Patent Publication Number: US-2011072468-A1

Title: Digital broadcast receiver and broadcast data display method for simultaneous display of multi-channel visual images

Description:
PRIORITY 
     This application is a Divisional Application of U.S. patent application Ser. No. 11/710,682, filed in the U.S. Patent and Trademark Office on Feb. 23, 2007, which claims priority under 35 U.S.C. §119(a) to applications filed in the Korean Intellectual Property Office on Feb. 23, 2006, and Sep. 15, 2006, and assigned Serial Nos. 2006-17793, and 2006-89505 respectively, the contents of each of which are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to a digital broadcast receiver and, more particularly, to a digital broadcast receiver and broadcast data display method wherein multi-channel visual images are simultaneously displayed to support easy channel selection and switching. 
     2. Description of the Related Art 
     In digital multimedia broadcasting (DMB), various multimedia signals including audios and videos are digitally modulated and delivered to users. Particularly, users in motion can receive various multimedia programs through portable personal or in-vehicle receivers equipped with an omni directional receiving antenna. 
     Advances in memories capable of storing vast amounts of digital multimedia data such as moving pictures and music videos, and popularization of mobile communication terminals, have enabled recent development and commercialization of mobile communication terminals having DMB reception capabilities, for example DMB phones. While in motion, users can watch or listen to DMB programs through DMB phones. 
     When a user receiving DMB desires to obtain information on channels other than the current reception channel or desires to switch the current reception channel to a different channel, the user may have to scan all available channels in sequence. In addition, because information on broadcast programs or channels is provided as text-based information including channel names and associated program schedules, the user may have difficulty in intuitively understanding program guide information of a particular channel. 
     To solve the above problem, an image-based broadcast information providing method has recently been developed. In this image-based method, visual images are pre-assigned to corresponding programs on individual channels or visual images are extracted on demand from video broadcasts on individual channels, to provide program information on a particular channel using the prepared visual images. 
     However, in such a conventional image-based approach, program information is provided using a fixed image for each program on a channel. Thus, program information that changes with the passage of time cannot be provided. Because up-to-date image information regarding broadcast programs of individual channels cannot be obtained, the user cannot utilize up-to-date image information to select a desired channel. 
     SUMMARY OF THE INVENTION 
     The present invention has been made in view of the above problems, and an object of the present invention is to provide a digital broadcast receiver and broadcast data display method that can simultaneously display up-to-date multi-channel visual images and facilitate channel selection of the user. 
     Another object of the present invention is to provide a digital broadcast receiver and broadcast data display method that can simultaneously display thumbnail images representing digital broadcasts of individual channels in corresponding display areas of a single screen and to facilitate channel selection and switching. 
     Another object of the present invention is to provide a digital broadcast receiver and broadcast data display method that can simultaneously display real-time broadcast of a major channel and up-to-date informational images of other remaining channels. 
     Another object of the present invention is to provide a digital broadcast receiver and broadcast data display method wherein a major channel display area for a real-time broadcast and multiple minor channel display areas for up-to-date visual images are simultaneously presented and selection of both the major channel display area and one of the minor channel display areas resulting in major/minor channel switching. 
     In accordance with the present invention, a broadcast data display method for a digital broadcast receiver is provided. In response to a broadcast reception request from a user, a channel list having identifiers of available channels is displayed. Broadcast data of a channel selected by the user from the channel list is displayed on a screen in a full-screen mode. In response to a request of all-channel view during channel list display or broadcast reception, the screen is divided into display areas corresponding to the individual available channels of the channel list. Real-time broadcast data of the selected channel is displayed in a corresponding display area of the screen. Still images of the remaining channels are displayed simultaneously or sequentially in their corresponding display areas. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects, features and advantages of the present invention will be more apparent from the following detailed description in conjunction with the accompanying drawings, in which: 
         FIG. 1  is an overview of a digital multimedia broadcasting (DMB) system; 
         FIG. 2  is a block diagram of a DMB receiver according to the present invention; 
         FIG. 3  is a block diagram of a DMB receiver according to another embodiment of the present invention; 
         FIG. 4  illustrates an I-frame information table for managing information on I-frames of minor channels in the receiver of  FIG. 2  or  FIG. 3 ; 
         FIG. 5  is a flow chart of a method of simultaneously displaying multi-channel visual images for the receiver of  FIG. 2  or  FIG. 3 ; 
         FIG. 6  is a block diagram of a DMB receiver according to another embodiment of the present invention; 
         FIG. 7  is a block diagram of a DMB receiver according to another embodiment of the present invention; 
         FIG. 8  is a flow chart of a method for simultaneously displaying multi-channel visual images for the receiver of  FIG. 6  or  FIG. 7 ; 
         FIG. 9  illustrates structures of MPEG video data processed by the receivers of  FIGS. 2 ,  3 ,  6  and  7 ; 
         FIGS. 10A and 10B  illustrate display screen layouts for presenting multi-channel visual images output by the receivers of  FIGS. 2 ,  3 ,  6  and  7 ; 
         FIG. 11  is a flow chart of a method for simultaneously displaying multi-channel visual images according to another embodiment of the present invention; 
         FIG. 12  is a flow chart of a method for simultaneously displaying multi-channel visual images according to another embodiment of the present invention; 
         FIG. 13  is the state transition diagram illustrating transitions in screen display mode in response to user events in the method of  FIG. 12 ; 
         FIG. 14  is the flow chart of a channel switching procedure in the method of  FIG. 12 ; 
         FIG. 15  illustrates the sequence of screen layouts for multi-channel visual images in response to user events; 
         FIG. 16  is a configuration of a DMB receiver for illustrating multi-channel visual image processing; 
         FIG. 17  illustrates the sequence of screen layouts for multi-channel visual images in response to user events; and 
         FIG. 18  illustrates the sequence of screen layouts for multi-channel visual images in response to user events. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Hereinafter, preferred embodiments of the present invention are described in detail with reference to the accompanying drawings. The same reference symbols identify the same or corresponding elements in the drawings. Detailed descriptions of constructions or processes known in the art may be omitted to avoid obscuring the invention in unnecessary detail. 
     First, a brief introduction to digital multimedia broadcasting (DMB) is provided. Although the present invention is applied to DMB, it may also be applied to any digital broadcasting, such as digital video broadcasting (DVB), and MediaFLO. 
     DMB services are based on digital audio broadcasting (DAB) technologies for digital radios, and further include multimedia broadcasting concepts to additionally deliver moving images and information services such as weather, news and location services. DMB services can provide compact disc (CD) or digital versatile disc (DVD)-like high quality audio and video broadcast data to users in motion through mobile or in-vehicle receivers, and they are attracting attention as next generation broadcasting services. 
     That is, DMB services enable users in motion to receive various multimedia broadcast data on multiple channels through mobile or in-vehicle terminals having an omni directional receiving antenna. 
     Compared with existing broadcasting services, DMB services can be characterized by mobility. DMB systems are divided by signal transmission mechanisms into terrestrial and satellite systems. DMB systems are compared with existing broadcasting systems and comparison results are summarized in Table 1. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 1 
               
             
            
               
                   
                   
               
               
                   
                 Mobility 
                   
               
            
           
           
               
               
               
               
            
               
                   
                 Fixed 
                 Mobile 
                 Comparison 
               
               
                   
                   
               
            
           
           
               
               
               
               
            
               
                 Transmission 
                 Existing public 
                 Terrestrial DMB 
                 Ground station 
               
               
                 mechanism 
                 broadcasting 
               
               
                   
                 Existing satellite 
                 Satellite DMB 
                 Artificial 
               
               
                   
                 broadcasting 
                   
                 satellite 
               
               
                 Comparison 
                 Middle to large 
                 Very small 
               
               
                   
                 receiver 
                 receiver 
               
               
                   
               
            
           
         
       
     
     As shown in Table 1, compared with existing broadcasting services, DMB services can be characterized by mobility and small size of receivers. Broadcasting services are provided though ground stations in terrestrial DMB systems, and are provided through artificial satellites in satellite DMB systems. 
     In a satellite DMB system as a new broadcast medium, programs are transmitted from a DMB broadcast center to a satellite, which then retransmits the programs to mobile DMB terminals in the wide coverage area of the satellite. Owing to the use of satellite, satellite DMB services are available in outdoor environments across a large area. Gap fillers or repeaters may be required to receive DMB signals and retransmit the received DMB signals in order to provide services to users in shadow areas such as underground or indoor regions. 
     In a terrestrial DMB system, programs are transmitted through spectrum suitable for terrestrial propagation. Unlike the satellite DMB system, broadcast signals are transmitted through base stations, which are similar to those for mobile terminals, on the ground. A terrestrial DMB service is a multimedia service combining video, audio and data broadcasting that is provided through terrestrial waves to users in motion. 
     Referring to  FIG. 1 , the DMB system includes a broadcasting center  10 , one or more satellites  20 , one or more base stations  30 , and a plurality of mobile, portable and fixed receivers such as vehicle receivers  40 , mobile terminals  50  and home receivers  60 . 
     The broadcasting center  10  compresses and modulates DMB signals representing audio, video and data signals, and transmits the modulated DMB signals to corresponding satellites  20  or base stations  30 . 
     Each satellite  20  or base station  30  receiving the DMB signals from broadcasting center  10  amplifies the received DMB signals, and retransmits the amplified DMB signals at different frequencies to receivers  40 ,  50  and  60 . 
     Each receiver  40 ,  50  or  60  receives the DMB signals from corresponding satellite  20  or base station  30 , and demodulates and decompresses the received DMB signals to output uncompressed audio, video and data signals. 
     Rapidly advancing digital broadcasting technologies have enabled users in fast motion to receive noise-free digital broadcast programs, and have demanded development of new added functions and services for greater user convenience. 
     A digital broadcast receiver of the present invention maintains one broadcast channel (&#39;major channel&#39;) to continuously deliver a digital broadcast, and at least one broadcast channel (&#39;minor channel&#39;) to deliver digital broadcasts in an alternating manner according to a preset channel switch condition. The channel switch condition is preferably one of a change request by the user, a preset change period, and detection of I-frames on minor channels, and is described later. 
     Referring to  FIG. 2 , DMB receiver  100  includes a DMB module  110 , a TS demultiplexer  120 , a major channel buffer  130 , a minor channel processor  140 , an A/V codec  150 , an image synthesizer  160 , a DMB output unit  170 , a channel setting unit  180 , and an input unit  190 . 
     DMB module  110  receives a multi-channel broadcast signal corresponding to broadcast channels selected by the user, and outputs transport stream (TS) data of the selected broadcast channels. In satellite DMB, DMB module  110  sets Walsh codes (a Walsh code is a code used to extract TS packets of a particular channel from broadcast data transmitted over an MPEG-2 transport stream) associated with a major channel and a minor channel on the basis of reception channel information from channel setting unit  180 , extracts TS data of the major and minor channels using the Walsh codes, and outputs the extracted TS data. Before output of the extracted TS data, DMB module  110  deinterleaves the extracted TS data using associated channel information. 
     TS demultiplexer  120  demultiplexes the TS data from DMB module  110  into major channel data and minor channel data, detects MPEG-4 format data from the major channel data and minor channel data, and outputs the major channel MPEG-4 data and minor channel MPEG-4 data to the major channel buffer  130  and minor channel processor  140  respectively. 
     Major channel buffer  130  stores broadcast data of the major channel from TS demultiplexer  120 . To separately store the audio portion and visual portion of the broadcast data, major channel buffer  130  preferably includes an audio buffer  131  for storing audio data in a digital form and video buffer  133  for storing video data in a digital form. 
     Minor channel processor  140  detects video data from the minor channel broadcast data from TS demultiplexer  120 , detects an I-frame from the detected video data, and stores the detected I-frame. Minor channel processor  140  preferably includes an I-frame detector  141  for detecting I-frames, and an I-frame storage  143  for storing detected I-frames and associated minor channel identifiers. 
     An MPEG-compressed video data stream includes intra-coded frames or I-frames, predictive frames or P-frames, and bidirectional frames or B-frames. I-frames are reference frames for MPEG compression and decompression, and are repeated in an MPEG-compressed video data stream by a preset period of time (0.5 seconds for the satellite DMB system). In addition, the size of an I-frame is greater than that of a P-frame or B-frame. For example, the P-frame size is about 1/10 of the I-frame size. 
     I-frame detector  141  detects an I-frame at each I-frame period in the minor channel broadcast data from TS demultiplexer  120 . The minor channel broadcast data fed to minor channel processor  140  can include both video data and audio data. Hence, I-frame detector  141  preferably detects video data in the minor channel broadcast data then detects an I-frame from the detected video data. 
     Preferably, I-frame detector  141  pre-stores I-frame periods to detect an image frame received at each I-frame period as an I-frame, or compares sizes of received image frames to detect a relatively large image frame as an I-frame. 
     I-frame storage  143  stores I-frames detected by I-frame detector  141  and associated minor channel identifiers. The stored I-frame of a current minor channel is updated at each I-frame period. 
     This is because image synthesizer  160  uses stored I-frames of minor channels (in particular, the previous minor channel) to display on a single screen I-frame images of the minor channels, which alternate with one another at a predetermined channel switch period. I-frame storage  143  preferably stores a quantity of I-frames greater than or equal to the quantity of preset minor channels to be received simultaneously with the major channel. I-frames arranged in a tabular format are illustrated in  FIG. 4 . Referring to  FIG. 4 , an I-frame information table  80  includes channel identifier fields  81  and I-frame fields  83  to store I-frames according to their corresponding channels. 
     A/V codec  150  decodes digital audio data and video data from major channel buffer  130 , and outputs decoded data as an audio signal and video signal. 
     Image synthesizer  160  combines major channel video data decoded by A/V codec  150  with multiple minor channel images from minor channel processor  140 . That is, the major channel video data is combined with I-frames of minor channels stored in I-frame storage  143 . Preferably, image synthesizer  160  stores the preset quantity of minor channels, and selects in sequence from I-frame storage  143  a quantity of I-frames for image synthesis equal to the preset quantity of minor channels. 
     DMB output unit  170  includes a speaker  171  for outputting an audio signal from A/V codec  150 , and a display section  173  for displaying a video signal from image synthesizer  160 . Display section  173  preferably simultaneously displays major channel video data and minor channel video data on a single screen using the output signal from image synthesizer  160 . 
     Channel setting unit  180  sets identifiers of major and minor channels to be received according to user selections through input unit  190 , and transmits the channel identifiers to DMB module  110 . Preferably, channel setting unit  180  pre-stores a channel ID list having a plurality of identifiers of minor channels selected by the user or a plurality of favorite channel identifiers automatically collected from channel reception histories, selects a channel identifier from the channel ID list in sequence according to a channel switch condition set in advance, and transmits the selected channel identifier to DMB module  110 . The channel ID list preferably includes a quantity of channel identifiers greater than or equal to the preset quantity of minor channels to be simultaneously output to a single screen. 
     The channel switch condition may be a change request by the user, a preset change period, or detection of an I-frame on the current minor channel. If the channel switch condition is a change request by the user, channel setting unit  180  preferably sets the current minor channel to a channel of a channel identifier accompanied by the change request. 
     If the channel switch condition is a change request by the user or a preset change period, channel setting unit  180  maintains the current minor channel until the channel switch condition is satisfied, and minor channel processor  140  updates the I-frame of the current minor channel stored in I-frame storage  143  at each I-frame period. 
     Accordingly, DMB output unit  170  both outputs broadcast data of the major channel fed via major channel buffer  130  and displays a preset quantity of minor channel images using minor channel I-frames stored in I-frame storage  143 , wherein the image of the current minor channel is updated and newly displayed at each I-frame period until the current minor channel is switched to another channel. 
     For a minor channel switch through I-frame detection, I-frame detector  141  preferably informs channel setting unit  180  of detection of an I-frame of a particular minor channel. Because an I-frame contains a reference image for MPEG compression and decompression, it is possible to create a visual image of the particular minor channel. That is, if an I-frame of the current minor channel is detected, a visual image of the current minor channel is updated with the detected I-frame image, and the current minor channel is switched to a next minor channel for video data reception. 
     Accordingly, in the present invention, while broadcast data of a major channel is being output, newly updated visual images of multiple minor channels can be delivered. 
     Instead of using such a channel ID list for a minor channel switch, channel setting unit  180  may directly set or modify minor channel identifiers according to information supplied by each user selection, and transmit the minor channel identifiers to DMB module  110 . 
     When a major channel change request is input through input unit  190 , channel setting unit  180  changes the major channel identifier according to information accompanied by the change request. That is, channel setting unit  180  sets identifiers of major and minor channels to be received by DMB module  110 , and controls DMB module  110  to alternate multiple minor channels while the major channel is fixed. 
     Referring to  FIG. 3 , DMB receiver  200  includes a DMB module  210 , a TS demultiplexer  220 , a major channel buffer  230 , a minor channel processor  240 , an A/V codec  250 , an image synthesizer  260 , a DMB output unit  270 , a channel setting unit  280 , and an input unit  290 . Compared with DMB receiver  100  of  FIG. 2 , DMB receiver  200  can simultaneously receive broadcast data of two minor channels if available channels exist. 
     Elements of DMB receiver  200  are similar in function to corresponding elements of DMB receiver  100  of  FIG. 2 . That is, DMB module  210 , TS demultiplexer  220 , major channel buffer  230 , minor channel processor  240 , A/V codec  250 , image synthesizer  260 , DMB output unit  270 , channel setting unit  280 , and input unit  290  of DMB receiver  200  shown in  FIG. 3  are similar in function, respectively, to DMB module  110 , TS demultiplexer  120 , major channel buffer  130 , minor channel processor  140 , A/V codec  150 , image synthesizer  160 , DMB output unit  170 , channel setting unit  180 , and input unit  190  of the DMB receiver  100  shown in  FIG. 2 . 
     However, with an increased number of minor channels to be received, operations of the elements in  FIG. 3  related to minor channel processing are different from those of corresponding elements in  FIG. 2 . 
     Channel setting unit  280  sets one major channel identifier and two minor channel identifiers, and transmits the three channel identifiers to DMB module  210 . In satellite DMB, DMB module  210  sets three Walsh codes on the basis of the major and minor channel identifiers, and extracts TS data corresponding to one major channel and two minor channels using the Walsh codes and outputs the extracted TS data. TS demultiplexer  220  separates major channel data, first minor channel data and second minor channel data from the TS data output from DMB module  210 , detects MPEG-4 data from the separated data, and outputs the detected MPEG-4 data. 
     To simultaneously process video broadcasts on multiple minor channels, minor channel processor  240  includes an I-frame detector for each minor channel. Minor channel processor  240  includes a first I-frame detector  241  for detecting an I-frame of a first minor channel, a second I-frame detector  242  for detecting an I-frame of a second minor channel, and an I-frame storage  243  for storing I-frames output from the first and second I-frame detectors  241  and  242 . 
     As described above, with an increased number of minor channels, operations of DMB module  210 , TS demultiplexer  220 , minor channel processor  240  and channel setting unit  280  in  FIG. 3  are different from those of corresponding elements in  FIG. 2 . Elements in  FIG. 3  other than those listed above are similar in operation to corresponding elements in  FIG. 2 , and a repeated description thereof is omitted. 
       FIG. 2  is a block diagram of a DMB receiver having one minor channel simultaneously received with a major channel, and  FIG. 3  is a block diagram of a DMB receiver having two minor channels. However, the present invention is not limited to a DMB receiver having one minor channel or two minor channels. The present invention relates to a DMB receiver that can simultaneously display visual images of a major channel and multiple minor channels, wherein each minor channel is selected in sequence according to a channel switch condition described above and the displayed image of the selected minor channel is continuously updated with a newly received image. The present invention is not limited by the quantity of minor channels simultaneously receivable with a major channel, and the quantity of minor channels can increase along with performance improvement of the DMB module. 
     Referring to  FIG. 5 , the method is described as follows. 
     The DMB receiver sets multiple channel identifiers for DMB reception in step S 105 . At this step, the DMB receiver sets a major channel identifier and a quantity of minor channel identifiers. Preferably, the DMB receiver pre-stores a channel ID list having a plurality of identifiers of minor channels selected by the user or a plurality of favorite channel identifiers automatically collected from channel reception histories, and selects a channel identifier from the channel ID list in sequence according to a preset channel switch condition to set the current minor channel to a channel of the selected channel identifier. The channel switch condition is described above in relation to  FIG. 2 . 
     When DMB reception is initiated in step S 115 , the DMB receiver receives broadcast data on multiple channels of the channel identifiers set at step S 105 , and separately extracts major channel data and minor channel data from the received broadcast data in step S 120  because the major channel data and minor channel data in the broadcast data received at step S 115  are in an interleaved form. This separate extraction operation is similar to the operation of TS demultiplexer  120  described in relation to  FIG. 2 . 
     After separate extraction of the major channel data and minor channel data at step S 120 , the DMB receiver stores the major channel data at step S 125 . An I-frame of the current minor channel is detected from the minor channel data at step S 130 , and the detected I-frame is stored according to its corresponding channel in step S 135 . Steps S 130  and S 135  for minor channel processing are similar to the operation of minor channel processor  140  described in relation to  FIG. 2 . 
     After storing the major channel data and I-frame detection, the DMB receiver combines the video portion of the major channel with a quantity of I-frame images equal to the preset quantity of the minor channels in step S 140 , and outputs the combined major/minor channel visual image with the audio data of the major channel in step S 145 . 
     While in DMB reception, namely, if reception of the fixed major channel is not terminated in step S 150 , if the channel switch condition is satisfied in step S 155 , the DMB receiver switches the current minor channel to another minor channel in step S 160 , and repeats steps S 115  through S 155  for continued DMB reception. 
     The condition to switch channels is preferably one of a change request by the user, a preset change period and detection of an I-frame on the current minor channel. The condition to switch channels at step S 160  to switch between minor channels are described in relation to channel setting unit  180  in  FIG. 2 . 
     Through steps described above, the DMB receiver of  FIG. 2  or  3  simultaneously displays up-to-date multi-channel visual images. In particular, up-to-date visual images of multiple minor channels are displayed during reception of a major channel, thereby facilitating channel selections of the user. 
       FIG. 6  illustrates a configuration of a DMB receiver according to another embodiment of the present invention. 
     Referring to  FIG. 6 , DMB receiver  300  includes a DMB module  310 , a TS demultiplexer  320 , a major channel buffer  330 , a minor channel processor  340 , an A/V codec  350 , an image synthesizer  360 , a DMB output unit  370 , a channel setting unit  380 , an input unit  390 , and a first switch SW 1 . Compared with DMB receiver  100  of  FIG. 2 , DMB receiver  300  performs switching between major and minor channels in response to a major/minor channel switch request, and further includes the first switch SW 1  to perform switching between major and minor channel data transmission paths. 
     Elements of DMB receiver  300  are similar in function to corresponding elements of DMB receiver  100  of  FIG. 2 . That is, DMB module  310 , TS demultiplexer  320 , major channel buffer  330 , minor channel processor  340 , A/V codec  350 , image synthesizer  360 , DMB output unit  370 , channel setting unit  380 , and input unit  390  of the DMB receiver  300  shown in  FIG. 6  are similar in function, respectively, to DMB module  110 , TS demultiplexer  120 , major channel buffer  130 , minor channel processor  140 , A/V codec  150 , image synthesizer  160 , DMB output unit  170 , channel setting unit  180 , and input unit  190  of DMB receiver  100  shown in  FIG. 2 . 
     Elements in  FIG. 6  other than channel setting unit  380  are similar in operation to corresponding elements in  FIG. 2 , and a repeated description thereof is omitted. In the case of channel setting unit  380 , it transmits a control signal for switching between major and minor channel data transmission paths to the first switch SW 1 . 
     Channel setting unit  380  outputs a control signal to the first switch SW 1  for switching data transmission paths on the basis of a user selection through input unit  390  or a major/minor channel switch condition set in advance. The major/minor channel switch condition is preferably a major/minor channel switch period or a major/minor channel switch time. If the condition to switch the major/minor channel is a major/minor channel switch period, channel setting unit  380  repeatedly outputs a control signal at regular intervals for switching between major and minor channels. If the condition to switch the major/minor channel is a major/minor channel switch time, channel setting unit  380  outputs a control signal at a specified time for switching between major and minor channels. 
     In response to a control signal from channel setting unit  380 , the first switch SW 1  changes current transmission paths. For example, before reception of a control signal by the first switch SW 1 , it is assumed that a first contact point SWp 1  and third contact point SWp 3  are interconnected to form a major channel data transmission path and a second contact point SWp 2  and fourth contact point SWp 4  are interconnected to form a minor channel data transmission path. After reception of the control signal, the first switch SW 1  forms a major channel data transmission path by interconnecting the first contact point SWp 1  and fourth contact point SWp 4 , and also forms a minor channel data transmission path by interconnecting the second contact point SWp 2  and third contact point SWp 3 . 
     As a result, before reception of the control signal, broadcast data passed through the first contact point SWp 1  and third contact point SWp 3  was processed as major channel data, and, after reception of the control signal, the broadcast data is directed to pass through the first contact point SWp 1  and fourth contact point SWp 4  and is processed as minor channel data; while broadcast data passed through the second contact point SWp 2  and fourth contact point SWp 4  was processed as minor channel data before reception of the control signal, and after reception of the control signal the broadcast data is directed to pass through the second contact point SWp 2  and third contact point SWp 3  and is processed as major channel data. 
     Accordingly, DMB receiver  300  of  FIG. 6  can perform switching between major and minor channel data transmission paths in response to a control signal from channel setting unit  380 . 
     Referring to  FIG. 7 , DMB receiver  400  includes a DMB module  410 , a TS demultiplexer  420 , a major channel buffer  430 , a minor channel processor  440 , an A/V codec  450 , an image synthesizer  460 , a DMB output unit  470 , a channel setting unit  480 , an input unit  490 , a second switch SW 2 , a third switch SW 3 , and a fourth switch SW 4 . Compared with DMB receiver  100  of  FIG. 2 , DMB receiver  400  performs switching between major and minor channels in response to a major/minor channel switch request, and stores minor channel data to minimize a major/minor channel switch time, and further includes a minor channel buffer  445  within minor channel processor  440  and the second to fourth switches SW 2  to SW 4  for changing transmission paths. 
     Elements in  FIG. 7  other than those related to a change of transmission paths and storage of minor channel data (the minor channel processor  440 , channel setting unit  480  and second to fourth switches SW 2  to SW 4 ) are similar in function to corresponding elements in  FIG. 2 . That is, DMB module  410 , TS demultiplexer  420 , major channel buffer  430 , A/V codec  450 , image synthesizer  460 , DMB output unit  470 , channel setting unit  480 , and input unit  490  of the DMB receiver  400  shown in  FIG. 7  are similar in function as DMB module  110 , TS demultiplexer  120 , major channel buffer  130 , A/V codec  150 , image synthesizer  160 , DMB output unit  170 , channel setting unit  180 , and input unit  190  of DMB receiver  100  shown in  FIG. 2 . 
     Compared with channel setting unit  180  in  FIG. 2 , channel setting unit  480  additionally outputs a control signal to the second to fourth switches SW 2  to SW 4  to change major and minor channel data transmission paths. 
     Channel setting unit  480  outputs a control signal CH.sig to the second, third and fourth switches SW 2 , SW 3  and SW 4  for switching transmission paths thereof on the basis of a user selection through input unit  490  or a major/minor channel switch condition set in advance. 
     In response to the control signal CH.sig, the second, third and fourth switches SW 2 , SW 3  and SW 4  toggle to new transmission paths. In  FIG. 7 , paths shown inside the switches with solid lines constitute initial transmission paths, and paths shown inside the switches with dotted lines constitute transmission paths to be formed in response to a major/minor channel switch request. 
     In DMB receiver  400  of  FIG. 7 , transmission path switching is performed at an input terminal of an I-frame detector  441  and output terminals of major channel buffer  430  and minor channel buffer  445 . 
     The second switch SW 2  makes an initial connection between the input terminal of I-frame detector  441  and the input terminal of minor channel buffer  445 . When channel setting unit  480  outputs a control signal in response to a major/minor channel switch request, the second switch SW 2  removes the connection between the input terminal of I-frame detector  441  and the input terminal of minor channel buffer  445  then makes a connection between the input terminal of I-frame detector  441  and the input terminal of major channel buffer  430 . That is, broadcast data fed to major channel buffer  430  before the occurrence of the major/minor channel switch request is now directed to I-frame detector  441  for I-frame detection. 
     At the same time, the third switch SW 3  and fourth switch SW 4  remove initial connections for audio and video outputs respectively from major channel buffer  430 , and make new connections for audio and video outputs respectively from minor channel buffer  445 . That is, the third switch SW 3  disconnects an initial transmission path from an audio buffer  431  of major channel buffer  430  to a speaker  471 , and then makes a new connection to form a transmission path from an audio buffer  447  of minor channel buffer  445  to speaker  471 . The fourth switch SW 4  disconnects an initial transmission path from a video buffer  433  of major channel buffer  430  to A/V codec  450 , and then makes a new connection to form a transmission path from a video buffer  449  of minor channel buffer  445  to A/V codec  450 . 
     As described above, the DMB receiver of  FIG. 7  buffers minor channel broadcast data in addition to buffering major channel broadcast data, and switches output of the buffered minor channel broadcast data and input to the I-frame detector in response to a major/minor channel switch request, thereby minimizing a time delay due to major/minor channel switching. 
       FIG. 8  is a flow chart of a method for simultaneously displaying multi-channel visual images for the DMB receiver of  FIG. 6  or  FIG. 7 . In particular, the flow chart of  FIG. 8  illustrates a method to perform switching between major and minor channels during simultaneous display of multi-channel visual images. Referring to  FIG. 8 , the method is described as follows. 
     The DMB receiver sets multiple channel identifiers for DMB reception in step S 205 . At this step, the DMB receiver sets a major channel identifier and a quantity of minor channel identifiers. Preferably, the DMB receiver pre-stores a channel ID list having a plurality of identifiers of minor channels selected by the user or a plurality of favorite channel identifiers automatically collected from channel reception histories, and selects a channel identifier from the channel ID list in sequence according to a preset channel switch condition to set the current minor channel to a channel of the selected channel identifier. The condition to switch the channel is described in relation to  FIG. 2 . 
     The DMB receiver receives broadcast data on multiple channels associated with the channel identifiers set at step S 205  and step S 215 , and the receiver separately extracts major channel data and minor channel data from the received broadcast data in step S 220  because the major channel data and minor channel data in the broadcast data received at step S 215  are in an interleaved form. This separate extraction operation is similar to the operation of TS demultiplexer  120  described in relation to  FIG. 2 . 
     After separate extraction of the major channel data and minor channel data at step S 220 , the DMB receiver stores the major channel data and minor channel data in a major channel buffer and minor channel buffer, respectively in step S 225 . 
     An I-frame of the current minor channel is detected from the minor channel data in step S 230 , and the detected I-frame is stored according to its corresponding minor channel in step S 235 . Steps S 230  and S 235  for minor channel processing are similar to the operation of the minor channel processor  140  described in relation to  FIG. 2 . 
     After I-frame detection from the minor channel data, the DMB receiver combines the video portion of the major channel with a quantity of I-frame images equal to the preset quantity of minor channels in step S 240 , and outputs the combined major/minor channel visual image with the audio data of the major channel in step S 245 . 
     While in DMB reception, namely, if reception of the fixed major channel is not terminated in step S 250 , if a major/minor channel switch request is input or a preset major/minor channel switch condition is satisfied in step S 255 , the DMB receiver performs switching between major and minor channel data transmission paths in step S 260 . That is, the DMB receiver of  FIG. 6  operates the first switch SW 1  as described with reference to  FIG. 6 , and the DMB receiver of  FIG. 7  operates the second to fourth switches SW 2  to SW 4  as described with reference to  FIG. 7 . 
     While in DMB reception, namely, major channel reception, if the condition to switch the channel is satisfied in step S 265 , the DMB receiver switches the current minor channel to another minor channel in step S 270 , and repeats steps S 215  through S 265  for continued DMB reception. 
     The condition to switch the channel is preferably one of a change request by the user, a preset change period and detection of an I-frame on the current minor channel. The condition to switch the channel and step S 270  of switching between major/minor channels are described in relation to channel setting unit  280  in  FIG. 2 . 
     Through steps described above, the DMB receiver of  FIG. 6  or  7  can both simultaneously display up-to-date multi-channel visual images and perform, in response to a major/minor channel switch request, switching between the major channel and a minor channel selected at the time of the request. In particular, the DMB receiver of  FIG. 7  can minimize the time delay due to major/minor channel switching. 
       FIG. 9  illustrates structures of MPEG video data processed by the receiver of  FIG. 2 ,  3 ,  6  or  7 . That is,  FIG. 9  shows examples of video streams composing typical MPEG video broadcasts receivable by the DMB receiver: a video stream (A) of a major channel, a video stream B) of a minor channel- 1 , a video stream (C) of a minor channel- 2 , a video stream (D) of a minor channel- 3 , a video stream (E) of a minor channel- 4 , a video stream (F) of a minor channel- 5 , a video stream (G) of a minor channel- 6 , a video stream (H) of a minor channel- 7 , and a video stream (J) of a minor channel- 8 . 
     As described above, the DMB receiver of the present invention receives video streams on multiple channels. In the case of minor channels, one of the minor channels is selected at a time, and only I-frames, which serve as reference image frames, are detected from broadcast data on the currently selected minor channel and stored. Referring to  FIG. 9 , if the condition to switch a channel is detection of an I-frame on the current minor channel, the DMB receiver continuously receives a video stream such as (A) on the major channel. During continuous reception on the major channel, the current minor channel is switched from ‘minor channel- 1 ’ to ‘minor channel- 2 ’ after detection of an I-frame on ‘minor channel- 1 ’ at time t 1 ; from ‘minor channel- 2 ’ to ‘minor channel- 3 ’ after detection of an I-frame on ‘minor channel- 2 ’ at time t 2 ; from ‘minor channel- 3 ’ to ‘minor channel- 4 ’ after detection of an I-frame on ‘minor channel- 3 ’ at time t 3 ; from ‘minor channel- 4 ’ to ‘minor channel- 5 ’ after detection of an I-frame on ‘minor channel- 4 ’ at time t 4 ; from ‘minor channel- 5 ’ to ‘minor channel- 6 ’ after detection of an I-frame on ‘minor channel- 5 ’ at time t 5 ; from ‘minor channel- 6 ’ to ‘minor channel- 7 ’ after detection of an I-frame on ‘minor channel- 6 ’ at time t 6 ; from ‘minor channel- 7 ’ to ‘minor channel- 8 ’ after detection of an I-frame on ‘minor channel- 7 ’ at time t 7 ; and from ‘minor channel- 8 ’ back to ‘minor channel- 1 ’ after detection of an I-frame on ‘minor channel- 8 ’ at time t 8 . Then, this process is repeated. Although an I-frame is received on ‘minor channel- 1 ’ and ‘minor channel- 6 ’, ‘minor channel- 2 ’ and ‘minor channel- 7 ’, and ‘minor channel  3 ’ and ‘minor channel  8 ’ at a same time, respectively, each minor channel is selected in order of precedence during updating an I-frame. Accordingly, the ‘minor channel- 1 ’, ‘minor channel- 2 ’ and ‘minor channel- 3 ’ are selected in sequence and the updated I-frame on the ‘minor channel- 6 ’, ‘minor channel- 7 ’ and ‘minor channel- 8 ’ is disregarded. 
     As a result, during output of major channel broadcast data, whenever broadcast data of a minor channel selected from the eight minor channels is output, an I-frame of the selected minor channel is updated, thereby enabling output of up-to-date visual images of minor channels. 
       FIGS. 10A and 10B  illustrate display screen layouts for presenting multi-channel visual images output by the DMB receivers of  FIGS. 2 ,  3 ,  6  and  7 . The DMB receiver outputs broadcast data received on multiple channels in screen layouts illustrated in  FIGS. 10A and 10B . As described with reference to  FIGS. 2 to 8 , broadcast data of minor channels is updated with associated I-frame images, thereby enabling delivery of up-to-date visual images of the minor channels. Switching between the major channel and a selected minor channel can be performed according to a user request. For example, if the user selects a display area associated with a minor channel, switching between the major channel and minor channel is performed. If the user selects a display area associated with the major channel, the selected display area is preferably enlarged. Preferably, the DMB receiver pre-stores display information for enlargement (for example, enlargement ratios and display locations), and enlarges the display area associated with the major channel using the display information. 
     In the description, although a DMB receiver simultaneously receives one major and one minor channel or one major and two minor channels, the DMB receiver may also simultaneously receive one major channel and two or more minor channels. Although the present invention addresses a DMB receiver, it may also be applied to a receiver for any digital broadcasting, such as DMB, digital video broadcasting—handheld (DVB-H), and MediaFLO. 
     A broadcast data display method according to another embodiment of the present invention is described. In the method, a single screen is divided into display areas corresponding to broadcast channels available in a DMB receiver; one of the available channels is automatically set as a major channel and the remaining channels are set as minor channels, on the basis of a channel reception history or a preset channel list; and broadcast data of the major channel is displayed in an associated display area and visual images of the minor channels are displayed in associated display areas, in the form of thumbnail images. 
     For example, in the case where two broadcast channels are available in a DMB receiver, the display screen is divided into two display areas, and broadcast data of one major channel is displayed in one of the display areas and an up-to-date visual image of one minor channel is displayed in the other display area. In the case where four broadcast channels are available in a DMB receiver, the display screen is divided into four display areas, and broadcast data of one major channel is displayed in one of the display areas and up-to-date visual images of the remaining three minor channels are displayed in their corresponding display areas, in the form of thumbnail images. 
     The broadcast data of a major channel may include video data and audio data. An up-to-date visual image of a minor channel may be a still image corresponding to an I-frame detected in the broadcast data of the minor channel. In the case of channel switching, the still image may also correspond to a raw image captured from the most recently decoded broadcast data of the former major channel. Preferably, the broadcast data of a major channel and up-to-date visual images of minor channels are resized according to positions and sizes of corresponding display areas in a single screen, and displayed in the form of thumbnail images. 
     Referring to  FIG. 11 , the method is described as follows. 
     When DMB reception is initiated by a user, a DMB receiver performs channel scan to identify available broadcast channels in step S 310 , and divides the screen into display areas corresponding to the individual available channels in step S 315 . The DMB receiver simultaneously receives broadcast data on the available channels in step S 320 , and resizes video images in the received broadcast data so that the video images can fit within their corresponding display areas in step S 325 . 
     The DMB receiver checks if a previous channel identifier exists in step S 330 . If a previous channel identifier exists, the DMB receiver sets a channel of the previous channel identifier as a major channel in step S 335 . If a previous channel identifier does not exist, the DMB receiver sets one of the available channels as a major channel in step S 336 . The DMB receiver sets the remaining available channels as minor channels, and detects I-frames in broadcast data of the minor channels in step S 340 . 
     The DMB receiver combines the detected I-frames with a video signal of the major channel into a screen output image, and displays the screen output image in step S 345 . That is, whereas video and audio signals of the major channel are reproduced as a broadcast stream, detected I-frames of the individual minor channels are displayed as up-to-date visual images. 
     The DMB receiver checks if the user requests to rescan broadcast channels in step S 350 . If the user requests to rescan, the DMB receiver repeats step S 310  and subsequent steps. If the user requests to switch major/minor channels in step S 355 , the DMB receiver exchanges the major channel and a minor channel selected by the user with each other in step S 360 , and repeats step S 345  and subsequent steps. That is, after step S 360 , video and audio signals of the new major channel are reproduced as a broadcast stream and a detected I-frame of the former major channel is displayed in the corresponding display area as an up-to-date visual image. If the user requests to terminate DMB reception in step S 365 , the DMB reception is terminated, otherwise the DMB receiver returns to step S 345  to continue display of the screen output image. 
     As described above, the DMB receiver of the present invention simultaneously displays up-to-date multi-channel images on a single screen. Broadcast data of one major channel and I-frames extracted from broadcast data of multiple minor channels are simultaneously displayed in corresponding display areas in the single screen. As a result, during viewing of the major channel broadcast, the user can easily perform channel selection or switching using up-to-date visual images. 
     Referring to  FIG. 12 , the method is described as follows. 
     When a user initiates DMB reception, a DMB receiver performs channel scan to identify available broadcast channels in step S 410 , and displays a list of the available channels in step S 415 . If a reception history having identifiers of previously received channels is present in the DMB receiver, step S 410  may be skipped. When the user selects a channel in the list, the DMB receiver reproduces broadcast data of the selected channel on the full screen in step S 420 . 
     During full screen display, if the user requests an all-channel view mode in step S 425 , the DMB receiver divides the screen into display areas corresponding to the individual available channels in step S 430 . The DMB receiver simultaneously receives broadcast data on the available channels in step S 435 , and resizes video images in the received broadcast data so that the video images can fit within the corresponding display areas in step S 440 . 
     After image resizing, the DMB receiver reproduces a video signal of the channel selected at step S 420  (major channel) as a broadcast stream in the corresponding display area in step S 445 , and displays in sequence detected I-frames of the remaining available channels (minor channels) as up-to-date visual images in the corresponding display areas in step S 450 . 
     During simultaneous display of multi-channel visual images, the DMB receiver can perform an operation requested by the user in step S 455 . User requested operations are described in connection with  FIGS. 13 and 14 . 
     Referring to  FIG. 13 , in an all-channel view mode, the DMB receiver displays major channel broadcast data and up-to-date minor channel visual images on the single screen. If the user selects a display area associated with the major channel, the DMB receiver transitions to an enlargement mode, enlarges the selected display area at a preset ratio, and displays video images in the major channel broadcast data that are preferably resized according to display area enlargement. If the user inputs a request of full-screen display, the DMB receiver makes a transition to a full-screen mode, and reproduces major channel broadcast data in the full screen. If the user inputs a request of major/minor channel switching, the DMB receiver switches major and minor channel data transmission paths, as later described with reference to  FIG. 14 . 
     In the enlargement mode, if the user selects a display area associated with the major channel, the DMB receiver enlarges the selected display area at a preset ratio within the screen size limit, and displays video images in the major channel broadcast data that are preferably resized accordingly. If the user inputs a request of full-screen display or if an enlargement event causes an associated display area to exceed the screen size limit, the DMB receiver makes a transition to the full-screen mode. 
     In the full-screen mode, the DMB receiver reproduces major channel broadcast data in the full screen. If the user inputs a request of all-channel view, the DMB receiver makes a transition to the all-channel view mode by performing operations described in connection with  FIG. 12 . If the user inputs a request of major/minor channel switching, the DMB receiver performs switching between the major and minor channels. 
     Sequences of screen layouts in response to user events are described later with reference to  FIGS. 15 to 18 . 
     Referring to  FIG. 14 , during an all-channel view mode in which major channel broadcast data and up-to-date minor channel visual images are displayed on the single screen, when the user requests to switch major/minor channels in step S 605 , the DMB receiver exchanges data transmission paths associated with the major channel and a selected minor channel with each other in step S 610 , detects an I-frame of the former major channel and displays the detected I-frame in the corresponding display area as an up-to-date visual image in step S 615 , and reproduces video and audio signals of the new major channel as a broadcast stream in step S 620 . During major/minor channel switching, visual images of the former major channel and new major channel may be resized according to their corresponding display areas. 
     Referring to  FIG. 15 , when the user initiates a DMB receiver, the DMB receiver receives information on available broadcast channels from broadcasting center  10  in  FIG. 1 , constructs a channel list using the channel information, and displays the constructed channel list as illustrated by an initial screen  510 . To construct a channel list, the DMB receiver may scan channel information for terrestrial DMB, use electronic program guide (EPG) information for satellite DMB, or use a channel reception history for favorite channels. 
     Thereafter, for display of multi-channel visual images, the DMB receiver divides the display screen into display areas corresponding to available broadcast channels as illustrated by screen layouts  520 ,  530  and  540 . Preferably, the number of display areas is equal to that of available broadcast channels. One of the display areas is associated with a broadcast channel selected as a major channel, and is used to display streaming broadcast data of the major channel. The remaining display areas are associated with broadcast channels other than the major channel (minor channels), and are used to display I-frames detected in broadcast data of the corresponding broadcast channels as up-to-date visual images. 
     Although, for the minor channels, I-frames are displayed as up-to-date visual images, streaming broadcast data may also be displayed. For minor channel streaming broadcast data, audio signals of the minor channel broadcast data are preferably removed to avoid possible collision with the major channel audio signal. 
     After division of the screen, streaming broadcast data, including video and audio signals, of the major channel selected with the initial screen  510  is displayed in the associated display area, and I-frames detected in broadcast data of the minor channels are displayed as up-to-date visual images in the display areas associated with the individual minor channels. 
     I-frames of the individual minor channels may be displayed at one time through buffering of the I-frames, or be sequentially displayed in order of channel identifiers of the channel list (or in order of thumbnail scanning) as illustrated in  FIG. 15 . 
     For example, as shown in screen layout  520 , streaming broadcast data of the major channel (Ch 1 ) is displayed in the display area associated with the major channel, and an I-frame of a minor channel (Ch 2 ) is displayed as an up-to-date visual image in the display area associated with the minor channel. After a preset time duration (N seconds), for example three frame periods, an I-frame of another minor channel (Ch 3 ) is displayed as an up-to-date visual image in the associated display area, as shown in screen layout  530 . After a preset time duration according to the number of minor channels to be displayed, I-frames of all minor channels are displayed as up-to-date visual images in the corresponding display areas, as shown in the screen layout  540 . 
     As described above, the DMB receiver combines a quantity of I-frames equal to the quantity of minor channels with video data of the major channel, and outputs the combined video data and audio data of the major channel. 
     Referring to  FIG. 16 , the DMB receiver includes a DMB module  610 , TS demultiplexer  620 , video codec  630 , audio codec  640 , image scaler  650 , speaker  660 , and display unit  680 . 
     Elements in the DMB receiver of  FIG. 16  are similar in function to corresponding elements in the DMB receiver of  FIG. 2 . That is, DMB module  610 , TS demultiplexer  620 , video and audio CODECs  630  and  640 , and speaker  660  and display unit  680  are similar in function to DMB module  110 , TS demultiplexer  120 , the A/V codec  150 , and DMB output unit  170  in  FIG. 2 . 
     The DMB receiver of  FIG. 16  includes image scaler  650  to perform video image resizing on broadcast data, and is a receiver simplified specifically for the purpose of illustrating multi-channel visual image processing, and therefore may include additional elements similar to those illustrated in  FIG. 2 . 
     Upon initiation of DMB reception, DMB module  610  receives a multi-channel broadcast signal corresponding to broadcast channels selected by the user, and outputs TS data of the selected broadcast channels. TS demultiplexer  620  demultiplexes the TS data from DMB module  610  into broadcast data for each broadcast channel, and separates the channel broadcast data into video and audio data. 
     Video codec  630  decodes the video data from TS demultiplexer  620  into a channel video signal. Audio codec  640  decodes the audio data from TS demultiplexer  620  into a channel audio signal. 
     Image scaler  650  resizes video images of channel video signals according to sizes and positions of corresponding display areas. To divide the display screen of display unit  680  into display areas corresponding to available broadcast channels, a screen divider (not shown) may be provided in image scaler  650  or as a separate element. 
     After resizing, a video signal  671  of a channel (Ch 1 ) selected as the major channel is output in a streaming form to an associated display area  681  for display, and an audio signal thereof is output in a streaming form to speaker  660  for reproduction. Detected I-frames (still images  673  to  677 ) of the remaining channels Ch 2  to Ch 9  (minor channels) are displayed as up-to-date visual images in their corresponding display areas  683  to  687 . 
     The DMB receiver of  FIG. 16  divides the display screen into display areas corresponding to broadcast channels, resizes the most recently decoded raw images of the individual broadcast channels, and displays the resized images as thumbnail images in their corresponding display areas. Hence, after channel scanning, thumbnail images can be displayed on the screen to represent corresponding broadcast channels, for example, in the form of a channel list, thereby enabling easy and rapid channel selection and switching for viewing. 
     Referring to  FIG. 17 , the screen layouts are related to manipulation of a display area associated with a major channel. When the user initiates a DMB receiver, the DMB receiver displays a channel list as illustrated by a screen layout  710 . The channel list may be constructed through channel scanning for terrestrial DMB, using electronic program guide (EPG) information for satellite DMB, or using a channel reception history for favorite channels. 
     If the user selects the identifier of a channel (Ch 1 ) as the major channel during display of the channel list, the DMB receiver outputs streaming broadcast data of the selected channel by displaying a video signal of the selected channel in a full screen mode as illustrated by a screen layout  720 , and by reproducing an audio signal thereof through a speaker. 
     If the user requests all-channel view during the full screen mode, the DMB receiver makes a transition to an all-channel view mode, and displays multi-channel visual images of available channels in their corresponding display areas of the screen, as shown in screen layout  731 ,  733  or  735  depending upon the quantity of available channels. The DMB receiver may also make a direct transition to the all-channel view mode in response to a request of all-channel view during display of the channel list. 
     During the all-channel view mode, the major channel selected for viewing is preferably distinguished from minor channels as illustrated by screen layout  731 . That is, streaming broadcast data of the major channel Ch 1  is displayed in the associated display area. Still images, such as I-frames detected in broadcast data of individual minor channels Ch 2  to Ch 9 , are displayed as up-to-date visual images in their corresponding display areas. 
     If the user selects the display area associated with the major channel during the all-channel view mode, the DMB receiver makes a transition to an enlargement mode, enlarges the associated display area at a preset ratio as illustrated by a screen layout  740 , and preferably resizes video images to be displayed according to enlargement of the associated display area. 
     If the user again selects the enlarged display area associated with the major channel Ch 1  during the enlargement mode, the DMB receiver transitions to the full screen mode, and enlarges the associated display area to the full screen as shown in screen layout  750 , and preferably resizes video images to be displayed in broadcast data of the major channel Ch 1  according to enlargement of the associated display area. 
     Although not shown in  FIG. 17 , the DMB receiver may make backward transitions from the current display mode to the previous display modes through, for example, a prior-mode function. 
     Referring to  FIG. 18 , the screen layouts relate to channel switching. Initially, as shown in screen layout  810 , one major channel Ch 1  is associated with a display area  811  and the DMB receiver is in an all-channel view mode. 
     During the all-channel view mode, in which multi-channel visual images of available broadcast channels are displayed, if the user moves the focus from display area  811  to a display area  812  for major/minor channel switching, the DMB receiver places the focus on display area  812  as illustrated by a screen layout  820 . If the user selects the focused display area  812  through a key input or the like, the DMB receiver performs major/minor channel switching as illustrated by a screen layout  830 . 
     That is, before the major/minor channel switching (screen layout  820 ), a streaming video signal of the major channel Ch 1  is displayed in display area  811 , and an I-frame of a minor channel Ch 2  is displayed in display area  812 . After the major/minor channel switching (screen layout  830 ), a streaming video signal of the new major channel Ch 2  is displayed in display area  812 , and a still image, such as an I-frame, of the former major channel Ch 1  is displayed as an up-to-date visual image in display area  811 . The still image may be an I-frame detected in the most recently decoded broadcast data of the former major channel Ch 1 , or be a raw image captured therefrom. The I-frame or raw image may be resized before being displayed according to the size and position of the corresponding display area. 
     During the all-channel view mode (screen layout  830 ), if the user selects the focused display area  812  associated with the current major channel Ch 2 , the DMB receiver makes a transition to an enlargement mode, enlarges display area  812  at a preset ratio as illustrated by a screen layout  840 , and preferably resizes video images to be displayed in broadcast data of the major channel Ch 2  according to enlargement of display area  812 . 
     During the enlargement mode (screen layout  840 ), if the user selects the enlarged display area  812  associated with the current major channel Ch 2 , the DMB receiver makes a transition to a full-screen mode, enlarges display area  812  to the full screen as illustrated by a screen layout  850 , and preferably resizes video images to be displayed in broadcast data of the major channel Ch 2  according to enlargement of display area  812 . 
     During the full-screen mode (screen layout  850 ), if the user requests channel switching between the current major channel Ch 2  and a minor channel Ch 1 , the DMB receiver displays streaming broadcast data of the new major channel Ch 1  on the full screen as illustrated by a screen layout  890 . 
     During the enlargement mode (screen layout  840 ), if the user moves the focus from display area  812  associated with the current major channel Ch 2  to display area  811  associated with a minor channel Ch 1 , the DMB receiver places the focus on display area  811  as illustrated by a screen layout  860 . If the user selects focused display area  811  associated with the minor channel Ch 1 , the DMB receiver makes a transition to the initial all-channel view mode, and performs major/minor channel switching as illustrated by a screen layout  870 . 
     That is, before the major/minor channel switching (screen layout  860 ), a streaming video signal of the major channel Ch 2  is displayed in display area  812 , and an I-frame of the minor channel Ch 1  is displayed in display area  811 . After the major/minor channel switching (screen layout  870 ), a streaming video signal of the new major channel Ch 1  is displayed in display area  811 , and a still image, such as an I-frame, of a new minor channel Ch 2  is displayed as an up-to-date visual image in the reduced display area  812 . The still image may be an I-frame detected in the most recently decoded broadcast data of the former major channel Ch 2 , or be a raw image captured therefrom. The I-frame or raw image may be resized before being displayed according to the size and position of the corresponding display area. 
     During the all-channel view mode (screen layout  870 ), if the user selects the focused display area  811  associated with the current major channel Ch 1 , the DMB receiver makes a transition to the enlargement mode, enlarges display area  811  at a preset ratio as illustrated by a screen layout  880 , and preferably resizes video images to be displayed in broadcast data of the major channel Ch 1  according to enlargement of display area  811 . 
     During the enlargement mode (screen layout  880 ), if the user selects the enlarged display area  811  associated with the current major channel Ch 1 , the DMB receiver makes a transition to the full-screen mode, enlarges the display area  811  to the full screen as illustrated by the screen layout  890 , and preferably resizes video images to be displayed in broadcast data of the major channel Ch 1  according to enlargement of display area  811 . 
     As apparent from the above description, the present invention provides a digital broadcast receiver and broadcast data display method enabling simultaneous display of multi-channel visual images. A video broadcast of a major channel and visual images of minor channels are simultaneously displayed and visual images of the minor channels are periodically updated on an I-frame period basis, thereby enabling simultaneous output of up-to-date multi-channel visual images. Hence, the user can easily select a desired channel. In addition, real-time video images of the major channel and up-to-date informational images of the minor channels are displayed together in their corresponding display areas of a single screen, and hence channel switching can be readily performed by selecting both the display area associated with the major channel and the display area associated with a target minor channel. Further, individual video broadcasts of available broadcast channels can be represented by thumbnail images; thereby enabling easy and rapid channel selection and channel switching. 
     While preferred embodiments of the present invention have been shown and described in this specification, it will be understood by those skilled in the art that various changes or modifications of the embodiments are possible without departing from the spirit and scope of the invention as further defined by the appended claims.