Abstract:
An apparatus and a method capable of receiving digital broadcasting without image discontinuity during channel switching. A digital multimedia broadcasting receiver buffers a previous channel while a new channel is buffered in a deinterleaver, thereby preventing image discontinuity during channel switching. The digital broadcasting receiver receives and deinterleaves broadcast data of a channel to be changed and stores the deinterleaved broadcast data in a buffer when a broadcast channel change is requested. The digital broadcasting receiver outputs and displays broadcast data of an initial channel stored in the buffer and stops output of the broadcast data of the initial channel and outputs the broadcast data of the channel to be changed, when the broadcast data of the channel to be changed are stored in the buffer by a predetermined buffering size.

Description:
PRIORITY  
       [0001]     This application claims priority to an application entitled “Apparatus And Method For Receiving Digital Multimedia Broadcasting Without Image Discontinuity During Channel Switching” filed in the Korean Intellectual Property Office on Sep. 20, 2004 and assigned Serial No. 2004-75136, the contents of which are incorporated herein by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates generally to digital broadcasting, and more particularly to an apparatus and a method capable of receiving digital broadcasting without image discontinuity during channel switching.  
         [0004]     2. Description of the Related Art  
         [0005]     Digital broadcasting, in particular, digital multimedia broadcasting (DMB) utilizing a system E scheme of an international telecommunication union (ITU) proposes convolutional interleaving/deinterleavirig. According to the convolutional interleaving, a DMB transmitter temporarily stores several input bits, delays the input bits for a predetermined period of time and outputs the delayed input bits when transmitting broadcasting data. Consequently, several bits delayed and output are interleaved between two bits adjacent to each other at the time of input. Accordingly, the DMB transmitter obtains a data stream having a sequence different from an input sequence through an interleaving and transmits the interleaved data stream.  
         [0006]     A DMB receiver deinterleaves the interleaved data stream received from the DMB transmitter and restores the data stream to an original input bit sequence. When a continuous burst error has occurred in a portion of the interleaved data stream transmitted from the DMB transmitter, the data stream, having been restored to the original input bit sequence through the deinterleaving process, has a random error changed from the burst error. Accordingly, a viterbi decoder of the DMB receiver can effectively perform an error correction.  
         [0007]     When a broadcasting channel is switched, the DMB transmitter fills buffers of a deinterleaver for a changed broadcasting channel (i.e., performs deinterleaving) and then displays the changed broadcasting channel. Accordingly, whenever a broadcasting channel is switched, a period of time is required for the buffer of the deinterleaver to empty and then fill. In the conventional DMB receiver, a period of time from 0.264 seconds at minimum to 6.514 seconds may be required for a deinterleaver buffering.  
         [0008]     Additionally, when considering a period of time for which the DMB receiver divides the deinterleaved and error-corrected broadcasting data into audio data and video data and processes the audio data and video data, the DMB receiver does not display anything for more than several seconds. Accordingly, a user&#39;s viewing is interrupted with image discontinuity such as blue screen every time prior to watching other broadcasting channels.  
       SUMMARY OF THE INVENTION  
       [0009]     Accordingly, the present invention has been designed to solve the above and other problems occurring in the prior art, and an object of the present invention is to provide an apparatus and a method for receiving a DMB capable of preventing image discontinuity during channel switching.  
         [0010]     In accordance with one aspect of the present invention, there is provided a method for changing broadcasting channels in a digital broadcasting receiver. The method includes the steps of: receiving and deinterleaving broadcasting data of a channel to be changed and storing the deinterleaved broadcasting data in a buffer, when a broadcasting channel change is requested; outputting and displaying broadcasting data of an initial channel stored in the buffer; and stopping output of the broadcasting data of the initial channel and outputting the broadcasting data of the channel to be changed, when the broadcasting data of the channel to be changed are stored in the buffer by a predetermined buffering size.  
         [0011]     In accordance with another aspect of the present invention, there is provided a digital broadcasting receiver including: a deinterleaver for receiving and deinterleaving broadcasting data of a channel to be changed when a broadcasting channel change is requested; a buffer for storing broadcasting data of an initial channel and outputting the broadcasting data of the initial channel until the broadcasting data of the channel to be changed are stored by a predetermined buffering size; and a display unit for providing a user with the broadcasting data output from the buffer. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]     The above and other objects, features, and advantages of the present invention will be more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which:  
         [0013]      FIG. 1  is a block diagram illustrating a DMB receiver according to an embodiment of the present invention;  
         [0014]      FIG. 2  is a flow diagram illustrating a DMB reception process according to an embodiment of the present invention;  
         [0015]      FIG. 3  is an exemplary view illustrating a screen displayed during channel switching according to an embodiment of the present invention; and  
         [0016]      FIG. 4  is a timing chart illustrating a state of buffering based on a DMB reception process according to an embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0017]     Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following description of the present invention, a detailed description of known functions and configuration incorporated herein will be omitted when it may make the subject matter of the present invention rather unclear.  
         [0018]      FIG. 1  is a block diagram illustrating a DMB receiver according to an embodiment of the present invention. Referring to  FIG. 1 , the DMB receiver includes a bit deinterleaver  400  for deinterleaving interleaved data by the bit and changing a bit unit of burst error to a random error, a viterbi decoder  410  for error-correcting the deinterleaved data, which are output from the bit deinterleaver  400 , by the bit, a byte deinterleaver  420  for deinterleaving the data output from the viterbi decoder  410  by the byte and changing a byte unit of burst error to a random error, a an RS decoder  430  for error-correcting the deinterleaved data, which are output from the byte deinterleaver  420 , by the byte, and a buffer  440 , which is disposed between the RS decoder  430  and a demux  450 . An existing memory provided in the DMB receiver may be used as the buffer  440  or a new memory may be provided. The data output from the RS decoder  430  is stored in the buffer  440  before being input to the demux  450 , which divides the data output from the buffer  440  into audio data and video data.  
         [0019]     An audio buffer  460  stores the audio data output from the demux  450  and a video buffer  470  stores the video data output from the demux  450 . A user interface  480  includes a key pad for receiving a key input for a user a speaker for outputting the audio data output from the audio buffer  460  as a sound signal capable of being recognized by the user, and a display unit for displaying the video data output from the video buffer  470  as an image capable of being recognized by the user.  
         [0020]      FIG. 2  is a flow diagram illustrating a DMB reception process according to an embodiment of the present invention. Referring to  FIG. 2 , when a user watching a DMB attempts broadcasting channel switching by means of the key pad of the user interface  480  of  FIG. 1  in step S 100 , the DMB receiver receives interleaved broadcasting data of the changed channel from a DMB transmitter. According to one embodiment of the present invention, it is possible to change the size (i.e., buffering size) of data, which must be stored in the buffer  440  for a display of the broadcasting data of the changed channel. In step S 110 , the DMB receiver determines a buffering size based on interleaving depth of the broadcasting data.  
         [0021]     The interleaving depth used in an interleaving indicated by an m-value. As the m-value increases, the DMB transmitter performs an interleaving process for broadcasting data to be transmitted more frequently. As a result, the ratio at which a burst error is changed to a random error increases and the viterbi decoder  410  has increased error correction ability. The DMB receiver can recognize the m-value through code division multiplexing (CDM) configuration information of a pilot channel  100 , that is, broadcasting channel configuration information.  
                                                     TABLE 1                       The number       Required           of m   Total bit   Time   Buffer Size                                53   67,575   0.264 s    44.8 packets   8.5   Kbytes       109   138,975   0.543 s    92.2 packets   17.3   Kbytes       218   277,950   1.086 s    184.5 packets   34.6   Kbytes       436   555,900   2.171 s    368.9 packets   69.3   Kbytes       654   833,850   3.257 s    553.4 packets   104   Kbytes       981   1,250,775   4.886 s    830.3 packets   156   Kbytes       1308   1,667,700   6.514 s   1106.9 packets   208   Kbytes                  
 
         [0022]     Table 1 shows the number of bits used in an interleaving according to the m-value, that is, the number of bits interleaved between adjacent two bits of broadcasting data by an interleaving, and the size of the buffer  440  corresponding to the number of bits. The DMB receiver can dynamically assign a memory according to the m-value.  
         [0023]     For example, in order to buffer broadcasting data transmitted through a service of a DMB provider, which selects an m-value  654  and provides the service, it is necessary to provide the buffer  440  having a size of 553.4 packets, that is, 104 Kbytes. Further, in order to deinterleave and error-correct the broadcasting data of the m-value  654  in the DMB receiver, 3.257 seconds are required. That is, 3.257 seconds are required for buffering the broadcasting data of the m-value  654  in the buffer  440 .  
         [0024]     In step S 120 , broadcasting data of a channel before the channel switching remaining in the buffer  440  is output to the demux  450 . The buffer  440  stores the broadcasting data corresponding to a buffering size determined based on an m-value of a previous channel. The demux  450  divides the input broadcasting data into the audio data and the video data, stores the audio data in the audio buffer  460 , and stores the video data in the video buffer  470 . The stored audio data and video data are output as a sound signal and an image capable of being recognized by a user through the speaker and the display unit of the user interface  480 . Step S 120  is continuously performed while the steps S 130  and S 140  are performed.  
         [0025]     In step S 130 , the DMB receiver deinterleaves and error-corrects the received broadcasting data of the changed channel and stores the broadcasting data in the buffer  440 . That is, the broadcasting data of the channel before the channel switching stored in the buffer  440  are output to the demux  450  through step S 120 .  
         [0026]     Simultaneously, the deinterleaved and error-corrected broadcasting data of the changed channel are stored in the empty space of the buffer  440  through step S 130 .  
         [0027]     In step S 140 , the DMB receiver determines if the broadcasting data of the changed channel corresponding to a buffering size determined based on an m-value has been stored in the buffer  440 . When a buffering has been completed, the broadcasting data stored in the buffer  440  is input to the demux  450 . That is, in step S 150 , the demux  450  divides the input broadcasting data into the audio data and the video data, stores the audio data in the audio buffer  460  and stores the video data in the video buffer  470 . The stored audio data and video data are output as a sound signal and an image capable of being recognized by the user through the speaker and the display unit of the user interface  480 .  
         [0028]     According to the present invention, the broadcasting data of the channel before the channel switching stored in the buffer  440  are continuously displayed until the broadcasting data of the changed channel are displayed, such that image discontinuity during the channel switching can be prevented.  
         [0029]     Although a case in which the buffering size is changed has been described in the present embodiment, it is noted that it is possible to fix the buffering size. For example, when the buffering size is fixed to a value corresponding to the largest m-value or the m-value can be fixed and S 110  can be omitted when the same m-value is used in all broadcasting channels.  
         [0030]     Meanwhile, although the user has changed a channel, the user may be confused due to the continuous display of a previous channel. A solution to this problem will be described herein below with reference to  FIG. 3 .  
         [0031]      FIG. 3  is an exemplary view illustrating a screen displayed during channel switching according to an embodiment of the present invention. Referring to  FIG. 3 , while the broadcasting data of the channel before the channel switching remaining in the buffer  440  are displayed, the display unit of the user interface  480  displays a message such as “Channel is being switched.” and prevents the user from being confused.  
         [0032]      FIG. 4  is a timing chart illustrating a state of buffering based on a DMB reception process according to an embodiment of the present invention. t is noted that the embodiment of  FIG. 4  illustrates using the service of the DMB provider, which selects the m-value  654  and provides the service as an example, and does not consider a time for processing audio/video data except for a delay time according to a deinterleaving and error correction time.  
         [0033]     Referring to  FIG. 4 , when the user attempts to watch a broadcasting by means of the key pad of the user interface  480  of  FIG. 1 , the DMB receiver receives broadcasting data of an initial set channel (‘CH#1’) from the DMB transmitter. The broadcasting data of the received CH# 1  are deinterleaved and error-corrected by the bit deinterleaver  400 , the viterbi decoder  410 , the byte deinterleaver  420 , and RS decoder  430 . A time required for performing the above process is 3.257 seconds (T 1 ), which is a delay time according to the m-value  654 .  
         [0034]     The DMB receiver stores the deinterleaved and error-corrected broadcasting data of CH# 1  in the buffer  440 . That is, the processed CH# 1  broadcasting data corresponding to 553.4 packets (i.e., 104 Kbytes) is stored in the buffer  440  according to the m-value  654 . After storing the 104 Kbyte broadcasting data of CH# 1  in the buffer  440 , the DMB receiver deinterleaves and error-corrects 104 Kbyte broadcasting data of CH# 1  following the stored data. A time required for performing this process is 3.257 seconds (T 2 ), which is the delay time according to the m-value  654 , similarly to T 1 .  
         [0035]     In a T 3 , the DMB receiver outputs the first 104 Kbyte broadcasting data of CH#1 stored in the buffer  440  to the demux  450  and simultaneously stores the second 104 Kbyte broadcasting data of CH# 1  in an empty buffer space of the buffer  440 . Further, the broadcasting data of CH# 1  output to the demux  450  is output as a sound signal and an image capable of being recognized by the user through the audio buffer  460 , the video buffer  470 , the speaker, and the display unit of the user interface  480 . Therefore, the broadcasting of CH# 1  starts (T 3 ).  
         [0036]     When the user changes CH# 1  to a CH# 2  (T′), the DMB receiver receives broadcasting data of CH# 2 . Further, the DMB receiver deinterleaves and error-corrects the interleaved broadcasting data of CH# 2  and outputs the broadcasting data of CH# 1  remaining in the buffer  440  to the demux  450 , while performing the deinterleaving and error-correction. Accordingly, the 104 Kbyte broadcasting data of CH# 1  according to the m-value  654  remains in the buffer  440  and the DMB receiver controls the broadcasting data to be displayed for 3.257 seconds, equal to the delay time according to the m-value  654  of the changed channel. The DMB receiver outputs the broadcasting data of CH# 1  remaining in the buffer  440  to the demux  450  and simultaneously stores the deinterleaved and error-corrected broadcasting data of CH# 2  in an empty space of the buffer  440 . Because the m-value of CH# 2  is identical to that of CH# 1 , a time for which the interleaved broadcasting data is deinterleaved and error-corrected is also 3.257 seconds. Accordingly, the time is identical to a broadcasting time of the remaining broadcasting data of CH# 1  (T 4 ).  
         [0037]     Herein, the display unit of the user interface  480 , which displays the broadcasting data of CH# 1  for T 4 , displays a message such as “Channel is being switched”, as illustrated in  FIG. 3  and prevents the user from being confused.  
         [0038]     When T 4  (i.e., 3.257 seconds) passes and all broadcasting data of CH# 1  remaining in the buffer  440  are transferred to the user, it becomes the time point T′ at which the broadcasting data of CH# 2  are continuously transferred to the user without image discontinuity during channel switching. That is, the time point ‘T’ is a time point at which all broadcasting data of CH# 1  remaining in the buffer  440  are output and the 104 Kbyte broadcasting data of CH# 2  stored in the buffer  440  are transferred to the user through the demux  450 , the audio buffer  460 , the video buffer  470 , the speaker, and the display unit of the user interface  480 . The broadcasting data of CH# 2  stored in the buffer  440  are transferred to the user and simultaneously the following broadcasting data of CH# 2  stored in an empty space of the buffer  440 . Therefore, deinterleaved and error-corrected broadcasting data of CH# 2  are continuously stored in the buffer  440  (T 5 ).  
         [0039]     Accordingly, the user does not watch a blank screen during the channel switching. Further, the DMB receiver performs the above processes, thereby continuously transferring the changed channel to the user without image discontinuity during the channel switching.  
         [0040]     According to the present invention as described above, when a user of a DMB receiver changes a channel, the broadcasting of the changed channel is provided to the user without image discontinuity.  
         [0041]     Further, according to the present invention, because a DMB service provider can provide a user with a broadcasting service without image discontinuity, the user does not experience a delay occurring during channel switching.  
         [0042]     Furthermore, according to the present invention, because a user can watch the next channel without image discontinuity and a blank screen, the user can accept the same feeling as that in the conventional terrestrial TV receiver. Accordingly, the satisfaction for a DMB service can increase.  
         [0043]     Although preferred embodiments of the present invention have been described for illustrative purposes, those skilled in the art will appreciate that various modifications, additions, and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims, including the full scope of equivalents thereof.