WO2005112330A1

WO2005112330A1 - Method and transmitter and receiver for transmitting digital information packets in a data network

Info

Publication number: WO2005112330A1
Application number: PCT/EP2005/052242
Authority: WO
Inventors: Jürgen PANDEL
Original assignee: Siemens Aktiengesellschaft
Priority date: 2004-05-14
Filing date: 2005-05-17
Publication date: 2005-11-24
Also published as: DE102004024124A1; DE102004024124B4

Abstract

The invention relates to a method for transmitting digital information packets in a data network comprising stations designed to exchange data from at least one transmitting station to at least two receiving stations. The information packets that are to be transmitted are divided up into one or more data packet groups in the transmitter station, and redundancy information in the form of redundant packets is added to each data packet group. If the receiver station receives a defective data packet, or if one of the packets in the data packet group is not received, the receiver station sends the transmitter station a negative acknowledgement protocol and the transmitter station initiates error protection measures. The transmitter station establishes a level of error protection for each receiver station on the basis of a statistical analysis of negative acknowledgement protocols received in connection with a given information packet. The invention also proposes a method wherein packets lost in a streaming scenario are retransmitted and stored in the network station so that if the streaming content is transmitted with errors the first time it can be used again later without errors. The invention further relates to a transmitter-receiver device for carrying out the claimed method.

Description

description

Method, transmitting and receiving device for the transmission of digital information packets in a data network

The invention relates to a method for transmitting digital information packets according to the preamble of claim 1 and a method according to the preamble of claim 13. The invention further relates to a transmitting device according to claim 14 and a receiving device according to claim 15.

The problem with digital data transmission is that data is lost during transmission due to poor transmission links or low bandwidths. In the case of packet-oriented data traffic in particular, incorrect or lost data leads to the loss of complete packets, as a result of which the content can no longer be reproduced correctly. Data loss is particularly problematic in so-called multimedia applications in which the

Data should often be displayed in real time without delay to the recipient.

From J. Rosenberg, H. Schulzrinne: "An RTP payload for at for generic forward error correction", IETF RFC 2733, Dec. 1999, methods for the reconstruction of lost data packets are known to solve this problem.

So-called broadcast and multicast data transmissions are also known, in which data are sent by a single transmitter and can be received by a large number of receivers. So-called Reed-Solomon codes can be used in these data transmissions for error protection, as known from Shu lin and Daniel Costello, "Error Control Coiding", Prentice Hall, 1983. With the help of the Reed-Solomon codes, redundancy is added to the data, so that the original data can be reconstructed if the receiver does not lose too much data. can be structured. Known error protection methods with the aid of Reed-Solomon codes are particularly suitable, for example, for those described in "DVB-H System Description", Doc. DVB-H153rl TM2939rl, 09.09.2003, specified DVB-H standard (Digital Video Broadcast - Handheld). For example, with the help of a (N, K) -Read Solomon code known from Shu Lin and Daniel Costello, "Error Control Coding", Prentice Hall, 1983, the data can also be reconstructed if out of a total of N packets, whereby K packets contain user data and NK parity (parity or redundancy) data, maximum NK any packets are lost. The disadvantage here is that Read Solomon codes based on Galois Field GF (2 ⁸ ) have a limitation in that N may have a maximum value of 255.

For package numbers going beyond this, the numbers in R.G. Gallager: "Low density parity check codes", IEEE Transactions on Information Theory, Vol. 8 (!), Jan. 1962, described Low Density Parity Check Codes (LDCP codes). However, these have the disadvantage that they are not as efficient as, for example, when using Read Solomon code-based methods; i.e. They cannot reconstruct all packets lost in the N-K.

It therefore follows that, in practice, not all lost or faulty packets can generally be reconstructed in the methods used in practice, so that additional packets of this kind are added again separately to point-to-point connections to the individual receiving subscribers (stations) to ship. For this purpose, the so-called NACK protocol (Not-ACKnoledge) - i.e. a negative acknowledgment of receipt - is sent by the receiving stations to the sending station (server) of the broadcast / multicast network in the event of lost (not received) or faulty packets NACK indicates which packet was faulty or not received so that the server knows which packets are received via the considered reliable point-to-point connection must be sent again to the individual receiving stations.

An alternative approach to this is from M. Luby et. al ..: "The use of forward error correction (FEC) in reliable multicast", IETF RFC 3453, Dec. 2002, is known, in which instead of repeating lost or faulty packets, only additional redundancy packets, which nevertheless make it possible to carry out a reconstruction of the packets, via the point-to-point

Send multipoint connection to all receiving subscriber stations. With this method, however, unnecessarily large amounts of data are transmitted over the point-to-multipoint connection, since, regardless of the actual number of receivers (receiving stations) which did not receive packets or received them only incorrectly, additional redundancy packets are always sent to all subscriber stations become.

The object on which the invention is based is to specify a method, a transmitting device and a receiving device for transmitting digital information packets in a data network, which ensure increased efficiency.

This object is achieved on the basis of the method according to the preamble of claim 1 by its characterizing features and the method according to the preamble of claim 13, the transmitting device according to claim 14 and the receiving device according to claim 15.

In the method according to the invention for the transmission of digital information packets in a data network, stations configured for data exchange are converted from at least one sending station to at least two receiving stations, in which the information packets to be transmitted are divided into one or more data packet groups in the sending station and the data packet groups each have redundancy information is added in the form of redundancy packets and in the event of incorrect or missing reception of a data packet of the data packet group by the receiving station, the transmitting station transmits a negative reception protocol to the sending station and this triggers measures for error protection by the sending station Station defines a degree of error protection measures as a function of a statistical evaluation of received negative reception protocols belonging to an information package per receiving station.

The inventive method adapts error protection measures to the current conditions of the data network, so that a more efficient use of resources is made possible. The statistical evaluation is preferably carried out by determining a statistical distribution of the received negative reception protocols. This enables the sending station to determine a number of necessary redundancy packets, which is necessary to ensure that a majority of the received stations can reconstruct the missing data packets with the help of the redundancy packets. This ensures that redundancy packets are not always transmitted to all receiving stations, but instead, for example, this is only done when it becomes necessary and only to an extent that does not burden the network or use resources efficiently.

This adaptation to the current circumstances can be specified if the statistical evaluation is supplemented by determining a statistical mean value belonging to the distribution and / or by determining a statistical standard deviation belonging to the distribution.

On the basis of the statistical evaluation, the sending station sets the level of the error protection measures in such a way that the sending station sets one for compliance with a determinable one If the required number of redundancy packets for the information packets to be transmitted is determined, further optimization of the method can be achieved by defining the criterion, the criterion being able to be determined, for example, by simulation or experimental approaches.

The criterion preferably specifies a number of those receiving stations which, by specifying the number of redundancy packets, should be able to reconstruct missing and faulty data packets based on the determined number of redundancy packets. In this way, a parameter for reducing the costs can be determined in a suitable manner, since the number of stations also determines the amount of data to be transmitted. It is therefore particularly advantageous, in addition, for the remaining receiving stations to have one of the error protection mechanisms known from the prior art, in particular that in which repeated transmission of data packets with negative reception protocols via a point-to-point to the respective remaining receiving station Connection is used, so that here overall a degree of error protection measures is defined by a distribution over known error protection measures. This makes it possible to find a suitable mixture that optimally allows compliance with given criteria.

In particular, if the efficiency to be achieved is a reduction in the cost factor, it is advantageous if the criterion is set in such a way that a cost value K _{qesarat is} minimized, the cost value being different

Kgeaamt S g _{e 3am} - - D _m K _m + DuK _u with D _u : = amount of data using point-to-point connection, D _m : = amount of data using point-to-multipoint connection, κ _u : = cost of Transmission of a specified amount of data via a point-to-point connection, K _ra : = costs for the transmission of a specified amount of data via a point-to-multipoint connection,

In addition, this further development has the advantage of being able to achieve precise optimization on the basis of a precise cost estimate in the case of data networks which are configured to point-to-point connections or to point-to-multipoint connections.

Especially if the sending station is a server for a download broadcast multicast service and at least some of the receiving stations use this service as a point over a point-to-multipoint connection, it is advantageous if during the transmission of an information data packet, received negative reception protocols are recorded, the statistical evaluation of the received negative reception protocols is carried out after the transmission of the information packet has been completed, and on the basis of the evaluation the number of data for transmission via the point-to-multipoint connection to meet the criterion required redundancy packets and the number of missing or faulty data packets to be retransmitted via a point-to-point connection is determined. Alternatively, the evaluation can also take place while the information packets are being sent out, so that this allows for faster processing and thus better adaptation in time-critical applications.

Contrary to what is described, in data networks in which the sending station is operated as a server for a streaming broadcast multicast service and at least part of the receiving station is used in the form of a point-to-multipoint connection, it is advantageous if one is used during the transmission Received negative reception protocols are recorded during the transmission of the information packet within a first time window statistical evaluation of the received negative reception protocols is carried out and the number of redundancy packets required for a transmission via the point-to-multipoint connection to meet the criterion is determined on the basis of the determination.

In this case, the duration of the first time window is preferably determined such that it is chosen to be less than the duration of a predetermined second time window. This takes into account the fact that in streaming systems a

There is a restriction regarding the permitted delay times, which is such that a delay must not exceed a predetermined time value. If, as proposed according to the further development, the first time window is selected such that its duration is shorter than the time restriction in streaming data networks, there is still enough time after the determination and transmission of redundancy packets to reconstruct at least some of the missing or faulty data packets , As an alternative, but above all in addition to the described methods, it is in a data network in which the sending station is operated as a server for a streaming broadcast multicast service and at least some of the received stations use this service in the form of a point-to-multipoint connection uses, the received station being designed for storing data, it is advantageous that missing and faulty data packets associated with information packets are sent again via a point-to-point connection and stored in the respective received station. This makes it possible for participating receiving stations to reproduce faulty data during the transmission, but to give a user of this service the opportunity to carry out an error-free reproduction of the data after the transmission has taken place.

The object is further achieved by a transmitting device and a receiving device, which means for the have management of the individual method steps according to the method according to the invention and, as a rule, both are implemented in one station, and have the advantage of enabling a station of the data network to carry out the method and thus to achieve the advantages of the method according to the invention mentioned above.

Further advantages and refinements of the invention are explained in FIGS. 1 to 3.

Show it:

Figure 1 is a schematic representation of a data network in which the inventive method is used;

FIG. 2 shows an exemplary flow chart of the method according to the invention;

Figure 3 histogram of participants in the above data network who have lost a number n packets.

FIG. 1 shows a preferred scenario in which the method according to the invention can be used. This involves the transmission of multimedia data from a broadcast service that sends data that can be received by several receivers (stations) at the same time. The multimedia data are provided by a broadcast multicast service center BM-SC and transmitted to an RAN (RAN = Radio Access Network) via an arbitrary intermediate network z. The mobile radio network RAN comprises a multiplicity of base stations B1 to B5, by means of which the multimedia data are transmitted to user terminals (receiving stations) UE1..UE3 (UΞ = user equipment) in the form of a cell phone via an air interface L. The broadcast multicast service center BM-SC generates information packets that include a header and a payload, the information pack kete are data packets which are transmitted using a transport layer in accordance with the OSI reference model, the transmission being carried out in this case in a wired and / or wireless manner. In the scenario shown in FIG. 1, data is therefore transmitted via a mobile radio network and, on the other hand, the data is transported in a packet-oriented manner via the transport layer.

Based on this preferred scenario, three possible exemplary embodiments of the method according to the invention will now be explained in more detail.

In a first exemplary embodiment, which is used in the broadcast multicast scenario mentioned, in a first step S1 the broadcast multicast service center BM-SC, which can also be regarded as a transmitting station, and which is the server of one in this broadcast The multicast scenario of the download service offered functions in such a way that all the useful data (information packets) are first transmitted via the broadcast channel, ie are transmitted via a point-to-multipoint connection to the received stations UE (only one station shown in the exemplary embodiment).

In parallel to the transmission, generally as an algorithm running as a background process, in a second step S2, negative reception protocols (NACKs, negative AC knowledges) are recorded by the server BM-SC.

In a third step S3, after the sending of the information packet by the server BM-SC, a statistical distribution of the negative reception protocol signals (NACK signals) is calculated.

This distribution is represented, for example, as a histogram of the number of stations received that have lost a number N of data packets. In a fourth step S4, the distribution is used to determine how many redundancy packets are sent out via the broadcast channel, ie via the point-to-multipoint connection, and also how many of the missing or faulty data packets are sent to the receiving subscribers a point-to-point connection must be sent repeatedly, ie in the fourth step S4 it is basically determined how the distribution from error protection measures, such as the incremental redundancy and the packet repetition, is to be determined.

It can be determined in a fifth step S5 that again data packets including redundancy packets have been lost and this in turn has been acknowledged by the receiving stations concerned with NACK signals, so that, for example, in a sixth step S6 the transmitting station BM-SC serving as the server can decide to forward redundancy packets until a sufficiently small amount of data packets to be repeated via point-to-point connections remains. Here, the server BM-SC always takes into account a quantity of data to be transmitted via the point-to-multipoint connection and a quantity of data to be transmitted via the point-to-point connection and can thus advantageously influence the total costs of the transmission that accrue as a result that these are ideally minimized.

The method is finally ended in a seventh step S7.

As an alternative to the exemplary embodiment described, in the same preferred scenario the calculation of the statistical distribution carried out in the third step S3 can also take place during the transmission of the user data, so that this statistic, which is based on the NACK signals, can already be used to start it early can send out further redundancy packages. A third exemplary embodiment of the method according to the invention results if a streaming service is offered in the underlying preferred scenario, that is to say the broadcast multicast system.

Such a streaming system is time-critical, so that a delay due to necessary reconstructions of data packets of the information packets based on additional redundancy packets sent is subject to a restriction, i.e. e.g. must not exceed a time of 5 s.

It is advantageous here that, as mentioned in the second exemplary embodiment, the additional redundancy packets are already sent out during the transmission of data packets belonging to the information packets, i.e. This means that the distribution or the statistics of the NACK signals are already evaluated during transmission for a given time window of, for example, 3 s, so that the number of redundancy packets to be output can be determined according to the invention within the time remaining until the maximum permitted delay. so that at least a predetermined relative number of the participating receiving stations, for example 95% of the stations, can reconstruct all lost user data packets. This high predetermined number is therefore necessary or in particular advantageous because, because of the delay restriction, it is not possible in the present exemplary embodiment to send missing packets again to the respective receiver via a point-to-point connection.

This is only possible if the receiving subscriber stations have the option, ie are designed in such a way that they can store the data associated with the streaming services. In such a case, the redundancy data packets are provided according to the invention during the transmission to save the streaming data. As a result, the received stations, i.e. those that did not have the option of reconstructing missing or faulty data packets in exemplary embodiment 3, can enable the data to be displayed error-free at least after transmission, that is to say after the streaming data has been received for the first time, the fourth exemplary embodiment described also being able to independent solution to the problem, namely the efficient use of the data networks can be designed, and specifically when the storage can be realized by all received subscriber stations and not only by those who cannot reconstruct lost data according to exemplary embodiment 3.

Claims

claims

1. Method for transmitting digital information packets in a data network with stations designed for data exchange from at least one transmitting station (BM-SC) to at least two receiving stations (UE), in which the information packets to be transmitted are in the transmitting station (BM-SC) ) are divided into one or more data packet groups and redundancy information is added to the data packet groups in the form of redundancy packets, and in the event of incorrect or missing reception of a data packet of the data packet group by the receiving station (UE), the receiving station (UE) sends a negative reception protocol to the sending station (BM- SC) and, as a result, measures for error protection are triggered by the sending station (BM-SC), characterized in that the sending station (BM-SC) measures the degree of error protection measures as a function of a statistical evaluation of those associated with an information packet received negative r receive protocols are defined for each receiving station.

2. The method according to claim 1, characterized in that a statistical distribution of the received negative reception protocols is determined as a statistical evaluation.

3. The method according to claim 2, characterized in that the static evaluation is supplemented by determining a statistical mean value associated with the distribution.

4. The method according to claim 2 or 3, characterized in that the static evaluation is supplemented by determining a statistical standard deviation associated with the distribution.

5. The method according to any one of the preceding claims, characterized in that the sending station (BM-SC) uses the static evaluation to set the level of the fault protection measures in such a way that the sending station (BM-SC) one for compliance with one The number of redundancy packets required for the information packets to be transmitted in the future is determined by a definable criterion.

6. The method as claimed in the preceding claim, characterized in that the criterion defines a quantity which represents the number of those receiving stations (UE) which, by specifying the number of redundancy packets, should be able to completely identify missing and faulty data packets to reconstruct the determined number of redundancy packages.

7. The method according to the preceding claim, characterized in that for the remaining receiving stations one of the error protection mechanisms known according to the prior art, in particular to the respective remaining receiving station, a repeated transmission of data packets with negative reception protocols via a point-to-point Point connection, is carried out.

8. The method according to one of the two preceding claims, characterized in that the criterion is set such that a cost value "K _gΘsamt" is minimized, whereby the value K _ge including from K _qesam t = D _m K _m + D _U K _U with D „: = amount of data using point-to-point connection, D _m : = amount of data using point-to-multi-point connection, K _u : = costs for the transmission of a predetermined

level of data via a point-to-point connection, κ _m : = costs for the transmission of a predetermined amount of data via a point-to-multipoint connection.

9. The method according to any one of the preceding claims, wherein the sending station is operated as a server for a "download broadcast / multicast" service and is used by at least some of the receiving stations in the form of a point-to-multipoint connection, characterized that a) during the transmission of information data packets, a reception of received negative reception protocols takes place, b) after completion of the transmission of the information packets, the statistical evaluation of the received negative reception protocols is carried out, c) on the basis of the evaluation cl) the number of transmissions for a transmission the point-to-multipoint connection required to meet the criterion and c2) the number of missing and faulty data packets to be retransmitted via a point-to-point connection is determined.

10. The method according to any one of the preceding claims, in which the sending station is operated as a server for a "broadcast / multicast" service and is used by at least some of the receiving stations in the form of a point-to-multipoint connection, characterized in that a ) during the transmission of information data packets, received negative reception protocols are recorded, b) during the transmission of the information packets, the statistical evaluation of the received negative reception protocols is carried out, c) on the basis of the evaluation cl) the number of redundancy packets required for transmission via the point-to-multipoint connection to meet the criterion, and c2) the number of Missing and faulty data packets to be retransmitted are determined via a point-to-point connection.

11. The method according to any one of the preceding claims, in which the sending station is operated as a server for a "broadcast / multicast" service and at least some of the receiving stations are used in the form of a point-to-multipoint connection, characterized in that a) during the transmission of information data packets, a reception of received negative reception protocols takes place, b) after the statistical transmission of the received negative reception protocols takes place within a first time window during the transmission of the information packets, c) on the basis of the evaluation, the number of times for a transmission via the Point-to-multipoint connection is required to meet the redundancy packages required to meet the criterion.

12. The method according to the preceding claim, characterized in that the duration of the first time window is less than a duration of a predetermined second time window.

13. Method, in particular according to one of the claims, in which the sending station acts as a server for a "download Broadcast / Multicast "service is operated and at least some of the receiving stations are used in the form of a point-to-multipoint connection, the receiving stations being designed for storing data, characterized in that missing and incorrectly received data packets associated with information data packets again via a Point-to-point connection can be sent and saved in the respective receiving station.

14. Transmitting device characterized by means for performing method steps of the method according to one of the preceding method claims.

15. receiving device characterized by means for performing method steps of the method according to one of the preceding method claims.