CN111431627A - Dynamic frequency selection method and underwater current field communication method based on dynamic multi-carrier - Google Patents

Dynamic frequency selection method and underwater current field communication method based on dynamic multi-carrier Download PDF

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CN111431627A
CN111431627A CN202010217665.3A CN202010217665A CN111431627A CN 111431627 A CN111431627 A CN 111431627A CN 202010217665 A CN202010217665 A CN 202010217665A CN 111431627 A CN111431627 A CN 111431627A
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chaotic
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CN111431627B (en
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李北明
贾佩松
安澄全
徐以东
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Harbin Engineering University
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/26—Systems using multi-frequency codes
    • H04L27/2601—Multicarrier modulation systems
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B13/00—Transmission systems characterised by the medium used for transmission, not provided for in groups H04B3/00 - H04B11/00
    • H04B13/02—Transmission systems in which the medium consists of the earth or a large mass of water thereon, e.g. earth telegraphy
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/001—Modulated-carrier systems using chaotic signals
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/26—Systems using multi-frequency codes
    • H04L27/2601—Multicarrier modulation systems
    • H04L27/2647—Arrangements specific to the receiver only
    • H04L27/2649—Demodulators
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/26—Systems using multi-frequency codes
    • H04L27/2601—Multicarrier modulation systems
    • H04L27/2647—Arrangements specific to the receiver only
    • H04L27/2655—Synchronisation arrangements
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/26—Systems using multi-frequency codes
    • H04L27/2601—Multicarrier modulation systems
    • H04L27/2647—Arrangements specific to the receiver only
    • H04L27/2655—Synchronisation arrangements
    • H04L27/2657—Carrier synchronisation

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Abstract

The invention belongs to the technical field of underwater current field communication, and particularly relates to a dynamic frequency selection method and an underwater current field communication method based on dynamic multiple carriers. The invention solves the problems of fixed transmitting frequency quantity and poor adaptive channel of the conventional parallel multi-carrier underwater current field communication method, enables each transmitting frequency to have larger energy, better solves the problem of influence of carrier energy on system transmission energy, and better solves the contradiction between transmission efficiency and carrier quantity. The complexity of the communication method of the present invention is increased in order to reduce the number of transmission frequencies, but is also acceptable in the case of the current rapid development of asic circuits.

Description

Dynamic frequency selection method and underwater current field communication method based on dynamic multi-carrier
Technical Field
The invention belongs to the technical field of underwater current field communication, and particularly relates to a dynamic frequency selection method and an underwater current field communication method based on dynamic multiple carriers.
Background
Modern underwater dredging deviceIncreasingly, there are increasing demands on communication efficiency and efficiency. The parallel multi-carrier underwater current field communication is an improved underwater current field communication mode, is an underwater current field communication mode with high communication efficiency, and inherits the advantages of strong anti-interference capability, severe surrounding environment, capability of realizing communication and the like of the conventional underwater current field communication. The number of frequencies transmitted each time by a conventional parallel multi-carrier underwater current field communication mode is fixed r, but when a channel is steep and bad, a large number of r frequencies are still transmitted, so that the receiving error rate is increased, and even communication is interrupted. In order to guarantee the receiving effect, a method of increasing the system power or reducing the number of transmission carriers is generally adopted. A more effective solution is that the number of the carriers sent each time is dynamically changed, and the number of the carriers sent each time is dynamically selected according to the amount of information by using a dynamic frequency selection technology, so that the change of a channel can be adapted, and each sending carrier can have the maximum energy. At present, the belief is that a chaotic array is used for constructing an underwater conduction current field communication system in the research on underwater conduction current field chaotic communication technology (master thesis of Harbin university of engineering, 2018.3, instructor: Libeiming), but the transmission efficiency is very low, only 1 bit of information can be transmitted each time, the safety and confidentiality are poor, and the chaotic array is very easy to crack. The invention provides a dynamic multi-carrier underwater current field communication method, which better solves the problem of influence of carrier energy on system transmission energy and the contradiction between transmission efficiency and carrier quantity. Reducing the number of sending carriers can make the receiving effect better, and is more favorable for distinguishing which carrier is sent to the bottom, so that the energy of each sending carrier can be increased, when r ismaxThe higher the transmission carrier number is, the larger the change of the number of each transmission carrier is, the more obvious the effect of reducing the number of transmission carriers is, and the method has a very wide application prospect.
Disclosure of Invention
The invention aims to provide a dynamic frequency selection method.
The purpose of the invention is realized by the following technical scheme: the method comprises the following steps:
the method comprises the following steps: inputting K bit parallel data, and converting the K bit parallel data into decimal value numerical values;
the K bits of parallel data are noted as:
d＝(dk,dk-1,…,d2,d1),di∈(1,0)；
converting the K bit parallel data into decimal value values according to the corresponding relation:
Figure BDA0002424998280000011
step two: according to the available frequency f of the underwater current field containing M underwater current fields1,f2,..fi..fMFrequency family of (1), successively comparing NdAnd
Figure BDA0002424998280000021
find out to satisfy
Figure BDA0002424998280000022
R ofsAs the minimum number of sequences to be transmitted this time;
rssatisfies the following conditions:
Figure BDA0002424998280000023
the invention also aims to provide the underwater current field communication method based on the dynamic multi-carrier, which solves the problems that the number of the sending frequencies of the conventional parallel multi-carrier underwater current field communication is fixed, the adaptive channel is poor, each sending frequency can have larger energy, the contradiction between the transmission efficiency and the number of the carriers can be better solved, and the number of the sending frequencies is effectively reduced.
The purpose of the invention is realized by the following technical scheme: the method comprises the following steps:
step 1: the transmitting end continuously transmits n frames of information source data according to a K bit frame, fixed synchronous head data is transmitted before the n frames of data are transmitted to carry out system quasi-synchronization, and n frames are transmitted after the synchronous head; the specific steps of the transmitting end for transmitting the signal are as follows:
step 1.1: the transmitting terminal converts every K bits of data in the information source data into parallel data through serial-to-parallel conversion, and the transmission duration of one frame of data is KTd，TdIs the period of the information source;
step 1.2: converting the K bit parallel data into decimal value values;
the K bits of parallel data are noted as:
d＝(dk,dk-1,…,d2,d1),di∈(1,0)；
converting the K bit parallel data into decimal value values according to the corresponding relation:
Figure BDA0002424998280000024
step 1.3: according to the available frequency f of the underwater current field containing M underwater current fields1,f2,..fi..fMFrequency family of (1), successively comparing NdAnd
Figure BDA0002424998280000025
find out to satisfy
Figure BDA0002424998280000026
R ofsAs the minimum number of sequences to be transmitted this time;
rssatisfies the following conditions:
Figure BDA0002424998280000027
step 1.4: selecting r from frequency family for K bit parallel data according to data-frequency selective mappersA frequency to be transmitted, rsEach frequency uses the same initial phase;
the frequency family comprises M usable frequencies f of underwater current fields1,f2,..fi..fMIn all, have
Figure BDA0002424998280000028
The transmission frequency is selectable to enable transmission
Figure BDA0002424998280000029
Bit information data, [ x ]]When the integer part is taken for x, the corresponding information data K transmitted at one time is:
Figure BDA00024249982800000210
step 1.5: extracting selected rsThe transmission frequency time domains are parallelly superposed together to form an underwater current field modulation signal of dynamic multi-carrier, and the superposition time is one frame of data continuous transmission time KTd(ii) a The underwater current field modulation signal of the dynamic multi-carrier is expressed as follows:
Figure BDA0002424998280000031
in the formula (I), the compound is shown in the specification,
Figure BDA0002424998280000032
r selected by data-frequency selective mapper according to transmission informationsA frequency to be transmitted, wherein i is 1,2s(ii) a The other frequencies are
Figure BDA0002424998280000033
Step 1.6: transmitting the underwater current field modulation signal of the dynamic multi-carrier through an underwater electric dipole antenna after power amplification; the underwater current field modulation signal of the dynamic multi-carrier after power amplification is as follows:
Figure BDA0002424998280000034
wherein P is the carrier power;
step 2: after the receiving end realizes quasi-synchronization through the synchronization head, the received signals are input into M chaotic demodulators, and each chaotic demodulator simultaneously inputs different local carrier waves fiFrequency fiFor one frequency in the frequency family, M chaos are obtainedAn output value of the demodulator;
under a Gaussian white noise channel, a receiving end underwater electric dipole antenna receives signals as follows:
r(t)＝s(t-τ)+n(t)+J(t)
in the formula, tau is communication propagation delay; n (t) is white Gaussian noise with double sideband power spectral density of N 02; j (t) is an interference signal;
if the input signal exceeds the range of 5 percent of the local carrier frequency, the chaotic demodulator outputs demodulation information V with the level approximate to 0LA level; if the input signal contains fiThen the chaotic demodulator outputs 1 signal VHA level; the output value of the chaotic demodulator is expressed by the formula:
Figure BDA0002424998280000035
wherein n'i+J′iIs the demodulation of the chaotic demodulator to noise and interference;
and step 3: selecting r with the largest absolute value from the obtained M output values of the chaotic demodulatorsAn output value of r to be selectedsThe frequency corresponding to each output value is used as the sent frequency combination and sent to a frequency-data inverse mapper to demodulate the sent information and restore the received K bit parallel data;
and 4, step 4: performing parallel/serial conversion on the K bit parallel data to obtain K bit reduction information source data; and restoring the n frame data continuously transmitted by the transmitting end into the source data frame by frame.
The present invention may further comprise:
the chaotic demodulator in the step 2 consists of an autocorrelation preprocessing module, a DUFFING chaotic oscillator processing module, a low-pass filtering module, a modulus taking module, a sampling judgment module and a statistic value interference elimination module; the chaotic demodulator realizes demodulation by utilizing the selectivity of the very narrow bandwidth of the DUFFING chaotic oscillator, and comprises the following specific steps:
step 2.1: inputting a received signal r (t) into an autocorrelation preprocessing module, and carrying out autocorrelation operation on r (t) and r (t-tau);
Figure BDA0002424998280000041
wherein τ is time shift, and the output of the autocorrelation operation is:
Figure BDA0002424998280000042
with increasing tau, the autocorrelation R of the noisen(τ) the attenuation is also faster and the noise is more suppressed, but the transmit frequency signal in the received signal is enhanced;
step 2.2: inputting a result R (tau) of the autocorrelation preprocessing module into a DUFFING chaotic oscillator processing module to obtain a value of a first order x in a differential equation of the DUFFING chaotic oscillator; the differential equation of the DUFFING chaotic oscillator is as follows:
Figure BDA0002424998280000043
wherein k is the damping ratio; -x3+0.8x5A non-linear restoring force;
Figure BDA0002424998280000044
is a built-in local carrier signal; gamma ray c1 is the amplitude of the local carrier frequency periodic perturbation force; the local carrier frequency is normalized to omegac＝1；
When the frequency of the input signal s (t) is normalizedsWhen 1 is consistent with local frequency, input signal amplitude is larger than gammasWhen 0.789599290618, the output enters a periodic state: after the frequency of the input signal s (t) exceeds the local frequency and is normalizeds< 0.95 or ωsWhen the output is more than 5% of 1.05, the output enters a chaotic state; the output of the chaotic demodulator can be composed of a chaotic state and a periodic state, and shows that an input signal is opposite to a local carrier fiVery narrow bandwidth with very strong weak signal; if the input signal exceeds the range of 5% of the local carrier frequency, the output is in a chaotic state;
step 2.3:inputting the value of the first order x into a low-pass filter module for filtering, wherein the cut-off frequency of the low-pass filter is less than the local carrier frequency f of the DUFFING chaotic oscillatori(ii) a When the output signal of the DUFFING chaotic oscillator is in a large-scale periodic state, the frequency of the output signal is concentrated on the local carrier frequency fiAnd a local carrier frequency fiAfter low-pass filtering, these signals will be filtered out; when the output signal of the DUFFING chaotic oscillator is in a chaotic state, a continuous spectrum exists on a frequency spectrum, and a low-frequency output signal still exists after low-pass filtering;
step 2.4: inputting the signal output by the low-pass filtering module into a module taking module for processing, and removing negative information;
step 2.5: inputting the signal output by the module taking module into a sampling judgment module, and performing amplitude judgment on the sampled signal after the module taking, wherein a judgment threshold is determined by an amplitude value corresponding to the output value without the signal; when the amplitude is larger than the decision threshold, the output is 0; when the amplitude is smaller than the decision threshold, the output is 1;
step 2.6: inputting the signal output by the sampling judgment module into a statistic value interference elimination module, and eliminating interference of the signal after amplitude judgment by using the statistic value; if the signal after the amplitude judgment comprises the corresponding local carrier frequency fiThen the corresponding output signal is 1 signal VHA high level; if the signal after the amplitude judgment does not comprise the corresponding local carrier frequency fiThe signal, the corresponding position output signal is the demodulation information V with the level of nearly 0LA level; when the input signal frequency exceeds the local frequency signal range by 5%, it is considered not to be within the local frequency signal range.
The synchronization header described in step 1 is designed to send f sequentially1,f2,..fi..fMA total of M frequency signals, each frequency having a duration Td(ii) a F is detected in M chaotic demodulators at a certain moment of a receiving endiA certain local frequency, and f is always detected in orderM(ii) occurs; the quasi-phase synchronization time is determined through synchronous head detection, and the quasi-phase synchronization time is shorter than T because a certain number of carriers are consumed by chaotic array demodulationdBut synchronization requirements can be achieved.
The invention has the beneficial effects that:
the invention solves the problems of fixed transmitting frequency quantity and poor adaptive channel of the conventional parallel multi-carrier underwater current field communication method, enables each transmitting frequency to have larger energy, better solves the problem of influence of carrier energy on system transmission energy, and better solves the contradiction between transmission efficiency and carrier quantity. Selecting r from M frequenciessThe frequency is transmitted in parallel, and the average energy of each sequence transmitted by the underwater current field communication of the conventional parallel multi-carrier is 1/r. The underwater current field communication method based on the dynamic multi-carrier can send r at one time under the same conditionsA sequence (r)sR) average energy per sequence to 1/rs. The complexity of the underwater current field communication method based on the dynamic multi-carrier is higher than that of the conventional parallel multi-carrier underwater current field communication, in order to reduce the number of sending frequencies, the complexity of the communication method is improved, but the complexity can be accepted under the condition of rapid development of the current application-specific integrated circuit.
Drawings
Fig. 1 is a structural diagram of a transmitting process of an underwater current field communication method based on dynamic multi-carrier waves.
Fig. 2 is a receiving process structure diagram of the underwater current field communication method based on dynamic multi-carrier of the present invention.
Fig. 3(a) is a time domain diagram of a chaotic oscillator with the same frequency as the input and local frequency and the amplitude exceeding.
Fig. 3(b) is a chaotic oscillator phase diagram with the same frequency as the input and local frequency.
Fig. 4(a) is a time domain diagram of the chaotic oscillator when the input frequency exceeds the frequency range by 5%.
Fig. 4(b) is a chaotic oscillator phase diagram when the input frequency exceeds the frequency range by 5%.
Fig. 5 is an internal structure view of the chaotic demodulator according to the present invention.
Fig. 6 is a time-frequency spectrum (input signal and local frequency are different) when the output of the improved DUFFING chaotic oscillator is in a chaotic state.
Fig. 7 is a time domain diagram of the signal after passing through the low pass filtering module.
Fig. 8 is a time domain diagram of a signal after passing through a modulus module.
Fig. 9 is a time domain diagram of a signal after passing through a sampling decision module.
Fig. 10 is a time domain diagram of the signal after the interference module is eliminated by statistics.
Detailed Description
The invention is further described below with reference to the accompanying drawings.
The number of the carriers sent by the parallel multi-carrier underwater current field communication method is fixed r, but when a channel is steep and severe, a large number of carriers are still sent, so that the receiving error rate is increased, and even communication is interrupted. In order to guarantee the receiving effect, a method of increasing the system power or reducing the number of transmission carriers is generally adopted. A more effective solution is that the number of the carriers sent each time is dynamically changed, and the number of the carriers sent each time is dynamically selected according to the amount of information by using a dynamic frequency selection technology, so that the change of a channel can be adapted, and each sending carrier can have the maximum energy.
The invention provides an underwater current field communication method based on dynamic multi-carrier, which utilizes a dynamic frequency selector to determine the least number r of sending carriers in the current transmission according to the information quantitysSatisfy r is not less than 1s≤rmax，rmaxThe maximum number of carriers may be transmitted for the system. The receiving end selects r with the maximum absolute value from output signals of M chaotic demodulatorssAn output value (generally these r)sThe frequency corresponding to the value of which is 2-5 times larger than the output value of the non-transmission frequency is used as the frequency combination of transmission, and is larger than a system starting threshold (V)H+n'i+J'i) The value of/2, r with the largest absolute value is selectedsThe frequency corresponding to each output value is used as the transmitted frequency combination, passes through a frequency-data inverse mapper, and is supplemented into K bit data through a dynamic selection restorer to obtain the transmitted data. Underwater based on dynamic multi-carrierThe current field communication method improves the parallel multi-carrier underwater current field communication method, improves the transmission effectiveness of the parallel multi-carrier underwater current field communication, and is superior to the parallel multi-carrier underwater current field communication. In order to improve the transmission effect of the parallel multi-carrier underwater current field communication and effectively reduce the number of transmitted carriers, the invention provides a dynamic multi-carrier underwater current field communication method, and simultaneously, the problem of influence of carrier energy on system transmission energy is well solved, and the contradiction between the transmission efficiency and the number of carriers is well solved. Reducing the number of sending carriers can make the receiving effect better, and is more favorable for distinguishing which carrier is sent to the bottom, so that the energy of each sending carrier can be increased, when r ismaxThe higher the number of each transmission carrier changes, the more obvious the effect of reducing the number of transmission carriers.
A dynamic frequency selector method for determining the least number r of transmitting frequencies in each transmissionsOnce transmitted K bits of data dk,dk-1,…,d2,d1And is recorded as:
d＝(dk,dk-1,…,d2,d1),di∈(1,0)；
converting the K bit data into decimal value values according to the corresponding relation:
Figure BDA0002424998280000071
successive comparisons NdAnd
Figure BDA0002424998280000072
satisfy the requirement of
Figure BDA0002424998280000073
Finding the minimum r satisfying the above formulasAs the minimum number of sequences to be transmitted this time:
rssatisfies the following conditions:
Figure BDA0002424998280000074
an underwater current field communication method based on dynamic multi-carrier waves comprises the following steps:
and a signal sending process:
step 1) the transmitting terminal continuously transmits the information source information according to K bits one frame, and K bit data of each frame transmitted is recorded as dk,dk-1,…,d2,d1Continuously sending n frame data, sending fixed synchronous head data before sending the n frame data to carry out system quasi-synchronization, and sending n frames after sending the synchronous head; every K bit data is firstly converted into parallel data through serial-parallel conversion, and one frame of data is sent for KTd，TdIs the period of the information source;
step 2) sending the K bit sending information sent each time into a serial/parallel converter to obtain K paths of parallel signals; converting the K bit data into decimal value values according to the corresponding relation:
Figure BDA0002424998280000075
successive comparisons NdAnd
Figure BDA0002424998280000076
satisfy the requirement of
Figure BDA0002424998280000077
Finding the minimum r satisfying the above formulasAs the minimum number of sequences to be transmitted this time:
rssatisfies the following conditions:
Figure BDA0002424998280000078
k bits of transmission information equivalent KdBit information (k)dK) or less, and KdThe highest bit of the bit information is 1;
step 3) k obtained in step 2)dPath signal and minimum number of carriers rs(ii) a Will kdThe parallel-path signal is derived from a frequency family (containing M usable frequencies f of underwater current field1,f2,..fi..fM) In which r is selected according to the data-frequency selective mappersOne frequency to be transmitted, in total
Figure BDA0002424998280000079
The transmission frequency is selectable to enable transmission
Figure BDA00024249982800000710
Bit information data, [ x ]]Denotes taking the integer part of x, and rsEach frequency uses the same initial phase; if the frequencies are in one-to-one correspondence with the information data, the information data K transmitted at one time is:
Figure BDA0002424998280000081
extracting selected rsThe transmission frequency time domains are parallelly superposed together to form a modulation signal, and the superposition time lasts for one frame of data transmission time KTdThereby forming a dynamic multi-carrier underwater current field sending signal:
Figure BDA0002424998280000082
in the formula (I), the compound is shown in the specification,
Figure BDA0002424998280000085
selecting r by data-frequency selective mapper according to transmission informationsOne frequency to be transmitted and the rest of the frequencies
Figure BDA0002424998280000086
Step 4) amplifying the power of the underwater current field modulation signal of the dynamic multi-carrier
Figure BDA0002424998280000083
In the formula, P is carrier power, and the obtained signal s (t) is transmitted out through an underwater electric dipole antenna;
and a signal receiving process:
and 5) under a Gaussian white noise channel, receiving signals received by the underwater electric dipole antenna at the receiving end are r (t) ═ s (t-tau) + n (t) + J (t)
In the formula, tau is communication propagation delay; n (t) is white Gaussian noise with double sideband power spectral density of N 02; j (t) is an interference signal; setting M carrier frequencies used by a sending end and a receiving end to be the same, and realizing quasi-synchronization through a synchronization head; inputting the received signals into M chaotic demodulators, and simultaneously inputting different local carriers f into each chaotic demodulatoriOf frequency fiFor one frequency in the frequency family, using the extreme sensitivity of the chaotic demodulator to frequency, the demodulation information V is output at a level of nearly 0 if the input signal is 5% out of the range of the local carrier frequencyLLevel if the input signal contains fiThe chaotic demodulator outputs a 1 signal VHLevel, then the output of the chaotic demodulator is
Figure BDA0002424998280000084
Wherein n'i+J'iIs the demodulation of the chaotic demodulation receiver to noise and interference, and the output of the chaotic demodulator enters n 'in extremely narrow bandwidth due to the extremely narrow bandwidth of the chaotic demodulator'i+J'iAt a very low level;
step 6) selecting r with the largest absolute value from the M output values of the chaotic demodulator obtained in the step 5)sAn output value (generally these r)sThe frequency corresponding to the output value with the value larger than the non-transmission frequency by 2-5 times) is used as the frequency combination of the transmission and is larger than a system starting threshold (V)H+n'i+J'i) The value of/2, r with the largest absolute value is selectedsThe frequency corresponding to each output value is used as the frequency combination to be transmitted and passes through a frequency-data inverse mapper to obtain kdBit parallel information (k)dK) or less, and KdThe highest bit of the bit information is 1;
step 7) kdBit parallel information is converted into k through parallel/serial conversiondBit serial information is supplemented to K bit data by a dynamic selection restorer, and the front end is supplemented with 0 and restored to K bit dataObtaining data sent this time for K bit data; the continuously transmitted n frames of information are restored into the source information frame by frame, and the number of frequencies transmitted each time may be different.
The chaotic demodulator demodulates by using a DUFFING chaotic oscillator; the mathematical model of the demodulation of the DUFFING chaotic oscillator is a differential equation:
Figure BDA0002424998280000091
where k is the damping ratio, -x3+0.8x5The non-linear restoring force is generated,
Figure BDA0002424998280000092
is a built-in local carrier signal, gamma c1 is the amplitude of the local carrier frequency periodic perturbation force, and the local carrier frequency is omegac1 (normalized), when the frequency ω of the input signal s (t)sWhen 1 (normalized) coincides with the local frequency, the input signal amplitude is greater than γs0.789599290618, and an initial value x is 1, and y is 1, the two-way time domain waveform diagram and the phase diagram of the improved system are shown in fig. 3(a) and fig. 3(b), and the output enters a periodic state:
when the frequency of the input signal s (t) exceeds the local frequency ωs< 0.95 or ωsWhen the value is greater than 5% of 1.05 (normalized), the initial value x is 1, the initial value y is 1, the chaotic critical state can be obtained through a differential equation, the time domain waveform diagram and the phase diagram are shown in fig. 4(a) and fig. 4(b), and the output enters the chaotic state;
the output of the chaotic demodulator can be composed of a chaotic state and a periodic state, and shows that an input signal is opposite to a local carrier fiThe signal has very strong weak signal and very narrow bandwidth, and if the input signal exceeds the range of 5% of the local carrier frequency, the output is in a chaotic state; the chaotic demodulator realizes demodulation by utilizing the selectivity of the extremely narrow bandwidth of the DUFFING chaotic oscillator, and consists of an autocorrelation preprocessing module, a DUFFING chaotic oscillator processing module, a low-pass filtering module, a modulus taking module, a sampling judgment module and a statistic value interference elimination module, as shown in FIG. 5;
step (ii) of2.1) inputting the received signal r (t) into an autocorrelation preprocessing module, and carrying out autocorrelation operation on r (t) and r (t-tau)
Figure BDA0002424998280000093
Where τ is time shifted, the output is:
Figure BDA0002424998280000101
with increasing tau, the autocorrelation R of the noisen(τ) the attenuation is also faster and the noise is more suppressed, but the transmit frequency signal in the received signal is enhanced;
step 2.2) inputting the signal of the step 2.1) into an improved DUFFING chaotic oscillator differential equation to obtain a first-order x value;
step 2.3) outputting a value of first order x, inputting the value into a low-pass filter for filtering, wherein the cutoff frequency of the low-pass filter is less than the local carrier frequency f of the improved DUFFING chaotic oscillatori(ii) a When the output signal of the DUFFING chaotic oscillator is in a large-scale periodic state, the frequency of the output signal is concentrated on the local carrier frequency fiAnd a local carrier frequency fiAfter low-pass filtering, these signals will be filtered out; when the output signal of the improved DUFFING chaotic oscillator is in a chaotic state, a continuous spectrum exists on a frequency spectrum, and a low-frequency output signal still exists after low-pass filtering, as shown in fig. 6;
a simulation graph obtained by low-pass filtering the output signal of the DUFFING chaotic oscillator is shown in fig. 6; it can be seen from the figure that if the input signal of the chaotic demodulator includes the corresponding local carrier frequency fiThe amplitude of the corresponding output signal is then almost zero, while the input signal does not include the corresponding local carrier frequency fiWhen the signal is present, the signal still exists, as shown in fig. 7;
step 2.4) performing modulus extraction on the output signal of the step 2.3) to remove negative information, as shown in fig. 8;
step 2.5) making amplitude judgment on the sampling signal subjected to modulus extraction in the step 2.4), wherein a judgment threshold is determined by an amplitude corresponding to an output value of no signal; the decision rule is as follows: when the amplitude is larger than the judgment threshold, the output is 0, and when the amplitude is smaller than the judgment threshold, the output is 1; the amplitude-decided signal, as shown in fig. 9:
step 2.6) eliminating interference of the signals after amplitude judgment by using the statistical value, filtering the signals smaller than the time length as burrs by using a smaller time mine mouth, and then negating the burrs, so that the corresponding local carrier frequency f is includediThen the corresponding output signal is 1 signal VHHigh level, without the input signal including the corresponding local carrier frequency fiThe signal, the corresponding position output signal is the demodulation information V with the level of nearly 0LLevel, as shown in FIG. 10;
compared with other chaotic signal judgment modes, the chaotic demodulator has stronger anti-interference performance, realizes soft judgment with wider application range, has digital signal input and output, and is more favorable for realizing chips such as an FPGA (field programmable gate array).
When the input signal frequency exceeds the local frequency signal range by 5%, it is considered not to be within the local frequency signal range.
The synchronous head is designed to sequentially send f in order to improve the detection effect1,f2,..fi..fMA total of M frequency signals, each frequency having a duration Td(ii) a F is detected in M chaotic demodulators at a certain moment of a receiving endiA certain local frequency, and f is always detected in orderM(ii) occurs; the quasi-phase synchronization time is determined through synchronous head detection, and the quasi-phase synchronization time is shorter than T because a certain number of carriers are consumed by chaotic array demodulationdBut synchronization requirements can be achieved.
The invention aims to provide a dynamic multi-carrier underwater current field communication method for effectively reducing the number of sending frequencies, which solves the problems that the number of sending frequencies of conventional parallel multi-carrier underwater current field communication is fixed, the adaptive channel is poor, each sending frequency can have larger energy, the contradiction between the transmission efficiency and the number of carriers can be better solved, and the receiving effect can be better by reducing the number of the sending carriers. Compared with the prior art, the method solves the problems of fixed transmitting frequency quantity and poor adaptive channel of the conventional parallel multi-carrier underwater current field communication method, enables each transmitting frequency to have larger energy, better solves the problem of influence of carrier energy on system transmission energy, and better solves the contradiction between transmission efficiency and carrier quantity.
Selecting r from M frequenciessTransmitting and transmitting in parallel by each frequency, wherein the average energy of each sequence transmitted by the underwater current field communication of the conventional parallel multi-carrier is 1/r; and a dynamic multi-carrier underwater current field communication method can send r under the same conditionsA sequence (r)sR) average energy per sequence to 1/rs. The complexity of the dynamic multi-carrier underwater current field communication method is higher than that of the conventional parallel multi-carrier underwater current field communication, and in order to reduce the number of sending frequencies, the complexity of the communication method is improved, but the complexity can be accepted under the condition of rapid development of the current application-specific integrated circuit.
Example 1:
with reference to fig. 1, the signaling process:
an underwater current field communication method based on dynamic multi-carrier adopts the same system parameters as the conventional parallel multi-carrier underwater current field communication method, and the information source period is vb0.02 sec, source rate vb50bps from a frequency family (ranging from 2000Hz to 5000Hz, respectively f1,f2,..fi..fM) The maximum frequency number r is selected from the available frequencies of the total containing M-16 underwater current fieldsmaxTransmitting at most 3 times
Figure BDA0002424998280000111
Bit data;
step 1), the transmitting terminal continuously transmits the information source information according to a frame with K being 9 bits, and 9 bits of data of each frame are recorded as dk,dk-1,…,d2,d1Continuously transmitting n frames of data, transmitting fixed sync header data before transmission of the n frames of dataCarrying out system quasi-synchronization, and sending n frames after synchronizing the head; every K bit data is firstly converted into parallel data through serial-parallel conversion, and the transmission duration of one frame of data is 9Td，TdFor the source period, assume that a certain frame transmits information dk,dk-1,…,d2,d1＝000001110；
Step 2) sending the 9-bit sending information sent each time into a serial/parallel converter to obtain 9 paths of parallel signals; and converting the 9-bit data into decimal value values according to the corresponding relation:
Figure BDA0002424998280000112
successive comparisons NdAnd
Figure BDA0002424998280000121
satisfy the requirement of
Figure BDA0002424998280000122
Finding the minimum r satisfying the above formulasAs the minimum number of sequences to be transmitted this time:
rssatisfies the following conditions:
Figure BDA0002424998280000123
Figure BDA0002424998280000124
9-bit transmission information equivalent kd4-bit information (k)dK is 4 ≦ K9), and K isdThe highest bit of the 4-bit information is 1;
step 3) k obtained in step 2)d4-channel signal and minimum carrier number r s1 is ═ 1; will kdFrom a frequency family (containing M16 underwater current field available frequencies f) 4 parallel signals1,f2,..fi..f16) In which r is selected according to the data-frequency selective mapper s1 frequency to be transmitted, in total
Figure BDA0002424998280000125
The transmission frequency is selectable to enable transmission
Figure BDA0002424998280000126
Bit information data, [ x ]]Denotes taking the integer part of x, and rsThe same initial phase is used for 1 frequency; and if the frequencies are in one-to-one correspondence with the information data, the corresponding information data K sent this time is as follows:
Figure BDA0002424998280000127
extracting selected r s1 transmitting frequency time domains are overlapped in parallel to form a modulation signal, and the overlapping time lasts for 9T of frame data transmitting timedThereby forming a dynamic multi-carrier underwater current field sending signal:
Figure BDA0002424998280000128
in the formula (I), the compound is shown in the specification,
Figure BDA0002424998280000129
selecting r by data-frequency selective mapper according to transmission information s1 frequency to be transmitted, the remaining frequencies being
Figure BDA00024249982800001210
Because the number of the frequencies which are dynamically selected to be sent is only 1, the carrier amplitude at the moment is larger than r than that of the original parallel multi-carrier underwater current field communication methodsThe carrier energy is increased, which is beneficial to receiving and judging;
step 4) amplifying the power of the underwater current field modulation signal of the dynamic multi-carrier
Figure BDA00024249982800001211
In the formula, P is carrier power, and the obtained signal s (t) is transmitted out through an underwater electric dipole antenna;
and a signal receiving process:
and 5) under a Gaussian white noise channel, receiving signals received by the underwater electric dipole antenna at the receiving end are r (t) ═ s (t-tau) + n (t) + J (t)
In the formula, tau is communication propagation delay; n (t) is white Gaussian noise with double sideband power spectral density of N 02; j (t) is an interference signal; setting M used by a sending end and a receiving end to be the same as 16 carrier frequencies, and realizing quasi-synchronization through a synchronization head; inputting the received signals into M-16 chaotic demodulators, and simultaneously inputting different local carriers f into each chaotic demodulatoriOf frequency fiFor one frequency in the frequency family, using the extreme sensitivity of the chaotic demodulator to frequency, the demodulation information V is output at a level of nearly 0 if the input signal is 5% out of the range of the local carrier frequencyLLevel if the input signal contains fiThe chaotic demodulator outputs a 1 signal VHLevel, then the output of the chaotic demodulator is
Figure BDA0002424998280000131
Wherein n'i+J'iIs the demodulation of the chaotic demodulation receiver to noise and interference, and the output of the chaotic demodulator enters n 'in extremely narrow bandwidth due to the extremely narrow bandwidth of the chaotic demodulator'i+J'iAt a very low level;
step 6) selecting r with the largest absolute value from the output values of 16 chaotic demodulators obtained in the step 5)s1 output value (typically these r s1 value greater than 2-5 times the output value without transmission frequency) as the frequency combination of transmission, and is greater than a system start threshold (V)H+n'i+J'i) The value of/2, r with the largest absolute value is selectedsThe frequency corresponding to 1 output value is used as the frequency combination of transmission to pass through a frequency-data inverse mapper to obtain kd4-bit parallel information (k)d9 or less), and kdHighest bit informationA bit is 1; (ii) a
Step 7) kdParallel-to-serial conversion of 4-bit parallel information to kdSupplementing the serial information into 9-bit data through a dynamic selection restorer, supplementing 0 to the front end of the serial information into K-9-bit data, and obtaining the data transmitted at this time; the continuously transmitted n frames of information are restored into the source information frame by frame, and the number of frequencies transmitted each time may be different.
The chaotic demodulator used in the underwater current field communication method based on the dynamic multi-carrier waves uses a DUFFING chaotic oscillator for demodulation; the synchronous head used in the underwater current field communication method based on the dynamic multi-carrier is designed to sequentially send f1,f2,..fi..f16And M is 16 frequency signals.
The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (4)

1. A method of dynamic frequency selection, comprising the steps of:
the method comprises the following steps: inputting K bit parallel data, and converting the K bit parallel data into decimal value numerical values;
the K bits of parallel data are noted as:
d＝(dk,dk-1,…,d2,d1),di∈(1,0)；
converting the K bit parallel data into decimal value values according to the corresponding relation:
Figure FDA0002424998270000011
step two: according to the available frequency f of the underwater current field containing M underwater current fields1,f2,..fi..fMFrequency family of (1), successively comparing NdAnd
Figure FDA0002424998270000012
find out to satisfy
Figure FDA0002424998270000013
R ofsAs the minimum number of sequences to be transmitted this time;
rssatisfies the following conditions:
Figure FDA0002424998270000014
2. an underwater current field communication method based on dynamic multi-carrier is characterized by comprising the following steps:
step 1: the transmitting end continuously transmits n frames of information source data according to a K bit frame, fixed synchronous head data is transmitted before the n frames of data are transmitted to carry out system quasi-synchronization, and n frames are transmitted after the synchronous head; the specific steps of the transmitting end for transmitting the signal are as follows:
step 1.1: the transmitting terminal converts every K bits of data in the information source data into parallel data through serial-to-parallel conversion, and the transmission duration of one frame of data is KTd，TdIs the period of the information source;
step 1.2: converting the K bit parallel data into decimal value values;
the K bits of parallel data are noted as:
d＝(dk,dk-1,…,d2,d1),di∈(1,0)；
converting the K bit parallel data into decimal value values according to the corresponding relation:
Figure FDA0002424998270000015
step 1.3: according to the available frequency f of the underwater current field containing M underwater current fields1,f2,..fi..fMFrequency family of (1), successively comparing NdAnd
Figure FDA0002424998270000016
find out to satisfy
Figure FDA0002424998270000017
R ofsAs the minimum number of sequences to be transmitted this time;
rssatisfies the following conditions:
Figure FDA0002424998270000018
step 1.4: selecting r from frequency family for K bit parallel data according to data-frequency selective mappersA frequency to be transmitted, rsEach frequency uses the same initial phase;
the frequency family comprises M usable frequencies f of underwater current fields1,f2,..fi..fMIn all, have
Figure FDA0002424998270000019
The transmission frequency is selectable to enable transmission
Figure FDA0002424998270000021
Bit information data, [ x ]]When the integer part is taken for x, the corresponding information data K transmitted at one time is:
Figure FDA0002424998270000022
step 1.5: extracting selected rsThe transmission frequency time domains are parallelly superposed together to form an underwater current field modulation signal of dynamic multi-carrier, and the superposition time is one frame of data continuous transmission time KTd(ii) a The underwater current field modulation signal of the dynamic multi-carrier is expressed as follows:
Figure FDA0002424998270000023
in the formula (I), the compound is shown in the specification,
Figure FDA0002424998270000024
r selected by data-frequency selective mapper according to transmission informationsA frequency to be transmitted, wherein i is 1,2s(ii) a The other frequencies are
Figure FDA0002424998270000025
Step 1.6: transmitting the underwater current field modulation signal of the dynamic multi-carrier through an underwater electric dipole antenna after power amplification; the underwater current field modulation signal of the dynamic multi-carrier after power amplification is as follows:
Figure FDA0002424998270000026
wherein P is the carrier power;
step 2: after the receiving end realizes quasi-synchronization through the synchronization head, the received signals are input into M chaotic demodulators, and each chaotic demodulator simultaneously inputs different local carrier waves fiFrequency fiObtaining output values of M chaotic demodulators for one frequency in a frequency family;
under a Gaussian white noise channel, a receiving end underwater electric dipole antenna receives signals as follows:
r(t)＝s(t-τ)+n(t)+J(t)
in the formula, tau is communication propagation delay; n (t) is white Gaussian noise with double sideband power spectral density of N02; j (t) is an interference signal;
if the input signal exceeds the range of 5 percent of the local carrier frequency, the chaotic demodulator outputs demodulation information V with the level approximate to 0LA level; if the input signal contains fiThen the chaotic demodulator outputs 1 signal VHA level; the output value of the chaotic demodulator is expressed by the formula:
Figure FDA0002424998270000027
wherein n'i+J′iIs the demodulation of the chaotic demodulator to noise and interference;
and step 3: selecting r with the largest absolute value from the obtained M output values of the chaotic demodulatorsAn output value of r to be selectedsThe frequency corresponding to each output value is used as the sent frequency combination and sent to a frequency-data inverse mapper to demodulate the sent information and restore the received K bit parallel data;
and 4, step 4: performing parallel/serial conversion on the K bit parallel data to obtain K bit reduction information source data; and restoring the n frame data continuously transmitted by the transmitting end into the source data frame by frame.
3. The underwater current field communication method based on the dynamic multi-carrier wave as claimed in claim 2, characterized in that: the chaotic demodulator in the step 2 consists of an autocorrelation preprocessing module, a DUFFING chaotic oscillator processing module, a low-pass filtering module, a modulus taking module, a sampling judgment module and a statistic value interference elimination module; the chaotic demodulator realizes demodulation by utilizing the selectivity of the very narrow bandwidth of the DUFFING chaotic oscillator, and comprises the following specific steps:
step 2.1: inputting a received signal r (t) into an autocorrelation preprocessing module, and carrying out autocorrelation operation on r (t) and r (t-tau);
Figure FDA0002424998270000031
wherein τ is time shift, and the output of the autocorrelation operation is:
Figure FDA0002424998270000032
with increasing tau, the autocorrelation R of the noisen(τ) the attenuation is also faster and the noise is more suppressed, but the transmit frequency signal in the received signal is enhanced;
step 2.2: inputting a result R (tau) of the autocorrelation preprocessing module into a DUFFING chaotic oscillator processing module to obtain a value of a first order x in a differential equation of the DUFFING chaotic oscillator; the differential equation of the DUFFING chaotic oscillator is as follows:
Figure FDA0002424998270000033
wherein k is the damping ratio; -x3+0.8x5A non-linear restoring force;
Figure FDA0002424998270000034
is a built-in local carrier signal; gamma rayc1 is the amplitude of the local carrier frequency periodic perturbation force; the local carrier frequency is normalized to omegac＝1；
When the frequency of the input signal s (t) is normalizedsWhen 1 is consistent with local frequency, input signal amplitude is larger than gammasWhen 0.789599290618, the output enters a periodic state: after the frequency of the input signal s (t) exceeds the local frequency and is normalizeds< 0.95 or ωsWhen the output is more than 5% of 1.05, the output enters a chaotic state; the output of the chaotic demodulator can be composed of a chaotic state and a periodic state, and shows that an input signal is opposite to a local carrier fiVery narrow bandwidth with very strong weak signal; if the input signal exceeds the range of 5% of the local carrier frequency, the output is in a chaotic state;
step 2.3: inputting the value of the first order x into a low-pass filter module for filtering, wherein the cut-off frequency of the low-pass filter is less than the local carrier frequency f of the DUFFING chaotic oscillatori(ii) a When the output signal of the DUFFING chaotic oscillator is in a large-scale periodic state, the frequency of the output signal is concentrated on the local carrier frequency fiAnd a local carrier frequency fiAfter low-pass filtering, these signals will be filtered out; when the output signal of the DUFFING chaotic oscillator is in a chaotic state, a continuous spectrum exists on a frequency spectrum, and a low-frequency output signal still exists after low-pass filtering;
step 2.4: inputting the signal output by the low-pass filtering module into a module taking module for processing, and removing negative information;
step 2.5: inputting the signal output by the module taking module into a sampling judgment module, and performing amplitude judgment on the sampled signal after the module taking, wherein a judgment threshold is determined by an amplitude value corresponding to the output value without the signal; when the amplitude is larger than the decision threshold, the output is 0; when the amplitude is smaller than the decision threshold, the output is 1;
step 2.6: inputting the signal output by the sampling judgment module into a statistic value interference elimination module, and eliminating interference of the signal after amplitude judgment by using the statistic value; if the signal after the amplitude judgment comprises the corresponding local carrier frequency fiThen the corresponding output signal is 1 signal VHA high level; if the signal after the amplitude judgment does not comprise the corresponding local carrier frequency fiThe signal, the corresponding position output signal is the demodulation information V with the level of nearly 0LA level; when the input signal frequency exceeds the local frequency signal range by 5%, it is considered not to be within the local frequency signal range.
4. The underwater current field communication method based on the dynamic multi-carrier wave as claimed in claim 2 or 3, characterized in that: the synchronization header described in step 1 is designed to send f sequentially1,f2,..fi..fMA total of M frequency signals, each frequency having a duration Td(ii) a F is detected in M chaotic demodulators at a certain moment of a receiving endiA certain local frequency, and f is always detected in orderM(ii) occurs; the quasi-phase synchronization time is determined through synchronous head detection, and the quasi-phase synchronization time is shorter than T because a certain number of carriers are consumed by chaotic array demodulationdBut synchronization requirements can be achieved.
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