RU2809343C1 - Method for combined transmission of analog and digital signals - Google Patents

Abstract

FIELD: modulation; demodulation.

SUBSTANCE: invention relates to the field of modulation and demodulation when transmitting analogue and digital information. The technical result is the possibility of joint transmission of an analogue audio signal and a digital signal in a narrow frequency range. To do this, on the transmitting side, a modulating analogue audio frequency signal with a constant component is fed to the input of a symmetrical full-wave modulator. The Manchester code is used as a carrier frequency signal, transmitting digital information. On the receiving side, the signal is fed in parallel to a full-wave detector, which acts as a symmetrical demodulator, and to a symmetrical voltage limiter. A low-frequency analogue signal will appear at the detector output, in which the high-frequency component is completely absent. At the output of the symmetrical limiter, a signal will appear in the form of a Manchester code, similar to the Manchester code on the transmission.

EFFECT: possibility of joint transmission of an analogue audio signal and a digital signal in a narrow frequency range.

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Description

The invention relates to the field of modulation and demodulation in the joint transmission of analog and digital information.

Currently, the transmission of analog and digital information over telephone lines is widely used. For example, simultaneous transmission of digital and analog information over two-wire telephone lines occurs in ADSL systems using frequency division of a voice transmission channel and two asymmetric data transmission channels to and from the network.

The closest in technical essence is pulse amplitude modulation, which is chosen as a prototype.

Suggested solution to the problem is to use pulse amplitude modulation (PAM) and pulse width modulation (PWM) together.

The technical result of the proposed invention is the possibility of joint transmission of an analog audio signal and a digital signal in a narrow frequency range over one two-wire telephone line.

The essence of the proposed method is in the use of a Manchester code digital signal as a carrier frequency in pulse-amplitude modulation of a low-frequency audio signal.

The known prototype method is carried out as follows.

Pulse amplitude modulation (PAM) is a type of pulse modulation (a sequence of pulses of the same shape, usually rectangular, is modulated), in which the average value of the output parameter is controlled by changing the amplitude of the pulses [1-4]. There are two types of AIM. With AIM-1, the amplitude of the pulse follows the change in the modulating function throughout the entire lifetime of this pulse. In the case of AIM-2, the amplitude modulation of pulses is determined by the instantaneous values of the message function, taken at the moment t _k = k×T _s , where T _s is the pulse repetition period. The pulse amplitude in this case is proportional to the instantaneous value of the modulating function at time t _k and remains constant during the pulse. If the pulse duration T _o << T _s , then the difference between AIM-1 and AIM-2 becomes insignificant. The pulse repetition rate is determined based on the acceptable accuracy of reconstruction of a continuous message during its demodulation [2].

Pulse amplitude modulation is used in telephone communications, radio broadcasting, transmission of television images, in measuring technology, biomedical equipment, telemetry and in other fields of technology. For high-frequency carrier waves, all radio frequency ranges are used. AIM is also used to transmit digital information in various types of Ethernet signals. In particular , 1000 BASE-T Gigabit Ethernet uses 5-level PAM-5 modulation [5]. In all cases under consideration, AIM is used to transmit either only analog or only digital information.

However, there are telephone lines that allow the transmission of signals in a narrow frequency range, but this requires the possibility of additional transmission of digital information. For example, some telephone lines operating in the field have a bandwidth of up to 30 kHz. Under these conditions, frequency separation of digital and analog channels using conventional linear filters becomes very problematic.

The proposed method is carried out as follows.

Figure 1 shows:

1- Analogue sound signal.

2- Manchester code digital signal.

3- Symmetrical bipolar modulator.

4- Manchester code signal, level modulated.

5- Full wave detector.

6- Symmetrical limiter detector.

7- Analogue sound signal.

8- Manchester code digital signal.

On the transmitting side, a low-frequency analog audio signal-1 of low frequency, having a constant component, is supplied to the first input of the symmetrical modulator-3. A bipolar signal in the form of a Manchester (or similar) digital code is supplied to the control input of symmetrical modulator-3. In modulator-3, signal-1 is alternately inverted in such a way that a symmetrical AIM-1 modulated signal-4 appears at the output of modulator-3, which enters a two-wire telephone line. There is no DC component in the transmitted signal, as a result of which galvanic isolation becomes possible. On the receiving side, the signal is supplied in parallel to a full-wave detector-5, which acts as a symmetric demodulator, and to a symmetrical voltage limiter-6. Ideally (in the absence of distortion in the line), a low-frequency analog signal-7 should appear at the output of the symmetrical limiter-detector-6, in which the high-frequency component is completely absent. In fact, due to linear distortion, the low-frequency signal-7 will contain a high-frequency component of low power, easily removed by a conventional linear filter (not shown in Fig. 1). At the output of the symmetrical limiter-6, a digital signal of the Manchester code will appear, similar to the Manchester code in the transmission.

In fact, in the proposed method, AIM and PWM are used together. At the same time, PWM is used to transmit digital information and has only 2 levels, which ensures high noise immunity when demodulating digital signals. In a demodulated analog signal, in the absence of linear distortion, ideally, there is no high-frequency component at all, which facilitates its subsequent filtering.

LITERATURE

1. https://ru.wikipedia.org/wiki Pulse amplitude modulation - Wikipedia.

https://de.ifmo.ru/bk_netra/page.php?dir=4&tutindex=11&index=42&layer=1.

2. Panfilov I. P., Dyrda V. E. Theory of electrical communication. – M.: Radio and Communications, 1991. – 344 p.

3. Kuleshov V. N., Udalov N. N., Bogachev V. M. Generation of oscillations and formation of radio signals. – M.: MPEI, 2008. – 416 p.

4. Berezovsky P. P. Fundamentals of radio engineering and communications. - Ekaterinburg: Ural State University, 2017. - 212 p.

5. Kartashevsky V.G., Lichtzinder B.Ya., Kireeva N.V., Buranova M.A. Computer networks : textbook. – Samara, PGUTI, 2016. – 265 p.

Claims (1)

A method for the joint transmission of analog and digital signals, which provides for the presence of pulse modulation in the communication channel, characterized in that during transmission an amplitude-modulated digital signal of the Manchester code is used, and at reception it is simultaneously full-wave detection to isolate the analog signal and symmetrically limited in level to isolate Manchester code digital signal.