KR20080047263A - Digital broadcasting system and error correction method thereof - Google Patents

Abstract

A digital broadcasting system and an error correction method thereof are provided to reduce a network load by transmitting a multicast packet of an FEC(Forward Error Correction) group including FEC data for lost packet recovery. A digital broadcasting system includes a server and a set-top box(40). The server groups a predetermined number of multicast packets to obtain FEC groups for digital broadcast data(MPEG TS) transmission, creates FEC data for each multicast packet using the digital broadcast data of the multicast packets in the FEC groups, and transmits the multicast packets including the FEC data on a network. The set-top box recovers respective digital broadcast data pieces of the lost multicast packet through digital broadcast data pieces of multicast packets except the lost multicast packet and combines the recovered digital broadcast data pieces to recover the lost multicast packet among multicast packets received on the network.

Description

Digital broadcasting system and error correction method of system {DIGITAL BROADCASTING SYSTEM AND ERROR CORRECTION METHOD THEREOF}

The present invention relates to a digital broadcasting system and an error correcting method of the system, and more particularly, to a digital broadcasting system and a method of error correcting a lost multicast packet through forward error correction. will be.

Digital broadcasting highly efficiently compresses the amount of information of programs for each channel based on the MPEG (Moving Picture Experts Group) coding standard, etc., and efficiently processes programs corresponding to a plurality of channels based on the digital modulation scheme of each transmission medium. Send multiplexed.

Therefore, digital broadcasting can broadcast dozens or hundreds of channels without using a large amount of repeaters, unlike analog broadcasting.

Such digital broadcasting includes digital terrestrial broadcasting, digital satellite broadcasting and cable digital broadcasting, depending on the transmission medium. Currently, digital satellite broadcasting is active worldwide, and digital terrestrial broadcasting is being piloted in some countries in the United States and Europe.

Most digital broadcasting services are provided using cables. However, at present, digital broadcasting services are being made through an Internet Protocol (IP) network according to the development of high speed Internet technology.

The digital broadcasting system for providing a digital broadcasting service is composed of a digital broadcasting server providing broadcast data through an IP network and a plurality of set-top boxes connected to the IP network to receive broadcast data provided from the digital broadcasting server and provide the user with the broadcast data. Can be.

The digital broadcasting server converts the analog broadcasting data received from the digital broadcasting station (System Operator) into digital broadcasting data through encoding and multicasts the compressed packet to the IP network. Here, the multicast packet transmitted to the IP network may be configured according to the Moving Picture Experts Group 2 (MPEG2) Transport Stream (TS) standard.

That is, the digital broadcast server multicasts broadcast data for an arbitrary channel to an IP network.

Accordingly, the set-top box provides digital television with digital broadcast data obtained by decoding the multicast packet received from the IP network through decoding.

As described above, the digital broadcast data is transmitted from the digital broadcast server to the set-top box through the multicast method through the IP network. Since the digital broadcast data (MPEG TS) is transmitted in a multicast manner, it cannot be retransmitted if it is lost in the IP network.

Accordingly, since the digital television connected to the set-top box cannot reproduce the lost digital broadcast data, noise is displayed in the reproduction area of the digital broadcast data lost on the screen.

One way to solve this problem is forward error correction (FEC). The FEC transmits multiple FEC packets together for the recovery of lost multicast packets between the multicast packet streams for digital broadcast data (MPEG TS), and the lost FEC packets are lost when the lost packets occur. A method of recovering lost multicast packets using neighboring packets of multicast packets.

This will be described in more detail with reference to FIG. 1.

As shown in FIG. 1, it can be seen that f (A, B) and f (B, C), which are FEC packets, are inserted between original multicast packet streams. At this time, f (A, B) = A XOR B and f (B, C) = B XOR C.

That is, the digital broadcasting server adds a plurality of FEC packets f (A, B) and f (B, C) between the original multicast packet streams A, B, C, D, E, ... Multicast over the network.

Meanwhile, the set-top box recovers lost multicast packets using FEC packets required for the recovery of lost multicast packets among the multicast streams transmitted through the IP network in the digital broadcasting server and neighboring packets of the lost multicast packets. .

For example, if a B packet is lost in a multicast stream transmitted through an IP network in a digital broadcasting server, the set-top box performs an exclusive OR (XOR) operation on the neighboring packet C and the FEC packet f (B, C). Recover B packets.

As described above, the digital broadcasting server transmits the FEC packet to the IP network by adding the FEC packet between the multicast packet streams on a packet basis in order to recover the lost packet in the set-top box. However, an overhead occurs in the IP network by the number of added FEC packets.

For example, adding FEC packets as shown in FIG. 1 incurs double overhead in the IP network compared to the original multicast packet stream.

In addition, when the FEC packet is added to recover the lost packet, the set-top box needs to add a task for processing it and a configuration for performing the task.

Thus, the present invention is intended to solve the above problems, errors, by sending, by including the FEC data for recovery of lost packets in the multicast packet in the FEC group reduced the load on the network, the digital broadcasting system and a system correction method The purpose is to provide.

According to an aspect of the present invention, there is provided a digital broadcasting system for setting a predetermined number of multicast packets to an FEC group for transmission of digital broadcast data (MPEG TS), and a multicast packet included in the FEC group. A server for generating forward error correction information of each multicast packet using the digital broadcast data (MPEG TS) of the multicast packet and including the same in the corresponding multicast packet and transmitting it through a network; If a multicast packet is lost among the multicast packets received through the network, the digital broadcast data (MPEG TS) fragment of the remaining multicast packets except for the lost multicast packet is recovered and the recovered digital broadcast data ( MPEG TS) fragments are assembled to recover lost multicast packets. And a set-top box for recovering the digital broadcast data (MPEG TS) of the multicast packet lost with the remaining packets except the lost multicast packet included in the FEC group.

The server may include: a Forward Error Correction (FEC) group setting unit configured to set a predetermined number of multicast packets to an FEC group for transmission of digital broadcast data (MPEG TS); A data dividing unit for dividing the digital broadcast data (MPEG TSs) of the multicast packets included in the FEC group by a predetermined number; A FEC header setting unit for setting a stream ID, a sequence number, a multicast packet order, and the like of the multicast packets to be included in the multicast packet; Forward error of each multicast packet by splitting the digital broadcast data (MPEG TS) of the multicast packets included in the FEC group into a predetermined number, respectively, and performing the exclusive OR (XOR) operation of the divided digital broadcast data (MPEG TS). An FEC information setting unit which sets correction information and includes the correction information in a corresponding multicast packet and transmits it through a network; And an FEC header setting unit for setting a stream ID, a sequence number, and an order of the multicast packets of the multicast packets in the FEC group to include in the multicast packet.

The set top box may determine the lost packet through a sequence number.

A server of a digital broadcasting system according to an aspect of the present invention for achieving the above object, the Forward Error Correction (FEC) group for setting a predetermined number of multicast packets to the FEC group for transmission of digital broadcast data (MPEG TS) Setting unit; A data dividing unit for dividing the digital broadcast data (MPEG TSs) of the multicast packets included in the FEC group by a predetermined number; And dividing the digital broadcast data (MPEG TSs) of the multicast packets included in the FEC group into a predetermined number, respectively, and forwarding the respective multicast packets by performing an exclusive logical sum (XOR) operation on the divided digital broadcast data (MPEG TSs). And an FEC information setting unit configured to set error correction information and include the same in a multicast packet and transmit the same through a network.

The server of the digital broadcasting system may further include an FEC header setting unit configured to set a stream ID, a sequence number, and an order of the multicast packets of the multicast packets in the FEC group to include in the multicast packet.

The set-top box of the digital broadcasting system according to an aspect of the present invention for achieving the above object, to determine whether the loss of the multicast packet among the multicast packets received through the network through the sequence number included in the multicast packet An error determination unit; At least one buffer; And an error correction unit for recovering the lost multicast packet through FEC data recovery of the remaining multicast packets except for the lost multicast packet in the FEC group.

In the digital broadcasting system according to an aspect of the present invention for achieving the above object, the information setting method for error correction of the server, the predetermined number of multicast packets for the transmission of digital broadcast data (MPEG TS) to the FEC group Doing; Dividing the digital broadcast data (MPEG TSs) of the multicast packets included in the FEC group by a predetermined number; Setting an FEC header constituting header information for recovery; The digital broadcast data (MPEG TS) of the multicast packets included in the FEC group is divided into a predetermined number, and the forward error correction information of each multicast packet is set by using the divided digital broadcast data (MPEG TS). Including in a multicast packet and transmitting over the network.

The step of transmitting through the network includes setting forward error correction information of each multicast packet through an exclusive OR (XOR) operation on the divided digital broadcast data (MPEG TSs).

An information setting method for error correction of a server in the digital broadcasting system may further include setting a stream ID, a sequence number, and a sequence of multicast packets in a multicast packet in an FEC group. .

In the digital broadcasting system according to an aspect of the present invention for achieving the above object, the error correction method of the set-top box, the sequence included in the multicast packet whether the loss of the multicast packet among the multicast packets received through the network Determining through the number; Recovers the lost digital broadcast data (MPEG TS) fragments of the lost multicast packet through the FEC data of the remaining multicast packets except the lost multicast packets in the FEC group, and combines the recovered digital broadcast data (MPEG TS) fragments. Recovering the made multicast packet.

As described above, according to the digital broadcasting system and the error correction method of the system of the present invention, it is possible to reduce the load on the network by including the FEC data for the recovery of lost packets in the multicast packet of the FEC group.

Hereinafter, a digital broadcasting system and an error correction method thereof according to the present invention will be described in detail with reference to the accompanying drawings.

In addition, it should be noted that the same reference numerals are given to the same elements, although belonging to different drawings for convenience of understanding.

2 is a diagram illustrating a configuration of a digital broadcasting system according to the present invention.

Since MPEG-TS was originally made based on the same network as cable broadcasting, when cable-to-MPEG transmission is divided into 188 bytes, error correction is performed by adding RS-CODE (Digital Video Broadcasting standard).

After this method is set as standard, broadcast equipments are mostly encoded using MPEG-TS, and IP TVs are mostly used based on 1316 bytes, which is 7 times 188 units, to conform to MPEG-TS.

Since the maximum value of one packet of Ethernet is 1500 bytes, the space of 156 bytes is left by using 1344 bytes as described above.

Therefore, in the present application, by using the remaining 156 bytes as the FEC field, it is possible to maximize the performance of many equipment set to 1500 bytes.

In other words, since many Ethernet devices are set to 1500 bytes, they cannot be raised above 1500. Therefore, use values as close to 1500 bytes as possible.

As shown in FIG. 2, the digital broadcasting system according to the present invention includes a stream server 20, an FEC server 30, and a plurality of set top boxes 40.

The stream server 20 converts the digital broadcast data (MPEG TS) provided by a broadcasting station (not shown) into a multicast packet of MPEG-TS format and provides it to the FEC server 30.

The FEC server 30 bundles the multicast packets provided by the stream server 20 into the FEC group by a certain number of units (for example, 10), and subtracts 1 from the number of multicast packets of the FEC group by multicast. The fragment size (fragment_size) is obtained by dividing the size of the digital broadcast data (MPEG TS) included in the packet.

The FEC server 30 generates FEC data for each multicast packet necessary for the recovery of the lost multicast packet by using the number of multicast packets and the fragment size of the FEC group, and generates the generated FEC data in the corresponding multicast. The packet is included in the packet and multicasted to the set-top box 40 through the IP network.

The set top box 40 provides the digital television with digital broadcast data obtained by decompressing a multicast packet transmitted through an IP network through decoding.

Meanwhile, when a lost multicast packet is generated among the multicast packets transmitted through the IP network, the set-top box 40 performs FEC data included in the multicast packet corresponding to the FEC group to recover the lost multicast packet. Recover the lost multicast packet using.

That is, when the multicast packet is lost among the multicast packets received through the network, the set-top box 40 loses the digital broadcast data (MPEG) lost through the FEC data of the remaining multicast packets except the lost multicast packet. Each piece of TS) is recovered and the recovered pieces of digital broadcast data (MPEG TS) are combined to recover lost multicast packets.

3 is a diagram illustrating a configuration of an FEC server according to the present invention.

As shown in FIG. 3, the FEC server according to the present invention includes an FEC group setting unit 31, an FEC header generating unit 32, a stream ID setting unit 33, a sequence number setting unit 34, and a sequence setting unit. 35, an FEC information setting unit 36 and a data partitioning unit 39.

The FEC group setting unit 31 sets the multicast packets provided from the stream server to the FEC group by a set number (for example, 10).

At this time, the format of the multicast packet provided from the stream server is shown in FIG.

As shown in FIG. 5, the multicast packet includes an IP address field 50, a UDP field 51, a digital broadcast data (MPEG TS) field 52, an FEC header field 53, and an FEC Data field 54. It consists of.

The IP address field 50 includes the IP address of the stream server that originated the multicast packet and the FEC group address to which the multicast packet is transmitted, and has a size of 20 (bytes).

The UDP field 51 indicates that the multicast packet is transmitted using the UDP protocol and has a size of 8 bytes.

The digital broadcast data (MPEG TS) field 52 includes digital broadcast data (MPEG TS) and has a size of 1316 bytes.

The FEC Header field 53 includes configuration information of the FEC generated for the recovery of the lost multicast packet and has a size of 8 bytes.

The FEC Data field 54 includes FEC data generated for the recovery of lost multicast packets and has a size of fragment_size of FIG. 6.

FIG. 6 includes information used when generating FEC data of a multicast packet and information capable of tracking lost packet information, and are information required when recovering a lost packet in a set-top box.

As shown in FIG. 6, the FEC header is divided into FEC group size (group_size), stream ID (stream_ID), multicast packet order (diff), fragment size (fragment_size), and sequence number in the FEC group. It is composed.

The FEC group size (group_size) is the total number of multicast packets of the FEC group is the FEC group size (group_size). Here, the FEC group is a defragmentation of digital broadcast data (MPEG TS) of multicast packets associated with mutually exclusive logical ORs used when composing FEC data. For example, when one multicast packet is lost, the digital broadcast data (MPEG TS) portion of the lost multicast packet is recovered to all other multicast packets in the FEC group. Since one lost packet per FEC group can be recovered, the smaller the FEC group size (group_size), the better the recovery rate but the higher the network overhead.

The stream ID (stream_ID) indicates an ID for distinguishing the digital broadcast data (MPEG TS) and other digital broadcast data (MPEG TS) included in the multicast stream.

The multicast packet order (diff) is the first multicast packet of one FEC group is 0 and is incremented by 1 from the next packet, and the last packet of the group has a value of group_size-1.

The fragment size (fragment_size) represents the size of dividing the digital broadcast data (MPEG TS) to generate the FEC data, and consequently coincides with the size of the FEC data.

The sequence number (sequence_number) represents a number assigned to each multicast packet and is used to identify lost multicast packets.

Hereinafter, a method of setting the FEC header field and the FEC data of FIG. 5 will be described.

6 is a diagram illustrating an FEC header field.

First, the FEC group size (group_size) is determined. A value within the range of 10 to 255 may be arbitrarily selected according to network conditions.

Since one lost multicast packet can be recovered per FEC group, the smaller the value, the better the recovery rate, but the higher the network overhead, the operator can choose from the appropriate line.

In the following, the case where group_size is 10 is taken as an example.

When the FEC group size is defined, the FEC header setting unit 32 sets a value defined in the group_size field, and fragments are positive integers within a range of values greater than 1316 / (group_size-1) and less than 148. Defines the size (fragment_size).

1316 / (group_size-1) <= fragment_size <= 148

Next, the FEC header setting unit 32 records the stream ID (stream_ID) through the stream ID setting unit 33.

The stream ID (stream_ID) is set to one channel for each digital broadcast stream. The value can be arbitrarily defined by the operator, and the multicast packet can be obtained by identifying a sequence number for streams having the same value in the set-top box. Since the loss is checked, it can be defined not to overlap with other channels.

When the stream ID setting is completed, the FEC header setting unit 32 assigns a sequence number (sequence_number) to the multicast packets belonging to the FEC group so as to correspond to the order of the digital broadcast data (MPEG TS). Set via. The sequence number is set to determine whether or not a multicast packet is lost in the set-top box. The sequence number is increased from 0 to 1, and the multicast packet after the maximum value 65535 is set to 0.

When the setting of the sequence number is completed, the FEC header setting unit 32 sets the order of the multicast packets included in the FEC group through the order setting unit 35. In this case, the multicast packet order (diff) in the group defines a distance value from the first packet in the FEC group. The first packet in the FEC group is 0, the second packet is 1, and then increases by 1, and the FEC group The last packet in it is a value of group_size-1.

When the multicast packet order setting 35 in the FEC group is completed, the FEC header setting unit 32 selects the set stream ID, each sequence number, group_size, multicast packet order, and fragment size, respectively. Included in the FEC header of the multicast packet.

Hereinafter, a method of setting the part of the FEC Data field shown in FIG. 5 will be described.

The FEC Data field 54 is a field for storing data generated by the FEC information setting unit 36, and the FEC information setting unit 36 is assigned to the FEC header of each multicast packet by the FEC header setting unit 32. When information setting is completed, the digital broadcast data (MPEG TS) included in the multicast packet is divided using the fragment size (fragment_size) set in the FEC header.

An example of the digital broadcast data (MPEG TS) divided by this fragment size is shown in FIG. 7. FIG. 7 shows content obtained by dividing the digital broadcast data (MPEG TS) when the fragment size (fragment_size) is 148. FIG. It can be seen that the digital broadcast data (MPEG TS) is divided into nine 148 bytes by the fragment size (148).

The FEC information setting unit 36 divides the digital broadcast data (MPEG TS) into fragment size pieces. Subsequently, FEC data to be inserted into the FEC Data area of the multicast packet shown in FIG. 5 is obtained.

This will be described in more detail.

First, the FEC information setting unit 36 divides the digital broadcast data MPEG TS into pieces, and then initializes the first buffer 37 and the second buffer 38. At this time, it is preferable that the first buffer 37 and the second buffer 38 have a fragment size.

If the order (n) of the multicast packets in the FEC group for recovering the FEC data and the order (diff) of the multicast packets for extracting the digital broadcast data (MPEG TS) fragments do not match, the FEC information setting unit 36 does not match. The "diff-1" th digital broadcast data (MPEG TS) fragment of the multicast packet n is stored in the second buffer 38.

The FEC information setting unit 36 performs an exclusive logical sum (XOR) operation on the FEC data stored in the first buffer 37 and the pieces of digital broadcast data (MPEG TS) stored in the second buffer 38, and the result value obtained by the calculation. Is stored in the first buffer 37.

If the order (n) of the multicast packets in the FEC group for recovering the FEC data and the order (diff) of the multicast packets for extracting the digital broadcast data (MPEG TS) fragments match, the FEC information setting unit 36 In order to extract the digital broadcast data (MPEG TS) fragment of the next multicast packet, the multicast packet n is increased by a set value '1'. That is, the multicast packet n is stored as "diff + 1" to extract the next piece of digital broadcast data (MPEG TS).

On the other hand, if the counter n order of the multicast packet increased by the set value and the FEC group size do not match, the FEC information setting unit 36 diff-diff digital broadcast data of the multicast packet corresponding to the counter n order. (MPEG TS) A piece is stored in the second buffer 38.

The FEC information setting unit 36 performs an exclusive logical sum (XOR) operation on the FEC data of the multicast packet n stored in the first buffer 37 and the pieces of digital broadcast data (MPEG TS) stored in the second buffer 38. The resultant value obtained by the calculation is stored in the first buffer 37.

If the current order (n = diff + 1) of the multicast packet and the FEC group size match in the FEC group, the FEC information setting unit 36 stores the value stored in the first buffer 37 in the FEC of the multicast packet n. Insert into the data area.

The FEC information setting unit 36 multicasts the corresponding multicast packet through the IP network when the value stored in the first buffer 37 is inserted into the FEC data area.

4 is a diagram illustrating a configuration of a set top box according to the present invention.

As shown in FIG. 4, the set top box 40 according to the present invention includes a network interface 41, an error determining unit 42, and an error correcting unit 43.

The error determining unit 42 determines the lost multicast packet using the sequence number among the streams of the multicast packet received through the IP network. When the multicast packet is lost, the error determining unit 42 is lost to the error correcting unit 43. Controls recovery of multicast packets.

The error correction unit 43 recovers the digital broadcast data (MPEG TS) included in the lost multicast packet, and lost the multicast through the FEC data of the remaining multicast packets except for the lost multicast packet in the FEC group. Recover the digital broadcast data (MPEG TS) fragment of the packet and combine the recovered digital broadcast data (MPEG TS) to recover the digital broadcast data (MPEG TS) of the lost multicast packet.

9 is a flowchart illustrating an operation of the FEC data setting method of the FEC server according to the present invention.

As shown in FIG. 9, the FEC server initializes a counter n order of multicast packets in the first buffer 37, the second buffer 38, and the FEC group (S90). At this time, it is preferable that the first buffer 37 and the second buffer 38 have a fragment size.

The FEC server checks whether the diff of the packet for setting the FEC data and the counter n of FIG. 9 match (S91). Here, diff means a diff value for generating the FEC data set in FIG. 6 and has the same value until the end of the flow. As shown in FIG. 9, when the counter 'n' generates FEC data through digital group data (MPEG TS) through XOR operation of "group_size-1", performing "group_size -1" XOR operation. I set up a counter, which is 'n'.

The FEC server corresponds to the counter (n) order in the FEC group if the counter (n) order of the multicast packets in the FEC group and the multicast diff in the FEC group of the multicast packet for setting the FEC data do not match. The diff-1 &lt; th &gt; digital broadcast data (MPEG TS) fragment of the multicast packet n to be stored is stored in the second buffer 38 (S92).

The FEC server performs an exclusive logical sum (XOR) operation on the fragment of the digital broadcast data (MPEG TS) stored in the first buffer 37 and the fragment of the digital broadcast data (MPEG TS) stored in the second buffer 38. The value is stored in the first buffer 37 (S93).

The FEC server increments the counter n by 1 (S94) to extract a fragment of the digital broadcast data (MPEG TS) of the next multicast packet, and then proceeds to step 91 (S91).

On the other hand, if the order (n) of the multicast packets and the order (diff) of the multicast packets to set the FEC data match in the FEC group, the FEC server indicates the order of the multicast packets to set the FEC data (diff). Is increased by a setting value of 1 to set the multicast packet n from which the digital broadcast data (MPEG TS) fragment is extracted to "diff + 1" (S95). That is, since the fragment of the digital broadcast data (MPEG TS) that the FEC server is to perform XOR operation on the first buffer is the same as the multicast packet to form the FEC data, if "n and diff" are equal, the next multicast packet is selected. Set 'n' to the value of "diff + 1".

The FEC server checks whether the counter n of the multicast packet increased by the set value and the FEC group size match (S96).

If the current order of multicast packets increased by the set value (n = diff + 1) and the FEC group size do not match, the FEC server corresponds to the current order of multicast packets increased by the set value (n = diff + 1). In the divided digital broadcast data (MPEG TS) fragments of the multicast packet, the digital broadcast data (MPEG TS) fragment corresponding to the sequence (diff) of the multicast packet for which FEC data is to be set is stored in the second buffer 38. Save (S97).

The FEC server calculates the fragment of the digital broadcast data (MPEG TS) stored in the first buffer 37 and calculates the fragment of the digital broadcast data (MPEG TS) stored in the second buffer 38 as an exclusive logical sum (XOR). The result value is stored in the first buffer 37 (S98).

The FEC server increments the counter n by 1 (S99) to extract a fragment of the digital broadcast data (MPEG TS) of the next multicast packet, and then proceeds to step 96 (S96).

On the other hand, the FEC server inserts a value stored in the first buffer 37 into the FEC data field if the current order (n = diff + 1) of the multicast packet in the FEC group matches the FEC group size. After that, when the insertion of the value stored in the first buffer 37 into the FEC data field is completed, the FEC server multicasts the corresponding multicast packet through the IP network (S100).

9 will be described in more detail with reference to FIG. 8 FEC data setting method of the FEC server according to the present invention.

8 is a diagram illustrating an FEC field of multicast packets included in an FEC group according to the present invention.

As shown in FIG. 8, it can be seen that the number of multicast packets included in the FEC group is 10 from A to J. Therefore, it can be seen that the FEC group size is "10". It can be seen that the sequence number set in the multicast packets included in the FEC group is set from 100 to 109.

It can be seen that the order of the multicast packets included in the FEC group is "0" for A, "1" for B, and "9" for J.

Meanwhile, digital broadcast data (MPEG TS) fragments for generating FEC data of multicast packets included in the FEC group are illustrated. For example, it can be seen that pieces of digital broadcast data (MPEG TS) for generating FEC data of multicast packet A include B0, C0, D0, E0, F0, G0, H0, I0, J0. Here, B in B0 denotes a multicast packet B, and a number "0" in B0 denotes a location of the first digital broadcast data (MPEG TS) fragment of the multicast packet B.

Hereinafter, the FEC setting method illustrated in FIG. 9 will be described by using FEC data setting of the multicast packet C as an example.

The FEC server initializes the counter n order of the multicast packets in the first buffer 37, the second buffer 38, and the FEC group (S90). At this time, it is preferable that the first buffer 37 and the second buffer 38 have a fragment size.

The FEC server checks whether the counter (n) order of multicast packets and the multicast packet order (diff) for setting FEC data in the FEC group match (S91).

The FEC server does not match the current order of multicast packets in the FEC group (n = 0) and the multicast order (diff = 2) in the FEC group of multicast packets for setting FEC data. n = 0) pieces of digital broadcast data (MPEG TS) of the multicast packet A corresponding to the sequence (diff = 2-1) of the multicast packets for which FEC data is to be set. A1 is stored in the second buffer 38 (S92).

The FEC server calculates and extracts the digital broadcast data (MPEG TS) pieces stored in the first buffer 37 and the digital broadcast data (MPEG TS) pieces stored in the second buffer 38 as an exclusive logical sum (XOR). The resultant value is stored in the first buffer 37 again (S93).

Thereafter, the FEC server increments the counter n order of the multicast packets in the FEC group by the set number " 1 " (S94) and proceeds to step 91 (S91).

Subsequently, in step 91, the FEC server sets the counter n order of the multicast packets to '1', and the multicast packet to set the FEC data is set to '2'. Proceed to S92.

That is, in step 92, the FEC server stores the second digital broadcast data (MPEG TS) fragment B1 of the multicast packet B in the second buffer 38.

Subsequently, the FEC server performs an XOR operation on the values of the first buffer and the second buffer (S93).

At this time, the value stored in the first buffer 37 is a result value of "0 XOR A1 XOR B1".

Thereafter, the FEC server increments the counter n order of the multicast packet by "1" and then proceeds to step 91 (S91).

In step S91, the FEC server proceeds to step 95 (S95) because the counter n order of the multicast packet matches "2" of the multicast packet to which FEC data is to be set as "2".

In step S95, the FEC server increments the sequence " 2 " of the multicast packets for which FEC data is to be set by the set number " 1 " and stores them in the counter n order of the multicast packets. Therefore, the order n of the multicast packets for which FEC data is to be set is "3". That is, since the order of the multicast packets for which FEC data is to be set is "diff (2) + 1", it becomes "3".

In step 96, the FEC server checks whether the order n of the multicast packets for which FEC data is to be set is equal to "3" and the FEC group size.

In step 96, the FEC server proceeds to step S97 because the sequence (n) "3" of the multicast packet for which FEC data is to be set and the FEC group size do not coincide with "10".

Therefore, the FEC server stores the third digital broadcast data (MPEG TS) fragment D2 of the multicast packet D in the second buffer 38, and proceeds to step 98 (S98).

The FEC server computes the value of the first buffer 37 and the value of the second buffer 38 as an exclusive logical sum (OR) in step 98 and stores the value in the first buffer 37 again. At this time, the value stored in the first buffer 37 is the operation result value of "0 XOR A1 XOR B1 XOR D2".

In step S99, the FEC server increments the counter n order of the multicast packets by "1" and proceeds to step 96 (S96).

Thereafter, the FEC server repeats steps 96 through S99 until the counter n order of the multicast packet matches the FEC group size.

The FEC server repeats steps 96 through 99 and if the current order of the multicast packets in the FEC group matches the size of the FEC group, the FEC server returns the value stored in the first buffer 37 in step S100. Insert into the FEC data field. After that, when the insertion of the value stored in the first buffer 37 into the FEC data field is completed, the FEC server multicasts the corresponding multicast packet through the IP network.

At this time, the value inserted into the FEC data field is a result of operation of "0 XOR A1 XOR B1 XOR D2 XOR E2 XOR F2 XOR G2 XOR H2 XOR I2 XOR J2".

10 is a flowchart illustrating an operation of an error detection and correction method of the set-top box according to the present invention.

Wait until all multicast packets of the FEC group are received.

Here, when receiving the multicast packet, it is checked whether the FEC group is changed by comparing the FEC header information of the multicast packet received immediately with the FEC header information just received. The checking method becomes the same FEC group if the following equation is satisfied.

Note: pre (x): x field of FEC Header of previous packet

     now (x): x field of the FEC Header of the current packet

{now (sequence_number)-pre (sequence_number)}

 -{now (diff)-pre (diff)} = 0

If the multicast packet is determined to be the same FEC group in S101 of FIG. 10, the digital broadcast data (MPEG TS) is stored in a TS buffer (not shown) in S102, and the header information is stored in an FEC header buffer.

If the packet is not the same FEC group in S101 of FIG. 10, the contents of the FEC header buffer are compared in S103 to check whether there is a missing packet in the FEC group.

If there is one packet lost in S103 of FIG. 10, the procedure goes to S104 through the recovery procedure S105 of FIG. 11, and if the packet is missing or exceeds one, the procedure goes to S104.

In S104 of FIG. 10, digital broadcast data (MPEG TS) and FEC Header information of a current packet are stored in a buffer as in S102, and digital broadcast data (MPEG TS) of a previous FEC group is transmitted to a decoder.

FIG. 11 is a flowchart illustrating a process of recovering a lost multicast packet in detail showing the 105 th step S105 of FIG. 10.

Here, 'm' is the number of multicast packets to be stored in the first buffer and to recover the FEC region and increases from 0 to "group_size-1".

Recovering lost packets requires information from all other multicast packets in the same FEC group, and is used to refer to these packets.

And 'P' means the location of the piece to recover. That is, since the digital broadcast data (MPEG TS) is divided by the fragment size when generating the FEC data, the number divided at that time is group_size-1. These divided pieces are as shown in FIG. 7, and 'P' means a piece number in FIG. 7.

In addition, 'n' is stored in the second buffer and refers to the count of multicast packets required for digital broadcast data (MPEG TS) fragment recovery and increases from 0 to group_size-1.

To recover lost packets, recover the 'P' th fragment from a specific packet 'm'. The process is as follows:

The 'm' packet extracts FEC data, and extracts a specific piece of digital broadcast data (MPEG TS) from all other packets, and XORs each other to recover the 'P' piece. At this time, a counter for sequentially selecting the remaining multicast packets other than the 'm' multicast packet used is 'n'.

First, in order to select the multicast packet m to be stored in the first buffer, the count 'm' is set to '0' (S110). This indicates that the order of multicast packets to be recovered first is diff '0'.

Thereafter, 'm' representing a multicast packet to be stored in the first buffer is compared with a diff of the lost packet (S111).

If 'm' is smaller than the diff of the lost packet in the comparing step S111, a fragment number P equal to 'm' is designated as a location to be stored in the third buffer (S114).

If the 'm' is greater than the diff of the lost packet in the comparing step S111, the fragment number P of 'm'-1 is designated as a position to be stored in the third buffer (S113).

Here, S113 and S114 determine the fragment position of the packet to be recovered.

Thereafter, it is determined whether 'm' is smaller than group_size (S115).

If 'm' is smaller than group_size, the first buffer is initialized with a fragment of digital broadcast data (MPEG TS) of the packet m, and the second buffer and 'n' are initialized with '0' (S117).

Thereafter, it is determined whether the multicast packet 'n' to be stored in the second buffer is smaller than the group_size (S119).

If the multicast packet 'n' is smaller than group_size, it is determined whether the multicast packet n to be stored in the second buffer and the diff of the lost packet are not the same (S121).

If the multicast packet n to be stored in the second buffer and the diff of the lost packet are not the same, the multicast packet m to be stored in the first buffer and the multicast packet n to be stored in the second buffer are compared (S122). ).

If the multicast packet n is smaller than the multicast packet m, the digital broadcasting data (MPEG TS) m-1th fragment of the 'n' th multicast packet in the current FEC group is stored in the second buffer. (S123). If the remaining part of the buffer is filled with '0'.

On the other hand, if the multicast packet n is larger than the multicast packet m, the m th piece of the digital broadcast data (MPEG TS) of the 'n' multicast packet in the current FEC group is stored in the second buffer (S124). . If the remaining part of the buffer is filled with '0'.

Thereafter, the first buffer and the second buffer are XORed and the result is stored in the first buffer (S125).

Subsequently, multicast packet n + 1 is performed (S118). That is, an operation for storing the fragment extracted from the next packet in the second buffer is performed.

Subsequently, when S119, S121, S122, S123, or S124, S125 is performed, and the multicast packet 'n' is equal to the group_size in step S119, it is determined whether the multicast packet 'n' is smaller than the group_size. In operation S120, the first buffer stores the information of the first buffer at the P th fragment position of the third buffer. That is, the fragment of the digital broadcast data (MPEG TS) is recovered from a multicast packet of one of the FEC groups.

Thereafter, the multicast packet m + 1 is performed (S112). That is, a process of recovering the FED data of the next multicast packet is performed.

Subsequently, the process proceeds to comparing the 'm' representing the packet to be recovered with the diff of the lost packet (S111).

Repeat these steps.

If 'm' is equal to group_size in the step S115 of determining whether 'm' is smaller than group_size, the contents of the third buffer are output to the TS buffer. That is, all lost packets are recovered.

Meanwhile, in the determining of whether the multicast packet n to be stored in the second buffer and the lost packet are not the same (S121), the diff of the multicast packet n to be stored in the second buffer and the lost packet are the same. In step S119, the multicast packet n is + 1ed so that the next multicast packet can be stored in the second buffer (S118). Since this is a case in which a piece of digital broadcast data (MPEG TS) cannot be obtained from the packet because it is a lost packet, an operation is performed on the next packet.

On the other hand, in the step (S122) comparing the diff of the multicast packet m to be stored in the first buffer and the multicast packet n to be stored in the second buffer, the multicast packet n is equal to the multicast packet m. If it is the same, "+1" is performed on the multicast packet n to store the next multicast packet in the second buffer (S118), and then the process proceeds to step 119 (S119). This is because the multicast packet providing the FEC data and the multicast packet providing the fragment are the same, so that the operation is performed on the next multicast packet.

1 is an illustration of forward error correction for recovering lost multicast packets in a digital broadcast system.

2 is a diagram illustrating a configuration of a digital broadcasting system according to the present invention.

3 is a diagram showing the configuration of an FEC server according to the present invention;

4 is a view showing a configuration for a set-top box according to the present invention.

5 illustrates a multicast packet in accordance with the present invention.

FIG. 6 is a diagram illustrating a configuration of an FEC header field shown in FIG. 5.

7 is an exemplary diagram of segmented digital broadcast data (MPEG TS) according to the present invention.

8 illustrates an FEC field of multicast packets included in an FEC group according to the present invention.

9 is a flowchart showing the operation of the FEC data setting method of the FEC server according to the present invention;

10 is a flowchart illustrating an operation of the error detection and correction method of the set-top box according to the present invention.

FIG. 11 is a flowchart illustrating a detailed operation of recovering an FEC region of a multicast packet in the error correction method of the set top box according to FIG. 10.

Claims (11)

In a digital broadcasting system, A certain number of multicast packets are set to the FEC group for transmission of the digital broadcast data (MPEG TS), and the forward direction of the respective multicast packets using the digital broadcast data (MPEG TS) of the multicast packets included in the FEC group. A server for generating error correction information and including the same in a multicast packet and transmitting the same through a network; Wow If the multicast packet is lost among the multicast packets received through the network, the digital broadcast data of the lost multicast packet through the pieces of digital broadcast data (MPEG TS) of the remaining multicast packets except for the lost multicast packet. (MPEG TS) A digital broadcast system comprising a set top box for recovering lost multicast packets by respectively recovering fragments and combining the recovered digital broadcast data fragments. The method of claim 1, The server, A Forward Error Correction (FEC) group setting unit for setting a predetermined number of multicast packets to an FEC group for transmission of digital broadcast data (MPEG TS); A data dividing unit for dividing the digital broadcast data (MPEG TSs) of the multicast packets included in the FEC group by a predetermined number; Each of the digital broadcast data (MPEG TSs) of the multicast packets included in the FEC group is divided into a predetermined number, and each of the divided digital broadcast data (MPEG TSs) is forwarded to each multicast packet through an exclusive OR. An FEC information setting unit configured to set error correction information and include the same in a multicast packet and transmit the same through a network; And And an FEC header setting unit configured to set a stream ID, a sequence number, and a sequence of multicast packets of the multicast packets in the FEC group to include in the multicast packet. The method of claim 2, The set top box, And determining the lost packet through a sequence number. In the server of a digital broadcasting system, A Forward Error Correction (FEC) group setting unit for setting a predetermined number of multicast packets to an FEC group for transmission of digital broadcast data (MPEG TS); A data dividing unit for dividing the digital broadcast data (MPEG TSs) of the multicast packets included in the FEC group by a predetermined number; And The digital broadcast data (MPEG TSs) of the multicast packets included in the FEC group are respectively divided into a predetermined number, and the respective digital broadcast data (MPEG TSs) are forwarded to the respective multicast packets through an exclusive OR (XOR) operation. A server comprising an FEC information setting unit for setting the error correction information to be included in the multicast packet for transmission over the network. The method of claim 4, wherein The server, And a FEC header setting unit for setting a stream ID, a sequence number, and a sequence of multicast packets of the multicast packets in the FEC group and including the multicast packets in the multicast packets. In a set top box of a digital broadcasting system, An error determination unit that determines whether the multicast packet is lost among the multicast packets received through the network through a sequence number included in the multicast packet; At least one buffer; And A set-top box including an error correction unit for recovering lost multicast packets through FEC data recovery of the remaining multicast packets except for the lost multicast packets in the FEC group. The method of claim 6, The error correction unit, The multicast packet to recover FEC data and the location of the digital broadcast data (MPEG TS) fragment of the multicast packet are identified, and the FEC data is stored in the first buffer, and the multicast packet storing the FEC data in the first buffer is lost. After extracting each piece of digital broadcast data (MPEG TS) required for recovery from the remaining multicast packets except for the multicast packet, the P-th digital broadcast data (MPEG) of the lost multicast packet is performed by performing an XOR operation stored in the first buffer. While recovering the fragments, the respective pieces of digital broadcast data (MPEG TS) of the lost multicast packets are recovered through the FEC data of the multicast packets except the lost multicast packets in the FEC group, and the recovered digital broadcast data ( Combining MPEG TS fragments to recover digital broadcast data (MPEG TS) of lost multicast packets. Set-top boxes. An information setting method for error correction of a server in a digital broadcasting system, Setting a predetermined number of multicast packets to an FEC group for transmission of digital broadcast data (MPEG TS); Dividing the digital broadcast data (MPEG TSs) of the multicast packets included in the FEC group by a predetermined number; And The digital broadcast data (MPEG TS) of the multicast packets included in the FEC group is divided into a predetermined number, and the forward error correction information of each multicast packet is set by using the divided digital broadcast data (MPEG TS). The information setting method for error correction of the server comprising the step of including in the multicast packet and transmitting through the network. The method of claim 8, Transmitting through the network, And setting forward error correction information of each of the multicast packets through an exclusive logical sum (XOR) operation of the divided digital broadcast data (MPEG TSs). The method of claim 8, And setting a stream ID, a sequence number, and an order of the multicast packets in the FEC group to include in the multicast packet. In the error correction method of a set-top box in a digital broadcasting system, Determining whether a multicast packet is lost among multicast packets received through a network through a sequence number included in the multicast packet; Wow Recovers the digital broadcast data (MPEG TS) fragments of the multicast packets lost through the FEC data of the remaining multicast packets except the lost multicast packets in the FEC group, and combines the recovered digital broadcast data (MPEG TS) fragments. An error correction method of a set top box comprising recovering a multicast packet.

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