CN109889262A - A kind of orthogonal frequency division multiplexing free space optical communication method based on wavelet transformation - Google Patents
A kind of orthogonal frequency division multiplexing free space optical communication method based on wavelet transformation Download PDFInfo
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Abstract
The present invention proposes a kind of orthogonal frequency division multiplexing free space optical communication method based on wavelet transformation.This method comprises: S1, selects sub-carrier number N, generates a data matrix；S2 carries out mapping the data matrix to obtain a complex matrix based on qam mode；S3 carries out discrete wavelet inverse transform to complex matrix to generate DWT-OFDM parallel signal, parallel signal is converted to serial signal；Serial signal is converted to optical signal and transmitted it in atmospheric channel by S4；S5 detects optical signal based on receiving end and the optical signal detected is converted to electric signal, electric signal is carried out A/D conversion acquisition digital signal, digital signal solution inversely processing is obtained the planisphere of demodulated signal and the bit error rate of system.This method has stronger anti-interference ability, and due to wavelet transformation limited length in the time domain, will not generate intersymbol interference, without introducing cyclic prefix, has the higher availability of frequency spectrum.
Description
Technical field
The present invention relates to the free space optical communication methods in optical communication system field, are specifically related to a kind of based on small echo
The orthogonal frequency division multiplexing free space optical communication method of transformation.
Background technique
With the rapid development of internet and related Data Services, people to the data transportation requirements of high-speed increasingly
Height, optic communication are paid attention to and are developed to the needs of traffic rate because it can greatly meet user.Optic communication is according to transmission
The difference of medium can be divided into two kinds, and one is the wire communications using optical fiber as transmission medium, and another kind is exactly directly to make
The free space optical communication of wireless communication link is established with atmospheric channel.Free space optical communication (FSO) has significant advantage,
But defect is equally obvious, mainly embody a concentrated reflection of atmospheric conditions extreme it is unstable on.Absorption, scattering and the turbulent flow effect of atmosphere
Communication quality should can be made to be greatly affected, so being considered as this when needing spectrum efficiency height, anti-atmospheric effect strong
Orthogonal frequency division multiplexing (OFDM) technology be applied to FSO system in.OFDM is a kind of multi-carrier modulation, traditional OFDM benefit
Composite signal is generated from one group of orthogonal index subcarrier with Fast Fourier Transform (FFT), but because Fourier transformation is in the time domain
Endless, when time window is inconsistent, it will result in the interference (ICI) and intersymbol interference (ISI) between subcarrier, so
OFDM must be introduced into cyclic prefix and go to avoid both interference.But it does so and also brings along additional power overhead, and reduce
The utilization rate of frequency.
Summary of the invention
Based on the above issues, the purpose of the present invention is intended to propose a kind of base to resist the unstability of atmospheric conditions
In orthogonal frequency division multiplexing (DWT-OFDM) free space optical communication method of wavelet transformation, this method has stronger anti-interference energy
Power.To achieve the above object, the present invention adopts the following technical scheme:
A kind of orthogonal frequency division multiplexing free space optical communication method based on wavelet transformation, which is characterized in that the method
The following steps are included:
S1 selects sub-carrier number N, generates a data matrix；
S2 carries out mapping the data matrix to obtain a complex matrix based on qam mode；
S3 will be described parallel to complex matrix progress discrete wavelet inverse transform to generate DWT-OFDM parallel signal
Signal is converted to serial signal；
The serial signal is converted to optical signal, and transmitted it in atmospheric channel by S4；
S5 detects the optical signal based on receiving end and the optical signal detected is converted to electric signal, will be described
Electric signal carries out A/D conversion acquisition digital signal and obtains the planisphere of demodulated signal and be the digital signal solution inversely processing
The bit error rate of system.
It preferably, also include that the road I and Q are carried out in numeric field respectively to the real and imaginary parts of the serial signal in the S4
Digital signal all the way is combined into after the up-conversion on road again, D/A conversion is carried out to the digital signal and generates electric signal, by the electricity
In signal modulation to light carrier, electro-optic conversion is carried out, generates optical signal.
Preferably, which is 128.
Preferably, which includes 16QAM.
Preferably, which includes that digital signal after converting A/D carries out Digital Down Convert, serioparallel exchange, small
Wave conversion and QAM demodulation.
Preferably, in the S4, by changing the intensity for the white Gaussian noise being added, to change the signal-to-noise ratio of channel, to obtain
Obtain the bit error rate under different signal-to-noise ratio.
Preferably, which is Haar wavelet inverse transformation.
Preferably, which is Haar wavelet transformation.
Scheme in compared with the existing technology, advantages of the present invention:
A kind of orthogonal frequency division multiplexing free space optical communication method based on wavelet transformation that the embodiment of the present invention proposes, phase
Than using OFDM (Fast Fourier Transform-based OFDM, FFT- based on Fourier transformation in existing
OFDM) there is stronger anti-interference ability, and due to wavelet transformation limited length in the time domain, intersymbol interference will not be generated,
Without introducing cyclic prefix, there is the higher availability of frequency spectrum.
Detailed description of the invention
The invention will be further described with reference to the accompanying drawings and embodiments:
Fig. 1 a show the process of the communication means based on wavelet transformation of the embodiment of the present invention；
Fig. 1 b show the orthogonal frequency division multiplexing free space optical communication method based on wavelet transformation of the embodiment of the present invention
Flow diagram；
Fig. 2 is FFT-OFDM principles of modulation and demodulation figure；
Fig. 3 is the DWT-OFDM principles of modulation and demodulation figure of the embodiment of the present invention；
Fig. 4 is under the 16QAM mapping of the embodiment of the present invention, using the error code of the FSO system of FFT-OFDM and DWT-OFDM
The curve of rate and transmission power；
Fig. 5 a is under 16QAM mapping, using the FSO system receiving terminal demodulated signal planisphere of FFT-OFDM；
Fig. 5 b is under 16QAM mapping, using the FSO system receiving terminal planisphere based on haar small echo DWT-OFDM.
Specific embodiment
Above scheme is described further below in conjunction with specific embodiment.It should be understood that these embodiments are for illustrating
The present invention and be not limited to limit the scope of the invention.Implementation condition used in the examples can be done such as the condition of specific producer into
One successive step, the implementation condition being not specified are usually the condition in routine experiment.
Please refer to Fig. 1 a, 1b describes the orthogonal frequency division multiplexing free space optical communication method based on wavelet transformation, such as schemes
1a show the orthogonal frequency division multiplexing free space optical communication method based on wavelet transformation of the application proposition, and one kind being based on small echo
The orthogonal frequency division multiplexing free space optical communication method of transformation comprising following steps:
S1 selects sub-carrier number N, generates a data matrix；
S2 carries out mapping the data matrix to obtain a complex matrix based on qam mode；
S3 will be described parallel to complex matrix progress discrete wavelet inverse transform to generate DWT-OFDM parallel signal
Signal is converted to serial signal；
The serial signal is converted to optical signal, and transmitted it in atmospheric channel by S4；
S5 detects the optical signal based on receiving end and the optical signal detected is converted to electric signal, will be described
Electric signal carries out A/D conversion acquisition digital signal and obtains the planisphere of demodulated signal and be the digital signal solution inversely processing
The bit error rate of system.In present embodiment, the system using the communication means includes transmitting terminal, receiving end；Transmitting terminal is based on S1-S4
Movement will treated that signal is transmitted in atmospheric channel, the reception device of receiving end is based on preset algorithm after receiving signal
Solution is inverse to obtain signal.
Next the flow diagram of communication means is described in detail in conjunction with Fig. 1 b, this method comprises:
Sub-carrier number N is selected, a data matrix is generated；The data matrix is mapped to obtain one by QAM modulation
A complex matrix carries out discrete wavelet inverse transform (IDWT) to the complex matrix and generates DWT-OFDM signal, DWT-OFDM is believed
Number parallel data is converted into serial data；The road I and the road Q are carried out in numeric field respectively to the real and imaginary parts of the serial signal
Be combined into again after up-conversion all the way digital signal to obtain the DWT-OFDM signal of real value；D/A conversion is carried out to the digital signal
Electric signal is generated, electric signal is modulated on light carrier, carries out electro-optic conversion, generates optical signal；The optical signal transmission is arrived
In atmospheric channel, white Gaussian noise is added in atmospheric channel and carrys out the noise in analog channel；The light letter that receiving end is detected
Number electric signal is converted to, electric signal progress A/D is converted to digital signal；The digital signal is carried out a series of inverse
Operation processing obtains the planisphere of demodulated signal and the bit error rate of system.QAM modulation is using 16QAM in present embodiment
(64QAM can also be used in other embodiments)；Wherein, solution inversely processing includes that the digital signal after converting A/D counts
Word down coversion, serioparallel exchange, wavelet transformation and QAM demodulation.Specifically the digital signal after A/D conversion is become by number is lower
Serioparallel exchange is carried out to it after frequency, converts serial data into parallel data, the parallel data is subjected to wavelet transform
(DWT), QAM demodulation finally is carried out to it, in this way recovery original data stream, handles data are received, obtains demodulated signal
Planisphere and system the bit error rate.
It is illustrated in figure 2 FFT-OFDM principles of modulation and demodulation figure.The cell signal of the carrier wave of traditional OFDM is defined as:
Wherein fkIt is the centre frequency of k-th of subcarrier, can be expressed asf0For tranmitting frequency, T is
The duration of ofdm signal.In transmitting terminal, FFT-OFDM is can be obtained into the superposition of orthogonal cosine carrier multiplication in digital baseband
Signal is embodied as
Wherein dkThe data symbol being assigned in k-th of subchannel is represented, rect (t) is rectangular window function.In receiving end,
Original data flow can be restored by input signal is multiplied by orthogonal sub-carriers being re-fed into integrator.
By above-mentioned derivation, the arithmetic expression and inverse discrete Fourier transform (IDFT) form of OFDM baseband signal are very
It is similar, so traditional OFDM, generates composite signal frequently with the IDFT of N point in transmitting terminal.Likewise, only being needed in receiving end
DFT is carried out to signal is received, so that it may restore data.OFDM is a kind of multi-carrier modulation technology, and signal generates process are as follows: will
The data flow of input is multiplied, finally by the subcarrier through ovennodulation after serioparallel exchange with mutually orthogonal subcarrier two-by-two
It is added, so that it may obtain ofdm signal.Traditional OFDM only needs to carry out the continuous signal of timing inverse direct computation of DFT in transmitting terminal
Leaf transformation (Inverse Discrete Fourier Transformation, IDFT) can modulate digital baseband signal
Onto mutually orthogonal subcarrier.Likewise, only needing to carry out discrete Fourier transform to reception signal in receiving end
(Discrete Fourier Transformation, DFT), so that it may restore data.In practical applications, it generallys use fast
Fast Fourier transform/inverse fast fourier transform (Fast Fourier Transformation/Inverse Fast
Fourier Transformation, FFT/IFFT) Lai Shixian DFT/IDFT, the complexity of ofdm system is reduced with this.
It can be convenient by Fourier transformation and efficiently complete OFDM modulation, but in wireless communications, multipath effect can bring time delay, by
Unlimited in time domain length in Fourier transformation, this can bring about intersymbol interference, reduce the anti-interference ability of system, it is therefore necessary to draw
Enter cyclic prefix.The length of the cyclic prefix needs the maximum delay greater than channel, could eliminate intersymbol interference, and maintain carrier wave
Orthogonality.But will increase bandwidth, the availability of frequency spectrum is reduced, and bring energy loss, cyclic prefix is longer, energy damage
It loses bigger.
It is illustrated in figure 3 the DWT-OFDM principles of modulation and demodulation figure of the application embodiment.In Fig. 3, h is a low pass filtered
Wave device, also referred to as scaling filter, g are a high-pass filter, also referred to as wavelet filter.It is in transmitting terminal, the N item of input is parallel
Data are divided into rate not several equal branches, and the rate of every branch is 2 power side, guarantees the rate of two branches most
It is small and equal in magnitude, it is considered as low frequency signal c for this twoj-1With detail signal dj-1, then can be used wavelet reconstruction algorithm by this
Two branches synthesize a branch cj, expression is as follows:
Above formula is wavelet reconstruction algorithm, and wherein ψ (t) is wavelet function,For scaling function, j represents resolution ratio, and 1/2j
Referred to as scale, it represents the number of plies where signal, Recursion Application is carried out to wavelet reconstruction algorithm, in transmitting terminal to N number of process
The subcarrier of modulation uses wavelet reconstruction algorithm to be superimposed again two-by-two, carries out log2N times iteration can synthesize DWT-OFDM all the way
Signal.
Similarly in receiving end, input signal is decomposed to obtain its low frequency signal and details using wavelet decomposition algorithm
Signal, obtained signal respectively correspond each branch, and expression formula is as follows
Above formula is wavelet decomposition algorithm, it can be seen that it is corresponding with wavelet reconstruction algorithm.Wavelet decomposition algorithm is passed
Return application, carries out log2N iteration can restore the original road N signal.Present embodiment mutually ties wavelet transformation with OFDM technology
It closes, cosine orthogonal basis function is replaced using orthogonal wavelet basis function, using inverse discrete wavelet transform/wavelet transform
(Inverse Discrete Wavelet Transform/Discrete Wavelet Transform, IDWT/DWT) replacement
IFFT/FFT in traditional OFDM.
Be illustrated in figure 4 under 16QAM mapping mode, using FFT-OFDM and DWT-OFDM FSO system the bit error rate with
The curve of signal-to-noise ratio.By changing the intensity for the white Gaussian noise being added, to change the signal-to-noise ratio of channel, such as add in the channel
After entering white Gaussian noise, the first signal-to-noise ratio of channel is obtained, it, will be electric by after the optical signal of atmospheric channel is converted to electric signal
Signal carries out A/D conversion, and the digital data transmission of conversion is carried out a series of inverse operations to receiving end, obtains the first signal-to-noise ratio
Under the bit error rate.Similarly, the second signal-to-noise ratio, third signal-to-noise ratio etc. are obtained by changing the intensity of addition Gaussian noise, respectively
Obtain the second signal-to-noise ratio, the bit error rate under the difference signal-to-noise ratio such as third signal-to-noise ratio.Above a band+number curve be to use
The ber curve of the FSO system of FFT-OFDM, below a band * curve be using using different wavelet basis DWT-
The ber curve of the FSO system of OFDM.As can be seen that being substantially better than use using the bit error rate of the FSO system of DWT-OFDM
The bit error rate of FFT-OFDM.Under 7% forward error correction (Forward Error Correction, FEC) threshold value, DWT- is used
Small 3dB of the signal-to-noise ratio of ofdm system than using FFT-OFDM system.This demonstrate the DWT-OFDM's proposed using the application
System has better noise robustness.
It is illustrated in figure 5 under 16QAM mapping mode, when signal-to-noise ratio is 15dB, FSO system receiving terminal demodulated signal constellation
Figure, wherein (a) is the FSO system receiving terminal planisphere using FFT-OFDM, (b) for using the DWT-OFDM of haar small echo
FSO system receiving terminal planisphere.It can be seen from the figure that the FSO system constellation figure polymerization using DWT-OFDM is clear, and
Compared with (a) figure, using the FSO system constellation figure of FFT-OFDM with respect to the DWT-OFDM energy that disperse, such the application propose
Enough noise jammings better against atmospheric channel.
In above embodiment, using inverse discrete wavelet transform/wavelet transform (Inverse Discrete
Wavelet Transform/Discrete Wavelet Transform, IDWT/DWT) replacement tradition OFDM in IFFT/
FFT.Wavelet transformation is extracted the minutia of signal using haar wavelet transformation, so DWT-OFDM exists compared to FFT-OFDM
Time domain and frequency domain have preferable Local Characteristic.The function that wavelet transformation translates on a timeline has orthogonality, and just
Each function base also meets orthogonality in intersection of subspace, so DWT-OFDM will not generate intersymbol interference, does not need to introduce circulation
Prefix has the higher availability of frequency spectrum.
In above embodiment, QAM is the abbreviation of Quadrature Amplitude Modulation, i.e. " orthogonal amplitude
Modulation ".The sub-carrier number selected is 128.
The above embodiments merely illustrate the technical concept and features of the present invention, and its object is to allow person skilled in the art
It is to can understand the content of the present invention and implement it accordingly, it is not intended to limit the scope of the present invention.All such as present invention essences
The equivalent transformation or modification that refreshing essence is done, should be covered by the protection scope of the present invention.
Claims (8)
1. a kind of orthogonal frequency division multiplexing free space optical communication method based on wavelet transformation, which is characterized in that the method packet
Include following steps:
S1 selects sub-carrier number N, generates a data matrix；
S2 carries out mapping the data matrix to obtain a complex matrix based on qam mode；
S3 carries out discrete wavelet inverse transform to generate DWT-OFDM parallel signal, by the parallel signal to the complex matrix
Be converted to serial signal；
The serial signal is converted to optical signal, and transmitted it in atmospheric channel by S4；
S5 detects the optical signal based on receiving end and the optical signal detected is converted to electric signal, by the telecommunications
Number to carry out A/D conversion obtain digital signal, by the digital signal solution inversely processing, obtains the planisphere and system of demodulated signal
The bit error rate.
2. the method according to claim 1, wherein also including in the S4, to the real part of the serial signal
Be combined into digital signal all the way again after the up-conversion that numeric field carries out the road I and the road Q respectively with imaginary part, to the digital signal into
Row D/A conversion generates electric signal, and the electric signal is modulated on light carrier, carries out electro-optic conversion, generates optical signal.
3. the method according to claim 1, wherein the sub-carrier number is 128.
4. the method according to claim 1, wherein the QAM modulation includes 16QAM.
5. the method according to claim 1, wherein the solution inversely processing includes the number letter after converting A/D
Number carry out Digital Down Convert, serioparallel exchange, wavelet transformation and QAM demodulation.
6. according to the method described in claim 5, it is characterized in that, the wavelet transformation is Haar wavelet transformation.
7. the method according to claim 1, wherein in the S4, by changing the white Gaussian noise being added
Intensity, to change the signal-to-noise ratio of channel, to obtain the bit error rate under different signal-to-noise ratio.
8. the method according to claim 1, wherein the wavelet inverse transformation is Haar wavelet inverse transformation.
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| CN114006677A (en) * | 2021-09-29 | 2022-02-01 | 广东电网有限责任公司韶关供电局 | Low-voltage power line carrier communication system resource coding method and system |
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| WO2022083591A1 (en) * | 2020-10-20 | 2022-04-28 | 华为技术有限公司 | Signal processing method and related device |
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| CN114006677A (en) * | 2021-09-29 | 2022-02-01 | 广东电网有限责任公司韶关供电局 | Low-voltage power line carrier communication system resource coding method and system |
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Application publication date: 20190614 |