JP2831153B2 - Spread spectrum communication system - Google Patents

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, and more particularly to a frequency hopping spread spectrum communication system in two-way communication.

[0002]

2. Description of the Related Art Conventionally, spread spectrum communication systems have been used in fields such as satellite communication and land communication because of their excellent interference resistance and confidentiality. One of the spread spectrum systems for performing this communication is a frequency hopping (hereinafter, referred to as FH) system. In the FH method, a carrier is spread by hopping according to a predetermined rule by a spreading code sequence. A transceiver based on a conventional two-way communication system using a spread spectrum communication system based on the FH system has been configured as shown in FIG. First, transmission will be described. The frequency synthesizer 13 outputs a signal of a random frequency in accordance with the spreading code sequence output from the spreading code sequence generator 11. The transmission data supplied to the transmission data input terminal 1 is spread by the multiplier 15 by the output of the frequency synthesizer 13 and amplified by the amplifier 17.
9 and transmitted from the antenna 20.

Next, in the case of reception, a signal received by an antenna 20 is separated from a transmission wave by a duplexer 19,
, And then input to the synchronization circuit 21 and the multiplier 16. The synchronization circuit 21 detects the clock phase of the spread code sequence and the phase of the spread code sequence from the received signal, and outputs a clock and a synchronization signal to the spread code sequence generator 12. The spreading code sequence generator 12 outputs a spreading code sequence according to the input clock and synchronization signal. The spread code sequence output from the spread code sequence generator 12 is supplied to a frequency synthesizer 14. Frequency synthesizer 14
Outputs a random frequency according to the input spreading code sequence. The multiplier 16 multiplies the received signal by the output of the frequency synthesizer 14 to despread the received signal, demodulates the received data by the demodulator 22, and outputs the demodulated received data from the received data output terminal 2. To perform two-way communication with such a transceiver, these transmitters and receivers operate simultaneously.

[0004]

The state of hopping in the above-mentioned conventional transceiver is as shown in FIG. In the figure, fT and fR indicate a transmission frequency and a reception frequency, respectively, and hop in the transmission frequency band and the reception frequency band indicated by broken lines asynchronously with time with each other. In FIG. 4, the transmission frequency and the reception frequency are separated at times t1 and t3, but approached at time t2. As described above, since the transmission frequency and the reception frequency hop independently at random, if the transmission and reception frequency bands are arranged too close to each other, interference due to mixing of the transmission wave into the receiver and suppression of the sensitivity of the receiver can be easily provided, Complicates receiver design. Conventionally, as a countermeasure for this, the transmission frequency band and the reception frequency band are separated, and the antennas of the transmitter and the receiver are separately provided and installed separately. However, there has been a problem that characteristics such as a decrease in reception speed, reception performance, particularly high selectivity and a wide dynamic range are required.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a spread spectrum communication system in which hopping on the transmission side and hopping on the reception side have a fixed relationship so that transmission waves do not interfere with the receiver due to hopping. .

[0006]

The spread spectrum communication system of the present invention is a two-way communication, and uses a frequency hopping system in which a carrier is hopped according to a predetermined rule by a spreading code sequence to perform spreading. In the spread spectrum communication system, the transmission frequency is characterized in that hopping is performed in parallel at a predetermined frequency interval from the reception frequency.

[0007]

According to the spread spectrum communication system of the present invention, the transmission frequency and the reception frequency are always separated by a constant frequency interval, so that the transmission wave is smaller than in the case where the hopping patterns of the transmitter and the receiver are independent. The receiver can be easily designed without giving any interference or suppression to the receiver.

[0008]

The present invention will be described below with reference to examples.

FIG. 1 is a block diagram showing the configuration of an embodiment to which the present invention is applied.

The transmitter in this embodiment supplies a spread code sequence output from a spread code sequence generator 11 to a frequency synthesizer 13. The frequency synthesizer 13 outputs a signal of a random frequency according to the input spread code sequence. The transmission data input to the transmission data input terminal 1 and the output of the frequency synthesizer 13
, The transmission data is spread by the output of the frequency synthesizer 13, the spread output is supplied to the amplifier 17, amplified, and then supplied to the antenna 20 via the duplexer 19,
The signal is transmitted from the antenna 20.

The receiver inputs the signal received by the antenna 20 to the duplexer 19 and separates it from the transmission wave by the duplexer 19, and supplies the separated received signal to the amplifier 18 for amplification and
The signal is supplied to the synchronization circuit 21 and the multiplier 16. Synchronous circuit 2
In 1, the clock of the spread code sequence and the phase of the spread code sequence are detected from the input received signal, and the clock and the synchronization signal are transmitted to the spread code sequence generator 11
To supply. The spread code sequence is supplied from the spread code sequence generator 11 having received the clock and the synchronization signal to the frequency synthesizer 14. The frequency synthesizer 14 receives the input spread code sequence and outputs a signal at a frequency separated by a certain frequency interval from the frequency generated by the frequency synthesizer 13 and at a random frequency according to the input spread code sequence. The received signal amplified by the amplifier 18 and the signal output from the frequency synthesizer 14 are supplied to a multiplier 16, and the multiplier 16 despreads the received signal. The despread signal output from the multiplier 16 is supplied to the demodulator 22 for demodulation, and the demodulated reception data is output from the reception data output terminal 2.

In the transceiver of this embodiment, there are two cases: two-way communication, a case of calling a partner station, and a case of responding to the partner station.

First, when calling the partner station, switch 2
3 is turned off and transmission is started. At this time, the spreading code sequence generator 11 generates a spreading code sequence according to the timing of its own station, and the frequency synthesizers 13 and 14 receive the same spreading code sequence, and according to the input spreading code sequence, 14 generates a transmission frequency and a reception frequency separated by a certain frequency interval, respectively, and hops in parallel with the transmission frequency and the reception frequency separated by a certain frequency interval.

Next, when responding to the partner station, the switch 23
Is turned on. In this state, the mobile station stands by at the reception frequency separated by a predetermined frequency interval from the transmission frequency, and the partner station transmits at this reception frequency. Upon receiving a call from the partner station, synchronization circuit 21 detects the clock phase of the spread code sequence and the phase of the spread code sequence from the received signal. The spread code sequence generator 11 having received the signal of the clock phase and the phase of the spread code sequence generates a spread code sequence synchronized with the received wave. Therefore, at the same time as the despreading is correctly performed on the receiving side, the transmission frequency and the reception frequency are hopped in parallel at a fixed frequency interval.

FIG. 2 shows how the transmission frequency and the reception frequency are hopped. Dashed lines indicate the transmission frequency band and the reception frequency band, respectively.
At time t2, the transmission frequency hops in the frequency increasing direction from time t1 while maintaining a constant frequency interval, and at time t2
In 3, the transmission / reception frequency hops in the frequency decreasing direction from time t2 while maintaining a constant frequency interval. That is, as is clear from the hopping at times t1, t2 and t3 shown in FIG. 2, the hopping on the transmission side and the hopping on the reception side are synchronized, and the transmission frequency and the reception frequency are always separated by a fixed frequency interval. Hopping. Since the transmission frequency and the reception frequency always have a fixed frequency interval, the transmission and reception frequency bands can be provided close to each other without having to make the characteristics of the duplexer 19 and the reception filter in the receiver so steep. Become.

In the above-described embodiment, the case where the output frequency of the frequency synthesizer 13 becomes the transmission frequency as it is, and the output frequency of the frequency synthesizer 14 becomes the reception frequency as it is. Generally, a frequency conversion circuit is often provided before and after a frequency synthesizer. In such a case, a frequency obtained by adding or subtracting a fixed frequency to or from the output frequency of the frequency synthesizer 13 and the output frequency of the frequency synthesizer 14 becomes a final transmission frequency and a reception frequency. Hopping in parallel.

[0017]

As described above, according to the spread spectrum communication system of the present invention, the transmission frequency is hopped in parallel at a predetermined frequency interval from the reception frequency, so that the transmission and reception frequency bands are arranged close to each other. Even so, there is no mixing of the transmitted wave into the receiver, and there is an effect of being free from severe requirements such as high selectivity and a wide dynamic range without receiving interference due to the mixing and suppressing the sensitivity of the receiver. Furthermore, the number of the spread code sequence generators can be reduced to one for transmission and reception, and the circuit size can be reduced.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an embodiment to which the method of the present invention is applied.

FIG. 2 is a schematic diagram showing a hopping state for explaining an operation of an embodiment to which the method of the present invention is applied.

FIG. 3 is a block diagram showing a configuration of a conventional example.

FIG. 4 is a schematic diagram showing a hopping state for explaining the operation of the conventional example.

[Explanation of symbols]

 11, 12 spreading code sequence generator 13, 14 frequency synthesizer 15, 16 multiplier 17, 18, amplifier 19, duplexer 20, antenna 21, synchronization circuit 22, demodulator 23, switch

Claims (1)

(57) [Claims] In a spread spectrum communication system which uses a frequency hopping system for spreading by spreading a carrier by hopping a carrier according to a predetermined rule by a spreading code sequence, a transmission frequency is changed from a reception frequency. A spread spectrum communication system characterized by hopping in parallel at a fixed frequency interval.