JPH04334237A - Demodulation device for orthogonal amplitude modulation system digital radio equipment - Google Patents

Abstract

PURPOSE:To prevent abnormal synchronism with simple configuration in the demodulation device of a multi-level orthogonal modulation system digital radio equipment to which a costas type carrier reproduction loop is applied. CONSTITUTION:In the demodulation device of the multi-level orthogonal modulation system digital radio equipment obtaining a demodulation base band signal by mixing a reproduced carrier with a reception signal by applying the costas type carrier reproduction loop, a means 11 supervising the step-out of the carrier detects step-out and an abnormal synchronism prevention means 13 decides normal synchronism and abnormal synchronism by using the detection output. At the time of abnormal synchronism, the carrier reproduction loop is prohibited for prescribed time and a selection means 7 outputs a prescribed reference signal as a control signal during that time. The reproduction carrier is given to an oscillation means 9 which has the carrier reproduction loop, oscillates with the oscillation frequency corresponding to the control signal and obtains the reproduction carrier for the prescribed period so as to obtain the reproduction carrier of the frequency which is extremely near normal synchronism. Then, the carrier reproduction loop is returned as before so as to constitute a system to normally execute synchronism.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention provides 22n (n=1, 2, 3
,...) relates to an abnormal synchronization prevention circuit used in a demodulator of a value-orthogonal amplitude modulation digital radio device.

0002

2. Description of the Related Art In recent years, various communication systems have been developed with the increase in communication needs and the development of communication technology, including digital microwave wireless communication systems. This type of system uses quadrature phase keying (QPSK;
Shift Keying) method and multi-value quadrature amplitude modulation (multi-value QAM; Quadrature Amplifier)
This system wirelessly transmits digital data by modulating it using the 2-degree modulation method, and enables high-quality data transmission at a lower cost than analog wireless transmission systems and wired digital transmission systems.

[0003] Here, Q
When considering AM, it is a method that changes both the amplitude and phase of the carrier wave, and by converting these two parameters simultaneously, it is possible to achieve more efficient modulation. . In principle, this is achieved by combining two orthogonal AM (amplitude modulation) waves, and the resulting signal is called a QAM wave. This Q
AM waves play an important role in multilevel transmission because they are created based on AM waves, which are the simplest and easiest to handle, and because any point on the phase plane can be selected as a code point, making it possible to achieve an ideal code arrangement. Fulfilling. The quantization values of two orthogonal AM waves are divided into two types: one in which the quantization values are binary, and the other in which the quantization values are multi-valued. The latter is called multi-value QAM.

[0004] Here, we will briefly touch on the basic principles of QAM. Although the characteristics of QAM are actually utilized in multi-value transmission of 16 or more values, for the sake of simplicity, we will focus on 4-value transmission. There are three basic modulation methods for modulating a sine carrier wave with a digital signal: amplitude modulation, phase modulation, and frequency modulation, just like analog modulation methods.
Keying; amplitude modulation), PSK (Phase
Shift Keying; FSK (F
It is also called frequency shift keying (frequency modulation). Generally, the phase of the carrier wave is expressed at equal intervals (2π/
The method of signal transmission using n code points arranged at intervals of n is called n-phase PSK, but in reality, the system used is
=2m (where m is a natural number), and in this case, transmission of m series of binary pulses becomes possible.

[0005] Currently, two two-phase PSK (Phase Sh
Ift Keying (phase modulation) waves are combined at right angles, a 4-phase PSK wave is obtained, but a 2-phase PSK wave is a binary A
Since it can be realized using SK waves, the 4-phase PSK signal can be
(t), the two two-phase PSK signals as e1 (t), e
2 (t), and the angular frequency is set as ωc, the formula (1
) can be expressed as

[0006]

[Equation 1] However, ψ1 (t) and ψ2 (t) are both independent 2
The value shows the waveform of the baseband signal (modulation signal),
Set it as follows.

[0007]

E(t) can also be written using the composite amplitude (envelope) and phase angle as follows.

[0008]

[Math 3]

[0009] The bandwidth of ψ1 (t) and ψ2 (t) is not unlimited, but is generally band-limited, so at times other than the center point of the pulse (sample time)
”, and therefore the absolute value of E(t) is also “1”.
This means that the locus of E(t) transitions on the square ABCD and its diagonals AC and BD, which means that E(t)
) is different from a pure PM wave, but since it satisfies the condition of constant amplitude at the sampling time, it can also be regarded as a PSK wave. The signal obtained by combining two orthogonal AM waves like this E(t) is, in other words,
It is a QAM wave.

FIG. 4 shows the code arrangement on the two-dimensional phase plane in 16
This is a lattice arrangement QAM. The lattice arrangement QAM has relatively good SN characteristics, and orthogonal modulation/demodulation technology that carries information on the sine and cosine components of a carrier wave can be applied. Since the lattice arrangement QAM is obtained by combining two orthogonal AM signal waves of n value (usually n=2m), it has n2 code points.

[0011] Let ψ1 (t) and ψ2 (t) be baseband pulses (modulated signals) each having an amplitude of n values, and the maximum value of the absolute values of ψ1 (t) and ψ2 (t), respectively. When is set to “1”, Q of unit amplitude is
The general formula for the waveform E(t) of the AM wave is the same as formula (1). Assuming that E(t) has 22m code points, when m=1, all four code points are equidistant from the origin, matching the code arrangement of 4-phase PSK. The case where m=2 is called 16QAM, the case where m=3 is called 64QAM, and the case where m=4 is called 256QAM.
It is called. Regarding QAM waves, those that satisfy the condition that information is included in both amplitude and phase have 16 values or more. Therefore, QAM waves of 16QAM or higher are used, and the modulation method widely used in recent digital radio systems is 16QAM.

[0012] When reproducing a digital radio signal modulated by multilevel QAM in this manner, since information is contained in both amplitude and phase, demodulation must be synchronous detection. Taking a 16QAM wave as an example, the received carrier wave is split into two, and two reference carrier waves with a 90° phase difference (QAM is a combination of two orthogonal AM waves, so one of the two orthogonal axes is used). With one as the I-axis and the other as the Q-axis, synchronous detection is performed using two types of reference carrier waves: a reference carrier wave having a phase in the I-axis direction and a reference carrier wave having a phase in the Q-axis direction. Then, by the detection output of each of the I-axis and Q-axis,
A discriminator determines which code has been received among the 16 codes, and reproduces four series of binary pulses depending on the type.

By the way, the following is a typical method for creating a reference carrier wave that provides a phase reference for synchronous detection. One method is to provide an independent carrier wave oscillator (usually using a voltage controlled oscillator VCO) in the receiver and obtain a reference carrier wave by controlling the phase of this carrier wave oscillator to a constant value. This is a method in which a part of the received signal is branched, delayed by one time slot, and used as a reference carrier wave for subsequent pulses. The latter method is used for differential detection, so the former method is generally used.

In the PSK synchronous detection method, the phase reference must be obtained from the received wave that is sent, but since the phase of the PSK received wave changes every moment due to modulation, a constant control signal that cancels out this modulation is used. The signal is fed back to the voltage controlled oscillator, thereby obtaining a reference phase. One method for eliminating the influence of the modulation is a frequency multiplication method or an inverse modulation method.

The frequency multiplication method is called a baseband processing type because it multiplies the demodulated signal in the baseband band, and the carrier wave regeneration circuit of this baseband processing type performs logical operations on the demodulated signal in the baseband band. There is a device that multiplies the phase in an equalizing manner and uses the output to control the phase of a reference oscillator, and this is also called a Costas type carrier wave recovery circuit.

[0016] In general, when the carrier wave regeneration circuit is of the Costas type, the circuit configuration can be made cheaper and simpler than the inverse modulation method, and it is advantageous in terms of economy and low power consumption, so it is widely used. be done. However, although it has such advantages, the Costas type carrier wave regeneration circuit has a problem that, in the case of low-speed transmission, abnormal synchronization occurs in which the carrier wave frequency becomes stable at a point different from the normal carrier wave frequency.

[0017]

[Problem to be solved by the invention] As mentioned above, multi-value QA
When reproducing a digital radio signal modulated by M,
Synchronous detection is performed, and this coherent detection requires a reference carrier wave that provides a phase reference. In order to obtain the reference carrier wave, a carrier wave regeneration circuit is used, and for this purpose an independent carrier wave oscillator (usually a voltage controlled oscillator VCO is used) is installed in the receiver, and the phase of this carrier wave oscillator is controlled to be constant. A method called the Costas type is used to obtain a reference carrier wave. The phase reference must be obtained from the received wave that is sent, but since the phase of the PSK received wave changes every moment due to modulation, a constant control signal that cancels out this modulation must be fed back to the voltage controlled oscillator. However, one economical method for eliminating the influence of the modulation component is to multiply the frequency.

The frequency multiplication method is called a baseband processing type, and the carrier wave regeneration circuit of this baseband processing type performs a logical operation on the demodulated signal in the baseband band to equalize the phase multiplication. There is a device that uses its output to control the phase of a reference oscillator, and this is also called a Costas type carrier wave recovery circuit.

[0019] In general, when the carrier wave regeneration circuit is of the Costas type, the circuit structure can be made cheaper and simpler than the inverse modulation method, and it is advantageous in terms of economy and low power consumption, so it is widely used. be done. On the other hand, however, carrier wave recovery circuits based on the Costas method have the disadvantage that if the carrier wave recovery loop characteristics are changed, the pull-in frequency and demodulation modulation characteristics, etc. deteriorate. The method of sampling the pattern with a double clock and determining whether normal synchronization or abnormal synchronization is performed based on the state of the demodulated eye pattern has the drawback that the detection circuit becomes complicated.

[0020] Therefore, the purpose of this invention is to
An object of the present invention is to provide a receiving device for a digital radio device that can prevent abnormal synchronization using a simple circuit at low cost and without changing transmission characteristics in the Costas system.

[0021]

[Means for Solving the Problems] In order to achieve the above object, the present invention is constructed as follows. That is, it is used for demodulating quadrature amplitude modulation type digital radio equipment, and it identifies the demodulated baseband signal, obtains a phase error signal from it, and oscillates at an oscillation frequency according to the control signal to obtain a recovered carrier wave. This phase error signal is given to the oscillation means as a control signal to control the oscillation, and this reproduced carrier wave is
° In a demodulation device that obtains a demodulated baseband signal by mixing each signal with a received signal with a phase difference, the first step is to monitor carrier synchronization loss based on the demodulation baseband signal, and to monitor carrier synchronization loss when it occurs. Then, a monitoring means outputs an alarm signal, an abnormal synchronization prevention means detects abnormal synchronization using the alarm signal and generates a signal for a predetermined period of time in the case of abnormal synchronization, and a reference carrier frequency close to the frequency of the phase error signal and the carrier wave. and a reference signal for oscillating a signal, normally selecting the phase error signal as the control signal, and selecting the reference signal as the control signal while receiving the signal generated by the abnormal synchronization prevention means. and a selection means for supplying the oscillation means to the oscillation means.

[0022] The second aspect includes a first monitoring means for monitoring carrier synchronization loss based on the demodulated baseband signal and outputting a carrier synchronization loss alarm signal when carrier synchronization loss occurs; a second monitoring means for monitoring frame asynchronization from received data demodulated based on the signal, and outputting a frame asynchronization alarm signal when frame asynchronization occurs; abnormal synchronization prevention means that detects abnormal synchronization from the above and generates a signal for a predetermined period of time in the event of abnormal synchronization; and receives a reference signal for oscillating a signal having a reference carrier frequency close to the frequency of the phase error signal and the carrier wave. , normally selecting the phase error signal as the control signal, and selecting the reference signal as the control signal and applying it to the oscillation means while receiving the signal generated by the abnormal synchronization prevention means. Configure.

[0023]

[Operation] In the above configuration, the demodulated baseband signal is identified, a phase error signal is obtained from it, this is given as a control signal to the oscillation means, and the oscillation means oscillates in response to the control signal to generate a reproduced carrier. The demodulated baseband signal is obtained by mixing the reproduced carrier waves with the received signal with a 90° phase difference, and the received data is reproduced based on this demodulated baseband signal, but at this time, If the reproduced carrier wave deviates from the carrier wave frequency of the received signal, the reproduced received data will not be correct due to loss of carrier synchronization or frame synchronization, so it is necessary to correctly phase match the frequency of the reproduced carrier wave. Then, carrier synchronization loss is monitored based on the demodulated baseband signal by the monitoring means (in the case of the first configuration) or the first monitoring means (in the case of the second configuration), and the carrier synchronization is monitored based on the demodulated baseband signal. In this case, the second monitoring means further monitors frame synchronization from received data demodulated based on the demodulated baseband signal, and issues a carrier synchronization loss alarm signal when carrier synchronization loss occurs. Then, a frame out-of-synchronization alarm signal is output from these monitoring means, so that the abnormal synchronization prevention means uses the above-mentioned alarm signal in the case of the first configuration, and the carrier-wave out-of-synchronization alarm signal and the frame out-of-synchronization alarm in the case of the second configuration. It detects abnormal synchronization from the signal and generates a signal for a predetermined period of time when abnormal synchronization occurs. The selection means receives the phase error signal and a reference signal for oscillating a signal with a reference carrier frequency close to the frequency of the carrier wave, and normally selects the phase error signal as the control signal. During the reception of the generated signal, the reference signal is selected as the control signal and applied to the oscillation means. As a result, when synchronization occurs, oscillation control of the oscillation means is performed based on the reference signal for a predetermined period of time, and then oscillation control of the oscillation means is performed using a phase error signal based on the demodulated baseband signal. be exposed. and,
Since the oscillation control of the oscillation means based on the reference signal is at a frequency approximate to the carrier frequency of the received signal, the demodulation system is in a state extremely close to the correct phase due to the regenerated carrier wave of this frequency, and from this state synchronization pull-in by the phase error signal is performed. , so you can get correct synchronization.

As described above, the present invention can detect normal synchronization by monitoring loss of carrier synchronization and loss of frame synchronization in a demodulator of a digital radio device using a multilevel orthogonal modulation method to which a so-called Costas method carrier recovery loop is applied. When abnormal synchronization is determined, the carrier wave regeneration loop is prohibited and the oscillation means (voltage controlled oscillator) is activated using a predetermined reference signal to oscillate at a frequency very close to normal synchronization, and then the carrier wave is regenerated. It is configured to perform normal synchronization by returning the loop to its original state.

In the carrier regeneration loop of the Costas method, in an abnormal synchronization state in the demodulation system, carrier wave synchronization is synchronized to a frequency different from normal, and therefore frame synchronization is not established. Therefore, in the present invention, carrier wave synchronization and frame synchronization are monitored. When abnormal synchronization is detected by processing the alarm signal that
A reference signal is temporarily applied to the carrier signal to oscillate the carrier wave signal at a frequency very close to normal synchronization, and then the loop is returned to its original state to pull in synchronization.This method has a simple configuration and also prevents abnormal synchronization. It can be prevented.

[0026]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing one embodiment of the present invention. In FIG. 1, 1 is an IF modulated wave input terminal into which a modulated IF (intermediate frequency) signal is input, and 2a and 2b are mixers, which receive the modulated IF signal input from the IF modulated wave input terminal 1, and It is mixed with the output of the power divider 10 and output.

3 is a clock recovery circuit, 4 is a discriminator, 5 is a demodulation logic circuit, 6 is a digital logic operation section, 7 is a data selector, 8 is an amplifier with a loop filter, 9 is a voltage controlled oscillator, 11 is a recovered carrier synchronization Reference numeral 12 designates a frame synchronization loss monitoring circuit, and reference numeral 13 represents an abnormal synchronization prevention circuit.

The discriminator 4 is an analog-to-digital converter (
A/D converter) converts the signals inputted from the mixers 2a and 2b into digital signals and outputs the digital signals. The 90° power divider 10 divides the carrier wave by 90°
It outputs two systems of signals with different phases by giving a phase difference, and the mixer 2a receives one of the 90° different outputs of the 90° power divider 10, and the mixer 2b receives the other output. are input, and the mixers 2a and 2b mix these and the modulated IF signal applied via the input terminal 1 and output a difference signal. Here, mixer 2a
The output of mixer 2b will be called Pch output, and the output of mixer 2b will be called Qch output.

The clock regeneration circuit 3 uses this Pch output and
The A/D converter on one side of the discriminator 4 operates in synchronization with the clock signal output from the clock regeneration circuit 3. The other A/D converter of the discriminator 4 operates in synchronization with the clock signal output from the clock regeneration circuit 3 to convert the Qch output into digital data. It is something to do.

One A/D converter of the discriminator 4 has a Pch
The demodulated baseband signal of the Qch series is given to the other A/D converter, and the demodulated baseband signal of the Qch series is given to the other A/D converter, and these A/D converters convert the demodulated baseband signal in synchronization with this clock signal. are converted into digital signals, and each of Pch and Qch is converted into, for example, three series of identification data SP1, SP2, SP3, SQ1, SQ2,
It is configured to output SQ3 separately (
4PSK example).

Now, if Pch is the horizontal axis of the orthogonal axes in FIG. Is there data in the 2nd quadrant, 3rd or 4th?
Depending on whether there is data in the quadrant, in the former case, for example, “1”,
In the latter case, the data is output as “0”, and SP2
outputs data as "1" in the former and "0" in the latter depending on whether the data is in the upper half or the lower half of the first and second quadrants or the third and fourth quadrants, and SP3 Depending on which half of the area the data is located in, the upper part of that section will be “1”.
”, the lower side shows “0”, and SQ1 outputs data as “1” if there is data in the first or fourth quadrant, and “0” if there is data in the second or third quadrant,
Also, in SQ2, depending on whether the data is in the right half or the left half of the first and fourth quadrants or the second and third quadrants, the former is set to "1", and the latter is "0".
”, and SQ3 outputs data as “1” on the right side and “0” on the left side depending on which half of the area the data is in. It is possible to identify whether a signal is appearing in the A/D converter output by A/D converter, which is obtained by A/D converting the P-axis and Q-axis signal levels at the resolution corresponding to each category. By making them correspond, data obtained by converting each channel component of P and Q using an A/D converter can be used as identification data.

The demodulation logic circuit 5 uses these identification data SP1.
, SP2 , SP3 , SQ1 , SQ2 , SQ3
This data is received and operated on to obtain demodulated data of each channel component of P and Q, and this demodulated data is output to the digital logic operation section 6.

Further, the data selector 7 outputs a phase error signal during normal synchronization, and outputs a predetermined reference bias signal during abnormal synchronization, and the abnormal synchronization prevention circuit 1
This switching is performed by the abnormal synchronization detection signal output from 3, and the output is switched. Therefore, the data selector 7 receives the phase error signal and the reference bias signal, selects the reference bias signal while receiving the abnormal synchronization detection signal, and selects and outputs the phase error signal when the abnormal synchronization detection signal disappears. It has become. Incidentally, the phase error signal is the identification data SP1, SP2, S output from the discriminator 4.
P3, SQ1, SQ2, SQ3 are calculated to obtain carrier wave phase information, and this is obtained by converting this into a voltage signal of a level corresponding to the carrier wave phase information,
Such a function is obtained by a processing circuit (not shown) provided within the data selector 7. Further, a reference bias signal is also obtained by a reference voltage generation circuit (not shown) provided in the data selector 7. Further, the reference bias signal is a signal that can provide a control voltage level that allows the VCO (voltage controlled oscillator) 9 to oscillate at an oscillation frequency that corresponds to a predetermined reference carrier frequency. The DC amplifier with loop filter 8 is connected to this data selector 7.
The level of the output signal is amplified.

Further, the VCO 9 generates a signal with a frequency corresponding to the level of this signal based on the signal of the level corresponding to the carrier wave phase information obtained from the DC amplifier with loop filter 8, and uses this as a recovered carrier wave signal to generate 90° power. It is given to the distributor 10. The 90° power divider 10 gives a 90° phase difference to this regenerated carrier wave signal, and one of the two regenerated carrier wave signals with the 90° phase difference is sent to the mixer 2.
a, and the other is input to mixer 2b as a local signal. By inputting the reproduced carrier wave signal given a 90° phase difference as a local signal to the mixers 2a and 2b and mixing it with the signal from the input terminal 1, the carrier wave can be removed and the data can be demodulated.

The regenerated carrier out-of-synchronization monitoring circuit 11 monitors out-of-synchronization of the carrier wave and outputs an alarm signal (out-of-synchronization alarm signal) when the out-of-synchronization occurs. Monitor for deviations. A frame out-of-sync monitoring circuit 12 monitors frame bits and sends an alarm signal (frame out-of-sync alarm signal) when out of frame out of frame.
This outputs the following. Further, the abnormal synchronization prevention circuit 13 receives the out-of-sync alarm signal and the out-of-frame out-of-sync alarm signal, determines that there is an abnormal synchronization when there is no out-of-sync alarm signal, and there is an out-of-frame out-of-sync alarm signal, and detects an abnormal synchronization for a predetermined period of time. It outputs a signal.

Next, the operation of the demodulation system having the above configuration will be explained. The IF modulated wave inputted from the IF modulated wave input terminal 1 is detected by mixers 2a and 2b to obtain a demodulated baseband signal. Here, a clock signal is generated in a clock regeneration circuit 3, and a discriminator 4 identifies the demodulated baseband signal at the synchronization timing while synchronizing with the clock, and converts it into identification data. This identification data is transmitted to the demodulation logic circuit 5.
The demodulating logic circuit 5 performs a logical operation on the identification data to obtain demodulated data. The obtained demodulated data is frame-synchronized by the digital logic operation section 6 and output.

Further, the carrier wave regeneration system detects carrier wave phase error information from the identification data output from the discriminator 4, and supplies it to the data selector 7 as a carrier wave phase error signal. During normal synchronization, the data selector 7 sends this carrier phase error signal to the amplifier 8 with a loop filter. The amplifier with loop filter 8 amplifies this error information signal and supplies it to the voltage controlled oscillator 9, so the voltage controlled oscillator 9 oscillates at an oscillation frequency corresponding to this error information signal, thereby regenerating in synchronization with the carrier clock. Generate a carrier wave. This regenerated carrier wave from the voltage controlled oscillator 9 is given to a 90° power divider 10, which gives this regenerated carrier wave a 90° phase difference and sends the carrier wave to a mixer 2a.
, 2b locally. and mixers 2a, 2b
Then, this local input and the received signal from input terminal 1 are mixed and detected.

The reproduced carrier out-of-synchronization monitoring circuit 11 monitors out-of-synchronization of carrier waves, and outputs an alarm signal when the out-of-synchronization occurs. Further, a frame out-of-sync monitoring circuit 12 monitors the frame bits and outputs an alarm signal when the frame out-of-sync occurs.

If the modulation phase is 0, π/2, π, 3π/2, the synchronized phase of the carrier wave mentioned above is always π
Odd multiple of /4 (π/4, 3π/4, 5π/4, 7π/4
).

Here, when abnormal synchronization occurs, the synchronized phase changes regularly by π/4 or π/2 for each data, causing signal distortion on the phase plane. However, since this twist matches the phase arrangement of the data, such as π/4 and π/2, there is no difference from normal synchronization at the data point. As described above, since the carrier wave is reproduced based on the phase error information of the identification data, it is difficult to detect abnormal synchronization using the carrier wave synchronization alarm. However, the twist on the phase displacement surface due to abnormal synchronization adds a change of every π/4 to the reproduced data,
Since the bit error rate is 0.5, frame bit detection is not possible and a frame out-of-sync alarm is generated.

FIG. 2 shows a specific embodiment of the abnormal synchronization prevention circuit 13 used in the present invention, in which 14 is a frame synchronization loss alarm signal, 15 is a carrier synchronization loss warning signal, and 16 is a specific embodiment of the abnormal synchronization prevention circuit 13 used in the present invention.
and 18 is an AND circuit, 17 and 19 are multivibrators, 20 is a phase error signal input terminal, 21 is a reference bias signal input terminal, 22 is a data selector switch in the data selector 7, 23 is a carrier wave regeneration circuit control signal output terminal, 24 is an inverting circuit.

The inverting circuit 24 outputs the carrier synchronization alarm signal 1.
5 is inverted and output to the AND circuit 16, and the data selector switch 22 is a changeover switch for selecting one of the phase error signal and the reference bias signal and outputting it to the carrier wave regeneration circuit control signal output terminal 23. It is.

The AND circuit 16 performs an AND logic between the frame synchronization loss alarm signal 14 and the inverted output of the carrier wave synchronization loss alarm signal 15, and the multivibrator 1
7 operates upon receiving the output of this AND circuit 16, and generates a signal (level "L") for a predetermined period of time.

The AND circuit 18 also outputs the A of the output pulse of the multivibrator 17 and the output of the AND circuit 16.
The multivibrator 19 receives the output from the AND circuit 18 and operates for a predetermined period of time.
It generates a signal. Further, the data selector switch 22 outputs the signal generated by the multivibrator 19 to the select signal input terminal of the data selector switch 22 as an abnormal synchronization detection signal.

Of these, the frame out-of-synchronization alarm signal 14 is an alarm signal output from the frame out-of-synchronization monitoring circuit 12 when the frame is out of synchronization, and the carrier out-of-synchronization alarm signal 15 is an alarm signal outputted when the regenerated carrier out of synchronization occurs. This is an alarm signal output from the regenerated carrier out-of-synchronization monitoring circuit 11, and the AND circuits 16 and 18, the multivibrator 1
The circuit consisting of 7 and 19 is the abnormal synchronization prevention circuit 13.
Configure.

Furthermore, as already explained, the phase error signal 20 corresponds to the identification data SP1, SP output from the discriminator 4.
2, SP3, SQ1, SQ2, and SQ3 to obtain carrier wave phase information, and converting this into a voltage signal of a level corresponding to the carrier wave phase information.Such a function is provided in the data selector 7. This is obtained by a processing circuit (not shown) provided in the. Further, the reference bias signal 21 is also obtained by a reference voltage generation circuit (not shown) provided in the data selector 7.

The abnormal synchronization prevention circuit 13 having such a configuration performs an AND (logical product) of the frame synchronization loss alarm signal 14 and the inverted signal of the carrier wave synchronization loss alarm signal 15 in the AND circuit 16, and generates a frame synchronization loss alarm. To prevent erroneous determination of carrier synchronization loss and abnormal synchronization by generating an output only when there is a signal and there is no carrier synchronization loss.

Since the frame synchronization loss alarm signal 14 and the carrier wave synchronization loss alarm signal 15 are unstable immediately after the power is turned on,
The output of the ND circuit 16 causes the multivibrator 17 to generate a signal for a certain period of time.

That is, immediately after the power is turned on, the circuit operation of the entire receiving system is unstable, and synchronization cannot be established from the frame out-of-sync monitoring circuit 12 and the reproduced carrier out-of-sync monitoring circuit 11 until the system is stabilized. Alarm signal 1
4 and the carrier synchronization loss alarm signal 15 are output, and during this period, the AND circuit 16 outputs an output, and this output causes the multivibrator 17 to keep the signal (“L”) for a predetermined period of time. Output.

On the other hand, by feeding the output of the AND circuit 16 and the output (“L”) of the multivibrator 17 to the AND circuit 18 and calculating the logical product of the two, the multivibrator 1
This is prohibited during the time when the output signal from the multivibrator 17 is being generated, thereby making it insensitive to out-of-synchronization due to temporary fluctuations, and when the output signal from the multivibrator 17 disappears after a certain period of time, the AND An output is generated from circuit 18. This ensures that the problem is not a temporary loss of synchronization, but
It becomes possible to generate an output from the AND circuit 18 in a state of abnormal synchronization.

The output from this AND circuit 18 is output to a multivibrator 19. This output causes the multivibrator 19 to generate a signal for a predetermined period of time. This output signal is given to the data selector 7 as an abnormal synchronization detection signal.

In this manner, when the frame synchronization is lost and the carrier waves are synchronized, the multivibrator 19 outputs an abnormal synchronization detection signal to the select signal input terminal of the data selector 7 for a certain period of time.

The data selector switch 22 in the data selector 7 outputs the phase error signal input from the phase error signal input terminal 20 to the carrier wave regeneration circuit control signal output terminal 23 during normal synchronization (that is, when not receiving an abnormal synchronization detection signal). This V
The reference carrier wave is regenerated from CO9.

When abnormal synchronization occurs here and an abnormal synchronization detection signal is input from the multivibrator 19, the data selector switch 22 in the data selector 7 is switched to the input side of the reference bias signal input terminal 21, and this reference bias A predetermined reference bias signal inputted from the signal input terminal 21 is outputted from the carrier wave regeneration circuit control signal output terminal 23. Then, after this reference bias signal is amplified by the DC amplifier with loop filter 8, it is applied to the VCO 9 as a reference voltage, so that the VCO 9 oscillates at a frequency corresponding to this reference bias signal. Since the level of the reference bias signal is set to a voltage level at which the reference carrier frequency is obtained, the VCO (voltage controlled oscillator) 9 oscillates at the reference carrier frequency. However, since it does not have phase error information, carrier synchronization is lost.

After a certain period of time, when the abnormal synchronization detection signal is no longer output from the multivibrator 19, the data selector switch 22 changes the input to the reference bias signal input terminal 21.
side to the phase error signal input terminal 20 side,
The data selector switch 22 again outputs the phase error signal inputted from the phase error signal input terminal 20 from the carrier wave regeneration circuit control signal output terminal 23 and applies it to the VCO 9 to start synchronization pull-in.

[0056] Until just before starting synchronization, the system was operating using a reference carrier wave with a frequency very close to the reference carrier wave oscillated by the reference bias described above.
The synchronization pull-in starts from the frequency of this reference carrier wave.

In this way, when the carrier recovery loop loses synchronization, it starts synchronization from a frequency very close to the reference carrier wave oscillated by the reference bias signal mentioned above, so it does not become abnormally synchronized and maintains normal synchronization. will be obtained.

As described above, the present invention is used for demodulating a quadrature amplitude modulation type digital radio device, identifies a demodulated baseband signal, obtains a phase error signal from this, and oscillates at an oscillation frequency according to a control signal. This phase error signal is applied as a control signal to an oscillation means for obtaining a recovered carrier wave to control oscillation, and the recovered carrier wave is mixed with a received signal with a 90° phase difference to obtain a demodulated baseband signal. In the apparatus, a first monitoring means for monitoring carrier synchronization loss based on the demodulated baseband signal and outputting a carrier synchronization loss alarm signal when carrier synchronization loss occurs; and demodulation based on the demodulation baseband signal. a second monitoring means that monitors frame asynchronization from the received data and outputs a frame asynchronization alarm signal when frame asynchronization occurs, and detects abnormal synchronization from the carrier desynchronization alarm signal and the frame asynchronization alarm signal. At the same time, abnormal synchronization prevention means generates a signal for a predetermined period of time in the case of abnormal synchronization, and receives the phase error signal and a reference signal for oscillating a signal with a reference carrier frequency close to the frequency of the carrier wave, and normally the phase error is detected. selecting a signal as the control signal and receiving the generated signal of the abnormal synchronization prevention means;
The apparatus further comprises a selection means for selecting the reference signal as the control signal and applying it to the oscillation means.

In such a configuration, the demodulated baseband signal is identified and a phase error signal is obtained from it,
This is given as a control signal to the oscillation means, the oscillation means oscillates in response to the control signal to obtain a regenerated carrier wave, and the regenerated carrier wave is mixed with the received signal with a 90° phase difference. A demodulated baseband signal is obtained, and received data is reproduced based on this demodulated baseband signal. At this time, if the reproduced carrier wave deviates from the carrier frequency of the received signal, the reproduced received data may be out of carrier synchronization or frame synchronization. Since the frequency of the reproduced carrier wave must be correct, the frequency of the reproduced carrier wave must be correct. The first monitoring means monitors carrier synchronization loss based on the demodulated baseband signal, and the second monitoring means monitors frame synchronization loss based on the demodulated received data based on the demodulation baseband signal. Then, when carrier synchronization loss occurs, a carrier synchronization loss alarm signal is output, and when frame synchronization loss occurs, a frame synchronization loss alarm signal is output from these monitoring means. Abnormal synchronization is detected from the frame synchronization loss alarm signal, and a signal is generated for a predetermined period of time when abnormal synchronization occurs. The selection means receives the phase error signal and a reference signal for oscillating a signal with a reference carrier frequency close to the frequency of the carrier wave, and normally selects the phase error signal as the control signal. During the reception of the generated signal, the reference signal is selected as the control signal and applied to the oscillation means.

As a result, when synchronization occurs, the oscillation of the oscillation means is controlled based on the reference signal for a predetermined period of time, and then the oscillation of the oscillation means is controlled using a phase error signal based on the demodulated baseband signal. However, since the oscillation control of the oscillation means based on the reference signal is at a frequency approximate to the carrier frequency of the received signal, the demodulation system is in a state extremely close to the correct phase due to the regenerated carrier wave of this frequency, and from this state Since synchronization pull-in using the phase error signal is started, correct synchronization can be obtained. It should be noted that the present invention is not limited to the embodiments described above and shown in the drawings, but can be implemented with appropriate modifications within the scope without changing the gist thereof.

[0061]

As described above, the present invention provides a demodulator for a multi-level orthogonal modulation type digital radio device to which a so-called Costas type carrier wave regeneration loop is applied, by monitoring carrier wave synchronization loss and frame synchronization loss. After determining normal synchronization and abnormal synchronization, and when abnormal synchronization occurs, the carrier wave regeneration loop is prohibited and the oscillation means (voltage controlled oscillator) is activated using a predetermined reference signal to oscillate at a frequency very close to normal synchronization. , it is configured to perform normal synchronization by restoring the carrier wave regeneration loop, and in the Costas type carrier wave regeneration loop, an abnormal synchronization state in the demodulation system is caused by the carrier wave synchronization being synchronized to a frequency different from the normal one. , since frame synchronization is not established, in the present invention, when abnormal synchronization is detected by processing an alarm signal for monitoring carrier synchronization and frame synchronization, the oscillation means (voltage controlled oscillator) provided in the carrier wave regeneration loop is temporarily activated. A reference signal is applied, a carrier signal is oscillated at a frequency very close to normal synchronization, and the loop is then returned to its original state to pull in synchronization, so it has a simple configuration and can prevent abnormal synchronization. can.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the overall configuration of an embodiment of the present invention.

FIG. 2 is a circuit diagram showing details of the abnormal synchronization prevention circuit of FIG. 1;

FIG. 3 is a diagram for explaining a four-phase PSK wave obtained by orthogonal synthesis of binary AM signals.

FIG. 4 is a phase plane layout diagram of QAM and PSK.

[Explanation of symbols]

1... IF modulated wave input terminal, 2a, 2b... mixer, 3... clock regeneration circuit, 4... discriminator, 5... demodulation logic circuit, 6...
Digital logic operation unit, 7...Data selector, 8...Amplifier with loop filter, 9...Voltage controlled oscillator, 10...90
°Power divider, 11...Regenerated carrier out-of-synchronization monitoring circuit, 1
2... Frame synchronization loss monitoring circuit, 13... Abnormal synchronization prevention circuit, 14... Frame synchronization loss alarm signal, 15... Carrier wave synchronization loss alarm signal, 16, 18... AND circuit, 17, 19
...Multivibrator, 20...Phase error signal input terminal,
21... Reference bias signal input terminal, 22... Data selector switch, 23... Carrier wave regeneration circuit control signal output terminal,
24...Inversion circuit.

Claims (2)

[Claims] Claim 1: Used for demodulating quadrature amplitude modulation digital radio equipment, which identifies a demodulated baseband signal, obtains a phase error signal from it, and oscillates and reproduces it at an oscillation frequency according to a control signal. In a demodulation device, the phase error signal is given as a control signal to an oscillation means for obtaining a carrier wave to control oscillation, and the reproduced carrier wave is mixed with a received signal with a 90° phase difference to obtain a demodulated baseband signal. monitoring means for monitoring loss of carrier synchronization based on the demodulated baseband signal and outputting an alarm signal when loss of carrier synchronization occurs; and monitoring means for detecting abnormal synchronization based on the alarm signal and for a predetermined period of time in the event of abnormal synchronization;
receiving an abnormal synchronization prevention means for generating a signal and a reference signal for oscillating a signal having a reference carrier frequency close to the frequency of the phase error signal and the carrier wave, and normally selecting the phase error signal as the control signal; A quadrature amplitude modulation type digital radio device, characterized in that it comprises a selection means for selecting the reference signal as the control signal and applying it to the oscillation means while receiving the signal generated by the abnormal synchronization prevention means. Demodulator. [Claim 2] A device used for demodulating quadrature amplitude modulation digital radio equipment, which identifies a demodulated baseband signal, obtains a phase error signal from it, and oscillates and reproduces it at an oscillation frequency according to a control signal. In a demodulation device, the phase error signal is given as a control signal to an oscillation means for obtaining a carrier wave to control oscillation, and the reproduced carrier wave is mixed with a received signal with a 90° phase difference to obtain a demodulated baseband signal. a first monitoring means for monitoring carrier synchronization loss based on the demodulated baseband signal and outputting a carrier synchronization loss alarm signal when carrier synchronization loss occurs; and received data demodulated based on the demodulation baseband signal. a second monitoring means that monitors frame asynchronization and outputs a frame asynchronization alarm signal when frame asynchronization occurs; detects abnormal synchronization from the carrier desynchronization alarm signal and frame asynchronization alarm signal; At the time of synchronization, the abnormal synchronization prevention means generates a signal for a predetermined period of time, and a reference signal for oscillating a signal with a reference carrier frequency close to the frequency of the phase error signal and the carrier wave is received. orthogonal amplitude, comprising a selection means for selecting the reference signal as the control signal and applying it to the oscillation means while receiving the signal generated by the abnormal synchronization prevention means. Demodulator for modulation digital radio equipment.