CN109450557A - Orthogonal multiple carrier code domain non-orthogonal multiple underwater sound communication downlink near-end user is without pilot-based channel estimation method - Google Patents
Orthogonal multiple carrier code domain non-orthogonal multiple underwater sound communication downlink near-end user is without pilot-based channel estimation method Download PDFInfo
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- 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
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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
- H04B1/7097—Interference-related aspects
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L25/00—Baseband systems
- H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
- H04L25/0202—Channel estimation
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L25/00—Baseband systems
- H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
- H04L25/0202—Channel estimation
- H04L25/022—Channel estimation of frequency response
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L25/00—Baseband systems
- H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
- H04L25/03—Shaping networks in transmitter or receiver, e.g. adaptive shaping networks
- H04L25/03006—Arrangements for removing intersymbol interference
- H04L25/03159—Arrangements for removing intersymbol interference operating in the frequency domain
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
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Abstract
The invention discloses a kind of orthogonal multiple carrier code domain non-orthogonal multiple underwater sound communication downlink near-end users without pilot-based channel estimation method, the reconstruction to remote subscriber frequency domain spread spectrum code is realized using the sparse property of underwater acoustic channel, and near-end user signal is carried out using reconstructed results as the pilot frequency information of near-end user balanced, and interference of the remote subscriber to near-end user is eliminated by SIC technology, to realize the demodulation completed under conditions of not adding pilot tone redundancy to near-end user information, effective solution NOMA communication process needs to add the decline problem of communication efficiency caused by pilot tone, the underwater sound communication for being suitble to communications bandwidth resources in short supply.
Description
Technical field
This method is related to the research of NOMA water sound communication technique, more specifically says, non-just for orthogonal multiple carrier code domain
It hands over multiple access water sound communication technique to need to add the problem of communication efficiency caused by pilot tone estimation channel reduces, proposes a kind of be suitble to
The access of downlink broadcast channel near-end user non-orthogonal multiple is applied to field of underwater acoustic communication without pilot-based channel estimation method.
Background technique
It is influenced by underwater sound communication distance field-effect, is located at that underwater sound local area network fringe node signal-to-noise ratio is low, performance is poor.
In orthogonal multicast, if the maximum capacity of simple pursuit system, it is located at underwater sound communication network fringe node quilt
The chance very little of scheduling;If improved to improve the handling capacity of underwater sound communication network fringe node edge customer power or
Increase transmission bandwidth, then the capacity of system can reduce accordingly.Therefore there is the orthogonal frequency division multiplexing of high spectrum utilization
(Orthogonal Frequency Division Multiplexing, OFDM) technology combines can be in underwater acoustic network child node
Under the premise of equality of opportunity, realize that the non-orthogonal multiple of communication network channel capacity boost accesses (Non-orthogonal
Multiple Access, NOMA) technology gradually attracts attention in recent years.By shallow water underwater acoustic channel multi-path propagation effects, NOMA letter
Pectination cycle decline is presented in the frequency domain response in road, and communication system needs to add pilot frequency information to realize and ring to time- variant channel
The estimation and tracking answered, lead to being remarkably decreased for underwater sound communication efficiency.
It is mentioned aiming at the problem that caused channel feedback information time-varying big propagation delay, the channel time-varying of underwater acoustic channel the characteristics of
A kind of OFDM modulation supercomposed coding method suitable for underwater sound downlink communication is gone out, this method utilizes subscriber channel by transmitting terminal
Statistical nature is two users' distribution power, utilizes the slow time-varying of pilot tone real-time tracing underwater acoustic channel.In two users' poor signal to noise
When different larger, under the resource allocation conditions of fair relatively, this method, which can be obtained, has perfect channel information than transmitting terminal
The bigger achievable rate region of orthogonal cut-in method, but this method need by addition Comb Pilot real-time tracking channel to
Communication efficiency is caused to decline.
In comb-type pilot channel estimation method, the NOMA downlink broadcast channel signal propagated by underwater acoustic channel is by channel
The interference of frequency domain comb filtering, it is therefore desirable to add pilot frequency information estimation channel and carry out equilibrium to signal is received, could connect
Receiving end realized using the method for matched filtering and demodulated to the integral of signal, so that communications bandwidth resources underwater sound communication in short supply can benefit
Communication bandwidth is narrower, to influence communication efficiency.
Summary of the invention
A kind of suitable downlink broadcast channel near-end user non-orthogonal multiple of being designed to provide of this method is accessed without pilot tone
Channel estimation methods, realization demodulates the estimation of near-end user channel and signal under the premise of not adding pilot frequency information, from
And effectively increase communication efficiency.
The core concept of method is to be realized using the sparse property of underwater acoustic channel to remote subscriber frequency domain spread spectrum in the present invention
The reconstruction of code, and equilibrium is carried out to near-end user signal using reconstructed results as the pilot frequency information of near-end user, and pass through SIC skill
Art eliminates interference of the remote subscriber to near-end user, completes under conditions of not adding pilot tone redundancy to near-end user to realize
The demodulation of information.
The solution of the present invention is as follows:
A kind of orthogonal multiple carrier code domain non-orthogonal multiple underwater sound communication downlink near-end user is without pilot channel estimation side
Method, comprising the following steps:
A. remote subscriber transmission includes the signal of spread spectrum data, and near-end user receives signal and simultaneously carries out time-frequency conversion;
B. the signal after time-frequency conversion is carried out spread spectrum identification by near-end user;
C. the spread-spectrum signal identified according to step B is found remote subscriber by sparse characteristic and is sent in conjunction with excessively complete dictionary
The corresponding M member spreading code serial number of spread spectrum, channel reconstructing is carried out by the spreading code serial number of searching;
D. serial interference elimination is carried out to near-end user received signal by power distribution, connecing after the interference that is eliminated
The collection of letters number;
E. the reception signal eliminated after interfering is demodulated.
Further, the step C the following steps are included:
C1. it definesTo work asWhen channel estimation value,It may be expressed as:
Wherein,I-th entrained (i ∈ [2 I]) in t-th of the OFDM symbol received for near-end user receiving end
The spread spectrum of q-th of transmission in a remote subscriber signal;
PmFor the row vector for the M member Spread Spectrum Matrix P that spreading length is N, Pm=[pm,0,pm,1,…,pm,N-1] in element
pm,nBe distributed on unit circle according to the mapping ruler arranged in advance (i.e. | | pm,n| |=1, n=0,1,2 ..., N-1);
fest() indicates channel estimation,For spread spectrumResponse;
C2. the excessively complete dictionary Ψ being made of multiple atom Φ is constructed, match tracing condition of sparse channel estimation technique pair is utilized
Channel estimation resultsMatching estimation is carried out, corresponding weighted factor storage vector is obtained
C3. it according to spread spectrum code identification principle, finds in i-th of remote subscriber signal entrained in t-th of OFDM symbol
The corresponding M member spreading code serial number m' of spread spectrum of q-th of transmission, that is, findM' corresponding to maximum value;
Wherein,For the spread spectrum pair of q-th of transmission in i-th of remote subscriber signal entrained in t-th of OFDM symbol
The M member spreading code serial number m' answered;
C4. after the completion of all non-near-end user spreading spectrum and decodings and channel coding verification, non-near-end user is verified and is completed
Information carry out channel coding and spread spectrum coding and obtain the frequency domain information of each non-near-end user transmission, by the frequency domain of each user
Frequency domain response is obtained after information adduction
C5. basisAnd receive signal Y1The channel that signal passes through is received to near-end user to be estimated to obtain
Further, the step D the following steps are included:
D1. to reception signal Y1Channel equalization is carried out to obtainThen according to formulaIt is rightIt carries out SIC demodulation and obtains near-end user reception signalWherein α is allocated to the power allocation factor of node 1.
Using above technical scheme, the application is had following technical effect that
This method can be realized under the premise of not adding pilot frequency information demodulates the estimation of near-end user channel and signal,
The transmission information for taking full advantage of remote subscriber realizes the weight to remote subscriber signal by the spread spectrum recognition methods of no pilot tone
It builds, and realizes the estimation to near-end user channel using the technology of match tracing as pilot tone, proximal end is used to realize
The demodulation of user data, effective solution NOMA communication process need to add the decline problem of communication efficiency caused by pilot tone, by
In not needing pilot tone, therefore the bigger of data is transmitted, is particularly suitable for communications bandwidth resources underwater sound communication in short supply.
Detailed description of the invention
Fig. 1 near-end user signal demodulating method block diagram.
Fig. 2 near-end user simulated channel impulse response.
Fig. 3 remote subscriber simulated channel impulse response.
Fig. 4 is without pilot channel estimation Comparative result.
The comparison of Fig. 5 comb-type pilot channel estimated result.
Two kinds of spread spectrum detection method performances of Fig. 6 remote subscriber compare.
Two kinds of underwater acoustic channel estimation method performances of Fig. 7 near-end user compare.
Fig. 8 near-end user channel response.
Fig. 9 remote subscriber channel response.
Figure 10 near-end user and transmitting terminal relative velocity.
Figure 11 remote subscriber and transmitting terminal relative velocity.
Two methods of Figure 12 remote subscriber demodulate Contrast on effect.
Two methods of Figure 13 near-end user demodulate Contrast on effect.
Specific embodiment
Following will be combined with the drawings in the embodiments of the present invention, and technical solution in the embodiment of the present invention carries out clear, complete
Site preparation description, it is clear that described embodiments are only a part of the embodiments of the present invention, instead of all the embodiments.It is based on
Embodiment in the present invention, it is obtained by those of ordinary skill in the art without making creative efforts every other
Embodiment shall fall within the protection scope of the present invention.
More detailed description is done to this method with specific embodiment with reference to the accompanying drawing.
1, spread spectrum code identification principle
Consider that spreading length is the M member Spread Spectrum Matrix P of N:
Its row vector Pm=[pm,0,pm,1,…,pm,N-1] in element pm,nIt is distributed according to the mapping ruler arranged in advance
On unit circle (i.e. | | pm,n| |=1, n=0,1,2 ..., N-1), it include the N in the OFDM symbol of K subcarrier using one
A subcarrier is to PmIt carries out carrier modulation and obtains time-domain signal s, S is its frequency domain response.Assuming that signal s is by one with sparse
The channel h of property obtains r in receiving end.If the circulating prefix-length of signal is greater than the maximum multipath time delay of channel h, signal r's
Frequency domain response R may be expressed as:
RQ=QH+V (2)
Wherein H is the frequency domain response of channel h, and V is Frequency domain noise interference.Receiving end only has known to R.Matrix P is utilized at this time
Middle M sample respectively estimates H, spreads the channel that sample is estimated using the m' at this timeIt may be expressed as:
Wherein ()HIndicate conjugate transposition, when m '=m,The estimation of channel at this timeWhen
Domain response is sparse.Since matrix P is the M member Spread Spectrum Matrix by design, as m ' ≠ m,May be considered has
It is similar to the property of noise, thereforeTime domain response be non-sparse.Pass through the sparse characteristic etc. using Shallow Water Acoustic Channels
Priori knowledge can efficiently identify the vector P of transmitting terminal transmission in the state that channel response is unknownm。
2, condition of sparse channel rebuilds principle
Shallow Water Acoustic Channels usually have sparse property, thus can use match tracing (matching pursuit,
MP) technology realizes the reconstruction to underwater acoustic channel H.Assuming that Ψ was complete dictionary, it is made of atom Φ, dictionary ΨKIt was complete
L × K corresponding to K subcarrier ties up matrix in dictionary Ψ.It is the l times matching from dictionary ΨKMiddle selection
Atom vector out, ωjFor weighted factor.Channel H is matched by following method flow at this time:
Step 1: being initialized, enable residual signals RH=H.
Step 2: being found and residual signals R in dictionary ΨHThe maximum atom φ of inner productl, and calculate its weighted factor ωj。
Step 3: updating weighted factor and store vector Wl=[Wl-1,ωl] and atom φlPosition vector U in dictionaryl
={ Ul-1,ul}。
Step 4: updating residual error
Step 2~4 are repeated until H is adequately broken.Channel frequency domain response vector of the system H after overmatchingIt can be with table
It is shown as:
Wherein L " is maximum number of iterations and has L " > L'.Formula (7) due to W contain all atoms in dictionary Ψ plus
Weight coefficient, the ω in the case where l ∈ SlValue is non-zero or much larger than 0.
3, serial interference elimination principle
Consideration one includes the NOMA underwater sound communication broadcasting link of I receiving node, it is assumed that node 1 is that distance signal is wide
The nearest receiving node of node is broadcast, reception signal frequency domain information is S1。S2For other I-1 receptions save other than node 1 in network
The adduction of point signal frequency domain information.NOMA underwater sound communication network broadcast node will be sent to the signal of each user through overpower point
Linear superposition is carried out after matching, is then sent using identical physical resource, and the complex baseband signal of equal value of transmission is
α is allocated to the power allocation factor of node 1.
Wherein, H1By for 1 channel frequency domain response of node, V1For the access noise of node 1.Node 1 utilizes SIC receiver
Detect S1When, it needs first to detect other I-1 receiving node signals respectively and merge to obtainIt can use channel coding when demodulation
Technology will receive signalMiddle I-1 component carries out the algebraic decoding of Soft Inform ation input respectively, enhances the reliability of each bit,
It is believed that the received I-1 of node 1 non-targeted signal demodulation results are sufficiently exact under reasonable power distribution.Then it passes through
It crosses soft and soft modulation symbol is madeThen willFrom reception signal Y1It is obtained after channel equalizationMiddle deletion, obtains:
4, this method is described in more detail below with reference to the method block diagram 1 of this method.
Assuming that i-th (i ∈ [2 I]) entrained in t-th of OFDM symbol that system near-end user receiving end receives is a
The spread spectrum of q-th of transmission in remote subscriber signalResponse beAccording to formula (1) it is found thatThere is M kind corresponding may reflect
It penetrates.
Step 1: definitionTo work asWhen channel estimation value,It may be expressed as:
Wherein fest() indicates channel estimation.
The excessively complete dictionary Ψ being made of multiple atom Φ is constructed, using match tracing condition of sparse channel estimation technique to channel
Estimated resultMatching estimation is carried out, corresponding weighted factor storage vector is obtained
Step 2: according to spread spectrum code identification principle, finding i-th of remote subscriber signal entrained in t-th of OFDM symbol
In q-th transmission the corresponding M member spreading code serial number of spread spectrum, that is, findM' corresponding to maximum value;
According to spread spectrum code identification principle, when m '=m,Time domain impulse responseJust there is sparse property,
Assuming that channelDegree of rarefication be L ', then its corresponding weighted factor stores vector at this timeIn only a weighted factor of L 'Value is non-zero or much larger than 0, that is to say, that a component of L ' in dictionary Ψ contains channelIn whole energy (assuming that
OFDM circulating prefix-length is greater than channel maximum multipath time delay);And as m' ≠ m,Without sparse property, therefore obtain
'sContain the channel matchedA maximum weighted volumes of L ' in dictionary Ψ, thereforeOnly contain channelPortion of energy.Due to | | Pm| | it is constant, according to formula (7)For constant, so that
Q-th of corresponding M of spread spectrum transmitted in i-th of remote subscriber signal entrained in t-th of OFDM symbol at this time
First spreading code serial numberIt may be expressed as:
Step 3: after the completion of all non-near-end user spreading spectrum and decodings and channel coding verification, non-near-end user having been verified
At information carry out channel coding and spread spectrum coding and obtain the frequency domain information of each non-near-end user transmission, by the frequency of each user
Frequency domain response is obtained after domain information adduction
Step 4: according toAnd receive signal Y1The channel that signal passes through is received to near-end user to be estimated to obtain
To reception signal Y1Channel equalization is carried out to obtainThen right according to formula (10)SIC demodulation is carried out to obtain
Signal is received to near-end user
This method can be realized under the premise of not adding pilot frequency information demodulates the estimation of near-end user channel and signal,
The transmission information for taking full advantage of remote subscriber spreads reconstruction of the recognition methods realization to remote subscriber signal by no pilot tone,
And the estimation to near-end user channel is realized using the technology of match tracing as pilot tone, to realize to near-end user number
According to demodulation, effective solution NOMA communication process needs to add the decline problem of communication efficiency caused by pilot tone, is suitble to logical
Believe bandwidth resources underwater sound communication in short supply.
5, emulation experiment explanation
In order to verify the feasibility and reliability of this method, using Matlab software to the NOMA underwater sound comprising 2 users
The communication of communication downlink broadcasting link has carried out Monte Carlo simulation.Under water at 15m, near-end user connects transmitting transducer when emulation
It receives hydrophone and remote subscriber receiving hydrophone is laid respectively at 17m under water and at underwater 21m, with transmitting terminal horizontal distance point
It Wei not d1=800m and d2=3450m, simulated channel mean depth of the sea 55m.Fig. 2,3 give by certain channel simulator Software Create
Near-end user and remote subscriber shallow sea channel impulse response.
Table 1 gives the major parameter of NOMA system emulation use.
1 NOMA system major parameter of table
Assuming that water sound communication signal presses spherical surface extension decaying, near-end user power allocation factor α=0.4 can be by formula at this time
(16) it is calculated.
It is calculated according to i-th of user's communication efficiency formula (17) it is found that near-end user and remote subscriber traffic rate difference
For 400bps and 100bps.
Figure 4 and figure 5 respectively show match obtained channel using this method and comb-type pilot channel estimation method are sparse
Impulse response, two methods can preferably estimate the tap position of simulated channel multidiameter delay.As shown in Figure 4, believe in height
It makes an uproar the ability for having high-accuracy spread spectrum demodulation than this method under environment, this is the basis of no pilot-based channel estimation method.
Fig. 6 gives pair that integral demodulation method after this method and comb-type pilot channel equilibrium is respectively adopted in remote subscriber
Than the demodulation to remote subscriber spread spectrum communications signals can be achieved in two methods.Signal-to-noise ratio (equivalent near-end user receive when
Signal-to-noise ratio) it is lower when two methods performance it is close;And in signal-to-noise ratio higher strip part, this method is significantly better than comb-type pilot channel
Equalization methods, this is because emulation when NOMA communication system addition Comb Pilot use even distribution pattern, cause system by
The influence of pilot tone resolution ratio forms higher error floor in high noise environment.
As shown in Figure 7, under the simulated conditions, using this method and comb-type pilot channel estimation method in high s/n ratio item
It can be realized the signal demodulation to near-end user under part.The result ten that two methods obtain signal equalization and demodulation taps
Closely, this is because carrier energy occupation proportion of the two methods for channel estimation is close.Assuming that an OFDM symbol is all sub
Carrier energy is ETotal, for comb-type pilot channel estimation method, it is used for the occupied carrier energy E of channel estimationComb
=ETotal×ηComb=1/3ETotal;And for this method, it is used for the occupied carrier energy E of channel estimationNo_Pilot=
(1-α)ETotal=0.6ETotal.Although ENo_Pilot> EComb, but this method is transmitted by near-end user simultaneously in channel estimation
The interference of information, therefore its channel estimation effect is close with using comb-type pilot channel estimated result.
6, lake, which is had a try, tests explanation
In order to verify the reliability of this method, lake examination verification experimental verification has been carried out within 2017.Locating waters is open when test, puts down
The equal depth of water is about 55m, and transmitting node energy converter is hung at 5m under water, and the receiving hydrophone of near-end user and remote subscriber is hung
It is placed at underwater 3m.Horizontal distance between transmitting node and near-end user and remote subscriber is respectively 500m and 1000m.
Near-end user and remote subscriber channel conditions when Fig. 8,9 give test, as seen from the figure, channel multi-path is complicated, believes
Road response quickly time-varying.Remote subscriber channel multi-path complexity is because under the water area condition, and signal receiving end is away from transmitting terminal 1km
The acoustic shadow of transmitting terminal is exactly in when nearby, direct sound wave signal energy is very weak.The quick time-varying of channel response is because proximal end is used
The carrier ship of family and remote subscriber is constantly drifted about by water currents, and as shown in Figure 10,11, near-end user movement velocity about exists
0.22m/s~0.38m/s, remote subscriber move speed about in 0.1m/s~0.24m/s.
When test, NOMA communication system major parameter is as shown in table 2.
2 orthogonal frequency division multiplexing spread spectrum communication system major parameter of table
Near-end user power allocation factor α=0.4 when test, transmitting terminal sends 7 frames altogether when communication, and every frame signal contains 10
OFDM symbol, practical each symbol includes near-end user data 64bit, includes remote subscriber data 16bit.Therefore test process
In, near-end user receives 4480bit effective information altogether, and remote subscriber receives 1120bit effective information altogether.According to communication efficiency public affairs
Formula (17) calculates it is found that near-end user and remote subscriber traffic rate are respectively 400bps and 100bps.
Figure 12 gives remote subscriber and integral demodulation method comparison after this method and comb-type pilot channel equilibrium is respectively adopted,
The demodulation to remote subscriber information can be achieved in two methods.It is influenced by remote subscriber channel status is poor, two methods expand
Raw Bit-Error-Rate after frequency demodulates is higher, respectively reaches 2.76 × 10-2With 3.57 × 10-2, distally used after convolutionally encoded demodulation
The error rates of data that family is obtained using this method is better than 8.93 × 10-4, and demodulation side is integrated after using comb-type pilot channel balanced
The error rates of data that method obtains is 3.9 × 10-3。
Figure 13 gives near-end user and this method and comb-type pilot channel estimation method is respectively adopted respectively to near-end user
After receiving signal equalization and the interference elimination of SIC remote subscriber, compared by the bit error rate of integral demodulation, two methods can be achieved
Demodulation to near-end user information, raw Bit-Error-Rate is respectively 2.24 × 10 after two methods spread spectrum demodulation-2With 1.45 × 10-2,
The error rates of data that remote subscriber is obtained using this method after convolutionally encoded demodulation is better than 1.4 × 10-3, and use Comb Pilot
It is 1.9 × 10 that the error rates of data that demodulation method obtains is integrated after channel equalization-3。
It although an embodiment of the present invention has been shown and described, for the ordinary skill in the art, can be with
A variety of variations, modification, replacement can be carried out to these embodiments without departing from the principles and spirit of the present invention by understanding
And modification, the scope of the present invention is defined by the appended.
Claims (3)
1. a kind of orthogonal multiple carrier code domain non-orthogonal multiple underwater sound communication downlink near-end user is without pilot-based channel estimation method,
Characterized by comprising the following steps:
A. remote subscriber transmission includes the signal of spread spectrum data, and near-end user receives signal and carries out time-frequency conversion;
B. the signal after time-frequency conversion is carried out spread spectrum identification by near-end user;
C. the spread-spectrum signal identified according to step B finds the expansion that remote subscriber is sent by sparse characteristic in conjunction with excessively complete dictionary
Frequently corresponding M member spreading code serial number carries out channel reconstructing by the spreading code serial number of searching;
D. serial interference elimination is carried out to near-end user received signal by power distribution, the reception letter after the interference that is eliminated
Number;
E. the reception signal eliminated after interfering is demodulated.
2. orthogonal multiple carrier code domain non-orthogonal multiple underwater sound communication downlink near-end user according to claim 1 is without leading
Frequency channel estimation methods, which is characterized in that the step C the following steps are included:
C1. it definesTo work asWhen channel estimation value,It may be expressed as:
Wherein,I-th entrained a distal end (i ∈ [2 I]) in t-th of the OFDM symbol received for near-end user receiving end
The spread spectrum of q-th of transmission in subscriber signal;
Pm is the row vector for the M member Spread Spectrum Matrix P that spreading length is N, Pm=[pm,0,pm,1,…,pm,N-1] in element pm,nIt presses
Be distributed on unit circle according to the mapping ruler arranged in advance (i.e. | | pm,n| |=1, n=0,1,2 ..., N-1);
fest() indicates channel estimation,For spread spectrumResponse;
C2. the excessively complete dictionary Ψ being made of multiple atom Φ is constructed, using match tracing condition of sparse channel estimation technique to channel
Estimated resultMatching estimation is carried out, corresponding weighted factor storage vector is obtained
C3. it according to spread spectrum code identification principle, finds in i-th of remote subscriber signal entrained in t-th of OFDM symbol q-th
The corresponding M member spreading code serial number m' of the spread spectrum of transmission, that is, findM' corresponding to maximum value;
Wherein,For the corresponding M of spread spectrum of q-th of transmission in i-th of remote subscriber signal entrained in t-th of OFDM symbol
First spreading code serial number m';
C4. after the completion of all non-near-end user spreading spectrum and decodings and channel coding verification, to the letter of non-near-end user verification completion
Breath carries out channel coding and spread spectrum coding obtains the frequency domain information of each non-near-end user transmission, by the frequency domain information of each user
Frequency domain response is obtained after adduction
C5. basisAnd receive signal Y1The channel that signal passes through is received to near-end user to be estimated to obtain
3. orthogonal multiple carrier code domain non-orthogonal multiple underwater sound communication downlink near-end user according to claim 2 is without leading
Frequency channel estimation methods, which is characterized in that the step D the following steps are included:
D1. to reception signal Y1Channel equalization is carried out to obtainThen according to formulaIt is rightIt carries out
SIC demodulation obtains near-end user and receives signalWherein α is allocated to the power allocation factor of node 1.
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