Abstract:
Disclosed is a method for receiving DMB services with a DMB receiving apparatus capable of operating both in first DMB receiving mode and in second DMB receiving mode in a weak electromagnetic field region. The method includes setting the DMB receiving apparatus to the first DMB receiving mode both to receive first DMB packet data and to detect second DMB packet data, checking detection of the second DMB packet data if an event occurs preventing reception of the first DMB packet data during the first DMB receiving mode, notifying the user of the DMB receiving apparatus of possibility of switching the apparatus from the first to the second DMB receiving mode if the second DMB packet data is detected, and switching the DMB receiving apparatus from the first to the second DMB receiving mode according to a user switching request.

Description:
PRIORITY 
   This application claims priority under 35 U.S.C. §119 to an application entitled “Method for Receiving Digital Multimedia Broadcasting in a Weak Electromagnetic Field Region and an Apparatus therefor” filed in the Korean Intellectual Property Office on Dec. 5, 2005 and assigned Ser. No. 2005-0117732, the contents of which are incorporated herein by reference. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a method and apparatus for receiving DMB (Digital Multimedia Broadcasting) services, and more particularly to a method and apparatus for effectively receiving DMB services even in a weak electromagnetic field region. 
   2. Description of the Related Art 
   DMB services represent the next generation digital broadcasting services to enable the user to enjoy high quality multichannel multimedia broadcasting. These DMB services may be provided through a variety of wireless communications sets such as a mobile terminal, vehicle-mounted wireless terminal, and home based television set. DMB services are generally divided into satellite DMB and terrestrial DMB according to the method of transmitting information. Satellite DMB utilizes satellite communications to enable subscribers to freely enjoy various multimedia contents through wireless terminals with a directional antenna, such as a personal mobile terminal and a vehicle-mounted wireless terminal, while they are moving outdoors. Terrestrial DMB generally provides multimedia services through the allotted frequencies of 204 to 210 MHz, VHF band corresponding to TV Channel Number  12 . 
   Referring to  FIG. 1 , which illustrates a conventional DMB system, satellite DMB services are provided by satellite DMB center  102  to send DMB signals of 13.824 to 13.883 GHz to satellite  100 , which in turn sends TDM (Time Division Multiplex) signals of 12.214 to 12.239 GHz for the terrestrial radio station  104  and signals of 2.630 to 2.665 GHz directly for a personal wireless terminal. The terrestrial radio station  104  is a system for providing the radio signals to a wireless terminal existing in a region not capable of receiving the signals directly from the satellite. Namely, the terrestrial radio station  104 , acting as gap filler, demodulates the TDM signals of 12.214 to 12.239 GHz received from the satellite  100 , and then modulates them into CDM (Code Division Multiplex) signals of 2.630 to 2.665 GHz to be received by the mobile terminal in a multiple fading environment such as a city or metropolis. 
   The DMB receiving terminal  106  may be a personal mobile terminal, vehicle-mounted wireless terminal, or fixedly mounted communications set to receive the signals directly from the satellite  100  or through the terrestrial radio station or gap filler  104 . The DMB signals received by the DMB receiving terminal  106  directly from the satellite  100  usually have a weak level. If the DMB receiving terminal  106  is far away from a metropolis with the gap filler  104 , it can only receive the signals from the satellite. Accordingly the region where the signals can received only from the satellite  100  is called a weak electromagnetic field region. The DMB signals received in the weak electromagnetic field region have a signal level of about −30 dBm to −100 dBm. On the contrary, if the DMB receiving terminal  106  is in a metropolis with the gap filler  104  or near to it, it can receive high-level DMB signals from the gap filler  104 . Accordingly the region where the DMB signals can be received from the gap filler  104  is called a strong electromagnetic field region. The DMB signals received in the strong electromagnetic field region have a signal level of about several tens to −50 dBm. Hence, it is necessary that the DMB receiving terminal  106  cover a wide range of signal levels extending from the strong electromagnetic field region to the weak electromagnetic field region. 
   In addition, the DMB receiving terminal  106  receives services from terrestrial DMB center  108  in the frequency band of 204 to 210 MHz. Thus, DMB services may be provided by both satellite and terrestrial broadcasting. Nevertheless, if the user of a DMB receiving terminal presently receiving satellite or terrestrial DMB services enters a weak electromagnetic field region, the DMB receiving terminal cannot receive the DMB signals, thus terminating the process of receiving the DMB services without providing advance notification of impossibility of receiving services. More specifically, because the DMB receiving terminal capable of receiving both satellite and terrestrial broadcasting can basically operate in terrestrial mode in a satellite weak electromagnetic field region, and in satellite mode in a terrestrial weak electromagnetic field region, it does not have to terminate the process of receiving the DMB services even if it enters either a satellite or terrestrial weak electromagnetic region when operating in either satellite or terrestrial mode. However, a conversion DMB receiving terminal will likely stop receiving the DMB services if it enters either satellite or terrestrial weak electromagnetic region when operating in either satellite or terrestrial mode. 
   SUMMARY OF THE INVENTION 
   It is an object of the present invention to provide a method and apparatus for receiving DMB services in a weak electromagnetic field region. 
   It is another object of the present invention to provide a method for switching a DMB receiving apparatus from the satellite mode to the terrestrial mode if the apparatus enters a satellite weak electromagnetic region when operating in the satellite mode and terrestrial DMB services may be received in that region. 
   It is still another object of the present invention to provide a method for switching a DMB receiving apparatus from the terrestrial mode to the satellite mode if the apparatus enters a terrestrial weak electromagnetic region when operating in the terrestrial mode and satellite DMB services may be received in that region. 
   According to an aspect of the present invention, a DMB receiving apparatus for receiving DMB (Digital Multimedia Broadcasting) services in a weak electromagnetic field region, includes a first DMB receiver for receiving first DMB packet data, a second DMB receiver for receiving second DMB packet data, a packet judgment unit for distinguishing the packet data received from the first and second DMB receivers into the first and the second DMB packet data, and a control unit for notifying the user of the DMB receiving apparatus of possibility of switching the apparatus from first to second DMB receiving mode if there occurs an event preventing the reception of the first DMB packet data during the first DMB receiving mode and the packet judgment unit detects the second DMB packet data, wherein the control unit switches the apparatus to the second DMB receiving mode according to a user switching request. 
   According to another aspect of the present invention, a method for receiving DMB services with a DMB receiving apparatus capable of operating both in first DMB receiving mode and in second DMB receiving mode in a weak electromagnetic field region, includes setting the DMB receiving apparatus to the first DMB receiving mode both to receive first DMB packet data and to detect second DMB packet data, checking detection of the second DMB packet data if there occurs an event preventing the reception of the first DMB packet data during the first DMB receiving mode, notifying the user of the DMB receiving apparatus of possibility of switching the apparatus from the first to the second DMB receiving mode if the second DMB packet data is detected, and switching the DMB receiving apparatus from the first to the second DMB receiving mode according to a user switching request. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawing in which: 
       FIG. 1  is a diagram of a conventional DMB system; 
       FIG. 2  is a block diagram for showing the structure of a DMB receiving terminal used for the present invention; 
       FIG. 3  is a flowchart illustrating the operation of a DMB receiving terminal in a weak electromagnetic region according to the present invention; and 
       FIGS. 4A to 4C  are display screens of a DMB receiving terminal displaying important operation phases according to the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Preferred embodiments of the present invention will be described below with reference to the accompanying drawings. In the drawings, the same or similar elements are denoted by the same reference numerals even though they are depicted in different drawings. In the following description, well-known functions or constructions are not described in detail to avoid obscuring the invention with unnecessary detail. 
   Referring to  FIG. 2 , a DMB receiving terminal or apparatus of the present invention includes a DMB receiving part  202 , terrestrial/satellite DMB packet judgment unit  200 , signal strength detector  201 , control unit  220 , DMB processing unit  209 , audio buffer  212 , and video buffer  214 . 
   The DMB receiving part  202  receives the DMB signals delivered to the DMB processing unit  209  under the control of the control unit  220 . The DMB receiving part  202  includes a terrestrial DMB receiver  206  for receiving terrestrial DMB packet data through an antenna and a satellite DMB receiver  204  for receiving satellite DMB packet data through an antenna. 
   The terrestrial/satellite DMB packet judgment unit  200  checks the packet data received from the DMB receiving part to determine whether the packet data from the DMB receiving part  202  is the terrestrial packet data from the terrestrial DMB receiver  206  or the satellite packet data from the satellite DMB receiver  204 , so that the terrestrial packet data from the terrestrial DMB receiver  206  is delivered to a terrestrial DMB processor  208  and the satellite packet data from the satellite DMB receiver  204  to a satellite DMB processor  210 . The signal strength detector  201  detects the strength of the signals received from the DMB receiving part  202  delivered to the control unit  220 . 
   The control unit  220  controls the whole functions of the DMB receiving terminal  106 , and, according to the present invention, notifies the user of the DMB receiving terminal of the possibility of switching the terminal from satellite DMB receiving mode to terrestrial DMB receiving mode if an event prevents reception of the satellite DMB packet data during the satellite DMB receiving mode and the terrestrial/satellite packet judgment unit  200  detects the terrestrial DMB packet data, and then switches the terminal to the terrestrial DMB receiving mode according to a user switching request. 
   The DMB processing unit  209  decodes the DMB signals received from the DMB receiving part  202  under the control of the control unit  220  according to the key data inputted by a key input device (not shown). Specifically the DMB processing unit  209  comprises terrestrial DMB processor  208  and satellite DMB processor  210  for respectively decoding the terrestrial and satellite DMB packet data received from the terrestrial/satellite packet judgment unit  200 . The video data and audio of the decoded DMB packet data are respectively delivered through a video buffer  214  and audio buffer  212  to their respective codecs. 
     FIG. 3  illustrates operation of the DMB receiving terminal  106  when having entered a weak electromagnetic field region during the satellite DMB receiving mode. Referring to  FIG. 3 , a description is provided of a process of continuously receiving the DMB services even when the terminal has entered a weak electromagnetic field region during operation in the satellite or terrestrial DMB receiving mode. 
   In step  300 , the DMB receiving terminal  106  is set to the satellite DMB receiving mode. The control unit  220  of the DMB receiving terminal  106  controls the terrestrial DMB receiver  206  and satellite DMB receiver  204  to output the DMB packet data to the terrestrial/satellite packet judgment unit  200 . In this case, the DMB receiving part  202  may change the header of the DMB packet data in order to distinguish the satellite and the terrestrial DMB packet data. For example, the satellite DMB receiver  204  maintains sync bytes of the satellite DMB packet data as “0×47” while the terrestrial DMB receiver  206  inserts a different number into the sync bytes of the terrestrial DMB packet data. Thus, the terrestrial/satellite packet judgment unit  200  distinguishes in step  302  the satellite and the terrestrial DMB packet data by checking the sync bytes contained in the packet data received from the terrestrial/satellite DMB receivers  204  and  206 . 
   In steps  300  to  302 , if the user sets the DMB receiving terminal to the satellite DMB receiving mode for receiving the satellite DMB services in step  300 , the terminal detects in step  302  the DMB packet of an RF-locked terrestrial DMB ensemble received on the background. In this case, the term “ensemble” means multiplexing multiple service components defined in “UHF Digital Radio Broadcasting Transmission and Reception Matching Standard” on a single physical transmission channel with a bandwidth of 1.536 MHz. Subsequently, the terrestrial/satellite (TS) packet received is delivered to the terrestrial/satellite packet judgment unit  200  to determine whether it is possible to receive the terrestrial DMB packet. If the terrestrial DMB packet is received, the next RF-fixed ensemble is checked to detect another TS packet. Likewise, all the ensembles are checked to repeatedly detect the terrestrial DMB packet data, thereby generating a list of the channels presently capable of providing the terrestrial DMB services. 
   In step  304 , the control unit  220  controls the signal strength detector  201  to check the strength of the present satellite DMB signals to be below a threshold value in order to determine whether the DMB receiving terminal is in a weak electromagnetic field region. If the DMB receiving terminal has entered a weak electromagnetic field region, the control unit  220  proceeds to step  306 , or otherwise returns to step  300  to continue the satellite DMB receiving mode. In step  306 , the control unit  220  controls the terrestrial/satellite packet judgment unit  200  to determine whether terrestrial DMB packet data is detected. 
   If the terrestrial DMB packet data is detected in the step  306 , the process goes to step  308 . The process otherwise goes to step  312  to notify the user that the terminal is in a region presently incapable of receiving the DMB services. When DMB packet data is not detected, the terminal may display on the screen a message of “Impossible to receive DMB. Operation terminated?”, as shown in  FIG. 4C . Subsequently, the control unit  220  may terminate the process in step  314  according to the user&#39;s request, or otherwise returns to step  300  to continue the satellite DMB receiving mode. However, returning to step  300  will not permit the user to enjoy the DMB services if the terminal travels out of a satellite weak electromagnetic field region incapable of providing the DMB services. Of course, if the terminal moves outside the satellite weak electromagnetic field region, it can provide the user with the DMB services. 
   Alternatively, if at step  306  of terrestrial DMB packet data, the control unit  220  proceeds to step  308  to notify the user of a possibility of switching the terminal from the satellite DMB receiving mode to the terrestrial DMB receiving mode. In this case, it may provide the terrestrial DMB channel information generated in step  302  of detecting the terrestrial DMB packet together with the notification of the switching. This enables the user to enjoy the terrestrial DMB services in a satellite weak electromagnetic field region. For example, the terminal may display on the screen a message of “Satellite DMB weak electromagnetic field region. Switching to terrestrial DMB receiving mode?” as shown in  FIG. 4A . 
   Subsequently, if the control unit  220  detects in step  310  a user request for switching the terminal from the satellite to the terrestrial DMB receiving mode, it proceeds to step  316 , or otherwise to step  312  to notify the user of impossibility of providing the satellite DMB services. If the user inputs a request of termination in step  314 , the control unit  220  terminates the operation, or otherwise returns to the step  300  to continue the satellite DMB receiving mode, as described above. 
   Meanwhile, if step  310  indicates the user request for switching, the control unit  220  proceeds to step  316  to switch the terminal to the terrestrial DMB receiving mode, and then to step  318  to detect satellite DMB packet data. More specifically describing the steps  316  to  318 , if the user switches the DMB receiving terminal to the terrestrial DMB receiving mode for receiving the terrestrial DMB services in step  316 , the terminal detects in step  318  the DMB packet of an RF-locked satellite DMB ensemble received on the background. Subsequently, the terrestrial/satellite (TS) packet received is delivered to the terrestrial/satellite packet judgment unit  200  to determine whether it is possible to receive the satellite DMB packet. If the satellite DMB packet is received, the next RF-fixed ensemble is checked to detect another TS packet. Likewise, all the ensembles are checked to repeatedly detect the satellite DMB packet data, thereby generating a list of the channels presently capable of providing the satellite DMB services. 
   In step  320 , the control unit  220  controls the signal strength detector  201  to check whether the present terrestrial DMB signal strength is below the threshold value in order to determine whether the DMB receiving terminal is in a weak electromagnetic field region. If the DMB receiving terminal has entered a weak electromagnetic field region, the control unit  220  proceeds to step  322 , or otherwise returns to step  316  to continue the terrestrial DMB receiving mode. In step  322 , the control unit  220  controls the terrestrial/satellite packet judgment unit  200  to determine whether satellite DMB packet data is detected. 
   If the satellite DMB packet data is detected in the step  322 , the process goes to step  324 . The process otherwise goes to step  312  to notify the user that the terminal is in a region presently incapable of receiving the DMB services. Subsequently, the control unit  220  terminates the process in step  314  according to the user&#39;s request, or otherwise returns it to the step  300  to continue the satellite DMB receiving mode. However, returning to the step  300  may not allow the user to enjoy the DMB services unless the terminal moves outside the satellite weak electromagnetic field region. Meanwhile, if the weak electromagnetic field region cannot receive both satellite and terrestrial DMB services, the terminal may continue the presently set DMB receiving mode, or switch to another DMB receiving mode according to the user&#39;s request. 
   Alternatively, if at step  322  satellite DMB packet data is detected, the control unit  220  proceeds to step  324  to notify the user of possibility of switching the terminal from the terrestrial DMB receiving mode to the satellite DMB receiving mode. In this case, it may provide the satellite DMB channel information generated in the step  318  of detecting the satellite DMB packet together with the notification of the switching. This enables the user to enjoy the satellite DMB services in a terrestrial weak electromagnetic field region. For example, the terminal may display on the screen a message of “Terrestrial DMB weak electromagnetic field region. Switching to satellite DMB receiving mode?”, as shown in  FIG. 4B . 
   Subsequently, if the control unit  220  detects in step  326  the user&#39;s request of switching the terminal from the terrestrial to the satellite DMB receiving mode, it returns to step  300  to perform the satellite DMB receiving mode, or otherwise to step  316 . 
   As described above, the invention enables the user to continuously enjoy DMB services by switching the DMB receiving terminal between terrestrial and satellite DMB receiving modes even when the terminal enters a terrestrial or satellite weak electromagnetic region during its operating in one of the two DMB receiving modes. 
   While the invention has been shown and described with reference to a certain preferred embodiment thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention. For example, the invention may be applied to European type DVB-H, Qualcomm Media Flow, Chinese type DMB, etc.