CN115499828A - Method for enhancing concealment of short wave voice signal and corresponding frequency offset estimation algorithm - Google Patents

Method for enhancing concealment of short wave voice signal and corresponding frequency offset estimation algorithm Download PDF

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CN115499828A
CN115499828A CN202211015468.9A CN202211015468A CN115499828A CN 115499828 A CN115499828 A CN 115499828A CN 202211015468 A CN202211015468 A CN 202211015468A CN 115499828 A CN115499828 A CN 115499828A
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synchronization sequence
embedded
original synchronization
colored noise
sequence
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张健
张凯
田杰
田甜
李怡呈
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Shaanxi Fenghuo Communication Group Co Ltd
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W12/00—Security arrangements; Authentication; Protecting privacy or anonymity
    • H04W12/03—Protecting confidentiality, e.g. by encryption
    • G—PHYSICS
    • G10—MUSICAL INSTRUMENTS; ACOUSTICS
    • G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
    • G10K11/00—Methods or devices for transmitting, conducting or directing sound in general; Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
    • G10K11/16—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
    • G10K11/175—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound
    • G10K11/1752—Masking
    • G10K11/1754—Speech masking
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L25/00—Baseband systems
    • H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
    • H04L25/0202—Channel estimation
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/0014—Carrier regulation
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/0014—Carrier regulation
    • H04L2027/0024—Carrier regulation at the receiver end
    • H04L2027/0026—Correction of carrier offset

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Abstract

The invention relates to the technical field of short wave communication, in particular to a short wave covert communication method based on an embedded synchronization sequence. According to the invention, the synchronization sequence is embedded into colored noise, a specific modulation mode is not required, the high complexity and difficult realization of modulation and demodulation caused by the specific modulation mode are avoided, and the strong concealment of the synchronization sequence can be realized; and a corresponding frequency offset estimation algorithm is provided, and the method has the advantages of high precision and easy implementation.

Description

Method for enhancing concealment of short wave voice signal and corresponding frequency offset estimation algorithm
Technical Field
The invention relates to the technical field of short wave communication, in particular to a short wave covert communication method based on an embedded synchronization sequence.
Background
With the rapid development of communication technology, more and more communication technologies and systems are emerging continuously, but the ancient and traditional communication mode of short-wave communication is still generally regarded by attention all over the world, and not only is the communication mode not eliminated, but also the communication mode is continuously and rapidly developed. As it has advantages not provided by other communication systems. First, shortwave is the only telecommunication means without network and relay constraints, for example, when a war or a disaster occurs, and a satellite is attacked, the survivability and the autonomous communication capability of shortwave are not comparable to those of other communication devices. Secondly, remote areas such as mountainous areas, gobi and oceans mainly rely on short waves for communication. Finally, the low communication cost also makes shortwave have a broad market. In summary, short-wave communication is still an important means for information transmission in the communication field at present.
Any communication system needs to transmit a synchronization sequence followed by user information. The synchronization sequence is used for enabling a receiver to acquire a synchronization starting point and calculate an accurate starting position of user information, and the user information can be processed only after the synchronization information is accurately acquired, so that synchronization acquisition is an initial step of communication of any communication system. When a synchronization sequence is transmitted, corresponding modulation (such as PSK, CPM, etc.) needs to be performed to adapt to the transmission characteristics of a channel, and paying attention to the special application scenario of short-wave communication, the factors such as signal concealment, interception, etc. need to be fully considered while information is transmitted between the two parties. However, due to the adoption of a modulation mode well known in the communication field, the signal has a special structure and does not have a hidden characteristic, so that the signal is easy to observe and intercept.
In order to extract useful information, the receiving end needs to down-convert the received high-frequency signal to a low-frequency signal, and this process needs a high-frequency carrier that is exactly the same as the frequency of the transmitting end. However, due to factors such as manufacturing process, material and electrical characteristics of the components, carrier frequencies generated at the transmitting end and the receiving end cannot be completely the same, and an error always exists. This error will affect the demodulation in the back end. The effect on the demodulator when the error is small is almost negligible; when the error is large, phase rotation occurs, which causes uncorrectable errors, and thus, the performance of the communication system is rapidly deteriorated. In order to solve the performance deterioration caused by the frequency error at the transmitting end and the receiving end, the common method is to perform frequency offset estimation on the signal before demodulation is not performed after down-conversion, and artificially remove the frequency offset estimation amount from the down-converted signal, so that the data entering the demodulator can be regarded as non-frequency offset data, and a correct result is obtained.
In summary, it is necessary to design a special synchronization sequence with characteristics of concealment, uneasy to be observed and intercepted, etc., and meanwhile, due to different carrier frequencies at the transmitting end and the receiving end, a corresponding frequency offset estimation algorithm needs to be provided for the special synchronization sequence. The invention can achieve the purpose of hiding in noise no matter the synchronous sequence is observed from a time domain or a frequency domain by embedding the synchronous information into colored noise in a distributed way, thereby greatly reducing the probability of being intercepted and intercepted.
Disclosure of Invention
Aiming at the problems in the prior art, the invention aims to provide a short-wave covert communication method based on an embedded synchronization sequence.
In order to achieve the purpose, the invention is realized by adopting the following technical scheme.
A method for enhancing concealment of short wave voice signals comprises the following steps:
step 1, generating colored noise with the same bandwidth as a short wave voice signal, the power of the colored noise is P, and the length of the colored noise is L at a transmitting end;
step 2, amplifying the amplitude of an original synchronization sequence with the length of K in the short wave voice signal to be P; the length L of the colored noise is far larger than the length K of the original synchronization sequence;
step 3, embedding the original synchronization sequence into colored noise;
step 4, intercepting the colored noise embedded into the original synchronization sequence from the first element of the original synchronization sequence to the last element of the original synchronization sequence as an embedded synchronization sequence;
and 5, replacing the original synchronization sequence in the short-wave voice signal by the embedded synchronization sequence by the transmitting terminal, and transmitting the replaced short-wave voice signal.
A frequency offset estimation algorithm is based on the method for enhancing the concealment of the short wave voice signal, and comprises the following steps:
step 1, obtaining a sinusoidal signal according to a local sequence and a synchronous segment structure
Figure BDA0003812357750000031
Step 2, non-uniformly sampled sinusoidal signal
Figure BDA0003812357750000032
Performing fast Fourier transform to obtain frequency offset estimation value
Figure BDA0003812357750000033
Step 3, according to the frequency deviation estimated value
Figure BDA0003812357750000034
Removing frequency deviation of the synchronous section;
step 4, reconstructing according to the local sequence and the synchronous segment after frequency deviation removal to obtain a sinusoidal signal
Figure BDA0003812357750000035
Returning to the step 1 until the maximum iteration times;
step 5, obtaining the frequency deviation estimated value of each iteration
Figure BDA0003812357750000036
Accumulating to obtain total frequency deviation estimated value
Figure BDA0003812357750000037
Compared with the prior art, the invention has the beneficial effects that: the synchronous sequence is embedded into colored noise, a specific modulation mode is not needed, the high complexity and difficult realization of modulation and demodulation caused by the specific modulation mode are avoided, and the strong concealment of the synchronous sequence can be realized; and a corresponding frequency offset estimation algorithm is provided, and the method has the advantages of high precision and easy implementation.
Drawings
The invention is described in further detail below with reference to the figures and the specific embodiments.
FIG. 1 is a schematic diagram of the structure of an embedded synchronization sequence according to the present invention;
FIG. 2 is a synchronization curve chart of the embedded synchronization head in the simulation result 1 of the present invention under the condition that the signal-to-noise ratio of the Gaussian channel is-5 dB;
FIG. 3 is a waveform diagram of the embedded synchronization head and the voice signal in the time domain according to simulation result 1 of the present invention;
fig. 4 is a graph of a change of a total frequency offset estimation value after each iteration of 30 iterations in total with a true frequency offset of 100Hz under the gaussian channel signal-to-noise ratio SNR = -5dB in simulation result 2 of the present invention.
Detailed Description
Embodiments of the present invention will be described in detail below with reference to examples, but it will be understood by those skilled in the art that the following examples are only illustrative of the present invention and should not be construed as limiting the scope of the present invention.
A method of enhancing concealment of short wave speech signals, comprising the steps of:
step 1, generating colored noise with same bandwidth as short wave voice signal, power P and length L = [ n ] at transmitting end 0 ,n 1 ,…,n L-1 ]；
Step 2, original synchronization sequence X = [ X ] with length of K in short wave voice signal 0 ,x 1 ,…,x K-1 ]Is amplified to P; the length L of the colored noise is far larger than the length K of the original synchronization sequence;
step 3, embedding the original synchronization sequence X into colored noise;
in particular, for the first element X of the original synchronization sequence X 0 ：
In colored noise, starting from the first element, the first element is found to belong to x 0 Neighborhood range of [ x ] 0 -r,x 0 +r]And replacing the element with x 0 ；
For the kth element X of the original synchronization sequence X k-1 ：
In colored noise, the first element belonging to x is found, starting with the element following the last replaced element k-1 Neighborhood range of [ x ] k-1 -r,x k-1 +r]And replacing the element with x k-1 ；
Wherein r is the fluctuation range.
The specific process is as follows:
for the first element X of the original synchronization sequence X 0 : in colored noise, n is the first element from 0 Initially, find the first at element x 0 Neighborhood range of [ x ] 0 -r,x 0 +r]The ith element n in (1) i-1 And n is i-1 Is replaced by x 0 ；
For the second element X of the original synchronization sequence X 1 : in colored noise, n is an element from the i +1 th i Initially, find the first at element x 1 Neighborhood range of [ x ] 1 -r,x 1 +r]The jth element n in (1) j-1 And n is j-1 Is replaced by x 1 ；
For the third element X of the original synchronization sequence X 2 : in colored noise, n is an element n from the j +1 th j Initially, find the first at element x 2 Neighborhood range of [ x ] 2 -r,x 2 +r]The qth element n in (1) q-1 N is to be q-1 Is replaced by x 2 ；
Similarly, the other elements X of the original synchronization sequence X are sequentially added 3 、x 4 、…、x K-1 Substitution into colored noise.
Step 4, intercepting the colored noise embedded into the original synchronization sequence from the first element of the original synchronization sequence to the last element of the original synchronization sequence as an embedded synchronization sequence;
and 5, replacing the original synchronization sequence in the short-wave voice signal by the embedded synchronization sequence by the transmitting terminal, and transmitting the replaced short-wave voice signal.
Further, the length of the embedded synchronization sequence obtained in step 4 is random, and in order to obtain the embedded synchronization sequence with the specified length, a step between step 4 and step 5 further includes: in the embedded synchronization sequence, any part of elements between any two adjacent original synchronization sequence elements are removed to obtain the embedded synchronization sequence with the specified length.
In order to more intuitively understand the construction process of the embedded synchronization sequence, fig. 1 gives a construction schematic diagram. It can be seen from the figure that in the colored noise, some sampling points are selected through comparison, sampling points which meet the conditions are marked, and the sampling points are embedded into the colored noise as actual synchronization points.
Simulation result 1
Referring to fig. 2, fig. 2 is a synchronization curve diagram of an embedded synchronization head at a gaussian channel signal-to-noise ratio of-5 dB; it can be seen that there is a very distinct peak in the synchronization curve, here corresponding to the receive sync header, so that the start of the data segment can be accurately determined.
Referring to fig. 3, fig. 3 is a waveform diagram of an embedded synchronization header and a voice signal in a time domain; it can be seen from the figure that the waveform of the embedded synchronization head is basically similar to the waveform of the voice signal, and a good concealing effect can be achieved.
The simulation result shows that the method for enhancing the concealment of the short-wave voice signal has strong concealment while ensuring correct synchronous capture.
When synchronous capture is carried out, a receiving end intercepts a series of received baseband signals, identifies the intercepted signals based on a local sequence and records an identification result; and traversing the received signals and drawing an identification result curve. The peak of the identification result curve corresponds to the start of the sync segment.
From the above principle, it can be seen that the process of acquiring the synchronization header is a process of identifying the input baseband signals one by one, and a common identification method is Fast Fourier Transform (FFT).
Since the local sequence X = (X) 0 ,Λ,x n ,Λ,x K-1 ) It is known that the phase variations can therefore be extracted from the intercepted received signal, thus obtaining a sequence
Figure BDA0003812357750000061
In which
Figure BDA0003812357750000062
Thus the sequence
Figure BDA0003812357750000063
It can be equivalent to a sinusoidal signal superimposed with noise, and the frequency of the signal is f. Then to
Figure BDA0003812357750000064
And carrying out fast Fourier transform to obtain a recognition result. Traversing the received signals and drawing an identification result curve. The peak of the identification result curve corresponds to the start of the sync segment. And identifying the frequency corresponding to the peak value of the result curve as the frequency deviation.
The embedded sync sequence is obtained by embedding the original sync sequence in colored noise in some random manner, so that the interval between any two elements in the embedded sync sequence is uncertain. The resulting-R can be seen as a non-uniformly sampled noisy sinusoidal signal.
For a sinusoidal signal with (frequency) offset and noise obtained by uneven sampling, a frequency offset value cannot be accurately obtained by directly utilizing FFT (fast Fourier transform). This is determined by the randomness of the embedding process (equivalent to non-uniform sampling).
From an information theory point of view, the non-uniformly sampled signal still contains information, but the information is non-uniformly distributed. Although not all information can be obtained, partial information can still be obtained from non-uniformly sampled signals.
A frequency offset estimation algorithm is based on the method for enhancing the concealment of the short wave voice signal, and comprises the following steps:
step 1, obtaining a sinusoidal signal according to a local sequence and a synchronous segment structure
Figure BDA0003812357750000071
Wherein the sinusoidal signal
Figure BDA0003812357750000072
Synchronous segment R = (R) 0 ,…,r n ,…,r K-1 ) Wherein
Figure BDA0003812357750000073
Representing frequency offset to a transmitted signal x k The influence of (2) belongs to multiplicative interference, and is a main factor of phase rotation generated by symbols;
Figure BDA0003812357750000074
indicating the magnitude of the additional phase of the kth symbol,
Figure BDA0003812357750000075
R sym represents a symbol transmission rate; w is a k Representing noise pairs x k The effect of (2) is an additive interference. w is a k Subject to mean of 0 and variance of σ 2 The two-dimensional noise sample values of the normal distribution. Based on the mathematical model, after the frequency error f at the transmitting and receiving ends is estimated, the operation of removing the frequency deviation can be carried out on the received signal, and the received signal is correspondingly rotated in a reverse way, namely
Figure BDA0003812357750000076
Step 2, non-uniformly sampled sinusoidal signal
Figure BDA0003812357750000077
Performing fast Fourier transform to obtain frequency offset estimation value
Figure BDA0003812357750000078
Step 3, according to the frequency deviation estimated value
Figure BDA0003812357750000079
Removing frequency deviation of the synchronous section;
step 4, reconstructing according to the local sequence and the synchronous segment after removing the frequency deviation to obtain a sinusoidal signal
Figure BDA00038123577500000710
Returning to the step 1 until the maximum iteration times;
step 5, obtaining the frequency deviation estimated value of each iteration
Figure BDA00038123577500000711
Accumulating to obtain the estimated value of total frequency deviation
Figure BDA00038123577500000712
Simulation result 2
Referring to fig. 4, fig. 4 is a graph of a change of a total frequency offset estimation value after each iteration of 30 iterations under the gaussian channel signal-to-noise ratio SNR = -5dB for a true frequency offset of 100 Hz; it can be seen that, as the number of iterations increases, the total frequency offset estimation value gradually approaches to the true value; the part of information (single frequency offset value) estimated by the first iteration is maximum, and then the information is gradually decreased; the sum estimate oscillates around the true frequency offset value at the late stage of the iteration. The method has the advantages that the estimated value of the frequency offset estimation iterative algorithm gradually approaches the true frequency offset value along with the increase of the iteration times, so that the method has the capability of frequency offset estimation, and the estimated value has the advantages of high precision and easiness in implementation.
Although the present invention has been described in detail in this specification with reference to specific embodiments and illustrative embodiments, it will be apparent to those skilled in the art that modifications and improvements can be made thereto based on the present invention. Accordingly, it is intended that all such modifications and alterations be included within the scope of this invention as defined in the appended claims.

Claims (4)

1. A method for enhancing concealment of short wave speech signals, comprising the steps of:
step 1, generating colored noise with the same bandwidth as a short-wave voice signal, P power and L length at a transmitting end;
step 2, amplifying the amplitude of an original synchronization sequence with the length of K in the short wave voice signal to be P; the length L of the colored noise is far larger than the length K of the original synchronization sequence;
step 3, embedding the original synchronization sequence into colored noise;
step 4, intercepting the colored noise embedded into the original synchronization sequence from the first element of the original synchronization sequence to the last element of the original synchronization sequence as an embedded synchronization sequence;
and 5, replacing the original synchronization sequence in the short-wave voice signal by the embedded synchronization sequence by the transmitting terminal, and transmitting the replaced short-wave voice signal.
2. Method for enhancing concealment of short wave speech signals according to claim 1, characterized in that the original synchronization sequence of step 3 is embedded in colored noise, in particular for the first element x of the original synchronization sequence 0 ：
In colored noise, starting from the first element, the first element is found to belong to x 0 Neighborhood range of [ x ] 0 -r,x 0 +r]And replacing the element with x 0 ；
For the kth element x of the original synchronization sequence k-1 ：
In colored noise, the first element belonging to x is found, starting with the element following the last replaced element k-1 Neighborhood range of [ x ] k-1 -r,x k-1 +r]And replacing the element with x k-1 ；
Wherein r is the fluctuation range.
3. The method for enhancing concealment of short wave speech signals according to claim 1, further comprising the steps between step 4 and step 5 of: in the embedded synchronization sequence, any part of elements between any two adjacent original synchronization sequence elements are removed to obtain the embedded synchronization sequence with the specified length.
4. A frequency offset estimation algorithm based on the method for enhancing concealment of short wave speech signal of any claim from 1 to 3, comprising the steps of:
step 1, sinusoidal signals are obtained according to the local sequence and the synchronous segment structure
Figure FDA0003812357740000021
Step 2, non-uniformly sampled sinusoidal signal
Figure FDA0003812357740000022
Performing fast Fourier transform to obtain frequency offset estimation value
Figure FDA0003812357740000023
Step 3, according to the frequency deviation estimated value
Figure FDA0003812357740000024
Removing frequency deviation of the synchronous section;
step 4, reconstructing according to the local sequence and the synchronous segment after frequency deviation removal to obtain a sinusoidal signal
Figure FDA0003812357740000025
Returning to the step 1 until the maximum iteration times;
step 5, obtaining the frequency deviation estimated value of each iteration
Figure FDA0003812357740000026
Accumulating to obtain total frequency deviation estimated value
Figure FDA0003812357740000027
CN202211015468.9A 2022-08-24 2022-08-24 Method for enhancing concealment of short wave voice signal and corresponding frequency offset estimation algorithm Pending CN115499828A (en)

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN117241361A (en) * 2023-11-13 2023-12-15 北京航空航天大学 Short wave hidden communication method based on power control

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN117241361A (en) * 2023-11-13 2023-12-15 北京航空航天大学 Short wave hidden communication method based on power control
CN117241361B (en) * 2023-11-13 2024-02-06 北京航空航天大学 Short wave hidden communication method based on power control

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