JPH10200499A - Network following device of digital audio broadcast receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform network following of a digital audio broadcast(DAB) receiver. SOLUTION: A digital audio broadcast receiver which is mounted on a mobile body and receives a transmitted signal from a transmitting station that divides data of plural audio programs into plural carriers, multiplexes the and sends them is provided with a high frequency receiving part 2 which has an oscillator that selects a sending frequency of the transmitting station, a Fourier transformer 3 which performs frequency analysis of plural carriers and demodulates them into data of an audio program and a control part 8 which checks the reception state of a transmitting signal and makes the part 2 select other transmitting station that sends the same audio program when the reception state is not satisfactory.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital audio broadcasting (DAB) receiver, and more particularly to a network follower for the receiver.

[0002]

2. Description of the Related Art Orthogonal frequency division multiplexing (OFDM) is adopted for digital audio broadcasting, and coded data is divided into several hundred or more carriers within a transmission bandwidth (about 1.5 MHz). It distributes, multiplexes, and transmits a plurality of audio programs. 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. In addition, this digital audio broadcasting includes modes I, II, II
There are four types, I and IV. Mode 1 is nationwide broadcasting by a single frequency network (SFN), mode II is local broadcasting, and mode III is used for satellite broadcasting and the like. 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 co-channel interference. In contrast, in a single frequency network, one channel covers a wide area. This is because the same audio program broadcast transmitted from a plurality of stations can be regarded as a signal from a multipath transmission path at the time of demodulation. In addition, if the delay time of each received signal is within the allowable range, a plurality of signals add to the reception strength in addition.

[0003]

The above-mentioned mode
For II, III, and IV, a single frequency network is not adopted, and each transmitting station uses a different transmission frequency as in the past. When the moving body approaches another transmitting station, the received power of the broadcast wave being received decreases. In this case, it is necessary to switch to the transmission frequency of the broadcast wave of another transmission station, but this must be done manually. However, there is a problem that this manual operation is complicated during the operation of the moving body.

Accordingly, the present invention has been made in view of the above problems, and has as its object to provide a network follower of a digital audio broadcasting receiver that can automatically switch to a transmitting station in modes II, III, and IV. Aim.

[0005]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a method for transmitting data from a plurality of audio programs into a plurality of carrier waves by dividing the data of a plurality of audio programs into a plurality of carrier waves. In a digital audio broadcasting receiver for receiving a transmission signal, a high-frequency receiving unit having an oscillator for selecting a transmission frequency of the transmitting station, and performing frequency analysis of the plurality of carriers to demodulate the data into the audio program data. A Fourier transformer for checking the reception status of the transmission signal, and if the reception status is poor, the high frequency reception unit controls the high frequency reception unit to select another transmission station transmitting the same audio program. It is characterized by having. By this means, Mode II, III
, IV, the switching to the transmitting station can be automatically performed.

The control unit determines that the reception condition is bad when the metric reliability formed based on the frequency analysis of the Fourier transformer becomes a predetermined number or more of a plurality of carrier waves which are below a predetermined value. By using the metric reliability as it is by this means, the configuration is simplified. The control unit determines that the reception condition is bad when the level of a plurality of carrier waves is equal to or more than a predetermined value based on the frequency analysis of the Fourier transformer. By this means, the determination of the reception status becomes earlier than the above.

[0007] The control unit checks the reception status by a cyclic redundancy check of the data of the audio program demodulated via 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 transmitting the same audio program data, and based on the list, the control unit performs the other transmission when the reception condition is poor. The selection of the station is determined. By this means, the search for the transmission frequency of the transmitting station to be received next can be easily performed.

The control unit switches the frequency of the oscillator of the high frequency receiving unit to another transmitting station, and after the switching, determines whether the audio program before and after the switching is the same before and after the switching based on the ID information of the audio program included in data from the other transmitting station. Check. By this means, there is no need to transmit the list of transmission frequencies from the transmitting station as described above. The control unit checks the reception status based on the S level indicating the reception electric field before switching to the other transmission station, and switches to another transmission station having a good reception status. By this means, the priority is given to switching to another transmitting station having a sufficient receiving electric field, so that useless time can be saved.

[0009] Current position information obtained from a current position information acquisition device mounted on a moving body is input, and a database of positions, transmission heights, and output power values of a plurality of transmitting stations is provided. The next transmitting station to be changed is determined based on the database. By this means, it becomes easy to search for a desired transmitting station with the maximum received power. The high-frequency receiver,
Two reception systems having the Fourier transformer are provided, and the control unit causes one reception system to perform normal reception, and the other reception system to check a current reception state and perform another transmission. The station is made to check the reception status when switching, and if another transmission station with a good reception status is found, the roles of the other reception system and the one reception system are switched. By this means, the current reception can be received as it is even while searching for another transmitting station.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram illustrating an example of a network follower of 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 a reception band (for example, L band, VHF band, etc.) and transmits the signal. To convert to baseband time series. The frequency is analyzed by a fast Fourier transformer (FFT) 3 composed of a DSP (Digital Signal Processor). The channel decoder 4 performs differential demodulation on the result of the frequency analysis, decodes the data into data, and 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.
As will be described later, the frequency control of the oscillator of the high-frequency receiving unit 2, the check of the reception status based on the conversion result of the fast Fourier transformer 3, the check of the transmission frequency of the same audio program, and the check of the reception electric field are performed. A user interface (uI) 9 gives an instruction of a control option performed by the control unit 8.

FIG. 2 is a diagram showing an example of the arrangement of the transmission frequencies of the transmitting stations selected by controlling the frequency of the oscillator of the high-frequency receiving section 2 in FIG. As shown in this figure, the transmission bandwidth is 1.5M
The transmission frequency of each transmitting station composed of a plurality of carrier waves in Hz is arranged so as to be located at a constant interval. FIG. 3 is a diagram illustrating an example of a digital audio broadcast frame from each transmitting station. As shown in the figure, a frame of digital audio broadcasting includes a high-speed information channel (FIC) and a main service channel (MSC). The high-speed information channel includes information such as an arrangement of multiplexing, names of services (such as audio programs), and cyclic redundancy check (CRC). The main service channel includes information of a plurality of service (audio program) IDs, and includes data multiplexed on a time axis.

FIG. 4 is a view for explaining an example of data added to a high-speed information channel or a main channel. In the transmitting station, as shown in the figure, for example, a list of transmission frequencies freq1, freq of transmitting stations transmitting the same service content ID1 to the high-speed information channel or the main channel.
q2, transmission frequency lists freq3 and freq4 of transmitting stations transmitting the same service content ID2 are additionally included. It is not always necessary to transmit this data every frame.

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 situation is normal, the frequency analysis result becomes flat and the metric reliability becomes flat. If the reception condition is bad due to the influence of multipath as shown in the upper part of this figure (b), distortion occurs in the frequency analysis result, and accordingly, the metric reliability also becomes 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.

FIG. 6 is a flow chart 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 a count number, and k represents the number of carriers in the transmission band. In step S3, it is determined whether Cr (k) <Cth holds. In step S4, if the above determination is satisfied, the count is increased to C = C + 1. Step S
At 5, it is determined whether C ≧ C0 holds. If the above determination is made in step S6, it is determined that the reception situation is bad, and the process is terminated. In step S7, step S
In the case of 3 or step S5, it is k = k0
Is determined, and if this determination is satisfied, the process ends. In step S8, if the above determination is not satisfied, k = k + 1 is counted up and the process returns to step S3.

In this manner, the metric reliability Cr of a predetermined number (C0) or more of the carriers in the transmission band is determined.
If (k) is the threshold value Cth, it is determined that the reception situation is bad.
As described above, when the control unit 8 determines that the reception condition is bad, the service I for broadcasting the same audio program is performed.
A search for a transmission frequency (transmitting station) belonging to D is performed, and the transmission frequency obtained by the search is set in the oscillator of the high frequency receiving unit 2. The reception status is determined in the same manner as described above using the transmission frequency set as described above. If the reception status is poor, another transmission frequency in the transmission frequency list is set. If the reception condition is poor at any transmission frequency in the list, the transmission frequency is returned to the original one.

According to the present invention, it is possible to automatically switch to the transmitting station even in modes II, III and IV by using the metric reliability as it is for the network follow and with a simple configuration. 5A and 5B.
Instead of the metric reliability at the bottom of FIG.
The reception state may be determined using the result of frequency analysis performed by the fast Fourier transform unit 3 in the upper part of (a) and (b). This allows you to check the reception status.
The time for calculating the metric reliability can be omitted.

Further, instead of the metric reliability and the frequency analysis of the fast Fourier transform described above, a cyclic redundancy check (CR) included in a frame of digital audio broadcast is performed.
The reception status may be determined based on C). In other words, by the cyclic redundancy check performed every time a frame is received, it is determined that the reception situation has deteriorated when an error is continuously detected in a plurality of frames. According to this embodiment,
By using the cyclic redundancy check in the frame, the reception status can be checked with a simple configuration.

Next, instead of the transmission frequency list of the transmission 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 multiplex configuration information includes information of the service ID to be provided. Change the transmission frequency when the reception situation is bad. After this change, if the multiplex configuration information is received and the same service ID information can be determined, the reception is continued as it is, and if different, the transmission frequency is further changed. This is repeated, and the transmission frequency is changed until the same service ID is received. If the multiplex configuration information cannot be obtained even if a plurality of frames are received over a long period of time, the frames are returned to the original transmitting station. This example is effective when the transmission frequency list cannot be transmitted on the transmission station side as described above.

In the above example, after changing the transmission frequency and before checking the multiplex configuration information, the S level (representing the received electric field) at the changed transmission frequency is checked and if it is equal to or less than the set threshold, the multiplex configuration information is acquired. Instead, change to the next transmission frequency. In this way, it is possible to save useless time by acquiring multiplex configuration information only for those for which a sufficient reception electric field is obtained.

FIG. 7 is a diagram for explaining another example of the network follower of the digital audio broadcast receiver according to the present invention. As shown in the figure, the antennas 1A, 1B,
High frequency receiving units 2A, 2B, fast Fourier transform units 3A, 3
B, two reception systems A and B are provided, and the control unit 8 causes the selector 10 to perform normal reception / decoding on one of the reception systems A and use the other reception system B to perform the above-described operation. As described above, the reception status is checked. When the reception condition deteriorates, the high-frequency reception unit 2B of the reception system B is caused to change to another transmission frequency, and when the reception condition is still bad after the change, it is changed to the next transmission frequency. When a transmission frequency with a good reception condition is obtained, the roles of the reception systems A and B are switched by the selector 10. That is, normal reception /
Decoding is performed, and the reception system A checks the reception status and the like.

In this way, since network follow is performed by two systems, the current service can be received as it is even while searching for another transmission frequency. Further, for example, by combining with a position information acquisition device such as a GPS (Global Positioning System) and providing the receiver with a database of the positions, transmission heights, and output power values of a plurality of transmitting stations, the position information acquisition device The transmitting station having the maximum received power at the current position may be determined from the current position obtained from the above and the database. Then, when the determined transmitting station can confirm the same service as described above, the transmission frequency is changed. If it cannot be confirmed, in the same manner as described above, except for the transmitting station determined by the previous calculation, the transmitting station having the next highest receiving power at the current position is determined. Repeat this procedure. As described above, since the transmitting station that can obtain the maximum received power is calculated, it becomes easy to search for the transmitting station that can receive the desired service with the maximum power.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an example of a network follower of a digital audio broadcast receiver according to the present invention.

FIG. 2 is a diagram illustrating an example of an arrangement of transmission frequencies of a transmission station selected by frequency control of an oscillator of a high-frequency receiving unit 2 in FIG. 1;

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 illustrating another example of the network follower of the digital audio broadcast receiver according to the present invention.

[Explanation of symbols]

 2, 2A, 2B: high-frequency receiving unit 3, 3A, 3B: fast Fourier transformer 8: control unit

Claims (9)

[Claims] 1. A digital audio broadcasting receiver mounted on a mobile unit and receiving a transmission signal from a transmitting station that divides data of a plurality of audio programs into a plurality of carrier waves and multiplexes and transmits the multiplexed data. A high-frequency receiving unit having an oscillator for selecting a transmission frequency, a Fourier transformer for performing frequency analysis of the plurality of carriers and demodulating the data into the audio program data, and checking a reception status of the transmission signal, A network follow-up device for a digital audio broadcast receiver, comprising: a control unit for causing the high-frequency receiving unit to select another transmitting station transmitting the same audio program when the receiving condition is poor. 2. The control unit determines that the reception condition 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 carriers. 2. The network follower of a digital audio broadcast receiver according to claim 1, wherein: 3. The method according to claim 1, wherein the control unit determines that the reception condition is bad when a plurality of carrier waves whose levels are equal to or less than a predetermined value exceed a predetermined number based on a frequency analysis of the Fourier transformer. The network follower for a digital audio broadcast receiver according to claim 1, wherein 4. The digital audio broadcasting system according to claim 1, wherein the control unit checks a reception status by a cyclic redundancy check of the data of the audio program demodulated through the Fourier transformer. Network follower for the receiver. 5. A transmission signal from the transmitting station includes a list of transmission frequencies of other transmitting stations transmitting the same audio program data. 2. The network follow-up device for a digital audio broadcast receiver according to claim 1, further comprising: determining whether to select the other transmitting station. 6. The control unit switches the frequency of the oscillator of the high-frequency receiving unit to another transmitting station, and after the switching, the audio program before and after the switching is determined by the ID information of the audio program included in data from the other transmitting station. 2. The network follower for a digital audio broadcast receiver according to claim 1, wherein the same is confirmed. 7. The control unit according to claim 1, wherein before switching to the other transmitting station, the control unit checks a reception status based on an S level indicating a reception electric field, and switches to another transmission station having a good reception status. 7. A network follower for a digital audio broadcast receiver according to item 6. 8. A current position information is input from a current position information acquisition device mounted on a moving body, and a database of positions, transmission heights, and output power values of a plurality of transmitting stations is provided. 7. The apparatus according to claim 6, wherein a next transmitting station to be changed is determined based on the database. 9. The radio frequency receiver and two receiving systems each including the Fourier transformer are provided, and the control unit causes one receiving system to perform normal reception and the other receiving system to perform normal reception. Check the current reception status, check the reception status when switching to another transmission station, and if another transmission station with a good reception status is found, the other reception system and the one reception system 2. The network follower for a digital audio broadcast receiver according to claim 1, wherein the role is switched.