JP2012034222A - Radio device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress unnecessary fluctuations of gain of a variable gain amplifier due to influence of noise when an input signal is weak.SOLUTION: A radio device 3 includes a variable gain amplifier 34 that amplifies an input signal and a gain control unit 35 that makes the gain of the variable gain amplifier 34 larger the smaller signal strength of the input signal is. The gain control unit 35 is configured such that in a first range where the signal strength is smaller than a first specified value, variations in the gain due to fluctuations in the signal strength becomes smaller than those in a second range where the signal strength is larger than the first specified value.

Description

  The present invention relates to a wireless device.

Patent Documents 1 and 2 disclose techniques related to feed-forward automatic gain control that automatically controls the gain of a digital variable gain amplifier that amplifies a received signal in accordance with the strength of the received signal.
Such automatic gain control increases the gain of the variable gain amplifier if the strength of the received signal is small, and decreases the gain of the variable gain amplifier if the strength of the received signal is large. Done to stabilize.

JP 2004-80455 A JP 2007-27357 A

In the conventional automatic gain control, as shown in FIG. 9, the relationship between the received signal strength (input power to the variable gain amplifier) and the gain is such that the gain of the variable gain amplifier is linear with respect to the received signal strength. It was a monotonous decrease.
When automatic gain control is performed as shown in FIG. 9, there is a problem that the gain fluctuates unnecessarily due to noise in a range where the received signal power is so low that the intensity of the received signal fluctuates due to the influence of noise.

  That is, when trying to increase the reception sensitivity of the wireless device (receiver), the wireless device also handles weak signals with very small received signal power. When the intensity of such a weak signal is reduced to the level of noise generated in the wireless device, the influence of noise included in the signal increases in the fluctuation of the signal intensity.

  In other words, even if the intensity of the received signal itself does not fluctuate or varies only slightly, the gain fluctuates unnecessarily due to the effects of noise, and the output of the variable gain amplifier fluctuates unnecessarily. Will do. As a result, the reception sensitivity may be deteriorated.

  Therefore, an object of the present invention is to suppress an unnecessary fluctuation in gain due to the influence of noise when a signal is a weak signal.

(1) The present invention includes: a variable gain amplifier that amplifies a received signal; and a gain control unit that increases the gain of the variable gain amplifier as the signal strength of the received signal decreases. In the first range in which the signal strength is smaller than the first predetermined value, the variation in the gain due to the variation in the signal strength is smaller than in the second range in which the signal strength is larger than the first predetermined value. The wireless device is configured.
According to the present invention, in the first range where the signal strength is small, the variation in the gain of the variable gain amplifier due to the variation in the signal strength is small. Therefore, even if the signal is a weak signal, unnecessary fluctuations in gain can be suppressed.

(2) It is preferable that the gain control unit makes the gain substantially constant in the first range regardless of the signal strength. In this case, in the first range, even if the signal intensity fluctuates due to the influence of noise, the gain becomes substantially constant, and the influence of noise can be suppressed.

(3) The first predetermined value is set to a value that is slightly larger than the level of noise added to the received signal in the analog signal processing unit that processes the analog received signal before the variable gain amplifier. Is preferred.
In this case, the first range can fix the gain of the entire range in which the influence of noise occurs, and can stabilize the output of the variable gain amplifier.

(4) The gain control unit is configured to obtain the gain according to the signal strength by referring to a reference table that defines a correspondence between the value indicating the signal strength and the gain, and further, the gain The control unit preferably refers to the reference table after setting a value indicating the signal strength as a constant value regardless of the signal strength for the signal strength within the first range. In this case, for the signal intensity within the first range, the value indicating the signal intensity is a constant value, so that the size of the reference table can be reduced.

(5) The gain control unit may determine the signal intensity within a third range in which the signal intensity is greater than the second predetermined value, which is greater than the first predetermined value, regardless of the signal intensity. It is preferable to refer to the reference table after setting the value indicating the signal strength to a constant value. In this case, for the signal intensity within the third range, the value indicating the signal intensity is a constant value, so that the size of the reference table can be reduced.

  According to the present invention, even if the signal is a weak signal, unnecessary fluctuations in gain can be suppressed.

It is a whole block diagram of a radio base station apparatus. It is a block diagram of a radio | wireless apparatus. It is a figure which shows the signal strength-gain characteristic for automatic gain control. (A) is a threshold table for obtaining an index from signal intensity, (b) is a graph representing the threshold table, and (c) is a reference table for obtaining a gain from the index. (A) is a threshold table for obtaining an index from signal intensity, (b) is a graph representing the threshold table, and (c) is a reference table for obtaining a gain from the index. It is a figure (1st modification) which shows the signal strength-gain characteristic for automatic gain control. It is a figure (2nd modification) which shows the signal strength-gain characteristic for automatic gain control. It is a figure (3rd modification) which shows the signal strength-gain characteristic for automatic gain control. It is a figure which shows the signal strength-gain characteristic for the conventional automatic gain control.

[1. Overall configuration of radio base station apparatus]
FIG. 1 shows a radio base station apparatus (radio communication apparatus) 1 for a mobile radio terminal such as a mobile phone. This radio base station apparatus 1 is configured by connecting a radio apparatus (RE: Radio Equipment) 3 with an optical fiber or an electric cable to a base station main body 2 having a baseband processing section (radio apparatus control section). ing. The wireless device 3 separated from the base station body 2 in this way is called a remote radio head (RRH). A radio transmission / reception antenna 4 is connected to the wireless device 3. The antenna 4 is installed in the antenna tower or the upper part of the building.
In addition, as the radio base station apparatus 1, the base station main body 2 and the radio apparatus 3 may be integrally formed.

  The base station body 2 mainly processes the baseband signal in the digital domain and controls the wireless device 3. The wireless device 3 includes a wireless transmitter and a wireless receiver, and transmits and receives wireless signals to and from mobile wireless terminals.

[2. Automatic gain control of radio equipment]
The receiver provided in the wireless device 3 has an automatic gain control function. FIG. 2 shows a receiver with an automatic gain control function. This receiver is set to have high reception sensitivity, and can receive a weak signal smaller than, for example, −100 dBm.

  The receiver includes an analog signal processing unit (analog block) 31 that processes an analog signal received by the antenna 4. The analog signal processing unit 31 includes elements such as an analog amplifier, a filter, and a frequency conversion unit, and outputs an analog reception signal subjected to analog signal processing by these elements.

The analog signal processing unit 31 is also a source of noise added to the analog reception signal. The analog circuit that constitutes the analog signal processing unit 31 inevitably generates noise due to its characteristics.
Therefore, the analog signal output from the analog signal processing unit 31 includes noise using the analog signal processing unit 31 as a noise generation source.

  Note that the level of noise with the analog signal processing unit 31 as a noise generation source depends on the circuit configuration of the analog signal processing unit 31 and its peripheral circuits, but is, for example, −hundred dBm. In order to measure the noise level, the input to the analog signal processing unit 31 is set to no input, and in this state, the power value of the signal output from the analog signal processing unit 31 (actually only noise) is measured. That's fine.

  The analog reception signal output from the analog signal processing unit 31 is converted into a digital reception signal by the A / D converter 32. Corresponding to the receiver handling weak signals as described above, the A / D converter 32 has a wide dynamic range.

  A digital reception signal output from the A / D converter 32 is input to a digital variable gain amplifier (VGA) 34 via a digital down converter 33. The digital down converter 33 can be omitted.

  The digital variable gain amplifier 34 amplifies the input digital reception signal. The digital variable gain amplifier 34 can change the gain under the control of the gain control unit 35. When the intensity of the signal input to the digital variable gain amplifier 34 is strong (power is large), the variable gain amplifier 34 reduces the gain to suppress the magnitude of the output signal, and conversely, the input signal intensity. Is weak (power is small), the gain is increased to increase the output signal.

  A gain control unit 35 that controls the gain of the digital variable gain amplifier 34 measures the power value (signal strength) of the input signal to the digital variable gain amplifier 34, determines the gain based on the power value, and determines the digital variable gain. The gain of the amplifier 34 is controlled. That is, this gain control is feedforward type automatic gain control.

  The gain control unit 35 of the present embodiment includes a power meter 36 that measures the power value (signal strength) of an input signal to the digital variable gain amplifier 34, and a range of power values measured by the power meter 36 (a predetermined range ( A power value limiting unit 37 for limiting to a second range A2), which will be described later, and a reference table 38 for determining a gain from the power value are provided.

  The power meter 36 is connected to the input side of the digital variable gain amplifier 34 and measures the power value of the digital reception signal (IQ data) input to the digital variable gain amplifier 34, that is, the amplitude value of the IQ data. Output.

Here, the minimum value that can be taken by the power value of the digital reception signal input to the digital variable gain amplifier 34 is defined as P _min . In the present embodiment, P _min is assumed to be a value smaller than −100 dBm.
Further, the maximum value that can be taken by the power value of the digital reception signal input to the digital variable gain amplifier 34 is defined as P _max .
In this case, the entire range A that can be taken by the digital input signal to the digital variable gain amplifier 34 is a range between P _min and P _max (see FIG. 3).
Therefore, the power value output from the wattmeter 36 takes an arbitrary value between P _min and P _max .

The power value limiting unit 37, the power value output from the power meter 36, the part in the entire range A range (the first from the predetermined value P ₁ second range of predetermined values P ₂₎ in the Limit to value. Note that P _min <P ₁ <P ₂ <P _max . In _addition, the range from _{P min} of less than _{P 1} is referred to as a "first range A1", the range from _{P 1} of _{P 2} is referred to as a "second range A2", "the first a range of up to _{P max} beyond the _{P 2} 3 range A3 ".

Specifically, the power value limiting section 37, power value output from the power meter 36, if within the first range A1 (if less than P _1), the first predetermined value of power values The power value is fixed to P ₁ and fixed within the third range A3, the power value is fixed to the _second predetermined value P2.
In other _words, the power values that can take a value between _{P min} of _{P max} is the power value limiting section 37, to a value within a second range A2 from the first predetermined value _{P 1} to a second predetermined value _{P 2} Will be limited.

  The reference table 38 of this embodiment is a table that defines the correspondence between power values (values indicating signal strength) and gains. In the second range, the reference table 38 is set so that the gain with respect to the power value linearly monotonously decreases so that the smaller the power value, the larger the gain, as in the conventional case. The gain control unit 35 refers to the reference table 38 based on the power value limited by the power value limiting unit 37 to determine a gain corresponding to the power value.

In the present embodiment, the power value is, because it is limited to a value within a second range from the first predetermined value P ₁ to a second predetermined value P _2, the power values defined in the lookup table 38 , suffice first value from a predetermined value P ₁ to a second predetermined value P _2.
When the power value takes an arbitrary value within the entire range A (range from P _min to P _max ) that the digital input signal to the digital variable gain amplifier 34 can take, the power value defined in the reference table As a result, many power values included in a wide range from P _min to P _max are required. In this case, the size of the reference table increases. On the other hand, in the present embodiment, the range A2 of the referenced power value is narrower than the range A of the power value actually input to the digital variable gain amplifier 34. Therefore, the size of the reference table 38 can be reduced. it can.

Now, in the present embodiment, wherein for defining a first range the first predetermined value P ₁ is the value of the noise level adjacent to a source of analog signal processing section 31, and than the noise level It is set to a large value. For example, the first predetermined value _{P 1} may be set to -100 dBm. This is a value slightly larger than that when the magnitude of noise generated from the analog signal processing unit 31 is −hundred dBm.

  When the power value input to the digital variable gain amplifier 34 is within the first range A1 (during weak input), the power value measured by the wattmeter 36 varies due to the influence of noise. Therefore, also in the first range A1, simply when the gain controller 35 varies the gain according to the power value, the output of the digital variable gain amplifier 34 unnecessarily varies due to noise. Therefore, although the intensity of the original received signal excluding noise is weak and it is necessary to increase the gain to increase the sensitivity, the apparent power value increases due to the noise, and conversely the gain decreases. May occur and reception sensitivity may be deteriorated.

In contrast, in the present embodiment, when the power value input to the digital variable gain amplifier 34 is within the first range A1 (during weak input), the gain does not vary even if the power value varies. A gain larger than the gain when the power value is in the second range is maintained.
Therefore, when the intensity of the original received signal excluding noise is weak, the gain can be maintained in a high state even if the power value fluctuates due to noise, and deterioration of the reception sensitivity can be prevented.

The predetermined value P ₂ of the second to define the third range, the power value of the digital received signal, it is set to the required value to be or near value thereof in the specification of the communication standards or wireless device Yes. When the power value of the received signal is larger than the value required in the communication standard or the wireless device specification, it is possible to contribute to the size reduction of the reference table 38 by not changing the gain.

[3. Gain determination process using threshold table]
FIG. 4 shows a first example of a technique using a threshold value table in order to determine the gain after limiting the range of power values in the gain control unit 35, and FIG. 5 shows a second example thereof. Is shown.
Here, for the sake of easy understanding, the range of the power value output from the wattmeter 36 is represented by 0 to 10,000 (P _min = 0, P _max = 10000). The first predetermined value _{P 1} and 1000, and the second predetermined value _{P 2} to 9000.

  4A and 4B and FIG. 5A and FIG. 5B are threshold value tables for converting the power value measured by the wattmeter 36 into an index value (another value indicating signal strength). Is shown. This index value is used to represent a certain range of power values as a single value. The gain control unit 35 converts the value measured by the wattmeter 36 into an index value by referring to the threshold value table. Further, the gain control unit 35 converts the index value into a gain by referring to a reference table (FIGS. 4C and 5C) for converting the index value into a gain.

  The threshold value table of FIG. 4 (a) (b) or FIG. 5 (a) (b) has a plurality of index values, and a threshold value corresponding to each index value is set. The gain control unit 35 compares the power value measured by the wattmeter 36 with the threshold value in the threshold value table. This comparison is performed in order from the threshold value with the largest value, and an index corresponding to the power value is determined.

In the case of the threshold value tables of FIGS. 4A and 4B, the plurality of index values are set such that a range of 100 power values is indicated by one index value. Therefore, the index value itself is not limited by the power value.
Therefore, as shown in FIG. 4C, the reference table 38 has a fixed gain value (minimum value) for index values = 1 to 10 corresponding to a range of power values = 10000 to 9000 (third range). The index value corresponding to the power value = 8999 to 1000 (second range) is gradually increased according to the index value until the power value = 999 to 0 (first range). The corresponding index values = 91 to 100 are set so that the gain becomes a fixed value (maximum value). Thereby, the relationship of FIG. 3 is realizable.

On the other hand, in the case of the threshold value tables shown in FIGS. 5A and 5B, for example, if the power value is between 10,000 and 9000, the index value = 1. If the power value is 8850, index value = 3. Further, if the power value is smaller than 1000, the index value = 82.
As described above, in the threshold value table of FIGS. 5A and 5B, a range with a power value of 10,000 to 9000 and a range of 999 or less corresponds to one index with a range of 1000. On the other hand, in the range from 8999 to 1000, a range having a width of 100 corresponds to one index.

  When the threshold value table as shown in FIGS. 5A and 5B is also provided, the range of index values is limited. Therefore, as the reference table 38, as shown in FIG. 5C, the gain increases linearly with respect to the index value, and the relationship shown in FIG. 3 can be realized.

[4. Modified example of signal strength-gain characteristics]
FIG. 6 shows a first modification of signal strength-gain. In FIG. 6, the entire range A of the received signal intensity is divided into two ranges, a first range A1 (P _{min to} P ₁ ) and a second range A2 (P _{1 to} P _max ).
In the first range A1, as in the case of FIG. 3, even if the signal intensity fluctuates due to noise, the gain is fixed and does not fluctuate. Therefore, the output of the digital variable gain amplifier 34 can be stabilized.
In FIG. 6, the third range is not provided as in FIG. 3, but since the first range is provided, it is possible to make the size of the reference table 38 smaller than in the past.

FIG. 7 shows a second modification of signal strength-gain. In FIG. 3, in the first range A1 and the third range A3, the gain is fixed at a constant value, and the gain variation with respect to the signal strength variation is suppressed to zero. On the other hand, in FIG. 7, the gain value varies somewhat even within the first range A1 or the third range A3. However, in the first range A1 or the third range A3, the gain fluctuation due to the fluctuation of the signal intensity is moderate compared to the second range.
For this reason, in the case of a weak signal whose signal intensity is within the first range A1, the degree of gain fluctuation due to the influence of noise can be suppressed to be small, and the influence of noise can be reduced.

FIG. 8 shows a third modification of signal strength-gain. In FIG. 3, the gain has only one value in the first range A1 and the third range A3, whereas in FIG. 8, the gain has two (plural) values in the first range A1. In the third range A3, two (plural) values are taken.
Thus, even if the gain is changed in stages in the first range A1, the gain fluctuation due to the fluctuation of the signal intensity is moderate compared to the second range. Therefore, in the case of a weak signal whose signal intensity is in the first range A1, the degree of fluctuation in gain due to the influence of noise can be suppressed to be small, and the influence of noise can be reduced.
Also in FIG. 8, the reference table size can be reduced.

[5. Addendum]
The embodiment disclosed this time is illustrative and not restrictive. The scope of the present invention is defined by the terms of the claims, and includes all modifications that are within the scope of the claims and equivalents.

DESCRIPTION OF SYMBOLS 1 Radio base station apparatus 2 Base station main body 3 Radio apparatus 4 Antenna 31 Analog signal processing part 32 A / D converter 33 Digital down converter 34 Digital variable gain amplifier 35 Gain control part 36 Watt meter 37 Power value restriction part 38 Reference table

Claims (5)

A variable gain amplifier that amplifies the received signal;
A gain control unit that increases the gain of the variable gain amplifier as the signal strength of the received signal decreases;
With
In the first range in which the signal strength is smaller than the first predetermined value, the gain control unit is configured to increase the gain due to the fluctuation of the signal strength in the second range in which the signal strength is larger than the first predetermined value. The wireless device is configured to reduce fluctuations in the frequency. The radio apparatus according to claim 1, wherein the gain control unit makes the gain substantially constant in the first range regardless of signal strength. 2. The first predetermined value is set to a value slightly larger than a level of noise added to a reception signal in an analog signal processing unit that processes an analog reception signal in a stage preceding the variable gain amplifier. Or the radio | wireless apparatus of 2. The gain control unit is configured to obtain the gain according to the signal strength by referring to a reference table that defines a correspondence between a value indicating the signal strength and the gain,
The gain control unit refers to the reference table after setting a value indicating the signal strength as a constant value regardless of the signal strength for the signal strength within the first range. The wireless device according to any one of claims. The gain control unit is configured to set the signal strength for a signal strength within a third range larger than a second predetermined value, the signal strength being greater than the first predetermined value, regardless of the signal strength. The wireless device according to claim 4, wherein the reference table is referred to after the indicated value is a constant value.

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