CN110300399B - Close-range multi-user covert communication method and system based on Wi-Fi network card - Google Patents

Close-range multi-user covert communication method and system based on Wi-Fi network card Download PDF

Info

Publication number
CN110300399B
CN110300399B CN201910548389.6A CN201910548389A CN110300399B CN 110300399 B CN110300399 B CN 110300399B CN 201910548389 A CN201910548389 A CN 201910548389A CN 110300399 B CN110300399 B CN 110300399B
Authority
CN
China
Prior art keywords
user
radio frequency
signal
csi
sequence
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Active
Application number
CN201910548389.6A
Other languages
Chinese (zh)
Other versions
CN110300399A (en
Inventor
牛进平
马跃
郭艺
张李
鱼跃华
陈�峰
尹晓燕
陈晓江
房鼎益
汤战勇
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Northwestern University
Original Assignee
Northwestern University
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Northwestern University filed Critical Northwestern University
Priority to CN201910548389.6A priority Critical patent/CN110300399B/en
Publication of CN110300399A publication Critical patent/CN110300399A/en
Application granted granted Critical
Publication of CN110300399B publication Critical patent/CN110300399B/en
Active legal-status Critical Current
Anticipated expiration legal-status Critical

Links

Images

Classifications

    • 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
    • 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
    • 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
    • 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

Landscapes

  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Quality & Reliability (AREA)
  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Mobile Radio Communication Systems (AREA)

Abstract

The invention discloses a close-range multi-user covert communication method and a system based on a Wi-Fi network card, wherein the method comprises the following substeps: step 1: the Wi-Fi signal source sends out a radio frequency signal, the receiving terminal receives the radio frequency signal and calculates CSI between the Wi-Fi signal source and the receiving terminal according to the radio frequency signal; step 2: the user side reflects radio frequency signals sent by the Wi-Fi signal source, each user loads information sequences which are respectively subjected to orthogonal coding to the radio frequency signals by using the network card at the same time, and comprehensive radio frequency signals are obtained through superposition; and step 3: and the receiving terminal receives the comprehensive radio frequency signal, calculates CSI between the Wi-Fi signal source and the receiving terminal according to the comprehensive radio frequency signal, establishes mapping from the CSI amplitude to the signal level to obtain a comprehensive signal level, and decodes the comprehensive signal level to obtain an information sequence of the user. The invention can transmit data of a plurality of users, help a receiver at a receiving end to separate important information of the plurality of users, and ensure the safety of the users in using public network connection to transmit the important information.

Description

Close-range multi-user covert communication method and system based on Wi-Fi network card
Technical Field
The invention belongs to the technical field of covert communication, and particularly relates to a near-distance multi-user covert communication method and system based on a Wi-Fi network card.
Background
In recent years, with the increasing popularization of wireless networks and mobile intelligent terminals, short-distance wireless data transmission has become an essential part of people's daily life. In a short distance situation, a great deal of user privacy information is mutually transferred among user equipment through methods such as Wi-Fi, Bluetooth, NFC and the like, and a huge security problem exists. According to a safety report of the first quarter of 2019 issued by a mobile safety laboratory in Tencent, the number of public Wi-Fi is up to 9.84 hundred million by 3 months, and the Wi-Fi coverage rate of the public places such as airports, hotels, large shopping malls and the like is 58.18 percent without risks, 41.82 percent of the Wi-Fi coverage rate of the risks and the number of the Wi-Fi coverage rate of the public places is close to 3.96 hundred million. Criminals may steal the private information of users by using the risk Wi-Fi and even threaten the property security of the users. Bluetooth is not only affected by denial of service attack, co-channel interference, message modification and resource abuse, but also has the disadvantage that the pairing time is as long as 6 seconds and only point-to-point communication is supported. The Wi-Fi and the Bluetooth are used in public places to transmit privacy information, such as identity information, an address list, account passwords and the like, which have great risks. However, the current mainstream technology of NFC is limited by cost and market, so that the mobile device with NFC function only accounts for 30% of the total device.
With the increasing awareness and research on information protection, a series of covert communication methods, such as schemes based on heat reflection and electromagnetic reflection, have appeared, and compared with earlier schemes based on sound and light, the covert communication methods have the advantage that no physical connection needs to be established, however, the solutions are applied to a certain extent in the respective applicable environments. The limitation is obvious, for example, the power is needed, the energy consumption is high, and the communication can be carried out by external equipment. In the prior art, sine waves from a router are reflected by different impedances when a network card is switched on and switched off, and self information is loaded on a received signal strength RSSI or transmitted to a receiving end, although the number of public Wi-Fi with the number of 9.84 hundred million and the popularity of the network card provide a hardware basis for the purpose, obvious problems exist correspondingly:
(1) the RSSI signal is greatly influenced by the environment, and the RSSI information can have larger change along with the change of time and space, and the reason is environmental multipath transmission;
(2) RSSI signals are easy to capture, RSSI information can be captured by any commercial network equipment in space, and hidden transmission of data is not facilitated;
(3) the data transmission rate is limited by the delay of the network card switch, and is only about 1 bps. Therefore, a low-cost, high-precision, easy-to-use covert communication solution has a very important research value.
Disclosure of Invention
The invention aims to provide a close-range multi-user covert communication method and system based on a Wi-Fi network card, which are used for solving the problems in the prior art in the research of covert communication schemes.
In order to realize the task, the invention adopts the following technical scheme:
a close-range multi-user covert communication method based on a Wi-Fi network card comprises the following substeps:
step 1: the Wi-Fi signal source sends out radio frequency signals, the receiving terminal receives the radio frequency signals and calculates original Channel State Information (CSI) between the Wi-Fi signal source and the receiving terminal according to the radio frequency signals;
step 2: the method comprises the following steps that a user side reflects a radio frequency signal sent by a Wi-Fi signal source, the user side comprises a plurality of users, and each user loads an information sequence which is subjected to orthogonal coding to the radio frequency signal by using a network card simultaneously to obtain a comprehensive radio frequency signal;
and step 3: and the receiving terminal receives the comprehensive radio frequency signal, calculates CSI between the Wi-Fi signal source and the receiving terminal according to the comprehensive radio frequency signal, establishes mapping from the CSI amplitude to the signal level to obtain a comprehensive signal level, and then decodes the comprehensive signal level to obtain an information sequence of each user.
Further, step 2 comprises the following substeps:
step 2.1: the user side, which reflects the radio frequency signal from the Wi-Fi signal source, includes K users, and in order to effectively separate the data from different users at the receiver, we use wkTo encode the transmitted data for user k. The data of each user comprises a plurality of information bits, and the l bit of the k user is expanded to form an information bit d'k(l) Expressed as:
d'k(l)＝μk(l)wk
where K is 1,2,3.. K and K denotes a total number of user terminals, l is 1,2,3.. L and L denotes a maximum number of bits of information, μk(l) Represents a bipolar bit and
Figure RE-GDA0002176930970000031
wkexpressed as a k-th row vector of a Walsh-Hadmard matrix, the Walsh-Hadmard matrix is a square matrix of N × N, the rows are orthogonal matrices, N is an integral power of 2, and N is more than or equal to 2 and is not less than the total number of users;
step 2.2: and constructing according to the number of users and simultaneously loading information sequences which are respectively subjected to orthogonal coding on the radio frequency signals to obtain the comprehensive radio frequency signals as shown in the formula I:
Figure RE-GDA0002176930970000032
wherein, βkRepresenting CSI power levels
Figure RE-GDA0002176930970000033
h0Original CSI, h for Wi-Fi signal source to receiverkFor the k user to receiver CSI, h0,kRepresenting CSI, p from Wi-Fi signal source to kth userkTransmission power of network card for k-th user, p0For the transmit power at the Wi-Fi signal source,
Figure RE-GDA0002176930970000034
and the attenuation coefficient for adjusting the working state of the network card is shown.
Further, step 3 comprises the following substeps:
step 3.1: and the receiving terminal receives the comprehensive radio frequency signal and calculates CSI between the Wi-Fi signal source and the receiving terminal by using a formula II according to the comprehensive radio frequency signal:
Figure RE-GDA0002176930970000035
wherein,
Figure RE-GDA0002176930970000041
and z "is a noise term;
step 3.2: establishing mapping from the amplitude value of the CSI between the Wi-Fi signal source and the receiving end to the signal level by using a formula III to obtain a comprehensive signal level d'k：
d”k＝μkN formula III
Wherein N ═ wT NwN，{·}TIs the transpose of a matrix, mukRepresents a bipolar sequence;
step 3.3: for integrated signal level d'kDecoding to obtain bipolar sequence mukAnd according to μkAnd obtaining the original information sequence of the kth user, and further obtaining the information sequences of all the K users.
Further, step 3.3 comprises the following sub-steps:
step 3.3.1: using the formula IV for the integrated signal level d'kDecoding to obtain bipolar sequence muk：
Figure RE-GDA0002176930970000042
Wherein,
Figure RE-GDA0002176930970000043
d'kis the information sequence of the k-th user after orthogonal coding and spreading.
Step 3.3.2: according to a bipolar sequence mukAnd obtaining the information sequence of the kth user according to the relation between the bipolar sequence and the information sequence shown in the formula V, and further obtaining the information sequences of all the K users:
Figure RE-GDA0002176930970000044
further, the radio frequency signal is sent to the receiving end by the Wi-Fi signal source depending on a data packet, and the data packet is structured into a packet detection sequence, a user identity identification sequence ID, a payload transmission sequence and a k-th user identification sequence IDkAs indicated by the general representation of the,
Figure RE-GDA0002176930970000045
wherein, K0≥K+1。
A close-range multi-user covert communication system based on a Wi-Fi network card comprises a Wi-Fi signal source, a user side and a receiving end;
the system comprises a Wi-Fi signal source, a user side and a receiving end;
the Wi-Fi signal source is used for sending a radio frequency signal to a receiving end;
the user side comprises a plurality of users, each user simultaneously loads information sequences which are respectively subjected to orthogonal coding to the radio frequency signals by using the network card, and the information sequences are reflected to a receiving end to be superposed with the original radio frequency signals to obtain comprehensive radio frequency signals;
the receiving terminal receives radio frequency signals sent by the Wi-Fi signal source and comprehensive radio frequency signals reflected by the user terminal, CSI between the Wi-Fi signal source and the receiving terminal is calculated, mapping from CSI amplitude to signal level is established according to amplitude change of the CSI to obtain comprehensive signal level, and then the comprehensive signal level is decoded to obtain an information sequence of each user.
Further, the user side reflects the radio frequency signal from the Wi-Fi signal source, said user side comprising K users, and in order to effectively separate the data from different users at the receiver, we use wkTo encode the transmitted data for user k. The data of each user includes a plurality of informationBit, information bit d 'of k-th user after l bit expansion'k(l) Expressed as:
d'k(l)＝μk(l)wk
where K is 1,2,3.. K and K denotes a total number of user terminals, l is 1,2,3.. L and L denotes a maximum number of bits of information, μk(l) Represents a bipolar bit and
Figure RE-GDA0002176930970000051
wkexpressed as a k-th row vector of a Walsh-Hadmard matrix, the Walsh-Hadmard matrix is a square matrix of N × N, the rows are orthogonal matrices, N is an integral power of 2, and N is more than or equal to 2 and is not less than the total number of users;
then, according to the number of users, information sequences which are respectively subjected to orthogonal coding are constructed and loaded on the radio frequency signals at the same time, and the comprehensive radio frequency signals are obtained as shown in the formula I:
Figure RE-GDA0002176930970000052
wherein, βkRepresenting CSI power levels
Figure RE-GDA0002176930970000053
h0CSI, h for Wi-Fi signal source to receiverkFor the k user to receiver CSI, h0,kRepresenting CSI, p from Wi-Fi signal source to kth userkTransmission power of network card for k-th user, p0For the transmit power at the Wi-Fi signal source,
Figure RE-GDA0002176930970000061
and the attenuation coefficient for adjusting the working state of the network card is shown.
Further, the receiving end receives the integrated radio frequency signal and calculates the CSI between the Wi-Fi signal source and the receiving end according to the integrated radio frequency signal by using a formula ii:
Figure RE-GDA0002176930970000062
wherein,
Figure RE-GDA0002176930970000063
and z "is a noise term;
the receiving end utilizes the formula III to establish the mapping from the CSI to the signal level to obtain the comprehensive signal level d'k：
d”k＝μkN formula III
Wherein N ═ wT NwN，{·}TIs the transpose of a matrix, mukRepresents a bipolar sequence;
the receiving end pair synthesizes signal level d'kDecoding to obtain bipolar sequence mukAnd according to μkAnd obtaining the information sequence of the kth user, and further obtaining the information sequences of all the K users.
Further, the receiving end pair utilizes the formula IV to synthesize the signal level d'kDecoding to obtain bipolar sequence muk：
Figure RE-GDA0002176930970000064
And according to a bipolar sequence mukAnd obtaining the information sequence of the kth user according to the relation between the bipolar sequence and the information sequence shown in the formula V, and further obtaining the information sequences of all the K users:
Figure RE-GDA0002176930970000065
further, the radio frequency signal is sent to the receiving end by the Wi-Fi signal source depending on a data packet, and the data packet is structured into a packet detection sequence, a user identity identification sequence ID, a payload transmission sequence and a k-th user identification sequence IDkAs indicated by the general representation of the,
Figure RE-GDA0002176930970000066
wherein, K0Greater than the 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, CSI of Wi-Fi devices has been widely applied to the field of environmental sensing. It is a finer grained channel characteristic than the received signal strength RSSI in Wi-Fi devices. The CSI can simultaneously capture fast fading and slow fading information, thereby reflecting frequency selective channel characteristics and multipath channel effects. Compared with the sensing method based on the RSSI, the sensing method based on the CSI has better sensing performance.
(2) In order to help extract important information of a user from the Wi-Fi CSI, a theoretical model is provided to show the relationship between the Wi-Fi CSI, a reflected radio frequency signal and the important information.
(3) In order to solve the problem that the Wi-Fi network card carries out multi-user covert communication and the problem that important information of a plurality of users cannot be separated when being superposed on a receiving end, the orthogonal coding and decoding technology helps a receiving end to separate the important information of the plurality of users.
(4) In order to theoretically simulate the relationship between the captured CSI and important information transmitted by a user, firstly, covert channel communication in a signal transmission process is analyzed through a wireless network card, then an analyzed CSI source (signal helper) and a wireless signal receiver at a receiving end are analyzed, and finally, a theoretical model is given to analyze the relationship between the CSI and transmission data.
(5) In order to facilitate the decoding of data by multiple users, a scheme capable of determining the number and identity of the users is provided.
Drawings
FIG. 1 is a diagram of the variation of CSI at the receiver when the user configures the Atheros 9580 network card;
FIG. 2 is a diagram of a user transmission packet structure;
FIG. 3 is a graph of received amplitude values for different frequency subcarriers;
FIG. 4 is a graph of the SNR of different frequency subcarriers after DC removal;
FIG. 5 is a CSI magnitude graph for different numbers of users;
FIG. 6 is a multi-user scenario diagram;
FIG. 7 is an experimental topology;
FIG. 8 is a user number identification performance diagram;
FIG. 9 is a user ID identification performance diagram;
FIG. 10 is a graph of bit error rate performance with a different number of users;
FIG. 11 is a diagram showing the relationship between the system transmission rate and the bit error rate corresponding to the network card switching interval;
figure 12 is a graph of the impact of the number of Wi-Fi access points in the environment on system performance.
Detailed Description
Example 1
The embodiment discloses a near-distance multi-user covert communication method based on a Wi-Fi network card, which comprises the following substeps:
step 1: the Wi-Fi signal source sends out a radio frequency signal, the receiving terminal receives the radio frequency signal and calculates the original CSI between the Wi-Fi signal source and the receiving terminal according to the radio frequency signal;
step 2: the method comprises the steps that a user side reflects radio-frequency signals sent by a Wi-Fi signal source, the user side comprises a plurality of users, each user loads information sequences which are respectively subjected to orthogonal coding to the radio-frequency signals by using a network card at the same time, and comprehensive radio-frequency signals are obtained through superposition;
and step 3: and the receiving terminal receives the comprehensive radio frequency signal, calculates CSI between the Wi-Fi signal source and the receiving terminal according to the comprehensive radio frequency signal, establishes mapping from the CSI amplitude to the signal level according to the amplitude change of the CSI to obtain a comprehensive signal level, and then decodes the comprehensive signal level to obtain information sequences of all users.
The invention adjusts the impedance of the Wi-Fi network card of the mobile user through the pre-installed software for controlling the impedance of the network card, thereby enabling the network card of the user to reflect the environment radio frequency signal (RF) signal in the surrounding environment. Then, the information in the user terminal can be carried by the reflected radio frequency signal and transmitted to the receiver at the receiving end, and the orthogonal coding and decoding are used to help the multi-user to decode the data at the receiving end.
First, how the Wi-Fi network card loads the information sequence is explained:
as shown in fig. 6, the incident signal from the Wi-Fi signal source will be transmitted directly to the receiving end. In addition, if the impedance of the user's network card changes from one state to another, the auxiliary signal may be reflected by the user's network card and transmitted to the receiving end. The present document is primarily directed to research on users of static network card configurations. In a static type network card, the envelope of the reflected radio frequency signal resembles a square wave of different power levels when the Wi-Fi network card is continuously enabled and disabled. As shown in fig. 1, the network card AR9850 belongs to a static network card. The signal received by one transmitting antenna of the signal source at user k can be represented as:
Figure RE-GDA0002176930970000091
wherein h is0,kFor the CSI, P from Wi-Fi signal source to user k0And x0Respectively the transmitted power and the transmitted signal at the Wi-Fi signal source, ZkIs white gaussian noise at user k.
Suppose that the user has installed the software for controlling the impedance of the network card in advance, and the software for controlling the impedance of the network card can control the working state of the network card of the user to be in an on/off state, so that the RF signal received by the user can be reflected. Different operating states of the network card may result in different amplitudes of the reflected rf signal, as shown in fig. 1. More specifically, received signal x'kWill reflect to user k:
Figure RE-GDA0002176930970000092
α 0 and α 1 are attenuation factors caused by adjusting the working state of the network card.
By utilizing the characteristic, sensitive information of a user can be modulated into a reflected radio frequency signal and then decoded at a receiving end of the receiving end. More specifically, the software for controlling the impedance of the network card, which is pre-installed in the mobile user, controls the working state of the user network card to be on or off according to the sensitive information of the user. Thus, the reflected signal at user k can be rewritten as:
Figure RE-GDA0002176930970000093
wherein d iskIs a sensitive information bit in user k. According to (2) and (3), the software controlling the impedance of the network card for user k will force the user's network card if the sensitive information transmission is' 0 'and the software controlling the impedance of the network card will force the user's network card if the bit transmitted information is '1'. In this way, sensitive information of the user can be modulated into a radio frequency signal and transmitted to a receiver at the receiving end.
If K users reflect Wi-Fi signals at the same time, the receiver at the receiving end receives signals from all K users in addition to the Wi-Fi signal source. Therefore, the signal received by the receiving end can be expressed as
Figure RE-GDA0002176930970000101
Wherein h is0CSI, h for Wi-Fi signal source to receiverkFor user k to receiver CSI, PkIs the transmit power of the network card for user k and z is white gaussian noise at the receiver.
The hidden channel communication coding scheme is mainly used for a plurality of mobile devices with static type network cards and based on the backward scattering of the Wi-Fi network cards. In order to allow multiple users to simultaneously spread data, the payload data before transmission is encoded using orthogonal coding techniques. In this way, different users can be distinguished by different orthogonal codes. Therefore, at the receiving end, the data can be separated from different users by using corresponding orthogonal decoding technology.
Specifically, step 2 includes the following substeps:
step 2.1: the user side, which reflects the radio frequency signal from the Wi-Fi signal source, includes K users, and in order to effectively separate the data from different users at the receiver, we use wkTo encode the transmitted data for user k. The data of each user comprises a plurality of information bits, and the l bit of the k user is expanded to form an information bit d'k(l) Watch (A)Shown as follows:
d'k(l)＝μk(l)wk
where K is 1,2,3.. K and K denotes a total number of user terminals, l is 1,2,3.. L and L denotes a maximum number of bits of information, μk(l) Represents a bipolar bit and
Figure RE-GDA0002176930970000102
wkexpressed as a K-th row vector of a Walsh-Hadmard matrix, the Walsh-Hadmard matrix is a square matrix of N × N, the rows are orthogonal matrices, N is an integral power of 2, and N is more than or equal to 2 and is not less than the total number of users (N is more than or equal to K);
for ease of explanation, the transmission payload data for each user is encoded using the rows of the Walsh-Hadmard matrix. The Walsh-Hadmard matrix is a square matrix with the rows being orthogonal vectors. Represents WNWalsh-Hadmard matrix for N × N it is then
Figure RE-GDA0002176930970000111
And
Figure RE-GDA0002176930970000112
where N is an integral power of 2, N>2 and is not less than the total number of users (namely N is more than or equal to K),
Figure RE-GDA0002176930970000113
is the Kronecker (Kronecker) product. Denotes wiIs a Walsh-Hadmard matrix HNThe ith row vector of (1). According to the definition of the Walsh-Hadmard matrix,
wiwj T＝0 (7)
and
wiwi T＝N (8)
to efficiently separate data from different users at the receiving end, w is utilizedNThe transmission data of user k is encoded.
Step 2.2: and (2) constructing and loading information sequences which are respectively subjected to orthogonal coding to the radio frequency signals according to the number of users, and obtaining the comprehensive radio frequency signals by superposition as shown in the formula I:
Figure RE-GDA0002176930970000114
wherein, βkRepresenting CSI power stage βk＝αηkCk，
Figure RE-GDA0002176930970000115
h0Original CSI, h for Wi-Fi signal source to receiverkFor the k user to receiver CSI, h0,kRepresenting CSI, p from Wi-Fi signal source to kth userkTransmission power of network card for k-th user, p0For the transmit power at the Wi-Fi signal source, αηkAnd the attenuation coefficient for adjusting the working state of the network card is shown.
For the case of one user, no orthogonal coding is required, so W is assumed for the case of one user 11. Note that other orthogonal coding schemes may also be used to support the transmission of signals by multiple users. For ease of explanation, the transmitted information is encoded using a Walsh-Hadmard sequence.
Specifically, step 3 includes the following substeps:
step 3.1: and the receiving terminal receives the comprehensive radio frequency signal and calculates CSI between the Wi-Fi signal source and the receiving terminal by using a formula II according to the comprehensive radio frequency signal:
Figure RE-GDA0002176930970000121
wherein,
Figure RE-GDA0002176930970000122
and z "is a noise term;
step 3.2: the amplitude of the CSI changes due to changes in the composite RF signal, and the composite signal level d' is obtained by using the formula III to establish the mapping from the composite CSI to the signal level "k：
d”k＝μkN formula III
Wherein N ═ wT NwN，{·}TIs the transpose of a matrix, mukRepresents a bipolar sequence;
step 3.3: for integrated signal level d'kDecoding to obtain bipolar sequence mukAnd according to μkAnd obtaining the information sequence of the kth user, and further obtaining the information sequences of all the K users.
Preferably, step 3.3 comprises the following sub-steps:
the coded information bits transmitted in d ' at user K have two possible values, ' 1 ' and ' -1 ', the received signal level of each coded information symbol "1" and "-1" is labeled as 1 and-1, respectively, assuming there are a total of K users, all transmitting data simultaneously, K (1 ≦ K) users transmitting coded information symbols "1", the remaining K-K users transmitting coded information symbols "-1", and then the overall received signal level associated with these transmitted symbols is defined as K × 1+ (K-K) × (-1) ═ K-2K.
Considering the packet structure and design, in superimposing the preamble sequence in which CSI is associated with the transmitter identity ID, the number level of CSI is equal to the number of users plus 1, K +1, and the number of signal levels is the same level of CSI. More specifically, the signal levels involved are K, K-2,.,. K-2(K-1),. K, where K-2(K-1) is the signal level corresponding to the Kth bit in the transmitter identification code ID.
The signal level is determined for each symbol of the received load based on the signal levels obtained in the preamble sequence. More specifically, the mean of the CSI amplitude samples in each symbol period is calculated, the calculated value is then compared with the CSI level associated with the sequence number, and finally the calculated value is updated to the latest CSI level. The calculated CSI levels are then mapped to corresponding signal levels. The calculated signal level corresponding to one information bit indicating a user not subjected to orthogonal coding is Ss.
Step 3.3.1: using the formula IV for the integrated signal level d'kDecoding to obtain bipolar sequence muk：
Figure RE-GDA0002176930970000131
Wherein
Figure RE-GDA0002176930970000132
Wherein d'kIs the information sequence of the k-th user after orthogonal coding and spreading.
Step 3.3.2: according to a bipolar sequence mukAnd obtaining the information sequence of the kth user according to the relation between the bipolar sequence and the information sequence shown in the formula V, and further obtaining the information sequences of all the K users:
Figure RE-GDA0002176930970000133
specifically, to maintain consistency of the description, "1" and "-1" are used to denote "1" and "0" in the preamble sequence, respectively. For packet detection, "-1, 1,1,1, -1" in the frame structure is used as a packet detection code. The data packet is then detected at the receiving end according to its coding structure. Other codes may also be used to facilitate packet detection.
Wireless carrier transmission of CSI, a CSI trace from the beginning if the time interval between the two CSI level changes abruptly equal three symbol durations, the initial abrupt change results in an increase in the CSI level, and the end abrupt change results in a decrease in the CSI standard, then three consecutive symbols "111" can be detected. The first and last symbols "-1" may also be determined because abrupt changes in CSI level are caused by differences in transmitted symbols. Once the symbol "-1111-1" is detected, it means that a new compression was transmitted.
In order to facilitate data decoding at the receiving end, the user number and identity after data packet detection must be determined first. Therefore, a user identification code is designed in the framework structure to solve this problem. More specifically, the sequence IDs are designed to identify different users for data decoding at the receiving end. Specifically, assume 11×kAnd-11×kIs as followsThere are 1 × k vectors with elements equal to 1 and-1, respectively.
The radio frequency signal is sent to a receiving end by a Wi-Fi signal source depending on a data packet, and the structure of the data packet is a packet detection sequence, a user identity identification sequence ID, a payload transmission sequence and a k-th user identification sequence IDkAs indicated by the general representation of the,
Figure RE-GDA0002176930970000141
wherein, K0Greater than the total number of users K, i.e. K0≥K+1。
In particular, a method for determining the number and identity of users
However, to decode the payload information of the receiver, it is first necessary to know the number of users and the identity of the users.
Once the symbol "1111-1" for packet detection is found, the location of the K +1 bit ID associated with the user identity can be determined from the packet structure. These K +1 symbols will be used to determine the number and identity of the user.
a) It was observed that since the CSI integrated levels of multiple users would be linearly superimposed, as also demonstrated in the measured data after L PF, as shown in fig. 5, if two users send reflected signals simultaneously, the CSI level obtained by the superimposed identity code would look like a staircase, and if all users send data simultaneously, the CSI level would change abruptly at the end of each bit duration.
b) User number determination, a matrix T is constructed, the rows of the matrix T are the identity codes of all users,
Figure RE-GDA0002176930970000142
wherein the k-th row vector is equal to the identification code of the k-th user. To determine the number of users, the number of abrupt changes in the CSI level at the end point boundary of each bit is detected by setting a CSI level change threshold. The number of simultaneous users transmitting data is equal to the number of abrupt changes in the CSI level for the symbol duration, corresponding to the user identity code.
c) And determining the user identity, namely according to experimental observation in the figure 5, the structure of the matrix T is that if the CSI level at the end boundary of the kth symbol of the position of the user identity code changes suddenly, the user sends data. For example, if only user 1 and user 3 of all K users participate in the backscatter transmission, the corresponding sub-matrix in the matrix T can be represented as:
Figure RE-GDA0002176930970000151
the CSI level of the CSI superimposed at the 1 st and 3 rd bit end positions of the user identification code will change.
Example 2
A close-range multi-user covert communication system based on a Wi-Fi network card comprises a Wi-Fi signal source, a user side and a receiving end;
the Wi-Fi signal source is used for sending a radio frequency signal to a receiving end;
the user side comprises K users, each user simultaneously loads respective information sequences to the radio frequency signals by using a network card, each user simultaneously loads respective orthogonally coded information sequences to the radio frequency signals by using the network card, and the information sequences are superposed to obtain comprehensive radio frequency signals which are reflected to a receiving end;
the receiving end receives radio frequency signals sent by the Wi-Fi signal source and comprehensive radio frequency signals reflected by the user end, CSI between the Wi-Fi signal source and the receiving end is calculated respectively, mapping from CSI amplitude to signal level is established according to amplitude change of the CSI to obtain comprehensive signal level, and then the comprehensive signal level is decoded to obtain information sequences of K users.
In particular, the user side, which reflects the radio frequency signal emitted by the Wi-Fi signal source, comprises K users, and in order to effectively separate the data from the different users at the receiver, we use wkTo encode the transmitted data for user k. The data of each user comprises a plurality of information bits, and the l bit of the k user is expanded to form an information bit d'k(l) Expressed as:
d'k(l)＝μk(l)wk
where K is 1,2,3.. K and K denotes a total number of user terminals, l is 1,2,3.. L and L denotes a maximum number of bits of information, μk(l) Represents a bipolar bit and
Figure RE-GDA0002176930970000161
wkthe method comprises the following steps of constructing and loading respective orthogonally coded information sequences to radio frequency signals according to the number of users, and obtaining comprehensive radio frequency signals by superposition, wherein the K-th row vector is expressed as a Walsh-Hadmard matrix, the Walsh-Hadmard matrix is a square matrix of N × N, the row of the matrix is an orthogonal matrix, N is an integral power of 2, and N is more than or equal to 2 and not less than the total number of the users (N is more than or equal to K):
Figure RE-GDA0002176930970000162
wherein, βkRepresenting CSI power levels
Figure RE-GDA0002176930970000163
h0Original CSI, h for Wi-Fi signal source to receiverkFor the k user to receiver CSI, h0,kRepresenting CSI, p from Wi-Fi signal source to kth userkTransmission power of network card for k-th user, p0For the transmit power at the Wi-Fi signal source,
Figure RE-GDA0002176930970000164
and the attenuation coefficient for adjusting the working state of the network card is shown.
Specifically, the receiving end receives the integrated radio frequency signal and calculates CSI between the Wi-Fi signal source and the receiving end according to the integrated radio frequency signal by using a formula ii:
Figure RE-GDA0002176930970000165
wherein,
Figure RE-GDA0002176930970000166
and z "is a noise term;
the receiving end utilizes the formula III to establish the mapping from the comprehensive CSI to the signal level to obtain the comprehensive signal level d'k：
d”k＝μkN formula III
Wherein N ═ wT NwN，{·}TIs the transpose of a matrix, mukRepresents a bipolar sequence;
the receiving end pair synthesizes signal level d'kDecoding to obtain bipolar sequence mukAnd according to μkAnd obtaining the information sequence of the kth user, and further obtaining the information sequences of all the K users.
Preferably, the receiving end pair utilizes the formula IV to synthesize the signal level d "kDecoding to obtain bipolar sequence muk：
Figure RE-GDA0002176930970000171
Wherein
Figure RE-GDA0002176930970000172
Wherein d'kIs the information sequence of the k-th user after orthogonal coding and spreading.
And according to a bipolar sequence mukAnd obtaining the information sequence of the kth user according to the relation between the bipolar sequence and the information sequence shown in the formula V, and further obtaining the information sequences of all the K users:
Figure RE-GDA0002176930970000173
specifically, the radio frequency signal is sent to the receiving end by the Wi-Fi signal source depending on a data packet, and the data packet has a structure of a packet detection sequence, a user identity identification sequence ID, a payload transmission sequence and a kth user identification sequence IDkAs indicated by the general representation of the,
Figure RE-GDA0002176930970000174
wherein, K0Greater than the total number of users K, i.e. K0≥K+1。
Example 3
Procedure of experiment
Firstly, a multi-user covert channel backscatter communication system is constructed in a 5GHz frequency band through commercial Wi-Fi equipment. We then collected data through the system to evaluate system performance. The experimental data acquisition is carried out in a common laboratory, and a plurality of Wi-Fi Access Points (APs) working in the same frequency band exist in surrounding rooms or corridors, so that the system is always interfered.
Evaluation and configuration
The experimental evaluation was designed according to the user scenario shown in fig. 6. Specifically, we used a commercial mini-desktop computer equipped with an Intel 5300Wi-Fi network card and a 5dBi omnidirectional antenna as the signal assistant and receiver, respectively. And a commercial mini desktop computer equipped with an Atheros AR9580Wi-Fi network card and a 5dBi omnidirectional antenna. The experimental evaluation was performed in an office environment, the topology of which is shown in fig. 7. The signal assistant generates a 5GHz help signal by transmitting User Datagram Protocol (UDP) packets. The transmission rate of the packets is 1000 packets/second. The receiver is running a CSI tool to acquire CSI tracking for the communication process. The user is located between the signal assistant and the receiver. Where d2 and d1 are the vertical distance of the signal assistor from the user's person and the vertical distance of the receiver from the user's person, respectively. The signal booster is at a distance of 1.2m from the receiver. The switching interval of the network card is default to 0.25 s.
CSI at the receiving end and received Signal-to-noise ratio (SNR)
It can be seen from the figure that not all Wi-Fi subcarriers carry sensitive data from the user, due to the frequency selectivity of the Wi-Fi channel.
Fig. 4 shows the snr of the CSI tracks of each subcarrier at two different time instants (corresponding to different packet numbers) after the dc component is removed, and it can be seen from the figure that the snr is frequency selective and time selective, but it is not easy to decode the user sensitive data on a subcarrier when the snr on the subcarrier is higher. Therefore, to facilitate decoding of sensitive data, the preamble characteristic is used to select subcarriers for decoding.
1) Detecting the number of users: the user number detection performance is closely related to the sensitive data decoding of the receiver, especially for multi-user human scenarios. Fig. 8 shows the performance of the user number detection when the distance d1 varies from 10cm to 40cm when 1,2,3 users are simultaneously participating in the system. As can be seen from the figure, the detection performance decreases as d1 increases. The reason for this is that the farther the user is from the receiver, the weaker the backscatter signal received by the receiver, thereby degrading the performance of the user number detection. It can also be seen from the figure that the lower the detection performance, the more users. At d1 ═ 10cm, the detection performance can reach almost 100% for different numbers of users.
2) User ID detection performance: FIG. 9 illustrates the performance of the user identification performance when 1,2 and 3 users participate in the system at the same time and the distance d1 is 10-40 cm. As can be seen from the figure, as d1 increases, the user ID detection performance decreases, which is similar to the trend in the figure. We can also see that the detection performance is lower and more users are obtained. When d1 is 10cm, the detection performance of the number of the examinees with different numbers of the examinees can almost reach 100%, which is similar to that in the figure.
3) System Bit Error Rate (BER): fig. 10 depicts the decoding performance of the system when the d1 distance varies from 10cm to 40cm when 1,2,3 users are simultaneously participating in the system. As can be seen, BER increases with increasing d 1. The reason for this is that the farther the user is from the receiver, the weaker the backscatter signal received by the receiver, and the decoding performance is reduced. It can be seen from the figure that the error rate is improved as the number of users increases. The bit error rate of a user can reach almost 0 when d1<20 cm. For 1,2 or 3 users involved in the system, the error code is less than 1% when d1 is 10 cm.
System data rate and network card switch switching interval
Figure 11 illustrates the effect of network card switching intervals on system data rate and bit error rate when one user is involved. An omnidirectional antenna with an antenna gain of 5dBi is disposed at the signal assistant, the user, and the receiving end, respectively, and d1 is 10 cm. As can be seen from the figure, both the data rate and the bit error rate increase as the network card switching interval decreases. By changing the switching frequency of the network card, the data transmission rate can reach 100 bits, and the error rate is very low; therefore, the system can also be applied to some near field communication scenes with low requirements on transmission rate.
Effect of interference on receiver signal-to-noise ratio
Fig. 12 shows an example of the effect of interference from the surrounding environment on the average signal-to-noise ratio of the receiver in the 1500 th packet after DC removal in CSI when d1 is 20 cm. These data were collected from a number of experimental measurements. In each experiment, we observed the number of Wi-Fi Access Points (APs) at 5GHz frequency using Wi-Fi diagnostic software. As can be seen from the figure, the signal-to-noise ratio decreases as the number of Wi-Fi APs increases. As the number of 5Ghz Wi-Fi APs increases, the interference of these Wi-Fi APs can severely interfere with the CSI trace, thereby causing the CSI trace to carry a reflected signal at the receiver, making decoding of sensitive data at the receiver more difficult. On the other hand, higher data rates are illustrated in fig. 11 when the surrounding environment is less disturbed.

Claims (4)

1. A close-range multi-user covert communication method based on a Wi-Fi network card is characterized by comprising the following substeps:
step 1: the Wi-Fi signal source sends out radio frequency signals, the receiving terminal receives the radio frequency signals and calculates original Channel State Information (CSI) between the Wi-Fi signal source and the receiving terminal according to the radio frequency signals;
step 2: the method comprises the following steps that a user side reflects a radio frequency signal sent by a Wi-Fi signal source, the user side comprises a plurality of users, and each user loads an information sequence which is subjected to orthogonal coding to the radio frequency signal by using a network card simultaneously to obtain a comprehensive radio frequency signal;
and step 3: the receiving terminal receives the comprehensive radio frequency signal, calculates CSI between the Wi-Fi signal source and the receiving terminal according to the comprehensive radio frequency signal, establishes mapping from a CSI amplitude value to a signal level to obtain a comprehensive signal level, and then decodes the comprehensive signal level to obtain an information sequence of each user;
step 2 comprises the following substeps:
step 2.1: the user side, which reflects the radio frequency signal from the Wi-Fi signal source, includes K users, and in order to effectively separate the data from different users at the receiver, we use wkEncoding the transmission data of user k, wherein the data of each user comprises a plurality of information bits, and the information bit d 'of the k-th user after the l bit expansion'k(l) Expressed as:
d'k(l)＝μk(l)wk
where K is 1,2,3.. K and K denotes a total number of user terminals, l is 1,2,3.. L and L denotes a maximum number of bits of information, μk(l) Represents a bipolar bit and
Figure FDA0002496192280000011
wkexpressed as a k-th row vector of a Walsh-Hadmard matrix, the Walsh-Hadmard matrix is a square matrix of N × N, the rows are orthogonal matrices, N is an integral power of 2, and N is more than or equal to 2 and is not less than the total number of users;
step 2.2: and constructing according to the number of users and simultaneously loading information sequences which are respectively subjected to orthogonal coding on the radio frequency signals to obtain the comprehensive radio frequency signals as shown in the formula I:
Figure FDA0002496192280000021
wherein, βkRepresenting CSI power levels
Figure FDA0002496192280000022
h0Original CSI, h for Wi-Fi signal source to receiverkFor the k user to receiver CSI, h0,kRepresenting CSI, p from Wi-Fi signal source to kth userkWork of transmission of network card for k-th userRate, p0For the transmit power at the Wi-Fi signal source,
Figure FDA0002496192280000023
representing the attenuation coefficient for adjusting the working state of the network card;
step 3 comprises the following substeps:
step 3.1: and the receiving terminal receives the comprehensive radio frequency signal and calculates CSI between the Wi-Fi signal source and the receiving terminal by using a formula II according to the comprehensive radio frequency signal:
Figure FDA0002496192280000024
wherein,
Figure FDA0002496192280000025
and z "is a noise term;
step 3.2: establishing mapping from the amplitude value of the CSI between the Wi-Fi signal source and the receiving end to the signal level by using a formula III to obtain a comprehensive signal level d'k：
d”k＝μkN formula III
Wherein N ═ wT NwN，{·}TIs the transpose of a matrix, mukRepresents a bipolar sequence;
step 3.3: for integrated signal level d'kDecoding to obtain bipolar sequence mukAnd according to μkObtaining an original information sequence of a kth user, and further obtaining information sequences of all K users;
step 3.3 comprises the following substeps:
step 3.3.1: using the formula IV for the integrated signal level d'kDecoding to obtain bipolar sequence muk：
Figure FDA0002496192280000026
Wherein,
Figure FDA0002496192280000031
d'kis the information sequence of the kth user after orthogonal coding and spreading;
step 3.3.2: according to a bipolar sequence mukAnd obtaining the information sequence of the kth user according to the relation between the bipolar sequence and the information sequence shown in the formula V, and further obtaining the information sequences of all the K users:
Figure FDA0002496192280000032
2. the Wi-Fi network card-based near-field multi-user covert communication method of claim 1, wherein the radio frequency signal is sent from the Wi-Fi signal source to the receiving end in dependence on a data packet, the data packet has a structure of a packet detection sequence, a user identity identification sequence (ID), a payload transmission sequence, and a kth user identification sequence (ID)kAs indicated by the general representation of the,
Figure FDA0002496192280000033
wherein, K0≥K+1。
3. A close-range multi-user covert communication system based on a Wi-Fi network card is characterized by comprising a Wi-Fi signal source, a user side and a receiving end;
the Wi-Fi signal source is used for sending a radio frequency signal to a receiving end;
the user side comprises a plurality of users, each user simultaneously loads information sequences which are respectively subjected to orthogonal coding to the radio frequency signals by using the network card, and the information sequences are reflected to a receiving end to be superposed with the original radio frequency signals to obtain comprehensive radio frequency signals;
the receiving terminal receives radio frequency signals sent by the Wi-Fi signal source and comprehensive radio frequency signals reflected by the user terminal, calculates CSI between the Wi-Fi signal source and the receiving terminal, establishes mapping from CSI amplitude to signal level according to amplitude change of the CSI to obtain comprehensive signal level, and then decodes the comprehensive signal level to obtain an information sequence of each user;
the user side, which reflects the radio frequency signal from the Wi-Fi signal source, includes K users, and in order to effectively separate the data from different users at the receiver, we use wkEncoding the transmission data of user k, wherein the data of each user comprises a plurality of information bits, and the information bit d 'of the k-th user after the l bit expansion'k(l) Expressed as:
d'k(l)＝μk(l)wk
where K is 1,2,3.. K and K denotes a total number of user terminals, l is 1,2,3.. L and L denotes a maximum number of bits of information, μk(l) Represents a bipolar bit and
Figure FDA0002496192280000041
wkexpressed as a k-th row vector of a Walsh-Hadmard matrix, the Walsh-Hadmard matrix is a square matrix of N × N, the rows are orthogonal matrices, N is an integral power of 2, and N is more than or equal to 2 and is not less than the total number of users;
then, according to the number of users, information sequences which are respectively subjected to orthogonal coding are constructed and loaded on the radio frequency signals at the same time, and the comprehensive radio frequency signals are obtained as shown in the formula I:
Figure FDA0002496192280000042
wherein, βkRepresenting CSI power levels
Figure FDA0002496192280000043
h0CSI, h for Wi-Fi signal source to receiverkFor the k user to receiver CSI, h0,kRepresenting CSI, p from Wi-Fi signal source to kth userkTransmission power of network card for k-th user, p0For the transmit power at the Wi-Fi signal source,
Figure FDA0002496192280000044
representing the attenuation coefficient for adjusting the working state of the network card;
and the receiving terminal receives the comprehensive radio frequency signal and calculates CSI between the Wi-Fi signal source and the receiving terminal by using a formula II according to the comprehensive radio frequency signal:
Figure FDA0002496192280000045
wherein,
Figure FDA0002496192280000046
and z "is a noise term;
the receiving end utilizes the formula III to establish the mapping from the CSI to the signal level to obtain the comprehensive signal level d'k：
d”k＝μkN formula III
Wherein N ═ wT NwN，{·}TIs the transpose of a matrix, mukRepresents a bipolar sequence;
the receiving end pair synthesizes signal level d'kDecoding to obtain bipolar sequence mukAnd according to μkObtaining an information sequence of a kth user, and further obtaining information sequences of all K users;
the receiving end pair utilizes the formula IV pair to synthesize the signal level d'kDecoding to obtain bipolar sequence muk：
Figure FDA0002496192280000051
And according to a bipolar sequence mukAnd obtaining the information sequence of the kth user according to the relation between the bipolar sequence and the information sequence shown in the formula V, and further obtaining the information sequences of all the K users:
Figure FDA0002496192280000052
4. the Wi-Fi network card based near field multi-user covert communication system of claim 3, wherein the radio frequency communication channelThe number is sent to a receiving end by a Wi-Fi signal source depending on a data packet, and the structure of the data packet is a packet detection sequence, a user identity identification sequence ID, a payload transmission sequence and a k-th user identification sequence IDkAs indicated by the general representation of the,
Figure FDA0002496192280000053
wherein, K0Greater than the total number of users K, i.e. K0≥K+1。
CN201910548389.6A 2019-06-24 2019-06-24 Close-range multi-user covert communication method and system based on Wi-Fi network card Active CN110300399B (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
CN201910548389.6A CN110300399B (en) 2019-06-24 2019-06-24 Close-range multi-user covert communication method and system based on Wi-Fi network card

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
CN201910548389.6A CN110300399B (en) 2019-06-24 2019-06-24 Close-range multi-user covert communication method and system based on Wi-Fi network card

Publications (2)

Publication Number Publication Date
CN110300399A CN110300399A (en) 2019-10-01
CN110300399B true CN110300399B (en) 2020-07-21

Family

ID=68028587

Family Applications (1)

Application Number Title Priority Date Filing Date
CN201910548389.6A Active CN110300399B (en) 2019-06-24 2019-06-24 Close-range multi-user covert communication method and system based on Wi-Fi network card

Country Status (1)

Country Link
CN (1) CN110300399B (en)

Citations (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2013166644A1 (en) * 2012-05-07 2013-11-14 Renesas Mobile Corporation Multi-cell periodic csi reporting
CN104067585A (en) * 2011-10-11 2014-09-24 阿尔卡特朗讯 Method and apparatus for self - interference cancellation
CN104737464A (en) * 2012-09-11 2015-06-24 瑞典爱立信有限公司 Finding channel state information with reduced codebook in a multi-antenna wireless communication system
CN104766427A (en) * 2015-04-27 2015-07-08 太原理工大学 Detection method for illegal invasion of house based on Wi-Fi
CN105232022A (en) * 2015-09-17 2016-01-13 太原理工大学 Non-invasive breath and heartbeat detection implementation method based on CSI (channel state information) signal strength in WiFi
CN105844216A (en) * 2016-03-11 2016-08-10 南京航空航天大学 Detection and matching mechanism for recognition of handwritten letters using WiFi signals
CN105873212A (en) * 2016-05-16 2016-08-17 南京邮电大学 Indoor-environment-person detection method based on channel state information
CN107025751A (en) * 2017-03-10 2017-08-08 深圳大学 The method and its system of indoor condition of a fire Detection And Warning based on transmission of wireless signals
CN108489509A (en) * 2018-06-06 2018-09-04 天津大学 A kind of non-contact single step-recording method and system based on commercial Wi-Fi
CN108988968A (en) * 2018-07-27 2018-12-11 河北工程大学 Human behavior detection method, device and terminal device

Family Cites Families (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US8170081B2 (en) * 2004-04-02 2012-05-01 Rearden, LLC. System and method for adjusting DIDO interference cancellation based on signal strength measurements
EP1971043A1 (en) * 2007-03-16 2008-09-17 Sony Deutschland GmbH Transmitting device and method for transmitting signals in a wireless communication system, receiving device and method for receiving signals in a wireless communication system
CN202102465U (en) * 2011-06-09 2012-01-04 国网信息通信有限公司 Wireless radio-frequency identification label and wireless radio frequency identification system
US9350293B1 (en) * 2015-01-16 2016-05-24 Raytheon Company Amplitude-noise reduction system and method for ultra-low phase-noise oscillators
US10484064B2 (en) * 2016-09-01 2019-11-19 Samsung Electronics Co., Ltd. Method and apparatus for downlink and uplink CSI acquisition

Patent Citations (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN104067585A (en) * 2011-10-11 2014-09-24 阿尔卡特朗讯 Method and apparatus for self - interference cancellation
WO2013166644A1 (en) * 2012-05-07 2013-11-14 Renesas Mobile Corporation Multi-cell periodic csi reporting
CN104737464A (en) * 2012-09-11 2015-06-24 瑞典爱立信有限公司 Finding channel state information with reduced codebook in a multi-antenna wireless communication system
CN104766427A (en) * 2015-04-27 2015-07-08 太原理工大学 Detection method for illegal invasion of house based on Wi-Fi
CN105232022A (en) * 2015-09-17 2016-01-13 太原理工大学 Non-invasive breath and heartbeat detection implementation method based on CSI (channel state information) signal strength in WiFi
CN105844216A (en) * 2016-03-11 2016-08-10 南京航空航天大学 Detection and matching mechanism for recognition of handwritten letters using WiFi signals
CN105873212A (en) * 2016-05-16 2016-08-17 南京邮电大学 Indoor-environment-person detection method based on channel state information
CN107025751A (en) * 2017-03-10 2017-08-08 深圳大学 The method and its system of indoor condition of a fire Detection And Warning based on transmission of wireless signals
CN108489509A (en) * 2018-06-06 2018-09-04 天津大学 A kind of non-contact single step-recording method and system based on commercial Wi-Fi
CN108988968A (en) * 2018-07-27 2018-12-11 河北工程大学 Human behavior detection method, device and terminal device

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
基于MPWFRFT的混沌加密卫星隐蔽通信研究;倪磊;《第十四届卫星通信学术年会论文集》;20180331;全文 *

Also Published As

Publication number Publication date
CN110300399A (en) 2019-10-01

Similar Documents

Publication Publication Date Title
Yang et al. Modulation in the air: Backscatter communication over ambient OFDM carrier
Wang et al. Ambient backscatter communication systems: Detection and performance analysis
Sheng et al. Detecting 802.11 MAC layer spoofing using received signal strength
Kang et al. Signal detection scheme in ambient backscatter system with multiple antennas
Angelosante et al. Neighbor discovery in wireless networks: A multiuser-detection approach
US11330434B2 (en) Security detection for a physical layer authentication system that considers signal-discriminating capability of an active adversary
Van Khuong et al. General expression for pdf of a sum of independent exponential random variables
Xu et al. FlipLoRa: Resolving collisions with up-down quasi-orthogonality
US20200169883A1 (en) Security Detection Method for Physical Layer Authentication System
EP1436854A2 (en) Method of detection of signals using an adaptive antenna in a peer-to-peer network
AU2002341656A1 (en) Method of detection of signals using an adaptive antenna in a peer-to-peer network
CN110381510B (en) Non-orthogonal multiple access authentication system based on superimposed physical layer authentication label
CN103997736B (en) The method for being used to detect listener-in in wireless communication system
US11818807B2 (en) Access point for estimating motion of objects using wlan sensing measurements
CN103684626A (en) Multi user cooperative frequency spectrum sensing data fusion method and device
MXPA03011587A (en) Transmittal of heartbeat signal at a lower level than heartbeat request.
Mi et al. CBMA: Coded-backscatter multiple access
CN109314689A (en) The method and apparatus being used for transmission
CN110300399B (en) Close-range multi-user covert communication method and system based on Wi-Fi network card
CN106209159B (en) data packet leader sequence and packet header, processing method thereof and data frame
CN110312255B (en) Parameter optimization method of non-orthogonal multiple access authentication system based on superimposed authentication tags
Annamalai et al. Analysis of equal-gain diversity receiver in correlated fading channels
Sharma et al. Performance comparison of hard and soft fusion techniques for energy efficient CSS in cognitive radio
Cai et al. Reliable High Throughput Aerial Acoustic Communication for Mobile Network
Wang et al. Channel State Information-Based Detection of Sybil Attacks in Wireless Networks.

Legal Events

Date Code Title Description
PB01 Publication
PB01 Publication
SE01 Entry into force of request for substantive examination
SE01 Entry into force of request for substantive examination
GR01 Patent grant
GR01 Patent grant