EP0624295A1

EP0624295A1 - Process for recovering test data transmitted over a transmission path for cellular digital streams

Info

Publication number: EP0624295A1
Application number: EP93902055A
Authority: EP
Inventors: Andreas Wolf
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 1992-01-31
Filing date: 1993-01-22
Publication date: 1994-11-17
Also published as: WO1993015575A1; NO942802D0; NO942802L; DE4203298C1; AU3343993A; CA2129224A1

Abstract

L'invention concerne un procédé pour récupérer dans des flux de données numériques ayant une structure cellulaire, des données d'essai transmises, à l'extrémité côté récepteur. Selon ce procédé, les données-test sont codées au moyen de mots codes, qui produisent une impulsion de Dirac en autocorrélation et il se produit une corrélation croisée côté récepteur en vue du décodage. Afin de pouvoir transmettre un nombre plus important de données d'essai sous une forme codée, un mot de valeur zéro (mémorisé à l'emplacement St = 1) binaire est ajouté aux mots codes côté émetteur et les différentes données d'essai (par ex. 11101) sont associées aux différents mots codes et au mot de valeur zéro côté récepteur, il est procédé en outre à une totalisation des chiffres des mots codes reçus et du mot de valeur zéro en vue de la corrélation croisée.The invention relates to a method for retrieving transmitted test data from the receiver side end in digital data streams having a cellular structure. According to this method, the test data are coded by means of code words, which produce a Dirac pulse in autocorrelation and there is a cross-correlation on the receiver side for decoding. In order to be able to transmit a larger number of test data in coded form, a binary word of value (stored at location St = 1) is added to the code words on the transmitter side and the various test data (for eg 11101) are associated with the various code words and with the zero value word on the receiver side, the digits of the code words received and the zero value word are also summed for cross-correlation.

Description

Method for recovering test data transmitted over a transmission link for digital data streams with a cell structure

The invention relates to a method for recovering test data transmitted from a transmitting end to a receiving end via a transmission link for digital data streams with a cell structure at the receiving end.

- In which the various test data at the transmission end of the transmission path by means of a binary code word, which gives a Dirac pulse in an auto-correlated manner, and by means of further binary code words generated from the code word by cyclically shifting the code word, and

- In which on the receiving side of the transmission path for decoding, a cross-correlation of the code word received in each case is carried out by evaluating the main maximum of the respective cross-correlation function in order to retrieve the test data. Such a method is used primarily in measurement technology for broadband ISDN transmission technology.

A known method of this type is described in DE 40 12 850 AI. In this known method for determining quality parameters of a transmission link for digital data streams, numbers of test cells introduced into the data stream are coded at the transmission end of the transmission link with a code word which, in an auto-correlated manner, gives a Dirac pulse; such a code word is, for example, an m-sequence or a code word from the code word stock of the Barker code. In addition, the code word is changed from test cell to test cell as part of the coding each shifted an equal distance. This means that further code words are formed by cyclically shifting the one code word. At the receiving end of the transmission link, a receiver is followed by a correlator which carries out a cross-correlation of the code word received in each case. The bit error rate is inferred from the height of the main maxima of the cross-correlation functions formed in this way, while the relative temporal position of the main maxima allows information about the test cell number, as a result of which the test data on the transmission side can be recovered. This is done very reliably in the known method, since it still works precisely even with a high bit error rate; With a 2 m sequence, for example as a code word, up to 7 bit errors can occur without impairing the reliability of the method.

The known method is also described in the journal "telcom report" 14 (1991) No. 2, pages 104 to 107. In the embodiment shown here, all further binary code words are formed by cyclically shifting from one code word.

The invention has for its object to further develop the known method so that it enables a safe recovery of a larger number of test data available on the transmission side on the receiving side.

To achieve this object, according to the invention in a method of the type specified at the outset

- on the transmit side the binary code word by cyclic

Moving the code word adds additional binary code words and a binary zero word and the different test data to the different code words and the zero word 1 assigned and

- On the receiving side of the transmission link for, "Decoding in addition to cross-correlation one

Cross-sum formation of the received code words and the 5 code word is carried out, whereby

- Above a predetermined value

Identify the main maxima of the cross-correlation function and use codewords to retrieve the assigned test data or 10 - a checksum below a predefined further value identifies the transmitted null word and is used to retrieve a test date assigned to the null value.

15 The main advantage of the method according to the invention is that by using the zero word (in this word all binary digits have a "0") the

One word is added to the pool of available encryption words. If, for example, 5 20 of a 2 m sequence is used, the invention leads to a total of 32 encryption words. This makes it possible to code a total of 32 different test data to be transmitted (that is to say each varying over a length of 5 bits) and to securely re-transmit them on the reception side

.25 win.

The supply of encryption words on the transmission side can be modified in one embodiment of the invention

Double the method in an advantageous manner in that

30 - from the binary code words on the transmission side

Invert inverse, binary code words are formed ^f and a binary one word is added to these inverse code words and further test data to the inverse

* Code words and the one-word are assigned,

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REPLACEMENTB - Identify the main maxima of the cross-correlation which are on the receiving side above a predetermined lower value and use codewords to retrieve the assigned test data, taking into account the signs of the main maxima, or

a cross-sum lying below a predetermined further value identifies the transmitted null word and is used to retrieve a test date assigned to the null word, or

- A checksum above an additional predetermined value identifies a one-word and is used to retrieve a test date assigned to the one-word. Of course, main maxima of different types can also be acquired by shifting the value range of the cross-correlation functions by such a value that the values of the main maxima of different types are always in the positive range.

The test data transmitted from the transmitting side and recovered on the receiving side can be further processed in various ways in the method according to the invention.

As with the known method described at the outset, the method according to the invention not only enables the test data to be retrieved on the receiving side, but also, by evaluating the level of the main maxima of the cross-correlation functions of the code words, a statement about the number of bit errors; Such a statement is also possible with regard to the zero word or the one word, because the number of bit errors can be determined from the checksum.

REPLACEMENTB To explain the invention is in

1 shows a block diagram of an embodiment of an arrangement for carrying out the method according to the invention, FIG. 2 shows a list of the encryption words, FIG. 3 shows an embodiment of a coder of an arrangement for a further embodiment of the method according to the invention, and FIG. 4 shows an embodiment of the receiving side of the same arrangement shown to carry out this further embodiment of the method according to the invention.

The exemplary embodiment shown in FIG. 1 contains an encryption generator 1 on the input side, which consists, for example, of an addressable memory.

In the example shown, this memory contains a 31-bit code word at position St = 2 (cf. FIG. 2),

5 which corresponds to a 2 m sequence. At further positions 3 to 31, a further 31 bit long code words are stored

5 arose by cyclically shifting the 2 m sequence; The resulting phases s of the code words are given in the second column of FIG. 2. In the

A 31-bit zero word is stored at position St = 1 of the memory and, as can be seen in FIG. 2, consist of zeros.

In total, there are 32 encryption words. As a result, 32 different test data can be encoded, which differ from one another in each case over a length of 5 bits. In block 2 of FIG. 1, therefore, only an uncoded, 5-bit data word is entered as a test date. The coded test data (block 3 in FIG. 1) generated by the encryption word generator 1 are transmitted via a transmission link 4 and, as coded test data, reach the receiving side 6 more or less corrupted (block 5 in FIG. 1), where they are decoded. This is done, inter alia, by cross-correlating the transmitted test data with reference data, for example an m-sequence m (block 8 in FIG. 1) in a cross-correlator 7. The resulting cross-correlation functions, which look essentially as it is shown in the aforementioned DE 40 12 850 AI, are examined in a module 9 for the position of the main maxima. The relative temporal position of the main maximum of the respective cross-correlation function contains the information about the respectively transmitted test date, so that the transmitted test date can be obtained from the determined relative temporal position of the respective main maximum via a further memory (not shown) on the receiving side 6; in this way, however, only 31 different test data can be recovered on the receiving side.

The zero word is recognized in block 10 and is done in such a way that a checksum is formed here. If the checksum is below a predefined value, for example in a 2 m sequence below the value 8, then this is an indication that the coded data transmitted is the null word. Accordingly, the associated test date can be retrieved in the course of the decoding by means of the memory (not shown) (block 11 in FIG. 1).

To determine the bit errors, the main maxima of the cross-correlation functions are examined for their height. It is ensured that this only applies to such

Main maxima occur, the height of which is above one

5 predetermined value; in the case of a 2 m sequence, only the main maxima are evaluated, the value of which lies above the number 16. This ensures that a main maximum based on the null word is not detected. The bit errors are determined from main maxima lying above the value 16 (block 12 in FIG. 1).

To determine the number of bit errors using the

The crossword is examined; their level is a direct measure of the number of bit errors.

In addition, it should be pointed out that the method according to the invention is not tied to the use of a 2 m sequence (with its cyclical shifts), but can also be carried out with other m sequences. It is also possible to use the Barker code, the Gordon, Mills and Welch sequence or the Gold code.

FIG. 3 shows another exemplary embodiment of an encryption word generator on the transmission side of a transmission path, not shown here, in the event that test data that vary over a length of 6 bits are to be encoded, that is to say a 6-bit data word D (x). exhibit.

The generator here has a feedback shift register 20 with several stages 21 to 24 and

Exclusive OR gates 25 and 26. A further exclusive OR gate 27 is arranged downstream of the shift register 20 in that it is connected with an input 28 directly to the output of the exclusive OR gate 26 and via one Changeover contact 29 in its position a can be connected to the output of stage 24. In the position b of the changeover contact 29, the one input 28 is acted upon by the signals of the lower five digits d-, d, - of the data word D (x). The further input 30 of the further exclusive OR gate 27 is acted upon by the signal of the uppermost (sixth) position of the data word D (x). The sixth position controls the inversion, so that, in deviation from the method according to FIGS. 1 and 2, 64 different encryption words are used here for assuming if a 2 m sequence is assumed as an example.

At the output 31 of the further exclusive-OR gate 27, data C (x) coded with the data words D (x) occurs in accordance with the test data to be transmitted, which - for example in addition to a 2 m sequence as the "basic code word" - 30 binary code words obtained cyclically, 31 further code words formed by inverting them, which may contain the zero word and the one word.

These coded data C (x) are transmitted via a transmission path (not shown) and reach the receiving end, the configuration of which is shown in FIG. 4. As in the exemplary embodiment according to FIGS. 1 and 2, a cross-sum formation of the transmitted, coded data C (x) is carried out in a block 40. This checksum is in turn examined in a subordinate block 42 to determine whether it is less than 8. If this is the case, then the transmitted test date is detected as a null word. If the checksum is greater than 23, it is a binary one-word (all binary digits have a "1"). In the cross-correlation of the other code words, inverse code words in this example result in negative main maxima of the cross-correlation functions; this allows the "normal" code words to be distinguished from the inverse code words when decoding. The amount of the main maxima is used here to distinguish the other code words from the zero or one word; amounts above a predetermined lower value

Main maxima characterize the other code words. At a

As in the exemplary embodiment described above, the 25 m sequence as the basic code word is 16.

In accordance with the exemplary embodiment according to FIGS. 1 and 2, the test data D (x) to be transmitted can be recovered on the receiving side in block 43.

Otherwise, the reception side according to FIG. 4 is constructed as shown in FIG. 1. The bit errors are determined in a corresponding manner. The codes listed above can also be used here.

Claims

1. Method for recovering test data transmitted via a transmission link for digital data streams with a cell structure from the transmitting end to the receiving end at the receiving end,

- In which, on the receiving side of the transmission path for decoding, a cross-correlation of the code word received in each case by evaluating the

Main maximums of the respective cross-correlation function for recovering the test data is made, that is, that

- a binary zero word (stored at St = 1) is added to the code words on the transmission side and the various test data (e.g. 11101) are assigned to the various code words and the zero word,

- On the receiving side (6) of the transmission link (4) for decoding, in addition to cross-correlation, a cross-sum of the received code words and the zero word is carried out, wherein

- identify the main maxima of the cross-correlation functions that are transmitted above a predetermined value and use them to retrieve the assigned test data (e.g. 11101) or

- A checksum lying below a predetermined further value identifies the transmitted zero word and for retrieving one of the zero word assigned test date is used.

2. The method of claim 1, d a d u r c h g e k e n n z e i c h n e t that

on the transmission side, inverse, binary code words are formed from the code words by inverting and a binary one word is added to these inverse code words and further test data are assigned to the inverse code words and the one word,

10 - on the reception side, above the predetermined maximum values of the main maxima of the cross-correlation functions, which are transmitted, identify code words transmitted and for retrieving the assigned test data, taking into account the signs of the

, ₅ main maxima are used or

₂ - a checksum lying above an additional predetermined value identifies a one-word and is used to retrieve a test date assigned to the one-word.

2 ~ 3. The method of claim 1, d a d u r c h g e k e n n z e i c h n e t that

- The height of the main maxima and the size of the checksum are evaluated as a measure of the bit error rate.

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