Abstract:
Each of channel searching means comprises means for judging, when a search for the subsequent channel is started, whether or not receivable channel information or information indicating that receiving is impossible is stored in a channel map with respect to the subsequent channel, means for starting the search for the subsequent channel when the receivable channel information or the information indicating that receiving is impossible is not stored in the channel map with respect to the subsequent channel, and means for terminating the channel search when the receivable channel information or the information indicating that receiving is impossible is stored in the channel map with respect to the subsequent channel.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a broadcasting receiver and a channel searching method in the broadcasting receiver, and more particularly, to a broadcasting receiver having two digital receiving units and a channel searching method in the broadcasting receiver having the two digital receiving units. 
     2. Description of the Prior Art 
     In recent years, ground wave digital television broadcasting has been developed. The transition from current analog broadcasting to digital broadcasting is being made. In a period of the transition, it has been expected that a channel map is frequently changed by newly opening a digital broadcasting station and changing frequencies, for example. Therefore, a receiver is required to make an efficient channel search. 
     On the other hand, smooth channel selection can be carried out by previously recognizing on which channel (frequency) broadcasting is being performed in the case of receiving, that is, on which channel broadcasting is receivable. Channels on which broadcasting is being performed differ for each area. Therefore, a channel map is produced by making a search over all broadcasting channels to determine on which channel broadcasting is being performed when a receiver is installed. 
     The channel search is made by tuning in to channels in a predetermined order with respect to a tuner and judging whether or not broadcasting is being performed on the channel based on whether or not a normal signal to be received can be obtained from the tuner. 
     Description is now made of an example of the channel searching operation of the receiver using  FIG. 1 . 
       FIG. 1  illustrates the configuration of a broadcasting receiver. 
     The broadcasting receiver comprises two groups of digital receiving units for receiving ground wave digital broadcasting. One of the digital receiving units comprises a first digital tuner  101 , a first digital demodulator  102 , and a first TS decoder  103 . The other digital receiving unit comprises a second digital tuner  201 , a second digital demodulator  202 , and a second TS decoder  203 . 
     A microcomputer  300  receives, through a remote control signal receiver  301  for receiving an operation signal transmitted by radio from a remote control  401  or a main body operation key  302 , the operation signal. The microcomputer  300  starts a channel searching operation by receiving an operation signal representing a channel search command. 
     The channel search has been conventionally made using the one digital receiving unit. That is, the microcomputer  300  outputs to the first digital tuner  101  a channel selection instruction for tuning in to a channel having the lowest frequency on which broadcasting may be performed when it receives the operation signal representing the channel search command. Out of signals inputted to the digital tuner  101  from the ground wave broadcasting antenna  100 , the signal selected by the digital tuner  101  is inputted to the first digital demodulator  102 , and is subjected to demodulation processing conforming to a modulation system. Generally, a digital TV broadcasting signal is subjected to OFDM (Orthogonal Frequency Demodulation Multiplexing) modulation, for example, and is subjected to OFDM demodulation by the first digital demodulator  102 . 
     If a normal signal is broadcast, it is outputted as an MPEG (Motion Picture Expert Group) transport stream after being previously subjected to processing for error correction. The demodulated MPEG transport stream is subjected to decoding processing by the first TS decoder  103 , and is outputted as elementary streams such as a video, an audio, etc., so that a video signal and an audio signal are restored by a video/audio decoder  104 . 
     The microcomputer  300  judges whether or not a normal digital signal is received on the channel which the digital tuner  101  is instructed to tune in to on the basis of the state of the first digital demodulator  102 . Specifically, it is judged whether or not the normal digital signal is broadcast depending on whether or not the first digital demodulator  102  can establish synchronization of the received digital signal. However, a method of judging whether or not the normal digital signal is received is not necessarily limited to the same. 
     Information such as a broadcasting station name sent from a broadcasting station is acquired on the basis of data obtained by the first TS decoder  103 . The presence or absence of broadcasting may be judged depending on whether or not the broadcasting station name can be specified. When it is judged that the normal digital signal is received, the microcomputer  300  stores in a memory  303  information for channel selection (receivable channel information) such as a frequency, a broadcasting station name, and a channel number. 
     The microcomputer  300  then outputs an instruction to tune in to a channel on the high frequency side adjacent to the current channel, for example. The microcomputer  300  judges whether or not the normal digital signal is received on the channel tuned in to in the same manner as described above, and stores in the memory  303  information for channel selection (receivable channel information) such as a frequency, a broadcasting station name, and a channel number when it is judged that the normal digital signal is received. Such an operation is repeated over all channels, to store in the memory  303  receivable channel information indicating on which channel broadcasting is being performed. 
     At the time of a normal operation, the microcomputer  300  receives a channel selection instruction from a user through the remote control signal receiver  301  or the main body operation key  302 , and refers to data in the memory  303 , thereby outputting to the first digital tuner  101  a channel selection instruction corresponding to the channel desired by the user. 
     As described in the foregoing, in the channel search for digital broadcasting, it is judged whether or not a normal signal can be received, and it is necessary to confirm the contents of digital data in order to extract a broadcasting station name or the like. Therefore, it generally takes much time to judge whether or not broadcasting is being performed on the channel. 
     Furthermore, in Japanese ground wave digital broadcasting, there are a plurality of types of broadcasting modes, and all combinations of the modes must be tried. Therefore, it takes more time to make the judgment. Thus, the channel search for digital broadcasting requires more time than the channel search for conventional analog broadcasting. When a channel search must be frequently made as in a period of transition to digital broadcasting, a viewer is forced to feel inconvenience. 
     An example of a VTR-integrated receiver is one comprising two groups of digital receiving units, as shown in  FIG. 1 . In such a receiver, it is considered that a channel search is made using the two digital receiving units. That is, channels to be searched for are previously divided into two groups, to search for each of the channels in the one group using the one digital receiving unit, while searching for each of the channels in the other group using the other digital receiving unit. 
     When a channel search is made by such a method, a processing time period can be made shorter, as compared with that in a case where a channel search is made using only one digital receiving unit. Even in the search for one channel, however, a search time period differs depending on whether or not there is broadcasting. When the number of channels handled by each of the digital receiving units is fixedly assigned, as described above, it takes longer to make the channel search using the one digital receiving unit than the channel search using the other digital receiving unit. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a broadcasting receiver capable of efficiently making a channel search and a channel searching method in the broadcasting receiver. 
     In a broadcasting receiver comprising a broadcasting receiving unit for receiving a television broadcasting signal, and a memory for storing a channel map storing for each of broadcasting channels receivable channel information or information indicating that receiving is impossible, the broadcasting receiving unit comprising a first digital receiving unit and a second digital receiving unit, a broadcasting receiver according to the present invention is characterized by comprising first channel searching means for tuning in to the broadcasting channels in a predetermined order using the first digital receiving unit, judging for each of the broadcasting channels whether or not broadcasting is receivable, and storing, with respect to the broadcasting channel on which broadcasting is receivable, the receivable channel information in the channel map, while storing, with respect to the broadcasting channel on which broadcasting is not receivable, the information indicating that receiving is impossible; and second channel searching means for tuning in to the broadcasting channels in an order opposite to the first channel searching means using the second digital receiving unit, judging for each of the broadcasting channels whether or not broadcasting is receivable, and storing, with respect to the broadcasting channel on which broadcasting is receivable, the receivable channel information in the channel map, while storing, with respect to the broadcasting channel on which broadcasting is not receivable, the information indicating that receiving is impossible, each of the channel searching means comprising means for judging, when a search for the subsequent channel is started, whether or not the receivable channel information or the information indicating that receiving is impossible is stored in the channel map with respect to the subsequent channel, means for starting the search for the subsequent channel when the receivable channel information or the information indicating that receiving is impossible is not stored in the channel map with respect to the subsequent channel, and means for terminating the channel search when the receivable channel information or the information indicating that receiving is impossible is stored in the channel map with respect to the subsequent channel. 
     The first channel searching means searches for the channels in ascending order of their frequencies, for example, and the second channel searching means searches for the channels in descending order of their frequencies, for example. 
     Each of the digital receiving units comprises a digital tuner for selecting a channel to be received, and a digital demodulator for demodulating a signal on the selected channel, and each of the channel searching means judges whether or not digital broadcasting is receivable on the channel to be received currently selected depending on whether or not the digital demodulator can establish synchronization of a received signal. 
     In a channel searching method in a broadcasting receiver comprising a broadcasting receiving unit for receiving a television broadcasting signal, and a memory for storing a channel map storing for each of broadcasting channels receivable channel information or information indicating that receiving is impossible, the broadcasting receiving unit comprising a first digital receiving unit and a second digital receiving unit, a channel searching method in a broadcasting receiver according to the present invention is characterized by comprising a first channel searching step for tuning in to the broadcasting channels in a predetermined order using the first digital receiving unit, judging for each of the broadcasting channels whether or not broadcasting is receivable, and storing, with respect to the broadcasting channel on which broadcasting is receivable, the receivable channel information in the channel map, while storing, with respect to the broadcasting channel on which broadcasting is not receivable, the information indicating that receiving is impossible, and second channel searching step for tuning in to the broadcasting channels in an order opposite to the first channel searching step using the second digital receiving unit, judging for each of the broadcasting channels whether or not broadcasting is receivable, and storing, with respect to the broadcasting channel on which broadcasting is receivable, the receivable channel information in the channel map, while storing, with respect to the broadcasting channel on which broadcasting is not receivable, the information indicating that receiving is impossible, each of the channel searching steps comprising the steps of judging, when a search for the subsequent channel is started, whether or not the receivable channel information or the information indicating that receiving is impossible is stored in the channel map with respect to the subsequent channel, starting the search for the subsequent channel when the receivable channel information or the information indicating that receiving is impossible is not stored in the channel map with respect to the subsequent channel, and terminating the channel search when the receivable channel information or the information indicating that receiving is impossible is stored in the channel map with respect to the subsequent channel. 
     The first channel searching step comprises the step of searching for the channels in ascending order of their frequencies, for example, and the second channel searching step comprises the step of searching for the channels in descending order of their frequencies, for example. 
     Each of the digital receiving units comprises a digital tuner for selecting a channel to be received, and a digital demodulator for demodulating a signal on the selected channel, and each of the channel searching steps comprises the step of judging whether or not digital broadcasting is receivable on the channel to be received currently selected depending on whether or not the digital demodulator can establish synchronization of a received signal. 
     The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram showing the configuration of a broadcasting receiver; 
         FIG. 2  is a flow chart showing the procedure for channel searching processing using a first digital receiving unit; and 
         FIG. 3  is a flow chart showing the procedure for channel searching processing using a second digital receiving unit. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to the drawings, an embodiment of the present invention will be described. 
     Also in the present embodiment, the configuration of a broadcasting receiver (a hardware configuration) is also the same as the configuration of the conventional broadcasting receiver shown in  FIG. 1 . 
       FIGS. 2 and 3  show the procedure for channel searching processing. 
       FIG. 2  shows the procedure for channel searching processing using a first digital receiving unit, and  FIG. 3  shows the procedure for channel searching processing using a second digital receiving unit. Both the channel searches are simultaneously started. 
     First referring to  FIG. 2 , the channel searching processing using the first digital receiving unit will be described. 
     When a channel search is started (step S 101 ), a microcomputer  300  clears the contents of a channel map stored in a memory  303  (step S 102 ). Further, the microcomputer  300  gives a first digital tuner  101  an instruction to tune in to a receivable channel having the lowest frequency (a channel selection instruction) (step S 103 ). As described later, it gives a second digital tuner  201  an instruction to tune in to a receivable channel having the highest frequency (a channel selection instruction). 
     The first digital tuner  101  selects a broadcasting signal corresponding to the channel which it is instructed to tune in to (step S 104 ). The selected broadcasting signal is demodulated by a first digital demodulator  102 , and is subjected to data separation processing by a first TS decoder  103 . At this time, it is judged whether or not there is broadcasting depending on whether or not synchronization can be ensured and whether or not a broadcasting station can be recognized from output data from the TS decoder  103  by the status of the first digital demodulator  102  (step S 105 ). 
     When it is judged in the foregoing step S 105  that there is broadcasting (synchronization can be ensured and a broadcasting station can be recognized), receivable channel information indicating that the current channel is one on which digital broadcasting is performed, which broadcasting station is performing broadcasting, and what modulation system is used, for example, is stored in the channel map inside the memory  303  (step S 106 ). The procedure then proceeds to the step S 108 . 
     When it is judged in the foregoing step S 105  that there is no broadcasting (no synchronization can be ensured or no broadcasting station can be recognized), information indicating that no broadcasting is being performed on the channel currently tuned in to (information indicating that receiving is impossible) is stored in the channel map inside the memory  303  (step S 107 ). The procedure then proceeds to the step S 108 . 
     In the step S 108 , the microcomputer  300  judges by referring to the channel map inside the memory  303  whether or not a search for a channel on the high frequency side adjacent to the current channel has already been terminated. That is, the microcomputer  300  judges that the search for the channel using the second digital receiving unit has already been terminated when receivable channel information or information indicating that no broadcasting is being performed is stored in the channel map with respect to the channel on the high frequency side adjacent to the current channel, while judging that the search for the channel using the second digital receiving unit has not been terminated when neither of the information is stored in the channel map. 
     When it is judged in the foregoing step S 108  that the search for the channel on the high frequency side adjacent to the current channel is not terminated, an instruction to tune in to the channel on the high frequency side adjacent to the current channel is given to the first digital tuner  101  (step S 109 ). The processing in the steps S 104  to S 108  is performed again. 
     When it is judged in the foregoing step S 108  that the search for the channel on the high frequency side adjacent to the current channel has already been terminated, the channel search using the first digital receiving unit is terminated (step S 110 ). 
     Referring now to  FIG. 3 , the channel searching processing using the second digital receiving unit will be described. 
     When a channel search is started (step S 201 ), the microcomputer  300  clears the contents of the channel map stored in the memory  303  (step S 202 ). Further, the microcomputer  300  gives the second digital tuner  201  an instruction to tune in to a receivable channel having the highest frequency (a channel selection instruction) (step S 203 ). 
     The second digital tuner  201  selects a broadcasting signal corresponding to the channel which it is instructed to tune in to (step S 204 ). The selected broadcasting signal is demodulated by a second digital demodulator  202 , and is subjected to data separation processing by a second TS decoder  203 . At this time, it is judged whether or not there is broadcasting depending on whether or not synchronization can be ensured and whether or not a broadcasting station can be recognized from output data from the TS decoder  203  by the status of the second digital demodulator  202  (step S 205 ). 
     When it is judged in the foregoing step S 205  that there is broadcasting (synchronization can be ensured and a broadcasting station can be recognized), receivable channel information indicating that the current channel is one on which digital broadcasting is performed, which broadcasting station is performing broadcasting, and what modulation system is used, for example, is stored in the channel map inside the memory  303  (step S 206 ). The procedure then proceeds to the step S 208 . 
     When it is judged in the foregoing step S 205  that there is no broadcasting (no synchronization can be ensured or no broadcasting station can be recognized), information indicating that no broadcasting is being performed on the channel currently tuned in to is stored in the channel map inside the memory  303  (step S 207 ). The procedure then proceeds to the step S 208 . 
     In the step S 208 , the microcomputer  300  judges by referring to the channel map inside the memory  303  whether or not a search for a channel on the low frequency side adjacent to the current channel has already been terminated. That is, the microcomputer  300  judges that the search using the first digital receiving unit has already been terminated when receivable channel information or information indicating that no broadcasting is being performed is stored in the channel map with respect to the channel on the low frequency side adjacent to the current channel, while judging that the search using the first digital receiving unit has not been terminated when neither of the information is stored in the channel map. 
     When it is judged in the foregoing step S 208  that the search for the channel on the low frequency side adjacent to the current channel is not terminated, an instruction to tune in to the channel on the low frequency side adjacent to the current channel is given to the second digital tuner  201  (step S 209 ). The processing in the steps S 204  to S 208  is performed again. 
     When it is judged in the foregoing step S 208  that the search for the channel on the low frequency side adjacent to the current channel has already been terminated, the channel search using the second digital receiving unit is terminated (step S 210 ). 
     According to the above-mentioned embodiment, the channel search can be efficiently made in the broadcasting receiver comprising the two digital receiving units. 
     Although the present invention has been described and illustrated in detail, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the spirit and scope of the present invention being limited only by the terms of the appended claims.