Dual-mode differential chaos shift keying method combining carrier and time slot index modulation

Abstract

The invention discloses a dual-mode differential chaos shift keying method combining carrier and time slot index modulation, and belongs to the technical field of communication. A chaotic signal generator is used at a transmitting end to generate a chaotic signal cx, a reference signal is generated after MS + 1 times of copying is achieved through Kronecker product operation, and Hilbert transformation is carried out on the chaotic signal cx to generate an orthogonal signal cy. The information index bit is a modulation bit transmitted by performing k combination mapping on a frequency domain and a time domain by using a carrier index and a time slot index and constructing two distinguishable signal modes of DCSK and QCSK. And finally, distributing the signals to subcarriers with different frequencies by adopting a multi-carrier technology to carry out overall signal transmission. And after the signal of each subcarrier is demodulated at a receiving end, the noise interference of the reference signal is reduced through a noise reduction module. And then, original input index information is recovered through related demodulation of carrier waves and time slots and a corresponding mapping rule, and finally, modulation bit information is recovered by adopting dual-mode demodulation.

Description

Technical Field

[0001] The invention belongs to the field of communication technology, and in particular is a dual-mode differential chaotic shift keying method of joint carrier and time slot index modulation. Background Art

[0002] As one of the three major discoveries in physics in the 20th century, chaos theory has been deeply applied to fields such as topography, economics, and communications. Especially in the modern society where communication networks are developing rapidly, information security issues have become an important issue in social life and national governance. The characteristics of chaotic signals, such as initial value sensitivity, quasi-randomness, and spectral characteristics, give them obvious advantages in modern chaotic communications. Chaotic communication uses chaotic signals as carriers in wireless digital communication systems, replacing traditional sine and cosine carriers, hiding or superimposing transmission signals on chaotic carriers, increasing communication security while directly realizing spectrum expansion. It has broad application prospects in confidential communications and spread spectrum communications.

[0003] Chaotic communication is usually divided into coherent and incoherent demodulation schemes according to whether the receiver needs to synchronize the demodulation signal. Since it is very difficult to achieve robust chaotic synchronization with coherent schemes, incoherent chaotic digital modulation technologies represented by differential chaos shift keying (DCSK) and correlated delay shift keying (CDSK) are commonly used. DCSK has a simple structure, low cost, and good bit error performance, but it only uses half of the time to transmit information alone, greatly reducing the information transmission rate. The CDSK transmitter uses an adder to replace the switch structure of DCSK and does not transmit the reference signal separately, which has a certain improvement in transmission rate and security, but the interference in the signal becomes larger, resulting in poor anti-noise performance. In subsequent research, in response to the problems of high bit error rate, low data rate and poor security in digital communication, the academic community has continuously proposed improved schemes based on DCSK and CDSK. In the Quadrature Chaos Shift Keying (QCSK) system proposed by the researchers, two orthogonal chaotic signals are generated through Hilbert transform, and the orthogonality is used to eliminate inter-code interference, thereby improving the system's error performance and the transmission rate is twice that of DCSK, but it also increases the complexity of the system. In 2013, Kaddoum Georges et al. proposed a multicarrier differential chaos keying (MC-DCSK) system that transmits the reference signal and multiple information-bearing signals simultaneously on different subcarriers, which not only solves the problem of radio frequency (RF) delay lines, but also improves the information transmission rate.

[0004] In order to further explore how to effectively improve the data rate and bit error performance of chaotic systems, index modulation (IM) technology has become an important means to solve these problems. Index modulation technology is an emerging communication technology that has high energy efficiency and anti-interference ability, and can significantly reduce hardware complexity. In modern communication systems, index modulation has been widely used in the Internet of Things, 5G and future 6G communications, providing new solutions for efficient, secure and reliable communications, showing great potential and application prospects. As representative index schemes in the time domain and frequency domain, the pulse position modulation DCSK (PPM-DCSK) system and the carrier index modulation DCSK (CI-DCSK) system use the time slot and subcarrier activation and deactivation states to map index resources. On the basis of transmitting traditional modulation bits, the index bits are transmitted from another dimension, which effectively improves the bit error performance.

[0005] In order to improve the transmission rate of the single index modulation system, the present invention combines the two signal modulation modes of QCSK and DCSK, and distributes the two signals through carrier and time slot index modulation technology, and proposes a dual-mode differential chaotic shift keying method of joint carrier and time slot index modulation.

[0006] In a paper on the same dual-mode modulation as the present invention, a dual-mode differential chaos shift keying (DM-DCSK-IM) system based on index modulation is proposed. At the transmitting end, the bit stream is divided into two parts, one part is the PPM mapping bit for selecting the activated time slot; the other part is for the dual-mode modulation bit, using the DCSK and QCSK modes to distinguish between activated and unactivated time slots, thereby increasing the data rate of the system. At the receiving end, a pair of distinguishable orthogonal reference signals are correlated and demodulated with the information in each time slot to restore the mapping bits and modulation bits. The differences between this paper and the present invention are as follows: 1. This paper only uses a time slot index based on PPM modulation, while the present invention uses carrier index and time slot index, and performs k-combination mapping from two dimensions, effectively increasing the number of index bits that can be transmitted. 2. The paper transmits DCSK signals in activated time slots and QCSK signals in inactivated time slots. The present invention transmits DCSK signals in activated time slots and QCSK signals in inactivated time slots (including the 0th time slot) on activated subcarriers. On inactivated subcarriers (including the 0th subcarrier), the opposite is true, which greatly improves the transmission rate while enhancing security. 3. The paper does not use noise reduction processing, while the present invention uses a noise reduction module to reduce reference signal noise interference and improve bit error performance. Summary of the invention

[0007] The present invention aims to solve the above problems of the prior art. A dual-mode differential chaotic shift keying method combining carrier and time slot index modulation is proposed. The technical solution of the present invention is as follows:

[0008] A dual-mode differential chaotic shift keying method for joint carrier and time slot index modulation comprises the following steps:

[0009] Step 1: Generate a chaotic signal using a chaos generator and copy it to obtain a reference signal;

[0010] Step 2: Carrier and time slot index modulation is performed in the frequency domain and time domain, and dual-mode modulation is combined to generate information-bearing signals;

[0011] Step 3: The reference signal and the information bearing signal are transmitted using a carrier wave;

[0012] Step 4: After the signal passes through the channel, carrier demodulation and noise reduction module are performed to obtain the reference signal and information signal.

[0013] Step 5: Recover the index information bits and modulation bits through two-dimensional index demodulation and dual-mode demodulation.

[0014] Furthermore, the step 1 uses a chaos generator to generate a chaotic signal, and copies the reference signal, which specifically includes:

[0015] At the transmitting end, the chaotic signal generator uses a second-order Logistic map, that is, c k is the mapping variable. Then the chaotic signal c with a length of θ is obtained by normalizing the sign function. x =[c x,1 ,c x,2 ,…,c x,θ ], c x,θ is the intermediate variable of the chaotic signal, which has the digital characteristics of mean 0 and variance 1; c x With a length of M S +1, perform Kronecker product on the matrix I with one row of all 1s to make it a replica of M S +1 times, get the reference signal The length is θ(M S +1), M S Indicates the number of system time slots (except the 0th time slot).

[0016] Further, the index modulation of the carrier and the time slot in the frequency domain and the time domain in step 2 specifically includes:

[0017] First, convert the binary carrier index bits and time slot index bits into decimal symbols, and use a one-to-one k combination mapping method to index the carrier and time slot; that is, for fixed n and m, all symbols can be represented by a strictly decreasing sequence J={α m +1,…,α1+1} means, Indicates a combination of formula operations α m represents a selected base, where α m >…>α1≥0, take the corresponding element from the set {1,…,n}, the formula is expressed as:

[0018]

[0019] in Indicates a combination of formula operations In the present invention, n=N S &M S ,m=N C &M C , N S is the number of optional carriers, N C is the number of activated carriers, M S is the number of optional time slots, M Cis the number of activated time slots, and the elements in set J are the selected activated resources; therefore, the carrier index bit Indicates a combination of formula operations in is the floor function, used to S Select N of the carriers C Carrier activation, slot index bit For M S Select M from the time slots C Time slot activation, Indicates a combination of formula operations

[0020] Furthermore, the dual-mode modulation in step 2 to generate the information bearing signal specifically includes:

[0021] In a dual-mode modulator, the active and inactive time slots on the active and inactive carriers transmit two distinguishable signals, namely, d u c y and a u c x +b u c y , where d u Indicates the mapping symbol of DCSK, a u , b u Respectively represent the mapping symbols of the real and imaginary parts in QCSK, c y is the orthogonal signal after the reference signal is Hilbert transformed. The information symbol carried by its corresponding signal is expressed as and The specific signal distribution is expressed as:

[0022] (1) On the activated subcarrier, the activated time slot transmission d u c y , the unactivated time slots include the 0th time slot transmission a u c x +b u c y ;

[0023] (2) On the inactive subcarriers, including the 0th subcarrier, the activated time slot transmits a u c x +b u c y , the unactivated time slots include the 0th time slot transmission d u c y ;

[0024] In the information bearing signal part, define the subcarrier index factor j=0,1,…,N S ,wNS An intermediate variable representing the subcarrier index factor, where w j =1 or w j = 0 means that the jth subcarrier is in an activated state or an inactivated state; similarly, the slot index factor is defined α=0,1,…,M S , v MS An intermediate variable representing the time slot index factor, where v α =1 or v α = 0 means that the αth time slot is in an activated state or an inactivated state; therefore, the expression e of the jth subcarrier j for:

[0025] (1) When w j =1, subcarrier is activated, e j =R j =[R j (0),R j (1),...,R j (α),...,R j (M S )],in R j It is expressed as the expression of activation of the jth subcarrier, R j (M S ) represents the intermediate variable of its time slot;

[0026] (2) When w j = 0, the subcarrier is not activated, e j =G j =[G j (0),G j (1),...,G j (α),...,G j (M S )],in G j It is expressed as the expression that the jth subcarrier is not activated, G j (M S ) represents the intermediate variable of its time slot.

[0027] Furthermore, the step 3 of transmitting the reference signal and the information bearing signal using a carrier wave specifically includes:

[0028] A pulse shaper is used to convert a discrete signal into a continuous signal, i.e. where h T (t-iT c ) is the impulse response generated by the pulse shaping filter with normalized energy of 1, h T represents the spectrum amplitude obtained by Fourier transform, T cis the chip time; then, the signal is transmitted on subcarriers of different frequencies; the reference signal is loaded to the center frequency f R The information signal is transmitted on a carrier with a center frequency of f j (j=0,1,…,N S ), so the total transmission signal at the transmitter can be expressed in the following form:

[0029]

[0030] where e R (t) represents the continuous reference signal, e j (t) represents the continuous information signal of the j-th subcarrier.

[0031] Furthermore, after the signal in step 4 passes through the channel, carrier demodulation and noise reduction module are performed to obtain a reference signal and an information signal, which specifically includes:

[0032] The transmitted signal passes through a multipath Rayleigh fading channel consisting of L independent, identically distributed slow Rayleigh fading paths; the impulse response function of this channel model is defined as Where L is the number of paths, λ l and τ l is the channel coefficient and path delay; when l = 1, λ l When =1, the Rayleigh fading channel behaves as an AWGN channel; therefore, the received signal is expressed as r(t)=s(t)*h(t)+n(t), where * is the convolution operator and n(t) is the AWGN noise with zero mean and variance N0 / 2.

[0033] After receiving the signal r(t), the receiving end multiplies it with each corresponding frequency carrier, and recovers the discrete information signal after sampling through the matched filter; then the first received signal is stored in the vector A, which can be expressed as: Represents the intermediate variable of the received reference signal. After the vector A is subjected to sample average denoising, a reference signal of length θ is obtained. where n R The mean is 0 and the variance is N0 / [2(M S +1)]; except for the first received signal, all other signal samples are stored in the matrix B as the information carrying signal matrix.

[0034] Further, the step 5 recovers the index information bits and the modulation bits by two-dimensional index demodulation and dual-mode demodulation, specifically including:

[0035] Step 5.1: 2D index demodulation: Then convert the reference signal After Hilbert transform, we get the orthogonal signal Since the 0th time slot and the 0th subcarrier of the information matrix B only carry the index result, the first column of the matrix B is divided by r 0,0 Take out the rest of the items and make it Divide the first row of matrix B by r 0,0 Take out the rest of the items and make it The reference signal With D ca and D ti Correlate each row of to obtain decision matrices Q1 and Q2. Find N from the decision variables of Q1 and Q2 respectively. C and M C The corresponding row number is mapped through k combinations to obtain the index symbol, and then the carrier and time slot index bit information is restored through decimal to binary conversion;

[0036] Step 5.2: Dual-mode demodulation: According to the recovered activated and inactivated subcarriers, the modulated bits are demodulated using the corresponding two signal modes in their activated and inactivated time slots respectively; that is, DCSK demodulation is used in the activated time slot of the activated subcarrier and the inactivated time slot (including the 0th time slot) of the inactivated subcarrier (including the 0th subcarrier), and its samples are compared with Correlate; QCSK demodulate the inactive time slots (including the 0th time slot) of the activated subcarrier and the active time slots on the inactive subcarrier (including the 0th subcarrier), and compare their samples with and Correlation is performed; the positive and negative results of the two cases are restored to the corresponding DCSK and QCSK modulated bits through inverse mapping.

[0037] An electronic device comprises a memory, a processor and a computer program stored in the memory and executable on the processor, wherein when the processor executes the program, a dual-mode differential chaotic shift keying method for joint carrier and time slot index modulation as described in any one of the claims is implemented.

[0038] A non-transitory computer-readable storage medium stores a computer program, wherein the computer program, when executed by a processor, implements a dual-mode differential chaotic shift keying method for combined carrier and time slot index modulation as described in any one of the items.

[0039] A computer program product, comprising a computer program, wherein when the computer program is executed by a processor, the dual-mode differential chaotic shift keying method for combined carrier and time slot index modulation as described in any one of the items is implemented. The advantages and beneficial effects of the present invention are as follows:

[0040] In order to ensure the superiority of the system bit error rate while greatly improving the transmission rate, the present invention proposes a dual-mode differential chaotic shift keying method of joint carrier and time slot index modulation, which performs index modulation through the two dimensions of carrier and time slot, and is not limited to a single sample index, but uses a k combination mapping method to select a single or multiple activated samples. Then, two different signals, DCSK and QCSK, are used to distinguish between each activated and unactivated sample, which increases the security of the system and makes it difficult to steal information. The signal is processed by a noise reduction module at the receiving end to effectively improve the anti-noise performance of the system. Then, the index recovery is performed on the 0th time slot and the carrier respectively, so that the two index demodulations do not interfere with each other, which improves the bit error performance and reduces the complexity to a certain extent, and finally, the DCSK and QCSK demodulation methods are used to recover the modulated bits respectively.

[0041] 1. Adopt two-dimensional index modulation technology, that is, joint carrier and time slot index modulation technology, and implement it through k combination mapping. Use the two available resources of frequency domain and time domain to transmit more index information bits, achieve higher bit error rate performance, and carry information in all activated and unactivated resources, avoiding the waste of subcarriers and time slots, and also avoiding the signal interference problem introduced during demodulation at the receiving end.

[0042] 2. Hilbert transform is used to generate a pair of orthogonal signals, which is convenient for constructing DCSK and QCSK signals. Since each time slot carries one or two modulation bits, it ensures that the information transmission rate is greatly improved under given spectrum resources. And through certain rules, DCSK and QCSK signals are placed in order in the carrier and time slot in two states, so that information transmission can be accurately demodulated while improving confidentiality performance, which plays a role in practicality and reliability in communication.

[0043] 3. Since DCSK modulation maps binary information bits to QCSK modulation maps binary information bits into The bit energy carried in the DCSK modulated resource block is less than 1, which enables the present invention to reduce the transmission energy consumed by the transmitting end under the same bandwidth condition.

[0044] 4. The receiving end adopts a noise reduction module. The present invention reduces the influence of reference signal noise by averaging the corresponding values ​​of the received signal in segments, thereby reducing the variance of the noise in the decision variable and achieving the effect of noise reduction. When the number of replications of the system increases with the number of time slots, not only the transmission rate of the system increases, but also the error performance is better.

[0045] 5. The index demodulation method adopted by the present invention is to make relevant decisions only through the 0th time slot and the carrier. This is because it carries index information, which ensures that the demodulation results between the two indexes do not affect each other, reducing the difficulty of demodulation. This makes the system's error performance better while reducing complexity. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 The present invention provides a preferred embodiment of the transmitting end structure diagram;

[0047] Figure 2 This is a schematic diagram of the information bearing signal frame structure of the present invention

[0048] Figure 3 is a block diagram of a receiving end of the present invention;

[0049] Figure 4 Comparison between system simulation value and theoretical value when θ=100, 200, 300 in the present invention;

[0050] Figure 5 The present invention is different from C ,M C The curve comparison of system BER under the value;

[0051] Figure 6 The present invention is different from b / N0 value, system N S ,M S The impact of changes on BER;

[0052] Figure 7 The BER curve comparison diagram of the present invention with DM-DCSK-IM and PPM-DCSK systems when m=4,8;

[0053] Figure 8 The BER curve comparison diagram of the present invention with CI-DCSK and MC-DCSK systems when n=5,10;

[0054] Fig. 9 It is a schematic diagram of a dual-mode differential chaotic shift keying method for combined carrier and time slot index modulation provided by a preferred embodiment of the present invention. DETAILED DESCRIPTION

[0055] The following will describe the technical solutions in the embodiments of the present invention in detail in conjunction with the accompanying drawings in the embodiments of the present invention. The described embodiments are only part of the embodiments of the present invention.

[0056] The technical solution of the present invention to solve the above technical problems is:

[0057] The following will describe the implementation of the present invention in detail with reference to the accompanying drawings. Figure 1The chaotic signal generator uses a second-order Logistic map, that is, Then the chaotic signal c with a length of θ is obtained by normalizing the sign function. x =[c x,1 ,c x,2 ,...,c x,θ ], this chaotic signal has digital characteristics with a mean of 0 and a variance of 1. x The signal is transformed by Hilbert to obtain the c y The signal is used for dual-mode modulation of the bit information transmission part.

[0058] On the information-bearing signal, the total transmitted bits are divided into three parts: carrier index bit k1, slot index bit k2 and modulation bit k3. k1 is used to obtain the S Select N of the carriers C carrier activation, k2 is used to activate S Select M from the time slots C The specific implementation is to first convert the binary carrier index bit and time slot index bit into decimal symbols, and then use the one-to-one k combination mapping method proposed in the literature

[18] to index the carrier and time slot. For fixed n and m, all symbols can be represented by a strictly decreasing sequence J={α m +1,…,α1+1}, where α m >…>α1≥0, take out elements from {1,…,n}, which can be achieved by the following formula:

[0059]

[0060] For example, when n=5, m=2, The mapping formula can be expressed as:

[0061]

[0062] By the above method, the decimal symbol obtained from the information bit mapping can correspond to the index carrier, such as Figure 2 As shown, when N S =4,N C = 2, the symbol mapped to the carrier index bit 10 is 2, and the two carriers with sequence numbers 3 and 2 are selected for activation. Similarly, when M S =5,M C = 2, the symbol mapped to the time slot index bit 111 is 7, and two time slots with sequence numbers 5 and 2 are selected for activation. Figure 2In the frame structure of the information-bearing signal, the 0th time slot and the 0th carrier are used to present the index result and are not included in the carrier and time slot index selection range, which also facilitates index demodulation at the receiving end.

[0063] In a dual-mode modulator, two distinguishable signals are transmitted in selected and unselected time slots on selected and unselected carriers, namely, d u c y and a u c x +b u c y , where the information symbol carried by the corresponding signal is expressed as and The specific signal distribution is as follows: Figure 2 As shown, on the activated subcarrier, the activated time slot transmission d u c y , inactive time slots (including time slot 0) transmit a u c x +b u c y ; On the inactive subcarriers (including the 0th subcarrier), the activated time slot transmits a u c x +b u c y , unactivated time slots (including time slot 0) transmit d u c y This method of carrying different signals in the frequency domain and time domain can effectively improve the transmission rate and increase the confidentiality of the system.

[0064] In the present invention, the transmission bits of the three parts are combined with each other through corresponding indexes and modulations to obtain the total transmission bit k T =k1+k2+k3. In the index bit part, due to the S N subcarriers are selected C subcarriers are activated, so the number of carrier indices is in is the floor function. Similarly, from M S In the time slots, M C time slots are activated, so the number of time slot indices In the modulation bit part, the number of modulation bits in the inactive time slot and the active time slot on the activated subcarrier is 2N respectively. C (M S -M C +1) and N C M C ; The number of modulation bits in the activated time slot and the inactivated time slot on the inactivated subcarrier is 2M respectively C (N S -N C+1) and (N S -N C +1)(M S -M C +1), so the total number of modulation bits k3 is expressed as:

[0065]

[0066] The transmission signal in the present invention is divided into two parts: a reference signal and an information-bearing signal. In the reference signal part, c x With a length of M S +1 all 1 sequence I is Kronecker product to make its copy M S +1 times, get the reference signal The length is θ(M S +1). In the information-bearing signal part, for the convenience of analysis, the subcarrier index factor W is defined as [w0,w1,…,w j ,…,w NS ],j=0,1,…,N S , where w j =1 or w j = 0 means that the jth subcarrier is in an activated state or an inactivated state. Similarly, the slot index factor is defined α=0,1,…,M S , where v α =1 or v α =0 indicates that the αth time slot is in an activated state or an inactivated state. Therefore, the expression of the jth subcarrier is:

[0067]

[0068] On the activated subcarrier, the expression for each time slot can be written as:

[0069]

[0070] On the inactive subcarriers, the expression for each time slot can be written as:

[0071]

[0072] A pulse shaper is used to convert a discrete signal into a continuous signal, i.e. where h T (t-iT c ) is the impulse response generated by the pulse shaping filter with normalized energy of 1, T c is the chip time. In addition, the paper also defines the spreading factor β = θ (M S +1). Then, the signal is transmitted on subcarriers of different frequencies. The reference signal is loaded to the center frequency f RThe information signal is transmitted on a carrier with a center frequency of f j The center frequency is assumed to be 1 / T. c multiples of and f>>1 / T c Therefore, the total transmission signal at the sender can be expressed in the following form:

[0073]

[0074] The transmitted signal passes through a multipath Rayleigh fading channel consisting of L independent, identically distributed slow Rayleigh fading paths. The impulse response function of this channel model is defined as Where L is the number of paths, λ l and τ l is the channel coefficient and path delay. When l = 1, λ l = 1, the Rayleigh fading channel behaves as an AWGN channel. In order to approximate the inter-symbol interference to zero, the channel delay is required to be much smaller than the expansion factor, that is, τ l <<β. Therefore, the received signal is expressed as:

[0075] r(t)=s(t)*h(t)+n(t) (7)

[0076] Where * is the convolution operator, and n(t) is the AWGN noise with zero mean and variance N0 / 2.

[0077] The receiving block diagram of the present invention is as follows Figure 3 As shown. After receiving the signal r(t), the receiving end multiplies it with the corresponding carrier of each channel, and recovers the discrete information signal after sampling through the matched filter. Then the first channel received signal is stored in the vector A, which can be expressed as: Vector A is the reference signal after sample averaging and denoising. Where n R The mean is 0 and the variance is N0 / [2(M S +1)]. Its working principle is to divide the signal into segments, take the sum of the values ​​of the same position in each segment and then calculate the average value to achieve the purpose of noise reduction. The length of the new signal is the same as the previous one. Then the reference signal After Hilbert transform, we get the orthogonal signal Except for the first received signal, all other signal samples are stored in matrix B as the information-carrying signal matrix, expressed as:

[0078]

[0079] Since the 0th time slot and the 0th subcarrier of the information matrix B are non-index objects and only carry the index results, the index information can be directly demodulated on the 0th time slot and the 0th subcarrier.0,0 Take out the rest of the items and make it Similarly, divide the first row of matrix B by r 0,0 Take out the rest of the items and make it The reference signal is compared with D ca and D ti Correlate each row of to obtain decision matrices Q1 and Q2:

[0080]

[0081] Find N from the decision variables of Q1 and Q2 respectively C and M C The corresponding row number is mapped through k-combination to obtain the index symbol, and then the carrier and time slot index bit information is recovered. According to the recovered activated and inactivated subcarriers, the modulated bits are demodulated using the corresponding two signal modes in their activated and inactivated time slots. Specifically, DCSK demodulation is used in the activated time slot of the activated subcarrier and the inactivated time slot (including the 0th subcarrier) of the inactivated subcarrier (including the 0th time slot), and its samples are compared with Correlate and recover the DCSK modulated bits; demodulate the inactive time slots (including the 0th time slot) of the activated subcarrier and the active time slots on the inactive subcarrier (including the 0th subcarrier) using QCSK, and compare their samples with and Perform correlation and recover the QCSK modulated bits.

[0082] The Gaussian approximation method is used to analyze the anti-noise performance of the present invention under Gaussian channels and multipath Rayleigh fading channels. Since the carrier index demodulation method and time slot index demodulation method are consistent, the decision variables of the two index demodulations are equal, so only one of the index decision variables needs to be derived. When the carrier index demodulation is correct, With c x,i The QCSK received signal samples are correlated and the decision variable It is expressed as:

[0083]

[0084] When the carrier index demodulation is incorrect, With only c y,i The DCSK received signal samples are correlated and the decision variable It is expressed as:

[0085]

[0086] When θ is large, the random variable and Obeying Gaussian distribution, the mean and variance of these two random variables can be calculated as:

[0087]

[0088] Where E[·] and Var[·] are mean and variance operations, respectively, and the average bit energy Where E s is the symbol energy, Δ can be specifically expressed as:

[0089]

[0090] Similarly, the decision variable and its mean variance of the time slot index demodulation can be derived through the above calculation steps, that is, when the time slot index demodulation is correct: When the slot index demodulation is incorrect:

[0091] In the demodulation of the present invention, the decision variable and All satisfy independent and identical distribution, definition

[0092] If the decision variable The minimum value is less than The maximum value, that is, I1<I2, then there is a carrier demodulation error; at the same time, define and where n3∈{1,2,…,M C}, n4∈{1,2,…,M S -M C}, if the decision variable The minimum value is less than The maximum value of I3, that is, I4, then a time slot demodulation error occurs. Thus, the probability of carrier demodulation error can be obtained and time slot demodulation error probability The expression is as follows:

[0093]

[0094] in and is the distribution function, and is the probability density function. Since the decision variable and are independent and identically distributed Gaussian random variables, so the random variables and Satisfying the folded Gaussian distribution, the distribution function and probability density function of the random variable are as follows:

[0095]

[0096] Where exp(·) is the exponential function and erf(·) is the error function, expressed as Then, the bit error rate P of carrier demodulation is ca and the bit error rate P of time slot demodulation ti It can be expressed as:

[0097]

[0098] Under the premise of correctly demodulating the carrier index and time slot index, the modulation mode of each signal sample can be obtained. First, the DCSK signal sample is compared with The correlation table shows the decision variable:

[0099]

[0100] Then the in-phase branch of the QCSK signal sample is compared with Related, reverse branch and Perform correlation. Since the two correlation forms are the same, only one can be expressed. The correlation decision variable of the in-phase branch is:

[0101]

[0102] The mean and variance of formulas (27) and (28) are derived respectively, namely: E[Z au ]=E[Z bu ]=μ1, Therefore, the modulation bit error probability corresponding to the DCSK and QCSK signal modes is derived as follows:

[0103]

[0104] in erfc(·) is the complementary error function, expressed as

[0105] Since the carrier index demodulation and time slot index demodulation of the system are independent of each other, and the modulation bit demodulation is related to the index result, the modulation bit error probability of the present invention is divided into four cases, namely, P mod =P mod1 +P mod2 +P mod3 +P mod4 , each case is specifically described as follows:

[0106] 1. When both the carrier index and the time slot index are demodulated correctly, the modulation bit error probability P mod1 for:

[0107]

[0108] in The calculation is as follows:

[0109]

[0110] 2. When the carrier index demodulation is correct and the time slot index demodulation is wrong, the modulation bit error probability P mod2 for:

[0111]

[0112] in The calculation is as follows:

[0113]

[0114] 3. When the carrier index demodulation is wrong and the time slot index demodulation is correct, the modulation bit error probability P mod3 for:

[0115]

[0116] in The calculation is as follows:

[0117]

[0118] 4. When both the carrier index and the time slot index are demodulated incorrectly, the modulation bit error probability P mod4 for:

[0119]

[0120] in The calculation is as follows:

[0121]

[0122] In summary, the bit error rate P of the present invention can be derived sys for:

[0123]

[0124] In a multipath Rayleigh fading channel, different paths are independent of each other and have the same channel gain. Let the signal-to-noise ratio gain of the lth path of the multipath Rayleigh fading channel be So the average signal-to-noise ratio gain is Then γ b The instantaneous probability density function can be expressed as follows:

[0125]

[0126] Finally, the average bit error rate formula of the present invention under the multipath Rayleigh fading channel can be expressed as:

[0127]

[0128] Figure 4 The influence of different chaotic sequence lengths θ on the BER performance of the dual-mode differential chaotic shift keying system with joint carrier and time slot index modulation in AWGN and multipath Rayleigh fading channels is analyzed. θ=100, 200, 300 are taken respectively, and other parameters are set to N S =5,N C =2,M S =5,M C =2, it can be seen from the figure that the simulation value is in good agreement with the theoretical value, verifying the correctness of the theoretical formula derivation. In addition, as θ increases, the BER performance of the system gradually deteriorates. This is because the noise component becomes larger as θ increases, causing noise interference to seriously affect the bit error performance. Figure 5 The analysis shows that the number of activated subcarriers N C and the number of activated time slots M C BER performance of dual-mode differential chaotic shift keying system with variable joint carrier and time slot index modulation in AWGN and multipath Rayleigh fading channels, with each parameter set to θ=100, N S =6,M S =8. As can be seen from the figure, the simulation results are basically consistent with the theoretical results. C Fixed, M C When it changes from 2 to 4, the bit error rate increases; when M C Fixed, N C When N changes from 1 to 3, the bit error rate also increases. This is because the probability of error in carrier and time slot index detection increases with N. C and M C As the BER increases, the overall BER performance deteriorates. Figure 6 The bit error rate of the dual-mode differential chaotic shift keying system with joint carrier and time slot index modulation under AWGN channel increases with the total number of index time slots M. S The curve of the change. Take the signal-to-noise ratio E b / N0 is 10dB and 12dB, and the relevant parameters are θ=100, N C =1,M C =1. From the curve in the figure, we can see that when M S As M increases, the bit error rate decreases and gradually tends to be flat. This is because when the total number of index time slots increases, the total number of bits that can be transmitted increases, resulting in a decrease in the system's bit error rate, but SThe increase in the number also means that more noise will be introduced, so the bit error rate reduction trend becomes smaller, and the impact of noise gradually becomes greater than the impact of the total number of transmitted bits. S When E increases, the system bit error rate also decreases, and E b / N0=12dB than E b When / N0=10dB, the BER reduction is greater, and the error performance is better when the signal-to-noise ratio is higher. Therefore, it can be concluded that the system error rate is greatly affected by the signal-to-noise ratio. Let the total number of carriers in the information transmission part be n, and the total number of time slots be m, that is: n=N S +1, m = M S +1. Figure 7 The bit error rate variation curves of dual-mode differential chaotic shift keying, DM-DCSK-IM and PPM-DCSK with joint carrier and time slot index modulation in AWGN and multipath Rayleigh fading channels are given with different time slot numbers m. The parameters are set to θ=100, N S =4,N C =1,M C =1. It can be seen from the figure that the present invention has better error performance than the other two systems in the two channels, and as m increases, the error performance of the dual-mode differential chaotic shift keying system and the PPM-DCSK system with joint carrier and time slot index modulation becomes better, while the error performance of the DM-DCSK-IM system becomes slightly worse. In the AWGN channel, when BER=10 -4 When m=4, the performance gain of the present invention compared with the DM-DCSK-IM system and the PPM-DCSK system is approximately 1.2 dB and 2.4 dB. Figure 8 The bit error rate variation curves of the dual-mode differential chaotic shift keying system, CI-DCSK system and MC-DCSK system with joint carrier and time slot index modulation in AWGN and multipath Rayleigh fading channels are given under different carrier numbers n. The other parameters are θ=100, M S =4,M C =1,N C =1. As can be seen from the figure, no matter in AWGN or multipath Rayleigh fading channel, the present invention is obviously better than other systems, and the bit error rate of all systems decreases with the increase of n. In AWGN channel, when BER=10 -4 When n=10, the present invention is compared with the E required by CI-DCSK and MC-DCSK. b / N0 is reduced by approximately 1 dB and 2.2 dB, so the present invention has better anti-noise performance.

[0129] The dual-mode differential chaotic shift keying method of joint carrier and time slot index modulation proposed in the present invention realizes the index of carrier and time slot through k combination mapping mode, and carries the information bit of index result on the 0th time slot and carrier, reducing the complexity of demodulating index bit. Then, two orthogonal sequences are generated by Hilbert transform to construct QCSK signal to carry modulation bits, and the other part of modulation bits are carried by DCSK signal. The two signals are used to distinguish the activated and unactivated time slots on each carrier, effectively improving the confidentiality of the system. At the same time, the receiving end adopts noise reduction operation to reduce noise interference to achieve better bit error performance. The present invention derives the BER formula under AWGN channel and multipath Rayleigh channel, and verifies the accuracy performance change trend of theoretical derivation through Monte Carlo simulation. Compared with DM-DCSK-IM, PPM-DCSK, CI-DCSK, and MC-DCSK systems, the present invention has lower bit error rate and better anti-noise performance, which proves the operability of the present invention in practical applications and promotes the rapid development of DCSK in practical communication applications.

[0130] The systems, devices, modules or units described in the above embodiments may be implemented by computer chips or entities, or by products with certain functions. A typical implementation device is a computer. Specifically, the computer may be, for example, a personal computer, a laptop computer, a cellular phone, a camera phone, a smart phone, a personal digital assistant, a media player, a navigation device, an email device, a game console, a tablet computer, a wearable device, or a combination of any of these devices.

[0131] Computer readable media include permanent and non-permanent, removable and non-removable media that can be implemented by any method or technology to store information. Information can be computer readable instructions, data structures, program modules or other data. Examples of computer storage media include, but are not limited to, phase change memory (PRAM), static random access memory (SRAM), dynamic random access memory (DRAM), other types of random access memory (RAM), read-only memory (ROM), electrically erasable programmable read-only memory (EEPROM), flash memory or other memory technology, compact disk read-only memory (CD-ROM), digital versatile disk (DVD) or other optical storage, magnetic cassettes, magnetic tape magnetic disk storage or other magnetic storage devices or any other non-transmission media that can be used to store information that can be accessed by a computing device. As defined herein, computer readable media does not include temporary computer readable media (transitory media), such as modulated data signals and carrier waves.

[0132] It should also be noted that the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, commodity or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, commodity or device. In the absence of more restrictions, the elements defined by the sentence "comprises a ..." do not exclude the existence of other identical elements in the process, method, commodity or device including the elements.

[0133] The above embodiments should be understood to be only used to illustrate the present invention and not to limit the protection scope of the present invention. After reading the contents of the present invention, technicians can make various changes or modifications to the present invention, and these equivalent changes and modifications also fall within the scope defined by the claims of the present invention.

Claims

1. A dual-mode differential chaotic shift keying method combining carrier and time slot index modulation, characterized in that: The following steps are involved: Step 1: Generate a chaotic signal using a chaos generator and copy it to obtain a reference signal; Step 2: Carrier and time slot index modulation is performed in the frequency domain and time domain, and dual-mode modulation is combined to generate information-bearing signals; Step 3: The reference signal and the information bearing signal are transmitted using a carrier wave; Step 4: After the signal passes through the channel, carrier demodulation and noise reduction module are performed to obtain the reference signal and information signal. Step 5: Recover the index information bits and modulation bits through two-dimensional index demodulation and dual-mode demodulation.

2. The dual-mode differential chaotic shift keying method of joint carrier and time slot index modulation according to claim 1 is characterized in that: The step 1 uses a chaos generator to generate a chaotic signal and copies the reference signal, which specifically includes: At the transmitting end, the chaotic signal generator uses a second-order Logistic map, that is, c k is the mapping variable; then the chaotic signal c with a length of θ is obtained by normalizing the symbol function x =[c x,1 ,c x,2 ,...,c x,θ ], c x,θ is the intermediate variable of the chaotic signal, which has the digital characteristics of mean 0 and variance 1; c x With a length of M S +1, perform Kronecker product on the matrix I with one row of all 1s, so that it replicates M S +1 times, get the reference signal The length is θ(M S +1), M S Indicates the number of system time slots except the 0th time slot.

3. The dual-mode differential chaotic shift keying method of joint carrier and time slot index modulation according to claim 1 is characterized in that: The index modulation of the carrier and the time slot in the frequency domain and the time domain in step 2 specifically includes: First, convert the binary carrier index bits and time slot index bits into decimal symbols, and use a one-to-one k combination mapping method to index the carrier and time slot; that is, for fixed n and m, all symbols can be represented by a strictly decreasing sequence J={α m +1,…,α1+1} means, Indicates a combination of formula operations α m represents a selected base, where α m >…>α1≥0, take the corresponding element from the set {1,…,n}, the formula is expressed as: in Indicates a combination of formula operations In the present invention, n=N S &M S ,m=N C &M C , N S is the number of optional carriers, N C is the number of activated carriers, M S is the number of optional time slots, M C is the number of activated time slots, and the elements in set J are the selected activated resources; therefore, the carrier index bit Indicates a combination of formula operations in is the floor function, used to S Select N of the carriers C Carrier activation, slot index bit For M S Select M from the time slots C Time slot activation, Indicates a combination of formula operations 4. The dual-mode differential chaotic shift keying method of joint carrier and time slot index modulation according to claim 1 is characterized in that: The dual-mode modulation in step 2 to generate the information-bearing signal specifically includes: In a dual-mode modulator, the active and inactive time slots on the active and inactive carriers transmit two distinguishable signals, namely, d u c y and a u c x +b u c y , where d u Indicates the mapping symbol of DCSK, a u 、b u Respectively represent the mapping symbols of the real and imaginary parts in QCSK, c y is the orthogonal signal after the Hilbert transform of the reference signal, and the information symbol carried by the corresponding signal is expressed as and The specific signal distribution is expressed as: (1) On the activated subcarrier, the activated time slot transmission d u c y , the unactivated time slots include the 0th time slot transmission a u c x +b u c y ; (2) On the inactive subcarriers, including the 0th subcarrier, the activated time slot transmits a u c x +b u c y , the unactivated time slots include the 0th time slot transmission d u c y ; In the information bearing signal part, define the subcarrier index factor An intermediate variable representing the subcarrier index factor, where w j =1 or w j = 0 means that the jth subcarrier is in an activated state or an inactivated state; similarly, the slot index factor is defined An intermediate variable representing the time slot index factor, where v α =1 or v α = 0 means that the αth time slot is in an activated state or an inactivated state; therefore, the expression e of the jth subcarrier j for: (1) When w j =1, subcarrier is activated, e j =R j =[R j (0),R j (1),...,R j (α),...,R j (M S )],in R j It is expressed as the expression of activation of the jth subcarrier, R j (M S ) represents the intermediate variable of its time slot; (2) When w j = 0, the subcarrier is not activated, e j =G j =[G j (0),G j (1),...,G j (α),...,G j (M S )],in G j It is expressed as the expression that the jth subcarrier is not activated, G j (M S ) represents the intermediate variable of its time slot.

5. The dual-mode differential chaotic shift keying method of joint carrier and time slot index modulation according to claim 1 is characterized in that: The step 3 uses a carrier wave to transmit the reference signal and the information bearing signal, specifically comprising: A pulse shaper is used to convert a discrete signal into a continuous signal, i.e. where h T (t-iT c ) is the impulse response generated by the pulse shaping filter with normalized energy of 1, h T represents the spectrum amplitude obtained by Fourier transform, T c is the chip time; then, the signal is transmitted on subcarriers of different frequencies; the reference signal is loaded to the center frequency f R The information signal is transmitted on a carrier with a center frequency of f j (j=0,1,…,N S ), so the total transmission signal at the transmitter can be expressed in the following form: where e R (t) represents the continuous reference signal, e j (t) represents the continuous information signal of the j-th subcarrier.

6. The dual-mode differential chaotic shift keying method of joint carrier and time slot index modulation according to claim 1 is characterized in that: After the signal in step 4 passes through the channel, carrier demodulation and noise reduction module are performed to obtain a reference signal and an information signal, which specifically includes: The transmitted signal passes through a multipath Rayleigh fading channel consisting of L independent, identically distributed slow Rayleigh fading paths; the impulse response function of this channel model is defined as Where L is the number of paths, λ l and τ l is the channel coefficient and path delay; when l = 1, λ l When =1, the Rayleigh fading channel behaves as an AWGN channel; therefore, the received signal is expressed as r(t)=s(t)*h(t)+n(t), where * is the convolution operator and n(t) is the AWGN noise with zero mean and variance N0 / 2. After receiving the signal r(t), the receiving end multiplies it with each corresponding frequency carrier, and recovers the discrete information signal after sampling through the matched filter; then the first received signal is stored in the vector A, which can be expressed as: Represents the intermediate variable of the received reference signal. After the vector A is subjected to sample average denoising, a reference signal of length θ is obtained. Where n R The mean is 0 and the variance is N0 / [2(M S +1)]; except for the first received signal, all other signal samples are stored in the matrix B as the information carrying signal matrix.

7. The dual-mode differential chaotic shift keying method of joint carrier and time slot index modulation according to claim 1 is characterized in that: The step 5 recovers the index information bits and the modulation bits by two-dimensional index demodulation and dual-mode demodulation, specifically including: Step 5.1: 2D index demodulation: Then convert the reference signal After Hilbert transform, we get the orthogonal signal Since the 0th time slot and the 0th subcarrier of the information matrix B only carry the index result, the first column of the matrix B is divided by r 0,0 Take out the rest of the items and make it Divide the first row of matrix B by r 0,0 Take out the rest of the items and make it The reference signal With D ca and D ti Correlate each row of to obtain decision matrices Q1 and Q2. Find N from the decision variables of Q1 and Q2 respectively. C and M C The corresponding row number is mapped through k combinations to obtain the index symbol, and then the carrier and time slot index bit information is restored through decimal to binary conversion; Step 5.2: Dual-mode demodulation: According to the recovered activated and inactivated subcarriers, the modulated bits are demodulated using the corresponding two signal modes in their activated and inactivated time slots respectively; that is, DCSK demodulation is used in the activated time slot of the activated subcarrier and the inactivated time slot (including the 0th time slot) of the inactivated subcarrier (including the 0th subcarrier), and its samples are compared with Correlate; QCSK demodulate the inactive time slots (including the 0th time slot) of the activated subcarrier and the active time slots on the inactive subcarrier (including the 0th subcarrier), and compare their samples with and Correlation is performed; the positive and negative results of the two cases are restored to the corresponding DCSK and QCSK modulated bits through inverse mapping.

8. An electronic device, characterized in that: It includes a memory, a processor and a computer program stored in the memory and executable on the processor, wherein when the processor executes the program, the dual-mode differential chaotic shift keying method with joint carrier and time slot index modulation as described in any one of claims 1 to 7 is implemented.

9. A non-transitory computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the dual-mode differential chaotic shift keying method with joint carrier and time slot index modulation as claimed in any one of claims 1 to 7 is implemented.

10. A computer program product, comprising a computer program, characterized in that When the computer program is executed by a processor, the dual-mode differential chaotic shift keying method with joint carrier and time slot index modulation as claimed in any one of claims 1 to 7 is implemented.

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