JP4442238B2 - Receiver - Google Patents

Description

  The present invention relates to a receiving apparatus such as a digital terrestrial broadcast receiver.

  As a method for modulating digital data, a modulation method called orthogonal frequency division multiplexing (hereinafter referred to as OFDM method; OFDM: Orthogonal Frequency Division Multiplexing) is known.

  With the OFDM modulation system, a large number of orthogonal subcarriers (subcarriers) are provided in the transmission band, and data is allocated to the amplitude and phase of each subcarrier by PSK (Phase Shift Keying) or QAM (Quadrature Amplitude Modulation), This is a digital modulation method.

  The OFDM system is often applied to terrestrial digital broadcasting that is strongly affected by multipath interference. As terrestrial digital broadcasting adopting the OFDM system, for example, there is a standard such as ISDB-T (Integrated Services Digital Broadcasting-Terrestrial) (see Non-Patent Document 1).

  Here, in the ISDB-T standard, a transmission method called hierarchical transmission is adopted.

  Hierarchical transmission, as shown in FIG. 4, can divide the inside of one channel (transmission band) into a plurality of regions (referred to as segments) and transmit broadcast signals with different modulation methods for each segment. In the case where the segment division method is adopted, a plurality of different broadcast signals are simultaneously broadcast on the same channel. Each segment transmits signals in a state where orthogonality is maintained, and on the receiving side, it is possible to collectively demodulate broadcast signals transmitted to a plurality of segments in one channel. Yes.

  In the ISDB-T standard, one channel (6 MHz band) is divided into 13 segments, one broadcast signal is modulated in one central segment, and one in 12 segments excluding the central segment. Hierarchical transmission system that modulates two broadcast signals is adopted. The hierarchy of the broadcast signal of one central segment is hereinafter referred to as A hierarchy, and the broadcast signal hierarchy of the segment excluding the A hierarchy is hereinafter referred to as B hierarchy.

  In the ISDB-T standard, the A layer broadcast signal is used for broadcasting for mobile terminals exclusively by making the A layer broadcast signal a signal with low transmission capacity (low image quality and low sound quality) and high error tolerance. By making the broadcast signal a signal with high transmission capacity (high image quality and high sound quality) and low error tolerance, the B layer is planned to be used exclusively for broadcasting for fixed reception. For example, the A layer modulation scheme is set to QPSK and the coding rate 2/3, and the B layer modulation scheme is set to 64 QAM and the coding rate 3/4.

  In addition, in the hierarchical transmission of the ISDB-T standard, there is a possibility of adopting a hierarchical transmission system in which the central three segments are the A hierarchy and the ten segments excluding the central three segments are the B hierarchy. is there.

JP 11-313290 A "Digital Terrestrial Broadcasting Transmission System ARIB STD-B30 Version 1.1", Radio Industry, formulated on May 31, 2001, July 29, 2003 1.5 revision

  By the way, in terrestrial digital broadcasting, there is a high possibility that the reception status will change every moment by receiving while moving, and the reception status may gradually deteriorate even though the reception status was good at first. . When the reception situation deteriorates, the video and audio are disturbed in the middle, resulting in a video that is very difficult to see and difficult to hear.

  Therefore, a general receiver does not output the decoded video signal as a moving image as it is, but displays a still image that holds the previous decoded image, thereby making it difficult to see the video when the reception state deteriorates. It is thought that it will cancel.

  However, since the audio signal cannot be processed as hold, if the same processing as the video signal is performed when the reception state deteriorates, the audio signal can only be muted. However, if the audio signal is muted in the middle, the sound is interrupted in the middle and becomes unintelligible.

  A technique for solving the problem of the audio signal when the reception state deteriorates is described in Patent Document 1. Patent Document 1 discloses an invention in which when a reception state deteriorates at the time of reception of a higher hierarchy (broadcast signal for fixed reception), the audio signal is switched to a lower hierarchy (broadcast signal for mobile body) and output. ing. With such an invention, the sound is not interrupted.

  However, in the ISDB-T standard, there is no guarantee that the broadcast signal modulated into one segment at the center of the channel and the broadcast signal modulated into 12 segments other than the center are the same source. There is a possibility that an audio signal that is completely unrelated to the previous audio signal is output. When an unrelated audio signal is output, it is not always friendly to the user, and conversely, it may be better to interrupt the audio.

  Therefore, the present invention is a receiving apparatus that receives an orthogonal frequency division multiplex signal that employs a hierarchical transmission method, and that eliminates the user's difficulty in hearing and provides a user-friendly audio signal. Objective.

The receiving apparatus according to the present invention divides a transmission channel into at least two layers, a first layer having high error resistance and a second layer having low error resistance, and adopts a hierarchical transmission method in which different data is transmitted respectively. In a receiving apparatus that receives a frequency division multiplexing (OFDM) signal, receiving means for receiving the OFDM signal transmitted to the transmission channel, and demodulating the received OFDM signal, and decoding a data stream from the demodulated signal Demodulating means, data separating means for separating the data stream into first layer data transmitted to the first layer and second layer data transmitted to the second layer, and the first layer A first decoding means for decoding an audio signal from the data, and a second decoding means for decoding the video signal and the audio signal from the second layer data. And means, the reception state of the received and are OFDM signals, and the reception state detecting means for detecting that according to the bit error rate calculated on the basis of the first decoding means and decoding the signals before and after the second decoding means Whether the audio signal decoded from the first layer data and the audio signal decoded from the second layer data are the same content is determined by referring to the identification information attached to the audio signal As a result of determination by the content determination unit and the reception state detection unit, when it is detected that the reception state is good, the video signal decoded by the second decoding unit and the second hierarchy data decoded from the second hierarchical data When the reception state is detected as a result of the process of outputting the audio signal 2 and the determination by the reception state detection unit, the content determination unit When it is determined that the audio signal decoded from the first layer data and the audio signal decoded from the second layer data have the same content, the first audio decoded by the first decoding unit A signal and a process of outputting a still image obtained from the video signal decoded by the second decoding unit immediately before, and an audio signal detected from a poor reception state and decoded from the first layer data And the process of outputting a message indicating that the reception state has deteriorated when it is determined that the audio signal decoded from the second layer data is not the same content. Ru and output means for selectively switched to output in response to the reception state and the audio signal decoded from the decoded audio signal and the second hierarchy data from.

  The output means detects that the reception state is bad by the reception state detection means, and the contents of the audio signal decoded from the first hierarchy data and the audio signal decoded from the second hierarchy data by the content discrimination means If it is determined that they are the same, the first audio signal is output.

  In the receiving apparatus according to the present invention configured as described above, in the normal reception state, the audio signal decoded from the second layer data is output, the reception state is poor, and the first layer data If the content of the audio signal decoded from the second hierarchy data is the same as the content of the audio signal decoded from the second hierarchy data, the audio signal decoded from the second hierarchy data is output.

  In the receiving apparatus according to the present invention, it is possible to output an audio signal that eliminates the difficulty of hearing even when the reception situation deteriorates, and prohibits the output of an audio signal that has nothing to do with it. Thus, a kind audio signal can be provided to the user.

  Hereinafter, a digital terrestrial broadcast receiving apparatus to which the present invention is applied will be described as an embodiment of the present invention.

  FIG. 1 shows a block diagram of a digital terrestrial broadcast receiving apparatus 10 to which the present invention is applied.

  As shown in FIG. 1, the terrestrial digital broadcast receiving apparatus 10 includes an antenna 11, a tuner 12, an OFDM demodulation / transmission path decoding unit 13, a demultiplexing unit 14, an A layer audio decoding unit 15, and a B layer video and audio. The decoding part 16, the audio | voice switching part 17, the content comparison part 18, and the reception condition judgment part 19 are provided.

  A broadcast signal broadcast from a broadcasting station is a signal corresponding to the ISDB-T standard. That is, the transport stream specified by ISO / IEC13818-1 is subjected to Reed-Solomon encoding, convolutional encoding, transmission path encoding processing for time and frequency interleaving, followed by IFFT (Inverse Fast Fourier Transform) calculation and This signal is subjected to OFDM modulation processing such as guard interval addition processing.

  Furthermore, a broadcast signal broadcast from a broadcast station includes two services by hierarchical transmission. In other words, one channel is divided into 13 segments in the frequency direction, and the content signal (video signal and audio signal) of A layer transmitted to one central segment is divided into segments other than the central one segment. B layer content signals to be transmitted are included. In addition, the broadcast signal of the A layer has a low transmission capacity (low image quality and low sound quality) and high error tolerance, and is a signal for mobile reception. On the other hand, the broadcast signal of the B layer is a signal for fixed reception having a high transmission capacity (high image quality and high sound quality) and low error tolerance.

  Such a broadcast wave signal is received by the antenna 11 of the receiving device 10 and supplied to the tuner 12 as an RF signal.

  The tuner 12 frequency-converts the RF signal received by the antenna 11 using a multiplier and a local oscillator, and then filters the RF signal using a bandpass filter to generate an IF signal. The IF signal output from the tuner 12 is supplied to the OFDM demodulation / transmission path decoding unit 13.

  The OFDM demodulation / transmission path decoding unit 13 performs A / D conversion processing, digital orthogonal demodulation processing, FFT calculation processing, carrier demodulation processing, frequency and time deinterleaving, Viterbi decoding processing, hierarchical processing on the input IF signal. Then, OFDM demodulation processing and transmission path decoding processing are performed by performing transport stream generation processing, Reed-Solomon decoding processing, and the like. The OFDM demodulation / transmission path decoding unit 13 can output a transport stream by performing OFDM demodulation processing and transmission path decoding processing. The transport stream output from the OFDM demodulation / transmission path decoding unit 13 is supplied to the separation unit 14.

  The separation unit 14 separates the input transport stream into data in the A layer and data in the B layer in units of TS packets. In the case of the ISDB-T standard, the ID (PID) of the TS packet including the content signal of the A layer has a fixed value. Therefore, the separation unit 14 refers to the PID of the TS packet. When the PID is the above-described fixed value, the separation unit 14 determines that the TS packet includes the A layer content signal, and the PID is other than that. If it is a value, it can be determined that the content signal of the B layer is included. The TS packet including the layer A content signal separated by the separation unit 14 is supplied to the layer A audio decoding unit 15, and the TS packet including the layer B content signal is supplied to the layer B video / audio decoding unit 16. Supplied.

  The A-layer audio decoding unit 15 selects only TS packets that include audio signals from all the input TS packets, performs decoding processing on the TS packets, and outputs audio signals in a predetermined audio format. Generate. The audio signal decoded by the A layer audio decoding unit 15 is supplied to the audio switching unit 17. The audio signal output from the A layer audio decoding unit 15 is hereinafter referred to as an A layer audio signal.

  The B-layer video / audio decoding unit 16 selects a TS packet including a video signal from all the input TS packets, performs a decoding process on the TS packet, and outputs a video signal of a predetermined video format. Generate. At the same time, the layer B video / audio decoding unit 16 selects only TS packets that include audio signals from all the input TS packets, performs decoding processing on the TS packets, and performs a predetermined audio format. Generates an audio signal. The video signal decoded by the B layer video / audio decoding unit 16 is supplied to a monitor or a recording device (not shown) via the video output terminal 21. The audio signal decoded by the B layer video / audio decoding unit 16 is supplied to the audio switching unit 17. The audio signal output from the B layer video / audio decoding unit 16 is hereinafter referred to as a B layer audio signal.

  The audio switching unit 17 selects one of the A layer audio signal and the B layer audio signal in accordance with the control from the reception status determination unit 19 and outputs the selected one audio signal. The audio signal output from the audio switching unit 17 is supplied to an audio output device or a recording device (not shown) via the audio output terminal 22.

  The content comparison unit 18 receives the service ID of the A layer audio signal and the service ID of the B layer audio signal. The service ID here is ID information for specifying a broadcast program, and is uniquely determined for each program. The content comparison unit 18 compares the input service IDs to determine whether the A layer audio signal and the B layer audio signal are the same as the content. The content comparison unit 18 gives the determination result (identical or non-identical) to the reception status determination unit 19.

  The reception status judgment unit 19 receives the bit error rate (BER) calculated by the OFDM demodulation / transmission path decoding unit 13 and the judgment result (identical / non-identical) of the content comparison unit 18. The bit error rate can be calculated, for example, by comparing data before Reed-Solomon decoding with data obtained by re-encoding data after Reed-Solomon decoding. The reception status determination unit 19 determines whether or not the reception state of the currently received broadcast signal is good based on the bit error rate and the same / non-identical content. The reception status judgment unit 19 performs switching control of the voice switching unit 17 based on these judgment results.

  Next, the operation of the terrestrial digital broadcast receiving apparatus 10 will be described with reference to the flowchart of FIG.

  First, the reception status determination unit 19 always determines whether or not the reception status is good (step S1). Specifically, it is detected whether or not the bit error rate (BER) is equal to or higher than a predetermined threshold, and if the bit error rate is equal to or higher than a predetermined value, it is determined that the reception status is bad. Judge that the reception status is good. Whether or not the reception state is good is used as an index for determining whether or not the content signal transmitted to the B layer can withstand viewing by the user. Therefore, the above threshold value of the bit error rate is set to a bit error rate that can withstand at least the user's viewing when the content signal transmitted to the B layer is demodulated.

  As a result of the determination, when the reception situation is good (the bit error rate is smaller than a predetermined threshold), the reception situation judgment unit 19 causes the B layer video / audio decoding unit 16 to decode the video signal and the audio signal as usual. Then, the B-layer video signal decoded as usual is output from the video output terminal 21. At the same time, the reception status determination unit 19 controls the audio switching unit 17 to switch the audio switching unit 17 to the B layer audio signal side, and outputs the B layer audio signal from the audio output terminal 22 (step S2).

  Therefore, in the terrestrial digital broadcast receiving apparatus 10, when the reception condition is good, the video signal and audio signal of the B layer are output.

  On the other hand, when the reception status is poor (bit error rate is equal to or higher than a predetermined threshold) as a result of the determination, the reception status determination unit 19 holds the previous image, not the moving image, for the B layer video / audio decoding unit 16. A still image like this is output. Then, a still image that holds the previous image is output from the video output terminal 21. Therefore, when the reception condition is poor, it is possible to display an image of good quality that has been decoded so far without displaying an image that has deteriorated to the extent that it cannot be viewed.

  If the reception status is poor, the reception status determination unit 19 refers to the comparison result of the content comparison unit 19 at the same time as processing the video, and whether the A layer audio signal and the B layer audio signal are the same as the content. It is determined whether or not (step S3). That is, it is determined whether or not the sound of the A layer and the sound of the B layer are the same. If the content is the same, the reception status determination unit 19 controls the audio switching unit 17 to output the A layer audio signal (step S4). If the content is not the same, for example, the audio signal output is stopped (muted) (Step S5).

  As described above, the terrestrial digital broadcast receiving apparatus 10 holds and outputs the video signal of the B layer when the reception state is bad, and if the audio signal is the same, the audio of the A layer has high error tolerance. If the audio signal is not the same, the audio is stopped. As a result, the terrestrial digital broadcast receiving apparatus 10 can output an audio signal that eliminates the difficulty of hearing even when the reception situation deteriorates when receiving the audio signal of the B layer. It is possible to provide a kind audio signal to the user by prohibiting the output of an audio signal that has nothing to do with the user.

The digital terrestrial broadcast receiving apparatus 10 determines whether or not the reception condition is good based on the bit error rate. However, since the bit error rate is a value that fluctuates drastically, the A layer audio signal and the B layer audio are used. Signal switching can occur frequently. Therefore, the reception status determination unit 19 may calculate a moving average of the bit error rate for each predetermined number of samples and determine whether the moving average value is equal to or greater than a predetermined threshold value. For example, the bit error rate is detected at intervals of 5 seconds, the detected bit error rate is moving averaged at intervals of 30 seconds, and whether or not the moving average value is, for example, “30 ⁻³ ” or more is detected. It may be determined whether or not is good.

  Further, whether or not the reception status is good is determined not only based on the bit error rate, but may be determined using, for example, the C / N of the received signal.

  The terrestrial digital broadcast receiving apparatus 10 compares the service ID of the A layer audio signal and the service ID of the B layer audio signal to determine whether the A layer audio signal and the B layer audio signal are the same. However, the present invention is not limited to this method, and determination may be made by comparing signal waveforms in steps as shown in FIG.

  That is, the A layer audio signal and the B layer audio signal are detected simultaneously (step S11). Subsequently, band limitation of the B layer audio signal having a wide band is performed, and the bands of the A layer audio signal and the B layer audio signal are matched (step S12). Subsequently, the A layer audio signal and the band-limited B layer audio signal are taken into the memory (step S13), and the waveforms of the two signals taken into the memory are compared (step S14). As a result of the waveform comparison, if the degree of coincidence of both is high, it is determined that the A layer audio signal and the B layer audio signal are the same, and if the degree of coincidence is low, it is determined that they are not the same (step S15).

  By performing such waveform comparison, even when the content is the same, it is possible to cope with a case where the service ID is different.

  Also, in the terrestrial digital broadcast receiving apparatus 10, when the reception status is poor and the A layer audio signal and the B layer audio signal are not the same, the audio signal is muted, but the audio signal is not muted and the user is not muted. A message with a content such as “Receiving condition has deteriorated. Is it okay to output other audio?” And outputs a layer A audio signal when the user performs a permission operation. You may make it do.

It is a block block diagram of the terrestrial digital broadcast receiver to which this invention is applied. It is a flowchart which shows operation | movement of a terrestrial digital broadcast receiver. It is the flowchart which showed the process for determining whether an A hierarchy audio | voice signal and a B hierarchy audio | voice signal are the same. It is a figure for demonstrating a hierarchical transmission system.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 Terrestrial digital broadcast receiver, 11 Antenna, 12 tuner, 13 OFDM demodulation / transmission path decoding part, 14 Separation part, 15 A hierarchy audio | voice decoding part, 16 B hierarchy audio | voice decoding part, 17 Audio | voice switching part, 18 Content comparison part , 19 Reception status judgment unit

Claims (4)

An orthogonal frequency division multiplexing (OFDM) signal adopting a hierarchical transmission scheme that divides a transmission channel into at least two layers, a first layer having high error resistance and a second layer having low error resistance, and transmitting different data respectively. In the receiving device for receiving,
Receiving means for receiving an OFDM signal transmitted to the transmission channel;
Demodulating means for demodulating the received OFDM signal and decoding a data stream from the demodulated signal;
Data separating means for separating the data stream into first layer data transmitted to the first layer and second layer data transmitted to the second layer;
First decoding means for decoding an audio signal from the first layer data;
Second decoding means for decoding the video signal and the audio signal from the second layer data;
Receiving state detecting means for detecting a receiving state of the received OFDM signal according to a bit error rate calculated based on signals before and after decoding by the first decoding means and the second decoding means ;
Content for determining whether the audio signal decoded from the first layer data and the audio signal decoded from the second layer data are the same content by referring to the identification information attached to the audio signal Discrimination means;
As a result of the determination by the reception state detecting means, when it is detected that the reception state is good, the video signal decoded by the second decoding means and the second audio signal decoded from the second layer data Is output from the first layer data and the second layer data decoded by the content determination unit when it is detected that the reception state is bad. When it is determined that the audio signal is the same content, it is obtained from the first audio signal decoded by the first decoding means and the video signal decoded by the second decoding means immediately before. The process of outputting the received still image and the reception state is detected to be poor, and the audio signal decoded from the first layer data and the second layer data are decoded. When it is determined that the audio signal is not the same content, the audio signal decoded from the first layer data and the first data are output so as to execute a process of outputting a message indicating that the reception state has deteriorated. receiving device Ru and output means for outputting selectively switched according to the reception state and the audio signal decoded from the second layer data. The first layer is disposed at the center of the transmission channel,
The second tier, receiving apparatus 請 Motomeko 1 wherein that are located in the frequency region other than the first hierarchy data out of the transmission channel. The reception state detecting means includes
The reception state of the received OFDM signal is detected according to the moving average of the bit error rate calculated for every fixed number of samples based on the signals before and after decoding by the first decoding means and the second decoding means. The receiving device according to claim 1 . The content discrimination means is
Comparing the waveform of the audio signal receiving apparatus 請 Motomeko 1, wherein you determine whether the same content.

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