Abstract:
This data transmission system is formed by:  
     at least a transmitting part ( 50 ) relating to equipment ( 2 ) which comprises transmission circuits for processing useful data for the purpose of forming series of information signals and  
     at least a receiving part ( 51 ) of other equipment ( 3 ), the receiving part comprising receiving circuits for processing said transmitted series of information signals.  
     In this system integrity verification means are provided for producing at least an error indication for the transmitted information signals and, in the receiving circuits, means for validating series of transmitted information signals even in the case where the error indication appears.  
     Thus it is possible to transmit image data in a system that has a small bandwidth.

Description:
FIELD OF THE INVENTION  
         [0001]    The invention relates to a transmission system for useful data, formed by  
           [0002]    at least a transmitting part comprising transmission circuits for processing the useful data for the purpose of forming series of information signals, and  
           [0003]    at least a receiving part comprising receiving circuits for processing said transmitted series of information signals, the receiving part comprising:  
           [0004]    integrity verification means for producing at least an error indication of the transmitted information signals.  
           [0005]    The invention also relates to a method of transmitting useful data.  
           [0006]    The invention further relates to electronic equipment comprising a transmitting part and a receiving part, so that it becomes possible to transmit and receive information signals from such equipment.  
         BACKGROUND OF THE INVENTION  
         [0007]    The invention finds interesting applications notably in mobile radio systems for which one wishes to transmit multi-media information signals. For this subject one may be referred to patent document PCT WO 99/02003, which describes a system for transmitting images. Thus, equipment forming a mobile telephone station may transmit and receive images.  
           [0008]    In this type of system one is confronted with problems of errors which are caused by the transmission of these information signals over rather narrow passband channels which satisfy, for example, standard UIT H.223.  
         SUMMARY OF THE INVENTION  
         [0009]    The present invention proposes a system of the type defined in the opening paragraph which permits easy transmission notably of multi-media type of information signals.  
           [0010]    For this purpose, such a system is characterized in that said receiving circuits comprise means for validating transmitted series of information signals even if the error indication appears.  
           [0011]    The idea of the invention is to tolerate several errors which are not of necessity fatal to the link and to recover information signals even if errors have been detected. It should also be borne in mind that several errors on an image have less importance than errors in management data, for example, those which manage the setting of communications of a GSM type of network. The latter are thus to be monitored more meticulously.  
           [0012]    According to another characteristic feature of the invention, such a system in which the transmission circuits form a header for each series, is characterized in that the integrity verification means influence said headers.  
           [0013]    This other characteristic feature thus proposes to limit the verification of series of information signals transmitted in this header, which simplifies the processing while a satisfactory result is produced.  
           [0014]    A transmission method that can be applied to such a system is characterized in that it comprises the following steps:  
           [0015]    positioning a header for the useful data to be transmitted,  
           [0016]    analysis of said header to produce an error indication of the header,  
           [0017]    acceptance of useful data for certain error indications. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]    These and other aspects of the invention are apparent from and will be elucidated, by way of non-limitative example, with reference to the embodiment(s) described hereinafter.  
         [0019]    In the drawings:  
         [0020]    [0020]FIG. 1 shows a system in accordance with the invention,  
         [0021]    [0021]FIG. 2 shows in a diagrammatic manner the transmitting and receiving parts of the system in accordance with the invention,  
         [0022]    [0022]FIG. 3 shows the organization of transmitted series of information signals,  
         [0023]    [0023]FIG. 4 shows a schematic diagram of the implementation of the invention in the framework of the standards cited above,  
         [0024]    [0024]FIGS. 5 and 6 show a flow chart explaining the operation of the receiving part.  
     
    
     DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0025]    In FIG. 1 is represented a system in accordance with the invention. Reference  1  indicates a base station and references  2  and  3 , mobile stations. These mobile stations comprise on their front face:  
         [0026]    a keypad  10 , a screen  11 , a microphone  12 , a loudspeaker  14  for station  2 ,  
         [0027]    a keypad  20 , a screen  21 , a microphone  22 , a loudspeaker  24  for station  3 , and installed on top:  
         [0028]    an antenna  30  and a television camera  31  for station  2 ,  
         [0029]    an antenna  40  and a television camera  41  for station  3 .  
         [0030]    Thanks to the system in accordance with the invention, the images captured by one of the cameras  31  or  41  may be made visible on the screen  11  or  21  of the other mobile station. These stations  2  and  3  are mobile radiotelephones that satisfy a standard of the GSM type. As, on the one hand, this standard allocates a passband that is small enough for the transmission of images and that, on the other hand, the transmission is made with comparatively reduced power, this image transmission is thus affected by errors.  
         [0031]    [0031]FIG. 2 shows the diagram of the transmission between the two mobile stations  2  and  3 . The transmission is considered of images in the direction from station  2  to station  3  while the base station  1  is passed along. The images in question are images captured by the camera  31  of station  2  to be displayed on screen  21  of station  3 . To the useful data, which solely relate to the images, are added other data for the transmission management with a view to forming series of information signals which will be analyzed at the receiving part of station  3 . All these data are multiplexed in the transmitting part  50  of the station  2  and are processed by the receiving part  51  of the station  3 .  
         [0032]    In FIG. 3 are represented two series of information signals S 1  and S 2 . This FIG. 3 shows the positioning of these management data, which is notably the positioning of a synchronization data FLG (HDLC), a series length data MPL and a Golay code data as recommended in said standard UIT H.223. This coding information is referred to as GOL. Thereafter, the useful data PDU are transmitted. The information MPL contained in the series S 1  permits to determine the time TA at which the series of information signals S 2  occurs.  
         [0033]    [0033]FIG. 4 summarizes the standards used in the example of embodiment described. Among the various boxes shown, C 1  to C 16 , certain boxes are represented in gray to indicate the parts modified by the measures according to the invention.  
         [0034]    Box C 1  represents the input/output connections of video equipment,  
         [0035]    Box C 2  represents the input/output connections of audio equipment,  
         [0036]    Box C 3  represents the applications relating to the user and involving data,  
         [0037]    Box C 4  represents the control system of the system,  
         [0038]    Box C 5  represents the assembly of the boxes explained by Recommendations H.234  
         [0039]    Box C 6  represents a video codec according to the Recommendations H.263/H.261  
         [0040]    Box C 7  represents an audio codec according to the Recommendations G.723/G.723C, this box has been modified to manage a delay indicated by box C 11 , so as to ensure that there is a synchronization between image and sound.  
         [0041]    Box C 8  relates to the protocols concerning data of the user, for example, the file transfer.  
         [0042]    Boxes C 9  and C 10  relate to the control protocol concerning the signaling of the system. It permits to control functions at either end of the link.  
         [0043]    Box C 12  represents the multiplexing and the demultiplexing of the various data. It is in this box that the headers are inserted, the length of the series of information signals and the encoding by means of the Golay code.  
         [0044]    Boxes C 13  and C 14  relate to the modem functions for transmitting and receiving the various data.  
         [0045]    Box C 15  represents the GSM network.  
         [0046]    Box K 16  represents the multi-point control unit.  
         [0047]    The operation of the system according to the invention is explained with the aid of flow charts of FIGS. 5 and 6.  
         [0048]    In FIG. 5, box K 1  indicates the analysis of the data stream with a view to the search for the indication FLG of the start of the series. This analysis is made of two octets. If these two octets do not contain the indication of synchronization (FLG) (box K 2 ), an examination is made whether the whole series has been received or not (box K 3 ). As long as the series has not been received, box K 1  is returned to. If the whole series has been processed and the indication FLG has not been found, box K 10  is proceeded to. In this box K 10  a sufficient number of octets is processed to apply the calculations determining the Golay code syndrome cited above. If this syndrome indicates &lt;&lt; 0 &gt;&gt;, box K 12 , then the information signals are estimated to be valid and the &lt;&lt;Robust&gt;&gt; mode is proceeded to, box K 14 . If this syndrome is not equal to &lt;&lt; 0 &gt;&gt;, a test is made in box K 16  whether or not one is in the &lt;&lt;Robust&gt;&gt; mode. If one is, box K 18  is proceeded to. If the series is validated there, the &lt;&lt;Uncertain&gt;&gt; mode is proceeded to. If the test of the box K 16  indicates a mode that is not the &lt;&lt;Robust&gt;&gt; mode, box K 19  is proceeded to. The start indication is ignored and the variable MPL is set to the maximum length value that a series can reach. From there, box K 1  is proceeded to.  
         [0049]    The test indicated in box K 2  may prove to be positive, operations shown in FIG. 6 are thus performed.  
         [0050]    In FIG. 6 the processing indicated in box K 30  is the same as that indicated in box K 10 . If the syndrome proves to be satisfactory, which is tested in box K 32 , box K 34  is proceeded to, which is a test of the position found relative to that contained in the variable MPL. If the result of the test is positive, box K 36  is proceeded to. There the &lt;&lt;Robust&gt;&gt; mode is changed to and the series of data is validated. If there is a conflicting situation with respect to these positions, tests are made in what mode one is (box K 38 ). If one is in the &lt;&lt;Robust&gt;&gt; mode, the header is ignored and one thinks that this is the information (box K 40 ). If one is not in this mode, an examination is made whether the option of standard H.223, which provides to send the information of the header of the preceding series in the header of the current series, is used (box K 42 ). If this is not the case, box K 44  is proceeded to, where the &lt;&lt;Robust&gt;&gt; mode is gone to and the series is rejected, otherwise the series is validated with the optional information contained in the current header and the &lt;&lt;Robust&gt;&gt; mode is proceeded to (box K 46 ).  
         [0051]    If the analyzed syndrome of box K 32  is not satisfactory, box K 50  is proceeded to and the position (the operating time of the information MPL) is examined. If this position is all right, box K 52  is proceeded to, where the series is validated, but the &lt;&lt;Uncertain&gt;&gt; mode is proceeded to. If this position is not all right, an examination is made in box K 54  in which mode one is. If one is not in the &lt;&lt;Robust&gt;&gt; mode, the header is ignored, one thinks that this is information (box K 56 ). If one is in the &lt;&lt;Uncertain&gt;&gt; mode, one remains there and rejects the series (box K 58 ).  
         [0052]    The indications of transmission errors are notably given by various tests indicated in FIGS. 5 and 6; for example, that of box K 2 , if the synchronization pattern has not been found, that of box K 12  and box K 32  when the syndrome is different from &lt;&lt; 0 &gt;&gt;.  
         [0053]    The invention covers any transmitter and any receiver that utilizes the concepts of the present invention.