JP2831154B2 - 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.
The signal is transmitted from the antenna 20 via 9A.

Next, in the case of reception, the signal received by the antenna 20 is separated from the transmission wave by the duplexer 19A,
After being amplified by 8, it is 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 timing 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 timing signals. The spread code sequence output from the spread code sequence generator 12 is supplied to a frequency synthesizer 14. The frequency synthesizer 14 outputs a random frequency according to the input spread 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.

According to the present invention, the hopping on the transmitting side and the hopping on the receiving side have a fixed relationship, and the hopping can reduce the occupied frequency bandwidth without causing the transmitted wave to interfere with the receiver and reduce the frequency utilization rate. It is an object of the present invention to provide a spread spectrum communication system capable of improving communication.

[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 transmitting wave and the receiving wave use the same frequency band, the transmitting frequency hops in parallel with the receiving frequency separated by half the occupied frequency bandwidth, and hops out of the occupied frequency band. Is characterized by hopping after folding back to the opposite band edge.

[0007]

According to the spread spectrum communication system of the present invention, since the same frequency band is used for the transmission frequency and the reception frequency, it is not necessary to provide the transmission frequency band and the reception frequency band separately as in the prior art. As a result, the occupied frequency bandwidth is reduced to half that of the conventional one, and effective frequency utilization can be achieved. Furthermore, the transmission frequency and the reception frequency are always separated by a half of the occupied frequency bandwidth and hop in synchronization, so that the transmission wave interferes and suppresses the receiver due to the hopping pattern of the transmitter and the receiver. Without giving, the receiver can be easily designed.

[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 the present embodiment supplies the spread code sequence output from the spread code sequence generator 11A to the 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 are
5, the transmission data is spread by the output of the frequency synthesizer 13, the spread output is supplied to the amplifier 17, amplified, supplied to the antenna 20 via the duplexer 19, and transmitted from the antenna 20. Here, in this embodiment, since the transmission and reception frequency bands are the same, the duplexer 19A utilizing the fact that the frequency bands are different as in the above-described conventional example cannot be used. As the duplexer 19, one that can change the center frequency according to the hopping pattern, for example, a YIG filter or the like is used.

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 step 1, the clock phase of the spread code sequence and the phase of the spread code sequence are detected from the input received signal, and the clock and timing signals are supplied to the spread code sequence generator 11A via the switch 23. The spread code sequence is supplied to the frequency synthesizer 14 from the spread code sequence generator 11A having received the clock and the timing signal. The frequency synthesizer 14 receives the input spread code sequence and generates a random frequency according to the input spread code sequence at a frequency separated from the frequency generated from the frequency synthesizer 13 by a half of the transmission / reception frequency bandwidth. Output a signal. 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.

Next, the configuration of a spread code sequence generator 11A for separating a transmission wave from a reception wave by a half of the occupied frequency bandwidth will be described.

FIG. 2 is a block diagram illustrating the configuration of the spreading code sequence generator 11A.

The spreading code sequence generator 11A includes a switch 2
3, a clock signal 3, a timing signal 4 and a selection signal 5 of logic "0" and logic "1" are supplied to generate a spread code sequence generator body 3 for generating a spread code sequence.
1 is added to the spreading code sequence output from the spreading code sequence generator main body 31 and a code sequence having a code sequence length of 拡 散 of the spreading code sequence length, and when the addition result exceeds the spreading code sequence length, A computing unit 32 for performing subtraction of the so-called spreading code sequence length to subtract the spreading code sequence length from the addition result, and a spreading code sequence output from the spreading code sequence generator 31 and a calculation output spread by the computing unit 32 A switch 33 for selectively allocating a code sequence to the frequency synthesizers 13 and 14 is provided. In FIG. 2, reference numeral 6 denotes a transmission spread code sequence output terminal supplied to the frequency synthesizer 13,
Reference numeral 7 denotes a reception spread code sequence output terminal to be supplied to the frequency synthesizer 14.

The switch 23 is switched off when calling the partner station, and is switched on when responding to the partner station. When the switch 23 is switched on, the clock 3, the timing signal 4 and the logic "1" are set. Is supplied to the spread code sequence generator 11A, and when it is switched to the off state, only the select signal 5 of logic "0" is supplied to the spread code sequence generator 11A. The spread code sequence generator main body 31 generates a spread code sequence according to its own timing when the input selection signal 5 is logic "0", and generates an external clock 3 when the selection signal 5 is logic "1". And a timing code 4 to generate a spread code sequence. For example, when the input spread code sequence is 11 bits (spread code sequence length 0 to 2047), the arithmetic unit 32 adds the fixed spread code sequence having a spread code sequence length of 1024. When the addition result exceeds the spread code sequence length (2047), the fixed code sequence having the spread code sequence length is subtracted. The switch 33 distributes the output of the spread code sequence generator main body 31 and the output of the arithmetic unit 32 to the transmission spread code sequence output terminal 6 and the reception spread code sequence output terminal 7, and the selection signal 5 is logic "0".
In this case, the spread code sequence output from the spread code sequence generator body 31 is supplied to the frequency synthesizer 13 and the spread code sequence output from the arithmetic unit 32 is supplied to the frequency synthesizer 14. Supply in reverse order.

First, the operation of the spread code sequence generator 11A will be described.

The spreading code sequence generator 11A generates a spreading code sequence having a spreading code sequence length of 7 bits. Therefore, the spreading code sequence generator main body 31 generates a 7-bit spreading code sequence, that is, an arbitrary number from 0 to 127.
The arithmetic unit 32 receives the input value and the half of the spread code sequence length of 6
4 is added. However, when the addition result exceeds 127, 128 is subtracted. Now, in the case of calling the other station, the output of the spread code sequence generator main body 31 is supplied to the frequency synthesizer 13 and the arithmetic unit 32
Is supplied to the frequency synthesizer 14. Table 1 shows an example of the output spreading code sequence from the spreading code sequence generator 11A in this case.

[0018]

[Table 1]

For example, when the output of the spread code sequence generator main body 31 is "14", the output of the arithmetic unit 32 is 14 + 64 =
112 + 64 = 176 (mod12) when the output of the spreading code sequence generator main body 31 is “112”.
8) = 48. Here, (mod128) is 1
Indicates the remainder divided by 28. That is, the input to the frequency synthesizers 13 and 14 always has a value of 0 to 127.
, And the frequency synthesizer 1
The input value to 3 and the input value to the frequency synthesizer 14 differ by half the value of the spread code sequence length (64 in the above example). Here, if the frequency synthesizers 13 and 14 assume that the output frequency changes linearly with a change in the input spread code sequence value, the input spread code sequence 0
The range of the output frequency corresponding to .about.127 is the transmission / reception frequency bandwidth. As shown in FIG. Just be away. Therefore, the spreading code sequence generator 11A is equivalent to the presence of a spreading code sequence generator that generates substantially two spreading code sequences that differ by half the value of the spreading code sequence length.

In the above-described transceiver of the present 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 11A generates a spreading code sequence at the timing of its own station. However, as described above, the transmission spread code sequence differs from the reception spread code sequence by half of the spread code sequence length, and the output frequency of the frequency synthesizer 13 to which the spread code sequence output from the spread code sequence generator main body 31 is input. The spreading code sequence output from the arithmetic unit 32 is hopped in parallel with the output frequency of the frequency synthesizer 14 to which it is input by a half of the occupied frequency bandwidth.

Next, when responding to the partner station, the switch 23 is used.
Is turned on. If there is a call from the partner station, the received wave is separated by the duplexer 19, and 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. Output a signal. A spread code sequence synchronized with the received wave is generated from the spread code sequence generator main body 31 which has received the clock and the timing signal via the switch 23. In this case, the received spread code sequence is a spread code sequence output from the spread code sequence generator main body 31 and is synchronized with the received wave. The received spread code sequence is supplied to the frequency synthesizer 14, and the received wave is received. At the same time, the received spreading code sequence is correctly despread on the side (in this case, the spreading code sequence output from the spreading code sequence generator body 31)
Is different from the transmission spread code sequence (in this case, the spread code sequence output from the arithmetic unit 32) by half of the spread code sequence length, and the output frequency of the frequency synthesizer 14 to which the received spread code sequence is input is the occupied frequency band. Perform hopping in parallel, separated by half the width.

FIG. 4 shows the state of hopping, where broken lines indicate transmission and reception frequency bands, respectively.
The transmission frequency band and the reception frequency band are the same frequency band.
The transmission frequency and the reception frequency are always hopping apart from each other by half of the transmission / reception frequency bandwidth, and hopping in the frequency increasing direction from time t1 to time t2, and at time t
The case where hopping is performed in the frequency increasing direction from time 2 to time t3 is shown. In the case of hopping from time t2 to time t3, a case where the addition result in the arithmetic unit 32 exceeds the spreading code sequence length is illustrated. Time t shown in FIG.
As is clear from the hopping at 1, t2 and t3, 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 hopped apart from each other by half the transmission / reception frequency bandwidth. I have. However, since the transmission frequency and the reception frequency are always separated by half the transmission / reception frequency bandwidth, the characteristics of the duplexer 19 and the reception filter in the receiver do not need to be so steep.

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 is illustrated. Generally, a frequency conversion circuit is often provided before and after the frequency synthesizer. In such a case, when a fixed frequency is added to or subtracted from the output frequency of the frequency synthesizer 13 and the output frequency of the frequency synthesizer 14, the final transmission frequency and the reception frequency are obtained, and when the same frequency band is used for transmission and reception, The transmission and reception frequencies are always separated by half the frequency of the occupied frequency bandwidth and hop in parallel.

[0025]

As described above, according to the spread spectrum communication system of the present invention, the transmission wave and the reception wave use the same frequency band, and the transmission frequency is separated from the reception frequency by a half of the occupied frequency bandwidth. Since hopping is performed in parallel and hopping outside the frequency band is turned back to the opposite band edge, hopping is performed even if the reception filter in the duplexer and the receiver does not have very steep characteristics. In addition to the effects of interference due to contamination and suppression of the sensitivity of the receiver, it is free from severe demands such as high selectivity and wide dynamic range, making it easier to design the receiver.
There is an effect that the transmission and reception frequency bandwidth is reduced to half of the conventional one.
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 block diagram showing a configuration of a spread code sequence generator in one embodiment to which the method of the present invention is applied.

FIG. 3 is a schematic diagram showing a relationship between a transmission / reception frequency bandwidth and an output frequency of a frequency synthesizer in one embodiment to which the method of the present invention is applied.

FIG. 4 is a schematic view showing a hopping state for explaining an operation of an embodiment to which the method of the present invention is applied.

FIG. 5 is a block diagram showing a configuration of a conventional example.

FIG. 6 is a schematic view showing a hopping state for explaining the operation of the conventional example.

[Explanation of symbols]

 11, 11A, 12 ... Spread code sequence generator 13, 14 ... Frequency synthesizer 15, 16 ... Multiplier 17, 18 ... Amplifier 19, 19A ... Duplexer 20 ... Antenna 21 ... Synchronous circuit 22 ... Demodulator 23, 33 ... Switch 31: Spread code sequence generator main body 32 ... Operation unit

Claims (1)

(57) [Claims] 1. A spread-spectrum communication system that uses a frequency hopping system for performing spread by spreading a carrier by hopping a carrier according to a predetermined rule by a spreading code sequence in a two-way communication. The same frequency band shall be used, and the transmitting frequency shall hop in parallel with the receiving frequency by half the occupied frequency bandwidth, and hopping outside the occupied frequency band shall be hopped back to the opposite end of the band. A spread spectrum communication system characterized by the following.