JPS5868340A - Fading generator - Google Patents

Abstract

PURPOSE:To estimate the amount of delay distortion in a fading generation period, to improve symmetry, and to evaluate equivalent characteristics accurately, by providing a delay equalizer to one of two paths for distributing an input signal. CONSTITUTION:An input signal from an input terminal 1 is distributed into two by a distributor 2 to the path composed of a delay line 3 and the path of a variable phase shifter 4, a variable attenuator 5, a delay equalizer 9, and a delay line 6; and the outputs of both the paths are synthesized by a synthesizer 7, whose output is outputted from an output terminal 8. This delay equalizer 9 is provided on the output side of the variable attenuator 5 to equalize delay distortion generated on a reflecting path, and the attenuation amount of frequency characteristics is made symmetrical on a prescribed frequency, thus evaluating equivalent characteristics accurately.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a fading generator that generates fading characteristics based on a two-wave interference model.

A fading generator is used, for example, when evaluating a fading equalizer for equalizing selective fading that occurs in wireless transmission, or when evaluating selective fading of the transmission path itself. Then, after dividing the input signal into two paths and applying an appropriate amount of phase shift using a variable phase shifter on one path,
Two paths are combined to obtain desired fading characteristics.

By the way, when realizing the above fading generator, it is required to be able to sufficiently simulate an ideal fading model, but this requirement has not always been met in conventional fading generators. That is,
If an attempt was made to make the dip in the fading characteristic appear continuously over a wide band, the resulting fading characteristic would become asymmetrical around the dip frequency and would not match the fading model.

Therefore, an object of the present invention is to provide a fading generator that has good symmetry with respect to the Fenong Dizzo frequency and matches the fading model based on two-wave interference.

In the fading generator according to the present invention, the cause of the aforementioned asymmetry in the fading characteristics back and forth around the dip frequency is that the variable phase shifter disposed on one path is generally narrow-band, which causes delay distortion. Because it is believed that this is the case, the present invention is characterized in that a delay equalizer for equalizing the delay distortion is provided in the path that generates this delay distortion.

A more detailed explanation will be given below with reference to nine drawings.

FIG. 1 is a block diagram of a conventional fading generator. In the figure, the input signal from input terminal 1 is passed through divider 2 to 2
a path consisting of a delay line 3 (hereinafter referred to as a direct path), a variable phase shifter 4, a variable attenuator 5, and a delay line 6.
(hereinafter referred to as the reflection path). By combining the direct path and the reflected path by the combiner 7, a selective fading characteristic based on a two-wave interference model is obtained, and multiple outputs are outputted from the output terminal 8. In order to obtain desired fading characteristics, the phase shift amount of the variable phase shifter 4, the attenuation amount of the variable attenuator 5, and the electrical length of the delay line are adjusted.

In the fading generator configured as shown in FIG. 1 above,
As I briefly explained earlier, if the fading characteristics of the Fa-Song characteristic are realized in a wide band and continuous manner, the fading characteristics that occur even though the amplitude characteristics of the direct path and the reflected path are both flat. The problem was that it became asymmetrical around the Ditsuno frequency, which caused it to no longer match the fading model, making it incompatible with ideal fading evaluations. First, I will explain the principle of selective fading, and then explain that the two factors that cause the above drawbacks are mainly the
The relationship with the asymmetry of fading characteristics due to delay distortion will be explained. Note that a specific example of the above-mentioned fading characteristics is illustrated along with the fading characteristics obtained by the present invention, which will be explained later.

FIG. 2 is a diagram showing the principle of selective fading caused by two-wave interference. Fading is a direct wave (A-B) and 0
It is generated by combining with the reflected waves (A to C-B) reflected by the point, and its amplitude characteristic X←) is the amplitude of the direct wave by 1
If so.

X(P)=[:1+r2+2rom(Δτω+θ)]2
−[1+r2+2r part (Δτ(ω-ω0)+π)]2・
...Represented by (1). Here r is the amplitude of the reflected wave, Δτ
represents the arrival time difference between the direct wave and the reflected wave, θ represents the phase difference between the direct wave and the reflected wave, and ω0 represents the angular frequency at which the dip occurs, respectively.

Since equation (1) is an even function with respect to Ditsuno's angular frequency ω0, the amplitude characteristics are symmetrical with respect to ωG. By the way, the variable phase shifter 4 included in the configuration of FIG. 1 is generally composed of an inductance L and a capacitance C, and when viewed over a wide band, delay distortion always occurs. As a result, in conventional fading generators, Δτ in equation (1) becomes a higher order function of ω, and if it is an odd order, the even symmetry with respect to ω0 of Fig. 3 is a block diagram showing an embodiment of a fading generator according to the present invention that eliminates the above-mentioned drawbacks.

In the figure, the two reflection paths include the delay distortion (
Mainly generated by the variable phase shifter. ) is provided, and other circuits with the same symbols as in FIG. 1 are the same as in FIG.

Here, in order to clarify the effect of the delay equalizer 9, let us consider the delay distortion generated in the two reflection paths.

Suppose that the delay characteristic τ←) at this time is expressed by the following equation.

On the other hand, assuming that there is no delay distortion in the direct path, that is, the delay time τ←) of the direct path is constant regardless of the frequency, the amplitude characteristic of fading when the two reflection paths have the delay characteristic of equation (2) is as follows. becomes.

X←)= (1+r2+2-Δτ(ω-056)+π9
(ω-ωo)2+? (ω-ωo)'+-))"...(
3) Next, as shown in Figure 3, the inverse characteristic of equation (2), that is, Ql19
Consider the case where a delay equalizer is inserted such that the sign of 2 is opposite to that of equation (2). In this case, τ←)=const, the fading characteristic is reduced to equation (1), and an ideal fading characteristic is obtained. The above is the principle of the fading generator according to the present invention.

FIG. 4 shows the amplitude characteristics of the fading generator according to the present invention shown in FIG.
40MHz, r=0.97 eΔT=1.67
2 is a diagram illustrating an example of the amplitude characteristic of the n5ec and an example of the amplitude characteristic of the conventional fading generator previously explained in FIG. 1. FIG. In the figure, failure p, Into is an example of the characteristics of a conventional fading generator, which is 1 nsec/40M per reflection path.
1 (indicates a case where first-order delay distortion of z occurs).

On the other hand, the solid line 11 is an example of the characteristics of the fading generator according to the present invention, and the delay equalizer produces 1nsee/40MH.
This is a case where the first-order delay distortion of z is equalized. As can be seen from this figure, in the conventional fading 3 generator, 1
Whereas the asymmetry at points 40 MHz ± 25 MHz apart was approximately 1.5 dB.

No asymmetry occurs in the fading generator according to the invention. In addition, the first-order delay distortion 1 of the reflection path shown in the specific example
The value n5ec/40MHz is an amount that occurs quite commonly when a variable phase shifter is implemented in the -140MHz band.

As explained above, according to the present invention, it is possible to provide a fading equalizer with good symmetry, and therefore, it is possible to more accurately evaluate the equalization characteristics of the fading equalizer. In addition, if a continuously variable type L generator is used as the delay etc., and the fading shape that actually occurs is realized by the fading generator according to the present invention, it is possible to estimate the amount of delay distortion in the fading interval. can.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a conventional fading generator. Fig. 2 is a diagram showing the principle of fading generation, Fig. 3 is a block diagram of an embodiment of the present invention, and Fig. 4 is a diagram comparing the characteristics of a conventional fading generator and a fading generator according to the present invention. A certain O Symbol explanation = 1 is an input terminal, 2 is a distributor, 3 is a delay line, 4 is a variable phase shifter, 5 is a variable attenuator, 6 is a delay line, 7
8 is a synthesizer, 8 is an output terminal, and 9 is a delay equalizer.

Claims (1)

[Claims] 1) In a fading generator configured based on a two-wave interference model, in which an input signal is distributed to two paths, one of which includes a variable phase shifter, and then combined to cause fading, a delay is added to one of the paths. A fading generator comprising an equalizer.