KR20070050664A - Terminal network synchronization acquisition apparatus for maintaining stable network synchronization and its method, and interactive satellite communication system using it - Google Patents

Abstract

1. TECHNICAL FIELD OF THE INVENTION

The present invention relates to an apparatus for obtaining a terminal of a terminal station for maintaining a stable network, and a method thereof, and a bidirectional satellite communication system using the same.

2. The technical problem to be solved by the invention

The present invention uses a DVB-S2 scheme for the forward link, and maintains a more stable network by inserting an NCR value in order to use the TDMA-based DVB-RCS scheme for the reverse link. It is an object of the present invention to provide an acquisition apparatus, a method thereof, and a bidirectional satellite communication system using the same.

3. Summary of Solution to Invention

The present invention provides a device for acquiring a mobile station of a terminal station for maintaining a stable network device, and converts a received signal transmitted from the outside into a baseband signal, performs demodulation and decoding, and inserts a network clock reference (NCR) value. Packet receiving means for filtering MPEG2-TS packets; A terminal network synchronizer acquiring unit for receiving a start-of-frame (SOF) flag, an MPEG2-TS packet including an NCR value, and other information transmitted from the packet receiving unit and performing terminal station synchronizer acquisition and maintenance; Reverse link transmitting means for transmitting data on a reverse link by using clock and time information transmitted through the terminal synchronizer obtaining means; And operating means for performing a basic function of the terminal station.

4. Important uses of the invention

The present invention is used for two-way satellite communication system.

Two-way satellite communication system, DVB-S2, terminal station, DVB-RCS, PCR, NCR, satellite broadcasting, STB, network synchronizer

Description

Terminal network synchronization acquisition apparatus for maintaining stable network synchronization and its method, and interactive satellite communication system using it

1 is a configuration diagram of an embodiment of a bidirectional satellite communication system according to the present invention;

2 is an explanatory diagram of a method for generating and inserting an NCR value in a system using a general DVB-S2 scheme, and a reference time point for generating an NCR;

3 is an explanatory diagram of an NCR extraction method and a reference time point in a terminal station when using a DVB-S2 scheme according to the present invention;

4 is a configuration diagram of an apparatus for obtaining a synchronizer of a terminal station for maintaining a stable synchronizer according to the present invention.

* Explanation of symbols for the main parts of the drawings

41: DVB-S2 receiver 42: terminal synchronizer acquirer

43: reverse link transmitter 44: STB operation and other components

The present invention relates to an apparatus for obtaining a terminal of a terminal station for maintaining a stable network, and a method and a bidirectional satellite communication system using the same. More specifically, the DVB (Digital Video Broadcasting) -S2 method using a forward link method Network of a terminal station for providing high-speed data communication and broadcasting service using a Digital Video Broadcasting-Return Channel via Satellite (DVB-RCS) method based on time division multiple access (TDMA) as a multiple access method on a reverse link The present invention relates to a synchronization acquisition device, a method thereof, and a bidirectional satellite communication system using the same.

In the prior art, a high-speed bidirectional satellite communication system using satellite uses a TDM DVB-S method as a forward link and a TDMA-based DVB-RCS method as a reverse link. In such a satellite broadcasting and communication system, a 42-bit timestamp value called a PCR (Program Clock Reference) generated by a 27 MHz clock, which is a reference clock of a central station, is used to recover a clock of a receiver. It is periodically included in the MPEG2-TS packet having a. The receiving side restores the 27 MHz clock, which is the reference clock of the central station, using the transmitted PCR value itself and the period of the received PCR, and uses it as the reference clock of the receiving side. In the bidirectional satellite communication system that complies with the DVB-RCS standard for configuring the reverse link through satellites, the timestamp indicating the reference time point of the central station required to maintain the clock and timing synchronization of the reverse link using the shape and characteristics of the PCR values is obtained. The information is periodically inserted by inserting it into a field that carries PCR values of MPEG standards.

In this way, the value inserted into the PCR field of the MPEG standard in order to maintain the clock and timing synchronization of the reverse link through the satellite is called NCR (Network Clock Reference). The terminal station recovers the 27 MHz clock which is the reference clock of the central station by using the intervals of the periodically received NCR values, and maintains absolute time synchronization with the central station by using the NCR value itself at the moment when the NCR value is received. do.

However, when the DVB-S2 scheme is used instead of the conventional broadcast scheme DVB-S as the forward link, the basic unit of the transmitted data is not the MPEG2-TS packet, but the DVB-S2 scheme that satisfies the DVB-S2 scheme. Frame. The DVB-S2 frame basically has a much larger length than the MPEG2-TS packet, and also does not always transmit the same data length, but the transmission data length varies depending on the modulation scheme and channel coding scheme to be transmitted.

Therefore, an MPEG2-TS packet containing an NCR value inserted for a clock and a synchronizer is temporarily stored in a buffer to constitute one DVB-S2 frame for transmission, and then delivered when one DVB-S2 frame is completed. It has a structure. In such a case, since the length of the data constituting the DVB-S2 frame can always be variable, the time stored in the buffer is also not constant and changes depending on the transmission modulation scheme and the channel coding scheme. Therefore, it is impossible to compensate for the delay factor for the received NCR value at the receiving terminal station, which causes a problem in determining the exact time point for reverse transmission.

Also, the frame of the DVB-S2 system does not always include an integer number of MPEG2-TS packets, but one MPEG2- having a specific PID is assigned to the NCR value for the network linker as in the case of using the existing DVB-S for the forward link. In the case of inserting and transmitting the TS packet, the MPEG2-TS packet including the NCR value is divided into two DVB-S2 frames and transmitted. In this case, the receiving terminal may recover both MPEG2-TS packets including one complete NCR value only after receiving both DVB-S2 frames. In case of using DVB-S as a forward link, NCR value is extracted by using MPEG2-TS packet reception time including NCR value as one reference time point.However, when DVB-S2 is used, When the MPEG2-TS packet including the NCR value arrives in two, a problem arises in that the reception time of the MPEG2-TS packet including the NCR value cannot be used as one reference time point.

In the case of general broadcasting service, the NCR or PCR value is used only for restoring the clock on the receiving side. Thus, even in the DVB-S2 method, a stable filter design does not cause a problem. It is used to find the exact time of data transmission on the reverse link as the information of clock recovery and NCR value arrives as one information. Therefore, if you do not know the exact value of the delay factor, and in some cases a problem such as splitting MPEG2-TS packet including NCR value into two DVB-S2 frames, it does not affect the recovery of the clock. However, there is a problem in finding the correct time to transmit data on the reverse link.

The present invention has been proposed to solve the above problems, and uses a DVB-S2 scheme for the forward link and a more stable network through the insertion of an NCR value in order to use the TDMA-based DVB-RCS scheme for the reverse link. An object of the present invention is to provide an apparatus for obtaining a network synchronizer of a terminal station and a method thereof, and a bidirectional satellite communication system using the same.

Other objects and advantages of the present invention can be understood by the following description, and will be more clearly understood by the embodiments of the present invention. Also, it will be readily appreciated that the objects and advantages of the present invention may be realized by the means and combinations thereof indicated in the claims.

In order to achieve the above object, the present invention provides a device for acquiring a network synchronizer of a terminal station for maintaining a stable network, and converts a received signal transmitted from the outside into a baseband signal, performs demodulation and decoding, and performs an NCR (Network Clock). Packet receiving means for filtering the MPEG2-TS packet with the inserted Reference) value; A terminal network synchronizer acquiring unit for receiving a start-of-frame (SOF) flag, an MPEG2-TS packet including an NCR value, and other information transmitted from the packet receiving unit and performing terminal station synchronizer acquisition and maintenance; Reverse link transmitting means for transmitting data on a reverse link by using clock and time information transmitted through the terminal synchronizer obtaining means; And operating means for performing a basic function of the terminal station.

In addition, the present invention provides a method for acquiring a network synchronizer of a terminal station for maintaining a stable network, and converts a signal received from the outside into a baseband signal, and converts an MPEG2-TS packet into which a demodulation and decoding function and an NCR value are inserted. A packet receiving step of filtering; The SOF flag and the continuous counter value transmitted from the packet receiving step are received, and the NCR latch flag and the MPEG2-TS packet having the NCR value inserted therein, and the continuous counter value reflecting the time delay in the decoder and the mode and stream de-adaptive part are received. A terminal manipulator obtaining step of acquiring and maintaining a terminal station synchronizer by obtaining a clock recovery and terminal time information of the central station; And a reverse link transmission step of transmitting data through a reverse link by using the clock and time information transmitted through the terminal synchronizer acquisition step.

On the other hand, the present invention, in the two-way satellite communication system using a network station acquisition device of the terminal station for maintaining a stable network, DVB-S2 scheme by receiving various types of MPEG2-TS packets for broadcast and two-way communication from the outside A central station transmitter that accepts multiple inputs and transmits them on a forward link in ACM mode using different degrees of protection for each input stream, and a signal input on a reverse link of a TDMA-based DVB-RCS scheme from a plurality of terminal systems. A central station system configured to receive and demodulate and decode a central station receiver; And a plurality of terminal station systems for receiving signals transmitted on the forward link from the central station system and transmitting data on the reverse link.

The above objects, features and advantages will become more apparent from the following detailed description taken in conjunction with the accompanying drawings, whereby those skilled in the art may easily implement the technical idea of the present invention. There will be. In addition, in describing the present invention, when it is determined that the detailed description of the known technology related to the present invention may unnecessarily obscure the gist of the present invention, the detailed description thereof will be omitted. Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a configuration diagram of an embodiment of a bidirectional satellite communication system according to the present invention.

As shown in FIG. 1, the bidirectional satellite communication system according to the present invention receives multiple types of MPEG2-TS packets for broadcast and bidirectional communication from the outside, receives multiple inputs among DVB-S2 schemes, and applies them to each input stream. Receives and demodulates signals received on the reverse link of the TDMA-based DVB-RCS scheme from a central station transmitter and a plurality of terminal stations 12 that transmit on the forward link in the adaptive coding and modulation (ACM) mode using different degrees of protection. It consists of a central station (11) consisting of a central station receiving unit performing a function of decoding, and a plurality of terminal stations (12) receiving signals transmitted on the forward link from the central station (11) and transmitting data on the reverse link.

Here, the central station 11 acquires a DVB-S2 / RCS PSI / SI table and a synchronizer, which are connected to the Internet for providing a two-way communication service and that a plurality of broadcast streams and all terminals should receive to provide a broadcast service. And receiving the MPEG2-TS packet having the NCR value inserted therein from the mode and stream adaptation unit of the DVB-S2 modulator and transmitting the same with different degrees of protection for each input stream, such as channel coding and modulation schemes. Demodulate the signal transmitted from the receiving terminal station.

In addition, the plurality of terminal stations 12 are provided with a bidirectional satellite communication service transmitted from the central station 11.

2 is an explanatory diagram of a method for generating and inserting an NCR value in a system using a general DVB-S2 scheme and a reference time point for generating an NCR, wherein the NCR value in a central station system in a forward link transmitted in a DVB-S2 scheme is illustrated in FIG. The method of generating and inserting a C and a reference time point of NCR generation.

As illustrated in FIG. 2, when the DVB-S2 scheme is used as a forward link, the problem of obtaining and maintaining a network synchronizer for the reverse link has been described because there is no information on the generation time and the extraction time of the NCR. . Among these problems, the central station extracts an NCR value and determines a time point for generating an MPEG2-TS packet including an NCR value and a reception time point for receiving an MPEG2-TS packet including an NCR value in a DVB-S2 frame. The above described problem can be solved by using the first SOF (Start Of Frame) signal. 3 illustrates a process of extracting an NCR value using an SOF generated by a modulator of the DVB-S2 modulator as an event, generating the MPEG-2 TS packet including the NCR value, and inserting the NCR value into a DVB-S2 frame.

That is, when SOF occurs in the modulator of the DVB-S2 modulator, it extracts the NCR value at this point, generates an MPEG2-TS packet including the NCR value, and inserts it into the DVB-S2 frame. However, since the SOF occurs when all input data is composed of one DVB-S2 frame and ends up channel coding, there is a problem that SOF cannot be inserted into the DVB-S2 frame in which the SOF is generated.

Therefore, the MPEG2-TS packet including the NCR value generated for the SOF of the Nth DVB-S2 frame is divided into one N + 2th DVB-S2 frame or N + 2nd and N + 3rd DVB-S2 frames. Will be sent.

That is, FIG. 3 finds an MPEG2-TS packet in which an NCR value is inserted in a terminal station receiving data transmitted from a central station in the same manner as in FIG. 2, and finds an exact time point of an NCR value transmitted from the central station based on the same. The method is illustrated and details thereof will be described with reference to FIG. 4.

FIG. 4 is a configuration diagram of an apparatus for acquiring a network synchronizer (terminal for bidirectional satellite communication) of a terminal station for maintaining a stable network device according to the present invention. As shown in FIG. 2, FIG. Fig. 3 shows the structure of the terminal station that extracts and uses the NCR value required for acquisition and maintenance of the network.

As shown in FIG. 4, the apparatus for obtaining a terminal of a terminal station for maintaining a stable network device according to the present invention (the terminal station for two-way satellite communication) converts a received signal transmitted through an antenna into a baseband signal and demodulates it. And an SOF flag given by the DVB-S2 receiver 41, a DVB-S2 receiver 41 for filtering an MPEG2-TS packet having an NCR value inserted therein, an MPEG2-TS packet having an NCR value inserted therein, and a decoding function. Receives other information, and transmits data on the reverse link by using the terminal synchronizer obtainer 42 for performing the acquisition and maintenance of the terminal station synchronizer and the clock and time information provided by the terminal synchronizer acquirer 42. Reverse link transmitter 43, and set-top box (STB) operation and other components 44 to perform the basic functions of the terminal station.

Here, the DVB-S2 receiver 41 receives the L-Band signal from the antenna and converts it into a baseband signal, and receives the baseband signal from the tuner 411 and receives the baseband signal from the DVB-S2. Demodulate according to a modulation scheme, generate an SOF flag indicating the start of a DVB-S2 frame, include a continuity counter value in each frame, and use it to obtain the terminal synchronizer obtainer 42 and decoder 413 The demodulator 412 and the demodulated data received by the demodulator 412 receive the demodulated data and then decode the LDB (Low Density Parity Check) and Bose-Chaudhuri-Hocquenghem (BCH) channel codings. The decoder 413 and the data output from the decoder 413 to restore the deleted null-packet and the MPEG2-TS packet header to restore the original MPEG2-TS packet header. A mode and stream de-adaptive unit 414 for converting to a TS stream; The PID filter 415 and the PID filter 415 which extract the MPEG2-TS packet having the NCR value inserted therefrom among the outputs of the mode and stream de-adaptive unit 414 and output a continuous counter value Each time a packet is received by receiving an MPEG2-TS packet with an NCR value inserted, the NCR PID flag signal, the NCR value of the MPEG2-TS packet with the NCR value inserted, and the first value of the NCR value are included in the DVB-S2 frame. NCR embedded MPEG2-TS output unit 416 for transmitting the continuous counter value to the local counter unit 421 of the terminal synchronizer obtainer 42.

In addition, the terminal synchronizer acquirer 42 outputs the SOF flag output from the demodulator 412 of the DVB-S2 receiver 41 and the continuous counter value, and the NCR output from the NCR-inserted MPEG2-TS output 416. MPEG-2 TS packet and decoder 413 with latch flag and NCR value inserted, and continuous counter value reflecting delay factor of mode and stream de-adaptive part 414 are inputted between SOF flag and NCR latch flag. Local counter unit 421 for calculating the time delay of the NCR value at the central station using the SOF flag and the NCR value and the time delay value between the SOF flag and the NCR latch flag output from the local counter unit 421. A clock synchronization unit 422 for restoring the 27 MHz clock used to generate the signal, and a time delay value between the SOF flag and the NCR value and the SOF flag and the NCR latch flag output from the local counter unit 421. Terminal station time at which the SOF flag occurred Beam calculation consists of the terminal time information acquisition unit 423 for transmitting the reverse link transmitter (43).

Here, the demodulator 412 of the DVB-S2 receiver 41 receives the waveform signal of FIG. 3 and generates a continuous counter value. Based on this, the demodulator 412 of FIG. Similarly, the SOF flag is generated and transmitted to the local counter unit 421 of the terminal synchronizer obtainer 42.

Then, the local counter unit 421 of the terminal synchronizer acquirer 42 calculates a t_delay value, which is a time difference between the SOF flag and the NCR PID flag in FIG. 3, based on the information provided from the DVB-S2 receiver 41. Then, the clock synchronization unit 422 recovers the 27 MHz clock of the central station and the terminal time information obtaining unit 423 obtains current time information of the terminal.

In addition, the clock synchronizer 422 calculates the actual time at which the NCR value is received based on the NCR latch flag, the NCR value, and the t_delay value transmitted from the local counter 421, and continuously delivers the NCR value. Restore the 27 MHz reference clock of the central station using.

The terminal time information obtaining unit 423 calculates the actual time at which the NCR value is received based on the NCR latch flag, the NCR value, and the t_delay value transmitted from the local counter unit 421, and calculates the reverse time of the reverse link transmitter ( 43).

The apparatus for obtaining a terminal of a terminal station for maintaining a stable network having the above structure (two-way satellite communication terminal) may use the DVB-S2 method instead of the conventional DVB-S method as a forward link transmission method. It is possible to reliably obtain and maintain the actual time information at the time when the 27 MHz clock, which is the central station reference clock, and the NCR value are received.

As described above, the method of the present invention may be implemented as a program and stored in a recording medium (CD-ROM, RAM, ROM, floppy disk, hard disk, magneto-optical disk, etc.) in a computer-readable form. Since this process can be easily implemented by those skilled in the art will not be described in more detail.

The present invention described above is capable of various substitutions, modifications, and changes without departing from the technical spirit of the present invention for those skilled in the art to which the present invention pertains. It is not limited by the drawings.

The present invention as described above, the DVB-S2 frame in the bidirectional satellite communication system using the DVB-S2 scheme for the forward link through the satellite, and the TDMA-based DVB-RCS scheme for the reverse link multiple access method By solving the problem of obtaining and maintaining the network synchronizer of the terminal station, which is different from the DVB-S scheme, it is possible to provide a more stable two-way satellite communication environment.

Claims (10)

In the apparatus for obtaining a network synchronizer of the terminal station for maintaining a stable network, Packet receiving means for converting a received signal transmitted from the outside into a baseband signal, performing demodulation and decoding, and filtering an MPEG2-TS packet into which a network clock reference (NCR) value is inserted; A terminal network synchronizer acquiring unit for receiving a start-of-frame (SOF) flag, an MPEG2-TS packet including an NCR value, and other information transmitted from the packet receiving unit and performing terminal station synchronizer acquisition and maintenance; Reverse link transmitting means for transmitting data on a reverse link by using clock and time information transmitted through the terminal synchronizer obtaining means; And Operation means for performing the basic function of the terminal station Device for obtaining a network synchronizer of the terminal station comprising a. The method of claim 1, The packet receiving means, Each time a packet is received in an MPEG2-TS packet with an NCR value inserted, a sequence of DVB-S2 frames containing the NCR PID flag signal, the NCR value of the MPEG2-TS packet with the NCR value inserted, and the first value of the NCR value The apparatus for obtaining a terminal of a terminal station, characterized in that it transmits an ordinary counter value to the terminal synchronizer obtaining means. The method according to claim 1 or 2, The packet receiving means, Signal conversion means for converting an L-band signal received through the antenna into a baseband signal; Demodulation means for demodulating the baseband signal transmitted through the signal conversion means according to a DVB-S2 modulation scheme; Decoding means for performing decoding on Low Density Parity Check (LDPC) and Bose-Chaudhuri-Hocquenghem (BCH) channel coding using DVB-S2 scheme using the demodulated data through the demodulation means; Mode and stream reverse adaptation means for receiving the data output from the decoding means, restoring the deleted null packet and restoring the MPEG2-TS packet header and converting the original MPEG2-TS stream into an original MPEG2-TS stream; Packet extraction means for extracting an MPEG2-TS packet having an NCR value inserted therefrom among the outputs of the mode and stream de-adaptive means, and outputting a continuous counter value; And The NCR PID flag signal, the NCR value of the MPEG2-TS packet into which the NCR value is inserted, and the first value of the NCR value are included each time the packet is received by receiving the MPEG2-TS packet including the NCR value through the packet extracting means. Packet forwarding means for delivering a continuous counter value of the DVB-S2 frame to the terminal synchronizer obtaining means Device for obtaining a network synchronizer of the terminal station comprising a. The method of claim 3, wherein The terminal network acquisition unit, The SOF flag output from the demodulation means and the continuous counter value, the MPEG2-TS packet including the NCR latch flag and the NCR value output from the packet transfer means, the decoding means and the mode and stream de-adaptive means. Local counting means for receiving a continuous counter value reflecting the delay factor and calculating a time delay between the SOF flag and the NCR latch flag; Clock restoring means for restoring a clock used when generating an NCR value at a central station by using a SOF flag and an NCR value output from the local counting means and a time delay value between the SOF flag and an NCR latch flag; And Computing terminal station time information at the time when the SOF flag is generated by using the SOF flag and the NCR value output from the local counting means and the time delay value between the SOF flag and the NCR latch flag, and forwarding the terminal station time information to the reverse link transmitting means. Terminal visual information acquisition means Device for obtaining a network synchronizer of the terminal station comprising a. The method of claim 4, wherein The demodulation means, And generating a SOF flag indicating the start of a DVB-S2 frame, and including a continuous counter value in each frame and transmitting the result to the local counting means and the decoding means. The method of claim 5, The terminal network acquisition unit, SOF flag and continuous counter value transmitted through the demodulation means and NCR latch flag given by the packet delivery means, MPEG2-TS packet with NCR value inserted, time delay in the decoding means and the mode and stream de-adaptive means And receiving the reflected continuous counter value to obtain the restoration of the 27 MHz clock of the central station and the terminal time information. A method for acquiring a network synchronizer of a terminal station for maintaining a stable network synchronizer, A packet receiving step of converting a signal received from the outside into a baseband signal and filtering MPEG2-TS packets into which a demodulation and decoding function and an NCR value are inserted; The SOF flag and the continuous counter value transmitted from the packet receiving step are received, and the NCR latch flag and the MPEG2-TS packet having the NCR value inserted therein, and the continuous counter value reflecting the time delay in the decoder and the mode and stream de-adaptive part are received. A terminal manipulator obtaining step of acquiring and maintaining a terminal station synchronizer by obtaining a clock recovery and terminal time information of the central station; And Reverse link transmission step of transmitting data on the reverse link by using the clock and time information transmitted through the terminal synchronizer acquisition step Method of obtaining a network synchronizer of the terminal station comprising a. The method of claim 7, wherein The packet receiving step, Each time a packet is received in an MPEG2-TS packet with an NCR value inserted, a sequence of DVB-S2 frames containing the NCR PID flag signal, the NCR value of the MPEG2-TS packet with the NCR value inserted, and the first value of the NCR value And obtaining a counter value to the terminal synchronizer obtaining step. In a two-way satellite communication system using a network station acquisition device of the terminal station for maintaining a stable network station,  A central station transmitter that receives various types of MPEG2-TS packets for broadcast and bidirectional communication from the outside and receives multiple inputs among DVB-S2 methods and transmits them on the forward link in ACM mode using different degrees of protection for each input stream. And a central station receiver configured to receive, demodulate and decode a signal input through a TDMA based DVB-RCS type reverse link from a plurality of terminal stations. And The plurality of terminal station systems for receiving signals transmitted on the forward link from the central station system and transmitting data on the reverse link Two-way satellite communication system using a network synchronizer acquisition device of a terminal station comprising a. The method of claim 9, The plurality of terminal station system, Packet receiving means for receiving a received signal transmitted from the outside and converting the received signal into a baseband signal, performing demodulation and decoding, and filtering an MPEG2-TS packet into which a network clock reference (NCR) value is inserted; A terminal network synchronizer acquiring unit for receiving a start-of-frame (SOF) flag, an MPEG2-TS packet including an NCR value, and other information transmitted from the packet receiving unit and performing terminal station synchronizer acquisition and maintenance; Reverse link transmitting means for transmitting data on a reverse link by using clock and time information transmitted through the terminal synchronizer obtaining means; And Operation means for performing the basic function of the terminal station Two-way satellite communication system using a network synchronizer acquisition device of a terminal station comprising a.

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