CN110266622A - A kind of orthogonal multiple carrier M member chaos phase modulation spread-spectrum underwater sound communication method - Google Patents
A kind of orthogonal multiple carrier M member chaos phase modulation spread-spectrum underwater sound communication method Download PDFInfo
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
- H04B1/69—Spread spectrum techniques
- H04B1/707—Spread spectrum techniques using direct sequence modulation
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/001—Modulated-carrier systems using chaotic signals
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/18—Phase-modulated carrier systems, i.e. using phase-shift keying
- H04L27/20—Modulator circuits; Transmitter circuits
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/18—Phase-modulated carrier systems, i.e. using phase-shift keying
- H04L27/22—Demodulator circuits; Receiver circuits
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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
- H04L27/2626—Arrangements specific to the transmitter only
- H04L27/2627—Modulators
- H04L27/2628—Inverse Fourier transform modulators, e.g. inverse fast Fourier transform [IFFT] or inverse discrete Fourier transform [IDFT] modulators
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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
- H04L27/2647—Arrangements specific to the receiver only
- H04L27/2649—Demodulators
- H04L27/265—Fourier transform demodulators, e.g. fast Fourier transform [FFT] or discrete Fourier transform [DFT] demodulators
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/32—Carrier systems characterised by combinations of two or more of the types covered by groups H04L27/02, H04L27/10, H04L27/18 or H04L27/26
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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
- H04L27/2647—Arrangements specific to the receiver only
- H04L27/2655—Synchronisation arrangements
- H04L27/2656—Frame synchronisation, e.g. packet synchronisation, time division duplex [TDD] switching point detection or subframe synchronisation
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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
- H04L27/2647—Arrangements specific to the receiver only
- H04L27/2655—Synchronisation arrangements
- H04L27/2657—Carrier synchronisation
Abstract
The invention discloses a kind of orthogonal multiple carrier M member chaos phase modulation spread-spectrum underwater sound communication methods, the described method includes: the input message sequence that information source issues is divided into the information sequence that K group length is a+2 by step 1) transmitting terminal, it is respectively fed in K burster, each burster, which respectively spreads preceding a progress M member chaos phase modulation, to be mapped, obtain a chaos phase modulation spreading code, the chaos phase modulation spreading code recycled after QPSK modulation progress band spectrum modulation, which is carried out, to latter 2 obtains baseband signal, then K group baseband signal is respectively mapped to carry out OFDM modulation on the subcarrier of OFDM symbol, it obtains digital signal to be launched and is emitted；Step 2) receiving end, as pilot signal, is carried out time-frequency two-dimensional search to received digital signal and completes Time and Frequency Synchronization using one section of chaos phase modulation spread-spectrum signal in OFDM symbol；Then it carries out OFDM demodulation and obtains K group baseband signal, input K combiner respectively and complete despreading and QPSK demodulation, obtain binary sequence.
Description
Technical field
The present invention relates to technical field of underwater acoustic communication, and in particular to a kind of orthogonal multiple carrier M member chaos phase modulation spread spectrum underwater sound
Communication means.
Background technique
Underwater acoustic channel is the letter that bandwidth is limited, Multi-path interference is complicated, the serious time-varying of ambient noise, space-variant and frequency become
Road, the complexity of channel seriously limit the communication performance of underwater sound communication.Spread spectrum communication has good due to the presence of spreading gain
Good antinoise and anti-multipath jamming characteristic, is widely used in remote water sound communication field.However due to by underwater acoustic channel
The limitation of bandwidth, spread spectrum communication traffic rate is lower, can only often meet tens bits per second even transmission of several bits
Rate, therefore practicability is by larger limitation.
It is difficult between the spreading code that data transfer rate is further improved, however is overlapped mutually using combination spread spectrum communication mode
It is completely orthogonal to guarantee, therefore there are interchannels to interfere with each other, and reduces the bit error rate performance of system；Utilize biorthogonal channel
Cyclic shift keying spread spectrum communication mode, by modulates information in symbol phases, using symbol phases size indicate information, one
Aspect further improves bandwidth availability ratio, on the other hand solves the problems, such as interchannel interference by orthogonal channel；Using just
Multi-carrier spread spectrum (Orthogonal Multi-carrier Spread Spectrum, the OMCSS) mode of friendship, by the letter after spread spectrum
Number simultaneously be modulated in multiple orthogonal sub-carriers, and combine cyclic shift keying and M member band spectrum modulation, further improve communication
Rate.However above-mentioned time domain spread spectrum scheme is limited for spread spectrum communication improved efficiency, and in the underwater sound condition of channel architecture complexity
Under, communication performance is restricted.Furthermore pseudorandom (Pseudo-Noise, PN) the sequence tool that above-mentioned traditional band spectrum modulation uses
There are the features such as apparent periodical and two-value, once signal is trapped, the individual features such as spreading rate and code period are easy quilt
Enemy extracts and utilizes, and leads to information leakage, does not have confidential nature.
Summary of the invention
It is an object of the present invention to further increase the logical of underwater sound spread-spectrum communication to solve above-mentioned the deficiencies in the prior art
Believe rate, while improving the security performance of spread-spectrum signal, provides a kind of high reliablity, good confidentiality, communication efficiency the high underwater sound
Communication means.
In order to achieve the above objectives, the present invention provides a kind of orthogonal multiple carrier M member chaos phase modulation spread-spectrum underwater sound communication method,
The method includes:
The input message sequence that step 1) transmitting terminal issues information source is according to every mono- group of carry out sequence string of (a+2) bit and turns
It changes, obtains K group length and be the information sequence of a+2, and be respectively fed in K burster, each burster is respectively to a first
The spread spectrum mapping of M member chaos phase modulation is carried out, a chaos phase modulation spreading code is obtained, to recycling after rear 2 progress QPSK modulation
To chaos phase modulation spreading code carry out band spectrum modulation obtain baseband signal, then by K group baseband signal be respectively mapped to OFDM accord with
Number subcarrier on carry out OFDM modulation, obtain digital signal to be launched, digital signal to be launched be finally converted into water
Acoustical signal is simultaneously emitted；
The underwater sound signal received is converted to digital signal by step 2) receiving end, using one section of chaos phase modulation in OFDM symbol
Spread-spectrum signal is as pilot signal, using the spreading gain of chaos phase modulation spreading code, carries out time-frequency two-dimensional search to digital signal
Complete Time and Frequency Synchronization；Then OFDM demodulation is carried out to the signal after completion Time and Frequency Synchronization and obtains K group baseband signal, input K respectively
A combiner completes despreading and QPSK demodulation, obtains binary sequence.
As a kind of improvement of the above method, the step 1) is specifically included:
Step 1-1) it maps to obtain original chaos sequence using Quadratic, M are thus generated for modulation intelligence sequence
Spreading code and one be used for Time and Frequency Synchronization pilot frequency sequence, spreading length is respectively N and D；M spreading code of generation is formed
One chaos phase modulation Spread Spectrum Sequence Set { c1,c2,...,cM}；
Step 1-2) the transmitting terminal input message sequence that issues information source according to per mono- group of progress sequence string of (a+2) bit simultaneously
Conversion obtains K group length and is the information sequence of a+2, and is respectively fed in K burster；
Step 1-3) each burster carries out segment processing to (a+2) bit information of input, will wherein before a progress M it is first
Mapping, remaining 2 information carry out QPSK mapping；Then k-th of burster obtains the M binary data x after the mapping of M memberk, select mixed
Xth in ignorant phase modulation frequency expansion sequence set in M frequency expansion sequencekA spreading code obtains corresponding spreading code as output
D (k) is obtained after QPSK mapping, and utilizes spreading codeTo obtaining base band corresponding with k-th of burster after d (k) band spectrum modulation
Signal b (n):
Wherein n=0,1..., KN, q=n-kN, k=1 ... K,Represent spreading codeQ-th of chip；
Step 1-4) each burster exports the baseband signal that a length is N, by K group baseband signal and pilot frequency sequence one
One is mapped on L subcarrier of OFDM symbol, obtains total baseband signal, IFFT transformation is carried out to total baseband signal, when obtaining
Domain signal S (t) are as follows:
Wherein, fnFor the frequency of each subcarrier, T is the time span of an OFDM symbol, TgFor the time of cyclic prefix
Length, T '=T+Tg；Complete M member CPM spread spectrum OFDM signal indicates are as follows:
Wherein, b (n, i) is the data modulated on n-th of subcarrier in i-th of symbol, and g (t) is the arteries and veins of each symbol
Waveform is rushed, is indicated are as follows:
As a kind of improvement of the above method, the step 1-1) it specifically includes:
Step 1-1-1) it maps to obtain original Constructing Chaotic Code using Quadratic, mapping equation indicates are as follows:
Y (m+1)=P-Qy2(m)
Wherein, as 3/4 < PQ < 2, original Constructing Chaotic Code y (m) ∈ (- 2/Q, 2/Q), Q=4, P=1/4, y (0) ∈ (-
0.5,0.5), (- 0.5,0.5) y (m) ∈, m is positive integer；
Step 1-1-2) y (m) quantified without two-value is modulated in complex exponential, generate chaos phase modulation spreading code c, c packet
Containing N number of chip, wherein q-th of chip are as follows:
C (q)=exp { j2 π y (q) }, q=0,1...N-1
Step 1-1-3) selection M mutually orthogonal chaos phase modulation spreading codes composition M member chaos phase modulation spread spectrum code sequence collection
Close { c1,c2,...,cM}；
Step 1-1-4) utilize original chaos sequence y (m) one section of fixed chaos phase modulation spreading code of generation, spread code length
For D, using the spreading code as pilot frequency sequence.
As a kind of improvement of the above method, the step 1-2) in a are as follows:
As a kind of improvement of the above method, the step 1-2) in K size by chaos phase modulation spreading code length N
Determine that relationship meets with the subcarrier number L of a multicarrier M member chaos phase modulation spread spectrum symbol S:
K×N+D≤L。
As a kind of improvement of the above method, the step 2) is specifically included:
Step 2-1) receiving end carries out Time and Frequency Synchronization to the ofdm signal that receives；
Step 2-2) Fourier transformation is done within the period [iT ', iT '+T] to the signal r (t) after synchronizing, it is obtained by formula (7)
Signal into i-th of symbol of output on n-th of subcarrier are as follows:
Wherein,For phase deviation caused by synchronous error；
Step 2-3) the M member coherently despreading on frequency domain is carried out to the spread-spectrum signal of distribution on different sub-carriers；
Assuming that the position of k-th of spread-spectrum signal to be de-spread on sub-carriers in i-th of OFDM symbol is γ=[0 1
... N-1], then the process of coherently despreading are as follows:
Wherein, rniAccording to k-th of spread-spectrum signal, the position in subcarrier carries out subcarrier pumping to i-th of OFDM symbol for representative
Baseband signal after taking, cpP-th of spreading code of M member chaos phase modulation frequency expansion sequence concentration is represented,Expression takes conjugate operation,
For rniWith cpThe result obtained after despreading；According toThe data x of available M systemkEstimated value:
To M systemIt carries out inverse mapping and obtains corresponding a bit information；
Step 2-4) it enablesIt is rightProgress QPSK inverse mapping, which can demodulate, obtains rear 2 bit informations；
Step 2-5) by a bit obtained in step 2-3) and step 2-4) and 2 bit informations input k-th of combiner into
Row combination obtains kth group information sequence；
Step 2-6) repeat step 2-5) demodulation obtains whole K group information sequences, and this K group information sequence is carried out and gone here and there
It is converted to final demodulating information sequence.
As a kind of improvement of the above method, the step 2-1) it specifically includes:
Step 2-1-1) with the time delay interception OFDM symbol to be synchronized of a time domain step-size in search, according to frequency domain Variable sampling
Algorithm carries out high-resolution FFT transform to time-domain OFDM symbol, obtains the frequency spectrum that each subcarrier is moved after by doppler interference；
Step 2-1-2) sub-carrier positions of pilot signal, and root are calculated with the Doppler factor of frequency domain search step-length
Above-mentioned frequency spectrum is extracted nearby according to obtained position, obtains baseband signal corresponding with pilot signal；
Step 2-1-3) above-mentioned baseband signal and the chaos phase modulation for being used for Time and Frequency Synchronization that receiving end generates are spread
Code carries out frequency domain spread spectrum despreading, finds out result of the energy value as this frequency domain search of despread result；
Step 2-1-4) with above-mentioned frequency domain search step-length update frequency domain search Doppler factor, in search range according to
Step 2-1-2) to the process iterative search of step 2-1-3), the maximum value of each secondary frequency domain search result is found out as this time domain
The result of search；
Step 2-1-5) with above-mentioned time domain step-size in search update time delay, according to step 2-1-1) to step in search range
Process iterative search 2-1-4), finds out the maximum value of each secondary time domain search result, and calculates this time and search for corresponding Doppler
The factor and time delay obtain the Domain Synchronous of Doppler's estimated value and OFDM symbol that signal demodulation needs as final output
Point.
The present invention has the advantages that
1, method of the invention is using CPM sequence as frequency domain spread spectrum code, and it is higher to combine orthogonal multiple carrier technology to obtain
Traffic rate, superposition QPSK modulation further improves band efficiency on M member spread spectrum；Remove system performance after CP is protected
It will not be decreased obviously, communication efficiency is further improved while not influencing reliability；In addition, CPM sequence takes full advantage of
The excellent correlation properties of chaos sequence overcome the bad disadvantage of regular PN sequence cross-correlation, while having generation simply, quantity
Huge feature；
2, method combination frequency domain M member of the invention spread spectrum and orthogonal multiple carrier technology, and introduce CPM sequence and propose that one kind is new
Orthogonal multiple carrier M member chaos phase modulation spread-spectrum underwater sound communication mode, greatly improved while guaranteeing communications errors performance
Traffic rate, and it is applicable to secrecy underwater sound communication.
Detailed description of the invention
Fig. 1 is orthogonal multiple carrier M member chaos phase modulation spread-spectrum underwater sound communication method flow chart of the invention；
Fig. 2 is that orthogonal multiple carrier M member chaos phase modulation spread-spectrum underwater sound communication Time and Frequency Synchronization of the invention realizes schematic diagram.
Specific embodiment
Below with reference to specific drawings and examples to a kind of orthogonal multiple carrier M member chaos phase modulation spread spectrum water provided by the invention
Acoustic communication method (M-ary Chaotic Phase Modulation Orthogonal Multi-carrier Spread
Spectrum, M-ary CPM-OMCSS) do further explaination.
Orthogonal multiple carrier M member chaos phase modulation spread-spectrum underwater sound communication method flow chart provided by the invention, as shown in Figure 1, tool
Body is described as follows:
Step 1: it maps to obtain original Constructing Chaotic Code using Quadratic, mapping equation indicates are as follows:
Y (m+1)=P-Qy2(m) (1)
Wherein, as 3/4 < PQ < 2, original Constructing Chaotic Code y (m) ∈ (- 2/Q, 2/Q), Q=4, P=1/4, y (0) ∈ (-
0.5,0.5), (- 0.5,0.5) y (m) ∈, m is positive integer；
The y (m) quantified without two-value is modulated in complex exponential, chaos phase modulation spreading code c is generated, c includes N number of chip,
Wherein q-th of chip are as follows:
C (q)=exp { j2 π y (q) }, q=0,1...N-1 (2)
M mutually orthogonal chaos phase modulation spreading codes are selected to form M member chaos phase modulation spread spectrum code sequence set { c1,
c2,...,cM}；
Step 2: utilization original Constructing Chaotic Code y (m) one section of fixed chaos phase modulation spreading code of generation, spread code length D,
Using the spreading code as pilot frequency sequence.
Step 3: input message sequence according to mono- group of carry out sequence serioparallel exchange of every a+2bit, is obtained K by communication transmitting terminal
Group length is the information sequence of a+2, and is respectively fed in K burster, as shown in Figure 1.Wherein the size of K is by chaos tune
The subcarrier number L of the length N of phase spreading code and a multicarrier M member chaos phase modulation spread spectrum symbol S determine that relationship meets:
K×N+D≤L。
Each burster carries out segment processing to (a+2) bit information of input, will wherein before a progress M member mappings, it is surplus
2 remaining information carry out QPSK mapping；Then k-th of burster obtains the M binary data x after the mapping of M memberk, select chaos phase modulation
Xth in frequency expansion sequence set in M frequency expansion sequencekA spreading code obtains corresponding spreading code as outputIt is wherein each
The selection mode of spreading code has M kind, therefore the value of corresponding a are as follows:
In formulaRepresent downward round numbers operation.
D (k) is obtained after QPSK mapping, and utilizes spreading codeTo being obtained after d (k) band spectrum modulation and k-th of burster pair
The baseband signal b (n) answered:
Wherein n=0,1..., KN, q=n-kN, k=1 ... K,Represent spreading codeQ-th of chip；
Step 4: the baseband signal that the above-mentioned corresponding length of each burster is N, by K group baseband signal and pilot tone sequence
Column are mapped to one by one on L subcarrier of OFDM symbol, total baseband signal that total length is K × N+D are obtained, to total baseband signal
It does IFFT transformation to carry out, time-domain signal S (t) can be obtained are as follows:
Wherein, fnFor the frequency of each subcarrier, T is the time span of an OFDM symbol, TgFor the time of cyclic prefix
Length, T '=T+Tg；To which complete M member CPM spread spectrum OFDM signal can indicate are as follows:
Wherein, b (n, i) is the data modulated on n-th of subcarrier in i-th of symbol, and g (t) is the arteries and veins of each symbol
Waveform is rushed, is defined as:
Step 5: receiving end carries out Time and Frequency Synchronization to it after receiving signal, as shown in Fig. 2, the Domain Synchronous includes:
Step 5-1) with the time delay interception OFDM symbol to be synchronized of a time domain step-size in search, it is calculated according to frequency domain Variable sampling
Method carries out high-resolution FFT transform to time-domain OFDM symbol, obtains the frequency spectrum that each subcarrier is moved after by doppler interference；
Step 5-2) with the sub-carrier positions of the Doppler factor calculating pilot signal of a frequency domain search step-length, and according to
Above-mentioned frequency spectrum is extracted in obtained position nearby, obtains baseband signal corresponding with pilot signal；
Step 5-3) the chaos phase modulation spreading code for being used for Time and Frequency Synchronization that generates above-mentioned baseband signal and receiving end
Frequency domain spread spectrum despreading is carried out, result of the energy value as this frequency domain search of despread result is found out；
Step 5-4) with the Doppler factor of above-mentioned frequency domain search step-length update frequency domain search, according to step in search range
Rapid 5-2) to the process iterative search of step 5-3), the maximum value of each secondary frequency domain search result is found out as domain search when this
As a result；
Step 5-5) with above-mentioned time domain step-size in search update time delay, according to step 5-1) to step 5-4) in search range
Process iterative search, find out the maximum value of each secondary time domain search result, and calculate this time search for corresponding Doppler factor and
Time delay obtains the Domain Synchronous point of Doppler's estimated value and OFDM symbol that signal demodulation needs as final output.
Fourier transformation is done to reception signal within the period [iT ', iT '+T] to the signal after synchronizing, is obtained by formula (7)
Signal in i-th of symbol of output on n-th of subcarrier are as follows:
Wherein, r (t) is the reception signal after synchronizing,For phase deviation caused by synchronous error.
Step 6: the M member coherently despreading on frequency domain is carried out to the spread-spectrum signal of distribution on different sub-carriers；
Assuming that the position of k-th of spread-spectrum signal to be de-spread on sub-carriers in i-th of OFDM symbol is γ=[0 1
... N-1], then the process of coherently despreading are as follows:
Wherein, rniAccording to k-th of spread-spectrum signal, the position in subcarrier carries out subcarrier pumping to i-th of OFDM symbol for representative
Baseband signal after taking, cpP-th of spreading code in M member CPM sequence sets is represented,Expression takes conjugate operation,For rniWith cp
The result obtained after despreading；According toThe data x of available M systemkEstimated value:
To M systemIt carries out inverse mapping and obtains corresponding a bit information；
Step 7: greatly enhancing the Signal to Interference plus Noise Ratio of baseband signal by the despreading of the frequency domain of step 6, is conducive to pair
The recovery of QPSK modulation intelligence d (k),
It is rightProgress QPSK inverse mapping, which can demodulate, obtains rear 2 bit informations.
Step 8: a bit obtained in step 6 and step 7 and 2 bit informations are inputted into k-th of combiner and carry out group
Conjunction obtains kth group information sequence.
Step 9: repeating step 8 and demodulate to obtain whole K group information sequences, and this K group information sequence is carried out and is gone here and there to turn
Get final demodulating information sequence in return.
It should be noted last that the above examples are only used to illustrate the technical scheme of the present invention and are not limiting.Although ginseng
It is described the invention in detail according to embodiment, those skilled in the art should understand that, to technical side of the invention
Case is modified or replaced equivalently, and without departure from the spirit and scope of technical solution of the present invention, should all be covered in the present invention
Scope of the claims in.
Claims (7)
1. a kind of orthogonal multiple carrier M member chaos phase modulation spread-spectrum underwater sound communication method, which comprises
The input message sequence that step 1) transmitting terminal issues information source is obtained according to per mono- group of carry out sequence serioparallel exchange of (a+2) bit
The information sequence for being a+2 to K group length, and be respectively fed in K burster, each burster is respectively to preceding a progress M
First chaos phase modulation spread spectrum mapping, obtains a chaos phase modulation spreading code, recycles what is obtained to mix after carrying out QPSK modulation to latter 2
Ignorant phase modulation spreading code carries out band spectrum modulation and obtains baseband signal, then K group baseband signal is respectively mapped to the son of OFDM symbol
OFDM modulation is carried out on carrier wave, obtains digital signal to be launched, digital signal to be launched is finally converted into underwater sound signal
And emitted；
The underwater sound signal received is converted to digital signal by step 2) receiving end, using one section of chaos phase modulation spread spectrum in OFDM symbol
Signal carries out time-frequency two-dimensional search to digital signal and completes as pilot signal using the spreading gain of chaos phase modulation spreading code
Time and Frequency Synchronization；Then OFDM demodulation is carried out to the signal after completion Time and Frequency Synchronization and obtains K group baseband signal, input K group respectively
Clutch completes despreading and QPSK demodulation, obtains binary sequence.
2. orthogonal multiple carrier M member chaos phase modulation spread-spectrum underwater sound communication method according to claim 1, which is characterized in that institute
Step 1) is stated to specifically include:
Step 1-1) it maps to obtain original chaos sequence using Quadratic, thus generate the M expansions for being used for modulation intelligence sequence
Frequency code and a pilot frequency sequence for Time and Frequency Synchronization, spreading length is respectively N and D；M spreading code of generation is formed one
Chaos phase modulation Spread Spectrum Sequence Set { c1,c2,…,cM}；
Step 1-2) the transmitting terminal input message sequence that issues information source according to per mono- group of carry out sequence serioparallel exchange of (a+2) bit,
It obtains K group length and is the information sequence of a+2, and be respectively fed in K burster；
Step 1-3) each burster carries out segment processing to (a+2) bit information of input, will wherein before a progress M members reflect
It penetrates, remaining 2 information carries out QPSK mapping；Then k-th of burster obtains the M binary data x after the mapping of M memberk, select chaos
Xth in phase modulation frequency expansion sequence set in M frequency expansion sequencekA spreading code obtains corresponding spreading code as outputQPSK
D (k) is obtained after mapping, and utilizes spreading codeTo obtaining baseband signal b corresponding with k-th of burster after d (k) band spectrum modulation
(n):
Wherein n=0,1..., KN, q=n-kN, k=1 ... K,Represent spreading codeQ-th of chip；
Step 1-4) each burster exports the baseband signal that a length is N, K group baseband signal reflected one by one with pilot frequency sequence
It is mapped on L subcarrier of OFDM symbol, obtains total baseband signal, IFFT transformation is carried out to total baseband signal, obtain time domain letter
Number S (t) are as follows:
Wherein, fnFor the frequency of each subcarrier, T is the time span of an OFDM symbol, TgIt is long for the time of cyclic prefix
Degree, T '=T+Tg；Complete M member CPM spread spectrum OFDM signal indicates are as follows:
Wherein, b (n, i) is the data modulated on n-th of subcarrier in i-th of symbol, and g (t) is the impulse wave of each symbol
Shape indicates are as follows:
3. orthogonal multiple carrier M member chaos phase modulation spread-spectrum underwater sound communication method according to claim 2, which is characterized in that institute
State step 1-1) it specifically includes:
Step 1-1-1) it maps to obtain original Constructing Chaotic Code using Quadratic, mapping equation indicates are as follows:
Y (m+1)=P-Qy2(m)
Wherein, as 3/4 < PQ < 2, original Constructing Chaotic Code y (m) ∈ (- 2/Q, 2/Q), Q=4, P=1/4, y (0) ∈ (- 0.5,
0.5), (- 0.5,0.5) y (m) ∈, m is positive integer；
Step 1-1-2) y (m) quantified without two-value is modulated in complex exponential, chaos phase modulation spreading code c is generated, c includes N number of
Chip, wherein q-th of chip are as follows:
C (q)=exp { j2 π y (q) }, q=0,1...N-1
Step 1-1-3) selection M mutually orthogonal chaos phase modulation spreading codes composition M member chaos phase modulation spread spectrum code sequence set { c1,
c2,...,cM}；
Step 1-1-4) utilization original chaos sequence y (m) one section of fixed chaos phase modulation spreading code of generation, spread code length D,
Using the spreading code as pilot frequency sequence.
4. orthogonal multiple carrier M member chaos phase modulation spread-spectrum underwater sound communication method according to claim 2, which is characterized in that institute
State step 1-2) in a are as follows:
5. orthogonal multiple carrier M member chaos phase modulation spread-spectrum underwater sound communication method according to claim 2, which is characterized in that institute
State step 1-2) in K size by chaos phase modulation spreading code length N and a multicarrier M member chaos phase modulation spread spectrum symbol S
Subcarrier number L determine, relationship meet:
K×N+D≤L。
6. orthogonal multiple carrier M member chaos phase modulation spread-spectrum underwater sound communication method according to claim 2, which is characterized in that institute
Step 2) is stated to specifically include:
Step 2-1) receiving end carries out Time and Frequency Synchronization to the ofdm signal that receives；
Step 2-2) Fourier transformation is done within the period [iT ', iT '+T] to the signal r (t) after synchronizing, it is obtained by formula (7) defeated
Signal in i-th of symbol out on n-th of subcarrier are as follows:
Wherein,For phase deviation caused by synchronous error；
Step 2-3) the M member coherently despreading on frequency domain is carried out to the spread-spectrum signal of distribution on different sub-carriers；
Assuming that the position of k-th of spread-spectrum signal to be de-spread on sub-carriers in i-th of OFDM symbol is γ=[0 1 ...
N-1], then the process of coherently despreading are as follows:
Wherein, rniIt represents after according to k-th of spread-spectrum signal, position carries out subcarrier decimation to i-th OFDM symbol in subcarrier
Baseband signal, cpP-th of spreading code of M member chaos phase modulation frequency expansion sequence concentration is represented,Expression takes conjugate operation,For rni
With cpThe result obtained after despreading；According toThe data x of available M systemkEstimated value:
To M systemIt carries out inverse mapping and obtains corresponding a bit information；
Step 2-4) it enablesIt is rightProgress QPSK inverse mapping, which can demodulate, obtains rear 2 bit informations；
Step 2-5) it a bit obtained in step 2-3) and step 2-4) and 2 bit informations is inputted into k-th of combiner carries out group
Conjunction obtains kth group information sequence；
Step 2-6) repeat step 2-5) demodulation obtains whole K group information sequences, and this K group information sequence is carried out parallel-serial conversion
Obtain final demodulating information sequence.
7. orthogonal multiple carrier M member chaos phase modulation spread-spectrum underwater sound communication method according to claim 6, which is characterized in that institute
State step 2-1) it specifically includes:
Step 2-1-1) with the time delay interception OFDM symbol to be synchronized of a time domain step-size in search, according to frequency domain Variable sampling algorithm
High-resolution FFT transform is carried out to time-domain OFDM symbol, obtains the frequency spectrum that each subcarrier is moved after by doppler interference；
Step 2-1-2) with the sub-carrier positions of the Doppler factor calculating pilot signal of a frequency domain search step-length, and according to
To position above-mentioned frequency spectrum is extracted nearby, obtain baseband signal corresponding with pilot signal；
Step 2-1-3) the chaos phase modulation spreading code for being used for Time and Frequency Synchronization that generates above-mentioned baseband signal and receiving end into
Line frequency domain despreading finds out result of the energy value as this frequency domain search of despread result；
Step 2-1-4) with the Doppler factor of above-mentioned frequency domain search step-length update frequency domain search, according to step in search range
2-1-2) to the process iterative search of step 2-1-3), the maximum value of each secondary frequency domain search result is found out as domain search when this
Result；
Step 2-1-5) with above-mentioned time domain step-size in search update time delay, according to step 2-1-1) to step 2-1- in search range
4) process iterative search, finds out the maximum value of each secondary time domain search result, and calculates this time and search for corresponding Doppler factor
With time delay as final output, the Domain Synchronous point of Doppler's estimated value and OFDM symbol that signal demodulation needs is obtained.
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