Abstract:
A TDM (Time Division Multiplexing) frame applicable to digital broadcast data transmission in an FTTH (Fiber To The Home) system and a method for transmitting and receiving the TDM frame is disclosed. The TDM frame and methods are applicable to transmit a plurality of digital broadcast data units having different synchronous clocks using a simple format. The TDM frame for multiplexing digital broadcast and communication signals having different synchronous signals in a broadcast/communication convergence system using an FTTH system comprises a framing bit field for identifying a start and end of the TDM frame seamlessly provided; two MPTS (Multiple-Program Transport Stream) fields respectively having at least one bit assigned for digital broadcast data transmission wherein an amount of input digital broadcast data is adjusted according to a difference between a multiplexing rate and an input rate associated with the digital broadcast data in the digital broadcast data transmission; and a fast Ethernet field having at least one bit assigned for communication data transmission.

Description:
CLAIM OF PRIORITY 
   This application claims priority, pursuant to 35 U.S.C. §119, to that patent application entitled “TIME DIVISION MULTIPLEXING FRAME FOR MULTIPLEXING DIFFERENT SYNCHRONOUS SIGNALS AND METHOD FOR TRANSMITTING AND RECEIVING THE SAME,” filed in the Korean Intellectual Property Office on Jan. 30, 2004 and assigned Ser. No. 2004-6177, the contents of which are hereby incorporated by reference. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to an FTTH (Fiber To The Home) systems, and more particularly to a TDM (Time Division Multiplexing) frame applicable for digital broadcast data transmission in an FTTH (Fiber To The Home) system and a method for transmitting and receiving the TDM frame. 
   2. Description of the Related Art 
   A broadcast services and communication services are currently provided independently to the home or office. Research on convergence of broadcast services and communication services is presently being conducted. Bi-directional HFC (Hybrid Fiber Coaxial) type system, and IP (Internet Protocol)-based system using an xDSL (x Digital Subscriber Line) network are known broadcast/communication systems. A system based on an FTTH (Fiber To The Home) is also be considered. 
   Because the broadcast/communication convergence system of the bi-directional HFC type uses a coaxial cable, there is a problem in that the bandwidth is limited due to a physical limit of the coaxial cable and a complex modulation scheme, such as a subcarrier modulation scheme, must be used. Moreover, as the IP-based broadcast/communication convergence system using the xDSL network that performs a transmission operation in units of packets, it is difficult for the broadcast service to be seamlessly provided. In this case, since a process for linking the packet units is required, time delay is incurred and a real-time broadcast service cannot be appropriately provided, such that QoS (Quality of Service) cannot be satisfied. In addition, because the xDSL uses a copper line as a transmission medium, there is a drawback in that a bandwidth is limited due to physical properties of the copper line. 
   For this reason, the broadcast/communication convergence system using the FTTH system is popular because of a wider bandwidth and faster transmission speed. 
   The broadcast/communication convergence system using the FTTH system uses a TDM transmission technique for convergence of the broadcast service and communication service. Here, the TDM transmission technique is to ensure a plurality of time slots is available and that there is appropriate transmission of desired data at each time slot. If a processing operation associated with the time slots is appropriately performed, broadcast streams can be seamlessly transmitted. 
   Where a digital broadcast based on the FTTH system is transmitted using the TDM transmission technique, synchronization between transmission data units is an important factor. In particular, transmission clock synchronization for a digital broadcast can be different for each broadcast provider or broadcast program. Where various clock signals are inputted, a need exists for a TDM frame format capable of synchronizing the different clock signals. 
   SUMMARY OF THE INVENTION 
   Therefore, one aspect of the present invention is to provide a TDM (Time Division Multiplexing) frame using a stuff bit and a method for transmitting and receiving the TDM frame that can transmit and receive a plurality of digital broadcast data units having different synchronous clocks using a simple format. 
   In accordance with another aspect of the present invention, a TDM (Time Division Multiplexing) frame for multiplexing digital broadcast and communication signals based on different synchronous signals in a broadcast/communication convergence system using an FTTH (Fiber To The Home) is provided and includes a framing bit field for identifying a start and end of the TDM frame seamlessly provided, two MPTS (Multiple-Program Transport Stream) fields respectively having at least one bit assigned for digital broadcast data transmission wherein an amount of input digital broadcast data is adjusted according to a difference between a multiplexing rate and an input rate associated with the digital broadcast data in the digital broadcast data transmission, and a fast Ethernet field having at least one bit assigned for communication data transmission. 
   In accordance with another aspect of the present invention, a method for transmitting a TDM (Time Division Multiplexing) frame in which different synchronous signals are multiplexed is provided and includes the steps of dividing data to be inputted to the TDM frame in a predetermined bit unit and inserting the divided data into the TDM frame, comparing an input rate of the data inserted in the predetermined bit unit with a multiplexing rate, and inserting a stuffing control field indicating a corresponding rate difference at every input data of the predetermined bit unit, and adjusting the number of last transmission bits of the TDM frame according to a value of the stuffing control field and carrying out a transmission operation. 
   In accordance with yet another aspect of the present invention, a method for receiving a TDM (Time Division Multiplexing) frame in which different synchronous signals are multiplexed is provided and includes the steps of comparing an input rate of transmission data inputted to the TDM frame with a multiplexing rate, extracting a stuffing control field indicating a corresponding rate difference, and confirming the number of bits included in the received TDM frame and extracting the transmission data from the received TDM frame according to the confirmed number of bits. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which: 
       FIG. 1  is a schematic block diagram illustrating a broadcast/communication convergence system based on an FTTH (Fiber To The Home) system to which the present invention is applied; 
       FIG. 2  shows a format of a TDM (Time Division Multiplexing) frame in accordance with an embodiment of the present invention; and 
       FIG. 3  shows MPTS (Multiple-Program Transport Stream) fields for accommodating a plurality of digital broadcast data units based on different synchronous signals in accordance with an embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Now, embodiments of the present invention will be described in detail with reference to the annexed drawings. In the drawings, the same or similar elements are denoted by the same reference numerals even though they are depicted in different drawings. For the purposes of clarity and simplicity, a detailed description of known functions and configurations incorporated herein will be omitted as it may make the subject matter of the present invention unclear. 
     FIG. 1  is a schematic block diagram illustrating a broadcast/communication convergence system based on an FTTH (Fiber To The Home) system to which the present invention is applied. As shown, the broadcast/communication convergence system based on the FTTH system to which the present invention is applied, includes an OLT (Optical Line Terminal)  11  serving as a subsystem positioned between users and a service node, an ONT (Optical Network Terminal)  12  serving as a device of a user side, and an optical cable connected between the OLT  11  and the ONT  12 . The OLT  11  electro-optically converts a plurality of broadcast and communication signals received from broadcast and communication providers into different wavelength signals λ 1 , λ 2 , . . . λ n , multiplexes the different wavelength signals into a single optical signal and sends the single optical signal so that broadcast/communication services such as digital broadcast, analog broadcast, voice telephone, video service, high-speed Internet, etc. can be provided to users. The ONT  12  transfers information received from the OLT  11  to the users in the form of time slot signals. 
   More specifically, the OLT  11  includes a plurality of E/O (Electrical-Optical) converters  101 - 1  to  101 -n each electro-optically converting a broadcast or communication signal; and an optical multiplexer  102  for multiplexing electro-optically converted signals based on a plurality of wavelengths into the single optical signal and transmitting the single optical signal. Moreover, the ONT  12  includes an optical demultiplexer  103  for demultiplexing the transmitted single optical signal into the electro-optically converted signals based on the plurality of wavelengths; and O/E (Optical-Electrical) converters  104 - 1  to  104 -n each converting the electro-optically converted signal into an electrical signal corresponding to the broadcast or communication signal. Hence, the broadcast signal and the communication signal are transferred to the ONT  12  and ONT  12  selects and switches the broadcast signal desired by a user and then delivers a TDM frame to the user. 
     FIG. 2  illustrates a format of a TDM (Time Division Multiplexing) frame in accordance with an embodiment of the present invention. In this illustrative embodiment of the present invention the frame format is capable of multiplexing two 27-Mbps MPEG-2 (Motion Picture Expert Group-2) TSs (Transport Streams) and 100-BASE-X fast Ethernet data, as will be more clearly explained. 
   As shown, the TDM frame in accordance with the present invention operates preferably at 162 MHz, and the TDM frame&#39;s length is 486 bits. In detail, the TDM frame includes an 8-bit framing bit field  201  necessary for identifying a start and end of the frame; a 2-bit scramble seed field  202  indicating scramble information associated with four types of polynomial expressions for scrambling; an 88-bit MPTS-1 (Multiple-Program Transport Stream-1) field  203  and an 88-bit MPTS-2 field  204  for transporting broadcast streams; and a 300-bit fast Ethernet field  205  for transporting communication data. In another aspect, the scramble seed field  202  can be replaced with other information in the TDM frame. 
   In a one specific embodiment, 8-bit framing bit field  201  is set to a value “10101010” (AA 16 ) and allows a demultiplexing stage to easily identify the start and end of the frame, and further allows an optical detection stage to easily perform a CDR (Clock and Data Recovery) operation. Of course, the set value “10101010” is only an example in the embodiment of the present invention. In the present invention, those skilled in the art can understand that a value of the framing bit field  201  is not limited to the value “10101010”. 
   Because the digital broadcast stream and fast Ethernet, i.e., communication, data include a plurality of consecutive 1&#39;s or 0&#39;s, respectively, a scrambling operation must be performed when an optical transmission operation is carried out. In accordance with the embodiment of the present invention, the 2-bit scramble seed field  202  is used for a stable scrambling operation and the four types of polynomial expressions are sequentially used, such that a stream of the consecutive 1&#39;s or 0&#39;s can be avoided. Scrambling is well-known in the communications art and need not be described in detail herein. 
   In order to include the two 27-Mbps MPEG-2 T Ss and the 100-BASE-X fast Ethernet data, the TDM frame includes the two 88-bit MPTS fields  203  and  204  and the 300-bit fast Ethernet field  205 . Here, in order to accommodate digital broadcast data units based on different synchronous signals, the MPTS fields include six stuffing control bits and one stuff bit in accordance with the present invention, respectively. The 88-bit MPTS fields are shown in  FIG. 3 . 
     FIG. 3  shows MPTS fields for accommodating digital broadcast data units based on different synchronous signals in accordance with an embodiment of the present invention. As shown, the MPTS field in accordance with the present invention includes a basic format consisting of six 12-bit data fields  301  for digital broadcast streams based on different synchronous signals and six stuffing control fields  302  necessary for a stuffing control operation according to a result of a determination as to synchronization in the data fields  301 , and a 1-bit stuff field  303  for compensating for broadcast data not synchronized with a 9-bit data field. 
   In accordance with the present invention, stuffing modes include three modes such as a normal mode, a positive mode and a negative mode. 
   With regard to the normal mode, this mode corresponds to the case wherein a broadcast signal input rate and a multiplexing rate are the same. In this normal mode, a transmission operation is carried out for a frame in which the last 9-bit data field is filled with data and the 1-bit stuff field  303  is empty. In  FIG. 3 , the frame referred to as (a) indicates a frame format in case of the normal mode. 
   With regard to the positive mode, this mode corresponds to the case wherein the broadcast signal input rate is higher than the multiplexing rate. In this positive mode, a transmission operation is carried out for a frame including the last 10-bit data field in which the 1-bit stuff field is filled with data. In  FIG. 3 , the frame referred to as (b) indicates a frame format in the case of the positive mode. 
   With regard to the negative mode, this mode corresponds to the case where the broadcast signal input rate is lower than the multiplexing rate. In this negative mode, a transmission operation is carried out for a frame including the 8-bit data field and the 2-bit stuff field  303  in which a 1-bit data field and a 1-bit stuff field are empty. In  FIG. 3 , the frame referred to as (c) indicates a frame format in the case of the negative mode. 
   As described above, the three modes are determined by the stuffing control fields  302 . Each of the stuffing control fields  302  used in the present invention is interleaved and inserted into the MPTS field every 12-bit data field. Exemplary values of the stuffing control fields  302  for discriminating the three modes are shown in the following Table 1. 
   
     
       
             
             
             
             
           
         
             
                 
               TABLE 1 
             
             
                 
                 
             
             
                 
               Mode 
               Mode detection condition 
               Pattern 
             
             
                 
                 
             
           
           
             
                 
               Positive 
               Number of 1&#39;s is equal to or larger than 5 
               111111 
             
             
                 
               Normal 
               Number of 1&#39;s is 2, 3 or 4 
               101010 
             
             
                 
               Negative 
               Number of 1&#39;s is 0 or 1 
               000000 
             
             
                 
                 
             
           
        
       
     
   
   Because a reception stage carrying out a demultiplexing operation detects a transmission mode using the number of 1&#39;s and the number of 0&#39;s in the six 1-bit stuffing control fields  302  as shown in the above Table 1, the error rate can be reduced. 
   In order to constitute a TDM (Time Division Multiplexing) frame so that digital broadcast signals including the stuff bit based on different synchronous clocks can be accommodated, data is inserted in a unit of 12 bits and a plurality of input digital broadcast signals are multiplexed. In this case, a multiplexing time and a broadcasting time are compared with each other. If the broadcasting time is earlier than the multiplexing time, a value of the stuffing control field  302  is set to “1”. All values of the stuffing control fields  302  are confirmed from the MPTS field  203  or  204 . If the mode detection condition corresponds to the positive mode, for example, if the number of 1&#39;s is equal to or larger than 5, a transmission operation is carried out for a frame including the last 10-bit field consisting of the 10-bit data field. Further, if the mode detection condition corresponds to the normal mode, for example, if the number of 1&#39;s is 2, 3 or 4, a transmission operation is carried out for a frame including the last 10-bit field consisting of the 9-bit data field and the 1-bit stuff field  303 . Furthermore, the mode detection condition corresponds to the negative mode, for example, if the number of 1&#39;s is 1 or 0, a transmission operation is carried out for a frame including the last 10-bit field consisting of the 8-bit data field and the 2-bit stuff field  303 . 
   Therefore, the reception stage confirms the stuffing control fields  302  from the transmitted MPTS fields  203  and  204 , and a transmission mode is confirmed. The last 10-bit field included in the MPTS field  203  or  204  is determined according to a corresponding mode, and a result of the determination is processed by the reception stage. 
   As apparent from the above description, the present invention can carry out a multiplexing operation for different digital broadcast signals based on different synchronous clocks using a simple format-based frame in a broadcast/communication convergence system for combining a plurality of digital broadcast signals and transmitting a result of the combining. 
   Although the embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope of the invention. Therefore, the present invention is not limited to the above-described embodiments, but the present invention is defined by the claims which follow, along with their full scope of equivalents. 
   In accordance with the embodiment of the present invention, there have been described a TDM (Time Division Multiplexing) frame including an 8-bit framing field, a 2-bit scramble seed field, two 88-bit MPTS (Multiple-Program Transport Stream) fields and a 300-bit fast Ethernet field, each 88-bit MPTS field including six 12-bit data fields, a 9-bit data field, six 1-bit stuffing control fields and a 1-bit stuff field. This description is only an example, and the present invention is not limited thereto. 
   That is, those skilled in the art can understand that bits of the TDM frame can be differently assigned according to an MPTS bandwidth and a fast Ethernet bandwidth.