Patent Publication Number: US-6714561-B1

Title: Adaptive multiplexing/demultiplexing method and multiplexer/demultiplexer therefor

Description:
This is a Divisional of application Ser. No. 09/393,362 filed Sep. 10, 1999, which is a Continuation-In-Part of Application Ser. No. 08/938,018 filed Sep. 22, 1997, now U.S. Pat. No. 6,034,968 the disclosure of which is incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an adaptive multiplexing/demultiplexing method, and a multiplexer/demultiplexer using the same in the H.324M system, and more particularly, to an adaptive multiplexing/demultiplexing method capable of being effectively used in an error-prone channel, and a multiplexer/demultiplexer using the method. 
     2. Description of the Related Art 
     In general, the H.324M recommendation prescribes a multiplexing of video and audio signals which is effective in an error-prone channel such as a wireless channel, and includes H.223 multiplexing, H.223/Annex C multiplexing, H.245 controlling, a H.263 video coder/decoder (CODEC) and a G.723.1 audio CODEC. Particularly, according to the H.223 recommendation, in order to achieve video telephone and video conferencing in a general digital telecommunication network by the ITU-T (the Telecommunication standardization sector of the International Telecommunication Union), video, audio and other data are adaptively multiplexed in protocol data units (PDU) and then later demultiplexed. An H.223 multiplexer/demultiplexer (MUX/DEMUX) can be used when a channel bit error rate is 10 −6  or less. An H.223/Annex C MUX/DEMUX is a new MUX/DEMUX capable of improving error robustness, obtained by adding rate compatible punctured convolutional coder/decoder (RCPC CODEC) and automatic retransmission on request (ARQ) functions to the H.223 MUX/DEMUX. According to the H.223/Annex C MUX/DEMUX, when an error occurs in a receiver, the RCPC-encoded data is retransmitted by a transmitter at different rates. 
     However, it is nearly impossible to use the H.223 MUX/DEMUX in an error-prone channel due to its low error-resiliency. Also, in the case of the H.223/Annex C MUX/DEMUX, channel throughput is steeply decreased due to the ARQ, and there is extremely high complexity due to the RCPC. A measure of complexity can be determined by the amount or type of error protection components included in a multiplexing/demultiplexing scheme, for example. 
     SUMMARY OF THE INVENTION 
     To solve the above problems, it is an object of the present invention to provide an adaptive multiplexing/ demultiplexing method and a multiplexer/demultiplexer (MUX/DEMUX) using the same, in which a plurality of MUX/DEMUXs having different complexities are defined between the H.223 MUX/DEMUX and the H.223/Annex C MUX/DEMUX, so that the multiplexing can be achieved selectively according to specific circumstances by selecting between the plurality of MUX/DEMUXs, to match a particular circumstance via a trade-off of overhead of the MUX/DEMUXs. 
     According to an aspect of the object, there is provided an adaptive multiplexing/demultiplexing method in an H.324M system, the method comprising the steps of: (a) performing a first multiplexing/demultiplexing process having at least one of: the complexity and performance of the H.223 recommendation; (b) performing a second multiplexing/demultiplexing process having at least one of: the complexity of the H.223/Annex C recommendation; and (c) inserting one or more of a third type of multiplexing/demultiplexing processing having at least one of different complexities and performance levels from the steps (a) and (b) 
     Preferably, the third multiplexing/demultiplexing process of the step (c) uses a high-level data link control (HDLC) flag including an extra pseudo-random noise (PN) code having more bits than the H.223 recommendation. 
     Preferably, the third multiplexing/demultiplexing process of the step (c) comprises the substeps of: (c1) using an HDLC flag including an extra PN code having more bits than the H.223 recommendation; and (c2) using a header having more bits than the H.223 recommendation. 
     Preferably, the third multiplexing/demultiplexing process of the step (c) comprises the substeps of: (c1) using an HDLC flag including an extra PN code having more bits than the H.223 recommendation; (c2) using a header having more bits than the H.223 recommendation; and (c3) using error protection bits in either an adaptation layer or a multiplexer layer. 
     According to another aspect of the object, there is provided an adaptive multiplexer/demultiplexer (MUX/DEMUX) in an H.324M system, comprising: an H.223 MUX/DEMUX; an H.223/Annex C MUX/DEMUX; and one or more intermediate MUX/DEMUXs between the H.223/Annex C MUX/DEMUX and the H.223 MUX/DEMUX, having different complexities to the H.223/Annex C MUX/DEMUX and the H.223 MUX/DEMUX. 
     Preferably, the one or more intermediate MUX/DEMUXs uses a high-level data link control (HDLC) flag including an extra pseudo-random noise (PN) code having more bits than the H.223 recommendation. 
     Preferably, the one or more intermediate MUX/DEMUXs uses an HDLC flag including an extra PN code having more bits than the H.223 recommendation, and a header-having more bits than the H.223 recommendation. 
     Preferably, the one or more intermediate MUX/DEMUXs uses an HDLC flag including an extra PN code having more bits than the H.223 recommendation, a header having more bits than the H.223 recommendation, and error protection bits in either an adaptation layer or a multiplex layer. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above object and advantages of the present invention will become more apparent by describing in detail preferred embodiments thereof with reference to the attached drawings in which: 
     FIG. 1 is a diagram showing the structure of the H.324M system for a public switched telephone network (PSTN), in which the present invention is applied; 
     FIG. 2A is a block diagram of the adaptive MUX/DEMUX of FIG. 1 according to an embodiment of the present invention; 
     FIG. 2B is a block diagram of the adaptive MUX/DEMUX of FIG. 1 according to another embodiment of the present invention; 
     FIG. 2C is a block diagram of the adaptive MUX/DEMUX of FIG. 1 according to still another embodiment of the present invention; 
     FIG. 3A is a diagram showing the structure of a multiplex protocol data unit (MUX-PDU) of a general H.223 MUX/DEMUX; 
     FIG. 3B is a diagram showing the structure of the MUX-PDU of a first MUX/DEMUX; 
     FIG. 3C is a diagram showing an example where a first flag is applied to a long HDLC flag of FIG. 3B; 
     FIG. 3D is a diagram showing the structure of the MUX-PDU of a second MUX/DEMUX; and 
     FIG. 3E is a diagram showing an example where a first flag and a second flag are applied to a long HDLC flag and a long header of FIG. 3D, respectively. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     An H.324M system for a public switched telephone network (PSTN), shown in FIG. 1, includes an adaptive multiplexer/demultiplexer (MUX/DEMUX)  110  and a transcoder  120 . First, media data (video, audio and other data) are coded, and the coded media data is then multiplexed by the adaptive MUX/DEMUX  110  and the transcoder  120  to form a protocol data unit (PDU) (not shown), and then transmitted through a channel. 
     FIG. 2A is a block diagram of the adaptive MUX/DEMUX  110  of FIG. 1 according to an embodiment of the present invention. The adaptive MUX/DEMUX  110  shown in FIG. 2A includes an H.223 MUX/DEMUX  210 , a first MUX/DEMUX  220  obtained by applying a long HDLC flag to the MUX-PDU of the H.223 MUX/DEMUX  210 , a second MUX/DEMUX  230  obtained by applying a long header to the MUX-PDU of the first MUX/DEMUX  220 , a third MUX/DEMUX  240  obtained by applying an error bit to the MUX-PDU of the second MUX/DEMUX  230 , and an H.223/Annex C MUX/DEMUX  250 . 
     In the adaptive MUX/DEMUX  110  according to the present invention, as shown in FIG. 2A, a transcoding option is inserted between the H.223 MUX/DEMUX  210  having lower and the H.223/Annex C MUX/DEMUX  250  having high complexity, to define a new multiplexing/demultiplexing method by using the plurality of MUX/DEMUXs having different complexities and performance levels, i.e., the first MUX/DEMUX  220 , the second MUX/DEMUX  230  and the third MUX/DEMUX  240 . 
     FIG. 3A is a diagram showing the structure of a multiplex-protocol data unit (MUX-PDU) of the general H.223 MUX/DEMUX  210 . The MUX-PDU of the H.223 MUX/DEMUX  210  includes an 8-bit high-level data link control (HDLC) flag  310  used for controlling transmission, an 8-bit header  320  including data information, and a payload  330  including video and audio data. Here, the MUX-PDU is the minimal unit generated by multiplexing the audio and video data in the MUX, and is generated before the channel interfacing. Also, the HDLC flag  310  is a unique bit pattern of six successive is (for example, 01111110), representing a start or end of a frame. 
     FIG. 3B is a diagram showing the structure of a MUX-PDU of the first MUX/DEMUX  220  which operates as a high-level MUX/DEMUX of the H.223 MUX/DEMUX  210 . The MUX-PDU of the first MUX/DEMUX  220  includes a long HDLC flag  342  of 8 bits or more having more bits than the H.223 recommendation, an 8-bit header  344  including data information, and a payload  346  including video and audio data. The first MUX/DEMUX  220  adopts an HDLC flag of more bits as shown in FIG. 3B in order to improve synchronization between video and audio signals in the MUX-PDU of the H.223 MUX/DEMUX  210 . Thus, in order to maximize the synchronization, an extra flag having bits similar to those of pseudo-random noise (PN) having a high auto-correlation is inserted in the portion of the HDLC flag. 
     FIG. 3C is a diagram showing an example where a first flag  343  is applied in the long HDLC flag  342  of FIG.  3 B. 
     FIG. 3D is a diagram showing the structure of a MUX-PDU of the second MUX/DEMUX  230  which operates as a high-level MUX/DEMUX of the first MUX/DEMUX  220 . The MUX-PDU of the second MUX/DEMUX  230  includes a long HDLC flag  352  having more bits than the H.223 recommendation, a long header  354  including more bits than the H.223 recommendation, and a payload  356  including video and audio data. The second MUX/DEMUX  230  adopts a header of more bits as well as the long HDLC-flag applied to the MUX-PDU of the first MUX/DEMUX  220 , in order to improve synchronization between video and audio signals. Here, the long header  354  may be used for error protection. 
     FIG. 3E is a diagram showing an example where first and second flags  343  and  355  are applied in the long HDLC flag  353  and the long header  354 , respectively. 
     The third MUX/DEMUX  240  of FIG. 2A operates a high-level MUX/DEMUX of the second MUX DEMUX  230  and a low-level MUX/DEMUX of the H.223/Annex C MUX/DEMUX  250 , and the MUX-PDU of the third MUX/DEMUX  240  additionally includes an error protection bit in an adaptation layer or a multiplex layer, as well as the components of the MUX-PDU of the second MUX/DEMUX  230 . Thus, the third MUX/DEMUX  240  increases the error-resiliency with respect to the channel CODEC. 
     FIG. 2B is a block diagram of the adaptive MUX/DEMUX  110  of FIG. 1 according to another embodiment of the present invention. Here, only a first MUX/DEMUX  514 , corresponding to the first MUX/DEMUX  220  of FIG. 2A, is inserted between an H.223 MUX/DEMUX  210  and an H.223/Annex C MUX/DEMUX  250 . 
     FIG. 2C is a block diagram of the adaptive MUX/DEMUX  110  of FIG. 1 according to still another embodiment of the present invention. 
     Here, a first MUX/DEMUX  524 , corresponding to the first MUX/DEMUX  220  of FIG. 2A, and a second MUX/DEMUX  526 , corresponding to the second MUX/DEMUX  230  of FIG. 2A, are inserted between an H.223 MUX/DEMUX  210  having lower complexity and an H.223/Annex C MUX/DEMUX  250  having high complexity. 
     As described above, in the adaptive multiplexing/demultiplexing method and a MUX/DEMUX using the same according to the present invention, a plurality of MUX/DEMUXs having different complexities are selectively inserted between an H.223 MUX/DEMUX and an H.223/Annex C MUX/DEMUX in an H.324M system, thereby improving error-resiliency and performance according to the circumstances. In other words, the intermediate MUX/DEMUXs have different complexities, which in turn provide intermediate performance levels than that provided by the less complex H.223 recommendation and the more complex H.223 Annex C recommendation. A measure of performance level can be determined by the amount of errors occurring in the received via the multiplexing/demultiplexing scheme, for example. 
     The multiplexing/demultiplexing described above with reference to FIGS. 2A-2C and  3 A- 3 E may be implemented by software stored to a computer readable medium. The software includes computer readable program means for implementing the multiplexing and demultiplexing according to the H.223 standard, which has relatively low complexity, and according to the H.223 Annex C standard, which has relatively high complexity. Multiplexing/demultiplexing of intermediate complexity and performance is disposed therebetween. The software further implements and responds to the various HDLC flags, PN codes and header information for the various levels of multiplexing and demultiplexing complexity and performance. 
     Though the above provides descriptions of preferred embodiments of the invention, the invention is not limited thereto. One skilled in the art would understand that various modifications can be made, which are within the spirit and scope of the appended claims. For instance, ongoing modifications to the standards mentioned herein are deemed to be within the scope of the appended claims.