Abstract:
The invention provides a method for receiving digital broadcast signals of a plurality of channels. The method comprises: storing a channel-parameter contrast table which includes parameter values of a plurality of parameters with which each of the plurality of channels is previously received; testing whether the digital broadcast signals of one of the plurality of channels can be received according to the parameter values stored in the channel-parameter contrast table to determine a receiving status; generating a plurality of channel numbers corresponding to each of the receivable channels of the plurality of channels according to the receiving statuses of the plurality of channels; and receiving the signals of a target channel according to the parameter values stored in the channel-parameter contrast table, wherein the target channel is one of the plurality of channels and selected by a user through the plurality of channel numbers.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to digital broadcasts, and more particularly to receiving digital broadcasts. 
     2. Description of the Related Art 
     Digital television can provide better video quality and audio quality. It can also provide value-added services derived from digital television broadcasts. Because the value-added services bring great profits, enterprises in advanced countries are competing to develop business in this field, and the television broadcasts is gradually being transformed from traditional analog systems to digital systems. If television signals are broadcasted from traditional analog systems, the signal strength tends to be subject to the landforms in the transmission path, but the television signals broadcast from digital systems are not interfered with by the landforms in the transmission path. Additionally, bandwidth utilization of digital broadcasting is more efficient than that of analog broadcasting. Most importantly, digital broadcasts can provide a variety of value-added services derived from data broadcasting. 
     The digital broadcast signal-transmission mediums include cable, satellite, microwave, and terrestrial. The current digital terrestrial television broadcasting (DTTB) standard includes the Advanced Television System Committee (ATSC) standard of the United States, the Digital Video Broadcasting-Terrestrial (DVB-T) standard of Europe, and the Integrated Services Digital Broadcasting-Terrestrial (ISDB-T) standard of Japan. The DVB-T standard was accepted by European Telecommunication Standard Institute (ETSI) in February 1997 as the digital terrestrial television broadcasting standard of Europe (ETS 300 744). Australia, New Zealand, Singapore and Taiwan have also adopted the DVB-T standard for DTTB. 
     Current DVB-T players provide an auto scan function for automatically scanning and setting DVB-T broadcast channels. The scanning mode of the auto scan function includes “all channel scan” for scanning the whole frequency band for all channels in the region, “frequency range scan” for scanning a frequency range for channels, and “programmable user channel” for scanning a single channel set by a user. The mentioned scanning modes scan all channels sequentially through a range of frequency band. Scanning a single channel, however, requires one or two minutes (the bandwidth of a single channel is about 6 MHz), and the time required to scan the entire frequency band depends on the scan range of the frequency band and is about several to ten minutes. This increased time required causes large power consumption when the DVB-T receiver is installed in a notebook computer as the available power is limited. Additionally, if parameters for receiving a channel are not correct and cause errors, the parameters cannot be automatically adjusted, causing further inconveniences. 
     BRIEF SUMMARY OF THE INVENTION 
     Often, the channel frequencies do not always change, and channels seldom need to be scanned before receiving broadcasts. Thus, only reception status of the channels needs to be rechecked so as to shorten the time spent on scanning channels. If the parameters for receiving the channels are incorrect and the channels cannot be received, the parameters can be adjusted according to old workable parameter values stored in a parameter table to try to receive the channels again. 
     The invention provides a method for receiving digital broadcast signals of a plurality of channels. An embodiment of the method comprises: storing a channel-parameter contrast table which includes parameter values of a plurality of previously used parameters with which each of the plurality of channels is previously received; testing whether the digital broadcast signals of one of the plurality of channels can be received according to the parameter values stored in the channel-parameter contrast table to determine a receiving status which indicates whether the one of the plurality of channels is receivable or unreceivable; storing a channel-receiving status contrast table which includes the receiving statuses of the plurality of the channels; generating a plurality of channel numbers corresponding to each receivable channel according to the receiving statuses of the plurality of channels; and receiving the signals of a target channel according to the parameter values stored in the channel-parameter contrast table, wherein the target channel is one of the plurality of channels and selected by a user through the plurality of channel numbers. 
     The invention also provides a device for receiving digital broadcast signals of a plurality of channels. An embodiment of the device comprises: a receiver, receiving the digital broadcast signals; and a controller, coupled to the receiver, storing a channel-parameter contrast table which includes parameter values of a plurality of parameters for receiving each of the plurality of channels in former times, testing whether the digital broadcast signals of one of the plurality of channels can be received by the receiver according to the parameter values stored in the channel-parameter contrast table to determine a receiving status which indicates whether the one of the plurality of channels is receivable or unreceivable, storing a channel-receiving status contrast table which includes the receiving statuses of the plurality of the channels, generating a plurality of channel numbers corresponding to each receivable channel according to the receiving statuses of the plurality of channels, and receiving the signals of a target channel according to the parameter values stored in the channel-parameter contrast table; wherein the target channel is one of the plurality of channels and selected by a user through the plurality of channel numbers. 
     A detailed description is given in the following embodiments with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein: 
         FIG. 1  is a flowchart of a method for receiving DTTB signals according to the invention; 
         FIG. 2  shows a channel-parameter contrast table according to the invention; 
         FIG. 3  shows a channel-receiving status contrast table according to the invention; and 
         FIG. 4  shows a channel-receiving status contrast table whose receiving status column and channel number column are updated after the automatic scan function is executed. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The following description is of the best-contemplated mode of carrying out the invention. This description is made for the purpose of illustrating the general principles of the invention and should not be taken in a limiting sense. The scope of the invention is best determined by reference to the appended claims. 
       FIG. 1  is a flowchart of a method  100  for receiving DTTB signals according to the invention. The method  100  can be implemented by a controller of a device which receives the DTTB signal. The device can receives signals of DTTB channels by implementing the method  100  and may be a DVB-T player, a DVB-T PCI card, a digital television (DTV), a mobile DTV receiver, a DVB-T set top box which transforms digital video signals to analog video signals, and a digital video recorder (DVR) or a personal video recorder (PVR) in which a DTV tuner is installed. The device may also be a DTV tuner installed on a motherboard of a personal computer, such as a personal computer installed with the Media Center operating system. Although the method  100  is illustrated here with the reception of DTTB or DVB-T signals, the method  100  can be implemented by a mobile phone conforming with the digital video broadcasting-handheld (DVB-H) standard to receive signals of DVB-H channels. Furthermore, the method  100  can also be used to receive signals of digital audio broadcasting (DAB) channels. 
     A selection item may be added to the user interface of the DVB-T player or other similar devices so as to be chosen for executing the function of the method  100 . The selection item may be referred to as “smart scan”. Before the smart scan function is executed, whether the frequency of DTTB channels is scanned for the first time must be first determined in step  102 . If the frequency of DTTB channels is scanned for the first time, a channel-parameter contrast table is not currently stored in the system. Thus, the traditional “all channel scan” function can be executed in step  104  to scan frequencies of all channels in the region. The parameters obtained in the scanning of step  104  can then be stored in a channel-parameter contrast table in step  106 . The channel-parameter contrast table records the channels found in the scanning step  104  and the corresponding parameters for receiving the channels. Otherwise, if the frequency of DTTB channels is not scanned for the first time, the system has stored the channel-parameter contrast table which includes parameters for receiving the corresponding channels, and the smart scan function can be directly executed in step  108  according to the parameters stored in the channel-parameter contrast table. 
       FIG. 2  shows a channel-parameter contrast table  200  according to the invention. The table  200  includes two columns: channel name  202  and the parameters  204  for receiving the corresponding channels. Each row of the table  200  corresponds to a channel found in the scanning step  104 . The parameters  204  may include a channel frequency parameter  210 , a channel bandwidth parameter  212 , a video packet identifier (video PID) parameter  214 , an audio packet identifier (audio-PID) parameter  216 , and other parameters  218 . For example, row  250  represents a first channel of Chinese Television System (CTS 1 ), and the parameters corresponding to the channel CTS 1  include a channel frequency of 533 MHz, a frequency bandwidth of 6 MHz, a video PID of 112 Dec (decimal format), an audio PID of 114 Dec (decimal format), and other parameters. 
     Because the channel-parameter contrast table  200  is present, the smart scan function can be executed. The channels  202  stored in each row of the table  200  is tested in step  108  for channel receiving one by one according to the corresponding parameters  204  stored in the table  200 . The receiving status of each channel tested in step  108  is recorded sequentially in a channel-receiving status contrast table in step  110 .  FIG. 3  shows a channel-receiving status contrast table  300  according to the invention. The table  300  includes three columns: channel name  302 , receiving status  304 , and channel number  306 . The channels stored in the channel name  302  column of table  300  are respectively correspondingly identical to those stored in the channel name  202  column of table  200 . For example, both the row  250  of table  200  and the row  250  of table  300  represent the CTS 1  channel. 
     In step  110 , the receiving status of each channel obtained in step  108  is recorded in the receiving status column  304  of table  300  according to the parameters of the tested channels. For example, if the signal of CTS 1  of row  250  is received successfully, the receiving status  304  of CTS 1  is recorded as “◯”. Otherwise, if the signals of CTS 1  of row  250  cannot be received according to the parameters  204  of table  200 , nothing is recorded in the receiving status column  304  of CTS 1 . After all channels of column  302  are tested, the receiving status column  304  of table  300  is completely recorded. The channel number  306  of each receivable channel which is recorded as “◯” is generated in step  110  according to the order of the channels appearing in column  210  of the table  200 . For example, the receiving status  304  corresponding to the CTS 1  channel of row  250  is recorded as “◯”, and the channel frequency  210  of CTS 1  in table  200  is 533 MHz, which is the channel with the smallest channel frequency among all channels in the region. Thus, CTS 1  channel of row  250  is assigned the channel number  306  of “01”. The second channel of Chinese Television System (CTS 2 ) next to the CTS 1  channel is then assigned the channel number  306  of “02”, because its channel frequency  210  is 539 MHz which is the second smallest channel frequency among all channel frequencies. The CTS 3  channel of row  252  is then assigned the channel number  306  of “03”. The Taiwan Public Television Service (PTS) channel of row  254  is not assigned a channel number  306 , because its receiving status  304  is not a “◯”. The DIMO TV channel of row  256  is then assigned the channel number  306  of “04”. The rest may be deduced by analogy. Thus, the channel number column  306  of table  300  is completed and can be taken as a reference for a user to select channels of the region. 
     Whether the receiving status column  304  includes an unreceivable channel is then determined in step  112 . For examples, the PTS channel of row  254 , the unknown channel of row  258 , and the first, second and third channels of Taiwan Television Company (TTV1, TTV2, and TTV3 channels) of row  262 ,  264 , and  266  are unreceivable channels because the respective receiving status  304  of those channels is not recorded as a “O”. If there are no unreceivable channels in receiving status column  304 , a target channel can be selected through the channel numbers  306  of table  300  for directly receiving the target channel according to the corresponding parameters  204  of table  200 . Otherwise, if there is at least one unreceivable channel, whether all of the unreceivable channels have been automatically scanned is determined in step  114  for updating the parameters in the following steps. If there is still an unreceivable channel, the frequency of which has not been automatically scanned, the frequency of the unreceivable channel is automatically scanned in step  116 . The method for scanning an unreceivable channel of table  300  is to search a frequency range from the channel frequency of the last channel to the channel frequency of the next channel for the channel frequency of the unreceivable channel. For example, the PTS channel of row  254  is situated between the CTS 3  channel of row  252  and the DIMO TV channel of row  256 , and the channel frequencies of the CTS 3  and DimoTV channel are respectively 545 and 557 MHz. Thus, the scan range of the PTS channel is from 545 to 557 MHz. For another example, the unknown channel of row  258  is situated between the Dimo TV channel of row  256  and the first channel of Formosa Television Company (FTV1) of row  260 , and the channel frequencies of the Dimo TV and FTV1 channel are respectively 557 and 575 MHz. Thus, the scan range of the unknown channel is from 557 to 575 MHz. 
     Step  118  determines whether the channel frequency of the unreceivable channel is found. If not, the receiving status  304  of the unreceivable channel is recorded as a “X” in step  122 .  FIG. 4  shows a channel-receiving status contrast table  400  whose receiving status column  404  and channel number column  406  is updated from the table  300  after the automatic scan function is executed. The original receiving statuses  304  of the unknown, TTV1, and TTV3 channels are empty in table  300 , and the channel frequencies of those channels still cannot be found in the scanning step  116 . Thus the receiving statuses  404  of those channels are recorded as a “X” Otherwise, if the channel frequency of the unreceivable channel can be found, the parameters  204  for receiving the channel is updated in step  120 , and the channel becomes a receivable channel. For example, the original channel frequency of the PTS channel of row  254  is 551 MHz in the table  200 , and the new channel frequency for receiving the PTS channel is 551.5 MHz. Thus, the channel frequency parameter  210  of the PTS channel is updated with 551.5 MHz. the receiving status  404  of the PTS channel is then updated with a “◯” in step  122  to indicate it&#39;s a receivable channel. For example, the original receiving statuses  304  of the PTS and TTV2 channels are empty in table  300 , but the channel frequencies of those channels are found in the scanning step  116 . Thus the receiving statuses  404  of those channels are recorded as a “◯” 
     Step  114  determines whether any unreceivable channel whose frequency has not been automatically scanned. If there is no unreceivable channel the channel frequency of which has not been scanned in step  114 , there is no empty in the receiving status column  404  of table  400 , and the auto scan function has been executed completely. The channel number  406  of table  400  is then updated in step  124  according to the updated receiving status  404 . The new channel number  406  is generated by sorting all of the receivable channels whose receiving status  404  is a “◯” according to its channel frequency and assigning each receivable channel a new channel number. The unreceivable channel whose receiving status  404  is a “X” is not assigned any channel number. For examples, the original channel number  306  of the PTS channel is empty, but the new channel number  406  of the PTS channel is “04”. The original channel number  306  of the Dimo TV channel of row  255  is “04”, but the new channel number  406  of the Dimo TV channel is “05” because the PTS channel is now receivable. Finally, the user can select a target channel according to the new channel numbers  406  of table  400  and receive the signals of the target channel according to the parameters  204  of the table  200  in step  126 . 
     The invention records the recent parameters for receiving the channels. Every time a user attempts to receive the DTTB signals, the receiving status of the channels are determined according to the stored parameters, and only the unreceivable channels need to be automatically scanned, Thus, the invention can reduce the scan time of channels to facilitate the DTTB reception. 
     While the invention has been described by way of example and in terms of preferred embodiment, it is to be understood that the invention is not limited thereto. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.