JP2000022646A - Fading simulator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To simulate shadowing including not only the median of a received electric field strength but also a change in a standard deviation due to the temporal change of the ratio of a stable component to a fluctuation component. SOLUTION: A distribution circuit 3 distributes an input from an input terminal 1 into two, the one is given to a Rayleigh modulator 4, and the other is directly given to a ratio variable synthesis circuit 5. The ratio variable synthesis circuit 5 synthesizes a fluctuation component from the Rayleigh modulator 4 to a stable component from the distribution circuit 3 while changing the ratio timely with an output of a standard deviation control means 6 and outputs the synthesized output via a median decision circuit 7. The standard deviation control means 6 can simulate a shadowing pattern where a probability distribution of the standard deviation of the amplitude of the synthesized reception electric field strength or the probability distribution of the standard deviation of the amplitude expressed in logarithm is distributed as a regular distribution.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fading simulator for simulating a radio wave propagation path.
The present invention relates to a fading simulator capable of correctly simulating electric field fluctuation due to shadowing or the like in a mobile communication field.

[0002]

2. Description of the Related Art In general, the propagation characteristics in a mobile radio propagation path are very complicated because the mobile station moves around since there is no line of sight between the base station and the mobile station. ", The Institute of Electronics, Information and Communication Engineers (199
1) P.I. 203-206). FIG. 6 is a diagram showing a model of received signal level fluctuation in mobile communication. The received signal level is basically determined by the distance between the base station and the terminal as shown in (3) of FIG. This is referred to as propagation distance fluctuation, and indicates average propagation loss distance characteristics for a target area. The received signal level determined as a result of this distance variation is referred to as a long section median. Looking a little closer,
As shown in (2) of FIG. 6, it has a relatively slow fluctuation component having a period of several tens ms due to the attenuation due to the influence of the building and the topography. This is called (short section) median value fluctuation. This variation is also called shadowing, and the distribution of the median is known to approximately follow a lognormal distribution.
Further, there is a severe fluctuation as shown in FIG. In a mobile propagation path, a radio wave transmitted from a base station is reflected or diffracted by a building or the like around the mobile station to form a standing wave on the road. When the receiving point moves in the standing wave, intense fading occurs in which the fluctuation width is 20 dB or more and the fluctuation frequency is several tens Hz. The fading caused by this standing wave is called instantaneous value fluctuation. It is known that the probability distribution of the instantaneous value of the received electric field strength often follows Nakagami-Rice distribution or Rayleigh distribution. That is, it is known that if the stable component in the received electric field strength is not negligible, it follows the Nakagami-Rice distribution, and if the stable component is very small and negligible, it follows the Rayleigh distribution.

As described above, in mobile communication, the received input voltage of a mobile device undergoes a change accompanied by extremely complicated fading. Therefore, a field test is required to confirm the characteristics of the mobile device. Required. But,
In an actual field test, there are various restrictions, and it is difficult not only to repeatedly execute a test with little variation, but also it is almost impossible to conduct an experiment in which various factors are separated. Therefore, a fading simulator capable of performing a test equivalent to an actual field test in a room is used. (Tadao Saito and Keiji Tachikawa, “Handbook of Mobile Communications” edited by Ohmsha, November 15, 1995, pp. 208-209). As an example of such a fading simulator, a Rayleigh fading simulator is known. FIG. 7 is a diagram showing a configuration example of the Rayleigh fading simulator. This Rayleigh fading simulator (Rayleigh modulator)
Is to vary the high-frequency signal so that the phase distribution becomes uniform and the amplitude becomes Rayleigh distribution. As shown in FIG. 7, it basically consists of two Gaussian noise generators and a quadrature modulator. Have been. The input carrier signal (sinωt) is divided into an in-phase component (sinωt) and a quadrature component (cosωt) by a divider.
Distributed (uncorrelated) baseband Gaussian noise signal a output from two Gaussian noise generators
(T), b (t), and then combine and output after balanced modulation. Thereby, the amplitude has a Rayleigh distribution,
It outputs a signal having a uniform phase distribution.

Further, a fading simulator considering the above-mentioned shadowing has also been proposed (Japanese Patent Laid-Open No. Hei 7 (1994)).
-177107). The proposed fading simulator is capable of simulating shadowing occurring in an interference wave between a desired wave and an N wave in consideration of an arbitrary combination of cross-correlations.

[0005]

As described above, Rayleigh fading does not include a direct wave or a stable radio wave from a fixed reflector, and is not reflected or diffracted by a moving body, or
It is considered that only the constantly changing component caused by the antenna itself moving in the standing wave of the radio wave.
In a complex urban radio wave environment, it is far enough from the transmission point,
Such fading is more likely to occur as the reflection and diffraction increase up to the reception point. However, actually, even if the mobile terminal is sufficiently far from the transmission point, a stable component is included in the radio wave received by the mobile object due to the surrounding radio wave environment. This occurs, for example, when a reflected wave from a fixed building arrives between the transmitting and receiving points. In such a case, it is known that the received electric field strength follows the Nakagami-Rice distribution. Therefore, in order to simulate general fading, it is necessary to add a stable component to the output of the Rayleigh modulator, that is, the fluctuation component of the received radio wave.

As described above, it is known that the median value of the received electric field intensity that constantly changes due to shadowing follows a log-normal distribution, but the standard deviation itself of the median value of the received electric field intensity is also a predetermined probability process. It has been clarified from the results of the experiments performed by the present inventors that the above conditions were satisfied. However, the above-described fading simulator in which shadowing is taken into consideration does not provide a configuration in which a shadowing pattern is provided only for the median value and the ratio between the stable component and the variable component of the received electric field strength can be varied. Therefore, shadowing including the change in the standard deviation of the received electric field strength was not correctly simulated. In addition, since the stable component and the variable component cannot be separately varied over time, the setting of the fading model is complicated and difficult to understand.

Therefore, the present invention correctly simulates shadowing including not only the median value of the received electric field strength but also a standard deviation change due to a temporal change of a ratio between a stable component and a variable component of the received electric field fluctuation. The purpose of the present invention is to provide a fading simulator capable of performing the following.

[0008]

In order to achieve the above object, a fading simulator according to the present invention comprises: a distributing means for distributing a high-frequency signal input from an input terminal into two signals; and one of outputs of the distributing means. Is input, and a Rayleigh modulator generates an output having a Rayleigh distribution in amplitude and a uniform distribution in phase. The other of the output of the Rayleigh modulator and the output of the distribution means is synthesized at a variable synthesis ratio. It has variable ratio synthesizing means, standard deviation control means for outputting a control signal for temporally varying the synthesizing ratio in the variable ratio synthesizing means, and median value determining means for determining the median value of the output signal. This allows
The ratio between the stable component and the variable component of the received electric field strength can be made variable with time, and it is possible to simulate shadowing more accurately than in the past.
In addition, since the stable component and the variable component are made to be temporally variable, the setting of the fading model becomes intuitive and easy to understand.

In another fading simulator of the present invention, a variable ratio distributing means for distributing a high frequency signal input from an input means to two output signals having variable output ratios,
One of the outputs of the variable ratio distributing means is input, the output has a Rayleigh distribution in amplitude and generates an output having a uniform phase distribution, and the other of the output of the Rayleigh modulator and the output of the variable ratio distributing means. , A standard deviation control means for outputting a control signal for temporally varying the ratio of the ratio variable distribution means, and a median value determining means for determining a median value of the output signal. As a result, the ratio between the stable component and the variable component of the received electric field strength can be made temporally variable, and more accurate shadowing can be simulated as compared with the related art. In addition, since the stable component and the variable component are made to be temporally variable, the setting of the fading model becomes intuitive and easy to understand.

Further, the standard deviation control means has a memory in which the control information is stored such that the probability distribution of the short-term standard deviation of the amplitude of the output signal becomes a normal distribution in a long section. Still further, the standard deviation control means has a memory in which the control information is stored such that the probability distribution of the short-term standard deviation of the value expressed in logarithm of the amplitude of the output signal becomes a normal distribution in the long term. is there. Furthermore, the standard deviation control means has a memory in which the control information corresponding to the short-term standard deviation of the amplitude obtained in the experiment is stored. These make it possible to provide the stochastic process in the long section of the short-term standard deviation of the instantaneous value constantly changing by shadowing by the standard deviation control means, and to provide the most likely probability distribution used. It becomes possible.

[0011]

FIG. 1 is a block diagram showing a configuration example of a first embodiment of a fading simulator according to the present invention. In this figure, reference numeral 1 denotes an input terminal, and 2 denotes an output terminal. When this fading simulator is used, for example, a transmitter is connected to the input terminal 1, and a receiver is connected to the output terminal 2, for example. 3 is a distribution circuit for distributing a high-frequency signal input from the input terminal 1 to two,
Is a Rayleigh modulator to which one of the outputs of the distribution circuit 3 is input, and has a configuration similar to that of the Rayleigh fading simulator shown in FIG.
Reference numeral 5 denotes a variable ratio synthesizing circuit, which synthesizes the output of the Rayleigh modulator 4 and the other output of the distribution circuit 3 at a ratio determined by a control signal supplied from a standard deviation control circuit 6. Reference numeral 7 denotes a median value determination circuit to which the output of the variable ratio combining circuit 5 is input.

In the thus configured fading simulator, the high-frequency signal input from the input terminal 1 is divided into two by the distribution circuit 3, and one of its outputs is input to the Rayleigh modulator 4. A high-frequency signal indicating a Rayleigh fading state in which the amplitude has a Rayleigh distribution and the phase has a uniform distribution is output.

As described above, in order to simulate general fading, it is necessary to add a stable component to the output of the Rayleigh modulator 4 (ie, the fluctuation component of the received radio wave). The variable ratio synthesizing circuit 5 is provided for that purpose, and makes the ratio of the constantly fluctuating output from the Rayleigh modulator 4 to the stable high-frequency signal from the other output of the distribution circuit 3 variable. Combine. As described above, the ratio between the stable component and the variable component needs to be changed with time. The standard deviation control circuit 6 is provided for this purpose. The standard deviation of the instantaneous value of the high-frequency signal output from the output terminal 2 is changed by changing the ratio between the stable component and the variable component with time. Control in a form similar to a pattern. For example,
If the ratio of the fluctuation component from the Rayleigh modulator 4 is increased, the standard deviation of the received electric field strength is increased,
If the ratio of the stable component from the distribution circuit 3 is increased, the standard deviation decreases.

FIG. 2 is a diagram showing an example of the configuration of the variable ratio synthesizing circuit 5. As shown in FIG. As shown in this figure, the ratio variable synthesis circuit 5 is a digital variable resistance attenuator 8 for controlling the level of an input 1 (a fluctuation component output from the Rayleigh modulator 4) and an input 2 (an output of the distribution circuit 3). Stable component)
, And a synthesizing circuit 10 for synthesizing the outputs of the digital variable resistance attenuators 8 and 9. The attenuation of each of the digital variable resistance attenuators 8 and 9 is controlled by a control signal supplied from the standard deviation control circuit 6. Here, the standard deviation control circuit 6 has a memory, for example, and stores a set of information for designating the amount of attenuation in the digital variable resistance attenuators 8 and 9 at each timing. Then, at a timing specified by simulation conditions or the like, a set of information specifying the attenuation is sequentially read from the standard deviation control circuit 6 and supplied to the digital variable resistance attenuators 8 and 9, whereby The ratio between the fluctuation component and the stable component synthesized by the synthesis circuit 10 is controlled, and the standard deviation of the instantaneous value fluctuation of the output signal can be controlled. As a result, a fading output having the standard deviation controlled by the standard deviation control circuit 6 is obtained from the synthesis circuit 10.

The fading output having the controlled standard deviation output from the variable ratio synthesizing circuit 5 is input to the median value determining circuit 7, where the median value changes with time. The signal is output to the output terminal 2. FIG. 3 is a block diagram showing a configuration example of the median value determination circuit 7. As shown in FIG. As shown in the figure, the median value determination circuit 7 includes a digital variable resistance attenuator 11 and a median information generation circuit 12 for controlling the attenuation of the digital variable resistance attenuator 11. Here, as the median information generating circuit 12, for example, a memory in which the median information is stored in a memory is used, and the amount of attenuation of the digital variable resistance attenuator 11 is determined by the information sequentially read out from the memory at a predetermined timing. A controlled fading signal having a median value corresponding to the lognormal distribution described above is output from the output terminal 2.

As described above, in the fading simulator of the present invention, both the standard deviation and the median of the high-frequency signal appearing at the output terminal 2 change with time according to a certain stochastic process. This stochastic process is determined by information in the memory of the standard deviation control circuit 6 and the memory of the median value determination circuit 12. As described above, in the fading simulator of the present invention, the stable component and the variable component are divided and made temporally variable. That is,
Since the standard deviation of the signal output from the output terminal 2 is determined by directly giving the ratio between the stable component and the variable component as information in the memory of the standard deviation control circuit 6, any model can be used for fading simulation. The feature is that it is easy to intuitively understand whether or not it is.

FIG. 4 is a block diagram showing a configuration example of the second embodiment of the present invention. In this figure, the same components as those in FIG. 1 are denoted by the same reference numerals to avoid duplication of description. As is apparent from FIG. 4, the difference between this embodiment and the embodiment shown in FIG. 1 is that the distribution circuit 3 is replaced with a variable ratio distribution circuit 13 and the variable ratio composition circuit 5 is composed. Circuit 14. Even with the configuration as shown in FIG. 4, a fading output similar to that of the embodiment shown in FIG. 1 can be obtained at the output terminal 2. In the case of the configuration as shown in FIG. 4, the ratio between the stable component and the variable component is controlled by the variable ratio distribution circuit 13. For example, from the variable ratio distribution circuit 13 to the Rayleigh modulator 4
If the level of the high-frequency signal going to the synthesis circuit 14 is made higher than the level of the high-frequency signal going to the synthesis circuit 14, the fluctuation component becomes large and the standard deviation becomes large.

FIG. 5 is a diagram showing a configuration example of the variable ratio distribution circuit 13. The input high frequency signal is divided by the distribution circuit 17 into two.
One is output to the output 1 via the digital variable resistance attenuator 15, ie, to the Rayleigh modulator 4, and the other is output to the output 2 via the digital variable resistance attenuator 17, ie, to the synthesis circuit 14. The attenuation in the digital variable resistance attenuators 15 and 16 is
It is controlled according to the contents of the memory of the standard deviation control circuit 6. Then, the output of the Rayleigh modulator 4 and the output 2 are combined by a combining circuit 14 and input to the median value determining circuit 7.

In the first and second embodiments described above, the median value determination circuit 7
Is provided on the output side, that is, immediately before the output terminal 2,
Even if this is provided on the input side, a similar fading output can be obtained. In this case, the median determination circuit 7 is provided between the input terminal 1 and the distribution circuit 3 in the embodiment of FIG. 1, and between the input terminal 1 and the variable ratio distribution circuit 13 in the embodiment of FIG. Becomes

Now, the first embodiment and the second embodiment will be described.
In the embodiment, the information in the memory of the standard deviation control circuit 6 provides a stochastic process in the long section of the short section standard deviation of the instantaneous value that constantly changes due to shadowing. As for the probability distribution, the probability distribution of the standard deviation of the amplitude or the probability distribution of the standard deviation of the logarithmic value of the amplitude is most likely to be normally distributed. The reason for this is that in a complex multipath propagation process in an urban area, the received electric field strength is represented by the sum of many reflected waves and diffracted waves (= stochastic variables), and the central limit theorem is easily established for the standard deviation. It is thought to be. Therefore, in the present invention,
As for the information in the memory of the standard deviation control circuit 6, the probability distribution of the standard deviation of the amplitude of the high frequency at the output terminal 2 or the probability distribution of the standard deviation of the logarithmic value of the amplitude can be selected. Has become. Also,
This standard deviation can be obtained experimentally. Therefore, in this case, the set of control information to the digital variable resistance attenuators 8 and 9 or 15 and 16 corresponding to the memory of the standard deviation control circuit 6 is set so as to become the value of the standard deviation experimentally obtained. Should be stored.

Further, some information in the median information generating circuit 12 in the median value determining circuit 7 can be selected. As mentioned earlier, for the median,
There are many known examples in which a logarithmic representation is normally distributed, and the corresponding control information to the digital variable resistance attenuator 11 may be stored in the memory of the median information generation circuit 12.

[0022]

As described above, the present invention relates to a fading simulator for use in mobile communication, in which not only the median value of the received electric field strength but also the standard deviation of the standard deviation determined by the ratio between the stable component and the variable component of the received electric field strength. Since the influence of shadowing is also simulated with respect to a temporal change, more realistic fading simulation can be performed as compared with the related art. In addition, by separating the stable component and the variable component and making them temporally variable, there is an effect that the setting of the fading model is intuitive and easy to understand.

[Brief description of the drawings]

FIG. 1 is a configuration diagram for explaining a first embodiment of the present invention.

FIG. 2 is a diagram illustrating a configuration example of a variable ratio combining circuit used in the present invention.

FIG. 3 is a diagram showing a configuration example of a median value determination circuit used in the present invention.

FIG. 4 is a configuration diagram for explaining a second embodiment of the present invention.

FIG. 5 is a diagram showing a configuration example of a variable ratio distribution circuit used in the present invention.

FIG. 6 is a diagram for explaining radio wave propagation in a mobile radio channel.

FIG. 7 is a diagram illustrating a configuration example of a Rayleigh fading simulator (Rayleigh modulator).

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Input terminal 2 Output terminal 3 Distribution circuit 4 Rayleigh modulator 5 Ratio variable composition circuit 6 Standard deviation control circuit (memory) 7 Median value determination circuit 8, 9 Digital variable resistance attenuator 10 Composition circuit 11 Digital variable resistance attenuator 12 Median value Information generation circuit (memory) 13 Variable ratio distribution circuit 14 Synthesis circuit 15, 16 Digital variable resistance attenuator 17 Distribution circuit

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5K042 AA06 BA11 CA02 CA13 DA01 EA13 FA15 FA22 GA11 GA12 LA11 5K067 AA02 BB02 DD47 EE02 EE10 EE32 LL08

Claims (5)

[Claims] 1. A high-frequency signal input from an input terminal is supplied to a second terminal.
A Rayleigh modulator to which one of the outputs of the distribution means is input and generates an output having a Rayleigh distribution in amplitude and a uniform phase distribution; an output of the Rayleigh modulator and the distribution Variable ratio combining means for combining the other output of the means with a variable combining ratio; standard deviation control means for outputting a control signal for varying the combining ratio in the variable ratio combining means with time; A fading simulator having a median determining means for determining a median of a signal. 2. A variable ratio distributing means for distributing a high-frequency signal input from an input means to two output signals having variable output ratios. One of the outputs of the variable ratio distributing means is input, and the amplitude has a Rayleigh distribution. A Rayleigh modulator for generating an output having a uniform phase distribution; a synthesizing unit for synthesizing the other of the output of the Rayleigh modulator and the output of the variable ratio distributing unit; and temporally varying a ratio of the variable ratio distributing unit. A fading simulator comprising: a standard deviation control means for outputting a control signal for setting the median value; and a median value determining means for determining a median value of the output signal. 3. The standard deviation control means includes a memory in which the control information is stored such that the probability distribution of the short-term standard deviation of the amplitude of the output signal becomes a normal distribution in a long section. 3. The fading simulator according to claim 1, wherein: 4. The standard deviation control means has a memory in which the control information is stored such that the probability distribution of the short-term standard deviation of the value representing the amplitude of the output signal in logarithm becomes a normal distribution in the long term. The fading simulator according to claim 1, wherein the fading simulator is used. 5. The standard deviation control means according to claim 1, wherein said standard deviation control means has a memory in which said control information corresponding to a short-term standard deviation of amplitude obtained in an experiment is stored. The fading simulator according to 1.