JPH08307174A - Automatic gain controller for multi-channel receiver - Google Patents

Abstract

PURPOSE: To make the receiver small and to reduce the cost by obtaining a power of a carrier demodulated digitally by a power arithmetic, section and controlling a gain of a variable gain amplifier depending on the magnitude of the power so as to eliminate the need for a band limit filter. CONSTITUTION: The controller is provided with an antenna 41 receiving a radio wave sent while dividing 16-value QAM symbol into plural carriers, a band pass filter 42 connecting to the antenna 41, a gain variable amplifier 43 to adjust the gain with respect to a reception signal level, and a power arithmetic section 61 receiving output signals I, Q from an I axis identification section 58 and a Q axis identification section 59, calculating the power of the symbol and controlling the gain of the variable gain amplifier 43 based on the result. Then the power arithmetic section 61 obtains the power of the carrier demodulated digitally and controls the gain of the variable gain amplifier depending on the magnitude of the power to obtain the automatic gain controller inexpensively comparatively simply without the need for a band control filter.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic gain control device (AGC) for a multi-channel receiver, and more particularly to an automatic gain control device capable of realizing miniaturization.

[0002]

2. Description of the Related Art FIG. 8 is a diagram showing an automatic gain control device in a conventional receiver. As shown in the figure, the reception signal from the receiver antenna 1 passes through the variable amplifier 3 via the bandpass filter 2. A mixer 4 is connected to the variable amplifier 3, and the mixer 4 mixes the signal from the local oscillator 5 with the variable amplifier 3.
The signal from is mixed and an intermediate frequency, for example, 10.7 MHz for FM broadcasting is formed. The intermediate frequency signal passes through the low pass filter 6 and is demodulated by the demodulator 7. The receiver is provided with an automatic gain control device 8. The automatic gain control device 8 includes a diode 9 for rectifying an intermediate frequency signal of the low pass filter 6 and a low pass filter 10 for smoothing the rectified signal to form a DC component.
And a reference voltage forming section 12 for outputting a reference voltage, and a differential amplifier 11 for controlling the gain of the variable amplifier based on the difference between the DC component and the reference voltage.

[0003]

However, the automatic gain control device for the above-mentioned receiver is arranged in an OFDM (Orthogonal Frequent
When applied to a multicarrier receiver such as ncy division multiplex), the following problems occur. First, with OFDM will be briefly described. FIG. 9 is a block diagram of an OFDM transmission / reception circuit. OFDM divides information (symbol) to be transmitted into a plurality of carriers (subcarriers) and transmits the information. As shown in the figure, the transmission circuit has, for example, 16-value QAM (Quadratureamplitude
(dulation) input symbol sequence is converted to the same degree of parallelism as the number of carriers, and a serial-parallel conversion circuit 21 and an inverse FFT (Fas (Fas)
t Fourier Transformation) 22, a circuit 23 that performs parallel-serial conversion to perform a D / A converter (Digital to Analog Converter) next, a low-pass filter 24 that is connected to the circuit 23 and outputs a baseband time series, Thereafter, a mixer 25 and a carrier oscillator 26 for converting to a desired RF carrier frequency
And a bandpass filter 27 connected to the mixer 25. The modulated signal is input to the bandpass filter 29 via the transmission line 28. The receiver circuit includes a mixer 30 and a local oscillator 3 in order to perform processing reverse to that of the transmitter circuit.
1. A circuit 32 that performs A / D conversion (Analog to Digital Conversion) and serial-parallel conversion, an FFT 33, and a parallel-serial conversion circuit 34 are provided to obtain a received symbol string.

FIG. 10 is a diagram showing a frequency spectrum of OFDM. OFDM is a digital modulation method aiming at both improvement of transmission rate per bandwidth and prevention of multipath interference and the like. As shown in FIG. 10, it is a multicarrier modulation method using hundreds of carriers. In OFDM, the carrier waves are orthogonal to each other, and the frequency components of the carrier waves overlap each other, so that many carrier waves can be packed and the frequency utilization efficiency becomes high. Digital modulation is performed after the serial-parallel converted encoded data is assigned to each of these carriers. By increasing the number of carriers, the transmission rate per bandwidth can be increased. Furthermore, since the effects of interleaving and error correction code extend over a plurality of carriers, the error correction capability is also improved. The digital modulation of each carrier is performed by converting the frequency domain into the time domain by the inverse FFT 22, and the digital demodulation of each carrier is performed by the FFT 33.
To convert from the time domain to the frequency domain. In a multi-channel receiver using such an OFDM, an automatic gain control device 8 as shown in FIG.
When the mixer 31 attempts to process the converted baseband time-series signal, the baseband time-series signal is composed of a large number of carrier waves, and thus it is like white noise. Thus, there is a problem that a band limiting filter is separately required for the automatic gain control device. For this reason,
This hinders downsizing and price reduction of the receiver.

Therefore, in view of the above problems, it is an object of the present invention to provide an automatic gain control device for a multi-channel receiver that does not require a band control filter in order to reduce the size and cost of the receiver. To do.

[0006]

In order to solve the above problems, the present invention provides an automatic gain control device for a multi-channel receiver having the following configuration. An automatic gain control device for a multi-channel receiver that digitally demodulates a large number of carriers included in a received signal into a symbol string is provided with a variable gain amplifier for adjusting the gain depending on the strength of the received signal level. The power calculation unit obtains the power of the digitally demodulated carrier wave and controls the gain of the variable gain amplifier according to the magnitude of the power.

The power calculator may average the powers of a plurality of carriers of one symbol to obtain the power of the carrier. The power calculator may average the powers of a plurality of carriers of a plurality of symbols to obtain the power of the carrier. When the quadrature conversion modulation signal is input to the multi-channel receiver, two variable amplifiers are provided in the I channel and the Q channel, and the gains of the two variable amplifiers are adjusted based on the levels of the output signals of the I channel and the Q channel. You may control.

[0008]

According to the automatic gain control device for a multi-channel receiver of the present invention, the power calculation unit obtains the power of the digitally demodulated carrier wave and determines the gain of the variable gain amplifier according to the magnitude of the power. By controlling
AGC can be realized relatively easily and inexpensively.

In order to obtain the power of the carrier wave, the power calculation unit averages the powers of a plurality of carrier waves of one symbol, so that not only a single carrier wave but also the average power of a plurality of carrier waves is used. By performing AGC,
Even if there is fading due to multipath and one carrier is lost, the power is not lost as described above, so that the AGC can be controlled.

The power calculation unit averages the powers of a plurality of carriers of a plurality of symbols in order to obtain the power of a carrier, so that there is fading due to multipath and there are many carriers in one symbol. The loss of power does not result in loss of power, so that the AGC can be controlled. When the quadrature conversion modulation signal is input to the multi-channel receiver, two variable amplifiers are provided in the I channel and the Q channel, and the gains of the two variable amplifiers are adjusted based on the levels of the output signals of the I channel and the Q channel. By controlling, it is possible to improve the demodulation accuracy by eliminating the level difference due to the difference in the efficiency processing system of the orthogonal transformation in the case of digital demodulation by the two FFTs.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing an automatic gain control device for a multi-channel receiver according to an embodiment of the present invention. The multi-channel receiver according to the present embodiment is based on the OFDM method, and for example, an antenna 4 that receives a radio wave transmitted by dividing a 16-value QAM symbol into a plurality of carriers.
1 and a bandpass filter 42 connected to the antenna 41.
A variable gain amplifier 43 for adjusting the gain with respect to the strength of the received signal level, an I channel mixer 44 on the side orthogonal to the received signal, and a Q channel mixer 45 on the in-phase side of the received signal. , A local oscillator 46 which generates an RF carrier frequency signal for conversion into a baseband time series and outputs the signal to the mixer 45, and a phase of the local oscillator 46 is 90
A 90 ° phase shifter 47 for phase shifting and outputting to the mixer 24,
The low-pass filters 48 and 49 connected to the mixers 44 and 45 for removing signals of unnecessary frequencies, the variable gain amplifiers 50 and 51 for adjusting the levels of the I channel and the Q channel, and the variable amplifiers 50 and 51, respectively. A / D conversion (Analog to Digital Conver)
circuits for performing serial-parallel conversion for converting the symbol string into the same degree of parallelism as the number of carriers, and serial-parallel conversion circuits 52 and 53 respectively connected to digital circuits by conversion from the time domain to the frequency domain. FFT5 for demodulation
4 and 55, and FFTs 54 and 55, respectively, and circuits 56 and 57 for performing parallel-serial conversion for outputting received symbols; and I-axis of codes connected to the parallel-serial conversion circuits 56 and 57 to form symbols And an I-axis identifying section 58 and a Q-axis identifying section 59 that identify between the Q-axis and the Q-axis, and a combining section 60 that forms data based on the codes identified by the I-axis identifying section 58 and the Q-axis identifying section 59. To do.

Further, the I-axis identifying section 58 and the Q-axis identifying section 5
A power calculator 61 is provided for inputting the output signals I and Q from 9 to calculate the power of the symbol and controlling the gain of the variable gain amplifier 43 based on the result. Further, output signals I and Q from the I-axis identification unit 58 and the Q-axis identification unit 59 are output.
To adjust the gains of the variable amplifiers 50 and 51 in order to adjust the imbalance of the I-axis and Q-axis levels by comparing the respective output signal levels.
Two are provided.

FIG. 2 is a diagram showing a code arrangement of 16AQAM. As shown in the figure, regarding the code of the 16QAM wave, there are three types of amplitudes of the received signal, and when the maximum amplitude is A, there are 5 ^1/2 A / 3 and A / 3 in addition. FIG. 3 is a diagram for explaining the processing in the FFTs 54 and 55 of FIG. As shown in the figure, the time-domain signal is input to the I-channel FFT 54 and the Q-channel FFT 55, and the frequency-domain signal is output. In these output signals, a peak of 1 indicates a carrier of 1 and the peak as a whole indicates one symbol on the I channel side or the Q channel side.

FIG. 4 is a flow chart for explaining the gain control by the power calculator 61 of FIG. In step S1, the following constants are set. That is, the powers c1 and c at the maximum amplitude and at other amplitudes corresponding to this
2. Set c3 as the reference power.

Here, c1 = A ² , c2 = 5A / 9, c3 = A / 9 c0 <c3.

In step S2, the power z of the received signal is calculated as follows. z = I ² + Q ^{2 In} step S3, it is determined whether or not c1 ≧ z> c2. If this determination is "YES", the process proceeds to step S2, and if "NO", the process proceeds to step S4.

In step S4, when the above judgment is established, Δ = c1−z is calculated. In step S5, the gain of the variable gain amplifier 43 is controlled based on this Δ, and the return processing is performed.

In step S6, if the determination in step S1 is not satisfied, it is determined whether or not c2 ≧ z> c3. If this determination is "YES", the process proceeds to step S7, and if "NO", the process proceeds to step S8. In step S7, when the above determination is satisfied, Δ = c2-z is calculated, and the process proceeds to step S5, in which the gain of the variable gain amplifier 43 is controlled based on this Δ.

In step S8, if the determination in step S6 is not satisfied, it is determined whether or not c3≥z> c0. If this judgment is "NO", the process proceeds to the return process. When z≤c0, fading occurs due to multipath and AGC is not performed because power is lost. If this determination is "YES", the process proceeds to step S9.

In step S9, when the above determination is established, Δ = c3−z is calculated, and the process proceeds to step S5. Based on this Δ, the gain of the variable gain amplifier 43 is controlled. In this way,
In the OFDM multi-channel receiver, the power is calculated using the result of the FFT processing at the time of demodulation, and the AG is calculated.
By performing C, AGC is relatively easy and inexpensive.
Can be realized.

FIG. 5 is a diagram for explaining another example of the processing of the power calculator 61. The power calculation unit 61 calculates the power z1 of the first carrier and the power z2 of the second carrier of one symbol in the power calculation of step S2 of FIG.
..., the power zn carrier of the n, as ^{_{follows, z1 = I 1 2 + Q}} 1 2, z2 = I 1 2 + Q 1 2, ... zn = I n 2 + Q n 2 obtains. Then, the average value zA of the power is obtained as follows.

ZA = (z1 + z2 + ... + zn) / n In this way, by performing the AGC using not only a single carrier but also the average of the powers of a plurality of carriers, there is fading due to multipath. Even if one carrier is lost, the power is not lost as described above, so that the AGC can be controlled.

FIG. 6 is a diagram showing another example of the processing of the power calculation unit 61. The power calculation unit 61 performs step S in FIG.
In the power calculation of 2, a plurality of symbols n, n + 1,
It is also possible to extract a plurality of carriers from n + m and obtain the average power in the same manner as described above. in this way,
Since power is not calculated in one symbol but AGC is performed in a plurality of symbols, even if there is fading due to multipath and many carriers in one symbol are lost, there is power loss. A
It becomes possible to control the GC.

FIG. 7 is a flow chart for explaining the operation of the balance adjusting section 62 of FIG. In step S11, D1 and D2 are set. In the quadrature demodulation, the I channel and the Q channel have two amplitudes, which are A / 2 ^1/2 and A / 3 · 2 ^1/2 with reference to FIG. Here, D1 = A / 2 ^1/2 and D2 = A / 3 · 2 ^1/2 .

In step S12, n = 1. In step S13, Δ1 (n) = 0 and Δ2 (n) = 0 are set.

In step S14, it is determined whether or not D1 ≧ I ≧ D2 and D1 ≧ Q ≧ D2. If this determination is "YES", the process proceeds to step S15, and if "NO", the process proceeds to step S16. In this judgment, I and Q are judged independently.

If the above determination is made in step S15, the processing of Δ1 (n) = D1−I, Δ2 (n) = D1−Q is performed, and the process proceeds to step S17. Step S16
In step S14, if the determination in step S14 is negative, Δ1 (n) = D2-I and Δ2 (n) = D2-Q are processed, and the process proceeds to step S17.

In step S17, Δ1 (n) = Δ1 (n-1) + Δ1 (n) and Δ2 (n) = Δ2 (n-1) + Δ2 (n) are processed. In step S18, it is determined whether or not n = n0. If this determination is "NO", the process proceeds to step S19, and if "YES", the process proceeds to step S20.

If the above determination is not satisfied in step S19, n = n + 1 is set and the process returns to step S14, and the following procedure is performed a predetermined number of times n.
0 Repeat. In step S20, step S18
When the determination is satisfied, the processing of Δ1A = Δ1 (n0) / n0 and Δ2A = Δ2 (n0) / n0 is performed.

In step S21, the gains of the variable amplifiers 50 and 51 are controlled based on Δ1A and Δ2A. In this way, it is possible to improve the demodulation accuracy by eliminating the level difference due to the difference in the efficiency processing system of the orthogonal transformation when the digital demodulation is performed by the FFTs 54 and 55.

[0031]

As described above, according to the present invention, the power calculator obtains the power of the digitally demodulated carrier wave and controls the gain of the variable gain amplifier according to the magnitude of this power. AGC can be realized easily and inexpensively. In order to obtain the power of the carrier waves, AGC is performed not only by using the power of a single carrier but also by averaging the powers of a plurality of carriers of one symbol. Even if one carrier is lost,
Since the power is not lost as described above, the AGC can be controlled. Since the powers of multiple carriers of multiple symbols are averaged to obtain the power of the carrier, even if there is fading due to multipath and many carriers in one symbol are lost, there is no power loss. Therefore, the AGC can be controlled. Since the gains of the two variable amplifiers are controlled based on the levels of the output signals of the I channel and the Q channel, by eliminating the level difference due to the difference in the efficiency processing system of the orthogonal transformation in the case of digital demodulation by two FFTs, It becomes possible to improve the demodulation accuracy.

[Brief description of drawings]

FIG. 1 is a diagram showing an automatic gain control device for a multi-channel receiver according to an embodiment of the present invention.

FIG. 2 is a diagram showing a code arrangement of 16AQAM.

FIG. 3 is a diagram illustrating a process in FFTs 54 and 55 of FIG.

4 is a flowchart illustrating gain control by a power calculation unit 61 of FIG.

FIG. 5 is a diagram illustrating another example of the processing of the power calculation unit 61.

FIG. 6 is a diagram showing another example of processing of the power calculation section 61.

FIG. 7 is a flowchart illustrating the operation of the balance adjustment unit 62 in FIG.

FIG. 8 is a diagram showing an automatic gain control device in a conventional receiver.

FIG. 9 is a block diagram of an OFDM transmission / reception circuit.

FIG. 10 is a diagram showing a frequency spectrum of OFDM.

[Explanation of symbols]

 43 ... Variable gain amplifier 50, 51 ... Variable amplifier 61 ... Power calculation unit 62 ... Balance adjustment unit

Claims (4)

[Claims] 1. An automatic gain control device for a multi-channel receiver that digitally demodulates a large number of carriers included in a received signal into a symbol string, and a variable gain amplifier for adjusting the gain depending on the strength of the received signal level ( 43) and the power of the carrier wave which has been digitally demodulated, and the variable gain amplifier (43) according to the magnitude of this power.
And a power calculation unit (61) for controlling the gain of the multi-channel receiver. 2. The multi-channel receiver according to claim 1, wherein the power calculator (61) averages the powers of a plurality of carriers of one symbol to obtain the power of the carriers. Automatic gain control device. 3. The multi-channel receiver according to claim 1, wherein the power calculation unit (61) averages powers of a plurality of carriers of a plurality of symbols to obtain the power of the carrier. Automatic gain control device. 4. When inputting a quadrature conversion modulation signal to the multi-channel receiver, variable amplifiers (50, 51) are provided for the I channel and the Q channel, and based on the levels of the output signals of the I channel and the Q channel. To control the gain of the variable amplifier (50, 51),
An automatic gain control device for a multi-channel receiver according to claim 1.