JP4316420B2 - Automatic gain control device, receiver and automatic gain control method - Google Patents

Description

  The present invention relates to an automatic gain control device for the purpose of extending a range in a mobile communication receiver.

By the way, this automatic gain control apparatus compensates for fluctuations in received power due to changes in propagation state in a digital modulation system mobile communication receiver in recent years, and keeps the power in the demodulator within the dynamic range that can maintain the demodulation quality. It plays a role to fit in. As a control method for received power, control is performed to lower the gain if the value of the input signal is higher than a certain threshold value, and to increase the gain if the input signal value is lower than another threshold value. In particular, a digitally modulated radio signal has a large peak factor, which is a ratio of the average power of the envelope to the peak power, and requires a device such as averaging.
A conventional automatic gain control device, for example, an automatic gain control device described in Patent Document 1, is characterized in that the output of the detection device is averaged, and then compared to a threshold value to determine whether the gain is up or down.
The automatic gain control device described in Patent Document 2 is characterized in that the output of the detection device is compared with a threshold value to make a gain up / down decision, and then the decision result is averaged.

In such an automatic gain control device, when a certain channel is selected and demodulated, the input signal of that channel is adjusted so that it is always input to the demodulator at the same average power level. Therefore, both when an analog circuit is used for power detection and when power is calculated after digitization by an A / D converter, automatic gain control is performed based on the average power.
However, in recent years, when the performance of A / D converters and the performance of digital signal processing have improved, it becomes possible to select a channel after taking a plurality of channels with the A / D converter and digitizing them. It is impossible to keep the control constant. This is because the average power of each channel varies without correlation. Then, automatic gain control that focuses on the control of the synthesized waveform is not distorted, that is, within the range of an element with a narrow dynamic range that operates linearly with respect to the input power, such as an A / D converter. It has become like this.

In recent years, it has become possible to process multiple channels at the same time by improving the performance of the demodulator, but a signal with multiple channels superimposed has a very large peak power because the peaks are voltage-added. become. For example, a signal obtained by adding two channels of digital modulated waves having an average power of 0 dBm and a peak power of 5 dBm has an average power of 3 dBm (power double = 3 dB increase) and a peak power of 10 dBm (voltage double = power quadruple = 6 dB), and the peak factor is 8 dB. Since a digital signal that bundles multiple channels in this way has a very large peak factor, the threshold for lowering the gain is lowered by the peak factor in order to avoid demodulator power saturation. It is necessary to set.
However, in mobile communications, it is rare for multiple channels to reach the receiver with the same power, and it is normal for the power of each channel to be different, such as there being channels that are not used at a certain point in time. Although the peak factor at the receiver changes from moment to moment, the threshold for lowering the gain is set low based on the maximum possible peak factor.
JP-A-63-99626 JP-A-7-263986

The conventional automatic gain control apparatus is configured as described above. When handling a plurality of inputs, a threshold for lowering the gain is set low based on the maximum possible peak factor, and the gain is increased accordingly. Since the difference from the threshold for increasing is narrowed, there is a problem that the number of times of gain control processing increases and the error rate of demodulated data increases.
In addition, since a plurality of channels are demodulated, a signal input to the demodulator has a wide frequency width, and an interference wave that does not need to be demodulated may be input to the demodulator. That is, if the power of the interference wave exceeds a threshold value for lowering the gain, there is a problem that the gain of the automatic gain control device is lowered and the channel being demodulated is suppressed, possibly causing a malfunction.

  The present invention has been made to solve the above-described problems, and has an object to obtain an automatic gain control device having a low demodulated data error rate even with a signal whose peak factor changes with time. An object of the present invention is to obtain an automatic gain control device that is less prone to malfunction.

An automatic gain control device according to the present invention includes a peak power calculator that calculates a peak power of an input signal on which a plurality of channel signals are superimposed,
A channel average power calculator for calculating the average power of the input signal for each channel;
When the peak power of the superimposed input signal calculated by the peak power calculator exceeds a first predetermined threshold, the input signal gain is decreased, and the input signal in any channel calculated by the channel average power calculator And a variable gain device that increases the gain of the input signal when the average power of the input signal becomes equal to or lower than a second predetermined threshold value.

According to the present invention, the gain of the automatic gain control device is controlled so as not to saturate the demodulator regardless of the peak factor of the signal input to the demodulator by comparing the threshold for reducing the gain with the peak power. To control. For this reason, it is possible to demodulate with an optimum gain, and to reduce the demodulation data error rate by reducing the number of gain control processes.
In addition, a second threshold value for lowering the gain is prepared, and only when the average power of the channel being demodulated is higher than the threshold value, the power determination result based on the peak power is validated, thereby There is an effect that malfunction of the automatic gain control device can be avoided.

Embodiment 1 FIG.
In the case of handling a plurality of inputs, a device for controlling the gain not only based on the summed peak power but also considering the average power of each channel will be described.
The automatic gain control apparatus according to Embodiment 1 of the present invention will be described below. In FIG. 1, a receiver 1 demodulates an input signal of each channel separated from the amplified input signal, and a signal amplifying unit 2 that amplifies the input signal with respect to an input on which a plurality of channel signals are superimposed. And a signal demodulator 3 for The variable gain device 4 as an internal component of the signal amplification unit 2 is a device that can change the gain using a variable gain amplifier or a variable attenuation amount attenuator.

The A / D converter 5 as an internal component of the signal demodulator 3 is a device that converts the output signal of the variable gain device into a digital signal. Similarly, the peak power calculator 6 as an internal component is a device that calculates the peak power for a signal obtained by synthesizing the input signals of a plurality of channels, digitized by the A / D converter 5. Similarly, the channel demodulator 7 is a demodulator provided for each channel to be received, and a plurality of channel demodulators 7 are provided according to the number of channels. The channel average power calculator 8 is a device that calculates the average power of the signals of the respective channels input to the channel demodulator 7.
The threshold 9 is a reference power value for comparison with the peak power, and is compared with the power calculated by the peak power calculator 6 in the power determiner 10.
The threshold 11 is a reference power value for comparison with the average power of each channel, and is compared with the power calculated by the channel demodulator 7 in the power determiner 12.

The operation of the apparatus having the configuration shown in FIG. 1 will be described with reference to the operation flowchart shown in FIG.
In FIG. 2, when the combined peak power calculated by the peak power calculator 6 is larger than the threshold value 9 in step S31, the gain of the variable gain unit 4 is lowered in S33.
Furthermore, when the power of each channel calculated by the channel demodulator 7 is smaller than the threshold 11 in step S32, the gain of the variable gain device 4 is increased in S34.
With this configuration, the gain is lowered so as not to saturate the signal demodulator 3, and the gain is increased so as to ensure the power higher than the minimum power required for demodulation of each channel, and input to the receiver 1. Even when the peak factor of the signal changes with time, since the signal demodulating unit 3 is not controlled to lower the gain until the threshold value 9 is actually saturated, the number of gain control operations can be reduced, and the demodulated data error rate can be lowered. .

This will be described with reference to FIG.
FIG. 3A is a diagram illustrating an example of average power of each channel, combined wave average power, and peak power, with an example in which six channels are combined and input. FIG. 3 (b) is a diagram showing the state of gain switching when the variable gain device is controlled using only the average power of the combined wave as in the prior art, and FIG. 3 (c) is a diagram in the present embodiment. It is a figure which shows the mode of gain switching. That is, if the peak power is detected and the variable gain device is controlled using the peak power, the limited dynamic range can be widely used, and the number of times the gain is varied can be reduced. That is, it is possible to control the synthesized waveform so as not to be distorted.
In the figure, the peak value of each channel is 10 dB for easy understanding. At time 0 to 3, since most of the composite wave average power is channel 1, the peak value is approximately 10 dB, but the peak value at time 8 when each channel is equal power is approximately 18 dB, and the peak value is It can be seen that is changing with time.

In this case, if automatic gain control is performed using only the conventional combined average power shown in FIG. 3B, the gain is lowered when the combined wave average power exceeds the threshold value of ○ 2 in FIG. , The gain is increased when the average power of each channel falls below the threshold value of 3. Therefore, since the combined wave average power exceeds the threshold value of ○ 2 at time 2, the gain is lowered, and since channel 1 becomes less than the threshold value of ○ 3 slightly before time 4, the gain is increased. Further, slightly before time 8, the combined wave average power exceeds the threshold value of ◯ 2, so the gain is lowered.
On the other hand, in the present embodiment, automatic gain control is also performed using the combined wave peak power, and the threshold value of ○ 1 in FIG. 3A corresponds to the threshold value of ○ 2. That is, the gain is decreased when the combined wave peak power exceeds the threshold value of ○ 1 before time 8, and the gain is increased when the average power of each channel is lower than the threshold value of ○ 3. In the case of FIG. 3, since there is no gain reduction command at time 2, the gain change is small once. In other words, according to the conventional method, the process of lowering the gain is performed where it is not necessary to lower the gain. Since a data demodulation error is likely to occur when the gain changes, automatic gain control using the peak power of the synthesized wave can be said to be a control in which an error is less likely to occur.

  In FIG. 1, the peak power calculator 6 may be configured such that the peak power detector is placed before the input of the A / D converter 5. Further, the peak power calculator 6 and the channel average power calculator 8 or the power determiners 10 and 12 include temporal averaging processing and calculation value selection processing (processing for omitting the maximum and minimum values in a certain time interval). Etc.), and the processing time and accuracy can be improved.

Embodiment 2. FIG.
A control device and method that further reduces the number of times of gain switching will be described.
FIG. 4 is a diagram showing a configuration of the automatic gain control apparatus according to the present embodiment. 1 is different from FIG. 1 in that a threshold 13 serving as a reference for switching is further added and compared with the power calculated by the channel demodulator 7 in the power determiner 14. When the power is higher than the threshold 13 and the power calculated by the peak power calculator 6 in the power determiner 10 is larger than the threshold 9, the gain of the variable gain unit 4 is decreased.

The gain control operation by the apparatus having the above configuration will be described.
FIG. 5 is a flowchart showing the operation. In the figure, the conditions for increasing the gain are different. In step S41, when the peak power is higher than the threshold 9 and the average power of each channel is higher than the predetermined threshold 13, the process proceeds to step S43, and the gain is set. Lower.
By doing so, the gain of the variable gain device 4 is reduced because the interference wave is input at a power higher than the threshold 9 although the power of the signal actually demodulated by each channel demodulator is low. Thus, it is possible to avoid a malfunction that the power of the signal demodulated by each channel demodulator is lowered, that is, a demodulated data error occurs.
The conditions and operation for increasing the gain are the same as those in the first embodiment.

As in the first embodiment, the peak power calculator 6 may be configured to place a peak power detector before the input of the A / D converter 5.
Further, the peak power calculator 6 and the channel average power calculator 8 or the power determiners 10 and 12 include temporal averaging processing and selection processing of calculated values (processing for omitting the maximum and minimum values in a certain time interval). Etc.) and the processing time and accuracy can be improved.

  As an application example of the present invention, the present invention can be applied to a mobile communication multi-channel receiver using the FDMA system particularly in digital communication. It can also be used when the peak factor of the received wave cannot be assumed at the time of design, such as a software defined radio.

It is a figure which shows the structure of the automatic gain control apparatus in Embodiment 1 of this invention. FIG. 5 is a diagram showing an operation flow in the first embodiment. 6 is a diagram for illustrating an operation in the first embodiment. FIG. It is a figure which shows the structure of the automatic gain control apparatus in Embodiment 2 of this invention. FIG. 10 is a diagram showing an operation flow in the second embodiment.

Explanation of symbols

  1 receiver, 2 signal amplification unit, 3 signal demodulation unit, 4 variable gain unit, 5 A / D converter, 6 point power calculator, 7 channel demodulator, 8 channel average power calculator, 9 threshold, 10 power Determinator, 11 threshold, 12 power determiner, 13 threshold, 14 power determiner, S31 step of comparing peak power and threshold 9, S32 comparing step of average power of each channel and threshold 11, S33 step of reducing gain , S34 a step of increasing the gain, S41 a step of comparing the peak power and the threshold 9 and each channel average power and the threshold 13, and S43 a step of decreasing the gain.

Claims (5)

A peak power calculator for calculating the peak power of an input signal on which a plurality of channel signals are superimposed;
A channel average power calculator for calculating the average power of the input signal for each channel;
When the peak power of the superimposed input signal calculated by the peak power calculator exceeds a first predetermined threshold, the input signal gain is decreased, and the input signal in any channel calculated by the channel average power calculator And a variable gain device that increases the gain of the input signal when the average power of the signal becomes equal to or less than a second predetermined threshold value.   The variable gain unit replaces the gain of the input signal when the peak power of the superimposed input signal calculated by the peak power calculator exceeds a first predetermined threshold, and calculates the superposition calculated by the peak power calculator. 2. The gain of an input signal is reduced when the input signal exceeds a first predetermined threshold and the average power of the input signal in each channel is equal to or greater than a third predetermined threshold. Automatic gain control device. A variable gain device for amplifying / attenuating an input signal on which a plurality of channel signals are superimposed;
A peak power calculator for calculating the peak power of the output signal from the variable gain unit;
A channel demodulator that demodulates and outputs the input signal for each channel;
A channel average power calculator for calculating an average power of an output signal from the channel demodulator,
The variable gain unit lowers the gain of the input signal when the peak power of the superimposed input signal detected by the peak power calculator exceeds a first predetermined threshold, and the channel average power calculator calculates A receiver characterized in that the gain of an input signal is increased when the average power of the input signal in the channel is equal to or lower than a second predetermined threshold value. As a gain control method of an automatic gain control device that amplifies / attenuates an input signal on which a plurality of channel signals are superimposed,
Calculating a peak power of an input signal on which a plurality of channel signals are superimposed, and reducing the gain of the input signal when the calculated peak power of the superimposed input signal exceeds a first predetermined threshold;
Calculating an average power of the input signal for each channel, and increasing the gain of the input signal when the calculated average power of the input signal of the channel is equal to or lower than a second predetermined threshold. Automatic gain control method. Instead of reducing the gain when the calculated peak power of the superimposed input signal exceeds the first predetermined threshold,
The step of lowering the gain when the calculated peak power of the superimposed input signal exceeds a first predetermined threshold and the average power of the input signal of each channel is greater than or equal to a third predetermined threshold. Item 5. The automatic gain control method according to Item 4.

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