JPH07297779A - Digital radio with automatic frequency control function - Google Patents

Abstract

(57) [Abstract] [Purpose] To prevent deterioration of reception sensitivity and deterioration of modulation frequency accuracy by preventing erroneous frequency control when line quality deteriorates. The error rate detection circuit 32 is provided in the AFC circuit in addition to the frequency deviation detection circuit 31, and the error rate detection circuit 3 is provided.
When the error rate BER detected in 2 is less than the predetermined value,
Frequency deviation Δ detected by the frequency deviation detection circuit 31
The oscillation frequency of the reference oscillator 21 is controlled in real time according to f, and when the error rate BER detected by the error rate detection circuit 32 increases above a predetermined value, this error rate B
The frequency deviation Δf detected by the frequency deviation detection circuit 31 is latched and held in the RAM immediately before the ER is increased, and thereafter, until the error rate BER is improved below a predetermined value,
The reference oscillator 2 according to the latched frequency deviation Δf
The oscillation frequency of 1 is controlled.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital wireless device used as, for example, a digital automobile / mobile phone or a digital cordless phone, and more particularly to a digital wireless device having an automatic frequency control function.

[0002]

2. Description of the Related Art In recent years, in wireless communication systems such as mobile wireless communication systems, systems adopting a digital modulation / demodulation system have been operated. This type of system digitally transmits not only control signals but also communication contents such as call voice signals when wireless communication is performed between a base station and a mobile station. It is possible to improve the compatibility with and effectively use radio frequency.

FIG. 3 is a circuit block diagram showing the configuration of a radio modulation / demodulation unit of a digital radio used as a mobile station in this type of system. In the figure, a radio frequency signal arriving via a radio line is received by an antenna 1, then input to a high frequency amplifier 3 via an antenna duplexer (DUP) 2, amplified by the high frequency amplifier 3, and further subjected to a high frequency filter. It is input to the first mixer 5 via 4. In the first mixer 5, the received radio frequency signal is mixed with the first local oscillation signal, whereby the frequency is converted into the first intermediate frequency signal. The first local oscillation signal is the first crystal oscillator 21 as a reference oscillator.
Is generated by the frequency synthesizer 22 composed of a PLL circuit based on the reference frequency signal generated from.

The first intermediate frequency signal output from the first mixer 5 has its unnecessary wave components removed by the first intermediate frequency filter 6 and is then input to the second mixer 7. And
In the second mixer 7, the second local oscillation signal is mixed and frequency-converted into a second intermediate frequency signal having a lower frequency than the first intermediate frequency signal. The second local oscillation signal is generated from an independent second crystal oscillator 23.

The second intermediate frequency signal output from the second mixer 7 has its unnecessary wave component removed by a second intermediate frequency filter 8 and is amplified by an intermediate frequency amplifier 9 before being quadrature demodulated (Q -DEM) 10. The quadrature demodulator 10 includes a distributor and two mixers,
The second intermediate frequency signal branched into two by the distributor is mixed with the local oscillation signal for quadrature demodulation in the two mixers, respectively, and demodulated into a reception baseband signal. The local oscillation signal for quadrature demodulation is generated from an independent third crystal oscillator 24. The demodulated received baseband signal is input to a digital demodulation circuit (DEM) 11 using a digital signal processing circuit (DSP). In the digital demodulation circuit 11, the received data RD is reproduced by subjecting the received baseband signal to the decoded signal processing.

On the other hand, the transmission data TD is converted into two systems of transmission baseband signals by a digital modulation circuit (MOD) 12 and then input to a quadrature modulator (Q-MOD) 13. The quadrature modulator 13 includes two mixers and a combiner, and mixes the transmission baseband signal with a local oscillation signal for quadrature modulation in each mixer to convert it into a transmission radio frequency signal. The local oscillation signals for quadrature modulation, which have a phase difference of 90 ° with each other, are generated by the frequency synthesizer 22. The transmission radio frequency signals output from the above mixers are combined into a transmission radio signal of one system by a combiner, and then power amplified by a transmission power amplifier 14. Then, the antenna 1 is connected to a radio line via an antenna duplexer 2. Sent to.

By the way, in a digital radio device adopting the QPSK system as a modulation / demodulation system, when the frequency of each reception local oscillation signal changes due to temperature change, secular change, or the influence of disturbance such as electromagnetic waves, an orthogonal plane of the reception baseband signal is obtained. There is a possibility that the phase is rotated above and an error occurs in the received data.

Therefore, this type of radio equipment is provided with an automatic frequency control (AFC) circuit. In this AFC circuit, for example, as shown in FIG. 3, the first crystal oscillator 21 is composed of a voltage-controlled temperature-compensated crystal oscillator (VCTCXO). Then, the frequency deviation detection circuit 25 attached to the digital demodulation circuit 11 detects the frequency error Δf from the amount of rotation of the phase of the received baseband signal, and the control voltage VS for making the frequency error Δf zero. The frequency of the transmission / reception local oscillation signal is corrected by generating the correction control circuit 26 and supplying it to the first crystal oscillator 21.

[0009]

However, the conventional digital radio equipment provided with such an AFC circuit has the following problems to be solved. That is, in a radio used in a mobile communication system, the reception electric field strength of a radio frequency signal may be significantly reduced due to the influence of multipath fading during communication. When the received electric field strength significantly decreases, a noise component appears in the demodulated baseband signal. Then, the frequency deviation detection circuit 25 detects a random frequency of the noise component as a frequency deviation, and thus the oscillation frequency of the reference oscillator 21 is corrected by the correction information including the noise component. For this reason,
The reception local oscillation frequency and the transmission local oscillation frequency fluctuate due to the noise component, and as a result, the reception sensitivity in the reception system is rapidly deteriorated. Further, in the transmission system, noise components are mixed in the transmission radio frequency, which leads to a decrease in modulation frequency accuracy.

The present invention has been made in view of the above circumstances, and its purpose is to prevent deterioration of reception sensitivity and modulation frequency accuracy by preventing erroneous frequency control when line quality deteriorates. Another object of the present invention is to provide a digital radio device having an automatic frequency control function capable of preventing the deterioration of the frequency and maintaining good transmission / reception characteristics.

[0011]

In order to achieve the above object, the present invention provides a demodulation data which is obtained by demodulating a received radio frequency signal into an intermediate frequency signal by a frequency conversion circuit and then by a digital demodulation circuit. In the digital radio equipped with the circuit system for, as the reference oscillating means for supplying the reference frequency signal to the local oscillating means for generating the local oscillating signal,
A frequency control type reference oscillating means capable of varying an oscillation frequency by a control voltage is provided, and a frequency deviation detecting means for detecting a frequency deviation from the demodulated data, and a line quality detecting means for detecting information indicating the line quality from the demodulated data. Means and
Frequency correction means is provided, and based on the information of the frequency deviation detected by the frequency deviation detection means by the frequency correction means and the information indicating the line quality detected by the line quality detection means, the frequency A control voltage for reducing the deviation is generated and supplied to the reference oscillation means.

According to the present invention, the line quality detecting means enables
The error rate of the demodulated data is detected as the information indicating the line quality, and the frequency correction unit detects the frequency deviation detected by the frequency deviation detection unit when the error rate detected by the line quality detection unit is less than a predetermined value. Based on this, the control voltage generated to bring the frequency deviation closer to zero is supplied to the reference oscillating means, while in the state where the error rate is a predetermined value or more, the control voltage value generated before this state is held. And is supplied to the reference oscillating means.

Further, according to the present invention, the line quality detecting means is provided with a table storing information representing the correspondence between the frequency deviation and the error rate, and the error rate corresponding to the frequency deviation detected by the frequency deviation detecting means is described above. Another feature is that it is obtained from a table.

[0014]

As a result, according to the present invention, the control voltage for controlling the oscillating frequency of the reference oscillating means has the information of the frequency deviation detected by the frequency deviation detecting means and the line quality detected by the line quality detecting means. Is generated on the basis of the information indicating the above, and is supplied to the reference oscillating means. Therefore, for example, the line quality is significantly deteriorated due to the influence of multipath fading, which causes the C / N of the demodulated baseband signal.
If the control signal is deteriorated, the control voltage is generated based on the information on the frequency deviation detected before the line quality deteriorates, without using the information on the frequency deviation detected in this state. Become. Therefore, it becomes possible to reduce the influence of the deterioration of the line quality and stably maintain the local oscillation signal frequency at an appropriate value at all times, thereby preventing the deterioration of the reception sensitivity and the deterioration of the accuracy of the transmission modulation frequency. it can.

According to the present invention, the error rate of the received data is detected as the line quality, and when the detected error rate is less than the predetermined value, the frequency deviation is generated so as to approach zero. When the control voltage is supplied to the reference oscillating means and the error rate is above a predetermined value,
The control voltage value generated immediately before this state is held and supplied to the reference oscillating means. Therefore, the local oscillation signal frequency can be maintained at a correct value even when the line quality is significantly deteriorated.

Further, according to the present invention, the error rate of the received data is detected by using the table storing the information indicating the correspondence between the frequency deviation and the error rate. Therefore, the error rate can be easily detected based on the detected value of the frequency deviation without performing complicated signal processing or arithmetic processing.

[0017]

1 is a circuit block diagram showing the configuration of a radio modulation / demodulation unit of a digital radio having an AFC function according to an embodiment of the present invention. In addition, in FIG.
The same parts as those in FIG.

The radio device of this embodiment has one reference oscillator 21 for local oscillation. This reference oscillator 21 is
It is a high-precision oscillator using a voltage-controlled temperature-compensated crystal oscillator (VCTCXO) and generates a reference frequency signal BS having a frequency according to the control voltage. This reference oscillator 21
The reference frequency signal BS generated by is supplied to the frequency synthesizers 22 and 27 and the frequency dividing circuit (÷ N) 28, respectively.

The frequency synthesizer 22 converts the reception frequency based on the reference frequency signal BS generated by the reference oscillator 21 according to the frequency division variable signal corresponding to the radio channel given from the control circuit (not shown). First local oscillation signal LO1 and transmission local oscillation signal LO for quadrature modulation
Generate T respectively. Then, the first local oscillation signal LO
1 is supplied to the first mixer 5, while the transmission local oscillation signal L
The OT is supplied to the quadrature modulator 13. Local oscillation signal L
The OT consists of two signals whose phases are orthogonal to each other.

The frequency synthesizer 27 generates a second local oscillation signal LO2 based on the reference frequency signal BS generated by the reference oscillator 21 according to a predetermined frequency division number, and the second local oscillation signal LO2 is generated. LO2 is supplied to the second mixer 7.

The frequency dividing circuit 28 divides the frequency of the reference frequency signal BS generated by the reference oscillator 21 by N to generate a local oscillation signal LO3 for quadrature demodulation. This local oscillation signal LO3 has two phases which are orthogonal to each other.
The two signals are supplied to the two mixers of the quadrature demodulator 10.

In the wireless device of this embodiment, the frequency deviation detection circuit (Δf-DE) is used as a component of the AFC circuit.
T) 31 and error rate detection circuit (BER-DET) 32
And a correction control circuit 30.

The frequency deviation detection circuit 31 detects the frequency deviation Δf based on the rotation amount of the phase point in the baseband signal after quadrature demodulation from the normal position. Error rate detection circuit 3
Reference numeral 2 has a memory that stores table information representing the correspondence between the frequency deviation Δf and the bit error rate BER of the received data. Then, the frequency deviation detection circuit 3
By giving the frequency deviation Δf detected by 1 to the memory as an address, the corresponding bit error rate B
Get the ER. Then, the bit error rate BER is compared with a preset threshold value to determine whether or not the threshold value is increased above the threshold value, and the determination information is output to the correction control circuit 30.

The correction control circuit 30 determines, based on the frequency deviation Δf detected by the frequency deviation detection circuit 31 and the determination information output from the error rate detection circuit 32,
The control voltage VS for controlling the oscillation frequency of the reference oscillator 21 is generated and supplied to the reference oscillator 21.

FIG. 2 is a circuit block diagram showing the configuration of the correction control circuit 30. The correction control circuit 30 includes a switch circuit 301, a RAM 302, a frequency / voltage conversion circuit (f / V) 303, and a digital / analog converter (D / A) 304.

The switch circuit 301 is turned on / off according to the determination information output from the error rate detection circuit 32. The RAM 302 has a function of latching the detection information of the frequency deviation Δf input via the switch circuit 301, and during the ON period of the switch circuit 301, the detection information of the frequency deviation Δf is directly frequency / voltage converted. Supply to the circuit 30. On the other hand, the switch circuit 3
When 01 is turned off, the detection information of the frequency deviation Δf input immediately before the switch circuit 301 is turned off is latched, and the detection information of the latched frequency deviation Δf is turned off by the switch circuit 301. The frequency / voltage conversion circuit 30 is continuously supplied during the period.

The frequency / voltage conversion circuit 303 has a memory in which table information representing the correspondence between the frequency deviation Δf and the control voltage VS is stored in advance. When the detection information of the frequency deviation Δf is input from the RAM 302 as an address, the digital control voltage VS corresponding to the frequency deviation Δf is read out and supplied to the digital / analog conversion circuit 304. The digital / analog conversion circuit 304 converts the digital control voltage VS supplied from the frequency / voltage conversion circuit 303 into an analog value and supplies the analog value to the reference oscillator 21.

Next, the AFC operation in the digital radio set as above will be described. When the communication is started, the frequency deviation detection circuit 31 detects the frequency deviation Δf from the change in the phase position of the demodulated baseband signal, and the error rate detection circuit 32 detects the bit error rate based on the detection information of the frequency deviation Δf. BER is detected. Then, based on these detection information, the correction control circuit 30 performs correction control of the oscillation frequency of the reference oscillator 21 as follows.

That is, first, when the quality of the wireless channel is good, the C / N of the demodulated baseband signal is high, so that the noise component mixed in the demodulated baseband signal corresponds to the frequency shift of the local oscillation signal. It is only an ingredient. Therefore, the frequency deviation Δf detected by the frequency deviation detection circuit 31 becomes relatively small corresponding to the frequency deviation of the local oscillation signal, and the bit error rate BER detected by the error rate detection circuit 32 is thereby reduced. It becomes a small value less than the threshold value. Therefore, the switch 301 of the correction control circuit 30 maintains the ON state (conduction state), and therefore the detection information of the frequency deviation Δf is directly input to the frequency / voltage conversion circuit 303 via the RAM 302.

Therefore, the frequency / voltage conversion circuit 303
Outputs a control voltage VS corresponding to the detection information of the frequency deviation Δf. The control voltage VS is converted into an analog signal by the digital / analog conversion circuit 304 and then supplied to the reference oscillator 21. That is, the reference oscillator 21
Is supplied in real time with a control voltage VS corresponding to the frequency deviation Δf detected from the demodulated baseband signal. Therefore, the oscillation frequency of the reference oscillator 21 is corrected so that the frequency deviation Δf becomes zero according to the control voltage VS.

As a method of correcting the frequency deviation Δf, the following method is used, for example. That is, when the frequency deviation Δf is detected, the rough adjustment is first performed. In this coarse adjustment, five predetermined coarse adjustment values + 2Δf ′, + Δf ′, related to the detected frequency deviation Δf,
0, -Δf ', -2Δf' (Δf '<Δf) are selected in order, and the control voltage V corresponding to this rough adjustment value is selected each time.
S is generated and supplied to the reference oscillator 21. Then, the coarse adjustment value when the frequency deviation Δf becomes the smallest is temporarily fixed. Next, fine adjustment values + Δf ″, −Δf ″ (Δf ″ <Δf ′) are set based on the temporarily fixed coarse adjustment value,
Control voltage V for each of these fine adjustment values + Δf ″ and −Δf ″
The oscillation frequency of the reference oscillator 21 is variably controlled by varying S. Thus, the frequency deviation Δf is corrected.

Now, it is assumed that the received electric field strength of the radio frequency signal is remarkably lowered due to the influence of multipath fading, and the C / N of the demodulated baseband signal is lowered. Then, the frequency deviation Δf detected by the frequency deviation detection circuit 31 is significantly increased, which causes the bit error rate BER detected by the error rate detection circuit 32.
Increases above the threshold. Therefore, the correction control circuit 3
The switch circuit 301 of 0 is turned off (non-conductive state), whereby the input of the detection information of the frequency deviation Δf to the RAM 302 is cut off. Therefore, the RAM 302
From the above, the detection information of the frequency deviation Δf input to the RAM 302 immediately before the switch circuit 301 is turned off is latched. Then, after that, the switch circuit 301
The control voltage VS corresponding to the latched detection information of the frequency deviation Δf is continuously output and is supplied to the reference oscillator 21 until is returned to the ON state. That is, during the period in which the C / N of the demodulated baseband signal is significantly reduced, instead of the frequency deviation Δf detected in this period,
The control voltage VS corresponding to the frequency deviation Δf immediately before the C / N decreases is supplied to the reference oscillator 21.

Therefore, even if the random noise component of the frequency mixed in the demodulated baseband signal due to the significant deterioration of C / N is detected as the frequency deviation, the local oscillation signal frequency can be accurately corrected without being affected by this. It becomes possible to do it.

As described above, in this embodiment, the error rate detection circuit 32 is provided in addition to the frequency deviation detection circuit 31, and when the error rate BER detected by this error rate detection circuit 32 is less than the predetermined value, the frequency deviation detection is performed. The reference oscillator 21 is real-time according to the frequency deviation Δf detected by the circuit 31.
When the error rate BER detected by the error rate detection circuit 32 increases above a predetermined value,
Just before the error rate BER increases, the frequency deviation Δf detected by the frequency deviation detection circuit 31 is latched and held,
Thereafter, until the error rate BER is improved to be less than a predetermined value, the reference oscillator 2 is responsive to the latched frequency deviation Δf.
The oscillation frequency of 1 is controlled.

Therefore, in the present embodiment, the line quality is remarkably deteriorated due to, for example, multipath fading, the C / N of the demodulated baseband signal is lowered, and the random noise component is detected as the frequency deviation Δf. Even in this case, it is possible to prevent erroneous AFC operation due to this frequency deviation Δf. Therefore,
The stability of the AFC operation can be improved, and thus the reception sensitivity can be prevented from deteriorating and the transmission modulation frequency accuracy can be prevented from decreasing.

Further, in the present embodiment, during the period when the line quality is remarkably deteriorated, the value of the frequency deviation Δf detected immediately before the deterioration of the quality is latched and held as described above, and according to the held value. The oscillating frequency of the reference oscillator 21 is held at this frequency. Therefore, the local oscillation signal can be stably generated even during the period when the line quality is deteriorated, and the normal AFC operation can be smoothly performed when the line quality is restored to a good state. ,
This makes it possible to maintain high communication stability.

By the way, when the line quality is deteriorated, the control voltage VS becomes indefinite during the period when the line quality is deteriorated in the case where the AFC operation is simply stopped without holding the control voltage VS. Therefore, the local oscillation frequency changes greatly, and as a result, it takes time to restore the AFC operation when the line quality returns to a good state.

Further, according to the present embodiment, the error rate detection circuit 32 is provided with a table storing information indicating the correspondence between the frequency deviation Δf and the error rate BER, and the error rate of the received data is estimated using this table. I am trying to do it. Therefore, the error rate BER can be easily detected based on the detected value of the frequency deviation Δf without performing complicated signal processing or arithmetic processing.

The present invention is not limited to the above embodiment. For example, although the error rate BER is determined by one threshold value in the above embodiment, the AFC operation may be stopped stepwise by using a plurality of threshold values. . As a specific example thereof, a configuration in which a plurality of time constants are set in the AFC loop and a large time constant is selected as the error rate BER increases can be considered.

Further, the threshold value for judging that the error rate has returned to a small state may be set to a value smaller than the threshold value for judging the increase of the error rate. With this configuration, a hysteresis characteristic can be provided between the line quality deterioration determination and the line quality restoration determination, and thereby more stable AFC stop control can be performed.

Further, as the line quality detecting means, other than the means for detecting the error rate BER, the opening of the eye pattern of the demodulated baseband signal may be measured, and other configurations of the reference oscillator and the frequency deviation detecting circuit are also possible. Also, the configuration of the frequency correction means, the control procedure and control contents, the type of the digital radio device and its configuration, etc. can be variously modified and implemented without departing from the scope of the present invention.

[0042]

As described above in detail, according to the present invention, as the reference oscillating means for supplying the reference frequency signal to the local oscillating means for generating the local oscillating signal, the voltage control type reference whose oscillation frequency can be varied by the control voltage is used. The frequency correction is provided by providing an oscillating means, a frequency deviation detecting means for detecting a frequency deviation from the demodulated data, a line quality detecting means for detecting information indicating the line quality from the demodulated data, and a frequency correcting means. Means for generating a control voltage for reducing the frequency deviation based on the information on the frequency deviation detected by the frequency deviation detecting means and the information indicating the line quality detected by the line quality detecting means. Is supplied to the reference oscillation means.

Therefore, according to the present invention, it is possible to prevent erroneous frequency control from being performed when the received electric field strength decreases, thereby preventing deterioration of receiving sensitivity and deterioration of modulation frequency accuracy. It is possible to provide a digital wireless device having an automatic frequency control function that can maintain excellent transmission / reception characteristics.

[Brief description of drawings]

FIG. 1 is a circuit block diagram showing a configuration of a digital wireless device including an AFC circuit according to an embodiment of the present invention.

FIG. 2 is a circuit block diagram showing a configuration of a correction control circuit of the AFC circuit shown in FIG.

FIG. 3 is a circuit block diagram showing an example of a configuration of a digital wireless device including a conventional AFC circuit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Antenna 2 ... Antenna duplexer 3 ... High frequency amplifier 4 ... High frequency filter 5 ... 1st mixer 6 ... 1st intermediate frequency filter 7 ... 2nd mixer 8 ... 2nd intermediate frequency filter 9 ... Intermediate frequency amplifier 10 ... Quadrature Demodulator 11 ... Digital demodulator 12 ... Digital modulator 13 ... Quadrature modulator 14 ... Transmission power amplifier 21 ... Reference oscillator 22, 27 ... Frequency synthesizer 28 ... Dividing circuit 30 ... Correction control circuit 31 ... Frequency deviation detection circuit (Δf -DET) 32 ... Error rate detection circuit (BER-DET) 301 ... Switch circuit 302 ... Latch RAM 303 ... Frequency / voltage conversion circuit (f / V) 304 ... Digital / analog converter (D / A) Δf ... Frequency deviation VS ... Control voltage BS ... Reference frequency signal BER ... Bit error rate

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location H04L 1/20 27/22

Claims (3)

[Claims] 1. A digital radio device equipped with a circuit system for frequency-converting a received radio frequency signal into an intermediate frequency signal by a frequency conversion circuit and then demodulating by a digital demodulation circuit to output demodulated data. Voltage-controlled reference oscillating means for generating a reference frequency signal having a corresponding frequency, and a local oscillating signal based on the reference frequency signal generated by the reference oscillating means to generate the frequency converting circuit and digital demodulation. Local oscillating means for supplying the circuit, frequency deviation detecting means for detecting frequency deviation from the demodulated data, line quality detecting means for detecting information indicating line quality from the demodulated data, and the frequency Information on the frequency deviation detected by the deviation detecting means and information indicating the line quality detected by the line quality detecting means. And a frequency correcting means for generating the control voltage for reducing the frequency deviation and supplying the control voltage to the reference oscillating means, the digital radio having an automatic frequency control function. Machine. 2. The line quality detecting means detects an error rate of demodulated data as information indicating the line quality, and the frequency correcting means, when the error rate detected by the line quality detecting means is less than a predetermined value, Based on the frequency deviation detected by the frequency deviation detecting means, a control voltage generated so as to bring the frequency deviation close to zero is supplied to the reference oscillating means. 2. The digital radio device with an automatic frequency control function according to claim 1, wherein the generated control voltage value is held and supplied to the reference oscillating means. 3. The line quality detecting means has a table storing information representing the correspondence between frequency deviation and error rate, and the error rate corresponding to the frequency deviation detected by the frequency deviation detecting means is calculated from the table. A digital radio having an automatic frequency control function according to claim 1 or 2, which is obtained.