JPH04280131A - Frequency hopping communication system - Google Patents

Abstract

PURPOSE:To prevent a hard of hearing state due to the deterioration in articulation caused by a change in a decoded voice occurred when digital cipher communication is applied to the frequency hopping communication system by implementing transmission reception with specific constitution. CONSTITUTION:In the frequency hopping communication system in which a voice signal is digital-coded to a prescribed frame length, a carrier frequency is hopped at a longer period than the length of the frame so as to implement communication, a sender side uses a timing control means to switch the hopping frequency near the middle of the frame for sending the frame and a receiver side decodes a code of a preceding frame as to the frame having the frequency changeover. That is, preceding frames F2, F6 are outputted in the case of frames F'3, F'6 having a changeover at a demodulated digital code (g) to obtain a code (i). Then a voice signal (j) is decoded, a sense of displeasure in a listening sense is prevented and the articulation is improved.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a frequency hopping communication system applying digital confidential communication.

0002

2. Description of the Related Art In frequency hopping communication systems, in order to prevent the transmission of radio waves with unstable frequencies that occur during frequency switching, transmission of radio waves is prohibited in regions where the frequencies are unstable. Furthermore, the difference in timing between frequency switching between reception and transmission is added, and the output of the received signal is intermittently interrupted. However, in the case of normal analog communication, this is not a particular problem.

0003

[Problem to be solved by the invention] If digital confidential communication is applied to such a method, in which voice is restored using the entire data of one frame, the data in the frame will be incorrect at the point when the signal output is interrupted, so it is necessary to respond to this frame. The decoded audio will be significantly different from the original audio. This difference reduces clarity and makes it difficult to hear.

[0004] This situation is shown in the time chart of FIG. In the figure, a is the waveform of the original audio signal, and b is the audio signal a divided into frames of 5 msec to 30 msec and digitally encoded, F1, F2,...
F7 represents a frame. c represents the control voltage of the voltage controlled oscillator that generates the transmission frequency, and f1, f2, f3
...represents the transmission frequency. α1 represents the time required for the change from f2 to f1, and α2 represents the time required for the change from f1 to f3. Therefore, the region of α1 and α2 shows a state in which the frequency is changing. d indicates the transmission power,
α1 and α2 indicate a state in which transmission power is prohibited. e represents the control voltage of a voltage controlled oscillator that generates the reception frequency, and f1, f2, f3, . . . represent the reception frequencies. β1 and β2 represent the time difference between the transmission frequency of c and the reception frequency of e. In e, α1 and α2 represent the times when the frequency switches from f2 to f1 and from f1 to f3, similar to the time chart in c. f represents the reception output, and since the transmission and reception frequencies do not match in the areas α1 +β1 and α2 +β2, noise is output (or nothing is output). g represents the demodulated digital code, and since reception is not performed normally at F3 and F6, the codes of F3 and F6 are F'3
, F'6. As a result, as shown in h, the audio signal restored based on F'3 and F'6 becomes different from the original audio signal, resulting in a decrease in intelligibility and difficulty in hearing.

[0005] An object of the present invention is to provide a frequency hopping communication system that prevents difficulty in hearing due to a decrease in intelligibility caused by changes in reconstructed speech that occur when digital confidential communication is applied to a frequency hopping communication system.

[0006]

[Means for Solving the Problems] The frequency hopping communication system of the present invention is a frequency hopping communication method in which an audio signal is digitally encoded into a fixed frame length and the carrier frequency is hopped at a cycle longer than the frame length. In a communication system, the transmitting side switches the frequency using a timing control means that switches the hopping frequency near the center of the frame and transmits the frame, and the receiving side decodes the code of the previous frame in a frame where there is a frequency switch. It is characterized in that the audio signal is restored by the control means.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a time chart when the present invention is implemented. In FIG. 1, g is the same as g in FIG. 6 and represents the demodulated digital code, and is the same as g in FIG.
, F'6 indicates that the data contents of frames F3 and F6 are incorrect. i is the output of F2 and F5 of the previous frame as F'3 and F'6, respectively,
j represents the recovered speech using these digital codes.

FIG. 2 is a block diagram of a transmission system according to the present invention when performing digital confidential communication using the frequency hopping communication system. In the figure, 1 is an encoder for audio signals, 2 is a modulator for digital transmission, 3 is a frequency converter, 4 is a power amplifier, and 5 is an oscillator, which generates a clock for driving the modulator 2. 6 is a local oscillator for frequency conversion, usually VC
A phase-locked loop (PLL) using O is used. 7 is a clock generator that drives the encoder 1, and 8 is a frequency switching controller that generates a frequency switching signal. The operation of this circuit is as follows.

The audio input is digitally encoded by an encoder 1, and the encoded signal is modulated by a modulator 2. The signal is input to the frequency converter 3 and converted into a transmission frequency by the frequency converter 3 using the frequency from the local oscillator 6 which is switched by the frequency switching signal from the frequency switching controller 8. The transmitted wave is amplified to a predetermined power by a power amplifier 4 and radiated from the antenna. Local oscillator 6
consists of a phase-locked loop including a voltage-controlled oscillator, and frequency hopping is performed by changing the control voltage of the voltage-controlled oscillator. Note that the clock from the clock generator 7 synchronizes the encoder 1 and the frequency switching controller 8, and controls the frequency switching so that it is in the middle of the frame constituted by the encoder 1. The frequency switching controller 8 also controls the power amplifier 4 to stop the transmission power radiation in an unstable frequency region when switching the frequency of the local oscillator 6.

FIG. 3 is a block diagram of a receiving apparatus according to the present invention. In the figure, 11 is a radio frequency amplifier (RFA), 12 is a frequency converter, 13 is an intermediate frequency amplifier including a filter, 14 is a digital demodulator (DEM), and 15 is a device that restores the digitally encoded audio signal. The decoder 16 is a local oscillator for frequency conversion, and is composed of a voltage controlled oscillator and a phase-locked loop. 17 is a frequency switching controller that outputs a frequency switching signal; 18 is a frame detector that detects a frame break of a digital code; and 19 is a clock generator. The operation of this receiving circuit is performed as follows.

The received signal from the antenna is transmitted to a high frequency amplifier 1.
1, mixed with a local oscillation frequency from a local oscillator 16 by a frequency converter 12, amplified by an intermediate frequency amplifier 13 including a filter, and then demodulated into digital information by a demodulator 14. A frame detector 18 detects a frame break from the signal, and a decoder 15 restores the audio signal frame by frame. On the other hand, clock generator 1
The local oscillator 1 consists of a phase-locked loop and a voltage-controlled oscillator, and operates the frequency switching controller 17 in synchronization with the frequency switching timing on the transmitting side using the signal from 9.
6 to make the frequency hop. Also, the clock from the clock generator 19 and the frame delimiter detector 18
In the process of detecting a frame with erroneous data based on the signal and restoring the audio signal in the decoder 15, the previous frame is output in the case of an erroneous frame.

FIG. 4 is a detailed circuit diagram of a part of the present invention, showing details of the decoder 15 and frame detector 18 of FIG. In the figure, 21 is a frequency change point detection circuit that detects a change point of a frequency hopping (frequency change) signal. 22 is a counter with set and reset functions that counts clock inputs. 23 is a serial/parallel conversion circuit. 24 is a frame detector that detects frame breaks in digital confidential communication. 25 is a temporary storage circuit for signals divided into frames, and the signal from the serial/parallel conversion circuit 23 is transferred to the frame detector 24.
Accumulates by latch signal from. A storage circuit 27 is the same circuit as the storage circuit 25, and shifts the signal from the storage circuit 25 and temporarily stores it. 26 is a switching controller that determines the counter value of the counter 22 and switches the switch of the switching circuit 28 based on the determined value. 29 is a demultiplexer, and 30 is a digital to analog converter (D/A converter).

FIG. 5 is a time chart showing signals at various parts of the circuit shown in FIG. In the figure, (a) is a frequency switching signal, (b) is a reset signal for the counter 22 made from the frequency switching signal in (a), (c) is a signal representing a frame break and is a set signal for the counter 22, (d) is a digital signal switched by the switching circuit 28 and is the storage circuit REG (1) 25 or the storage circuit REG (2) 27.
Output the contents from either.

The operation will be explained with reference to FIGS. 4 and 5. The frequency switching signal shown in (a) of FIG.
1, the conversion point (H→L, L→H) is detected and input to the counter 22 as a reset signal (b). On the other hand, the input signal is input to the serial/parallel converter 23 and the frame detector 24, and the detector 24 performs frame detection to obtain the set pulse (c) for each frame division. The serial signal input to the serial/parallel conversion circuit 23 is converted from serial data to parallel data by a set pulse from the frame detector 24, and is latched in REG (1) 25. At the same time, the data in REG (1) 25 is converted to REG. (2)2
Shifted to 7. Further, the counter 22 starts counting the clock signal from the count value 0 by the set signal,
If the reset signal does not come, it counts up to the specified value. If a reset signal is received, the counter operation is stopped. The switching controller 26 determines whether the value of the counter is smaller than or equal to a predetermined value, and if it is equal, it is determined that there is no conversion point in the frame, and it remains as RE(1)2.
The switching circuit 28 is switched so that the signal No. 5 is outputted to the demultiplexer 29 and passed to the D/A converter 30. On the other hand, if the counter value is small, it is determined that the frequency has been switched within the frame, and in that case, it is determined that the data is incorrect, and the current frame is not output and the REG (2) 2 of the previous frame is
The switching circuit 28 is switched so as to output the data accumulated in the D/A converter 3, and the switching circuit 28 is switched to output the data accumulated in the D/A converter 3.
0, it is converted to an analog signal.

[0015]

[Effects of the Invention] As explained in detail above, the following effects can be obtained by implementing the present invention. (1) Auditory discomfort can be prevented. (2) The above can improve clarity.

[Brief explanation of the drawing]

[Figure 1] Time chart of frequency hopping communication system according to the present invention

FIG. 2 is a block diagram showing an example of the configuration of the transmitting side of the present invention.

[Figure 3
]Block diagram showing an example of the configuration of the receiving side of the present invention

FIG. 4 is a block diagram showing some details of the present invention.

[Figure 5] Time chart showing waveforms of each part in Figure 4

[Figure 6] Time chart of conventional frequency hopping communication method

[Explanation of symbols]

1 Encoder 2 Modulator 3 Frequency converter 4 Power amplifier 5 Oscillator 6 Local frequency oscillator 7 Clock generator 8 Frequency switching controller 11 High frequency amplifier 12 Frequency converter 13 Intermediate frequency amplifier 14 Demodulator 15 Decoder 16 Local frequency oscillator 17 Frequency switching controller 18 Frame detector 19 Clock generator 21 Frequency change point detection circuit 22 Counter 23 Serial/parallel conversion circuit 24 Frame detector 25 Accumulation circuit (1) 26 Switching controller 27 Accumulation circuit (2) 28 Switching circuit 29 Demultiplexer 30 D/A converter

Claims (1)

[Claims] Claim 1. In a frequency hopping communication method in which an audio signal is digitally encoded into a fixed frame length and communication is carried out by hopping a carrier frequency at a cycle longer than the length of the frame, the transmitting side performs communication near the center of the frame. The audio signal is transmitted by switching the frequency using a timing control means that switches the hopping frequency, and on the receiving side, in a frame in which the frequency is switched, the audio signal is restored by the control means that decodes the code of the previous frame. Frequency hopping communication method.