DE102006045311A1 - Method and device for reconstructing at least one data packet - Google Patents

Abstract

The invention relates to a method for reconstructing at least one data packet of a two-dimensional block code, wherein in each x-th row of the two-dimensional block code the associated data packets and at least a first redundancy packet with a systematic code and every y-th column of the two-dimensional block code, the associated data packets and at least a second redundancy packet is coded with a parity code, wherein for several lines of the two-dimensional block code (a1) the data packets of the xth line are decoded with systematic codes in intermediate packets, these intermediate packets being erroneous or error-free, (a2) a respective position of one erroneous intermediate packet is stored, (a3) at least one end packet is generated by applying the encoding rule of the parity code to at least one of the error-free intermediate packets and at least one of the end packets, and after performing these steps for the lines at least for one of the columns of the two-dimensional block code (b1), a number of defective intermediate packets per column is determined from at least one of the stored positions (POS), and (b2) corrects the erroneous intermediate packet into the data packet using the parity code using the at least one final packet if the number equals 1. The invention also relates to a device for carrying out the method.

Description

The Invention busy with a method and apparatus for reconstructing at least one data packet.

Currently is the standardization of digital television over the Internet vehemently advanced, e.g. as part of DVB (DV - Digital Video broadcast). The to be transferred digital television signals are thereby in data packages with the help of the IP standard (IP - Internet Protocol) from a transmitter to one or a plurality of receivers. The transmission takes place in the access network for example about DSL (DSL - Digital Subscriber Line). Due to disturbances in the transmission networks it can come to transmission errors, wherein erroneous data packets are discarded, for example. causes for transmission errors are for example overload from routers in the network, interfering signals on broadband access lines, or transmission errors in wireless Home networks, such as WLAN (WLAN - Wireless Local Area Network).

One Loss of data packets due to digital television signals compressed multimedia data can be represented, e.g. due to error propagation during decoding, too massive Quality losses lead. Especially at payment services, such as Video on Demand, one is possible error-free reconstruction in the receiver even with transmission errors to ensure.

It is a variety of methods for error protection and reconstruction erroneous data known, with the help of the protected Data packets additional redundant data packets (redundancy packets) are generated, the Error detection and / or erroneous reception at the receiver for reconstruction Data packets can be used. The coding and the decoding takes place here, for example blockwise, being a reconstruction property of data packets can be improved, the more data packets in a data block, considered in the coding or decoding, into consideration is pulled.

The Use of large Data blocks shows however, the disadvantage of having a large storage space in one Apparatus for carrying out the decoding must be provided. This disadvantage is additionally characterized strengthened that faster RAM (Random Access Memory) over external Hard disk space relatively expensive is so in today's computing units the RAM is replaced by a virtual one RAM is extended, where the data is on a slow disk be outsourced.

Of the Invention is therefore the object of a device and to specify a method with which both the reconstruction property by Use large data blocks as well as a memory efficiency for the reconstruction of the data blocks improved becomes.

These Task is by the claims 1 and 6 solved. Other developments of the invention are given in the dependent claims.

The The invention relates to a method for reconstructing at least one Data packets of a two-dimensional block code, where in each xth line of the two-dimensional block code the associated data packets and at least a first redundancy package with a systematic one Code and every y-th column of the two-dimensional block code the associated Data packets and at least a second redundancy packet with a parity Code are encoded, where for several lines of the two-dimensional block code (a1) the data packets the xth line with systematic codes are decoded into intermediate packets, these intermediate packages are faulty or error free, (a2) stored a respective position of a faulty intermediate packet (a3) at least one end packet by applying the encoding rule the parity code on at least one of the error-free intermediate packets and on at least one of the end packages is generated and after performing this Steps for the lines at least for one of the columns of the two-dimensional block code (b1) respectively a number of faulty intermediate packets per column based on at least one of the stored positions (POS) is determined, and (b2) the erroneous intermediate packet into the data packet by means of the parity code is corrected using the at least one end packet, if the number equals 1. The invention also relates to a Device for performing of the procedure.

By this method, the erroneous intermediate packets are corrected by using the parity code, ie, an encoding rule of the parity code and the associated second redundancy packets, and using the at least one end packet. This shows the advantage that to correct the faulty intermediate packet, i. h for reconstructing the corresponding data packet, only a small number of data, ie data packets, is made possible in a second decoding module carrying out this correction with a low memory outlay. By using the small memory requirement, an efficiency for the reconstruction of the data packets is improved, since a time-consuming reading and / or writing of faulty or error-free intermediate packets is considerably reduced. This efficiency in the reconstruction remains guaranteed even if a large number of data packets in the two-dimensional block code is used. Furthermore, the use of a large number of data packets can significantly reduce an unreconstructible residual error in transmitted data packets.

Preferably is at least a faulty intermediate package before performing the Step a1 by a predeterminable value, in particular a binary value 0, preallocated. This ensures that when creating the Final value no distinction into erroneous and / or error-free Intermediate packages performed must become. This can accelerate the reconstruction erroneous data packets because of a time-consuming query, whether an interim package is faulty or error free when creating the end package can be dispensed with. In general, can be faulty Intermediate packages also with binary values or other values not equal to 0, as long as the predefinable Value ensures that at a link This value with the end value does not change a content of the final value takes place. Especially when using the parity code generates a binary zero with one of the end packages exactly the contents of the end package.

Becomes preferably before the first execution of step a3 on or several end packages to a predetermined additional value, in particular on a binary further value 0, preassigned, then the reconstruction of incorrectly transmitted Data packets, i. faulty intermediate packages, further accelerated become. Will the end packages for the first time without this extension generated, so is the coding rule of the parity code not applicable to the error-free intermediate packages and end packages. Due to the pre-assignment with the predeterminable further value is therefore achieved that no query must be made whether the creation of the End values performed the first time , whereby an acceleration of the process for the correction of faulty intermediate packages, d. H. for reconstruction at least one of the data packets is realized.

In a further training after the implementation of steps a) and b) clears the position of the at least one defective intermediate packet, the faulty intermediate package, which was corrected, by doing so replaced corresponding error-free intermediate package and then the Steps of the procedure to be carried out again. Through this extension, i.e. re-running through the steps of the method according to the invention is a further reduction in faulty intermediate packages or one Increase in reconstructed data packets allows. In particular, by this iterative repetition of the steps the first time through reconstructed faulty intermediate packets used to further correct incorrect intermediate packages.

moreover Preferably, the steps are repeated until no faulty intermediate packets can be corrected, or until all faulty Intermediate packages have been reconstructed. With the help of this extension the iterative development of the invention can then be aborted if no further improvement is achieved in an iteration step becomes. Hereby can unnecessary iterative repetitions of the steps avoided and thus an acceleration the reconstruction can be achieved.

• – ein erstes Dekodiermittel zum Dekodieren der Datenpakete der x-ten Zeile mittels des systematischen Codes in Zwischenpakete, wobei diese Zwischenpakete fehlerhaft oder fehlerfrei sind;
• – ein erstes Speichermittel zum Speichern einer Position eines jeweiligen fehlerhaften Zwischenpakets;
• – ein Akkumulatormittel zum Generieren von zumindest einem Endpaket durch Anwenden der Kodierungsvorschrift des Paritätskodes auf zumindest ein fehlerfreies Zwischenpaket und auf zumindest eines der Endpakete;
• – ein zweites Dekodiermittel zum Ermitteln jeweils einer Anzahl an fehlerfreien Zwischenpaketen pro Spalte anhand zumindest der im ersten Speichermittel abgelegten Position, und zum Korrigieren des fehlerhaften Zwischenpakets in das Datenpaket mittels des Paritätskodes unter Verwendung des zumindest einen Endpakets, falls die Anzahl gleich Eins ist.

The invention also relates to an apparatus for reconstructing at least one data packet of a two-dimensional block code, wherein in each x-th row of the two-dimensional block code the associated data packets and at least a first redundancy packet with a systematic code and in each y-th column of the second dimensional block codes the associated data packets are encoded with a parity code, the device comprising the following means:

• A first decoding means for decoding the data packets of the x-th row by means of the systematic code in intermediate packets, these intermediate packets being erroneous or error-free;
• A first storage means for storing a position of a respective defective intermediate packet;
• - accumulator means for generating at least one end packet by applying the encoding rule of the parity code to at least one error-free intermediate packet and to at least one of the end packets;
• A second decoding means for determining in each case a number of error-free intermediate packets per column based on at least the position stored in the first memory means, and for correcting the erroneous intermediate packet in the data packet by means of the parity code using the at least one end packet if the number is equal to one.

With Using this device, the method can be implemented and realized become.

The Invention and its developments are based on drawings explained in more detail.

It demonstrate:

1 a construction of a two-dimensional block code;

2 a flow chart for performing a method for decoding a data packet;

3 an apparatus for performing the method of decoding the data packet;

4A - 4D Positions of erroneous data packets during iterative run of the procedure.

Elements with the same function and mode of action are in the 1 to 4 provided with the same reference numerals.

With the aid of a first embodiment of the invention will be explained in more detail. Here, a feature film is to be transmitted as part of a video-on-demand service from a video-on-demand server to a set-top box of a recipient. The transmission takes place with the help of the DVB standard. For this purpose, the movie is divided into data packages. A data packet comprises one or more symbols of a predefinable length. In the present exemplary embodiment, each data packet D (x, y) comprises exactly one symbol of length 1 bit, wherein a position of the data packet in a two-dimensional block code ZDB is denoted by a reference symbol x for a line and a reference symbol y for a column of the two-dimensional data Block codes ZDB features. M = 15 consecutive data packets become a line Z of a two-dimensional block code ZDB according to 1 summarized. Furthermore, the two-dimensional block code N = 5 lines Z of data packets, ie the data packets D (1,1), ..., D (5,15).

For each line of the two-dimensional block code, T = 3 first redundancy packets R (1,1), ..., R (5,3) are formed in each case. These first redundancy packets are generated using a systematic code SC, such as a Rapter code or a Low Density Parity Check code. One skilled in the art of channel coding is aware of other systematic codes, so will not be discussed further here. Furthermore, at least one second redundancy packet S (1),..., (S15) is generated for the data packets per column. For this purpose, a parity code PC is used. The parity code PC indicates that the respective second redundancy packet S (y) is generated by binary XOR combination of the binary symbols of the respective data packets of each line Z, eg y = 10, of the two-dimensional block code. The second redundancy symbols S are thus generated as follows: S (y) = D (1, y) XOR D (2, y) XOR ... XOR D (5, y) (1)

Of the Transmitter, i. the Video-on-Demand server, next sends the Data packets D1 (1,1), ..., D (5,15), the first and second redundancy packets R (1,1), ..., R (5,3), S (1), ..., S (15) to the receiver. The Order of the packets in the concrete transmission is for the invention without meaning.

Due to a disruption of the transmission, one or more of the packets, such as the data packets D (3,15), reach the receiver incorrectly. If a packet is lost during transmission, this packet is marked as faulty. The flowchart according to 2 , which allows reconstruction of faulty data packets, is started in state STA. Here are the steps:

step S1: An index counter i is set to 1, i = 1. Further, in a later step, too setting the endpacts to 0, i. E (i) = 0, E (2) = 0,. E (M = 15) = 0. The index counter characterizes the current line of the two-dimensional Block codes. This is followed by a step S2.

Step S2: In this step, for the i-row of the two-dimensional block code, a decoding of the M = 15 data packets by means of the systematic code using the first redundancy packets of the i-th row in M = 15 intermediate packets Z (i, 1), ..., Z (i, M) decodes. This results in faulty intermediate packets Z1 and error-free intermediate packets Z2. For the reconstruction of at least one faulty intermediate packet can according to 2 be proceeded. It follows a step S3.

step S3: The faulty intermediate packets from the second step S2 become and their position POS (x, y) within the two-dimensional block code with the coordinates (x, y) stored in a first memory module SM1. It follows a step S4.

Step S4: In this step, the error-free intermediate packet Z2 is linked with the corresponding end packets by applying the encoding rule of the parity code PC, so that the end packets E (1), ..., E (15) are generated. For example, the final packet E (1) is formed by the following rule: E (1) = E (1) XOR Z2 (i, 1) (2)

For the others error-free intermediate packets and end packets of the i-th line become analog proceed. It follows step S5.

step S5: This step checks if the Steps S2 to S4 for all lines have been performed are. If this is not the case, i ≠ N, thus, step S6 is proceeded to. Otherwise, the next step S7 executed.

step S6: This becomes the index counter i increased by 1, i = i + 1, and subsequently proceeded to the second step S2.

Step S7: The seventh step becomes the index counter is set to 1, ie i = 1. In the following, the index counter restricts the column of the two-dimensional block code to be processed. It follows a step S8.

step S8: In step S8, for the column i of the two-dimensional block code has a number A of defective ones Intermediate packages per column i determined. This determination is made by analyzing the stored positions POS (x, y). Then it will be a step S9 is performed.

step S9: In the ninth step S9, it is analyzed whether the number A = 1. If this is the case, then proceeds to step S10, otherwise with step S11.

Step S10: In step S10, the erroneous intermediate packet of the column i is corrected into an error-free intermediate packet by means of the associated second redundancy packet S (15) of the parity code PC using the associated end packet E (15). For example, the faulty intermediate packet Z1 (3,15) with the position POS (x = 3, y = 15). For this purpose, the faulty intermediate packet Z1 (3,15) is reconstructed into the error-free intermediate packet Z2 (3,15) by means of the following equation: Z2 (3,15) = D (3,15) = E (15) XOR (3)

For further faulty intermediate packages will proceed analogously. The above equation results from the coding rule of the parity code PC.

step S11: In the eleventh step S11, it is checked if the last columns of the two-dimensional block code ZDB is reached, i.e. if i = M. If this is the case, then the flowchart becomes finished in the END state. Otherwise, step S10 is executed.

step S12: In this step, the index i is incremented by 1, i. i = i + 1. Further will after execution of step S12, the flowchart continues in step S8.

In the flowchart according to 2 In step S4, only the error-free intermediate packets were taken into account for the creation of the final packets. In an extension, all intermediate packages for the preparation of the final packages can be taken into account, if the faulty intermediate packages, eg Z1 (5,15), are pre-assigned by a predeterminable value W before the final packages are created, the value W being used to generate one of the final values faulty intermediate packet causes no change in the final value before generation. In particular, the binary value W = 0 is set. Due to the pre-assignment with the value W = 0, no change in the newly determined final value takes place during the XOR operation.

There both for Codes SM, PC used systematic codes for two-dimensional block code are, the error-free intermediate packet Z2 (x, y) is identical to the corresponding data packet D (x, y), e.g. D (1.5) = Z2 (1.5).

To Reconstruction of all intermediate packets, i. Data packets, these can in the receiver's set-top box be further processed. For example, they are by a MPEG2 (MPEG - Motion Picture Expert Group) Decoder decodes and the decoded picture visually displayed on a user's monitor.

In 3 An apparatus DV for carrying out the method for reconstructing a data packet is to be seen. The two-dimensional block code ZDB is first transferred to a first decoding module DM1. The first decoding module executes steps S1 to S6 according to the flowchart 2 by. The position POS (x, y) of the respective defective intermediate packet is stored in the first memory module SM1 organized. At least the faulty intermediate packets Z2 (1,1),..., Z (N, M) are stored in the second memory module SM2. An accumulator module AM executes the generation of the end packets E (1), ..., E (M) according to step S4 after decoding each line of the two-dimensional block code 2 by. The final packets are buffered in the accumulator module.

In a second decoding module DM2, the steps S7 to S12 of the flowchart become 2 carried out. In this case, the second redundancy packets S (1), ..., S (M) are supplied by the first decoder module DM1, the positions of faulty intermediate packets from the first memory module SM1 and the respective end packets from the accumulator module to the second decoder module DM2. From this, it determines the number A of defective intermediate packets in columns and, if the number is equal to one, corrects the faulty intermediate packet. The corrected, ie error-free, intermediate packet is transmitted to the second memory module for overwriting the faulty intermediate packet at the same position x, y.

The Device DV can be in hardware, software or in combination be implemented and realized from hardware or software. Furthermore, this is in a portable terminal, such as a mobile phone according to GSM standard (GSM-Global System for Mobile Communications) or a stationary terminal, for example a set-top box integrated.

In a further development can after Correction of one of the faulty intermediate packets a re-run of steps S1 to S12 take place. For this purpose, the flowchart according to 2 after the state "J" of step S11 in step S13. In this case, the positions POS (x, y) for the faulty intermediate packets are removed from the first memory module, and in the second memory module the corrected or incorrect intermediate packets are replaced by the associated error-free intermediate packets. Subsequently, the steps S1 to S12 are executed. The iteration of this development can be continued until all intermediate packets, ie data packets, are error-free, or until after another iteration no further faulty intermediate packets have been corrected.

The improvement achieved by this development will be described below with reference to 4A - 4D explained in more detail. In this case, faulty intermediate packets Z1 (x, y) with a symbol "X" and error-free intermediate packets Z2 (x, y) or D (x, y) are marked with a symbol "_". Starting from 4A be first in accordance with the comments 2 Corrects faulty intermediate packets, wherein the systematic code and the parity code, ie parity code, are designed such that a faulty intermediate packet can only be corrected if it is the only faulty intermediate packet in a row or column. Thus, a correction is performed line by line and then column by column. The final result is in 4B to see. Only in the first and fourth column could a faulty intermediate package be corrected, ie reconstructed. Subsequently, the steps according to the comments to 2 again on the intermediate packages of 4B applied. The constellation of 4C results after passing through the steps S1 to S6, ie correction by means of the systematic code, and the 4D after completing the flowchart in the END state.

Thus, after two passes through the steps 2 all faulty intermediate packets have been corrected, ie all data packets have been reconstructed.

The invention is based on 1 to 4 have been shown in more detail. The numbers of data, first and second redundancy symbols used here represent only one embodiment and are not limited thereto. In general, data packets may have one or more bits. Furthermore, each row of the two-dimensional block code may comprise a different number of data packets, taking into account only those data packets for forming the second redundancy packet (s) located in a column of the two-dimensional block code. Furthermore, the first and the second redundancy packets may each have different numbers per row or per column, for example in the second column three and in the fourth column five second redundancy packets. In addition, one or more end packets per column of the two-dimensional block code may generally be used.

literature

• [1] M. Bassert, channel coding, publishing house BG Teubner, Stuttgart 1992, ISBN 3-518-06143-0 (Parity check code, example 1.1, P. 16-17)

Claims (6)

Method for reconstructing at least one data packet (D (3,15)) of a two-dimensional block code (ZDB), wherein in each x-th row (Z) of the two-dimensional block code (ZDB) the associated data packets (D (x, 1 ), ..., D (x, M)) and at least a first redundancy packet (R (x, 1), ..., R (x, T)) with a systematic code (SK) and in every yth Column (S) of the two-dimensional block code (ZDB) the associated data packets (D (1, y), ..., D (N, y)) and at least a second redundancy packet (S (1), ..., ( S (15)) are encoded with a parity code (PC), characterized in that a) the following steps a1) -a3) are carried out for a plurality of lines of the two-dimensional block code (ZDB): a1) decoding of the data packets (D (x, 1 ), ..., D (x, M)) of the x-th row (Z) by means of the systematic code (SM) in intermediate packets (Z (x, 1), ..., Z (x, M)), these intermediate packets are faulty or error free; a2) storing a respective position (POS (x, y)) of a faulty intermediate packet (Z1 (3,15)); a3) generating at least one end packet (E (1), ..., E (M)) by applying the coding specification of the parity code (PC) to at least one of the error-free intermediate packets (Z2 (3,1), ..., Z2) (3,14)) and on at least one of the end packets (E (1), ..., E (M)); b) after performing step a) for the rows, the steps b1) -b2) are carried out for at least one of the columns of the two-dimensional block code (ZDB): b1) determining in each case a number (A) of defective intermediate packets (Z1 (3 , 15)) per column (S) based on at least one of the stored positions (POS); b2) correcting the erroneous intermediate packet (Z1 (3,15)) into the data packet (D (3,15)) by means of the parity code (PC) using the at least one end packet (E (15)) if the number (A) equals one. A method according to claim 1, characterized in that in step a) faulty intermediate packets (Z (5,15)) by a predetermined value (W), in particular by a binary value zero, pre-assigned become. Method according to one of the preceding claims, characterized characterized in that before the first execution of step a3) an or several end packages (1, ..., EM) to a presettable further value (V), especially on a binary further value (V) zero, be pre-assigned. Method according to one of the preceding claims, characterized marked that - to Carry out the steps a) and b) the position of the at least one faulty Intermediate packages deleted, - the faulty one Intermediate packet (Z1 (3,15)), which was corrected by the error-free Intermediate package (Z2 (3,15)) is replaced, and - then steps a) and b) executed again become. Method according to claim 4, characterized in that that the steps of claim 4 are repeated until - by doing Step b) no faulty intermediate packages are corrected, or - to Step b) all faulty intermediate packets have been corrected. Device (DV) for reconstructing at least one Data packets (D (3,15)) of a two-dimensional block code (ZDB), where in every xth row (Z) of the two-dimensional block code (ZDB) the associated Data packets (D (x, 1), ..., D (x, M)) and at least a first redundancy packet (R (x, 1), ..., R (x, T)) with a systematic code (SK) and in each y-th column (S) of the two-dimensional block code (ZDB) the associated data packets (D (1, y), ..., D (N, y)) and at least one second redundancy packet (S (1), ..., (S (15)) with a parity code (PC), in particular for performing a method according to a of the preceding claims, thereby marked that the device comprises the following means: - a first Decoding means (DM1) for decoding the data packets (D (x, 1), ..., D (x, M)) of the xth row (Z) by means of the systematic code (SM) in intermediate packets (Z (x, 1), ..., Z (x, M)), these intermediate packets are faulty or error free; A first storage means (SM1) for storing a position (POS (x, y)) of a respective defective intermediate packet (Z1 (3.15)); - one Accumulator means (AM) for generating at least one end packet (E (1), ..., E (M)) by applying the encoding rule of the parity code (PC) to an error-free intermediate packet (Z2 (3,1), ..., Z2 (3,14)) and on at least one of the end packets (E (1), ..., E (M)); - a second Decoding means (DM2) for determining a number (A) of erroneous ones respectively Intermediate packages (Z1 (3,15)) per column (S) on the basis of at least the first storage means (SM1) stored position (POS), and for correction of the faulty intermediate packet (Z1 (3,15)) into the data packet (D (3,15)) by means of the parity code (PC) using the at least one end packet (E (15)) if the number (A) equals one.