JPH09186630A - Channel switching code generating system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily generate many codes by generating plural codes from analog signals obtained through repeating specific mapping to vary an initial value of the repetitive mapping. SOLUTION: A channel code is switched at a time interval of k, k+1, k+2,... and a value Xk of an analog signal at a time (k) is a code representing one channel. Which channel the code represents is decided by rounding the value Xk . In the case of an FH communication, it is handled that the value Xk represents 6 channels and the frequencies prepared corresponding to 6 channels are used for local oscillation frequencies at a transmitter side and a receiver side. The analog signal is converted into a discrete value and each discrete value is used for a code representing the channel, then many codes caused at random without periodicity are obtained. Since the channel is decided by rounding the discrete value, the receiver side conducts similar rounding.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a communication device requiring channel switching, and more particularly to a system for generating a channel switching signal in a communication device of frequency hopping spread spectrum communication system.

[0002]

2. Description of the Related Art The principle of frequency spreading in a frequency hopping communication system is to randomly and randomly sweep a carrier of a signal modulated by information within a given communication band. That is, the frequency of the carrier is not fixed to a specific frequency, but spreads are realized by switching from one frequency to another frequency one after another.

The original modulated wave is restored from the spread spectrum signal as follows. Received wave is R
The frequency is converted from the F frequency to the IF frequency. that time,
The local oscillation frequency supplied to the frequency converter is switched in synchronization with the hopping pattern of the received wave. By this operation, the broadband spread spectrum signal is
The original modulated wave is obtained by frequency conversion into a narrow band signal having a frequency.

Since the frequency hopping communication system has the frequency spreading / despreading process as described above, the frequency channel switching code is required to have the following properties in constructing the communication system.

(1) There are many kinds of codes so that the codes can be assigned to a plurality of users. (2) Decoding is performed as randomly and as long as possible so that unrelated third parties cannot intercept the communication contents. It is required that (3) transmission waves of other users and transmission waves of the own station collide with each other so that collisions do not occur as much as possible so that error rate characteristics are not deteriorated.

As a frequency switching code in a frequency hopping communication system, a conventional R.S. D. Yates
Mr. One Coincidence Code (OOC)
What is called is known. Also, 1980, 11
There is a modified one-coincidence code described in the article "A few properties of one-coincidence code" published by Miyake et al. In the "Information Theory and Its Application Study Group" in May. The modified one-coincidence code will be described below with reference to FIG. This code is expressed by the following equation using a prime number P and an arbitrary integer i of 1 or more smaller than P, and an arbitrary integer j of 0 or more smaller than P.

FIG. 2A shows the case where C _i (j) = (i × j) mod P P = 7. As shown in FIG. 2A, the modified one-coincidence code has a multi-valued number P, a period P, and a code word number P-1, and only one position matches at most within one code period.

Regarding the modified one-coincidence code, its code generator is shown in Japanese Patent Application No. 57-85968, "Spreading Coder for Frequency Hopping". This is an address generation circuit that outputs an arbitrary integer value of 0 or more smaller than P to a prime number P as an address signal, a counter that counts a clock signal modulo the above prime number P, the above address signal and counter output. And a multiplication circuit for multiplying and by modulo the above prime number P.

[0009]

From the above, the modified one-coincidence code is FH (frequency hopping).
When used as a frequency switching code for a communication system, it seems that an FH communication system can be obtained which collides only once within one cycle of the code, that is, with a probability of 1 / the number of frequency channels. However, this is the case when the respective users start communication at substantially the same time, and it does not occur depending on the time lag of the communication start of each station. One example thereof is shown in FIG.

In reality, since the time when each user starts communication is random, the user capacity is the number P of code words.
It must be sufficiently smaller than -1. Therefore,
This problem can be solved if the period P is sufficiently long with respect to the number of users in one communication section required by the communication system, but this corresponds to increasing the number N of frequency channels in the FH communication system. .

It can be said that the number of users allowed depends on the number N of frequency channels regardless of the frequency switching code used, and the modified one-coincidence code does not solve this dependence. . This is because the modified one coincidence code has periodicity.

In addition, the modified one-coincidence code is poor in randomness and has a periodic characteristic, so that it cannot be said that the code is not easily decipherable. If this code is used in the FH communication system, the communication can be intercepted. The sex is relatively large. Further, the modified one-coincidence code has a limitation that the number of codes that can be created is smaller than the total number N of frequency channels, and when the total number N of frequency channels is not a prime number, all frequency channels cannot be used. .

It is an object of the present invention to provide a method of generating a large number of codes, which have essentially no periodicity and are rich in randomness, in an order of magnitude more than the conventional code generation method.

Further, the present invention makes it possible to provide a code set having a small correlation, which makes it difficult for a collision of transmission waves to occur in an FH communication system, with a small dependence on how to combine the codes.

Another object of the present invention is to construct an FH communication system that is much more confidential than before.

[0016]

In order to achieve the above object, in the channel switching code generation system of the present invention, the mapping represented by the difference equation X _{k + 1} = f (X _k ) is repeated. A deterministic, but deterministic, irregular, complex, period-free and unpredictable chaotic behavior of an analog signal is distributed, for example, with a total number N of frequency channels. The code obtained by digitizing is the frequency channel switching code.

In this way, the specific difference equation X
A method of generating a plurality of codes by changing an initial value of an iterative mapping of an analog signal obtained by iterating a mapping represented by _{k + 1} = f (X _k ), and a difference equation X _{k + 1} = f
A method of generating a plurality of codes by using a plurality of different iterative mappings of analog signals of the iterative mappings that can be _{represented by} (X _k ), and a repetitive method represented by a specific difference equation X _{k + 1} = f (X _k ). An extremely large number of mapping signals can be created by shifting the position k of the discrete section where the analog signal corresponding to a specific initial value is used as a code, and by simultaneously using the above three methods for generating a large number of switching codes. It is possible to easily generate the code of.

Further, the code generated by the above-mentioned code generation method preserves the chaotic property which is irregular, complicated, and has no period and has unpredictable behavior. The dependency makes it possible to provide a set of codes that makes it less likely that a transmitted wave will collide in an FH communication system.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, the principle of the channel switching code generation system of the present invention will be described with reference to FIG.
(A) is a schematic diagram which shows the chaotic analog signal obtained by iterative mapping. FIG. 1B is a schematic diagram showing a method of obtaining a channel switching code by converting the analog signal of FIG. 1A into discrete values when the number of channels is changed from 1 to 9. As shown in FIG. 1B, in the present invention, a channel switching code is obtained by first calculating and obtaining a chaotic analog signal and then digitizing it to match the channel number. .

Since it is known that the analog signal shown in FIG. 1A has a size within a predetermined range, the range is divided by the number of channels. In the case of FIG. 1B, 9
It is divided by the number of individual channels.

Now, the channel code is k, k + 1, k +
It is assumed that switching is performed at time intervals of 2, ...
The value Xk of the analog signal at the time k is a code representing one channel, and which channel this code represents is determined by rounding off the value Xk.
That is, in FIG. 1B, Xk exists between channels 5 and 6, but when rounded off, it becomes 6 channels.

Therefore, in FH communication, Xk is treated as representing 6 channels, and the frequencies prepared for the 6 channels on the transmitting side and the receiving side are used as the local oscillation frequency. Similarly, X _{k + 1} is 7 channels for _{k + 1 and} X _{k + 2 is for k + 2.}
Has 6 channels, and with k + 3, X _{k + 3} has 4 channels.

As described above, by converting the analog signal into discrete values and using each of the discrete values as a code representing a channel, it is possible to obtain many codes that have no periodicity and occur randomly. In the above embodiment, since the channels are decided by rounding off the discrete values, the rounding off must be done on the receiving side as well.

Therefore, when the transmitting side rounds off and determines the corresponding channel, a value matching the channel may be transmitted as the channel switching code. In this case, since the code itself corresponds to the channel, the receiving side does not need to perform the rounding operation to determine the channel.

The analog signal produced by the iterative mapping is
Many studies have been conducted on the difference equation having chaos property. One of them is: Logistic mapping: X _{k + 1} = aX _k (1-X _k ) Trigonometric mapping: X _{k + 1} = aSIN ( X _k ) Furthermore, · X _{k + 1} = aX _k ² −1 · X _{k + 1} = bX _k ; 0 ≦ X _k ≦ 1 / b = −X _k / (1-1 / b) + b / (1 -b); 1 / b ≦ X k ≦ 1 · X k + 1 = bX k; 0 ≦ X k ≦ 1 / b = X k / (1-1 / b) -1 / (1-b); 1 / b ≦ X _k ≦ 1. However, it is well known that not all analog signals of the iterative mapping are chaotic for arbitrary values of the parameters a and b.

Here, in FIG. 3A, an analog signal of the repetitive mapping of the logistic mapping is represented by a = 4, X ₀ = 0.8,
The case of k = 801 to k = 1000 is shown. FIG.
FIG. 3B shows the analog signal of FIG. As can be seen from FIG. 3 (b), even if the chaotic analog signal is converted into discrete values, the chaotic property having irregularity, complexity, and aperiodicity is not lost.
Further, it is obvious that the chaotic property is maintained because the larger the integer value to be discretized, the closer to the original analog signal.
Therefore, it can be said that a code obtained by converting a chaotic analog signal into a discrete value is irregular, complicated, aperiodic, and unpredictable.

The analog signal of the logistic map is shown in FIG. 4 (a), where a = 4, X ₀ = 0.2, k = 801 to k =
In the case of 1000, the discrete value is shown in 24. In FIG. 4B, analog signals of the logistic map are represented by a = 4, X ₀ = 0.21, k = 801 to k = 10.
In the case of 00, it is a discrete value in 24. It is known that the chaotic analog signal is sensitive to the initial value, but it can be seen from FIG. 4 that the chaotic analog signal does not lose the initial value sensitivity even when it is discretized. Therefore, it can be said that a very large number of codes as many as the number of possible initial values can be obtained even by using a specific iterative mapping.

The analog signal of the logistic map is shown in FIG. 5 (a), where a = 4, X ₀ = 0.9, k = 801 to k =
In the case of 1000, the discrete value is shown in 24. FIG. 5B shows the difference equation X _{k + 1} = 2Xk ₂ −.
The analog signal of the iterative mapping represented by 1 is a = 4, X0
In the case of = 0.9, k = 801 to k = 1000, the discrete value is converted into 24. As can be seen from FIG. 5, different iterative mappings result in different codes. Therefore, it can be said that a large number of codes can be obtained by using different iterative maps.

The analog signal of the logistic map is shown in FIG. 6A, where a = 4, X0 = 0.6, k = 101 to k =
In the case of 300, the discrete value is shown in 24. FIG. 6B shows the output value series of the logistic mapping, which is converted into discrete values at 24 in the case of a = 4, X0 = 0.6, k = 801 to k = 1000. It is known that the autocorrelation of a chaotic analog signal converges to 0 as the time difference increases. Further, as can be seen from FIG. 6, it can be seen that a set of code sequences having a small correlation can be obtained by changing the value of k that is used as a code sequence.

Next, FIG. 7 shows a simple example of an FH communication device using the channel switching code of the present invention. Then, the operation will be briefly described. FIG. 7A is a block diagram of a main part of the FH transmitter, and FIG. 7B is a block diagram of a main part of the FH receiver. In the figure, reference numeral 20 is a channel switching code generator, which comprises a counter section 1, a ROM section 2, and a latch section 3. Reference numeral 4 is a hopping synthesizer, 5 is a primary modulator, 6 is a mixer, 7 is a BPF (band pass filter), and 8 is an antenna. Further, 9 is an antenna, 10
Is a wide band BPF, 11 is a mixer, 12 is a narrow band BPF,
Reference numeral 13 is a detector. 14 is a counter unit, 15 is a ROM
The reference numeral 16 designates a latch portion which constitutes a channel switching code generator on the receiver side. 17 is a hopping synthesizer.

The operation of the transmitter will be briefly described with reference to FIG. The counter unit 1 counts the number of clocks (not shown) common to the circuit blocks and outputs the counted clocks to the ROM unit 2 as an address signal. The ROM section 2 stores data obtained by converting a channel switching code obtained by performing a calculation for converting a chaotic analog signal into a discrete value in advance so as to correspond to the input data format of the hopping synthesizer 4.

The latch unit 3 holds several bits of data output from the ROM unit 2 according to the address signal from the counter unit 1 in accordance with the input data format of the hopping synthesizer 4, and then collectively stores the data in the hopping synthesizer 4. Output. Hopping synthesizer 4
Sequentially outputs the local oscillation frequency according to the input data.
The primary modulator 5 primary-modulates the transmission data by an appropriate narrow band modulation. The mixer 6 multiplies the primary modulation signal and the output of the hopping synthesizer 4 and then passes through a band pass filter (hereinafter, BPF) 7 having an appropriate frequency characteristic,
It transmits from the antenna 8.

As a result, the signal arriving at the receiver is received by the antenna 9 and the broadband BPF 10 removes the interference wave from the unnecessary band and proceeds to the mixer 11. The mixer 11 multiplies the output (local oscillation signal) of the hopping synthesizer 17 by the received signal and despreads the product. Counter section 14, ROM section 1
5, the operation of the channel switching code generator including the latch unit 16 is the same as that described on the transmitter side. And
The despread reception signal passes through the narrow band BPF 12 and is detected by the wave detector 13.

At this time, the channel switching code described above has essentially no cycle, but it has a cycle depending on the storage capacity of the ROM section 2. However, in the currently widely used PLL-IC, the serial data for setting the comparison frequency divider is about 20 bits at most, so that the data amount required for one hop is about 20 bits. Therefore, the ROM capacity required for a cycle of 2000 hops is only about 40 kbits. Therefore, the ROM section 2
The period depending on the storage capacity of is much longer than the period of the modified one coincidence code.

The hopping synthesizer 17 on the receiver side needs to perform hopping in synchronization with the same channel switching code as the hopping synthesizer 4 on the transmitter side.
Sharing the same channel switching code between the transmitter and the receiver can be done by putting information of the same channel switching code in the ROM section 2 on the transmitter side. Although not described in detail here, hopping synchronization can be realized by a general synchronization capturing circuit and a synchronization tracking circuit.

Finally, a method of selecting a plurality of channel switching codes in constructing the FH communication system will be additionally mentioned.
First, an analog signal generated by an iterative mapping and having a deterministic but chaotic behavior that is irregular, complicated, and has no period is discretized with the total number N of frequency channels. Of a discrete interval which starts with a different initial value in a particular iterative map, or uses a plurality of different iterative maps, or starts using an analog signal as a code for a particular initial value of a particular iterative map. Preliminary calculations are made by shifting the position k, and by simultaneously using the above-mentioned three methods for generating a large number of switching codes, a lot of them are obtained. Then, the number of sets of channel switching codes required for the communication system used is selected by examining the cross-correlation.

[0037]

As described above, in the present invention,
The deterministic, but irregular, complex, and period-free unpredictable behavior generated by iterating a map represented by the difference equation X _{K + 1} = f (X _k ). A channel switching code is a discrete value of an analog signal having a chaotic property. Therefore, it is possible to generate a large number of codes that have essentially no periodicity and are rich in randomness, which is orders of magnitude higher than that of conventional code generation methods. Further, it is possible to provide a code set having a small correlation that makes it difficult for a collision of transmission waves to occur in a frequency hopping communication system. Further, it becomes possible to construct an FH communication system which is much more confidential than before.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating the concept of a system for generating a channel switching code according to the present invention.

FIG. 2 is a diagram showing an example of a conventional frequency channel switching code.

FIG. 3 is a diagram showing an example of digitization in the channel switching code generation method of the present invention.

FIG. 4 is a diagram showing an example of digitization in the channel switching code generation method of the present invention.

FIG. 5 is a diagram showing an example of digitization in the channel switching code generation method of the present invention.

FIG. 6 is a diagram showing an example of digitization in the channel switching code generation method of the present invention.

FIG. 7 is a block diagram of a frequency hopping communication device using the channel switching code generation method of the present invention.

[Explanation of symbols]

 1: Counter part 2: ROM part 3: Latch part 4: Hopping synthesizer 5: 1st order modulator 6: Mixer 7: Bandpass filter 8: Antenna 9: Wideband bandpass filter 10: Narrowband bandpass filter 11: Detector

Claims (5)

[Claims] 1. A channel switching code is obtained by digitizing an analog signal having a chaotic property of irregular and unpredictable behavior obtained by repeatedly performing mapping. Channel switching code generation method. 2. A channel switching code generation system for generating a carrier switching code in a frequency hopping spread spectrum communication system in which a plurality of carriers having different frequencies are sequentially switched to transmit a signal by repeating mapping. A channel-switching code generation method characterized in that a channel-switching code is obtained by digitizing an obtained analog signal having a chaotic property that causes irregular and unpredictable behavior. 3. The channel switching code generating system according to claim 1, wherein the analog signal is digitized according to the number of channels. 4. The channel switching code generation system according to claim 3, further comprising means for calculating to which channel the value of the analog signal at a predetermined time interval corresponds. 5. The channel switching code generation method according to claim 1, wherein a plurality of different iterative mappings are used.