JPH11261449A - Radio communication system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain synchronism in a short time without using a highly accurate oscillator in a radio communication system of a frequency hopping system. SOLUTION: A transmission side and a reception side are mutually linked by using an ALE function and, when an actual spread communication is started, time information on the transmission side is transmitted by an ALE modulation system. A control part 5 outputs the time information supplied by a time generation part 1 by way of an ALE modulation part 6. On the other hand, on the reception side RX, an ALE modulation part 21 outputs an information bit which is recognized to include the time information to an analysis part. In the analysis part, the time information in the received information bit is read and is transmitted to a control part 16. The control part which has received this time information instructs a time generation part 12 to bing the time of its own station to be in synchronism with the time on the transmission side, time of the time generation part 12 is corrected. On the reception side, so that synchronism of a PN pattern is obtained on the basis of this corrected time information.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a radio communication system for performing spread spectrum communication by frequency hopping, and more particularly to a method for synchronizing the time of a PN code between a transmitting side and a receiving side.

[0002]

2. Description of the Related Art A frequency hopping system is known as one of spread spectrum communication systems. In the frequency hopping method, a carrier frequency of a signal modulated with information to be transmitted is switched randomly and discretely based on a PN code and supplied, thereby spreading a signal band and performing highly confidential communication. On the other hand, on the receiving side, the same P
It is necessary to demodulate using the N code, and when converting the received signal to the intermediate frequency, the signal is correctly demodulated by switching the local oscillation frequency supplied to the frequency conversion unit to be synchronized with the PN code of the received wave. You.

[0003] A system employing this frequency hopping system for communication in the HF band has been proposed and being realized. As is well known, the characteristic that HF band radio waves are reflected by the ionosphere enables long-distance communication without using any additional means. Although extremely effective in realizing communication, it has the following problems.

[0004]

Generally, in the frequency hopping system, the longer the PN cycle and the more types, the higher the confidentiality. In particular, HF communication is mostly used for long-distance communication. In this case, the PN cycle is set to be extremely long so that information is not stolen during the information propagation, and highly confidential communication is performed. However, when the PN cycle becomes extremely long, there is a problem that it takes time to acquire the PN code synchronously. Therefore, it is impossible to capture in a short time (several minutes) by means such as a generally used sliding correlator and a matched filter.
Therefore, there is a method of allocating a PN pattern to a standard time and synchronizing all the radios with the standard time in order to acquire the synchronization in a short time. In this case, even if the PN cycle is long, the spread demodulation can be started from the position of the PN code corresponding to the current time, so that the synchronization can be acquired in a short time.

[0005] However, in order to synchronize with the standard time, there is a problem that an extremely high-precision oscillator of about 10 ^-9 is required for each radio, and frequent time calibration is required. The present invention has been made to solve the above-described problem, and has as its object to provide a radio communication system using a frequency hopping method that can achieve synchronization acquisition in a short time without using a high-precision oscillator.

[0006]

In order to achieve the above object, a wireless communication system according to the present invention comprises an optimum frequency selecting means (ALE means) for establishing a mutual link between transmission and reception, and spread spectrum communication by frequency hopping. In order to perform, the transmitting device and the receiving device, a time generating means, and a hopping pattern generating means for generating a hopping pattern based on the time information output from the time generating means, and the transmitting device, the transmitting device, the link After the establishment, the time signal of the own station is transmitted through the ALE means, and the information signal to be transmitted is spread and modulated according to the hopping pattern. The hopping pattern is received through the ALE means, and the time generation means of the own station is calibrated based on the time information. It is characterized by demodulating a more received spread modulation signal.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail based on illustrated embodiments. FIG. 1 is a block diagram showing an example of a configuration of a wireless communication system using a frequency hopping method according to the present invention. In the figure, TX indicates a transmitting device, and RX indicates a receiving device.

In the transmitting device TX, a time generator 1 generates a time based on a clock output from an oscillator 2. The PN generating unit 3 generates a PN pattern according to the current time based on the time supplied from the time generating unit 1.

The memory unit 4 stores a plurality of PN patterns assigned according to time. See Figure 2 for details.
As shown in the figure, a plurality (four in this example) of PN codes A to
D hops at a predetermined cycle T and is allocated to each of the frequencies f1 to f4 that are not easily affected by the ionosphere. For example, P
Looking at the N code A, the hopping pattern has the frequency f 1 → f 3 → f 2 → f 3 → f 1.
An N-code hopping pattern (PN pattern) is stored in the memory unit 4 of FIG. The control unit 5 controls each component.

The ALE modulator 6 is a modulation means having an optimum frequency selection function (Automatic Link Establishment). As described above, the communication in the HF band uses the reflection of the ionosphere and the like, and the communicable frequency changes every moment due to environmental changes. Therefore, the modulation is performed by selecting the optimum frequency at the time of communication.

The data modulation section 7 modulates transmission data using a modulation scheme such as PSK or FSK. The changeover switch 8 supplies one output of the ALE modulator 6 or the data modulator 7 to one input terminal of a later-described spread modulator 10 in response to an instruction from the controller 5.
The FH synthesizer 9 generates a signal having a frequency corresponding to the PN pattern output from the PN generator 3. The spread modulation unit 10 spreads and modulates the signal from the switch 8 with the frequency signal from the FH synthesizer 9. 11 is an antenna.

On the other hand, in the receiving device RX, the time generator 12 generates time based on the clock output from the oscillator 13. The PN generation unit 14 generates a P based on the current time based on the time supplied from the time generation unit 12.
This is for generating N patterns.

The memory unit 15 stores the same PN pattern as the memory unit 4 on the transmitting side. The control unit 16 controls each component. The synthesizer 17 for FH
This is to generate a signal of a frequency corresponding to the PN pattern output from the PN generation unit 14. The spread demodulation unit 18 converts the signal received by the antenna 19 into the FH synthesizer 17.
Is spread-spectrum modulated with a frequency signal from

The changeover switch 20 supplies the output of the spread demodulation section 18 to one of the ALE demodulation section 21 and the data demodulation section 23 in response to an instruction from the control section 16. The ALE demodulation unit 21 is a demodulation unit having an ALE function corresponding to the ALE modulation unit 6. The analysis unit 22 supplies the extracted time information to the control unit 16. The data demodulation unit 23 demodulates a signal by a demodulation method corresponding to the data modulation unit 7.

The operation of the communication apparatus configured as described above will be described. First, the transmitting side and the receiving side recognize that they are in a linked state using the ALE function. A method for establishing this link state will be described below. FIG. 3 is a diagram showing a data format used for ALE communication.
In the data, the first three bits are used as a command code, and the remaining 45 bits are used as information bits. For example, the sender T
The ALE signal from X is a command code 101 as shown in (a), and the contents of the information bits include information such as a frequency channel. A plurality of transmission frequency channels for ALE data are prepared in the HF band.
Send data.

An ALE signal shown in (a) is output from the transmitting side TX, and when this is received by the receiving side RX, the RX outputs a response signal. The response signal is assumed to have a command code of 100 as shown in (b), for example, and the content of the information bit includes information indicating that the ALE signal has been successfully received. If this response signal is sent on the transmitting side TX, the link is established, and the subsequent communication is performed on this channel. If the receiving side RX cannot receive the ALE signal, no response signal is output, so the transmitting side TX switches to another channel and establishes the link again. As described above, the link is established on the channel most suitable for communication. Although the configuration for receiving the response signal on the transmitting side TX is omitted, the receiving side RX
Needless to say, an ALE demodulation unit or the like may be provided in the same manner as described above.

When starting the actual spread communication,
To perform synchronization acquisition of the PN pattern, the transmitting device TX
Transmits the time information of its own station by the ALE modulation method.
The switch 8 is connected to the ALE modulator 6 in advance. At this time, the controller 5 converts the time information supplied from the time generator 1 into a predetermined format shown in FIG. Output to the modulator 6. That is, the command code is set to 110 indicating time, and the contents of the information bits are month, day,
Hours, minutes, seconds, milliseconds, the number of times of transmission of time information, and the like are represented by a code string having a predetermined bit length, and these are represented by an ALE modulator 6.
Output to The ALE modulating unit 6 modulates this with a channel in a link state and outputs it.

On the other hand, the receiving side RX is in a link state with the transmitting side TX and always waits for the ALE signal. The information bits are recognized as being included, and the information bits are output to the analysis unit 22. Analysis unit 2
In step 2, the time information in the received information bits is read and sent to the control unit 16. By inputting this time information, the control unit 16 instructs the time generation unit 12 to synchronize the time of its own station with the time of the transmission side, so that the time generation unit 12
Time is calibrated.

The transmitting device TX repeats the transmission of the time information described above a predetermined number of times. For example, as shown in FIG. 4, the time information is transmitted three times, and the receiving side performs synchronization acquisition during that time. Then, when the transmission of the time information is completed, the control unit 5 on the transmission side starts the synchronization of the PN pattern. First, the control unit 5 switches the switch 8 to the data modulation unit 7 side,
It instructs the PN generator 3 to transmit a PN pattern. The PN generator 3 generates a pattern corresponding to the current time among the PN patterns assigned to the absolute time by using the FH synthesizer 9.
To supply. The FH synthesizer 9 outputs a frequency signal corresponding to the PN pattern. On the other hand, data modulator 7
Outputs modulated transmission data. As a result, the spread modulator 10 spread-modulates the output from the data modulator 7 with the output of the FH synthesizer 9, and the frequency-hopped signal is transmitted from the antenna 11.

On the other hand, the receiving side RX also generates a PN pattern based on the time synchronized with the transmitting side TX, and spreads and demodulates the received signal using this. That is, the control unit 16 switches the switch to the data demodulation unit 23 side, and the PN generation unit 1
4 is instructed to transmit a PN pattern. PN generator 14
Supplies the pattern corresponding to the current time among the PN patterns assigned to the absolute time to the synthesizer 17 for FH. The FH synthesizer 17 outputs a frequency signal corresponding to the PN pattern. As a result, the spread demodulated transmission data is output from the spread demodulation unit 18 and the data is demodulated by the data demodulation unit 23 to obtain correct data.

As described above, in the radio communication system using the frequency hopping method of the above-described embodiment, time information is transmitted from the transmission side using the ALE function required in HF communication, and the reception side transmits time information based on the time information. Is corrected to perform synchronous capture of the PN pattern, so that the synchronous capture of the hopping pattern can be performed in a short time.

Although the above embodiment has been described by taking as an example the case where frequency hopping is performed in the HF band, the present invention is not limited to this, and can be applied to any spread spectrum modulation system that performs ALE communication. is there.
The format in the ALE communication is not limited to this, and any format may be used as long as the format including time information is transmitted in the ALE communication. Also, it is obvious that the number of times of transmission of the time information is not limited to three, but may be any number as long as the time information can be transmitted reliably.

[0023]

As described above, the radio apparatus according to the present invention sends time information from the transmitting side using the ALE function used for HF communication, and the receiving side corrects the time based on this time information. Synchronous acquisition of the PN pattern by using this method makes it possible to acquire the synchronization in a short time, and it is not necessary to mount a high-precision oscillator in each wireless device, so a remarkable effect in providing a low-cost wireless device. To play.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an example of a configuration of a wireless communication system using a frequency hopping method according to the present invention.

FIG. 2 is a diagram showing a PN pattern (hopping pattern) stored in a memory unit of the wireless communication system according to the present invention.

FIG. 3 is a diagram showing a frame configuration of an ALE signal.

FIG. 4 is a signal output diagram for explaining the operation of the wireless communication system according to the present invention.

[Explanation of symbols]

 1, 12: time generation unit 2, 13: oscillation unit 3, 14: PN generation unit 4, 15: memory unit 5, 16: control unit 6: ALE modulation unit 7 ··· Data modulators 8 and 20 ··· Switch 9 and 17 ··· Synthesizer for FH 10 and 18 ··· Spread modulators 11 and 19 ··· Antenna 21 ··· ALE demodulator 22 ··· Analysis unit 23: Data demodulation unit

Claims (1)

[Claims] In a wireless communication system provided with an optimum frequency selecting means (ALE means) for establishing a mutual transmission / reception link, a time generating means is provided in a transmitting apparatus and a receiving apparatus for performing spread spectrum communication by frequency hopping. And a hopping pattern generating means for generating a hopping pattern based on the time information output from the time generating means, and the transmitting device establishes the link and, after establishing the link, transmits the time of its own station via the ALE means. While transmitting a signal and spread-modulating and transmitting an information signal to be transmitted by the hopping pattern, the receiving device,
Receiving time information from the transmitting device via the ALE means,
A wireless communication system, comprising: calibrating a time generation means of the own station based on the time information; and demodulating a spread modulation signal received by the hopping pattern.