JPH07307689A - Communication system and transmission equipment - Google Patents

Abstract

PURPOSE:To provide a communication system which quickly restores synchronism to keep the communication even in the case of a failure of reception of a preamble at the time of transmission start and to provide the transmission equipment used in this system. CONSTITUTION:A timing control circuit 14 connects switches 17 and 21 to terminals 17a and 21a for a prescribed time after the fall time of an oscillation output signal (b) and connects them to terminals 17b and 21b thereafter, and this switching is repeated synchronously with the oscillation output signal (b) having a certain period. When the modulation signal of the output modulated wave of a modulating circuit 18 is a synchronizing signal, a frequency conversion circuit 23 subjects a carrier to frequency hopping by a pattern based on the preamble code to output it to an output terminal 24. When the modulation signal of the output modulated wave of the modulating circuit 18 is data which is compressed by a memory circuit 13 with respect to time, the frequency conversion circuit 23 subjects the carrier to frequency hopping by a pattern based on a spreading code to output it to the output terminal 24.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a communication system and a transmitter, and more particularly to a communication system for transmitting and receiving digital data by a spread spectrum system using frequency hopping and a transmitter used therefor.

[0002]

2. Description of the Related Art Conventionally, a frequency hopping method has been known as an example of a digital communication method, which is one of the spread spectrum methods for broadening the frequency band of a signal to improve noise resistance and interference resistance. (For example,
JP-A-58-21939).

FIG. 4 shows a block diagram of an example of a conventional transmission apparatus that performs this frequency hopping. This conventional device
A synchronization signal generation circuit 16 that generates a preamble signal for shortening the synchronization time on the reception side at the start of transmission, switches 17 and 21, a modulation circuit 18 that performs modulation by a predetermined modulation method, and a spreading that generates a spreading code. Code generation circuit 19
2, a preamble code generation circuit 20, a frequency synthesizer 22 for performing frequency hopping, a frequency conversion circuit 23 for frequency conversion of an input signal into a transmission frequency band, and a timing control circuit 25.

To explain the operation of this conventional device,
The transmission control signal a shown in FIG. 5A is input to the timing control circuit 25 from the input terminal 12. When the input timing control signal a becomes low level, the timing control circuit 25 determines that it is in the transmission state, activates the synchronization signal generation circuit 16 and the preamble code generation circuit 20, respectively, connects the switch 17 to the terminal 17a side, and , Switch 2
1 is connected to the terminal 21a side.

As a result, the synchronization signal output from the synchronization signal generation circuit 16 is transmitted through the switch 17 to the modulation circuit 18
Is supplied to the frequency conversion circuit 23 after being modulated. On the other hand, the preamble code is output from the preamble code generation circuit 20 and supplied to the frequency synthesizer 22 via the switch 21. The frequency synthesizer 22 frequency-converts this preamble code and supplies it to the frequency conversion circuit 23.

The frequency conversion circuit 23 frequency-converts the output modulated wave of the modulation circuit 18 based on the preamble code from the frequency synthesizer 22, and performs frequency hopping based on a pattern having a relatively short period or a specific pattern. Output.

The timing control circuit 25 switches and connects the switch 17 to the terminal 17b side and the switch 21 to the terminal 21b after holding the connection state of the switches 17 and 21 for the preamble transmission period. As a result, the input data input to the input terminal 11 is changed to the switch 1
The spread code, which is supplied to the modulation circuit 18 via the switch 7 and the spread code generated by the spread code generation circuit 19, is transmitted via the switch 21 and the frequency synthesizer 22 to the frequency conversion circuit 23.
Is supplied to.

As a result, after the lapse of the preamble transmission period, the modulated wave modulated by the input data is supplied to the frequency conversion circuit 23 and frequency-converted by the spread code,
The frequency is hopped by the spread code having an extremely long period and transmitted from the output terminal 24. Therefore, as shown in FIG. 4B, the output terminal 24 has a preamble 31
Is output for a predetermined period of time, a signal obtained by frequency-hopping the modulated wave of the input data is extracted.

On the receiving side, since the synchronization of the data part can be established by establishing the synchronization with the preamble signal, it is possible to achieve the synchronization in a short time even if the spreading code with a long cycle is used.

[0010]

However, in the above-mentioned conventional transmitting apparatus, the preamble 31 is transmitted only once at the start of transmission, and therefore, when the preamble cannot be received by the receiving apparatus due to fading of the wireless line, If the synchronization is lost during the communication, the receiving apparatus cannot obtain the preamble signal, so that the synchronization cannot be established and it takes a long time for the communication to be interrupted or to be recovered.

The present invention has been made in view of the above points,
If the preamble could not be received at the start of transmission,
An object of the present invention is to provide a communication system and a transmission device capable of quickly recovering synchronization and maintaining communication even if synchronization is lost during communication.

[0012]

In order to achieve the above object, in the communication system of the present invention, the modulation wave having the synchronizing signal as the modulation signal is selected from the modulation waves output from the modulation circuit by the second selecting means. Modulated by the frequency hopping pattern determined by the preamble code and transmitted, and the modulated wave using the digital data as the modulation signal is modulated by the frequency hopping pattern determined by the spreading code selected by the second selecting means and transmitted. Having a frequency hopping transmission means on the transmission side, and demodulating a synchronization signal from the received signal using the preamble code from the generation unit that generates the same preamble code and spreading code as the transmission side to establish synchronization, and then the generation unit In a communication system having a frequency hopping receiving means for demodulating digital data using a spread code from Time compression means for intermittently outputting the time compression data obtained by time compression of the time data to the first selecting means is provided on the transmitting side, and the first selecting means is the non-input period of the time compression data. And outputs a time-series combined signal in which a synchronization signal is inserted, the second selecting means performs the selecting operation in synchronization with the selecting operation of the first selecting means, and the receiving side decompresses the time-compressed data demodulated. It is configured to return to the original time axis.

Further, in the transmitter of the present invention, the time compression means for time-compressing the digital data to be transmitted, the synchronization signal generation circuit for generating the synchronization signal for shortening the synchronization time on the receiving side, and the synchronization signal modulation time A preamble code generation circuit for determining the hopping pattern of the data, a spreading code generation circuit for determining the hopping pattern at the time of data modulation, and a first code for selecting one of the output time compressed data of the time compression means and the output synchronization signal of the synchronization signal generation circuit. 1 switch, a second switch that selects one of the preamble code from the preamble code generation circuit and the spreading code from the spreading code generation circuit, a modulation circuit that modulates the output signal of the first switch, and a modulation circuit The frequency at which the output modulated wave is frequency-hopping and transmitted with the hopping pattern based on the output code of the second switch. And hopping means, so when the synchronization signal by the first switch is selected preamble code is selected by the second switch, the first and second
And a timing control signal generating means for generating a timing control signal for switching control of the first and second switches in a constant time cycle.

[0014]

In the system of the present invention, the first selection means extracts a signal obtained by time-sequentially combining the synchronization signal and the time-compressed data, and the combined signal is frequency-hopping transmitted through the modulation circuit. Since it is input to the means, the frequency hopping transmission means transmits and receives a preamble (modulated wave having a synchronization signal as a modulation signal) having a hopping pattern determined by a preamble code a plurality of times at a fixed time period from the start of transmission.

Further, in the transmitting apparatus of the present invention, the first
Since the selecting means can be realized by the first switch and the timing control signal generating means, and the second selecting means can be realized by the second switch and the timing control signal generating means, the hopping pattern can be realized by the preamble code by the frequency hopping means. The preamble for which is determined can be transmitted a plurality of times in a fixed time period from the start of transmission.

[0016]

EXAMPLES Next, examples of the present invention will be described. FIG. 1 shows a schematic block diagram of an embodiment of a communication system according to the present invention. As shown in the figure, the time base compression means 1 time-compresses the digital data to be transmitted, and intermittently outputs the compressed data at regular time intervals. The synchronization signal generating means 2 generates a synchronization signal for shortening the synchronization time on the receiving side. First
When the transmission is started, the selection means 3 of the
Is selected for the first fixed time, the compressed data from the time compression means 1 is selected for the second fixed time, and then the synchronization signal from the sync signal generating means 2 is selected for the first constant time. The operation of doing is repeated. As a result, the synchronization signal (preamble), which is conventionally transmitted only once at the start of transmission, is inserted into the non-transmission period (first fixed time) of the compressed data and is transmitted periodically multiple times. Become.

The signal picked up by the first selecting means 3 is modulated by the modulating circuit 4 and then supplied to the frequency hopping transmitting means 5 to generate a frequency based on the preamble code or the spreading code from the second selecting means 6. Is hopping. That is, the second selecting means 6 selects the preamble code during the period in which the modulated wave having the synchronizing signal as the modulation signal of the output modulated waves of the modulation circuit 4 is input to the frequency hopping transmitting means 5, and the preamble code is selected. Modulated by the frequency hopping pattern determined by, and transmitted, the spread code is selected during the period in which the modulated wave using the digital data as the modulation signal is input, and the spread code is modulated by the frequency hopping pattern determined by the spread code. Send it.

The transmitted signal is received by the frequency hopping receiving means 7, where the preamble code generated by the generator 8 which generates the same preamble code and spreading code as the transmitting side is used to synchronize the fixed pattern synchronization signal from the received signal. , And establishes synchronization, and then uses the spreading code from the generator 8 to demodulate the time-compressed data.

The time compressed data demodulated by the frequency hopping receiving means 7 is supplied to the time expanding means 9 and expanded on the original time axis. The time compression means 1 can be realized, for example, by setting the read frequency higher than the write clock frequency of the digital data to the memory circuit, and the time expansion means 9 corresponds to the write clock frequency of the time compressed data to the memory circuit. This can be realized by setting the read frequency lower by a ratio corresponding to the time compression ratio.

Thus, according to the present embodiment, the preamble is transmitted and received intermittently a plurality of times, so that even if a part of the preamble cannot be received at the time of radio line failure due to fading, the radio line of the radio line cannot be received. Since the preamble transmitted after the failure recovery can be received, synchronization can be established and communication can be maintained in a short time.

Next, an embodiment of the transmitting apparatus according to the present invention will be described with reference to FIGS. 2 is a block diagram of an embodiment of the transmitting apparatus according to the present invention, and FIG. 3 is a time chart for explaining the operation of the main part of FIG. 2, those parts that are the same as those corresponding parts in FIG. 4 are designated by the same reference numerals. As shown in FIG. 2, this embodiment further includes a memory circuit 13 and an oscillating circuit 15 for compressing modulated data in a conventional transmitter, and a timing control circuit 14 outputs an output signal of the oscillating circuit 15 at regular intervals. It is designed to be operated intermittently.

The memory circuit 13 constitutes the time compression means 1, and the synchronization signal generation circuit 16 comprises the synchronization signal generation means 2.
Are configured. Further, the timing control circuit 14, the oscillation circuit 15 and the switch 17 make it possible to use the first selecting means 3
The timing control circuit 14, the oscillation circuit 15 and the switch 21 constitute the second selecting means 6. Further, the frequency synthesizer 22 and the frequency conversion circuit 2
Reference numeral 3 constitutes the frequency hopping transmission means 6.

Next, the operation of this embodiment will be described.
The oscillator circuit 15 oscillates and outputs a symmetrical square wave having a constant period (for example, 250 ms), as indicated by b in FIG. 3B. The timing control circuit 14 is shown in FIG.
The transmission control signal a shown in (A) and the oscillation output signal b of the oscillation circuit 15 described above are received as input signals, respectively, and in synchronization with the fall of the oscillation output signal b during the low level of the transmission control signal a: The operation of.

That is, the timing control circuit 14 judges that the transmission control signal a is in the transmission state when the transmission control signal a becomes the low level,
The synchronization signal generation circuit 16 is operated for a predetermined period (for example, 10 ms, which is the same as the conventional preamble transmission period) from the time of the fall of the oscillation output signal b immediately after the fall of the transmission control signal a.
At the same time that the preamble code generation circuit 20 is activated, the switch 17 is connected to the terminal 17a side and the switch 21 is connected to the terminal 21a side.

As a result, the synchronizing signal output from the synchronizing signal generating circuit 16 passes through the switch 17 and the modulating circuit 18
To the preamble code generation circuit 2 at the same time.
The preamble code output from 0 is supplied to the frequency synthesizer 22 via the switch 21. Modulation circuit 1
The modulated wave of which the modulated signal is the synchronizing signal extracted from 8 is supplied to the frequency conversion circuit 23, where the carrier wave is frequency hopped in a pattern based on the preamble code and output to the output terminal 24. The output signal d at this time is the preamble signal indicated by I in FIG. The sync signal is a signal for shortening the sync time on the receiving side as described above, and the pattern itself may not be fixed and may be time information or the like.

After 10 ms of the preamble transmission period, the timing control circuit 14 inverts the polarity of the timing control signal to switch the switch 17 to the terminal 17b side and switch 21 to the terminal 21b side. As a result, the data read from the memory circuit 13 is supplied to the modulation circuit 18 via the switch 17, and at the same time, the spread code output from the spread code generation circuit 19 is supplied to the frequency synthesizer 22 via the switch 21. To be done. The initial phase of the spread code output from the spread code generating circuit 19 at the time of the above switching is set to a certain phase according to the content of the preamble code.

At this time, the signal supplied to the modulation circuit 18 is
When the transmission control signal a becomes low level, the digital data A shown in FIG. 3 (C) which is input to the memory circuit 13 through the input terminal 11 and written at the write clock frequency f _W is set to the write clock frequency. The time-compressed data A ^* is read by a read clock having a frequency f _R higher than f _W , and this time-compressed data A ^* is modulated by the modulation circuit 18.

A modulated wave whose modulated signal is the time-compressed data A ^* extracted from the modulation circuit 18 is supplied to the frequency conversion circuit 23, where the carrier wave has a frequency with a pattern having an extremely long period based on the spread code. It is hopped and output to the output terminal 24. The output signal d at this time is the time compression data A ^* shown by II in FIG.

The timing control circuit 14 then outputs 1 from the second falling time of the oscillation output signal b of the oscillation circuit 15.
During the period of 0 ms, the switch 17 is switched and connected again to the terminal 17a side, and the switch 21 is switched and connected to the terminal 21a side. As a result, as is clear from the above explanation,
The carrier wave of the modulated wave in which the modulated signal is the synchronizing signal is frequency-hopped in a pattern based on the preamble code and output to the output terminal 24. The output signal d at this time is shown in FIG.
It is a preamble signal indicated by III in (D).

After the preamble transmission period of 10 ms, the timing control circuit 14 inverts the polarity of the timing control signal again to switch and connect the switch 17 to the terminal 17b side and the switch 21 to the terminal 21b side. As a result, the carrier wave of the modulated wave, which is the time-compressed data B ^* obtained by time-compressing the input digital data B of the input terminal 11 by the memory circuit 13, is used as the modulated signal in the pattern having an extremely long cycle based on the spread code. The hopping signal is output from the frequency conversion circuit 23 to the output terminal 24.
Is output to. The output signal d at this time is the time compression data B ^* indicated by IV in FIG. The data A and B shown in FIG. 3C are data in which information is continuous.

Subsequently, the switches 17 and 21 are switched again, the preamble signal indicated by IV in FIG. 3D is output to the output terminal 24, and the same operation as described above is repeated thereafter. As a result, according to the present embodiment, the preamble signal is transmitted not only once at the start of transmission but also a plurality of times during one transmission time (which cannot be generally stated because it varies depending on the data, for example, 3 to 4 seconds). Therefore, even if the reception device cannot receive one preamble signal, or even if the synchronization is lost during the communication, the preamble signal can be received after that,
The synchronization can be recovered quickly and the communication can be maintained.
Therefore, the present embodiment is suitable for application to land mobile communication that is easily affected by fading.

The modulation method of the modulation circuit 18 can be, for example, PSK modulation, QPSK modulation, or QAM modulation. Further, the present invention is not limited to the above embodiment, and it goes without saying that the preamble signal output period and the compressed data output period are not limited to the embodiment shown in FIG.

[0033]

As described above, according to the present invention,
By transmitting the preamble signal multiple times during one transmission, even if the reception device cannot receive one preamble signal or if synchronization is lost during communication, the preamble signal is received after that. Since it is possible to do so, it is possible to quickly recover the synchronization and maintain the communication in the receiving device.
It is particularly preferable to apply the present invention to land mobile communication that is easily affected by fading.

[Brief description of drawings]

FIG. 1 is a schematic block diagram of an embodiment of the method of the present invention.

FIG. 2 is a block diagram of an embodiment of the device of the present invention.

FIG. 3 is a time chart for explaining an operation of a main part of FIG.

FIG. 4 is a block diagram of an example of a conventional device.

5 is a time chart for explaining the operation of the main part of FIG.

[Explanation of symbols]

 1 time compression means 2 synchronization signal generation means 3 first selection means 4, 18 modulation circuit 5 frequency hopping transmission means 6 second selection means 7 frequency hopping reception means 8 code generation section 9 time expansion means 11 digital data input terminal 12 Transmission control signal input terminal 13 Memory circuit 14 Timing control circuit 15 Oscillation circuit 16 Synchronization signal generation circuit 17, 21 Switch 19 Spread code generation circuit 20 Preamble code generation circuit 22 Frequency synthesizer 23 Frequency conversion circuit 24 Output terminal

Claims (2)

[Claims] 1. The first selecting means selects a synchronizing signal for shortening the synchronizing time on the receiving side for a fixed time from the start of transmission and supplies the synchronizing signal to the modulating circuit, and then selects digital data to select the modulating circuit. Of the output modulated wave of the modulation circuit, the modulated wave having the synchronizing signal as the modulated signal is modulated by the frequency hopping pattern determined by the preamble code selected by the second selecting means, and transmitted. A modulated wave having digital data as a modulation signal has frequency hopping transmitting means on the transmitting side for modulating and transmitting with a frequency hopping pattern determined by the spread code selected by the second selecting means, the same as the transmitting side. After establishing the synchronization by demodulating the synchronization signal from the received signal using the preamble code from the generating unit that generates the preamble code and the spread code, In a communication system having a frequency hopping receiving means for demodulating the digital data by using a spread code from the generator on a receiving side, time-compressed data obtained by time-compressing the digital data is intermittently supplied in a constant time cycle. The time compression unit for outputting to the first selection unit is provided on the transmission side, and the first selection unit outputs the time-series combined signal in which the synchronization signal is inserted in the non-input period of the time compression data, The second selecting means performs the selecting operation in synchronization with the selecting operation of the first selecting means, and uses the spread code from the generating section to demodulate the time compressed data by the frequency hopping receiving means into the original time axis. A communication system characterized in that a time expansion means for expanding the communication is provided on the receiving side. 2. A time compression means for time-compressing digital data to be transmitted, a sync signal generation circuit for generating a sync signal for shortening a sync time on the receiving side, and a hopping pattern for modulating the sync signal. A preamble code generation circuit, a spreading code generation circuit that determines a hopping pattern during data modulation, and a first switch that selects one of the output time compressed data of the time compression means and the output synchronization signal of the synchronization signal generation circuit. A second switch that selects one of a preamble code from the preamble code generation circuit and a spread code from the spread code generation circuit; a modulation circuit that modulates an output signal of the first switch; The output modulated wave is frequency-hopping and transmitted by a hopping pattern based on the output code of the second switch. Frequency hopping means, and the first and second switches are interlocked so that when the synchronization signal is selected by the first switch, the preamble code is selected by the second switch. And a timing control signal generating means for generating a timing control signal for switching control and switching control of the first and second switches in a constant time cycle.