CN115967463A - Network time synchronization message transmission method and device applied to any channel environment - Google Patents

Abstract

The invention discloses a network time synchronization message transmission method and a device applied to any channel environment, wherein the method comprises the following steps: classifying data bits of a time synchronization message to be transmitted to obtain public information bits and secret information bits, and performing Polar coding on the data of the time synchronization message to obtain a first coding sequence; dividing all data subcarriers in a transmission bandwidth range into subblocks according to the number of legal receiving ends, dividing each subblock to obtain clusters, performing IM modulation on each cluster, and determining the active subcarrier index of each cluster; based on the total frequency domain channel matrix characteristic of a preset channel simulation system, interleaving symbol vectors obtained by modulating the first coding sequence; and modulating the interleaved symbol vector to the active subcarrier selected by each subblock to complete OFDM-IM modulation, and sending the modulated OFDM-IM signal to each legal receiving end. The invention solves the problems of poor network time synchronization message transmission safety and application scene limitation.

Description

Network time synchronization message transmission method and device applied to any channel environment

Technical Field

The present invention relates to the field of communications technologies, and in particular, to a method and an apparatus for secure transmission of a network time synchronization packet applied to an arbitrary channel environment.

Background

The network time synchronization technology is a technology for realizing time synchronization of a computer or an instrument device accessed to a network by using the network as a medium through message interaction. The Network Time synchronization Protocol includes a Network Time Protocol (NTP) and a Precision Time Protocol (Precision Time Protocol, PTP, IEEE 1588). At present, the standardization work of NTP and PTP security mechanisms is continuously carried out, and from the standardization results of the NTP and PTP security mechanisms which are newly released, these mechanisms can provide basic security functions, such as identity authentication, data integrity protection, replay attack suppression, and the like, but still have significant defects, such as great limitation in the aspect of time delay attack, and the timestamp in the time synchronization message is publicly transmitted in the network and is vulnerable to tampering attack; the safety and the precision of time synchronization cannot be considered; and the current mode cannot be completely applied to the identity authentication mechanism of network time synchronization.

Therefore, the application range of the current network time synchronization message transmission method is limited, and certain security holes exist.

Disclosure of Invention

In view of the above problems, the present invention provides a method and an apparatus for transmitting a network time synchronization packet applied to any channel environment, which can be applied to any channel environment and solve the problem of application scenario limitation in the secure transmission of the network time synchronization packet.

In order to achieve the purpose, the invention provides the following technical scheme:

a network time synchronization message transmission method applied to any channel environment comprises the following steps:

classifying data bits of a time synchronization message to be transmitted to obtain public information bits and secret information bits;

performing Polar coding on data bits of the time synchronization message based on the public information bits and the secret information bits to obtain a first coding sequence;

carrying out constellation modulation on the first coding sequence to obtain a symbol vector;

dividing all data subcarriers in a transmission bandwidth range into a plurality of subblocks according to the number of legal receiving ends, dividing each subblock to obtain a plurality of clusters, performing IM modulation on each cluster, and determining the active subcarrier index of each cluster;

interleaving the symbol vectors based on the total frequency domain channel matrix characteristics of a preset channel simulation system, and determining active subcarrier indexes for bearing the symbol vectors;

modulating the interleaved symbol vector to the active sub-carrier selected by each sub-block to complete OFDM-IM modulation and obtain an OFDM-IM signal;

and sending the OFDM-IM signal to each legal receiving end.

Optionally, the method further comprises:

determining an information bit channel, wherein the information bit channel comprises a secret bit channel and a public bit channel, the secret bit channel is used for transmitting the secret information bits, the public bit channel is used for transmitting the public information bits, and the sum of the information bit channel and the frozen bit channel is a total bit channel;

determining an information bit channel index set, a public bit channel index set, a secret bit channel index set, a frozen bit channel index set based on the bartacurie sub-parameters of each bit channel in the total bit channels.

Optionally, the performing Polar coding on the data bits of the time synchronization packet based on the public information bits and the secret information bits to obtain a first coding sequence includes:

generating a Polar code generating matrix;

extracting corresponding rows of the generated matrix according to each index set to obtain each submatrix, wherein each index set comprises an information bit channel index set, a public bit channel index set, a secret bit channel index set and a frozen bit channel index set;

and performing Polar coding on data bits of the time synchronization message based on the secret information bits and the secret information bit vector corresponding to the message forwarding indication vector, the public information bit vector corresponding to the public information bits, the freezing vector and each submatrix to obtain a first coding sequence.

Optionally, the dividing each sub-block to obtain a plurality of clusters includes:

acquiring the number of sub-links included in an actual transmission link from a sending end to a legal receiving end in a network;

determining a number of clusters based on the number of child links;

and dividing each subblock according to the number of the clusters to obtain a plurality of clusters, wherein a specific number of clusters are reserved for link safety information transmission, and the rest clusters are used for transmitting time synchronization message data.

Optionally, performing IM modulation on each cluster, and determining an active subcarrier index of each cluster includes:

numbering a plurality of clusters of each subblock respectively to enable IM data of each numbered cluster to bear different information, wherein the IM data of the first 3 clusters bear a transmitting end identification code, a receiving end identification code and the numbers of all sub-links contained in a preset route respectively, the IM data of the rest clusters bear channel simulation system indicating data of the sub-links respectively, and the channel simulation system indicating data of the sub-links are used for indicating the numbers and the passing sequence of a channel simulation system which needs to be passed by a time synchronization message on the sub-links;

and performing IM modulation on each cluster according to the information to be carried by each cluster, and determining the active subcarrier index of each cluster.

Optionally, the interleaving the symbol vector based on the total frequency domain channel matrix characteristic of the preset channel simulation system, and determining an index of an active subcarrier carrying the symbol vector, includes:

determining a total frequency domain channel matrix of each channel simulation system based on a transfer function preset for each channel simulation system;

calculating the channel gain of each active sub-carrier in each sub-block added by the channel simulation system based on the total frequency domain channel matrix of the channel simulation system;

interleaving the symbol vectors based on the channel gains, and determining active subcarrier indexes carrying the symbol vectors.

Optionally, the modulating the interleaved symbol vector to the active subcarriers selected by each sub-block to complete OFDM-IM modulation, and obtaining an OFDM-IM signal includes:

determining the noise vector length of each sub-block based on the symbol vector length and the number of active sub-carriers of each sub-block, and generating a noise vector;

generating a frequency domain vector based on the link security information vector, the message data symbol vector and the noise vector;

generating a time domain vector based on the frequency domain vector;

and carrying out OFDM-IM modulation based on the frequency domain vector and the time domain vector to obtain an OFDM-IM signal.

Optionally, the method further comprises:

in the signal transmission process, each channel simulation system and each switching device in the transmission process the OFDM-IM signals based on a special link working mechanism.

Optionally, the method further comprises:

responding to a legal receiving end to receive the OFDM-IM signal, processing the OFDM-IM signal based on a reverse processing mode matched with a generation processing mode of the OFDM-IM signal to obtain the time synchronization message, wherein the reverse processing mode at least comprises OFDM demodulation, IM demodulation, generation of a total frequency domain channel matrix of a channel simulation system, de-interleaving, constellation demodulation, pline decoding and message transmission safety judgment according to an error rate of a message forwarding indication vector.

A network time synchronization packet transmission apparatus applied to an arbitrary channel environment, the apparatus comprising:

the classification unit is used for classifying data bits of the time synchronization message to be transmitted to obtain public information bits and secret information bits;

a Polar coding unit, configured to perform Polar coding on data bits of the time synchronization packet based on the public information bits and the secret information bits to obtain a first coding sequence;

the constellation modulation unit is used for carrying out constellation modulation on the first coding sequence to obtain a symbol vector;

the first determining unit is used for dividing all data subcarriers in a transmission bandwidth range into a plurality of subblocks according to the number of legal receiving ends, dividing each subblock to obtain a plurality of clusters, performing IM modulation on each cluster, and determining the active subcarrier index of each cluster;

a second determining unit, configured to interleave the symbol vector based on a total frequency domain channel matrix characteristic of a preset channel simulation system, and determine an index of an active subcarrier carrying the symbol vector;

an OFDM modulation unit, configured to modulate the interleaved symbol vector to an active subcarrier selected by each sub-block to complete OFDM-IM modulation, so as to obtain an OFDM-IM signal;

a signal transmitting unit for transmitting the OFDM-IM signal to each legal receiving end

Compared with the prior art, the invention provides a network time synchronization message transmission method and a device applied to any channel environment, which are applied to a sending end, and comprise the following steps: classifying data bits of a time synchronization message to be transmitted to obtain public information bits and secret information bits; performing Polar coding on data of the time synchronization message based on the public information bit and the secret information bit to obtain a first coding sequence; carrying out constellation modulation on the first coding sequence to obtain a symbol vector; dividing all data subcarriers in a transmission bandwidth range into a plurality of subblocks according to the number of legal receiving ends, dividing each subblock to obtain a plurality of clusters, performing IM modulation on each cluster, and determining the active subcarrier index of each cluster; interleaving the symbol vectors based on the total frequency domain channel matrix characteristics of a preset channel simulation system, and determining active subcarrier indexes for bearing the symbol vectors; modulating the interleaved symbol vectors to active subcarriers selected by each subblock to complete OFDM-IM modulation, and sending modulated OFDM-IM signals to each legal receiving end; in the signal transmission process, each channel simulation system and each switching device process OFDM-IM signals according to a special link working mechanism. And the legal receiving end carries out OFDM demodulation, IM demodulation, generation of a total frequency domain channel matrix of a channel simulation system, de-interleaving, constellation demodulation and Plour decoding on the received OFDM-IM signal. And judging the safety of message transmission according to the bit error rate of the message forwarding indication vector. The invention controls the frequency selectivity of the transmission channel through the channel simulation system and the matched special link working mechanism thereof, can be applied to any channel environment, and solves the problems of poor network time synchronization message transmission safety and application scene limitation.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the provided drawings without creative efforts.

Fig. 1 is a schematic block diagram illustrating a principle of implementing OFDM modulation by IFFT according to an embodiment of the present invention;

fig. 2 is a schematic block diagram of an implementation of OFDM demodulation through FFT according to an embodiment of the present invention;

fig. 3 is a schematic diagram of a frequency domain model for OFDM transmission and reception according to an embodiment of the present invention;

FIG. 4 is a schematic diagram of a first-order tap frequency domain equalizer according to an embodiment of the present invention;

fig. 5 is a schematic flowchart of a network time synchronization packet transmission method applied to an arbitrary channel environment according to an embodiment of the present invention;

fig. 6 is a schematic diagram of an NTS protected NTPv4 data packet format according to an embodiment of the present invention;

fig. 7 is a schematic diagram of a security algorithm link according to an embodiment of the present invention;

fig. 8 is a schematic diagram of a dedicated link communication frame structure according to an embodiment of the present invention;

fig. 9 is a schematic structural diagram of a network time synchronization packet transmission apparatus applied to an arbitrary channel environment according to an embodiment of the present invention.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

The terms "first" and "second," and the like in the description and claims of the present invention and in the above-described drawings, are used for distinguishing between different objects and not for describing a particular order. Furthermore, the terms "include" and "have," as well as any variations thereof, are intended to cover a non-exclusive inclusion. For example, a process, method, system, article, or apparatus that comprises a list of steps or elements is not set forth for a listed step or element but may include steps or elements not listed.

The embodiment of the invention provides a network time synchronization message transmission method applied to any channel environment, which introduces OFDM-IM modulation on the basis of Polar coding and constructs the channel quality difference between a legal main channel and an illegal tapping channel by controlling the frequency selectivity of a transmission channel. The method solves the safety problem caused by the fact that the channel quality of an illegal wiring channel is close to that of a legal main channel, and a secret bit channel cannot be constructed or the number of the secret bit channels cannot meet the actual requirement.

In order to facilitate description of technical features in the embodiments of the present invention, a related art to which the present invention is applied will now be explained.

Polar code technique:

polar code is a channel coding proposed by erdal. Arikan, university of turkey bickent (Bilkent University) in 2007, by Polar coding the original information bits, N successive applications (serially transmitting an N-bit vector) of a given binary input discrete memoryless channel (B-DMCs) W can be merged and split into N bit channels with polarization effect

Polar codes are a special form of block codes (also known as block codes). The data block length N is defined as N =2 ⁿ (N ≧ 0), for any N-bit original data block

The Polar coding data block is shown as formula (1).

Wherein G is _N Generating a matrix for the N order;

I _N is an N-order identity matrix; r _N Representing a permutation operation; />

Represents kronecker product (Kroneckerproduct) _ live>

Kronecker power (Kronecker)

Is defined as->

(for all n ≧ 1). According to customary practice, is>

For any subset a of {1, …, N }, equation (1) can be written as:

wherein, G _N (A) Is G _N The corresponding row index is determined by A;

indicating modulo-2 addition.

If A and u are fixed _A Let u stand for _A For free variables, a block u of source data is available _A To the coded data block

To (3) is performed. This mapping is called coset coding: coset code generator matrix is G _N (A) Given a vector u _A G _N (A) To determine coset, this class of codes is collectively referred to as G _N -a coset code. G _N The coset code may be passed through a parameter vector (N, K, A, u) _A ) Uniquely determining, wherein K is the dimension of the code, and the parameter determines the size of A; K/N is called code rate R; a is an information bit index set; u. u _A The vector is frozen for N-K bits.

Polar code gives specific rules in the selection of information set a based on the above coding mode: given B-DMC channel W, when the set of information bit indices A is chosen from all K element subsets of {1, …, N }, such that j ∈ A for all i ∈ A, j ∈ A ^c All have Bhattacharyya parameter

The parameter vector is (N, K, A, u) _A ) G of (A) _N The coset code is called polar code of channel W.

Polar coding realizes channel polarization, and code words after coding

Any bit x of _i Will be via the bit channel W ⁽ⁱ⁾ _N To the receiving end. Bit channel +>

Has the polarization characteristics that: when N is larger, the capacity of a part of channels will tend to 1, while the capacity of the rest of channels will tend to 0, and the ratio of the channels with the capacity of 1 to the total number of channels is just the capacity I (W) of the original binary input discrete channel. This means that in the N bit channels there is ∑ located>

A single bit channel enables error-free transmission of information bits. Original data block->

In the actual number of information bits->

The OFDM modulation technology:

an Orthogonal Frequency Division Multiplexing (OFDM) technique, which is abbreviated as OFDM technique, is a multi-carrier baseband modulation technique, and has the following basic characteristics:

(1) A large number of narrowband subcarriers (subcarriers) are used. OFDM modulation techniques divide the effective transmission bandwidth into a number of mutually orthogonal narrowband subcarriers, each of which may carry a separate information stream. Thousands of sub-carriers are allowed to transmit simultaneously on the same transmission link.

(2) The frequency spectrum utilization rate is high. The subcarriers in the frequency domain are closely arranged, and the subcarrier interval is delta f =1/T _u Wherein T is _u Is the duration of the modulation symbols carried in each subcarrier.

(3) The implementation complexity is low. OFDM can achieve low complexity modulation and demodulation through efficient IFFT (Inverse Fast Fourier Transform) and FFT (Fast Fourier Transform) operations.

In time domain, OFDM is based on fast modulation, and in each OFDM symbol interval, N is total _c The modulation symbols are transmitted in parallel, which is also the reason that OFDM modulation can achieve higher data transmission efficiency, and the modulation symbols may adopt any constellation modulation scheme, such as BPSK (Binary Phase Shift Keying) modulation, QPSK (Quadrature Phase Shift Keying) modulation, and the like.

In the frequency domain, OFDM divides the effective transmission bandwidth into a series of orthogonal and mutually overlapped narrow-band subcarriers, the frequency spectrum of each subcarrier is a sine-square spectrum, and can be described by a sinc function (sinc (x) = sin (x)/x). The subcarrier spectrum is characterized by a narrow main lobe and infinite continuation of side lobes in the + ∞ and- ∞ directions. To avoid carrier leakage, the center frequency of each subcarrier is typically distributed on both sides of the center frequency of the signal (zero frequency of the baseband signal). Since the bandwidth of each subcarrier (the main lobe width of the sinc function) is narrow, even if there is channel distortion over the entire transmission bandwidth, the channel can be considered flat for each subcarrier within its spectral main lobe.

The OFDM modulation method is called OFDM, and its orthogonality is mainly reflected in that any two OFDM modulated sub-carriers are at time interval mT _u ≤t≤(m+1)T _u All are mutually orthogonal, i.e.:

thus, OFDM can be viewed as being formed by a series of orthogonal functions φ _k (t) modulation by:

OFDM can achieve low complexity modulation through efficient IFFT operations. Assume a time-discrete (sampled) OFDM signal with a sampling rate fs that is an integer multiple of the subcarrier spacing Δ f, i.e.: f. of _s ＝1/T _s = N · Δ f, the parameter N should be chosen with sufficient consideration for the sampling rate f _s The sampling theorem is satisfied. Due to N _c Δ f can be considered as the nominal bandwidth of the OFDM signal, which means that the value of N should be chosen to be greater than N _c And a sufficient margin is ensured.

According to the above assumptions, the time-discrete OFDM signal can be described as:

wherein the content of the first and second substances,

thus, the sequence x _n I.e. the sampled OFDM signal, is the original block of modulation symbols a ₀ ,a ₁ ,…,a _Nc-1 The length is extended to N by complementing 0, and then the obtained product is subjected to Inverse Fourier Transform (IDFT) of N points. Thus, OFDM modulation can be achieved by inverse fourier transform followed by digital to analog conversion, as shown in fig. 1. In particular, when the number of points for IDFT is selected to be 2 ^m (m is an arbitrary integer), OFDM modulation can be achieved by an efficient radix-2-IFFT.

Similar to OFDM modulation, OFDM demodulation can also be achieved by an efficient FFT, i.e. the analog signal is sampled (f) _s ＝1/T _s ) And then becomes a discrete signal and then is implemented by DFT/FFT with the number of points N, as shown in fig. 2.

The orthogonality between the sub-carriers will be, at least partly, lost under the influence of a real complex channel. The time domain is embodied in an integration period of a demodulator, and the integration period not only comprises an integer period of a complex exponential corresponding to a certain subcarrier, but also comprises a fractional period, so that the orthogonality among the subcarriers is influenced; in the frequency domain, each subcarrier is considered to have a special spectral structure. Even if the frequency domain impulse response of the channel is constant in the main lobe bandwidth range of each OFDM subcarrier, the distortion of the channel only damages the side lobe of the subcarrier, but because the side lobe range of each OFDM subcarrier is much larger than the main lobe, the distortion of the side lobe inevitably causes the loss of the orthogonality among the subcarriers, thereby causing the interference among the subcarriers.

In order to ensure the orthogonality between the OFDM signal subcarriers in the actual channel environment, the OFDM technology adopts a simple method, i.e., inserting a cyclic prefix. The method refers to copying an end portion of an OFDM symbol and inserting it into a front end of the OFDM symbol. Therefore, inserting the cyclic prefix increases the length of the OFDM symbol from Tu to T _u +T _CP Wherein T is _CP Is the cyclic prefix length. Therefore, after inserting the cyclic prefix, the symbol rate of OFDM is reduced accordingly.

In practice, cyclic prefix insertion is performed after IFFT, so cyclic prefix insertion can be understood as understanding the last N of the IFFT output block of length N _CP Copying and inserting the samples in front of the block to increase the length of the block from N to N + N _CP . At the receiving end, the samples of the cyclic prefix portion are removed prior to OFDM demodulation (DFT/FFT processing).

Assuming that the cyclic prefix is sufficiently long, one integration period T in the demodulator _u The linear convolution of the channel may be considered as a circular convolution. The combination of OFDM modulation (IFFT processing), channel and OFDM demodulation (FFT processing) can be regarded as a frequency-domain channel, as shown in fig. 3, where the frequency-domain channel taps H ₀ ,…,H _NC-1 May be generated directly from the channel impulse response.

Output b of the demodulator in fig. 3 _k Is a modulation signal a at the transmitting end _k Via complex frequency domain channel tap H _k After weighting and phase rotation, a noise interference term n is added _k And (4) obtaining the product. For further processing of the received signal to be correctThe original data bits are recovered, that is, constellation demodulation is performed, and the receiving end needs to compensate for the distortion of the amplitude and the phase of the received signal caused by the channel, which is called equalization, and fig. 4 shows a schematic diagram of a first-order tap frequency domain equalizer.

After inserting the cyclic prefix, the received symbol can be regarded as a cyclic convolution of the transmitted symbol and the channel from the perspective of the receiver, so that no overlap-and-discard (overlap-and-discard) processing is required at the receiving end. The taps of the frequency domain equalizer can be calculated directly by estimating the samples of the channel frequency response, for example, in an MMSE equalizer, the frequency domain filter taps can be calculated by equation (9).

In the formula, N ₀ Is the noise power; h _k Is a discrete channel frequency response.

Through equalization, the influence of non-ideal channel characteristics on received signals can be effectively inhibited, and the orthogonality among subcarriers is ensured.

OFDM-IM modulation technique:

an OFDM-IM (OFDM with index modulation) modulation technology is developed and proposed on the basis of an OFDM technology, and compared with the traditional OFDM technology, the technology mainly aims to expand a mode of taking a subcarrier index as new bearing information.

In OFDM-IM modulation, N is added _c Sub-carriers equally divided into N _g Clusters, each cluster having N subcarriers, N _c ＝n·N _g . Different from the traditional OFDM technology (N) _c All subcarriers are used for carrying data symbols), only k subcarriers are selected for data transmission at a time from n subcarriers of each cluster, and are called active subcarriers (active subcarriers), and k is less than or equal to n. The combination of active subcarriers of each cluster is called an IM symbol (IM symbol), and different combinations of active subcarriers within a cluster constitute different IM symbols. The number of IM symbols that can be expressed by the index of the active sub-carrier per cluster is

Number of bits ≧ or equivalent to the number of active subcarrier indices per cluster that can be carried>

(/>

Indicating rounding down). The index set of the active subcarriers of the β -th cluster may be expressed as:

I _β ＝{i _β,0 ,…,i _β,k-1 } (10)

wherein i _β,u E {1,2, …, n }, and u =0,1, …, k-1.

After the active subcarriers are determined, as in the conventional OFDM modulation, each active subcarrier can carry one data symbol, and assuming that the constellation modulation order of the data symbol is/(e.g., l =1 for BPSK; l =2 for QPSK), the number of bits carried by the active subcarrier in each cluster is B ₂ K · l. Thus, the total number of bits transmitted per cluster is B ₁ +B ₂ 。

Denote the OFDM-IM symbol vector as

Wherein x _β ＝[x _β (0),…,x _β (n-1)] ^T Refers to the transmission symbol vector of the beta cluster. For x _β (i) If I ∈ I _β Then x _β (i) Is a data symbol; on the contrary, x _β (i)＝0。

The modulation and demodulation process of the OFDM-IM technology is similar to that of OFDM, except that clustering and active subcarrier selection are added before IFFT of a modulation part, and an IM demodulation link is added after FFT of a demodulation part. The basic idea is to detect all sub-carriers one by one, determine whether they carry non-zero data symbols, and if so, the sub-carrier is the active sub-carrier. Currently, there are a Maximum Likelihood detector (ML) detector, a log Likelihood Ratio detector (LLR) detector, a coherent OOK detector, and the like.

Specifically, referring to fig. 5, a schematic flow chart of a network time synchronization packet transmission method applied to any channel environment according to an embodiment of the present invention is provided, where the method includes the following steps:

s101, classifying data bits of a time synchronization message to be transmitted to obtain public information bits and secret information bits.

S102, based on the public information bits and the secret information bits, polar coding is carried out on the data bits of the time synchronization message to obtain a first coding sequence.

S103, carrying out constellation modulation on the first coding sequence to obtain a symbol vector.

S104, dividing all data subcarriers in the transmission bandwidth range into a plurality of subblocks according to the number of legal receiving ends, dividing each subblock to obtain a plurality of clusters, performing IM modulation on each cluster, and determining the active subcarrier index of each cluster.

And S105, interleaving the symbol vectors based on the total frequency domain channel matrix characteristics of a preset channel simulation system, and determining the active subcarrier indexes bearing the symbol vectors.

S106, modulating the interleaved symbol vectors to the active subcarriers selected by each subblock to complete OFDM-IM modulation and obtain OFDM-IM signals.

S107, the OFDM-IM signals are sent to the legal receiving ends.

It should be noted that, in the signal transmission process, each channel simulation system and each switching device process the OFDM-IM signal according to the dedicated link working mechanism. Correspondingly, the legal receiving end carries out OFDM demodulation, IM demodulation, total frequency domain channel matrix generation of a channel simulation system, de-interleaving, constellation demodulation and Plour decoding on the received OFDM-IM signal. And judging the message transmission safety according to the bit error rate of the message forwarding indication vector. The detailed description of this section will be described in detail in the following examples of the present invention.

In the embodiment, an OFDM-IM modulation technology is introduced into a Polar code-based network time synchronization data packet, and the degradation of an illegal connecting channel is realized by utilizing the special time-frequency domain structure and orthogonal characteristic of an OFDM signal, so that the system safety rate is improved.

First, in step S101, data bits of the time synchronization packet to be transmitted are classified, so that security of information bits that need to receive transmission protection can be further improved. The information bits to be protected by transmission are divided into secret information bits, and the other bits are divided into public information bits. Taking NTP (Network Time Protocol) as an example, the packet format is shown in fig. 6.

In FIG. 6, LI: a leap second indication, a 2-bit unsigned integer, indicating whether a positive leap second or a negative leap second will be implemented for the last minute of the current month; VN: version number, 3-bit unsigned integer, currently 4; mode: working mode, 3-bit unsigned integer; stratum: level number, 8-bit unsigned integer, indicating levels 1-15; poll:8 bit signed integer indicating maximum time interval between successive time sync messages, log ₂ (x) Calculating the second; precision:8 bit signed integer indicating the accuracy of the system clock, in log ₂ (x) Calculating the second; root Delay: total bidirectional time delay from the reference clock; root Dispersion: total time offset from a reference clock; reference ID: a 32-bit code sequence to indicate a particular server or reference clock; reference Timestamp: a reference timestamp indicating the time of the last calibration of the system clock; origin Timestamp: the time synchronization request message sending timestamp indicates the time when the request message leaves the client and is sent to the server, and the client time is taken as reference; receive Timestamp: receiving a timestamp by the time synchronization request message, indicating the time when the request message reaches the server, and taking the server time as reference; transmit Timestamp: the time synchronization response message sending timestamp indicates the time when the response message leaves the server and is sent to the client, and the server time is taken as reference; destination Timestamp: the time synchronization response message receiving timestamp indicates the time when the response message reaches the client, and the client time is taken asReference is made to. It should be noted that the Destination Timestamp field is not included in the response packet, but is determined by the client and written into the corresponding data structure of the client packet buffer. The above fields are conventional parts of NTP packets, for a total of 12 x 32 bits.

This is followed by an extension portion (optional) of the NTP packet, containing 4 new extension fields for NTS, which serves to provide NTS protection for the NTP packet. The format of the extended field for NTS authentication and encryption starts from the Nonce Length field. Nonce Length: a 16-bit unsigned integer to indicate the length of the Nonce field; ciphertext Length: a 16-bit unsigned integer indicating the length of the ciphertext field; the nonces: providing nonces required by the AEAD algorithm, and filling zeros if the nonces are less than 32 bits; ciphertext: the output of AEAD algorithm, the structure of the field is determined by the actually adopted algorithm, but usually all contain an authentication tag and an actual ciphertext, and if the number of the authentication tag is less than 32 bits, zero padding is carried out; additional Padding: the extension part of the packet may require the inclusion of this field if the nonce length used by the client is less than the maximum length allowed by the AEAD algorithm employed.

The current NTP data packet format is plaintext except NTS authentication and encryption extension domain, i.e. the content of the message is not encrypted and only protected by authentication. From the viewpoint of suppressing Timestamp tampering attack and being compatible with the current security mechanism, the 4 Timestamp fields in fig. 5, i.e., reference Timestamp, origin Timestamp, receive Timestamp, and Transmit Timestamp, should be divided into secret information bits, and other message fields are divided into public information bits. It should be noted that after Polar coding, the public information bits are transmitted through the public bit channel, and there is no essential difference from the current transmission mechanism. This means that the fields included in the public information bit set are still protected by the current security mechanism, but the network time synchronization security algorithm based on Polar code proposed by the present invention focuses on enhancing the weak links of the current security mechanism, i.e. the security of the timestamp data.

In step S102, after the public information bits and the secret information bits are obtained, the bit channel parameters are combined, that is, an information bit channel is first determined, where the information bit channel includes a secret bit channel and a public bit channel, the secret bit channel is used for transmitting the secret information bits, the public bit channel is used for transmitting the public information bits, and the sum of the information bit channel and the frozen bit channel is a total bit channel. Then based on the baratropiy parameters of each bit channel in the total bit channels, a set of information bit channel indices, a set of public bit channel indices, a set of secret bit channel indices, a set of frozen bit channel indices may be determined. And then Polar coding is carried out on the bit data of the time synchronization message based on various information bits, the frozen vector and the corresponding index set to obtain a first coding sequence. For example, in one embodiment, an information bit channel is determined, which includes a secret bit channel and a public bit channel. The secret bit channel is used for transmitting the secret information bits, and the public bit channel is used for transmitting the public bit channel. The sum of the information bit channel and the frozen bit channel is a total bit channel; determining an information bit channel index set, a public bit channel index set, a secret bit channel index set, a frozen bit channel index set based on the bartacurie sub-parameters of each bit channel in the total bit channels.

The above information may be utilized in the process of Polar encoding at step S103. In an embodiment, performing Polar coding on data bits of the time synchronization packet based on the public information bits and the secret information bits to obtain a first coding sequence, including: generating a Polar code generating matrix; extracting corresponding rows of the generated matrix according to each index set to obtain each submatrix, wherein each index set comprises an information bit channel index set, a public bit channel index set, a secret bit channel index set and a frozen bit channel index set; and performing Polar coding on the data bits of the time synchronization message based on the secret information bits and the secret information bit vector corresponding to the message forwarding indication vector, the public information bit vector corresponding to the public information bits, the frozen vector and each submatrix to obtain a first coding sequence.

Specifically, after the public information bits and the secret information bits are determined, the number of secret bit channels K is determined _s Number of public bit channels K _p Information bit channel number K and total bit channel number N.

Taking NTP as an example, the number of secret bit channels K _s The method is characterized by comprising the steps of determining the total bit number of timestamp data by 64 multiplied by 4 and the length of a message forwarding indication vector, wherein the message forwarding indication vector is designed into a random sequence, and the length of the sequence is determined by actual physical channel bandwidth resources, channel quality and performance requirements on delay attack and timestamp tampering attack suppression. In order to avoid introducing large additional complexity, delay uncertainty and new security risk due to sharing of the message forwarding indication vector between the client and the server, the client key or the truncated sequence thereof can be used as the message forwarding indication vector in combination with the NTS protocol. The length of the client key is 256 bits, and if the client key is used as a message forwarding indication vector, the number K of the secret bit channels can be determined _s Is 512 bits.

Number of public bit channels K _p Determined by the total number of bits in all fields except the timestamp field in the NTP packet.

The number K of channel bits should satisfy K ≧ K _s +K _p The number of the waiting symbols can be set in consideration of transmission efficiency, and can be appropriately larger than the number of information bits actually transmitted in consideration of security.

The total number of bit channels N, which is also the code length of Polar codes, needs to satisfy the following constraints:

wherein W is a given channel, and wherein N =2 ⁿ (ii) a I (W) is the symmetric capacity of channel W;

indicating a rounding down.

Further, the above-mentioned Polar technique may be usedFormula (2) and formula (3) in the related information of the operation characteristics calculate Polar code generating matrix G _N 。

Computing the Bartay-Charier sub-parameters for each bit channel

If W is the BEC channel (deletion probability ε), the parameter->

Can be obtained by recursive calculation, i.e.

/>

Wherein the content of the first and second substances,

parameter->

Equaling a channel +>

The deletion probability of (2).

Among the Barattacharyya (Bhattacharyya) parameters of N bit channels, K minimum ones are selected

The corresponding index constitutes the information bit channel index set +>

Is at>

In selecting K _p The smallest->

The corresponding index constitutes a public information bit channel index set +>

Selection of K _s Maximum->

The corresponding index constitutes a set of secret information bit channel indices +>

The bit channels corresponding to the rest indexes can be reserved for other necessary information bit transmission which is not mentioned in the invention; />

The complement of (4) is recorded as>

To freeze a set of bit channel indices, the corresponding bit channel is used to transmit the frozen vector.

According to index set

And & ->

Extracting the generator matrix G _N Corresponding row of, generating a sub-matrix

And &>

A secret information bit vector is formed by the timestamp data bit and the message forwarding indication vector and is marked as u _s (ii) a Other message fields form a public information bit vector, denoted as u _p (ii) a Frozen vector set toZero vector, is

The codeword after Polar encoding of the original time synchronization packet->

Is composed of

After the first coding sequence is obtained in step S103, constellation modulation may be performed on bits in the first coding sequence to obtain a symbol vector.

For code word

Performing constellation modulation to obtain a symbol vector>

Wherein N is _c The number of OFDM data subcarriers required for transmitting a time synchronization message.

Where k is a modulation symbol vector

The index of (2); x is a radical of a fluorine atom _k,m The index is the bit of the code word which is mapped into the k modulation symbol, and m is the index of the code word; />

A constellation modulation function is referred to; l is the modulation order, e.g. with BPSK modulation, l =1. If QPSK modulation is used, l =2.

In step S104, all data subcarriers within the transmission bandwidth range are divided into a plurality of sub-blocks according to the number of legal receiving ends, each sub-block is divided to obtain a plurality of clusters, each cluster is IM-modulated, and an active subcarrier index of each cluster is determined.

Wherein, the dividing each sub-block to obtain a plurality of clusters includes: acquiring the number of sub-links included in an actual transmission link from a sending end to a receiving end in a network; determining a number of clusters based on the number of sublinks; and dividing each subblock according to the number of the clusters to obtain a plurality of clusters, wherein a specific number of clusters are reserved for link safety information transmission, and the rest clusters are used for transmitting time synchronization message data. Correspondingly, performing IM modulation on each cluster, and determining an active subcarrier index of each cluster, includes: numbering a plurality of clusters of each subblock respectively, wherein IM data of each numbered cluster bear different information, the IM data of the first 3 clusters bear a sending end identification code, a receiving end identification code and the numbers of all sublinks contained in a preset route respectively, the IM data of the subsequent rest clusters bear channel simulation system indicating data of the sublinks respectively, and the sublink information simulation system indicating data are used for indicating the numbers and the passing sequence of the channel simulation systems which the time synchronization message needs to pass through on the sublinks; and performing IM modulation on each cluster according to the information to be carried by each cluster, and determining the active subcarrier index of each cluster.

In particular, considering all the working modes defined by the NTP, PTP protocol, from the perspective of message transmission, two basic modes are involved, namely one-to-one and one-to-many, unicast and broadcast. The difference between the two is that one legal receiving end or a plurality of legal receiving ends.

The invention regards unicast as a special form of broadcast. Without loss of generality, consider one sender and η receivers. If unicast, η =1; broadcast, then η>1. In step S103, N is occupied by the time synchronization message sent to each receiving end _c A data sub-carrier.

All data subcarriers N contained in one OFDM-IM symbol _D Dividing into eta sub-blocks, one sub-block being used for transmitting a time synchronization message to a legal receiving end R _i (i is more than or equal to 1 and less than or equal to eta). Each sub-block divisionN _g,j A plurality of clusters, each cluster containing n _i And (1) each data subcarrier (i is more than or equal to 1 and less than or equal to eta). N is a radical of hydrogen _g,j Equal to R from the sending end to the receiving end in the network _i The number of sub-links included in the actual transmission link (predetermined route) (considering the switching devices such as switches, routers, and repeaters in the network, all the links from the sending end to the switching device, from the switching device to the switching device, and from the switching device to the receiving end are sub-links) is added by 3.N is a radical of _g,j In each cluster, the first 3 clusters are reserved for link safety information transmission, and the rest clusters are used for transmitting message data. Considering time synchronization message transmission requirements, requirement (N) _g,j -3)·n _i >N _c (1≤i≤η)。

N of each sub-block _g,j The serial numbers of the clusters are 1,2, … and N _g,j . An IM data bearer sender identifier code (pre-allocated, unique in system) of the cluster numbered 1, an IM data bearer receiver identifier code (pre-allocated, unique in system) of the cluster numbered 2, and IM data bearer routing information, i.e., 1 st to nth routing information, of the cluster numbered 3 _g,j Sub-link numbers (pre-assigned, uniquely identifying each sub-link in the network) for 3 sub-links, numbered 4 to N _g,j In total of N _g,j 3 clusters corresponding to 1 st, 2 nd, … …, jth to Nth of the actual transmission link _g,j The IM data of the 3 sub-links carries sub-link channel simulation system indication data, which is used to indicate the number (pre-assigned, different channel simulation system numbers, different corresponding transfer functions) and the sequence (passing through in the sequence of numbers) of the channel simulation system that the time synchronization message needs to pass through on the sub-link. In accordance with the above design, the active subcarrier index for each cluster is determined

(1≤j≤N _g,j ,1≤p _j,i <n _i )。

In the embodiment, a plurality of frequency selective Rayleigh channel simulation systems with transfer functions H are required to be pre-deployed on all physical sublinks in the network _j,v (4≤j≤N _g,i V is more than or equal to 1 and less than or equal to r) is shown as formula (17), and r is the number of channel simulation systems deployed on a certain sub-link. The channel simulation system on the sublinks corresponding to the subblocks i and the cluster j only acts on n of the cluster _i A data subcarrier. The first 3 clusters of each sub-block do not experience any channel simulation system.

In step S105, the symbol vector may be interleaved based on the total frequency domain channel matrix characteristic of a preset channel simulation system, an active subcarrier index carrying the symbol vector is determined, then OFDM-IM modulation is performed based on step S106, and the obtained OFDM-IM signal is sent to each legal receiving end in step S107.

In one embodiment, the interleaving the symbol vectors and determining the indexes of the active subcarriers carrying the symbol vectors based on the total frequency domain channel matrix characteristics of the preset channel simulation system includes: determining a total frequency domain channel matrix of each channel simulation system based on a transfer function preset for each channel simulation system; calculating the channel gain of each active sub-carrier in each sub-block added by the channel simulation system based on the total frequency domain channel matrix of the channel simulation system; interleaving the symbol vectors based on channel gains of the active subcarriers, and determining an index of the active subcarriers carrying the symbol vectors. Further, modulating the interleaved symbol vector to an active subcarrier selected by each sub-block to complete OFDM-IM modulation, and obtaining an OFDM-IM signal, including: determining the noise vector length of each sub-block based on the symbol vector length and the number of active sub-carriers of each sub-block, and generating the noise vector; generating a frequency domain vector based on the link security information vector, the message data symbol vector and the noise vector; and generating a time domain vector based on the frequency domain vector, and carrying out OFDM-IM modulation based on the frequency domain vector and the time domain vector to obtain an OFDM-IM signal.

In the signal transmission process, each channel simulation system and each exchange device process OFDM-IM signals according to a special link working mechanism. And the legal receiving end carries out OFDM demodulation, IM demodulation, generation of a total frequency domain channel matrix of a channel simulation system, de-interleaving, constellation demodulation and Plour decoding on the received OFDM-IM signal. And judging the message transmission safety according to the bit error rate of the message forwarding indication vector.

Specifically, before sending a time synchronization message each time, a sending end determines in advance a route to each receiving end, a channel simulation system to be traveled by the message on each sub-link, and a travel sequence. The link diagram is shown in fig. 7.

In the embodiment of the present invention, it is assumed that the channel simulation system and the intermediate device on all the sublinks are trusted and are connected through the dedicated link to form an independent security net, which is shielded from all the terminals. The channel simulation systems deployed on the various links, and the channel simulation systems and the switching equipment can communicate through dedicated links. The dedicated link communication frame structure is shown in fig. 8. Each legal receiving end corresponds to a special link communication frame, the first 2 fields of each frame respectively bear the identification codes of the sending end and the legal receiving end, and then each subframe is formed. Each subframe corresponds to one sublink, subframe 1 corresponds to a first sublink, subframe 2 corresponds to a second sublink, … …, and so on. The subframe consists of 4 fields, the first field carries a sub-link number, and the mapping relation between each sub-link and an actual sub-link is specified; the 2 nd and 3 rd fields respectively bear the current sending equipment number and the destination equipment number of the frame, and may be a channel simulation system or a switching device; the 4 th field carries the serial number and the sequence of the channel simulation system that the time synchronization message needs to go through on the sub-link.

The method comprises the steps that a sending end firstly sends a time synchronization message to a first channel simulation system, after the first channel simulation system receives an OFDM-IM signal, channel equalization is carried out on the signal according to a channel estimation result in an earlier stage (channel estimation between each device and adjacent devices can be carried out periodically), IM data of a corresponding subblock are demodulated, and a sending end identification code, a receiving end identification code, each sublink number and a sublink channel simulation system number and sequence through which each sublink needs to pass are obtained. The first channel simulation system generates a dedicated link communication frame based on the above information while applying frequency selective fading to the OFDM-IM signal. After the processing is finished, the special link communication frame ( fields 2 and 3 of the subframe 1) is updated according to the IM information, and the special link communication frame and the OFDM-IM signals are sent to a second channel simulation system.

The second channel simulation system receives the dedicated link communication frame and the OFDM-IM signal, and records the arrival times of the dedicated link communication frame and the OFDM-IM signal, respectively. And according to the result of the channel estimation in the previous period, carrying out channel equalization on the OFDM-IM signal, demodulating IM data corresponding to the first 2 clusters of the subblocks, and comparing the demodulated IM data with the identification code of the transmitting end and the identification code of the receiving end of the special link communication frame. If the time difference of arrival of the dedicated link communication frame and the OFDM-IM signal is not over-limit, the OFDM-IM signal is judged to be normal, and frequency selective fading is applied to the OFDM-IM signal. And after the processing is finished, updating the special link communication frame according to the IM information, and sending the special link communication frame and the OFDM-IM signal to a third channel simulation system. The third and subsequent channel simulation systems are handled exactly the same as the second one until they are transmitted to the switching device at the end of the sublink 1. Otherwise, if the identification codes are not consistent, the transmission of the OFDM-IM signals and the communication frames of the special link is stopped; if the special link communication frame is not received, the system is always in a silent state, and the OFDM-IM signal is continuously transmitted on the sub-link; if the OFDM-IM signal is not received, the transmission of the special link communication frame is stopped; if the arrival time difference exceeds the limit, the channel simulation system judges that the signal is abnormal, does not apply frequency selective fading to the OFDM-IM signal, and updates the dedicated link communication frame and directly sends the dedicated link communication frame and the OFDM-IM signal to the switching equipment at the tail end of the sublink 1.

After the exchange equipment at the tail end of the sublink 1 receives the special link communication frame and the OFDM-IM signal (if the special link communication frame is not received, the OFDM-IM signal transmission is terminated, if the OFDM-IM signal is not received, the special link communication frame transmission is terminated), the channel equalization is carried out on the OFDM-IM signal according to the early-stage channel estimation result, the identification codes of a sending end and a receiving end carried by the OFDM-IM signal and the special link communication frame are compared, and if the identification codes are not consistent, the signal transmission is terminated; if the two sub-links are consistent, the frequency selective fading applied by all the channel simulation systems of the sub-link is equalized according to the 4 th field of the sub-frame 1 of the dedicated link communication frame. Normally, the OFDM-IM signal passes through all the preset channel simulation systems of the sublink, and at the switching device at the end, the frequency selective fading influence introduced by the channel simulation systems can be completely equalized. In abnormal conditions, the OFDM-IM signal is directly transmitted to the end switching device without going through all channel simulation systems, and new frequency selective fading will be introduced during the equalization process of the switching device. After the processing of the switching device at the end of the sublink 1 is completed, the dedicated link communication frame ( fields 2 and 3 of the subframe 2) is updated according to the field 1 and the field 4 of the subframe 2 of the dedicated link communication frame, and the dedicated link communication frame and the OFDM-IM signal are sent to the first channel simulation system of the sublink 2. The processing process of the sub-link 2 and the subsequent sub-links is the same as that of the sub-link 1 until the last channel simulation system before the transmission to the legal receiving end.

After receiving the special link communication frame and the OFDM-IM signal, the processing process of the last channel simulation system before the legal receiving end and the exchange equipment perform channel equalization on the OFDM-IM signal according to the early-stage channel estimation result, compare the sending end identification code and the receiving end identification code carried by the OFDM-IM signal and the special link communication frame, and terminate signal transmission if the sending end identification code and the receiving end identification code are inconsistent; if they are consistent, the sub-frame N is communicated according to the special link communication frame _g,i And 4 th field of-3, which is used for equalizing the frequency selective fading applied by all channel simulation systems of the sublink. And after the processing is finished, sending the OFDM-IM signal to a legal receiving end according to the identification code of the receiving end.

In the above safety mechanism, except for the first channel simulation system and the last channel simulation system, the processing procedures of the other channel simulation systems are the same; the process is the same for all switching devices.

The deployment of the channel simulation system and the design of the working mechanism of the channel simulation system in the embodiment of the invention aim to control the frequency selectivity between the OFDM-IM signal (legal signal) transmitted by the legal main channel and the OFDM-IM signal (illegal signal) transmitted by the illegal lapping channel, thereby controlling the equivalent signal-to-noise ratio. The reasonable degradation of the channel capacity of the illegal tap channel is realized on the premise of not influencing the capacity of the legal main channel.

In the OFDM-IM modulation process, the data subcarrier channel gain determined by the channel simulation system in each sub-block is calculated according to a predetermined routing and channel simulation system scheme (it should be noted that, in the embodiment of the present invention, the actual physical channel is not considered, and the influence of the actual physical channel is removed in the channel equalization performed by each stage of equipment), as shown in formulas (18) and (19).

In the formula, H _Ri The fingers correspond to legitimate receivers R _i Of the sub-blocks of the channel simulation system total frequency domain channel matrix, H _n,Ri Is H _Ri The nth diagonal element of (a); r is _j Simulating the number of systems for the channel experienced by the jth cluster of the sub-block; the other symbols have the same meanings as above.

Refers to the transmission of OFDM-IM symbols from a transmitting end to a receiving end R _i In the process at N _g,i -total transfer function of the channel simulation system experienced on 3 sub-links.

In the formula (I), the compound is shown in the specification,

to correspond to a legal receiver R _i The index of the jth cluster of the subblock is q _j Channel gain of active subcarriers (determined only by the channel simulation system); q _j,i The active subcarrier index set for the jth cluster of the sub-block is determined in step S104.

Taking subblocks as a unit, active subcarriers of the first 3 clusters are specially used for bearing link safety information, and the rest clusters areAll of (2)

The channel gains of the active sub-carriers are ordered from high to low, using the first N _c The constellation symbol vector ≥ in the highest-gain active subcarrier modulation step S103>

This process may be equivalent to interleaving. Here, to distinguish different sub-blocks, the constellation symbol vector is denoted as &>

And has->

Remaining->

The active subcarriers can modulate noise according to actual needs; or pseudo constellation symbols are modulated, and the symbols do not carry information, so that the purpose of confusing an illegal receiving end can be achieved, and the illegal receiving end cannot judge which are normal message data symbols and which are pseudo data symbols.

Take the modulation noise vector as an example. Recording the Gaussian white noise vector modulated in the residual active subcarrier of each subblock as

Its single-sided power spectral density is N ₀ The one-dimensional probability density function is shown in equation (20). After the noise vector is modulated, from the time domain perspective, the data symbols of the normal message are mixed with white noise transmission, even the transmission is submerged in the white noise, and an attacker can hardly recognize and intercept the processed time synchronization message.

In the formula, mu _n As a mean value, μ is usually taken _n ＝0；σ _n ² Is the variance, when the mean value μ _n At 0, the average power of the noise is equal to the variance σ _n ² 。

The frequency domain vector generated according to the above algorithm is shown in equation (21).

In the formula (I), the compound is shown in the specification,

the method comprises a link safety information vector, a message data symbol vector, a Gaussian white noise vector and a zero vector (the non-modulated data vector of the non-active sub-carrier is embodied as the zero vector).

Determining the number N of IFFT points in OFDM modulation _IFFT And generating a complete frequency domain vector. To be able to employ an efficient radix-2-IFFT, N _IFFT It needs to be an integer power of 2. Meanwhile, the suppression of the out-of-band scattering is considered,

N _IFFT >N _D . Definition of N _IFFT Sub-carriers other than the N _D The subcarriers except the data subcarrier are virtual subcarriers, and the number N of the virtual subcarriers _x ＝N _IFFT -N _D The data carried is zero, and is distributed on both sides of the data subcarrier. After considering the virtual sub-carriers, the complete frequency domain vector

As shown in equation (22).

Vector the frequency domain

Performing serial-to-parallel conversion, performing IFFT conversion and parallel-to-serial conversion to obtain N _IFFT Time domain vector of points &>

For time domain vector

Insertion of N _cp Cyclic prefix of point, get N _OFDM ＝(N _OFDM +N _IFFT +N _cp ) Point OFDM-IM modulation vector ≧>

N _cp The value of (a) can be set according to the total frequency domain channel matrix (considering the actual physical channel and each channel simulation system).

OFDM-IM signal

Via each main channel W _R To each legal receiver R _i (1 ≦ i ≦ η), and will be pre-designed to traverse several levels of channel modeling systems on each sublink during transmission.

Will be the main channel W _R Is expressed as

In the case of a temporal attack scenario,

may also be attacked E _k (the number of attackers is unknown, k may be equal to 1 or greater than 1) interception, tampering and forwarding, where the transmission channel via which it is based is taken on the pickup channel->

Let the channel output vector of the attacker side be recorded as

The Gaussian white noise vector in the time synchronization message reduces the probability of identifying and intercepting the time synchronization message by an attacker to a certain extent. Even if the signal is successfully intercepted and forwarded, under the safety mechanism designed by the algorithm, the forwarding will probably cause the transmission of the OFDM-IM signal to be terminated, an illegal signal cannot reach a legal receiving end, or the time difference between the OFDM-IM signal and a special link communication frame reaching a next-stage channel simulation system exceeds the limit, so that additional frequency selective fading is introduced at the position of the sublink switching equipment; or in the case of missing dedicated link communication frames, the data goes through each channel simulation system and the switching device, so that the switched device terminates transmission and cannot reach a legal receiving end. For a legal receiving end R _i Record the illegal tap channel output vector as

Receiving end R _i For received signal (

Or->

) After CP removal, serial-to-parallel conversion and FFT conversion, IM demodulation is carried out on the sub-block i, and then each sub-link channel simulation system which the signal passes through is determined according to IM data. Calculating the total frequency domain channel matrix H of the channel simulation system of the sub-block according to the transfer function of each sub-link channel simulation system which the signal passes through _Ri As shown in equation (18).

If received is a normal signal

In the signal transmission process, each channel simulation system and the switching equipment balance the frequency selective fading introduced by the actual physical channel and the channel simulation system, so that the receiving end R _i After FFT transformation, the signal energy can be directly detected by detecting the subcarrierIM demodulation is carried out to obtain a correct frequency domain channel matrix H _Ri . Then according to H _Ri The channel gain of the active sub-carrier is calculated (as shown in formula (19)), and after the gain is sequenced, the correct message data symbol position and sequence (de-interleaving) can be obtained.

If an illegal signal is received

Safety mechanism according to the invention>

One or a plurality of clusters in the system are bound to have frequency selective fading, and the frequency selective fading causes a receiving end R _i When IM demodulation is performed, erroneous judgment occurs, and erroneous IM data is obtained. Erroneous IM data will indicate the erroneous channel simulation system number, such that R _i The correct frequency domain channel matrix H cannot be obtained _Ri And thus cannot be deinterleaved correctly.

After de-interleaving, performing parallel-to-serial conversion, message data symbol extraction and constellation demodulation on the frequency domain vector of the subblock to obtain a corresponding Polar codeword sequence

Or>

When legal receiving end R _i After receiving the OFDM-IM signal modulated by the transmitting end through Polar coding, a target channel simulation system and OFDM-IM, the receiving end needs to demodulate and decode the signal to obtain data of the time synchronization message, and it should be noted that the receiving end processes the received OFDM-IM signal of the transmitting end, and the receiving end performs reverse processing on the OFDM-IM signal generated by the transmitting end.

Specifically, the legal receiving end R _i Using SC decoder to receive vector: (

Or->

) And decoding is carried out. Based on the polarization characteristic of Polar codes and the performance difference between a legal main channel and an illegal tapping channel which are artificially constructed, the polarization characteristic of Polar codes is combined with the performance difference of the illegal main channel and the performance difference of the illegal tapping channel, and the polarization characteristic of Polar codes is combined with the performance difference of the illegal tapping channel>

After decoding, the secret information bit has a lower error rate; if the data packet is maliciously forwarded by an attacker (corresponding codeword sequence)

) The message forwarding indication vector will have a higher error rate. Therefore, a proper error rate threshold value can be set according to the quality of the actual legal main channel, the error rate of the message forwarding indication vector is detected packet by packet, when the error rate of the indication vector is greater than or equal to the threshold value, the data packet is considered to be forwarded by an attacker, and the data packet is discarded; otherwise, the data packet is considered not to be attacked by the forwarding class, and the data packet is accepted, as shown in equation (23).

In the formula u _d Indicating a message forwarding indication vector; u. of _di Refers to the ith bit of the message forwarding indication vector,

is an estimated value thereof; />

The bit quantity of error codes in the message forwarding indication vector is indicated; num (u) _d ) Indicating the total bit number of the message forwarding indication vector; and E is the set bit error rate threshold value.

The security strategy leads the bit channel quality (binary symmetric capacity or Bhattacharyya parameter) after polarization corresponding to a legal main channel to be basically unaffected by introducing Polar coding, OFDM-IM modulation, a sub-link channel simulation system and message data symbol interleaving based on a channel simulation system transfer function, and the bit channel with higher original channel quality corresponding to a considerable part of an illegal connecting channel is degraded into a bit channel with poorer channel quality, thereby greatly improving the security rate, solving the limitation in the aspect of the channel quality difference between the legal main channel and the illegal connecting channel, and expanding the application range of the method to any channel scene.

It should be noted that, in the embodiment of the present invention, on the basis of Polar coding and decoding, at the sending end and the legal receiving end R _i When the transmitted OFDM-IM signal cannot pass through the subsequent sublink channel simulation system chain due to interception and forwarding of an attacker, an equalization function at the side of the switching equipment is not matched with a transfer function of the channel simulation system actually passed by the signal, so that extra frequency selective fading is introduced into a corresponding cluster to cause errors of IM demodulation and de-interleaving at a receiving end, the constellation demodulation error rate is greatly increased, which is equivalent to reducing the signal-to-noise ratio of each application of a physical channel in a pure Polar coding and decoding system, thereby causing the channel quality of a considerable part of polarization bit channels with good channel quality to be degraded, and improving the system safety rate.

In the embodiment of the invention, polar codes are related to channels, through OFDM-IM modulation and demodulation, polar code words are equivalent to a physical channel which passes through binary input and binary output, the channel can be modeled as a BSC channel, the transition probability of the BSC channel is determined by the error rate of constellation demodulation, and the error rate can be determined in advance through experiments, so that the Polar codes can be constructed.

When the physical channel environment is severe and the channel state response changes rapidly with time, in order to ensure the transmission quality of the time synchronization data message, it may be considered to insert pilot frequencies (pilot frequency patterns are predetermined) at specific positions of the OFDM-IM subblocks, and the OFDM-IM modulation of the message data symbols is still performed according to the above description. Each channel simulation system and each switching device perform channel estimation, interpolation and physical channel equalization by means of pilot frequency, and inhibit the increase of the demodulation error rate of time synchronization message data symbols brought by physical channel distortion. Each channel simulation system does not act on the pilot symbols, i.e. the pilot symbols are guaranteed to reflect the situation of the real physical channel.

The network time synchronization message transmission method applied to any channel provided by the embodiment of the invention can effectively inhibit message delay attack and timestamp tampering attack; unicast and broadcast oriented transmission modes; the method can effectively inhibit a single or a plurality of attackers, external attackers and internal attackers in the network, and ensures the safety of time message transmission from a physical layer; polar coding and decoding, OFDM-IM modulation and demodulation, signal processing of a channel simulation system and switching equipment and a special link working mechanism all have lower complexity and smaller processing time delay, and the physical layer of the switching equipment directly realizes the control of the route, thereby avoiding the storage of a route table and the table look-up of an upper layer and having little influence on the time synchronization precision; independent of system time synchronization; and the method is compatible with the current NTP and PTP security mechanisms. Meanwhile, the working scene limitation of the network time synchronization message safety transmission method is broken through, namely the wireless network synchronous transmission method can work in wired and wireless network environments, and the difference of the channel quality of a legal main channel and an illegal connecting channel is not required.

Correspondingly, an embodiment of the present invention further provides a schematic structural diagram of a network time synchronization packet transmission apparatus applied to an arbitrary channel environment of a sending end, and referring to fig. 9, the apparatus may include:

a classifying unit 901, configured to classify data bits of a time synchronization packet to be transmitted, so as to obtain public information bits and secret information bits;

polar coding unit 902, configured to perform Polar coding on data bits of the time synchronization packet based on the public information bits and the secret information bits to obtain a first coding sequence;

a constellation modulation unit 903, configured to perform constellation modulation on the first coding sequence to obtain a symbol vector;

a first determining unit 904, configured to divide all data subcarriers within a transmission bandwidth range into a plurality of sub-blocks according to the number of legal receiving ends, divide each sub-block to obtain a plurality of clusters, perform IM modulation on each cluster, and determine an active subcarrier index of each cluster;

a second determining unit 905, configured to interleave the symbol vector based on a total frequency domain channel matrix characteristic of a preset channel simulation system, and determine an index of an active subcarrier carrying the symbol vector;

an OFDM modulation unit 906, configured to modulate the interleaved symbol vector onto an active subcarrier selected by each sub-block to complete OFDM-IM modulation, so as to obtain an OFDM-IM signal;

a signal transmitting unit 907, configured to transmit the OFDM-IM signal to each of the legal receiving ends.

Optionally, the apparatus further comprises:

a third determining unit, configured to determine an information bit channel, where the information bit channel includes a secret bit channel and a public bit channel, where the secret bit channel is used to transmit the secret information bits, the public bit channel is used to transmit the public information bits, and a sum of the information bit channel and the frozen bit channel is a total bit channel;

a fourth determining unit, configured to determine an information bit channel index set, a public bit channel index set, a secret bit channel index set, and a frozen bit channel index set based on the baryta curie sub-parameter of each bit channel in the total bit channels.

Optionally, the Polar encoding unit comprises:

the first generating subunit is used for generating a Polar code generating matrix;

the extraction subunit is used for extracting corresponding rows of the generated matrix according to each index set to obtain each submatrix, wherein each index set comprises an information bit channel index set, a public bit channel index set, a secret bit channel index set and a frozen bit channel index set;

and the coding subunit is used for carrying out Polar coding on the data bits of the time synchronization message based on the secret information bit vector corresponding to the secret information bit and the message forwarding indication vector, the public information bit vector corresponding to the public information bit, the freezing vector and each submatrix to obtain a first coding sequence.

Optionally, the first determining unit includes a sub-block sub-dividing unit, configured to divide each sub-block to obtain a plurality of clusters, where the sub-block sub-dividing unit is specifically configured to:

acquiring the number of sub-links included in an actual transmission link from a sending end to a legal receiving end in a network;

determining a number of clusters based on the number of sublinks;

and dividing each sub-block according to the number of the clusters to obtain a plurality of clusters, wherein a specific number of clusters are reserved for link safety information transmission, and the rest clusters are used for transmitting time synchronization message data.

Correspondingly, the first determining unit further includes an IM modulation subunit, configured to perform IM modulation on each cluster, and determine an active subcarrier index of each cluster, where the IM modulation subunit is specifically configured to:

numbering a plurality of clusters of each subblock respectively to enable IM data of each numbered cluster to bear different information, wherein the IM data of the first 3 clusters bear a sending end identification code, a receiving end identification code and the numbers of all sublinks contained in a preset route respectively, the IM data of the rest clusters bear channel simulation system indicating data of the sublinks respectively, and the channel simulation system indicating data of the sublinks are used for indicating the numbers and the passing sequence of a channel simulation system which a time synchronization message needs to pass through on the sublink;

and performing IM modulation on each cluster according to the information to be carried by each cluster, and determining the active subcarrier index of each cluster.

Optionally, the second determining subunit is specifically configured to:

determining a total frequency domain channel matrix of each channel simulation system based on a transfer function preset for each channel simulation system;

calculating the channel gain of each active sub-carrier in each sub-block added by the channel simulation system based on the total frequency domain channel matrix of the channel simulation system;

interleaving the symbol vectors based on the channel gains, and determining active subcarrier indexes carrying the symbol vectors.

Optionally, the OFDM modulation unit is specifically configured to:

determining the noise vector length of each sub-block based on the symbol vector length and the number of active sub-carriers of each sub-block, and generating a noise vector;

generating a frequency domain vector based on the link security information vector, the message data symbol vector and the noise vector;

generating a time domain vector based on the frequency domain vector;

and carrying out OFDM-IM modulation based on the frequency domain vector and the time domain vector to obtain an OFDM-IM signal.

Optionally, the apparatus further comprises:

and the first processing unit is used for processing the OFDM-IM signals by each channel simulation system and each switching device in the transmission process based on a dedicated link working mechanism in the signal transmission process.

Optionally, the apparatus further comprises:

and the second processing unit is used for responding to the reception of the OFDM-IM signal by a legal receiving end, processing the OFDM-IM signal based on a reverse processing mode matched with the generation processing mode of the OFDM-IM signal, and obtaining the time synchronization message, wherein the reverse processing mode at least comprises OFDM demodulation, IM demodulation, generation of a total frequency domain channel matrix of a channel simulation system, deinterleaving, constellation demodulation, pline decoding and message transmission safety judgment according to the error rate of a message forwarding indication vector.

Based on the foregoing embodiments, an embodiment of the present invention further provides a storage medium, where the storage medium stores executable instructions, and the instructions, when executed by a processor, implement the network time synchronization packet transmission method applied to any channel environment as described in any one of the above.

An embodiment of the present invention further provides an electronic device, including:

a memory for storing a program;

a processor, configured to execute the program, where the program is specifically configured to implement the network time synchronization packet transmission method applied to any channel environment as described in any one of the above.

In the present specification, the embodiments are described in a progressive manner, each embodiment focuses on differences from other embodiments, and the same and similar parts among the embodiments are referred to each other. The device disclosed by the embodiment corresponds to the method disclosed by the embodiment, so that the description is simple, and the relevant points can be referred to the method part for description.

The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims (10)

1. A network time synchronization message transmission method applied to any channel environment is characterized by comprising the following steps:

classifying data bits of a time synchronization message to be transmitted to obtain public information bits and secret information bits;

performing Polar coding on data bits of the time synchronization message based on the public information bits and the secret information bits to obtain a first coding sequence;

carrying out constellation modulation on the first coding sequence to obtain a symbol vector;

dividing all data subcarriers in a transmission bandwidth range into a plurality of subblocks according to the number of legal receiving ends, dividing each subblock to obtain a plurality of clusters, performing IM modulation on each cluster, and determining the active subcarrier index of each cluster;

interleaving the symbol vectors based on the total frequency domain channel matrix characteristics of a preset channel simulation system, and determining active subcarrier indexes for bearing the symbol vectors;

modulating the interleaved symbol vectors to active subcarriers selected by each subblock to complete OFDM-IM modulation and obtain OFDM-IM signals;

and sending the OFDM-IM signal to each legal receiving end.

2. The method of claim 1, further comprising:

determining an information bit channel, wherein the information bit channel comprises a secret bit channel and a public bit channel, the secret bit channel is used for transmitting the secret information bits, the public bit channel is used for transmitting the public information bits, and the sum of the information bit channel and the frozen bit channel is a total bit channel;

determining an information bit channel index set, a public bit channel index set, a secret bit channel index set, a frozen bit channel index set based on the bartacurie sub-parameters of each bit channel in the total bit channels.

3. The method according to claim 2, wherein said performing Polar coding on data bits of said time synchronization packet based on said public information bits and said secret information bits to obtain a first coding sequence comprises:

generating a Polar code generating matrix;

extracting corresponding rows of the generated matrix according to each index set to obtain each submatrix, wherein each index set comprises an information bit channel index set, a public bit channel index set, a secret bit channel index set and a frozen bit channel index set;

and performing Polar coding on the data bits of the time synchronization message based on the secret information bits and the secret information bit vector corresponding to the message forwarding indication vector, the public information bit vector corresponding to the public information bits, the frozen vector and each submatrix to obtain a first coding sequence.

4. The method of claim 1, wherein the dividing each sub-block into a plurality of clusters comprises:

acquiring the number of sub-links included in an actual transmission link from a sending end to a legal receiving end in a network;

determining a number of clusters based on the number of child links;

and dividing each sub-block according to the number of the clusters to obtain a plurality of clusters, wherein a specific number of clusters are reserved for link safety information transmission, and the rest clusters are used for transmitting time synchronization message data.

5. The method of claim 4, wherein performing IM modulation on each cluster and determining the active subcarrier index of each cluster comprises:

numbering a plurality of clusters of each subblock respectively to enable IM data of each numbered cluster to bear different information, wherein the IM data of the first 3 clusters bear a sending end identification code, a receiving end identification code and the numbers of all sublinks contained in a preset route respectively, the IM data of the rest clusters bear channel simulation system indicating data of the sublinks respectively, and the channel simulation system indicating data of the sublinks are used for indicating the numbers and the passing sequence of a channel simulation system which a time synchronization message needs to pass through on the sublink;

and performing IM modulation on each cluster according to the information to be carried by each cluster, and determining the active subcarrier index of each cluster.

6. The method of claim 5, wherein the interleaving the symbol vectors and determining the indexes of active subcarriers carrying the symbol vectors based on the total frequency domain channel matrix characteristics of a preset channel simulation system comprises:

determining a total frequency domain channel matrix of each channel simulation system based on a transfer function preset for each channel simulation system;

calculating the channel gain of each active sub-carrier in each sub-block added by the channel simulation system based on the total frequency domain channel matrix of the channel simulation system;

interleaving the symbol vectors based on the channel gains, and determining active subcarrier indexes carrying the symbol vectors.

7. The method of claim 6, wherein modulating the interleaved symbol vectors onto selected active subcarriers of each sub-block to perform OFDM-IM modulation to obtain an OFDM-IM signal comprises:

determining the noise vector length of each sub-block based on the symbol vector length and the number of active sub-carriers of each sub-block, and generating a noise vector;

generating a frequency domain vector based on the link security information vector, the message data symbol vector and the noise vector;

generating a time domain vector based on the frequency domain vector;

and carrying out OFDM-IM modulation based on the frequency domain vector and the time domain vector to obtain an OFDM-IM signal.

8. The method of claim 1, further comprising:

in the signal transmission process, each channel simulation system and each switching device in the transmission process the OFDM-IM signals based on a special link working mechanism.

9. The method of claim 1, further comprising:

responding to a legal receiving end to receive the OFDM-IM signal, processing the OFDM-IM signal based on a reverse processing mode matched with a generation processing mode of the OFDM-IM signal to obtain the time synchronization message, wherein the reverse processing mode at least comprises OFDM demodulation, IM demodulation, generation of a total frequency domain channel matrix of a channel simulation system, de-interleaving, constellation demodulation, pline decoding and message transmission safety judgment according to an error rate of a message forwarding indication vector.

10. A network time synchronization packet transmission apparatus applied to an arbitrary channel environment, the apparatus comprising:

the classification unit is used for classifying data bits of the time synchronization message to be transmitted to obtain public information bits and secret information bits;

a Polar coding unit, configured to perform Polar coding on data bits of the time synchronization packet based on the public information bits and the secret information bits to obtain a first coding sequence;

the constellation modulation unit is used for carrying out constellation modulation on the first coding sequence to obtain a symbol vector;

the first determining unit is used for dividing all data subcarriers in a transmission bandwidth range into a plurality of subblocks according to the number of legal receiving ends, dividing each subblock to obtain a plurality of clusters, performing IM modulation on each cluster, and determining the active subcarrier index of each cluster;

a second determining unit, configured to interleave the symbol vector based on a total frequency domain channel matrix characteristic of a preset channel simulation system, and determine an index of an active subcarrier carrying the symbol vector;

an OFDM modulation unit, which is used for modulating the symbol vector after interleaving to the active sub-carrier selected by each sub-block to complete OFDM-IM modulation and obtain an OFDM-IM signal;

and the signal sending unit is used for sending the OFDM-IM signal to each legal receiving end.

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