JPS6227577B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a fading simulator that simulates selective fading that occurs in a wireless transmission path.

In general, for communications performed via a wireless transmission path, it is necessary to consider the influence of fading that occurs on the transmission path. Regarding this problem, in parallel with theoretical analysis, measurement of transmitter-receiver characteristics on a transmission path where fading exists is required. What is needed in such cases is a fading simulator that can generate fading that occurs in nature in a laboratory.

Fading can be broadly divided into Rayleigh fading, in which the level of the entire transmission band changes;
It can be classified as selective fading, in which a portion of the level within the transmission band changes.

Conventionally, regarding simulation devices for the former,
Various methods have become known, but regarding the latter, there is no known method that characterizes selective fading with a small number of parameters.

An object of the present invention is to provide a selective fading simulator that can characterize selective fading with a small number of parameters. The present invention includes a first orthogonal noise modulation circuit that applies amplitude modulation to an input signal and a signal having a phase difference of 90 degrees from the input signal using independent Gaussian noise, and a first orthogonal noise modulation circuit that applies amplitude modulation to the input signal and a signal having a phase difference of 90 degrees from the input signal; and a second orthogonal noise modulation circuit that inputs the output of the attenuator through an attenuator, and an addition circuit that adds the outputs of the first and second orthogonal noise modulation circuits, the delay amount of the delay element and The fading simulator is characterized in that a signal subjected to pseudo-selective fading whose characteristics can be changed depending on the amount of attenuation is obtained from the output of the adder circuit. According to this invention, various types of selective fading can be generated by changing two parameters: the delay amount of the delay element and the attenuation amount of the attenuator.

Next, the present invention will be explained in detail with reference to the drawings.

FIG. 1 shows a fading simulation circuit 990 that generates Rayleigh fading.

The basic principle of this circuit is explained in "Fading Simulation Radar for Mobile Radio" in Materials CS74-96 (published in 1974) of the Communication Systems Study Group of the Institute of Electronics and Communication Engineers.

〓〓〓〓
The operation of the circuit is explained below.Input terminal 1
The input signal from 00 is divided into two parts, one is multiplier 1, the other is passed through π/2 phase shift circuit 10 and added to multiplier 2, and Gaussian noise from independent Gaussian noise generators 8 and 9 is added to multiplier 2. is applied through terminals 104 and 105. The outputs of multipliers 1 and 2 are added by adder 5 and appear at output terminal 101. The output signal that appears is a so-called Rayleigh fading signal whose envelope has a Rayleigh distribution in amplitude distribution and a flat phase distribution.

FIG. 2 shows the mechanism by which selective fading occurs. A signal from transmitter 200 is transmitted to receiver 300 by direct wave 400. Generally, in addition to the direct wave 400, a reflected wave 500 (or refracted wave) having a longer path than the direct wave 400 is generated by a reflecting object (refracting object), etc., and is superimposed on the direct wave 400. Then, due to the time difference between the direct wave 400 and the reflected wave 500, the signals transmitted by both waves are added in opposite phases in a specific band within the band, and the level of only that band is significantly lower than that of other bands. The degree of decrease in this level is reflected wave 50
Depending on the intensity of 0.

This is so-called selective fading based on the two-wave model, and generally, fading based on multi-paths is often represented by this two-wave model.

FIG. 3 is a block diagram showing one embodiment of the present invention, which embodies the two-wave model described above. In other words, the two Rayleigh fading simulating circuits 990 and 980 simulate a propagation path corresponding to the direct wave 400, the latter a propagation path corresponding to the reflected wave 500, and each is a propagation path in which Rayleigh fading exists. be.

In front of the Rayleigh fading simulation circuit 980 corresponding to the reflected wave 500, a delay element 12,
An attenuator 13 is provided, and the former can change the time difference due to the path difference between the direct wave and the reflected wave, and the latter can change the intensity of the reflected wave. Block 9 in the diagram
90 is the same as that in FIG. 1; block 980 has the same configuration as block 990 in that it shares adder 5; The circuits 6 and 7 correspond to 8 and 9, and the π/2 phase shift circuit 11 corresponds to 10, respectively. In the figure, block 1000 shows the portion excluding Gaussian noise generators 6, 7, 8, and 9.
By making the output spectra of the Gaussian noise generators 6, 7 and 8, 9 different, more natural fading can be generated.
In this embodiment, by making the first two spectrums wider than those of the latter two, the movement of the in-band depth due to selective fading is made faster than that of Rayleigh fading.

FIG. 4 shows an example of an application of the present invention, which is a fading simulation circuit that simultaneously generates selective fading that is correlated with the selective fading that occurs in the previous example of FIG. 3. A block diagram is shown.

Blocks 1000, 1000' are the same as block 1000 in FIG. 3, and blocks 6', 7', 8',
Reference numeral 9' denotes a Gaussian noise generator that has a certain correlation with the Gaussian noise output from the Gaussian noise generators 6, 7, 8, and 9, respectively. In this application example, output terminals 101, 1
This is for experimenting with the diversity effect using 01' as two inputs.

As described above, according to the present invention, a fading simulator that generates selective fading characterized by two parameters can be obtained.

Also, the Gaussian noise generator shown in the example is PN
It is possible to create a digital circuit using a code generator, digital filter, and D/A converter, and the band of the Gaussian noise generated at this time can be easily changed by changing the clock frequency that drives the digital circuit.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a Rayleigh fading simulation circuit, in which 1 and 2 are multipliers, 5 is an adder, 10 is a π/2 phase shift circuit, and 8 and 9 are Gaussian noise generators. FIG. 2 is a diagram illustrating the mechanism by which selective fading occurs, and FIG. 3 is a block diagram showing an embodiment of the present invention.
980 is the Rayleigh fading simulation circuit shown in FIG. 1, in which the adder 5 is shared, 13 is a delay element, and 12 is an attenuator. FIG. 4 shows an example of application of the present invention, in which 1000 and 100
0' is the same as block 1000 in FIG.
6, 7, 8, 9, 6'7', 8', 9' are Gaussian noise〓〓〓〓
It is a generator. 〓〓〓〓

Claims (1)

[Claims] 1. A first orthogonal noise modulation circuit that applies amplitude modulation to an input signal and a signal having a phase difference of 90 degrees from the input signal using independent Gaussian noise, and modulates the amplitude of the input signal and a signal having a phase difference of 90 degrees from the input signal, and a second orthogonal noise modulation circuit that inputs the output of the attenuator through the attenuator, and an addition circuit that adds the outputs of the first and second orthogonal noise modulation circuits, the delay amount of the delay element and the attenuation A fading simulator characterized in that a signal subjected to pseudo-selective fading whose characteristics can be changed depending on the amount of attenuation of the adder is obtained from the output of the adder circuit.