CN108809444A - Utilize the experimental method of shock tube simulation communication performance under plasma sheath channel - Google Patents
Utilize the experimental method of shock tube simulation communication performance under plasma sheath channel Download PDFInfo
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
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- H04B17/00—Monitoring; Testing
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- H04B17/0087—Monitoring; Testing using service channels; using auxiliary channels using auxiliary channels or channel simulators
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- H—ELECTRICITY
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- H04B—TRANSMISSION
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- H04B17/30—Monitoring; Testing of propagation channels
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Abstract
The present invention proposes a kind of experimental method using shock tube simulation communication performance under plasma sheath channel, belongs to communication experiment field.This method builds communication experiment system first；Modulation system to be compared is generated to communicate baseband signal all the way and import communication experiment system using frequency division multiplexing mode and carries out shock tube experiment, the reception signal waveform after being influenced by plasma is obtained and is sent to data processing terminal；Data processing terminal docking is received signal waveform and is handled, and the achievable rate of each modulation system under plasma channel is obtained, and completes the assessment that different modulating mode communication performance under channel is covered to plasma sheath.The present invention carries out simulated experiment using shock tube to high dynamic plasma sheath channel communication, the performance that different communication modulator approach under plasma sheath channel can be compared, to obtain the communication means that the tool in existing communication modulation mode is adapted to plasma sheath channel.
Description
Technical field
The invention belongs to communication experiment fields, more particularly to utilize shock tube simulation communicativeness under plasma sheath channel
The experimental method of energy.
Background technology
It is formed near space (being the space field apart from 20 to 100 kilometers of earth surface) high-speed aircraft flight course
Plasma sheath be a kind of special complex electromagnetic environment, often lead to the communication disruption of aircraft.And near space
For high-speed aircraft, continuous continual same ground is needed to keep communication unimpeded.Therefore, the presence of plasma sheath can be serious
Threaten the flight safety of aircraft.Realize the reliable information transfer under plasma sheath channel, it has also become development near space is high
One of the bottleneck problem that fast aircraft need to be solved primarily, and current study frontier both domestic and external.
Plasma sheath is one layer of plasma for being coated on aircraft surface, is that hypersonic aircraft is closing on sky
Between flight when, due to air severe friction, aircraft surface forms shock wave, and high temperature makes gas ionization, while thermal insulation layer is burnt
Erosion is peeled off, and plasma sheath is constituted.Charged particle in plasma sheath can absorb, reflect and scatter electromagnetic wave so that letter
Number amplitude fading and phase offset occurs, causes communication quality to deteriorate, cause information link to be interrupted when serious, it is existing to form " black barrier "
As.It is still to restrict hypersonic aircraft to develop key subjects urgently to be resolved hurrily to communicate black barrier so far.Plasma sheath channel
The numerous complicateds random processes such as characteristic is extremely complex, and the attitudes vibration of aircraft, turbulent flow, pressure fluctuation, ablation are peeled off it is close
Coupling causes the three-dimensional spatial distribution in plasma flow field to be a complicated random process.The plasma sheath of this Special complex
Three kinds of characteristics will be presented in channel：Channel time selectivity caused by the time-varying characteristics of plasma sheath；Plasma sheath set dispersion is drawn
The frequency selectivity risen；Spatial selectivity caused by the distortion of dynamic plasma sheath antenna direction.Plasma sheath electromagnetic propagation
Existing high dynamic characteristic so that conventional channel model is difficult to be suitable for plasma sheath medium.
An important parameter for weighing communication system basic performance is the achievable rate of system information transmissions.It indicate be
Communication system is when ensureing error free transmission information, maximum communication rate that system can reach.Achievable rate has weighed one
Ability of a channel to the carrying of signal transmission.The achievable rate of one channel and the state of channel have directly closes closely
The case where being, therefore in general needing to know channel when calculating channel achievable rate.In traditional achievable rate meter
In calculation method, channel probability distribution situation is known, and channel needs theoretical model, on the basis of theoretical model
It is upper to derive the information transmission achievable rate for acquiring channel.And under plasma sheath scene, a kind of this method is no longer applicable.Cause
For under plasma sheath scene, channel status and plasma physics parameter are closely related, the probability distribution of channel is according to different
Parameter can change a lot.And for plasma sheath channel, the theory of complete set is not worth with one yet at present
The model firmly believed describes the characteristic of channel.Therefore, for sheath channel, the above method can not be used to calculate the reachable of channel
Rate
Since practical flight communication experiment is of high cost, it is difficult to carry out practical flight communication experiment under present circumstances, because
This needs to design a communication simulation experiment on the ground and carries out survey under simulation plasma sheath channel to entire communication plan
Examination.But how to be still at present a very difficult project in ground environment simulation plasma sheath high dynamic channel circumstance.
Shock tube be it is a kind of using pressure difference generate shock wave device, be currently used primarily in measurement and study its generation etc.
Relevant physical parameter of gas ions, such as electron density, collision frequency, electron temperature etc..Its generated shock wave is in certain journey
High dynamic channel circumstance can be simulated on degree, still, at present about the experimental study of shock tube, essentially consists in plasma phase
Close physical parameter measurement, such as to shock tube generate plasma electron density, collision frequency measurement.And for such as
What experimentally still belongs to blank by what shock tube directly applied to communication performance research.
Since practical flight communication experiment is of high cost, it is difficult to carry out practical flight communication experiment under present circumstances, because
This realizes that shock tube high dynamic channel communication simulation test becomes active demand.Shock tube high dynamic channel communication simulation test
There are three key difficulties：1) by the restrictive condition that shock tube self character is determined, lead to the experiment cost ratio of shock tube
Larger, experiment every time will adjust the state of shock tube and complete pipeline cleaning and vacuumize reinflated whole process, and
The state for being difficult to shock tube in experiment twice is completely the same；2) the signal of communication of receiving terminal by shock tube generate etc.
After ion decaying, dynamic range of signals is bigger, theoretically more than 40dB, acquisition precision is caused to be difficult to improve；3) due to shock wave
Pipe has the communications status time existing for plasma short, only 0.2ms or so, causes the data volume received less, therefore using mistake
Code check is difficult under these conditions as communication performance index.
Invention content
In place of to fill up the blank of the prior art, proposition is a kind of to be simulated using shock tube in plasma
The experimental method of communication performance under sheath channel.The present invention carries out mould using shock tube to high dynamic plasma sheath channel communication
Draft experiment can compare the performance of different communication modulator approach under plasma sheath channel, to obtain adjusting in existing communication
Tool is adapted to the communication means of plasma sheath channel in mode processed.
The present invention proposes a kind of experimental method using shock tube simulation communication performance under plasma sheath channel, special
Sign is that this approach includes the following steps：
1) communication experiment system is built；
The communication experiment system includes：Intermediate-freuqncy signal generates equipment, and the first frequency variation signal transmitting equipment, the first frequency conversion are set
Standby, transmitting antenna, shock tube, the second frequency variation signal transmitting equipment, the second frequency conversion equipment, bandpass filter, reception antenna, data
Sample devices and data processing terminal；
The output end that the intermediate-freuqncy signal generates equipment connects the input terminal of the first frequency conversion equipment by IF interface, and first
Frequency variation signal emits the output end of equipment while connecting another input terminal of the first frequency conversion equipment；The output end of first frequency conversion equipment
Transmitting antenna is connected by radio frequency interface, transmitting antenna connects data against shock tube experiment window, the control interface of shock tube
Sample devices, the reception antenna of the shock tube other end connect the input terminal of the second frequency conversion equipment, the second frequency conversion by radio frequency interface
Signal emits another input terminal of output end the second frequency conversion equipment of connection of equipment；The output end of second frequency conversion equipment passes through intermediate frequency
Interface connects the input terminal of bandpass filter；The input terminal of the output end connection data acquisition equipment of bandpass filter；Data are adopted
The output end for collecting equipment connects data processing terminal；
2) the different modulating mode for selecting pending comparison, is generated different modulating mode all the way using frequency division multiplexing mode
Communications baseband signal to be sent；
3) the communications baseband signal steps for importing 1 to be sent for generating step 2)) in the communication experiment system built
Frequency signal generating apparatus carries out shock tube experiment using the communication experiment system, obtains the reception signal after being influenced by plasma
Waveform is simultaneously sent to data processing terminal；Specific workflow is as follows：
The communications baseband signal to be sent that step 2) is obtained generates equipment by intermediate-freuqncy signal and generates analog intermediate frequency signal,
Carrier signal is generated by the first frequency variation signal transmitting equipment, forming radiofrequency signal after being handled by the first frequency conversion equipment passes through transmitting
Antenna is sent to shock tube, and radiofrequency signal reaches the second frequency conversion equipment after shock tube by reception antenna, by the second frequency conversion
Signal emits equipment and generates carrier signal, by forming the intermediate-freuqncy signal received after the second frequency conversion equipment, then is filtered by band logical
Wave device forms the intermediate-freuqncy signal not with outer clutter, and to reach data sampling devices, data sampling devices do not have to what is received
There is the intermediate-freuqncy signal with outer clutter to carry out data acquisition, obtains the reception signal waveform after being influenced by plasma and be sent to data
Processing terminal；
4) data processing terminal docking is received signal waveform and is handled, and obtains what step 2) under plasma sheath channel was selected
The achievable rate of each modulation system completes the assessment that different modulating mode communication performance under channel is covered to plasma sheath.
The features of the present invention and advantageous effect are：
The characteristic that the present invention utilizes influence of the shock tube high dynamic channel to Electromagnetic Wave Propagation more consistent in very wide-band,
Communication simulation is generated using the method for frequency division multiplexing and sends signal, transmission as much as possible is obtained in limited call duration time
Information；Using instruments such as arbitrary waveform generator, frequency mixer, filter, A/D sample devices with shock tube together by building one
A communication simulation experimental system comprising shock tube, to be simulated to plasma sheath set channel；Utilize shock tube communication simulation
The data that experiment obtains calculate the achievable rate of different modulating mode, using achievable rate as the index of assessment communication performance.This
Invention has the following advantages：
1) method for utilizing frequency division multiplexing, devises the signal of communication of shock tube communication experiment, solves shock tube communication
Time is short, many experiments channel status be difficult to ensure it is consistent caused by the signal of multiple modulation system can not be carried out simultaneously it is real
The difficulty tested；
2) characteristic of plasma sheath channel can be simulated to a certain extent by utilizing shock wave caused by shock tube, and
Communication experiment method is devised on the basis of this, the simulation of plasma sheath channel is realized in ground environment, and required is flown
Row device transmission communication channel completes simulation in laboratory, and expense needed for experiment is greatly saved；And to A/D sampling modules into
Row optimization, solves the difficulty that dynamics of channels range is big in shock tube experiment.
3) using experiment institute measured data, obtain the signal of communication of various modulation systems by plasma sheath channel can
Up to rate, is selected for the communication mode on high dynamic channel and excellent provide support.
Description of the drawings
Fig. 1 is the communication experiment system structural schematic diagram based on shock tube of the present invention.
Fig. 2 is the computational methods flow chart of achievable rate in the present invention.
Fig. 3 is the communications baseband signal spectrum distribution diagram to be sent of the embodiment of the present invention.
Fig. 4 is communications baseband signal actual spectrum figure to be sent of the embodiment of the present invention.
Specific implementation mode
Experimental method proposed by the present invention using shock tube simulation communication performance under plasma sheath channel is tied below
It is as follows to close the drawings and specific embodiments further description.
The present invention is directed to three difficult points of shock tube experiment, uses following solution：1) by Different Modulations
Signal is combined to be compared in each experiment；2) receiving terminal to the acquisition precisions of data sampling devices acquire frequency into
Row optimization design；3) communication performance under different modulating mode is assessed using achievable rate index.
Experimental method proposed by the present invention using shock tube simulation communication performance under plasma sheath channel, this method
Include the following steps：
1) communication experiment system is built；
The communication experiment system structure is as shown in Figure 1, include：Intermediate-freuqncy signal generates equipment, the transmitting of the first frequency variation signal
Equipment, the first frequency conversion equipment, transmitting antenna, shock tube, the second frequency variation signal transmitting equipment, the second frequency conversion equipment, bandpass filtering
Device, reception antenna, data sampling devices and data processing terminal；
The output end that the intermediate-freuqncy signal generates equipment connects the input terminal of the first frequency conversion equipment by IF interface, and first
Frequency variation signal emits the output end of equipment while connecting another input terminal of the first frequency conversion equipment；The output end of first frequency conversion equipment
Transmitting antenna is connected by radio frequency interface, (experiment window is the pipe of shock tube to transmitting antenna against shock tube experiment window
Opposite two sides, can be used to receiving and transmitting signal), the control interface of shock tube connects data sampling devices, and the shock tube other end connects
The input terminal that antenna connects the second frequency conversion equipment by radio frequency interface is received, the second frequency variation signal emits the output end connection the of equipment
Another input terminal of two frequency conversion equipments；The output end of second frequency conversion equipment connects the input of bandpass filter by IF interface
End；The input terminal of the output end connection data acquisition equipment of bandpass filter；At the output end connection data of data acquisition equipment
Terminal is managed, handled by data processing terminal completion final data and obtains result.Shock tube connects data by control interface and adopts
The triggering input interface of sample equipment gives data sampling devices one trigger signal when shock tube works by control interface.
Each composition components/devices needed for this pilot system realize that function is as follows：
Intermediate-freuqncy signal generates equipment：Using arbitrary waveform generator, arbitrary waveform generator is for exporting self-defined frequency division
Multiplexed signals, it is ensured that the transmitting of intermediate-freuqncy signal emits required all kind of modulations composite signal.
Frequency variation signal emits equipment：Using vector signal generator, for emitting carrier signal, to adapt to selected by experiment
Rf frequency.
Frequency conversion equipment：It is responsible for carrying out frequency spectrum shift using frequency mixer, this pilot system is using frequency mixer working frequency in institute
The radio frequency band needed, such as S-band, C-band.
Shock tube：Using multi-functional shock tube, formula experimental facilities temporarily is rushed to meet, high-temperature gas is uniform, and parameter is controllably
It is required that.
Bandpass filter：Using passive bandpass filters, the present invention generates larger after double conversion and by channel
Noise and a plurality of mirror image frequency are general.Filter band logical bandwidth of operation is at least 60~80MHz, input power≤0.5W, by multistage
Filtering can filter most of unwanted frequency.
Data sampling devices：Usable oscillograph is sampled.The present invention uses equipment requirement sampling rate to 200MSa/
It is more than s or more and 50Mpts storage depths, sampling precision 14bit or more.
Data processing terminal：Data processing terminal obtains different modulating mode for handling collected data
Under shock tube experiment under communication achievable rate, complete the assessment of different modulating mode communication performance under reciprocity ion channels,
The computer of common model can be used.
2) the different modulating mode for selecting pending comparison, is generated different modulating mode all the way using frequency division multiplexing mode
Communications baseband signal (the present embodiment uses and generates communications baseband signal to be sent with MATLAB) to be sent, i.e., will be required
The mode of the signal frequency division multiplexing of the different modulating mode of comparison designs generation intermediate-freuqncy signal all the way；
3) the communications baseband signal steps for importing 1 to be sent for generating step 2)) in the communication experiment system built
Frequency signal generating apparatus carries out shock tube experiment using the communication experiment system, obtains the reception signal after being influenced by plasma
Waveform is simultaneously sent to data processing terminal.Specific workflow is as follows：
The communications baseband signal to be sent that step 2) is obtained generates equipment by intermediate-freuqncy signal and generates analog intermediate frequency signal,
Carrier signal is generated by the first frequency variation signal transmitting equipment, forming radiofrequency signal after being handled by the first frequency conversion equipment passes through transmitting
Antenna is sent to shock tube, and radiofrequency signal reaches the second frequency conversion equipment after shock tube by reception antenna, by the second frequency conversion
Signal emits equipment and generates carrier signal, by forming the intermediate-freuqncy signal received after the second frequency conversion equipment, then is filtered by band logical
Wave device forms the intermediate-freuqncy signal not with outer clutter, and to reach data sampling devices, data sampling devices do not have to what is received
Having the intermediate-freuqncy signal with outer clutter to carry out data acquisition, (when work, shock tube sends out control signal trigger data sampling when opening
Equipment, data sampling devices carry out data acquisition), it obtains the reception signal waveform after being influenced by plasma and is sent at data
Manage terminal.
In the present embodiment, designed frequency-division multiplex singal is imported into intermediate-freuqncy signal and generates equipment (arbitrary waveform generator)
In, shock tube, the control signal trigger data sample devices (oscillograph CX3300) provided by shock tube are opened, AD is sampled as
14bit, sample frequency 500MHz, sampling time length are 1ms.The oscillograph that data sampling devices use in the present embodiment
CX3300。
4) data processing terminal docking is received signal waveform and is handled, and obtains what step 2) under plasma sheath channel was selected
The achievable rate of each modulation system completes the assessment that different modulating mode communication performance under channel is covered to plasma sheath.It is reachable
Higher rate is effective transmission data rate higher of the modulation system, i.e. communication performance in the case where similarly sending character rate
Better.
Step 4) flow is as shown in Fig. 2, be as follows：
First, the information transmission achievable rate expression formula of channel is as follows：
I(X；Y)=H (X)-H (X | Y)
=H (Y)-H (YX)
Wherein, H (X) is the comentropy for sending signal collection X, and H (Y) is the comentropy for receiving signal collection Y, and H (X/Y) is known
The conditional entropy of X under signal collection Y is received, H (Y/X) is the conditional entropy of Y under known transmission signal collection X.
H (Y)=- ∫ p (y) logp (y) dy
Wherein, H (Y) is the comentropy for receiving signal collection Y, and p (y) is the probability density distribution of Y.And H (X/Y) and H (Y/X)
Respectively conditional entropy.
H (Y/X)=∑ p (xi)H(Y/xi)
H(Y/xi)=- ∫ p (y/xi)·logp(y/xi)dy
Wherein, xiFor i-th of transmission symbol, p (xi) it is xiProbability density distribution, p (y/xi) it is known transmission symbol xi
In the case of receive the conditional probability density distribution of symbol y.H (Y/xi) is known transmission symbol xiThe conditional entropy of lower Y.
Information to acquire sheath channel transmits achievable rate, it is necessary to acquire p (y), p (x firsti), p (y/xi), especially
Condition of acceptance probability density distribution.In conventional method, above-mentioned distribution is obtained by theory analysis and channel model.For
Sheath channel does not have theory analysis and lacks the case where model describes, and simulation numerical is used for the achievable rate of sheath channel
The method of calculating.p(y/xi) be expressed from the next：
Wherein hiIndicate the plasma sheath channel status at i-th of moment.It is obtained using the shock tube experiment of step 3)
Signal waveform is received, is distributed by the conditional probability density counted under current shock tube plasma channel status, that is, p (y |
xi, hi).In addition the probability distribution i.e. p of the state that can obtain channel are counted to the state of the channel in experiment
(hi).Pass through the process of above-mentioned numerical computations, you can obtain condition of acceptance probability density distribution p (y | xi)。
It further calculates to obtain the probability distribution p (y) for receiving symbol y, as follows：
P (y)=∑ p (y/xi)p(xi)
After having an above-mentioned probability distribution, you can corresponding comentropy and conditional entropy are acquired, to be calculated up to speed
Rate.
With reference to a specific embodiment, that the present invention is described in more detail is as follows.
The present embodiment proposes a kind of experimental method using shock tube simulation communication performance under plasma sheath channel,
It is characterized in that, this approach includes the following steps：
1) communication experiment system is built；
The communication experiment system includes：Intermediate-freuqncy signal generates equipment, and the first frequency variation signal transmitting equipment, the first frequency conversion are set
Standby, transmitting antenna, shock tube, the second frequency variation signal transmitting equipment, the second frequency conversion equipment, bandpass filter, reception antenna, data
Sample devices and data processing terminal；
The output end that the intermediate-freuqncy signal generates equipment connects the input terminal of the first frequency conversion equipment by IF interface, and first
Frequency variation signal emits the output end of equipment while connecting another input terminal of the first frequency conversion equipment；The output end of first frequency conversion equipment
Transmitting antenna is connected by radio frequency interface, transmitting antenna connects data against shock tube experiment window, the control interface of shock tube
Sample devices, the reception antenna of the shock tube other end connect the input terminal of the second frequency conversion equipment, the second frequency conversion by radio frequency interface
Signal emits another input terminal of output end the second frequency conversion equipment of connection of equipment；The output end of second frequency conversion equipment passes through intermediate frequency
Interface connects the input terminal of bandpass filter；The input terminal of the output end connection data acquisition equipment of bandpass filter；Data are adopted
The output end for collecting equipment connects data processing terminal；
The unit type for each building block of system that the present embodiment uses is as follows：
Intermediate-freuqncy signal generates equipment：Using arbitrary waveform generator, M8190A12GSa/s, arbitrary waveform generator is responsible for
The output of the required self-defined frequency-division multiplex singal of experimental system, it is ensured that pilot tone has been added for emitting in the transmitting of intermediate-freuqncy signal
The all kind of modulations composite signal such as QPSK, FSK, PPM.
Frequency variation signal emits equipment：Using vector signal generator, E4438CESG, for emitting carrier signal, to adapt to
Rf frequency needed for channel.
Frequency conversion equipment：Using ZX05-83LH-S+ frequency mixers, for working frequency in 1.7GHz~8GHz, local oscillator input range can
For 7dbm, 10dbm, 13dbm, effect of the present invention is optimal when 13dbm.
Shock tube：Using multi-functional shock tube, temporarily to rush formula experimental facilities, high-temperature gas is uniform, and parameter is controllable.It can be produced
The electron density of raw plasma reaches as high as 10^14/cm^3, and for collision frequency up to 100GHz, experimental period is tens of
Us magnitudes are to 0.2ms magnitudes.
Bandpass filter：Using BIF-70+ filters, bandwidth of operation is 58M~82MHz, and input power≤0.5W is passed through
Multiple-stage filtering can filter most of unwanted frequency.
Data sampling devices：Use oscillograph CX3300.The present embodiment using equipment can reach 500MSa/s sample rates and
256Mpts storage depths, sampling precision 14bit.
Data processing terminal：It completes, to collected data processing, to obtain not using association notebook ThinkPadT480
With the communication achievable rate under the shock tube experiment under modulation system, different modulating mode communicativeness under reciprocity ion channels is completed
The assessment of energy.
2) the different modulating mode for selecting pending comparison, is generated different modulating mode all the way using frequency division multiplexing mode
Communications baseband signal (the present embodiment uses and generates communications baseband signal to be sent with MATLAB) to be sent, i.e., will be required
The mode of the signal frequency division multiplexing of the different modulating mode of comparison designs generation intermediate-freuqncy signal all the way；
The communications baseband signal to be sent that the present embodiment uses is by simple signal, frequency shift keying 4KSK, quadrature phase shift key
Control QPSK, the frequency-division multiplex singal that pulse position modulation 4PPM is constituted, spectrum distribution is as shown in Figure 3.The transmission letter specifically generated
The design of number frequency spectrum is as follows:
(a) .QPSK signals；
If QPSK signal center frequencies are fcQPSK, that is, have
Wherein, XQPSK(t) it is QPSK signals, A is signal amplitude, A=1 in experiment；aI(t),aQ(t) ∈ { 1, -1 } is hair
The symbol for sending I, Q two-way is determined by transmission bit.H (t) is filter coefficient, is herein radical sign raised cosine roll off molding filtration
Device coefficient；Rolloff-factor takes 0.5.F is taken in experimentcQPSK=61.25MHz, corresponding QPSK signal bandwidths are 1.5M.
(b) .4PPM signals；
If 4PPM signal center frequencies are fcPPM, that is, have：
Wherein, XPPM(t) it is PPM signal, A is signal amplitude, A=1 in experiment；aPPM(t) ∈ { 1,0 } is the PPM sent
Symbol is determined by transmission bit.H (t) be filter coefficient, be herein Gaussian pulse formed filter coefficient, three dB bandwidth with
The product of symbol period is BT=0.4.Centre frequency f is taken in experimentcPPM=66MHz, corresponding 4PPM signal bandwidths are 6M left
It is right.
(c) .4FSK signals；
If 4FSK signal frequency points are fFSK,i, i=1 ..., 4, then have：
Wherein, XFSK(t) it is fsk signal, middle A is signal amplitude, A=1 in experiment；aFSK,i(t) ∈ { 1,0 } is to send
FSK symbols are determined by transmission bit.H (t) is filter coefficient, is herein radical sign raised cosine roll off formed filter coefficient,
Rolloff-factor takes 0.5.Frequency interval Δ f=2MHz, f are taken in experimentFSK,i=70M+i Δ f, bandwidth 8M, frequency range
For 71M -79M.
It is f that intermediate frequency, which is arranged, in the present embodimentcTri- signals of above-mentioned QPSK, PPM, FSK are added up, and are superimposed with by=70M
The simple signal of 70M, then can obtain intermediate-freuqncy signal s (t) to be sent is：
S (t)=XFSK(t)+XPPM(t)+XQPSK(t)+exp(1j·2πfct)
Fig. 3 gives the frequency spectrum distribution diagram of communications baseband signal to be sent in the present embodiment, and signal total bandwidth is 20M, in
Frequency of heart is 70M.
In the present embodiment, by the actual spectrogram of communications baseband signal to be sent caused by MATLAB as shown in figure 4,
Wherein the centre frequency of QPSK signals is 61.25MHz, bandwidth 1.5M；PPM signal centre frequency is 66MHz, bandwidth 6M；
The bandwidth of fsk signal is 8M, and frequency range is 71M -79M.
3) the communications baseband signal steps for importing 1 to be sent for generating step 2)) in the communication experiment system built
Frequency signal generating apparatus carries out shock tube experiment using the communication experiment system, obtains the reception signal after being influenced by plasma
Waveform is simultaneously sent to data processing terminal；Specific workflow is as follows：
The communications baseband signal to be sent that step 2) is obtained generates equipment by intermediate-freuqncy signal and generates analog intermediate frequency signal,
Carrier signal is generated by the first frequency variation signal transmitting equipment, forming radiofrequency signal after being handled by the first frequency conversion equipment passes through transmitting
Antenna is sent to shock tube, and radiofrequency signal reaches the second frequency conversion equipment after shock tube by reception antenna, by the second frequency conversion
Signal emits equipment and generates carrier signal, by forming the intermediate-freuqncy signal received after the second frequency conversion equipment, then is filtered by band logical
Wave device forms the intermediate-freuqncy signal not with outer clutter, and to reach data sampling devices, data sampling devices do not have to what is received
There is the intermediate-freuqncy signal with outer clutter to carry out data acquisition, obtains the reception signal waveform after being influenced by plasma and be sent to data
Processing terminal；
In the present embodiment, the control interface of shock tube is connected with data sampling devices, and data sampling devices are set
Trigger signal.
Shock tube point, which is fought, starts data sampling, i.e., trigger data sample devices when shock tube is lighted a fire, to data sampling
Equipment starts to acquire current Received Signal oscillogram；Collected data are the voltage value of oscilloprobe, to be connect
Receive signal waveforms.
4) data processing terminal docks receipts signal waveform using MATLAB softwares and is handled, and obtains plasma sheath channel
The achievable rate of each selected modulation system of lower step 2) is completed to cover different modulating mode communicativeness under channel to plasma sheath
The assessment of energy.
If data sampling devices successfully adopt data, that is, imports data to data processing terminal and complete data processing, i.e.,
Corresponding achievable rate can be obtained, experiment is completed.If collecting data not successfully, that is, resets shock tube trigger signal and lay equal stress on
New experiment.
In the present embodiment, collected data are finally passed into data processing terminal, to can be obtained under plasma channel
The achievable rate calculations of different modulating mode.The present embodiment respectively by frequency range 60.5M-62M, 63M-69M, 71M-79M's
Bandpass filter filters out QPSK, PPM, fsk signal；It is obtained receiving signal by matched filter again, to which respective symbol can be obtained
Conditional probability density, obtain required distribution function there are two types of mode：Statistics with histogram directly is done to receiving symbol, to
Obtain the numerical approximation of distribution function；It is approximate with logarithm normal distribution or Gaussian mixtures, it is only necessary to estimate corresponding model
Parameter.Finally, the distribution function approximate solution for having corresponding symbol, then can be obtained the achievable rate of corresponding modulation system.
Claims (2)
1. a kind of experimental method using shock tube simulation communication performance under plasma sheath channel, which is characterized in that the party
Method includes the following steps：
1) communication experiment system is built；
The communication experiment system includes：Intermediate-freuqncy signal generate equipment, the first frequency variation signal emit equipment, the first frequency conversion equipment,
Transmitting antenna, shock tube, the second frequency variation signal transmitting equipment, the second frequency conversion equipment, bandpass filter, reception antenna, data are adopted
Sample equipment and data processing terminal；
The output end that the intermediate-freuqncy signal generates equipment passes through the input terminal of IF interface the first frequency conversion equipment of connection, the first frequency conversion
Signal emits the output end of equipment while connecting another input terminal of the first frequency conversion equipment；The output end of first frequency conversion equipment passes through
Radio frequency interface connects transmitting antenna, and transmitting antenna connects data sampling against shock tube experiment window, the control interface of shock tube
Equipment, the reception antenna of the shock tube other end connect the input terminal of the second frequency conversion equipment, the second frequency variation signal by radio frequency interface
The output end for emitting equipment connects another input terminal of the second frequency conversion equipment；The output end of second frequency conversion equipment passes through IF interface
Connect the input terminal of bandpass filter；The input terminal of the output end connection data acquisition equipment of bandpass filter；Data acquisition is set
Standby output end connects data processing terminal；
2) the different modulating mode for selecting pending comparison, is generated different modulating mode using frequency division multiplexing mode pending all the way
The communications baseband signal sent；
3) by communications baseband signal steps for importing 1 to be sent that step 2) generates) intermediate frequency of communication experiment system built believes
Number generate equipment, using the communication experiment system carry out shock tube experiment, obtain the reception signal waveform after being influenced by plasma
And it is sent to data processing terminal；Specific workflow is as follows：
The communications baseband signal to be sent that step 2) is obtained generates equipment by intermediate-freuqncy signal and generates analog intermediate frequency signal, by the
One frequency variation signal emits equipment and generates carrier signal, and forming radiofrequency signal after being handled by the first frequency conversion equipment passes through transmitting antenna
It is sent to shock tube, radiofrequency signal reaches the second frequency conversion equipment after shock tube by reception antenna, by the second frequency variation signal
Emit equipment and generate carrier signal, by forming the intermediate-freuqncy signal received after the second frequency conversion equipment, then passes through bandpass filter
The intermediate-freuqncy signal not with outer clutter is formed, to reach data sampling devices, data sampling devices are to receiving without band
The intermediate-freuqncy signal of outer clutter carries out data acquisition, obtains the reception signal waveform after being influenced by plasma and is sent to data processing
Terminal；
4) data processing terminal docking is received signal waveform and is handled, and obtains selected each of step 2) under plasma sheath channel
The achievable rate of modulation system completes the assessment that different modulating mode communication performance under channel is covered to plasma sheath.
2. the method as described in claim 1, which is characterized in that achievable rate expression formula is as follows in the step 4)：
I(X；Y)=H (X)-H (X | Y)
=H (Y)-H (Y | X)
Wherein, H (X) is the comentropy for sending signal collection X, and H (Y) is the comentropy for receiving signal collection Y, and H (X/Y) is known reception
The conditional entropy of X under signal collection Y, H (Y/X) are the conditional entropy of Y under known transmission signal collection X；
H (Y)=- ∫ p (y) logp (y) dy
Wherein, p (y) is the probability density distribution of Y；
H (Y/X)=∑ p (xi)H(Y/xi)
H(Y/xi)=- ∫ p (y/xi)·logp(y/xi)dy
Wherein, xiFor i-th of transmission symbol, p (xi) it is xiProbability density distribution, p (y/xi) it is known transmission symbol xiFeelings
The conditional probability density distribution of symbol y is received under condition；H (Y/xi) is known transmission symbol xiThe conditional entropy of lower Y；
p(y/xi) be expressed from the next：
Wherein, hiIndicate the plasma sheath channel status at i-th of moment；The reception obtained using the shock tube experiment of step 3)
Signal waveform, by count the conditional probability density distribution p under current shock tube plasma channel status (y | xi, hi), and to reality
The state of channel in testing carries out the probability distribution p (h that statistics obtains the state of channeli), obtain condition of acceptance probability density point
Cloth p (y | xi)；
It further calculates to obtain the probability distribution p (y) for receiving symbol y, as follows：
P (y)=∑ p (y/xi)p(xi)。
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