DE10220370A1 - Method and device for recovering a code word from a received, defective code word, method and device for generating a code word, and transmission system - Google Patents

Abstract

In a method and a device for recovering a code word from a received, incorrect code word, the incorrect code word is first received. The code word comprises code units and was derived from one or more information units using a redundancy code. After receiving the faulty code word, faulty or nonexistent code units are determined in the code word and a deposition pattern is set in response thereto. The received, defective code word is then punctured on the basis of the set depuncturing pattern, so that the defective or non-existing code unit is depunctured in the code word.

Description

The present invention relates to a method and a device for recovering code words from a received, incorrect code word, and in particular to a method and an apparatus for Retrieve a code word that has a lossy packet-oriented connection network was transmitted and a Has a plurality of packages. Furthermore, the present invention on a method and on a Device for generating a plurality of packets for Transmission over a packet-oriented connection network as well on a transmission system. The present invention is particularly suitable for the transmission of multimedia data via a lossy channel, in particular Channels are considered where both packet loss and also individual, randomly distributed bit errors in the Data stream occur.

When transmitting multimedia data, i.e. from Voice data, image data, video data and audio data is the trend in the development of future communication systems away from connection-oriented transmission a packet-oriented transmission. This means that for a connection between two communication partners is not a permanent connection is switched exclusively, but that all participants share all lines use. This requires that the data stream of a Participant is divided into packages and the split Packages are sent sequentially to the recipient. The single packet looks for itself in the network its way to the recipient.

• - Paketverluste, z. B. aufgrund überlasteter Netzknoten,
• - unterschiedliche Laufzeiten der einzelnen Pakete, da nicht garantiert ist, dass alle Pakete den gleichen Weg in dem Netz wählen, und
• - ein empfangenes Paket enthält mit hoher Sicherheit keine Bitfehler.

The following effects can occur in such networks:

• - packet losses, e.g. B. due to overloaded network nodes,
• different transit times of the individual packets, since it is not guaranteed that all packets choose the same route in the network, and
• - a received packet contains with high certainty no bit errors.

Below is the packet-based transmission of Multimedia data viewed via a communication system which to a wired core network (landline) and a radio network (mobile network) exists. The core network takes over bridging long distances, while the radio network wireless accessibility of a mobile subscriber on the "last mile" guaranteed.

A concrete example of such a transmission system would be z. B. the combination of the Internet with a modern one Mobile radio system, e.g. B. GSM-GPRS / UMTS, which is often called mobile internet is called.

• - Paketverluste in dem Kernnetz, da Knotenpunkte des Kernnetzes überlastet sein können oder einzelne Pakete nicht rechtzeitig an dem Empfänger ankommen, und
• - Bitfehler bei der Übertragung durch das Funknetz.

The following effects occur when transmitting multimedia data over such a data network:

• Packet losses in the core network, since nodes of the core network may be overloaded or individual packets may not arrive at the recipient in time, and
• - Bit error in the transmission through the radio network.

In such a communication system, the recipient is thus faced with a data stream in which, on the one hand Packets may be missing and packets received can contain individual bit errors.

When transmitting multimedia data via a system of the above type exist in the prior art different procedures, which are essentially in the following five classes can be classified.

I. Error concealment at the recipient

Procedures in this class aim to Detect transmission errors on the receiver side and by a to disguise suitable signal interpolation. This Procedures deliver very good results at low Bit error rates or individual packet losses fail, however mostly with higher bit error rates as well as with multiple consecutive packet losses.

An example of such a method is, for example in ITU-T Recommendation G.711 - Appendix I, "A high quality low-complexity algorithm for packet loss concealment with G. 711 ", ITU-U, 1988

II. Interleaving / multiplexing at the transmitter

Methods of this class spread the before the transmission Data of one package over several packages (interleaving) or Bundle the data streams of several participants (multiplexing). This is associated with a delayed transmission of the data (Buffering). This can be especially the case with dialog-oriented Data transmission, e.g. B. telephony, too intolerable Lead to delays. These methods are particularly suitable for transmission over packet loss channels, since one at the Transmission of lost packet (bundle error) too leads to individual, distributed bit errors in the data stream, which then works well with the one described above Error concealment procedure obscured or with the following described channel coding method are corrected can.

An example of such a method is given by S. V. Anderson. u. a., "Multiplexed Predictive Coding of Speech" in Proc. Of ICASSP 2001, Salt Lake City, Utah, May 2001, Vol. III, pages 741 to 744.

III. channel coding

Methods of this class specifically add one to the transmitter Redundancy (channel coding) in the data stream Help at the receiver detected transmission errors and can be corrected.

An example of this method is e.g. B. by M. Luby, u. a. "Practical Loss Resilient Codes" in Proc. 9th Annual ACM-SIAM Symposium on Discrete Algorithms, January 1998 described.

IV. Multiple Descriptions

Methods of this class generate from a data packet several, usually two, descriptions of the same. Becomes Now only a part of the descriptions can be received Decoding done with reduced quality. Everyone will Received descriptions, the decoding takes place in the original quality. These procedures are suitable everything for transmission via packet loss channels, have so far however, little application was found.

Such a process is described, for example, by W. Jiang, u. a. "Multiple description speech coding for robust communication over lossy packet networks ", in International Conference on Multimedia and Expo, New York, NY, USA, August 2000, Vol. II, pages 444-447.

V. ARQ procedure

Methods of this class recognize on the recipient side lost packages and request them again from the Transmitter on. This requires a return channel from the receiver to the transmitter. Another disadvantage of these procedures is that there is a significant delay until all packets could actually be received.

An example of such a method is from J. Hagenauer, "Rate-Compatible Punctured Convolutional Codes (RCPC Codes) and their Applications ", IEEE Transactions on Communications, Vol. 36, No. 4, pp. 389-400, April 1988 described.

Depending on the specific application, it is too possible to use the methods described in more detail above combine.

The disadvantage of the methods described above is in that these no longer exist at high bit error rates can provide the necessary correction, too intolerable delays or no safe delays Enable transmission.

Based on this state of the art present invention the task, in a simplified manner and secure data transmission with a to enable improved quality.

This object is achieved by a method according to claim 1, an apparatus according to claim 11, a method according to Claim 21, a device according to claim 22 and by a transmission system according to claim 25 solved.

• a) Empfangen des Codeworts;
• b) Bestimmen einer fehlerhaften oder nicht-vorhandenen Codeeinheit in dem Codewort;
• c) ansprechend auf die im Schritt (b) bestimmte fehlerhafte oder nicht-vorhandene Codeeinheit, Einstellen eines Depunktierungsmusters; und
• d) Depunktieren des empfangenen, fehlerhaften Codeworts mittels des eingestellten Depunktierungsmusters, so dass die fehlerhafte oder nicht-vorhandene Codeeinheit in dem Codewort depunktiert wird.

The present invention provides a method for retrieving a code word from a received, faulty code word, a code word comprising code units and being derived from one or more information units by means of a redundancy code, with the following steps:

• a) receiving the code word;
• b) determining a faulty or non-existent code unit in the code word;
• c) in response to the defective or non-existing code unit determined in step (b), setting a deposition pattern; and
• d) depuncturing the received, defective code word by means of the set depuncturing pattern, so that the defective or non-existing code unit is depunctured in the code word.

The present invention also provides an apparatus for recovering a code word from a received, incorrect code word, wherein a code word comprises a plurality of code units and was generated by means of a redundancy code
a signal processing unit which receives the defective code word, which determines a defective or non-existent code unit in the code word, which sets a depuncturing pattern in response to the defective or non-existent code unit, and which punctures the received code word based on the set depuncturing pattern so that the defective or non-existent code unit is depunctured in the code word.

• a) Empfangen der Informationseinheiten;
• b) Codieren jeder Informationseinheit, um für jede Informationseinheit eine Mehrzahl von Codeeinheiten zu erzeugen; und
• c) Anordnen der erzeugten Codeeinheiten derart in dem Codewort, dass ein Verlust einer Codeeinheit oder mehrerer Codeeinheiten in dem Codewort zu einer Codeeinheiten-Folge führt, die einem auf das ursprüngliche Codewort anwendbaren Punktierungsmuster entsprechen, das auch einem Empfänger des Codeworts bekannt ist.

The present invention further provides a method for generating a code word, which contains code units, which are generated based on information units by a redundancy code, for transmission over a lossy connection network, with the following steps:

• a) receiving the information units;
• b) coding each information unit to generate a plurality of code units for each information unit; and
• c) arranging the generated code units in the code word such that a loss of one or more code units in the code word leads to a code unit sequence which corresponds to a puncturing pattern applicable to the original code word, which is also known to a recipient of the code word.

The present invention further provides a device for generating a code word, which contains code units which are generated based on information units by a redundancy code, for transmission over a lossy connection network, comprising:
an input for receiving the information units;
an encoder for encoding each information unit to generate a plurality of code units for each information unit; and
a processing device for arranging the generated code units in the code word such that a loss of one or more code units in the code word leads to a code unit sequence which corresponds to a puncturing pattern applicable to the original code word, which is also known to a recipient of the code word.

According to a preferred embodiment, a Generates a plurality of packets which contain code units, which are based on information units by one Redundancy code are generated, and via a packet-oriented Connection network are transmitted. Here, the Information units received and each of the received Information units is made using a plurality encoded by generators, with an information unit each of the generators is applied and each of the Generators a code unit for an adjacent Unit of information generated. The code units are a plurality of Associated packets, with code units by the same generators, the same packages assigned, and the packets generated are provided.

The present invention also provides a transmission system for transmitting information units
a transmitter which comprises a device for generating a code word or comprises a device which operates according to the inventive method for generating a code word;
a transmission medium that receives and transmits the code words generated by the transmitter; and
a receiver which receives the code words transmitted by the transmission medium, the receiver comprising a device for recovering code words according to the present invention, or a device which operates according to the method according to the invention for recovering the code words.

The present invention is basically the above assign described channel coding method and based on dotted channel codes, also from J. Hagenauer, "Rate-Compatible Punctured Convolutional Codes (RCPC Codes) and their Applications ", IEEE Transactions Communications, Vol. 36, No. 4, pp. 389-400, April 1988 are. It is also possible for further optimization that inventive method also with one or more of the to combine the transmission method described above, in particular the error concealment procedure, the interleaving / multiplexing process and the ARQ Procedures come into consideration.

With regard to puncturing, it should be pointed out that this is understood to mean the systematic removal of bits before the transmission of a data stream. If the decoder has knowledge of which bits have been removed (punctured) on the transmitter side, the decoder can still decode the data stream. The performance of a punctured channel code of rate r, which was obtained from a parent code at rate R _M , is only slightly worse than a real channel code of rate r. By puncturing, a code of any rate r can be generated very easily from a mother code of the rate R _M , where 1>r> R _M applies.

In conventional systems, the Mother codes always immediately after the channel encoder on the Transmitter side according to a defined puncturing pattern, which is known to both the sender and the receiver is. The present invention leaves this approach and according to the invention there is no puncturing of the channel code on the transmitter side. This means that basically everyone Bits of the generated mother code are sent. Different to in the prior art, the technique of Dotting is not used on the transmitter side, but is shifted to the receiving end, whereby the puncturing actually occurring, i.e. rejection of certain bits, caused by transmission losses, ie in that during the transmission of a bit stream one or more bits are lost, i.e. not with the Arrive recipient. This can be the case with the Transmission occurs over a packet loss channel.

The essence of the present invention is therefore that the puncturing virtually from the transmitter to the receiver is shifted, the actual puncturing by Transmission network losses. Preferably The present invention relates to the use of Convolutional codes, because the puncturing technique is special for this suitable is. However, the present invention is not limited to this.

This is an example for the further explanation Packet loss channel considered, but it is obvious that the present invention is not based on such Packet loss channel is limited, but to everyone lossy transmission channel and the associated Transfer procedures can be applied.

Now look at the packet loss channel and kick actually a loss in transmission over the same of a package, so on the receiving end which for example, includes an FEC decoder (FEC = Forward Error Correcting = assumed, that all bits of the lost packet at the transmitter were virtually dotted. However, since the packet losses are pure happen randomly and are hardly predictable for the recipient, the recipient must be informed whether a particular Package is lost or not. This is what it is about However, this is only a small additional information that very easily via a control channel or an inband can be signaled. The same can be achieved by those packages that do not after a certain time arrived at the FEC decoder as dotted be explained (time out).

The method according to the invention can thus be carried out in one step very efficient both packet loss and individual, Correct randomly distributed bit errors.

Basically, the method according to the invention can any channel coding method can be applied, e.g. B. Convolutional codes, turbo codes etc. should preferably be used for the corresponding channel code a decoder with a soft input or at least one erasure decoder To be available.

The method according to the invention thus leads in comparison conventional commercial processes as described above have been described for a substantially secure transmission of the data, which is the case, for example, when transmitting Multimedia data depending on the application in one clear improved speech quality, audio quality, picture quality or Expresses video quality.

Previous FEC procedures were always only one limited special channel. So z. B. for the Transmission via packet loss networks, especially Reed-Solomon codes, which, however, do not or only partially with considerable Have the effort decoded soft-in / soft-out. In contrast to are convolutional codes because of their code properties not suitable for correcting packet loss, for that they can be decoded very well soft-in / soft-out. In the Transmission over cellular networks, in which individual, distributed bit errors occur are particularly suitable Convolutional codes, whereas Reed-Solomon codes or block codes rather are unsuitable.

The method according to the invention processes the data in accordance with a preferred embodiment before sending already in such a way that a packet loss becomes an optimal one Puncturing the convolutional code leads. This is due to optimal Distribution of the encoded data over a plurality of Packages reached. This ensures that a Packet loss, usually caused by a convolutional code would not have been correctable, nevertheless - up to one certain packet error rate - remains correctable. Through the Preprocessing at the transmitter can be done at the receiver guaranteed that M 'packets sent are lost can go, where M '<M, and still a error-free decoding result can be achieved. M 'hangs the code rate N and the code used.

According to a preferred embodiment, this takes place The inventive method on a combination of landlines and cellular network application, but it works inventive method also according to another Exemplary embodiment for pure packet loss networks or pure Mobile networks. Use in the above combination of However, two networks is particularly suitable because here both Packet losses of the fixed network as well as the bit errors of the Cellular network in one step with the same code can be corrected, which, as already explained above, was not possible in the prior art.

• - es können sowohl Paketverluste als auch Einzelfehler behandelt werden,
• - die Erfindung basiert auf durch Paketverlust punktierten Kanalcodes,
• - bei einem Paketverlust erfolgt die Punktierung virtuell auf der Empfängerseite,
• - es ist kein Rückkanal erforderlich,
• - es wird keine zusätzliche Verzögerung des Datenstroms hervorgerufen,
• - als Kanalcode können beliebige, punktierbare Verfahren eingesetzt werden,
• - optional kann an einer Basisstation bei einer Ausgestaltung des Übertragungsnetzwerks als Kombination eines Festnetzes und eines Mobilnetzes eine Neucodierung eingesetzt werden, ohne dass der Empfänger Kenntnis hiervon haben muss,
• - der Sender kann die Paketanzahl und Länge beliebig variieren, ohne dass der Empfänger Kenntnis davon besitzen muss, so dass das System sehr flexibel an Übertragungsqualität und Kapazität der einzelnen Teilnetze angepasst werden kann,
• - dem Empfänger muss lediglich der Verlust eines Pakets signalisiert werden,
• - aufgrund der Struktur müssen sämtliche Anpassungen des Systems, wie z. B. Modus, Rate, Träger, nicht an den Empfänger signalisiert werden, so dass diese Anpassung flexibel und lastabhängig erfolgen können,
• - Anpassungen an dem Mobilfunknetz müssen nicht dem Sender signalisiert werden, wie z. B. das Verwerfen von Paketen, da die Mobilfunkverbindung weniger Fehler aufweist,
• - an der Basisstation muss kein echtes, rechenaufwendiges Transcodieren erfolgen.

The present invention has the following advantages:

• - both packet loss and individual errors can be handled,
• the invention is based on channel codes punctured by packet loss,
• - in the event of a packet loss, puncturing takes place virtually on the receiving end,
• - no return channel is required,
• there is no additional delay in the data stream,
• - Any puncturable methods can be used as the channel code,
• a coding can optionally be used on a base station in a configuration of the transmission network as a combination of a fixed network and a mobile network, without the recipient having to be aware of this,
• the sender can vary the number and length of packets as desired, without the recipient needing to be aware of it, so that the system can be adapted very flexibly to the transmission quality and capacity of the individual subnets,
• - the recipient only needs to be informed of the loss of a packet,
• - Due to the structure, all adjustments to the system, such as B. mode, rate, carrier, are not signaled to the receiver, so that this adaptation can be done flexibly and depending on the load,
• - Adjustments to the mobile network do not have to be signaled to the transmitter, such as. B. discarding packets because the cellular connection has fewer errors,
• - There is no need for real, computationally complex transcoding at the base station.

Further developments of the present invention are in the Subclaims defined.

Preferred embodiments of the present invention are described below with reference to the accompanying Drawings explained in more detail. Show it:

Fig. 1 is a flow diagram of the method according to the invention according to a preferred embodiment;

FIG. 2 shows a transmission system according to a preferred embodiment of the invention with the inventive receiver;

Fig. 3 shows the behavior of the transmission system shown in Fig. 2 without re-encoding the code words received in the base station;

FIG. 4 shows the behavior of the transmission system shown in FIG. 2 with re-coding of the code words received in the base station;

FIG. 5 shows a conventional transmission system for packet-oriented transmission between sender and receiver;

Fig. 6 illustrates the behavior of the conventional transmission system shown in Fig. 5; and

Fig. 7 is a tabular comparison of the behavior of the conventional transmission system and the transmission system according to the invention.

In the following description of the preferred Embodiments become similar or equivalent elements in the individual figures with the same reference numerals Mistake.

A preferred exemplary embodiment of the method according to the invention for recovering a code word is explained in more detail with reference to FIG. 1. This method assumes that the data stream transmitted from a transmitter to a receiver comprises a plurality of code words, with individual code words having a plurality of packets, with a plurality of code units, e.g. B. bits are included, which were generated on the transmitter side by a suitable coding method and were distributed to individual packets according to a predetermined scheme.

In step S100, the code words are received and in Step S102 checks whether all packets of the code word were received. If this is the case, the procedure continues to step S104, in which the received code word decodes is so the information units which the coding on which the transmitter was based, to regain, that is transmitted multimedia data. Then the decoded data for further processing, e.g. B. advertisement, Manipulation etc., forwarded.

It is determined in step S102 that not all packets of the code word have been received, the method goes to Step S110 further in that for the received code word it is determined how many packets have not been received and on which position / position the same in the code word are arranged. Based on this information, the following step S112 found that the received Codeword, at least from the perspective of the recipient, on the transmitter obviously according to a predetermined puncturing pattern was dotted. Based on this information, the chooses The method according to the invention is suitable in step S112 Depuncture pattern, which in the subsequent step S114 is used for depuncturing the code word, which completes the code word again. After that Code word has been completed, the procedure goes to Step S104, in which the required decoding of the Code words can be performed.

According to a preferred embodiment, the Step S102 decision made on the Number of packets received on another Information signal, which indicates whether a certain packet from a set of transmitted packets was received or Not. Alternatively, a period of time can be monitored during which the packets of a code word are expected, and in the event that one or more packages are outside received during this period, they are received rated.

It is possible to decode a received code word, if a packet was received without errors. However, it is not generally required that really a package was received without errors. Situations can exist in which several packets were received, each with some of the data contained is error-free. In this In this case, error-free decoding would also be possible.

A preferred exemplary embodiment of a transmission system which uses the method according to the invention for retrieving a code word and thus enables the advantages described above for the transmission of data is explained in more detail below with reference to FIG. 2. In the exemplary embodiment shown in FIG. 2, the transmission of multimedia data to a mobile receiver via a combined packet loss network and mobile radio network is described.

The multimedia data to be transmitted are from various multimedia sources, e.g. B. a camera 100 a or a microphone 100 b, provided to a multimedia encoder 102 . The multimedia encoder 102 generates a plurality of information units based on the signals present from the multimedia sources 100 a, 100 b, which are forwarded to a channel coding unit 106 via a connection 104 . The channel coding unit 106 comprises an FEC encoder 108 , a packet distribution unit 110 and a multiplexer 112 . The FEC encoder 108 receives the information units at its input via the connection 104 and generates N code units for each information unit, e.g. B. Bits that are forwarded to the packet distribution unit 110 via the connections shown in FIG. 2. The packet distribution unit 110 distributes the received N code units to M packets, preferably M ≥ N. The M packets are passed on to the multiplexer 112 , which then provides them serially at its output. The output of the channel coding unit 106 , that is to say the output of the multiplexer 112 , provides the packets generated to a packet loss network, that is to say a packet-oriented connection network 114 , which serially transmits the packets to a base station 116 . The base station 116 comprises a demultiplexer 118 which provides the M packets transmitted via the network 114 in parallel at an output thereof. Optionally, a re-coding unit 120 can be provided in the base station 116 , in which case the M packets present in parallel at the output of the demultiplexer 118 are made available in parallel to the re-coding unit 120 .

The base station transmits the received M packets, either the M packets received directly at the base station or the M packets newly encoded in the base station, to an FEC decoder 124 in the mobile receiver via a radio network shown only schematically at 122 in FIG . The FEC decoder 124 generates the information units initially provided to the channel coding unit 106 from the received M packets and transmits them via the connection 126 to a multimedia decoder 128 , which decodes the received information units and provides corresponding multimedia devices which are suitable for reproducing the corresponding multimedia data. z. B. the screen 130 a or the speaker 130 b.

The transmission system shown by way of example in FIG. 2 further comprises a controller 132 for the packet loss network and a controller 134 for the mobile network. As can be seen from FIG. 2, the controller 134 for the mobile network receives the DQI signal (DQI = Downlink Quality Indication) from the FEC decoder 124 and issues a carrier command to the base station 116 . As indicated by the connection 136 , the controller 132 for the fixed network and the controller 134 for the mobile network exchange information which will be discussed later. The controller 132 for the fixed network receives the parameter PER from the packet loss network, ie the packet error rate (PER = packet error rate), ie the rate at which packets are lost on the network 114 . Based on the received information, the controller for the fixed network 132 issues the channel coding unit 106 with the rate command, which is used to determine the rate at which the packets are sent to the packet loss network 114 . The controller for the landline 132 also issues a mode command to the multimedia encoder 102 to determine a mode thereof.

In a further preferred exemplary embodiment, as is also shown in FIG. 2, provision can be made to provide an optional return channel between the FEC decoder 124 and the channel coding unit 106 . Provision can also be made to forward the information provided to the base station 116 about the receipt of a faulty packet to the FEC decoder 124 , as indicated by the optional connection “BFI 1-M” (BFI = Bad Frame Indicator).

The functionality of the transmission system according to the invention according to the illustrated embodiment is explained in more detail below with reference to FIG. 2.

As mentioned, FIG. 2 shows the transmission system according to a preferred exemplary embodiment in a possible application scenario of the present invention. In the embodiment shown in FIG. 2, the data sources, e.g. B. provided by the camera 100 a or the microphone 100 b, digitized source data processed by the multimedia encoder 102 . The original data is compressed. In general, it is assumed that the degree of compression on the multimedia encoder 102 is adjustable, so that the data rate at the output of the multimedia encoder can be adjusted in several stages by the mode command that is present at a control input of the multimedia encoder 102 . The compressed data is then made available via the connection 104 to the channel coding unit 106 . Here the data is processed by means of the channel encoder or FEC encoder 108 , which has a rate of 1 / N. This means that L bits at the input of the FEC encoder produce 108 N times L coded bits at the output thereof. The rate of the FEC encoder 108 is set by means of the rate command which is present at a control input of the FEC encoder 108 . The encoded bits are now provided to the packet distribution unit 110 , which divides the encoded bits into M packets.

Since packet loss on the decoder side is interpreted as puncturing the convolutional code, it is necessary to distribute the N by L coded bits among the M packets in such a way that packet loss when transmitted over the packet-oriented network 114 to a channel code received at the decoder leads, which is optimally punctured for this. In other words, it is necessary to generate at the output of the channel coding unit 106 a data stream to be transmitted to the decoder in the form of a code word, a loss of a packet in the code word and in the decoder being recognized as a punctured code word, with regard to the arrangement of the Packets in the code word can be accessed using known puncturing methods without actual puncturing naturally taking place.

The so-called free distance d _free , which the punctured code has, and its range of distances are preferably used to assess puncturing patterns with regard to their "optimality". The distance spectrum consists of two components a _d and c _d . Here a _d indicates the number of paths in the trellis that build a Hamming distance d to the null word and c _d the sum of the bit errors on these paths of distance d.

Both the largest possible free distance d _free and the smallest possible values a _d and c _d are considered optimal. See also z. BJ Hagenauer: "Rate Compatible Punctured Convolutional Codes and their Applications".

The problem with this is the optimal puncturing pattern in usually only through complex computer simulations are determined. Hang on the application used here the puncturing patterns of the code, the code rate, the Packet length and the number of lost packets. at Convolutional codes are preferred, the punctured bits to distribute as evenly as possible over a block.

Examples of the optimal mentioned above Puncturing patterns are punctured by J. Hagenauer, "Rate-Compatible Convolutional Codes (RCPC Codes) and their Applications ", IEEE Transactions on Communications, Vol. 36, No. 4, pp. 389-400, April 1988; by J. Hagenauer, u. a., "Channel Coding and Transmission Aspects for Wireless Applications ", IEEE Special Issue Video Transmission gor Mobile Multimedia Applications, vol. 87, pages 176-1777. October 1999, and by C. White, "Error Correcting with Tail-Biting Convolutional Codes ", dissertation, TU Munich, December 2001.

After the bits are distributed among the M packets, the M packets are sequentially sent over the packet loss channel 114 .

By returning the packet error rate (PER) of the packet loss network 114 to the network control unit 132 , it is possible to adaptively set both the compression of the multimedia encoder 102 and the rate of the FEC encoder 108 . This makes it possible to adaptively adapt both the number of packets and the length of the packet to the current packet loss probability of the network.

The received data packets are transmitted at the base station (BS) 116 via the carriers of a mobile radio network 122 . The only additional information that has to be transmitted to the receiver is the signaling BFIX (Bad Frame Indication = display of a bad frame), which indicates whether a certain packet x has arrived at the base station (in good time) and has thus been transmitted via the radio channel or not. A control or control channel or in-band signaling can be used for this. The same can be achieved if the packets that have not arrived are declared punctured by the FEC decoder 124 after a certain time ("time out").

In addition, in another exemplary embodiment, decoding with subsequent re-coding 120 (optional re-coding) can optionally be carried out on the base station 116 before transmission via the radio channel 112 . As a result, the packet losses occurring in the packet loss network 114 are corrected before the radio transmission. This becomes a clear gain in particular if the bit error probability on radio channel 122 is high.

By returning the transmission quality DQI on the radio channel to the network control unit 134 of the mobile radio system, it is possible to adaptively adapt the number of carriers of the mobile radio system used to the current channel state of the radio channel. An exchange of feedback information between the two network control units 132 and 134 serves to optimize the transmission quality of the overall system. If an optional return channel (ARQ) is available, incremental redundancy can also be requested if there is a high probability of packet loss by retransmitting some of the M sub-packets.

The received data is then decoded in the FEC decoder 124 at the receiver end and passed on to the multimedia decoder 128 , which decompresses it.

Although a preferred embodiment of the Application of the method according to the invention has been explained to point out that the inventive method basically used in every communication system can be, but it is especially for the systems is suitable, where the transmission characteristics both Packet loss as well as individual, randomly distributed bit errors in the corresponding data stream.

As particularly suitable embodiments for the present invention will use voice transmission Internet and GSM-GPRS, the voice / audio / image / video transmission via Internet and UMTS, the voice / audio / image / Watched video transmission over the Internet and GSM EDGE. Furthermore, when using chained Channel codes very efficient data over the above System transfer (file transfer).

The transmission properties and the behavior of the transmission system described with reference to FIG. 2 according to a preferred implementation of the same are explained in more detail below. For the implementation of the transmission system from FIG. 2, the example of the transmission of voice over the mobile Internet was considered. The term "mobile Internet" means the above-described combined network consisting of a packet-oriented network part and an additional radio channel connection section. As already mentioned above, the transmission system opens up a very flexible adaptation of the transmission characteristics depending on the losses on the packet-oriented network and the connection capacity of the mobile network. As mentioned, packet loss at the receiver is considered puncturing the convolutional code, so the only additional information to be transmitted to the decoder is the bad frame indication mentioned above.

The Multimediacodierer causes 102 a coding language based on the AMR voice codec which is based on the CELP technology, which up to eight rates between 4.75 kbit / s to 12.2 kbit / s. The subjectively pure voice quality of the 12.2 kbit / s mode is comparable to the G.711 codec. In addition, a 6-bit CRC is applied to the most important bits. This CRC is used on the speech decoder for the detection of defective frames of a speech frame and controls the error concealment of defective speech frames. This leads to a total bit rate of 5.05 kbit / s to 12.5 kbit / s after the coding of the speech by the encoder 102 .

In addition, the encoder 102 can also pass on source significance information (SSI) to the channel coding unit 106 , which is then used, for example, for the unequal error protection (UEP) of the voice data. A recursive systematic convolutional code (RSC = RSC = Recursive Systematic Convolutional) with the rate 1 / N is subsequently applied to the data 104 output by the encoder 102 in the encoder 108 . After a packet loss on the receiver side is regarded as puncturing the convolutional code, the packet formation of the coded bits should preferably be carried out according to an optimal puncturing pattern of the generated code.

In the exemplary embodiment shown, it is assumed that the packet formation is carried out in such a way that all bits which come from a specific generator polynomial G _x (D) are assigned to the same packet x. Thus, at the output of packet distribution unit 110, there is one packet containing the systematic bits and N-1 different packets, each containing the bits generated by a particular generator polynomial.

The N packets are then serially transmitted over the lossy packet-oriented network 114 . By returning the PER signal, the speech coding mode and the rate of the RSC code can be adjusted adaptively, and consequently the number and length of the packets transmitted can be set.

At the base station 116 , the received packets are transmitted via the carriers N ₁ to N _{N of} the wireless network or radio network 122 . In this exemplary embodiment, the only information that must additionally be transmitted is the bad frame indicator (BFIx), which indicates whether a specific packet x = 1,. , ., N has arrived at the base station 116 in good time and has, as a result, been transmitted via the wireless network or not. In addition, the optional re-encoding described above can be performed at base station 116 prior to transmitting the received packets. This is very helpful in dealing with the loss of packets on the landline 114 , which can improve the overall behavior of the system.

Feedback of the DQI signal from decoder 124 to the base station via a control unit of the mobile radio network can be used to adaptively adapt the number of carriers used for the wireless connection.

The received packets are decoded on the receiver side, that is to say in the decoder 124 , and the decoder 128 is designed as a speech decoder which receives the decoded packets. It should be noted that it is sufficient if only one random packet from the N packets, which is received without errors, is required to enable error-free decoding. If there is any remaining redundancy in the speech-coded data, iterative source and channel decoding can alternatively or additionally be used.

The method according to the invention was analyzed on the basis of the implementation of the transmission system explained in FIG. 2 just described. The number of packets N was chosen such that the packet distribution is comparable both in the packet according to the invention, ie also in a reference system, which will be described later. The delay of the two systems is also the same. In order to have a suitable comparison between the two systems, all feedback information and adjustments in the system according to the invention have been neglected for the coding experiment.

The AMR mode MR122 was used as the speech encoder, with a fixed rate of 12.2 kbit / s. In addition, the 6-bit CRC described above was applied to the most important bits, resulting in a total bit rate of 12.5 kbit / s after the speech coding. The source significance information mentioned above was not used in this example. A code with the rate 1/5 was selected as the recursive systematic convolutional code, with the following generator polynomials:

So five packets were created from one speech frame, sent over the packet-based network. The Total rate after packet distribution was 62.5 kbps.

A simple model of a lossy packet-oriented network accepted, this simple model being statistically independent Packet loss, and additive channels for wireless connection with white distributed noise (AWGN).

The spectral distance (SD = SD = Spectral Distance) was assumed as the measured value for the speech quality, which is described, for example, by RM Gray, inter alia "Distorsion Measures for Speech Processing" in IEEE Transactions on Acoustics, Speech and Signal Processing, Vol. 28, No. 4, pages 367 to 376, August 1980.

S _x (ω) and S _y (ω) are the amplitude spectra of the original, error-free transmitted system and the signal output of the speech decoder. W denotes the signal bandwidth. Based on this assumption, only distortions due to the transmission are considered, distortions due to the speech coding are neglected. In the above equation, a small value d indicates little or little distortion of the signal transmitted without error, and consequently high speech quality. A high value of d indicates high distortion and consequently poor speech quality.

FIG. 3 shows the behavior of the system described in more detail in FIG. 2 according to the implementation mentioned above, wherein no re-coding was carried out in the base station 116 here. The spectral distance SD is plotted along the z-axis as a measure of the speech quality, the packet error rate PER occurring on the network 114 is plotted along the x-axis and the signal-to-noise ratio is plotted on the mobile network along the y-axis.

As can be seen from FIG. 3, packet losses on the packet-oriented network essentially do not affect the quality over a large range of packet error rates, with slight distortions only occurring at high packet error rates of greater than 10%. Furthermore, the RSC code is able to correct most errors caused by the wireless connection. The speech quality only decreases at low signal-to-noise ratios (E _s / N ₀ <-1 dB). However, it should be noted that even in the worst or worst case, namely if PER = 0.25 and E _s / N ₀ is -4 dB, the transmitted speech or the transmitted speech signal is still understandable.

The behavior of the transmission system described above will now be described with reference to FIG. 4 if the optional re-coding is additionally carried out in the base station. As can be seen, this additional re-encoding means that all packet losses are avoided during transmission over the packet-oriented network, only the distortions due to transmission over the wireless network remain.

A reference system is explained in more detail below with reference to FIG. 5, which also transmits coded speech data to a mobile subscriber via a lossy packet-oriented network and via a wireless connection, but uses a conventional approach to correcting packet losses, namely signal interpolation. In Fig. 5, an encoder 202 is shown, which passes via a connection 204, the coded data to a packet distributing unit 210 that distributes the received data to a plurality of packets which are then transmitted over the network 214 to a base station 216. The received packets are transmitted to the mobile receiver via a radio channel 220 , the received packets being demultiplexed in the demultiplexer 224 and passed on to the decoder 228 . In the reference system shown in FIG. 5, the G.711 codec was selected as the speech codec and the encoded data stream was distributed over N packets in such a way that adjacent samples were introduced into adjacent packets. As a result, packet loss leads to a distribution of the sample signal losses and not to a complete loss of samples. A packet loss can then be concealed at the decoder simply by interpolating between the distributed sampling losses. The packets are transmitted over the same mobile Internet channel as in the embodiment of the present invention described above.

FIG. 6 shows the behavior of the transmission system shown in FIG. 5, and as can already be seen from a superficial comparison of FIGS. 3 and 4 with FIG. 6, the behavior of the reference system has a significantly poorer speech quality in areas , in which the system according to the invention still leads to the generation of intelligible language during transmission. As can be seen from Fig. 6, the system suffers greatly from the uncoded transmission of the voice data over the wireless link. But even with low bit error rates or a high signal-to-noise ratio, the system is still very susceptible to transmission errors as far as the voice quality is concerned. If you now consider the packet error rate of the lossy packet-oriented network, you can see that the reference system is also very sensitive to packet losses. Thus, a packet loss rate of 10 ^-3 already leads to a decrease in the speech quality, wherein, starting from a packet error rate of 10 ^-3 with increasing packet error rate, the transmission quality is getting worse. Compared with the system according to the present invention without re-coding, it can be established that with the reference system, even with an increasing packet error rate from 10 ^-3, a significant decrease in the voice quality can be determined, which does not occur in the system according to the invention.

In order to verify the results obtained with reference to FIGS. 3, 4 and 6, informal hearing tests were carried out, the parameter SD being used as a measure of the speech quality. The G.711 reference system ( FIG. 6) was compared with the transmission system which implements the method according to the invention for recovering faulty code words (without re-coding), see FIG. 2. The table in FIG. 7 shows for the two systems what percentage of the test listeners preferred which system. The superiority of the new system with the approach according to the invention for recovering faulty code words is readily apparent, and based on a comparison of the signal-to-noise ratios and packet error values shown in FIG. 7 with FIGS . 3 and 6 is not surprising.

Referring to Figs. 1 to 7, preferred embodiments of the present invention have been described, in particular, the implementation of the inventive method and the inventive device is described in a transmission system which is a combination of a radio network and a fixed network. The present invention is not limited to this application, but can be applied in general to any transmission networks, fixed networks or mobile radio networks. Furthermore, the present invention is not limited to the RSC coding described above, but any type of coding which inserts redundancy into the code words to be transmitted can be used with the method according to the invention, provided that the available code can be punctured (not on the transmitter) so that losses in transmission can be recognized by the receiver as puncturing.

In addition, the present invention is also applicable Apply systems where increasing the Transmission capacity, puncturing the generated codes is carried out, with an additional loss in the Transmission as additional puncturing from the receiver is seen.

The loss of the packets or the code units can include in the transmission also in the receiver and / or after the Generation are caused in the transmitter.

Claims (27)

1. A method for recovering a code word from a received, incorrect code word, wherein a code word comprises code units and is derived from one or more information units by means of a redundancy code, with the following steps: a) receiving (S100) the code word; b) determining (S110) an incorrect or non-existing code unit in the code word; c) in response to the defective or non-existing code unit determined in step (b), setting (S112) a depuncturing pattern; and d) depuncturing (S114) the received, defective code word by means of the set depuncturing pattern, so that the defective or non-existing code unit is depunctured in the code word. 2. The method according to claim 1 with the following step: a) decoding (S104) the depunctured code word to recover the one or more information units. 3. The method according to claim 1 or 2, wherein a faulty code unit or a loss of a code unit in the transmission channel ( 114 ) is caused after the generation of the code word. 4. The method according to claim 3, in which a defective code unit or a loss of a code unit in a transmitter ( 102 , 110 ) is caused after the generation of the code word and / or when the code word is transmitted to a receiver ( 116 ). 5. The method according to any one of claims 1 to 4, wherein a code unit is a packet with a plurality of bits, so that the received code word comprises a plurality of packets, wherein in step (b) it is determined whether a packet of the code word at transmission of the code word via a packet loss network ( 114 ) has been lost. 6. The method according to claim 4 or 5, wherein the Depuncture pattern depending on the number of lost packages and depending on their position in the Code word is set. 7. The method according to any one of claims 4 to 6, in which the step of (b) receiving one Includes information signal (BFI) indicating that a packet has been lost. 8. The method according to any one of claims 4 to 6, in which step (b) monitoring a period of time includes, during which a package must arrive, whereby at Expiration of the time without the package arrived is a loss of the package is determined. 9. The method according to any one of claims 1 to 8, in which the received code word is transmitted via a radio network ( 112 ) to a mobile receiver and in which steps (b), (c) and (d) are carried out in the receiver. 10. The method of claim 9, wherein prior to transmitting the received code word to the mobile receiver, the received code word is re-encoded ( 122 ). 11. Device for recovering a code word from a received, incorrect code word, wherein a code word comprises a plurality of code units and was generated by means of a redundancy code with
a signal processing device ( 116 ; 124 ) which receives the defective code word, which determines a defective or non-existent code unit in the code word, which sets a depuncturing pattern in response to the defective or non-existent code unit, and which receives the received one based on the set defuncturing pattern Depunits the codeword so that the defective or non-existing code unit is depunctivated in the codeword. 12. The device according to claim 11, having a decoder ( 124 , 128 ) which receives the depunctured code word and which recovers the one or more information units from the depunctured code word. 13. The apparatus of claim 11 or 12, wherein the transmission channel ( 114 ) causes the incorrect code word after generating the code word. 14. The apparatus of claim 13, wherein a transmitter ( 102 , 110 ) and / or a transmission medium ( 114 ) between the transmitter ( 102 , 110 ) and a receiver ( 116 ; 124 , 128 ) causes the incorrect code word. 15. The apparatus according to any one of claims 11 to 14, wherein a code unit is a packet having a plurality of bits so that the received code word comprises a plurality of packets, the signal processing unit determining whether a packet of the code word is transmitted during the transmission of the code word lost via a packet loss network ( 114 ). 16. The apparatus of claim 14 or 15, wherein the Signal processing unit the depuncturing pattern depending on the number of packets lost and depending on their position in the code word established. 17. The device according to one of claims 14 to 16, at which the signal processing unit Receives information signal (BFI) indicating that a packet has been lost. 18. The device according to one of claims 14 to 16, at of the signal processing unit a period of time monitors during which a packet must arrive, whereby the signal processing device when the Time without the package arriving, one Indicates loss of the package. 19. Device according to one of claims 11 to 18 with a radio network ( 122 ) to transmit the receiving code word to a mobile receiver ( 124 , 128 ), which comprises the signal processing unit. 20. The apparatus according to claim 19 with a coding unit ( 120 ) which re-codes the received code word before transmission to the mobile receiver. 21. A method for generating a code word that contains code units that are generated based on information units by a redundancy code for transmission via a lossy connection network, comprising the following steps: a) receiving the information units; b) coding each information unit to generate a plurality of code units for each information unit; and c) arranging the generated code units in the code word such that a loss of one or more code units in the code word leads to a code unit sequence which corresponds to a puncturing pattern applicable to the original code word, which is also known to a recipient of the code word. 22. The method of claim 21, wherein
generating a plurality of packets containing code units, which are generated based on information units by a redundancy code, for transmission over a packet-oriented connection network ( 114 ),
in step (b) each of the information units is coded using a plurality of generators, the information unit being applied to each of the generators, and each generator generating a code unit for an adjacent information unit, and
in step (c) the code units are assigned to a plurality of packets, code units which have been generated by the same generators being assigned to the same packets; and
the packets generated are made available for transmission. 23. Device for generating a code word, which contains code units which are generated based on information units by a redundancy code, for transmission via a lossy connection network, comprising:
an input for receiving the information units;
an encoder ( 108 ) for encoding each information unit to generate a plurality of code units for each information unit; and
a processing device ( 110 , 112 ) for arranging the generated code units in the code word such that a loss of one or more code units in the code word leads to a code unit sequence which corresponds to a puncturing pattern applicable to the original code word, which also corresponds to a receiver of the Code word is known. 24. The device according to claim 23 for generating a plurality of packets containing code units, which are generated based on information units by a redundancy code, for transmission over a packet-oriented connection network ( 114 ),
wherein the encoder ( 108 ) has a plurality of generators to which the information unit is applied, each of the generators generating a code unit for the applied information unit; and
wherein the processing means ( 110 , 112 ) which receives from the encoder for each information unit applied to the encoder the assigned code units and assigns a plurality of packets, the processing means code units generated by the same generator in the encoder to the same packet assigns, and which provides the complete packets for transmission. 25. Transmission system to transmit information units with
a transmitter ( 102 , 110 ) which receives the information units and uses a redundancy code to derive a code word with a plurality of code units from the information units, the transmitter comprising a device according to one of claims 21 to 24;
a transmission medium ( 114 ) that receives and transmits the code words generated by the transmitter ( 102 , 110 ); and
a receiver ( 116 ; 124 , 128 ) receiving the code words transmitted from the transmission medium ( 114 ), the receiver comprising a device according to any one of claims 11 to 20. 26. The transmission system of claim 23, wherein the transmission medium is a packet-oriented connection network ( 114 ). 27. Transmission system according to claim 24, wherein said communication system further comprises a radio network (122), wherein a base station (116) is arranged between the packet-oriented connection network (114) and the radio network (122), and wherein the receiver is mobile.