JP2008172577A - Digital broadcasting receiver - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a receiver in which uncomfortable feeling of videos and audios is not given to a viewing audience at the time of switching an antenna as well as reducing a size and manufacturing cost of the receiver in a digital broadcasting receiver equipped with a plurality of antennae. <P>SOLUTION: The receiver is equipped with two antennae 1, 2; a digital TV tuner 12 which outputs video signals and audio signals from OFDM signals received by the antennae; an antenna switching unit 11 which selects one of the two antennae 1, 2 to change a connection with the digital TV tuner 12; a BER detecting circuit 13 which detects a BER in order to detect a demodulation level of the digital TV tuner 12; and a video bit rate detecting circuit 14 which detects a video bit rate of a TS in order to detect a scene change. When the detected result of the BER detecting circuit 13 has become unable to be subjected to demodulation and a scene change has been detected due to the demodulation failure, the antenna switching unit 11 selects the other antenna. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a digital broadcast receiving apparatus, and more particularly to a digital broadcast diversity receiving apparatus suitably used for a moving body such as a vehicle with a simplified configuration and a reduced size.

  In analog televisions (hereinafter referred to as “TVs”) mounted on mobile objects such as automobiles, diversity antennas are installed to ensure directivity, and video quality is ensured by switching to antennas with high reception sensitivity as needed. is doing. Generally, this antenna switching is performed by checking each antenna terminal voltage in accordance with the timing of updating the video frame and switching to the antenna having the highest terminal voltage. For this reason, there is a moment when no antenna is connected when checking the terminal voltage and switching the antenna, but since this time is extremely short, the viewer of the television does not recognize the interruption of the video.

  However, if the phase difference is included in the video signal between the antennas when the antenna is switched, a phenomenon occurs in which the video appears to swing from side to side. Therefore, as a diversity device that prohibits unnecessary antenna switching when it is determined that the received image is good and prevents deterioration of image quality and sound quality due to switching, a plurality of antennas are detected by detecting the relative received electric field level of the antenna. A diversity apparatus for mobile television has been proposed that selects an antenna with the maximum reception level from among the antennas and prohibits a diversity operation based on the reception status of multiple waves detected from a video signal (see Patent Document 1).

  Incidentally, in recent years, with the start of digital terrestrial television broadcasting, in-vehicle televisions and car navigation systems equipped with digital terrestrial television tuners have become widespread. Recently, one segment (hereinafter referred to as “One Seg”) broadcasting, which is not as high-quality as terrestrial digital TV broadcasting but useful for mobile TVs, etc. has started, and those equipped with one-segment digital TV tuners have become widespread. ing. These digital broadcasts employ an OFDM (Orthogonal Frequency Division Multiplexing) scheme that is resistant to multipath, and MPEG2 and ITU-T H are used as video compression and coding schemes to enable transmission and reception of enormous amounts of video data. .264 etc. are adopted. Video compression encoding techniques include “DCT (Discrete Cosine Transform)” technology that extracts and encodes still image features, “Motion Compensation” technology that extracts changes in motion between frames, and the like. A video without any sense of incongruity is provided by reproducing a TS (Transport Stream) while reducing the amount of transfer data by compressing data at a variable bit rate when encoding the video.

  These tuners that handle digital broadcast waves may take several seconds to stream once the connection with the antenna is interrupted, and the video is interrupted during this time. Therefore, in a television system compatible with digital broadcasting provided with a diversity antenna for a mobile body or the like, tuners are incorporated as many as the number of diversity antennas. Then, after the broadcast waves received by the respective antennas are converted into digital signals, they are combined in a complementary manner to ensure continuous image quality.

As a receiving device for a mobile body having such a plurality of antennas and a plurality of signal processing groups for processing broadcast waves received by the respective antennas, the terrestrial digital broadcasting or the like is best performed according to the current location of the mobile body Based on the transmitter station position information and the mobile object position information, the arrival direction of the interference wave and the desired wave is estimated based on the transmitter station position information and the mobile body position information, and diversity combining is performed based on the estimation result and the reception state of the broadcast wave. There has been proposed a receiving apparatus that selects a method and processes output signals of the plurality of signal processing groups in a diversity unit (see Patent Document 2).
JP 11-225293 A JP 2006-115318 A

  However, in the diversity device for mobile TV of Patent Document 1, when the terminal voltage of each antenna is confirmed, there is a moment when it is not connected to any antenna. Therefore, when this is applied to a receiving device for digital broadcasting, the antenna The video / audio is interrupted each time the switch is made and the antenna terminal voltage is confirmed. On the other hand, the receiving device of Patent Document 2 includes tuners as many as the number of antennas, so that the size of the device itself is increased and an increase in manufacturing cost is inevitable.

  The present invention has been made in view of such a background, and in a digital broadcast wave receiving device having a plurality of antennas, the size of the device is reduced and the manufacturing cost is reduced, and a sense of incongruity due to switching between video and audio antennas is provided. It is an object of the present invention to provide a receiving device that does not give a viewer a message.

  In order to solve the above problems, a receiving apparatus according to the present invention includes a diversity antenna and a single tuner, and a receiving antenna is clearly unable to receive a signal due to a change in radio wave environment (medium / weak electric field, The antenna is switched when a delay wave or radio wave interference occurs. In addition, by optimizing the timing of antenna switching, the uncomfortable feeling of antenna switching is reduced.

  According to a first aspect of the present invention, there is provided a digital broadcast receiving apparatus that includes a plurality of antennas used for receiving digital broadcast waves, and a digital television that demodulates the digital broadcast waves received by the antennas and outputs a video signal and an audio signal. A tuner; antenna switching means for selecting one of the plurality of antennas to switch connection to the digital TV tuner; and demodulation level detection means for detecting a demodulation level of the digital TV tuner. The means is characterized in that the selection is performed according to a detection result of the demodulation level detection means.

  According to a second aspect of the present invention, in the digital broadcast receiving apparatus according to the first aspect, the antenna switching means selects another antenna when the detection result of the demodulation level detecting means is not demodulated. .

  According to a third aspect of the present invention, there is provided the digital broadcast receiving apparatus according to the first or second aspect, further comprising a scene change detecting means for detecting a change in a video scene from a digital broadcast wave received by the antenna, and the antenna switching means. Is characterized in that when the detection result of the demodulation level detection means is equal to or less than a predetermined value, another antenna is selected when the scene change detection means detects a scene change.

  According to a fourth aspect of the present invention, in the digital broadcast receiving apparatus according to any one of the first to third aspects, the antenna switching means is configured so that when the demodulation level after antenna switching is lower than the demodulation level before antenna switching, An antenna is selected.

  According to the first aspect of the present invention, it is possible to reduce the size of the apparatus and reduce the manufacturing cost by using one digital TV tuner in the digital broadcast receiving apparatus having a plurality of antennas. According to the invention of claim 2, by switching the antenna when the digital TV tuner cannot demodulate to the digital signal, the antenna can be provided without giving the viewer a sense of incongruity when switching the video and audio antennas. Can be switched. According to the third aspect of the present invention, the digital television tuner can demodulate the digital signal, but when the reception state is not good, the antenna is switched in accordance with the timing of the scene change, so that the video antenna is changed. The antenna can be switched without giving the viewer a sense of incongruity due to the switching. According to the fourth aspect of the present invention, the antenna is switched again when the reception state is deteriorated due to the antenna switching. Therefore, it is possible to switch to the optimum antenna without giving the viewer a sense of discomfort due to the antenna switching of the video.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

<< Configuration of Embodiment >>
FIG. 1 is a schematic configuration diagram of an automobile equipped with a digital broadcast receiver 3. The automobile 10 has film antennas 1 and 2 having different directivities attached to the left side of the windshield and the right side of the rear glass, respectively. The antennas 1 and 2 are for receiving a terrestrial digital television broadcast signal (digital broadcast wave) that is an OFDM signal, and are connected to the tuner unit 4.

  In the automobile 10, the tuner unit 4 is mounted in a trunk room, a display 5 and an operation unit 6 are installed on a dashboard, and speakers 7a and 7b are installed on left and right doors. The occupant can view the TV video and audio from the tuner unit 4 via the display 5 and the left and right speakers 7a and 7b by operating a button (not shown) on the operation unit 6, a touch panel operation on the display 5, or operating a remote control. .

  The tuner unit 4 includes a board on which a microcomputer, a ROM, a RAM, a peripheral circuit, an input / output interface, various drivers, and the like are mounted, an antenna switching unit that switches connection with the antennas 1 and 2, as described later, A digital TV tuner and the like that generate and output a video signal and an audio signal from the broadcast wave of the OFDM signal input from the antennas 1 and 2 are incorporated. The display 5 and the left and right speakers 7 a and 7 b are connected to the tuner unit 4, and video and audio signals are output from the tuner unit 4.

  FIG. 2 is a block diagram of the digital broadcast receiving apparatus 3. The tuner unit 4 includes an antenna switching unit 11 (antenna switching means) that switches between the antennas 1 and 2, a digital television tuner 12 that demodulates the received OFDM signal, and a BER (detection level) for detecting the demodulation level of the digital television tuner 12. A BER detection circuit 13 (demodulation level detection means) that detects a Bit Error Rate (bit error rate) and a video bit rate detection circuit 14 (scene change detection means) that detects a video bit rate of the TS are main components. . The digital television tuner 12 includes a tuner unit 21, a synchronization processing circuit 22, a detection processing circuit 23, an error correction circuit 24, and a decoder 25.

  The antenna switching unit 11 electrically connects only one antenna to be selected from the antennas 1 and 2 to which the terminals are connected to the digital television tuner 12, and inputs a digital broadcast wave received by the selected antenna to the tuner unit 21. To do.

  The tuner unit 21 extracts the OFDM signal of the selected channel from the broadcast wave of the OFDM signal received by the antenna. The synchronization processing circuit 22 converts the OFDM signal of the extracted channel into a digital signal by an AD converter, performs quadrature demodulation, obtains the correlation between the effective symbol period and the guard interval period using a one-symbol delay memory, and calculates the carrier frequency Correct the error and sampling frequency error between the transceiver. The detection processing circuit 23 stores the FFT (Fast Fourie Transform) operation corresponding to the transmission mode and the information of one symbol before in the memory and performs differential detection. The error correction processing circuit decodes the control signal indicating the transmission parameter used in each layer, and based on the decoded result, the error of the detection result de-mapping, various de-interleavers, Viterbi decoding and Reed-Solomon decoding Make corrections, play TS and output. The decoder 25 decodes the output TS and outputs a video signal and an audio signal.

  The BER detection circuit 13 communicates with the error correction processing circuit 24 to detect the BER using the Viterbi signal and Reed-Solomon complex error correction in order to detect the demodulation level of the digital TV tuner 12, and the detection result is transmitted to the antenna. Input to the switching unit 11. The video bit rate detection circuit 14 detects the video bit rate of the streamed TS in order to detect a scene change, and inputs the detection result to the antenna switching unit 11. Based on the detection result of the BER detection circuit 13, the antenna switching unit 11 sets the demodulation level of the digital television tuner 12 to “demodulation is impossible” when the converted digital data cannot be demodulated, and when the BER is equal to or higher than a predetermined value, If the BER is less than or equal to a predetermined value, it is assigned to “good demodulation”. The antenna switching unit 11 performs switching control of the antenna switching unit 11 based on the determination result of the BER detection circuit 13 and the detection result of the video bit rate detection circuit 14.

<< Operation of Embodiment >>
FIG. 3 is a flowchart showing an antenna switching procedure when demodulation failure occurs during reception. When the automobile 10 is started or the digital television system is switched on by the operation unit 6 or the like, the tuner unit 4 starts receiving the digital television broadcast signal using the antenna 1 set as the primary antenna, The audio signal is output and the flowchart shown in FIG. 4 is executed.

  In step ST11, the antenna switching unit 11 determines whether the BER is large or small. If the BER is not greater than or equal to the threshold (ie, “demodulation is good”), the process proceeds to return and the procedure is repeated. On the other hand, if the BER is greater than or equal to the threshold (that is, “demodulation failure”), the process proceeds to step ST12, where the antenna switching unit 11 determines the detection result of the video bit rate detection circuit 14. In step ST12, when the video bit rate is less than the predetermined value (that is, when no scene change is detected), the process proceeds to return and the above procedure is repeated. On the other hand, when the video bit rate is equal to or higher than the predetermined value (that is, when a scene change is detected), the process proceeds to step ST13, and the antenna switching unit 11 switches the connection to the antenna 2 set as the secondary antenna. In step ST14, the antenna switching unit 11 determines the magnitude of the BER after the antenna switching compared to before the antenna switching. When the BER after the antenna switching is smaller than that before the antenna switching, the reception by the antenna 1 is continued, the process proceeds to return, and the above procedure is repeated. If the BER after antenna switching is larger than that before antenna switching in step ST14, the process proceeds to step ST15 where the antenna switching unit 11 switches the connection to the original antenna 1 and repeats the above procedure.

  In this embodiment, the two antennas 1 and 2 attached to the front and rear of the automobile 10 are used. However, three or more antennas may be arranged on the front and rear, right and left of the automobile 10. For example, if four antennas are attached, one antenna is set as the primary antenna, the antenna opposite to the primary antenna is set as the first secondary antenna, and the remaining antennas are set as the third and fourth secondary antennas. After setting the priority order, the antenna is switched in the same procedure as the above flow. Specifically, switching to the first secondary antenna in step ST13, switching to the second secondary antenna in step ST15, and switching to the third secondary antenna when the demodulation level of the second secondary antenna does not become maximum are performed. .

  FIG. 4 is a time chart showing an example of antenna switching of the digital broadcast receiving apparatus 3 according to the embodiment. The horizontal axis represents time, and the vertical axis represents the demodulation level (small BER) of the digital television tuner by the two antennas 1 and 2. Note that in the actual digital broadcast receiving apparatus 3, only the demodulation level for one antenna is detected, but here, the demodulation levels for both antennas 1 and 2 are shown to indicate changes in the reception intensity of each antenna. Yes. The numbers in the lower column indicate the code of the selected antenna, the white triangle indicates the scene change time t detected from the video bit rate, and the black triangle indicates the antenna switching time.

At the time when the tuner unit 4 starts reception at t ₀ , the antenna 1 that is the primary antenna is selected. Since the demodulation level of the antenna 1 is equal to or higher than the threshold value, the tuner unit 4 repeats only step ST11 of FIG. 3 and continues reception. Although a scene change is detected at t ₁ , since the demodulation level of the antenna 1 is equal to or higher than the threshold value, reception by the antenna 1 is continued. Thereafter, the demodulation level of the antenna 1 falls below the threshold value, but since there is no scene change, reception by the antenna 1 is continued (step ST12). While this state subsequently repeats the steps ST11 and step ST12, the scene change at _{t 2} is detected, the antenna switching unit 11 switches the connection from the antenna 1 to the antenna 2 (step ST13). However, when the digital television broadcast signal is received by the antenna 2 and streaming is performed, it is found that the demodulation level of the antenna 2 is lower than the demodulation level of the antenna 1 (BER is large) (step ST14). Is switched to the antenna 1 (step ST15). Because demodulation level of the antenna 1 is lower than the threshold value, the repeats steps ST11 and step ST12, the next scene change is detected at t _3. The antenna switching unit 11 switches the connection from the antenna 1 to the antenna 2 in the same manner as at t ₂ , but at this time, the demodulation level of the antenna 1 is lower than that of the antenna 2 (step ST14). Continues reception while switching to. If step ST11 and step ST12 are repeated, the demodulation level of antenna 2 has exceeded the threshold value, and therefore only step ST11 is repeated at both t ₄ and t ₅ .

  Next, an antenna switching procedure when demodulation is impossible during reception will be described with reference to FIG. The flowchart of FIG. 5 is processed in parallel with the flowchart of FIG. 3, but is programmed so that this flowchart is applied with priority. The tuner unit 4 starts receiving a digital television broadcast signal using the antenna 1 set as a primary antenna, outputs a video signal / audio signal, and executes the flow of FIG.

  In step ST21, the antenna switching unit 11 determines whether the digital television broadcast signal received by the antenna 1 can be demodulated to the TS. If demodulation is possible (that is, “demodulation is good” or “demodulation is bad”), the process proceeds to return and this procedure is repeated. In this case, the flow shown in FIG. 3 is performed in parallel. On the other hand, when the digital television broadcast signal cannot be demodulated to TS (that is, when “demodulation is impossible”), the process proceeds to step ST22, and it is determined whether or not the non-demodulation time continues for a predetermined value t or more. In this case, the flow shown in FIG. 3 is not executed and this flow is preferentially applied. Setting the predetermined non-demodulable time prevents frequent antenna switching even when radio waves are temporarily blocked by entering the shadow of a building while traveling in an urban area, etc. Because. The predetermined value t may be set to be changed according to the operating state. If it is determined in step ST22 that the non-demodulable time does not exceed the predetermined value t, the process proceeds to return and the above procedure is repeated. On the other hand, if the time during which demodulation is impossible becomes equal to or greater than the predetermined value t in step ST22, the process proceeds to step ST23, where the antenna switching unit 11 switches the connection to the antenna 2 set as the secondary antenna. In step ST24, the antenna switching unit 11 determines whether the digital television broadcast signal received by the antenna 2 can be demodulated to the TS. If demodulation is possible, go to return and repeat this procedure. On the other hand, if it cannot be demodulated, the process proceeds to step ST25, and demodulation cannot be performed using either antenna 1 or 2. Therefore, the tuner unit 4 displays "cannot receive" on the display 5 and repeats the above procedure.

  Next, although not shown, the embodiment in the flow of FIG. 5 will be described as described with reference to FIG. When the tuner unit 4 starts reception, the antenna 1 that is a primary antenna is connected by the antenna switching unit 11. When the demodulation level at the antenna 1 is equal to or higher than the threshold value, the antenna 1 is continuously connected. For example, the automobile 10 enters a tunnel or is hidden in the shade at the end of a broadcast area where the radio wave is weak, so that the tuner unit 4 cannot demodulate the digital TV broadcast signal received by the antenna 1 and enters a “demodulation disabled” state. (Step ST21) When this state continues for a predetermined time or longer (Step ST22), the antenna switching unit 11 switches the connection from the antenna 1 to the antenna 2 (Step ST23). If the digital TV broadcast signal received by the antenna 2 can be demodulated, the process proceeds to return and step ST21 is repeated. However, if the digital TV broadcast signal from the antenna 2 cannot be demodulated for a predetermined time or more, the tuner unit 4 Displays “cannot be received” on the display 5 and repeats steps ST21 to ST23. That is, the antenna switching is repeated until demodulation is possible. When the automobile 10 comes out of the tunnel and becomes ready for demodulation, the flow shown in FIG. 3 is performed.

  As described above, the digital broadcast receiving device 3 includes the plurality of antennas 1 and 2 and the single digital TV tuner 12, thereby reducing the size of the device and reducing the manufacturing cost. Also, when the demodulation of the digital signal becomes impossible for a predetermined time or more, the antenna is switched, and when the demodulation of the digital signal is poor, the antenna is switched in accordance with the timing of the scene change, The antenna can be switched without giving the viewer a sense of incongruity due to the antenna switching. Furthermore, when the reception state becomes worse when the antenna is switched, the antenna can be switched again so that the optimum antenna can be adopted without giving the viewer a sense of discomfort.

  Although the description of the specific embodiment is finished above, the present invention is not limited to the above embodiment. For example, in the above embodiment, the digital receiving device is applied to a digital television system mounted on a car, but the present invention may be applied to other transportation means and a portable television. In the above embodiment, a BER (Bit Error Rate) detection circuit is used as a demodulation level detection means, but other information such as a carrier wave noise power ratio (reception of a received signal) is used as an element for determining the demodulation level. C / N), detection information of received power, or a combination thereof may be used. Similarly, in the above embodiment, a video bit rate detection circuit is employed as the scene change detection means, and the scene change is detected based on the video bit rate detected thereby. However, MER (modulation error rate) or constellation is detected. The present invention can be applied with appropriate modifications without departing from the spirit of the present invention.

Schematic configuration diagram of a car equipped with a digital broadcast receiver Block diagram of digital broadcast receiver Flow chart showing the antenna switching procedure in case of demodulation failure Time chart showing an example of antenna switching Flow chart showing the antenna switching procedure when demodulation is not possible

Explanation of symbols

1, 2 Antenna 3 Digital broadcast receiver 4 Tuner unit 11 Antenna switching unit (antenna switching means)
12 Digital TV tuner 13 BER detection circuit (demodulation level detection means)
14 Video bit rate detection circuit (scene change detection means)
15 Antenna switching control circuit (antenna switching control means)

Claims (4)

A plurality of antennas for receiving digital broadcast waves;
A digital television tuner that demodulates a digital broadcast wave received by the antenna and outputs a video signal and an audio signal;
An antenna switching means for selecting one of the plurality of antennas and switching the connection to the digital TV tuner;
Demodulation level detection means for detecting the demodulation level of the digital TV tuner,
The digital broadcast receiving apparatus according to claim 1, wherein the antenna switching means performs the selection according to a detection result of the demodulation level detection means.   2. The digital broadcast receiving apparatus according to claim 1, wherein the antenna switching unit selects another antenna when the detection result of the demodulation level detection unit is not demodulated. A scene change detecting means for detecting a change in the video scene from the digital broadcast wave received by the antenna;
The antenna switching means selects another antenna when the scene change detection means detects a scene change when the detection result of the demodulation level detection means is a predetermined value or less. The digital broadcast receiver according to claim 1 or 2.   The digital antenna according to any one of claims 1 to 3, wherein the antenna switching means selects another antenna when the demodulation level after antenna switching is lower than the demodulation level before antenna switching. Broadcast receiving device.

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