DE2524034A1 - CODE WORD RECEPTION PROCEDURE - Google Patents

Description

Licentia Patent-Verwaltungs-GmbH PT-BK / Wgr / jo

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Code word reception method

In data transmission systems, in addition to the useful information to be transmitted, certain code words usually have to be used (unique words) with defined content and agreed meaning, e.g. to define certain points in time to identify the beginning of a longer sequence of signals or to be transmitted as an address.

The specific code words should be able to be recognized on the receiving side with the greatest possible certainty. this will makes the noise and interfering signals superimposed by the signals more difficult, in particular when transmitting with multiphase modulation. In the case of two-phase modulation, on the other hand, certain code words can be determined more reliably.

In that by Ogawa, A. and Ohkawa, M. under the title: ^N A

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New Eight-Phase Modem System for TDMA "as contribution Dk in the conference report of the Second International Conference on Digital Satellite Communication, Paris, Nov. 1972, the specific code words are therefore transmitted with two-phase modulation. A special two-phase demodulator is provided for receiving the specific code words , the input of which is connected in parallel to the input of the polyphase demodulator.The effort for this is low on the transmitting side, but appears too high on the receiving side.

In a B-phase modulation, where m is generally a power of 2, a number of successive bit positions of the data to be transmitted which is equal to the logarithm of two ld m are combined to form a code word, and when each of the m possible code words is transmitted by a phase position assigned to it Carrier frequency marked against a reference frequency. The phase angles of the modulated signals can be even-numbered or, as is usually the case, odd-numbered multiples of the angle π / m. On the receiving side, the step rate can be recovered more reliably from signals with odd multiples of the angle π / m. It is known and customary to obtain the odd-numbered multiples from the even-numbered multiples of the angle x / m by means of an axis transformation.

Two-phase signals for the specific code word result

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if this is structured in such a way that when combining Id m bit positions, only two predeterminable code words are created, in the simplest case, if in the specific code word an integer multiple of Id m successive bit positions are equal to one another, or in other words, if the step act for the specific code word Id m times is longer than the step rate of the data to be transferred.

The object leading to the invention was to provide a method by which, in a simple manner, the code words contained therein and transmitted by two-phase signals from the four-phase or multi-phase signals smallest error probability can be determined.

In the known method for m-phase demodulation the reference carrier required for this has any one of m possible phase positions with respect to the received carrier. It however, no method is known by which the reference carrier is simply converted into the specific, for demodulation the two-phase signals forces the necessary phase position.

The method according to the invention for achieving the object is described in claim 1. It assumes that none of the coordinate values takes on the value zero, ie that the received signals with respect to the reference carrier phase angle approximately equal to the odd multiples of the angle % / m

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have or, as explained, previously transformed to such angles.

According to the method, the values characterizing the coordinates of the signal in the phase star result at only two possible phase positions, regardless of their actual phase positions, only ever with one of two values same amount and different signs. It can be shown that when using the method the signal-to-noise ratio for the newly obtained value improved by at least 3 db (at m a 4, increasing with m). That The specific code word to be determined can therefore be recognized more reliably in the case of noisy reception signals.

The figure shows, in a simplified overview circuit diagram, the most important assemblies of the receiving part of a conventional multiphase modem, which are essential for understanding, and therein in a dash-dotted frame a exemplary arrangement for performing the method described.

The phase-modulated signals arriving via the input E are replaced by the signals from the carrier frequency F. 90 phase shift controlled demodulators Dl resp. D2 demodulates and results in the coordinate values χ and y. The subsequent data receiver DE wins from

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returns the original useful information for the values χ and y, outputs this via output A, and also supplies a clock derived from the received signals T. The figure also shows the assemblies evaluator B, which are also known for determining a certain code word in a signal sequence, the sampling switch AS controlled by the clock T and the correlator K which, after the certain code word has been determined, generates a signal, e.g. as Supplies the start character to the data receiver DE.

Since the designations χ and y are arbitrarily assigned to the coordinate values, they can be interchanged in the given specification and in the circuit example.

Assemblies known per se from analog computer technology can be used to carry out the described method will. The arrangement shown in the dash-dotted frame of the figure consists of a divider Q, a multiplier H and a summer S, each with two inputs and an integrator I. A first of the two coordinate values is first a first, the dividend input of the divider and secondly one first entrance of the multiplier and the second coordinate value is fed firstly to the second, the divisor input of the divider and secondly to a first input of the adder. To the

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The output of the divider is the integrating element, for example a simple low-pass filter connected downstream of the quotient values integrated from several previous cycle times.

The output of the integrator is connected to the second input of the multiplier and the output of the multiplier with the second input of the adder. The value of the two-phase signal to be evaluated is at the output of the adder detachable.

The only decisive factor for evaluating the values obtained by the described arrangement is their sign. Methods and arrangements suitable for this are known. The figure shows as evaluator B a sign element without Consideration of the amount added to him solely depending on the sign of the value +1 or -1 returns values.

The output signals of the evaluator are queried by a sampling switch AS controlled by the clock T and sent to the correlator K, which upon receipt of a certain code word that is to be regarded as correct with an evasive probability sends a signal z. B. supplies the data receiver DE as a start signal.

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Claims (2)

- 7 claims (1 · / Method for determining a specific code word (unique word) in the received signals of a working with four or multi-phase or four or multi-phase difference modulation and coherent demodulation Transmission system, the characters of the specific code word being transmitted with only two phase positions shifted by 180 relative to one another, characterized in that from the demodulation initially obtained, the coordinates of a received signal in the phase star according to size and sign reproducing two voltage values χ and y a single one, according to The magnitude of the two-phase signal whose sign is to be assessed is formed by the fact that a first of the two Coordinate values, multiplied by the ratio of the first to the second coordinate value, is added to the second coordinate value. 2. Circuit for performing the method according to claim. 1, characterized in that a first of the two coordinate values is converted into the Relation to the second is set that the quotient obtained by a multiplier (M) with the first BK 75/21 - 8 - 609849/0575 Coordinate value is multiplied so that the second coordinate value is added to the product by a summer (S) is added, and that the output signal of the adder is the value of the two-phase signal to be assessed represents. BK 75/21 609849/0575