JP4242753B2 - Broadcast receiver - Google Patents

Description

  The present invention relates to a broadcast receiving apparatus that receives a broadcast signal transmitted by an OFDM (orthogonal frequency division) method and then decodes the broadcast signal.

  In recent years, digital television broadcasting has begun to be used in place of conventional analog television broadcasting. In digital television broadcasting, it is necessary to transmit and receive a large amount of digital data at high speed. An OFDM (orthogonal frequency division) method has attracted attention as a method for efficiently transporting a large amount of digital data.

  In the OFDM system, a digital signal is serial-parallel converted into a plurality of parallel symbols on the transmission side, and further subjected to inverse Fourier transform to obtain a plurality of orthogonal subcarriers of different frequencies, and this is D / A converted OFDM A signal is transmitted. The receiver side performs A / D conversion on the received OFDM signal, obtains parallel symbols by Fourier transformation, and further obtains a decoded digital signal by parallel-serial conversion. Since the subcarriers are orthogonal to each other in the OFDM scheme, the frequency bands of the subcarriers may partially overlap, so that a large amount of data can be transmitted in a limited frequency band.

  On the other hand, in communication including the OFDM system and analog broadcasting, a so-called diversity system is often employed in which signal quality is improved by using a plurality of antennas having different directivities in order to prevent signal attenuation. Diversity systems can be broadly classified into switched diversity systems and composite diversity systems.

  The switching diversity system uses only a signal with the least deterioration among signals received from a plurality of antennas. The switching diversity system has been conventionally employed in analog broadcast receiving apparatuses.

  The combining diversity system increases the signal level by combining signals received from a plurality of antennas. However, the arrival times of signals received from a plurality of antennas differ depending on the signal reception path. That is, the signal reflected on the building or the like arrives slightly later than the signal received directly from the transmitter. (Hereafter, the signal that arrives first is called a desired wave, and the signal that arrives late is called a delayed wave.)

  In the OFDM scheme, when a delay wave is combined with a desired wave, the previous symbol overlaps, and the characteristics deteriorate when demodulating the data of each symbol. In order to prevent such deterioration, a signal margin period called a guard interval is added to each subcarrier during signal transmission, for example, as in the configuration of Patent Document 1. The guard interval is a cyclic addition of a part of the waveform of the symbol, and if the delay time of the delay wave is within the guard interval time, the effect of overlapping of its own symbols is inevitable, Demodulation can be performed while avoiding the overlap of the previous symbol. That is, by adding a guard interval, it is possible to prevent deterioration due to delayed waves to some extent and obtain a signal with higher signal quality than when no diversity system is used.

In this way, a high-quality signal can be obtained by using both the OFDM scheme and the combining diversity system. In addition, the quality of the received signal increases as the number of antennas increases.
JP-A-10-107777

  However, in the OFDM system, it is necessary to prepare a circuit (OFDM demodulation circuit) for performing signal processing such as tuner and Fourier transform for each antenna. In particular, the OFDM demodulation circuit is an expensive circuit that performs high-speed signal processing, and there is a problem that if a large number of antennas are provided in order to obtain a high-quality signal, the cost of the receiving apparatus increases significantly. On the other hand, it has been difficult to apply the switching diversity system to the OFDM system in terms of antenna switching timing.

  In view of the above circumstances, an object of the present invention is to provide a low-cost broadcast receiving apparatus that can obtain a high-quality signal.

In order to solve the above problem, the broadcast receiving apparatus of the present invention decodes an OFDM signal received from a master antenna to obtain a master symbol, and an OFDM signal received from one of a plurality of slave antennas. A slave OFDM unit that obtains a slave symbol by decoding, a combining unit that combines the master symbol and the slave symbol to obtain a combined symbol, and a slave that the slave OFDM unit should receive an OFDM signal based on a predetermined criterion Selecting means for selecting an antenna. Further, the predetermined criterion includes that the bit error rate of the composite symbol exceeds a first predetermined value, and that the electric field strength of the OFDM signal received from the master antenna exceeds a second predetermined value. .

  Therefore, according to the broadcast receiving apparatus of the present invention, a slave antenna that receives the highest quality OFDM signal can be selected. In addition, the broadcast receiving apparatus of the present invention is low-cost in that the number of OFDM units is the same as that of the conventional broadcast receiving apparatus. Therefore, according to the present invention, a high-quality signal can be obtained, and a low-cost broadcast receiving apparatus can be realized.

Further, the predetermined criterion may be that the electric field strength of the OFDM signal currently received by the slave OFDM unit is lower than a third predetermined value.

Further, whether or not the electric field strength of the OFDM signal received from the master antenna exceeds the second predetermined value can be determined from the auto gain control level of the master tuner that tunes the OFDM signal received from the master antenna. Good.

Also, whether the field strength of the OFDM signal currently received by the slave OFDM unit is below the third predetermined value depends on whether the OFDM signal received from the slave antenna currently receiving the OFDM signal by the slave OFDM unit is received. This may be determined from the auto gain control level of the slave tuner that performs tuning.

The broadcast receiver tunes the OFDM signal received from the master antenna, processes the OFDM signal and sends it to the master OFDM unit, and the OFDM signal received from any one of the plurality of slave antennas. A slave-side tuner that performs tuning and processes the OFDM signal and sends it to the slave OFDM unit, and the selection means selects a slave antenna from which the slave-side tuner should receive the OFDM signal based on the predetermined criterion It is good also as a structure.

  With such a configuration, only two tuners that perform tuning of the FDM signal, process the OFDM signal, and send the signal to the OFDM unit may be used, thereby realizing a broadcast receiver with lower cost.

Alternatively, the broadcast receiving apparatus tunes the OFDM signal received from the master antenna and tunes the OFDM signal received from each of the plurality of slave antennas and the master tuner that processes the OFDM signal and sends it to the master OFDM unit. And a plurality of slave-side tuners that process the OFDM signal and selectively send it to the slave OFDM unit, and the selection means transmits the processed OFDM signal to the slave OFDM unit based on the predetermined criterion The slave side tuner may be selected from a plurality of slave side tuners. In addition, the predetermined criterion is that the field strength of the OFDM signal received by the slave tuner currently selected by the selection means is lower than the field strength of the OFDM signal received by another slave tuner. Including that.

  With such a configuration, the phenomenon that the field intensity of the OFDM signal received by the slave tuner after switching is lower than that before switching does not occur, so that unnecessary switching can be prevented.

Whether the field strength of the OFDM signal received by the slave tuner currently selected by the selection means is lower than the field strength of the OFDM signal received by the other slave side tuners It may be determined from the auto gain control level of the tuner.

The selection means switches the slave antenna to which the slave OFDM unit should receive the OFDM signal after the slave antenna has received the OFDM signal corresponding to the specific symbol, and the OFDM signal by the slave antenna after the switching is completed. May be restarted from the beginning of the next symbol.

  With such a configuration, it is possible to prevent a phenomenon in which radio waves received on the slave side are switched discontinuously.

  FIG. 1 is a diagram showing a schematic configuration of a digital television broadcast receiving apparatus according to a first embodiment of the present invention. The receiving apparatus 100 of the present embodiment employs a combining diversity system that combines a master signal received by the master antenna 10a and a slave signal received by one of the slave antennas 10b and 10c. The antennas 10a, 10b, and 10c are antennas having different directivities.

  The OFDM signal received by the master antenna 10a is sent to the tuner unit 20a. The tuner unit 20a performs OFDM signal tuning, band filtering, down-conversion, and the like using a PLL, and generates an analog signal that can be easily processed by the master OFDM unit 30a. The generated analog signal is sent to the master OFDM unit 30a.

  The master OFDM unit 30a sequentially performs A / D conversion, serial-parallel conversion, and fast Fourier transform on the analog signal sent from the tuner unit 20a to obtain a plurality of symbols.

  On the other hand, the slave antennas 10 b and 10 c are connected to the switch 60. The switcher 60 is a device that switches between the OFDM signal received by the slave antenna 10b and the OFDM signal received by the slave antenna 10c to be sent to the tuner unit 20b. Which signal is sent to the tuner unit 20b is controlled by the microcomputer 40 (described later).

  The tuner unit 20b performs tuning, band filtering, down-conversion, and the like of the OFDM signal using the PLL, and generates an analog signal that can be easily processed by the slave OFDM unit 30b. The generated analog signal is sent to the slave OFDM unit 30b.

  The slave OFDM unit 30b sequentially performs A / D conversion, serial-parallel conversion, and fast Fourier transform on the analog signal sent from the tuner unit 20b to obtain a plurality of symbols. Then, the plurality of symbols are sent to the master OFDM unit 30a.

  The master OFDM unit 30a combines a plurality of symbols decoded by the master OFDM unit 30a and a plurality of symbols sent from the slave OFDM unit 30b to obtain a symbol with little deterioration. Then, the plurality of symbols are returned to single carrier data. Through the above procedure, video information that is single carrier data is decoded. This video information is an MPEG format data stream. Next, the decoded video information is sent to the MPEG unit 50.

  The MPEG unit 50 converts the video information into a video signal and an audio signal such as an analog video signal and a DV signal, and outputs them. A monitor and a speaker (not shown) are connected to the MPEG unit 50, and the user of the receiving apparatus 100 can view a moving image with sound.

  The procedure for switching the slave antenna by the microcomputer 40 will be described below. FIG. 2 is a flowchart of an antenna switching routine executed by the microcomputer 40. This routine is executed periodically (for example, every frame or every second). When this routine starts, step S101 is first executed. When the receiving apparatus 100 is activated, the OFDM signal received by the slave antenna 10b is sent to the tuner unit 20b.

  In step S101, the process waits until a plurality of symbols decoded by the master OFDM unit 30a and a plurality of symbols sent from the slave OFDM unit 30b are combined. Next, the process proceeds to step S102.

In step S102, the BER (bit error rate) of the synthesized symbol is calculated. Here, if the BER exceeds a certain standard (for example, 10 ⁻² ), it is determined that the signal is greatly deteriorated (S102: YES), and the process proceeds to step S103. On the other hand, if the BER is lower than the predetermined standard, it is determined that there is almost no signal degradation (S102: NO), and this routine is finished (slave antenna switching is not performed).

  In step S103, the AGC (auto gain control) outputs of the tuner units 20a and 20b are acquired, and the AGC levels of both are checked. If the AGC level of the master-side tuner unit 20a exceeds the predetermined value x and the AGC level of the slave-side tuner unit 20b is lower than the predetermined value y (S103: YES), the process proceeds to step S104, and the tuner unit 20b The slave antenna that receives the signal to be sent to is switched, and then this routine is terminated. On the other hand, if the AGC level of the master-side tuner unit 20a is lower than the predetermined value x or the AGC level of the slave-side tuner unit 20b is higher than the predetermined value y (S103: NO), this routine is terminated.

  The AGC level is an index indicating the electric field strength of the received OFDM signal, and the electrolytic strength increases as the AGC level increases. That is, the low AGC level of the tuner unit 20b on the slave side means that the radio wave received by the slave antenna is weak and therefore contains a lot of noise components. On the other hand, when switching the slave antenna, video information must be temporarily decoded using only the OFDM signal received by the master antenna 10a, so that the electric field strength of the OFDM signal received by the master antenna 10a is sufficiently large. There must be. Accordingly, in step S104, it is determined whether or not to switch the slave antenna using not only the AGC level on the slave side but also the AGC level on the master side.

  As described above, according to this routine, the deterioration of the synthesized symbol is larger than a reference value, the electric field strength of the OFDM signal received by the master antenna 10a is sufficiently large, and the electric field strength of the OFDM signal received by the slave antenna. Is less than a predetermined value, the slave antenna is switched.

  The procedure for switching the antenna in step S104 will be described below. FIG. 3 shows symbols obtained by Fourier transform by the master OFDM unit 30a and symbols obtained by Fourier transform by the slave OFDM unit 30b arranged in chronological order. Symbol 1 is converted first, and symbol 3 is converted last.

  As shown in FIG. 3, the antenna switching process is performed while the master OFDM unit 30a obtains the symbol 2 by performing the Fourier transform. That is, on the slave side, the antenna is switched after the reception of the signal corresponding to symbol 1 is completed, and the switching process is completed before the signal corresponding to symbol 3 reaches the receiving apparatus 100. The signal corresponding to symbol 3 is received by the slave antenna after switching. Note that the slave OFDM unit 30b does not process the signal corresponding to the symbol 2.

  In this way, the slave antenna receives signals on the slave side by switching the antenna after completing reception of a signal corresponding to a specific symbol and restarting reception of a signal corresponding to the next symbol after switching. Prevents the phenomenon of radio wave switching discontinuously. If the signal received on the slave side is discontinuously switched while receiving a signal corresponding to a certain symbol, the symbol decoded from that signal is likely to be significantly different from that at the time of transmission. The quality of the product may deteriorate. In the present embodiment, the phenomenon that the radio waves received on the slave side are switched discontinuously by the above-described method is prevented, so that high-quality video information can be obtained even when the antenna is switched.

  As described above, according to the present embodiment, the slave antenna is automatically switched when it is determined that the quality of the OFDM signal received from the plurality of slave antennas is low. Therefore, since combining diversity can be performed using a higher quality OFDM signal, the obtained video information is high quality information with less noise components.

  In the present embodiment, the switching device 60 is configured to switch between the two slave antennas 10b and 10c, but the switching device may be configured to switch between three or more slave antennas.

  The first embodiment of the present invention described above is a low-cost receiving apparatus having a configuration that is almost the same as a receiving apparatus using a conventional combining diversity system, in which there are only two tuner sections and two OFDM sections. Despite being, it is possible to obtain higher quality video information. However, in the first embodiment, when the slave AGC level after switching is lower than that before switching, it is necessary to switch the slave antenna again. The second embodiment of the present invention prevents such unnecessary switching of the slave antenna.

  FIG. 4 is a diagram showing a schematic configuration of a digital television broadcast receiving apparatus according to the second embodiment of the present invention. Note that elements having the same or similar functions as those of the first embodiment of the present invention are given the same or similar reference numerals as those of the first embodiment.

  In the receiving apparatus 200 of the present embodiment, the slave antenna 10b is connected to the tuner unit 20b, and the slave antenna 10c is connected to the tuner unit 20c. The switcher 60 switches an analog signal to be sent to the slave OFDM unit 30b among the analog signals generated by the tuner units 20b and 20c. Which signal is sent to the tuner unit 20b is controlled by the microcomputer 40 (described later).

  As in the first embodiment, the symbols obtained by the processing of the slave OFDM unit 30b are combined with the symbols obtained by the processing of the master OFDM unit 30a, and further converted into a predetermined video / audio signal by the MPEG unit 50. Is done.

  The procedure for switching the slave tuner unit by the microcomputer 40 will be described below. FIG. 5 is a flowchart of an antenna switching routine executed by the microcomputer 40. This routine is executed periodically (for example, every frame or every second). When this routine starts, step S201 is first executed. When the receiving apparatus 200 is activated, an analog signal generated by the tuner unit 20b is sent to the slave OFDM 30b.

  In step S201, the process waits until the plurality of symbols decoded by the master OFDM unit 30a itself and the plurality of symbols transmitted from the slave OFDM unit 30b are combined. Next, the process proceeds to step S202.

In step S202, the BER (bit error rate) of the synthesized symbol is calculated. Here, when the BER exceeds a certain standard (for example, 10 ⁻² ), it is determined that the signal is greatly deteriorated (S202: YES), and the process proceeds to step S203. On the other hand, if the BER is below the predetermined standard, it is determined that there is almost no signal degradation (S202: NO), and this routine is terminated (the slave tuner unit is not switched).

  In step S203, the AGC (auto gain control) outputs of the tuner units 20a, 20b, and 20c are acquired, and the AGC levels of both are checked. The level of the AGC output from the tuner unit that is currently supplying signals to the slave 30b is “first slave AGC level”, and the level of the AGC output from the tuner unit that is not currently supplying signals to the slave 30b is “first”. 2 slave AGC levels ”. When the AGC level of the tuner unit 20a on the master side exceeds the predetermined value x and the first slave AGC level is lower than the second slave AGC level and the predetermined value y (S203: YES), the process proceeds to step S204, and the slave The tuner unit that receives a signal to be sent to the OFDM unit 30b is switched, and then this routine ends. On the other hand, when the AGC level of the tuner unit 20a on the master side is lower than the predetermined value x, the first slave AGC level is higher than the second slave AGC level, or the first slave AGC level is higher than the predetermined value y. (S203: NO), this routine is terminated.

  Therefore, according to this routine, the deterioration of the synthesized symbol is larger than a certain reference value, the electric field strength of the OFDM signal received by the master antenna 10a is sufficiently large, and the tuner unit sending the current signal to the slave OFDM unit 30b The field strength of the OFDM signal received by the connected slave antenna is smaller than the field strength of the OFDM signal received by another slave antenna, and the OFDM signal received by the slave antenna that is currently sending the signal to the slave OFDM unit 30b When the electric field strength is less than a predetermined value, the slave antenna is switched. Note that the switching timing and the like are the same as those in the first embodiment, and a description thereof will be omitted.

  As described above, according to the present embodiment, the OFDM signal received by the slave antenna connected to the tuner unit that has seen the reference in the first embodiment and is currently sending the signal to the slave OFDM unit 30b. The slave antenna is switched only when the electric field strength is lower than the electric field strength of the radio wave received by another slave antenna. Therefore, although it is necessary to provide a tuner unit for each slave antenna, the phenomenon that the slave-side AGC level after switching is lower than that before switching does not occur. Therefore, according to the present embodiment, it is possible to realize a receiving apparatus that does not wastefully switch slave antennas and that can obtain video information with higher quality than the conventional one.

It is a figure showing schematic structure of the digital television broadcast receiver of the 1st Embodiment of this invention. 4 is a flowchart of an antenna switching routine according to the first embodiment of the present invention. In the first embodiment of the present invention, symbols obtained by Fourier transform by the master OFDM unit and symbols obtained by Fourier transform by the slave OFDM unit are arranged in time series. It is a figure showing schematic structure of the digital television broadcast receiver of the 2nd Embodiment of this invention. 7 is a flowchart of an antenna switching routine according to a second embodiment of the present invention. It is an example of the menu for order displayed on the screen of the liquid crystal monitor of a car navigation apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10a Master antenna 10b, 10c Slave antenna 20a Master side tuner part 20b, 20c Slave side tuner part 30a Master OFDM part 30b Slave OFDM part 40 Microcomputer 50 MPEG part 60 Switcher 100, 200 Digital television broadcast receiver

Claims (9)

A master OFDM unit that obtains a master symbol by decoding an OFDM signal received from a master antenna;
A slave OFDM unit that decodes an OFDM signal received from one of a plurality of slave antennas to obtain a slave symbol;
Combining means for combining the master symbol and the slave symbol to obtain a combined symbol;
Selection means for selecting a slave antenna from which the slave OFDM unit should receive an OFDM signal based on a predetermined criterion;
The predetermined criterion includes a bit error rate of the combined symbol exceeding a first predetermined value and an electric field strength of an OFDM signal received from the master antenna exceeding a second predetermined value. A broadcast receiver characterized by that. Whether the field intensity of the OFDM signal received from the master antenna exceeds the second predetermined value is determined from the auto gain control level of the master tuner that tunes the OFDM signal received from the master antenna. The broadcast receiving apparatus according to claim 1 , wherein: The broadcast reception according to claim 1 or 2 , wherein the predetermined criterion includes that an electric field strength of an OFDM signal currently received by the slave OFDM unit is lower than a third predetermined value. apparatus. Whether the field strength of the OFDM signal currently received by the slave OFDM unit is lower than the third predetermined value is determined based on the OFDM signal received from the slave antenna from which the slave OFDM unit is currently receiving the OFDM signal. 4. The broadcast receiving apparatus according to claim 3 , wherein the broadcast receiving apparatus is determined from an auto gain control level of a slave tuner that performs tuning. The broadcast receiving device is:
Tuning the OFDM signal received from the master antenna, processing the OFDM signal and sending it to the master OFDM unit;
A slave-side tuner that tunes the OFDM signal received from any one of the plurality of slave antennas and that processes the OFDM signal and sends it to the slave OFDM unit;
Have
The selection means selects a slave antenna from which the slave tuner should receive an OFDM signal based on the predetermined criterion.
The broadcast receiving apparatus according to any one of claims 1 to 4 , wherein the broadcast receiving apparatus is characterized. The broadcast receiving device is:
Tuning the OFDM signal received from the master antenna, processing the OFDM signal and sending it to the master OFDM unit;
A plurality of slave-side tuners that tune the OFDM signals received from each of the plurality of slave antennas and that process the OFDM signals and selectively send them to the slave OFDM unit;
The selecting means selects, from the plurality of slave-side tuners, a slave-side tuner that is to transmit the processed OFDM signal to the slave OFDM unit based on the predetermined criterion.
The broadcast receiving apparatus according to any one of claims 1 to 4 , wherein the broadcast receiving apparatus is characterized. The predetermined criterion is that the field strength of the OFDM signal received by the slave tuner currently selected by the selection means is lower than the field strength of the OFDM signal received by another slave tuner. The broadcast receiving apparatus according to claim 6 , comprising: Whether the field strength of the OFDM signal received by the slave tuner currently selected by the selection means is lower than the field strength of the OFDM signal received by the other slave side tuners is determined by the plurality of slave sides. The broadcast receiving apparatus according to claim 7 , wherein the broadcast receiving apparatus is determined from an auto gain control level of a tuner. The selection means switches the slave antenna from which the slave OFDM unit should receive an OFDM signal after the slave antenna has received an OFDM signal corresponding to a specific symbol,
After the switching is completed, the reception of the OFDM signal by the slave antenna is resumed from the beginning of the next symbol.
The broadcast receiving apparatus according to any one of claims 1 to 8 , wherein the broadcast receiving apparatus is provided.

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