JPH04344730A - Spread spectrum communication system - Google Patents

Abstract

PURPOSE:To realize the spread spectrum communication system in which secrecy is sufficiently improved even when a length of a spread code string is reduced. CONSTITUTION:In the spread spectrum communication system in which a transmitter 10 spreads an information signal by modulating a carrier modulated by a spread code series by using the information signal and sends the result and a receiver side 20 uses the same spread code series as the sender side to implement inverse spread for taking correlation with a reception signal thereby demodulating the information signal, the transmitter 10 and the receiver 20 use hopping pattern setting sections 11, 27 and hopping time interval setting sections 12, 28 so as to apply hopping to a spread code series in a preset prescribed order at a preset prescribed period.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spread spectrum communication system used for confidential communications, and more particularly to a spread spectrum communication system that improves confidentiality when the length of a spreading code string is shortened.

0002

[Prior Art] In general, spread spectrum communication systems are
On the transmitting side, the information signal is spread and transmitted by modulating a carrier wave modulated with a spreading code sequence called a pseudo-noise code sequence, which has a sufficiently wider spectrum width than the information signal, with the information signal, and on the receiving side, the information signal is spread and transmitted. The information signal is demodulated by performing despreading to correlate with the received signal using the same spreading code string as the information signal. In this spread spectrum communication system, when despreading is performed on the receiving side using a different spreading code sequence than on the transmitting side,
Since it becomes broadband noise, it is used for confidential communication, etc.

0003

[Problem to be Solved by the Invention] However, in the above-mentioned spread spectrum communication system, it is preferable to make the spread code string sufficiently long in order to improve confidentiality, but in reality, it is difficult to spread the code due to the circuit size allowed by the equipment. There are cases where it is not possible to make the code string sufficiently long. In this way, if the spreading code string cannot be made long enough, the spreading code string becomes short, and in this case, the number of codes that can be generated decreases, which raises the problem of increasing the possibility of eavesdropping by a third party. .

SUMMARY OF THE INVENTION An object of the present invention is to provide a spread spectrum communication system that can sufficiently improve confidentiality even when the length of the spreading code string is shortened.

[0005]

[Means for Solving the Problems] In order to achieve the above object, the present invention spreads and transmits an information signal by modulating a carrier wave modulated with a spreading code sequence with an information signal on the transmitting side, and transmits the information signal on the receiving side. In a spread spectrum communication system in which the information signal is demodulated by performing despreading to correlate with the received signal using the same spreading code string as that on the transmitting side, the spreading code string is used on the transmitting side and the receiving side. It is characterized by hopping at a preset predetermined period and in a preset predetermined order.

[0006]

[Operation] On the transmitting side and the receiving side, the spreading code string is hopped at a predetermined period and in a predetermined order. This makes it possible to sufficiently improve confidentiality even when the length of the spreading code string is shortened.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be explained below based on the drawings.

FIG. 1(a) shows an embodiment of a transmitter configured by applying the spread spectrum communication method according to the present invention, and FIG. 1(b) shows a transmitter configured by applying the spread spectrum communication method according to the present invention. This figure shows an example of a receiver configured by applying the communication method.

In FIG. 1A, the transmitter 10 of this embodiment includes a hopping pattern setting section 11, a hopping time interval setting section 12, a central processing unit (CPU) 13,
It is configured to include a pseudo noise code generator (PN code generator) 14, a mixer 15, an oscillator 16, and an antenna 17.

[0010] Here, the hopping pattern setting section 11 sets the order of the pseudo-noise code string that is the spreading code string to be transmitted, and the hopping time interval setting section 12 sets the time at which the pseudo-noise code string changes. The central processing unit 13 controls the entire transmitter 10, and the pseudo noise code generator 14 controls the central processing unit 1.
The mixer 15 and the oscillator 16 modulate the output of the pseudo-noise code generator 14 with the carrier wave output from the oscillator 16 and transmit the signal to the antenna. 17 to convert it into a high frequency signal for output as radio waves.

In addition, in FIG. 1(b), the receiver 20 of this embodiment includes an antenna 21, a mixer 22, and an oscillator 2.
3. SS demodulator 24, pseudo-noise code generator (PN code generator) 25, central processing unit (CPU) 26, hopping pattern setting section 27, hopping time interval setting section 2
8.

Here, the mixer 22 and the oscillator 23 convert the high frequency signal received by the antenna 21 into SS waves, and the SS demodulator 24 is a pseudo noise code generator 25.
The central processing unit 26 is a unit that performs spectrum despreading, that is, demodulates the SS wave output from the mixer 22 in accordance with the pseudo-noise code string formed by the above, a central processing unit 26 is a unit that controls the entire receiver 20, and a hopping pattern setting unit. Reference numeral 27 sets the order of the pseudo-noise code string, which is a spreading code string, and a hopping time interval setting section 28 sets the time at which the pseudo-noise code string changes.

Next, the operation of this embodiment will be explained with reference to examples of transmitted data and received data shown in FIG.

In the transmitter 10 shown in FIG. 1(a), information representing the order of pseudo-noise code sequences to be transmitted is preset in the hopping pattern setting section 11 and pseudo-noise codes set in the hopping time interval setting section 12. The information representing the time at which the sequence changes is taken into the central processing unit 13, and the central processing unit 13 processes the information representing the order of the pseudo-noise code sequence to be transmitted and the information representing the time at which the pseudo-noise code sequence changes. A control signal is formed based on the signal, and this control signal is applied to the pseudo noise code generator 14.

[0015] Furthermore, before the start of data transmission, the central processing unit 13 generates a predetermined idle pattern with a synchronization frame added to the rear end as transmission data, and applies this to the pseudo noise code generator 14. .

The pseudo-noise code generator 14 generates a pseudo-noise code string that changes at regular time intervals, that is, at a predetermined period and in a predetermined order, based on the control signal and transmission data applied from the central processing unit 13. Transmission data modulated with the hopped pseudo-noise code string is output. The output of the pseudo-noise code generator 14 is a carrier wave generated by the oscillator 16, which is modulated by the mixer 15 and sent out from the antenna 17.

In this state, the central processing unit 13
When a transmission signal is applied to the central processing unit 13, the central processing unit 13 forms transmission data corresponding to this transmission signal, converts it into an idle pattern, and outputs it.

FIG. 2(a) shows that the transmitter 1
2 shows an example of transmission code sequence transmission data transmitted from 0. That is, the transmitter 10 first outputs a fixed signal a1 consisting of an idle pattern and a synchronization signal, then a signal a2 consisting of data 1 and a synchronization signal, then a signal a3 consisting of data 2 and a synchronization signal,
A signal a4 consisting of data 3 and a synchronization signal is sequentially output.

In the receiver 20 shown in FIG. 1(b), the hopping pattern setting section 27 and the hopping time interval setting section 28 include the hopping pattern setting section 11 and the hopping time interval setting section 28 shown in FIG. 1(a). Part 1
Information representing the order of the pseudo-noise code strings and information representing the time at which the pseudo-noise code strings change are set in advance, and the received code sequence received data as shown in FIG. 2(b) is set in advance. receive. This received code series received data is mixed with the signal generated from the transmitter 23 by the mixer 22, frequency converted, and becomes an SS wave.
It is added to the SS demodulator 24.

[0020]The SS demodulator 24 is connected to the central processing unit 26.
demodulates the input SS wave according to the pseudo-noise code string generated from the pseudo-noise code generator 25 under the control of Form. Here, the central processing unit 26 monitors the synchronization signal included in the SS wave, and obtains information indicating the order of the pseudo-noise code strings set in the hopping pattern setting section 27 and the hopping time interval setting section 28, and the pseudo-noise code string. The pseudo-noise code string generated by the pseudo-noise code generator 25 is sequentially switched in accordance with the information representing the time at which the pseudo-noise code generator 25 changes, and the pseudo-noise code string is hopping at a predetermined period and in a predetermined order similar to that on the transmitter side. form.

In this way, the received data output from the SS demodulator 24 is applied to the central processing unit 26,
The central processing unit 26 outputs a reception signal corresponding to this reception data.

[0022]

[Effects of the Invention] As explained above, according to the present invention, spreading code sequences are hopping at a predetermined cycle and in a predetermined order on the transmitting side and the receiving side. With this configuration, it is possible to sufficiently improve confidentiality even when the spreading code string length is shortened.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a transmitter and a receiver constructed by applying an embodiment of a spread spectrum communication system according to the present invention.

FIG. 2 is a timing chart explaining the operation of the embodiment shown in FIG. 1;

[Explanation of symbols]

10 Transmitter 11 Hopping pattern setting unit 12 Hopping time interval setting unit 13 Central processing unit (CPU) 14 Pseudo-noise code generator (PN code generator) 15 Mixer 16 Transmitter 17 Antenna 20 Receiver 21 Antenna 22 Mixer 23 Transmission Unit 24 SS demodulator

Claims (1)

[Claims] Claim 1: On the transmitting side, an information signal is spread and transmitted by modulating a carrier wave modulated with a spreading code sequence with an information signal, and on the receiving side, the same spreading code sequence as that on the transmitting side is used to combine the received signal with the information signal. In a spread spectrum communication system that demodulates the information signal by performing despreading that takes the correlation of
A spread spectrum communication system characterized in that the transmitting side and the receiving side hop the spreading code string at a predetermined period and in a predetermined order.