog broadcast wave has a digital modulation wave or not. (That is, whether or not an IBOC broadcast station exists), and if a digital modulation wave exists, the IBOC broadcast wave is demodulated and further demodulated by a process called “blend”. The broadcast wave is switched to the IBOC broadcast wave and the IBOC broadcast wave is output. On the other hand, if there is no digital modulation wave, the demodulated analog broadcast wave is output as it is.
[0005]
In a digital audio broadcasting (DAB) system adopting the IBOC method, there are two methods for transmitting the broadcast wave, a hybrid method and an all-digital method. FIG. 1 shows the broadcast wave transmission form, and schematically shows the relationship between each frequency assignment of the FM modulated broadcast signal component and the IBOC DAB signal component and the power spectral density. As shown in FIG. 1A, the hybrid system is an analog / digital hybrid system in which an IBOC DAB signal (digital modulation wave) is added to the upper sideband and lower sideband of an analog broadcast carrier wave (FM analog signal), respectively. This is a method used in the current technology. The IBOC DAB signal added to both sidebands of the FM analog signal is composed of, for example, 95 equally spaced orthogonal frequency division modulation (OFDM) subcarriers, and is approximately 129 kHz to 198 kHz away from the FM center frequency as shown. Occupies the spectrum. Also, the DAB output of the OFDM subcarrier in each sideband is typically set to about -25 dB relative to the FM analog output.
[0006]
On the other hand, as shown in FIG. 1B, the all-digital system is a system in which an additional digital signal band is arranged in the frequency band occupied by the FM analog signal in the hybrid system. This method is expected to be used on behalf of As shown in the figure, the sideband in the all-digital system is wider than the sideband in the hybrid system, and the power spectral density of the sideband of the all-digital IBOC signal is acceptable in the hybrid IBOC sideband. The value is set to about 10 dB higher than the level to be set. Furthermore, the power spectral density of the extended all-digital signal is set to a value about 15 dB lower than the level of the hybrid IBOC sideband. This minimizes the problem of interference with adjacent hybrid or all-digital IBOC signals.
[0007]
The IBOC DAB system embodies the digital terrestrial broadcasting system adopted in the United States. Currently, FM broadcast stations in the United States are provided with a frequency interval of 200 kHz, so seek by the receiver. The frequency step at that time is 200 kHz.
[0008]
When performing a seek operation when receiving a hybrid IBOC broadcast wave (see FIG. 1A), as described above, first tune to a frequency at which an analog broadcast wave can be received, and then an IBOC broadcast wave exists. If there is an IBOC broadcast wave, the IBOC broadcast is decoded and output; otherwise, the analog broadcast wave is output as it is.
[0009]
On the other hand, when a seek operation is performed in the case of receiving an all-digital IBOC broadcast wave (see FIG. 1B), it is determined whether or not an IBOC broadcast wave exists by tuning to each frequency once. If there is an IBOC broadcast wave, the IBOC broadcast is decoded and output. However, if there is no IBOC broadcast wave, the operation shifts to the next frequency, performs a seek operation again, and finally reaches a frequency at which the IBOC broadcast wave can be received. Repeat seek operation until synchronized.
[0010]
As a technology related to the above-described conventional technology, for example, Ivyquity discloses a modulation format (hybrid method, all-digital method) for FM IBOC DAB and a broadcasting method and system using such a modulation format ( For example, see Patent Literature 1 and Patent Literature 2).
[0011]
[Patent Document 1]
JP-T-2001-520479 [Patent Document 2]
Japanese translation of PCT publication No. 2002-510897
[Problems to be solved by the invention]
As described above, in order to receive an all-digital IBOC broadcast wave, the conventional technique requires a process of tuning to each frequency once to determine the presence or absence of an IBOC broadcast station. If a wave is not included, it is necessary to shift to the next frequency and perform a seek operation again, and this seek operation must be repeated until it is finally tuned to a frequency at which an IBOC broadcast wave can be received. For this reason, it takes considerable time to specify the target IBOC broadcast wave and output it. That is, there is a problem that the time required for all seek operations from the start to the end of the seek operation is relatively long.
[0013]
Such a problem may also occur when an original analog broadcast wave (analog FM broadcast wave in a hybrid system, existing analog broadcast wave) is received by the IBOC broadcast receiver.
[0014]
The present invention was created in view of the problems in the prior art, and in receiving an IBOC broadcast wave including an existing analog broadcast wave, the time required for a station search (seek) operation for specifying the broadcast wave is reduced. An object is to provide an IBOC broadcast receiver that can be shortened.
[0015]
[Means for Solving the Problems]
In order to solve the above-described problems of the prior art, according to the present invention, an IBOC broadcast receiver adapted to receive a broadcast wave transmitted in an IBOC modulation format, each received through an antenna. Broadcast selection means for selectively outputting a broadcast wave tuned in frequency from among broadcast waves, received electric field strength detection means for detecting an electric field strength level of a received signal corresponding to a frequency set at the time of station search, and the broadcast selection means And a control means operatively connected to the received electric field strength detection means, wherein the control means performs a station search by shifting the reception frequency to the broadcast selection means in a predetermined step unit. , detected received field strength level at a predetermined level or higher in the reception electric field strength detecting means for the frequency set during the station search, and the frequency is defined If it corresponds to a wave number step, it is determined that an analog broadcast wave is included in the signal of the reception frequency, the broadcast wave is selectively output, the reception field strength level is equal to or higher than a predetermined level, and the frequency Is not equivalent to the specified frequency step, it is determined whether or not an IBOC broadcast wave is included in a signal having a frequency step away from the reception frequency by a predetermined frequency step. An IBOC broadcast receiver is provided that selectively outputs the IBOC broadcast wave .
[0016]
According to the IBOC broadcast receiver according to the present invention, the control means causes the broadcast selection means to shift the reception frequency in units of predetermined steps and perform a station search (seek) operation. As can be seen, the broadcast wave (existing analog broadcast wave, IBOC broadcast wave) is specified as compared with a seek operation that requires processing for determining the presence or absence of each broadcast station by tuning to each frequency once. Therefore, the time required for the seek operation can be shortened. At this time, based on the result (received electric field strength level) detected by the received electric field strength detecting means, it is determined whether the broadcasting station providing the broadcasting service is an existing analog broadcasting station or an IBOC broadcasting station. Can be determined.
[0017]
As described above, according to the present invention, when a target broadcast wave (for example, an all-digital IBOC broadcast wave) is received, a frequency that becomes the broadcast wave (for example, an IBOC all-digital broadcast wave) is set to a predetermined step. By limiting to the frequency shifted in units, the total time required from the start to the end of the seek operation can be greatly shortened.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 2 schematically shows the configuration of an IBOC broadcast receiver according to an embodiment of the present invention.
[0019]
The IBOC broadcast receiver 10 according to the present embodiment is used for in-vehicle use, receives a broadcast wave transmitted from an analog broadcast station that provides a service such as an existing FM broadcast, and digital audio by the IBOC method. It is adapted to receive broadcast waves transmitted in a predetermined modulation format from an IBOC broadcast station that provides broadcast (DAB) services. As described above, there are two forms of broadcast waves sent from an IBOC broadcast station: those using the hybrid system (see FIG. 1 (a)) and those using the all-digital system (see FIG. 1 (b)). Therefore, for the sake of convenience, the IBOC broadcasting station related to the hybrid system will be called “hybrid station” and the IBOC broadcasting station related to the all digital system will be called “all digital station”.
[0020]
In the IBOC broadcast receiver 10, reference numeral 11 denotes a control unit configured by a microcomputer or the like, and has a function of controlling processing related to a seek operation performed by the receiver 10, as will be described later. Reference numeral 12 denotes an antenna for receiving a broadcast wave (analog broadcast wave, IBOC broadcast wave) transmitted from each broadcasting station, and 13 is communicably connected to the control unit 11 and is received through the antenna 12. A tuner unit (RF front end) for performing frequency tuning on the broadcast wave, and an analog / digital (A / D) conversion unit 14 for digitizing the broadcast wave selected and output from the tuner unit 13.
[0021]
Reference numeral 15 denotes an FM demodulator that is communicably connected to the control unit 11. Basically, an FM analog signal is transmitted to a broadcast wave that is selectively output from the tuner unit 13 through the A / D conversion unit 14. If included, it has the function of digitally demodulating the FM analog signal. Further, the FM demodulator 15 has a built-in S meter 15a, and the frequency set at the time of station search (seek) based on the control from the controller 11 (that is, the frequency is shifted in predetermined step units as will be described later). The field intensity level (also referred to as “S meter value”) of the received signal corresponding to the frequency) is detected. In the present embodiment, the case where the S meter 15a is built in the FM demodulator 15 is taken as an example, but this is not necessarily built in the FM demodulator 15, and may be built in the tuner unit 13, for example. .
[0022]
Reference numeral 16 denotes an IBOC decoder that is communicably connected to the control unit 11. The IBOC digital audio broadcasting (DAB) system has a well-known functional block. In the illustrated example, the IBOC decoder 16 includes a digitally modulated wave (that is, an orthogonal frequency division modulation (OFDM) subcarrier) included in the broadcast wave selected and output from the tuner unit 13 through the A / D conversion unit 14. An OFDM demodulator 16a for demodulating the OFDM subcarrier, and an FEC decoder 16b for decoding forward error correction (FEC) added due to digital encoding or audio compression performed on the broadcasting station side; And an audio decoder 16c. The OFDM demodulator 16a performs its demodulation function when an OFDM subcarrier (digital modulated wave) is included in the broadcast wave selected and output as described above. In this sense, the output of the OFDM demodulator 16a indicates that synchronization with the digital modulation wave has been achieved.
[0023]
A signal output from the IBOC decoder 16 (audio decoder 16c) is supplied to the blend processing unit 17 as a blend control signal BC and controls the blend function. The blend processing unit 17 basically uses the IBOC broadcast wave (digital modulation) from the audio signal (analog broadcast wave) demodulated through the FM demodulation unit 15 based on the state (ie, level) of the blend control signal BC. The function of outputting by switching to (wave) is provided. The control unit 11 can also directly monitor the state (level) of the blend control signal BC by communication with the IBOC decoder 16.
[0024]
Reference numeral 18 denotes a digital / analog (D / A) conversion unit that converts the digitized audio signal output through the blend processing unit 17 into an analog audio signal. Although not specifically shown, the audio output from the D / A converter 18 is amplified through an audio amplifier and then heard by the user through a speaker. Reference numeral 19 denotes a memory unit such as a RAM connected to the control unit 11. The memory unit 19 stores data relating to broadcast frequencies of receivable broadcast stations (analog stations, hybrid stations, or all digital stations). In addition, based on the control from the control unit 11, data of the electric field intensity level (S meter value) of the received signal detected by the S meter 15 a in the FM demodulation unit 15 is temporarily stored.
[0025]
In the IBOC broadcast receiver 10 according to the present embodiment configured as described above, the control unit 11 is the “control unit”, the tuner unit 13 is the “broadcast selection unit”, and the FM demodulation unit 15 is the “first demodulation unit”. The S meter 15a incorporated in the FM demodulator 15 is “reception field strength detection means”, the IBOC decoder 16 is “second demodulation means”, and the blend processing unit 17 is “audio output switching means”. Each corresponds.
[0026]
Hereinafter, the processing related to station search (seek) and broadcast reception performed by the IBOC broadcast receiver 10 according to the present embodiment will be described with reference to FIGS. 3 and 4 showing an example thereof. In this processing flow, one frequency step at the time of seek is 100 kHz.
[0027]
Referring first to FIG. 3, in the first step S1, the tuner unit 13 tunes to a set frequency (frequency shifted in a predetermined step unit) based on control from the control unit 11 (seek operation). start).
[0028]
In the next step S2, in the control unit 11, the S meter value at the frequency is equal to or higher than a predetermined level (seek stop level), and the frequency is a specified frequency step (in this case, a USA specified frequency step: 200 kHz). ) (NO) or NO (NO). If the determination result is YES (for example, 98.1 MHz in the example of FIG. 4), the process proceeds to step S3. If the determination result is NO (for example, 98.2 MHz in the example of FIG. 4), the process proceeds to step S4.
[0029]
In step S3, the tuner unit 13 performs a seek stop operation based on the control from the control unit 11, and receives a broadcast wave (analog broadcast wave) of the hybrid station or an existing analog FM station. Then, this processing flow is “END”.
[0030]
On the other hand, in step S4, the control unit 11 temporarily stores the data of the S meter value at the frequency (98.2 MHz in this case) detected in step S2 in the memory unit 19. In this case, the memory unit 19 detects the S meter value a plurality of times (a total of three times in the present embodiment) at predetermined time intervals based on the control from the control unit 11 after the process of step S2, and averages the values. The one taken is stored. The reason for taking the average value by detecting three times in this way is that the reception state is likely to change with time, and the electric field strength level (S meter value) of the received signal may also vary accordingly. This is because it is more reliable to take the average value of a plurality of detection data than the detection data.
[0031]
In the next step S5, based on the control from the control unit 11, the tuner unit 13 shifts the reception frequency (in this case, 98.2 MHz) to the next step (200 kHz) frequency (that is, 98.4 MHz). .
[0032]
In the next step S6, the control unit 11 determines whether the S meter value at the frequency (98.4 MHz in this case) is equal to or higher than a predetermined level (seek stop level) (YES) or not (NO). . If the determination result is yes, the process proceeds to step S8, and if the determination result is no, the process proceeds to step S7.
[0033]
In step S7, based on the control from the control unit 11, the tuner unit 13 shifts the reception frequency (in this case, 98.4 MHz) to the next step (100 kHz) frequency (ie, 98.5 MHz). Then, it returns to step S1 and repeats said process.
[0034]
On the other hand, in step S8, the S meter value data at the frequency (in this case, 98.4 MHz) detected in step S6 is temporarily stored in the memory unit 19 by the control unit 11 in the same manner as the processing performed in step S4. Store. In this case, similarly, the memory unit 19 stores the value obtained by detecting the S meter value three times and taking the average value.
[0035]
In the next step S9, the control unit 11 stores two S meter value data stored in the memory unit 19 (that is, the S meter value at the frequency 98.2 MHz and the frequency 98.4 MHz in the example of FIG. 4). Each S meter value) is referred to, and the two are compared to determine whether the error is within 500 mV (YES) or not (NO). That is, it is determined whether or not the S meter values (the electric field intensity levels of the received signals) at the two frequencies are close to each other (if there is an error, at most about 500 mV). If the determination result is YES, the process proceeds to step S11, and if the determination result is NO, the process proceeds to step S10.
[0036]
In step S10, in the same manner as the processing performed in step S7, the reception frequency (in this case, 98.4 MHz) is set to the next frequency (in the case of 98.4 MHz) for the tuner unit 13 based on the control from the control unit 11. That is, it is shifted to 98.5 MHz. Then, it returns to step S1 and repeats said process.
[0037]
On the other hand, in step S11, based on the control from the control unit 11, the tuner unit 13 is subjected to an intermediate frequency between the two frequencies (in this case, 98.2 MHz and 98.4 MHz) compared in step S9 ( That is, it is shifted to 98.3 MHz).
[0038]
In the next step S12, the control unit 11 determines the presence or absence of an IBOC broadcast wave using IBOC “Acquire” (a command for confirming the presence or absence of an IBOC station) based on communication performed with the IBOC decoder 16. Then, it is determined whether an IBOC broadcast wave is included in the signal of the reception frequency (YES) or not (NO). If the determination result is YES, the process proceeds to step S13, and if the determination result is NO, the process proceeds to step S14.
[0039]
In step S13, similarly to the process performed in step S3, the tuner unit 13 receives a broadcast wave (all digital broadcast wave) of the IBOC station based on the control from the control unit 11. Then, this processing flow is “END”.
[0040]
On the other hand, in step S14, similarly to the process performed in step S5, based on the control from the control unit 11, the tuner unit 13 is caused to shift the reception frequency to the next frequency (200 kHz). Then, it returns to step S1 and repeats said process.
[0041]
As described above, according to the IBOC broadcast receiver 10 according to the present embodiment, based on the control from the control unit 11, the tuner unit 13 shifts the reception frequency in units of a predetermined step (100 kHz or 200 kHz). Compared with the case of the seek operation that requires processing to determine the presence or absence of each broadcast station by tuning to each frequency once as in the past, the broadcast wave (existing The time required for the seek operation for specifying (analog broadcast wave, IBOC broadcast wave) can be shortened. At this time, the control unit 11 monitors the reception electric field intensity level (S meter value) detected by the S meter 15a through communication with the FM demodulation unit 15 to provide the broadcast service. It is possible to determine whether the station is an existing analog FM station or an IBOC station.
[0042]
As described above, according to the IBOC broadcast receiver 10 of the present embodiment, when receiving a target broadcast wave (for example, an all-digital IBOC broadcast wave), the broadcast wave (for example, an IBOC all-digital broadcast wave) and The total time required from the start to the end of the seek operation can be significantly reduced by limiting the frequency to be a frequency that is shifted in units of a predetermined step (100 kHz or 200 kHz).
[0043]
Further, when it is determined in step S2 (FIG. 3) that the frequency does not correspond to the specified frequency step, the tuner unit 13 is caused to shift the reception frequency to the next frequency of 2 steps (200 kHz) in step S5. ing. The reason for shifting to the next frequency of 2 steps (200 kHz) is that a signal spectrum is generated at a frequency where a broadcasting station originally does not exist due to the influence of so-called inter-modulation (modulation interference), and the signal spectrum is not erroneously detected. Because.
[0044]
In the above-described embodiment, the case where one frequency step at the time of seek is set to 100 kHz has been described as an example (FIG. 3). However, as is apparent from the gist of the present invention, one frequency step is not limited to 100 kHz. Of course.
[0045]
【The invention's effect】
As described above, according to the present invention, an IBOC broadcast wave including an existing analog broadcast wave is received by performing a seek operation by shifting the reception frequency in predetermined steps while monitoring the electric field strength of the received signal. In doing so, it is possible to shorten the time required for the seek operation for specifying the broadcast wave.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram of a broadcast wave transmission method (hybrid method, all-digital method) used in an IBOC digital audio broadcasting (DAB) system.
FIG. 2 is a block diagram schematically showing a configuration of an IBOC broadcast receiver according to an embodiment of the present invention.
FIG. 3 is a flowchart showing an example of processing related to station search (seek) and broadcast reception performed by the IBOC broadcast receiver of FIG. 2;
FIG. 4 is a diagram for supplementarily explaining the processing flow of FIG. 3;
[Explanation of symbols]
10 ... IBOC broadcast receiver,
11: Control unit (control means),
12 …… Antenna,
13. Tuner part (broadcast selection means),
15 ... FM demodulator (first demodulator),
15a ... S meter (received electric field strength detecting means),
16 ... IBOC decoder (second demodulation means),
17 ... Blend processing unit (audio output switching means),
BC: Blend control signal.

Claims (7)

An IBOC broadcast receiver adapted to receive a broadcast wave transmitted in an IBOC modulation format,
Broadcast selection means for selecting and outputting a frequency-tuned broadcast wave from among the broadcast waves received through the antenna;
A reception field strength detection means for detecting a field strength level of a reception signal corresponding to a frequency set at the time of station search;
Control means operably connected to the broadcast selection means and the received electric field strength detection means,
The control means detects the received electric field strength detection means with respect to the frequency set at the time of station search when the station selection is performed by shifting the reception frequency to the broadcast selection means in a predetermined step unit . When the received electric field strength level is equal to or higher than a predetermined level and the frequency corresponds to a specified frequency step, it is determined that an analog broadcast wave is included in the signal of the received frequency, and the broadcast wave is selectively output. If the received electric field strength level is equal to or higher than a predetermined level and the frequency does not correspond to a predetermined frequency step, the signal having a frequency step away from the received frequency by a predetermined frequency step includes an IBOC broadcast wave. IBOC release handset, characterized in that to selectively output the IBOC broadcast wave when it is determined that the dolphin whether determined by a contains IBOC broadcast wave Machine. The received electric field strength detection means detects the received electric field strength level a plurality of times for the frequency set by the control means,
2. The IBOC broadcast receiver according to claim 1 , wherein the control unit uses an average value of the detected plurality of received field strength levels as a received field strength level value at the frequency. When the control means determines that the frequency set at the time of station search does not correspond to the specified frequency step, the control means only sets the reception frequency to a frequency sufficient to avoid the influence of modulation interference. The IBOC broadcast receiver according to claim 1 , wherein the IBOC broadcast receiver is shifted to the next frequency. The control means compares each received electric field strength level value at the frequency shifted by a frequency step sufficient to avoid the influence of the modulation interference and the frequency before the shift, and the error between the two is within a predetermined value. 4. The IBOC broadcast receiver according to claim 3 , wherein the broadcast selection unit shifts the reception frequency to a frequency intermediate between the two frequencies to be compared. The control means selects and outputs the IBOC broadcast wave to the broadcast selection means when it determines that the IBOC broadcast wave is included in the received signal having a frequency intermediate between the two frequencies to be compared. The IBOC broadcast receiver according to claim 4 , wherein: A first demodulation unit that is operatively connected to the control unit and demodulates the analog signal when the broadcast signal selected and output from the broadcast selection unit includes an analog signal;
A second demodulating means that is operatively connected to the control means and demodulates the digital modulated wave when the broadcast wave selected and output from the broadcast selecting means contains a digital modulated wave;
2. The audio output switching means for switching and outputting the audio signal demodulated by the first demodulating means and the audio signal demodulated by the second demodulating means. IBOC broadcast receiver.   The IBOC broadcast receiver according to claim 1, wherein the IBOC broadcast receiver is mounted on a vehicle.

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