GB2339372A

GB2339372A - Transmitting digitized data

Info

Publication number: GB2339372A
Application number: GB9912315A
Authority: GB
Inventors: Bernd Boelike; Diethard Haensgen; Jochen Antkowiak; Peter Pogrzeba
Original assignee: Deutsche Telekom AG
Current assignee: Deutsche Telekom AG
Priority date: 1998-05-27
Filing date: 1999-05-26
Publication date: 2000-01-19
Anticipated expiration: 2019-05-26
Also published as: GB2339372B; DE19825398A1; GB9912315D0; FR2780834A1

Description

2339372 TRANSMITTING DIGITIZED DATA The invention relates to a method of

transmission of digital data, including error protection, and to a device for use in such a method. A method of this type is, for example, described in the standard "Digital video Broadcasting (DVB); Microwave Multipoint Distribution Systems (MMDS) below 10 GHz11, No.: EN 300 749 V1.1.2 1997-08.

Before being passed to a transmission section, digitized signals are provided with an error protection so that they can be restored even if disturbances occur. One of the most frequently used correction methods is the Reed- Solomon coding method (RS-coding) which makes it possible, up to a certain correction limit, to eliminate errors in the data stream upon decoding. RS codes are used, for example, in ATM (ATM:

Asynchronous Transfer Mode) transmissions, DVB-S (Digital Video Broadcasting-Satellite) transmissions, DVB-C (Digital Video BroadcastingCable) transmissions, DVB-T(Digital Video Broadcasting-Terrestrial) transmissions, PDH (Plesiochronous Digital Hierarchy) transmissions and SDH (Synchronous Digital Hierarchy) transmissions. If there is sufficient error protection, the signal is restored completely and without errors at the end of the section after the decoding.

There is the problem that, while the decoded received signal appears to be received completely perfectly even if there is an error influencing on the transmission section that is possibly already considerable, it fails completely without warning when the limit of the error protection is exceeded only slightly.

The following approaches to solving this problem are known:- with a gradual coding and the associated decoding, the "graceful degradation", there is no immediate complete failure in the case of an increase in the transmission disturbances, for example in the case of video signals, but first a deterioration in the picture quality.

For MPEG signals (MPEG signals: picture signals, sound signals and data signals which are coded according to the regulations of the Motion Pictures Experts Group), there are test sequences and evaluating devices by various manufacturers. Their main aim is to determine syntactical errors which occur in the coding devices and decoding devices. This technique can also be used for testing the capability of transmission sections for MPEG signals, but the transmission errors cannot be detected completely.

In the case of ATM sections, the absence of ATM cells is often determined. This method can be used only for ATM signals and allows only the checking of the corresponding subsystem.

For new interactive systems, a QoS (Quality of Service) proposal has been made. In this connection, the ability to be transmitted of a certain data rate within a section is guaranteed.

All known methods, however, have the defect that they render possible only partial solutions. For a network operator, however, determining the status of the input signals is important. Moreover, items of information about the data integrity are required for each partial section and for the backward-channel sections. The data integrity can be characterised by the ratio of the efficiency of the error-correction method which is used to the data corruptions inserted on the transmission section or the distance between error-correction limit and disturbance level (here called transmission reserve). The integrity for the data to be transmitted must be ensured independently of the data structure (for example MPEG, ATM or IP).

The object of the invention consists in determining the transmission reserve for all relevant partial transmissions. With the invention, a universally applicable method for determining the transmission reliability for data is to be created.

According to a first aspect of the present invention, there is provided a method for transmitting digitized data, which is provided with an error protection before the transmission and restored thereafter using said error protection, wherein at the receiving end:

the status of the error correction is evaluated and an error-correction signal formed therefrom; a section-identification signal is formed for each section; the error-correction signal and the section identification signal are added to the data; and there is formed from the error-correction signal and the section-identification signal an item of data integrity information.

According to a second aspect of the present invention, there is provided a device for transmitting digitized data, in which there is inserted in the decoder an error-correction circuit, characterised in that an output of the error-correction circuit in the decoder and the signals of a section-identification signal transmitter are connected to the input of a multiplexer.

With the aid of the invention, it is possible in a surprisingly simple way to use the available errorcorrection circuits also for determining the data transmission reliability. The contradiction that, on the one hand, the errors which occur during transmission have to be eliminated completely while, on the other hand, information about the system reserve is necessary, is overcome by the double use of the errorcorrection circuits and the addition of the sectionidentification signals. In this way, the formation of the information for the system reserve about data transmission reliability is possible.

In the following, the invention is explained in greater detail with the aid of exemplary embodiments and illustrated in the associated drawings:

Figure 1 shows the basic modules for forming the necessary signals for determining the data integrity; Figure 2 shows the use of the invention in a partial 30 section with the formation of the errorcorrection information, the sectionidentification signal SAI, the multiplexer and the output-side demultiplexer with evaluating device; and Figure 3 shows the use of the invention in a transmission chain with inclusion of the backward-channel sections.

In accordance with Figure 1, in order to generate the information for the data integrity of the partial section, the error-correction information F(n) is taken from the error-correction circuit RS (Reed-Solomon Decoder). This signal is, if necessary, converted in a parallel-serial (P/S) converter into a data stream and combined with the useful signal in a multiplexer. In order to identify the partial section, the sectionidentification signal SAI is formed and likewise combined with the useful signal. The output signal from the multiplexer, I(n), results from the input signal I and the additional signal Z(n).

I(n) = I + Z(n), (n) - identification of the partial section, z (n) = SAI (n) + F (n) + Z (n - 1).

Figure 2 shows the use of the invention in a partial section with the formation of the error-correction information, the section-identification signal SAI, the multiplexer and the output-side demultiplexer with evaluating device.

Figure 3 shows the advantageous use of the invention in a transmission chain with inclusion of the backwardchannel sections.

The use of the method is not limited to certain types of transmission section. It can be used universally on the section segments to be monitored (cable connections, directional radio links, HF connections to subscribers).

In exceptional cases where the FEC (Forward Error Correction) according to the RS coding is not used, a digital test line, i.e. a known item of data information, can, as an exception, be inserted as an alternative in the coding circuit, which digital test line is evaluated on the decoder side and from which the same error- correction information F(n) is formed.

The transmission reliability is part of the network reliability. With the use of the invention, there can be determined for digital networks a measure of the data integrity or transmission reliability on the partial sections which are used and thus for the overall transmission reliability.

The use of the invention is possible in digital networks of a wide variety of types, in particular with real-time transmissions without the possibility of signal repetitions. Thus, sections of the primary and secondary distribution can be combined. High-speed networks and access networks can likewise be included in the determination of the network reliability.

Advance evaluations for compressing the signals required for determining the data integrity information and also central monitorings are possible without alterations to the useful data stream.

Claims

1. Method for transmitting digitized data, which is provided with an error protection before the transmission and restored thereafter using said error protection, wherein at the receiving end: the status of the error correction is evaluated and an error-correction signal formed therefrom; a section-identification signal is formed for each section; the error-correction signal and the sectionidentification signal are added to the data; and there is formed from the error-correction signal and the section-identification signal an item of data- integrity information.

2. Method according to claim 1, characterised in that error-correction signals and section-identification signals are formed separately for each partial section.

3. Method according to claims 1 and 2, characterised in that errorcorrection signals and sectionidentification signals are also formed for the signals supplied from outside.

4. Method according to claims 1 and 2, characterised in that, at the end of the transmission section, the error-correction signals which are present and the associated section-identification signals are separated from a useful-signal data stream and added to a backward-channel data stream.

5. Method according to claims 1 and 2, characterised in that errorcorrection signals and the associated section-identification signals are also formed for the backward-channel sections and added to the data.

6. A device for transmitting digitized data, in which there is inserted in the decoder an error-correction circuit, characterised in that an output of the errorcorrection circuit in the decoder and the signals of a section-identification signal transmitter are connected to the input of a multiplexer. 10

7. A device as claimed in claim 6, wherein the ouput of the error-correction circuit is connected to the input of the multiplexer through a parallel-serial converter. 15

8. A method of data transmission, substantially as herein described with reference to the accompanying drawings.

9. A device for transmitting digitized data, substantially as herein described with reference to, or as shown in, any of the accompanying drawings.