Abstract:
A digital cable broadcast system includes a broadcast receiver, a broadcast transmitter, and an alternative data receiver. The broadcast transmitter transmits a new emergency alert message associated with an emergency alert event if the broadcast receiver is not plugged into a power supply. More particularly, the transmitter transmits a status request to a cable mode or an out of band (OOB) included in the broadcast receiver, and it determines that the receiver is not plugged into the power supply if no response is received from the receiver. The alternative data receiver receives the new emergency alert message from the transmitter and displays the new emergency alert message in order to inform users.

Description:
[0001]     This application claims the benefit of Korean Patent Application No. 10-2005-0109678, filed on Nov. 16, 2005, which is hereby incorporated by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to Emergency alert signaling method and digital cable broadcast system.  
         [0004]     2. Discussion of the Related Art  
         [0005]     Generally, for TV sets on the market in North America, a basic protocol for handling an emergency alert message is laid down to prepare against an urgent situation or emergency.  
         [0006]     Meanwhile, for cable digital televisions, a basic protocol for receiving an emergency alert message transmitted from a cable digital broadcasting station correctly and for handling the received message is laid down as well.  
         [0007]     Differing from a digital TV receiving regular terrestrial broadcasting only, the cable digital TV is capable of receiving an emergency alert message via a specific frequency of terrestrial or cable broadcasting. In case that the emergency alert message arrives at a viewer watching the cable digital TV, the cable digital TV carries out a process for switching a current channel to a specific channel of the terrestrial or cable broadcasting and outputting the emergency alert message to efficiently provide the information about an emergency.  
         [0008]     And, a basic protocol deals with various and complicated situations such as a method of returning to a channel a viewer has watched if an emergency ends and the like.  
         [0009]     However, the related art method of handling the emergency alert message in cable broadcasting has the following problems.  
         [0010]     First of all, if a power of a broadcast receiver capable of receiving cable digital broadcasting is turned off and if the receiver is in a plugged-out mode, there exists no method of notifying a user of information indicating an emergency occurrence.  
         [0011]     Secondly, although a power of a broadcast receiver capable of receiving cable digital broadcasting is turned on, if the receiver is in a standby mode or if the receiver is outputting another data input source (e.g., the receiver is outputting A/V data received from a DVD player), it is unable to notify a user of information indicating an emergency occurrence.  
       SUMMARY OF THE INVENTION  
       [0012]     Accordingly, the present invention relates to Emergency alert signaling method and digital cable broadcast system.  
         [0013]     An object of the present invention is to provide a method of processing an emergency alert message in bi-directional cable digital broadcasting, data structure thereof and broadcast receiver thereof, by which a user can be informed of an emergency occurrence if a power of a broadcast receiver capable of receiving cable digital broadcasting is turned off and if the receiver is in a plugged-out mode.  
         [0014]     Another object of the present invention is to provide a method of processing an emergency alert message in bi-directional cable digital broadcasting, data structure thereof and broadcast receiver thereof, by which a user can be informed of an emergency occurrence if a power of a broadcast receiver capable of receiving cable digital broadcasting is turned on and if the receiver is in a standby mode or if the receiver is outputting another data input source (e.g., the receiver is outputting A/V data received from a DVD player).  
         [0015]     Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objectives and other advantages of the invention may be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.  
         [0016]     To achieve these objects and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, a digital cable broadcast system includes a broadcast transmitter, a broadcast receiver, and an alternative data receiver. The broadcast transmitter initially determines whether the broadcast receiver is plugged into a power supply. In order to determine this, the transmitter transmits a status request to the broadcast receiver to determine whether a cable card included in the broadcast receiver is active or not. If no response is received from the broadcast receiver, the transmitter determines that the cable card is not active and the broadcast receiver is not plugged into the power supply.  
         [0017]     If the broadcast transmitter determines that the broadcast receiver is not plugged into the power supply, it transmits a new emergency alert message associated with an emergency alert event into the alternative data receiver. The data receiver receives the new emergency alert message from the broadcast transmitter and displays the message. Upon display of the alert message, a user is informed of the emergency alert event and can plug the broadcast receiver into a power supply.  
         [0018]     After the broadcast receiver is plugged into the power supply, a controller included in the broadcast receiver determines whether the broadcast receiver is on a power-on mode or power-off mode. If it is on the power-off mode, the controller controls operation of a tuner included in the broadcast receiver to periodically tune to a predefined emergency alert channel to receive an emergency alert table (EAT). If the emergency alert table includes a new emergency alert message, the controller automatically sets the broadcast receiver on the power-on mode and further control operation of the tuner to tune to the emergency alert channel.  
         [0019]     It is to be understood that both the foregoing general description and the following detailed description of the present invention are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0020]     The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the principle of the invention. In the drawings:  
         [0021]      FIG. 1  is a block diagram of an emergency alert message processing system in bi-directional cable digital broadcasting according to one embodiment of the present invention;  
         [0022]      FIG. 2  is a block diagram of a broadcast receiver equipped with an emergency alert message processing function in bi-directional cable digital broadcasting according to one embodiment of the present invention;  
         [0023]      FIG. 3  is a flowchart of a method of processing an emergency alert message in bi-directional cable digital broadcasting according to one embodiment of the present invention;  
         [0024]      FIG. 4  is a diagram of a bit stream syntax of an emergency alert table according to one embodiment of the present invention;  
         [0025]      FIG. 5  is a diagram of a meaning of “alert_priority” value according to one embodiment of the present invention; and  
         [0026]      FIG. 6  is a flowchart of a method of processing an emergency alert message in bi-directional cable digital broadcasting according to another embodiment of the present invention.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0027]     Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.  
         [0028]     First of all, for the clear explanation of the present invention, description about a method of processing EAM (emergency alert message) and the like in case that a power of a bi-directional cable DTV (digital television) is turned off’ and ‘description about a method of processing EAM (emergency alert message) and the like in case that a power of a bi-directional cable DTV (digital television) is in a standby mode’ are respectively explained as follows.  
       First Embodiment  
       [0029]      FIG. 1  is a block diagram of an emergency alert message processing system in bi-directional cable digital broadcasting according to one embodiment of the present invention. In case that a bi-directional cable DTV is off (plugged-out mode), a system capable of providing an emergency associated message to a user is explained in a general way with reference to  FIG. 1  as follows.  
         [0030]     Referring to  FIG. 1 , a cable broadcasting station  102  is connected to a cable broadcast receiver  101  via a cable. Even if a plug (not shown in the drawing) for supplying a power to the cable broadcast receiver  101  is off (plugged-out mode), the cable broadcasting station  102  can communicate with the cable broadcast receiver  101  via the cable.  
         [0031]     Hence, the cable broadcasting station  102  decides whether the cable broadcast receiver  101  is in the plugged-out mode or not via communications.  
         [0032]     Besides, the cable broadcast receiver  101  can be a bi-directional cable DTV capable of transmitting/receiving broadcast associated signals or the like for example.  
         [0033]     The cable broadcasting station  102 , which is connected to the cable broadcast receiver  101  to bi-directionally transmit/receive normal broadcast signals and data, can be a cable MSO (multiple system operator) or the like for example.  
         [0034]     In case that the cable broadcast receiver  101  is in the plugged-off mode as a result of the decision made by the cable broadcasting station  102  and if information indicating that an emergency has occurred is confirmed, the cable broadcasting station  102  transmits the information indicating that the emergency has occurred to an EAM receiving medium  103 . In doing so, the cable broadcasting station  102  confirms the information indicating that the emergency has occurred using an EAT (emergency alert table) and the like for example.  
         [0035]     The EAM receiving medium  103  having received the information indicating that the emergency has occurred outputs the information in a format of text or the like.  
         [0036]     In this case, the EAM receiving media  103  includes a wire phone, a mobile phone, a PDA or the like of a user of the cable broadcast receiver  101 . Meanwhile, the EAM receiving medium  103  can be registered using information of a cable broadcasting subscriber. Alternatively, a user of the cable broadcast receiver can separately specify the EAM receiving medium  103  to register.  
         [0037]      FIG. 2  is a block diagram of a broadcast receiver equipped with an emergency alert message processing function in bi-directional cable digital broadcasting according to one embodiment of the present invention. In case that a bi-directional cable DTV is in a plugged-out mode, a system capable of providing an emergency associated message to a user is explained in detail with reference to  FIG. 2  as follows.  
         [0038]     Referring to  FIG. 2 , a cable broadcast receiver  101  includes an RF switch  201 , a tuner  204 , a demodulator  205 , a demultiplexer  206 , an A/V decoder  207 , a display unit  208 , a cable modem  209 , a PSI/PSIP database  210 , a PSI/PSIP decoder  211 , a channel manager  212 , an application &amp; UI controller  213 , a channel map  214 , a flash memory  215 , a cable card module  216  and a microcomputer  217 . For example, the cable broadcast receiver  101  includes a bi-directional digital television (DTV) or the like.  
         [0039]     The tuner  204  receives a broadcast signal including a PSI/PSIP (program and system information/program and system information protocol) table. Yet, the PSIP table includes an EAT 9 emergency alert table) for example.  
         [0040]     And, an operation of the tuner  204  is controlled by the channel manager  212 .  
         [0041]     In particular, the tuner includes an IB (in-band) tuner  202  receiving an in-band signal and an OOB (out-of-band) tuner  203  receiving an out-of-band signal.  
         [0042]     Yet, the EAT will be explained with reference to  FIG. 4  later.  
         [0043]     The tuner  204  records a result of receiving the broadcast signal in the channel manager  212 .  
         [0044]     The demodulator  205  is operative in modulating a signal tuned by the tuner  204  into a VSB/EVSB (vestigial side band/enhanced vestigial side band) signal.  
         [0045]     The demultiplexer  206  is operative in demultiplexing the signal modulated by the demodulator  205  into audio data, video data and PSI/PSIP table data.  
         [0046]     Demultiplexing of the audio/video data is controlled by the channel manager  212 . And, demultiplexing of the PSI/PSIP table data is controlled by the PSI/PSIP decoder  211 .  
         [0047]     The demultiplexed PSI/PSIP table is transferred to the PSI/PSIP decoder  211 . The demultiplexed audio/video data is transferred to the A/V decoder  207 . And, the A/V decoder  207  decodes the received data.  
         [0048]     The PSI/PSIP decoder  211  parses a PSI/PSIP section. The PSI/PSIP decoder  211  reads the rest of actual section data failing in section filtering of the demultiplexer  206  and then records the read data in the PSI/PSIP database  210 .  
         [0049]     The PSI/PSIP decoder  211  can parse EAT information included in the PSI/PSIP while parsing the PSI/PSIP section. In this case, according to the parsed information, the application &amp; UI controller  213  controls the display unit  208  to output a text associated with an emergency.  
         [0050]     The display unit  208  outputs audio or video data and outputs an OSD (on screen display) video.  
         [0051]     Moreover, differing from a general broadcast receiver, the cable broadcast receiver  101  further includes the cable modem  29  and the cable card module  216  to receive a cable broadcast signal from the cable broadcasting station  102 .  
         [0052]     An emergency alert message (EAM) can be received via the OOB tuner  203  if a cable card is inserted in the cable broadcast receiver  101 . If the cable card is not inserted in the cable broadcast receiver  101 , the emergency alert message can be received via the IB tuner  202  as well.  
         [0053]     The received emergency alert message can avoid an overlapping check of the received emergency alert message according to a reception band.  
         [0054]     For instance, after a current emergency alert message has been received, if it is decided that a reception band of the current emergency alert message is different from a reception band of a previously received emergency alert message, it can be confirmed that a new emergency has occurred. Hence, by clearing “sequence_number” of an EAT shown in  FIG. 4 , an overlapping check of an emergency alert message needs not to be performed separately.  
         [0055]     On the other hand, if the current emergency alert message is received via the same band of the previous emergency alert message, the overlapping check of an emergency alert message is carried out. As a result of the overlapping check, if it is an overlapped message, it can be confirmed that a new emergency has not occurred. Hence, it is unnecessary to process the emergency alert message anymore.  
         [0056]     Meanwhile, since the cable broadcast receiver  101  is in a plugged-out mode, in case that a power is not supplied to the cable broadcast receiver  101  at all, the cable broadcasting station  102  decides whether the cable broadcast receiver  101  is in the plugged-out mode in a following manner.  
         [0057]     First of all, the cable broadcasting station  102  can decide whether a plug of the cable broadcast receiver  101  is put into a socket using the fact that the cable broadcasting station  102  can bi-directionally communicate with the cable broadcast receiver  101  via the cable.  
         [0058]     If the plug of the cable broadcast receiver  101  is put into the socket, the able card module  216  can detect that a cable card is in an active mode. And, the application &amp; UI controller  213  can recognize the active mode of the cable card by transacting control signals with the cable card module  216 .  
         [0059]     In this case, if the cable broadcasting station  102  sends a request signal making a request for information indicating whether the cable card is in the active mode via the RF switch  201 , the request signal is delivered to the application &amp; UI controller  213  via the OOB tuner  203  or the cable modem  209 .  
         [0060]     In case of receiving the request signal, the application &amp; UI controller  213  transfers information detecting that the cable card is in the active mode to the cable broadcasting station  102  via the cable modem  209  or the OOB tuner  203 .  
         [0061]     This considers that bi-directional communications can be achieved between the cable broadcast receiver  101  and the cable broadcasting station  102  via the cable modem or OOB tuner  209  or  203  of the cable broadcast receiver  101 .  
         [0062]     Meanwhile, in case that the plug of the cable broadcast receiver  101  is not put into the socket, a signal flow of the plugged cable broadcast receiver  101  is not generated.  
         [0063]     Hence, the cable broadcasting station  102  transfers a signal that requests information indicating whether the cable card is in the active mode to the cable broadcast receiver  101 . If any response signal is not received from the cable broadcast receiver  101 , the cable broadcasting station  102  decides that the cable broadcast receiver  101  is in the plugged-out mode.  
         [0064]     As a result of the decision made by the cable broadcasting station  102 , if the cable broadcast receiver  101  is in the plugged-out mode, the cable broadcast receiver  101  is unable to receive an emergency alert message despite that an emergency has occurred. Hence, the cable broadcasting station  102  transmits information associated with the emergency not to the plugged-out cable broadcast receiver  101  but to the EAM receiving medium  103  as a different medium.  
         [0065]     The cable broadcasting station  102  can transmit the information associated with emergency to the EAM receiving medium  103  by wire or wireless communications.  
         [0066]     If the EAM receiving medium  103  is a wire phone for example, the emergency occurrence news can be outputted as sound. If the EAM receiving medium  103  is a mobile phone or PDA (personal digital assistants) for example, the emergency occurrence news can be outputted as at least one of sound and text.  
         [0067]     Namely, no special limitation is put on the EAM receiving medium  103 . All kinds of devices, which can receive and output the emergency associated information if the cable broadcast receiver  101  is in the plugged-out mode, can become the EAM receiving medium  103 .  
         [0068]     Meanwhile, the cable broadcasting station  102  decides a specific type of the EAM receiving mode  103  to transmit the emergency associated information in the following two manners for example.  
         [0069]     First of all, a user of the cable broadcast receiver  101  subscribes for the cable broadcasting station  102  to watch cable broadcasting. The type of the EAM receiving medium  103  is randomly decided using the user information acquired from the subscription.  
         [0070]     For instance, in case that user&#39;s home or mobile phone number is registered as the user information, the cable broadcasting station  102  transmits the emergency associated information to a phone of the user&#39;s home phone number or a mobile phone of the user&#39;s mobile phone number. So, the home or mobile phone having received the information outputs the received information in at least one of audio and video data formats.  
         [0071]     Secondly, a user can set a type of the EAM receiving medium  103  by himself.  
         [0072]     For instance, in case that the cable broadcast receiver  101  is in the plugged-out mode, the user directly designates a specific phone, a mobile phone, a PC, a laptop, a PDA or the like as the EAM receiving medium  103  to receive the emergency associated information.  
         [0073]     Of course, the first and second methods can be combined together as well. In particular, the type of the EAM receiving medium  103  is preferentially decided using the previously registered information of the user. Yet, if no information of the user exists or if the user intends to change the information randomly, the type of the EAM receiving medium  103  is set changeable.  
         [0074]      FIG. 3  is a flowchart of a method of processing an emergency alert message in bi-directional cable digital broadcasting according to one embodiment of the present invention. A method of transmitting an emergency alert message to a different medium in case that a cable broadcast receiver is in a plugged-out mode is explained in a sequence of time flow with reference to  FIG. 3  as follows.  
         [0075]     Referring to  FIG. 3 , a unique ID granted cable card is lent to a user of a receiver capable of receiving cable digital broadcasting if the user subscribes for a cable broadcasting station (not shown in the flowchart).  
         [0076]     The cable broadcasting station  102  maintains and manages a pair of the lent cable card&#39;s ID and a host ID of the user&#39;s cable broadcast receiver using a database IS 301 ).  
         [0077]     In case that an EAM (emergency alert message) needs to be transmitted due to an emergency occurrence, if the cable broadcast receiver  101  is in a plugged-out mode, an EAM receiving medium  103  capable of receiving the EAM instead of the cable broadcast receiver  101  is registered to the cable broadcasting station  102  (S 302 ).  
         [0078]     The EAM contains information associated with an emergency and can be outputted in at least one of audio and video data formats.  
         [0079]     The EAM receiving medium  103  is registered to the cable broadcasting station  102  in the aforesaid manner. In particular, a phone number registered in subscribing for the cable broadcasting station is used for the registration. Alternatively, an EAM receiving medium  103  newly changed and registered by a user in direct is used for the registration.  
         [0080]     The cable broadcasting station  102  transmits regular broadcasting to the cable broadcast receiver  101  having subscribed for the cable broadcasting station (S 303 ).  
         [0081]     The cable broadcasting station  102  decides whether an emergency occurs using an EAT (emergency alert table) while transmitting regular broadcasting (S 304 ).  
         [0082]     As a result of the decision (S 304 ), if the emergency does not occur, the cable broadcasting station  102  keeps transmitting the regular broadcasting normally.  
         [0083]     As a result of the decision (S 304 ), in case that the emergency has occurred, the cable broadcasting station  102  decides whether the cable broadcast receiver  101  subscribed for the cable broadcasting station  102  is in a plugged-in mode (S 305 ).  
         [0084]     As mentioned in the foregoing description of  FIG. 2 , the deciding step S 305  is carried out in a following manner. First of all, while transmitting regular broadcasting to the cable broadcast receiver  101  subscribed for the cable broadcasting station  102 , if an emergency situation occurs, the cable broadcasting station  102  periodically polls a signal inquiring whether the cable card, which is lent to the cable broadcast subscriber and is loaded in the cable broadcast receiver  101 , is in an active mode. If a response signal is not received within a predetermined duration, it is decided that the subscriber&#39;s cable broadcast receiver  101  (e.g., host TV) is in an plugged-out mode.  
         [0085]     As a result of the decision (S 305 ), if the cable broadcast receiver  101  subscribed for the cable broadcasting station  102  is in the plugged-out mode, a message containing emergency associated information is transmitted to the registered EAM receiving medium  103  (S 306 ).  
         [0086]     In this case, the emergency associated information can be outputted in at least one of audio and video data formats via the EAM receiving medium  103 .  
         [0087]     A user recognizing a situation of the emergency occurrence via the EAM receiving medium  103  or the like can put a plug of the cable broadcast receiver  101  into a socket to turn on a power to acquire detailed information of the emergency. Hence, the turned-on cable broadcast receiver  101  is automatically tuned to an emergency alert channel to provide more information to a viewer.  
         [0088]     Meanwhile, as a result of the decision (S 305 ), in case that the cable broadcast receiver  101  subscribed for the cable broadcasting station  102  is in the plugged-in mode, the cable broadcast receiver  101  receives an EAT associated with the emergency and the like (S 307 ).  
         [0089]      FIG. 4  is a diagram of a bit stream syntax of an emergency alert table (EAT) according to one embodiment of the present invention.  
         [0090]      FIG. 5  is a diagram of a meaning of “alert_Priority” value according to one embodiment of the present invention.  
         [0091]     A method of transmitting emergency associated information to an EAM receiving medium according to an urgent extent, a significant extent and the like of an emergency despite a plugged-out mode of a cable broadcast receiver is explained with reference to  FIG. 4  and  FIG. 5  as follows.  
         [0092]     In this case, an EAT can be defined by a PSIP (program and system information protocol) and the like in cable broadcasting.  
         [0093]     The EAT is transmitted from a cable broadcasting station  102 . A cable broadcast receiver  101  then parses the transmitted EAT to decide whether an emergency has occurred.  
         [0094]     In the present invention, “alert_priority” shall be newly defined. In particular, the EAT can be directly utilized by the cable broadcast receiver  101 .  
         [0095]     And, the “alert_priority” means a syntax representing a priority or significance.  
         [0096]     A method of using an EAM receiving medium  103 , a shown in  FIG. 5 , is appended for an pulled-out mode of the cable broadcast receiver  101 .  
         [0097]     For instance, if the cable broadcast receiver  101  is in the plugged-out mode and if “alert_priority” has a value equal to or greater than ‘11’ (high priority, maximum priority), the emergency associated information is transmitted to the EAM receiving medium  103 .  
         [0098]     This is not to transmit the emergency associated information is to the EAM receiving medium  103  if the priority of the emergency is relatively low (low priority, medium priority).  
         [0099]     And, it is a matter of course that the emergency associated information can be set to be transmitted to the EAM receiving medium  103  in case of an occurrence of any kind of emergency.  
       Second Embodiment  
       [0100]      FIG. 2  is a block diagram of a broadcast receiver equipped with an emergency alert message processing function in bi-directional cable digital broadcasting according to one embodiment of the present invention.  
         [0101]      FIG. 4  is a diagram of a bit stream syntax of an emergency alert table according to one embodiment of the present invention.  
         [0102]     A method of operating an emergency alert system in case of a standby mode of a cable broadcast receiver and the like is explained with reference to  FIG. 2  and  FIG. 4  as follows.  
         [0103]     First of all, the second embodiment of the present invention mainly deals with an EAS operating method for the case of a plugged-in cable broadcast receiver in a standby mode or for the case of a cable broadcast receiver that is outputting another input source (e.g., data output via DVD player), which differs from the first embodiment of the present invention dealing with the EAS operating method for the case of the plugged-out broadcast receiver.  
         [0104]     Of course, the first and second embodiments of the present invention can be separately implemented or can be combined together to be implemented as one invention.  
         [0105]     Besides, elements shown in  FIG. 2  are already explained in the description of the first embodiment of the present invention. Hence, detailed description of the elements shown in  FIG. 2  will be skipped in the following.  
         [0106]     The microcomputer  217 , as shown in  FIG. 2 , is operated when the plugged-in cable broadcast receiver  101  is in a standby mode. This is because in the standby mode of the cable broadcast receiver  101 , an operational power of the microcomputer  217  should be in an active mode to control other elements by receiving signals of a remote controller and the like.  
         [0107]     Hence, in the standby mode of the cable broadcast receiver  101 , the microcomputer  217  can control other elements to operate them under its control.  
         [0108]     In case that the cable broadcast receiver  101  is in the standby mode, the microcomputer  217  controls the channel manager  212 . And, the channel manager  212  controls the tuner  204  to be tuned to a predetermined emergency alert channel periodically.  
         [0109]     The emergency alert channel is a channel carrying news associated with an emergency. The emergency alert channel can employ a conventional frequency channel of a broadcasting station or can be set to a new frequency channel additionally.  
         [0110]     Over the emergency alert channel, an EAT (emergency alert table) containing information about a presence or non-presence of an emergency occurrence, a priority of an emergency and the like to the cable broadcast receiver  101 . An example of the EAT is shown in  FIG. 4 .  
         [0111]     The PSI/PSIP decoder  211  decides a presence or non-presence of an emergency occurrence, a priority of an emergency and the like by parsing the EAT transmitted from the cable broadcasting station  102 . According to a decision result, an emergency associated text is outputted via the display unit  208 . Or, the cable broadcast receiver  101  is switched to a normal mode from the standby mode and is then tuned to the emergency alert channel by controlling the tuner  204 .  
         [0112]     In this case, the normal mode means a state that a cable broadcast video is outputted via a screen of the cable broadcast receiver  101 .  
         [0113]      FIG. 5  is a diagram of a meaning of “alert_Priority” value according to one embodiment of the present invention.  
         [0114]      FIG. 6  is a flowchart of a method of processing an emergency alert message in bi-directional cable digital broadcasting according to another embodiment of the present invention.  
         [0115]     A method of operating an emergency alert system is explained in a time flow sequence with reference to  FIG. 5  and  FIG. 6  as follows. In this case, 1) a cable broadcast receiver is in a plugged-out mode, 2) a plugged-in cable broadcast receiver is in a standby ode, 3) a plugged-in cable broadcast receiver outputs an external input source, or 4) a plugged-in cable broadcast receiver outputs a cable broadcast.  
         [0116]     First of all, it is decided whether a cable broadcast receiver  101  is in a plugged-in mode (S 601 ). N this case, the cable broadcast receiver  101  includes a bi-directional cable DTV or the like for example.  
         [0117]     As a result of the decision (S 601 ), if the cable broadcast receiver  101  is not in the plugged-in mode but in a plugged-out mode, an emergency alert message is transmitted to a registered EAM receiving medium  103  (S 602 ).  
         [0118]     Yet, the steps S 601  and S 602  are explained in the description of the first embodiment of the present invention, of which detailed explanation will be skipped in the following description.  
         [0119]     As a result of the decision (S 601 ), if the cable broadcast receiver  101  is in the plugged-in mode, it is decided whether the cable broadcast receiver  101  is in a standby mode (S 603 ).  
         [0120]     In the standby mode, the cable broadcast receiver  101  is not operative in video output and the like since a power of the cable broadcast receiver  101  is turned off despite that a plug of the cable broadcast receiver  101  is put into a socket.  
         [0121]     As a result of the decision (S 603 ), if the cable broadcast receiver  101  is in the standby mode, the tuner  204  is controlled to be periodically tuned to an emergency alert channel (S 604 ).  
         [0122]     The emergency alert channel is a channel carrying news associated with an emergency. The emergency alert channel can employ a conventional frequency channel of a broadcasting station or can be set to a new frequency channel additionally. In particular, the emergency alert channel means a channel carrying such a table as an EAT (emergency alert table) and the like.  
         [0123]     The tuner  204  is periodically tuned to the emergency alert channel and the PSI/PSIP decoder  211  decides whether an emergency has occurred by parsing the EAT and the like (S 605 ).  
         [0124]     As a result of the decision (S 605 ), in case that the emergency has occurred, a power of the cable broadcast receiver  101  is turned on (S 606 ).  
         [0125]     According to an urgent or significant extent (not shown in “alert_priority” of  FIG. 5 ), a power of the cable broadcast receiver  101  can be set to be turned on or to maintain the standby mode.  
         [0126]     For instance, in the table shown in  FIG. 5 , only if “alert_Priority” has a value equal to or greater than 11 (high priority, maximum priority), the power of the cable broadcast receiver  101  is turned on. If “alert_Priority” has a value smaller than 11, the cable broadcast receiver  101  is kept in the standby mode.  
         [0127]     Namely, in case that the priority of the emergency is relatively low (low priority, medium priority), it is convenient for a user to keep the power of the cable broadcast receiver  101  in the standby mode.  
         [0128]     Alternatively, it can be designed that the power of the cable broadcast receiver  101  is turned on in case of any emergency occurrence.  
         [0129]     By continuously keeping the cable broadcast receiver  101  tuned to the emergency alert channel, emergency associated information received over the emergency alert channel is provided to a user. Of course, if a user tunes the cable broadcast receiver  101  to another channel, the cable broadcast receiver  101  is tuned to the corresponding channel according to a user&#39;s manipulation.  
         [0130]     As a result of the decision (S 603 ), if the cable broadcast receiver  101  is not in the standby mode but in a power-on mode, it is decided whether the cable broadcast receiver  101  is outputting a received cable broadcast (S 608 ).  
         [0131]     As a result of the decision (S 608 ), if the cable broadcast receiver  101  is outputting not the cable broadcast but another input source (e.g., A/V data output via DVD player), the tuner  204  is controlled to be periodically tuned to the emergency alert channel (S 609 ).  
         [0132]     The tuner  204  is periodically tuned to the emergency alert channel and the PSI/PSIP decoder  211  decides whether an emergency has occurred by parsing the EAT and the like (S 610 ).  
         [0133]     As a result of the decision (S 610 ), in case that the emergency has occurred, a tuning to the emergency alert channel is continuously maintained to provide emergency associated information received over the emergency alert channel to a user (S 607 ).  
         [0134]     Of course, if a user tunes the cable broadcast receiver  101  to another channel, the cable broadcast receiver  101  is tuned to the corresponding channel according to a user&#39;s manipulation.  
         [0135]     According to an urgent or significant extent (not shown in “alert_priority” of  FIG. 5 ), it can be designed that the cable broadcast receiver  101  keeps outputting another input source instead of being switched to the emergency alert channel if the urgent or significant extent is relatively low.  
         [0136]     If a user is viewing A/V data outputted via specific external input source, the currently viewed A/V data may be very important. Hence, by controlling the cable broadcast receiver  101  to be tuned to the emergency alert channel only in case of a relatively very high significance of the emergency, user&#39;s convenience can be enhanced.  
         [0137]     As a result of the decision (S 608 ), if a cable broadcast is being outputted, the PSI/PSIP decoder  211  decides whether an emergency has occurred by parsing the EAT and the like (S 611 ).  
         [0138]     The decision of the step S 611  is enabled because information containing EAT and the like can be received via the tuner  204  in cable broadcasting no matter what cable broadcast channel a user is watching.  
         [0139]     As a result of the decision (S 611 ), in case that an emergency has occurred, the broadcast receiver  101  is tuned to the emergency alert channel to provide emergency associated information to a user (S 607 ).  
         [0140]     Of course, if a user tunes the cable broadcast receiver  101  to another channel, the cable broadcast receiver  101  is tuned to the corresponding channel according to a user&#39;s manipulation.  
         [0141]     According to an urgent or significant extent (not shown in “alert_Priority” of  FIG. 5 ), it can be designed that the cable broadcast receiver  101  keeps outputting the currently-viewed cable broadcast instead of being switched to the emergency alert channel if the urgent or significant extent is relatively low.  
         [0142]     If a user of the cable broadcast receiver  101  is viewing a pay-per-view cable broadcast or an expensive cable broadcast charging a separate contents view, the currently viewed video may be more important than the emergency associated video.  
         [0143]     Hence, by controlling the cable broadcast receiver  101  to be tuned to the emergency alert channel only in case of a relatively very high significance of the emergency, user&#39;s convenience can be enhanced.  
         [0144]     Meanwhile, terminologies used in the description of the present invention are defined as considering functions in the present invention, which are variable according to usual practice or intentions of those who skilled in the art. Hence, their definitions shall be given based on the overall contents of the present invention.  
         [0145]     Accordingly, the present invention provides the following effects.  
         [0146]     Firs of all, if the power of the broadcast receiver capable of receiving cable digital broadcasting is turned off and if the broadcast receiver is in the plugged-out mode, the information indicating the emergency occurrence can be notified to a user.  
         [0147]     Secondly, if the power of the broadcast receiver capable of receiving cable digital broadcasting is turned on and if the broadcast receiver is in the standby mode or is outputting another data input source (e.g., outputting A/V data received from DVD player), the information indicating the emergency occurrence can be notified to a user.  
         [0148]     It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the inventions. Thus, it is intended that the present invention covers the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.