Patent Document

CLAIM OF PRIORITY 
       [0001]    This application claims the benefit under 35 U.S.C. §119(a) from an application entitled “System for Providing a Video Service, and Apparatus and Method for the Same,” filed in the Korean Intellectual Property Office on Oct. 25, 2006 and assigned Serial No. 2006-103807, the contents of which are hereby incorporated by reference in its entirety. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a system, apparatus, and method for providing a video service. More particularly, the present invention relates to an apparatus and a method for providing a multimedia video service in real time to a mobile terminal connected by a wireless network. 
         [0004]    2. Description of the Related Art 
         [0005]    In order to provide multimedia application service when the available bandwidth is relatively limited, techniques such as the MPEG4/H.264 compression technology uses schemes such as a motion compensation and prediction scheme, discrete cosine transform, vector quantization, variable length encoding, etc., to reduce the bandwidth required when providing multimedia service. 
         [0006]    The prediction scheme is used to provide inter-coding, and thereby has a large impact on improving compression efficiency. Inter-coding is a method that compares a macro block of a previous frame with a macro block of a current frame in order, and encodes the difference value on the basis of the prediction scheme. 
         [0007]    More particularly, an inter-coding method of a moving picture includes one I-frame (intra-frame) and a plurality of P-frames (predict-frames) for each time. In coding, the I-frame is independently encoded regardless of adjacent frames (intra-coded), and P-frames are predict-frames referring to a temporally adjacent I-frame or P-frame. Typically, the intra-coding is used for coding of the I frame, and the inter-coding is used for coding of the P-frame. However, if a new part, which is not included in the I-frame, is found in the P-frame, then intra-coding can be performed for the corresponding P-frame. Therefore, the moving picture is encoded by using the intra-coding and inter-coding together at the specific ratio. 
         [0008]    Accordingly, in order to restore the inter-coded frame, a frame that was previously encoded and reconstructed is used as a basis for the restoration. However, the loss of information in one frame can have a considerable effect on image quality of a subsequent frame. Therefore, even a slight transmission error can have considerable impact, sometimes breaking a video bit stream. Therefore, the prediction scheme of inter-coding is particularly vulnerable to transmission problems, as the error may be spread to a subsequent reference frame unless special solutions are not provided. 
         [0009]    To this end, Automatic Repeat Request (ARQ), Forward Error Correction (FEC) and error concealment have been developed to provide some limited means of preventing the complete break-down of a video bit stream. However, it is very difficult to implement the aforementioned compression and prediction schemes and completely prevent temporal error propagation. 
       SUMMARY OF THE INVENTION 
       [0010]    Accordingly, the present invention has been made in part at least to solve some of the above-mentioned problems occurring in the prior art, as well as provide other advantages. The present invention provides a system, apparatus and method for providing a video service that is resistant to error propagation. 
         [0011]    In accordance with an exemplary aspect of the present invention, there is provided a method for providing a video service of a video service system, which provides a multimedia video service in real time, to a mobile terminal connected by a wireless network. the method including the steps of: transmitting a video frame to a mobile terminal demanding the video service, in which the frame is coded by a coding scheme comprising a first coding scheme and a second coding scheme together at a predetermined ratio; receiving coding scheme change determining information for determining whether or not to change the coding scheme of the video frame from the mobile terminal during transmitting the video frame; and changing the coding scheme of the video frame to be transmitted to the mobile terminal according to the result of analyzing the coding scheme change determining information. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    The above and other exemplary aspects, features and advantages of the present invention will become more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which: 
           [0013]      FIG. 1  illustrates a communication system according to the present invention; 
           [0014]      FIG. 2  is a block diagram illustrating a server according to an embodiment of the present invention; 
           [0015]      FIG. 3  is a control flowchart illustrating a method of providing a video service from the server according to an embodiment of the present invention; 
           [0016]      FIG. 4  is a block diagram illustrating a mobile terminal according to an embodiment of the present invention; and 
           [0017]      FIG. 5  is a control flowchart illustrating a method of providing a video service from a mobile terminal according to an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0018]    Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings for explanatory purposes. As the embodiments are not the only manner in which the invention may be practiced, a person of ordinary skill in the art understands that invention is not limited to the examples shown and described. For the purposes of clarity and simplicity, a detailed description of known functions and configurations incorporated herein will be omitted when it may obscure the subject matter of the present invention by their inclusion. 
         [0019]      FIG. 1  illustrates one example of a communication system according to the present invention. 
         [0020]    Referring to  FIG. 1 , a server  100  is connected to a mobile terminal  200  through a wireless network  300 . The server  100  codes a moving picture according to a coding scheme using both an intra-coding and inter-coding scheme at a predetermined ratio and transmits the coded picture, and the mobile terminal  200  receives and decodes the coded moving picture. 
         [0021]    In addition, according to the present invention, the mobile terminal  200  while decoding the moving picture transmitted from the server, determines whether there is an error regarding the received frame, e.g., whether there is packet loss regarding the received frame. 
         [0022]    Further, the mobile terminal  200  can monitor an overflow or underflow occurrence. If an error occurs, the mobile terminal  200  provides the server  100  with information about an error occurrence and a position in which the error has occurred. At this time, the information identifying the position in which the error has occurred is provided for each macro block received by the mobile terminal  200 . The video frame includes a plurality of macro blocks, and the coding is performed for each macro block. 
         [0023]    Furthermore, the mobile terminal  200  transmits to the sever  100  other information, such as a received signal electric field strength or Received Signal Strength Indicator (RSSI), a Carrier to Interference and Noise Ratio_(CINR) and a buffer&#39;s own state, etc. Hereinafter, the information related to a receipt of the video frame from the mobile terminal, such as the RSSI, CINR and the buffer&#39;s own state, may be the receiving environment information. 
         [0024]    The server  100  receives from the mobile terminal  200  the error occurrence and the position in which the error has occurred, and then performs coding according to a changed coding scheme from a subsequent macro block of the macro block in which the error has occurred. For example, the server  100  performs intra-coding from the subsequent macro block of the macro block in which the error has occurred or thereafter. Or the server  100  performs coding by adjusting the ratio of the intra-coding and the inter-coding, when the error has occurred, the ratio of the intra-coding is increased. 
         [0025]    Still referring to  FIG. 1 , the server  100 , in turn, receives the information regarding the reception environment from the mobile terminal  200  as described above, analyzes the reception environment information, and determines whether or not to change the coding scheme. The change in the coding scheme might be required, or optional, depending on the information about the reception environment. If the information about the reception environment includes the RSSI or CINR, the server  100  can determine how far the terminal is away from a base station. As an analyzed result, if it is determined that the mobile terminal is relatively close to the base station, the server  100  typically maintains the current coding scheme. If it is determined that the mobile terminal  200  is relatively far from the base station, the server  100  typically changes the current coding scheme because of the possibility of a packet loss, or because a packet loss ratio is high or has increased by a predetermined value. 
         [0026]    Furthermore, according to the present invention, if the coding scheme change determining information indicates that a buffer has a large available capacity capable of storing a video frame of the terminal, the server  100  may change a current coding scheme to an intra-coding scheme that allows the information to include many coded frames. 
         [0027]      FIG. 2  provides a block diagram of the described server  100  shown in  FIG. 1 . Referring to  FIG. 2 , the server  100  includes an encoder  110 , an output buffer  130 , a server controller  140  and a transmitting/receiving unit  150 . Under the control of the server controller  140 , the encoder  110  typically codes the video for each macro block according to a coding scheme using both the intra-coding and the inter-coding at a predetermined ratio and provides the coded video frames to the transmitting/receiving unit  150  through the output buffer  130 . The transmitting/receiving unit  150  subsequently transmits the coded video frames retrieved from the output buffer  130  to the mobile terminal. Further, the transmitting/receiving unit  150  receives the coding scheme change determining information transmitted from the mobile terminal and transmits the received information to the server controller  140 . 
         [0028]    Here, the coding scheme change determining information typically includes information such as information about the reception environment of the mobile terminal (i.e. receiving environment information), an error occurrence, and the position in which the error has occurred. However the coding scheme change determining information is not limited to the aforementioned items, and it is to be understood by a person of ordinary skill in the art that any information related to the change determination on the coding scheme where the change of the coding scheme is necessary may also be included. 
         [0029]    Still referring to  FIG. 2 , the server controller  140  receives the coding scheme change determining information. The coding scheme change determining information indicates a specific error occurrence and the position in which the error has occurred, and the server controller  140 , in response to the coding scheme change determining information received from the mobile terminal  100  (via the wireless network  300 ) typically performs coding according to a changed coding scheme continuing from the macro block or the subsequent macro block of the corresponding macro block in which the error has occurred. 
         [0030]    As an alternative to changing the coding scheme as described herein above, the server controller  140  may perform coding in which the ratio of the intra-coding and the inter-coding is changed/controlled. 
         [0031]    Furthermore, if the coding scheme change determining information comprises some or all of the receiving environment information, the server controller  140  analyzes the receiving environment information and determines whether or not to change the coding scheme. If it is determined that the mobile terminal is within an acceptable range from (relatively close to) the base station as the result of the analysis, the server controller  140  typically maintains the current coding scheme. However, if it is determined that the mobile terminal is outside or close to an unacceptable range from the base station, the server typically changes the current coding scheme when the possibility of a packet loss, or a packet loss ratio has increased or is high (for reached a certain predetermined threshold). 
         [0032]    As described above, the change of the coding scheme can be accomplished by performing intra-coding from the subsequent macro block of the macro block which the error has occurred or thereafter, or by decreasing the ratio of the inter-coding and increasing the ratio of the intra-coding. A person of ordinary skill in the art understands and appreciates that the changes in ratios of the inter-coding and intra-coding also potentially impacts the bandwidth requirements for transmissions, as well as storage requirements of the buffer at the server, and must also take in account the capabilities/capacities of the mobile terminal. 
         [0033]      FIG. 3  provides a flow chart illustrating an example of one way control flow of the server controls changing of according scheme according to the present invention. 
         [0034]    Referring to  FIG. 3 , in step  310 , the server  100  (shown in  FIG. 1 ) codes the input video for each macro block according to a certain coding scheme using both the intra-coding and inter-coding at a predetermined ratio. Thereafter, in step  320 , the server  100  receives the coding scheme change determining information and at step  330  determines whether or not to receive the coding scheme change determining information transmitted from the mobile terminal  200 . 
         [0035]    With regard to step  330 , after receiving the coding scheme change determining information from the mobile terminal  200  via the wireless network  300 , the server  100  proceeds determines whether or not to necessitate the change of the coding scheme. If the coding scheme change determining information from the mobile terminal indicates the occurrence of an error and the position in which the error has occurred, changing of the coding scheme is typically necessary. In addition, if the coding scheme change determining information comprises or includes the receiving environment information (indicating information about the reception environment of the mobile terminal), the server determines at step  330  whether or not to necessitate the change of the coding scheme according to the context of the receiving environment information. 
         [0036]    At step  340 , if the coding scheme change determining information indicates the occurrence of an error occurrence and the position in which the error has occurred, the server  100  changes the coding scheme performed of only the macro block in which the error has occurred or thereafter. Otherwise, the server controller  140  performs coding by adjusting the ratio of the intra-coding and the inter-coding. In the above two cases, the coding scheme is changed in order for the transmitted video frames to be resistant to packet loss. 
         [0037]    If the coding scheme change determining information comprises or includes the receiving environment information, and the receiving environment information indicates that the terminal is in a position where the possibility of the packet loss occurrence is high according to the result of analyzing the information on the receiving environment, the server  100  changes the coding scheme in order for the transmitted video frames to be resistant to packet loss. 
         [0038]    Still referring to  FIG. 3 , at step  350  the server  100  determines whether or not the transmission of the video frame is complete, and if the transmission of the video frame is not complete, the server  100  performs step  320  again. 
         [0039]    In the meantime,  FIG. 4  illustrates a block diagram of the mobile terminal  200  shown in  FIG. 1  and typically used with the present invention. Referring to  FIG. 4 , the mobile terminal includes a key input unit  210 , a controller  240 , a memory  220 , a wireless transmitting/receiving unit  250 , a RSSI measurement unit  260 , a display unit  230 , an error detector  270  and a decoder  280 . 
         [0040]    According to the present invention, the controller  240  of the mobile terminal  200  generally controls the functions of the mobile terminal. In addition, the transmitting/receiving unit  250  outputs received video frames to the decoder  280 . The decoder  280  decodes the video frames for each macro block. If the macro block of the input video frame is coded according to an intra-coding or inter-coding scheme, the decoder  280  appropriately decodes the macro block according to the respective scheme used. The error detector  270  monitors the decoder  280  and determines whether or not an error has occurred during the decoding, typically that a packet loss occurred. If packet loss has occurred, the error detector  270  provides to the controller  240  the packet loss occurrence and the position where the packet loss occurred. 
         [0041]    Further, the RSSI measurement unit  260  measures the RSSI, which indicates the strength of signals from the base station of the mobile terminal, and provides the measured RSSI to the controller  240 . Furthermore, the mobile terminal further includes a Carrier to Interference-plus-Noise Ratio (CINR) measurement unit (not shown) if necessary to measure the CINR, and provides the measurement result to the controller  240 . 
         [0042]    The controller  240  receives information from the error detector  270  regarding the occurrence of packet loss and the position where the packet loss occurred, and the RSSI from the RSSI measurement unit  260 , and then instructs the wireless transmitting/receiving unit  250  to transmit to the server  100  that is transmitting the video frames the information regarding packet loss and position, and typically the RSSI information. The server  100 , in turn using the information received to make any necessary adjusts to the transmission to the mobile terminal. 
         [0043]    As described above, the video frame typically includes a plurality of macro blocks, and the coding is performed for each macro block, so that it is preferable that the packet loss position information, i.e., the position in which the error has occurred, is the position of the macro block. 
         [0044]    The wireless transmitting/receiving unit  250  converts voice data and control data into wireless signals and transmits the wireless signals, receives the wireless signals, and converts the received wireless signals into voice data and control data and outputs the converted data. The key input unit  210  includes a plurality of number and context keys, and provides an input of a keyword for searching for a telephone number by a user, and outputs a keyword input signal to the controller  240 . 
         [0045]    The display unit  230  may typically comprise a Liquid Crystal Display (LCD), a Thin Film Transistor (TFT), an organic electroluminescence (organic EL) or the like, and displays various data and videos under the control of the controller  240 . The memory  220  includes a non-volatile memory such as a Read Only Memory (ROM), a Random Access Memory (RAM), a voice memory or the like, for storing a plurality of programs and information necessary when controlling the operation of the mobile terminal  200 . 
         [0046]      FIG. 5  provides a flowchart illustrating one example of the steps that can be used by the server to control the changing of the coding scheme according to the present invention. 
         [0047]    Referring to  FIG. 5 , at step  410  the mobile terminal  200  decodes the video frames received from the server  100  for each macro block. The mobile terminal  200  appropriately decodes the macro block according to whether the input video frame is code by intra-coding or inter-coding. 
         [0048]    At step  420 , the mobile terminal  200  determines whether or not the packet loss occurred during decoding of the video frame. 
         [0049]    At step  430 , if packet loss has occurred, the mobile terminal  200  transmits to the server  100  data indicating the occurrence of the packet loss and the position where the packet loss occurred as the coding scheme change determining information. Alternatively or in addition thereto, if the mobile terminal  200  measures the RSSI, the mobile terminal  200  transmits to the server  100  the RSSI information as the coding scheme change determining information. 
         [0050]    At step  440 , the mobile terminal  200  receives from the server  100  the video frames coded by the coding scheme in a different way than the video frames coded by the previous coding scheme, and appropriately performs decoding. 
         [0051]    At step  450 , the mobile terminal  200  determines whether or not the transmission of the video frame was complete, and if the transmission of the video frame is not complete, to the method returns to step  420  to determine whether the video frame receiving information. 
         [0052]    As described above, the present invention provides for changing the coding scheme according to the transmitting/receiving state of the video between the terminal and the server and thus can correspond to the breakdown of the video in the wireless environment. 
         [0053]    The invention has been shown and described with reference to certain exemplary embodiments thereof. The exemplary embodiments of the present invention are applied to the server and the video transmission/reception between the server and the terminal. However, it is a matter of course that the present invention also can be applied to the video transmission/reception between servers or between terminals. Thus, the scope of the invention is not limited by the described embodiments and the scope of the invention as defined by the appended claims.

Technology Category: 5