CN109379320A - A kind of time shift frequency division multiplexing underwater sound communication modulator approach - Google Patents
A kind of time shift frequency division multiplexing underwater sound communication modulator approach Download PDFInfo
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- CN109379320A CN109379320A CN201811305999.5A CN201811305999A CN109379320A CN 109379320 A CN109379320 A CN 109379320A CN 201811305999 A CN201811305999 A CN 201811305999A CN 109379320 A CN109379320 A CN 109379320A
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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
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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
- 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
- H04L27/2602—Signal structure
- H04L27/2605—Symbol extensions, e.g. Zero Tail, Unique Word [UW]
- H04L27/2607—Cyclic extensions
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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
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Abstract
The invention discloses a kind of time shift frequency division multiplexing underwater sound communication modulator approaches, the method reduces cyclic prefix used in orthogonal frequency division multiplexing, the following steps are included: transmitting terminal: binary bit stream to be transmitted is encoded, become complex symbol d by modulation symbol mapping, d is the vector (N=K*M) of N*1, N number of element is modulated onto K orthogonal sub-carriers group, and each orthogonal sub-carriers group is orthogonal sub-carriers time shift M times formation in the time domain；Send the superposition that signal is the modulated symbol on all subcarriers；Transmission vector finally is obtained plus cyclic prefix in transmitting terminalReceiving end: vector is sentBy underwater acoustic channel, the data markers that receiving end receives areCyclic prefix is removed, signal y is obtained, obtains vector z by channel equalization, the subsequent demodulated device of vector z is decoded as vectorFinally output signal is obtained by demapping and decoding.The present invention improves the spectrum efficiency of communication system, efficiently utilizes bandwidth, reduces the bit error rate, further increases the flexibility of system.
Description
Technical field
The present invention relates to underwater sound communication digital multi-carrier transmission technical fields, and the present invention is in orthogonal frequency division multiplexing (OFDM)
On the basis of, it is extended in the time domain, proposes a kind of time shift frequency division multiplexing (TS-FDM) time shift frequency division multiplexing underwater sound communication modulation
Method.
Background technique
Underwater sound communication becomes marine major wireless communications mode, and is applied to collect oceanographic data, environment
Monitoring and long-range control etc..But underwater acoustic channel is still considered as one of channel most challenged, underwater acoustic channel it is main
Problem is: limited bandwidth, serious time-varying multipath fading, environmental noise, time domain and frequency domain double selectivity etc., this also leads
Cause the transmission rate of underwater sound communication low.
Orthogonal frequency division multiplexing (OFDM) modulation-demodulation technique has high rate data transmission, anti-multipath jamming, impulsive noise ability
By force, the advantages such as availability of frequency spectrum height, and the characteristics of combination underwater acoustic channel, it is widely used in underwater sound communication, becomes and grinds
Study carefully hot spot.OFDM significant effect in underwater sound communication can carry out high-speed biography with orthogonal subcarrier in limited bandwidth
It is defeated, but it has strict demand to orthogonality.In order to eliminate inter-sub-carrier interference and intersymbol interference, cyclic prefix (CP) becomes
The necessary a part of OFDM, CP length generally to account for OFDM symbol length 1/6th to a quarter and its length has sternly
Lattice require-it is greater than maximum delay, this is necessarily to reduce spectrum efficiency as cost.
Therefore resource shared by CP how is reduced, further increasing spectrum efficiency underwater sound communication limited for bandwidth has
Significance.
Summary of the invention
The present invention provides a kind of time shift frequency division multiplexing underwater sound communication modulator approaches, and the present invention is based on underwater sound communication
OFDM multicarrier transmission systems propose time shift frequency division multiplexing (TS-FDM) novel multi-carrier modulation skill in conjunction with time domain expansion concept
Art, it is intended to improve the spectrum efficiency of communication system, efficiently utilize bandwidth, reduce the bit error rate, further increase system flexibility, in detail
See below description:
A kind of time shift frequency division multiplexing underwater sound communication modulator approach, the method reduce circulation used in orthogonal frequency division multiplexing
Prefix the described method comprises the following steps:
Transmitting terminal:
Binary bit stream to be transmitted is encoded, and becomes complex symbol d by modulation symbol mapping, d is N*1's
Vector (N=K*M), N number of element are modulated onto K orthogonal sub-carriers group, and each orthogonal sub-carriers group is that orthogonal sub-carriers exist
Time shift M times formation in time domain；Send the superposition that signal is the modulated symbol on all subcarriers；In finally adding for transmitting terminal
Cyclic prefix obtains sending vector
Receiving end:
Send vectorBy underwater acoustic channel, the data markers that receiving end receives areCyclic prefix is removed, letter is obtained
Number y, obtains vector z by channel equalization, the subsequent demodulated device of vector z is decoded as binary output vectorsFinally by solution
Mapping and decoding obtain output signal.
Further, the subcarrier group are as follows:
N=0,1,2,3 ... ..., N-1
M=0,1,2,3 ... ..., W-1
K=0,1,2,3 ... ..., K-1
Wherein, k=0,1 ..., K-1 represent the sequence number of subcarrier, and m=0,1 ..., M-1 indicate the subcarrier group of extension
Internal symbol sequence number, n=0,1 ..., M-1 are sample index, and δ [n] is unit pulse, gK, m[n] is by δ [n] in time and frequency
Displacement in rate and constitute, mod is remainder operation.
Wherein, a symbol of the method can transmit N=K*M data, identical as OFDM symbol occupancy
Bandwidth.
It is further, described to send the superposition that signal is the modulated symbol on all subcarriers specifically:
Wherein, dK, mIndicate m-th of subsymbol in vector d in k-th of subcarrier group.
Wherein, the signal y specifically:
Y=Hx+ ω=HAd+ ω
Wherein, H is the Channel cyclical convolution matrix of a N*N, and ω is the white Gaussian noise vector of N*1, and y is equal by channel
Weighing apparatus obtains vector z, then z=H-1HAd+H-1ω=Ad+H-1ω。
The beneficial effect of the technical scheme provided by the present invention is that: the present invention improves the spectrum efficiency of communication system, reduces
Cyclic prefix used in OFDM technology (CP) efficiently utilizes bandwidth, reduces the bit error rate, further increases the flexibility of system.
Detailed description of the invention
Fig. 1 is a kind of flow chart of time shift frequency division multiplexing underwater sound communication modulator approach；
Fig. 2 is TS-FDM symbol and the schematic diagram that OFDM symbol compares；
Fig. 3 is the schematic diagram for increasing spectral efficiency gain of the TS-FDM with respect to OFDM with M；
Fig. 4 is the bit error rate (BER) performance that TS-FDM and OFDM changes under different orthogonal sub-carrier number with signal-to-noise ratio
Schematic diagram.
Specific embodiment
To make the object, technical solutions and advantages of the present invention clearer, embodiment of the present invention is made below further
Ground detailed description.
The embodiment of the present invention proposes TS-FDM modulation technique.If TS-FDM symbol is that M times of OFDM symbol time domain extension obtains
It arrives, then under transmission data and the identical situation in orthogonal sub-carriers interval, the bandwidth ratio OFDM of TS-FDM reduces M times, this
It is significant for the underwater acoustic channel of bandwidth critical constraints.And a TS-FDM transmission block includes multiple subcarriers and multiple sons
Symbol, entire block only need a CP, spectrum efficiency can be substantially improved.OFDM itself have excellent noiseproof feature, quickly
Fourier inversion (IFFT) algorithm quickly transmit and suitable for underwater sound communication transmission real number the advantages of, these features exist
It still is able to embody in TS-FDM.
Embodiment 1
The embodiment of the present invention devises a kind of time shift frequency division multiplexing underwater sound communication modulator approach, and this method is retaining OFDM's
On the basis of good characteristic, cyclic prefix (CP) used in OFDM is reduced to improve spectrum efficiency, this method comprises:
Needing to keep stringent orthogonality between each carrier frequency in orthogonal frequency division multiplexing (OFDM) system, essence
It is exactly that transmitting terminal is weighted to serial complex exponential signal with data to be modulated and then synthesizes a complex signal, OFDM carrier wave is raw
It is as follows at formula:
Wherein, N is total number of sub-carriers, and n is the sampling time, and k is sub-carrier indices number.If bandwidth used in transmission data is
B, the orthogonal sub-carriers number used are K, and subcarrier spacing is Δ f=B/K.And time shift frequency division multiplexing (TS-FDM) technology is exactly base
Obtained from OFDM, the K subcarrier of OFDM is extended M times in time domain, so TS-FDM subcarrier generates as follows:
N=0,1,2,3 ... ..., N-1
M=0,1,2,3 ... ..., M-1
K=0,1,2,3 ... ..., K-1
Wherein, k=0,1 ..., K-1 represent the sequence number of subcarrier, and m=0,1 ..., M-1 indicate the subcarrier of extension
Group internal symbol sequence number, n=0,1 ..., N-1 are sample index, and δ [n] is unit pulse, gK, m[n] be by δ [n] in the time and
Displacement in frequency and constitute, mod is remainder operation.So TS-FDM symbol can transmit N=K*M data, but and
OFDM occupies identical bandwidth B.
In conclusion the embodiment of the present invention proposes time shift frequency division multiplexing (TS-FDM) novel multi-carrier modulation technology, purport
In the spectrum efficiency for improving communication system, bandwidth is efficiently utilized, the bit error rate is reduced, further increases system flexibility.
Embodiment 2
The scheme in embodiment 1 is further introduced below with reference to Fig. 1, specific calculation formula, it is as detailed below
Description:
In transmitting terminal, if TS-FDM is by time shift M times in the time domain of K subcarrier, in TS-FDM transmitting terminal, Jiang Yaochuan
The binary bit stream sent is encoded, and becomes complex symbol d by modulation symbol mapping later, and d is the vector (N=K* of N*1
M), d=(d0 T..., dK-1 T) T, dk=(d0, k..., dM-1, k)T.Wherein, N=K*M indicates that this N number of element is modulated onto K
In orthogonal sub-carriers, and each orthogonal sub-carriers extend M times in time domain and form one group of orthogonal sub-carriers group.
It sends signal x=(x [n])TFor the superposition of the modulated symbol on all subcarriers, it may be assumed that
Wherein, dK, mIndicate m-th of subsymbol in vector d in k-th of subcarrier group, T is transposition.
If enabling A=(g0,0..., g0, M-1, g1,0..., gK-1, M-1) then formula (2) can be write as vector form:
X=Ad (4)
Wherein, d is transmission data vector, gK-1,M-1For subcarrier represented by formula (1), x is modulated by TS-FDM
Signal.It to obtain sending vector plus cyclic prefix in the last x of transmitting terminalThen send vector
Send vectorBy underwater acoustic channel, the data markers that receiving end receives areThereafter first before removal circulation
Sew, obtain signal y, can indicate are as follows:
V=Hx+ ω=HAd+ ω (5)
Wherein, H is the Channel cyclical convolution matrix of a N*N, and ω is the white Gaussian noise vector of N*1.Y is equal by channel
Weighing apparatus obtains vector z, then z=H-1HAd+H-1ω=Ad+H-1ω.The demodulated device of subsequent vector z, the process may be expressed as:
It is decoded as binary output vectorsFinally output signal is obtained by demapping and decoding.
In conclusion the embodiment of the present invention proposes time shift frequency division multiplexing (TS-FDM) novel multi-carrier modulation technology, purport
In the spectrum efficiency for improving communication system, bandwidth is efficiently utilized, the bit error rate is reduced, further increases system flexibility.
Embodiment 3
Feasibility verifying is carried out to the scheme in Examples 1 and 2 below with reference to Fig. 1-Fig. 4, specific formula for calculation, example,
It is described below:
The embodiment of the present invention is the characteristics of combining underwater acoustic channel on the basis of OFDM, more effectively to utilize limited band
Width improves spectrum efficiency.As shown in Fig. 2, bandwidth shared by each TS-FDM symbol is identical with OFDM symbol, phase is transmitted in the two
In the case where with data, each OFDM symbol will have a CP, in contrast, the TS-FDM technology that the embodiment of the present invention proposes
Very big improvement is carried out to this, each TS-FDM symbol also only needs the CP with OFDM symbol equal length.
Such as: as M=4, OFDM needs four CP, as long as one CP of TS-FDM symbol, CP length is identical and meets item
Part, this provides for improved spectrum efficiencies.
Assuming that the CP length of OFDM and TS-FDM is identical, then spectral efficiency gain of the TS-FDM compared to OFDM are as follows:
Wherein, NCPFor the CP length of OFDM and TS-FDM.
As the increase TS-FDM of M can also become larger for the frequency gain of OFDM, and increasing when M tends to infinity
It is beneficial maximum, i.e. limM→∞ρ=5/4.
The value of M can be selected in practical application as the case may be.Fig. 3 is to increase frequency spectrum of the TS-FDM with respect to OFDM with M to imitate
Rate gain, wherein CP length is the 1/4 of orthogonal sub-carriers number, i.e.,Spectral efficiency gain speedup is located at 2- in M
Very fast among 10, with the increase of M, spectral efficiency gain tends towards stability.More importantly TS-FDM is improving spectrum efficiency
Error performance is improved simultaneously, as shown in figure 4, spreading factor M=4 in figure, CP length are the 1/4 of orthogonal sub-carriers number, i.e.,The availability of frequency spectrum improves 1.114, and guarantees bandwidth shared by OFDM and TS-FDM all in 8-14K range
It is interior.On the whole, the bit error rate performance of TS-FDM is better than OFDM, and in 15dB, TS-FDM performance, which becomes apparent from, is better than OFDM.Therefore
TS-FDM bit error rate performance while spectrum efficiency increases gets a promotion, and is more suitable for the limited underwater acoustic channel of bandwidth.It is bright
Aobvious to find out, as K=256, since CP length is unsatisfactory for the requirement greater than maximum delay, bit error rate performance is significantly deteriorated, but TS-
The still well OFDM of FDM performance.In addition, TS-FDM can increase CP length, such as N(TS-FDM_CP)=K/2, even so TS-FDM phase
Spectral efficiency gain for OFDM is still 1.111 times, and bit error rate performance performance is significantly better than OFDM, such as black curve institute
Show.OFDM symbol length is small, and CP is it is difficult to ensure that be greater than maximum delay, or can guarantee that its CP length but other performances can be by
To seriously affecting.But TS-FDM can be while guaranteeing that spectrum efficiency is greater than OFDM, i.e. the CP symbol lengths of TS-FDM are less than
The a quarter of its symbol lengths, TTS-FDM_CP≤TTS-FDM/ 4, it can also guarantee that cyclic prefix is greater than maximum delay, performance obtains
It improves, it is opposite that there is advantageous property.
It will be appreciated by those skilled in the art that attached drawing is the schematic diagram of a preferred embodiment, the embodiments of the present invention
Serial number is for illustration only, does not represent the advantages or disadvantages of the embodiments.
The foregoing is merely presently preferred embodiments of the present invention, is not intended to limit the invention, it is all in spirit of the invention and
Within principle, any modification, equivalent replacement, improvement and so on be should all be included in the protection scope of the present invention.
Claims (5)
1. a kind of time shift frequency division multiplexing underwater sound communication modulator approach, which is characterized in that the method reduces orthogonal frequency division multiplexing
Cyclic prefix used, the described method comprises the following steps:
Transmitting terminal:
Binary bit stream to be transmitted is encoded, and becomes complex symbol d by modulation symbol mapping, d is the vector of N*1
(N=K*M), N number of element is modulated onto K orthogonal sub-carriers group, and each orthogonal sub-carriers group is orthogonal sub-carriers in time domain
Upper time shift M times formation；Send the superposition that signal is the modulated symbol on all subcarriers；In the last plus circulation of transmitting terminal
Prefix obtains sending vector
Receiving end:
Send vectorBy underwater acoustic channel, the data markers that receiving end receives areCyclic prefix is removed, signal y is obtained,
Vector z is obtained by channel equalization, the subsequent demodulated device of vector z is decoded as binary output vectorsFinally pass through demapping
Output signal is obtained with decoding.
2. a kind of time shift frequency division multiplexing underwater sound communication modulator approach according to claim 1, which is characterized in that the sub- load
Wave group are as follows:
N=0,1,2,3 ..., N-1
M=0,1,2,3 ..., M-1
K=0,1,2,3 ..., K-1
Wherein, K=0,1 ..., K-1 represent the sequence number of subcarrier, and m=0,1 ..., M-1 are indicated in the subcarrier group of extension
Symbol sebolic addressing number, n=0,1 ..., N-1 are sample index, and δ [n] is unit pulse, gK, m[n] is by δ [n] in time and frequency
On displacement and constitute, mod be remainder operation.
3. a kind of time shift frequency division multiplexing underwater sound communication modulator approach according to claim 1, which is characterized in that the method
A symbol can transmit N=K*M data, with can only transmit K data orthogonal frequency division multiplexing (OFDM) symbol occupy phase
Same bandwidth.
4. a kind of time shift frequency division multiplexing underwater sound communication modulator approach according to claim 2, which is characterized in that the transmission
Signal is the superposition of the modulated symbol on all subcarriers specifically:
Wherein, dK, mIndicate m-th of subsymbol in vector d in k-th of subcarrier group.
5. a kind of time shift frequency division multiplexing underwater sound communication modulator approach according to claim 1, which is characterized in that the signal
Y specifically:
Y=Hx+ ω=HAd+ ω
Wherein, H is the Channel cyclical convolution matrix of a N*N, and ω is the white Gaussian noise vector of N*1, and y is obtained by channel equalization
To vector z, then z=H-1HAd+H-1ω=Ad+H-1ω。
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN112910814A (en) * | 2021-01-14 | 2021-06-04 | 天津大学 | Underwater acoustic communication multi-carrier modulation method based on partial response |
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