JPH08321855A - Digital radio wave receiver applying multilevel frequency shift modulating system - Google Patents

Abstract

PURPOSE: To normally make possible correct level judging in accordance with a reception state in a case under a strong reception electric field or a weak reception electric field. CONSTITUTION: A reception electric field strength degree detected by a reception electric field strength detecting circuit 21 is monitored in a threshold value control circuit 20a under the usage of a four-phase FSK radio wave receiver and a code judging threshold value is adaptively and variably controlled in accordance with the change of the reception electric field strength so as to be supplied to a decoder 16.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to multilevel frequency shift keying (multilevel FS) as a modulation system such as a selective call receiver.
The present invention relates to improvement of a digital radio receiver adopting the K) system.

[0002]

2. Description of the Related Art In recent years, a multi-value modulation system has been widely adopted in mobile communication equipment, and accordingly, a radio receiver giving a good sensitivity to the multi-value modulation is required. For example,
The selective call receiving system adopts a four-value FSK system in order to increase the data transmission capacity, and the selective call receiver used in this system is required to have a receiving sensitivity close to that of a conventional binary FSK receiver. .

FIG. 10 shows a four-valued F that has been conventionally considered.
It is a circuit block diagram which shows the principal part structure of a SK radio receiver. In the figure, a reception signal received by an antenna (not shown) and then frequency-converted into an intermediate frequency signal by a mixer is amplified by an intermediate frequency amplifier (IF) 11 and input to a detector (DISC) 13 including a discriminator. To be done. In this detector 13, the received signal is a phase shifter (φ).
Quadrature detection is performed based on the received signal that is phase-shifted by π / 2 at 12. The demodulated signal output from the detector 13 is passed through a bit rate filter (FIL) 14 and then input to an analog / digital (A / D) converter 15, where it is converted into a digital signal and then to a decoder 16. Is entered. In the decoder 16, 3 stored in advance in the memory 17
The level of the digital signal is judged based on the two threshold values Vth1, Vth2 and Vth3.

By the way, the above threshold values Vth1 and Vth2
, Vth3 are conventionally set as follows, for example. Note that the 2-bit information "00", "01", "10", and "11" transmitted by the four-valued FSK system is now frequency f1, f2, f3, f4 as shown in FIG. 11, for example.
Be assigned to. The horizontal axis of FIG. 11 represents the demodulated signal voltage as well as the frequency.

The selective call receiver receives a training signal (repetition signal of "00" and "10") as shown in FIG. 11 transmitted from the base station as a preamble signal, and the peak of demodulation output of this training signal. Value is A /
The D converter 15 samples and holds. Then, based on the sampled and held peak value, each threshold value Vth1,
Set Vth2 and Vth3. At that time, the central threshold value Vth2 among the above threshold values Vth1, Vth2, and Vth3.
With respect to, there is a case where the direct current component of the demodulated signal output from the integration circuit 18 is input to the A / D converter 15 via the changeover switch 19 and the direct current component is sampled and held to set. Also, the central threshold value Vth2
May be set using the training signal, and the other threshold values Vth1 and Vth3 may be set by adding or subtracting predetermined amplitude information based on the center threshold value Vth2.

That is, in any conventional setting method, when a threshold value is set, the threshold value is fixedly stored in the memory, and thereafter, the threshold value is continuously used to obtain a demodulated signal. The level is judged.

[0007]

However, such a conventional receiver uses a fixed threshold value as described above. Therefore, for example, if the threshold value is set in a state where the received electric field strength is sufficiently large, when the received electric field strength decreases, such as when the receiving station is far away from the base station or when fading occurs, the decoder It becomes impossible to make an accurate level judgment. On the other hand, if the threshold value is set and used in a state where the received electric field strength is lowered, accurate level determination cannot be performed when the received electric field strength is sufficiently large.

The present invention has been made in view of the above circumstances, and a first object thereof is to always obtain an accurate level according to the reception state at that time both in a strong receiving electric field and in a weak receiving electric field. It is an object of the present invention to provide a digital radio receiver to which a multivalued frequency shift keying method that can make a determination is applied.

A second object of the present invention is to provide a multi-valued frequency deviation capable of making an accurate level judgment above an allowable level under a strong receiving electric field and a weak receiving electric field without requiring complicated threshold control. It is an object of the present invention to provide a digital radio receiver to which a transmodulation method is applied.

A third object of the present invention is to provide a digital radio receiver to which a multilevel frequency shift keying system which can make accurate level determination for any data transmission rate is applied.

[0011]

In order to achieve the above first object, a first invention comprises a receiving state detecting means for monitoring a receiving state of a radio frequency signal, and a threshold control means. The threshold value control means selectively and variably controls a plurality of threshold values based on the reception state detected by the reception state detection means.

Further, according to the present invention, the reception state detecting means detects the reception electric field strength of the radio frequency signal, and the threshold value controlling means detects a plurality of signals based on the reception electric field strength detected by the reception state detecting means. The feature is that the threshold value is selectively variably controlled.

Further, according to the present invention, the reception state detecting means monitors the synchronization state of the received digital data, and the threshold value controlling means detects the plurality of thresholds based on the synchronization state detected by the reception state detecting means. It is also characterized by selectively variably controlling the value.

Further, according to the present invention, the reception state detecting means monitors the reception electric field strength of the radio frequency signal and the synchronization state of the reception digital data, respectively, and the threshold control means detects the reception detected by the reception state detecting means. It is also characterized in that the plurality of thresholds are selectively variably controlled based on the electric field strength and the synchronization state.

Further, the threshold value control at that time is performed by a plurality of threshold values when the reception electric field strength detected by the reception state detecting means falls below a predetermined level and the synchronization acquisition rate falls below a predetermined value. May be selectively switched from a preset first value to a second value.

On the other hand, in order to achieve the above-mentioned second object, the second invention comprises a threshold value generating means for storing a plurality of threshold values preset in accordance with the received electric field strength near the receiving sensitivity. The threshold value stored in the threshold value generating means is used for determining the level of the demodulated signal.

Further, according to the present invention, the threshold value generating means detects a demodulated signal level under a received electric field strength equal to or higher than a predetermined level, and sets a first threshold value group based on the detected level. Based on the detection level, the demodulation signal level under the reception electric field strength near the reception sensitivity is estimated, and the second value corresponding to the reception electric field strength near the reception sensitivity is estimated from the estimated value and the first threshold value group. Means for generating and storing a threshold value group, and the second threshold value group stored in this means is used for the level determination of the demodulated signal.

In order to achieve the above-mentioned third object, the third invention is such that, when digital data of a plurality of different transmission rates can be respectively received, the threshold value generating means for each of the plurality of transmission rates. , A plurality of threshold groups preset according to the received electric field strength near the receiving sensitivity are stored respectively, and these threshold groups are selectively read according to the transmission rate to determine the level of the demodulated signal. It is characterized by offering to.

[0019]

As a result, according to the first aspect of the present invention, the reception state of the radio frequency signal coming from the base station is monitored, and the threshold value is variably controlled according to the change of the reception state. For this reason, a threshold value is set according to the demodulated signal level at that time under a strong received electric field. On the other hand, when the received electric field strength decreases due to the effect of fading, etc., the threshold value becomes low according to the demodulated signal level at that time. It will be changed to the value. Therefore, the optimum threshold value is always set regardless of the state of the received electric field, which enables the accurate determination of the demodulated signal level.

At this time, if the received electric field strength is monitored as a receiving state and threshold control is performed, for example, the detection output of the received electric field strength detection circuit already provided for displaying outside the reception area is used as it is. Is possible,
As a result, the present invention can be realized without providing a new circuit.

Further, even if the synchronization state of the received digital data is monitored as the reception state and the threshold value control is performed, for example, the synchronization acquisition rate as the synchronization state is substantially proportional to the change of the reception electric field strength, so that the reception electric field strength is The threshold value can always be set to the optimum value as in the case where the threshold value is set based on. Moreover, when the synchronization state is monitored as the reception state, it is possible to detect a reception field strength lower than in the case where the reception field strength is directly monitored, so that the threshold value control can be performed in a wider range of the reception field strength. Becomes

Further, if the threshold value is controlled by monitoring the reception electric field strength and the synchronization status as the reception status, the threshold value can be changed only when both the reception electric field strength and the synchronization status are deteriorated. Becomes For example, in the case where the reception electric field strength does not decrease as in the case where control intermodulation or sensitivity suppression occurs, but the synchronization acquisition rate decreases, unnecessary threshold value change is prevented. be able to.

On the other hand, according to the second aspect of the invention, the level of the demodulated signal is determined based on the threshold value fixedly set in advance according to the received electric field strength near the receiving sensitivity. Therefore, when the received electric field strength is low, more accurate level judgment is possible compared to the case where a fixed threshold value is used in the strong received electric field, and the noise component is originally small in the strong received electric field. It is possible to maintain good level determination accuracy even if the threshold value does not become optimal according to the strong reception electric field. Moreover, according to the present invention, once the threshold value according to the received electric field strength near the receiving sensitivity is set, it is not necessary to adaptively perform the threshold value control thereafter. Therefore, it becomes possible to make threshold control unnecessary or significantly simple.

Further, according to the third invention, when receiving and determining data having different transmission rates, a threshold value set in advance for each transmission rate is selectively used. Therefore, even when data is received at any transmission speed, it is possible to accurately determine the level above the allowable level by the threshold value set near the reception sensitivity.

[0025]

【Example】

(First Embodiment) FIG. 1 is a circuit block diagram showing a main configuration of a four-value FSK radio receiver according to the first embodiment of the present invention. In the figure, the same parts as those in FIG. 10 are designated by the same reference numerals and detailed description thereof will be omitted.

The four-level FSK radio receiver of this embodiment is newly provided with a reception field strength detection circuit (RSSI) 21 and a threshold control circuit 20a. The reception electric field strength detection circuit 21 detects the reception electric field strength of the radio frequency signal arriving from the base station based on the amplitude level of the reception intermediate frequency signal obtained in the intermediate frequency amplifier 11, and sets the detection signal as a threshold value. It is supplied to the control circuit 20a.

The threshold control circuit 20a constantly or periodically receives the decoding determination threshold V during reception of the radio frequency signal.
The th1, Vth2, and Vth3 are variably controlled. The thresholds Vth1, Vth2, and Vth3 are variably controlled by variably controlling the initial threshold value stored in advance in the memory 17, based on the detection signal supplied from the reception electric field strength detection circuit 21.

Next, the operation of the receiver configured as above will be described. Prior to using the receiver, the initial threshold value is first set. That is, for example, the receiver is brought near a base station where a strong reception electric field can be obtained, where the training signal transmitted from the base station is received and the amplitude level of the demodulated signal is detected by the A / D converter 15. To do. Then, the amplitude information detected by the A / D converter 15 is stored in the memory 17, and based on this amplitude information, the initial threshold values Vth1, Vth2, Vth3 under a strong reception electric field are stored.
Set and memorize. These initial threshold values Vth1, V
For example, as shown in FIG. 3A, th2 and Vth3 are set so as to be in the middle of the amplitude levels of the respective codes “00”, “01”, “11” and “10”.

When the receiver starts to be used in this state, the threshold control circuit 20a supplies the initial thresholds Vth1, Vth2 and Vth3 stored in the memory 17 to the decoder 16. The decoder 16 starts the level judgment of the demodulated signal based on the initial threshold values Vth1, Vth2, Vth3.

Now, assume that the user carrying the receiver moves to a position far away from the base station in this state, and the received electric field strength of the radio wave coming from the base station is thereby lowered.
This decrease in the electric field strength of the received radio wave is detected by the received electric field strength detection circuit (RSSI) 21, and the threshold control circuit 20a
Conveyed to. Then, the threshold control circuit 20a
The detected value of the received electric field strength transmitted from the received electric field strength detection circuit 21 and the characteristic data representing the change of the demodulated signal voltage value with respect to the received electric field strength stored in advance are stored in the memory 17. Initial threshold Vth1,
Change Vth2 and Vth3.

For example, the characteristic data as shown in FIG. 2 is previously stored as characteristic data representing the change in the demodulated signal voltage value with respect to the received electric field strength. In this state, the detected value of the received electric field strength changes from S0 to S1. Suppose it has changed. Then, the threshold control circuit 20a obtains the demodulated signal voltage value v1 corresponding to the detected value S1 of the received electric field strength from the characteristic data, and changes the threshold value to the optimum value based on the demodulated signal voltage value v1. . For example, if the demodulation signal voltage is
If the value is changed to the value shown in (c), the threshold value Vth1 is set so as to be positioned at the intermediate value of each code as shown in FIG.
', Vth2, Vth3'. Then, the threshold value control circuit 20a subsequently determines the changed threshold value Vth1.
', Vth2, Vth3' are given to the decoder 16 to make level determination of the demodulated signal.

As described above, in this embodiment, the receiving electric field strength detected by the receiving electric field strength detecting circuit 21 in the threshold value control circuit 20a is monitored while the receiver is in use, and the received electric field strength is changed according to the change in the receiving electric field strength. The threshold is adaptively variably controlled. Therefore, even if the amplitude level of the demodulated signal changes due to a change in the characteristics of the wireless transmission line such as movement of the receiver or fading, the threshold adaptively changes according to this change. Therefore, the decoder 1
In 6, it is always possible to perform accurate level determination according to the optimum threshold value.

Incidentally, if the threshold value given to the decoder 16 is fixed to the initial threshold values Vth1, Vth2, and Vth3 as in the conventional case, the amplitude level of the demodulated signal obtained under the weak reception electric field strength and the threshold value Vth1. , Vth2,
The relationship with Vth3 becomes improper as shown in FIG. 3B, and it becomes difficult to accurately determine "00" and "10".

Further, in this embodiment, since the received electric field strength is detected and the threshold value is variably controlled, the following effects can be obtained. That is, for example, a selective call receiver is generally provided with a received electric field strength detection circuit for performing an out-of-range display. Therefore, with such a receiver, the threshold value control can be performed by using the existing reception electric field strength detection circuit as it is, and thus there is an advantage that it can be realized without causing the circuit scale to be complicated or large. is there.

In the above description, the threshold value is controlled to be stepless or close to it in accordance with the change in the received electric field strength. However, in order to judge the change in the received electric field strength, one or more judgment levels are set. May be set in advance, the received electric field strength detection value may be compared with these determination levels for determination, and the threshold value may be switched to a corresponding threshold value in accordance with the determination result.

Further, as a modification of the above FIG. 1, the following can be considered. FIG. 6 is a circuit block diagram showing the configuration. In the figure, the demodulation signal and integration circuit 1
The output signal of 8 is amplified by the amplitude amplifier (AC) 23 and then supplied to the A / D converter 15. Further, the A / D converter 15 receives the DC voltage obtained by rectifying the output of the amplitude amplifier 23 by the rectifier 24 as a reference level.

With such a configuration, the circuit scale is increased by the provision of the rectifier 24, but since the demodulation signal level is amplified by the amplitude amplifier 23 to directly obtain the amplitude level, the received electric field strength and the amplitude level are obtained. The conversion of can be eliminated.

(Second Embodiment) In this embodiment, the bit synchronization acquisition rate is monitored while the receiver is in use, and the threshold value is variably controlled according to the change of the bit synchronization acquisition rate. Is.

FIG. 4 is a circuit block diagram showing a main configuration of a four-value FSK radio receiver according to this embodiment. In addition,
In the figure, the same parts as those in FIG. 10 are designated by the same reference numerals, and detailed description thereof will be omitted.

The four-valued FSK radio receiver of this embodiment is newly provided with a bit synchronization state monitor circuit (SYNC) 22 and a threshold control circuit 20b. The bit synchronization state monitoring circuit 22 monitors the bit synchronization state in the decoder 16 and supplies the threshold control circuit 20b with information indicating a change in the bit synchronization acquisition rate.

The threshold control circuit 20b sets the initial threshold values Vth1, Vth2, Vth3 stored in advance in the memory 17 in accordance with the change in the bit synchronization acquisition rate detected by the bit synchronization state monitoring circuit 22. It is variably controlled and supplied to the decoder 16.

With such a configuration, the received electric field strength of the radio frequency signal coming from the base station is lowered due to the change of the characteristic of the radio transmission path such as the movement of the receiver or the fading, and the bit synchronization is accompanied with this. When the capture rate decreases, the threshold value supplied from the threshold value control circuit 20b to the decoder 16 changes.

Therefore, the threshold value is adaptively variably controlled in accordance with the change in the bit synchronization acquisition rate, whereby the demodulation is performed in accordance with the change in the characteristics of the wireless transmission path such as the movement of the receiver and fading. Even if the amplitude level of the signal changes, the decoder 16 can always make an accurate level determination according to the optimum threshold value.

Further, in this embodiment, since the threshold value is controlled based on the bit synchronization acquisition rate, it is possible to detect a low reception input level which is generally difficult to detect by the reception electric field strength detection circuit. This enables threshold control over a wider range.

In the above description, the threshold value is controlled to be stepless or close to it in accordance with the change in the bit synchronization acquisition rate, but one or a plurality of values may be set in order to determine the change in the bit synchronization acquisition rate. A determination level may be set in advance, the detected value of the bit synchronization acquisition rate may be compared with these determination levels for determination, and control may be performed to switch to a corresponding threshold value according to the determination result.

Further, instead of the bit synchronization acquisition rate, the bit synchronization loss rate may be detected and the threshold value may be controlled according to the detection result. (Third Embodiment) In the present embodiment, both the reception electric field strength and the bit synchronization acquisition rate of a radio frequency signal are monitored, and a threshold value is set based on each detection result of the reception electric field strength and the bit synchronization acquisition rate. Is variably controlled.

FIG. 5 is a circuit block diagram showing a main configuration of a four-value FSK radio receiver according to this embodiment. In addition,
In the figure, the same parts as those in FIGS. 1 and 2 are designated by the same reference numerals, and detailed description thereof will be omitted.

The receiver of this embodiment comprises a received electric field strength detection circuit 21, a bit synchronization state monitoring circuit 22 and a threshold control circuit 20c. Threshold control circuit 20c
Prepares a threshold value for lowering the received electric field strength in advance, and when the detected value of the received electric field strength and the bit synchronization acquisition rate each fall below a predetermined level, the initial threshold value stored in the memory 17 is stored. Instead of the values Vth1, Vth2, and Vth3, the threshold for lowering the weak received electric field strength is supplied to the decoder 16.

With such a configuration, the received electric field strength of the radio frequency signal arriving from the base station drops below a predetermined level due to a change in the characteristics of the radio transmission path such as movement of the receiver or fading, which causes When the bit synchronization acquisition rate also drops below a predetermined level, the threshold control circuit 2
The threshold value supplied from 0c to the decoder 16 is the initial threshold value V for the strong receiving electric field stored in the memory 17.
The thresholds for lowering the weak reception electric field strength are switched from th1, Vth2, and Vth3.

On the other hand, when only the bit synchronization acquisition rate decreases due to the effect of intermodulation or sensitivity suppression, the threshold value control circuit 20c does not confirm the decrease in the received electric field strength, so that the threshold value is changed. Absent.

Therefore, according to the present embodiment, even if the received electric field strength changes due to the change in the characteristics of the wireless transmission line such as the movement of the receiver or the fading, the decoder 16 has a strong received electric field strength and a weak received electric field strength. Under the strength, the level judgment is performed according to the respective appropriate threshold values, which allows more accurate demodulation signal level judgment than the conventional receiver in which the threshold value is fixed to one value. it can.

Further, for example, when only the bit synchronization acquisition rate is lowered due to the influence of intermodulation or sensitivity suppression, it is possible not to judge that this is an immediate reduction of the received electric field strength, and thereby the inappropriate threshold is set. It is possible to prevent value switching.

In the above description, a threshold value for lowering the strong reception electric field strength and a threshold value for lowering the weak reception electric field strength are prepared so that both the bit synchronization acquisition rate and the reception electric field strength are below a predetermined level. When it falls to 0, the threshold value supplied to the decoder 16 is switched from the threshold value for lowering the strong receiving electric field strength to the threshold value for lowering the weak receiving electric field strength. However, not limited to this, in a state where both the bit synchronization acquisition rate and the received electric field strength are reduced to below a predetermined level,
The threshold value may be changed steplessly or in plural steps according to the detected value of the received electric field strength or the detected value of the bit synchronization acquisition rate. Further, instead of the bit synchronization acquisition rate, the bit synchronization loss rate may be detected.

(Fourth Embodiment) In the present embodiment, the demodulation signal voltage under strong reception electric field strength is measured, and the measured value of the demodulation signal voltage, the reception electric field strength and the demodulation signal voltage stored in advance. Is used to set the decoding judgment threshold value such that the error rate characteristics under the weak reception electric field strength near the sensitivity of the receiver become the optimum value, and the decoding judgment threshold value is set. Is fixedly used to determine the level of the demodulated signal.

FIG. 7 is a circuit block diagram showing a main configuration of a four-value FSK radio receiver according to this embodiment. In addition,
In the figure, the same parts as those in FIG. 10 are designated by the same reference numerals, and detailed description thereof will be omitted.

The receiver of the present embodiment has a threshold value generating circuit 3
It has 0a. This threshold value generating circuit 30a represents the amplitude information of the demodulated signal stored in the memory 17 under the strong received electric field strength and the relationship between the received electric field strength and the demodulated signal voltage stored in advance at the time of initial setting. Using the characteristic data, the received electric field strength near the sensitivity, that is, FIG.
As shown in FIG. 5, the optimum threshold values Vth1 ″, Vth2 ″, V are set in the received electric field strength (for example, S1) in the area below the received electric field strength S0 at which the demodulated signal voltage cannot hold a constant value.
TH3 ″ is determined, and thereafter, this optimum threshold value Vth is determined.
1 ″, Vth2 ″ and Vth3 ″ are fixedly applied to the decoder 16.

With this configuration, when the receiver coordinator positions the receiver under the strong reception electric field strength at the time of initial setting, the training signal transmitted from the base station has a good S / N ratio. The received amplitude information of the demodulated signal is sampled and held by the A / D converter 15 and stored in the memory 17.

Then, the threshold value generating circuit 30a uses the amplitude information of the demodulated signal stored in the memory 17 and the characteristic data representing the relationship between the received electric field strength and the demodulated signal voltage stored in advance, Received electric field strength near sensitivity,
For example, the optimum threshold values Vth1 ″, V in S1 of FIG.
th2 ″ and VTH3 ″ are determined. Then, thereafter, the optimum threshold values Vth1 ″, Vth2 ″, Vth3 ″ are fixedly given to the decoder 16.

Therefore, when the receiver is started to be used thereafter, the decoder 16 determines during reception that the error rate characteristic under the weak receiving electric field strength near the sensitivity is optimized in the threshold generating circuit 30a. Optimum threshold value Vth
The level of the demodulated signal is determined according to 1 ″, Vth2 ″ and Vth3 ″.

Therefore, in the state where the received electric field strength is lowered, for example, when the receiver is moved to a place far away from the base station, the decoder 16 is suitable for a weak received electric field strength near the above sensitivity. Threshold Vth1 ″, Vth2
Since the level of the demodulated signal is determined according to ", Vth3", correct level determination is possible.

On the other hand, in the state where a sufficiently strong received electric field strength is obtained as in the case where the receiver moves to a position relatively close to the base station, the threshold values Vth1 ″, Vth are set.
Although 2 ″ and Vth3 ″ are not the optimum threshold values under strong receiving electric field strength, the received code under strong receiving electric field strength is originally low in noise, so even if it is not the optimum threshold value, there are few errors. , The error rate is within the allowable range.

FIG. 8 is a diagram for explaining the above-mentioned effects and effects. The received codes "10", "11", "01",
The distribution of the demodulated signal voltage when noise is added to "00" is shown. It should be noted that the figure does not include variations in demodulated signal level due to intersymbol interference.

First, assuming that the threshold values Vth1, Vth2, and Vth3 are set to be optimum under the strong reception electric field strength, FIG. 8A shows the case of judging the reception code received under the strong reception electric field strength. As shown, almost no reception error occurs. The shaded area in the figure represents the error rate. However, if an attempt is made to judge the reception code received under the weak reception electric field strength using the threshold values Vth1, Vth2, and Vth3, as shown in FIG.
Since th1 and Vth3 are greatly deviated from the central position between the received codes “10” and “11” and the central position between “01” and “00”, respectively, the error rates are shown by the shaded portions in the figure. Increase.

Therefore, if the threshold values Vth1 ", Vth2", and Vth3 "are set so that the error rate characteristics in the weak receiving electric field strength near the receiving sensitivity are optimized as in the present embodiment, FIG.
As shown in (d), the thresholds Vth1 ″ and Vth3 ″ are the reception codes “10” and “1” under the weak reception electric field strength, respectively.
It is located near the central position between 1 "and near the central position between" 01 "and" 00 ".
The error rate of the received code is reduced. Also, the above threshold Vth
When the received code is judged under the strong received electric field strength by using 1 ″, Vth2 ″ and Vth3 ″, the thresholds Vth1 ″ and Vth3 ″ are respectively received codes “10” and “10” as shown in FIG. 8C. Although it will deviate from the central position between 11 "and the central position between" 01 "and" 00 ", relatively few errors occur as shown in the figure. This is because the noise generated in the received code is originally small under the strong received electric field strength, and even if the threshold value is slightly shifted, the noise is not so much affected.

As described above, according to the present embodiment, the threshold values Vth1 ", Vth2", and Vth3 "are set so that the error rate characteristics at the weak receiving electric field strength near the receiving sensitivity are optimum, and this threshold is set. Since the received code is determined according to the values Vth1 ″, Vth2 ″, and Vth3 ″, the error rate can be reduced especially under a weak received electric field strength, which allows the received electric field strength to exceed the allowable value over a wide range. Sign determination accuracy can be obtained.

Further, the threshold values Vth1 ", Vth2", Vth
Since 3 ″ can be fixed, it is not necessary to adaptively control the threshold value according to the received electric field strength and the like, and thus the configuration for the threshold value control can be simplified.

(Fifth Embodiment) In the present embodiment, in a receiver capable of selectively receiving digital data of a plurality of different transmission rates, as shown in FIG. 2, the sensitivity is generally S1, Focusing on the fact that S2 is different, the optimum thresholds are set in accordance with the sensitivities corresponding to the selected transmission rates.

FIG. 9 is a circuit block diagram showing a main configuration of a four-value FSK radio receiver according to this embodiment. In addition,
In the figure, the same parts as those in FIG. 7 are designated by the same reference numerals, and detailed description thereof will be omitted.

The receiver of this embodiment comprises a bit rate control circuit 25 and a threshold value generating circuit 30b. The bit rate control circuit 25 receives the decoder 16 according to the speed information input via a transmission speed selection terminal (not shown).
And the transmission rate is specified for the threshold value generation circuit 30b.

The threshold value generation circuit 30b stores the transmission rate designation information given from the bit rate control circuit 25 every time a new setting or change operation of the transmission rate is performed.
Using the amplitude information of the demodulated signal under the strong received electric field strength stored in the memory 17 and the characteristic data representing the relationship between the received electric field strength and the demodulated signal voltage stored in advance, the specified transmission rate is met. An optimum threshold value is determined for the received electric field strength near the sensitivity (for example, S2 in FIG. 2).
Then, thereafter, this optimum threshold value is fixedly provided to the decoder 16.

With such a configuration, in the threshold value generating circuit 30b, an optimum threshold value when receiving a weak electric field near the sensitivity is set for each transmission speed of data to be received. The decoder 16 determines the code according to the threshold value. Therefore,
(EN) Provided is a radio receiver capable of reducing an error rate, particularly under a weak reception electric field strength, and obtaining a code determination accuracy equal to or more than an allowable value over a wide range of the reception electric field strength, regardless of the transmission speed. it can.

The present invention is not limited to the above embodiments. For example, in each of the first to third embodiments, when adaptively variably controlling the threshold value in accordance with at least one of the received electric field strength and the bit synchronization acquisition rate,
The threshold value may be variably controlled in consideration of the set transmission rate.

In addition, the modulation method, type of radio receiver, application, configuration, threshold setting control procedure and control contents thereof can be variously modified and implemented without departing from the scope of the present invention.

[0074]

As described in detail above, according to the first aspect of the present invention, it is provided with the reception state detecting means for monitoring the reception state of the radio frequency signal and the threshold control means. By means of the means for selectively variably controlling a plurality of threshold values based on the reception state detected by the reception state detection means, both under strong reception electric field and under weak reception electric field, It is possible to provide a digital radio receiver to which a multi-value frequency shift keying system that can always make an accurate level determination according to the reception state at that time is applied.

According to the second aspect of the invention, there is provided a threshold value generating means for storing a plurality of threshold values preset according to the received electric field strength near the receiving sensitivity, and the threshold value generating means stores the threshold value. By using the generated threshold value for the level judgment of the demodulated signal, it is possible to obtain an accurate level above the allowable level under both strong and weak receiving electric fields without requiring complicated threshold control. It is possible to provide a digital radio receiver to which a multilevel frequency shift keying system that can perform level determination is applied.

Further, according to the third aspect of the invention, when the digital data of a plurality of different transmission rates can be respectively received, the threshold value generating means sets the reception electric field strength near the reception sensitivity for each of the plurality of transmission rates. According to the present invention, a plurality of threshold groups set in advance are stored respectively, and these threshold groups are selectively read according to the transmission rate to be used for the level judgment of the demodulated signal. It is possible to provide a digital radio receiver to which a multivalued frequency shift keying method that can accurately determine a level even at a data transmission rate is applied.

[Brief description of drawings]

FIG. 1 is a circuit block diagram showing a main part configuration of a four-level FSK radio receiver according to a first embodiment of the present invention.

FIG. 2 is a diagram showing an example of a change characteristic of a demodulated signal voltage with respect to a received electric field strength.

FIG. 3 is a diagram showing an example of setting a threshold value in the reception shown in FIG.

FIG. 4 is a circuit block diagram showing a main part configuration of a four-value FSK radio receiver according to a second embodiment of the present invention.

FIG. 5 is a circuit block diagram showing a main part configuration of a 4-level FSK wireless receiver according to a third embodiment of the present invention.

6 is a circuit block diagram showing a modified example of the receiver shown in FIG.

FIG. 7 is a circuit block diagram showing a main part configuration of a 4-level FSK radio receiver according to a fourth embodiment of the present invention.

FIG. 8 is a diagram for explaining the operational effects of the receiver shown in FIG.

FIG. 9 is a circuit block diagram showing a main part configuration of a 4-level FSK radio receiver according to a fifth embodiment of the present invention.

FIG. 10 is a circuit block diagram showing an example of a conventional four-level FSK wireless receiver.

FIG. 11 is a diagram showing an example of setting a conventional threshold value.

FIG. 12 is a diagram showing a configuration example of a training signal.

[Explanation of symbols]

 11 ... Intermediate frequency amplifier 12 ... Phase shifter 13 ... Detector (DISC) 14 ... Bit rate filter (FIL) 15 ... Analog / digital (A / D) converter 16 ... Decoder 17 ... Memory 18 ... Integration circuit 19 ... Switching Switches 20a, 20b, 20c ... Threshold control circuit 21 ... Reception electric field strength detection circuit (RSSI) 22 ... Synchronous state monitoring circuit (SYNC) 23 ... Amplitude amplifier (A / C) 24 ... Rectifier 30a, 30b ... Threshold value Generator circuit

Claims (8)

[Claims] 1. A multi-valued device for decoding digital data by receiving a radio frequency signal which has been multi-valued frequency shift keying modulated, demodulating the frequency and then judging the level of the demodulated signal based on a plurality of threshold values. In a digital radio receiver to which a frequency shift keying method is applied, a plurality of reception state detection means for monitoring the reception state of the radio frequency signal, and a plurality of the reception states detected by the reception state detection means are provided. A digital radio receiver to which a multilevel frequency shift keying method is applied, comprising: a threshold control means for selectively variably controlling a threshold. 2. A reception state detection means detects a reception electric field strength of the radio frequency signal, and a threshold value control means based on the reception electric field strength detected by the reception state detection means. 2. A digital radio receiver to which the multilevel frequency shift keying system according to claim 1, wherein the threshold value is selectively variably controlled. 3. A reception state detection means monitors a synchronization state of the reception digital data, and a threshold value control means based on the synchronization state detected by the reception state detection means, the plurality of threshold values. 2. The digital radio receiver to which the multivalued frequency shift keying system according to claim 1 is selectively variably controlled. 4. The reception state detection means monitors the reception electric field strength of the radio frequency signal and the synchronization state of the reception digital data, respectively, and the threshold value control means receives the reception electric field detected by the reception state detection means. 2. The digital radio receiver to which the multilevel frequency shift keying system according to claim 1, wherein the plurality of threshold values are selectively variably controlled based on the strength and the synchronization state. 5. The threshold value control means sets a plurality of threshold values when the reception electric field strength detected by the reception state detection means falls below a predetermined level and the synchronization acquisition rate falls below a predetermined value. 5. The digital radio receiver to which the multilevel frequency shift keying system according to claim 4, wherein the preset first value is selectively switched to the second value. 6. A multi-valued device for decoding digital data by receiving a radio frequency signal which has been multi-valued frequency shift keying modulated, demodulating the frequency, and then judging the level of the demodulated signal based on a plurality of threshold values. In a digital radio receiver to which a frequency shift keying method is applied, a plurality of thresholds fixedly set according to the received electric field strength near the reception sensitivity are stored, and these thresholds are used to determine the level of the demodulated signal. A digital radio receiver to which a multi-valued frequency shift keying system is applied, which is provided with a threshold value generation means for use in. 7. The threshold value generating means detects a demodulated signal level under a received electric field strength equal to or higher than a predetermined level, and sets a first threshold value group based on the detected level.
Based on the detection level, the demodulation signal level under the reception electric field strength near the reception sensitivity is estimated, and the estimated value and the first
And a means for generating and storing a second threshold value group corresponding to the received electric field strength near the receiving sensitivity from the threshold value group and the second threshold value group stored in the means. 7. A digital radio receiver to which a multilevel frequency shift keying system according to claim 6 is applied, which is used for signal level judgment. 8. When the digital data at different transmission rates can be received respectively, the threshold value generating means is preset for each of the transmission rates according to the received electric field strength near the receiving sensitivity. 8. A multi-valued frequency according to claim 7, wherein a plurality of threshold value groups are respectively stored, and these threshold value groups are selectively read according to the transmission rate and used for level determination of the demodulated signal. Digital radio receiver using shift keying method.