JP3853002B2 - Network follower for digital audio broadcast receiver - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a receiver for digital audio broadcasting (DAB), and more particularly to a network follow device for this receiver.
[0002]
[Prior art]
The digital audio broadcasting employs orthogonal frequency division multiplexing (OFDM), which divides the encoded data and distributes and multiplexes it into several hundred or more carriers within the transmission bandwidth (about 1.5 MHz). A plurality of audio programs are transmitted. This method is resistant to multipath interference during transmission and is suitable for mobile reception. In digital audio broadcasting used in Europe, several channels are provided in one transmission band. There are four types of digital audio broadcasting, Modes I, II, III, and IV. Mode 1 is national broadcasting by a single frequency network (SFN), Mode II is regional broadcasting, and Mode III is satellite. It is used for broadcasting. The mode I single frequency network is a system in which relay transmission is performed at the same transmission frequency (channel) or simultaneous broadcasting is performed by a plurality of stations. In a conventional relay system, different transmission frequencies (channels) are used to avoid interference between the same channels. In contrast, a single frequency network covers a wide area with a single channel. This is because the same audio program broadcast transmitted from a plurality of stations can be regarded as a signal from a multipath transmission line at the time of demodulation. If the delay time of each received signal is within an allowable range, a plurality of signals additionally contribute to the received intensity.
[0003]
[Problems to be solved by the invention]
By the way, a single frequency network is not adopted for the modes II, III, and IV, and different transmission frequencies are used in the respective transmitting stations as in the prior art. When a mobile object approaches another transmitting station, the received power of the broadcast wave being received is reduced. In this case, it is necessary to switch to the broadcast wave transmission frequency of another transmitting station, but it must be done manually. However, there is a problem that this manual operation is complicated during operation of the moving body.
[0004]
Therefore, in view of the above problems, an object of the present invention is to provide a digital audio broadcast receiver network follow device capable of automatically switching to a transmitting station in modes II, III, and IV. .
[0005]
[Means for Solving the Problems]
In order to solve the above problems, the present invention is for digital audio broadcasting that is mounted on a mobile body and receives a transmission signal from a transmitting station that divides and multiplexes data of a plurality of audio programs into a plurality of carriers and transmits the data. In the receiver, a high-frequency receiving unit having an oscillator for selecting a transmission frequency of the transmitting station, a Fourier transformer for performing frequency analysis of the plurality of carriers and demodulating the audio program data, and the transmission The signal reception status is checked, and when the reception status is bad, the high frequency reception unit is provided with a control unit for selecting another transmission station transmitting the same audio program. By this means, switching to the transmitting station can be automatically performed in modes II, III and IV.
[0006]
The control unit determines that the reception state is bad when the metric reliability formed based on the frequency analysis of the Fourier transformer becomes a predetermined number or more for a plurality of carrier waves. By using the metric reliability as it is by this means, the configuration is simplified.
Based on the frequency analysis of the Fourier transformer, the control unit determines that the reception status is poor when the level of a plurality of carrier waves is equal to or lower than a predetermined value. By this means, the determination of the reception status becomes faster than the above.
[0007]
The control unit checks the reception status by a cyclic redundancy check of the data of the audio program demodulated through the Fourier transformer. By this means, the configuration is simplified by using the cyclic redundancy detection as it is.
The transmission signal from the transmission station includes a list of transmission frequencies of other transmission stations that transmit the data of the same audio program, and the control unit is configured to transmit the other transmission when the reception status is bad based on the list. Make a station selection decision. By this means, a search for the transmission frequency of the transmission station to be received next can be easily performed.
[0008]
The control unit switches the frequency of the oscillator of the high-frequency receiving unit to another transmitting station, and after switching, confirms whether the audio program is the same before and after switching by the ID information of the audio program included in the data from the other transmitting station. . This means eliminates the need to transmit a list of transmission frequencies from the transmitting station as described above. The control unit checks the reception status based on the S level representing the received electric field before switching to the other transmission station, and switches to another transmission station having a good reception status. By this means, switching is preferentially performed to another transmitting station having a sufficient reception electric field, so that useless time can be saved.
[0009]
The present position information obtained from the present position information acquisition device mounted on the mobile body is input, and a database of positions, transmission heights, and output power values of a plurality of transmitting stations is provided. Based on the current position information and the database Next, the next transmitting station to be changed is determined. By this means, it becomes easy to search for a desired transmitting station with the maximum received power.
Two reception systems having the high-frequency receiver and the Fourier transformer are provided, and the control unit causes one reception system to perform normal reception, and the other reception system has a current reception status. Check and check the reception status when switching to another transmission station, and if another transmission station with good reception status is found, switch the role of the other reception system and the one reception system . By this means, the current reception can be received as it is even while searching for another transmitting station.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a diagram for explaining an example of a network follower for a digital audio broadcast receiver according to the present invention. From the digital audio broadcast signal received via the antenna 1, the radio frequency (RF) unit 2 changes the reference transmission frequency of the oscillator (OSC) in the reception band band (for example, L band, VHF band, etc.) and transmits Select to convert to baseband time series. This result is subjected to frequency analysis by a fast Fourier transformer (FFT) 3 constituted by a DSP (Digital Signal Processor). The channel decoder 4 performs differential demodulation on the result of the frequency analysis, decodes it into data, and further decodes this data into desired channel data. The audio decoder 5 decodes desired channel data into a PCM (pulse code modulation) signal. This result is output from the speaker 7 via the power amplifier 6. The control unit 8 (CPU) controls the high-frequency receiving unit 2, the fast Fourier transformer 3, the channel decoder 4, and the audio decoder 5, and further controls the frequency of the oscillator of the high-frequency receiving unit 2, the fast Fourier, as will be described later. Based on the conversion result of the converter 3, the reception status is checked, the transmission frequency of the same audio program is checked, and the reception electric field is checked. The user interface (uI) 9 gives an instruction for options of control performed by the control unit 8.
[0011]
FIG. 2 is a diagram showing an example of the arrangement of the transmission frequencies of the transmission stations selected by the frequency control of the oscillator of the high frequency receiver 2 of FIG. As shown in the figure, the transmission frequency of each transmission station composed of a plurality of carriers with a transmission bandwidth of 1.5 MHz is arranged at a constant interval.
FIG. 3 is a diagram for explaining an example of a digital audio broadcast frame from each transmitting station. As shown in the figure, a frame of digital audio broadcasting is composed of a high-speed information channel (FIC) and a main service channel (MSC). The high-speed information channel includes information such as multiplexing arrangement, service (audio program, etc.) name, and cyclic redundancy check (CRC). The main service channel includes information on a plurality of service (audio program) IDs and includes data multiplexed on the time axis.
[0012]
FIG. 4 is a diagram for explaining an example of data added to the high-speed information channel or the main channel. As shown in the figure, the transmitting station transmits, for example, a list of transmission frequencies freq1 and freq2 and the same service content ID2 of the transmitting station transmitting the same service content ID1 to the high-speed information channel or the main channel. Station frequency lists freq3 and freq4 are additionally included. It is not always necessary to transmit this data every frame.
[0013]
FIG. 5 is a diagram for explaining an example of checking the reception status. In the fast Fourier transform 3, the metric reliability Cr for evaluating the frequency analysis result is shown in the lower part of the frequency analysis result in the upper part of FIG. When the reception status is normal, the frequency analysis result is flat and the metric reliability is flat. As shown in the upper part of this figure (b), if the reception condition is bad due to the influence of multipath, the frequency analysis result is distorted, and accordingly, the metric reliability is also distorted as shown in the lower part of this figure (b). . The control unit 8 sets a threshold value Cth for the metric reliability and checks the reception status as follows.
[0014]
FIG. 6 is a flowchart for explaining an example of checking the reception status based on the metric reliability. In steps S1 and S2, C and k are initialized. Here, C is the count number, and k represents the number of carriers in the transmission band. In step S3, it is determined whether Cr (k) <Cth. In step S4, if the above determination is satisfied, the count is incremented to C = C + 1. In step S5, it is determined whether C ≧ C0 is satisfied. If the above determination is established in step S6, it is determined that the reception status is bad, and the process is terminated. If it is determined in step S7 that the condition is not satisfied in step S3 or step S5, it is determined that k = k0 is satisfied. If this determination is satisfied, the process is terminated. In step S8, if the above determination is not satisfied, the count is incremented to k = k + 1 and the process returns to step S3.
[0015]
In this way, if the metric reliability Cr (k) of the predetermined number (C0) or more of the carriers in the transmission band is the threshold value Cth, it is determined that the reception situation is bad.
If the control unit 8 determines that the reception condition is poor as described above, the control unit 8 searches for a transmission frequency (transmission station) belonging to the service ID that broadcasts the same audio program, and the transmission frequency obtained by the search is received at a high frequency. Set to the oscillator of part 2. The reception status is determined in the same manner as described above with the transmission frequency set in this way, and if the reception status is worse, another transmission frequency in the transmission frequency list is set. If the reception status is poor at any transmission frequency in the list, the original transmission frequency is restored.
[0016]
According to the present invention, the metric reliability can be used for network follow as it is, and the switching to the transmitting station can be automatically performed in the modes II, III, and IV with a simple configuration.
In addition, instead of the metric reliability in the lower part of FIGS. 5A and 5B, the reception status is obtained by using the result of frequency analysis by the fast Fourier transform unit 3 in the upper part of FIGS. 5A and 5B. You may make it judge. As a result, the time for calculating the metric reliability can be omitted to check the reception status.
[0017]
Further, instead of the above-described metric reliability and fast Fourier transform frequency analysis, the reception status may be determined based on a cyclic redundancy check (CRC) included in a digital audio broadcast frame. That is, it is determined that the reception situation has deteriorated when an error is continuously detected in a plurality of frames by a cyclic redundancy check performed every time a frame is received. According to this embodiment, the reception status can be checked with a simple configuration by using the cyclic redundancy check in the frame.
[0018]
Next, in place of the transmission frequency list of the transmitting station as described above, the multiplex configuration information (MCI) existing in the high-speed information channel (FIC) of the digital audio broadcast frame may be used. That is, the information on the service ID to be provided is included in the multiple configuration information. Change the transmission frequency when reception is bad. After this change, if the multiplex configuration information is received and it can be determined that the service ID information is the same, the reception is continued as it is, and if it is different, the transmission frequency is further changed. This is repeated and the transmission frequency is changed until the same service ID is received. If multiple configuration information cannot be obtained even if a plurality of frames are received over time, the frame is returned to the original transmitting station. As described above, this example is effective when the transmission frequency list cannot be transmitted on the transmission station side.
[0019]
In the above example, after checking the multiplex configuration information after changing the transmission frequency, the S level (representing the received electric field) at the changed transmission frequency is checked and the multiplex configuration information is not acquired if it is below the set threshold value. Change the transmission frequency. In this way, wasted time can be saved by acquiring the multiplex configuration information only for those for which a sufficient received electric field is obtained.
[0020]
FIG. 7 is a diagram for explaining another example of a network follow device for a digital audio broadcast receiver according to the present invention. As shown in this figure, two receiving systems A and B are provided, such as antennas 1A and 1B, high-frequency receiving units 2A and 2B, and fast Fourier transform units 3A and 3B. Normal reception / decoding is performed in the reception system A, and the reception status is checked using the other reception system B as described above. When the reception situation deteriorates, the high frequency receiving unit 2B of the reception system B is changed to another transmission frequency, and after the change, if the reception situation is bad, it is changed to the next transmission frequency. When a transmission frequency with a good reception condition is obtained, the selector 10 switches the roles of the reception systems A and B. That is, the reception system B performs normal reception / decoding, and the reception system A checks the reception status.
[0021]
In this way, since network follow is performed in two systems, the current service can be received as it is even while searching for other transmission frequencies.
Further, for example, a position information acquisition device that is combined with a position information acquisition device such as GPS (Global Positioning System) and has a database of positions, transmission heights, and output power values of a plurality of transmission stations on the receiver side. The transmitting station that has the maximum received power at the current position may be determined from the current position obtained from the above and the database. Then, if the determined transmitting station can be confirmed as the same service as described above, the transmission frequency is changed. If it cannot be confirmed, the transmitting station that has the maximum received power at the current position is determined in the same manner as described above, except for the transmitting station that has been determined in the previous calculation. Repeat this procedure. In this way, since the transmitting station that can obtain the maximum received power is determined by calculation, it is easy to search for a transmitting station that can receive a desired service with the maximum power.
[Brief description of the drawings]
FIG. 1 is a diagram for explaining an example of a network follower for a digital audio broadcast receiver according to the present invention.
FIG. 2 is a diagram illustrating an example of arrangement of transmission frequencies of transmission stations selected by frequency control of an oscillator of the high-frequency receiving unit 2 in FIG.
FIG. 3 is a diagram illustrating an example of a digital audio broadcast frame from each transmitting station.
FIG. 4 is a diagram illustrating an example of data added to a high-speed information channel or a main channel.
FIG. 5 is a diagram illustrating an example of checking a reception status.
FIG. 6 is a flowchart illustrating an example of checking a reception status based on metric reliability.
FIG. 7 is a diagram for explaining another example of a network follow device for a digital audio broadcast receiver according to the present invention.
[Explanation of symbols]
2, 2A, 2B ... high frequency receiver 3, 3A, 3B ... fast Fourier transformer 8 ... controller

Claims (3)

In a receiver for digital audio broadcasting that is mounted on a mobile unit and receives a transmission signal from a transmission station that divides and multiplexes data of a plurality of audio programs into a plurality of carrier waves,
A high frequency receiver having an oscillator for selecting a transmission frequency of the transmitting station;
A Fourier transformer for performing frequency analysis of the plurality of carrier waves and demodulating the audio program data;
The reception status of the transmission signal is checked, and when the reception status is bad, the high frequency reception unit includes a control unit that selects another transmission station that is transmitting the same audio program,
The control unit determines that the reception condition is bad when the metric reliability formed based on the frequency analysis of the Fourier transformer is less than a predetermined value for a plurality of carrier waves exceeds a predetermined number. Network follower for digital audio broadcast receiver. In a receiver for digital audio broadcasting that is mounted on a mobile unit and receives a transmission signal from a transmission station that divides and multiplexes data of a plurality of audio programs into a plurality of carrier waves,
A high frequency receiver having an oscillator for selecting a transmission frequency of the transmitting station;
A Fourier transformer for performing frequency analysis of the plurality of carrier waves and demodulating the audio program data;
The reception status of the transmission signal is checked, and when the reception status is bad, the high frequency reception unit includes a control unit that selects another transmission station that is transmitting the same audio program,
The digital audio broadcasting, wherein the control unit determines that the reception condition is bad when a predetermined number or less of a plurality of carrier wave levels becomes a predetermined number or more based on frequency analysis of the Fourier transformer Follow-up device for receiver. In a receiver for digital audio broadcasting that is mounted on a mobile unit and receives a transmission signal from a transmission station that divides and multiplexes data of a plurality of audio programs into a plurality of carrier waves,
A high frequency receiver having an oscillator for selecting a transmission frequency of the transmitting station;
A Fourier transformer for performing frequency analysis of the plurality of carrier waves and demodulating the audio program data;
The reception status of the transmission signal is checked, and when the reception status is bad, the high frequency reception unit includes a control unit that selects another transmission station that is transmitting the same audio program,
The control unit the frequency of the oscillator of the high-frequency receiving unit is switched to another transmission station, switching back and forth of the audio program to check the same by the ID information of the audio programs included in the data from the other transmitting station after the switching ,
Current position information is input from a current position information acquisition device mounted on a mobile body, and a database of positions, transmission heights, and output power values of a plurality of transmitting stations is provided. Based on the current position information and the database A network follower for a digital audio broadcasting receiver , characterized in that the next transmitting station to be changed is determined .

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