JP2010200163A - Demodulation device, demodulation method, demodulation program, and computer-readable recording medium - Google Patents

Abstract

A demodulator capable of reducing power consumption during demodulation is realized.
An OFDM demodulator 1 detects a reception quality of a received signal of a digital broadcast, in which a demodulation unit 4a of a broadcast demodulation system a and a demodulation unit 4b of a broadcast demodulation system b perform demodulation processing, respectively. The hierarchy is selected according to the quality detection unit 29 and the modulation error ratio as a detection value indicating the reception quality detected by the reception quality detection unit 29, and one of the broadcast demodulation systems a and b is activated and the other is deactivated. And an activation control unit 50.
[Selection] Figure 1

Description

  The present invention relates to a demodulating device, a demodulating method, a demodulating program, and a computer-readable recording medium capable of suppressing power consumption and selecting and demodulating an optimal digital broadcast.

  In digital terrestrial television broadcasting using terrestrial waves, a transmission method called an Orthogonal Frequency Division Multiplex (hereinafter referred to as “OFDM”) that can efficiently transmit video signals and audio signals is used. .

  Specifically, a digital broadcast receiving apparatus that receives this digital broadcast wave has a receiving function in addition to a stationary receiving apparatus (hereinafter referred to as a “fixed receiving apparatus”) that is fixedly installed in a house. It is assumed to be used as a receiving device (hereinafter referred to as “portable receiving device”) intended to be used in a mobile device or a moving body such as a car. For this reason, in digital broadcasting, it is considered to perform hierarchical transmission using a plurality of different transmission path encodings as well as broadcasting with a single transmission path encoding.

  In this hierarchical transmission, ARIB STD-B31, which is a transmission standard for terrestrial digital television broadcasting, specifies ISDB-T (Integrated Services Digital Broadcasting-Terrestrial), which is a broadcasting system for terrestrial digital television broadcasting. (See Non-Patent Document 1). ISDB-T is a method of dividing a transmission band of one physical channel in which broadcasting is performed into 13 frequency bands (OFDM segments) and setting transmission parameters and information to be transmitted for each band.

  Specifically, in the ISDB-T, the OFDM segment is divided into a maximum of three layers (in order of lower required C / N ratio, the strong layer, the middle layer, and the weak layer). For example, strong hierarchy broadcasting and / or middle hierarchy broadcasting is performed. That is, in ISDB-T, the fixed receiver is configured to be able to receive all layers, while the portable receiver is configured to be able to receive strong and / or middle layers. The Of the portable receivers, mobile receivers (for example, in-vehicle receivers) are configured to be capable of receiving the middle and strong layers, and are portable receivers (for example, mobile phones). And a receiving device mounted on a PDA (Personal Digital Assistant) are configured to be able to receive a strong hierarchy.

  In Japan, terrestrial digital broadcasting based on the above standards has been started in December 2003. In this terrestrial digital broadcasting in Japan, one segment of the 13 segments in the one physical channel band is used, and one segment broadcasting using the remaining 12 segments and fixed broadcasting using the remaining 12 segments are performed. Are broadcast for portable receivers, and the fixed broadcast is broadcast for fixed receivers. These two digital broadcasts are currently being simultaneously broadcast with the same video and audio.

  FIG. 9 is a graph for explaining a hierarchical structure in OFDM. As shown in FIG. 9, the one-segment broadcasting is broadcasting using one segment (0.43 MHz) located in the center of the 13-segment frequency band (5.57 MHz). In FIG. 9, reference numeral 80 indicates a one-segment broadcasting band, and reference numeral 81 indicates a fixed broadcasting band. As shown in [Table 1], one-segment broadcasting has a required C / N ratio (Carrier to Noise Ratio) of 10 dB or more lower than that of fixed broadcasting, so it is highly resistant to noise and fading and is specialized for portable receivers. It can be said that it was broadcast. As shown in [Table 1], one-segment broadcasting is an H.264 standard as an image compression method (image compression standard) for transmitting moving images with a small amount of data. The H.264 system is used. This H. The H.264 system is a system for realizing, for example, a compression efficiency more than twice that of the MPEG (Motion Picture Experts Group) -2 system used for the fixed broadcasting. For this reason, in the one-segment broadcasting, it is possible to provide high-quality video and audio that could not be realized in the conventional analog broadcasting even in the portable receiver. [Table 1] below shows broadcast parameters for one-segment broadcasting and fixed broadcasting, respectively.

  From now on, processing on the transmitting side (digital broadcasting station) that transmits digital broadcasting using the OFDM transmission method will be described. On the transmission side, a digital signal sequence of a broadcast wave of a digital broadcast to be transmitted is combined into several bits and mapped to a complex signal by using a modulation method based on the QPSK method, 16QAM method, or 64QAM method. Next, on the transmission side, a baseband OFDM signal is obtained by performing an inverse fast Fourier transform (IFFT) on the mapped N complex signals.

  Each transmission symbol included in the OFDM signal is divided into a plurality of segments. Each segment includes a data carrier, an SP (Scattered Pilot) carrier, a TMCC (Transmission and Multiplexing Configuration Control) carrier, an AC (Auxiliary Channel) 1 carrier, and an AC2 carrier.

  The SP carrier is a carrier for transmitting an SP signal used as a reference for waveform equalization with respect to the OFDM signal, and is periodically inserted into each transmission frame. The period in which this SP carrier is arranged is determined in advance. Specifically, the SP carrier is inserted at a period of one in 12 carriers for the carrier direction and one for four symbols in the symbol direction in the segment structure of the OFDM signal. Is done.

  The TMCC carrier is a carrier for transmitting a TMCC signal including a synchronization word and transmission parameters. The AC1 carrier or the AC2 carrier is a carrier for transmitting an AC1 signal or an AC2 signal for transmitting additional information. Unlike the SP carrier, the TMCC carrier, the AC1 carrier, and the AC2 carrier are aperiodically inserted in each transmission frame.

  As described above, in terrestrial digital television broadcasting, reception by a portable receiver (or a mobile receiver) is realized, but the following problems arise. Specifically, when receiving a digital broadcast by a portable receiver, reception quality may be increased due to fading, impulse noise, multipath, C / N ratio deterioration, and the like. In particular, the degree of degradation of reception quality increases as the moving speed of the portable receiver increases. When the reception quality is greatly deteriorated, the portable receiving apparatus cannot correct the received digital broadcast error, and the video and audio cannot be prevented from being deteriorated. Therefore, in digital terrestrial television broadcasting, when a portable receiving device receives a high-quality layer (fixed broadcasting), video and audio disturbances (for example, regarding video) due to the deterioration in reception quality. (Ghost disturbance) increases.

  Therefore, in Patent Documents 1 and 2, in order to solve the above problem, when the reception quality of a high-quality digital broadcast is deteriorated, the digital broadcast is switched to a signal of a receivable layer or a receivable channel. A receiving device is disclosed.

  FIG. 10 is a block diagram showing a schematic configuration of the digital broadcast receiving apparatus 100 disclosed in Patent Document 1. As shown in FIG. The digital broadcast receiving apparatus 100 includes an antenna 101, a demodulator 102, a monitor 113, an amplifier 115, and a speaker 117 that receive a digital broadcast in which one or more layers exist in the same physical channel. The demodulator 102 of the digital broadcast receiving apparatus 100 extracts a channel selection channel signal from the received signal received by the antenna 101, and performs demodulation processing on the extracted signal. The video signal and the audio signal obtained by the demodulation process are output to the monitor 113 and the amplifier 115, respectively.

  Further, the demodulator 102 includes a layer 1 demodulator 107a, a layer 2 demodulator 107b,..., A layer N demodulator 107n (hereinafter referred to as “layer demodulator 107”), a frequency tuning unit 103, The reception quality determination unit 108, the switching unit 109, and the mode display unit 111 are provided.

  Hierarchy demodulating section 107 performs demodulation processing for each hierarchy on the channel selection signal extracted by frequency tuning section 103. Reception quality determination section 108 determines the reception quality of the demodulated signal for each layer. Switching section 109 selects any one of layer demodulation sections 107 based on information indicating the optimum reception layer output from reception quality determination section 108. The mode display unit 111 transmits a signal output from the hierarchical demodulation unit 107 selected by the switching unit 109 to the monitor 113 and the amplifier 115.

  According to the above configuration of Patent Document 1, the digital broadcast receiving device 100 switches to a signal of a receivable layer or a receivable channel even when the reception quality of a high-quality digital broadcast is deteriorated. Can do.

  FIG. 11 is a block diagram showing a schematic configuration of the digital broadcast receiving apparatus 120 disclosed in Patent Document 2. As shown in FIG. The digital broadcast receiving device 120 receives at least a weak layer broadcast of the digital broadcast and generates video and audio, and receives a digital broadcast middle layer and / or strong layer broadcast and generates video and audio. The selection means 125 that selects the video / audio output signal of the second reception unit 126B to be performed, the first reception unit 126A, and the second reception unit 126B and supplies the selected video / audio output signal to the video display unit and the audio output unit (both not shown). And a control unit 124 for giving a selection command signal to the selection unit 125, and is configured to be portable. The digital broadcast receiving apparatus 120 includes a plurality of tuners 122A and 122B as frequency selection means and OFDM demodulation means. Each of the tuner 122A of the first receiving unit 126A and the tuner 122B of the second receiving unit 126B includes reception quality determining means (not shown), and the control means 124 receives the received signal quality (reception state information) determined by the reception quality determining means. ) To give the selection command signal.

  According to the above configuration of Patent Document 2, the digital broadcast receiving apparatus 120 can switch between fixed broadcast and one-segment broadcast because the first receiver 126A and the second receiver 126B can simultaneously operate and present video and audio. As a result, the received video can be presented stably.

  The digital broadcast receiving apparatus 120 is driven by a battery (not shown) that is attached, and the control unit 124 stops energization of the first receiving unit 126A when the remaining battery level falls below a predetermined value. At the same time, the video / audio output from the second receiving unit 126B may be selected. Further, a switch (not shown) operated by the user is provided, and the control unit 124 stops energization to the first reception unit 126A and performs the second reception when the low power consumption mode is selected by the switch. The video / audio signal output from the unit 126B may be selected. Furthermore, it is configured as a vehicle-mounted type, and when the control unit 124 detects engine OFF, the control unit 124 may stop energization of the first receiving unit 126A and select the video / audio signal output from the second receiving unit 126B. Good.

Japanese Unexamined Patent Publication No. 2000-165766 (released on June 16, 2000) Japanese Patent Laying-Open No. 2005-252512 (published on September 15, 2005)

Japan Radio Industry, “Transmission Method for Digital Terrestrial Television Broadcasting ARIB STD-B31 Version 1.5”, First Edition May 31, 2001, Revised 1.7 Version September 26, 2007

  However, when a user views a one-segment broadcast on a small monitor used in a mobile phone, particularly when viewing a moving image, there arises a problem that block noise peculiar to the digital broadcast tends to appear. In addition, in the one-segment broadcasting, there is a user's need to view a high-definition fixed broadcast even if the mobile phone has a small monitor.

  As described above, with the implementation of one-segment broadcasting that is highly resistant to noise and fading, users can view digital broadcasting using a mobile phone over a wide range. However, the transmission rate of one-segment broadcasting is about 1/40 of that of fixed broadcasting as shown in [Table 1].

  In general, the quality of video in digital broadcasting is determined by the transmission rate of the transmitted digital broadcast, and the transmission rate is determined by the modulation method and coding rate. Specifically, in the receiving apparatus, when the transmission rate is high, the frame rate of the moving image increases and the image quality of the image becomes high definition, while when the transmission rate is low, the frame rate of the moving image decreases and the video The image quality is also rough. In other words, one-segment broadcasting, which has a lower transmission rate than fixed broadcasting, has made it possible to view digital broadcasting on a mobile phone by enhancing resistance to noise and fading. In order to provide this, it is necessary to further take measures against the block noise described above.

  Further, when the receiving apparatus is a mobile receiving apparatus, there are no restrictions on the circuit scale and power consumption. On the other hand, in the case of a portable receiver mounted on a mobile phone or the like, the size, such as the area and thickness of parts of the portable receiver, and the power consumption that can be used for the portable receiver are limited. It becomes.

  Here, the digital broadcast receiving apparatus 100 of Patent Document 1 receives and demodulates a digital broadcast composed of a plurality of layers having different broadcast parameters. For this reason, as shown in FIG. 10, the digital broadcast receiving apparatus 100 has a configuration in which the frequency tuning unit 103 is common but the hierarchical demodulating unit 107 has a plurality of hierarchical demodulating units 107 a to 107 n arranged in parallel. Further, the hierarchical demodulation units 107a to 107n mounted in parallel perform demodulation processing at the same time. For this reason, in the digital broadcast receiving apparatus 100, power consumption increases compared to a configuration in which only the hierarchical demodulator that performs demodulation processing of the signal of the optimum hierarchy among the hierarchical demodulators 107a to 107n can be operated. Problems arise. In general, the power consumption of the hierarchical demodulator that demodulates a layer with a high transmission rate is larger than the power consumption of the hierarchical demodulator that demodulates a layer with a low transmission rate.

  Furthermore, since the digital broadcast receiving apparatus 100 performs the same processing for any hierarchy regardless of the hierarchy selection process in the switching unit 109, the power consumption when demodulating a hierarchy with a low transmission rate is This is the same as the power consumption when demodulating a layer with a high transmission rate. For this reason, in the digital broadcast receiving apparatus 100, even when demodulating a layer with a low transmission rate, the power consumption is the same as when demodulating a layer with a high transmission rate, so that power consumption is wasted. A problem occurs.

  Further, the digital broadcast receiving device 120 of Patent Document 2 receives and demodulates a digital broadcast composed of a plurality of layers having different broadcast parameters. Therefore, the digital broadcast receiving apparatus 120 has a configuration in which a plurality of tuners 122A and 122B and decoder units 123A and 123B are arranged in parallel as shown in FIG. The digital broadcast receiving device 120 always demodulates a plurality of layers at the same time except when the remaining battery level is smaller than a predetermined value, when the user operates a switch, and when the engine of the automobile is turned off. Since the tuners 122A and 122B basically operate by receiving power supply at the same time, the tuners 122A and 122B eventually have the same problem as the digital broadcast receiving apparatus 100 disclosed in Patent Document 1.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a demodulation device, a demodulation method, a demodulation program, and a computer-readable recording medium that can reduce power consumption during demodulation. Is to provide.

  In order to solve the above-described problem, the demodulator according to the present invention is a demodulator that demodulates a digital broadcast in which a plurality of hierarchies exist in the same physical channel at a specific hierarchy, and the received signal of the digital broadcast A channel processing unit that performs channel selection processing of the physical channel by extracting the frequency component of the specific physical channel from the channel, and demodulation that performs demodulation processing on the received signal having the frequency component extracted by the channel selection processing unit A reception demodulating system comprising: a plurality of broadcast demodulation systems; and a reception quality detection for detecting the reception quality of the received signal demodulated by the demodulation processing means of each broadcast demodulation system. And a hierarchy selected according to a detection value indicating the reception quality detected by the reception quality detection means, and at least one of the broadcast demodulation systems corresponding to the selected hierarchy Is characterized by comprising, a start control means for starting the.

  In order to solve the above problem, the demodulation method according to the present invention includes a plurality of broadcast demodulation systems for demodulating a digital broadcast having a plurality of layers in the same physical channel at a specific layer. A demodulation method by a demodulation device provided, a channel selection processing step for performing channel selection processing of the physical channel by extracting a frequency component of a specific physical channel from the received signal of the digital broadcast, and the channel selection processing step And performing a demodulation process step for performing a demodulation process on the received signal having the frequency component extracted in step 5 for each of the plurality of broadcast demodulation systems. A reception quality detection step for detecting the reception quality of the received signal subjected to demodulation processing, and the reception quality detected in the reception quality detection step. Select the hierarchy in accordance with a detection value indicated is characterized in that it comprises an activation control step of activating only the broadcast demodulating system of at least one channel corresponding to the selected hierarchy, a.

  According to the above configuration, in the demodulating apparatus and the demodulating method according to the present invention, in each broadcast demodulation system, the hierarchy is selected and selected according to the detection value indicating the reception quality of the received signal that has been demodulated. Since only the broadcast demodulation system corresponding to the hierarchy is activated, it becomes possible to reduce power consumption during demodulation.

  In the demodulation device according to the present invention, the activation control unit includes a determination unit that determines whether a detection value indicating the reception quality received from the reception quality detection unit is equal to or greater than a preset threshold value. The hierarchy is selected according to the determination result of the determination means, and supplied to each broadcast reception system so as to supply a power supply voltage and / or an operation clock only to the broadcast demodulation system corresponding to the selected hierarchy. And a start selection means for controlling the power supply voltage and / or the operation clock to be provided.

  According to said structure, a determination means determines whether the detection value which shows reception quality is more than the preset threshold value, and a starting selection means selects a hierarchy according to this determination result. Further, the activation selection means controls the power supply voltage to be supplied to each broadcast receiving system so as to supply the power supply voltage only to the broadcast demodulation system corresponding to the selected hierarchy. As the threshold value, any value may be set as long as the activation control unit satisfies a criterion capable of selecting an optimum hierarchy of digital broadcasting. Thereby, the activation control means can activate only the broadcast demodulation system corresponding to the hierarchy selected according to the determination result.

  Further, according to the above configuration, as in the above configuration for controlling the power supply voltage, whether or not to supply an operation clock to each broadcast demodulation system is controlled as activation control of each broadcast demodulation system. Thereby, the activation control means can activate only the broadcast demodulation system corresponding to the hierarchy selected according to the determination result. When the power supply voltage is supplied to the broadcast demodulation system to be activated and the operation clock is supplied, the demodulator according to the present invention quickly selects the selected broadcast demodulation system simultaneously with the operation clock supply. The effect of driving is obtained. Further, by stopping the supply of the operation clock to the broadcast demodulation system that does not need to be activated, the demodulator according to the present invention can reduce power consumption in the broadcast demodulation system.

  The demodulator according to the present invention is characterized in that a plurality of the threshold values are set in the determination means.

  According to the above configuration, since a plurality of threshold values are set in the determination unit, it is possible to reduce the frequency of selecting a hierarchy as compared with a case where only one threshold value is set. In general, when the detection value indicating the reception quality changes in the vicinity of a threshold value, no error occurs in the output from the demodulation processing means even when the demodulator receives a digital broadcast without switching the hierarchy. Or even if it occurs, it is often very small. From the above, the demodulating device can stabilize the reception rate of digital broadcasting.

  Further, in the demodulator according to the present invention, the activation selection unit determines that the detection unit indicates that a detection value indicating the reception quality is equal to or more than a first threshold which is one of the plurality of thresholds. When the result is obtained, the power supply voltage and / or operation clock to be supplied to each broadcast reception system is controlled so that the power supply voltage and / or operation clock is supplied to two or more broadcast demodulation systems. Then, the hierarchy is selected according to the determination result of the determination means, which determines whether or not the detection value indicating the reception quality is equal to or higher than a second threshold different from the first threshold, and the selected hierarchy The power supply voltage and / or the operation clock to be supplied to each broadcast reception system is controlled so that the power supply voltage and / or the operation clock is supplied only to the broadcast demodulation system corresponding to the above.

  According to the above configuration, the activation selection means can provide a period in which two or more broadcast demodulation systems are activated simultaneously when switching to the broadcast demodulation system to be used. As a result, it is possible to stabilize the reception rate of digital broadcasting. At this time, it is preferable that the first and second threshold values are appropriately set in consideration of the variation of the detected value with respect to the elapsed time, the time response of the demodulator itself, and the like.

  Further, the demodulating apparatus according to the present invention is characterized in that the reception quality detecting means obtains a modulation error ratio as a detection value indicating the reception quality. Further, the demodulating apparatus according to the present invention is characterized in that the reception quality detecting means uses a determination index obtained from a modulation error ratio as a detection value indicating the reception quality. The demodulating apparatus according to the present invention is characterized in that the reception quality detecting means uses a statistic obtained from the statistics of the modulation error ratio as a detection value indicating the reception quality.

  According to the above configuration, in the demodulation device according to the present invention, when the reception quality detection unit receives a digital broadcast including a plurality of layers, the detection value indicating the reception quality is obtained from the modulation error ratio and the modulation error ratio. By obtaining either the obtained determination index or the statistic obtained from the statistics of the modulation error ratio, and the activation control means determines whether or not the detected value is equal to or greater than a preset threshold value , Selection of hierarchy and activation control of each broadcast demodulation system. Thereby, the activation control means can perform the selection of the hierarchy and the activation control of each broadcast demodulation system with high accuracy. If the detected value is a value obtained from the modulation error ratio, for example, a required C / N ratio is set as the threshold value in the activation control means.

  Further, the demodulating apparatus according to the present invention is characterized in that the activation control means stops a broadcast demodulation system that does not correspond to the selected hierarchy.

  According to the above configuration, since the activation control unit stops the broadcast demodulation system that does not correspond to the selected hierarchy, that is, the broadcast demodulation system that does not need to be activated, the power consumption can be further reduced.

  The demodulating device according to the present invention further includes a storage device, and the storage device stores data obtained by performing demodulation processing on the received signal output from each broadcast demodulation system. It is characterized by being.

  According to the above configuration, data (for example, TSP) obtained by performing demodulation processing on a digital broadcast reception signal output from each broadcast demodulation system is stored in the storage device in advance. This makes it possible to appropriately control the time at which each broadcast demodulation system starts demodulating each digital broadcast having a different hierarchy.

  The demodulating device may be realized by a computer. In this case, a control program for a broadcast demodulating device that causes the demodulating device to be realized by the computer by operating the computer as the respective means, and recording the program. Such computer-readable recording media also fall within the scope of the present invention.

  As described above, the demodulator according to the present invention is a demodulator that demodulates a digital broadcast in which a plurality of hierarchies exist in the same physical channel in a specific hierarchy, and is based on a specific physical channel from the received signal of the digital broadcast. Channel selection processing means for performing the channel selection processing of the physical channel by extracting the frequency component of, and demodulation processing means for performing demodulation processing on the received signal having the frequency component extracted by the channel selection processing means, A plurality of broadcast demodulation systems, reception quality detection means for detecting reception quality of the received signal demodulated by the demodulation processing means of each broadcast demodulation system, and the reception The hierarchy is selected according to the detection value indicating the reception quality detected by the quality detection means, and only at least one broadcast demodulation system corresponding to the selected hierarchy is activated. And turning control means, comprising a.

  Further, the demodulation method according to the present invention is a demodulation method by a demodulator having a plurality of broadcast demodulation systems for demodulating a digital broadcast having a plurality of layers in the same physical channel at a specific layer. A channel selection processing step of performing channel selection processing of the physical channel by extracting a frequency component of a specific physical channel from the received signal of the digital broadcast, and reception having the frequency component extracted in the channel selection processing step A received signal obtained by performing a demodulation process step for performing a demodulation process on a signal for each broadcast demodulation system of a plurality of systems, and performing a demodulation process in the demodulation process step of each broadcast demodulation step A reception quality detection step for detecting the reception quality of the received signal, and the hierarchy according to a detection value indicating the reception quality detected in the reception quality detection step Selected, including an activation control step of activating only the broadcast demodulating system of at least one channel corresponding to the selected hierarchy, a.

  Therefore, there is an effect that power consumption during demodulation can be reduced.

It is a block diagram which shows schematic structure of the demodulation apparatus which concerns on this invention. It is a block diagram which shows schematic structure of the tuner with which the said demodulation apparatus was equipped. It is a block diagram which shows schematic structure of the FEC part with which the said demodulation apparatus was equipped. It is a graph for demonstrating the calculation method of the MER value in a reception quality detection part in case a modulation system is a QPSK system. It is a flowchart which shows the flow of a process in a demodulation apparatus when the said demodulation apparatus receives the digital broadcast which consists of 1seg broadcasting and fixed broadcast. FIG. 6A is a diagram showing an example of control by the activation control unit using a graph showing a change in MER value with time, and FIG. 6A is a graph showing a case where control is performed with one threshold, and FIG. b) is a graph showing a case where control is performed with a plurality of threshold values. FIG. 7A is a graph showing the flow of processing in the demodulator that activates only the selected broadcast demodulation system after activating all broadcast demodulation systems at a plurality of threshold values. FIG. FIG. 7B is a graph showing a case where one of the demodulation systems is activated, and FIG. 7B is a graph showing a case where the other of the two broadcast demodulation systems is activated. It is a graph which shows the point which makes the statistic obtained from the statistic of MER as a modulation error ratio the detection value which shows reception quality. It is a graph for demonstrating the hierarchical structure in OFDM. 1 is a block diagram illustrating a schematic configuration of a digital broadcast receiving device disclosed in Patent Document 1. FIG. FIG. 10 is a block diagram illustrating a schematic configuration of a digital broadcast receiving device disclosed in Patent Document 2. FIG. 6 is a flowchart illustrating an example in which the flowchart illustrated in FIG. 5 is expanded when the number of layers is three or more.

  FIG. 1 is a block diagram showing a schematic configuration of a demodulator according to the present invention.

  An OFDM demodulator (demodulator) 1 shown in FIG. 1 receives digital broadcasts having a plurality of hierarchies in the same physical channel output from a broadcast station, when the antennas 2a and 2b respectively receive the digital broadcasts. The received signal indicating the digital broadcast of the desired channel is selected and demodulated. Further, the OFDM demodulator 1 outputs the demodulated received signal as a TSP (Transport Stream Packet) to a monitor (not shown) and an amplifier (not shown) provided in the subsequent stage of the OFDM demodulator 1 It is. The OFDM demodulator 1 receives and demodulates a digital broadcast wave transmitted by an orthogonal frequency division multiplex system (OFDM) defined by a terrestrial digital television broadcast system (ISDB-T). The OFDM demodulator 1 is, for example, a stationary receiver (fixed receiver) that is fixedly installed in a house, or a receiver (portable receiver) mounted on a portable device having a function of receiving digital broadcasting. Device), a receiver mounted on a mobile body such as a car (receiver for mobile body). An example of the fixed receiving device is a television receiver, an example of the portable receiving device is a mobile phone and a PDA, and an example of a moving body receiving device is an in-vehicle receiving device.

  The OFDM demodulator 1 includes antennas 2a and 2b, tuners (channel selection processing means) 3a and 3b, demodulation units (demodulation processing means) 4a and 4b, an activation control unit (activation control unit) 50, and a clock source 40. And a voltage control unit 42. The antennas 2a and 2b may be shared, that is, may be realized as a single antenna.

  Here, the tuner 3a and the demodulator 4a constitute one system of a broadcast demodulation system (hereinafter referred to as “broadcast demodulation system a”) for demodulating the received signal of the digital broadcast received by the antenna 2a. . Further, the tuner 3b and the demodulator 4b are provided with a single broadcast demodulation system (hereinafter referred to as “broadcast demodulation system b”) different from the broadcast demodulation system a for demodulating the received signal of the digital broadcast received by the antenna 2b. This is configured. That is, the OFDM demodulator 1 can be interpreted as having a plurality of systems (here, two systems) of broadcast demodulation systems a and b for demodulating received digital broadcast signals. Here, as an example, a one-segment broadcast demodulation system for demodulating the one-segment broadcast received by the broadcast demodulation system a is configured, and a fixed broadcast demodulation system for demodulating the fixed broadcast received by the broadcast demodulation system b. The description will be made on the assumption that it is configured.

  Each of the demodulation units 4 a and 4 b includes a baseband signal processing unit (hereinafter referred to as “BB unit”) 6 and an error correction processing unit (hereinafter referred to as “FEC unit”) 7. Specific descriptions of the BB unit 6 and the FEC unit 7 will be described later.

  The clock source 40 uses an operation clock as a clock for operating the broadcast demodulation system a as a tuner 3a and a demodulation unit 4a, and an operation clock as a clock for operating the broadcast demodulation system b as a tuner 3b and a demodulation unit 4b. And are supplied through the clock line 41, respectively.

  The voltage control unit 42 has a voltage source (not shown). From the voltage source, a predetermined power supply voltage necessary for starting the broadcast demodulation system a is broadcast demodulated to the tuner 3a and the demodulation unit 4a. A predetermined power supply voltage necessary for starting the system b is supplied to the tuner 3b and the demodulator 4b through the voltage supply line 43, respectively.

  The antenna 2a receives a digital broadcast having a plurality of hierarchies within the same physical channel output from the broadcast station as an RF (Radio Frequency) signal, and receives the RF signal (received signal of the digital broadcast). This is supplied to the tuner 3a. Similar to the antenna 2a, the antenna 2b receives a digital broadcast having a plurality of hierarchies within the same physical channel output from the broadcasting station as an RF signal, and supplies the RF signal to the tuner 3b.

  The tuner 3a extracts the frequency component of a specific physical channel from the RF signal from the antenna 2a, and performs channel selection processing for the physical channel. Similar to the tuner 3a, the tuner 3b extracts a frequency component of a specific physical channel from the RF signal from the antenna 2b, and performs channel selection processing of the physical channel.

  From here, the schematic configuration of the tuners 3a and 3b will be described with reference to FIG.

  The tuner 3 shown in FIG. 2 is a tuner suitably used as the tuner 3a or 3b. The tuner 3 includes a filter (first filter) 11, a variable gain amplification unit (first variable gain amplification unit) 12, a frequency conversion unit 13, a filter (second filter) 14, and a variable gain amplification unit (first filter). 2 variable gain amplifying unit) 15.

  The filter 11 extracts a desired frequency component from the supplied RF signal from the antenna 2a when the tuner 3 is used as the tuner 3a, and from the antenna 2b when the tuner 3 is used as the tuner 3b (other than digital broadcast waves). This is a band-pass filter provided to remove the RF signal. The filter 11 transmits the RF signal having the extracted frequency component to the variable gain amplifying unit 12.

  The variable gain amplifying unit 12 is provided to amplify or attenuate the RF signal from the filter 11 based on a gain adjustment signal supplied from an automatic gain control unit (hereinafter referred to as “AGC unit”) 26 described later. It is a low noise amplifier (low noise amplifier). The variable gain amplifier 12 transmits the amplified or attenuated RF signal from the filter 11 to the frequency converter 13.

  The frequency converter 13 converts the RF signal into an IF (Intermediate Frequency) signal by performing frequency conversion on the RF signal from the variable gain amplifier 12. The frequency conversion unit 13 transmits the IF signal of the selected desired channel to the filter 14.

  The filter 14 is a low-pass filter provided for extracting a desired frequency component from the IF signal of the frequency converter 13 (removing unnecessary physical channel signals again). That is, the filter 14 can be interpreted as a filter for extracting a frequency component of a specific physical channel (that is, selecting a desired channel). The filter 14 transmits the IF signal having the extracted frequency component to the variable gain amplification unit 15.

  The variable gain amplifying unit 15 amplifies the IF signal from the filter 14 to a voltage that can be input to the demodulator at the subsequent stage, based on a gain adjustment signal supplied from the AGC unit 26 described later. Here, the “demodulation unit at the subsequent stage” means a demodulation unit 4a when the tuner 3 is used as the tuner 3a, and a demodulation unit 4b when the tuner 3 is used as the tuner 3b. The variable gain amplifier 15 transmits the amplified IF signal to the demodulator at the subsequent stage.

  The tuner 3 shown in FIG. 2 is configured to include the filters 11 and 14, but may be configured to omit the filter 11 and include only the filter 14.

  In addition, when the frequency bandwidth for performing a channel selection process for a specific physical channel is increased from a received signal of digital broadcasting, the tuner 3 also increases power consumption. In consideration of this, the power consumption of the tuner 3b of the broadcast demodulation system b constituting the fixed broadcast demodulation system is larger than the power consumption of the tuner 3a of the broadcast demodulation system a constituting the one-segment broadcast demodulation system.

  When receiving the IF signal from the tuner 3a, the demodulator 4a demodulates the IF signal. That is, the demodulator 4a performs demodulation processing on the received signal having the frequency component extracted by the tuner 3a. Similar to the demodulator 4a, the demodulator 4b demodulates the IF signal when receiving the IF signal from the tuner 3b. That is, the demodulator 4b performs a demodulation process on the received signal having the frequency component extracted by the tuner 3b.

  Regarding the schematic configuration of the demodulating units 4a and 4b, and the operation of the demodulating unit 4a and the operation of the demodulating unit 4b when an IF signal is input from the variable gain amplifying unit 15 (see FIG. 2) of the tuner 3, Since they are the same as each other, they will be described together below.

  The IF signal from the variable gain amplification section 15 (see FIG. 2) of the tuner 3 is first supplied to the BB section 6 of the demodulation section 4a or 4b.

  From here, the schematic configuration of the BB unit 6 will be described with reference to FIG.

  The BB unit 6 converts the IF signal supplied from the tuner 3 (see FIG. 2) into a baseband OFDM signal, and performs demodulation processing on the baseband OFDM signal. The obtained data signal group and TMCC information are supplied to the FEC unit 7. That is, the BB unit 6 can be interpreted as a unit that converts a digital broadcast reception signal into a baseband signal and performs demodulation processing.

  The BB unit 6 has the same configuration in the demodulating unit 4a and the demodulating unit 4b. The analog-digital converting unit (hereinafter referred to as “ADC unit”) 20, the quadrature detecting unit 21, the narrow band carrier frequency error correcting unit 22, and the high speed A Fourier transform unit (hereinafter referred to as “FFT unit”) 23, a waveform equalization unit 24, a symbol synchronization unit 25, an AGC unit 26, a broadband carrier frequency error correction unit 27, and a TMCC decoding unit 28 are provided.

  The ADC unit 20 converts the IF signal supplied from the variable gain amplification unit 15 (see FIG. 2) of the tuner 3 from an analog signal to a digital signal, and supplies the converted signal to the quadrature detection unit 21.

  The quadrature detection unit 21 performs quadrature detection on the IF signal, which is a digital signal, supplied from the ADC unit 20 using a carrier signal having a preset carrier frequency, thereby realizing a real axis component (so-called I-axis component). A baseband OFDM signal which is a complex signal composed of a channel signal) and an imaginary axis component (so-called Q channel signal) is obtained, and the baseband OFDM signal is supplied to the narrowband carrier frequency error correction unit 22.

  The narrowband carrier frequency error correction unit 22 corrects the baseband OFDM signal by detecting a narrowband carrier frequency error from the baseband OFDM signal supplied from the quadrature detection unit 21. The narrowband carrier frequency error correction unit 22 performs, for example, complex multiplication of the baseband OFDM signal and a carrier frequency error correction signal supplied from a numerically controlled oscillator (not shown) to thereby calculate the baseband OFDM signal. Correct the carrier frequency. In addition, the narrow band carrier frequency error correction unit 22 may perform correction using a phase rotation circuit represented by a CORDIC (COordinate Rotation Digital Computer) circuit. In this case, the phase rotation circuit calculates and inputs the phase correction amount of each sampling point from the narrowband carrier frequency error, and rotates the input baseband OFDM signal by the phase correction amount. Narrow band carrier frequency error is corrected. The narrowband carrier frequency error correction unit 22 supplies the baseband OFDM signal whose carrier frequency is corrected to the FFT unit 23, the symbol synchronization unit 25, and the AGC unit 26.

  The FFT unit 23 extracts a signal corresponding to the effective symbol period from the baseband OFDM signal by referring to the start timing of each effective symbol specified by the symbol synchronization unit 25, and applies the extracted baseband OFDM signal to the extracted baseband OFDM signal. Fast Fourier transform is performed. For example, the FFT unit 23 may use an arbitrary point within the guard interval period in the baseband OFDM signal as a start point of the baseband OFDM signal that is extracted as a target to be subjected to the fast Fourier transform. The FFT unit 23 performs fast Fourier transform on the baseband OFDM signal, so that N complex signals modulated on each carrier including the data signal, SP signal, TMCC signal, and the like from the baseband OFDM signal. Get. The FFT unit 23 supplies N complex signals obtained from the baseband OFDM signal to the waveform equalization unit 24 and the TMCC decoding unit 28.

  The waveform equalization unit 24 performs waveform equalization processing on the N complex signals supplied from the FFT unit 23 based on the timing indicated by the synchronization establishment signal supplied from the TMCC decoding unit 28. . Here, the waveform equalization processing means processing for equalizing the amplitude and phase of N complex signals. Specifically, the waveform equalization unit 24 calculates a transfer function of the communication path (function corresponding to vibration fluctuation and phase rotation generated in the communication path) based on the expected value of the SP signal group supplied from the FFT unit 23. presume. Then, the waveform equalization unit 24 obtains a waveform equalized data signal group by complex-dividing each data signal by the transfer function obtained by this estimation. The waveform equalization unit 24 supplies the waveform equalized data signal group to the FEC unit 7 and a reception quality detection unit 29 described later.

  The symbol synchronization unit 25 extracts transmission parameters such as a transmission mode and a guard interval ratio from the baseband OFDM signal with the carrier frequency corrected supplied from the narrowband carrier frequency error correction unit 22. Thereby, the symbol synchronizer 25 specifies the head timing of each effective symbol included in the baseband OFDM signal (baseband signal).

  The AGC unit 26 receives an IF signal input from the baseband OFDM signal supplied from the narrowband carrier frequency error correction unit 22 and corrected for the carrier frequency to the demodulation unit 4a or 4b in which the AGC unit 26 is provided. The optimum intensity is calculated, and the calculation result is supplied to the variable gain amplifying units 12 and 15 (see FIG. 2) of the tuner 3 as the above-described gain adjustment signal. The AGC unit 26 of the demodulation unit 4a supplies the gain adjustment signal to the tuner 3a, and the AGC unit 26 of the demodulation unit 4b supplies the gain adjustment signal to the tuner 3b.

  The broadband carrier frequency error correction unit 27 corrects the complex signal by detecting the broadband carrier frequency error from the complex signal to be supplied from the FFT unit 23 to the waveform equalization unit 24. Specifically, when the broadband carrier frequency error correction unit 27 detects the broadband carrier frequency error, the complex signal modulated on a carrier in a specific frequency band determined based on the broadband carrier frequency error among the complex signals. Only the waveform equalizer 24 is controlled to be supplied. When the complex signal is supplied from the FFT unit 23 to the waveform equalizing unit 24 and a signal indicating that the complex signal is in the desired OFDM band is output to the waveform equalizing unit 24, the complex signal by the broadband carrier frequency error correcting unit 27 is output. No correction to the signal is necessary.

  The TMCC decoding unit 28 performs DBPSK demodulation on the TMCC signal supplied from the FFT unit 23, and identifies a synchronization word included in the result of the DBPSK demodulation, thereby specifying the start timing of each transmission frame. Is. In addition, the TMCC decoding unit 28 obtains TMCC information that defines transmission parameters and the like by performing error correction decoding (specifically, difference set cyclic decoding) on the TMCC signal. The TMCC decoding unit 28 supplies a synchronization establishment signal indicating the head timing of each identified transmission frame to the waveform equalization unit 24 and the FEC unit 7, and supplies the TMCC information to the FEC unit 7.

  Note that the N complex signals output from the FFT unit 23 are not limited to the configuration directly supplied to the waveform equalizing unit 24, and after being corrected by the wideband carrier frequency error correcting unit 27, the waveform equalizing unit 24. May be supplied. In this case, the broadband carrier frequency error correction unit 27 extracts only the complex signal within the carrier number band specified based on the broadband carrier frequency error from the complex signal, and extracts the extracted complex signal as a desired OFDM signal. The signal is supplied to the waveform equalizing unit 24 as a complex signal of a band.

  In the digital broadcasting having the hierarchical structure shown in [Table 1], the number of carriers for fixed broadcasting is 12 times the number of carriers for one-segment broadcasting. Accordingly, the power consumption of the BB unit 6 of the broadcast demodulation system b constituting the fixed broadcast demodulation system is larger than the power consumption of the BB unit 6 of the broadcast demodulation system a constituting the one-segment broadcast demodulation system.

  Next, a schematic configuration of the FEC unit 7 will be described with reference to FIG.

  The FEC unit 7 shown in FIG. 3 is an FEC unit provided in the demodulation unit 4a or 4b. The FEC unit 7 restores the transmission bit string of the data signal group from the BB unit 6 (see FIG. 1), performs error correction decoding using the error correction code included in the restored transmission bit string, and thereby performs the TSP. The generated TSP is supplied to a subsequent monitor and amplifier (not shown). That is, the FEC unit 7 can be interpreted as performing error correction processing on the baseband signal demodulated by the BB unit 6.

  3 includes a demapping unit 30, a bit deinterleaving unit 31, a frequency deinterleaving unit 32, a time deinterleaving unit 33, a depuncturing unit 34, a Viterbi decoding unit 35, a byte deinterleaving unit 36, and an energy despreading unit. Unit 37, TSP generation unit 38, and RS (Reed Solomon) decoding unit 39.

  The demapping unit 30 performs a mapping demodulation process on the data signal group waveform-equalized by the waveform equalization unit 24. That is, the demapping unit 30 restores the transmission bit string of the data signal group mapped to the complex signal by any one of QPSK, 16QAM, and 64QAM. The demapping unit 30 transmits a data signal group having the restored transmission bit string to the bit deinterleaving unit 31.

  The bit deinterleave unit 31 performs a bit interleaving cancellation process on the data signal group from the demapping unit 30. Here, interleaving is for distributing error input signals for error correction decoding, and is for rearranging the order according to the regularity defined by the ISDB-T described above. That is, the bit deinterleaving unit 31 rearranges the order of the transmission bit strings included in the data signal group in units of bits. The bit deinterleave unit 31 transmits the data signal group subjected to the bit interleave cancellation process to the frequency deinterleave unit 32.

  The frequency deinterleaving unit 32 performs frequency interleaving cancellation processing of the data signal group from the bit deinterleaving unit 31, that is, rearranges the order of the carriers. The frequency deinterleaving unit 32 transmits the data signal group subjected to the frequency interleaving cancellation process to the time deinterleaving unit 33.

  The time deinterleaving unit 33 performs time interleaving cancellation processing of the data signal group from the frequency deinterleaving unit 32, that is, rearranges the order of the demodulated data signals. The time deinterleaving unit 33 transmits the data signal group subjected to the time interleaving cancellation process to the depuncture unit 34.

  When the inner code of the error correction code included in the restored transmission bit string that the data signal group from the time deinterleaving unit 33 has is a punctured convolutional code, the depuncturing unit 34 converts the convolutional code into the convolutional code. On the other hand, depuncture processing is performed. Here, the depuncture is to insert a provisional value into a redundant signal area that has been thinned in advance on the transmission side, and the thinning method is defined by ISDB-T. The depuncture unit 34 transmits the data signal group subjected to the depuncture process to the Viterbi decoding unit 35.

  The Viterbi decoding unit 35, when the inner code of the error correction code included in the restored transmission bit string included in the data signal group from the depuncture unit 34 is convolutionally encoded, is subjected to the convolutional encoding. It decodes encoded data and corrects errors. The Viterbi decoding unit 35 transmits to the byte deinterleaving unit 36 a data signal group that has been subjected to decoding of encoded data and error correction.

  The byte deinterleave unit 36 performs byte interleaving cancellation processing on the data signal group from the Viterbi decoding unit 35, that is, rearranges the order of the transmission bit strings of the data signal group in units of bytes. The byte deinterleaving unit 36 transmits the data signal group subjected to the byte interleaving cancellation process to the energy despreading unit 37.

  The energy despreading unit 37 performs an energy despreading process on the data signal group from the byte deinterleave unit 36. Here, the energy despreading processing is to give randomness to the data signal group by eliminating the bias of the signal polarity, and reversely multiply the pseudo noise sequence multiplied on the transmission side. Means. The energy despreading unit 37 transmits the data signal group subjected to the energy despreading process to the TSP generation unit 38.

  The TSP generation unit 38 generates a TSP having a predetermined size (for example, 204 bytes) from the data signal group from the energy despreading unit 37. The TSP generation unit 38 transmits the generated TSP to the RS decoding unit 39.

  The RS decoding unit 39 performs Reed-Solomon encoding when the outer code of the error correction code included in the restored transmission bit string that the TSP from the TSP generation unit 38 has is Reed-Solomon encoded. The encoded data is decoded and error-corrected. The RS decoding unit 39 supplies the TSP that has been subjected to the decoding and error correction of the encoded data to the subsequent monitor and amplifier. The TSP supplied from the RS decoding unit 39 is H.264. The image is input to a decoder (not shown) that performs image compression using an H.264 or MPEG-2 image compression method, and is demodulated by the decoder. As a result, the monitor that receives the TSP realizes video display, and the amplifier that receives the TSP realizes audio output via a speaker connected to the monitor.

  In the digital broadcasting having the hierarchical structure shown in [Table 1], the data transmission rate of the fixed broadcast is 40 times the data transmission rate of the one-segment broadcasting. Accordingly, the power consumption of the FEC unit 7 of the broadcast demodulation system b constituting the fixed broadcast demodulation system is larger than the power consumption of the FEC unit 7 of the broadcast demodulation system a constituting the one-segment broadcast demodulation system.

  Further, the BB unit 6 detects the reception quality of the received signal of the digital broadcast, which is demodulated by the demodulation units 4a and 4b, and supplies the detection result to the activation control unit 50 to be described later. Unit (reception quality detection means) 29 is provided. In the present embodiment, it is assumed that reception quality detection unit 29 is provided in both demodulation unit 4a and demodulation unit 4b.

  Specifically, the reception quality detection unit 29 calculates a modulation error rate (hereinafter referred to as “MER value”) based on the data signal group waveform-equalized by the waveform equalization unit 24. Thus, the reception quality of the data signal group is detected. The reception quality detection unit 29 supplies the calculated MER value to the activation control unit 50 as a detection value indicating the reception quality.

Here, the MER value means the power conversion value of the waveform-equalized data signal (complex signal) X _EQ (n, k) and the ideal constellation point X _EQ 'of the data signal X _EQ (n, k). This is the ratio of the vector error δX _EQ (n, k) indicating the deviation from (n, k) to the power conversion value. The MER value for the data signal X _EQ (n, k) is defined by the following equations (1) to (4).

Note that, in the subscripts used in the above formulas, n represents a symbol number and k represents a carrier number. In addition, the sum obtained by Equation (1) is the sum of the subscripts n and k. In order to obtain a highly accurate MER value, the above n and k may be increased and the sum of these may be obtained. On the other hand, when real time property is required, the sum may be obtained only for all carriers in one symbol or only for a specific carrier. Furthermore, the ideal constellation point X _EQ ′ (n, k) for the data signal X _EQ (n, k) is all possible constellation points X _m (0 ≦ m <M) determined according to the modulation method. of the data signal X _EQ (n, k) the distance between the _{d m (n, k) =} | is that of the minimum constellation point _{X m | X EQ (n,} k) -X m.

  From here, a method of calculating the MER value in the reception quality detection unit 29 when the modulation method is, for example, the QPSK method will be described. FIG. 4 is a graph for explaining a MER value calculation method in the reception quality detection unit 29 when the modulation method is the QPSK method.

When the data signal X _EQ (n, k) waveform-equalized by the waveform equalizing unit 24 is at the position shown in FIG. 4, the ideal constellation point X _EQ ′ (n, k) at this time is the above-described value. from the description, it is determined that constellation points X ₁ shown in FIG. The reception quality detection unit 29 includes P _Signal (distance between the data signal X _EQ (n, k) and the origin), P _Noise (data signal X _EQ (n, k), constellation point X ₁ ) shown in FIG. The MER value is calculated by substituting in the denominator and numerator of the logarithm part of the common logarithm shown in the above formula (1).

Since the MER value is a power ratio between P _Signal and P _Noise shown in FIG. 4 as shown in the above formula (1), it can be interpreted as corresponding to a C / N ratio (carrier to noise power ratio). . That is, the MER value can be used as an index indicating the reception quality of the digital broadcast wave received by the OFDM demodulator 1.

  In the present embodiment, the reception quality detection unit 29 is provided in the BB unit 6. However, the present invention is not limited to this, and the reception quality detection unit 29 does not impair reception quality detection processing. Any position (block) may be provided in any position of the OFDM demodulator 1. Furthermore, in the present embodiment, the reception quality detection unit 29 is provided in both the broadcast demodulation system a and the broadcast demodulation system b. That is, the OFDM demodulator 1 is provided with two reception quality detection units 29. However, only one reception quality detection unit 29 is provided in the OFDM demodulator 1, and the reception quality detection unit 29 calculates the reception quality in both the broadcast demodulation system a and the broadcast demodulation system b. There may be.

  Further, the OFDM demodulator 1 includes an activation control unit 50. The activation control unit 50 selects a hierarchy according to the detection value indicating the reception quality of the received signal of the digital broadcast detected by the reception quality detection unit 29, and performs the detection so as to perform only the demodulation corresponding to the selected hierarchy. Depending on the value, one of the broadcast demodulation systems a and b is activated and the other is deactivated. However, as long as the hierarchy is selected, there may be a period in which both broadcast demodulation systems a and b are activated. That is, the activation control unit 50 can be interpreted as switching between the broadcast demodulation system a and the broadcast demodulation system b in accordance with the reception quality of the broadcast wave of the digital broadcast received by the OFDM demodulator 1. .

  The activation control unit 50 includes a determination unit (determination unit) 51 and an activation selection unit (activation selection unit) 52.

  The determination unit 51 determines whether or not the detection value indicating the reception quality of the received signal of the digital broadcast received from the reception quality detection unit 29 is greater than or equal to a preset threshold value. When the determination unit 51 receives the MER value supplied from the reception quality detection unit 29, the determination unit 51 determines whether the MER value is equal to or greater than a preset threshold value, and transmits the determination result to the activation selection unit 52. To do. Although details will be described later, it is preferable that a threshold value to be referred to in the determination is stored in the determination unit 51 in advance.

  The start selection unit 52 generates a stop start signal indicating that the broadcast demodulation system a and the broadcast demodulation system b are to be started or stopped according to the determination result of the determination unit 51, the clock source 40 and the voltage control unit 42. To supply.

  The voltage control unit 42 supplies a power supply voltage or supplies a power supply voltage to each of the broadcast demodulation system a and the broadcast demodulation system b according to the stop activation signal supplied from the activation selection unit 52. To stop. Further, the clock source 40 supplies an operation clock or supplies an operation clock to each of the broadcast demodulation system a and the broadcast demodulation system b in accordance with the stop activation signal supplied from the activation selection unit 52. Stop.

  Subsequently, for each process in the OFDM demodulator 1 when the OFDM demodulator 1 receives a so-called mode 3 digital broadcast having a hierarchical structure shown in [Table 1] and consisting of a one-segment broadcast and a fixed broadcast. This will be described with reference to FIG.

  FIG. 5 is a flowchart showing a flow of processing in the OFDM demodulator 1 when the OFDM demodulator 1 receives a digital broadcast composed of a one-segment broadcast and a fixed broadcast.

  The OFDM demodulator 1 receives a digital broadcast composed of a one-segment broadcast and a fixed broadcast. The activation selection unit 52 controls the voltage control unit 42 using the stop activation signal so as to activate the broadcast demodulation system a at the time of one-segment broadcast demodulation and the broadcast demodulation system b at the time of fixed broadcast demodulation. The start selection unit 52 supplies the voltage control unit 42 with the stop start signal for starting or stopping each of the broadcast demodulation system a and the broadcast demodulation system b. The voltage control unit 42 controls whether to start or stop each of the broadcast demodulation system a and the broadcast demodulation system b in accordance with the stop activation signal supplied from the activation selection unit 52.

  First, when the OFDM demodulator 1 is activated (step S0), the activation selector 52 supplies the voltage controller 42 with the stop activation signal indicating the activation of the broadcast demodulation system a. When receiving the stop activation signal, the voltage control unit 42 supplies (or supplies) the predetermined power supply voltage necessary for starting the broadcast demodulation system a to the tuner 3a and the demodulation unit 4a. The broadcast demodulation system a is activated by raising the power supply voltage (step S1).

  Subsequently, the tuner 3a selects a channel desired by the user from the RF signal indicating the digital broadcast received by the antenna 2a, and converts the frequency band of the RF signal indicating the selected channel into an IF signal limited to one segment. The IF signal is converted and supplied to the demodulator 4a. When the IF signal is supplied from the tuner 3a, the demodulator 4a tries the initial synchronization of the IF signal, and confirms whether the IF signal is synchronized, thereby confirming whether the synchronization is established in the broadcast demodulation system a. Confirm (step S2).

  In other words, in step S2, the TMCC decoding unit 28 of the broadcast demodulation system a performs DBPSK demodulation on the TMCC signal of the IF signal, and detects the synchronization word included in the TMCC signal, whereby the IF signal It is determined whether or not synchronization can be established. When the TMCC decoding unit 28 of the broadcast demodulation system a determines that the synchronization of the IF signal can be established, that is, determines that the synchronization of the IF signal is established, it indicates that synchronization is established (that is, the beginning of the transmission frame). A synchronization establishment signal (indicating timing) is transmitted to the waveform equalization unit 24 of the broadcast demodulation system a.

  When the demodulation unit 4a determines that the synchronization of the IF signal supplied from the tuner 3a is not established (synchronization NG) (the result of step S2 is NO), the activation control unit 50 receives from the TMCC decoding unit 28 of the broadcast demodulation system a. A synchronization establishment signal indicating no synchronization establishment is supplied. When activation control unit 50 receives the synchronization establishment signal indicating that synchronization is not established, activation selection unit 52 determines that neither one-segment broadcasting reception nor fixed broadcasting reception is possible, and both broadcast demodulation systems a and b The stop start signal indicating the stop is supplied to the voltage control unit 42. When receiving the stop activation signal, the voltage control unit 42 supplies the above-described predetermined power supply voltage necessary for starting the broadcast demodulation system a to the tuner 3a and the demodulation unit 4a, and broadcast demodulation. The broadcast demodulating system stops supplying the predetermined power supply voltage necessary for starting up the system b to the tuner 3b and the demodulator 4b (or lowering the power supply voltage). Both a and b are stopped, and the OFDM demodulator 1 is stopped (step S11).

  On the other hand, when the demodulation unit 4a determines that the synchronization of the IF signal supplied from the tuner 3a is established (synchronization is OK) (the result of step S2 is YES), the broadcast demodulation system a remains active, that is, the broadcast demodulation system a While maintaining the above operation, the process of step S3 is performed. At this time, the voltage control unit 42 naturally maintains the supply of the predetermined power supply voltage to the tuner 3a and the demodulation unit 4a of the broadcast demodulation system a.

  In step S3, when the broadcast demodulation system b is activated (demodulates), the broadcast demodulation system b is stopped while maintaining the operation of the broadcast demodulation system a. Specifically, the start selection unit 52 supplies the voltage control unit 42 with the stop start signal indicating the stop of the broadcast demodulation system b. When receiving the stop activation signal, the voltage control unit 42 stops supplying the predetermined power supply voltage necessary for starting the broadcast demodulation system b to the tuner 3b and the demodulation unit 4b ( Alternatively, the broadcast demodulation system b is stopped by lowering the power supply voltage.

  At this time, in the broadcast demodulation system a, if the demodulation unit 4a determines that the synchronization of the IF signal is established, the TMCC decoding unit 28 of the broadcast demodulation system a sends a synchronization establishment signal indicating the establishment of synchronization to the broadcast demodulation system a. To the waveform equalization unit 24. When the waveform equalization unit 24 of the broadcast demodulation system a receives this synchronization establishment signal from the TMCC decoding unit 28 of the broadcast demodulation system a, the waveform equalization unit 24 converts the data signal included in the complex signal supplied from the FFT unit 23 of the broadcast demodulation system a. A waveform equalization process is performed on the signal. Then, the waveform equalization unit 24 of the broadcast demodulation system a transmits the waveform-equalized data signal to the reception quality detection unit 29 of the broadcast demodulation system a.

  When the reception quality detection unit 29 of the broadcast demodulation system a receives the data signal waveform-equalized by the waveform equalization unit 24 of the broadcast demodulation system a, the reception quality detection unit 29 detects the reception quality of the data signal. That is, the reception quality detection unit 29 calculates the MER value of the received data signal in the manner described above shown in FIG. 4 and the like (reception quality detection step S4), and supplies the calculated MER value to the activation control unit 50. To do.

  When the determination unit 51 receives the MER value, the activation control unit 50 refers to a preset threshold value and determines whether the MER value is equal to or greater than the threshold value (“activation control step according to the present invention” Step S5). The threshold value is, for example, the required C / N ratio of fixed broadcasting shown in [Table 1], and is the value with the highest required C / N ratio in the hierarchy of digital broadcasting demodulated by the OFDM demodulator 1. It is preset as the required C / N ratio of the hierarchy.

  If the determination unit 51 determines that the MER value is greater than or equal to the threshold value (YES in step S5), the determination unit 51 supplies the determination result to the activation selection unit 52. Upon receiving a determination result indicating that the MER value is equal to or greater than the threshold value, the activation selection unit 52 activates the broadcast demodulation system b (activation control step S6). That is, in step S6, the start selection unit 52 supplies the voltage control unit 42 with the stop start signal indicating the start of the broadcast demodulation system b. When receiving the stop activation signal, the voltage control unit 42 supplies (or supplies) the predetermined power supply voltage necessary for starting the broadcast demodulation system b to the tuner 3b and the demodulation unit 4b. The broadcast demodulation system b is activated by increasing the power supply voltage.

  In step S6, the tuner 3b selects a channel desired by the user from the RF signal indicating digital broadcast received by the antenna 2b, and the frequency band of the RF signal indicating the selected channel is limited to 13 segments. The signal is converted into an IF signal, and the IF signal is supplied to the demodulator 4b. Then, when the IF signal is supplied from the tuner 3b, the demodulator 4b tries to establish initial synchronization of the IF signal and confirms whether or not the IF signal is synchronized, thereby synchronizing the broadcast demodulation system b. The presence or absence of establishment is confirmed (step S7).

  In other words, similarly to the synchronization processing described above for the broadcast demodulation system a in step S2, in step S7, the TMCC decoding unit 28 of the broadcast demodulation system b performs DBPSK demodulation on the TMCC signal of the IF signal. By detecting a synchronization word included in the TMCC signal, it is determined whether or not synchronization of the IF signal can be established. When the TMCC decoding unit 28 of the broadcast demodulation system b determines that the synchronization of the IF signal can be established, that is, determines that the synchronization of the IF signal is established, it indicates that synchronization is established (that is, the beginning of the transmission frame). A synchronization establishment signal (indicating timing) is transmitted to the waveform equalization unit 24 of the broadcast demodulation system b.

  When the TMCC decoding unit 28 of the broadcast demodulation system b determines whether or not IF signal synchronization can be established, and determines that the IF signal synchronization is not established, that is, the demodulation unit 4b does not establish IF signal synchronization. When it is determined that (synchronization is NG) (NO in step S7), a synchronization establishment signal indicating no synchronization is supplied to the activation control unit 50. When receiving the synchronization establishment signal, the activation control unit 50 performs the process of step S1 for activating the broadcast demodulation system a.

  On the other hand, when the TMCC decoding unit 28 of the broadcast demodulation system b determines that IF signal synchronization is established, that is, when the demodulation unit 4b determines that IF signal synchronization is established (synchronization OK) (the result of step S7 is YES). ), The process of step S8 is performed. Specifically, similar to the reception quality detection process described above in step S4 in the broadcast demodulation system a, in step S8, the waveform equalization unit 24 in the broadcast demodulation system b is changed from the TMCC decoding unit 28 in the broadcast demodulation system b. When a synchronization establishment signal indicating that synchronization is established is received, waveform equalization processing is performed on the data signal included in the complex signal supplied from the broadband carrier frequency error correction unit 27 of the broadcast demodulation system b, and the waveform equalization is performed. The data signal is transmitted to the reception quality detection unit 29 of the broadcast demodulation system b. Then, the reception quality detection unit 29 of the broadcast demodulation system b calculates the MER value of the data signal waveform-equalized by the waveform equalization unit 24 of the broadcast demodulation system b (reception quality detection step S8), and the calculated MER The value is supplied to the activation control unit 50.

  In the activation control unit 50, when the determination unit 51 receives the MER value obtained in step S8, the threshold value set in advance is referred to and the MER value is greater than or equal to the threshold value as in the process in step S5. It is determined whether or not there is (step S9, which is one of the “startup control steps” according to the present invention).

  If the determination unit 51 determines that the MER value is smaller than the threshold value (NO in step S9), the determination unit 51 supplies the determination result to the activation selection unit 52. When receiving the determination result indicating that the MER value is smaller than the threshold value, the activation selection unit 52 supplies the voltage control unit 42 with the stop activation signal indicating the activation of the broadcast demodulation system a. When receiving the stop activation signal, the voltage control unit 42 supplies (or supplies) the predetermined power supply voltage necessary for starting the broadcast demodulation system a to the tuner 3a and the demodulation unit 4a. The broadcast demodulation system a is activated by raising the power supply voltage (returning to step S1).

  On the other hand, the determination part 51 supplies the said determination result to the starting selection part 52, when it determines with the said MER value being more than the said threshold value (the result of step S9 is YES). When receiving the determination result indicating that the MER value is equal to or greater than the threshold value, the start selection unit 52 supplies the voltage control unit 42 with the stop start signal indicating the stop of the broadcast demodulation system a. When receiving the stop activation signal, the voltage control unit 42 stops supplying the predetermined power supply voltage necessary for starting the broadcast demodulation system a to the tuner 3a and the demodulation unit 4a ( Alternatively, the power supply voltage is lowered, the broadcast demodulation system a is stopped (startup control step S10), and the process of step S7 is performed to check whether synchronization is established in the broadcast demodulation system b.

  In addition, in the process in step S5, when the determination unit 51 determines that the MER value is smaller than the threshold (the result in step S5 is NO), the process in step S2 is performed.

  From here, an example of the control performed by the activation control unit 50 in the processing in step S5 and step S9 described above will be described with reference to FIG.

  FIG. 6 is a diagram illustrating an example of control by the activation control unit 50 using a graph showing a change in the MER value with time.

  FIG. 6A is a graph showing a case where the activation control unit 50 performs control with one threshold value.

  As illustrated in FIG. 6A, when the determination unit 51 determines that the MER value supplied from the reception quality detection unit 29 is equal to or greater than the threshold value S, the activation selection unit 52 activates the broadcast demodulation system b. Based on the determination result, the stop activation signal indicating activation of the broadcast demodulation system b is supplied to the voltage control unit 42. Further, in this case, the activation selection unit 52 supplies the voltage control unit 42 with the stop activation signal indicating the suspension of the broadcast demodulation system a based on the determination result in order to stop the broadcast demodulation system a.

  On the other hand, when the determination unit 51 determines that the MER value is smaller than the threshold value S, the activation selection unit 52 indicates the activation of the broadcast demodulation system a based on the determination result to activate the broadcast demodulation system a. An activation signal is supplied to the voltage control unit 42. Further, in this case, the activation selection unit 52 supplies the voltage control unit 42 with the stop activation signal indicating the suspension of the broadcast demodulation system b based on the determination result, in order to stop the broadcast demodulation system b.

  Furthermore, since the OFDM demodulator 1 can demodulate a digital broadcast by a demodulation system that is optimal for viewing, the power consumption can be made the same as when a single broadcast demodulator dedicated to each layer is used. That is, the OFDM demodulator 1 can suppress power consumption when demodulating the one-segment broadcasting than when demodulating the fixed broadcasting.

  Therefore, the OFDM demodulator 1 integrates the existing one-segment broadcast demodulation LSI (Large-Scale Integration) and the fixed broadcast demodulation LSI and adds a control circuit, thereby suppressing power consumption and optimal hierarchy of digital broadcasting. Can be selected and demodulated. In other words, the OFDM demodulator 1 does not need to design a new LSI, uses the resources of the existing one-segment broadcast demodulation LSI and the fixed broadcast demodulation LSI, and only adds a control circuit to suppress power consumption. Digital broadcasting can be demodulated with a demodulation system that is optimal for viewing.

  In the OFDM demodulator 1 according to the present embodiment, the same OFDM demodulator 1 receives a plurality of layers having different required C / N ratios, detects the MER value as the reception quality of the broadcast wave, and selects the optimum layer. It becomes possible to receive. Furthermore, it is possible to control the power consumption so that the power consumption of the OFDM demodulator 1 when selecting each layer is the same as the value of the OFDM demodulator dedicated to each layer.

  In this embodiment, the MER value is described as an example of the index indicating the reception quality. However, the index is a BER (Bit Error Rate) of the Viterbi decoding unit 35 or the RS decoding unit 39 or the detected narrowness. The synchronization quality such as fluctuation of the band carrier frequency error may be used. In other words, any physical quantity or parameter may be used as the index as long as a specific threshold value can be defined for switching control between hierarchies.

  The OFDM demodulator 1 shown in FIG. 1 can be interpreted as an example in the case where the activation control unit 50 is provided as an independent processing block. However, as an example of a configuration in which the OFDM demodulator 1 is applied to a mobile phone or the like, There is a configuration in which the OFDM demodulator 1 is controlled by a CPU via a data bus. In this case, the activation control unit 50 may be realized by software control by the CPU. That is, in this case, the CPU may include the activation control unit 50.

  In the present embodiment, each quadrature detection unit 21 of the demodulation units 4a and 4b performs quadrature detection of the IF signal. However, the present invention is not limited to this, and instead of the quadrature detection unit 21, for example, quadrature detection is performed by the tuner 3. The structure provided with a part may be sufficient. In this case, the output signal from the tuner 3 is supplied to the demodulator at the subsequent stage as a baseband signal having an IQ component instead of an IF signal.

  In addition, as described above, the OFDM demodulator 1 uses the IF method of obtaining a baseband signal after converting an RF signal into an IF signal. However, the present invention is not limited to this, and the baseband signal is obtained directly from the RF signal. The zero IF method (so-called direct conversion method) may be used. In the digital broadcasting with the hierarchical structure shown in [Table 1], the number of fixed broadcasting carriers is 12 times that of one-segment broadcasting, so the RAM (Random Access Memory) area required for deinterleaving processing is also 12 times, and consumption is accordingly increased. Power also increases.

  In the above description related to FIG. 6A, the description has been made assuming that the threshold value is one (only the threshold value S), but the threshold value is not limited to one, and may be plural.

  When the threshold value is one, the activation control unit 50 switches between the broadcast demodulation system a and the broadcast demodulation system b because the MER value slightly vibrates near the threshold value.

  In the so-called mode 3 digital broadcasting described above, a difference in demodulation time occurs between the one-segment broadcasting and the fixed broadcasting. Therefore, when the frequency of switching between the broadcast demodulation system a and the broadcast demodulation system b increases, a time lag occurs until the user can view the broadcast due to the difference in the demodulation time, and the broadcast is viewed. There is a risk of discomfort for some users.

  Therefore, in the OFDM demodulator 1, a storage unit (not shown) such as a buffer (data buffer) is provided in a decoding unit (not shown) for decoding video, image, and audio, Each TSP (data obtained by demodulating the received signal) of one-segment broadcasting (demodulated by the broadcast demodulation system a) and fixed broadcasting (demodulated by the broadcast demodulation system b) is stored. Then, information about each TSP time of one-segment broadcasting and fixed broadcasting is extracted, and each stored TSP is stored in the storage device so as to cancel the difference in demodulation time (equalize the time until the output of each TSP). While the output timing is adjusted, the storage device writes and reads data according to a so-called FIFO (First-In First-Out) method in which the most recently stored data is extracted last.

  Thereby, the OFDM demodulator 1 can quickly and continuously (seamlessly) switch between the broadcast demodulation system a and the broadcast demodulation system b. The storage device stores information related to the demodulation method by the OFDM demodulator 1 (see FIG. 5) regarding each of one-segment broadcasting (demodulated by the broadcast demodulation system a) and fixed broadcasting (demodulated by the broadcast demodulation system b). Since the OFDM demodulator 1 adjusts the activation timing of each of the broadcast demodulation systems a and b in accordance with the information related to the demodulation method, the processing load on the decoding unit increases and the power consumption is instantaneous. Increase. For this reason, it is preferable to reduce the frequency of switching between the broadcast demodulation system a and the broadcast demodulation system b as much as possible. Therefore, in the OFDM demodulator 1, it is preferable to set a plurality of threshold values.

  For example, a threshold value Sa for switching from the broadcast demodulation system a to the broadcast demodulation system b is a threshold value Sa, and a threshold value for switching from the broadcast demodulation system b to the broadcast demodulation system a is a threshold value Sb. Set Sb. The activation control unit 50 performs switching between the broadcast demodulation system a and the broadcast demodulation system b based on both the comparison between the MER value and the threshold value Sa and the comparison between the MER value and the threshold value Sb.

  FIG. 6B is a graph showing a case where the activation control unit 50 performs control with a plurality of threshold values (here, two threshold values Sa and Sb). In FIG. 6A and FIG. 6B, the time change of the MER value is the same.

  As illustrated in FIG. 6B, when the determination unit 51 determines that the MER value supplied from the reception quality detection unit 29 is equal to or greater than the threshold value Sa, the activation selection unit 52 activates the broadcast demodulation system b. Based on the determination result, the stop activation signal indicating activation of the broadcast demodulation system b is supplied to the voltage control unit 42. Further, in this case, the activation selection unit 52 supplies the voltage control unit 42 with the stop activation signal indicating the suspension of the broadcast demodulation system a based on the determination result in order to stop the broadcast demodulation system a.

  On the other hand, if the determination unit 51 determines that the MER value is smaller than the threshold value Sa, which is different from the threshold value Sa (here, smaller than the threshold value Sa), the activation selection unit 52 activates the broadcast demodulation system a. The stop activation signal indicating activation of the broadcast demodulation system a is supplied to the voltage control unit 42 based on the determination result. Further, in this case, the activation selection unit 52 supplies the voltage control unit 42 with the stop activation signal indicating the suspension of the broadcast demodulation system b based on the determination result, in order to stop the broadcast demodulation system b. However, according to the time-dependent change of the MER value according to FIG. 6B, there is no period in which the MER value is smaller than the threshold value Sb during the activation of the broadcast demodulation system b. No signal is supplied.

  When the control is performed with one threshold, the frequency of switching between the broadcast demodulation system a and the broadcast demodulation system b is increased as shown in FIG. On the other hand, when control is performed with two threshold values, the frequency of switching between the broadcast demodulation system a and the broadcast demodulation system b can be reduced as shown in FIG.

  Note that when the difference between the threshold value Sa and the threshold value Sb increases, the frequency of switching between the broadcast demodulation system a and the broadcast demodulation system b decreases. However, if the threshold value Sb is made too small, the broadcast demodulation system b is activated in spite of difficulty in demodulating the received signal by the broadcast demodulation system b from the viewpoint of reception quality. There is a possibility that the demodulation mode for demodulating the fixed broadcast is maintained by b. In consideration of this, it is preferable to determine each of the plurality of threshold values using the OFDM test wave generator or the fading simulator after actually configuring the OFDM demodulator 1.

  The activation control unit 50 is not limited to a form in which the MER value itself is used as a detection value for comparison with a threshold value, and the differential value of the MER value, the integral value of the MER value, the interpolated value of the MER value, The determination index as the detected value may be calculated from the filter output of the MER value, and the determination index may be compared with the threshold value to switch between the broadcast demodulation system a and the broadcast demodulation system b.

  In an electronic device equipped with the OFDM demodulator 1, the radio wave is blocked by a building or the like by moving while the OFDM demodulator 1 is activated, and enters the region where the radio wave cannot propagate (radio wave shadow). Due to the obstruction of reception of radio waves from the outside of the electronic device, the electric field strength of the reception waves of the antennas 2a and / or 2b is momentarily stopped, and accordingly, the MER value is instantaneously deteriorated. There is a risk of it. However, when the deterioration of the MER value is instantaneous, it is spread in time by the frequency deinterleaving unit 32 (see FIG. 3) of the FEC unit 7 of the corresponding demodulating unit 4a and / or 4b, so the Viterbi decoding unit In some cases, 35 and the RS decoding unit 39 can completely perform error correction. In this case, considering that reception is not possible during initial synchronization, it may be better to activate the corresponding broadcast demodulation system a or b and maintain the demodulation mode. The OFDM demodulator 1 calculates a determination index as the detected value from the differential value of the MER value, the integral value of the MER value, the interpolated value of the MER value, the filter output of the MER value, and the like. By selecting the reception layer by comparing the exponent and the threshold, even if the MER value slightly fluctuates or instantaneously deteriorates as shown in FIG. 6B, the deterioration is affected. Therefore, it is possible to maintain the demodulation mode without performing stable reception.

  Note that the tuners 3a and 3b and the demodulation units 4a and 4b of the OFDM demodulator 1 may be realized by independent LSIs. Further, the tuner 3a and the demodulator 4a and / or the tuner 3b and the demodulator 4b of the OFDM demodulator 1 may be realized by an integrated LSI. Further, all of the tuners 3a and 3b and the demodulation units 4a and 4b of the OFDM demodulator 1 may be realized by one LSI. The configuration is not limited to the above as long as it is configured by a plurality of tuners and demodulation units (that is, a plurality of broadcast reception systems) and can perform the same processing as the processing flow.

  In the processing flow described above, the activation selection unit 52 transmits the stop activation signals of the broadcast demodulation systems a and b to the voltage control unit 42. The voltage control unit 42 receives the stop activation signal and controls the voltage supplied to each broadcast demodulation system a and b. As a result, the start and stop of the broadcast demodulation systems a and b are controlled. At that time, whether or not to supply a voltage to an internal core (not shown) that performs actual processing while supplying a voltage to an I / O (Input / Output) unit (not shown) of the LSI is determined. You may control. At this time, since the I / O unit remains activated, the LSI is activated immediately. In addition, since the power consumption of the internal core is the largest, the power consumption is suppressed by stopping the internal core.

  In addition, the clock source 40 operates an operation clock for operating each broadcast demodulation system for each of the broadcast demodulation system a and the broadcast demodulation system b in response to the stop activation signal supplied from the activation selection unit 52. Or the supply of the operation clock is stopped.

  The activation control unit 50 may further control the operation clock using the clock source 40 in the same manner as the control of the power supply voltage using the voltage control unit 42, or the power supply using the voltage control unit 42. It may be performed instead of voltage control. That is, when starting or stopping the broadcast demodulation systems a and b by the start control unit 50, the start or stop method may be a method of supplying or stopping a power supply voltage, or supplying an operation clock or It may be a method of stopping, or a method of supplying or stopping both the power supply voltage and the operation clock.

  When supplying the power supply voltage to a certain broadcast demodulation system (broadcast demodulation system a or b) and supplying the operation clock, the broadcast demodulation system performs processing immediately after the supply of the operation clock is started. Has the advantage that can be started. Further, the broadcast demodulation system to which the operation clock is not supplied suppresses power consumption by stopping the processing.

  By the way, when the reception quality detection unit 29 detects the MER value, a plurality of pieces of carrier information are required, and therefore the detection result of the MER value is updated every measurement period. The reception quality detection unit 29 measures the m-th MER value from the reception of a certain reception signal from the output signal of the waveform equalization unit 24 provided in the same broadcast demodulation system as the reception quality detection unit 29 itself. Y (m) indicating data is detected as a MER value. Here, m is an arbitrary natural number.

  When the power supply voltage and the operation clock are supplied to the broadcast demodulation system a (that is, the tuner 3a and the demodulation unit 4a) and / or the broadcast demodulation system b (that is, the tuner 3b and the demodulation unit 4b), the power supply voltage and In the broadcast demodulation system a and / or the broadcast demodulation system b supplied with the operation clock, the tuner 3a and / or the tuner 3b selects a desired channel, and the BB unit 6 of the demodulation unit 4a and / or the demodulation unit 4b is a symbol. A valid TSP is output only after the synchronization and frame synchronization are established and the FEC unit 7 finishes the time deinterleaving process, the Viterbi decoding process, and the RS decoding process. The period from the supply of the power supply voltage and the operation clock to the output of TSP depends on the mounting procedure of the tuners 3a and 3b and the demodulating units 4a and 4b, but it is the broadcast demodulation system a or the broadcast demodulation system b. Regardless of whether or not there is, it is about 1 to 3 seconds.

  In addition, the following three are mentioned as a factor (specific example of the mounting procedure which can depend) which influences the period until the said TSP output.

  The first factor is the time required for the synchronization processing that is first performed after the power and clock are supplied. If this synchronization process is not completed (synchronization is established), the process for extracting the output TSP cannot be started. Specifically, in this synchronization processing, processing such as gain adjustment AGC, carrier frequency error correction AFC (Automatic Frequency Control), symbol synchronization, and frame synchronization is performed. In order to synchronize with a certain frame, it is necessary to detect and synchronize a synchronization word at the beginning of the frame. For this purpose, a synchronization word detection period for at least two frames is required, and this synchronization word detection period affects the period until TSP output.

  The second factor is a delay caused by the demodulation process in the waveform equalizer 24. The waveform equalizing unit 24 corrects the influence due to fading received by each data carrier on the communication path with reference to the SP (Scattered Pilot) carrier. At this time, the number before and after the data to be corrected Correction is performed using the SP of the symbol. Therefore, the waveform equalizer 24 is provided with data of about 1 to 10 symbols and an SP storage area. Note that the storage capacity of the SP storage area varies depending on the waveform equalization algorithm. In other words, the waveform equalization unit 24 causes a delay of 1 symbol to 10 symbols or more by correcting the influence due to fading.

  The third factor is a delay caused by the demodulation process in the time deinterleaving unit 33 (see FIG. 3) of the FEC unit 7. The time deinterleaving unit 33 performs time interleaving cancellation processing. Here, according to the standard defined in Non-Patent Document 1 described above, time interleaving is performed every 1 to 8 frames. Therefore, the time deinterleaving unit 33 can perform the time interleaving cancellation process for the first time by accumulating data of about 1 to 8 frames. In other words, the time deinterleaving unit 33 causes a delay of at least about 1 to 8 frames or more.

  Although the specific time varies depending on the broadcasting parameters due to the above three factors, the time required to obtain the TSP output after the power supply and the clock are supplied is a time corresponding to a total of 3 to 11 frames. In the case of the above-described mode 3 digital broadcasting, the time required for obtaining the TSP output is approximately 1 to 3 seconds. However, in some cases, it may take more than 3 seconds, so the period from supply of power supply voltage and operation clock to TSP output is assumed to be 1 to 3 seconds or more. It is preferable to keep it.

  Furthermore, as shown in FIG. 9, the one-segment broadcasting 80 and the fixed broadcasting 81 are broadcast together in the digital broadcasting shown in [Table 1]. However, even in the simulcast described above, the timing at which the output signals after the video and audio demodulation processing are obtained may differ between the one-segment broadcast 80 and the fixed broadcast 81, and the time difference between the video and audio demodulation processing Depending on the architecture, it varies from about 1 second to several tens of seconds.

  Therefore, when switching between the broadcast demodulation system a for demodulating the one-segment broadcast and the broadcast demodulation system b for demodulating the fixed broadcast, the output signals are continuously transmitted so as to cancel out the time difference. Unless the broadcast demodulation system to be stopped is further activated for the time required for output, continuous layer switching (in other words, between the broadcast demodulation system a and the broadcast demodulation system b) is performed. It becomes difficult.

  In general, the required C / N ratio in fixed broadcasting is larger than the required C / N ratio in one-segment broadcasting. The process of switching the one-segment broadcast to the fixed broadcast is performed when the MER value increases and the radio wave condition becomes good. At this time, the demodulation process of the one-segment broadcast (activation of the broadcast demodulation system a) Even if the operation is continued, since the radio wave condition is good, the demodulation process is hardly adversely affected. On the other hand, the process of switching the fixed broadcast to the one-segment broadcast is performed when the MER value becomes small and the radio wave condition deteriorates. At this time, the fixed broadcast demodulation process (activation of the broadcast demodulation system b) If the operation is continued, the radio wave condition has deteriorated, so there is a high possibility that the demodulation process will be adversely affected.

  Therefore, in the OFDM demodulator 1, as shown in FIG. 6B, when a plurality of threshold values are used, according to the determination result of the MER value and a certain threshold value (first threshold value), Supply a power supply voltage to both broadcast demodulation systems a and b, and supply a power supply voltage only to one of the broadcast demodulation systems a and b according to the determination result of another threshold value (second threshold value). Therefore, it is preferable to switch between the broadcast demodulation system a and the broadcast demodulation system b.

  When the OFDM demodulator 1 is activated, the broadcast demodulation system a is first activated (see steps S0 and S1 in FIG. 5).

  When only the broadcast demodulation system a is activated, the activation control unit 50, when the determination unit 51 receives the MER value, as shown in FIG. 7A, the MER value is Y (m) ≧ Y1a (first When the threshold value is reached, the start selection unit 52 supplies the voltage control unit 42 with the stop operation signal to start the broadcast demodulation system b. In response to the stop operation signal, the voltage control unit 42 supplies power to the tuner 3b and the demodulation unit 4b to activate them. At this time, the voltage demodulation system a and the broadcast demodulation system b Both are activated (see period L1 from the activation start timing). If Y (m) ≧ Y1b (second threshold value) is satisfied during the period L1, the activation selection unit 52 enters the fixed broadcast demodulation mode, that is, the activation selection unit 52 stops the broadcast demodulation system a. In response to the stop operation signal, the voltage control unit 42 stops supplying the power supply voltage to the tuner 3a and the demodulation unit 4a (or the power supply voltage). Descent). Further, when Y (m) <Y1b is always satisfied during the period L1, the activation selection unit 52 continues the one-segment broadcast demodulation mode, that is, the activation selection unit 52 stops the broadcast demodulation system b. The stop operation signal is supplied to the voltage control unit 42, and the voltage control unit 42 stops the supply of the power supply voltage to the tuner 3b and the demodulation unit 4b (or drops the power supply voltage) according to the stop operation signal. .

  Next, when only the broadcast demodulation system b is activated, the activation control unit 50, when the determination unit 51 receives the MER value, the MER value is Y (m) ≦ Y2b as shown in FIG. When (first threshold value) is reached, the activation selection unit 52 supplies the voltage control unit 42 with the stop operation signal to activate the broadcast demodulation system a. In response to the stop operation signal, the voltage control unit 42 supplies a power supply voltage to the tuner 3a and the demodulation unit 4a to activate them, but at this time, the broadcast demodulation system a and the broadcast demodulation system b Both are activated (see period L2 from the activation start timing). If Y (m) ≦ Y2a (second threshold value) is satisfied during the period L2, the activation selection unit 52 enters the one-segment broadcast demodulation mode, that is, the activation selection unit 52 stops the broadcast demodulation system b. In response to the stop operation signal, the voltage control unit 42 stops supplying the power supply voltage to the tuner 3b and the demodulation unit 4b (or the power supply voltage). Descent). Further, when Y (m)> Y2a is always satisfied during the period L2, the activation selection unit 52 continues the fixed broadcast demodulation mode, that is, the activation selection unit 52 stops the broadcast demodulation system a. The stop operation signal is supplied to the voltage control unit 42, and the voltage control unit 42 stops the supply of the power supply voltage to the tuner 3a and the demodulation unit 4a (or drops the power supply voltage) according to the stop operation signal. .

  For convenience, in FIGS. 7A and 7B, the period during which the broadcast demodulation system a or b is clearly activated is the period during which the broadcast demodulation system a or b is clearly stopped by the solid arrow at the top of the graph. Without an arrow at the top of the graph, it is not clear whether the broadcast demodulation systems a and b are activated (that is, the period during which one of the broadcast demodulation systems a or b is activated and the other is stopped). These are indicated by broken arrows at the top of the graph.

  By repeatedly performing each process according to FIG. 7A and each process according to FIG. 7B, the OFDM demodulator 1 can demodulate digital broadcasting in a demodulation system optimal for viewing. The power consumption can be made the same as when a single demodulator dedicated to a hierarchy is used.

Here, when the required C / N ratio in fixed broadcasting is Y _QEF , the threshold value Y1b shown in FIG. 7A is a condition for switching from the broadcast demodulation system a to the broadcast demodulation system b. It is necessary to satisfy the condition> Y _QEF . The threshold value Y1b is a condition for further starting the broadcast demodulation system b in the one-segment broadcast demodulation mode, that is, a condition necessary for starting both the broadcast demodulation systems a and b. Therefore, Y1b> Y1a is set. If satisfied, there are no special restrictions on the numbers.

  However, if the difference between Y1a and Y1b is small, the determination unit 51 selects the fixed broadcast demodulation mode before the broadcast demodulation system b is activated and synchronized. However, in this case, since the one-segment broadcasting can be demodulated continuously by the broadcast demodulation system a, both the broadcast demodulation systems a and b are activated and an effective TSP is received from the FEC unit 7 of the broadcast demodulation system b. It is preferable to stop the broadcast demodulation system a after the output is obtained. Conversely, if the difference between Y1a and Y1b is too large, the period during which both broadcast demodulation systems a and b are activated becomes too long, resulting in an increase in power consumption.

When the required C / N ratio in fixed broadcasting is Y _QEF , the threshold value _Y2a shown in FIG. 7B is a condition for switching from the broadcast demodulation system b to the broadcast demodulation system a. It is necessary to satisfy Y _QEF . The threshold Y2b is a condition for further starting the broadcast demodulation system a in the fixed broadcast demodulation mode, that is, a condition necessary for starting both the broadcast demodulation systems a and b. Therefore, Y2b> Y2a is set. If satisfied, there are no special restrictions on the numbers.

  However, if the difference between Y2a and Y2b is small, the determination unit 51 selects the one-segment broadcast demodulation mode before the broadcast demodulation system a is activated and synchronized. In this case, since it is difficult to demodulate the fixed broadcast by the broadcast demodulation system b, if the fixed broadcast demodulation mode is continued, there is a high possibility that the demodulation process will be adversely affected. Here, if the difference between Y2a and Y2b is increased, the risk of adverse effects is reduced, but the period during which both broadcast demodulation systems a and b are activated becomes too long, resulting in a reduction in power consumption. It will increase. In other words, the relationship between the stability of the demodulation process and the power consumption is a so-called trade-off relationship. Considering the trade-off relationship, the difference between Y2a and Y2b is preferably set to about 1 to 2 dB in order to reduce the possibility of the adverse effect in the OFDM demodulator 1.

  The threshold values Y1a, Y1b, Y2a, and Y2b are determined by taking into account the above-described conditions as appropriate, and the time variation of the MER value during fading, and between the decoding unit and the OFDM demodulator 1 described above. It is preferable to determine after actually configuring the OFDM demodulator 1 taking various time evaluations using a fading simulator or the like into consideration, considering the time lag of the time response. When the decoding unit has the storage device having a capacity large enough to ignore the time difference regarding the timing at which an output signal is obtained in one-segment broadcasting and fixed broadcasting, each of the broadcast demodulation systems a and b It is sufficient to consider only the synchronization time (that is, the period from the supply of the power supply voltage and the operation clock to the TSP output). Therefore, the period L1 (see FIG. 7 (a)) and the period L2 (see FIG. 7 (b)) are set to about 1 second to several seconds, so that the continuous demodulation (in other words, broadcast demodulation) Switching between system a and broadcast demodulation system b) can be realized sufficiently. On the other hand, when the capacity of the storage device is small, it is necessary to further consider the time difference regarding the timing at which the output signal is obtained between the one-segment broadcasting and the fixed broadcasting. For this reason, in order to realize continuous layer switching (in other words, between the broadcast demodulation system a and the broadcast demodulation system b), the period L1 (see FIG. 7A) and the period L2 (FIG. 7) are realized. (Refer to (b)) requires about 1 second to several tens of seconds.

  Note that the periods L1 and L2 may be the same value or different values. The periods L1 and L2 can be appropriately set according to various characteristics of the decoding unit and the OFDM demodulator 1 that are actually used, and the threshold values Y1a, Y1b, Y2a, and Y2b that are set. is there.

  The reception quality detection unit 29 may use a statistic obtained from MER statistics as a modulation error ratio as a detection value indicating reception quality.

  Below, the point which makes the statistics obtained from the statistics of MER as a modulation error ratio the detection value which shows reception quality is demonstrated with reference to FIG.

First, the reception quality detection unit 29 divides the detection time of the MER value for each specific detection period (measurement period: for example, the period L11 shown in FIG. 8) for obtaining the statistic of the MER value. Then, within each detection period, the average value Y _av (t) of the MER values Y (m) is measured by the following mathematical formula (5), and the standard deviation σ _Y (t) is measured by the following mathematical formula (6). Here, t is a parameter indicating the number of times that the statistical detection period has elapsed from the start of reception (the number of detection periods counted from the start of reception).

  Here, the parameter “N” is a natural number indicating the total number of data Y (m) to be summed.

Then, from the average value Y _av (t) and the standard deviation σ _Y (t), a determination index Z (t) is calculated by the following formula (7). Note that γ is a constant.

  Here, assuming that the distribution of the MER value Y (m) with respect to time is a Gaussian distribution (normal distribution), due to the nature of the distribution function of a general Gaussian distribution, when γ = 1, the measurement data of the MER value Of these, about 84.1% of Y (m) satisfies Y (m) ≧ Z. In addition, when γ = 2, about 97.7% of Y (m) in the measurement data of the MER value satisfies Y (m) ≧ Z. Furthermore, when γ = 3, about 99.87% of Y (m) in the measurement data of the MER value satisfies Y (m) ≧ Z.

That is, when γ ≧ 2 and Z ≧ threshold Y _TH is satisfied, about 97% or more of the measurement data Y (m) of the MER value satisfies Y (m) ≧ threshold Y _TH . It will be.

Further, consider the case where Y _QEF , which is the required C / N ratio, is selected as the threshold Y _TH . The required C / N ratio is equal to the C / N ratio when the BER at the output time of the Viterbi decoding unit 35 is 2 × 10 ⁻⁴ and the BER at the output time of the RS decoding unit 39 is 10 ⁻¹¹ or less. In the period of Y (m) ≧ threshold _YTH , the digital broadcast reception rate is 100%. However, even if Y (m) is smaller than the threshold _YTH , if the difference is small, the reception rate Is approximately 100% (see FIG. 8).

From the above, regarding the t-th detection period counted from the start of reception, if Z (t) ≧ Y _TH is satisfied, the reception rate during the t-th detection period can be regarded as 100%. .

The reception quality detection unit 29 detects the statistic in a specific detection period t, detects the determination index Z (t) based on the formula (7), and based on the determination index Z (t), The activation control unit 50 performs switching control between the broadcast demodulation system a and the broadcast demodulation system b in the detection period (t + 1) next to the detection period t. In the control, the average value Y _av (t) and the standard deviation σ _Y (t) in the detection period t are used as the average value Y _av (t−1) and the standard value in the detection period (t−1) immediately before the detection period t. The control is performed under the precondition that the deviations σ _Y (t−1) are approximated. According to this control, it is possible to statistically guarantee the stability of the demodulation process.

Each control in the detection period t described above obtains a comparison between the MER value (that is, Y (m)) and the threshold value (that is, the threshold value Y _TH ) from the MER value in steps S4 and S8 according to FIG. It can be interpreted that the determination index (that is, Z (t−1)) as a calculated statistic is replaced with a comparison between the threshold value (that is, the threshold value Y _TH ). For example, Y _QEF which is a required C / N ratio of fixed broadcasting can be applied as the threshold Y _TH . When the determination index Z (t-1) is larger than the threshold _YTH , the broadcast demodulation system b is activated and the broadcast demodulation system a is stopped, and the determination index Z (t-1) is greater than the threshold _YTH . If it is smaller, the switching between the broadcast demodulation system a and the broadcast demodulation system b is controlled so that the broadcast demodulation system a is started and the broadcast demodulation system b is stopped. According to this control, as described above, the stability of the demodulation process can be statistically ensured. In addition, when implementing the said control using MER value Y (m), each process which concerns on the flowchart shown in FIG. 5 is implemented for every period which detects a MER value. On the other hand, when the control is performed using the determination index Z (t), each process according to the flowchart illustrated in FIG. 5 is performed in a specific detection period (that is, illustrated in FIG. 8) for obtaining a statistic of the MER value. It will be carried out every period L11).

So far, the average value _Y av of MER value in the average value _Y av (t) and the detection period of the MER value in the detection period t (t-1) (t -1), is, as being approximately equal The average value Y _av (t) of the MER value in the detection period t is the average value in the period before the detection period t (that is, each of the detection periods 1 to (t−1)). _{Y av (1) ~Y av (} t-1) results inferred from, or may be obtained. As an example of this, as shown in the following mathematical formula (8), the average value Y _av (t) of the MER value in the detection period t is set to the two previous detection periods, that is, the detection period (t−1) and the detection period. This is a method of estimating by a differential method using each average value Y _av (t−1) and Y _av (t−2) of MER values in (t−2).

Further, the average value Y _av (t) of the MER values in the period t may be estimated using an interpolation filter such as a Lagrange interpolation filter or a spline filter, or an adaptive filter such as an LMS (Least Mean Square) may be used. You may guess with various digital filters. However, since these estimation points can be realized by a known technique, a detailed description thereof will be omitted.

Furthermore, not only the average value Y _av (t) of the MER value in the detection period t but also the standard deviation σ _Y (t) of the MER value in the detection period t is the same as the estimation method of the average value Y _av (t). You may guess in the way.

Here, it is assumed that the distribution of the MER value Y (m) with respect to time is a Gaussian distribution (normal distribution). However, the distribution of the MER value Y (m) with respect to time is not limited to this. It may be assumed that the distribution is a probability distribution according to a distribution function, such as binomial distribution, Poisson distribution, Bernoulli distribution, etc., or Rayleigh distribution function or Rice distribution used as a fading distribution function It may be assumed that it is a function or the like. That is, for example, 95% or more of the MER value Y (m) with _respect to time satisfies the determination index Z (t) and various determination conditions (the average in each statistical distribution, and Y (m) ≧ Y _QEF , and If the dispersion properties, etc. are determined, stable control similar to that assumed when a Gaussian distribution is assumed is possible.

Further, in the present embodiment, the selected threshold value is not limited to the required C / N ratio as long as it is a value that allows switching between broadcast demodulation system a and broadcast demodulation system b. . The required C / N ratio is defined as the C / N ratio when the BER of the TSP output of the RS decoding unit 39 satisfies 10 ⁻¹² or less. When it is required from the specifications of the entire receiving and demodulating system including the OFDM demodulator 1 to reduce the allowable value of the BER to be satisfied, the threshold may be larger than the required C / N ratio, If there are few problems even if the allowable value is increased, the threshold value may be smaller than the required C / N ratio. In the present embodiment, the required C / N ratio is adopted as a control threshold, but this required C / N ratio varies depending on the modulation scheme and the coding rate. The required C / N ratio also changes depending on the processing capabilities of the BB unit 6 and the FEC unit 7. For this reason, if the processing algorithm of the BB unit 6 and / or the FEC unit 7 is different for each OFDM demodulator 1, the required C / N ratio is also different for each OFDM demodulator 1. Therefore, the threshold value needs to be a value corresponding to each OFDM demodulator 1. Furthermore, when using a plurality of thresholds, when using statistics as a threshold, and when demodulating a broadcast having three or more layers, the threshold to be used is the required C / N ratio. (Or a statistic obtained from the required C / N).

  Furthermore, the hierarchical structure of the digital broadcasting according to the present embodiment has been described as having two layers of one-segment broadcasting and fixed broadcasting as shown in [Table 1]. However, the hierarchical structure is not limited to the two-layer structure. That is, the present invention can be applied to a digital broadcast having an arbitrary hierarchical configuration as long as it is a digital broadcast including two or more (a plurality of) layers having different modulation methods and coding rates with different required C / N ratios. . When the number of layers is 3 or more, the same control as in FIG. 5 can be performed by extending the reception quality detection step and the activation control step in the flowchart shown in FIG. 5 according to the number of layers. There may be cases where the number of thresholds cannot be one.

  FIG. 12 shows an example in which the flowchart shown in FIG. 5 is expanded when the number of hierarchies is three or more.

  The flowchart shown in FIG. 12 assumes an OFDM demodulator having broadcast demodulation systems a to c that respectively receive digital broadcasts including three layers. In addition to the flowchart shown in FIG. It is carried out.

  First, in step S3, the broadcast demodulation system c is further stopped (step S31). Further, binary values of T1 and T2 are prepared as threshold values, and MER is compared with threshold value T1 in steps S5 and S9 (steps S51 and S91). Then, after step S91, the MER is compared with the threshold value T2, and the same processing as steps S31 to S91 is performed (steps S12 to S18), except that the broadcast demodulation system to be activated or stopped is different. Then, the same processing as step S31 is performed again (step S19).

  The case of having three layers corresponds to, for example, the case where the layers are QPSK, 16QAM, and 64QAM.

  Finally, the OFDM demodulator 1, in particular, the reception quality detection unit 29 and the activation control unit 50 may be configured by hardware logic, or may be realized by software using a CPU as follows.

  That is, the OFDM demodulator 1 includes a CPU that executes instructions of a control program that realizes each function, a ROM (read only memory) that stores the program, a RAM (random access memory) that expands the program, the program, and various programs A storage device (recording medium) such as a memory for storing data is provided. An object of the present invention is a recording medium on which a program code (execution format program, intermediate code program, source program) of a control program of the OFDM demodulator 1 which is software for realizing the functions described above is recorded so as to be readable by a computer. This can also be achieved by supplying to the OFDM demodulator 1 and reading and executing the program code recorded on the recording medium by the computer (or CPU or MPU).

  Examples of the recording medium include tapes such as magnetic tapes and cassette tapes, magnetic disks such as floppy (registered trademark) disks / hard disks, and disks including optical disks such as CD-ROM / MO / MD / DVD / CD-R. Card system such as IC card, IC card (including memory card) / optical card, or semiconductor memory system such as mask ROM / EPROM / EEPROM / flash ROM.

  The OFDM demodulator 1 may be configured to be connectable to a communication network, and the program code may be supplied via the communication network. The communication network is not particularly limited. For example, the Internet, intranet, extranet, LAN, ISDN, VAN, CATV communication network, virtual private network, telephone line network, mobile communication network, satellite communication. A net or the like is available. Also, the transmission medium constituting the communication network is not particularly limited. For example, even in the case of wired such as IEEE 1394, USB, power line carrier, cable TV line, telephone line, ADSL line, etc., infrared rays such as IrDA and remote control, Bluetooth ( (Registered trademark), 802.11 wireless, HDR, mobile phone network, satellite line, terrestrial digital network, and the like can also be used. The present invention can also be realized in the form of a computer data signal embedded in a carrier wave in which the program code is embodied by electronic transmission.

  The present invention is not limited to the above-described embodiments, and various modifications can be made within the scope shown in the claims. That is, embodiments obtained by combining technical means appropriately modified within the scope of the claims are also included in the technical scope of the present invention.

  According to the present invention, in a demodulator that selects and demodulates an optimum hierarchy of digital broadcasting, power consumption at the time of demodulation can be optimized and minimized with respect to the selected hierarchy. The present invention can be applied to a receiving device having a demodulating device that demodulates the signal. In particular, the demodulating device according to the present invention is effective when applied to a small portable receiving device (for example, a mobile phone, a PDA) among the above receiving devices. Further, the demodulator according to the present invention is a demodulator that receives and demodulates a signal according to the OFDM transmission method, for example, a demodulator for a wireless LAN, a demodulator for receiving BS digital broadcast or CS digital broadcast, and a cable. The present invention can also be applied to a demodulator for receiving a television broadcast.

1 OFDM demodulator (demodulator)
3, 3a, 3b tuner (channel selection processing means)
4a, 4b Demodulator (demodulation processing means)
29 Reception quality detection unit (reception quality detection means)
40 clock source 50 start control unit (start control means)
51 determination part (determination means)
52 Start selection section (start selection means)
a, b Broadcast demodulation system

Claims (15)

A demodulator that demodulates a digital broadcast in which a plurality of layers exist in the same physical channel at a specific layer,
Channel selection processing means for performing channel selection processing of the physical channel by extracting the frequency component of the specific physical channel from the received signal of the digital broadcast, and the reception signal having the frequency component extracted by the channel selection processing means A demodulation processing means for performing demodulation processing, a broadcast demodulation system comprising a plurality of systems of the broadcast demodulation system,
Reception quality detection means for detecting the reception quality of the received signal demodulated by the demodulation processing means of each broadcast demodulation system;
Activation control means for selecting the hierarchy according to the detection value indicating the reception quality detected by the reception quality detection means, and activating only at least one broadcast demodulation system corresponding to the selected hierarchy. A demodulating device characterized by that. The activation control means includes
Determination means for determining whether or not a detection value indicating the reception quality received from the reception quality detection means is greater than or equal to a preset threshold;
The power supply voltage to be supplied to each broadcast receiving system is selected so that the hierarchy is selected according to the determination result of the determination means, and the power supply voltage is supplied only to the broadcast demodulation system corresponding to the selected hierarchy. The demodulation apparatus according to claim 1, further comprising activation selection means for controlling.   The demodulator according to claim 2, wherein a plurality of the threshold values are set in the determination means. The activation selection means is
When the determination result of the determination means that the detection value indicating the reception quality is equal to or higher than a first threshold which is one of a plurality of the thresholds, two or more broadcast demodulation systems After controlling the power supply voltage to be supplied to each broadcast receiving system so as to supply the power supply voltage,
It is determined whether or not the detection value indicating the reception quality is equal to or higher than a second threshold value different from the first threshold value, and the hierarchy is selected according to the determination result of the determination unit, and corresponds to the selected hierarchy 4. The demodulator according to claim 3, wherein the power supply voltage to be supplied to each broadcast receiving system is controlled so that the power supply voltage is supplied only to the broadcast demodulating system. The activation control means includes
Determination means for determining whether or not a detection value indicating the reception quality received from the reception quality detection means is greater than or equal to a preset threshold;
The operation clock to be supplied to each broadcast receiving system is selected so that the hierarchy is selected according to the determination result of the determination means, and the operation clock is supplied only to the broadcast demodulation system corresponding to the selected hierarchy. The demodulation apparatus according to claim 1, further comprising activation selection means for controlling.   6. The demodulator according to claim 5, wherein a plurality of the threshold values are set in the determination means. The activation selection means is
When the determination result of the determination means that the detection value indicating the reception quality is equal to or higher than a first threshold which is one of a plurality of the thresholds, two or more broadcast demodulation systems After controlling the operation clock to be supplied to each broadcast receiving system so as to supply the operation clock to
It is determined whether or not the detection value indicating the reception quality is equal to or higher than a second threshold value different from the first threshold value, and the hierarchy is selected according to the determination result of the determination unit, and corresponds to the selected hierarchy 7. The demodulator according to claim 6, wherein the operation clock to be supplied to each broadcast reception system is controlled so that the operation clock is supplied only to the broadcast demodulation system.   The demodulation apparatus according to claim 1, wherein the reception quality detection unit obtains a modulation error ratio as a detection value indicating the reception quality.   The demodulator according to any one of claims 1 to 7, wherein the reception quality detection means uses a determination index obtained from a modulation error ratio as a detection value indicating the reception quality.   The demodulator according to any one of claims 1 to 7, wherein the reception quality detection means uses a statistic obtained from statistics of a modulation error ratio as a detection value indicating the reception quality. The activation control means includes
The demodulation apparatus according to any one of claims 1 to 10, wherein a broadcast demodulation system that does not correspond to the selected hierarchy is stopped. A storage device;
12. The storage device stores data obtained by performing demodulation processing on the received signal output from each broadcast demodulation system, respectively. The demodulator according to 1. A demodulation method by a demodulator having a plurality of broadcast demodulation systems for demodulating a digital broadcast in which a plurality of layers exist in the same physical channel at a specific layer,
A channel selection processing step for performing channel selection processing of the physical channel by extracting a frequency component of a specific physical channel from the received signal of the digital broadcast, and a reception signal having the frequency component extracted in the channel selection processing step. And performing a demodulation process step for performing a demodulation process on each of the plurality of broadcast demodulation systems,
A reception quality detection step of detecting the reception quality of the received signal that has been demodulated in the demodulation processing step of each broadcast demodulation step;
An activation control step of selecting the hierarchy according to the detection value indicating the reception quality detected in the reception quality detection step, and activating only at least one broadcast demodulation system corresponding to the selected hierarchy; A demodulating method.   A demodulation program for operating the demodulation device according to any one of claims 1 to 12, wherein the demodulation program causes a computer to function as each of the means.   The computer-readable recording medium which recorded the demodulation program of Claim 14.

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