JPH07235884A - Delay wave eliminating device - Google Patents

Abstract

PURPOSE:To eliminate a delay wave even in a case where a transmission pattern is unknown. CONSTITUTION:A 1st FFT circuit 10 applies the Fourier transformation to an input signal whose fundamental wave is synthesized with a delay wave with respect to time. A 2nd FFT circuit 14 applies the Fourier transformation to an output signal from the 1st FFT circuit 10 with respect to frequency to generate delay time data of the delay wave and delay wave level data. A delay waveform synthesis circuit 18 applies a delay and a level change to the input signal based on the delay time data of the delay wave and delay wave level data to synthesize delay waves. A differential amplifier 20 inverts the synthesized delay wave and adds it to the input signal.

Description

Detailed Description of the Invention

[0001]

[Industrial application] Delay waves are generated because radio waves propagate through a plurality of routes in wireless communication. The present invention relates to a delayed wave removing device that removes a delayed wave component from a received signal that interferes with this delayed wave to reproduce a fundamental wave.

[0002]

2. Description of the Related Art In wireless communication such as mobile phones, radio waves are used to propagate information. When propagating radio waves on the ground,
A plurality of propagation paths are created by a reflector such as a building between the radio wave transmitter and receiver, and the arrival time of the radio wave from the transmitter to the receiver varies depending on which path is propagated. Therefore, the receiving device receives a plurality of radio waves whose phases are shifted from each other. Generally, the radio wave propagating along the shortest path is received first and has the strongest intensity. Therefore, in the following description, the radio wave propagating along this shortest path is used as the fundamental wave, and the radio wave received with a delay compared with this is the fundamental wave. Will be called a delayed wave. That is, the fundamental wave and the delayed wave have the same transmission pattern, but their phases are deviated from each other.
When radio waves whose phases are shifted from each other by passing through a plurality of propagation paths are received, the received signal is distorted because a plurality of delayed waves interfere (combine) with the fundamental wave. In particular, when the transmitting device or the receiving device moves, the relative position of the reflector changes with respect to the position of the transmitting / receiving device, resulting in large distortion.

Interference due to delayed waves will be considered more specifically. When the time is t, the fundamental wave of a certain frequency f can be expressed as cos (2πft). The delayed wave having the delay time τ can be expressed as cos {2πf (t + τ)}. For example, the received signal χ (t) obtained by combining one delayed wave with the fundamental wave
Is expressed by the following equation 1.

[0004]

## EQU1 ## χ (t) = cos (2πft) + αcos {2πf
(t + τ)}

Here, α is the amplitude of the delayed wave, and since it should have propagated over a longer distance than the fundamental wave in general, 0 <α <1
And Addition theorem of the triangular function to the second term on the right side of Equation 1, co
If s (A + B) = cosAcosB-sinAsinB is applied, it can be transformed as shown in Formula 2.

[0006]

## EQU2 ## χ (t) = {1 + αcos (2πfτ)} cos
(2πft) −αsin (2πfτ) sin (2πft)

Here, the replacement is performed as follows. In addition, "
^ "Means exponentiation. For example, a ^ 2 means a squared a.

[0008]

## EQU3 ## a = 1 + αcos (2πfτ)

(4) b = αsin (2πfτ)

(5) tan θ = b / a

## EQU6 ## c = (a ^ 2 + b ^ 2) ^ (1/2)

From the above expressions 3 to 6, a and b can be expressed by the following expressions 7 and 8.

[0010]

[Equation 7] a = c · cos θ

[Formula 8] b = c · sin θ

Substituting equations 7 and 8 into equation 2,

[0012]

Χ (t) = c · cos θ cos (2πft) −c · sin θ sin (2πft) = c · cos (2πft + θ)

From Equation 9, it is understood that the received signal χ (t) obtained by combining one delayed wave with the fundamental wave has an amplitude c and a phase shift of θ with respect to the fundamental wave. Next, when the amplitude c is expressed by using α, f, and τ, the expression 10 is obtained.

[0014]

C = [{1 + αcos (2πfτ)} ^ 2 + {αsin (2πfτ)} ^ 2] ^ (1/2) = {1 + α ^ 2 + 2αcos (2πfτ)} ^ (1/2)

Equation 10 shows that the amplitude of χ (t) changes as the frequency f changes. That is, c can be considered as a function of frequency f.

[0016]

C (f) = {1 + α ^ 2 + 2αcos (2πτ
f)} ^ (1/2)

Χ (t) has a periodicity corresponding to the frequency f because of cos (2πτf). FIG. 6 shows the characteristic curve of Eq. As the frequency f is changed, periodical distortion as shown in FIG. 6 occurs. That is, c (f) is the frequency f
Represents the change in the amplitude of χ (t) when is changed.
Equation 11 shows a received signal in which one delayed wave is combined with the fundamental wave, but when a plurality of n delayed waves are further combined into the fundamental wave, the same calculation gives the following Equation 12. .

[0018]

[Equation 12]

In equation 12, n = 2, τ1 = 0 and α1
It can be seen that when = 1, it becomes equal to Eq.

By the way, in a mobile phone or the like, information is put on a carrier wave by phase modulation. In this case, the spectrum energy is dispersed around the frequency of the carrier wave, and when this is displayed in the frequency domain, the solid line in FIG. 7 is obtained. For example, if a carrier wave having a frequency of 6 GHz is phase-modulated at 200 Mbps (megabits per second), the spectrum energy is centered at 6 GHz and is approximately +/- 100 MHz.
Disperse into. The phase-modulated signal is also used in the case of simultaneously measuring a frequency band having a certain width by taking advantage of this characteristic. For example, if a signal as shown in FIG. 7 is transmitted from the transmitting device to the receiving device, about +/− 10 centering around 6 GHz.
The characteristics of the transmitter / receiver at a frequency of 0 MHz can be measured at the same time.

When the delay time is sufficiently shorter than the period (= 1 / f), that is, when τ << (1 / f),
As can be seen from Equation 11, the change in cos (2πτf) is small, so that it is observed as a level variation rather than distortion in the frequency characteristic as shown by the broken line in FIG. On the contrary, when the delay time τ becomes large and approaches the period (modulation speed), “waviness” as shown in FIG. 8 begins to occur. That is, the waveform shown in FIG. 7 appears to have the periodic distortion as shown in FIG. 6, and the magnitude (amplitude) of each frequency component changes according to c (f). When undulation (distortion) occurs in the reception signal as shown in FIG. 8, the transmission signal cannot be reproduced even if the reception level is sufficient. For example, in digital wireless communication, FIG.
When the transmission signal pattern shown in FIG. 10 interferes with the delayed wave, the pattern of the reception signal becomes as shown in FIG. Both FIG. 9 and FIG. 10 are displayed in the time domain.

Therefore, various attempts have been made to identify the delayed wave. One of the methods is to obtain the delay as shown in FIG. 11 by taking the difference of the spectrum of the received signal as shown in FIG. 8 containing the delayed wave from the reference spectrum as shown by the solid line in FIG. 7 which does not include the delayed wave. Only the distortion of the frequency characteristic due to the wave can be obtained. The difference spectrum is subjected to Fourier transform with respect to frequency, and the delay time is analyzed. However, the reference spectrum at the time of transmission as shown in FIG. 7 needs to be known in advance.

As another method, there is a method of calculating a correlation between a transmission signal waveform which is known in advance and a reception signal waveform which has been interfered by a delayed wave. Thereby, the degree of mixing of the delayed wave is calculated, and the delayed wave is specified. However, even in this method, it is necessary to previously know the pattern of the transmission signal as shown in FIG. 9, especially the modulated wave.

[0024]

When undulations occur in the received signal as shown in FIG. 8, the transmitted signal cannot be reproduced even if the received level is sufficient. For example, in the field of digital communication, when the transmission signal shown in FIG. 9 interferes with a delayed wave, the reception signal becomes as shown in FIG. Therefore, it is necessary to remove the delayed wave that interferes with the fundamental wave. However, conventionally, the delayed wave cannot be specified unless the pattern of the transmitted transmission signal (fundamental wave) is known in advance. That is, since the carrier wave is assigned in advance between the transmitter and the receiver, the carrier wave component of the delayed wave can be specified by the conventional method. However, since the information to be placed on the carrier wave by the modulation (for example, the voice information in the mobile phone) is not known in advance, the conventional method of taking the correlation with respect to the transmission signal pattern shown in FIG. 9 cannot be applied. The distortion due to the modulated wave component of the delayed wave could not be removed.

Therefore, an object of the present invention is to provide a delayed wave removing apparatus which removes a delayed wave that interferes with a transmission pattern (fundamental wave) of a transmission signal. Another object of the present invention is to provide a delayed wave removing apparatus that can remove a delayed wave even when the transmission pattern (fundamental wave) of the transmission signal is unknown.

[0026]

First, referring to FIG.
The Fourier transform means 10 Fourier transforms the input signal in which the delayed wave is combined with the fundamental wave with respect to time. The second Fourier transforming means 14 Fourier transforms the output of the first Fourier transforming means 10 with respect to frequency to generate delay time data of delayed waves and delayed wave level data. The delay and level changing means (delayed wave synthesizing circuit) 18 adds delay and level to the input signal according to the delay time data and the delayed wave level data. Adder (differential amplifier) 20
Inverting the output of the delay and level changing means 18 and adding it to the input signal.

In the case of an input signal in which many delayed waves are combined with the fundamental wave, the most accurate delay time data and delayed wave level data cannot be specified once from the output of the second Fourier transform means 14. There is. Referring to FIG. 3, in this case, the peak detecting means 15 detects the peak value of the second signal output from the second Fourier transforming means 14, and obtains the delay time data and the delay wave level data corresponding to the peak value. . Further, the waveform synthesis circuit 11 synthesizes the signal components of the first signal corresponding to the delay time data and the delay wave level data, and the differential amplifier 12 inverts and adds the first signal to the second signal, and the second signal is omitted. Repeat until constant. The differential amplifier 11 and the waveform synthesizing circuit 12 form a first adding unit that performs addition processing. The storage means (delayed wave component table) 16 stores the delay time data and the delayed wave level data used in the addition processing. The delay and level changing means (delay wave synthesizing circuit) 18 adds delay and level changes to the input signal from one or more sets of delay time data and delay wave level data. The second adding means (differential amplifier) 20 inverts the output of the delay and level changing means 18 and adds it to the input signal.

[0028]

When the Fourier transform is applied to the input signal that causes the interference with the delayed wave as described above, the spectrum has periodicity with respect to the frequency f. This periodicity is related to the delay time. Therefore, in the present invention, in order to analyze the periodicity with respect to the frequency f, the first signal obtained by Fourier transforming the input signal by the first Fourier transform means is further Fourier transformed with respect to the frequency f by the second Fourier transform means. The period (frequency) of one signal is calculated. Obtaining this cycle (frequency) is performed by using the above-mentioned formulas 11 and 12
It is to find the delay time as can be seen from. Then, since the delayed wave level corresponding to the delay time is also obtained at the same time, after delaying and changing the level of the input signal and approximately combining the delayed waves, the phase is inverted and added to the input signal to significantly delay the delayed signal. Remove.

[0029]

1 is a block diagram of a preferred embodiment of a delayed wave removing apparatus according to the present invention. First fast Fourier transform (FF
T) The circuit 10 Fourier transforms the input signal with respect to time. The input signal is, for example, a signal obtained by receiving a radio wave that has passed through the above-described plurality of propagation paths and converting it into an electric signal.
In the signal in which one delayed wave is combined as shown in Expression 11, as the frequency f changes, the level (amplitude) of each frequency becomes a periodic "swell" as shown in FIG. In order to analyze such a period with respect to the frequency f of the output signal of the first FFT (first signal), the first signal is Fourier-transformed with respect to the frequency f by the second fast Fourier transform circuit 14. Note that the Fourier transform is usually performed with respect to time, but in this case, it is performed with respect to the frequency f instead of time.

Since the periodicity of the first signal output from the first FFT circuit 10 is due to cos (2πτf) in the example of Expression 11, it can be seen that the period T is T = 1 / τ. To describe more generally, the number 11 or the number 12
Fourier transform of c (f) with respect to frequency f
If expanded to the Fourier series, it is expressed by the following Expression 13. "F" means Fourier transform.

[0031]

[Equation 13] C (τ) = F {c (f)} = C0 + ΣCncos (2πnτ / T + ψn)

Here, Σ means a sum when n is changed from 1 to infinity. Also, the terms sin and cos are collectively expressed by an arbitrary phase angle ψn. From Equation 13, it can be seen that the Fourier transform of the first signal with respect to the frequency f yields the delay time nτ and the corresponding delayed wave level Cn. That is, the second FFT circuit 1
By Fourier-transforming the first signal in step 4, the delay time data and the delayed wave level data corresponding thereto can be obtained. FIG. 2 is a graph showing the second signal output by the second FFT circuit 14. This may be considered in the same manner as the spectrum when the waveform on the time axis is Fourier-transformed with respect to time, except that the Fourier transform is performed with respect to the frequency f. Delay wave synthesis circuit (delay and level changing means) 18
Delays and changes the level of the input signal from the delay time data and the delay wave level data to approximately combine the delay waves. The delayed wave that is approximately combined is the differential amplifier 2
The phase is inverted at 0 and then added to the input signal. Therefore, the output signal of the differential amplifier 20 is a signal obtained by removing the delayed wave component from the input signal to a considerable extent.

The input signal is composed of not only the fundamental wave but also the delayed wave. Therefore, when delay and level change are applied to the input signal in the delay wave synthesis circuit 18, not only the fundamental wave component but also the delay wave component is delayed and the level is changed, so that an accurate delayed wave cannot be synthesized. However, in digital wireless communication, for example, if the delayed wave component is largely removed and the fundamental wave can be reproduced at a predetermined level or higher, the transmitted information can be reproduced, which poses no practical problem. If the fundamental wave cannot be reproduced at a predetermined level or higher, the circuit shown in FIG. 1 may be connected in series before the differential amplifier 20 and the same process may be repeated a plurality of times.

FIG. 3 is a block diagram of another embodiment of the present invention. When the number of interfering delay waves is small and the delay time is relatively long, the delay wave level can be discretely decomposed for each delay time as shown in FIG. However, when a plurality of delayed waves interfere with each other with a relatively short delay time, the second signal has a continuous spectrum as shown in FIG. Therefore, the peak detection circuit 15 detects one or more peak values of the second signal and obtains delay time data and delayed wave level data corresponding to the peak values. The obtained data is
It is stored in the delayed wave component table 16. If the delay time data and the delay wave level data are known, the signal component of the first signal corresponding thereto can be specified. Therefore, the waveform synthesizing circuit 1
2, the signal components are combined, inverted by the differential amplifier 11, added to the first signal, and then applied to the second FFT circuit 14. This reduces the periodic distortion of the first signal.
The differential amplifier 11, the waveform synthesis circuit 12, and the peak detection circuit 15 collectively function as an antiphase waveform addition circuit.

If a large peak appears in the second signal even after the addition process is performed once, the addition process is repeated a plurality of times.
This is because the delay time data and the delay wave level data at the peak value do not always correspond exactly to the delay time and the delay wave level of the delay wave. Figure 5
The anti-phase waveform adding circuit alternately shows the waveform of the signal applied to the second FFT circuit 14 and the waveform of the second signal, and the above-mentioned addition process is repeated to show how the second signal converges in a substantially constant time series. It is represented by. Since the delay time data and the delay wave level data used when repeating the addition processing are stored in the delay wave component table 16, the waveform synthesis circuit 12 causes the first delay time data and the delay time in the first addition processing. Synthesize waveform from wave level data,
In the second time, in addition to the first delay time data and the delayed wave level data, the data corresponding to the peak value newly detected by the peak detection circuit 15 is used to synthesize two waveforms from two sets of data. The same operation is repeated after the third time. A storage unit such as a RAM may be used for the delayed wave component table 16.

The delayed wave synthesizing circuit 18 uses one or more pieces of delay time data and delayed wave level data stored in the delayed wave component table 16 to approximate and delay the input signal. Synthesize delayed waves. The differential amplifier 20 inverts the delayed wave synthesized as described above and adds it to the input signal. The fact that the delay wave synthesizing circuit 18 uses the set of the delay time data and the delay wave level data for making the second signal substantially constant means that the delay wave for preventing the periodic distortion from occurring in the first signal can be synthesized. That's what it means. Therefore, the delayed wave component can be largely removed from the input signal.

The present invention may be implemented in, for example, a microprocessor system. In this case, the first and second FFT
The circuit can be realized by performing arithmetic processing with a microprocessor. Further, it may be realized by connecting a DSP (digital signal processing device) to the bus of the microprocessor system. If the DSP is used, the fast Fourier transform operation of an arbitrary input signal can be performed at higher speed. Furthermore, F
The FT circuit may be realized by the superheterodyne method used in the spectrum analyzer.

The delayed wave removing apparatus of the present invention may be configured as a dedicated integrated circuit (IC). If integrated into an IC, it can be applied to small devices such as those mounted on a mobile phone. Also,
Although the present invention has been described above with respect to wireless communication, the present invention can also be applied to wired communication using a cable or the like.

[0039]

According to the present invention, it is not necessary to check the correlation with the transmission signal or the like in order to specify the delayed wave. Therefore, the delayed wave can be removed even if the transmission pattern of the transmission signal is not known in advance. Further, the configuration is suitable for integration into an integrated circuit (IC) and can be applied to small devices.

[Brief description of drawings]

FIG. 1 is a block diagram of one preferred embodiment of the present invention.

FIG. 2 is a second output of the second FFT circuit 14 shown in FIG.
It is a graph which shows a signal.

FIG. 3 is a block diagram of another preferred embodiment of the present invention.

FIG. 4 is a second output of the second FFT circuit 14 shown in FIG.
It is a graph which shows a signal.

FIG. 5 is a diagram showing, in time series, the waveform of the signal applied to the second FFT circuit 14 by the anti-phase waveform addition circuit 12 and the waveform of the second signal when the addition process is repeated.

FIG. 6 is a diagram showing a characteristic curve of Expression 11.

FIG. 7 is a diagram showing the waveform of a phase-modulated carrier wave in the frequency domain.

FIG. 8 is a diagram showing a state in which a phase-modulated carrier wave is distorted by a delayed wave.

FIG. 9 is a diagram showing an example of a transmission pattern in digital wireless communication.

FIG. 10 is a diagram showing an example of a received signal that interferes with a delayed wave in digital wireless communication.

FIG. 11 is a diagram showing a waveform obtained by subtracting the waveform shown in FIG. 8 from the waveform shown in FIG. 7 in order to identify a delayed wave by a conventional method.

[Explanation of symbols]

 10 First Fourier Transforming Means 11, 12 First Adding Means 14 Second Fourier Transforming Means 15 Peak Detecting Means 16 Delayed Wave Component Table (Storage Means) 18 Delayed Wave Combining Circuit (Delay and Level Changing Means) 20 Differential Amplifier (First 2 addition means)

Claims (2)

[Claims] 1. A first Fourier transforming means for Fourier transforming an input signal in which a delayed wave is combined with a fundamental wave with respect to time, and a delay time of the delayed wave by Fourier transforming an output of the first Fourier transforming means with respect to frequency. Second Fourier transform means for generating data and delayed wave level data; delay and level changing means for delaying and changing the level of the input signal in accordance with the delay time data and the delayed wave level data; And a delay wave removing device comprising an adding means for inverting the output of the level changing means and adding the inverted signal to the input signal. 2. A first Fourier transforming means for Fourier-transforming an input signal in which a delayed wave is combined with a fundamental wave with respect to time, and a second Fourier-transforming with respect to frequency the first signal output by the first Fourier transforming means. Fourier transforming means, peak detecting means for detecting the peak value of the second signal output by the second Fourier transforming means, and obtaining delay time data and delayed wave level data corresponding to the peak value; First adding means for repeating an adding process of inverting and adding the signal component of the first signal corresponding to the delayed wave level data to the first signal until the second signal becomes substantially constant, and the adding process. Storage means for storing the delay time data and the delayed wave level data used for the above, and the input from the delay time data and the delayed wave level data. A delay and level changing means adds a delay and level change in the signal, the delay wave removal device comprising a second addition means for inverting the output of the delay and level changing means for adding to the input signal.