JP2003110385A - Communication device - Google Patents

Abstract

(57) [Summary] To provide a communication device capable of improving line quality. An output of A / D converters (903, 904) is monitored, a saturation frequency is measured, and when the saturation frequency exceeds a threshold, control is performed so as to reduce the gain of a variable gain amplifier (903). The despreading unit 107 monitors the line quality and uses the adaptive filter 1 provided in the feedback loop.
The AGC time constant is automatically controlled to an optimum value for each reception environment by updating the 15 filter coefficients as needed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a receiving system demodulator of a wireless communication system, and more particularly to an AGC circuit which stably supplies electric power suitable for a receiving environment.

[0002]

2. Description of the Related Art Conventionally, in a wireless communication system such as a digital mobile phone system, a CDMA (Code Division Multiple Access) system has been used as one of access methods.

The overall configuration of a conventional CDMA system will be described with reference to FIG. FIG. 3 shows an overall configuration diagram of the CDMA system. In FIG. 3, the base station 310 includes a wireless reception device 311 inside and receives wireless signals from the terminals 300A, B, and C. The base station 310 has a communication area as a range in which wireless communication is possible. The reception power received at the base station side constantly changes according to the distance between the base station and the mobile terminal and the surrounding environment. For example, when there is another system 320 that uses a narrow band signal around the base station 310, when fading occurs when moving at high speed like the terminal 300A, and when shadowing occurs by hiding in the shadow of a building like the terminal 300B. It may occur.

When the base station receives a signal from a terminal that is moving at high speed such as the terminal 300A, the received power repeats a rapid increase and decrease due to the effect of fading. Also, when communicating with a terminal in an environment where shadowing is likely to occur, such as the terminal 300B, the received power that has been stable until then suddenly drops by several tens of dB, or A phenomenon such as an increase occurs. When the above-described phenomenon occurs, the wireless receiver 311 in the base station 310 temporarily receives power that exceeds the allowable range.

Further, one of the characteristics of the CDMA system is that the reception power is made uniform by controlling the transmission power of each mobile terminal. In the case where, for example, another system 320 using a narrow band signal exists in the communication area of the base station,
Of course, since the transmission power of the other system 320 cannot be controlled, if the interference signal 301 is strong, high power will be received for a long time.

One of the further characteristics of the CDMA system is that the peak factor (Peak Factor: average power to peak power ratio) of the received signal changes depending on the number of terminals communicating at the same time. Originally, a CDMA signal has a high peak factor because it is noisy, but since a plurality of terminals communicate at the same frequency, the peak factor of the received signal of the base station depends on the number of terminals communicating or each terminal. It depends on the combination of spreading codes assigned.

As described above, the reception state of the base station changes from moment to moment with changes in the reception environment.

FIG. 4 shows the configuration of a conventional base station. In FIG. 4, the base station selects the channel of the received signal received by the antenna 404 that receives the signal, by the frequency using the channel selection filter 402. The quadrature demodulator 408 demodulates the selected channel signal, the variable gain amplifier 403 amplifies the signal, the A / D converter 401 converts the analog signal into a digital signal, and the digital signal received by the digital signal processing unit 400. Is being processed.

As described above, when the received power suddenly increases due to fading or shadowing, the A / D (analog-digital) converter 401 in the preceding stage of the digital signal processing section 400 is saturated or the bit resolution is lowered. Causes the SNR (signal to noise ratio) to deteriorate, and causes the line quality of the FER (Frame Error Rate) characteristic to deteriorate in the despreading unit. For this reason, conventionally, the variable gain amplifier 40 is provided before the A / D converter 401.
3 is used, the input level is kept constant and the saturation of the A / D converter 401 is suppressed. Further, even if a narrow band interference signal from another system exists in the vicinity of the own system band, a method of frequency blocking is used by using a channel selection filter 402 having a steep blocking characteristic so as not to be affected by it. ing. Alternatively, even if there is an interference signal in the own system band, each component of the wireless reception device 311 is configured to minimize the influence of the interference signal.
In particular, a method of selecting a device having a wide dynamic range is used for the A / D converter. Furthermore, even when the peak factor of the received signal is large, the A / D
To prevent frequent saturation of converter 401,
The output power of the variable gain amplifier 403 is the A / D converter 401.
For the maximum input amplitude range of, a method is used in which the peak factor is taken into consideration and the level is kept low.

FIG. 5 shows a conventional example of an AGC (Automatic Gain Control) system for controlling the gain of a variable gain amplifier. Received main signal IF (Intermediate
Frequency) 500 is the quadrature demodulator 501 for I signal and Q
After being orthogonally demodulated into two signals, the A / D converter I5
03 and A / D converter Q504 respectively perform A / D conversion and output to despreading section 507. BB (Base Ban
d) A part of the signals I and Q is output from the power calculator 51.
At 0, the instantaneous power calculation (I ² + Q ² ) is performed. The difference between this instantaneous power and the control target value P513 is calculated by the filter 5
15 and D / A (digital-analog) converter 50
The control voltage 517 is instructed to the variable gain amplifier 502 via 8.509. The AGC time constant is adjusted according to the response characteristics of the control target value P513 and the filter 515, so that the setting is suitable for the reception environment at the base station installation location.

[0011]

In the above-mentioned prior art, the output power of the variable gain amplifier 502 secures a margin considering the maximum possible peak factor with respect to the maximum input amplitude range of the A / D converter in the subsequent stage. And then set lower. That is, the dynamic range of the A / D converter is used while being narrowed by the margin. When narrow-band interference signals of other systems overlap within the own system band, it is not possible to block them in frequency with the channel filter, so both the interference signal and the desired signal are
It will be quantized by the / D converter. When receiving a high power interference signal, the desired signal to interference signal ratio deteriorates,
The bit resolution of the desired signal is reduced. Therefore A / D
Although it is desired to make the most effective use of the dynamic range of the converter, a certain margin must be secured in consideration of the reception state having a large peak factor as described above. That is, when determining the convergence value of the signal amplitude, a trade-off between the saturation of the A / D converter and the dynamic range of the A / D converter becomes a problem. Further, since the reception environment such as fading and shadowing varies depending on the installation location of the base station or the state of the terminal in communication, it is desirable to optimize the control target value of AGC or the filter characteristic according to the reception environment. With a fixed control target value or filter characteristics, depending on the reception environment, FE
There is a possibility that communication is performed in a state where the line quality such as R, PER (Packet Error Rate) or throughput is deteriorated.

In order to solve the above problems, it is an object of the present invention to provide a communication device capable of improving the line quality.

[0013]

In order to solve the above problems, the communication device of the present invention has a transmitting section for transmitting a signal and a receiving section for receiving the signal. The receiving unit includes a variable amplifier that amplifies a received signal at a designated amplification factor, a gain controller that instructs the variable amplification unit to the amplification factor, and a predetermined quality for the received signal. And a computing unit to be obtained. The gain controller is provided with an adaptive filter means for indicating a time constant indicating a response characteristic and for instructing the variable amplifier of the amplification factor, and a coefficient control means for instructing a time constant of the adaptive filter means.

The coefficient control means changes the time constant according to the quality obtained by the arithmetic unit. As the predetermined channel quality, for example, FER, PER, throughput or the like can be obtained.

According to the present invention, a predetermined channel quality is monitored, and the time constant of the adaptive filter provided in the gain controller is updated at any time to set the optimum AGC time constant for each receiving environment. This makes it possible to reduce the deterioration of the line quality due to the saturation of the A / D converter or the deterioration of the line quality due to the high power interference signal.

[0016]

DETAILED DESCRIPTION OF THE INVENTION A first embodiment of the present invention will be described below with reference to the drawings.

FIG. 9 shows the configuration of a base station which is a wireless communication device in the first embodiment. In FIG. 9, the base station includes an antenna 904 that transmits and receives a signal, and a duplexer 9 that transmits a transmission signal and receives a reception signal.
05, a transmitter 930, a receiver 940, and a digital processor 9 for digitally processing a transmission signal and a reception signal.
00 and. The receiving unit 940 amplifies the received signal with an LNA (amplifier) 906 that amplifies the received signal, a mixer 907 that performs frequency modulation, a channel selection filter 902 that selects a predetermined channel, and a designated amplification factor. A variable gain amplifier 903, a quadrature demodulator 908 for quadrature demodulating a received signal, A / D converters 920 and 921 for converting an analog signal into a digital signal,
AGC circuit 9 for controlling the amplification factor of the variable gain amplifier 903
And 50. The transmission unit 930 also includes a D / A converter 914 that converts the digital signal processed by the digital signal processing unit 900 into an analog signal, a variable gain amplifier 913 that amplifies the transmission signal, and a quadrature that orthogonally modulates the transmission signal. Modulator 912 and mixer 911 for performing frequency modulation
And an HPA 910 that amplifies a transmission signal.

In FIG. 9, an antenna 90 is provided at the base station.
The received signal received in 4 is converted into the channel selection filter 902.
Select the channel by frequency. The signal of the selected channel is amplified by the variable gain amplifier 903, and the quadrature demodulator 9
Quadrature demodulation at 08, A / D converters 920 and 921 convert the analog signal into a digital signal, and the digital signal processing unit 900 processes the received digital signal. The AGC circuit 950 includes A / D converters 920 and 92.
The I signal and the Q signal from 1 are received, the amplification factor of the variable gain amplifier 903 is obtained from the electric energy, and the obtained amplification factor is instructed to the variable gain amplifier 903 by the control voltage.

At the time of transmission, the transmission signal processed by the digital signal processing unit 900 is converted into an analog signal by the D / A converter 914, the transmission signal is amplified by the variable gain amplifier 913, and transmitted by the quadrature modulator 912. Quadrature modulate the signal. This transmission signal is frequency-modulated by the mixer 911, and HP
A910, Duplexer 905 and antenna 90
The transmission signal is transmitted via the transmission line 4.

Next, the AGC circuit according to the present embodiment will be described. FIG. 1 shows a functional block diagram of an AGC circuit 950 of a wireless communication device in a CDMA system.

In FIG. 1, the AGC circuit 950 is a BB
A power calculation unit 110 that calculates a power value from the signal I105 and the BB signal Q106, and A / D converters 920 and 921.
Amplitude saturation detection unit 109 for detecting the saturation frequency of the signal and the time constant indicating the response characteristic are instructed, and the amplification factor is set to the variable amplifier 903.
An adaptive filter 115 for instructing the above, a coefficient control unit 118 that controls the coefficient of the adaptive filter 115, and a coefficient table 112 that stores a predetermined coefficient.

In the present embodiment, the A / D converter 9
In order to prevent the saturation of 20 · 921, the amplitude saturation detection unit 109
At, the saturation frequency of the A / D converters 920 and 921 is detected, and the amplification factor of the variable gain amplifier is adjusted so as not to be saturated when it is saturated frequently. In addition, FER1 that indicates the line quality so that it can adapt to a receiving environment that changes over the long term.
19 is detected, and if the FER 119 increases and the quality deteriorates, the speed at which the feedback loop converges is adjusted by adjusting the time constant of the adaptive filter 115.

In FIG. 1, the main signal IF10 of the received signal is shown.
0 is output by the variable gain amplifier 903 to the AGC circuit 95.
It is amplified or attenuated at the amplification factor indicated by 0. The main signal IF100 is subjected to quadrature demodulation by the quadrature demodulator 908 and then A / D.
By the converter I920 and the A / D converter Q921,
The signals are A / D converted into digital signals of BB signal I105 and BB signal Q106, respectively, and input to the despreading unit 107 of the digital signal processing 900. Despreading unit 107
Calculates the FER by despreading the BB signal I 105 and the BB signal Q 106, and supplies the FER to the coefficient control unit 118.

The coefficient control unit 118 uses the coefficient table 112.
By applying the coefficient selection signal 111 to the adaptive filter 11
The filter coefficient of 5 is updated to control the time constant of the AGC. FIG. 10 shows a configuration example of the adaptive filter 115, and FIG. 11 shows a specific example of the stored contents of the coefficient table 112. In FIG. 10, an adaptive filter 115 includes taps a0 to ak which are filter coefficients and delay circuits 1001 to 100.
0K, adders 1011 to 101K, and an amplifier 1020 whose amplification factor is indicated by the power deviation Δ. In addition, as shown in FIG.
2 stores the time constant and the filter coefficient of each tap of the adaptive filter 115 corresponding to the coefficient selection signal. The coefficient table 112 is provided with the filter coefficient of the filter having the characteristic shown in FIG. 6 so that the AGC time constant β can be varied in each range of β1 to β2 by Δβ.

A method of controlling the time constant in the coefficient controller 118 will be described with reference to FIG. Selection signal AGC
A control flowchart of the time constant is shown in FIG. In the present embodiment, when the FER increases, the AGC time constant is decreased, and when the FER further increases, the AGC time constant β is increased by Δβ and the time constant is changed according to the FER. The time constant is controlled to the optimum value.

The AGC time constant β is determined by the despreading unit 107 as FE.
The coefficient control unit 118 calculates the average value of R every predetermined time Δt (for example, a long time such as 10,000 frames). The coefficient control unit 118
The increase / decrease of FER is monitored, and the value of FER (t) corresponding to the current AGC time constant β is stored (S700). FER
The value of (t) and FER (t- which is the value calculated immediately before.
1) is compared (S701), and if the current FER value is improved and the quality is improved, that is, FER (t−
If 1)> FER (t), t is updated to t + 1 (S
702), and shifts to the next FER monitoring (S70).
0). If the current FER value increases and the quality deteriorates, the coefficient selection signal 111 is instructed to decrease the current AGC time constant β by Δβ, and the coefficient table 112.
The coefficient is instructed to the adaptive filter 115 via (S70).
3).

After that, after changing the filter coefficient of the adaptive filter, the average value of FER (β-Δβ) is monitored again (S7).
04), and compares it with the FER (β) before the change (S70).
5). If the changed FER value is improved and the quality is improved, the coefficient selection signal 111 is instructed to further reduce the AGC time constant β by Δβ (S706), and the adaptive filter is supplied via the coefficient table 112. The coefficient is designated to 115 (S703). If the changed FER value increases and the quality deteriorates, change the AGC time constant β to Δβ.
The coefficient selection signal 111 to increase
The coefficient is instructed to the adaptive filter 115 via the coefficient table 112 (S707).

Further, after changing the filter coefficient of the adaptive filter, the average value of FER (β + Δβ) is monitored again (S7).
08), and compares it with the FER (β) before the change (S70)
9). If the changed FER value is improved and the quality is improved, the coefficient selection signal 111 is instructed to further increase the AGC time constant β by Δβ (S710), and the adaptive filter is supplied via the coefficient table 112. The coefficient is designated to 115 (S707). If the changed FER value increases and the quality deteriorates, the coefficient selection signal 111 is instructed to select the AGC time constant β, and the coefficient is sent to the adaptive filter 115 via the coefficient table 112. Instruct (S711). The average value of FER is monitored again (S71
2), the current FER (β) which is the value is FER (t)
(S713). Thus, the AGC time constant β
When the optimum value of is determined, the FER monitoring is started again.

By the processing as described above, the AGC time constant is changed according to the line quality, so that the optimum value can be controlled.

Next, the control of the target power value will be described. FIG. 8 shows a control flowchart of the target power value.

The BB signal I105 and the BB signal shown in FIG.
The signal Q106 is an amplitude saturation detection unit 109 and a power calculation unit.
110 is input. The power calculator 110 uses A / D conversion
Of the converter I920 and A / D converter Q921
Instantaneous power (I²+ Q ²) 114 is calculated. Shun
Hour power (I²+ Q²) 114 and control target value P113
The force deviation Δ116 is the same as that of the adaptive filter 115 shown in FIG.
Input to XA and variable gain via D / A converter 108
It becomes a gain control signal in the amplifier 903.

In FIG. 8, the amplitude saturation detector 109 is
By detecting the frequency (the number of times at a predetermined time) when the MSB (Most Significant Bit) of the instantaneous power 114 calculated from the BB signal I105 and the BB signal Q106 becomes '1' (the maximum value of the A / D converter). A /
The saturation frequency of the D converter is detected (S800). The predetermined time may be one frame, for example. When the saturation frequency exceeds a predetermined threshold value S (S801), the power control target value is set to P-Δ.
By changing to P to reduce the amplification factor (S802), this value is given to the feedback loop, and the A / D converter I90
3 and the saturation frequency of the A / D converter Q904 are suppressed.
For example, when considering the peak factor of 10 dB, the threshold value S is set so that the saturation frequency of the quadrature demodulator 203 or the A / D converters 103 and 104 is 1% or less. If the saturation frequency does not exceed the threshold value S even if it exceeds a predetermined time, the control target value P + ΔP is given to the feedback loop (S803), and the A / D converter I903 and the A / D converter Q904 are provided. The dynamic range of.

As described above, according to the first embodiment, by using the line quality such as FER, PER or throughput as the AGC control parameter in the despreading unit, the AGC time constant most suitable for the receiving environment is automatically set. It is possible to reduce the dependence of the design parameters of the base station on the reception environment and maintain good communication quality.

According to the first embodiment, the A / D
The saturation frequency of the A / D converter can be detected from the converter digital output, and the AGC gain control target value can be set so as not to saturate the A / D converter. This eliminates the need to always secure the peak factor margin of the A / D converter, so that the dynamic range of the A / D converter can be effectively used. For example, even if there is a high-power narrow-band interference signal in the own system band, if the peak factor is not large, the peak factor margin of the A / D converter is reduced and the dynamic range is expanded to cause interference signals. It is possible to minimize the influence and reduce the deterioration of communication quality.

Next, a second embodiment will be described with reference to the drawings. Also in the second embodiment, the wireless communication device shown in FIG. 9 which is referred to for explaining the first embodiment can be applied. In FIG. 9, the position of the quadrature demodulator is A
It may be arranged after the / D converter. FIG. 2 shows a functional block diagram of an AGC circuit using an adaptive filter according to the second embodiment.

In FIG. 2, the AGC circuit 2010 has a B
A power calculation unit 210 that calculates a power value from the B signal I204 and the BB signal Q205, an average power calculation unit 209 that integrates the power amounts calculated by the power calculation unit 210 to obtain an average value, and an average of the calculated powers. Power saturation detection unit 212 that detects when the value exceeds a predetermined threshold value
And an adaptive filter 215 for instructing a variable amplifier 903 of a gain and a time constant indicating a response characteristic, and a cycle control unit 216 for periodically instructing the adaptive filter 215 of a reset signal. The adaptive filter 215 includes an integral counter, and the time constant is determined by the instruction of the periodic reset signal. The time constant β is set in advance so as to correspond to the value of the FER so that the time constant β of the AGC is controlled within the range shown in FIG.

In the second embodiment, in order to prevent saturation of the A / D converter 202, the average power calculation unit 209 detects the average power of the A / D converter 920 and the average power is predetermined. The power saturation detection unit 212 detects that the threshold is exceeded, and adjusts the amplification factor of the variable gain amplifier so as not to saturate when saturated. In addition, the FER that indicates the line quality so that it can adapt to the receiving environment that changes over the long term.
When 217 is detected and the FER 217 increases and the quality deteriorates, the speed at which the feedback loop converges is adjusted by adjusting the time constant of the adaptive filter 215.

In FIG. 2, the main signal IF 200 is amplified or attenuated by the variable gain amplifier 201 at the amplification factor instructed by the AGC circuit 2010. After that, the main signal IF 200 is A / D converted into a digital signal by the A / D converter 202 and orthogonally demodulated by the orthogonal demodulator 203. The BB signal I204 and the BB signal Q205 are input to the despreading unit 206, respectively. Despreader 206
Calculates the FER by despreading the BB signal I204 and the BB signal Q205, and gives the calculation result to the cycle control unit 216. The cycle control unit 216 uses the adaptive filter 215.
Reset signal 214 to the integration counter of
The AGC time constant β is controlled in the range as shown in FIG. 6 by giving an instruction in a cycle determined corresponding to the value of ER.
Further, the cycle control unit 216 controls the F to the AGC time constant β.
Store the value of ER.

BB signal I204 or BB signal Q205
Of the instantaneous power (2
I ² ) or (2Q ² ) 211 is calculated. The instantaneous power (2I ² ) 211 is supplied to the adaptive filter 215 and the D / A.
A gain control signal is provided to the variable gain amplifier 201 via the converter 207. A part of the instantaneous power (2I ² ) 211 is input to the average power calculation unit 209. In the average power calculation unit 209, the average power value Pa2133 is calculated by integrating the instantaneous power 2I ² 211 for a predetermined time T.
To calculate. The calculated average power value Pa213 is given as the digital gain Pa / 2I ² of the adaptive filter 215. The MSB of the average power value Pa213 is input to the power saturation detection unit 212, and the frequency at which the MSB becomes '1' is monitored for a predetermined time. When the bit resolution of the A / D converter 202 is M bits, when Pa ≧ 2 ^{M +1} , M
SB becomes '1' and the A / D converter 202 determines that it is saturated. MS with average power value Pa213
When the frequency of B becoming “1” exceeds the threshold value S, the control target value is increased by ΔP by increasing the integration time by ΔT. If the saturation frequency does not exceed the threshold value S even if the predetermined time is exceeded, the integration time is decreased by ΔT and the control target value is decreased by ΔP. A / D
By converging the saturation frequency of the converter close to the threshold value S but not exceeding it, the dynamic range of the A / D converter can be expanded.

As described above, according to the second embodiment, the despreading unit automatically uses the line quality such as FER, PER or throughput as the AGC control parameter to automatically set the AGC time constant most suitable for the receiving environment. It is possible to reduce the dependence of the design parameters of the base station on the reception environment and maintain good communication quality.

According to the first embodiment, the A / D
The saturation frequency of the A / D converter can be detected from the converter digital output, and the AGC gain control target value can be set so as not to saturate the A / D converter. This eliminates the need to always secure the peak factor margin of the A / D converter, so that the dynamic range of the A / D converter can be effectively used. For example, even if there is a high-power narrow-band interference signal in the own system band, if the peak factor is not large, the peak factor margin of the A / D converter is reduced and the dynamic range is expanded to cause interference signals. It is possible to minimize the influence and reduce the deterioration of communication quality.

[0042]

As described above, according to the present invention, it is possible to realize a communication device capable of improving line quality and always maintaining good call quality under various receiving environments.

[Brief description of drawings]

FIG. 1 is a configuration diagram according to a first embodiment of the present invention.

FIG. 2 is a configuration diagram according to a second embodiment of the present invention.

FIG. 3 is an overall system configuration diagram.

FIG. 4 is a conventional base station configuration diagram.

FIG. 5 is a block diagram of a conventional AGC system.

FIG. 6 is an explanatory diagram showing filter characteristics.

FIG. 7 is a flowchart for AGC time constant control.

FIG. 8 is a flowchart for control target power value control.

FIG. 9 is a base station configuration diagram according to the first and second embodiments.

FIG. 10 is a configuration diagram of an adaptive filter according to the first embodiment.

FIG. 11 is an explanatory diagram of contents of a coefficient table according to the first embodiment.

[Explanation of symbols]

903 ... Variable gain amplifier 908 ... Quadrature demodulator 903/904 ... A / D converter 107 ... Despreading unit 108 ... D / A converter 109 ... Amplitude saturation detector 110 ... Power calculation unit 115 ... Adaptive filter 112 ... Coefficient table 118 ... Coefficient control unit.

Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) H04B 1/707 H04J 13/00 D (72) Inventor Michiaki Ueda 216 Totsuka-cho, Totsuka-ku, Yokohama-shi, Kanagawa Hitachi Ltd. (72) Inventor Tsuyoshi Yamaguchi, 216 Totsuka-cho, Totsuka-ku, Yokohama-shi, Kanagawa, Ltd.Hitachi, Ltd. Communications Division, (72) Yasuyuki Asara, 393, Totsuka-cho, Totsuka-ku, Yokohama-shi, Kanagawa Electronic company F term (reference) 5J023 DA03 DB01 DD01 DD07 5J100 JA01 LA01 LA08 LA11 QA01 SA02 5K022 EE01 EE31 5K061 AA11 BB12 CC52 JJ24

Claims (5)

[Claims] 1. A communication device having a transmitting section for transmitting a signal and a receiving section for receiving the signal, wherein the receiving section includes a variable amplifier for amplifying the received signal at a designated amplification factor, and the variable amplification. A gain controller for instructing the amplification factor with respect to the means, and the received signal, comprising an arithmetic unit for obtaining a predetermined quality, the gain controller is instructed time constant indicating a response characteristic,
An adaptive filter means for instructing the amplification factor to the variable amplifier, and a coefficient control means for instructing a time constant of the adaptive filter means are provided, wherein the coefficient control means is in accordance with the quality obtained by the arithmetic unit. A communication device characterized by changing a time constant. 2. The communication device according to claim 1, wherein the gain controller further includes power calculation means for obtaining a power amount of the received signal, and control means for changing the amplification factor according to the power amount. The communication device, wherein the adaptive filter means uses the amplification factor changed by the control means as a gain of the adaptive filter. 3. The communication device according to claim 2, wherein the control means detects the number of times the power amount exceeds a predetermined power amount within a predetermined time, and the number of times is a predetermined number. When it exceeds, the communication device is controlled to reduce the amplification factor. 4. The communication device according to claim 2, wherein the control means averages the power amounts and detects the number of times the averaged power amount exceeds a predetermined power amount in a predetermined time. A communication device, which controls to reduce the amplification factor when the number of times exceeds a predetermined number. 5. A communication device having a transmitter for transmitting a signal and a receiver for receiving the signal, wherein the receiver has a variable amplifier for amplifying the received signal at a designated amplification factor, and the variable amplifier. A gain controller for instructing the amplification factor with respect to the gain controller, the gain controller according to the frequency of the power calculation means for obtaining the power amount of the received signal, and the power amount exceeds a predetermined power amount. A communication device comprising: a control unit that controls the amplification factor.