JPH06311189A - Demodulator - Google Patents

Abstract

PURPOSE:To reduce reproduction synchronizing time by providing a band width switching means for a low-pass filter and permitting a carrier reproducing means to make the band width of LPF narrow by the band width switching means when a frame synchronization detecting means detects the sending of an asynchronous signal. CONSTITUTION:The modulated wave of an intermediate frequency band is inputted to an orthogonal wave detector 12 by way of an AGC amplifier 11. The wave detector 12 fetches the base band signal of Ich and Qch by orthogonally detecting input modulated wave by receiving the reference carrier wave whose phase is different by 90 degree from VCO 3 and sends identification data to a transversal equalizer 17 by way of LPE 13, 15 and A/D converter 14, 16. The equalizer identification data to output reproduction data of Ich and Qch to a frame synchronization circuit 2, the equalizer 17, a carrier wave reproducing circuit 6 and an alarm detection circuit 5. At the time of switching a switch on the side of transmission, the circuit 2 sends out the asynchronous signal to the circuit 6. The circuit 6 turns a switch SW3 on, short-circuits a resistence R3 and makes the band width of LPF 6 narrow.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a demodulator used in a digital multiplex radio system having a standby system.

In a digital multiplex radio system,
As the method of configuring the protection line, the line is configured by distinguishing it into (N + 1) system, Twin-path system, Hot-stanby system (also called set protection system), etc. In this case, switching to the protection line is performed immediately. At this time, it is necessary to reduce the resynchronization time.

[0003]

2. Description of the Related Art FIG. 4 is an example of an operation diagram of a digital multiplex radio system using a hot standby system, FIG. 5 is a block diagram of a demodulator of a conventional example, and FIG. 6 is an alarm detection circuit diagram of FIG. (a) is a main part configuration diagram, and (b) is an operation explanatory diagram. FIG. 7 is a diagram for explaining the operation of the carrier recovery circuit in FIG. 5, where (a) is a carrier recovery circuit configuration diagram and (b) is a low-pass filter configuration diagram in (a).

First, in FIG. 4, since the switches SW ₁ and SW ₂ are in the state of solid lines, the transmission data is modulated by the modulator 8.
It is taken out as received data from the demodulation device 86 through the 1, transmission device 82, and reception device 85. However, for example, when a failure occurs in the transmission device 82, the switch SW ₁ is in the state of the dotted line, so that the transmission data is taken out as the reception data from the demodulation device 88 through the modulation device 83, the transmission device 84, and the reception device 87. .

Although the nominal transmission frequency is the same for both the working and standby systems, the transmitter local oscillators 821 and 841 are provided independently as shown in the figure, so they do not exactly match and are deviated by Δf. Also, since the hot standby method is used,
The waiting device is in the on state.

Next, referring to FIG. 5, the modulated wave in the intermediate frequency band (for example, 16QAM wave) is an AGC (automatic gain control) amplifier 11
Then, the signal is amplified to a predetermined level and added to the quadrature detector 12. Since a quadrature detector also receives a reference carrier with a 90-degree phase difference from a voltage controlled oscillator (hereinafter abbreviated as VCO) 3, it quadrature-detects the input modulation wave and performs Ich and Qch baseband. The signal is extracted and the low pass filter
Analog-to-digital (A / D) converter 14, via 13, 15
Send to 16.

Since the A / D converter discriminates and sends it to the transversal equalizer 17, this equalizer performs waveform shaping and Ich conversion.
, Qch reproduction data is output to the frame synchronization circuit 2, transversal equalizer 17, carrier wave reproduction circuit (hereinafter abbreviated as CR circuit) 6, and alarm detection circuit 5. Therefore, the frame sync circuit sends a sync signal if the frame sync signal in the reproduced data can be detected, and sends an asynchronous signal if it cannot detect the frame sync signal, and the transversal equalizer uses an internal tap coefficient so that optimum waveform equalization is performed. Control.

Further, after the equivalent phase multiplication is performed using the reproduced data in the well-known Costas type arithmetic processing section 181 in the CR circuit shown in FIG. 7 (a), the low-pass signal shown in FIG. 7 (b) is passed. A control signal for reproducing a carrier wave is generated through the filter 182.

Further, the alarm detection circuit 5 shown in FIG. 6 counts the signals entering the opening (hatched portion) of the eye pattern, and the count number corresponds to the bit error rate (hereinafter abbreviated as BER) 10 ^-2 . When it becomes larger than the value, it is determined that the synchronization is out of sync, an out-of-sync alarm is displayed, and the sweeper 4 is activated.

As a result, the phase locked loop starts the pull-in operation for reproducing the carrier wave, but when the out-of-sync alarm is recovered, the sweeper is stopped because the pull-in operation is completed and the synchronization is established.

It should be noted that the alarm detection circuit is provided with hysteresis such that the out-of-sync alarm is restored when the aperture ratio of the eye pattern is such that the BER is 10 ^-3 . In addition, the signals that enter the opening are D ₁ and D ₃ in the case of 16QAM waves, and when they enter, the output of the EX-OR gate 51 becomes H.

When the demodulator shown in FIG. 4 is used in the hot standby system, switching is performed in the following steps. At the same time as switching the switch SW ₁ from the solid line to the dotted line,
Since modulated waves having different frequencies are input to the demodulator 86, the carrier recovery circuit in the demodulator tries to follow. At this time, the received data becomes a momentary interruption, and the alarm detection circuit is activated. The out-of-sync alarm from the alarm detection circuit activates the sweeper. Resync after sweeper sweep.

At this time, the following problems occur at each step. The carrier recovery circuit that forms the step phase-locked loop has a loop bandwidth of, for example, 0.3 to 12 KHz for tracking fading or for auxiliary signal transmission (analog service channel for transmitting a meeting signal etc.). Is becoming wider. Therefore, when modulated waves with different frequencies are input, the oscillation frequency of the VCO is rapidly changed in response to this. Step, the aperture ratio of the eye pattern decreases in response to this change, and the alarm detection circuit sends out-of-synchronization alarm, so the sweeper is activated. The sweep cycle of the sweeper is, for example,
It is 100 to 300 ms, and during this period, synchronization is not established and the system is disconnected.

[0014]

As described above, there is a problem that the pull-in time at the time of system switching becomes the sweep period of the sweeper (for example, 100 to 300 ms) or more, and it takes too much time to resynchronize.

The present invention needs to reduce the resynchronization time.

[0016]

FIG. 1 is a block diagram showing the principle of the first and second aspects of the present invention. In the figure, 3 is a voltage controlled oscillator for transmitting a carrier wave having a frequency corresponding to the applied control signal, 1
Is a demodulation / equalization means for extracting a baseband signal from the input modulated wave using the carrier wave sent from the voltage controlled oscillator, identifying and waveform-shaping the reproduced data, and 2 is a frame synchronization signal in the reproduced data. Is a frame synchronization detecting means for transmitting a synchronous / asynchronous signal corresponding to the detection state of.

The carrier reproducing means 6 performs a predetermined logical operation on the reproduced data and then generates and sends out the control signal via the low-pass filter so that the carrier becomes the reference carrier. Alarm detecting means for sending an alarm signal when it is detected that the bit error rate of the reproduced data has deteriorated below a predetermined value, and 4 is a sweeper means for starting and sending a sweeper output as the control signal when the alarm signal is applied. , 61 are bandwidth switching means for narrowing the bandwidth by a predetermined width, and 7 is a gate means.

According to the first aspect of the present invention, the carrier recovery means drives the bandwidth switching means to narrow the bandwidth of the low-pass filter when the frame synchronization detecting means detects that the asynchronous signal is transmitted. To

According to a second aspect of the present invention, when the carrier regenerating means detects that the frame synchronizing means has transmitted an asynchronous signal, the gate means is turned off until a predetermined time elapses after the detection, and the alarm signal is sent by the sweeper. The means is not applied.

[0020]

According to the first aspect of the present invention, when the carrier wave reproducing means detects that the frame synchronization detecting means has transmitted an asynchronous signal, it drives the bandwidth switching means to reduce the bandwidth of the low-pass filter. , The phase-locked loop did not make a sudden response when switching the switch (when switching the protection line). It should be noted that switch switching is performed on the transmitting side, but on the receiving side, an asynchronous signal indicating asynchronization of the corresponding data frame is used.

In the second aspect of the present invention, when the bandwidth of the phase locked loop is narrowed as described above, it is not necessary to activate the sweeper if resynchronization is possible. Therefore, when the carrier wave reproducing means detects that the frame synchronizing means has sent out an asynchronous signal,
After the detection, the gate means is turned off until a predetermined time elapses so that the alarm signal is not applied to the sweeper means. If the alarm signal is applied even after a lapse of a predetermined time, the gate means is turned on, and the sweeper means is activated.

As a result, the resynchronization time can be shortened.

[0023]

FIG. 2 is a block diagram of a demodulator of the first and second embodiments of the present invention, FIG. 3 is an operation explanatory diagram of FIG. 2, (a) is a block diagram of a bandwidth switching means, (b), (c) is an operation explanatory view of the phase locked loop.

A resistor R ₃ , a capacitor C ₂ , a switch SW
₃ is a component of the bandwidth switching means 61. Also, FIG.
The dotted lines in (b) and (c) show the conventional example for comparison. The operation of FIG. 2 will be described below with reference to FIG. 3, but the parts described in detail above will be briefly described, and the part of the present invention will be described in detail.

First, the modulated wave in the intermediate frequency band is an AGC amplifier.
It is added to the quadrature detector 12 via 11. Quadrature detector
Since a reference carrier with a 90-degree phase difference from each other is also added from VCO 3, the input modulated wave is quadrature-detected and Ich and
Extracts the Qch baseband signal, and passes low-pass filter 1
The identification data is sent to the transversal equalizer 17 via the 3, 15, A / D converters 14, 16.

The transversal equalizer performs waveform shaping and Ic
The reproduced data of h and Qch are output to the frame synchronization circuit 2, the transversal equalizer 17, the carrier wave reproduction circuit 6 and the alarm detection circuit 5.

Therefore, if the frame synchronizing circuit cannot detect the frame synchronizing signal in the reproduced data, it sends an asynchronous signal, and the transversal equalizer controls the internal tap coefficient so that optimum waveform equalization is performed. Then, the carrier wave reproduction circuit 6 performs an equivalent phase multiplication by using the reproduction data in the internal Costas type arithmetic processing unit, and then the low pass filter to which the bandwidth switching means 61 shown in FIG. 3 (a) is added. A control signal for reproducing the carrier wave is generated via. Here, the bandwidth switching unit 61 is as shown in FIG. 3 (a), when the switch SW ₃ is in an off state kept charged up capacitor C ₂ through the resistor R ₃ of high resistance value.

In the first aspect of the present invention, when the switch (not shown) is switched on the transmission side, the asynchronous signal is sent from the frame synchronizing circuit 2 to the carrier wave reproducing circuit 6 as described above. When the carrier recovery circuit detects an asynchronous signal, when the switch SW ₃ is turned on, the resistor R ₃ is short-circuited, the capacitor C ₁ and the capacitor C ₂ are connected in parallel, and the bandwidth is, for example, 0.3 to 12 KHz to 0.3 to It becomes as narrow as 2 KHz.

As a result, the response speed of the phase-locked loop decreases, and the control signal sent from the carrier recovery circuit changes according to the response speed, as shown in FIG. 3 (b). If you can resynchronize within, do not start the sweeper.

In the second aspect of the present invention, a gate means 7 having a timer 71 of 10 to 20 ms and an AND gate 72 is provided. Then, when the carrier recovery circuit 6 detects the asynchronous signal, it turns on the switch SW ₃ as described above and simultaneously starts the timer. When the timer does not start, it outputs H output, but when it is operating, it outputs L output, so the gate is off during timer operation, and the out-of-sync alarm from the alarm detection circuit is output by sweeper 4. Not sent to.

However, if the operation of the timer is stopped, the AND gate is turned on. At this time, if the out-of-sync alarm is continuously sent, the sweeper is activated by the out-of-sync alarm as in the conventional example ( That is, in the hot standby system, the bandwidth of the phase locked loop is narrowed at the time of system switching, and the sweeper is stopped for a predetermined time to shorten the pull-in time. As a result, it is possible to reduce the line interruption rate and improve the quality.

[0032]

As described in detail above, according to the present invention, there is an effect that the resynchronization time can be shortened.

[Brief description of drawings]

FIG. 1 is a principle configuration diagram of first and second aspects of the present invention.

FIG. 2 is a block diagram of a demodulation device of the first and second embodiments of the present invention.

3 (a) is a configuration diagram of a bandwidth switching means, and FIGS. 3 (b) and 3 (c) are operation explanatory diagrams of a phase locked loop.

FIG. 4 is an example of an operation explanatory diagram of a digital multiplex wireless system using a hot standby system.

FIG. 5 is a block diagram of a conventional demodulation device.

6A and 6B are explanatory diagrams of an alarm detection circuit in FIG. 5, in which FIG. 6A is a configuration diagram of a main part and FIG.

7A and 7B are operation explanatory diagrams of the carrier recovery circuit in FIG. 5, where FIG. 7A is a carrier recovery circuit configuration diagram, and FIG. 7B is a low-pass filter configuration diagram.

[Explanation of symbols]

1 demodulation / equalization means 2 frame synchronization detection means 3 voltage controlled oscillator 4 sweeper means 5 alarm detection means 6 carrier recovery means 7 gate means 61 bandwidth switching means

Claims (2)

[Claims] 1. A baseband signal is extracted from an input modulated wave using a voltage-controlled oscillator (3) for transmitting a carrier wave having a frequency corresponding to a control signal to be applied, and a carrier wave transmitted from the voltage-controlled oscillator, Demodulation / equalization means (1) for identifying and shaping the waveform and outputting the reproduced data, and frame synchronization detection means (2) for transmitting the synchronous / asynchronous signal corresponding to the detection state of the frame synchronous signal in the reproduced data Carrier wave reproduction means (6) for generating and transmitting the control signal such that the carrier wave becomes a reference carrier wave through a low pass filter after performing a predetermined logical operation on the reproduced data, Alarm detection means for sending an alarm signal when it is detected that the bit error rate of the reproduced data has deteriorated below a predetermined value.
(5) and, when the alarm signal is applied, a sweeper means for starting and sending a sweeper output as the control signal
(4) In a hot standby demodulator having (4), the low-pass filter is provided with bandwidth switching means (61) for narrowing the bandwidth by a predetermined width, and the carrier recovery means is the frame synchronization detection means. A demodulation device having a structure in which the bandwidth switching means is driven to narrow the bandwidth of the low-pass filter when it detects that the asynchronous signal has been transmitted. 2. A gate means (7) is provided, and when the carrier wave reproducing means detects that the frame synchronizing means has sent out an asynchronous signal, the gate means is turned off until a predetermined time elapses after the detection. The demodulator according to claim 1, wherein the alarm signal from the alarm detecting means (5) is not applied to the sweeper means (4).