RU1800623C - Device for transmitting and receiving information - Google Patents

Abstract

The invention relates to telecommunications, in particular to the transmission of information over interfering communication channels. The goal is to increase noise immunity. For this, two delay units 2 and 10, a spectrum analyzer 9, and a second subtraction unit 14 are introduced into the device. 10 ill.

Description

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The invention relates to radio engineering and communication and can be used in the transmission of signals over communication channels with interference.

The purpose of the invention is to increase the immunity of the device when exposed to interference with a monotonically increasing and monotonically decreasing frequency spectrum, as well as when changing the plot of the transmitted information. The proposed device is intended to increase the noise immunity of the transmitted information only under the influence of slowly varying over time interference, when the inertia of the control channels and feedback does not affect the operation of the device.

Figure 1 is a structural diagram of a device for transmitting and receiving information; figure 2 is a structural diagram of a spectrum analyzer; Fig. 3 is an electrical functional diagram of a predistortion filter; figure 4 is an electrical functional diagram of a correction filter; Fig. 5a shows a change in the transfer function of the high-pass filter (block 23 and block 22) depending on the control signal; Fig. 5b shows the change in the transfer function of the low-pass filter (the predistorting part of the predistorting filter 3 and the whitening part of the correction filter) depending on the control signal; in FIG. Figures 6-10 show the characteristics of the transfer functions of the predistortion and correction filters, as well as the shape of the spectra of signals and noise at the output of the signal source, in the communication channel and at the input of the receiver. In FIG. 6-10 depict the following spectra; a) the spectrum of the information signal at the source output is Gc, the interference spectrum acting on the communication channel is GPKC, b) the transfer function of the predistortion part of the predistortion filter, c) the transfer function of the 23-Kapp block; d) the spectrum of the information signal transmitted to the communication channel — GCKC, the spectrum of the interference acting on the communication channel — Spx, e) the transfer function of the whitening part of the correction filter — K2kf, e) the transmission function of block 22 — Kif; g) the spectrum of the information signal received by the receiver -Gcnp, the interference spectrum at the input of the receiver is Gnnp.

The structure of the device’s block diagram (FIG. 1) includes t: 1 — information source; 2 - the first block delay; 3 - predistortion filter; 4 - communication channel; 5 - correction filter; 6 - information receiver; 7 - the first spectrum analyzer; 8 - second

spectrum analyzer; 9 - the third spectrum analyzer; 10 - the second block delay; 11 is a first subtraction block; 12 is a feedback channel; 13 is a control channel; 14 is a second subtraction block.

The composition of the structural diagram of the spectrum analyzer (Fig.2) includes: 15, 20 - narrow-band filters; 16, 21 - amplitude detectors; 17 - matching device; 18 - subtractive device; 19 - integrator.

The composition of the predistortion filter 3, (Fig. H) includes: block 22 — the correction part of the filter 5; DA1, DA2 - operational amplifiers; R1 ... R6 - resistors; YD1, YD2 - diodes; C1 is a capacitor; VT1 transistor; L1 - inductor.

The composition of the correction filter 5 (Fig. 4) includes: block 23 — the compensating part of the filter 3; DA3, DA4 - operational amplifiers; R7 ... R12 -resistors; VD3, VD4 diodes; C2 - capacitor; VT2 transistor; L2 - inductor,

Moreover, in the device for transmitting and receiving information, the information source 1, the first delay unit 2, the predistortion filter 3, the communication channel 4, the correction filter 5, the information receiver 6 are connected in series. The output of the predistortion filter 3 is connected to the second spectrum analyzer 8, the second delay unit 10, the first subtraction unit 11, and the second subtraction unit 14 connected in series. The output of the communication channel 4 through the series-connected third spectrum analyzer 9 and the feedback channel 12 is connected to the second input block 11, and the output of the information source 1 through the first spectrum analyzer 7 is connected to the second input of block 14, the output of which is connected to the control input of the predistortion filter 3 and through the control channel 13 with the control in Odom equalizing filter 5.

To accomplish the task of improving noise immunity, the proposed device uses the adaptive predistortion and signal correction method. This method improves the noise immunity of the transmitted information while maintaining the average power of the transmitted signal. In the proposed device, the predistortion filter changes the spectrum of the signal (in the application, the spectrum of the signal means the envelope of the signal spectrum) so that in the communication channel the spectrum of the predistorted signal in the transmitted frequency band is parallel to the interference spectrum (the interference spectrum also means the bending interference spectrum ) If the spectrum

the signal will not be parallel to the interference spectrum (in energy level) will exceed the spectrum of the signal, which will lead to loss of information at these frequencies. From the output of communication channel 4, a mixture of the information signal and interference passes sequentially through the whitening part of the correction filter, the transfer function of which is reciprocal to the transfer function of block 23 and through the correction part of the correction filter 5, the transfer function of which is reciprocal to the transfer function before the distorting part predistortion filter. Thus, the information signal passes the entire path from block 1 to block 6 without distortion.

The device includes 3 spectrum analyzers (blocks 7-9), each of which contains (see Fig. 7-9), each of which contains (see, Fig. 2) 17 - matching device connected to narrow-band filters 15 and 20, highlighting narrow sections of the spectrum of the transmitted signal, where the dependence of the steepness of the spectrum envelope on frequency is most manifested. For example, for a television signal, it is advisable to choose the lower bandpass filter in the frequency domain (fo + 0.7, ..., fo + 1) MHz, where fo is the carrier frequency, and the upper bandpass filter (fo + 2 ... о + 4 ) MHz. Block 15 is connected through the amplitude detector 16 to the first input of the subtraction unit 18, and block 20 is connected through the amplitude detector 21 to the second input of the block 18. In the subtractor 18, the signal transmitted by the block 16 transmitted through the upper bandpass filter 15 is subtracted from the signal transmitted through the lower bandpass filter 20 and detector 21. The output of block 18 is connected to an integrator 19 designed to reduce the static error, the output of which is the output of the spectrum analyzer. The purpose of the spectrum analyzer is to generate a signal proportional to the steepness of the spectrum envelope of the signal fed to its input. Since the information signal in the spectrum analyzer is filtered and then detected, the signal at the output of the spectrum analyzer will occupy a frequency band much smaller than the information signal, so the bandwidth of the control channels is much smaller than the communication channels. This will result in significant noise immunity of the control signal and eliminates the need to consider the effect of interference on the control signal in the control channel and the feedback channel.

Let us consider how a control signal is generated for tuning blocks 3, 5. At the input of communication channel 4, spectrum analyzer 8 generates a signal proportional to

the steepness of the spectral envelope of the information signal processed by block 3. At the output of the communication channel, the spectrum analyzer 9 performs the same operation for a mixture of signal and additive interference. In block 11

0, the signal from block 8 is subtracted from the signal from block 9. As a result of subtraction, the signal component characterizing the steepness of the spectrum of the information signal is compensated, since the steepness

5, the spectrum of the information signal at the input and output of the communication channel is equal. At the output of block 11, a signal is generated proportional to the steepness of the interference spectrum operating in the communication channel. At the output of block 7

0, a signal is generated proportional to the steepness of the information signal spectrum. In block 14, the signal from block 11 is subtracted from the signal from block 7, so that a signal is generated at the output of the second subtraction block 14, which characterizes the difference between the slope of the spectrum of the information signal at the output of block 1 and the slope of the interference spectrum in the communication channel. If at the output of block 14 the signal has a positive polarity, then such a signal should go to the control input of block 23 and the control input of the whitening part of the correction filter, while to the control inputs of the predistortion part of the predistortion

5 of the filter and block 22, a zero signal will be given. If the signal at the output of block 14 has a negative polarity, then such a control signal goes to the control input of the predistortion part of the predistortion filter and through block 13 to the control input of block 22, while to the control inputs of block 23 and the whitening part of the correction filter a zero signal will be given. The control signal formers, which are part of blocks 3 and 5, are based on a non-inverting amplifier assembled on a DA2 (DA4) operational amplifier and R5, R6 (R11, R12) resistors in a standard connection

0 (see Fig. 3, 4), while the diodes VD1 and VD2 (VD3 and VD4) are connected to the amplifier output in the opposite connection. The output of the diode VD1 (VD4) is connected to the control input of the predistortion part of the predistortion filter 5 (block 22), and the output of the diode VD2 (VD3) is connected to the control input of block 23 (the whitening part of the correction filter).

In the proposed device, two delay units are used. The second delay block 10 serves to delay the signal from the spectrum analyzer 8 in order to more accurately compensate for the signal component in block 11. The delay time of the signal in block 11 is determined by the sum of the time the information signal travels through communication channel 4 and the signal transit time from the analyzer spectrum 9 through feedback channel 12. The first delay block 2 serves to delay the information signal in front of block 3 in order to more accurately predistort the signal. The signal delay time in block 2 is determined by the sum of the time needed to analyze the signal in block 7, the signal passing through block 14, and also adaptive filter tuning of block 3.

In the proposed device used predistortion and corrective filters. The electrical schematic diagram of the predistortion and filter is shown in Fig. 3, g of the correction filter in Fig. 4. In this case, the blocks 23 and 22 are T-shaped high-pass filters, for the adjustment of which field-effect transistors are used, which are switched on in the controlled resistance mode. The predistorting part of the predistorting filter is made on the basis of block 22 included in the negative feedback circuit of the amplifier with a high gain (see Fig. 3), and the whitening part of the correction filter is made on the basis of block 23 included in the negative feedback circuit of the amplifier ( see figure 4). The circuit thus implemented is shown in FIG. 6.10, p. 223 books of Marigodov V.K., Baburova E.F. Synthesis of optimal radio systems with adaptive predistortion and signal correction. - M.: Radio and Communications, 1985, p. 248. This scheme provides high accuracy of reciprocity of the transfer functions of the predistortion and correction filters,

Let us consider how the transmission characteristics of the filters are tuned depending on the control signal. In the proposed device, the high-pass filter is used as the predistorting part of the predistortion filter, and the low-pass filter is used as block 23, therefore, the low-pass filter is used as block 22, and the high-pass filter is used as the whitening part of the correction filter . As the low-pass filter, the lower part of the transfer function of the band-pass filter, i.e. from TH to fe (see figure 5). If a zero signal is applied to any of the control inputs of the predistortion filter, the transfer function of the filter is changed so that the entire information signal passes without distortion (see Fig. 6 a, b, curve 1). If the control signal is on the control the input of block 23 and the whitening part of the correction filter becomes greater than zero, this indicates that the slope of the spectrum of the information signal at the source output exceeds the slope of the interference spectrum in the communication channel, therefore it is necessary to amplify the information signal low frequencies and lower the low frequencies so that the steepness of the signal spectrum in the communication channel is equal to the steepness of the interference spectrum. Block 23 performs this function. Moreover, the greater the difference between the slope of the spectrum of the information signal at the output of block 1 and the slope of the interference spectrum in the communication channel, the greater the control signal and the greater the slope of the transfer function of block 23. This can be seen from FIG. .5, a. For curve 4, the control signal is greater than for curve 3; for curve 3 more than for curve 2, etc.

The predistortion portion of the predistortion filter and block 22 are controlled by a negative signal. Moreover, the more the negative control signal differs from zero, the greater the difference between the slope of the interference spectrum and the signal, the greater the steepness of the transfer function of the predistortion part of the predistortion filter (see Fig. 5, b for curve 4, the control signal is more different from zero, than for curve 3, etc.).

The device operates as follows.

The spectrum analyzer 8 at its output generates a signal proportional to the steepness of the spectrum of the information signal supplied to its input. A spectrum analyzer 9 of a mixture of an information signal supplied to its input and interference acting in a communication channel. From the output of the spectrum analyzer 8, the signal goes to the second delay unit 10, where it is delayed by the time necessary for the signal to pass through the communication channel 4 and feedback channel 12. As a result, 2 signals simultaneously pass to the first subtraction unit 11: information a signal transmitted through spectrum analyzer 8 and a delay line 10, and the same information signal but transmitted through communication channel 4, spectrum analyzer 9 and feedback channel 12, in total with the additive interference acting on the communication channel. As a result of the subtraction in block 11, the components of one information signal arriving at two different inputs are mutually compensated, and a signal proportional to the steepness of the interference spectrum acting in the communication channel appears at the output of block 11. This signal is fed to the second subtraction unit 14. In this case, from the output of block 1, the information signal is sent to the first delay block 2, where it is delayed until the transfer functions of the predistortion and correction filters are tuned, and to the first spectrum analyzer 7, at the output of which a signal proportional to the steepness of the spectrum is generated information signal at the output of block 1. At the output of block 14, as a result of subtraction, a signal is generated proportional to the difference in the steepness of the spectrum of the information signal at the output of block 1 from the steepness of cn The interference channel in the communication channel. This control signal goes to block 3 and adjusts the transfer function of the predistortion filter so that in the communication channel 4 the slope of the information signal spectrum is equal to the slope of the interference spectrum. At the same time, the same control signal passes through control channel 13 to block 5 and reconstructs the transfer function of the correction filter so that at the input of receiver 6 the information signal spectrum is completely restored. After the filters are tuned, the information signal from the delay line passes the predistortion filter 3, the communication channel 4 and the correction filter 5 to the information receiver 6, at the input of which the slope of the information signal spectrum will coincide with the slope of the interference spectrum, which will increase the noise immunity of the transmitted information.

Consider the operation of the device of the invention with various forms of the spectrum of the information signal and interference in the communication channel.

Assume that the spectrum of the information signal at the output of block 1 is uniform, the spectrum of the interference acting in the communication channel is also uniform (see Fig. 6). In this case, the slope of the signal spectrum coincides with the slope of the interference spectrum and is equal to zero. In this case, the signal at all control inputs of filters 3 and 5 is equal to zero, therefore, the transfer function of all filters will be uniform in the transmitted frequency band, and the information signal from block 1 to block 8 will be transmitted without changes (see Fig. 6, a , ..., g).

Assume that the plot of the transmitted information has changed, and the signal spectrum has become monotonically decreasing (see Fig. 7). As can be seen from Fig. 8, at higher frequencies the interference spectrum is superior to the signal spectrum. At the output of block 11, zero will be formed

signal because the interference spectrum is uniform. A positive signal will be generated at the output of the spectrum analyzer 7, the same signal will be generated at the output

block 14, and therefore at the control inputs of block 23 and the whitening part of the correction filter. Moreover, at the control inputs of the predistortion part of the predistortion filter and block 22 will be

0 zero control signal. Thus, the transfer function of the block 23 and the whitening part of the correction filter will be uniform in the transmitted frequency band from fH to fB, and the transfer function

5 of block 23 will be such that the slope of the information signal spectrum in the communication channel coincides with the slope of the interference spectrum, i.e. raising the amplitude of the upper frequencies and decreasing the amplitude of the lower ones. The whitening part of the correction filter will restore the initial signal spectrum at the receiver input. The steepness of the information signal spectrum will coincide with the steepness of the interference spectrum, which

5 provides noise-free transmission of information.

Assume that the interference spectrum in the communication channel has become monotonically increasing in frequency (see Fig. 8). As can be seen from Fig. 8,

0 the spectrum of interference at higher frequencies exceeds the spectrum of the signal. A negative polarity signal will be generated at the output of block 11. As a result of subtraction, a positive signal is generated at the output of block 14, which is larger in amplitude than in the case shown in Fig. 7. This will cause the transfer function of the second predistortion filter to become even more uneven, raising the amplitude

0 high frequencies and decreasing the amplitude of the lower ones. Which is necessary to ensure the same slope of the signal spectrum and interference in the communication channel (see Fig. 8d). Pass through correction filter 5, signal spectrum

5 restores its original shape, since the transfer characteristics of the corresponding parts of the predistortion and correction filters are mutually inverse.

0 Assume that the interference spectrum in the communication channel is uniform, and the signal spectrum has become monotonically increasing (see Fig. 9). In this case, at the output of block 11 there will be a zero signal, and at the output of block 7 - a signal of negative polarity, then at the output of block 14 there will be the same negative signal. This signal will be transmitted to the control inputs of the predistortion part of the predistortion filter and block 26, which will rebuild their transfer functions. At

this first predistortion filter provides suppression of the amplitude of the high frequencies and the amplification of the lower. This will make it possible to obtain the steepness of the signal spectrum in the communication channel equal to the steepness of the interference spectrum, which will increase the noise immunity of the device. At the same time, a zero signal will be supplied to the control inputs of block 27 and the whitening part of the correction filter, which will ensure uniform transfer functions of block 27 and the whitening part of the correction filter in the transmitted frequency band.The restoration of the original shape of the signal spectrum will be performed by block 26.

Assume that the interference spectrum in the communication channel has become monotonically decreasing (see FIG. 10). At lower frequencies, the interference spectrum is superior to the signal spectrum. In this case, a positive polarity signal will be generated at the output of block 11, and a negative polarity at the output of block 7. As a result of subtracting from the signal from block 7 the signal from block 11 at the output of subtracting block 14, a negative signal of a larger amplitude will be formed than in the previous case (see Fig. 9). This control signal will rebuild the transfer function of the predistortion part of the predistortion filter so that it amplifies the amplitude of the low-frequency signal and suppresses the amplitude of the high-frequency signal, and the unevenness of the transfer function is greater than in the previous case (see Fig. 9). In the communication channel, the steepness of the signal spectrum will be equal to the steepness of the interference spectrum, which will ultimately lead to an increase in the noise immunity of the transmitted information.

Let us conclude the calculation of the gain in noise immunity of the proposed device compared to the prototype device. Since the main disadvantage of the prototype is its low noise immunity for interference having a monotonically decreasing spectrum, we determine the effectiveness of the proposed device and prototype with such interference acting in the information and control channels. We will calculate the gain in noise immunity for the information channel, assuming that the control and feedback channels due to their narrowband and simplicity of the control signals have significantly greater noise immunity compared to the information channel.

Assume that the optimal adaptive correction filter in the prototype and the proposed device is an optimal Kolmogorov-Wiener linear filter. Then the minimum standard error for both devices is determined by the well-known formula

l

Cmin -

 G (α) N (fl) () In 0 G (α o) + N (u) (

where G (ftJ), N (o) are the spectral power densities of the signal and additive noise, respectively, at the input of the optimal linear filter;

Dy) - effective bandwidth of the information channel,

Let the information channel in the prototype device and the proposed device be influenced by interference concentrated in the low-frequency region of the signal spectrum, i.e. interference with a monotonically declining spectrum.

N (o) 1 / $ w,

(2)

where} Ј is a constant coefficient characterizing the frequency selective properties of the information receiver.

In the prototype device, the input of the optimal correction filter (Kolmogorov-Wiener optimal linear filter) receives an additive mixture of the interference bleached in the bleaching part of the correction filter with the spectrum N (o) No const and the signal with the uniform spectrum G (w) Go const predistorted signal through two series-connected filters (block 23 - in the transmitting path and the whitening part of the correction filter in the receiving).

In accordance with (1) for the prototype, we obtain the following value of the minimum mean square error

  AftjGoN0, 6 & 2gr (C0 + Mo) (3)

For the proposed device according to the expression (1) with a monotonically decreasing additive noise (2) we find

2 go w ...

Јmin - -7Г- J -------- 5-- (4) At 27Г о 1 + G0 + $ 0)

After integration and the simplest converted we get

BMIN "

4INu

In 11 + G0 + уЈЛм | , (5)

The gain in noise immunity of the proposed device compared to the prototype device is determined from the ratio

X Јminp / Јminu,

Using expressions (3) (5) and (6), we obtain

AujGp% (1 + q) ln (G0} ЈAu)

where q Go / No is the signal-to-noise ratio (power).

If we take 10, then from (7) we find

4.35

From the expression (8) it follows that the gain of the proposed device in noise immunity in comparison with the prototype increases with decreasing signal-to-noise ratio. So for q 1 # 2.18; at q 0.1% 3.96. The marginal payoff at q-1 is; 4.35.

Thus, under the most unfavorable conditions of the interference environment (low noise immunity of signals), the proposed device has a significant positive effect compared to the prototype device.

In addition to the obtained calculation of the gain, it should be noted that in the prototype it is completely impossible to carry out normal operation when switching from monotonically decreasing, since the first subtraction unit in the prototype device cannot fundamentally generate control signals

channels corresponding to different signs of the steepness of the change in the interference spectrum. In the proposed device, the presence of an additional second subtraction unit, as well as the structural refinement of the predistortion and correction filters, make it possible to eliminate this drawback, which also confirms the positive effect of the proposed device.

Claims (1)

.10 Claims A device for transmitting and receiving information, comprising a source of information, a series-connected predistortion filter, a communication channel, a correction filter, an information receiver, as well as first and second spectrum analyzers, a feedback channel, a subtraction unit and a control channel, characterized in that , in order to increase the noise immunity 20, two delay units, a third spectrum analyzer and a second subtraction unit are introduced, the information source being connected to the inputs of the first spectrum analyzer and the first delay unit, output 25 which is connected to the input of the prediction filter, the input of which is connected to the communication channel and to the input of the second spectrum analyzer, the output of which is connected to the input of the second delay unit, the output of the second delay unit 30 is connected to the first input of the first subtraction unit, the output of the first subtraction unit connected to the first input of the second subtraction unit, the second input of which is connected to the output 35 of the first spectrum analyzer, the output of the second subtraction unit is connected to the control input of the predistortion filter and to the input of the control channel, the output of which is connected to the control input of the correction filter, the input of which is connected to the output of the communication channel and to the input of the third spectrum analyzer, the output a third spectrum analyzer is connected to the input of the feedback channel, the output of which is connected to the second input of the first subtraction unit. Fi g. 2 L, L B about "22 I G K1pf x ° Kz i lz f. . (fen f I "1pf X l  I I B FIG. 7 1ig. B