CN109743107A - A kind of orthogonal frequency division multiplexing free-space optical communication system based on wavelet transformation - Google Patents
A kind of orthogonal frequency division multiplexing free-space optical communication system 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 system based on wavelet transformation.The system includes: mapping block；Wavelet inverse transformation module carries out wavelet inverse transformation to the complex matrix after mapping；Parallel serial conversion module converts serial data for the parallel data after wavelet transformation and obtains ofdm signal；Digital Up Convert module is combined into digital signal all the way after the real and imaginary parts of ofdm signal to be carried out to the up-conversion on the road I and the road Q respectively again；Digital signal input arbitrary waveform generator is carried out D/A conversion by arbitrary waveform generator；Mach increases Dare modulator, and the electric signal of arbitrary waveform generator output is converted into optical signal through driving input modulator；Variable optical attenuator connects modulator, for adjusting the transmission power for the optical signal being transferred in atmospheric channel by collimating mirror；Photodetector detects simultaneously transmitting photo-signal and the signal of conversion is transmitted to off-line processing system to obtain the bit error rate of the planisphere of demodulated signal and system.
Description
Technical field
The present invention relates to the free-space optical communication systems in a kind of optical communication system field, are specifically related to one kind and are based on
The orthogonal frequency division multiplexing free-space optical communication system of wavelet 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 system of wavelet transformation, which uses compared to existing
The FSO system of OFDM (FFT-OFDM) based on Fourier transformation 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, have higher spectrum efficiency.To realize
Above-mentioned purpose, the present invention adopts the following technical scheme:
A kind of orthogonal frequency division multiplexing free-space optical communication system based on wavelet transformation, which is characterized in that the system
Include:
The data matrix of input is carried out the complex matrix after QAM modulation is mapped by mapping block；Wavelet inverse transformation
Module carries out wavelet inverse transformation to the complex matrix after mapping；
Parallel data after wavelet transformation is converted to serial data, obtains ofdm signal by parallel serial conversion module；
The real and imaginary parts of the ofdm signal of parallel serial conversion module output are carried out I by Digital Up Convert module respectively
It is combined into digital signal all the way again after the up-conversion on road and the road Q；
The input arbitrary waveform generator of digital signal all the way of synthesis is carried out D/A conversion by arbitrary waveform generator；
Electrooptic modulator, the electric signal of the arbitrary waveform generator output are converted through input modulator of overdriving
For optical signal；
Variable optical attenuator connects the modulator, for adjusting the light letter being transferred in atmospheric channel by collimating mirror
Number transmission power；
Photodetector, optical signal in atmospheric sounding channel are simultaneously converted to electric signal, the electric signal are passed through number
Storage oscillograph carries out A/D conversion, and the signal of conversion is transferred to off-line processing system, obtains planisphere and the bit error rate.
Preferably, the laser generates light carrier and is modulated to the electric signal that the arbitrary waveform generator exports
On the light carrier, optical signal is converted to.
Preferably, which includes that Mach increases Dare modulator, and the laser is outside cavity gas laser.
Preferably, which also includes collimating mirror, and the optical signal is transferred to atmospheric channel by the collimating mirror of transmitting terminal
In.
Preferably, which includes avalanche photodide.
Preferably, which includes Digital Down Converter Module, serioparallel exchange module, the reconciliation of wavelet transformation module
Mapping block, the Digital Down Converter Module to be input to digital storage oscilloscope carry out A/D conversion after signal carry out
Digital Down Convert extracts the in-phase component and quadrature component of signal, is then combined into complex signal all the way again,
The serioparallel exchange module is to convert serial data into parallel data, and by the parallel data transmission after conversion
Wavelet transform is carried out to the wavelet transformation module, is transferred to demapping through the transformed signal of wavelet transformation module
Module carries out QAM demodulation and restores input signal, obtains the planisphere of demodulated signal and the bit error rate of system.
Preferably, which includes 16QAM/64QAM modulation.
Scheme in compared with the existing technology, advantages of the present invention:
Orthogonal frequency division multiplexing free-space optical communication system proposed by the present invention based on wavelet transformation will be become based on small echo
The OFDM changed replaces the OFDM based on Fourier transformation to be applied among FSO system, compares Fourier transformation, small echo is in the time domain
Length is limited, and adjacent OFDM subcarrier will not generate interference after wavelet modulation, therefore not need cyclic prefix, is had more
High spectrum efficiency.
Detailed description of the invention
The invention will be further described with reference to the accompanying drawings and embodiments:
Fig. 1 show the orthogonal frequency division multiplexing free-space optical communication system based on wavelet transformation of the embodiment of the present invention
System block diagram；
Fig. 2 is the FSO system block diagram using FFT-OFDM；
Fig. 3 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. 4 is under the 64QAM 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 is FSO system receiving terminal demodulated signal planisphere under the 16QAM mapping of the embodiment of the present invention；
Fig. 6 is FSO system receiving terminal demodulated signal planisphere under the 64QAM mapping of the embodiment of the present invention.
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 that Fig. 1 show orthogonal frequency division multiplexing free-space optical communication system the present invention is based on wavelet transformation is
System block diagram, the system include mapping block, wavelet inverse transformation module, parallel/serial conversion module, arbitrary waveform generator (AWG), tune
Device processed, variable optical attenuator (VOA), photodetector (APD) and digital storage oscilloscope (DSO) and receiving end processed offline
System composition, wherein the mapping block is used to carrying out the data matrix of input into the plural square after QAM modulation is mapped
Battle array；In one embodiment, the modulator be Mach increase Dare modulator (MZM), the mapping block include 16QAM and
64QAM modulation, the sub-carrier number selected is 128.It will be inverse small echo will to be sent by the modulated complex matrix of 16QAM/64QAM
Conversion module carries out discrete wavelet inverse transform (IDWT), and in one embodiment, wavelet inverse transformation module is Haar wavelet inverse transformation
Module.Parallel data after discrete wavelet inverse transform (IDWT) is converted to serial data after entering parallel/serial conversion module, because
The light modulation and demodulation mode that the radio optical communication system is examined using straight straightening, so the signal being modulated on light is necessary for
Real number signal.After the up-conversion that real and imaginary parts of the numeric field to the OFDM complex signal of generation carry out the road I and the road Q respectively again
It is combined into digital signal input arbitrary waveform generator (AWG) all the way and carries out D/A conversion.
The above-mentioned electric signal exported after arbitrary waveform generator (AWG) conversion, which is overdrived, inputs Mach increasing Dare tune
The light carrier of device (MZM) processed, external laser cavity (ECL) output is modulated, and optical signal is converted electrical signals to, in the present invention
In, Mach is connected with variable optical attenuator (VOA) after increasing Dare modulator (MZM), for adjusting the hair of the optical signal after converting
Power is penetrated, the optical signal is transferred in atmospheric channel by the collimating mirror of transmitting terminal, the collimating mirror that optical signal passes through receiving end
After being detected by photodetector, it is input into digital storage oscilloscope (DSO) and carries out A/D conversion, and the signal of conversion is transmitted
To off-line processing system, planisphere and the bit error rate are obtained.In one embodiment, processed offline includes Digital Down Convert, goes here and there and turns
It changes, wavelet transform (DWT) and QAM demodulation finally obtain the planisphere of demodulated signal and the bit error rate of system.It please refers to
Shown in Fig. 1, specifically, it is defeated after Digital Down Convert to be input to the signal that digital storage oscilloscope (DSO) is carried out after A/D conversion
Enter to string and conversion module, converts serial data into parallel data, and the parallel data after conversion is passed through into discrete wavelet transformer
(DWT) it is transferred to De-mapping module and carries out QAM demodulation, wherein QAM demodulation includes that 16QAM/64QAM is demodulated, and finally obtains demodulation
The planisphere of signal and the bit error rate of system.
Presently filed embodiment changes the transmission power of light, such as pass through tune by adjusting variable optical attenuator (VOA)
Section variable optical attenuator (VOA) is the first transmission power come the transmission power for adjusting light, and photodetector (APD) detects optical signal
And after being converted into electric signal, electric signal is input to digital storage oscilloscope (DSO) and carries out A/D conversion, and by the number of conversion
Word signal is transferred to off-line processing system, obtains planisphere and the bit error rate under the first transmission power.Similarly, variable by adjusting
The transmission power adjustment of light is the second transmission power by optical attenuator (VOA), and third transmission power etc. obtains the second transmitting respectively
Power, planisphere and the bit error rate under the different capacities such as third transmission power.
In one embodiment, processed offline includes Digital Down Convert, serioparallel exchange, wavelet transform (DWT) and QAM
Demodulation, finally obtains the planisphere and error rate of system of demodulated signal.It please refers to shown in Fig. 1, specifically, being input to stored digital
The signal that oscillograph (DSO) carries out after A/D conversion is input to serioparallel exchange module after Digital Down Convert, and serial data is turned
It is changed to parallel data, and the parallel data after conversion is transferred to mapping block by discrete wavelet transformer (DWT) and carries out QAM solution
It adjusts, wherein QAM demodulation includes that 16QAM/64QAM is demodulated, and finally obtains the planisphere of demodulated signal and the bit error rate of system.
In one embodiment, photodetector uses 10Gb/s avalanche photodetector (APD), and small echo uses three kinds of small echos
Base is made comparisons analysis, including Haar, db4 and sym4.Air link length is 30cm, wavelength of transmitted light 1550.12nm, is sent
Rate is 1Gb/s, sampling rate 10GS/s.
It is illustrated in figure 2 the FSO system block diagram for using FFT-OFDM in the prior art, the difference of the system and Fig. 1 exist
In the Fourier transformation of the prior art replaces with wavelet transformation, because FFT-OFDM can generate intersymbol interference, turns carrying out D/A
It must be introduced into cyclic prefix before changing to go to avoid interfering.Likewise, needing to remove circulation before receiving end carries out Fourier transformation
Prefix, the number of cyclic prefix are 32.Because Fourier transformation is unlimited in time domain length, this can bring about intersymbol interference, reduce
The anti-interference ability of system, it is therefore necessary to introduce cyclic prefix to resist intersymbol interference, but bandwidth can also be paid by doing so
Cost reduces the availability of frequency spectrum, and brings energy loss.Cyclic prefix is longer, and energy loss is bigger.Therefore by small echo
Transformation replaces Fourier transformation, because length is limited small echo in the time domain, adjacent OFDM subcarrier is not after wavelet modulation
Interference can be generated, therefore does not need cyclic prefix, there is higher spectrum efficiency, there is stronger anti-noise jamming ability.
QAM demodulation includes that 16QAM/64QAM is demodulated, and is illustrated in figure 3 under 16QAM mapping mode, using FFT-OFDM and
The bit error rate of the FSO system of DWT-OFDM and the curve of transmission power.The top mark point is to use FFT- for circle
The ber curve of the FSO system of OFDM, below three be using using different wavelet basis DWT-OFDM FSO system
Ber curve.As can be seen that being substantially better than using the bit error rate of the FSO system of DWT-OFDM using FFT-OFDM's.From
It is in figure it can also be seen that minimum using the bit error rate of the FSO system of the DWT-OFDM using Haar small echo, in 7%FEC threshold value
Under, the low 5dB of transmission power ratio FFT required for the system using Haar small echo.Use the system of db4 and sym4 small echo
Bit error rate size is close, 4dB lower than transmission power needed for FFT under 7%FEC threshold value.
Be illustrated in figure 4 under 64QAM mapping mode, using FFT-OFDM and DWT-OFDM FSO system the bit error rate with
The curve of transmission power.The top mark point is the ber curve for using the FSO system of FFT-OFDM for circle, below
Three are the ber curves for using the FSO system of the DWT-OFDM using different wavelet basis.As can be seen that compared to
Under 16QAM, 64QAM mapping mode, using DWT-OFDM FSO system the bit error rate compared to use FFT-OFDM error code
Rate advantage is more obvious.From this figure it can be seen that using the bit error rate of the FSO system of the DWT-OFDM using Haar small echo most
Low, under 7%FEC threshold value, transmission power required for the system using Haar small echo is -11dBm.And when transmission power reaches
When maximum value -4dBm, 7%FEC threshold value is not reached also using the error rate of system of FFT, the system that this explanation uses Haar small echo
Low 7dB of the required transmission power at least than using FFT system.Using db4 small echo error rate of system slightly higher than with
Sym4 small echo, under 7%FEC threshold value, the low 0.8dB of transmission power ratio sym4 required for the system using db4 small echo.
It is illustrated in figure 5 under 16QAM mapping mode, FSO system receiving terminal demodulated signal planisphere, wherein (a) is to use
The FSO system receiving terminal planisphere of FFT-OFDM, (b), (c) and (d) be respectively to use to use Haar small echo, db4 small echo
With the FSO system receiving terminal planisphere of the DWT-OFDM of sym4 small echo.It can be seen from the figure that using the application embodiment
DWT-OFDM the polymerization of FSO system constellation figure it is clear, which use the constellation point congregational rate of Haar small echo is best, and adopt
More serious with the FSO system constellation figure disperse of FFT-OFDM, it is dry that this illustrates that DWT-OFDM can preferably resist atmospheric channel
It disturbs.
It is illustrated in figure 6 under 64QAM mapping mode, FSO system receiving terminal demodulated signal planisphere, wherein (a) is to use
The FSO system receiving terminal planisphere of FFT-OFDM, (b), (c) and (d) be respectively to use to use Haar small echo, db4 small echo
With the FSO system receiving terminal planisphere of the DWT-OFDM of sym4 small echo.It can be seen from the figure that 64QAM reflects compared to 16QAM
It penetrates under mode, the FSO system constellation figure disperse of FFT-OFDM is more more serious, and uses the FSO system star of DWT-OFDM
Seat figure polymerization is more visible, and which use the constellation point congregational rate of Haar small echo is best.
The orthogonal frequency division multiplexing free-space optical communication system based on wavelet transformation that the application proposes will be become based on small echo
The OFDM changed replaces the OFDM based on Fourier transformation to be applied among FSO system, which is based on FFT- compared to existing
The FSO system of OFDM has stronger anti-noise jamming ability, the function translated on a timeline due to wavelet transformation and just
The each function base of its in intersection of subspace is all satisfied orthogonality, so intersymbol interference will not be generated when facing multidiameter delay, and
Without introducing cyclic prefix, there is the higher availability of frequency spectrum and better bit error rate performance.
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 (7)
1. a kind of orthogonal frequency division multiplexing free-space optical communication system based on wavelet transformation, which is characterized in that the system packet
It includes:
The data matrix of input is carried out the complex matrix after QAM modulation is mapped by mapping block；
Wavelet inverse transformation module carries out wavelet inverse transformation to the complex matrix after mapping；
Parallel data after wavelet transformation is converted to serial data, obtains ofdm signal by parallel serial conversion module；
The real and imaginary parts of the ofdm signal of parallel serial conversion module output are carried out the road I and Q by Digital Up Convert module respectively
Digital signal all the way is combined into after the up-conversion on road again；
The input arbitrary waveform generator of digital signal all the way of synthesis is carried out D/A conversion by arbitrary waveform generator；
Electrooptic modulator, the electric signal of the arbitrary waveform generator output are converted into light through input modulator of overdriving
Signal；
Variable optical attenuator connects the modulator, for adjusting the optical signal being transferred in atmospheric channel by collimating mirror
Transmission power；
Photodetector, optical signal in atmospheric sounding channel are simultaneously converted to electric signal, the electric signal are passed through stored digital
Oscillograph carries out A/D conversion, and the signal of conversion is transferred to off-line processing system, obtains planisphere and the bit error rate.
2. system according to claim 1, which is characterized in that also include laser, generate light carrier and described will appoint
The electric signal of meaning waveform generator output is modulated on the light carrier, is converted to optical signal.
3. system according to claim 2, which is characterized in that the electrooptic modulator includes that Mach increases Dare modulator,
The laser is outside cavity gas laser.
4. system according to claim 1, which is characterized in that also include collimating mirror, the optical signal passes through transmitting terminal
Collimating mirror is transferred in atmospheric channel.
5. system according to claim 1, which is characterized in that the photodetector includes avalanche photodide.
6. system according to claim 1, which is characterized in that the off-line processing system include Digital Down Converter Module,
Serioparallel exchange module, wavelet transformation module, De-mapping module,
The Digital Down Converter Module to be input to digital storage oscilloscope carry out A/D conversion after signal carry out number under
Frequency conversion extracts the in-phase component and quadrature component of signal, is then combined into complex signal all the way again,
The serioparallel exchange module is to convert serial data into parallel data, and by the parallel data transmission after conversion to institute
It states wavelet transformation module and carries out wavelet transform, be transferred to De-mapping module through the transformed signal of wavelet transformation module
It carries out QAM demodulation and restores signal, obtain the planisphere of demodulated signal and the bit error rate of system.
7. system according to claim 1, which is characterized in that the QAM modulation includes 16QAM/64QAM modulation.
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