CN110300399A - A kind of short distance multi-user concealed communication method and system based on Wi-Fi network interface card - Google Patents
A kind of short distance multi-user concealed communication method and system based on Wi-Fi network interface card Download PDFInfo
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- CN110300399A CN110300399A CN201910548389.6A CN201910548389A CN110300399A CN 110300399 A CN110300399 A CN 110300399A CN 201910548389 A CN201910548389 A CN 201910548389A CN 110300399 A CN110300399 A CN 110300399A
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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
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L1/00—Arrangements for detecting or preventing errors in the information received
- H04L1/0001—Systems modifying transmission characteristics according to link quality, e.g. power backoff
- H04L1/0009—Systems modifying transmission characteristics according to link quality, e.g. power backoff by adapting the channel coding
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L1/00—Arrangements for detecting or preventing errors in the information received
- H04L1/0001—Systems modifying transmission characteristics according to link quality, e.g. power backoff
- H04L1/0023—Systems modifying transmission characteristics according to link quality, e.g. power backoff characterised by the signalling
- H04L1/0026—Transmission of channel quality indication
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W4/00—Services specially adapted for wireless communication networks; Facilities therefor
- H04W4/80—Services using short range communication, e.g. near-field communication [NFC], radio-frequency identification [RFID] or low energy communication
Abstract
The invention discloses a kind of short distance multi-user concealed communication methods and system based on Wi-Fi network interface card, method includes following sub-step: step 1:Wi-Fi signal source issues radiofrequency signal, and receiving end receives radiofrequency signal and calculates the CSI between Wi-Fi signal source and receiving end according to radiofrequency signal；Step 2: user terminal reflects the radiofrequency signal that Wi-Fi signal source issues, and each user loads the information sequence for respectively passing through orthogonal coding using network interface card in radiofrequency signal simultaneously, obtains comprehensive radiofrequency signal by superposition；Step 3: receiving end receives comprehensive radiofrequency signal and calculates the CSI between Wi-Fi signal source and receiving end according to comprehensive radiofrequency signal, the mapping for establishing CSI amplitude to signal level obtains integrated signal level, integrated signal level is decoded, the information sequence of user is obtained.The present invention can transmit the data of multiple users, and the recipient of receiving end is helped to separate the important information of multiple users, guarantee user using public network connection transmission important information safety.
Description
Technical field
The invention belongs to Covert Communication Technology fields, and in particular to a kind of short distance multi-user based on Wi-Fi network interface card is hidden
Cover communication means and system.
Background technique
In recent years, becoming increasingly popular with wireless network and mobile intelligent terminal, near radio data are transmitted
Become essential a part in people's daily life.There is a large amount of user privacy information to pass through in short distance
The methods of Wi-Fi, Bluetooth, NFC mutually transmitting between the subscriber devices, wherein there is huge safety problems.According to rising
" first quarter safety message in the 2019 " display for interrogating Mobile safety laboratory publication, ends March, public Wi-Fi quantity is high
Up to 9.84 hundred million, the public places such as covering airport, hotel, shopping mall market do not find the Wi-Fi accounting 58.18% of risk, and
Risk Wi-Fi accounting 41.82%, quantity is close to 3.96 hundred million.The privacy that offender can steal user using risk Wi-Fi is believed
Breath, or even threaten user's property safety.Bluetooth not only can be by Denial of Service attack, co-channel interference, message modification and resource
The influence of abuse also has the pairing time up to 6 seconds, and the drawbacks of only support point-to-point communication.Wi-Fi is used in public places
Privacy information is transmitted with Bluetooth, such as identity information, address list, account number cipher all have greater risk.And conduct
The mainstream technology NFC of near-field communication at present, due to the limitation in cost and market, the mobile device Zhan with NFC function is always set
Standby 30%.
With the enhancing of people's information protection consciousness and going deep into for research, there are a series of concealed communication methods, such as
Based on the schemes such as heat reflection and ELECTROMAGNETIC REFLECTION, this concealed communication method compared to the scheme based on early sound and light there is
Do not need to establish the advantage of physical connection, however, these solutions all obtained in the environment of each self application it is a degree of
Using.Its limitation is obvious, for example needs power supply, energy consumption are high, need external equipment just to can be carried out communication.Lead in the prior art
Impedance when crossing network interface card switch is different, reflects the sine wave from router, and self information is loaded into received signal strength
RSSI is upper or is transferred to receiving end, although the public Wi-Fi quantity of 9.84 hundred million quantity and the popularization of network interface card provide firmly thus
Part basis, but it is corresponding there is a problem that it is obvious:
(1) RSSI signal is affected by environment big, and RSSI information will appear bigger change with the variation in time and space
Change, the reason is that environment Multipath Transmission；
(2) RSSI signal is easy captured, and RSSI information can be captured by business networking devices any in space, unfavorable
In the hided transmission of data；
(3) message transmission rate is limited to the delay of network interface card switch, only 1bps or so.Therefore, a kind of inexpensive, high-precision
Degree, the covert communications solution easily used have very important researching value.
Summary of the invention
The purpose of the present invention is to provide a kind of short distance multi-user concealed communication method based on Wi-Fi network interface card and it is
System, to solve the problems, such as the prior art to covert communications project study.
In order to realize above-mentioned task, the invention adopts the following technical scheme:
A kind of short distance multi-user's concealed communication method based on Wi-Fi network interface card, including following sub-step:
Step 1:Wi-Fi signal source issues radiofrequency signal, and receiving end receives radiofrequency signal and calculates Wi- according to radiofrequency signal
Original channel status information CSI between Fi signal source and receiving end；
Step 2: user terminal reflects the radiofrequency signal that Wi-Fi signal source issues, and the user terminal includes multiple users, each
User loads the information sequence for respectively passing through orthogonal coding using network interface card in radiofrequency signal simultaneously, obtains comprehensive radiofrequency signal；
Step 3: receiving end receives comprehensive radiofrequency signal and calculates Wi-Fi signal source and receiving end according to comprehensive radiofrequency signal
Between CSI, the mapping for establishing CSI amplitude to signal level obtains integrated signal level, then carries out to integrated signal level
Decoding, obtains the information sequence of each user.
Further, step 2 includes following sub-step:
Step 2.1: user terminal reflects the radiofrequency signal that Wi-Fi signal source issues, and the user terminal includes K user, is
Efficiently separate the data from different user at receiver, we utilize wkTo encode the transmission data of user k.Each
The data of user include multiple information bits, the information bit d' after the l Bits Expanding of k-th of userk(l) it indicates are as follows:
d'k(l)=μk(l)wk
Wherein, k=1,2,3...K and K indicate user terminal total number of users, and l=1,2,3...L and L indicate information bit most
Big digit, μk(l) indicate bipolarity position andwkIt is expressed as the kth of Walsh-Hadmard matrix
Row vector, Walsh-Hadmard matrix are the square matrix of N × N, and row is orthogonal matrix, the integral power that N is 2, N >=2 and not small
In total number of users；
Step 2.2: according to the building of user's number and while the respective information for passing through orthogonal coding of load in radiofrequency signal
Sequence obtains comprehensive radiofrequency signal such as formula I:
Wherein, βkIndicate CSI power stageh0For Wi-Fi signal source to reception
Hold the original CSI, h of receiverkFor the CSI of k-th of user to receiver, h0,kIndicate Wi-Fi signal source to k-th user's
CSI, pkFor the transmission power of the network interface card of k-th of user, p0For the transmission power at Wi-Fi signal source,It indicates to adjust network interface card
The attenuation coefficient of working condition.
Further, step 3 includes following sub-step:
Step 3.1: receiving end receives comprehensive radiofrequency signal and according to comprehensive radiofrequency signal, calculates Wi-Fi using formula II and believes
CSI number between source and receiving end:
Wherein,And z " is noise item；
Step 3.2: the amplitude of the CSI established between Wi-Fi signal source and receiving end using formula III to signal level is reflected
It penetrates to obtain integrated signal level d "k:
d”k=μkN formula III
Wherein, N=wT NwN, { }TIt is the transposition of matrix, μkIndicate bipolar sequence；
Step 3.3: to integrated signal level d "kIt is decoded to obtain bipolar sequence μk, and according to μkObtain k-th of use
The original information sequence at family, and then obtain the information sequence of whole K users.
Further, step 3.3 includes following sub-step:
Rapid 3.3.1 step by step: using formula IV to integrated signal level d "kIt is decoded, obtains bipolar sequence μk:
Wherein,d'kIt is information sequence of k-th of user after orthogonal coding extends.
Step 3.3.2: according to bipolar sequence μk, according to the relationship of bipolar sequence shown in formula V and information sequence, obtain
To the information sequence of k-th of user, and then obtain the information sequence of whole K users:
Further, the radiofrequency signal relies on data packet and is sent to receiving end, the data packet by Wi-Fi signal source
Structure be that packet detection sequence, user identity identification serial ID and payload transmit sequence, the identification sequence of k-th of user
IDkIt is expressed as,Wherein, K0≥K+1。
A kind of short distance multi-user's convert communication system based on Wi-Fi network interface card, including Wi-Fi signal source, user terminal, connect
Receiving end；
Including Wi-Fi signal source, user terminal, receiving end；
The Wi-Fi signal source is for issuing radiofrequency signal to receiving end；
The user terminal includes multiple users, and each user is loaded respectively by just using network interface card in radiofrequency signal simultaneously
The information sequence of coding is handed over, and is reflected into receiving end and is overlapped to obtain comprehensive radiofrequency signal with original radio frequency signal；
The receiving end receives the synthesis radiofrequency signal of the radiofrequency signal that Wi-Fi signal source is sent and user terminal reflection,
CSI between Wi-Fi signal source and receiving end is calculated, is changed according to the amplitude of CSI, establishes the mapping of CSI amplitude to signal level
Integrated signal level is obtained, then integrated signal level is decoded, obtains the information sequence of each user.
Further, the radiofrequency signal that user terminal reflection Wi-Fi signal source issues, the user terminal includes K user,
In order to efficiently separate the data from different user at receiver, we utilize wkTo encode the transmission data of user k.Often
The data of a user include multiple information bits, the information bit d' after the l Bits Expanding of k-th of userk(l) it indicates are as follows:
d'k(l)=μk(l)wk
Wherein, k=1,2,3...K and K indicate user terminal total number of users, and l=1,2,3...L and L indicate information bit most
Big digit, μk(l) indicate bipolarity position andwkIt is expressed as the kth of Walsh-Hadmard matrix
Row vector, Walsh-Hadmard matrix are the square matrix of N × N, and row is orthogonal matrix, the integral power that N is 2, N >=2 and not small
In total number of users；
Then the information sequence for respectively passing through orthogonal coding is simultaneously loaded in radiofrequency signal simultaneously according to the building of user's number,
Obtain comprehensive radiofrequency signal such as formula I:
Wherein, βkIndicate CSI power stageh0For Wi-Fi signal source to reception
Hold the CSI, h of receiverkFor the CSI of k-th of user to receiver, h0,kIndicate CSI, p of the Wi-Fi signal source to k-th of userk
For the transmission power of the network interface card of k-th of user, p0For the transmission power at Wi-Fi signal source,It indicates to adjust network interface card work shape
The attenuation coefficient of state.
Further, the receiving end receives comprehensive radiofrequency signal and according to comprehensive radiofrequency signal, calculates Wi- using formula II
CSI between Fi signal source and receiving end:
Wherein,And z " is noise item；
The receiving end obtains integrated signal level d " using the mapping that formula III establishes CSI to signal levelk:
d”k=μkN formula III
Wherein, N=wT NwN, { }TIt is the transposition of matrix, μkIndicate bipolar sequence；
The receiving end is to integrated signal level d "kIt is decoded to obtain bipolar sequence μk, and according to μkIt obtains k-th
The information sequence of user, and then obtain the information sequence of whole K users.
Further, the receiving end is to utilization formula IV to integrated signal level d "kIt is decoded, obtains bipolar sequence
μk:
And according to bipolar sequence μk, according to the relationship of bipolar sequence shown in formula V and information sequence, obtain k-th of use
The information sequence at family, and then obtain the information sequence of whole K users:
Further, the radiofrequency signal relies on data packet and is sent to receiving end, the data packet by Wi-Fi signal source
Structure be that packet detection sequence, user identity identification serial ID and payload transmit sequence, the identification sequence of k-th of user
IDkIt is expressed as,Wherein, K0Greater than total number of users K, i.e. K0≥K+1。
Compared with the prior art, the invention has the following beneficial effects:
(1) in recent years, the CSI of Wi-Fi equipment has been widely used in environmentally sensitive field.With connecing in Wi-Fi equipment
It receives signal strength RSSI to compare, it is a more fine-grained channel characteristic.CSI can capture rapid fading and slow fading letter simultaneously
Breath, to reflect frequency-selective channel feature and multipath channel effect.It is of the invention compared with the method for sensing based on RSSI
Method for sensing based on CSI has better sensing capabilities.
(2) in order to help the important information for extracting user from Wi-Fi CSI, a theoretical model is given to show
Relationship between Wi-Fi CSI, reflected radio-frequency signal and important information.
(3) in order to solve the problems, such as that Wi-Fi network interface card carries out the covert communications of multi-user, the important information of multiple users is superimposed upon
Receiving end can not separate this problem, and orthogonal encoding and decoding technique helps recipient to separate the important information of multiple users.
(4) it for the relationship theoretically between the CSI of analog capture and the important information of user's transmission, analyzes first
The private communication channel communication of signals transmission passes through wireless network card, the source CSI then analyzed (signal assisting device) and receiving end
Wireless signal receiver finally gives theoretical model analysis CSI and transmits the relationship between data.
(5) data of multi-user decode for convenience, propose a kind of scheme that can determine number of users and identity.
Detailed description of the invention
Fig. 1 is the variation diagram of the CSI at receiver when user configuration 9580 network interface card of Atheros；
Fig. 2 is that user transmits packet structure figure；
Fig. 3 is the different frequency subcarrier range value figure received；
Fig. 4 is the different frequency sub-carrier signal-noise ratio figure by DC processing；
Fig. 5 is the CSI map of magnitudes for different user quantity；
Fig. 6 is multi-user scene figure；
Fig. 7 is experiment topological diagram；
Fig. 8 is number of users recognition performance figure；
Fig. 9 is User ID recognition performance figure；
Figure 10 is the bit error rate performance figure there are different number user；
Figure 11 is system transfer rate bit error rate relation figure corresponding with network interface card switch gap；
Figure 12 is influence of the Wi-Fi access point number to system performance in environment.
Specific embodiment
Embodiment 1
A kind of short distance multi-user's concealed communication method based on Wi-Fi network interface card is disclosed in the present embodiment, including such as
Lower sub-step:
Step 1:Wi-Fi signal source issues radiofrequency signal, and receiving end receives radiofrequency signal and calculates Wi- according to radiofrequency signal
Original CSI between Fi signal source and receiving end；
Step 2: user terminal reflects the radiofrequency signal that Wi-Fi signal source issues, and the user terminal includes multiple users, each
User loads the information sequence for respectively passing through orthogonal coding using network interface card in radiofrequency signal simultaneously, obtains synthesis by superposition and penetrates
Frequency signal；
Step 3: receiving end receives comprehensive radiofrequency signal and calculates Wi-Fi signal source and receiving end according to comprehensive radiofrequency signal
Between CSI, changed according to the amplitude of CSI, the mapping for establishing CSI amplitude to signal level obtains integrated signal level, then
Integrated signal level is decoded, the information sequence of all users is obtained.
The present invention adjusts the impedance of mobile subscriber's Wi-Fi network interface card by the software of preassembled control network interface card impedance,
Ambient radio-frequency signal (RF) signal to make the network interface card of user be able to reflect in ambient enviroment.Then, the information in user terminal
The receiver that can be carried by the radiofrequency signal reflected and be transmitted to receiving end helps multi-user to exist using orthogonal coding and decoding
Receiving end carries out data decoding.
Firstly, to Wi-Fi network interface card, how load information sequence is done to explain:
As shown in fig. 6, the incoming signal from Wi-Fi signal source will be transmitted directly to receiving end.In addition, if user
The impedance of network interface card is from a kind of state change to another state, then auxiliary signal may be reflected by the network interface card of user, then passes
It is defeated to arrive receiving end.It is studied herein mainly for the user of static network card configuration.In static type network interface card, enable when continuous and
When disabling Wi-Fi network interface card, the square wave of the envelope of reflected radio-frequency signal as a different capacity grade.As shown in Figure 1, network interface card
AR9850 belongs to static network interface card.The signal that one transmitting antenna of the signal source receives at user k can indicate are as follows:
Wherein h0,kFor CSI of the Wi-Fi signal source at user k, P0And x0Transmission power respectively at Wi-Fi signal source
With transmitting signal, ZkFor the white Gaussian noise at user k.
Assuming that user is mounted with the software of control network interface card impedance in advance, and the software for controlling network interface card impedance can be controlled
The working condition of user's network interface card processed, is at open/close state, thus can reflect out the RF signal that user receives.Net
The amplitude that the different working condition of card will lead to reflected radio-frequency signal is different, as shown in Figure 1.More specifically, the letter received
Number x'kIt will be reflected to user k:
Wherein α 0 and α 1 is decay factor caused by adjusting network interface card working condition.
Using this characteristic, the sensitive information of user can be modulated into the radiofrequency signal of reflection, then in receiving end
Receiving end decoding.More specifically, the software of the control network interface card impedance in mobile subscriber is pre-installed according to the sensitivity of user
The working condition that information controls user's network interface card is on or off.Therefore, the reflection signal at user k can be rewritten are as follows:
Wherein dkIt is the sensitive information position in user k.According to (2) and (3), the software of the control network interface card impedance of user k will
The network interface card of user is forced, if if the software that sensitive information transmission is ' 0 ' and controls network interface card impedance will force the network interface card of user
The information of position transmission is " 1 ".In this way, the sensitive information of user can be modulated into radiofrequency signal, and pass to and connect
The receiver of receiving end.
If K user reflects Wi-Fi signal simultaneously, the receiver of receiving end comes from Wi-Fi signal in addition to receiving
Outside the signal in source, the signal from all K users can be also received.Therefore, the signal that receiving end receives can be expressed as
Wherein h0For Wi-Fi signal source to the CSI of receiving end receiver, hkFor the CSI of user k to receiver, PkFor with
The transmission power of the network interface card of family k, z are the white Gaussian noise at receiver.
Mainly for more mobile devices of configuration static types network interface card, the hidden letter based on Wi-Fi network interface card back scattering
Road communication code scheme.In order to allow multiple users simultaneously propagation data, using orthogonal coding technology to the payload before transmission
Data are encoded.In this way, different users can be distinguished with different orthogonal codes.Therefore, in receiving end, it can use phase
The quadrature decoder technology answered separates data from different users.
Specifically, step 2 includes following sub-step:
Step 2.1: user terminal reflects the radiofrequency signal that Wi-Fi signal source issues, and the user terminal includes K user, is
Efficiently separate the data from different user at receiver, we utilize wkTo encode the transmission data of user k.Often
The data of a user include multiple information bits, the information bit d' after the l Bits Expanding of k-th of userk(l) it indicates are as follows:
d'k(l)=μk(l)wk
Wherein, k=1,2,3...K and K indicate user terminal total number of users, and l=1,2,3...L and L indicate information bit most
Big digit, μk(l) indicate bipolarity position andwkIt is expressed as the kth of Walsh-Hadmard matrix
Row vector, Walsh-Hadmard matrix are the square matrix of N × N, and row is orthogonal matrix, the integral power that N is 2, N >=2 and are not less than
Total number of users (N >=K)；
For the ease of explaining, encoding the transport payload number of each user using the row of Walsh-Hadmard matrix
According to.Walsh-Hadmard matrix is a square matrix, and row is orthogonal vectors.Indicate WNFor the Walsh-Hadmard square of N × N
Battle array.Then, it is
With
The wherein integral power that N is 2, N > 2, and it is not less than total number of users (i.e. N >=K),It is Kronecker (Kronecker)
Product.Indicate wiFor Walsh-Hadmard matrix HNThe i-th row vector.According to the definition of Walsh-Hadmard matrix,
wiwj T=0 (7)
With
wiwi T=N (8)
In order to effectively separate data from different users in receiving end, w is utilizedNTo the transmission data of user k
It is encoded.
Step 2.2: the information sequence of orthogonal coding, warp are constructed and respectively passed through to radiofrequency signal load according to user's number
It crosses superposition and obtains comprehensive radiofrequency signal such as formula I:
Wherein, βkIndicate CSI power stage βk=αηkCk,h0For Wi-Fi signal source to receiving end
The original CSI, h of receiverkFor the CSI of k-th of user to receiver, h0,kIndicate Wi-Fi signal source to k-th user's
CSI, pkFor the transmission power of the network interface card of k-th of user, p0For the transmission power at Wi-Fi signal source, αηkIt indicates to adjust network interface card
The attenuation coefficient of working condition.
The case where for a user, orthogonal coding is not needed, it is therefore assumed that W in the case where a user1=1.Note
Meaning, other orthogonal coding schemes can be used for supporting the signal of multiple users to transmit.For the ease of explaining, using Walsh-
Hadmard sequence encodes the information of transmission.
Specifically, step 3 includes following sub-step:
Step 3.1: receiving end receives comprehensive radiofrequency signal and according to comprehensive radiofrequency signal, calculates Wi-Fi using formula II and believes
CSI number between source and receiving end:
Wherein,And z " is noise item；
Step 3.2: the variation of comprehensive radiofrequency signal can cause the amplitude of CSI to change, and establish comprehensive CSI to letter using formula III
The mapping of number level obtains integrated signal level d "k:
d”k=μkN formula III
Wherein, N=wT NwN, { }TIt is the transposition of matrix, μkIndicate bipolar sequence；
Step 3.3: to integrated signal level d "kIt is decoded to obtain bipolar sequence μk, and according to μkObtain k-th of use
The information sequence at family, and then obtain the information sequence of whole K users.
Preferably, step 3.3 includes following sub-step:
There are two possible values for the encoded information bits transmitted at the user k in d': ' 1 ' and ' -1 '.By each encoded information
The reception signal rank of symbol " 1 " and " -1 " is respectively labeled as 1 and -1.Assuming that a total of K user, all users send simultaneously
Data, a user of K (1≤k≤K) send encoded information symbol " 1 ", remaining K-k user sends encoded information symbol " -1 ".So
Afterwards, overall received signal level relevant to these transmission symbols is defined as (K-k) × (- 1) k × 1+=K-2k.
In view of the structure and design of packet, in superposition CSI preamble sequence relevant to transmitter identification codes ID, the number of CSI
The quantity that amount level is equal to user adds 1, K+1, and the quantity of signal level is the level of the same CSI.More specifically, involved
And signal level are as follows: K, K-2 ..., K-2 (K-1) ... ,-K wherein K-2 (K- 1) be transmitter identification codes ID in K
Corresponding signal level.
It is to receive each symbol loaded to determine signal level according to the signal level obtained in preamble sequence.More specifically
Ground is said, the mean value of CSI amplitude sample in each symbol period is calculated, then by calculated value and CSI water relevant with sequence number sequence
It is flat to be compared, finally calculated value is updated horizontal to nearest CSI.Then, the CSI being calculated grade is mapped to accordingly
Signal grade.The corresponding calculating signal level of an information bit for indicating the user without orthogonal coding is Ss.
Step 3.3.1: using formula IV to integrated signal level d "kIt is decoded, obtains bipolar sequence μk:
WhereinWherein d'kIt is information sequence of k-th of user after orthogonal coding extends.
Step 3.3.2: according to bipolar sequence μk, according to the relationship of bipolar sequence shown in formula V and information sequence, obtain
To the information sequence of k-th of user, and then obtain the information sequence of whole K users:
Specifically, the consistency in order to keep description, use " 1 " and " -1 " respectively indicate " 1 " in preface sequence and
"0".Packet is detected, using " -1,1,1,1, -1 " in frame structure as packet detection code.Then according to the coding of data packet
Structure is in receiving end detection data packet.Other codes can also be used for that data packet is facilitated to detect.
The wireless carrier of CSI transmits, if the time interval CSI of CSI trace between the two from the beginning is horizontal suddenly
Variation is equal to three symbol durations, and sudden change causes CSI level to increase at the beginning, and ending suddenly change leads to CSI
Standard reduces, and then continuous three symbols " 111 " can be detected.First and last symbol " -1 " can also be true
It is fixed, because caused by the mutation of CSI level is difference as transmission symbol.Once detecting symbol " -1111-1 ", it is meant that
Transmit new compression.
Data decoding is carried out in receiving end for convenience, it is necessary to Customs Assigned Number and identity after first determining data packet detection.
Therefore, user identification code is devised in frame structure to solve the problems, such as this.More specifically, implementation sequence ID, to know
Not different user, in order to carry out data decoding in receiving end.Specifically, it is assumed that 11×kWith -11×kIt is all elements difference
1 × k-vector equal to 1 with -1.
The radiofrequency signal relies on data packet and is sent to receiving end by Wi-Fi signal source, and the structure of the data packet is
Packet detection sequence, user identity identification serial ID and payload transmit sequence, the identification serial ID of k-th of userkIt is expressed as,Wherein, K0Greater than total number of users K, i.e. K0≥K+1。
Specifically, the method for determining user number and identity
However, wanting the payload information of receiver decoder, it is necessary first to know the number of user and the identity of user.
Once finding the symbol " -1111-1 " for wrapping detection, so that it may related to user identity according to pack arrangement determination
The position K+1 ID position.These K+1 symbols will be used to determine the number and identity of user.
A) observe: since the CSI level of aggregation of several users is by linear superposition, this can also be in the measured data after LPF
In be proven, as shown in Figure 5.If two users send the signal reflected simultaneously, obtained by the identity code being superimposed
CSI level will as stair, if all users simultaneously send data, in the end of each bit duration
Unexpected variation can all occur for time, CSI level.
B) number of users determines: one matrix T of construction, row is the identity code of all users,
Wherein row k vector is equal to the identification code of k-th of user.It is horizontal by setting CSI in order to determine the quantity of user
Change threshold detects the mutation quantity of the endpoint boundary CSI level of each bit.The number of users etc. of data is sent simultaneously
In the mutation quantity of CSI level in symbol duration, correspond to user identity code.
C) user identity determines: according to Germicidal efficacy in Fig. 5, the structure of matrix T is, if the of user identity code position
CSI level mutates at the end boundary of k symbol, then user sends data.For example, if in all K users only
User 1 and user 3 take part in backscatter transmission, then corresponding submatrix can indicate in matrix T are as follows:
The variation of CSI rank will occur in the CSI that the 1st of CUSTOMER ID and the 3rd end position are superimposed.
Embodiment 2
A kind of short distance multi-user's convert communication system based on Wi-Fi network interface card, including Wi-Fi signal source, user terminal, connect
Receiving end；
The Wi-Fi signal source is for issuing radiofrequency signal to receiving end；
The user terminal includes K user, and each user loads respective information using network interface card in radiofrequency signal simultaneously
Sequence, each user loads the information sequence for respectively passing through orthogonal coding using network interface card in radiofrequency signal simultaneously, by superposition
It obtains the comprehensive radiofrequency signal of comprehensive radiofrequency signal and reflexes to receiving end；
The receiving terminal receives the synthesis radiofrequency signal of the radiofrequency signal that Wi-Fi signal source is sent and user terminal reflection,
The CSI between Wi-Fi signal source and receiving end is calculated separately, is changed according to the amplitude of CSI, establishes CSI amplitude to signal level
Mapping obtain integrated signal level, then integrated signal level is decoded, obtains the information sequence of K user.
Specifically, the radiofrequency signal that user terminal reflection Wi-Fi signal source issues, the user terminal includes K user, in order to
The data from different user are efficiently separated at receiver, we utilize wkTo encode the transmission data of user k.Each
The data of user include multiple information bits, the information bit d' after the l Bits Expanding of k-th of userk(l) it indicates are as follows:
d'k(l)=μk(l)wk
Wherein, k=1,2,3...K and K indicate user terminal total number of users, and l=1,2,3...L and L indicate information bit most
Big digit, μk(l) indicate bipolarity position andwkIt is expressed as the row k of Walsh-Hadmard matrix
Vector, Walsh-Hadmard matrix are the square matrix of N × N, and row is orthogonal matrix, the integral power that N is 2, N >=2 and are not less than
Total number of users (N >=K)；The information sequence of orthogonal coding, warp are constructed and respectively passed through to radiofrequency signal load according to user's number
It crosses superposition and obtains comprehensive radiofrequency signal such as formula I:
Wherein, βkIndicate CSI power stageh0For Wi-Fi signal source to reception
Hold the original CSI, h of receiverkFor the CSI of k-th of user to receiver, h0,kIndicate Wi-Fi signal source to k-th user's
CSI, pkFor the transmission power of the network interface card of k-th of user, p0For the transmission power at Wi-Fi signal source,It indicates to adjust network interface card
The attenuation coefficient of working condition.
Specifically, the receiving end receives comprehensive radiofrequency signal and according to comprehensive radiofrequency signal, Wi-Fi is calculated using formula II
CSI between signal source and receiving end:
Wherein,And z " is noise item；
The receiving end obtains integrated signal level d " using the mapping that formula III establishes comprehensive CSI to signal levelk:
d”k=μkN formula III
Wherein, N=wT NwN, { }TIt is the transposition of matrix, μkIndicate bipolar sequence；
The receiving end is to integrated signal level d "kIt is decoded to obtain bipolar sequence μk, and according to μkIt obtains k-th
The information sequence of user, and then obtain the information sequence of whole K users.
Preferably, the receiving end is to utilization formula IV to integrated signal level d "kIt is decoded, obtains bipolar sequence μk:
WhereinWherein d'kIt is information sequence of k-th of user after orthogonal coding extends.
And according to bipolar sequence μk, according to the relationship of bipolar sequence shown in formula V and information sequence, obtain k-th of use
The information sequence at family, and then obtain the information sequence of whole K users:
Specifically, the radiofrequency signal, which relies on data packet, is sent to receiving end by Wi-Fi signal source, the data packet
Structure is that packet detection sequence, user identity identification serial ID and payload transmit sequence, the identification serial ID of k-th of userk
It is expressed as,Wherein, K0Greater than total number of users K, i.e. K0≥K+1。
Embodiment 3
Experimentation
Multi-user's private communication channel backscattering communication system is constructed in 5GHz frequency range by commercial Wi-Fi equipment first.
Then, we collect data by system come assessment of system performance.Experimental data acquisition be in a common laboratory into
Capable, there are multiple work in the room or corridor of surrounding in the Wi-Fi access point (APs) of same frequency range, makes always to system
At interference.
Assessment and configuration
Experimental evaluation is that user's scene according to shown in Fig. 6 is designed.Specifically, we are respectively using outfit
The commercial mini desktop computer of Intel 5300Wi-Fi network interface card and 5dBi omnidirectional antenna is as signal assistant and receiver.And
The commercial mini desktop computer for being equipped with Atheros AR9580Wi-Fi network interface card and 5dBi omnidirectional antenna is user.Experimental evaluation
It is to be carried out under working environment, topological structure is as shown in Figure 7.Signal assistant passes through transmission User Datagram Protocol (UDP)
Packet generates 5GHz and helps signal.The transmission rate of packet is 1000 packet/seconds.Recipient is currently running CSI tool and is used for capture
The CSI of communication process is tracked.User is between signal assistant and receiver.Wherein d2 and d1 is respectively that signal assistor arrives
The vertical range of the vertical range of user people and receiver to user people.Signal assistor is 1.2m at a distance from receiver.Net
The switch gap of card is defaulted as 0.25s.
The CSI of receiving end and the signal-to-noise ratio received (SNR)
Fig. 3 shows the track CSI of multiple subcarriers and the corresponding signal-to-noise ratio of receiver after LPF.The volume leaked from user
Code sensitive data is related with the square of the track CSI in Fig. 3.It can be seen from the figure that and not all Wi-Fi subcarrier all
Sensitive data from the user is carried, this is because the frequency selectivity of Wi-Fi channel.Therefore, from the user in order to decode
Sensitive data needs to carry out sub-carrier selection.
Fig. 4 be respectively after DC component removal each subcarrier in two moment different moments (corresponding different Bale No.s) CSI rail
The signal-to-noise ratio of mark is not to say that a subcarrier it can be seen from the figure that signal-to-noise ratio is frequency selectivity and time selectivity
On signal-to-noise ratio it is higher, it is easier decode the subcarrier on user sensitive data.Therefore, for the ease of to sensitive data into
Row decoding is decoded using leading characteristic selection subcarrier.
1) number of users detects: the decoding of the sensitive data of number of users detection performance and receiver is closely related, especially right
In multi-user people's scene.Fig. 8 shows that d1 distance changes from 10cm to 40cm when 1,2,3 user simultaneously participates in system
When, the performance of number of users detection performance.It can be seen from the figure that detection performance declines with the increase of d1.The reason is that
The distance of user to receiver is remoter, and the back-scattered signal that receiver receives is weaker, to reduce number of users detection
Performance.From figure we it can also be seen that detection performance is lower, user is more.In d1=10cm, to the use of different number
Family, detection performance almost can achieve 100%.
2) User ID detection performance: Fig. 9 illustrates when 1,2,3 user people simultaneously participates in system, d1 distance for 10~
When 40cm, the performance of user's person part recognition performance.It can be seen from the figure that with the increase of d1, under User ID detection performance
Drop, this is similar to trend in figure.We obtain more users it can also be seen that detection performance is lower.In d1=10cm
When, the subject number detection performance of different subject numbers almost can achieve 100%, similar to figure.
3) it error rate of system (BER): Figure 10 describes when 1,2,3 user simultaneously participates in system, d1 distance is from 10cm
To the decoding performance of system when 40cm variation.It can be seen from the figure that BER increases with the increase of d1.To find out its cause, with
The distance of family to receiver is remoter, and the backscatter signal that receiver receives is weaker, to reduce decoding performance.From figure
It can also be seen that with the increase of user number, the bit error rate is also increased accordingly.The bit error rate of one user people is in d1 < 20cm
It almost can achieve 0.For 1,2 or 3 user involved in system, error code when d1=10cm is less than 1%.
System data rates and network interface card switching interval
Figure 11 illustrates when being related to a user, shadow of the network interface card switch gap to system data rates and the bit error rate
It rings.Antenna gain is that the omnidirectional antenna of 5dBi is arranged respectively at signal assistant, user and receiving end, d1=10cm.It can from figure
To find out, data rate and the bit error rate all increase with the reduction of network interface card switching interval.By changing the switching frequency of network interface card,
Message transmission rate can reach 100, and the bit error rate is very low；Therefore, which can also be applied to some pairs of transmission rate requests
Lower near-field communication scene.
Interfere the influence to receiver signal-to-noise ratio
Figure 12 gives an example, illustrates as d1=20cm, in the 1500th data packet, when DC is removed in CSI
Afterwards, influence of the interference from ambient enviroment to receiver average signal-to-noise ratio.These data are collected from many experiments measurement
's.In each experiment, we observe the quantity of Wi-Fi access point (APs) under 5GHz frequency using Wi-Fi diagnostic software.From
As can be seen that signal-to-noise ratio is reduced with the increase of Wi-Fi AP quantity in figure.When 5Ghz Wi-Fi APs quantity increases, this
The interference meeting severe jamming CSI trace of a little Wi-Fi APs, thus the reflection signal for carrying CSI trace at receiver, so that
Sensitive data decoding at receiver becomes more difficult.On the other hand, higher data rate is in Figure 11 when ambient enviroment
It interferes less.
Claims (10)
1. a kind of short distance multi-user's concealed communication method based on Wi-Fi network interface card, which is characterized in that including following sub-step:
Step 1:Wi-Fi signal source issues radiofrequency signal, and receiving end receives radiofrequency signal and calculates Wi-Fi letter according to radiofrequency signal
Original channel status information CSI number between source and receiving end；
Step 2: user terminal reflects the radiofrequency signal that Wi-Fi signal source issues, and the user terminal includes multiple users, each user
It loads the information sequence for respectively passing through orthogonal coding in radiofrequency signal simultaneously using network interface card, obtains comprehensive radiofrequency signal；
Step 3: receiving end receives comprehensive radiofrequency signal and is calculated between Wi-Fi signal source and receiving end according to comprehensive radiofrequency signal
CSI, the mapping for establishing CSI amplitude to signal level obtains integrated signal level, then decodes to integrated signal level,
Obtain the information sequence of each user.
2. short distance multi-user's concealed communication method based on Wi-Fi network interface card as described in claim 1, which is characterized in that step
Rapid 2 include following sub-step:
Step 2.1: user terminal reflect Wi-Fi signal source issue radiofrequency signal, the user terminal includes K user, in order to
The data from different user are efficiently separated at receiver, we utilize wkTo encode the transmission data of user k.Each user
Data include multiple information bits, the information bit d' after the l Bits Expanding of k-th of userk(l) it indicates are as follows:
d'k(l)=μk(l)wk
Wherein, k=1,2,3...K and K indicate user terminal total number of users, and l=1,2,3...L and L indicate the dominant bit of information bit
Number, μk(l) indicate bipolarity position andwkBe expressed as the row k of Walsh-Hadmard matrix to
Amount, Walsh-Hadmard matrix are the square matrix of N × N, and row is orthogonal matrix, the integral power that N is 2, N >=2 and are not less than user
Sum；
Step 2.2: simultaneously load the information sequence for respectively passing through orthogonal coding in radiofrequency signal simultaneously according to the building of user's number,
Obtain comprehensive radiofrequency signal such as formula I:
Wherein, βkIndicate CSI power stageh0It is terminated for Wi-Fi signal source to reception
The original CSI, h of receipts machinekFor the CSI of k-th of user to receiver, h0,kIndicate CSI, p of the Wi-Fi signal source to k-th of userk
For the transmission power of the network interface card of k-th of user, p0For the transmission power at Wi-Fi signal source,It indicates to adjust network interface card work shape
The attenuation coefficient of state.
3. short distance multi-user's concealed communication method based on Wi-Fi network interface card as claimed in claim 2, which is characterized in that step
Rapid 3 include following sub-step:
Step 3.1: receiving end receives comprehensive radiofrequency signal and according to comprehensive radiofrequency signal, calculates Wi-Fi signal source using formula II
CSI between receiving end:
Wherein,And z " is noise item；
Step 3.2: the amplitude of the CSI established between Wi-Fi signal source and receiving end using formula III to signal level is mapped
To integrated signal level d "k:
d”k=μkN formula III
Wherein, N=wT NwN, { }TIt is the transposition of matrix, μkIndicate bipolar sequence；
Step 3.3: to integrated signal level d "kIt is decoded to obtain bipolar sequence μk, and according to μkObtain k-th of user's
Original information sequence, and then obtain the information sequence of whole K users.
4. short distance multi-user's concealed communication method based on Wi-Fi network interface card as claimed in claim 3, which is characterized in that step
Rapid 3.3 include following sub-step:
Step 3.3.1: using formula IV to integrated signal level d "kIt is decoded, obtains bipolar sequence μk:
Wherein,d'kIt is information sequence of k-th of user after orthogonal coding extends.
Step 3.3.2: according to bipolar sequence μk, according to the relationship of bipolar sequence shown in formula V and information sequence, obtain kth
The information sequence of a user, and then obtain the information sequence of whole K users:
5. short distance multi-user's concealed communication method described in claim 1 based on Wi-Fi network interface card, which is characterized in that described
Radiofrequency signal relies on data packet and is sent to receiving end by Wi-Fi signal source, and the structure of the data packet is packet detection sequence, uses
Family identification serial ID and payload transmit sequence, the identification serial ID of k-th of userkIt is expressed as,Wherein, K0≥K+1。
6. a kind of short distance multi-user's convert communication system based on Wi-Fi network interface card, which is characterized in that including Wi-Fi signal source,
User terminal, receiving end；
The Wi-Fi signal source is for issuing radiofrequency signal to receiving end；
The user terminal includes multiple users, and each user is loaded in radiofrequency signal respectively using network interface card by orthogonal volume simultaneously
The information sequence of code, and be reflected into receiving end and be overlapped to obtain comprehensive radiofrequency signal with original radio frequency signal；
The receiving end receives the synthesis radiofrequency signal of the radiofrequency signal that Wi-Fi signal source is sent and user terminal reflection, calculates
CSI between Wi-Fi signal source and receiving end, changes according to the amplitude of CSI, and the mapping for establishing CSI amplitude to signal level obtains
Then integrated signal level decodes integrated signal level, obtain the information sequence of each user.
7. short distance multi-user's convert communication system based on Wi-Fi network interface card as claimed in claim 6, which is characterized in that use
Family end reflect Wi-Fi signal source issue radiofrequency signal, the user terminal includes K user, in order at receiver effectively
The data from different user are separated, we utilize wkTo encode the transmission data of user k.The data of each user include multiple
Information bit, the information bit d' after the l Bits Expanding of k-th of userk(l) it indicates are as follows:
d'k(l)=μk(l)wk
Wherein, k=1,2,3...K and K indicate user terminal total number of users, and l=1,2,3...L and L indicate the dominant bit of information bit
Number, μk(l) indicate bipolarity position andwkBe expressed as the row k of Walsh-Hadmard matrix to
Amount, Walsh-Hadmard matrix are the square matrix of N × N, and row is orthogonal matrix, the integral power that N is 2, N >=2 and are not less than user
Sum；
Then it simultaneously loads the information sequence for respectively passing through orthogonal coding in radiofrequency signal simultaneously according to the building of user's number, obtains
Comprehensive radiofrequency signal such as formula I:
Wherein, βkIndicate CSI power stageh0It is terminated for Wi-Fi signal source to reception
The CSI of receipts machine, hkFor the CSI of k-th of user to receiver, h0,kIndicate CSI, p of the Wi-Fi signal source to k-th of userkIt is
The transmission power of the network interface card of k user, p0For the transmission power at Wi-Fi signal source,It indicates to adjust network interface card working condition
Attenuation coefficient.
8. short distance multi-user's convert communication system based on Wi-Fi network interface card as claimed in claim 7, which is characterized in that
The receiving end receives comprehensive radiofrequency signal and according to comprehensive radiofrequency signal, calculates Wi-Fi signal source using formula II and connects
CSI between receiving end:
Wherein,And z " is noise item；
The receiving end obtains integrated signal level d " using the mapping that formula III establishes CSI to signal levelk:
d”k=μkN formula III
Wherein, N=wT NwN, { }TIt is the transposition of matrix, μkIndicate bipolar sequence；
The receiving end is to integrated signal level d "kIt is decoded to obtain bipolar sequence μk, and according to μkObtain k-th of user
Information sequence, and then obtain the information sequence of whole K users.
9. short distance multi-user's concealed communication method based on Wi-Fi network interface card as claimed in claim 8, which is characterized in that institute
Receiving end is stated to utilization formula IV to integrated signal level d "kIt is decoded, obtains bipolar sequence μk:
And according to bipolar sequence μk, according to the relationship of bipolar sequence shown in formula V and information sequence, obtain k-th of user's
Information sequence, and then obtain the information sequence of whole K users:
10. short distance multi-user's concealed communication method as claimed in claim 6 based on Wi-Fi network interface card, which is characterized in that described
Radiofrequency signal relies on data packet and is sent to receiving end by Wi-Fi signal source, and the structure of the data packet is packet detection sequence, uses
Family identification serial ID and payload transmit sequence, the identification serial ID of k-th of userkIt is expressed as,Wherein, K0Greater than total number of users K, i.e. K0≥K+1。
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