JPS591024B2 - Code word detection method - Google Patents

Description

[Detailed description of the invention] In a data transmission system, a predetermined code word (unique word) having a certain content and a unique meaning is used as effective information to be transmitted.
For example, it must be transmitted additionally or as an address for the detection of a predetermined point in time, which identifies the start of a relatively long signal sequence.

A given code word must be detected as reliably as possible at the receiving end. This is difficult due to the noise superimposed on the signal and the superimposed interference signals, for example in transmission by polyphase phase modulation. On the other hand, in the case of binary phase modulation, a predetermined code word can be detected more reliably. Contribution paper D4 to the proceedings of the 2nd International Conference on Digital Hygiene Communication (Paris, November 1972) “8 Phases for TDMA”
The system described in New Modem System-1 (article by Mr. Ogawa and Mr. Okawa) can transmit a predetermined code word by two-phase phase modulation.

A special two-phase phase demodulator is provided for receiving the predetermined code word, the input of which is connected in parallel with the input of the polyphase phase demodulator. The expense required for this is small on the sending side, but too high on the receiving side. In m-phase modulation, where m is generally a power of 2, successive bit digits of the data to be transmitted, as many as the base 2 logarithm ldm, are grouped into one code word and Each of the m codewords is characterized by a phase state belonging to the codeword of the carrier wave relative to a reference frequency.
The phase angle of the modulated signal is usually an even or odd multiple of the angle π/m. On the receiving side, the clock is at an angle of π/m
is reliably reproduced from a signal having an odd multiple of . Angle π/
It is known to obtain odd multiples of m from even multiples of the angle π/m by axial transformation. A given code word is bit digit ld
If m is configured such that only two given codewords hold true when summarizing, a biphasic phase signal will result for a given codeword.

In the simplest case, in a given code word, the integral multiples of successive bit digits ldm are mutually equal, or in other words, the advancing clock for a given code word is 1 dm times the advancing clock of the data to be transmitted. It's a long time. The present invention provides four-phase phase modulation or polyphase phase modulation or four-phase differential modulation or polyphase differential modulation and coherent transmission in which the signs of a given code word are transmitted by only two phase positions shifted by 18' from each other. The invention starts from a method for detecting a predetermined code word (unique word) in a received signal of a data signal transmission system in which detailed demodulation (synchronous detection) is performed.

In this case, the received signals of the transmission system each consist of four-phase or polyphase modulated carrier waves.

In addition, in the case of phase modulation other than 4-phase phase modulation, for example, 8-phase phase modulation, not only 4 phase modulations are used for information transmission,
For example, 8 phase angles are 0°, 45°, 900,
135 phase, 1800, etc. are used. In the case of phase differential modulation, only the changes in the useful information are detected and converted into digital bits, which are then transmitted using quadrature or polyphase phase modulation. In the case of polyphase phase modulation or polyphase differential modulation, as in the case of 4-phase phase modulation or 4-phase differential modulation, the transmission of the symbol of a given code word is carried out by 18' This is done by using only two shifted phase aberrations.

It is assumed that a predetermined code word is detected in the same way for each modulation on the receiving side.

However, it is an object of the present invention to provide a method for easily detecting a predetermined code word transmitted by a two-phase signal contained therein from a four-phase phase signal or a multi-phase phase signal without error. It is. In the known method of m-phase phase demodulation, is it necessary? The reference carrier wave has m phase changes with respect to the received carrier wave. However, there is no known method for simply forcing the reference carrier wave to a predetermined phase position necessary for demodulating a two-phase signal. The above problem is solved as follows by the present invention.

That is, from the two voltage values x and y that are first obtained during demodulation and represent the coordinates of the received signal according to the magnitude and sign in the data point phase map, the first coordinate value of the two coordinate values is is evaluated according to its sign by multiplying the value of the ratio of the first coordinate value to the second coordinate value, integrated over the clock time of , and adding the multiplied value to the second coordinate value. power, so as to form a unique magnitude of the two-phase signal. At that time, none of the coordinate values takes the value 0,
That is, either the received signal has a phase angle with respect to the reference carrier that is the same as an odd multiple of the angle π/m, or it is converted to such an angle in advance, as described above. According to the method of the present invention, from the values representing the coordinate values of the signal of the data point phase diagram, it is possible to obtain two Only one of the two values always occurs.

Using the method of the present invention, the noise figure is at least 3 db
(When m=4. It increases as m increases.) The predetermined codeword to be detected is reliably detected from the noisy received signal. Next, embodiments of the present invention will be described in detail with reference to the drawings.

The illustrated circuit is suitable, for example, not only for four-phase phase modulation, but also for n-phase phase modulation with n>4.

This is because the circuit shown has only 2 out of n phase variations.
It is concerned only with the transmission of a given code word using only two phase variations, and two demodulators D1 and D2 as shown are sufficient for the demodulation of the code word. Of course, in the case of polyphase phase modulation further demodulators are provided, but they are not used for the demodulation of a given code word. For 8-phase phase modulation, 8 phases correspond to 3 bits, so for demodulation of useful information three demodulators are provided;
In that case as well, only the two illustrated demodulators D1 and D2 are
Used for demodulating a given code word.

In short, the illustrated quadrature demodulators D1 and D2 are part of an n-phase phase demodulator (n≧4), and therefore the illustrated experimental example is the same regardless of the number of n. However, it is also possible to use only one demodulator for the demodulation of a given code word.

That is, the two demodulators decompose a carrier wave having an instantaneous phase position into sine and cosine components. These two components are then used to determine the carrier amplitude. The use of two demodulators makes it possible to extract the amplitude optimally and efficiently during demodulation.

The phase-modulated signal supplied via input E is demodulated by demodulators D1 and D2 which are controlled by a carrier frequency F with a phase shift of approximately 9'.

The coordinate values X and y are then generated. The connected data receiver DE recovers the original useful information from the value For the detection of a predetermined code word, a suplink switch ASl, controlled by a known evaluator B1 clock T, supplies a signal after the detection of a predetermined code word to a data receiver DE, for example as a start signal. A vessel K is illustrated.XI:
．． Since y is arbitrarily assigned to a coordinate value, it can be interchanged depending on predetermined specifications and circuit embodiments. In order to implement the above-described scheme, well-known commercially available components of analog and computer technology are used.

The devices in the frame surrounded by broken lines in the figure are divider Q1 and multiplier M.
It consists of one adder S and an integrating element. The first of the two coordinate values is first supplied to the dividend input of the divider and the first input of the multiplier, and the second coordinate value is first supplied to the second divisor input of the divider and A first input of the adder is supplied.

An integrated element, for example a simple low-pass filter, follows the output of the divider and integrates the value of the quotient over a plurality of preceding clock times. The output side of the integrated element is connected to the second input side of the multiplier, and the output side of the multiplier is connected to the second input side of the adder.
connected to the input side of the

At the output of the adder, the magnitude of the two-phase phase signal to be evaluated can be extracted. It is only its sign that is decisive for the evaluation of the values obtained by the above-mentioned device. Methods suitable for this are known. The figure shows a code discriminator as evaluator B. The sign discriminator will send out +1 or -1 depending on the sign of the value applied to it, regardless of the magnitude applied to it. The output signal of the evaluator is read out at predetermined intervals by a sampling switch AS controlled by a clock T and fed to a correlator K. The correlator K supplies a signal, for example as a star 1 signal, to the data receiver DE upon reception of a predetermined code word that is considered to be correct with sufficient certainty. Using these correlators K or data receivers DE, the phase ambiguity of the entire received signal is removed.

[Brief explanation of the drawing]

The figure is a block diagram of a receiving section including the device of the invention. B...Evaluator, AS...Sampling switch, K...Correlator, DE...Data receiver, Dl, D2... Demodulator.

Claims (1)

[Claims] 1 Four-phase phase modulation or polyphase phase modulation or four-phase differential modulation or polyphase differential modulation and coherent demodulation are performed in which the sign of a given code word is transmitted by only two phase positions shifted by 180° from each other. the predetermined code word (unique word) in the received signal of the data signal transmission system
In the method of detecting By multiplying the coordinate value by a value of the ratio of the first coordinate value to the second coordinate value, integrated over a plurality of clock periods, and adding the multiplied value to the second coordinate value, the sign is determined. A code word detection method is characterized in that a unique magnitude of a two-phase signal is formed to be evaluated according to the magnitude of the two-phase signal.