JPH11326426A - Noise adding method, and device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To allow use of an effective value measuring means of relatively narrow dynamic range. SOLUTION: An attenuation amount of variable attenuators 13, 16 is made zero, an average value of signals is detected by a detection means 31 and multiplied by a constant to find an effective value VRS. An average value of noises is detected by the detection means 31, and multiplied by a constant to find an effective value VRN, and gains of an amplifier 15 are controlled to make the VRN equal to the VRS. At least, one of the attenuators 13, 16 is regulated in response to a desirable S/N ratio, and outputs of the attenuators 13, 16 are totalized to be output from a terminal 21.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used, for example, in a communication system for a test for guaranteeing how much noise interference interference will cause the system to operate. / N) for adding a noise to a signal for outputting a signal having the same.

[0002]

2. Description of the Related Art FIG. 3 shows a conventional noise adding device. The signal from the signal source 11 is amplified by an amplifier 12 as necessary, and a variable attenuator 13 as a signal level adjusting means is provided.
Supplied to On the other hand, the noise from the noise source 14 is supplied to a variable attenuator 16 as a noise level adjusting means through a variable gain amplifier 15 and also to a detector 17, the level of which is detected, and a gain controller 18 according to the detected level.
Controls the gain of the variable gain amplifier 15, and the noise level input to the variable attenuator 16 is kept substantially constant.

The outputs of the variable attenuators 13 and 16 are added to an adder 19
And output to the output terminal 21 as a noise-added signal. The output of the adder 19 is also supplied to a power detector 22, and the output of the power detector 22 is input to a control unit 23 having a CPU. To output a desired S / N noise-added signal, the S / N and the signal level (effective value) are input and set to the control unit 23, only the signal is output, and the detection power of the power detector 22 is detected. Control unit 2
3 is read, and this value becomes the set value inputted.
Adjust the variable attenuator 13 and then output only noise,
The control unit 2 controls the signal output level of the power detector 22 so that the adjusted signal output level is set to the input / output S / N ratio.
3 adjusts the variable attenuator 16. After that, the signal and the noise are simultaneously output to obtain a noise-added signal of a desired S / N at the output terminal 21.

[0004]

Each time the S / N is set, the effective value of the signal and the effective value of the noise are measured to obtain a noise-added signal of a desired level and a desired S / N. Therefore, accurate S / N cannot be obtained unless each effective value of the signal and noise is large or small. Therefore, a power detector 22 having a wide dynamic range and excellent linearity is required. In particular, noise has a high crest factor (large crest factor), so that a power detector having a wider dynamic range is required.

From this point, a thermocouple type expensive and complicated circuit configuration has been used as the power detector.
Although the effective value can be calculated and calculated by a DSP (Digital Signal Processor), it can be measured only at a low frequency such as a baseband band, that is, it can be used only for adding noise in a low frequency band, and It becomes complicated and expensive.

[0006]

According to the present invention, the noise level input to the noise level adjusting means is adjusted so that the signal before noise addition and the noise have the same effective value, respectively. , At least one of the noise level adjusting means and the signal level adjusting means is adjusted, and the outputs of these adjusting means are added and output.

[0009] The measurement of the effective value is obtained by detecting the average value by the average value detecting means and multiplying the average value by a constant corresponding to a signal or noise. This average value detection means can be shared by switching to both noise and signal. The variable adjusting means for adjusting the noise level input to the noise level adjusting means is controlled such that the variable adjusting means maintains a constant value in accordance with the output of the average value detecting means for obtaining the effective value, thereby stabilizing the noise level. To

Further, adjustment to the same effective value, and subsequent S /
Control means for fully automatically adjusting at least one of the signal level adjusting means and the noise level adjusting means according to N may be provided.

[0009]

FIG. 1 shows an embodiment of the present invention.
Parts corresponding to those in FIG. 3 are denoted by the same reference numerals. In this embodiment, an average value detecting means 31 is provided. The average value detecting means is, for example, a double-wave detection circuit 32 composed of a diode.
And a low-pass filter 33 of CR. Switches 34 and 35 are connected between the input side of the average value detecting means 31 and each input side of the variable attenuator 13 as a signal level adjusting means and the variable attenuator 16 as a noise level adjusting means. The output of the average value detecting means 31 is an AD converter 37
Is input to the control unit 38 having a CPU through The control unit 38 can set an attenuator for each of the variable attenuators 13 and 16. The control unit 38 converts the digital value into an analog value by the DA converter 39, and controls the variable gain amplifier 1 through the gain control unit 18 according to the analog value.
5 can be controlled. Further, the output of the average value detecting means 31 can be supplied to the gain control section 18 to control the gain of the variable gain amplifier 15 according to the detected average value.

Next, the procedure of a noise adding process by this device will be described with reference to FIG. First, the control unit 38 turns on the switch 34, detects the average value of the signal by the average value detection means, and reads this as a digital value through the AD converter 37. If the signal is a sine wave, the effective value (RMS) /
Since there is a relation of average value (MAD) = π / (2√2) = 1.111, the control unit 38 sets the read average value to 1.111.
To obtain the effective value _{VRS of the} signal (S1).

Next, the controller 38 turns off the switch 34.
Then, by turning on the switch 35, noise (for example, white
The average value of Gaussian noise) is detected by the detection means 31,
This average value is read as a digital value,
Multiplied by 53, the effective value V of the noise _RN(S2). What
Effective value / flat when the noise is white Gaussian noise
Average = √ (π / 2) = 1.253.

The control unit 38 controls the DA converter 3 so that the measured effective value V _RN of the noise becomes equal to the measured effective value V _{RS of the} signal.
9 is provided with a digital value, and the gain of the variable gain amplifier 15 is controlled through the gain control unit 18 (S3). In this way, in a state where the effective values of the signal and the noise are equal to each other, at least one of the variable attenuators 13 and 16 is adjusted according to the S / N preset by the input means 43 (S
4). That is, the attenuation amount AT _S (d
B), the amount of attenuation AT _N (dB) given to the variable attenuator 16 and the amount of AT _N -AT _S may be made equal to the S / N expressed in dB. Variable attenuator 1 adjusted in this way
The sum signal of the outputs 3 and 16 is output to the output terminal 21 at the desired S / S level.
It is output as N noise-added signals.

This noise-added signal is used, for example, as a test signal for a communication system.
In some cases, the test is performed with a test signal in which / N is changed by a predetermined value. In such a case, at least one of the variable attenuators 13 and 16 may be sequentially adjusted so as to obtain each S / N. That is, it is not necessary to measure the effective value each time. In the embodiment shown in FIG. 1, while the test signal is being output from the output terminal 21, the switch 3 is set so that the noise level is stably maintained.
5 is turned on, the detection output of the average value detection means 31 is input to the gain control section 18, and the gain of the variable gain amplifier 15 is controlled.

When the signal from the signal source 11 is different from a sine wave, the effective value / average value of the signal waveform may be obtained in advance by an experiment. Although the effective value is obtained by the average value detection and the multiplication of a constant, the effective value may be directly measured using a power detector as shown in FIG. Depending on the frequency band to which noise is added, an effective value may be calculated by a DSP, or an average value may be calculated and multiplied by a constant to obtain an effective value. The control for making the effective value of the noise equal to the effective value of the signal may be performed by adjusting the gain of the amplifier 12 instead of the amplifier 15.

[0015]

As described above, according to the present invention,
With the signal level adjusting means and the noise level adjusting means having the same set value, the effective value V _RS of the signal is measured, and the noise is adjusted so that the measured effective value V _RN of the noise becomes equal to the effective value V _RS. The level is adjusted. Thereafter, when the S / N is set, the effective value is not measured, but the level is adjusted by the level adjusting means. Therefore, the effective value is measured by the effective value V of the signal.
_It suffices if the _RS and the effective value V _{RN of the} noise can be correctly measured. Since they are the same, it is only necessary to be able to perform a correct measurement near this level. There is no need to make a determination in a wide level range, for example, and the dynamic range may be relatively narrow. Therefore, the effective value can be measured using a power detector or DSP having a simple configuration at a low cost.

Since the S / N error is almost determined by the error of the level adjusting means, it is possible to increase the noise-added band up to the usable frequency band of these level adjusting means. In particular, when the effective value is obtained by the average value measurement and the constant multiplication as in the above-described embodiment, an inexpensive and simple configuration can be obtained as the related art. When the average value detecting means 31 is used, the output of the average value detecting means 31 may be used for the gain control of the variable gain amplifier 15 in order to stably maintain the noise level while the noise-added signal is being output. In the result shown in FIG. 3, the level detector 17 does not need to be provided, and the configuration becomes simpler.

Further, as described above, the whole process can be automatically performed by the control unit 38 without manual operation.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of the apparatus of the present invention.

FIG. 2 is a flowchart showing a procedure of an embodiment of the method of the present invention.

FIG. 3 is a block diagram showing a conventional noise adding device.

Claims (6)

[Claims] 1. A method for inputting a signal and noise to obtain a noise-added signal having a desired signal-to-noise ratio, comprising: signal level adjusting means for adjusting the level of the signal before the input addition; Setting the noise level adjusting means for adjusting the level of the noise before input addition to the same predetermined value; measuring the effective value of the input signal of the signal level adjusting means; Measuring the effective value of the input noise of the adjusting means, based on the measured noise effective value or signal effective value,
Adjusting the level or signal level of the noise input to the noise level adjusting means or the signal level adjusting means so that the noise effective value is equal to the signal effective value. And adjusting at least one of the signal level adjusting means and the noise level adjusting means according to the signal-to-noise ratio and adding and outputting the outputs of the two adjusting means. Addition method. 2. The signal from a signal source is level-adjusted by a signal variable level adjuster, and the noise from a noise source is level-adjusted by a noise variable level adjuster. A noise adding device for adding noise by an adding means and outputting the desired signal to noise as a noise added signal; a means for measuring an effective value of an output signal of the signal level adjusting means; and a noise level adjusting means. Means for measuring the effective value of the output noise of the noise level inserted between the noise source and the variable level adjusting means for noise or between the signal source and the variable level adjuster for the signal, Variable level adjusting means for adjusting the signal effective value and the noise effective value, and initial level adjusting means for controlling the variable level adjusting means so that the effective value of the noise becomes the same value. Signal the signal level adjusting means in response to noise ratio, noisy anda S / N setting means at least controlling the one of said noise level-adjusting means. 3. The signal effective value measuring means comprises: mean value detecting means for detecting an average value of the signal; and means for obtaining an effective value by multiplying the detected average value by a constant. The means comprises an average value detecting means for detecting an average value of noise, and a means for multiplying the detected average value by a constant to obtain an effective value. The means for detecting the average value of the signal and the means for detecting the average value of the noise 3. A switching means for switching and connecting an input side of the signal level adjusting means and an input side of the noise level adjusting means to the shared average value detecting means. Noise adding device. 4. The noise addition device according to claim 2, further comprising a fluctuation suppressing means for controlling said variable level adjusting means to suppress a fluctuation of a noise level inputted to said noise level adjusting means. apparatus. 5. The noise adding apparatus according to claim 4, wherein said fluctuation suppressing means is means for controlling said variable level adjusting means with a detection output of said average value detecting means in said noise effective value measuring means. 6. An effective value of the signal is measured, an effective value of the noise is measured, and the variable level adjusting means is controlled so that a measured effective value of the noise is equal to a measured effective value of the signal. The noise adding apparatus according to claim 2, further comprising a control unit that automatically controls the S / N setting unit.