RU2804430C1 - Single phase difference modulation method - Google Patents

Abstract

FIELD: radio engineering.

SUBSTANCE: invention can be used in data transmission systems with phase-shift keyed signals. The method of single phase-difference modulation consists in converting the transmitted sequence of binary data into a sequence in which the modulo sum of two elements lagging behind each other by one element is equal to the transmitted data. The transformed sequence is manipulated in phase with the carrier signal. The elements of the transformed sequence are inverted through one and the second carrier frequency signal phase-shifted relative to the first by ninety degrees is manipulated in phase. The two phase-shift keyed signals are summed.

EFFECT: absence of phase jumps by 180 degrees in the modulated signal while maintaining the noise immunity of signal reception.

1 cl, 1 dwg

Description

The invention relates to the field of radio engineering and can find application in data transmission systems using phase-shift keyed signals.

In some systems, such as satellite systems, in addition to requirements for the level of out-of-band spectral components of the signal, there are requirements for the constancy of their envelopes. In such systems, four-phase (quadrature) phase shift keying (FMS, OQPSK) is used, the advantage of which is the absence of 180-degree phase jumps in the modulated signal [1, p. 151]. When filtering a signal to suppress out-of-band spectral components, a slight rolloff of the envelope occurs in the region of phase transitions by ±90 degrees. With further limitation in a nonlinear transmitter power amplifier or satellite repeater, the envelope is restored, and the spectral components are not amplified [2, p. 580].

In binary differential phase shift keying (DBPSK), also called single-shot phase difference modulation [3], the initial phases of adjacent signal bursts are the same or differ by 180 degrees. The presence of phase jumps of 180 degrees leads to the fact that when filtering signals, deep amplitude modulation occurs, until the envelope turns to zero. If the signal subsequently passes through a nonlinear transmitter power amplifier or satellite repeater, the envelope is restored, and along with it the suppressed spectral components [2, p. 580].

The purpose of the invention is to develop a method of single phase-difference modulation in which the modulated signal does not have 180-degree phase jumps, and the noise immunity of signal reception does not deteriorate. The achieved result is the possibility of use in satellite systems and systems with a nonlinear transmitter power amplifier.

The closest in terms of the number of matching features to the proposed method is second-order phase-difference modulation, which is a method of generating a phase-shift keyed signal in which information is embedded in the value of second-order differences in the initial phase of signal transmissions [3, p. 41; 4].

The mathematical representation of a phase-shift keyed signal is:

where T is the duration of signal transmissions,

- initial phase of the n-th parcel.

Second order difference of the initial phase of signal transmissions [3, p. 41]

With phase difference modulation of the second order of magnitude is assigned a value determined by the transmitted information symbol and belonging to the set corresponding to the modulation multiplicity.

In case of single modulation can only take two values. To ensure the greatest noise immunity, choose 0 degrees and 180 degrees. In this case, the initial phases of the sendings take two values that differ by 180 degrees, and the sequence can be represented in the form

,

Where - a binary sequence of zeros and ones.

The second order difference is transformed to the form:

therefore, up to

.

If the transmitted binary information is a sequence , That

,

hence

.

Thus, single second-order phase difference modulation can be described as a method of generating a phase-shift keyed signal, which consists in the fact that the sequence of transmitted binary data is converted into a sequence in which the modulo sum of two elements lagging each other by one element is equal to the transmitted data, and the converted sequence is manipulated 180 degrees out of phase with the carrier frequency signal.

The disadvantage of the prototype method is the presence of phase jumps of 180 degrees.

To solve the problem posed in the invention in the method of single phase difference modulation, which consists in the fact that the sequence of transmitted binary data is converted into a sequence in which the modulo sum of two elements spaced from each other by one element is equal to the transmitted data, and the converted sequence is manipulated according phase shift of the carrier frequency signal by 180 degrees, according to the invention, a second carrier frequency signal is generated, phase-shifted relative to the first by 90 degrees, the elements of the converted sequence are inverted through one and the resulting sequence is manipulated in phase by 180 degrees of the second carrier frequency signal, and both phase-shift keyed ones are summed signal.

The method of single phase difference modulation consists in sequentially performing the following operations.

- Sequence of transmitted binary data convert to sequence , in which the sum modulo two of elements spaced one element apart is equal to the transmitted data, that is . In this case, the first two elements of the sequence - arbitrary zeros or ones, and the remaining elements of the transformed sequence can be calculated using the recurrence formula .

- The elements of the transformed sequence are inverted through one (every second), forming a sequence such that

(1)

- Two carrier signals are generated, shifted in phase by 90 degrees: And

- One of the carrier signals is manipulated in phase by 180 degrees in a sequence , and the second - by the sequence .

- Both phase-shift keyed signals are summed.

Thus, the generated signal over the time interval

has the form:

,

where T is the duration of one message.

As a result of transformations, the signal can be reduced to the form:

,

Where determined from the condition

.

By enumerating binary values And it is possible to prove the identity

.

Where - sum modulo two.

Let us introduce the notation , Then

, (2)

and taking into account (1)

,

that is, the sequence is a sequence of alternating zeros and ones.

The difference in the initial phases (2) of two adjacent parcels is equal to

.

Since the difference equal to 1 or 1, difference up to can only take two values And . Thus, the modulated signal does not have 180 degree phase jumps.

Let's consider methods for receiving data transmitted using the modulation method under consideration. The difference in the initial phases (2) of parcels spaced from each other by one parcel is equal to

Because , then when And are identical and the phase difference is zero. At And are different, so the phase difference is . Hence and the data can be received by comparing the initial phases of bursts spaced one burst apart.

Note that with single phase difference modulation of the first order, data is received by comparing the initial phases of adjacent messages. Consequently, to receive data transmitted by the claimed method, similar algorithms and demodulator circuits can be used [3, p. 36, Fig. 1.8, 1.9]. The difference is that the signal delay in the corresponding blocks doubles (instead of T - 2T). In this case, the noise immunity of demodulation algorithms does not change.

It is known [3, p. 42] that second-order phase-difference modulation makes it possible to receive data under conditions of significant detuning of the signal carrier frequency. This is explained by the fact that the second-order difference in the initial phase of signal transmissions is invariant to the carrier frequency [3, p. 43].

Signals generated by the claimed method have the same property. Indeed, if the deviation of the carrier frequency from the nominal value is equal to , That:

therefore, up to

Consequently, the second-order difference in the initial phase of the signal transmissions does not depend on the magnitude of the deviation of the signal carrier frequency. Receiving inverted data possible using autocorrelation signal demodulators with single phase difference modulation of the second order [3, p. 215, Fig. 5.16, 5.17].

Let's consider one more property of signals generated by the proposed method. Taking into account (2), the square of the signal is equal to

Thus, the square of the signal contains an alternating component, which is a harmonic oscillation of twice the carrier frequency, manipulated in phase by a sequence of alternating zeros and ones. This signal does not depend on the transmitted data, so its use in a symbol synchronization circuit can increase the efficiency (accuracy, noise immunity, etc.) of the circuit.

An example of a technical implementation of a phase-difference modulator corresponding to the proposed method is shown in Fig. 1.

The modulator contains:

1, 5 - modulo two adder;

2, 3, 4 - D-trigger;

6,7 - level converter;

8, 10 - multiplier;

9 - phase shifter;

11 - adder.

The modulator works as follows. Transferred binary data arrive at one of the inputs of the modulo two adder 1, and the clock pulses (TI), to the edges of which they are linked, arrive at the clock inputs of D-flip-flops 2, 3, 4. The output signal of the modulo two adder 1 is delayed in D-flip-flops 2 , 4 for two clock periods and is fed to its second input. If the sequence of binary pulses at the output of the adder modulo two 1 is denoted as , then the sequence at the output of D-trigger 2 will look like , and the output of the D-flip-flop is 4 . Since in a modulo two 1 adder the sequences are summed And , That , that is

, which corresponds to the rule for converting the sequence of transmitted data in the proposed method.

D-trigger 3 operates in divider by two mode and a square wave is formed at its output, the period of which is equal to two periods of the clock frequency. A square wave from the output D-flip-flop 3 is supplied to one input of the modulo two 5 adder, and a sequence is supplied to the second input from the output of the adder modulo two 1.

In a modulo 5 adder, every second element of the sequence is inverted The output signals of the modulo two adders 1 and 5 are converted to bipolar form in level converters 6 and 7 and are fed to the inputs of multipliers 8 and 10. The carrier frequency signal is supplied to the second input of multiplier 8, and the carrier frequency signal, shifted, is supplied to the second input of multiplier 10 in phase by 90 degrees in phase shifter 9.

At the output of multiplier 8, a carrier frequency signal is generated, phase-manipulated by 180 degrees by the converted sequence of transmitted binary data At the output of multiplier 10, a carrier frequency signal is generated, phase-shifted by 90 degrees and phase-shifted by 180 degrees by the sequence , in which every second element is inverted.

In adder 11, phase-shift keyed signals from the outputs of multipliers 8 and 10 are summed.

SOURCES OF INFORMATION

Noise immunity and efficiency of information transmission systems / A.G. Zyuko, A.I. Falko, I.P. Panfilov, V.L. Banquet, P.V. Ivashchenko; Ed. A.G. Zyuko. - M.: Radio and Communications, 1985. - 272 p., ill.

Sklyar B. Digital communication. Theoretical foundations and practical application. Ed. 2nd, rev.: Trans. from English - M.: Williams Publishing House, 2004. - 1104 p.

Okunev Yu.B. Digital transmission of information using phase-shift keyed signals. - M.: Radio and communication, 1991. - 296 p.

USSR Author's Certificate 177450. Method of transmitting discrete messages with relative phase shift keying. Published 12/18/1965. Bull. No. 1.

Claims (1)

A method of single phase difference modulation, which consists in the fact that the sequence of transmitted binary data is converted into a sequence in which the modulo sum of two elements lagging each other by one element is equal to the transmitted data, and the converted sequence is manipulated in phase by 180 degrees by the carrier frequency signal , characterized in that a second carrier frequency signal is generated, phase-shifted relative to the first by 90 degrees, the elements of the converted sequence are inverted through one and the resulting sequence is manipulated in phase by 180 degrees of the second carrier frequency signal, and both phase-shifted signals are summed.