CN109379154A - A kind of safe transmission scheme based on time reversal technology - Google Patents
A kind of safe transmission scheme based on time reversal technology Download PDFInfo
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- CN109379154A CN109379154A CN201811181405.4A CN201811181405A CN109379154A CN 109379154 A CN109379154 A CN 109379154A CN 201811181405 A CN201811181405 A CN 201811181405A CN 109379154 A CN109379154 A CN 109379154A
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B17/00—Monitoring; Testing
- H04B17/30—Monitoring; Testing of propagation channels
- H04B17/391—Modelling the propagation channel
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B17/00—Monitoring; Testing
- H04B17/30—Monitoring; Testing of propagation channels
- H04B17/309—Measuring or estimating channel quality parameters
- H04B17/336—Signal-to-interference ratio [SIR] or carrier-to-interference ratio [CIR]
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B7/00—Radio transmission systems, i.e. using radiation field
- H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
- H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
- H04B7/06—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station
- H04B7/0613—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission
- H04B7/0615—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission of weighted versions of same signal
- H04B7/0617—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission of weighted versions of same signal for beam forming
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/32—Carrier systems characterised by combinations of two or more of the types covered by groups H04L27/02, H04L27/10, H04L27/18 or H04L27/26
- H04L27/34—Amplitude- and phase-modulated carrier systems, e.g. quadrature-amplitude modulated carrier systems
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W12/00—Security arrangements; Authentication; Protecting privacy or anonymity
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Abstract
Wireless communication may steal information in communication process by open free space, eavesdropping user.For the information leakage problem of multi-user downlink, a kind of safe transmission scheme that wave beam forming (BF) technical optimization is used based on time reversal (TR) technology is proposed.The program establishes multiple input single output (MISO) tapping channel model to maximize safe capacity as multi-user communication criterion.One side base station enhances signal in the direction indicated using beamforming technique, sends desired signal for desired user；On the other hand due to time reversal technology be to environment it is adaptive, the signal of base station will pass through time reversal chamber before transmission, and focusing makes energy focus on legitimate receipt side when sky, and security performance is more excellent.Theory analysis and simulation result show: compared with existing safety of physical layer scheme, suggested plans safe capacity is higher, and bit error rate is lower.
Description
Technical field
The present invention relates to wireless communication technology field, in particular to a kind of safe transmission side based on time reversal technology
Case.
Background technique
Physical-layer techniques constantly explore innovation in recent years, have accumulated the technology base of a large amount of physical layer information safe transmission researchs
Plinth, therefore the research of radio physical layer safety has obtained many research institutions and the attention of scholar, it has also become wireless communication field
A research hotspot.Safety of physical layer transmission technology is a kind of mode of lifting system safe capacity, is guaranteed in wireless transmission
Maximum safe capacity be one of important goal of secure communication.Safe capacity indicates that information is transmitted to desired user security in base station
Maximum rate, be the important indicator measured system and realize safety of physical layer communication capacity.When the channel quality of eavesdropping side
Than legitimate receipt side bad channel quality when, there are the safe capacities of non-zero；Conversely, safe capacity is zero, i.e. base station and expectation
The communication link of a safety is not present between user.In order to overcome the defect that safe capacity is zero under above situation, people is studied
Member has carried out the research of theoretical property to the safety of physical layer under multiple-input and multiple-output (MIMO).Research shows that when desired user receives
When information, eavesdropping user can eavesdrop the communication by tapping channel, and safe capacity can be improved using beamforming technique.Wave beam
Figuration technology can be believed in a specified direction by the amplitude and phase of each array element signals of control, the signal for emitting antenna
Number enhancing, for it is expected user transmission desired signal.Some researchers consider rayleigh fading channel, the results showed that when base station is sent out
When penetrating number of antennas increase, even if eavesdropping user is equipped with more antennas, security performance is still significantly improved.In addition there are also research people
Safe rate when beamforming technique and united beam form-endowing technology and a certain item technology is only used in member's comparison physical layer, point
Analysis demonstrates united beam form-endowing technology and the security performance of system can be improved in a certain item technology.
Time reversal technology attracts extensive attention in wireless communication research because of its good electromagnetic property.It can be uniform
Or adaptive room and time synchronizing focus is realized in inhomogeneous medium, i.e., only believe within the scope of the room and time of very little
Number reach most strong, and it is extremely faint beyond its room and time focusing range signal.Expert focuses when proposing using sky, and the time is anti-
Low complex degree communication may be implemented in artistic skills art.Researcher compare mimo system in using time reversal technology and when not in use between
Safe capacity when inversion technique, analysis demonstrate time reversal technology and the security performance of system can be improved.Though existing research
Time reversal technology and beamforming technique are so combined, but have mutually been tied without exploring time reversal technology with beamforming technique
Close the application in terms of safety of physical layer.
Wireless communication may steal information in communication process by open free space, eavesdropping user.Needle
To the information leakage problem of multi-user downlink, propose that a kind of time reversal (TR) technology that is based on uses wave beam forming (BF) skill
The safe transmission scheme of art optimization.The program establishes multiple input single output to maximize safe capacity as multi-user communication criterion
(MISO) tapping channel model.One side base station enhances signal in the direction indicated using beamforming technique, for expectation
User sends desired signal；On the other hand due to time reversal technology be to environment it is adaptive, the signal of base station is in transmitting
Before will pass through time reversal chamber, focusing makes energy focus on legitimate receipt side when sky, and security performance is more excellent.
Summary of the invention
For the information leakage problem of multi-user downlink, correlation and channel shape between combine antenna of the present invention
System modelling is downlink MISO tapping channel model to maximize safe capacity as multi-user communication criterion by state.It is proposed one kind
The safe transmission scheme of beamforming technique optimization is used based on time reversal technology, reduces the wind that information is ravesdropping user's eavesdropping
Danger.The mentality of designing of scheme are as follows: firstly, base station uses wave beam forming in a descending multi-user MISO tapping channel model
Technology emits signal to K expectation user, selects an optimal user k to be communicated according to safe capacity, eavesdropping user can lead to
Cross tapping channel steal information；Secondly, the signal of every antenna of base station will pass through a time reversal chamber before transmission.
The present invention, which suggests plans, studies the performances such as Signal to Interference plus Noise Ratio (SINR), safe capacity, and makes a concrete analysis of correlation and use between antenna
Influence of the beamforming technique to communication security.Safe transmission scheme based on time reversal the following steps are included:
Step 101: descending multi-user MISO tapping channel model of the building based on time reversal；
Step 102: equivalent secure transmission technique is the beamforming technique based on MISO-TR；
Step 103: system performance analysis is specifically analyzed in terms of two: safe capacity and bit error rate.
The descending multi-user MISO tapping channel model of step 101 building based on time reversal includes: according to the time
Inverting downlink transmission model, using MISO working method, the descending multi-user MISO tapping channel model packet suggested plans
Include a base station, K expectation user and an eavesdropping user.Base station is equipped with M root antenna, it is expected that user and eavesdropping user are all equipped with
Single antenna legitimate channel and tapping channel are mutually indepedent, and obey Rayleigh fading.Assuming that all channel fading coefficients in system
All obey CN (0,0.5) distribution.
The reception signal for receiving signal and eavesdropping user of expectation user will be derived respectively below:
In Multi-users MIS O tapping channel model, eavesdropping user only carries out passive wiretapping, the channel status of eavesdropping user
Information is unknown.Channel impulse response (CIR) between base station and user is obtained in the time reversal detection phase, due to multipath channel
With complexity, it is therefore assumed that known to CIR.CIR can be indicated are as follows:
In formula: 1≤m≤M；U indicates K expectation user and an eavesdropping user；L is the number of distinguishable multipath；
hMu, lIndicate the amplitude of the l articles multipath；τMu, lIndicate the time delay of the l articles multipath；Channel impulse response is discrete in the time domain to turn to square
Battle array hmu∈CL×1, it may be assumed that
hmu=[hmu[0], hmu[1] ..., hmu[L-1]]T
To each of the links, hmu[l] is Cyclic Symmetry multiple Gauss (CSCG) stochastic variable, is met:
E[hmu[l]]=0
In formula: TsFor system communication cycle, σTFor channel root mean square delay extension.
Assuming that base station sends the independent unit energy symbol s of a secretkTo desired user k, then all K expectation users
Transmission symbol are as follows:
S=[s1, s2..., sK]T
Time reversal chamber can indicate are as follows:
hk-TR(t)=[hmk[L-1], hmk[L-2] ..., hmk[0]]T/||hmk||
hmk(t)∈CL×1For the channel vector between base station and expectation user k.As can be seen from the above formula that time reversal
The shock response of chamber is that (so-called time reversal is exactly in the time domain to received for the time reversal of respective channels shock response
Signal carries out backout, and phase conjugation is equal on frequency domain) and normalize.Normalized purpose is in order to ensure transmitting
Energy remains unchanged.
Therefore, each transmitting symbol of Base Transmitter to desired user k will undergo an equivalent channel:
gmk=hk-TR*hmk
In formula: * indicates convolution；gmkChannel length be hmk2 demultiplications 1, i.e. 2L-1, it is being total to about center
Yoke symmetric sequences, it may be assumed that
It might as well enable:
Central value gMk, 0For real number.
In descending multi-user MISO tapping channel model, recipient is single-antenna subscriber.This is because time reversal
Chamber can only once be handled a specific channel, that is to say, that a time reversal chamber cannot be simultaneously to two or two
Above different channels are handled.
The equivalent secure transmission technique of step 102 is that the beamforming technique based on MISO-TR includes: to beg for separately below
By based on beamforming technique and the reception signal based on MISO-TR using beamforming technique optimization two schemes.
When only with beamforming technique, it is expected that the reception signal of user k are as follows:
Base station utilizes the channel state information (CSI) in channel detection stage, that is, hmk(t), it is (so-called to obtain wave beam forming
Beam figuration is exactly the weight that wave beam forming is selected using the instantaneous characteristic of channel, is pre-processed to signal is sent, and then will
Power is sent to concentrate on recipient and reduce signal-to-noise ratio (SNR) the vector W of eavesdropping sidek, it can be calculated by following formula:
(.)HIndicate Hermitian conjugate transposition；||.||FIndicate Frobenius norm.
After beam forming processing, the reception signal of eavesdropping user are as follows:
Therefore, it is desirable to the received signal to noise ratio of user k are as follows:
Assuming that CIR is generated at random, then it is expected that the intersymbol interference power of user k and inter-user interference power are respectively as follows:
The received signal to noise ratio of eavesdropping user are as follows:
In formula: the intersymbol interference power and inter-user interference power of eavesdropping user are respectively as follows:
When being optimized based on MISO-TR using beamforming technique, it is expected that the reception signal at user k are as follows:
Above formula is made of four parts: (1) desired signal (Signal)；(2) intersymbol interference (ISI)；(3) inter-user interference
(IUI)；(4) additive white Gaussian noise (Noise).
Therefore, it is desired to the received signal to noise ratio of user k are as follows:
In formula: the intersymbol interference power and inter-user interference power of expectation user k is respectively as follows:
Base station emits signal, after time reversal chamber, the reception signal of eavesdropping user using beamforming technique are as follows:
Similarly:
Therefore, the received signal to noise ratio of eavesdropping user are as follows:
In formula: the intersymbol interference power and inter-user interference power of eavesdropping user are respectively as follows:
As the above analysis, beamforming technique is not still either used using beamforming technique, it is expected that user
The signal power received is greater than the signal power that eavesdropping user receives certainly.Base station is using beamforming technique transmitting letter
Number, after time reversal chamber, signal power, intersymbol interference power and inter-user interference power are all changed.When adopting
When with time inversion technique, the signal of Base Transmitter can focus on legitimate receipt side, prevent the information side of being ravesdropping from stealing.
Step 103 system performance analysis includes: that the present invention will be next pair in terms of safe capacity and bit error rate two
System performance is analyzed.The analytic expression of safe capacity is obtained by theory analysis and the derivation of equation.According to bit error rate formula
Derivation mode is modulated using quadrature amplitude modulation (QAM), makes a concrete analysis of the bit error rate of system.
The capacity of legitimate channel are as follows:
Ck=log2(1+RSIN, k)
The capacity of tapping channel are as follows:
CE=log2(1+RSIN, E)
When then base station is communicated with desired user k, the safe capacity of system are as follows:
As can be seen from the above equation, under desired user and the identical situation of eavesdropping user noise power, with signal-to-noise ratio
Increase, safe capacity will be gradually increased.
The safe capacity of system is the difference of the capacity of legitimate channel and the capacity of tapping channel, be can be realized most when greater than zero
Big safe capacity, eavesdropping user can not steal informations；Safe capacity is zero when equal to or less than zero, and eavesdropping user can theoretically lead to
Cross the information that the information stolen decodes out base station transmission.The channel status of legitimate channel and tapping channel determines the safety of system
Property, capacity is bigger when the channel status of legitimate channel is more preferable, i.e. safe capacity is positive value, and secure communication may be implemented in system.
Using optimized safe capacity as communication criteria, the best expectation user k then selected meets:
Assuming that legitimate channel and tapping channel noise power are equal, it may be assumed that
Nk=NE
Base station uses qam mode, when only with beamforming technique, it is expected that the mean receiving power of user k are as follows:
Therefore, average signal-to-noise ratio are as follows:
RSN, k=Pk/Nk
Bit error rate are as follows:
μkIt can be calculated by following formula:
As can be seen that being gradually increased μ with signal-to-noise ratiokAlso it is gradually increased, bit error rate will be smaller and smaller.
When being optimized based on MISO-TR using beamforming technique, according to above-mentioned analysis it is found that being averaged for user k of expectation connects
Receive power are as follows:
As Bit Error Rate Computation formula when bit error rate is with only with beamforming technique.
The beneficial effects of the present invention are: the present invention is directed to the information leakage problem of multi-user downlink, it is contemplated that day
Correlation, channel status and multi-user communication criterion between line construct a descending multi-user MISO tapping channel model, propose
A kind of safe transmission scheme based on time reversal.The experimental results showed that compared with existing safety of physical layer scheme, present invention peace
Full capacity is higher, and bit error rate is lower.
Detailed description of the invention
The put row Multi-users MIS O tapping channel illustraton of model of Fig. 1 present invention；
Fig. 2 present invention proposes the safe transmission implementation flow chart based on time reversal；
The simulation comparison figure that Fig. 3 present invention and existing scheme safe capacity change with correlation factor；
The simulation comparison figure that Fig. 4 present invention and existing scheme safe capacity change with signal-to-noise ratio；
The simulation comparison figure that Fig. 5 present invention and existing scheme safe capacity change with number of antennas；
Fig. 6 present invention and existing scheme bit error rate are with signal-to-noise ratio.
Specific embodiment
To make the object, technical solutions and advantages of the present invention express to be more clearly understood, with reference to the accompanying drawing and specifically
Case study on implementation is described in further details the present invention.
The put row Multi-users MIS O tapping channel illustraton of model of Fig. 1 present invention, specifically includes:
For the information leakage problem of multi-user downlink, correlation and channel shape between combine antenna of the present invention
System modelling is downlink MISO tapping channel model to maximize safe capacity as multi-user communication criterion by state.It is proposed one kind
The safe transmission scheme of beamforming technique optimization is used based on time reversal technology, reduces the wind that information is ravesdropping user's eavesdropping
Danger.The mentality of designing of scheme are as follows: firstly, base station uses wave beam forming in a descending multi-user MISO tapping channel model
Technology emits signal to K expectation user, selects an optimal user k to be communicated according to safe capacity, eavesdropping user can lead to
Cross tapping channel steal information；Secondly, the signal of every antenna of base station will pass through a time reversal chamber before transmission.
The present invention, which suggests plans, studies the performances such as Signal to Interference plus Noise Ratio (SINR), safe capacity, and makes a concrete analysis of correlation and use between antenna
Influence of the beamforming technique to communication security.
According to time reversal downlink transmission model, using MISO working method, the descending multi-user suggested plans
MISO tapping channel model includes a base station, K expectation user and an eavesdropping user.Base station is equipped with M root antenna, it is expected that using
Family and eavesdropping user are all equipped with single antenna.Legitimate channel and tapping channel are mutually indepedent, and obey Rayleigh fading.Assuming that system
In all channel fading coefficients all obey CN (0,0.5) distribution.
Fig. 2 present invention proposes the safe transmission implementation flow chart based on time reversal, comprising the following steps:
Step 101: descending multi-user MISO tapping channel model of the building based on time reversal；
Step 102: equivalent secure transmission technique is the beamforming technique based on MISO-TR；
Step 103: system performance analysis is specifically analyzed in terms of two: safe capacity and bit error rate.
The descending multi-user MISO tapping channel model of step 101 building based on time reversal includes: according to the time
Inverting downlink transmission model, using MISO working method, the descending multi-user MISO tapping channel model packet suggested plans
Include a base station, K expectation user and an eavesdropping user.Base station is equipped with M root antenna, it is expected that user and eavesdropping user are all equipped with
Single antenna.Legitimate channel and tapping channel are mutually indepedent, and obey Rayleigh fading.Assuming that all channel fading coefficients in system
All obey CN (0,0.5) distribution.
The reception signal for receiving signal and eavesdropping user of expectation user will be derived respectively below:
In Multi-users MIS O tapping channel model, eavesdropping user only carries out passive wiretapping, the channel status of eavesdropping user
Information is unknown.Channel impulse response (CIR) between base station and user is obtained in the time reversal detection phase, due to multipath channel
With complexity, it is therefore assumed that known to CIR.CIR can be indicated are as follows:
In formula: 1≤m≤M；U indicates K expectation user and an eavesdropping user；L is the number of distinguishable multipath；
hMu, lIndicate the amplitude of the l articles multipath；τMu, lIndicate the time delay of the l articles multipath；Channel impulse response is discrete in the time domain to turn to square
Battle array hmu∈CL×1, it may be assumed that
hmu=[hmu[0], hmu[1] ..., hmu[L-1]]T
To each of the links, hmu[l] is Cyclic Symmetry multiple Gauss (CSCG) stochastic variable, is met:
E[hmu[l]]=0
In formula: TsFor system communication cycle, σTFor channel root mean square delay extension.
Assuming that base station sends the independent unit energy symbol s of a secretkTo desired user k, then all K expectation users
Transmission symbol are as follows:
S=[s1, s2..., sK]T
Time reversal chamber can indicate are as follows:
hk-TR(t)=[hmk[L-1], hmk[L-2] ..., hmk[0]]T/||hmk||
hmk(t)∈CL×1For the channel vector between base station and expectation user k.As can be seen from the above formula that time reversal
The shock response of chamber is that (so-called time reversal is exactly in the time domain to received for the time reversal of respective channels shock response
Signal carries out backout, and phase conjugation is equal on frequency domain) and normalize.Normalized purpose is in order to ensure transmitting
Energy remains unchanged.
Therefore, each transmitting symbol of Base Transmitter to desired user k will undergo an equivalent channel:
gmk=hk-TR*hmk
In formula: * indicates convolution；gmkChannel length be hmk2 demultiplications 1, i.e. 2L-1, it is being total to about center
Yoke symmetric sequences, it may be assumed that
It might as well enable:
Central value gMk, 0For real number.
In descending multi-user MISO tapping channel model, recipient is single-antenna subscriber.This is because time reversal
Chamber can only once be handled a specific channel, that is to say, that a time reversal chamber cannot be simultaneously to two or two
Above different channels carry out processing
The equivalent secure transmission technique of step 102 is that the beamforming technique based on MISO-TR includes: to beg for separately below
By based on beamforming technique and the reception signal based on MISO-TR using beamforming technique optimization two schemes.
When only with beamforming technique, it is expected that the reception signal of user k are as follows:
Base station utilizes the channel state information (CSI) in channel detection stage, that is, hmk(t), it is (so-called to obtain wave beam forming
Beam figuration is exactly the weight that wave beam forming is selected using the instantaneous characteristic of channel, is pre-processed to signal is sent, and then will
Power is sent to concentrate on recipient and reduce signal-to-noise ratio (SNR) the vector W of eavesdropping sidek, it can be calculated by following formula:
(.)HIndicate Hermitian conjugate transposition；||.||FIndicate Frobenius norm.
After beam forming processing, the reception signal of eavesdropping user are as follows:
Therefore, it is desirable to the received signal to noise ratio of user k are as follows:
Assuming that CIR is generated at random, then it is expected that the intersymbol interference power of user k and inter-user interference power are respectively as follows:
The received signal to noise ratio of eavesdropping user are as follows:
In formula: the intersymbol interference power and inter-user interference power of eavesdropping user are respectively as follows:
When being optimized based on MISO-TR using beamforming technique, it is expected that the reception signal at user k are as follows:
Above formula is made of four parts: (1) desired signal (Signal)；(2) intersymbol interference (ISI)；(3) inter-user interference
(IUI)；(4) additive white Gaussian noise (Noise)
Therefore, it is desired to the received signal to noise ratio of user k are as follows:
In formula: the intersymbol interference power and inter-user interference power of expectation user k is respectively as follows:
Base station emits signal, after time reversal chamber, the reception signal of eavesdropping user using beamforming technique are as follows:
Similarly:
Therefore, the received signal to noise ratio of eavesdropping user are as follows:
In formula: the intersymbol interference power and inter-user interference power of eavesdropping user are respectively as follows:
As the above analysis, beamforming technique is not still either used using beamforming technique, it is expected that user
The signal power received is greater than the signal power that eavesdropping user receives certainly.Base station is using beamforming technique transmitting letter
Number, after time reversal chamber, signal power, intersymbol interference power and inter-user interference power are all changed.When adopting
When with time inversion technique, the signal of Base Transmitter can focus on legitimate receipt side, prevent the information side of being ravesdropping from stealing.
Step 103 system performance analysis includes: that the present invention will be next pair in terms of safe capacity and bit error rate two
System performance is analyzed.The analytic expression of safe capacity is obtained by theory analysis and the derivation of equation.According to bit error rate formula
Derivation mode is modulated using quadrature amplitude modulation (QAM), makes a concrete analysis of the bit error rate of system, and carry out simulating, verifying.
The capacity of legitimate channel are as follows:
Ck=log2(1+RSIN, k)
The capacity of tapping channel are as follows:
CE=log2(1+RSIN, E)
When then base station is communicated with desired user k, the safe capacity of system are as follows:
As can be seen from the above equation, under desired user and the identical situation of eavesdropping user noise power, with signal-to-noise ratio
Increase, safe capacity will be gradually increased.
The safe capacity of system is the difference of the capacity of legitimate channel and the capacity of tapping channel, be can be realized most when greater than zero
Big safe capacity, eavesdropping user can not steal informations；Safe capacity is zero when equal to or less than zero, and eavesdropping user can theoretically lead to
Cross the information that the information stolen decodes out base station transmission.The channel status of legitimate channel and tapping channel determines the safety of system
Property, capacity is bigger when the channel status of legitimate channel is more preferable, i.e. safe capacity is positive value, and secure communication may be implemented in system.
Using optimized safe capacity as communication criteria, the best expectation user k then selected meets:
The present invention uses the downlink tapping channel model of Multi-users MIS O, uses wave beam forming skill based on MISO-TR
Art optimization, is compared with existing safe transmission scheme, and the safe transmission scheme that simulating, verifying proposes is improving safe capacity
On advantage, and carry out performance evaluation.In emulation, legitimate channel and tapping channel obey multi-path Fading Channel typical case
Channel length L is 80-150, therefore L=110 is arranged.The present invention analyzes suggested plans safe capacity from many aspects, imitates
True result is as shown in Figures 3 to 5.
Safe capacity is that there are the functions that security of system is measured when eavesdropping user.Fig. 3 is safe capacity under multipath channel
With the simulation result that correlation factor changes, transmitting antenna number is set as 2, and number of users is set as 2, and signal-to-noise ratio is set as
10dB.Safe capacity is averaged to obtain by 10000 independent Monte Carlo simulation results.From figure 3, it can be seen that identical item
Under part, safe capacity of the invention is consistently higher than the safe capacity of existing scheme, and security performance is more preferable.Under conditions of certain, with
The increase of correlation factor α, safe capacity first increases and then decreases.Should the result shows that, there are an optimal channel correlation coefficients
Keep safe capacity maximum, focusing improves legitimate receipt side's performance when the present invention utilizes the sky of time reversal.
Fig. 4 is the simulation result that safe capacity changes with signal-to-noise ratio under multipath channel under correlation factor α=0.3, transmitting
Antenna number is set as 2.It can be seen from the figure that signal-to-noise ratio is bigger, safe capacity first improves to be changed slowly afterwards, and three kinds of sides
Variation is slow after the difference of case is first increasing.Should the result shows that, when using correlation factor α=0.3, the present invention connects to legal
The improvement result of debit's performance is also become better and better, and is gradually changed slowly with the difference of existing scheme, security performance of the invention
Always optimal.
Fig. 5 is also the simulation result that safe capacity changes with number of antennas under multipath channel under correlation factor α=0.3,
Signal-to-noise ratio is set as 10dB.It can be seen from the figure that number of antennas is more, safe capacity is bigger.It is of the invention under the same terms
Safe capacity is consistently higher than the safe capacity of existing scheme.Should the result shows that, when using correlation factor α=0.3, safe capacity
It is improved with increasing for number of antennas.
Assuming that legitimate channel and tapping channel noise power are equal, it may be assumed that
Nk=NE
Base station uses qam mode, when only with beamforming technique, it is expected that the mean receiving power of user k are as follows:
Therefore, average signal-to-noise ratio are as follows:
Bit error rate are as follows:
μkIt can be calculated by following formula:
As can be seen that being gradually increased μ with signal-to-noise ratiokAlso it is gradually increased, bit error rate will be smaller and smaller.
When being optimized based on MISO-TR using beamforming technique, according to above-mentioned analysis it is found that being averaged for user k of expectation connects
Receive power are as follows:
As Bit Error Rate Computation formula when bit error rate is with only with beamforming technique.This means that the present invention mentions
Scheme Security performance out is more preferable.Bit error rate is to measure the function of system performance.Fig. 6 be under QAM modulation legitimate channel and steal
Listen the bit error rate of channel with signal-to-noise ratio change as a result, Base Transmitter number of antennas M=8, it is expected that user and eavesdropping user are equal
Using maximum-likelihood decoding.It can be seen from the figure that signal-to-noise ratio is bigger, bit error rate is gradually decreased.Compared with existing scheme, this
The bit error rate of invention is lower.Should the result shows that, scheme proposed by the present invention reduces bit error rate, improves the safety of system
Performance.
The present invention analyzes the parameter safe capacity for measuring security of system, and peace is analyzed in terms of different
Full capacity.Analysis can obtain the increase with signal-to-noise ratio, and safe capacity is also gradually promoted；The transmitting antenna of correlation factor α and base station
Number M has large effect to safe capacity, and safe capacity of the invention is consistently higher than existing scheme.The present invention is also to accidentally ratio
Special rate is analyzed, it is known that bit error rate will be smaller and smaller with the increase of signal-to-noise ratio, and is consistently less than existing side
Case.
The present invention proposes a kind of based on the use of time reversal technology for the information leakage problem in multi-user downlink
The safe transmission scheme of beamforming technique optimization, and the expression formula based on Signal to Interference plus Noise Ratio SINR is derived from the table of safe capacity
Up to formula.Simulation analysis obtains, and the safe capacity suggested plans is obviously improved, and bit error rate is lower.Therefore, which can be with
Improve the security performance of communication system.
Claims (4)
1. a kind of safe transmission scheme based on time reversal technology, which is characterized in that for the information of multi-user downlink
Leakage problem, correlation and channel status between combine antenna of the present invention, to maximize safe capacity as multi-user communication standard
It then, is downlink MISO tapping channel model by system modelling；It is proposed that a kind of time reversal technology that is based on uses beamforming technique
The safe transmission scheme of optimization reduces the risk that information is ravesdropping user's eavesdropping；The mentality of designing of scheme are as follows: firstly, at one
In descending multi-user MISO tapping channel model, base station emits signal to K expectation user using beamforming technique, according to peace
Full capacity selects an optimal user k to be communicated, and eavesdropping user can pass through tapping channel steal information；Secondly, base station is every
The signal of root antenna will pass through a time reversal chamber before transmission；The present invention, which suggests plans, studies Signal to Interference plus Noise Ratio
(SINR), the performances such as safe capacity, and make a concrete analysis of correlation and the shadow using beamforming technique to communication security between antenna
Ring, the safe transmission scheme based on time reversal the following steps are included:
Step 101: descending multi-user MISO tapping channel model of the building based on time reversal；
Step 102: equivalent secure transmission technique is the beamforming technique based on MISO-TR；
Step 103: system performance analysis is specifically analyzed in terms of two: safe capacity and bit error rate.
2. safe transmission scheme according to claim 1, which is characterized in that step 1 building is based on time reversal
Descending multi-user MISO tapping channel model include: according to time reversal downlink transmission model, using MISO working method,
The descending multi-user MISO tapping channel model suggested plans includes a base station, K expectation user and an eavesdropping user, base
It stands and is equipped with M root antenna, it is expected that user and eavesdropping user are all equipped with single antenna legitimate channel and tapping channel is mutually indepedent, and take
From Rayleigh fading, it is assumed that all channel fading coefficients all obey CN (0,0.5) distribution in system；
In Multi-users MIS O tapping channel model, eavesdropping user only carries out passive wiretapping, the channel state information of eavesdropping user
It is unknown；Channel impulse response (CIR) between base station and user is obtained in the time reversal detection phase, since multipath channel has
Complexity, it is therefore assumed that CIR is it is known that CIR can be indicated are as follows:
In formula: 1≤m≤M；U indicates K expectation user and an eavesdropping user；L is the number of distinguishable multipath；hMu, lIt indicates
The amplitude of the l articles multipath；τMu, lIndicate the time delay of the l articles multipath；Channel impulse response is discrete in the time domain to turn to matrix hmu∈
CL×1, it may be assumed that
hmu=[hmu[0], hmu[1] ..., hmu[L-1]]T
To each of the links, hmu[l] is Cyclic Symmetry multiple Gauss (CSCG) stochastic variable, is met:
E[hmu[l]]=0
In formula: TsFor system communication cycle, σTFor channel root mean square delay extension；
Assuming that base station sends the independent unit energy symbol s of a secretkTo desired user k, then the hair of all K expectation users
Send symbol are as follows:
S=[s1, s2..., sK]T
Time reversal chamber can indicate are as follows:
hk-TR(t)=[hmk[L-1], hmk[L-2] ..., hmk[0]]T/||hmk||
hmk(t)∈CL×1For the channel vector between base station and expectation user k；As can be seen from the above formula that time reversal chamber rushes
Hit response be respective channels shock response time reversal (so-called time reversal be exactly in the time domain to received signal into
Row backout is equal to phase conjugation on frequency domain) and normalize, normalized purpose is in order to ensure the energy of transmitting is protected
It holds constant；
Therefore, each transmitting symbol of Base Transmitter to desired user k will undergo an equivalent channel:
gmk=hk-TR*hmk
In formula: * indicates convolution；gmkChannel length be hmk2 demultiplications 1, i.e. 2L-1, it be about center conjugation it is symmetrical
Sequence, it may be assumed that
It might as well enable:
Central value gMk, 0For real number；
In descending multi-user MISO tapping channel model, recipient is single-antenna subscriber, this is because time reversal chamber one
It is secondary a specific channel to be handled, that is to say, that a time reversal chamber cannot be simultaneously to two or more
Different channels handled.
3. safe transmission scheme according to claim 1, which is characterized in that the equivalent secure transmission technique of step 2 is
Beamforming technique based on MISO-TR includes: to discuss to use wave with based on MISO-TR based on beamforming technique separately below
The reception signal of beam figuration technical optimization two schemes；
When only with beamforming technique, it is expected that the reception signal of user k are as follows:
Base station utilizes the channel state information (CSI) in channel detection stage, that is, hmk(t), obtaining wave beam forming, (so-called beam is assigned
Shape is exactly the weight that wave beam forming is selected using the instantaneous characteristic of channel, is pre-processed to signal is sent, and then will be sent
Power concentrates on recipient and reduces signal-to-noise ratio (SNR) the vector W of eavesdropping sidek, it can be calculated by following formula:
(.)HIndicate Hermitian conjugate transposition；||·||FIndicate Frobenius norm；
After beam forming processing, the reception signal of eavesdropping user are as follows:
Therefore, it is desirable to the received signal to noise ratio of user k are as follows:
Assuming that CIR is generated at random, then it is expected that the intersymbol interference power of user k and inter-user interference power are respectively as follows:
The received signal to noise ratio of eavesdropping user are as follows:
In formula: the intersymbol interference power and inter-user interference power of eavesdropping user are respectively as follows:
When being optimized based on MISO-TR using beamforming technique, it is expected that the reception signal at user k are as follows:
Above formula is made of four parts: (1) desired signal (Signal)；(2) intersymbol interference (ISI)；(3) inter-user interference
(IUI)；(4) additive white Gaussian noise (Noise)；
Therefore, it is desired to the received signal to noise ratio of user k are as follows:
In formula: the intersymbol interference power and inter-user interference power of expectation user k is respectively as follows:
Base station emits signal, after time reversal chamber, the reception signal of eavesdropping user using beamforming technique are as follows:
Similarly:
Therefore, the received signal to noise ratio of eavesdropping user are as follows:
In formula: the intersymbol interference power and inter-user interference power of eavesdropping user are respectively as follows:
As the above analysis, beamforming technique is not still either used using beamforming technique, it is expected that user receives
To signal power be greater than the signal power that eavesdropping user receives certainly；Base station emits signal, warp using beamforming technique
After crossing time reversal chamber, signal power, intersymbol interference power and inter-user interference power are all changed；Between when employed
When inversion technique, the signal of Base Transmitter can focus on legitimate receipt side, prevent the information side of being ravesdropping from stealing.
4. safe transmission scheme according to claim 1, which is characterized in that step 103 system performance analysis includes:
The present invention will analyze system performance in terms of safe capacity and bit error rate two；It is pushed away by theory analysis and formula
Lead the analytic expression for obtaining safe capacity；It according to bit error rate derivation of equation mode, is modulated using quadrature amplitude modulation (QAM), specific point
The bit error rate of analysis system；
The capacity of legitimate channel are as follows:
Ck=log2(1+RSIN, k)
The capacity of tapping channel are as follows:
CE=log2(1+RSIN, E)
When then base station is communicated with desired user k, the safe capacity of system are as follows:
As can be seen from the above equation, under desired user and the identical situation of eavesdropping user noise power, with the increase of signal-to-noise ratio,
Safe capacity will be gradually increased；
The safe capacity of system is the difference of the capacity of legitimate channel and the capacity of tapping channel, can be realized maximum peace when greater than zero
Full capacity, eavesdropping user can not steal informations；Safe capacity is zero when equal to or less than zero, and eavesdropping user theoretically can be by stealing
The information taken decodes out the information of base station transmission；The channel status of legitimate channel and tapping channel determines the safety of system,
Capacity is bigger when the channel status of legitimate channel is more preferable, i.e., safe capacity is positive value, and secure communication may be implemented in system；
Using optimized safe capacity as communication criteria, the best expectation user k then selected meets:
Assuming that legitimate channel and tapping channel noise power are equal, it may be assumed that
Nk=NE
Base station uses qam mode, when only with beamforming technique, it is expected that the mean receiving power of user k are as follows:
Therefore, average signal-to-noise ratio are as follows:
RSN, k=Pk/Nk
Bit error rate are as follows:
μkIt can be calculated by following formula:
As can be seen that being gradually increased μ with signal-to-noise ratiokAlso it is gradually increased, bit error rate will be smaller and smaller；
When being optimized based on MISO-TR using beamforming technique, according to above-mentioned analysis it is found that the average received function of expectation user k
Rate are as follows:
As Bit Error Rate Computation formula when bit error rate is with only with beamforming technique.
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