JP2002319990A - Automatic gain control system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make the set processable time of AFC longer than conventional one. SOLUTION: A received signal S1 is a data signal obtained by imposing quadrature modulation by adding a preamble including data for frequency synchronization at the head of a frame. A step variation type variable attenuator 1 is an attenuator and controlled by an attenuation control part 3 to roughly adjust the level of the received signal S1 in a short time. An AFC part 8 performs automatic frequency control according to the preamble of a quadrature detection output signal which is digitally converted by an A/D conversion part 7. A coefficient generation part 10 receives the digitally-converted quadrature detection output signal to start operating in parallel to the AFC part 8, and computes and outputs the ratio of the signal level value of the preamble and a fixed constant level value as a gain control coefficient. A multiplication part 9 multiplies the digital signal which has its frequency automatically controlled by the AFC part 8 by the gain control coefficient and outputs the result as an output signal S2 having been controlled to the constant level.

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 method for a digital receiving apparatus applied to a communication system such as a wireless LAN, and more particularly to a method for transmitting a quadrature-modulated data signal by adding a preamble for frequency synchronization to the head of a frame. The present invention relates to an automatic gain control method of a digital receiving apparatus which receives and performs setting processing of automatic frequency control (AFC) within a preamble period.

[0002]

2. Description of the Related Art FIG. 2 is a block diagram showing an example of a conventional automatic gain control system for a digital receiver of this kind.

Here, the received signal S1 is a data signal with a preamble added to the beginning of a frame, as shown in FIG. 4, for example, and the preamble contains data for frequency synchronization.

In FIG. 2, a digital receiver includes a variable attenuator 1 for coarsely adjusting the signal level of an input received signal S1.
And a bandpass filter (BPF) for removing unnecessary signal components
2, an attenuation control unit 3 for controlling the variable attenuation unit 1, and an AGC amplification unit 4 for finely adjusting the signal level to a predetermined constant level.
A quadrature detector 5 for quadrature detecting the output signal of the AGC amplifier 4 and demodulating it into data signals orthogonal to each other, an AGC controller 6 for controlling the AGC amplifier 4, and an A for digitally converting the quadrature detection output signal. A / D conversion unit 7 and an AFC unit 8 that receives the digitally converted quadrature detection output signal, performs AFC processing, and outputs the result as an output signal S2.

The variable attenuator 1 is a variable step attenuator. The attenuation control unit 3 detects the head level of the preamble, sets the attenuation of the variable attenuation unit 1 stepwise so that the received signal level becomes an appropriate value within a predetermined allowable value in a short time, and sets an excessive signal level. Sparse adjustment is performed so as to prevent the occurrence of distortion due to.

The AGC control unit 6 receives the digital signal output from the A / D conversion unit 7, detects the signal level of the preamble, and controls the AGC amplification unit 4 so that the signal level becomes constant.
Fine-tune the gain of the.

[0007] The AFC unit 8 receives the digitally converted quadrature detection output signal and detects a phase difference from a reference phase during the preamble period based on the real part and the imaginary part of the quadrature detection output of the frequency synchronization data included in the preamble. The automatic frequency control is performed by setting and holding the phase and correcting the phase.

The AFC section 8, as shown in FIG. 3, for example, detects a phase difference from a reference phase based on the amplitudes of a real part and an imaginary part, and corrects the detected phase difference. And a phase shift circuit 32. When the data signal passes through the phase shift circuit 32, the data signal is synchronously adjusted to the reference frequency.

[0009]

In the above-mentioned conventional example,
AFC processing is performed based on a preamble of a signal that has been AGC-controlled to a predetermined constant level.

However, O which is generally used in a wireless LAN
Since the preamble period of the FDM signal is very short, A
The operable time allowed when the FC unit performs the AFC setting process is short. To detect the phase difference and set the phase correction amount within the preamble period, the AFC process needs to be speeded up, and the circuit configuration is There is a problem that it becomes complicated.

SUMMARY OF THE INVENTION An object of the present invention is to provide an automatic gain control system capable of making the setting processing time of AFC longer than before, relaxing the AFC processing speed and simplifying the circuit configuration.

[0012]

According to the automatic gain control method of the present invention, a data signal orthogonally modulated by adding a preamble for frequency synchronization to the head of a frame is received, and orthogonally detected to perform a data signal orthogonal to each other. Digital demodulation after demodulation, an automatic gain control system of a digital receiving device that performs automatic frequency control processing based on the preamble of the digitally converted quadrature detection output signal, wherein the digitally converted quadrature detection output signal Means for generating the coefficient based on the signal level of the preamble, and a multiplication means for fine-adjusting the gain by multiplying the signal subjected to automatic frequency control processing based on the digitally converted quadrature detection output signal by the coefficient, The process of calculating the coefficient and the automatic frequency control process are performed in parallel.

More specifically, a variable attenuating means for detecting the level of a quadrature-modulated received signal with a frequency synchronization preamble added to the beginning of a frame and performing gain coarse adjustment stepwise, and this variable attenuating means. Quadrature detection means for orthogonally detecting a signal whose gain has been coarsely adjusted and demodulating the signal into data signals orthogonal to each other, A / D conversion means for digitally converting an output signal of the orthogonal detection means, and digital conversion by the A / D conversion means. AFC means for performing automatic frequency control processing based on the preamble of the converted quadrature detection output signal, wherein the gain control coefficient is based on the preamble of the digitally converted quadrature detection output signal. Coefficient generating means for generating the AFC
Multiplying means for multiplying the output signal of the means by the gain control coefficient and finely adjusting the output signal to a predetermined constant level.

The AFC means and the coefficient generating means simultaneously receive the digitally converted quadrature detection output signals and operate in parallel with each other.

Further, the coefficient generation means detects the signal level of the preamble of the digitally converted quadrature detection output signal, calculates a ratio with the predetermined constant level, and generates the gain control coefficient.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the present invention, in which the same components as those in the conventional example shown in FIG. The difference from the conventional example is that the digital signal subjected to the AFC processing by the AFC unit 8 is digitally operated by the multiplication unit 9 to perform fine level adjustment.

In FIG. 1, a digital receiver includes a variable attenuator 1 for coarsely adjusting the signal level of an input received signal S1.
And a bandpass filter (BPF) for removing unnecessary signal components
2, an attenuation control unit 3 for controlling the variable attenuation unit 1, an orthogonal detection unit 5 for orthogonally detecting the output signal of the band-pass filter (BPF) 2 and demodulating it into data signals orthogonal to each other, and digitally outputting the orthogonal detection output signal. An A / D conversion unit 7 for performing conversion, an AFC unit 8 for performing automatic frequency control processing (AFC) based on a preamble of the digitally converted quadrature detection output signal,
A multiplication unit 9 that multiplies the output signal of the FC unit 8 by a gain control coefficient and outputs the multiplied signal as an output signal S2 of a predetermined constant level, and a coefficient generation unit 10 that generates a gain control coefficient.

Here, the received signal S1 is a data signal that is orthogonally modulated by adding a preamble for frequency synchronization to the head of the frame, for example, as shown in FIG.

The variable attenuator 1 is a step variable attenuator, and is controlled by the attenuation controller 3 to attenuate the received signal level stepwise.

The attenuation control unit 3 detects the head level of the preamble, and sets the attenuation of the variable attenuation unit 1 stepwise so that the received signal level becomes an appropriate value within a predetermined allowable value in a short time. Sparse adjustment is performed to prevent the occurrence of distortion due to an excessive signal level.

The AFC unit 8, for example, as shown in FIG.
Phase difference detection circuit 31 for detecting a phase difference from a reference phase based on the amplitudes of the real part and the imaginary part of the quadrature detection output signal
And a phase shift circuit 32 for correcting the detected phase difference.

The AFC section 8 receives the digitally converted quadrature detection output signal, and detects a phase difference from the reference phase based on the real part and imaginary part of the quadrature detection output of the frequency synchronization data included in the preamble. Then, the detected phase difference is set and held in the phase shift circuit within the preamble period, and the automatic frequency control of the data signal is performed.

Next, the operation will be described.

The input received signal S1 is roughly adjusted in level in a short time by the variable attenuator 1, and is subjected to a bandpass filter (BP).
F) After the required signal components are extracted by 2, the orthogonal signal is orthogonally detected by the orthogonal detector 5 and demodulated into data signals orthogonal to each other.

The quadrature detection output signal is converted into a digital signal by an A / D converter 7 and input to an AFC unit 8 where it is automatically frequency-controlled. And output as an output signal S2.

In general, in AFC processing,
It is less affected by variations in input level. Therefore, even if the signal level is coarsely adjusted by the variable attenuator 1, the frequency can be controlled.

According to the present invention, the signal that has been subjected to the AFC processing is finely adjusted to a predetermined constant level by digital operation, so that the processable time within the preamble period in the AFC section 8 is made longer than before. For this purpose, a multiplier 9 and a coefficient generator 10 are provided.

Here, the AFC unit 8 and the coefficient generation unit 10
, Simultaneously input the quadrature detection output signals digitally converted by the A / D converter 7 and start operations in parallel.

The coefficient generator 10 calculates the signal level value by integrating the signal values of the preambles of the real part and the imaginary part of the digital quadrature detection output signal, and calculates the ratio between the signal level value and a predetermined constant level value. Then, it is stored as a gain control coefficient and output to the multiplication unit 9.

The multiplication unit 9 multiplies the digital signal subjected to automatic frequency control in the AFC unit 8 by a gain control coefficient, and outputs an output signal S2 finely adjusted to a predetermined constant level.

The timing at which the coefficient generation section 10 calculates and outputs the gain control coefficient is earlier than the timing at which the AFC section outputs the signal subjected to the AFC processing, and the multiplication section 9 performs gain control on the information data of the frame. By multiplying by the coefficient, fine adjustment of the signal level that could not be controlled by the variable attenuator 1 can be performed.

[0033]

As described above, according to the present invention, A
The digital signal after the FC processing is multiplied by a gain control coefficient to finely adjust the digital signal to a predetermined constant level. In this case, by performing the gain control coefficient calculation processing and the AFC processing in parallel, the preamble is obtained. Since the AFC processing possible time within the period can be made longer than before, the AFC processing speed can be made slower than before and the circuit configuration can be simplified.

[Brief description of the drawings]

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

FIG. 2 is a block diagram showing a conventional example.

FIG. 3 is a block diagram illustrating an example of an AFC unit 8;

FIG. 4 is a diagram illustrating an example of a frame configuration of a received signal.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Variable attenuation part 2 Band-pass filter (BPF) 3 Attenuation control part 5 Quadrature detection part 7 A / D conversion part 8 AFC part 9 Multiplication part 10 Coefficient generation part

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H04B 1/16 H04L 27/00 F

Claims (6)

[Claims] An orthogonally modulated data signal having a frequency synchronization preamble added to the beginning of a frame is received, orthogonally detected, demodulated into mutually orthogonal data signals, and then digitally converted. An automatic gain control method for a digital receiver that performs automatic frequency control processing based on the preamble of a detection output signal, wherein a coefficient for gain control is calculated based on the digitally converted quadrature detection output signal, and the automatic frequency control is performed. An automatic gain control method, wherein a gain is finely adjusted to a predetermined constant level by multiplying the processed signal by the coefficient. 2. The automatic gain control method according to claim 1, wherein the processing for calculating the coefficient is executed in parallel with the automatic frequency control processing. 3. A means for generating the coefficient based on the signal level of the preamble of the digitally-converted quadrature detection output signal, and an automatic frequency control processing based on the digitally-converted quadrature detection output signal. 2. The automatic gain control method according to claim 1, further comprising a multiplication means for multiplying a coefficient to finely adjust the gain. 4. A variable attenuator for detecting the level of a quadrature-modulated received signal with a frequency synchronization preamble added to the beginning of a frame and performing a coarse gain adjustment stepwise, and a coarse gain adjustment by the variable attenuator. Orthogonal detection means for orthogonally detecting the demodulated signal and demodulating it into data signals which are orthogonal to each other; and A for digitally converting the output signal of the orthogonal detection means
An automatic gain control method for a digital receiving apparatus comprising: a digital-to-analog (D / D) conversion unit; and an AFC unit that performs automatic frequency control processing based on a preamble of the quadrature detection output signal digitally converted by the A / D conversion unit. A coefficient generating means for generating a gain control coefficient based on the preamble of the converted quadrature detection output signal, and a multiplying means for multiplying the output signal of the AFC means by the gain control coefficient and finely adjusting the output signal to a predetermined constant level are provided. An automatic gain control method characterized in that: 5. The automatic gain control method according to claim 4, wherein said AFC means and said coefficient generating means simultaneously receive said digitally converted quadrature detection output signals and operate in parallel with each other. 6. The gain generation means for detecting a signal level of a preamble of the digitally converted quadrature detection output signal, calculating a ratio of the preamble to a predetermined constant level, and generating the gain control coefficient. The automatic gain control method according to claim 5, wherein