A continuous phase modulation secure communication method and system

Abstract

This invention relates to a continuous phase modulation secure communication method and system. The communication system of this invention communicates in time slots and employs a combined transmitting and receiving communication device capable of obtaining accurate time synchronization. The method is as follows: First, the communication delay between the transmitting and receiving parties is estimated; then, based on the current time information obtained by the transmitting device, the set time slot length, and the one-way transmission delay between the transmitting and receiving devices, a randomization seed for the time slot is set, and waveform coefficients such as the transmission rate of the original symbol in the time slot, the truncation position and length of the spread spectrum pseudo-random sequence, and the periodic dwell time of the spread spectrum pseudo-random sequence chip are randomized; the original symbol is spread spectrum modulated, and then subjected to a novel continuous phase modulation; finally, the receiving device modulates the received signal, and then generates waveform coefficients consistent with those of the transmitting device based on the obtained current time information, despreads the demodulated signal, recovers the original symbol, and realizes keyless transmission of information.

Description

Technical Field

[0001] This invention belongs to the field of physical layer secure communication technology, specifically relating to a keyless, novel continuous phase modulation secure communication method and system. Background Technology

[0002] Security is a crucial indicator for evaluating the performance of a communication system. Secure communication refers to ensuring reliable communication between legitimate users while preventing unauthorized eavesdropping on their communications. Physical layer security encompasses two aspects: firstly, the use of encryption, perturbation, and anti-interference techniques on open air interface signals to conceal signal characteristics and ensure secure transmission, thereby reducing the probability of interception; secondly, leveraging the rich and unique "fingerprint" characteristics of wireless channels for key distribution, enhanced authentication, and security enhancement design of upper-layer security systems. In low-probability-of-interception (LPI) communication systems, spread spectrum and continuous phase modulation techniques are commonly used to hide information. However, conventional spread spectrum techniques contain repeatable elements, and these signal characteristics can allow unauthorized users to reconstruct the entire signal from fragments. Therefore, random perturbation of the signals transmitted at the physical layer is an effective way to ensure physical layer signal security. This can eliminate inherent waveform characteristics, increase waveform randomness, conceal transmitted signal parameters, and guarantee a low interception rate. Discontinuous phase signals produce more cyclic spectral lines and pulse responses in the spectrum, making their signal characteristics easier for adversaries to identify. Therefore, continuous phase signals are widely used in secure communication systems. However, with the development of blind identification technology, conventional continuous phase modulations, such as MSK and GMSK modulation, can be accurately identified and interfered with. Meanwhile, traditional key encryption technology protects the secure transmission of communication information through encryption algorithms. Specific keys are used to encrypt information, ensuring that the information is transmitted in ciphertext form from sender to receiver, thus improving communication security. When the encryption algorithm is sufficiently complex, the time it takes for an eavesdropper to crack the encryption system will far exceed the validity period of the encrypted signal. However, with the continuous improvement of computing power and the advent of quantum computers, its security is facing increasing challenges, making the key itself a weak link in system security. Summary of the Invention

[0003] Because existing secure communication systems suffer from drawbacks such as easily identifiable signals and easily cracked keys, this invention proposes a keyless, novel continuous phase modulation secure communication method and system. The secure communication method and system proposed in this invention can avoid the problem of key system breaches due to key leakage, and the novel continuous phase modulation method is difficult for adversaries to identify.

[0004] The communication system of the present invention uses equipment with the following characteristics: it combines transmitting and receiving, adopts spread spectrum communication, and has a GPS or Beidou module that can obtain accurate time synchronization.

[0005] The specific technical solution of this invention is as follows:

[0006] A continuous phase modulation secure communication method includes the following steps:

[0007] Step 1: Estimate the communication delay between the sender and receiver to complete time base synchronization;

[0008] Step 2: Based on the current time information obtained by the sending end, the set time slot length, and the one-way transmission delay between the sending and receiving parties, set the randomization seed for the time slot, and randomize the waveform coefficients such as the transmission rate of the original symbol in the time slot, the truncation position and truncation length of the spread spectrum pseudo-random sequence, and the dwell time of the spread spectrum pseudo-random sequence chip period.

[0009] Step 3: Spread spectrum modulation is performed on the original symbols, followed by continuous phase modulation;

[0010] Step 4: The receiving end modulates the received signal, and then generates waveform coefficients consistent with those of the sending end based on the acquired current time information. The demodulated signal is then despread to recover the original symbol, thus realizing keyless transmission of information.

[0011] Preferably, in step one, before the information communication begins, the time t when communication device 1 (i.e., the sending end) sends the synchronization sequence to communication device 2 (i.e., the receiving end) is recorded. send After receiving the synchronization sequence, the receiving part of communication device 2 immediately closes the loop and forwards it to communication device 1 through its transmitting part. Communication device 1 records the time t when it receives the return signal. receive Let the processing delay of the transmitting section of this type of communication equipment be t. e The signal transmission delay in the medium is t. p The processing delay of the receiving part of this type of communication equipment is t. r The total round-trip delay of the signal is t. D The one-way transmission delay is t delay Therefore, the following relationship exists:

[0012] t D =t receive -t send (1)

[0013]

[0014] Preferably, in step two, the information from communication device 1 is communicated in time slots, with a time slot length of t. slot Before transmitting information in each time slot, the transmitting unit determines the current time based on the acquired information and the one-way transmission delay t between the transceiver devices. delayThe randomization seed for the waveform coefficients of the transmitted signal in this time slot is set based on the relationship between the two parameters. The waveform coefficients include the transmission rate of the original symbol, the starting position and truncation length of the spread spectrum pseudo-random sequence, and the dwell time of the spread spectrum pseudo-random sequence chip period. The randomization of the waveform coefficients is detailed below. When t... send <t delay At that time, based on the current time information t send (i.e., the time of the synchronization sequence) serves as the randomization seed for the waveform coefficients of the current time slot, when t send ≥t delay At that time, with As a randomization seed for the waveform coefficients of the current time slot, This is the floor function.

[0015] The binary sequence to be transmitted is converted into quaternary symbols, then serial-to-parallel conversion is performed to split it into I / Q paths. Based on the randomization seed of the current time slot waveform coefficients, the transmission rate R of the randomized original symbols is determined. symbol The symbol period is Suppose that X symbols can be transmitted in the I / Q channels in the current time slot, then

[0016] The starting position P of the spread spectrum pseudo-random sequence is randomized based on the randomization seed of the current time slot waveform coefficients. I With P Q The truncation length M of the spread spectrum pseudo-random sequence and the periodic dwell time S of the spread spectrum pseudo-random sequence chip. Let the lengths of the two complete spread spectrum pseudo-random sequences ISeq and QSeq be L, then 1 ≤ P I ≤L, 1≤P Q ≤L, When P I When M ≤ L, the sequence ISeq is extracted from P. I To P I +M-1 position obtains the spread spectrum pseudo-random sequence Seq1 of path I, when P I When M > L, then the sequence ISeq is extracted from P. I Return to position L and cycle back from 1 to M-L+P. I -1 position obtained. When P Q When M ≤ L, extract the sequence QSeq from P. Q To P Q +M-1 position obtains the spread spectrum pseudo-random sequence Seq2 of the Q path, when P Q When M > L, then the sequence QSeq is extracted from P. Q Recycle back from position L to M-L+P Q -1 position obtained.

[0017] Preferably, in step three, after the waveform coefficients of the current frame are generated, the 1st, 2nd, ..., Xth original symbols of the I-path are XORed with Seq1 to obtain the expanded symbols of the I-path. k (k = 1, 2, 3, ..., MX), the 1st, 2nd, ..., Xth original symbols of the Q-path are XORed with Seq2 to obtain the expanded symbol Q of the Q-path. k Then, Gaussian white noise is filled into the remaining time period at the end of the current time slot, which is insufficient to transmit a single symbol, thus forming the expanded symbol of the entire time slot.

[0018] Phase modulation is applied to the spread symbols. Assuming that each spread symbol in a different time slot contains a fixed m carrier cycles, then the signal carrier frequency... The signal expression is shown in (3):

[0019] s k (t)=cos(2πf c t+θ k (3)

[0020] Where, θ k The symbol modulation phase is represented by the formula shown in (4):

[0021]

[0022] To maintain phase continuity, the modulated signal waveform in equation (3) is changed according to the phase difference between the preceding and following symbols. The modulated signal is then divided into three parts within one symbol period according to equation (5). Figure 2 As shown, the general formula for the new continuous phase modulation can be obtained:

[0023]

[0024] Where, θ k-1 θ k θ k+1 t represents the phase of the previous symbol, the current symbol, and the next symbol, respectively. x t y Let represent the duration of the first part and the third part, respectively. The calculation formulas are shown in equations (6) and (7):

[0025]

[0026] f h f e Let represent the first part carrier frequency and the third part carrier frequency respectively. The calculation formulas are shown in equations (8) and (9):

[0027]

[0028] The corrected phase of the first part is represented by the formula shown in equation (10):

[0029]

[0030] Preferably, in step four, the receiving section of communication device 2 generates an r signal with the same waveform as in equation (5). k (t) is used to demodulate the received signal to obtain the baseband symbol.

[0031] The receiving part of communication device 2 uses the current timing information as the randomization seed of the current time slot to generate waveform coefficients consistent with step two, and despreads the demodulated baseband symbols to recover the original symbols.

[0032] A keyless, novel continuous phase modulation secure communication process has been completed.

[0033] This invention also discloses a continuous phase modulation secure communication system, based on the above method, comprising the following modules:

[0034] Communication delay estimation module: Estimates the communication delay between the sender and receiver;

[0035] Waveform coefficient randomization module: Based on the current time information obtained by the transmitting end, the set time slot length, and the one-way transmission delay between the transmitting and receiving parties, the randomization seed of the time slot is set, and the waveform coefficients such as the transmission rate of the original symbol of the time slot, the truncation position and truncation length of the spread spectrum pseudo-random sequence, and the dwell time of the spread spectrum pseudo-random sequence chip period are randomized.

[0036] Continuous phase modulation module: Spread spectrum modulation is performed on the original symbol, followed by continuous phase modulation;

[0037] Original symbol recovery module: The receiver modulates the received signal and generates waveform coefficients consistent with those of the transmitter based on the acquired current time information. The demodulated signal is then despread to recover the original symbol.

[0038] The beneficial effects of this invention are:

[0039] This invention eliminates the key distribution process for communicating parties, preventing the key system from being compromised due to key theft by eavesdroppers and ensuring the confidentiality of communication. During signal transmission, continuous phase modulation signals have fewer cyclic spectral lines and no impulse response. Furthermore, as a novel continuous phase shift keying method, it is difficult for adversaries to crack, thus improving communication security. Attached Figure Description

[0040] Figure 1 This is a schematic diagram of a preferred embodiment of the time base signal compensation acquisition scheme of the present invention.

[0041] Figure 2 This is a schematic diagram of the time period variable of the modulation symbol in a preferred embodiment of the present invention.

[0042] Figure 3 This is a block diagram of a continuous phase modulation secure communication system according to a preferred embodiment of the present invention. Detailed Implementation

[0043] The present invention will be further described below with reference to the accompanying drawings.

[0044] This embodiment presents a keyless, novel continuous phase modulation secure communication method, applicable to the following... Figure 1-2 The aforementioned communication transceiver system. The specific steps of this embodiment are as follows:

[0045] Step 1: Before information communication begins, record the time t when communication device 1 sends the synchronization sequence to communication device 2. send After receiving the synchronization sequence, the receiving part of communication device 2 immediately closes the loop and forwards it to communication device 1 through its transmitting part. Communication device 1 records the time t when it receives the return signal. receive Let the processing delay of the transmitting section of this type of communication equipment be t. e The signal transmission delay in the medium is t. p The processing delay of the receiving part of this type of communication equipment is t. r The total round-trip delay of the signal is t. D The one-way transmission delay is t delay Therefore, the following relationship exists:

[0046] t D =t receive -t send (1)

[0047]

[0048] Step 2: Communication equipment 1 communicates information in time slots, with a time slot length of t. slot Before transmitting information in each time slot, the transmitting unit determines the current time information obtained by the timing module and the one-way transmission delay t between the transceiver devices. delay The randomization seed for the waveform coefficients of the transmitted signal in this time slot is set based on the relationship between the two parameters. The waveform coefficients include the transmission rate of the original symbol, the starting position and truncation length of the spread spectrum pseudo-random sequence, and the dwell time of the spread spectrum pseudo-random sequence chip period. The specific steps for randomizing the waveform coefficients are detailed below. When t... send <t delay At that time, based on the current time information t send This serves as the randomization seed for the waveform coefficients of the current time slot, when t send ≥t delay At that time, with As a randomization seed for the waveform coefficients of the current time slot, This is the floor function.

[0049] The binary sequence to be transmitted is converted into quaternary symbols, then serial-to-parallel conversion is performed to split it into I / Q paths. Based on the randomization seed of the current time slot waveform coefficients, the transmission rate R of the randomized original symbols is determined. symbol The symbol period is Suppose that X symbols can be transmitted in the I / Q channels in the current time slot, then

[0050] The starting position P of the spread spectrum pseudo-random sequence is randomized based on the randomization seed of the current time slot waveform coefficients. I With P Q The truncation length M of the spread spectrum pseudo-random sequence and the periodic dwell time S of the spread spectrum pseudo-random sequence chip. Let the lengths of the two complete spread spectrum pseudo-random sequences ISeq and QSeq be L, then 1 ≤ P I ≤L, 1≤P Q ≤L, When P I When M ≤ L, the sequence ISeq is extracted from P. I To P I +M-1 position obtains the spread spectrum pseudo-random sequence Seq1 of path I, when P I When M > L, then the sequence ISeq is extracted from P. I Recycle back from position L to M-L+P I -1 position obtained. When P Q When M ≤ L, extract the sequence QSeq from P. Q To P Q +M-1 position obtains the spread spectrum pseudo-random sequence Seq2 of the Q path, when P Q When M > L, then the sequence QSeq is extracted from P. Q Recycle back from position L to M-L+P Q -1 position obtained.

[0051] Step 3: After the waveform coefficients of the current frame are generated, the 1st, 2nd, ..., Xth original symbols of the I-path are XORed with Seq1 to obtain I. k (k = 1, 2, 3, ..., M·X), the 1st, 2nd, ..., Xth primitive symbols of the Q path are XORed with Seq2 to obtain Q. k Then, Gaussian white noise is filled into the remaining time period at the end of the current time slot, which is insufficient to transmit a single symbol, thus forming the expanded symbol of the entire time slot.

[0052] Phase modulation is applied to the spread symbols. Assuming that each spread symbol in a different time slot contains a fixed m carrier cycles, then the signal carrier frequency... The signal expression is shown in (3):

[0053] s k (t)=cos(2πf c t+θ k (3)

[0054] Where, θ k The symbol modulation phase is represented by the formula shown in (4):

[0055]

[0056] To maintain phase continuity, the modulated signal waveform in equation (3) is changed according to the phase difference between the preceding and following symbols. The modulated signal is then divided into three parts within one symbol period according to equation (5). Figure 2 As shown, the general formula for the new continuous phase modulation can be obtained:

[0057]

[0058] Where, θ k-1 θ k θ k+1 t represents the phase of the previous symbol, the current symbol, and the next symbol, respectively. x t y Let represent the duration of the first part and the third part, respectively. The calculation formulas are shown in equations (6) and (7):

[0059]

[0060]

[0061] f h f e Let represent the first part carrier frequency and the third part carrier frequency respectively. The calculation formulas are shown in equations (8) and (9):

[0062]

[0063] The corrected phase of the first part is represented by the formula shown in equation (10):

[0064]

[0065] Step 4: In the receiving section of communication device 2, generate r with the same signal waveform as in equation (5). k (t) is used to demodulate the received signal by performing autocorrelation through a matched filter to obtain the baseband symbol.

[0066] The receiving part of communication device 2 uses the current timing information as the randomization seed of the current time slot to generate waveform coefficients consistent with step two, and despreads the demodulated baseband symbols to recover the original symbols.

[0067] This embodiment of a keyless, novel continuous phase modulation secure communication method has been completed.

[0068] like Figure 3 As shown, this embodiment discloses a continuous phase modulation secure communication system, which, based on the above method embodiment, includes the following modules:

[0069] Communication delay estimation module: Estimates the communication delay between the sender and receiver;

[0070] Waveform coefficient randomization module: Based on the current time information obtained by the transmitting end, the set time slot length, and the one-way transmission delay between the transmitting and receiving parties, the randomization seed of the time slot is set, and the waveform coefficients such as the transmission rate of the original symbol of the time slot, the truncation position and truncation length of the spread spectrum pseudo-random sequence, and the dwell time of the spread spectrum pseudo-random sequence chip period are randomized.

[0071] Continuous phase modulation module: Spread spectrum modulation is performed on the original symbol, followed by continuous phase modulation;

[0072] Original symbol recovery module: The receiver modulates the received signal and generates waveform coefficients consistent with those of the transmitter based on the acquired current time information. The demodulated signal is then despread to recover the original symbol.

[0073] Other aspects of this embodiment can be found in the above method embodiments.

[0074] The above-described embodiments are merely preferred embodiments of the present invention and are not intended to limit the present invention in any way. Other variations and modifications are possible without exceeding the technical solutions described in the claims.

Claims

1. A continuous phase modulation secure communication method, characterized in that, Includes the following steps: Step 1: Estimate the communication latency between the sender and receiver; Step 2: Based on the current time information obtained by the sending end, the set time slot length, and the one-way transmission delay between the sending and receiving parties, set the randomization seed for the time slot, and randomize the transmission rate of the original symbol in the time slot, the truncation position and truncation length of the spread spectrum pseudo-random sequence, and the waveform coefficients of the chip period dwell time of the spread spectrum pseudo-random sequence. Step 3: Spread spectrum modulation is performed on the original symbols, followed by continuous phase modulation; Step 4: The receiving end demodulates the received signal, and then generates waveform coefficients consistent with those of the transmitting end based on the acquired current time information. The demodulated signal is then despread to recover the original symbol. Step one is as follows: Record the time t when the sending end sends the synchronization sequence to the receiving end. send After receiving the synchronization sequence, the receiving end forwards it to the sending end, and the sending end records the time t when it receives the return signal. receive Let the processing delay of the transmitting part of the communication equipment be t. e The signal transmission delay in the medium is t. p The processing delay of the receiving part of the communication equipment is t. r The total round-trip delay of the signal is t. D The one-way transmission delay is t delay The following relationship exists: t D =t receive -t send (1) Step two is as follows: The sending end communicates information in time slots, and let the length of one time slot be t. slot Before sending information in each time slot, the sending end determines the current time based on the acquired information and the one-way transmission delay t between the sending and receiving ends. delay The randomization seed for the waveform coefficients of the transmitted signal in this time slot is set by the relationship between the two factors. The waveform coefficients include the transmission rate of the original symbol, the starting position and truncation length of the spread spectrum pseudo-random sequence, and the dwell time of the spread spectrum pseudo-random sequence chip period. When t send <t delay At that time, based on the current time information t send This serves as the randomization seed for the waveform coefficients of the current time slot, when t send ≥t delay At that time, with t serves as the randomization seed for the waveform coefficients of the current time slot. slot It is the duration of a time slot. This is the floor function.

2. The continuous phase modulation secure communication method as described in claim 1, characterized in that: The randomization of the transmission rate of the original symbol is as follows: After converting the binary sequence to be transmitted into quaternary symbols, a serial-to-parallel conversion is performed to split it into I / Q paths. Based on the randomization seed of the waveform coefficients in the current time slot, the transmission rate R of the original symbol is randomized. symbol The symbol period is Suppose that X symbols can be transmitted in the I / Q channels in the current time slot, then 3. The continuous phase modulation secure communication method as described in claim 1 or 2, characterized in that: The randomization of the truncation position and length of the spread spectrum pseudo-random sequence, as well as the chip period dwell time of the spread spectrum pseudo-random sequence, is as follows: The starting position P of the spread spectrum pseudo-random sequence is randomized according to the randomization seed of the current time slot waveform coefficients. I With P Q The truncation length M of the spread spectrum pseudo-random sequence and the chip dwell time S of the spread spectrum pseudo-random sequence; Let the lengths of the two complete spread spectrum pseudo-random sequences ISeq and QSeq be L, then 1 ≤ P I ≤L, 1≤P Q ≤L, When P I When M ≤ L, the sequence ISeq is extracted from P. I To P I +M-1 position obtains the spread spectrum pseudo-random sequence Seq1 of path I, when P I When M > L, then the sequence ISeq is extracted from P. I Recycle back from position L to M-L+P I -1 position obtained; when P Q When M ≤ L, extract the sequence QSeq from P. Q To P Q +M-1 position obtains the spread spectrum pseudo-random sequence Seq2 of the Q path, when P Q When M > L, then the sequence QSeq is extracted from P. Q Recycle back from position L to M-L+P Q -1 position obtained.

4. The continuous phase modulation secure communication method as described in claim 3, characterized in that: Step 3 is as follows: After the waveform coefficients of the current frame are generated, the 1st, 2nd, ..., Xth original symbols of the I-path are XORed with Seq1 to obtain I. k (k=1, 2, 3,...,M·X), I k The expanded symbol of the I-path and the Xth original symbols of the Q-path are XORed with Seq2 to obtain Q. k Q k The expanded symbol of the Q path is then filled with Gaussian white noise into the remaining time period at the end of the current time slot, which is insufficient to transmit a single symbol, thus forming the expanded symbol of the entire time slot. Phase modulation is applied to the spread symbols; assuming that the spread symbols in different time slots always contain m carrier cycles, then the signal carrier frequency... The signal expression is shown in (3): s k (t)=cos(2πf c t+θ k ) (3) Where t represents time, θ k The symbol modulation phase is represented by the formula shown in (4): Based on the phase difference between the preceding and following symbols, the waveform of the modulated signal in equation (3) is changed, and the modulated signal is divided into three parts within one symbol period according to equation (5), resulting in the general formula for continuous phase modulation: Where, θ k-1 θ k θ k+1 t represents the phase of the previous symbol, the current symbol, and the next symbol, respectively. x t y Let represent the duration of the first part and the third part, respectively. The calculation formulas are shown in equations (6) and (7): f h f e Let represent the first part carrier frequency and the third part carrier frequency respectively. The calculation formulas are shown in equations (8) and (9): The corrected phase of the first part is represented by the formula shown in equation (10):

5. The continuous phase modulation secure communication method as described in claim 4, characterized in that: In step four, the receiving end generates a signal waveform r that is the same as that in equation (5) in step three. k (t), the received signal is demodulated to obtain the baseband symbol; The receiving end uses the current timing information as the randomization seed for the current time slot to generate the same waveform coefficients as in step two, and despreads the demodulated baseband symbols to recover the original symbols.

6. A continuous phase modulation secure communication system, based on the method according to any one of claims 1-5, characterized in that, Includes the following modules: Communication delay estimation module: estimates the communication delay between the sender and receiver; specifically, it records the time t it takes for the sender to send the synchronization sequence to the receiver. send After receiving the synchronization sequence, the receiving end forwards it to the sending end, and the sending end records the time t when it receives the return signal. receive Let the processing delay of the transmitting part of the communication equipment be t. e The signal transmission delay in the medium is t. p The processing delay of the receiving part of the communication equipment is t. r The total round-trip delay of the signal is t. D The one-way transmission delay is t delay The following relationship exists: t D =t receive -t send (1) Waveform coefficient randomization module: Based on the current time information obtained by the transmitter, the set time slot length, and the one-way transmission delay between the transmitter and receiver, the randomization seed of the time slot is set, and the transmission rate of the original symbol in the time slot, the truncation position and length of the spread spectrum pseudo-random sequence, and the dwell time of the spread spectrum pseudo-random sequence chip period waveform coefficients are randomized; specifically as follows: the information of the transmitter is communicated in time slots, and a time slot length is set to t. slot Before sending information in each time slot, the sending end determines the current time based on the acquired information and the one-way transmission delay t between the sending and receiving ends. delay The randomization seed for the waveform coefficients of the transmitted signal in this time slot is set by the relationship between the two factors. The waveform coefficients include the transmission rate of the original symbol, the starting position and truncation length of the spread spectrum pseudo-random sequence, and the dwell time of the spread spectrum pseudo-random sequence chip period. When t send <t delay At that time, based on the current time information t send This serves as the randomization seed for the waveform coefficients of the current time slot, when t send ≥t delay At that time, with t serves as the randomization seed for the waveform coefficients of the current time slot. slot It is the duration of a time slot. For floor functions; Continuous phase modulation module: Spread spectrum modulation is performed on the original symbol, followed by continuous phase modulation; Original symbol recovery module: The receiver demodulates the received signal, generates waveform coefficients consistent with those of the transmitter based on the acquired current time information, despreads the demodulated signal, and recovers the original symbol.

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