Description

SYSTEM AND METHOD FOR DIGITAL MULTIMEDIA

BROADCASTING

Technical Field

[1] The present invention relates to a system for broadcasting and a method thereof.

[2] The present invention is designed from a project that was supported by the IT R&D program of MICfITTA [2006-S-017-02, Development of advanced transmission technology for the terrestrial DMB system]. Background Art

[3] DMB (digital multimedia broadcasting) is a multimedia service that provides audio having sound quality of a CD (compact disk) and high-quality video when objects are in motion.

[4] In order to transmit a variety of services provided from a DMB service provider via one DMB channel, the services are transmitted in an ensemble in which services are integrated.

[5] In general, a system for DMB multiplexes a number of services into an ensemble using an ensemble multiplexer, generates an ETI (ensemble transport interface) signal for the ensemble, modulates the signal using a COFDM (coded orthogonal frequency division multiplexing) encoder, and transmits the modulated signal as a DMB broadcasting signal.

[6] However, when the same ETI is transmitted via different network channels in the system for DMB, the network may be disconnected by a transmission error due to differences of the channels, or by unexpected accidents. As a result, DMB recipients may not be provided with a smooth DMB service due to the disconnected network. Disclosure of Invention Technical Problem

[7] The present invention has been made in an effort to provide stable broadcasting to

DMB recipients by synchronizing ETI streams of different networks of a system for DMB.

Technical Solution

[8] A method for digital media broadcasting according to an exemplary embodiment of the present invention includes: receiving a first ETI (ensemble transport interface) signal from a first network; receiving a second ETI signal from a second network; searching the same frames while comparing the first ETI signal and the second ETI signal; determining differences in delay time between the same frames; and synchronizing the first ETI signal and the second ETI signal according to the difference in

delay time.

[9] The method for digital multimedia broadcasting may further include examining errors of the first ETI signal; examining errors in the second ETI signal; and selecting and transmitting another ETI signal when either one of the first ETI signal and the second ETI signal has an error.

[10] Further, the searching of the same frames may include searching the same frames while comparing count field values included in frames of the first ETI signal and frames of the second ETI signal.

[11] A system for digital multimedia broadcasting according to an exemplary embodiment of the present invention includes: a first frame error examiner that receives a first ETI (ensemble transport interface) signal from a first network; a second frame error examiner that receives a second ETI signal from a second network; a frame comparing unit that compares field values of frames of the first ETI signal and frames of the second ETI signal and determines differences in delay time between the same frames; and a frame output switching unit that synchronizes the first ETI signal and the second ETI signal according to the differences in delay time.

Advantageous Effects

[12] According to an exemplary embodiment of the present invention, since the ETI stream synchronization device switches the output for the same ETI stream received through another network including the same ETI stream, when an unexpected accident occurs due to disconnection of a network in a system for DMB, the broadcasting is continued without being cutting off and the ETI stream can be transmitted without disconnection of the transmission network. Brief Description of the Drawings

[13] An exemplary embodiment of the present invention will be described in detail with reference to the accompanying drawings for clear understanding of advantages of the present invention, wherein:

[14] FIG. 1 is a diagram schematically showing the configuration of a system for DMB according to an exemplary embodiment of the present invention;

[15] FIG. 2 is a diagram schematically showing a hierarchical structure of an ensemble transmission interface according to an exemplary embodiment of the present invention;

[16] FIG. 3 is a diagram schematically showing the configuration of a synchronization output switching device according to an exemplary embodiment of the present invention;

[17] FIG. 4 is a flowchart illustrating a schematic process of an ETI signal switching method of the synchronization output switching device according to an exemplary embodiment of the present invention;

[18] FIG. 5 is a flowchart illustrating a schematic process of an ETI signal synchronization outputting method of a synchronization output switching device according to an exemplary embodiment of the present invention; and

[19] FIG. 6 is a diagram schematically showing the structure of ETI(LI) frame which is the common part of both ETI(NI) and ETI(NA). Mode for the Invention

[20] In the following detailed description, only certain exemplary embodiments of the present invention have been shown and described, simply by way of illustration. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention. Accordingly, the drawings and description are to be regarded as illustrative in nature and not restrictive. Like reference numerals designate like elements throughout the specification.

[21] It will be further understood that the terms "comprises" and/or "comprising," when used in this specification, specify the presence of stated components, but do not preclude the presence or addition of one or more other components, unless specifically stated. In addition, the terms "-er", "-or", "module", and "block" described in the specification mean units for processing at least one function and operation, and can be implemented by hardware components or software components, and combinations thereof.

[22] Hereafter, a system for stable broadcasting and a method thereof according to an exemplary embodiment of the present invention are described in detail with reference to the accompanying drawings.

[23] FIG. 1 is a diagram schematically showing the configuration of a system for DMB according to an exemplary embodiment of the present invention.

[24] As shown in FIG. 1, a system for DMB includes a video service encoder 110, an audio service encoder 120, a data service encoder 130, an ensemble multiplexer 200, and a transmitter 300.

[25] The video service encoder 110 provides a video service, the audio service encoder

120 provides an audio service, and the data service encoder 130 provides a data service. The video service encoder 110, the audio service 120, and the data service encoder 130 are operated by a service provider.

[26] The ensemble multiplexer 200 is operated by an ensemble provider and generates an

ETI signal by multiplexing a video service, an audio service, and a data service that are inputted through different networks into an ensemble.

[27] The transmitter 300 is operated by a transmission network provider, and modulates the ETI signals provided from the ensemble multiplexer 200 using a COFDM method

and then transmits them.

[28] FIG. 2 is a diagram schematically showing a hierarchical structure of an ensemble transmission interface according to an exemplary embodiment of the present invention.

[29] As shown in FIG. 2, the ETI, an output signal of the ensemble multiplexer 200, is a basic interface in a DMB transmission network.

[30] The hierarchical structure of the ETI is defined into three hierarchies of an LI (logical interface) hierarchy, an NI (network independent) hierarchy, and an NA (network adaptation) hierarchy.

[31] The LI hierarchy defines basic information for generating an ensemble as a basic logical structure.

[32] The NI hierarchy is simply a physical interface hierarchy that maps the LI and includes a basic interface of equipment involved in the ETI.

[33] The NA hierarchy is a physical interface hierarchy that is protected from errors to be used in a network environment that easily makes an error as compared with the NI hierarchy, and is mapped with the LI hierarchy.

[34] Further, various types of interfaces, such as ETI (NI, G.703), ETI (NI, V.11), and

ETI (NA, G.704), exist according to the signal types of the interfaces that are used, and the ETI(NI, G.703) is the minimum requirement for any equipment producing or accepting an ETI signal, i.e., a standard input interface of a COFDM modulator.

[35] FIG. 3 is a diagram schematically showing the configuration of a synchronization output switching device according to an exemplary embodiment of the present invention.

[36] As shown in FIG. 3, the synchronization output switching device 310 includes a first frame error examiner 311, a second frame error examiner 313, a first frame buffer 315, a second frame buffer 317, a frame comparing unit 319, and a frame synchronization output switching unit 321. The synchronization output switching device 310 may be an independent device or be included in the transmitter 300.

[37] The first frame error examiner 311 and the second frame error examiner 313 respectively receive a first ETI signal and a second ETI signal from a first ETI transmission network and a second ETI transmission network and examine errors in transmission, and then send the error examination results to the frame synchronization output switching unit 321. Further, when no error is detected, the first frame error examiner 311 and the second frame error examiner 313 store the frames of the first ETI signal and the frames of the second ETI signal into the first frame buffer 315 and the second frame buffer 317, respectively.

[38] The frame comparing unit 319 searches the same frames by comparing the frames of the ETI signals stored in the first frame buffer 315 and the second frame buffer 317, and determines differences in delay time dA and dB between the same frames.

[39] The frame synchronization output switching unit 321 receives the differences in delay time dA and dB from the frame comparing unit 319, searches the same frames of the first ETI signal from the first ETI transmission network and the second ETI signal from the second ETI transmission network, and then synchronizes the first ETI signal and the second ETI signal, and thereafter transmits either one of the first ETI signal and the second ETI signal. Further, when an error occurs in either one of the first ETI transmission network and the second ETI transmission network, the frame synchronization output switching unit 321 switches the ETI signal of the first ETI network and the ETI signal of the second ETI network for stable broadcasting, such that the broadcasting is continued without being cut off.

[40] Hereafter, a broadcasting output switching method using the synchronization output switching device shown in FIG. 3 is described in detail with reference to FIG. 4.

[41] FIG. 4 is a flowchart illustrating a schematic process of an ETI signal switching method of the synchronization output switching device according to an exemplary embodiment of the present invention.

[42] As shown in FIG. 4, the first frame error examiner 311 and the second frame error examiner 313 of the synchronization output switching device 310 respectively receive a first ETI signal and a second ETI signal that are the same, from a first network and a second network (Sl 10).

[43] The first frame error examiner 311 and the second frame error examiner 313 receiving the first ETI signal and the second ETI signal examine transmission errors and abnormal errors for the ETI frames included in the first ETI signal and the second ETI signal, respectively (S 120).

[44] It is assumed in this embodiment that the existing broadcasting uses the first ETI signal of the first network.

[45] When an error is detected in the first ETI signal of the first network by the first frame error examiner 311, an error message is transmitted to the frame synchronization output switching unit 321 (S 130).

[46] The frame synchronization output switching unit 321 that has received the error message switches the first ETI signal with an error of the first network and the second ETI signal stored in the second frame buffer 317 of the second network that is a frame of another network without an error, and then outputs the second ETI signal (S 140).

[47] When no error is detected from the first ETI signal and the second ETI signal, the first frame error examiner 311 and the second frame error examiner 313 transmit the received first and second ETI signals to the first frame buffer 315 and the second frame buffer 317, respectively. The first frame buffer 315 and the second frame buffer 317 that have received the first ETI signal and the second ETI signal, respectively, store the first ETI signal and the second ETI signal, respectively (S 150), and output an ETI

signal to the frame synchronization output switching unit 321 in response to a request for transmission from the frame synchronization output switching unit 321 (S 160).

[48] Hereafter, an ETI signal synchronization method using the synchronization output switching device shown in FIG. 3 and an ETI frame are described in detail with reference to FIG. 5 and FIG. 6.

[49] FIG. 5 is a flowchart illustrating a schematic process of an ETI signal synchronization outputting method of a synchronization output switching device according to an exemplary embodiment of the present invention. FIG. 6 is a diagram schematically showing the structure of ETI(LI) frame which is the common part of both ETI(NI) and ETI(NA).

[50] As shown in FIG. 5, the first frame error examiner 311 and the second frame error examiner 313 of the synchronization output switching device 310 respectively receive a first ETI signal and a second ETI signal from the first network and the second network that are different (S210). At this time, the first ETI signal is equal to the second ETI signal. The first frame error examiner 311 and the second frame error examiner 313 examine errors in the received first and second ETI signals, and then store the first ETI signal and the second ETI signal to the first frame buffer and the second frame buffer of a corresponding network, respectively.

[51] The first frame buffer 315 and the second frame buffer 317 that have received the first and second ETI signals without an error each store the ETI frames that are included in the first and second ETI signals and then transmit the first and second ETI signals to the frame comparing unit 319 for ETI signal synchronization.

[52] The frame comparing unit 319 compares the ETI frames of the first ETI signal and the second ETI signal to find the same frames of the ETI signals for synchronization of the first ETI signal of the first frame buffer 315 and the second ETI signal of the second frame buffer 317 (S230). The frame comparing unit 319 compares three specific field values of the ETI frame of the first ETI signal with those of the ETI frame of the second ETI signal and searches the same frames to find the same frames in the first and second ETI signals for ETI signal synchronization.

[53] In the ETI frames of the first and second ETI signals that have a structure as shown in FIG. 6, the frame comparing unit 319 first compares the values of frame counter (FCT) fields 411 included in frame characterization (FC) fields 410 of the ETI frames 400 of the first and second ETI signals. The value of the frame counter field 411 is in the range of 0 to 249, and the count value increases or decreases by 1 before or after a frame. Accordingly, for the same frames, the values of the two frame counter fields 411 are the same. Therefore, it is possible to search ETI frames having the same values of the counter field 411 by moving ETI frames to be compared forward and backward by 250.

[54] Next, the frame comparing unit 319 that has estimated the approximate position of the frame from the values of the frame counter field 411 compares the values of header cyclic redundancy checksums (CRC h ) 431 included in the fields of end of headers (EOH) 430 of the ETI frames 400 of the first and second ETI signals.

[55] Finally, the frame comparing unit 319 determines whether the frames are the same, by comparing the values of cyclic redundancy checksums (CRC) 451 included in the fields of end of frames (EOF) 450 of the ETI frames 400 of the first and second ETI signals.

[56] In the ETI frame 400 shown in FIG. 6, the reference numerals 420, 430, 440, and 460 denote a stream characterization field (STC), an end of header field (EOH), a main stream field, and a time stamp field (TIST), respectively.

[57] The frame comparing unit 319 generates differences in delay time dA and dB between the same frames and transmits them to the frame synchronization output switching unit 321 (S240). The frame comparing unit may estimate differences in delay time dA and dB between the same frames using the position (index) of buffers where the same frames are stored.

[58] Subsequently, the frame synchronization output switching unit 321 removes the frames of the first and second ETI signals corresponding to the differences in delay time dA and dB, for synchronization of the first ETI signal of the first network and the second ETI signal of the second network, and synchronizes the ETI signals, and thereafter transmits the synchronized ETI signals (S250).

[59] In FIG. 3, a reference character "dS" is delay time generated in the synchronization output switching device 310.

[60] The embodiment of the present invention described above is not implemented by only the method and apparatus, but it may be implemented by a program for executing the functions corresponding to the configuration of the exemplary embodiment of the present invention or a recording medium having the program recorded thereon. These implementations can be realized by the ordinarily skilled person in the art from the description of the above-described exemplary embodiment.

[61] While this invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.