CN112187373B - Concealed channel communication method based on gyroscope resonance - Google Patents
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Abstract
The invention discloses a hidden channel communication method based on gyroscope resonance, which is characterized in that a communication channel from a loudspeaker to a gyroscope is established, the inter-axis characteristics of the gyroscope during resonance are found for the first time, the elimination of channel noise and motion interference is realized on the basis of the inter-axis characteristics, the hidden channel communication method of motion robustness across protocols is realized, and the motion robustness of a motion sensor recycling system is realized for the first time. The invention uses the low-cost loudspeaker and the gyroscope to realize the cross-protocol Internet of things communication, does not need to additionally increase peripheral equipment, does not have the requirement of physical contact or fixed position, can realize higher communication rate and accuracy, supports multi-channel/multi-user simultaneous transmission, and simultaneously meets the requirements of convenience and practicability.
Description
Technical Field
The invention relates to the field of covert channel communication, in particular to a covert channel communication system based on gyroscope resonance and used for sending signals by a microphone and receiving signals by a gyroscope.
Background
With the development of global economy and technology, the technology of internet of things attracts more and more attention. The smart home, the smart city system and the industrial 2.0 are brought forward, so that no deep people can embody the concept of the internet of things. In a plurality of application occasions in the field of internet of things such as data monitoring, intelligent perception, man-machine interaction and industrial assembly lines, data transmission of wireless nodes is an essential link. Under different application scenarios, the nodes of the internet of things support one or more communication protocols. However, at present, internet of things communication protocols are various and are not compatible with each other, for example, WiFi and bluetooth are widely used in the field of mobile communication, ZigBee and MQTT are suitable for small data stream transmission under the condition of resource limitation, EnOcean and 6LowPan are commonly used in the field of smart homes, and AMQP and COAP are widely used in the field of industrial internet of things. In snow, all large manufacturers build and use more exclusive communication protocols to build own ecosystems in order to attract consumers, and the situation that the communication protocols of the internet of things are not compatible is further aggravated.
In response to the above problems, researchers have utilized physical features to construct a bypass communication system regardless of communication protocols between wireless nodes without physical or logical connections. For example, a communication system is established using a vibration motor and accelerometer, chip temperature variation, or channels such as an ultrasonic speaker and microphone. These systems, however, are limited by problems such as the presence of mating peripherals (e.g., speakers and microphones), physical contact (e.g., the shock motor and accelerometer need to be placed in the same plane), or the inability to change position (e.g., chip temperature measurements).
A gyroscope, by its nature, resonates for acoustic signals at a particular frequency. That is, within a certain range, the microphone emits sound wave signals of a specific frequency band, and the gyroscope generates additional low-frequency output. Based on this characteristic, a covert channel communication system from the microphone to the gyroscope can be established. The purpose of inertial sensor systems (e.g., gyroscopes, accelerometers, etc.) is to measure and record the motion of the device, however, such motion is an additional noise to data mining and recycling systems that utilize inertial sensor systems, and the robustness to motion noise is an urgent problem to be solved by such systems.
Disclosure of Invention
Aiming at the problems in the prior art, the invention provides a motion robust hidden channel communication method based on gyroscope resonance, which utilizes a common commercial loudspeaker and a gyroscope with built-in nodes to achieve cross-protocol signal transmission through signal modulation and demodulation, does not need to additionally increase peripheral equipment, does not have the requirements of physical contact or fixed position, can realize higher communication rate and accuracy, and simultaneously meets the requirements of convenience and practicability.
The invention is realized by the following technical scheme: a hidden channel communication method based on gyroscope resonance comprises the following steps:
the method comprises the following steps: sound wave coding: the resonance characteristic of a gyroscope in the target receiving equipment determines the communication frequency, the coding mode is adjusted based on the idea of pulse interval coding, and the signal is modulated on the target frequency band and played by a loudspeaker.
Step two: channel noise elimination: including frequency drift and random error cancellation. Based on the inter-axis characteristics of the gyroscope during resonance, two pieces of on-axis data are selected to form a combined channel through a multiplier and a mean value filter, and frequency drift and gyroscope random errors generated by gyroscope sampling rate drift are eliminated.
Step three: and (3) decoding: and (4) defining a threshold value by using a maximum acoustic threshold value algorithm and decoding to obtain data transmitted in a channel.
Further, the communication frequency band selection method in the first step specifically includes:
(1.1) prediction: a chirp is played by the microphone with the step size set to 1Hz and readings on each axis of the gyroscope are observed. And when the reading is greatly improved and does not accord with Gaussian distribution, the resonance is considered to occur, and the amplitude peak value and the corresponding frequency of each axis are recorded. Two points f with an amplitude of 0.707 times the peak value are found on the respective axesstart、fendThe corresponding frequency is recorded as the point at which resonance occurs, i.e. the point at which resonance occurs
(1.2) selecting frequency bands: selecting a frequency band which enables at least two axes to resonate, i.e. a frequency band for communication, as the frequency band
The communication frequency may be selected to be any frequency within the communication band.
Further, the frequency bands where only two axes resonate are selected as the frequency bands of the multi-channel/multi-user communication, i.e. the frequency bands of the multi-channel/multi-user communication
To support multi-channel/multi-user data transmission.
Further, by adopting the interleaving technology for coding, the blocking noise on the line of sight can be eliminated, so as to reduce the signal transmission error caused by the channel interference.
Further, the inter-axis characteristics of the resonance of the gyroscope in the second step are specifically as follows:
when different axes in a gyroscope generate resonance under the same sound wave, resonance can occur simultaneously, and resonance data on the different axes have the same vibration frequency and fixed phase difference.
Further, the method also comprises a step of eliminating the sound source motion noise, specifically:
and (3) a dynamic threshold dividing technology is used, namely, a maximum acoustic threshold algorithm is used for dividing the threshold in a short time period so as to eliminate the amplitude change of the resonance data caused by the motion of the sound source.
Further, the method also comprises a step of eliminating the motion noise of the target receiving device, and specifically comprises the following steps:
two-dimensional motion of the target receiving device: selecting an axis without motion as one axis in a joint channel to form the joint channel, and eliminating extra numerical interference caused by two-dimensional motion through mean filtering;
three-dimensional motion of the target receiving device: the additional numerical interference caused by three-dimensional motion is eliminated through wavelet analysis, blind source separation and signal recovery based on the resonance inter-axis characteristics.
Further, the method for eliminating the three-dimensional motion interference of the target receiving device specifically includes:
(a) wavelet analysis: and preliminarily eliminating low-frequency motion noise.
(b) Single-channel blind source separation: and taking data on one axis of the gyroscope as an observation matrix, and taking resonance data and motion data as a source matrix to establish a blind source separation model. And decomposing and dimension increasing the one-dimensional observation matrix by using ensemble empirical mode decomposition, and solving the model by using a principal component analysis method to obtain a high-dimensional solution matrix with the same dimension.
(c) And (3) signal recovery: and (c) repeating the steps (a) and (b) on the other axis, and fitting resonance data between different axes into an elliptic curve based on the characteristics that the frequency is the same and the phase difference is fixed when the gyroscope resonates. And traversing all combinations in a solution matrix for summation, finding out the positions of the high levels by utilizing the characteristics of the positions of the high levels in the coding rule for fitting, selecting a group of combinations which can be fitted into an ellipse and have the largest elliptical area as signals, and considering the rest parts as noise interference caused by motion.
The method has the advantages that the characteristic that the sound wave with specific frequency induces the resonance of the gyroscope is utilized, and a user sends a modulated sound wave signal to the gyroscope, so that the communication of the hidden channel across protocols is realized. Furthermore, the invention excavates the inter-axis characteristics of the gyroscope in resonance, can establish robust communication in a moving environment, and is the first system for realizing motion robustness based on the function re-development of the inertial sensor. The invention can realize lower error rate and simultaneously meet the requirements of convenience, usability and safety, users do not need to change the original hardware structure of equipment or add special equipment, and the invention has no limitations of traditional hidden channel communication such as fixed layout, physical contact, immobility, non-selective broadcast and the like, thereby realizing high-precision and long-distance communication.
Drawings
FIG. 1 is a system flow diagram;
FIG. 2 is a communication diagram;
FIG. 3 is a graph of resonance bands for an example of 8 BMI160 gyroscopes;
FIG. 4 is a schematic illustration of encoding;
FIG. 5 is a schematic diagram of multiplier-based channel noise cancellation;
FIG. 6 is a plot of the combined channel signal-to-noise ratio trend versus distance;
FIG. 7 is a diagram of multi-channel/multi-user support;
fig. 8 is a system communication example.
Detailed Description
The invention provides a concealed channel communication method based on gyroscope resonance, which comprises the following steps:
the method comprises the following steps: sound wave coding: the resonance characteristic of a gyroscope in the target receiving equipment determines the communication frequency, the coding mode is adjusted based on the idea of pulse interval coding, and the signal is modulated on the target frequency band and played by a loudspeaker.
Step two: channel noise elimination: including frequency drift and random error cancellation. Based on the inter-axis characteristics of the gyroscope during resonance, two pieces of on-axis data are selected to form a combined channel through a multiplier and a mean value filter, and frequency drift and gyroscope random errors generated by gyroscope sampling rate drift are eliminated.
Step three: and (3) decoding: and (4) defining a threshold value by using a maximum acoustic threshold value algorithm and decoding to obtain data transmitted in a channel.
Fig. 2 is a communication diagram, since in practice, there may be movement of the sound source, the target receiving device, etc., generating corresponding motion noise, and therefore, a motion noise cancellation step may be included, as shown in fig. 1, the motion noise cancellation: the method comprises the steps of sound source movement, visual range obstruction and receiving equipment movement, and a denoising technology based on a dynamic threshold technology, an interleaving technology and a multiplier foundation and a fitting denoising technology based on single-channel blind source separation respectively.
The present invention will now be described in further detail with reference to the attached drawings, which are illustrative, but not limiting, of the present invention.
As a preferred scheme, the first step: sound wave coding: the communication frequency is determined by the resonance characteristics of the gyroscope in the target receiving device, and the signal is modulated on the target frequency band and played by the speaker. The method comprises the following steps:
(1.1) prediction: a chirp is played by the microphone with the step size set to 1Hz and readings on each axis of the gyroscope are observed. And when the reading is greatly improved and does not accord with Gaussian distribution, the resonance is considered to occur, and the amplitude peak value and the corresponding frequency of each axis are recorded. Two points f with an amplitude of 0.707 times the peak value are found on the respective axesstart、fendI.e. the energy is reduced to half, the corresponding frequency is recorded as the point at which resonance occurs, i.e. the point at which resonance occurs
(1.2) selecting frequency bands: referring to fig. 3, a frequency band selected to allow at least two axes to resonate may be used as a communication frequency band, that is, a communication frequency band
(1.3) pulse encoding: referring to fig. 4, the data is encoded by defining different time interval widths between rising edges of pulses, where a short interval represents a "1" and a long interval represents a "0".
The second step is as follows: channel noise elimination: including frequency drift and random error cancellation. Based on the inter-axis characteristics of the gyroscope during resonance, two pieces of on-axis data are selected to form a combined channel through a multiplier and a mean filter, so that frequency drift and gyroscope random errors generated by gyroscope sampling rate drift are eliminated, and reference is made to fig. 5. The method specifically comprises the following steps:
(2.1) interaxial characteristics: when different axes in a gyroscope generate resonance under the same sound wave, resonance can occur simultaneously, and resonance data on the different axes have the same vibration frequency and fixed phase difference. I.e. knowing the resonance signal components on both axesIs other than x1And x2(1,2∈{x,y,z})，x1And x2Having the same vibration frequency and a fixed phase difference, i.e.
x1＝A1sin(2πft+φ1)
x2＝A2sin(2πft+φ2)
Δφ＝φ1-φ2
Wherein f and delta phi are constants and are determined by the acoustic frequency inducing resonance and the sampling rate of the gyroscope; a. the1And A2The amplitudes on the two axes are respectively determined by the sound intensity and frequency at the receiving device and the resonance frequency of the gyroscope;
(2.2) frequency drift cancellation: the output is a down-sampled output of the resonant frequency when the gyroscope is considered to be resonant, which can cause the output frequency to drift when the sampling rate is jittered. Selection of x1And x2After multiplication, obtain
Using mean filtering of appropriate window length, high frequency components are removed to obtain a combined signal upper signal of
Y is a constant and is irrelevant to frequency, so that the influence caused by frequency drift generated by gyroscope sampling rate drift is avoided, and the stability of communication is ensured;
(2.3) channel noise cancellation: taking into account random errors e of gyroscope readings, i.e.
Wherein e is1And e2Respectively, random errors on corresponding axes, and conforms to Gaussian white noise. After multiplication, obtain
Using mean filtering of appropriate window length, high frequency components are removed to obtain a combined signal upper signal of
Therefore, the influence caused by random errors is eliminated, the signal-to-noise ratio of the channel is improved, and the transmission quality of the channel is improved, referring to fig. 6.
The motion noise elimination: the method comprises the following steps of sound source movement, obstruction on visual range, receiving equipment movement, denoising technology based on a dynamic threshold technology, an interleaving technology and a multiplier foundation and fitting denoising technology based on single-channel blind source separation, and the specific method comprises the following steps:
(1) the sound source moves: a dynamic threshold dividing technology is used, namely, a maximum sound threshold algorithm is used for dividing a threshold in a short time period so as to eliminate the amplitude change of resonance data caused by the motion of a sound source;
(2) obstruction in the viewing distance: in the initial coding stage, an interleaving technology is adopted for coding, so that signal transmission errors caused by channel interference can be reduced; the technique allocates transmission bits of information in the time domain or the frequency domain or both. It changes the information structure to the maximum extent without changing the content. In this way, the decoder can treat these errors as random errors, which means that it maximally disperses the concentrated errors during the channel transmission. One of the most common methods is a block interleaver. The process can be summarized as writing an input sequence into an m x n matrix in row order and then reading the data in columns. In addition, the reordering is performed by exchanging the read/write objects of the previous step. The mapping function is expressed as
Where i (j) is the position of the jth (j ═ 1,2, … …, B) data in the original arrangement, m and n are the number of rows and columns, respectively,
b — m × n represents an interleaving length. The method disperses burst errors in the channel transmission process to the maximum extent, and effectively reduces errors caused by burst blocking;
(3) two-dimensional motion of the target receiving device: and (5) selecting an axis without motion as one axis in the joint channels to form the joint channels, and eliminating the extra numerical interference caused by the two-dimensional motion. I.e. the gyroscope resonates, the readings on each axis are
Wherein A isiFor the amplitude of the vibration of the gyroscope due to resonance,
the vibration frequency of the gyroscope due to resonance, f0For input acoustic frequency, k is the index, Fs is the gyroscope sampling rate, Mi[·]Gyroscope readings are generated for motion. The example of motion being centered on the XoY plane is illustrated, which means here Mz[k]Is always zero. Multiplying data on the X and Z axes to establish a channel, i.e.
Scomb[k]＝Rx[k,Mx]×Rz[k,0]
＝Rx[k,0]×Rz[k,0]+Mx[k]×Rz[k,0]
Wherein the former Rx[k,0]×Rz[k,0]I.e. the signal, the latter term Mx[k]×Rz[k,0]When R isz[k,0]Low when it is low, when R is lowz[k,0]Filtering by mean filtering when the level is high;
(4) three-dimensional motion of the target receiving device: the additional numerical interference caused by three-dimensional motion is eliminated through wavelet analysis, blind source separation and signal recovery based on the resonance inter-axis characteristics. The method specifically comprises the following steps:
(4.1) wavelet analysis: preliminarily eliminating low-frequency motion noise;
(4.2) the blind Source separation model can be written as
X＝AS
Wherein X ═ X1[k],x2[k],……,xN[k]]TIs an observation matrix obtained by separating data on one axis of the gyroscope, S ═ S1[k],s2[k],……,sM[k]]TA is an N M matrix for the corresponding source matrix. In general, it requires that the number of independent observers is not less than the number of sources, i.e., N ≧ M. The goal is to search the inverse matrix to estimate
In this case
The readings (mixture of resonance data and motion data) on a single axis are taken as the subject of observation. Due to frequency offset and modulation, there are multiple independent source vectors, i.e., M > 2. Decomposition matrix observation is necessary because here N-1 < M.
(4.3) Single channel observations should be decomposed into a multi-channel matrix: in order to meet the requirement of the dimension of the observation matrix, an integrated empirical mode decomposition (EEMD) method is adopted to decompose the single-channel mixed data into Intrinsic Mode Functions (IMFs) components.
Empirical Mode Decomposition (EMD) is the basic method of decomposing data into IMFs. Unlike fourier transforms, EMD can handle non-stationary signal analysis. It is based on the data itself and does not require any basis functions, making it more suitable for arbitrary data. EMD may obtain a series of IMFs from an input x [ k ], as shown below
Wherein n1 is the number of IMFs obtained by decomposition, rn1[k]As a residual amount after decomposition.
EEMD is a noise-aided improved EMD algorithm. In short, the basic idea is to add various white gaussian noises to the raw data and periodically apply EMD. These noises are then removed and all the decomposition results are recovered. It introduces a series of white noise with the same standard deviationnum[k](num ═ 1,2, … …, K). Then using xnum[k]＝x[k]+noisenum[k]Replacing x [ k ] in the above formula]I.e. by
Due to the characteristic of zero-mean noise, after multiple averaging calculations, the noise will cancel each other out. After K cycles, the final IMFsimfi[k]Is that
Generally, EEMD decomposes single-channel data into a multi-channel matrix, IMFs is an observation matrix X, and the requirement that N is equal to N1 and is larger than or equal to M is met;
(4.4) Signal recovery: we used fast independent component analysis (FastICA), a widely used solution for blind source separation stabilization, and obtained the result as an n1 dimensional matrix C ═ C1[k],c2[k],cn1[k]]. However, due to the complexity of the motion residuals, the number of sources is not yet clear, nor is there a rule to follow how these vectors are incorporated into the resonance data and motion. Since the phase difference is fixed, any two pairs of resonance data can be fitted to a circle, or ellipse. We repeat the above process for the blended data from the other axis and list all possible combinations. Due to the encoding scheme used in step two, resonance data must occur in odd-numbered pulse widths and the variance is larger thanThe segment of the mean variance can be considered high. These segments are selected for fitting, where the largest area and mean square error approved combination contains only resonance data.
Step four: and (3) decoding: and (4) defining a threshold value by using a maximum acoustic threshold value algorithm and decoding to obtain data transmitted in a channel. The basic idea is to find the maximum entropy and use the corresponding threshold as the final threshold. Specifically, for a channel with a resolution r and a maximum value L · r, we determine the threshold q as follows
max H(q)＝H1(q)+H2(q),
q＝l×r,0≤l≤L
Where p (-) is the probability density function. L represents the maximum multiple, and when a point corresponds to a value greater than the threshold, it is deemed high, and vice versa.
As another preferred scheme, in the step one, the frequency bands with resonance of only two axes are selected as the frequency bands of the multi-channel/multi-user communication respectively, that is, the frequency bands with resonance of only two axes are selected as the frequency bands of the multi-channel/multi-user communication respectively
Independent denoising on two frequency bands is realized by using a denoising technology based on a multiplier, so that different contents are transmitted on the two frequency bands respectively, and multi-channel transmission/multi-user simultaneous transmission can be supported by referring to fig. 6-7.
The above-mentioned contents are only for illustrating the technical idea of the present invention, and the protection scope of the present invention is not limited thereby, and any modification made on the basis of the technical idea of the present invention falls within the protection scope of the claims of the present invention.
Claims (8)
1. A hidden channel communication method based on gyroscope resonance is characterized by comprising the following steps:
the method comprises the following steps: sound wave coding: determining a communication frequency band by the resonance characteristic of a gyroscope in target receiving equipment, coding by adopting different time interval widths between pulse rising edges, modulating a signal on the target frequency band and playing by a loudspeaker;
step two: channel noise elimination: including frequency drift and random error cancellation; based on the inter-axis characteristics of the gyroscope during resonance, selecting two-axis data, multiplying the two-axis data through a multiplier, and then carrying out mean filtering by using a mean filter to eliminate high-frequency components to form a combined channel, so as to eliminate frequency drift and gyroscope random errors generated by gyroscope sampling rate drift;
step three: and (3) decoding: using a maximum acoustic threshold algorithm to define a threshold and decoding the threshold to obtain data transmitted in a channel; the method for defining the threshold by using the maximum sound threshold algorithm specifically comprises the following steps:
for a channel with a resolution r and a maximum value L · r, the threshold q is determined as follows
max H(q)＝H1(q)+H2(q)，
q＝l×r，0≤l≤L
Wherein p (-) is a probability density function; l represents the maximum multiple, and when a point corresponds to a value greater than the threshold, it is deemed high, and vice versa.
2. The gyro resonance-based covert channel communication method of claim 1, wherein in said first step, the communication band selection method specifically comprises:
(1.1) prediction: playing chirp with a loudspeaker, setting step length, and observing readings on each axis of the gyroscope; when the reading is greatly improved and does not accord with Gaussian distribution, the resonance is considered to occur, and the amplitude peak value and the corresponding frequency of each axis are recorded; two points f with an amplitude of 0.707 times the peak value are found on the respective axesstart、fendThe corresponding frequency is recorded as the point at which resonance occurs, i.e. the point at which resonance occurs
(1.2) selecting frequency bands: selecting as the communication band a band which enables resonance of at least two axes, i.e.
3. The method of claim 2, wherein in step (1.2), the frequency bands with resonance only in two axes are selected as the frequency bands for multi-channel/multi-user communication, i.e. the frequency bands for multi-channel/multi-user communication are selected
To support multi-channel/multi-user data transmission.
4. The method of claim 1, wherein in the first step, the encoding is performed by interleaving to eliminate the blocking noise at the line of sight, so as to reduce the signal transmission error caused by channel interference.
5. The hidden channel communication method based on gyroscope resonance as claimed in claim 1, wherein the inter-axis characteristics of gyroscope resonance in the second step are as follows:
when different axes in a gyroscope generate resonance under the same sound wave, resonance can occur simultaneously, and resonance data on the different axes have the same vibration frequency and fixed phase difference.
6. The hidden channel communication method based on gyroscope resonance as claimed in claim 1, further comprising the step of eliminating the sound source motion noise, specifically:
and (3) a dynamic threshold dividing technology is used, namely, a maximum acoustic threshold algorithm is used for dividing the threshold in a short time period so as to eliminate the amplitude change of the resonance data caused by the motion of the sound source.
7. The gyro resonance-based covert channel communication method of claim 1, further comprising the step of removing motion noise of a target receiving device, specifically comprising:
two-dimensional motion of the target receiving device: selecting an axis without motion as one axis in a joint channel to form the joint channel, and eliminating extra numerical interference caused by two-dimensional motion through mean filtering;
three-dimensional motion of the target receiving device: the additional numerical interference caused by three-dimensional motion is eliminated through wavelet analysis, blind source separation and signal recovery based on the resonance inter-axis characteristics.
8. The gyro resonance-based covert channel communication method of claim 7, wherein the method for eliminating the interference of the three-dimensional motion of the target receiving device is as follows:
(a) wavelet analysis: preliminarily eliminating low-frequency motion noise;
(b) single-channel blind source separation: taking data on one axis of a gyroscope as an observation matrix, and taking resonance data and motion data as a source matrix to establish a blind source separation model; decomposing and dimension increasing the one-dimensional observation matrix by using ensemble empirical mode decomposition, and solving the model by using a principal component analysis method to obtain a high-dimensional solution matrix with the same dimension;
(c) and (3) signal recovery: repeating the steps (a) and (b) on the other axis, wherein resonance data between different axes can be fitted into an elliptic curve based on the characteristics of the same frequency and fixed phase difference of the gyroscope during resonance; and traversing all combinations in a solution matrix for summation, finding out the positions of the high levels by utilizing the characteristics of the positions of the high levels in the coding rule for fitting, selecting a group of combinations which can be fitted into an ellipse and have the largest elliptical area as signals, and considering the rest parts as noise interference caused by motion.
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