JPS6043928A - Automatic frequency distortion compensating device - Google Patents

Abstract

PURPOSE:To compensate automatically transmission distortion by inserting the transmission distortion produced on a transmission line due to multi-path fading to a receiver having a specific transmission characteristic. CONSTITUTION:A transmission distortion compensating circuit DCC-2 consists of hybrid circuits H-3, H-4, circuit rho having the vibrating ratio rho between a direct wave and an interference wave, circuit tau having a time difference tau between the direct wave and the interference wave, and a circuit phi producing a phase difference phi. Then a feedback loop is constituted via a control section CONT-2. The transmission distortion is compensated automatically by using the feedback loop by reducing the transmission characteristic of the circuit DCC-2 to Hc(omega)=1/ (1+rhoexp-j(omegatau+phi)).

Description

DETAILED DESCRIPTION OF THE INVENTION [a) Technical Field of the Invention The present invention relates to a frequency distortion compensator, and particularly to a propagation distortion compensator applied to a multilevel digital radio device.

(+)) Conventional technology and problems When sending a digital radio signal at a diagonal speed to the other station using a digital wireless device, the direct wave and the interference generated depending on the propagation path condition are simultaneously transmitted to the receiver of the other station. Join, Figure 2 tal
As shown in the figure, a tip may occur in the reception level.

Frequency distortion caused by such multipath fading V is caused by, for example, two-phase or four-phase PSK (Phase Shift
Keying) It is not a problem for waves, but 1
This has a very large effect on multi-level modulated waves such as 6-fold orthogonal width modulated waves, and the line quality deteriorates.

FIG. 1 is a schematic block connection diagram for implementing a conventional propagation distortion compensation method, and FIG. 2 is a diagram for explaining the operation of the block connection diagram of FIG. 1.

The operation shown in FIG. 1 will now be explained with reference to FIG.

First, a received wave with a dip caused by multipath fading as shown in Figure 2+a+ is applied to a receiver (not shown), and the propagation distortion shown in Figure 1 is applied to the rear cylinder such as amplification 9 and frequency conversion. 1 added to the compensation circuit DCC-1. This circuit is a parallel resonant circuit consisting of a capacitor C and a wire ring, which is connected between the connection point of the series-connected amplifiers A-1 and A-2 and the ground. 12, the frequency characteristics are the opposite of the shape shown in FIG. 2 (al), as shown in FIG. 2 (1).

In addition, Fig. 2 (shape of the dip of al and center frequency f-
0, in order to match the Q and resonant frequency of the parallel resonant circuit shown in Figure 1, a part of the output signal of amplifier A-2)
In addition to l+Ii control unit C0NT-4, this control unit C0NT
t['l! from -1 This is done by changing the values of the variable resistor R and variable capacitor C using a control signal.

However, in order to compensate for the propagation distortion due to deep fading that causes steep dips, the Q of the parallel resonator must be increased, which inevitably results in The insertion loss increases, and due to the asymmetric resonance characteristics of the resonator, it cannot be completely compensated, and as shown in Figure 2 fc), an equalization residual remains and the bit error rate worsens. There were other problems.

(C1 Purpose of the Invention The present invention has been made in view of the above-mentioned problems of the prior art.It is an object of the present invention to provide a propagation distortion compensation method for preventing line quality from deteriorating even if multipath fading occurs in a propagation path. The purpose is

fdl Structure of the Invention The object of the above invention is to provide a receiver with a circuit having transmission characteristics such as -j(ωτ+φ) He(ω)=1/(1+ρe) to reduce the propagation distortion caused in the propagation path due to multipath fading. This is achieved by providing a propagation distortion compensator characterized by fully automatically compensating propagation distortion.

Embodiment of the Invention FIG. 3 is a diagram of an equivalent circuit of multipath 117 aging.

In the figure, ρ is the circuit where the amplitude ratio of the direct wave and interference wave is ρ,
τ is a circuit where the time difference between the propagation paths of direct waves and interference waves is τ, φ is a circuit that provides a phase difference φ, H-1 and H-2 are hybrid circuits, 1 is an input terminal, and 2 is a circuit that provides a phase difference φ. The output terminals are shown respectively.

In Figure 3, the wave applied to input terminal 1 is Hypuri,
The signal is divided into a direct wave with an amplitude of 1 passing through the path 1 and an interference wave with an amplitude 1 passing through the path 2 in the path H-1.

The direct wave continues as it is and is added to the hybrid circuit H-2. On the other hand, the interference wave that has proceeded to the path ■ undergoes changes such that the amplitude becomes ρ in the circuit ρ, the time difference with the direct wave becomes τ in the circuit τ, and the phase difference becomes φ in the circuit φ, and then the hybrid circuit H-
The direct wave and interference wave added here are taken out from the output terminal 2 as output waves.

This output wave Y is expressed as follows.

-Nωτ+φ) y=x+xρe Here, the first term indicates a direct wave, and the second term indicates an interference wave.

Therefore, the transmission characteristic H-1(ω) of this equivalent circuit is as follows.

-j(ωτ+φ) H-1(ω)=X/Y=1+ρe In other words, this transmission characteristic H-1(ω) exhibits a fading characteristic, and a circuit with completely opposite transmission characteristics should be inserted into all receivers. If so, this aging characteristic can be completely compensated for and its shadow can be eliminated.

Therefore, the transmission characteristics of the propagation distortion compensation circuit are expressed by the following formula. VC compensation can be provided.

Further, τ is set to the average path difference length of the propagation path.

FIG. 4 is a block connection diagram for implementing the present invention.

In the figure, ■-3 and H-4 are hybrid circuits, DCC
-2 indicates a propagation distortion compensation circuit, and C0NT-2 indicates a control section.

Note that the same symbols as in Figures 2g and 3 represent the same parts.1 This circuit includes the propagation distortion compensation circuit DCC-2 and the 1tll control unit C0NT-.
2, and the transmission characteristics of the former circuit DCC-2 are expressed as (
This circuit forms a feedback loop in order to make the transmission characteristics the same as shown in equation 1).

Note that if ρ>1, this system will oscillate, so it must be ρ>1. Further, the output signal is not limited to the output of the hybrid 4, and may be extracted from any of the outputs of the phase shifter φ, the attenuator ζ, and the hybrid 3. Further, the ρ, φ, and τ portions can each be configured with a variable attenuator, a phase shifter, and a delay line, and this propagation distortion compensation circuit is inserted, for example, between the intermediate frequency amplifier and demodulator of the receiver.

Fig. 5 is a diagram showing the performance of the propagation distortion correction circuit DCC-2 shown in Fig. 4. Fig. 5 fal shows the frequency characteristics of this circuit, and Fig. 5 (()) shows the performance of the propagation distortion correction circuit DCC-2. The frequency characteristics of the subsequent received waves are shown respectively.

FIG. 6 is a diagram for explaining a control method of the ft1lj controller C0NT-2 to completely compensate for propagation distortion as shown in FIG. 5(1)).

Generally, when looking at the spectrum of a modulated wave modulated by a digital signal over time, it has a flat top surface as shown at 181 in FIG.

Therefore, as shown in the figure, if the energy around frequencies f-2, f-1, and f-3 on both sides of the spectrum is extracted using a narrow band filter with exactly the same characteristics, the extracted power will all be the same. -I know.

Now, when propagation distortion is applied, the waveform shown in FIG. 6 181 is distorted, and the corresponding power is extracted.

For example, if the power shown in Figure 6 (bl) is obtained,
Comparing the power extracted at points f-1 and f-3, the power at f-3 is greater, so the center frequency is f-2.
I understand that it is more to the left, so I need to move it to the right.

Also, since the magnitude of the dip is the difference between the power of (f-1)+(f-3)/2 and the power of f-2, it is necessary to increase Q to make the dip zero.

Since the direction to be controlled has been decided, f-1゜f-2, f
The parts of ρ and φ are controlled so that the respective powers of -3 are equal.

ffl As described in detail, according to the present invention, propagation distortion caused by half-path fading can be completely compensated for by inserting a circuit having the transmission characteristics shown in equation (1) into the receiver. This makes it possible to prevent the quality of digital transmission lines from deteriorating.

[Brief explanation of drawings]

Figure 1 is a conventional professional connection diagram for implementing the propagation distortion compensation method, and Figure 2 is a diagram for explaining the function of Figure 1.
Figure 3 shows how many circuits with multipath fading are used.
Figure 5 shows a block connection diagram for implementing the present invention'fc.
This figure shows the performance of FIG. 4, and FIG. 6 shows a diagram for explaining the control method of the control section shown in FIG. 4. In the figure, ρ is a circuit where the amplitude ratio is ρ, τ is a circuit where the time difference between the propagation paths of the direct wave and interference wave is τ, and φ is the phase difference φ
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〉1...No. ” is corrected as follows. "If ρ>l, this system will oscillate, so it must be ρ<l." (3) "Attenuator ζ" on page 7, line 2 of the specification should be replaced with "attenuator ρ
” he corrected. (4) Revise Figure 2 of the drawing as shown in the attached sheet. Figure 2 (a) (b) (C) ta1

Claims (1)

[Claims] Means for appropriately adding a received input signal subjected to frequency adjustment to the received input signal through a variable delay circuit, a phase shifter, and a variable attenuator, and so that the spectrum of the output signal after synthesis becomes a predetermined spectrum. and means for automatically controlling a variable attenuator and a variable phase shifter.