JP4345508B2 - 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 method, a 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. 3, can divide the inside of one channel (transmission band) into a plurality of areas (referred to as segments) and transmit broadcast signals with different modulation schemes 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 a receiver mounted on a mobile body such as a car, it is considered that it is normal to receive a broadcast signal of A layer intended for the mobile terminal because of its wide range of activity. However, since the broadcast signal of the A layer has a low video bit rate to be transmitted, the image quality is not sufficient for a vehicle-mounted receiver having a relatively larger screen than a portable device.

  Therefore, the present invention provides a receiving apparatus that receives an orthogonal frequency division multiplex signal that employs a hierarchical transmission scheme, and outputs a high-quality content signal for a fixed terminal when the reception quality is good, and when the reception quality is insufficient. By outputting low-quality content signals for normal mobile terminals, it is possible to ensure high image quality and a wide service area, suppress frequent switching, and enable high-quality content signals. An object of the present invention is to provide a receiving apparatus that is adjusted so that a high-quality content signal is output as much as possible.

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 / decoding means, data separating means for separating the decoded data stream into first layer data transmitted to the first layer and second layer data transmitted to the second layer; a first decoding means for outputting a first content signal by decoding the first layer data, the first co-decodes the second layer data Second decoding means for outputting a second content signal having a higher quality than the content signal, reception quality detecting means for detecting the reception quality of the received OFDM signal, and the first content signal or the second content. Output means for switching and outputting either one of the signals, wherein the output means is configured to selectively output the second content signal decoded from the second layer having low error tolerance, It is periodically determined whether or not the reception quality detected by the detection means is better than the first threshold value. If the reception quality is better than the first threshold value, the second content signal is continuously output. a first processing Ru switching the content signal for selecting and outputting the first content signal if, not selectively outputs the first content signal error resistance is decoded from a high first hierarchy Occasionally, whether the reception quality detected by the reception quality detection means is better than the second threshold value is a value higher than the first threshold value periodically determines, when the reception quality is better than the second threshold value If the reception quality is worse than the second threshold value and the reception quality is rising in the direction of good reception, the content signal to be selected and output is switched to the second content signal; otherwise, the first content signal and executes a second process that continues to output.

In the receiving apparatus according to the present invention configured as described above, the reception quality is better than the first threshold when the second content signal decoded from the second layer with low error tolerance is selectively output. In this case, the second content signal is continuously output. In other cases, the content signal to be selectively output is switched to the first content signal. In the receiving apparatus, when the first content signal decoded from the first layer having high error tolerance is selectively output, the reception quality is better than the second threshold and the direction in which the reception quality is good. When the content signal is increased, the content signal to be selected and output is switched to the second content signal. In other cases, the first content signal is continuously output.

  The receiving apparatus according to the present invention outputs a high-quality content signal for a fixed terminal when the reception quality is good, and outputs a low-quality content signal for a mobile terminal when the reception quality is insufficient. High image quality and a wide service area can be secured.

  Furthermore, in the receiving apparatus according to the present invention, hysteresis is set in the determination of the reception quality, and at the same time, if the reception quality rises in a good direction even when the reception quality is insufficient, a high level for the fixed terminal is provided. Outputs a content signal with image quality. As a result, in the receiving apparatus according to the present invention, frequent switching of the content signal is suppressed, and furthermore, a content signal with as high a picture quality as possible can be output.

  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 content decoding unit 15, and a B layer content decoding. A unit 16, a switching output unit 17, and a switching control unit 18 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. That is, one channel is divided into 13 segments in the frequency direction, and the content signal (video signal, audio signal, etc.) of the A layer transmitted to one central segment, and segments other than the central one segment B-layer content signals transmitted to the network. The A layer is a layer (strong layer) in which a signal with low transmission capacity (low image quality and low sound quality) and high error resistance is modulated (strong layer). For example, a broadcast signal for mobile reception is modulated. On the other hand, the B layer is a layer (weak layer) in which a signal with high transmission capacity (high image quality and high sound quality) and low error tolerance is modulated (weak layer), for example, a broadcast signal for fixed reception is modulated. .

  Such a broadcast signal is received by the antenna 11 of the receiving apparatus 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.

  Further, the OFDM demodulation / transmission path decoding unit 13 measures the S / N ratio of the received signal and the bit error rate (BER) of the transport stream to be output at regular time intervals. The OFDM demodulation / transmission path decoding unit 13 sends the S / N ratio (signal / noise ratio) and bit error rate obtained by measurement to the switching control unit 18 at regular intervals. The bit error rate can be calculated, for example, by comparing the data before Reed-Solomon decoding with the data obtained by re-encoding the data after Reed-Solomon decoding.

  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 content decoding unit 15, and the TS packet including the layer B content signal is supplied to the layer B content decoding unit 16. Is done.

  The A layer content decoding unit 15 decodes the input TS packet to generate a video signal of a predetermined video format and an audio signal of a predetermined audio format. The video signal and the audio signal decoded by the A layer content decoding unit 15 are supplied to the switching output unit 17. The video signal and the audio signal output from the A layer content decoding unit 15 are hereinafter referred to as an A layer content signal.

  The B layer content decoding unit 16 performs a decoding process on the input TS packet, and generates a video signal of a predetermined video format and an audio signal of a predetermined audio format. The video signal and the audio signal decoded by the B layer content decoding unit 16 are supplied to the switching output unit 17. Note that the video signal and the audio signal output from the B layer content decoding unit 16 are hereinafter referred to as a B layer content signal.

  The switching output unit 17 selects one of the A layer content signal and the B layer content signal in accordance with the control from the switching control unit 18 and outputs the selected one content signal. The content signal output from the switching output unit 17 is supplied via a video / audio output terminal 20 to a not-shown video display device, audio output device, or recording device.

  The switching control unit 18 receives the S / N ratio of the received signal and the bit error rate (BER) of the output transport stream from the OFDM demodulation / transmission path decoding unit 13 at regular time intervals. The switching control unit 18 determines whether to output the A layer content signal or the B layer content signal based on the input S / N ratio and the bit error rate, and according to the determination, the switching output unit 17 Perform switching control.

  The terrestrial digital broadcast receiving apparatus 10 configured as described above receives an OFDM broadcast signal including two services (content signals) by hierarchical transmission, and receives one of the two services (contents). Signal) can be output.

  Next, switching control of the switching control unit 18 will be described with reference to the flowchart of FIG.

  First, when reception is started, the switching control unit 18 refers to the S / N ratio of the received signal at that time, and determines whether or not the S / N ratio is equal to or higher than a first threshold (for example, 20 dB). (Step S1). That is, in step S1, the switching control unit 18 determines whether or not the quality of the received signal is better than the first threshold value.

Subsequently, when the switching control unit 18 determines in step S1 that the S / N ratio of the received signal is equal to or higher than the first threshold (for example, 20 dB), it is next included in the weak hierarchy (B hierarchy). The bit error rate of the transport stream is referred to, and it is determined whether or not the bit error rate is smaller than a predetermined value (for example, 10 ⁻³ ) (step S2). This predetermined value (for example, 10 ⁻³ ) is the maximum error rate that can be viewed when viewing the content signal included in the B layer. That is, the switching control unit 18 determines whether or not the transport stream included in the B layer has been restored to a level that allows viewing.

Subsequently, when the switching control unit 18 determines in step S2 that the bit error rate of the B layer is smaller than a predetermined value (for example, 10 ⁻³ ), the content signal included in the weak layer (that is, B The switching output unit 17 is set so as to output (hierarchical content signal) (step S3). When the switching output unit 17 is set to output the B layer content signal, the switching unit 17 selects the B layer content signal output from the B layer content decoding unit 16 and outputs it to the outside via the terminal 20.

Thereafter, the switching control unit 18 repeats the above-described processing from step S1 to step S3 at regular intervals (for example, every S / N ratio transfer interval). Therefore, the switching control unit 18 until the S / N ratio of the received signal becomes smaller than the first threshold value (for example, 20 dB) or the bit error rate of the B layer becomes a predetermined value (for example, 10 ⁻³ ) or more. , B level content signal continues to be output. In other words, if the reception quality is kept at a certain level or higher, a content signal with high image quality, high sound quality, and low error resistance that is modulated in a weak hierarchy is output.

On the other hand, when it is determined in step S1 that the S / N ratio of the received signal is smaller than the first threshold (for example, 20 dB), or in step S2, the bit error rate of the B layer is a predetermined value (for example, 10 ⁻³ ) or more. If it is determined that there is, the process exits the loop from step S1 to step S3 and proceeds to step S4.

  In step S4, the switching control unit 18 sets the switching output unit 17 to output the A layer content signal (step S4). When the switching output unit 17 is set to output the A layer content signal, the switching unit 17 selects the A layer content signal output from the A layer content decoding unit 15 and outputs it to the outside via the terminal 20.

  Subsequent to step S4, the switching control unit 18 refers to the S / N ratio of the received signal at that time, and determines whether or not the S / N ratio is equal to or greater than a second threshold (for example, 24 dB) (step S4). S5). That is, the switching control unit 18 determines whether the quality of the received signal is better than a predetermined threshold value. Note that the second threshold value is set to a value sufficiently higher than the first threshold value in order to provide hysteresis.

  Subsequently, when the switching control unit 18 determines in step S5 that the S / N ratio of the received signal is smaller than a second threshold (for example, 24 dB), next, it calculates a moving average of the S / N ratio. Then, it is determined whether or not the changing direction of the moving average value is increasing (step S6). That is, it is determined whether or not a value obtained by taking a moving average of the reception quality is changed in a direction in which the reception quality is good.

  The moving average value of the S / N ratio is a value obtained by taking the past predetermined samples of the value of the S / N ratio measured at certain time intervals and calculating the average. By calculating the moving average in this way, even when the S / N ratio fluctuates greatly due to mobile reception, the influence of the fluctuation can be reduced and an average value with good responsiveness can be output. Can do.

  In this way, the switching control unit 18 determines whether or not the quality of the received signal is changing by determining whether or not the moving average value of the S / N ratio is increasing. ing.

Subsequently, the switching control unit 18 determines in step S5 that the S / N ratio of the received signal is greater than or equal to a second threshold value (for example, 24 dB), or the moving average value of the S / N ratio in step S6. If it is determined that the change direction is increasing, the bit error rate of the transport stream including the B layer content signal is referred to, and the bit error rate is a predetermined value (for example, 10 ⁻³ ). It is determined whether it is smaller (step S7). That is, the switching control unit 18 determines whether or not the content signal of the B layer has been decoded to the extent that viewing is possible.

If the switching control unit 18 determines in step S7 that the bit error rate of the B layer is smaller than a predetermined value (for example, 10 ⁻³ ), the switching control unit 18 goes from step S4 to step S7 and proceeds to step S3. The switching output unit 17 is set so as to output a hierarchical content signal.

When it is determined in step S6 that the change direction of the moving average value of the S / N ratio has not increased, or in step S7, the switching control unit 18 determines that the bit error rate of the B layer is a predetermined value (for example, 10 ⁻³ ) or more. If it is determined that, it returns to step S4.

Thereafter, the switching control unit 18 repeats the processing from step S4 to step S7 at regular time intervals (for example, every S / N ratio transfer interval). Therefore, the switching control unit 18 determines that the S / N ratio of the received signal is equal to or higher than the second threshold (for example, 24 dB) or the moving average value of the S / N ratio is increased, and the bit error rate of the B layer is The A-layer content signal is continuously output until it becomes smaller than a predetermined value (for example, 10 ⁻³ ). That is, it continues to output low-quality and low-quality content signals for mobile terminals.

  As described above, at the start of reception, the switching control unit 18 determines whether the S / N ratio of the received signal is equal to or higher than the first threshold (that is, whether the reception quality is better than the first threshold). ), If the S / N ratio is equal to or higher than the first threshold, the content signal decoded from the weak layer (layer having low error resistance) is output, and if the S / N ratio is smaller than the first threshold, The content signal decoded from the strong hierarchy (hierarchy with high error tolerance) is output.

  In addition, when the switching control unit 18 outputs a weak layer signal (B layer content signal), whether or not the S / N ratio of the received signal is equal to or higher than the first threshold (that is, the reception quality is the first level). Whether or not it is better than a threshold value of 1) at regular intervals, and if the S / N ratio is greater than or equal to the first threshold value, a content signal decoded from a weak layer (layer with low error resistance) is output. Subsequently, when the S / N ratio becomes lower than the first threshold, the output signal is switched from the strong layer (layer having high error tolerance) to the decoded content signal.

  In addition, the switching control unit 18 determines whether or not the S / N ratio of the received signal is equal to or higher than the second threshold when the strong layer signal (A layer content signal) is output (that is, the reception quality is Whether or not it is better than the second threshold) is output at regular intervals, and if the S / N ratio is lower than the second threshold, a content signal decoded from a strong layer (layer having high error resistance) is output. If the S / N ratio continues to be greater than or equal to the second threshold, the output signal is switched from the weak layer (layer having low error tolerance) to the decoded content signal.

  By performing the above processing, the terrestrial digital broadcast receiving apparatus 10 can adaptively output a signal of a weak layer or a strong layer according to the reception quality.

  Further, in the switching control unit 18, the S / N ratio (second threshold) that is the threshold for switching from the strong hierarchy to the weak hierarchy is higher than the S / N ratio (first threshold) that is the threshold for switching from the weak hierarchy to the strong hierarchy. Hysteresis is set in the switching control by increasing the threshold value of (). Thus, the terrestrial digital broadcast receiving apparatus 10 is set so that frequent switching is not performed.

  Further, the switching control unit 18 moves the S / N ratio even when the S / N ratio is smaller than the second threshold when outputting the content signal of the strong hierarchy (hierarchy with high error tolerance). Since the average value is increasing, when it is expected that the S / N ratio is recovered and the reception quality is improved, switching to the weak layer side is performed. As a result, the terrestrial digital broadcast receiving apparatus 10 can output a weak-layer content signal as much as possible in a situation where a weak-layer content signal is possible, and can receive a high-quality and high-quality content signal. The possible range can be expanded.

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 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 content decoding part, 16 B hierarchy content decoding part, 17 Switching output part, 18 Switching control part

Claims (6)

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 / decoding means for demodulating the received OFDM signal and decoding a data stream from the demodulated signal;
Data separating means for separating the decoded 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 the first layer data and outputting a first content signal;
Second decoding means for decoding the second layer data and outputting a second content signal of higher quality than the first content signal ;
Reception quality detection means for detecting the reception quality of the received OFDM signal;
Output means for switching and outputting either the first content signal or the second content signal,
The output means is
Whether or not the reception quality detected by the reception quality detection means is better than the first threshold when the second content signal decoded from the second layer having low error tolerance is selectively output. determining, in the case the reception quality is better than the first threshold continues to output the second content signal, the first process the content signal for selectively outputting the otherwise Ru switched to the first content signal And
When the first content signal decoded from the first layer having high error tolerance is selectively output, the reception quality detected by the reception quality detection unit is higher than a first threshold value. It is periodically determined whether or not it is better than the threshold value, and when the reception quality is better than the second threshold value and when the reception quality is worse than the second threshold value and the reception quality is rising in the better direction, it is selectively output. switching the content signal to the second content signal, in other cases, receiving apparatus for executing a second process that continues to output the first content signal. Receiving the reception quality detecting means detects the quality, the receiver of the S / N ratio der Ru請 Motomeko 1, wherein the received signal. The output means calculates a moving average of the S / N ratio of the received signal, if it rises its moving average, the 請 Motomeko 2 wherein you determined that the reception quality has risen for the better Receiver device. The output means is
Detecting the bit error rate of the data stream demodulated by the demodulating means;
If the detected bit error rate is equal to or higher than a predetermined value , the first content signal decoded from the first layer having high error tolerance is output regardless of the reception quality detected by the reception quality detection means. The receiving device according to claim 2, wherein: The output means is
At the start of the reception operation, it is periodically determined whether or not the reception quality detected by the reception quality detection means is better than the first threshold. If the reception quality is better than the first threshold, the second content signal The receiving apparatus according to claim 1, wherein the first content signal is output in other cases. The first layer is disposed at the center of the transmission channel,
The receiving apparatus according to claim 1, wherein the second layer is arranged in a frequency domain excluding the first layer data in the transmission channel.

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