CN105610759B - The new method of XCTD channel transmission rate is improved based on OFDM technology - Google Patents
The new method of XCTD channel transmission rate is improved based on OFDM technology Download PDFInfo
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- CN105610759B CN105610759B CN201610044211.4A CN201610044211A CN105610759B CN 105610759 B CN105610759 B CN 105610759B CN 201610044211 A CN201610044211 A CN 201610044211A CN 105610759 B CN105610759 B CN 105610759B
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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
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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
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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
- H04L27/263—Inverse Fourier transform modulators, e.g. inverse fast Fourier transform [IFFT] or inverse discrete Fourier transform [IDFT] modulators modification of IFFT/IDFT modulator for performance improvement
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L5/00—Arrangements affording multiple use of the transmission path
- H04L5/003—Arrangements for allocating sub-channels of the transmission path
- H04L5/0044—Arrangements for allocating sub-channels of the transmission path allocation of payload
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Abstract
The present invention is to walk deserted temperature of navigating, salinity, the transmission channel of depth section instrument is prototype, the method for improving XCTD channel transmission rate is proposed using OFDM technology, XCTD channel mainly uses the frequency band transmission mode of single carrier at present, wherein as investigation depth and transmission frequency increase, Signal-to-Noise substantially reduces, limit the transmission rate of channel, OFDM is a kind of typical case of multi-carrier modulation, it can make full use of the finite bandwidth of XCTD, higher snr gain is obtained in a manner of reducing single carrier wave transmission rate, channel bandwidth utilization ratio is improved to increase the quantity of carrier wave, improve the message transmission rate of XCTD, the present invention constructs OFDM algorithm flow chart, by changing investigation depth, signal-to-noise ratio etc. carrys out the observation signal bit error rate and analyzes its reason, this Invention is had great importance using OFDM technology for improving XCTD message transmission rate.
Description
Technical field
The present invention using walk deserted temperature of navigating, salinity, depth (XCTD) section plotter transmission channel as prototype, proposing makes
The new method of XCTD channel transmission rate is improved with OFDM technology.
Background technique
XCTD is a kind of relatively advanced conductivity developed and be rapidly developed in recent years both at home and abroad, temperature profile survey
Equipment is measured, has the characteristics that boat, real-time, large area, low cost and high-acruracy survey, it passes through emitter for measuring probe
Be thrown into it is marine, probe at the fast speed drop during by the collected cross-sectional data of built-in sensors by transmission line real-time Transmission simultaneously
It is handled, and then analyzes the parameters in series such as the temperature of different depth marine environment, salinity, XCTD transmission line is about by diameter
The single bifilar enameled wire of 0.1mm is constituted, be wound in the form of spiral inductance two spools be separately mounted to underwater probe and
On ship inside emitter, since XCTD probe decrease speed is fast, the transmission line being wrapped on spool constantly discharges, transmission channel
Parameter constantly change with unwrapping wire length, be in high order linear time-varying characteristics, with the increase of investigation depth, channel width is increasingly
It is narrow, and message transmission rate is higher, and signal amplitude decaying is more serious, and signal-to-noise ratio will be lower, as shown in Figure 1, XCTD signal
Transmission rate be largely restricted.
OFDM is a kind of typical case of multi-carrier modulation, it breaks a channel into several orthogonal sub-channels, by high-speed data
Signal is converted into parallel low speed sub-data flow, is modulated on every sub-channels and is transmitted, can be abundant by OFDM technology
Using the finite bandwidth of XCTD, higher snr gain is obtained in a manner of reducing single carrier wave transmission rate, to increase
The quantity of carrier wave improves the bandwidth availability ratio of channel, and then improves the message transmission rate of XCTD.
Summary of the invention
Present invention aim to address the problems for improving XCTD channel transmission rate, propose OFDM orthogonal frequency division multiplexing skill
Art improves this method of the bandwidth availability ratio of XCTD channel, and constructs OFDM algorithm flow chart, by changing investigation depth, passing
Defeated rate, signal-to-noise ratio etc. carry out the observation signal bit error rate, and the present invention has great importance for improving XCTD message transmission rate.
The algorithm flow provided by the invention that XCTD channel transmission rate is improved based on OFDM technology, as shown in Fig. 2, algorithm
The mentality of designing of process is:
1, planisphere map modulation
XCTD channel is low pass narrow-band filtering characterized channel, and frequency increases, and signal amplitude decaying is serious, and signal-to-noise ratio reduces,
Entire channel is divided into several orthogonal sub-channels by OFDM technology, can be selected according to the different characteristics of different subchannels different
Modulation system, the preferable channel of characteristic, can suitably increase message transmission rate, it is possible to select after meeting certain signal-to-noise ratio
16QAM is selected, the high-order modulatings such as 64QAM, in the place of characteristic of channel difference, channel SNRs are low, to reduce data transmission speed
Rate may be selected by QPSK, the low-order-modulateds mode such as 2PSK modulation, so can be each according to XCTD using OFDM technology in this way
Subchannel feature makes equilibrium between efficiency of transmission and noise margin, in complicated marine environment, has selected non fouling
It can stronger QPSK modulation mapping mode.
2, number of subcarriers
XCTD channel is narrowband systems, this is also the one of the major reasons of restricting channel message transmission rate, and OFDM skill
The art feature most prominent with respect to single carrier modulation system is exactly to increase the availability of frequency spectrum, and entire channel is divided by OFDM technology
Several subchannels, every sub-channels are modulated with the mutually orthogonal subcarrier of different frequency, it is possible to be carried by reducing son
Wave frequency rate interval increases number of subcarriers, and then improves the bandwidth availability ratio of XCTD channel, final improve data transfer rate,
In order to guarantee the orthogonality between each subcarrier, the frequency interval minimum between adjacent sub-carrier takes the inverse of symbol period, and can only
Its integral multiple is taken, selecting subcarrier spacing after many tests is 83.33kHz.
3, IFFT algorithm
The data of each subchannel transmission enter before channel, need common hair that each subchannel information is stacked up
It penetrates, and IFFT algorithm has simplified the complexity of this superposition significantly, but this algorithm is long using needing to meet input data
The integral number power that degree is 2, it is possible to before the ifft, meet the requirements data length by serioparallel exchange.
4, protection interval
XCTD channel is wire channel, is made of bifilar enameled wire, and multidiameter delay is not present, but due to channel frequency itself
Shifting and phase-shift characterisitc, there are intersymbol interferences in transmission process for digital signal, can generate trailing phenomenon between OFDM symbol at this time
And influence next symbol, the measure for solving intersymbol interference be exactly add protection interval between two ofdm symbols, thus
It can reduce the bit error rate, length is generally the 1/8-1/4 of symbol period length.
5, it encodes
Channel decoding is conducive to signal and is reliably transmitted to stay of two nights module from information source module, can fight to a certain extent
Channel fading and interchannel noise, linear block codes are one of most common channel coding methods, and RS coding is a kind of multi-system
Linear block codes, have very strong error correcting capability, most significant feature is can to correct burst error, in identical transmission
Under efficiency, the error correcting capability of RS coding is strongest.
6, over-sampling
In ofdm system the IFFT operation of N point is carried out to OFDM symbol, obtained N number of output under normal circumstances is adopted
It is readily generated false signal when sample value is transferred in D/A converter, N merely is carried out to OFDM symbol in Fourier transformation
The secondary obtained sample point of sampling cannot really reflect the situation of change of continuous OFDM symbol.And XCTD channel has
The low pass narrow-band filtering characteristic of 1500Hz cutoff frequency, high frequency signal attenuation are serious, it is therefore desirable to adopt to OFDM symbol
Sample adds some sampled points again between N number of sampled point of original ofdm signal, constitute pN (p is integer) a sampled value.
For IFFT operation, (p-1) N number of zero only need to be added among N number of input value of system, useful signal is made to be in low frequency
Section, while improving time-domain sampling rate.
The advantages of the present invention:
The limited bandwidth of XCTD can be made full use of by OFDM technology, is come in a manner of reducing single carrier wave transmission rate
Higher snr gain is obtained, improves channel bandwidth utilization ratio to increase the quantity of carrier wave, improves the data transmission of XCTD
Rate has built the Transmission system of OFDM, such as Fig. 3 herein from the channel characteristic of XCTD on the emulation platform of MATLAB
It is shown, by changing signal transmission frequencies, investigation depth and signal-to-noise ratio etc. come the observation signal bit error rate, and its reason is analyzed,
It finally obtains, as shown in figure 4, in conjunction with surveyed channel width range, suitably being protected within the scope of certain number of subcarriers
Interval, as number of subcarriers increases, data effective transmission speed is gradually increased, and the present invention is to carry out the hydrology using XCTD instrument
The detection of data provides a kind of new method, while correctly can improve XCTD transmission speed using OFDM technology for engineers and technicians
Rate has important theory directive significance.
Detailed description of the invention
Fig. 1 is to walk boat to jettison the Formula X CTD course of work and narrow band analyzing.
Fig. 2 is OFDM algorithm basic procedure.
Fig. 3 is the simulink simulated program that OFDM technology is applied on XCTD channel.
Fig. 4 is that the beneficial effect that OFDM technology is applied on XCTD channel is shown.
Specific embodiment
This new method of XCTD channel transmission rate is improved to OFDM technology using simulink simulation software to emulate,
As shown in Figure 3.
1, coding mode is determined, as a kind of multi-system primitive BCH code, RS coding has very strong error correcting capability, dashes forward
Feature is can to correct burst error out, chooses RS (7,3) here and is encoded, and the basic thought of RS code is to choose one properly
Generator polynomial g (x), and the codeword polynome that each message segment is calculated to be made to be times formula of g (x),
To make numeral deconv with the residue result of g (x) for 0, therefore, when the codeword polynome received is divided by the residue of g (x)
Be 0 when, can illustrate receive code word residue there are mistakes.The key of RS coding techniques is the selection of generator polynomial,
The selection of decoding algorithm is equally also most important, including calculates syndrome, solves key equation, errors present and error value.
2, determine that modulation system, OFDM technology will select different modulating mode, general low-order-modulated side according to channel characteristic
Formula selects QPSK, and high-order modulating then selects 16QAM or 64QAM, and signal before modulation, can will be whole by serioparallel exchange
A channel is divided into several orthogonal sub-channels, and the lower channel signal attenuation amplitude of carrier frequency is small, and noise is relatively high, can choose
The examination of the high order modulation side 16QAM, 64QAM comes up data rate raising, and the higher channel of data rate is then narrow due to channel
Band low-frequency filter characteristics, signal amplitude decaying is serious, therefore cannot try improve data transfer rate by high order modulation side again, and
It is to make signal with lower speed rates by low-order-modulated mode, to increase snr gain, in selecting modulation mode,
QPSK modulation system may due to channel phase-shift characterisitc and so that demodulating process is affected, can be special according to the phase shift of channel
Property, solve planisphere mapping when change judgment condition, observe the bit error rate variation reach it is optimal, eventually pass through debugging and it is excellent
Change, so that modulation system is accomplished equilibrium in subchannel selection and rate selection, make minimum bit-error rate.
3, number of subcarriers is determined, the integral number power for adjusting number of subcarriers, and number of carrier wave being made to meet 2, in order to improve
The availability of frequency spectrum of channel, number of subcarriers needs increase, but bandwidth shared by each carrier wave reduces after number of carrier wave increase, will
Meeting is so that system is more sensitive for Doppler frequency shift, and furthermore number of carrier wave increases, and peak-to-average force ratio also will increase, will necessarily be to transmitting
End requires to increase, so number of carrier wave cannot be set as arbitrarily large, but needs to accomplish the equilibrium between number of subcarriers and channel,
In a certain range number of carrier wave limitation.
Estimate that number of carrier wave method can be with reference to using following methods:
(1) parameters such as number of carrier wave are determined by channel estimation, XCTD channel increases with depth, and channel width gradually subtracts
It is small, therefore the entire characteristic of channel for declining process cannot be summarized by when one depth of estimation the characteristics of channel, it can choose
Several typical depth carry out channel estimation, finally analyze in channel estimation results, test, compare optimal case.
(2) consider that investigation depth, the parameters such as data rate select different sub-carrier quantity to be tested, and analyze and compare
Optimal case out.
4, protection interval is determined, XCTD channel is made of bifilar enameled wire, multidiameter delay is not present, but due to channel sheet
Body frequency displacement and phase-shift characterisitc, there are intersymbol interferences in transmission process for digital signal, can generate hangover between OFDM symbol at this time
Phenomenon and influence next symbol, the measure for solving intersymbol interference is exactly to add protection interval between two ofdm symbols,
Since XCTD channel does not have multidiameter delay, it is thus determined that protection interval length and symbol period length cannot from when elongatedness come it is true
It is fixed, that is, protection interval not can determine that an exact value, only by entering before channel and data after channel out
Observation comparison, gradually debugs, finds out suitable protection interval length.
5, data are encoded by RS, planisphere mapping, zero padding, IFFT, after the processes such as addition protection interval enter channel, are needed
Corresponding inverse transformation is wanted to restore data, i.e., deprotection interval, FFT zero-suppress, and demodulate, and the processes such as RS decoding finally integrate each mould
Block parameter, optimizes communication system.
Claims (3)
1. a kind of method for improving XCTD channel transmission rate based on OFDM technology, it is characterised in that comprise the concrete steps that:
The first step, planisphere mapping and De-mapping module
XCTD channel is low pass narrow-band filtering characterized channel, and frequency increases, and signal amplitude decaying is serious, and signal-to-noise ratio is lower and lower,
Equilibrium is made between efficiency of transmission and noise margin according to the every sub-channels feature of XCTD, in the place of characteristic of channel difference, choosing
QPSK, 2PSK modulation system are selected, the preferable channel of characteristic selects 16QAM, and 64QAM modulation system is meeting certain signal-to-noise ratio
Suitably increase message transmission rate afterwards；
Second step, serioparallel exchange and parallel serial conversion module
Entire channel is divided by several subchannels using OFDM technology, the mutually orthogonal son of every sub-channels different frequency carries
Wave is modulated, and increases number of subcarriers by reducing subcarrier spacing, and then improve the bandwidth availability ratio of XCTD channel,
Final improve data transfer rate；
Third step, IFFT transformation and FFT transform module
The data of each subchannel transmission enter before channel, need common transmitting that each subchannel information is stacked up,
IFFT algorithm simplifies the complexity of this superposition significantly；
4th step, up-conversion and down conversion module
It will be transmitted on the carrier wave of the modulates baseband signals of low speed to upper frequency.
2. a kind of method for improving XCTD channel transmission rate based on OFDM technology according to claim 1, feature exist
In, since XCTD channel does not have multipath delay, determine between two OFDM symbols protection interval cannot from when elongatedness confirm,
Only by gradually debugging, finding out suitable protection interval length to the observation of data compares before entrance channel and out after channel.
3. a kind of method for improving XCTD channel transmission rate based on OFDM technology according to claim 1, feature exist
In, number of carrier wave is determined by channel estimation, 200,800,1000,1800,2000 meters of depth is selected to carry out channel estimation, and
Consider that investigation depth, transmission rate parameter select different sub-carrier quantity to be tested, analysis compares optimal case.
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| CN106230506A (en) * | 2016-07-19 | 2016-12-14 | 中国科学技术大学 | A kind of orthogonal frequency-division complex modulation method being applied to visible light communication |
| CN106230766B (en) * | 2016-08-08 | 2019-11-05 | 华南师范大学 | The synthesis adaptive transmission method of visible light communication |
| CN106791704B (en) * | 2017-01-22 | 2019-10-29 | 天津航天中为数据系统科技有限公司 | A kind of multi-mode UAV TT & C communication system and method |
| CN112134822B (en) * | 2020-09-22 | 2023-06-23 | 天津工业大学 | Method for improving multi-user transmission performance of marine inductive coupling anchor chain based on OFDM+FDMA technology |
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| CN103944848A (en) * | 2014-01-08 | 2014-07-23 | 华南理工大学 | Underwater acoustic anti-Doppler multicarrier modulation and demodulation method based on linear frequency modulation and device thereof |
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| CN103944848A (en) * | 2014-01-08 | 2014-07-23 | 华南理工大学 | Underwater acoustic anti-Doppler multicarrier modulation and demodulation method based on linear frequency modulation and device thereof |
| CN103984837A (en) * | 2014-05-30 | 2014-08-13 | 天津工业大学 | Method for analyzing influence of time-varying channel of deep sea navigation XCTD on transmission performance |
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| OFDM基本原理及其在移动通信中的应用;李向宁等;《重庆邮电学院学报》;20030630;第15卷(第2期);第25-30页 |
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