JP3505790B2 - Digital radio receiver - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radio receiver, and more particularly to a digital radio receiver that demodulates a digital modulated wave after frequency conversion into a low frequency band.

[0002]

2. Description of the Related Art An example of a conventional digital radio receiver is shown in FIG.
It shows in 0.

In a conventional digital radio receiver, after the received digital modulated wave is frequency-converted into an IF frequency band,
It was demodulated into a digital signal by the demodulator.

Generally, in digital wireless communication, time division multiplex transmission, code compression and expansion are performed. Code compression,
When decompression is performed, the digital output of the demodulator is generally decoded by a code decoder.

In FIG. 10, an RF band received signal composed of a plurality of channels is band-limited by an RF band bandpass filter 2 via an antenna 1, and an RF variable gain amplifier 3 is provided.
Entered in. RF amplified by the RF variable gain amplifier 3
The reception signal 17 is input to the first mixer 4, mixed with the local oscillation frequency of the first local oscillator 10, and frequency-converted to the first IF band. The first IF signal 18 frequency-converted to the first IF band is band-limited by the first IF band bandpass filter 5, amplified by the first IF band amplifier 16, and then input to the second mixer 6. The signal is mixed with the local oscillation frequency of the second local oscillator 11 in the second mixer 6, and the second IF signal 1
After being frequency-converted to 9, it is input to the demodulator 12. The demodulator 12 demodulates the signal into a digital signal, which is then input to the code decoder 13 and decoded. The decoded received data is output from the output terminal 15.

Now, at the antenna input terminal 21, a signal desired to be demodulated (hereinafter referred to as a desired wave) and two signals (hereinafter referred to as intermodulation interference wave) which are interference signals whose third-order intermodulation distortion signals match the desired wave. And) are entered.
The spectrum is shown in FIG. In the figure, f _D is the frequency of the desired wave and f _U is the frequency of the intermodulation interference wave. In the figure, the pass band and the attenuation band are separated by the dotted line,
The interference signal is within the pass band of the RF band band pass filter 2.

The mechanism of intermodulation interference generation will now be described. It is assumed that the desired frequency is f1, the interference wave frequencies are f2 and f3, and f1, f2, and f3 have the following relationship.

[0008]

[Equation 1]

At this time, 3 out of the intermodulation waves due to 2 interference waves
If only the second-order component is taken out, the third-order components fi1 and fi2 are given by the following expressions.

[0010]

[Equation 2]

Thus, fi1 becomes equal to f1,
It interferes with the desired wave and deteriorates the reception sensitivity.

In wireless communication, a multi-channel access method is mainly used for effective use of frequencies. As described above, the channel interval frequency is df, and f to f1.
A situation occurs where 2 and f3 are input to the antenna. Therefore, immunity to intermodulation interference is an important issue for wireless receivers.

In addition, the two intermodulation interference waves cause
Most of the secondary distortion is generated in the first mixer 4, and at this time, the spectrum of the output (first IF signal 18) of the first mixer 4 is as shown in FIG.
, Which deteriorates the reception sensitivity. In order to improve this intermodulation interference, the first IF level detector 2
5, desired wave level detector 7 (This detector is
ceive Signal Strength Indicator) circuit),
The level of the RF variable gain amplifier 3 is controlled by using the level determiner 8 and the gain controller 9.

The operation will be described below. First, FIG. 13 shows the output 20 (hereinafter referred to as RSSI) of the desired wave level detector 7 and the bit error rate indicating the reception sensitivity in digital radio in the absence of interference. Show. In this state, the first IF
The spectrum of the signal 18 is as shown in FIG.
The detection result of the F level detector 25 is small. The level determiner 8 does not output the gain switching signal to the gain controller 9 while the detection result is small.

Next, when there is an intermodulation interference wave as shown in FIGS. 11 and 12, the detection result of the first IF level detector 25 is large, and since the interference is received, the bit error rate is 14, the bit error rate is deteriorated as compared with the bit error rate shown by the dotted line when there is no interference. At this time, when the RSSI increases and exceeds the threshold value A, the level determiner 8 outputs a gain switching signal to the gain controller 9 and lowers the gain of the RF variable gain amplifier 3. As a result, the desired wave interference ratio (hereinafter referred to as the D / U ratio) of the first mixer input signal decreases, and the bit error rate approaches the value when there is no interference as the antenna input level increases.

The third-order intermodulation distortion level that deteriorates the error rate has a relationship of being reduced by 3 dB when the signal level at the mixer input point is reduced by 1 dB. Therefore, by lowering the gain of the RF variable gain amplifier 3 by 1 dB, the third-order intermodulation distortion level is reduced. The intermodulation distortion level is lowered by 3 dB, and the error rate can be greatly improved.

In this way, deterioration of reception sensitivity due to intermodulation interference is reduced.

[0018]

In the prior art, gain control is performed when there is an input of an interfering wave that causes third-order intermodulation distortion, but there is an input signal that does not cause third-order intermodulation distortion. Even in this case, there is a problem of performing gain control.

That is, as shown in FIG. 16, df1 ≠ d
When the two signals f _U that are f2 are input to the antenna input terminal 21, the third-order intermodulation distortion does not match the desired wave f _D, and therefore the reception sensitivity does not deteriorate. However, in this case, as shown in FIG. 17, there are two signals even at the output of the first mixer, and the detection result of the first IF level detector 25 becomes large, so that the gain is lowered. Therefore, as shown in FIG. 18, the bit error rate cannot be improved.

As described above, there is a problem that the gain control may not be effective.

[0021]

In order to solve the above-mentioned problems, the present invention comprises a variable gain amplifier which can input a signal of a first frequency received by an antenna and vary the gain by a control signal, In a digital radio receiver for converting the output of the variable gain amplifier into a signal having a second frequency lower than the first frequency, demodulating the signal converted to the second frequency into digital data, and decoding the digital data. , Above second
Received signal strength detector for detecting the level of the signal after being converted to the second frequency, and the error rate of the signal after being converted to the second frequency
The error rate detector that detects the
Detected signal level and detected by the above error rate detector
The gain of the variable gain amplifier depends on the error rate
A control unit for outputting a control signal for controlling the profit,
The control unit controls the signal level detected by the received signal strength detector.
As the reference value to be compared with the bell, the first reference value and this
A second reference value smaller than the first reference value and receiving the above
The signal level detected by the signal strength detector is increasing.
When using the above-mentioned first reference value,
If the signal level detected by the output device decreases,
It is characterized in that the comparison is performed using the second reference value .

[0022]

[0023]

[0024]

[0025]

[Action] With the above-described configuration, since the control gain of both by and variable gain amplifier with the quality level and the error rate of the signal after the conversion to a second frequency, strength against intermodulation interference
In addition, a digital wireless receiver with high reception sensitivity can be realized.

[0026]

1 is a block diagram showing the configuration of a first embodiment of a digital radio receiver according to the present invention.

The receiver of this embodiment, as shown in FIG.
The first IF level detector 25 in the conventional receiver shown in FIG. 10 is deleted, and the code decoder 13, the bit error rate calculation unit 14, the desired wave level detector 7 for detecting the IF signal level, and the desired wave level are detected. A level determiner 8 for comparing the output of the detector 7 with a reference level and a bit error rate with the reference bit error rate, and RF according to the output of the level determiner 8.
The gain controller 9 controls the gain of the variable gain amplifier 3.

An example of the encoder / decoder 13 is described in detail in RCR STD-27B issued by the Radio System Development Center, which is a standard for digital car telephones in Japan.

In this embodiment, since the code decoder 13 has a bit error rate calculation function, the bit error rate calculation unit 1
Although 4 is built in the code decoder 13, it goes without saying that it may be made independent instead of being built in.

Next, the operation of each of the above parts will be described. The level determiner 8 stores the reference level and the reference error rate in advance, compares the output of the desired wave level detector 7 with the reference level, and determines the output of the bit error rate calculator 14 and the reference error rate. The comparison is performed, and an instruction for switching the gain of the RF variable gain amplifier 3 is output to the gain controller 9 according to the comparison result. The gain controller 9 receives the instruction from the level determiner 8 and switches the gain of the RF variable gain amplifier 3.

This gain switching operation is performed by, for example, RF.
The variable gain amplifier 3 is provided with a high gain amplifier and a low gain amplifier, and these amplifiers are selectively switchable so that the level detected by the desired wave level detector 7 is a preset reference level. When it is smaller than A (below threshold A), the RF variable gain amplifier 3 uses a high gain amplifier, the desired wave level exceeds the reference level A, and the bit error rate is below the reference bit error rate B (below threshold A). When it is larger than B), it is controlled to switch to the low gain amplifier. Further, as an example of the configuration of the RF variable gain amplifier 3, it is the same even if it is configured by using a variable attenuator and a linear amplifier. The following will be described as a configuration including a high gain amplifier and a low gain amplifier.

First, consider the case where there is no intermodulation interference wave.
When the antenna input level increases as shown in FIG. 2, the desired wave level is initially below the threshold A and the bit error rate is worse than the threshold B. As the antenna input level increases, the bit error rate becomes better than the threshold B.
When the antenna input level further increases, the desired wave level becomes higher than the threshold value A. In this change, the level determiner 8 does not output the gain switching signal, and the initial high gain remains.

When the antenna input level decreases next, the opposite of the above description is true. At first, the desired wave level is equal to or higher than the threshold value A, and the bit error rate is better than the threshold value B. The gain is high. When the antenna input level decreases as shown in FIG. 3, the desired wave level becomes smaller than the threshold value A. When the antenna input level further decreases, the bit error rate becomes worse than the threshold value B. When the antenna input level further decreases, the desired wave level becomes smaller than the threshold value C. In this change, the level determiner 8 does not output the gain switching signal, and the initial high gain remains.
The reason why the thresholds of the desired wave level are set to A and C as described above will be described later.

Next, consider the case where there is an intermodulation interference wave.
Considering the case where both the desired wave and the interfering wave increase and the antenna input level increases, the desired wave level is initially below the threshold A and the bit error rate is the threshold as shown in FIG. Worse than value B. As the antenna input level increases, the desired wave level becomes higher than the threshold value A. At the time of this change, the level determiner 8 outputs a gain switching signal, and the gain controller 9 lowers the gain of the RF variable gain amplifier 3. By this control, the input level of the first mixer 4 is lowered, the third-order intermodulation distortion signal included in the output signal of the first mixer 4 is reduced, and the bit error rate is the error rate without intermodulation interference (in the figure, Error rate of the dotted line).

As the antenna input level further increases,
The bit error rate is better than the threshold B. in this way,
The bit error rate can be improved by switching the gain.

Next, when the antenna input level decreases, this is contrary to the above explanation. As shown in FIG. 5, when the antenna input level decreases, the bit error rate becomes worse than the threshold value B. When it is further decreased, the desired wave level becomes smaller than the threshold value A, but the gain is not switched here. When the desired wave level becomes smaller than the threshold value C, the level determiner 8 outputs a gain switching signal and the gain controller 9 outputs R.
The gain of the F variable gain amplifier 3 is increased. Here, by switching with the threshold value C smaller than the threshold value A,
It is possible to keep the area where the intermodulation interference is reduced for a long time, and to reduce the adverse effect on the demodulation system due to the frequent switching of the gain with respect to the variation of the antenna input level near the point A.

The above operation will be summarized with reference to FIGS. 6 and 7. FIG. 6 shows a combination of the desired wave level and the bit error rate. The desired wave level is “small” and the bit error rate is “bad”. The changes are defined as numbers 1-8. FIG. 7 shows how the gain of the RF variable gain amplifier 3 changes with changes 1 to 8. For example, when in a high gain state,
The change 5 from "small evil" to "major evil" puts the gain in a low state. This corresponds to the case where there is intermodulation interference and the antenna input level increases (characteristic in FIG. 4) as described above.

In the above description, the threshold value A is used to increase the antenna input level and the threshold value C is used to decrease the antenna input level, and the so-called hysteresis characteristic is provided. Using a threshold value E such that C <E <D, 2
It should be added that even if it has a stepwise hysteresis characteristic, it is one embodiment of the present invention.

A second embodiment in which the reference level and the reference bit error rate set in the level determiner 8 described above can be freely set will be described with reference to FIG. From the viewpoint of the circuit scale, it is effective to set the reference level and the reference bit error rate as fixed values in the level determiner 8 in advance, but considering the versatility of the level determination and the gain control, It is also effective that the input / output characteristics can be changed by an external signal according to the above.

FIG. 8 is a block diagram of a digital radio receiver in which a memory circuit 22 which is writable by an external signal via an input terminal 23 is added. The memory circuit 22 has a writable structure, and stores the reference level and the reference bit error rate used in the level determiner 8 in advance, so that the memory information is written from an externally connected keyboard or the like via the external input terminal 23. To do so. Level judge 8
Compares the reference level stored in the storage circuit 22 with the output of the desired wave level detector 7, and compares the reference bit error rate and the bit error rate of the bit error rate calculation unit 14 stored in the storage circuit 22. In comparison, a gain switching signal is output to the gain controller 9. As a result, the gain control can be changed according to the situation. In addition, as a feature of the memory circuit 22,
It is desirable that the stored information can be retained even when the power of other circuits is turned off.

Further, a part of the memory circuit is constituted by a read-only memory circuit, and the read-only memory circuit stores basic information (this information is generally called a default value).
As long as the information is not input to the writable storage circuit by an external signal, the basic information stored in the read-only storage circuit can be used as the reference level and the reference bit error rate for gain control.

Next, a case where the above-mentioned receiver performs intermittent reception will be described.

Intermittent reception follows a preset time period,
This is a receiving method in which the receiving state and the dormant state are repeated. In the sleep state, the power of the receiving unit is generally turned off except for the control unit. Therefore, unless a special function is added, once the stop state is entered, the gain of the RF variable gain amplifier described above returns to the initial state.

When receiving intermittently in a relatively short cycle, the desired wave level rarely changes abruptly. Therefore, it is highly possible that the desired wave level close to that in the previous reception state is high when the reception state is entered and then the stop state is entered again. Therefore, by storing the information about the gain control state in the previous reception state until the next reception state, the gain control can be promptly performed when the next reception state is entered.

FIG. 9 is a diagram showing a block configuration of a third embodiment which is an embodiment of a receiver for performing such intermittent reception. A memory circuit 24, which is different from the memory circuit 22 in FIG. 8, is a writable memory circuit that can retain stored information even when the power of the wireless reception unit is turned off. The output information of the level determiner 8 is stored in the storage circuit 24. The gain controller 9 switches the gain of the RF variable gain amplifier 3 according to the information stored in the storage circuit 24.

When the sleep state is entered, the power to the circuits other than the memory circuit 24 is cut off, and the gain control information (for example, "high" or "low" information) stored in the memory circuit 24 at this time.
Is retained. When the next reception state is entered, the gain controller 9 uses the gain control information stored in the storage circuit 24 to switch the gain of the RF conversion gain amplifier 3 in the same manner as in the previous reception state.

On the other hand, the level determiner 8 refers to the gain control state stored in the storage circuit 24, determines which state the gain of the RF variable gain amplifier 3 is, and determines the reference level and reference bit used for the level determination. Select the error rate. Na
The specific effects are as follows. First
In addition, the received bit error rate itself was used as the judgment value.
Therefore, it is possible to reliably detect the occurrence of intermodulation interference,
It is possible to maintain good reception sensitivity. Secondly,
Reference level and reference bit error rate in level discriminator
Can be set by an external signal,
The degree of freedom regarding output characteristics is increased. This allows you to receive
Versatility when installed in a machine or integrated into an IC
Can be widened. When the present invention is applied to an intermittent receiver,
By storing the gain control information in the receiving state,
When the next reception state is entered after the stop state, the stored information is used.
The required gain control state can be quickly achieved. this
To start gain control when entering the reception state.
Time is reduced. Also, the signal after conversion of the second frequency
The variable gain is increased by both the signal level and the error rate.
Controls the gain of the width device, so that intermodulation interference is generated
Sometimes, it is possible to prevent the bit error rate from decreasing, and
Gain control when there is an input signal that does not cause interference
It is possible to maintain a good bit error rate by not performing
It In addition, it is strong against intermodulation interference and has high reception sensitivity.
It is possible to realize a digital wireless receiver with low power consumption and a small configuration.
It

[0048]

As described above, according to the present invention,
Resistant to intermodulation interference, a high reception sensitivity digital radio receiver can realize.

[0049]

[0050]

[Brief description of drawings]

FIG. 1 is a block configuration diagram of a first embodiment of a digital wireless receiver according to the present invention.

FIG. 2 is a first diagram showing input / output characteristics in the digital wireless receiver according to the present invention.

FIG. 3 is a second diagram showing input / output characteristics in the digital wireless receiver according to the present invention.

FIG. 4 is a third diagram showing the input / output characteristics of the digital wireless receiver according to the present invention.

FIG. 5 is a fourth diagram showing the input / output characteristics of the digital wireless receiver according to the present invention.

FIG. 6 is a diagram for explaining changes in determination conditions in the digital wireless receiver according to the present invention.

FIG. 7 is a gain state transition diagram of an RF variable gain amplifier in a digital radio receiver according to the present invention.

FIG. 8 is a block configuration diagram of a second embodiment of a digital wireless receiver according to the present invention.

FIG. 9 is a block configuration diagram of a third embodiment of a digital wireless receiver according to the present invention.

FIG. 10 is a block diagram of a conventional digital wireless receiver.

FIG. 11 is a first diagram showing a spectrum of an RF variable gain amplifier in a conventional digital radio receiver.

FIG. 12 is a first diagram showing a spectrum of a first mixer output in a conventional digital radio receiver.

FIG. 13 is a first diagram showing input / output characteristics in a conventional digital wireless receiver.

FIG. 14 is a second diagram showing input / output characteristics in the conventional digital wireless receiver.

FIG. 15 is a second diagram showing a spectrum of a first mixer output in a conventional digital wireless receiver.

FIG. 16 is a second diagram showing a spectrum of an RF variable gain amplifier in a conventional digital radio receiver.

FIG. 17 is a third diagram showing the spectrum of the first mixer output in the conventional digital wireless receiver.

FIG. 18 is a third diagram showing the input / output characteristics of the conventional digital wireless receiver.

[Explanation of symbols]

1 ... Antenna 2 ... RF band bandpass filter 3 ... RF variable gain amplifier 4 ... First mixer 5 ... First IF band bandpass filter 6 ... Second mixer 7 ... Desired wave level detector 8 ... Level determiner 9 ... Gain control Device 10 ... First local oscillator 11 ... Second local oscillator 12 ... Demodulator 13 ... Code decoder 14 ... Bit error rate calculator 15 ... Output terminal 16 ... First IF band amplifier 17 ... RF reception signal 18 ... First IF signal 19 ... second IF signal 20 ... RSSI 21 ... antenna input terminal 22 ... memory circuit 23 ... external input terminal 24 ... memory circuit 25 ... first IF level detector

Continuation of the front page (56) Reference JP-A-8-8782 (JP, A) JP-A-4-328906 (JP, A) JP-A-5-129862 (JP, A) JP-A-6-104670 (JP , A) (58) Fields surveyed (Int.Cl. ⁷ , DB name) H03G 3/20 H04B 1/10

Claims (4)

(57) [Claims] 1. A variable gain amplifier which receives a signal of a first frequency received by an antenna and whose gain can be varied by a control signal, and outputs the variable gain amplifier having a second frequency lower than the first frequency. Convert to frequency signal, this second
In a digital radio receiver that demodulates a signal converted to the frequency into digital data and decodes it, a received signal strength detector that detects the level of the signal converted to the second frequency ; Error in detecting the error rate of the signal after conversion to frequency
A rate detector Ri, depending on the situation of the detected error rate at the level of the detected signal and the error rate detector by the receiving signal strength detector, output a control signal for controlling the gain of the variable gain amplifier
And a control unit for applying a signal, the control unit being a signal detected by the received signal strength detector.
As the reference value to be compared with the level, the first reference value and this
Has a second reference value smaller than the first reference value of
The signal level detected by the signal strength detector increases
When using the above-mentioned first reference value, the received signal strength
When the signal level detected by the detector decreases
A digital radio receiver characterized in that comparison is performed using the second reference value . 2. A variable gain amplifier which receives a signal of a first frequency received by an antenna and whose gain can be varied by a control signal, and outputs the variable gain amplifier having a second frequency lower than the first frequency. Convert to frequency signal, this second
In a digital radio receiver that demodulates a signal converted into the frequency into digital data and decodes it, a received signal strength detector that detects the level of the signal converted into the second frequency; An error rate detector that detects the error rate of the signal after frequency conversion, and the level of the signal detected by the received signal strength detector and the error rate detected by the error rate detector A control unit for outputting a control signal for controlling the gain of the variable gain amplifier, wherein the control unit has a first reference value and a reference value as a reference value to be compared with the signal level detected by the received signal strength detector. The variable gain amplifier has a second reference value smaller than the first reference value, and the variable gain amplifier uses the first amplification reference and the second amplification reference value smaller than the first amplification reference value as a reference for amplifying the gain. Have the above When the level of the signal detected by the signal strength detector increases, it is smaller than the first reference value, and when the error rate detected by the error rate detector is larger than a predetermined error rate, When the level of the signal detected by the received signal strength detector decreases using the first amplification reference value of the variable gain amplifier, between the second reference value and the first reference value, A digital radio receiver characterized in that when the error rate detected by the error rate detector is larger than a predetermined error rate, the second amplification reference value of the variable gain amplifier is used. 3. A variable gain amplifier, which receives a signal of a first frequency received by an antenna and whose gain can be varied by a control signal, has an output of the variable gain amplifier which is lower than the first frequency. Convert to frequency signal, this second
In a digital radio receiver that demodulates a signal converted into the frequency into digital data and decodes it, a received signal strength detector that detects the level of the signal converted into the second frequency; An error rate detector that detects the error rate of the signal after frequency conversion, and the level of the signal detected by the received signal strength detector and the error rate detected by the error rate detector A control unit for outputting a control signal for controlling the gain of the variable gain amplifier, wherein the control unit detects the error rate detector at the level of an arbitrary signal detected by the received signal strength detector. When the error rate is less than the reference value, a control signal for controlling the gain of the variable gain amplifier to be the first gain is output, and when the error rate detected by the error rate detector is not less than the reference value, Variable gain above Digital radio receiver, characterized in that the gain width unit outputs a control signal for controlling so as to be lower gain than the first gain. 4. The control section, when the level of the signal detected by the received signal strength detector increases, the error rate detected by the error rate detector at the level of the arbitrary signal is a reference value. When it is less than, a control signal for controlling the gain of the variable gain amplifier to be the first gain is output, and when the error rate detected by the error rate detector is equal to or more than a reference value, the gain of the variable gain amplifier is When a level of the signal detected by the received signal strength detector decreases, a control signal for controlling the gain is lower than the first gain is output at a level lower than the level of the arbitrary signal. Regardless of the value of the error rate detected by the error rate detector,
The digital radio receiver according to claim 3, wherein a control signal for controlling the gain of the variable gain amplifier to be a first gain is output.