JPH0568130B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a squelch device used in a digital radio device or the like that digitizes voice and modulates and demodulates it for communication.

Configuration of Conventional Example and Its Problems FIG. 1 is a block diagram of a digital radio including a conventional squelch device. In FIG. 1, an analog input signal 1 is converted by an encoder 2 into a digital signal such as PCM or Delci modulation. This digital signal is modulated into an FM signal by a modulator 4 using a carrier signal 3, powered up by a transmitter 5, and radio waves are transmitted from an antenna 6. This radio wave is received by a receiver 8 via an antenna 7. This received signal is demodulated into a digital signal by a demodulator 9, converted into an analog signal by a decoder 10, amplified to a predetermined level by an audio amplifier 11, and outputted as an analog output signal 12.

On the other hand, the signal from the receiver 8 is discriminated by the frequency discriminator 13, and only the noise component is detected by the squelch circuit 15 of the squelch device 14. This squelch circuit 1
5 detects a large amount of noise components, enters a squelch operation and cuts off the output of the audio amplifier 11. Also,
The digital signal detection circuit 16 inputs the demodulated signal of the demodulator 9, and cuts off the output of the audio amplifier 11 if it is not a digital signal. In this manner, the conventional squelch device 14 performs a squelch operation by connecting and disconnecting the audio amplifier 11 depending on the amount of noise components and the presence or absence of a digital signal.

However, in the conventional example described above, the digital signal detection circuit 16 simply detects the presence or absence of a digital signal, so in the case of a digital signal having a similar data signal format, it cannot detect the arrival of the data signal. Then, the audio amplifier 11 is connected. At this time, since the data signal format is different from a predetermined one, the decoder 10 generates a noise-like signal, which is output as the analog output signal 12, which is a drawback.

Purpose of the Invention The present invention eliminates the drawbacks of the conventional example described above, and aims to provide an excellent squelch device that cuts off the output of an audio amplifier when receiving radio waves in a format other than a predetermined digital signal format. shall be.

Composition of the Invention In order to achieve the above object, the present invention provides that the amplitude level of the noise component of the frequency-discriminated signal is smaller than the voltage set by the squelch volume, and that the demodulated digital signal is The structure detects the presence of a frame synchronization signal, controls the connection/disconnection of the audio amplifier, and outputs an analog output signal, so even if the reception input exceeds the reception input set by the squelch volume, It has the advantage of not outputting an analog output signal when there is no frame synchronization signal and the predetermined digital signal format is not satisfied.

DESCRIPTION OF EMBODIMENTS The configuration of an embodiment of the present invention will be described below with reference to the drawings. FIG. 2 is a block diagram of a digital radio including a squelch device according to an embodiment of the present invention, FIG. 3 is a diagram showing one frame of a digital signal of this embodiment, and FIG. 4 is a noise squelch circuit of this embodiment. FIG. 5 is a signal waveform diagram of the squelch device of this embodiment when interference waves are added.

In Figures 3 to 5, 1 is an analog input signal such as voice, 2 is an encoder that converts the analog input signal into a digital signal such as PCM or delta modulation, and 4
converts this digital signal to FM using carrier signal 3.
A modulator 5 performs modulation, etc., and a transmitter 5 transmits this modulated signal as a radio wave via an antenna 6.
8 is a receiver that receives the radio waves via the antenna 7, converts the frequency, and outputs it as an intermediate frequency; 9
is a demodulator that converts the received signal into a digital signal, 1
0 is a converter (CODEC) that converts this digital signal into an analog signal, and 11 is a converter (CODEC) that amplifies the analog signal, the output can be connected or disconnected by a control signal, and it has a built-in low-pass filter that removes unnecessary components. 12 is an analog output signal.

On the other hand, 13 is a frequency discriminator that discriminates the signal of the receiver 8, 17 is a squelch device according to an embodiment of the present invention, 18 is a high-pass filter that extracts only high-frequency components from the discrimination signal, and 19 is the amplitude of the high-frequency signal. This is an amplitude detection circuit that detects the level. Note that this amplitude detection voltage changes in proportion to the radio signal to band noise ratio (C/N ratio). A comparison circuit 20 compares this amplitude detection signal with the voltage set by the squelch volume 20a. 21 inputs the digital signal of the demodulator 9 and outputs one frame (320
frame synchronization detection circuit that detects the first frame synchronization signal (8 bits), 22 is 1
Frame synchronization signal (8 bits) at the beginning of the frame
This is a state holding circuit that holds the detection result of the frame synchronization detection circuit after detecting the frame synchronization detection circuit until the next frame arrives. 23 is an AND circuit which inputs the signal from the state holding circuit 22 and the signal from the comparison circuit 20 and sends a control signal to the control terminal of the audio amplifier 11.

Next, the operation of the above embodiment will be explained. Second
4, an analog input signal 1 is converted by an encoder 2 into a digital signal such as PCM or delta modulation. This digital signal is modulated into an FM signal by a modulator 4 using a carrier signal 3, and then sent to a transmitter 5.
The power is increased and radio waves are transmitted from the antenna 6. This radio wave is sent to a receiver 8 via an antenna 7.
Receive at. This received signal is demodulated and converted into a digital signal by a demodulator 9, converted into an analog signal by a decoder 10, amplified to a predetermined level by an audio amplifier 11, and outputted as an analog output signal 12.

On the other hand, the signal from the receiver 8 is discriminated by the frequency discriminator 13, the high frequency component (noise component) is extracted by the high frequency filter 18 of the squelch device 17, the amplitude level is detected by the amplitude detection circuit 19, and the comparison circuit At step 20, the voltage is compared with the voltage set by the squelch volume 20a. Here, if the amount of noise is large and the amplitude level signal is larger than the voltage set by the squelch volume 20a, the comparison circuit 20 outputs "0". If the amplitude level signal is small, the comparison circuit 20 outputs "1".

In addition, the frame synchronization detection circuit 21 detects the first 8 bits of the one frame digital signal (320 bits) output from the demodulator 9, and if it is a frame synchronization signal, the remaining part of one frame is detected. also outputs "1" from the state holding circuit.

Therefore, if the AND circuit 23 has a strong receiving input voltage and a predetermined digital signal system,
Both inputs become "1", and the audio amplifier 11 outputs an analog output signal 12. In addition, in the case of a weak received input voltage or if the predetermined digital signal system is not used, the input of the AND circuit 23 includes "0", the output becomes "0", and the audio amplifier 11 does not output an analog output signal. .

Note that detailed aspects of this embodiment will be explained below.

The noise detection voltage has large level fluctuations, and
Since the fluctuation period is also random, the time constant is increased to prevent malfunctions. As shown in Fig. 4, when a radio wave arrives, the amplitude detection voltage a of the noise is set by the squelch volume 20a, and when it passes the value b,
The audio amplifier 11 is connected and the communication path is turned on. The signal speed is 16Kbit/s, and 20mS is 1
If it is a frame, the total number of bits is 320 bits.
Here, if the frame synchronization signal is 8 bits, the remaining
312 bits are data bits. The frame synchronization signal is generally 2 m times or 2 raised to the n power, but if there are many synchronization bits, the communication data bits will be compressed, so normally about 2 to 16 bits are used. In this embodiment, it is set to 8 bits.

To explain the signal format here, the audio
Coded at 15.6Kbit/s, encoded at 20mS,
The signal is divided into 312 bits, converted to a signal speed of 16 Kbit/s, and then assembled into a continuous signal by adding an 8-bit synchronization code. Please note that the audio is 16Kbit/
If encoded in seconds, the signal may be converted to a rate of 16.4 Kbit/sec and 8 bits may be added to make it a continuous signal.

When receiving the above signal, the 312 bits after detecting the 8 bit synchronization signal are received as digital data, the signal speed is changed, the signal is processed as a continuous signal, and the data is converted into an analog signal.

FIG. 5 explains a state in which an interference wave of the same frequency is added to the digital data signal.

In FIG. 5, A is the arrival period of the desired received wave, and B is the arrival period of the interfering radio wave. During period (b), communications were disrupted and noise was generated due to interference.

The band noise of the frequency discriminator 13 is reduced in noise level by the arrival of the desired reception wave, and the noise level is reduced by the standard radio wave adjuster h.
The voltage becomes lower than the reference voltage set by the comparator circuit 20.
The output of becomes "1". Therefore, the audio amplifier 11
is turned ON, and the analog signal obtained by decoding the digital data of the desired received wave is output to 12.

Next, in (b) when a jamming wave arrives, the combined level of the received level changes depending on the phase relationship with the desired received wave, but when the received level increases, the out-of-band noise remains reduced. At this time, the received data is confused due to interference and generates noise, but the noise is output from the audio amplifier 11 as it is.

In the present invention, the frame synchronization detection circuit 21 of the squelch device 17 receives the frame synchronization signal (8 bits), and when this signal is received, there is a delay of 20 mS until the reception of the next frame synchronization signal is completed.
During this period, the state holding circuit 22 outputs "1",
AND circuit 23 along with the output “1” of the noise detection circuit
In addition, the audio amplifier 11 is connected, but if interference radio waves arrive, the frame synchronization signal cannot be received, and if interference occurs, the output of AND23 will be "0".
Since the audio amplifier 10 is turned off, even if an interference wave arrives immediately after the arrival of a frame synchronization signal, the noise can be immediately removed by missing the next frame synchronization signal. The noise generation time in this case is approximately 20 mS. Instead of detecting a loss of frame synchronization signal and immediately performing a squelch operation,
It is also possible to cause the squelch operation to be performed when the squelch operation occurs a number of times that does not significantly impede communication. This time can be changed according to the requirements of the communication system.

A dotted line box c indicates the noise generation time that occurs when a large number of allowed asynchronous times when frame synchronization is lost is set. Increasing the allowable number of synchronizations to a certain extent in this way is necessary in order to prevent the playback output from being disconnected more than necessary when quality deterioration of the line occurs rapidly and intermittently due to fading or the like. However, in this case, it naturally takes time to detect the radio wave interruption, and a noise generation section shown in C occurs when the call ends. Here, by using the noise squelch signal in combination, this noise at the end of the call can be suppressed, and this is the advantage of using the noise squelch in combination.

Effects of the Invention As is clear from the above-mentioned embodiments, the present invention provides a method in which the amplitude level of the noise component of the frequency-discriminated signal is smaller than the voltage set by the squelch volume.
and detecting that the demodulated digital signal has a predetermined frame synchronization signal for each frame,
Since the analog output signal is output by controlling the connection/disconnection of the audio amplifier, even if there is a reception input that is higher than the reception input set by the squelch volume, there is no frame synchronization signal and the specified digital signal format is met. When not, it has the effect of not outputting an analog output signal.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a digital radio device including a conventional squelch device, FIG. 2 is a block diagram of a digital radio device including a squelch device according to an embodiment of the present invention, and FIG. 3 is a block diagram of a digital radio device including a squelch device according to an embodiment of the present invention. FIG. 4 is a signal waveform diagram of the noise squelch circuit of this embodiment, and FIG. 5 is a signal waveform diagram of the squelch device of this embodiment when interference waves are added. 1... Analog input signal, 2... Encoder, 3... Carrier signal, 4... Modulator, 5... Transmitter, 6... Antenna, 7... Antenna, 8... Receiver, 9... Demodulator, 1
0...Decoder, 11...Audio amplifier, 12...Analog output signal, 13...Frequency discriminator, 17...Squelch device, 18...High-pass filter, 19...Amplitude detection circuit, 20...Comparison circuit, 21...Frame synchronization detection circuit , 22...state holding circuit, 23...AND circuit.

Claims (1)

[Claims] 1. An amplitude detection circuit that extracts high-frequency components from frequency-discriminated received input and detects the amplitude level, a comparison circuit that compares the voltage set by the squelch volume and the signal of the amplitude detection circuit, and a demodulation circuit. a frame synchronization detection circuit that detects a frame synchronization signal included in one frame of a digital signal; and a state holding circuit that maintains a detection state until one frame ends after the frame synchronization detection circuit detects the frame synchronization signal. , inputting the signal of the comparison circuit and the signal of the state holding circuit,
The output controls the output of the analog output signal.
A squelch device equipped with an AND circuit.