JPS62179229A - Propagation distortion compensation system - Google Patents

Abstract

PURPOSE:To equalize the amplitude and delay corresponding to various fading characteristics by using a tap coefficient so as to decide the fading characteristic and controlling an equalizing section so as to form an opposite characteristic to the fading characteristic depending on the result of deciding thereby compensating the propagation distortion. CONSTITUTION:A waveform of a reception signal demodulated by a demodulation section 4 is equalized automatically by a transversal automatic equalizer 1, a fading discrimination section 2 compares and references plural tap coefficients of the transversal automatic equalizer 1 to decide the fading characteristic depending on the quantity of the amplitude of a dielectric wave and an interruption amplitude, the result of deciding controls the equalizing section 3 equalizing a reception signal thereby compensating the propagation distortion. That is, each tap coefficient is controlled corresponding to the waveform distortion in the transversal automatic equalizer 1 and since the waveform distortion changes depending on the fading characteristic, the fading deciding section 2 compares and references the tap coefficients of the transversal automatic equalizer 1 so as to decide the fading characteristic whether or not the amplitude of the direct wave has a larger fading than the interference wave amplitude.

Description

[Detailed Description of the Invention] [Summary] Since each tap coefficient of the transversal automatic equalizer is controlled to compensate for waveform distortion, the fading characteristics are determined using the tap coefficients, and the fading characteristics are determined. The equalizer is controlled based on the determination result so that the characteristics are inverse to the fading characteristics, thereby compensating for propagation distortion, and the amplitude and delay can be equalized in response to various fading characteristics. .

[Industrial application field]

The present invention relates to a propagation distortion compensation method for compensating for deterioration of propagation path characteristics during fading in a digital wireless communication method.

Wireless communication systems often receive two or more radio waves with different propagation path lengths due to reflection or refraction, and fading occurs in which the combined electric field strength and amplitude/delay frequency characteristics vary depending on the phase difference between each received wave. occurs. This fading distorts the demodulated waveform, increases code amount interference, and causes errors in identification codes, which seriously affects the digital wireless communication system. Therefore,
It is necessary to compensate for the deterioration of propagation path characteristics due to fading.

[Conventional technology]

Fading caused by the direct wave and the interference wave has the characteristics shown in FIG. 12 when the direct wave amplitude is larger than the interference wave amplitude. That is, the frequency r.

In this case, the amplitude characteristic Hc decreases and the delay characteristic τ becomes a large delay characteristic. On the other hand, when the direct wave amplitude is smaller than the interference wave amplitude, as shown in FIG. 13, the amplitude characteristic Hc decreases at the frequency fo, but the delay characteristic τ becomes a leading characteristic.

In order to compensate for such fading characteristics, conventionally,
Various methods have been adopted. For example, a variable resonance automatic equalizer is used to change the resonance frequency and sharpness (Q) based on the detection information of, for example, three points in the spectrum of the equalized output. A characteristic opposite to the amplitude characteristic Hc was formed, thereby compensating for the depressed amplitude characteristic.

[Problems to be solved by the invention] Compensation for propagation distortion by a conventional equalizer is as shown in FIG.
This is done using a characteristic opposite to the amplitude characteristic Hc shown in Figure 3, and if the direct wave amplitude is always larger than the interference wave amplitude,
This can be compensated for by using the aforementioned variable resonance automatic equalizer, etc., but if the amplitude of the interference wave becomes large and the fading characteristics shown in Fig. 13 occur, when the amplitude characteristic Hc is compensated, the delay characteristic τ becomes Since the case is inverted with respect to the case of FIG. 12, the delay characteristic of the resonant circuit is further added to the delay characteristic τ of the propagation path, which has the disadvantage that the delay characteristic is further deteriorated.

The present invention identifies fading characteristics by using tap coefficients of a transversal automatic equalizer that performs waveform equalization,
The purpose of this is to enable compensation of amplitude characteristics without deteriorating delay characteristics.

[Means for solving problems]

In the propagation distortion compensation method of the present invention, waveform distortion occurs depending on the fading characteristics, and the tap coefficient of the transversal automatic equalizer changes in response to the waveform distortion, so this tap coefficient is used to determine the fading characteristics. The first
This will be explained with reference to the figures. Transversal automatic equalizer 1
The waveform of the received signal demodulated by the demodulator 4 is automatically equalized by
The fading characteristic based on the magnitude relationship between the direct wave amplitude and the interference wave amplitude is determined, and the equalization unit 4 that equalizes the received signal is controlled based on the determination result to compensate for propagation distortion.

[Effect]

The transversal automatic equalizer 1 controls each tap coefficient in response to waveform distortion, and since the waveform distortion changes depending on fading characteristics, the transversal automatic equalizer 1 is controlled in the fading determination section 2. By comparing and referring to each tap coefficient, fading characteristics such as whether the direct wave amplitude is fading larger than the interference wave amplitude are determined. For example, when the notch frequency is at the center of the band, fading characteristics can be determined based on the magnitude relationship of the in-phase tap coefficients. The equalizer 3 is controlled based on the determination result of this fading characteristic. For example, in the case of fading characteristics where the interference wave amplitude is larger than the direct wave amplitude, equalization by the variable resonance automatic equalizer is stopped. , it is possible to prevent deterioration of delay characteristics.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 2 is a block diagram of an embodiment of the present invention, in which 11 is a transversal automatic equalizer, 12 is a fading determination section, 13 is a variable resonance automatic equalizer, 14 is a demodulation section, 1
5 is a variable resonance circuit, 16 is an equalization control section, 17 and 18 are amplifiers, 19 is a variable attenuator composed of a PIN diode, etc., 20 is a variable capacitor composed of a varactor diode, etc., and 21 is a resonance circuit together with the variable capacitor 20. is the inductance that makes up the

The equalization control unit 16 of the automatic equalizer 13 detects the dip frequency due to fading of the intermediate frequency signal, and controls the variable attenuator 19 based on the detection information of the three points of the spectrum of the equalized output to achieve variable resonance. The Q of the circuit 15 is set to a value corresponding to the amount of dip, and the variable capacitor is controlled so that the resonance frequency becomes the dip frequency, and amplitude equalization is performed so that the spectrum of the equalized output becomes flat.

Further, the intermediate frequency equalized output signal of the automatic equalizer 13 is sent to the demodulator 1.
4 and applied to the transversal automatic equalizer 11, where waveform equalization is performed.

Each tap coefficient of the transversal automatic equalizer 11 is applied to a fading determination section 12, and fading characteristics are determined.

As described above, the variable resonance automatic equalizer 13 can compensate for the fading characteristics when the direct wave amplitude is larger than the interference wave amplitude, so the fading determination unit 12 determines that the fading characteristics are the same. Then, the variable resonance circuit 15 is controlled by the equalization control section 16. However, this variable resonance automatic equalizer 13 cannot compensate for fading characteristics when the interference wave amplitude is larger than the direct wave amplitude, so when determining such fading characteristics, the fading determination section 12 Equalization control section 1
6 to make the amount of attenuation by the variable attenuator 19 zero. This eliminates the influence of the resonant circuit and the received signal is directly applied to the demodulator 14, thereby preventing the delay characteristics from deteriorating.

FIGS. 3 and 4 are block diagrams of a 5-tap transversal automatic equalizer. In the same figure.

, 22-29 are delay circuits (T), 30-49 are coefficient units,
50.51 is an adder, 52.53 is a discriminator, 54-61
is a delay circuit (T), 62 is a group of exclusive OR circuits, 63 is an integrator, 64 is an amplifier, 65 is an integrator 63. amplifier 64
This is the circuit containing.

The demodulated in-phase signal Iin is sequentially delayed by delay circuits 22 to 25 and applied to coefficient multipliers 30 to 39, and the orthogonal signal Qin is sequentially delayed by delay circuits 26 to 29 and applied to coefficient multipliers 40 to 49. . The in-phase components passed through the coefficient units 35 to 39 and the orthogonal components passed through the coefficient units 40 to 44 are added to an adder 50, and the output signal AI is added to a discriminator 52. Further, the in-phase components via the coefficient units 30 to 34 and the orthogonal components via the coefficient units 45 to 49 are added to an adder 51, and the output signal AQ is applied to a discriminator 53.

The discriminators 52 and 53 discriminate the levels of the addition output signals AI and AQ, for example, the 2-bit signals IPI and 2-bit signals, respectively.
IP2. QPI and QP2 are output and transferred to a subsequent processing circuit (not shown). Further, the discriminators 52 and 53 apply the error signal to the delay circuits 54 and 58, and the polarity signal to the delay circuit 5.
It will be added to 6.60. A correlation detection circuit is configured by exclusive OR circuit group 62 and circuit 65, and control signals 2CI, ICI, OCI, -IC1, -2CI.

2Dr, ID1. ODI, -IDI, -2DI.

2CQ, ICQ, OCQ, -ICQ, -2CQ.

2DQ, IDQ, ODQ, -IDC, and -2DQ are applied to coefficient multipliers 30 to 49, respectively. Thereby, the tap output signals from the delay circuits 22 to 25 and 26 to 29 are controlled by the coefficient multiplier, and waveform equalization is performed.

FIGS. 5 and 6 are explanatory diagrams of examples of in-phase tap coefficients and quadrature tap coefficients in the transversal automatic equalizer configured as described above, and the delay time is 6.3n S s Center frequency fo = 12.5 MHz So, the curve a w in Figure 5
h is the notch frequency f. +0゜・・・fo+7(MH
z) and curve 3-g in FIG. 6 is the notch frequency f. 10, ... Regarding fo+6 (MHz),
Other in-phase tap coefficients C,, C, for the central in-phase tap coefficient C8 when the direct wave amplitude is larger than the interference wave amplitude.

c-1t Amplitude ratio with C-z (Fig. 5) and orthogonal tap coefficients Do, D+, Dz, I)-1t
It shows the amplitude ratio (FIG. 6) with D-z.

Contrary to the cases shown in FIGS. 5 and 6, when the interference wave amplitude is larger than the direct wave amplitude, the center tap coefficient C8, Do
The polarities of the tap coefficients C9 and c, c2 and CZ, Dl and D-I, and D2 and D-2, which are located symmetrically to each other, do not change in polarity, but their respective values become opposite. Also, if the notch frequency is lower than the center frequency fo, the in-phase tap coefficient Co+
C++Cz+C-I and C-2 do not change, but the polarities of the orthogonal tap coefficients D0, D+, Dz, D-+ and D-z are reversed.

Therefore, when the notch frequency matches the center frequency fo, as can be seen from the curve a in FIG.
−+ or C2>c−, it can be determined that the direct wave amplitude is larger than the interference wave amplitude, and the fading determination unit 12 causes the equalization control unit 12 to perform normal equalization control. to control. Also, contrary to the above condition, C, <C
-, or C2<C-2, it is determined that the direct wave amplitude is smaller than the interference wave amplitude, and the fading determination unit 12 controls the equalization control unit 16 to 16 controls the attenuation amount of the variable attenuator 19 to be zero. As a result, the equalization operation is stopped, and deterioration of the delay characteristics can be prevented.

If the notch frequency is other than the center frequency, as shown by the curve C+g*h in FIG. 5, it will be difficult to make a determination using only the above-mentioned conditions. In that case, the relationship between the orthogonal tap coefficients shown in FIG. 6 is also used for determination. Therefore,
The fading determination unit 12 may be configured with a comparison circuit for comparing tap coefficients and a logic circuit, or its function may be realized by a program-controlled processor.

FIG. 7 is a block diagram of another embodiment of the present invention, 71
72 is a transversal automatic equalizer; 72 is a fading determination unit; 73a and 73b are automatic equalization units each having different equalization characteristics and opposite propagation path characteristics; 74 is a demodulation unit;
75a and 75b are switching circuits. The automatic equalizer 73a includes, for example, an amplifier 76 and an adder 7, as shown in FIG.
7 and a feedback circuit 78, the input signal Vin is converted to 1/a by an amplifier 76 and is applied to the adder 77, and the output signal Vout is applied to the adder 77 via the feedback circuit 78 having a characteristic of b6-Jlllτ. So, the transfer function Hb
(ω) becomes .

Further, the automatic equalizer 73b, for example, as shown in FIG.
Amplifier 79. Consisting of an adder 80 and a circuit 81, the adder 80 adds the input signal Vin passed through the amplifier 79 with a gain of -1/a and the output signal Vout, and
)e-" output signal Vout through the circuit 81 with the characteristic of T.
The transfer function Hb(ω)1 is as follows. That is, the automatic equalizers 73a and 73b have opposite characteristics.

When the fading determination unit 72 determines that the direct wave amplitude is larger than the interference wave amplitude, as shown in the figure, the automatic equalizer 73a is connected by the switching circuit 75a to perform automatic equalization, and vice versa. When it is determined that the interference wave amplitude is larger than the direct wave amplitude as fading, the switching circuit 73a is turned off, the switching circuit 73b is turned on, and the automatic equalizer 73b is connected to perform automatic equalization. In this case, since the automatic equalizer 73b can form a characteristic opposite to the propagation path characteristic, amplitude equalization can be performed without deteriorating the delay characteristic.

FIG. 10 is a block diagram of an automatic equalizer, showing an example of the configuration for realizing the functions shown in FIG. 8. In the figure, 82 is an amplifier with a gain of 1/a, and 83 is a 3 dB
Directional coupler, 84 is a 10 dB directional coupler, 85 is a low-pass Soil 4 router with delay time τ, 86 is a variable attenuator, 8
7 is an amplifier. A feedback circuit 7B is configured by the low-pass filter 85, variable attenuator 86, and amplifier 87, and the output signal Vout separated by the 10 dB directional coupler 84 is applied to this circuit. Also, 3dB directional coupler 8
3 constitutes an adder 77, and the output signal Vout via the feedback circuit is added to the input signal Vin via the amplifier 82. Therefore, an adaptive automatic equalizer having characteristics opposite to the amplitude characteristics and delay characteristics shown in FIG. 12 described above is constructed.

FIG. 11 is an example block diagram for realizing the functions shown in FIG. 9, where 88 is an amplifier with a gain of 1/a, and 89 is a 3
B directional coupler, 90 is an amplifier with gain l/b, 91 is a variable attenuator, 92 is a low-pass filter with delay time τ, 93
is a 10 dB directional coupler. The circuit 81 in FIG. 9 is configured by the amplifier 90, the variable attenuator 91, and the low-pass filter 92, and the adder 80 is configured by the 3 dB directional coupler 89.
An output signal VOut separated by a 10 dB directional coupler 93 is added to in. Therefore, an adaptive automatic vase having amplitude characteristics and delay characteristics opposite to those shown in FIG. 13 is constructed.

In the above embodiment, the automatic equalizers 73a and 73b with different equalization characteristics are connected in parallel to the input signal, and the switching circuits 75a and 75b connect the automatic equalizers 73a and 73b. It is also possible to connect automatic equalizers in series and switch to stop the equalization operation of either one according to the determination result of the fading determination section 72.

〔Effect of the invention〕

As explained above, the present invention compares and refers to a plurality of tap coefficients of the transversal automatic equalizer l, thereby determining fading characteristics in which the magnitude relationship between the direct wave amplitude and the interference wave amplitude is different, and determining the fading characteristics. It performs equalization control according to the characteristics, and in the case of fading characteristics where the interference wave amplitude becomes large, the equalization operation by the normal automatic equalizer is stopped to prevent the delay characteristics from deteriorating. Alternatively, equalization control can be performed by switching and connecting automatic equalizers with characteristics opposite to the propagation path characteristics in this case. Therefore, there is an advantage that the fading characteristics in the digital wireless communication system can be determined and propagation distortion can be compensated for without deteriorating the delay characteristics.

[Brief explanation of drawings]

Figure 1 is a block diagram of the principle of the present invention, Figure 2 is a block diagram of an embodiment of the present invention, Figures 3 and 4 are block diagrams of a transversal automatic equalizer, and Figure 5 is an in-phase tap coefficient. FIG. 6 is an explanatory diagram of orthogonal tap coefficients, FIG. 7 is a block diagram of another embodiment of the present invention, FIGS. 8 and 9 are functional block diagrams of an automatic equalizer, and FIG. 11 is a block diagram of the automatic equalizer, and FIGS. 12 and 13 are explanatory diagrams of fading characteristics. 1 is a transversal automatic equalizer, 2 is a fading judgment section, 3 is an equalization section, 4 is a demodulation section, 11゜71 is a transversal automatic equalizer, 12.72 is a fading judgment section, 13 is a variable resonance type 73a and 73b are automatic equalizers with different characteristics, and 14, 74.75a and 75b are switching circuits.

Claims (2)

[Claims] (1) A fading determination section (2) is provided which compares and refers to a plurality of tap coefficients of the transversal automatic equalizer (1) to determine fading characteristics of a received wave, and the fading determination section (2) an equalizer (3) that equalizes the received signal according to the fading characteristics determined in the step;
) is a propagation distortion compensation method. (2) The propagation distortion compensation method according to claim 1, wherein the equalization section (3) has a configuration in which the equalization characteristic can be switched by the fading determination section (2).