EP0058318B1 - Procédé de permutation de bandes partielles - Google Patents

Procédé de permutation de bandes partielles Download PDF

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Publication number
EP0058318B1
EP0058318B1 EP82100607A EP82100607A EP0058318B1 EP 0058318 B1 EP0058318 B1 EP 0058318B1 EP 82100607 A EP82100607 A EP 82100607A EP 82100607 A EP82100607 A EP 82100607A EP 0058318 B1 EP0058318 B1 EP 0058318B1
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Prior art keywords
modulators
frequency
band
partial bands
signal
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Expired
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EP82100607A
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German (de)
English (en)
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EP0058318A1 (fr
Inventor
Heinz Dipl.-Ing. Göckler
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Bosch Telecom GmbH
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ANT Nachrichtentechnik GmbH
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04K—SECRET COMMUNICATION; JAMMING OF COMMUNICATION
    • H04K1/00—Secret communication
    • H04K1/04—Secret communication by frequency scrambling, i.e. by transposing or inverting parts of the frequency band or by inverting the whole band

Definitions

  • the invention relates to a method for exchanging subbands of the same width of a signal frequency band according to the preamble of patent claim 1.
  • Such methods are known, for example from German patent specification 2,426,451, in which a circuit arrangement for obtaining interchangeable frequency grids for the harmonics of fundamental speech frequencies in devices for subband interchanging, in which on the transmission side a speech signal band is divided into subbands of equal width and by a swap of the subbands a transmission band is formed, in which the subbands contained therein can be inverted, the swap made on the receiving side being reversed, which is characterized in that the frequency at the lower limit of the voice band and half the sub-bandwidth Stand in relation to two whole numbers.
  • This circuit arrangement has five modulators which break up the speech band into five subbands by means of suitably selected upper carrier frequencies at the outputs of the downstream unit filters. The subbands obtained in this way are converted back into the original frequency position of the voice band with the aid of a further five downstream modulators, with the subbands being interchanged by supplying the modulators with a selectable selection of five out of ten carrier frequencies.
  • US Pat. No. 2,408,692 describes a transmission system with obfuscation by converting sub-bands into the frequency range of one of the sub-bands and then converting them into length-modulated pulses which are transmitted in multiples of time.
  • the known bandpass methods require a relatively high level of circuitry.
  • the object of the present invention was therefore to specify a method for the subband swapping of the type mentioned at the outset which enables time-discrete or digital signal processing with less circuitry.
  • the method according to the invention specifies how the frequency values for the carrier oscillations are to be selected as a function of the division into subbands and the sampling frequency, so that time-discrete or digital signal processing can be carried out in an uncomplicated manner.
  • Both rectangular and sinusoidal carriers can be used at relatively low sampling frequencies and a simple modulator circuit.
  • favorable values for concealing a CCITT voice channel are specified, which are divided into five subbands.
  • the basic block diagram of a speech concealment system based on the five-band swap is shown in FIG. 1.
  • the input spectrum of the speech signal Xin (f) to be concealed can be affected by undesired higher-frequency spectral components, which may have to be suppressed by an input-side low-pass filter TP 1 in order to be able to comply with the sampling theorem, for example, in the case of discrete-time signal processing with a predetermined sampling frequency fS.
  • the resulting band-limited spectrum X (f) is divided into five sub-bands in the next step using the same band passes BP 1 to BP 5. This requires prior modulation with corresponding carrier frequencies w 1, w 2, etc.
  • Y (f) is the spectrum of the disguised continuous Output signal.
  • the system for decrypting disguised speech signals also has the block structure shown in FIG. 1, with the reception-side random generator ZG having to deliver the same random sequence as the transmitter and synchronized with it for correct decryption.
  • FIG. 2a shows the spectrum of the speech signal (telephone quality), the control position fully representing the continuous-time signal and the additional spectral components occurring symmetrically to integer multiples of the sampling frequency fS (here the reverse position is shown below fS) with time-discrete processing.
  • the range of speech to be scrambled thus extends from B to 11 B (0.31 to 3.41 kHz). 2 2
  • the minimum value of the rectangular carrier frequency must not fall below 4 B, since otherwise, due to the hermeticity of the spectra of real signals, disturbing spectral overlaps occur. This condition also arises in the same way on the basis of the line spectrum of the rectangular carrier wave according to Fourier.
  • 3 shows a simple modulator implementation with 2 multipliers, only with the two values and 1 manages with both signs and 0, and the sample signal value x (kT) to be evaluated is routed to the corresponding one of the two inputs of one of these multiplier amplifiers or to zero potential by means of a selection switch, which is controlled by a control logic of the analog switch.
  • the sampling frequency thus results
  • the sampling frequencies can be reduced even further if sinusoidal carrier oscillations are used for the conversion, which can be combined into corresponding sequences from only a few samples with different amounts. Relationships (3) and (4) also apply here. The following applies to the sampling frequencies or
  • Claim 5 specifies a low-effort modulator implementation by means of multipliers, with depending on the integer ratio f, / fS between 1/2 and 1/6, for 1/8, 1/10 and 1/12 only 1 to 3 absolute values for one or both Signs are required (Table 4).
  • An exemplary embodiment for f ⁇ / fS 1/8 is shown in FIG. 3 described above.

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  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Compression, Expansion, Code Conversion, And Decoders (AREA)
  • Transmission Systems Not Characterized By The Medium Used For Transmission (AREA)
  • Position Fixing By Use Of Radio Waves (AREA)
  • Synchronisation In Digital Transmission Systems (AREA)

Claims (5)

1. Procédé de permutation de bandes partielles, de même largeur, d'une bande de fréquence d'un signal au moyen de modulateurs (X), en aval desquels sont montés des filtres passe-bande identiques (BP 1 à BP 5) ainsi que d'autres modulateurs (X), étant précisé que des fréquences porteuses définies (f 1 à f 4) correspondent aux modulateurs (X) et étant précise qu'entre les filtres passe-bande (BP 1 à BP 5) et les modulateurs (X) montés en aval, il est prévu, pour le cryptage, par découpage en fonction du temps, des bandes partielles, une matrice de couplage (matrice de cryptage) asservie à un générateur de nombres aléatoires (générateur de hasard), caractérisé en ce que les fréquences porteuses présentent les valeurs
Figure imgb0027
avec ν=1, 2... bandes partielles de largeur de bande B et i, I et ny ⊂|N=1, 2... (éléments e de l'ensemble des nombres naturels N) comme paramètres de choix libre, étant précisé que i et n peuvent également prendre les valeurs 0; et en ce que les modulateurs (X) travaillent en fonction discrète du temps et en ce que, pour la fréquence de balayage des ondulations porteuses on a la relation
Figure imgb0028
2. Procédé selon la revendication 1, caractérisé en ce que les porteuses sont sinusoïdales et en ce qu'on choisit ka fréquence de balayage sous la forme:
Figure imgb0029
KGV étant le plus petit commun multiple, ou sous la forme
Figure imgb0030
3. Procédé selon la revendication 1, où la bande de fréquence de signal est le canal vocal de la CCITT (0,3 à 3,4 kHz), caractérisé en ce que l'on forme n = bandes partielles de largeur de bande B=620 Hz; et en ce que la conversion de fréquence, avec des porteuses rectangulaires selon l'une des possibilités suivantes du tableau 1:
Figure imgb0031
4. Procédé selon la revendication 1 ou la revendication 2, caractérisé en ce que l'on forme n=5 5 bandes partielles de largeur de bande B=620 Hz; et en ce que la conversion de fréquence avec des porteuses sinusoidales se fait selon l'une des possiblités suivantes du tableau 3:
Figure imgb0032
5. Procédé selon la revendication 2 ou la revendication 4, caractérisé en ce que les modulateurs (X) sont constitués d'un circuit de multiplexeurs qui, au rythme de la fréquence de balayage fS, multiplient le signal, pour f,/fS ou pour un mutliple entier, par l'un des facteurs indiqués selon le tableau 4 suivant:
Figure imgb0033
EP82100607A 1981-02-13 1982-01-29 Procédé de permutation de bandes partielles Expired EP0058318B1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DE3105214 1981-02-13
DE19813105214 DE3105214A1 (de) 1981-02-13 1981-02-13 "teilbandvertauschungsverfahren"

Publications (2)

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EP0058318A1 EP0058318A1 (fr) 1982-08-25
EP0058318B1 true EP0058318B1 (fr) 1984-08-08

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EP82100607A Expired EP0058318B1 (fr) 1981-02-13 1982-01-29 Procédé de permutation de bandes partielles

Country Status (7)

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EP (1) EP0058318B1 (fr)
CA (1) CA1186380A (fr)
DE (2) DE3105214A1 (fr)
DK (1) DK52682A (fr)
ES (1) ES8302387A1 (fr)
FI (1) FI820393L (fr)
PT (1) PT74410B (fr)

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS6424648A (en) * 1987-07-21 1989-01-26 Fujitsu Ltd Privacy call equipment

Family Cites Families (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2408692A (en) * 1942-04-29 1946-10-01 Rca Corp Signaling system
CH248975A (de) * 1946-02-04 1947-05-31 Patelhold Patentverwertung Verfahren und Einrichtung zur Verschleierung der einzelnen Gespräche einer Mehrkanalanlage.
DE1273002B (de) * 1963-09-11 1968-07-18 Siemens Ag Einrichtung zur verschluesselten UEbertragung von Sprachsignalen durch Vertauschung von Teilbaendern
DE2652607A1 (de) * 1976-11-19 1978-05-24 Licentia Gmbh Verfahren zum verschleierten uebertragen von nachrichtensignalen

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DE3260506D1 (en) 1984-09-13
FI820393L (fi) 1982-08-14
DE3105214A1 (de) 1982-09-09
ES509565A0 (es) 1982-12-16
ES8302387A1 (es) 1982-12-16
PT74410B (de) 1983-10-28
PT74410A (de) 1982-03-01
DK52682A (da) 1982-08-14
EP0058318A1 (fr) 1982-08-25
CA1186380A (fr) 1985-04-30

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