Chaotic filter based time index communication modulator, demodulator and method

Abstract

The application discloses a time index communication modulator and demodulator based on a chaotic filter and a method thereof. The modulator adopts a double information coding mechanism, maps a bit index bit to one of time slot positions, inserts a bit 0 in the specific time slot, and transmits bipolar modulation bits in the remaining time slot positions, so as to realize hybrid modulation. The application directly transmits the symbol sequence generated by a PPM modulator through a channel after pulse shaping by using a chaotic shaping filter, does not need to transmit a reference signal, can transmit more data under the same transmission energy, improves transmission efficiency, performs chaotic matching filtering on a received signal at a receiving end, samples and extracts at a best signal-to-noise ratio point, maximizes signal detection performance, and enhances the anti-noise and anti-interference capability of the system. Compared with an existing second-order hybrid differential chaotic shift keying system, the application reduces the bit error rate of the system without transmitting a reference signal.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of communication technology, in particular to a time-indexed communication modulator and demodulator based on a chaotic filter and a method. BACKGROUND

[0002] Non-coherent demodulation has been widely used in chaotic communication because it avoids the difficulty of chaotic synchronization due to channel interference and system parameter mismatch in coherent demodulation. The classical method of non-coherent demodulation is differential chaos shift keying (DCSK), which has good robustness and better bit error rate performance because the reference signal and the information signal experience the same channel distortion. However, the message transmission rate of this method is relatively low because the reference signal uses half of the time slots for transmission.

[0003] Chaotic communication shows its advantages, such as using the simplest matched filter to maximize the signal-to-noise ratio and improving the resistance to multipath interference. Chaotic shape-forming filter (CSF) is used to generate chaotic baseband signals in wireless communication, which can generate chaotic signals as spreading sequences in chaotic shift keying and encode information in the sequences. Second order hybrid system differential chaos shift keying (SOHS-DCSK) applies chaotic shape-forming filter to the traditional chaotic differential keying scheme, and the corresponding matched filter can be used to maximize the signal-to-noise ratio of the receiver and improve the reliability of information transmission in the DCSK system. Since SOHS-DCSK needs to send a reference signal every time information is transmitted, it has low energy efficiency.

[0004] Chaotic shape-forming filter improves the practicality and compatibility of chaotic signals through spectrum optimization, and PPM modulation enhances the concealment and energy efficiency of chaotic communication from the perspective of time domain coding. The combination of the two has unique advantages in anti-interference, low power consumption and high security scenarios. The present application directly transmits the symbol sequence generated by the PPM modulator through the channel after pulse shaping using the chaotic shape-forming filter, without the need to transmit a reference signal, which can transmit more data under the same transmission energy and improve the energy efficiency. SUMMARY

[0005] The purpose of the present application is to provide a time-indexed chaotic communication modulator and demodulator based on a chaotic shape-forming filter and a method, which does not need to transmit a reference signal and further improves the bit error rate performance of SOHS-DCSK.

[0006] To achieve the above purpose, the present application adopts the following technical solutions:

[0007] A time-indexed chaotic communication modulation method based on a chaotic shaping filter, comprising the following steps:

[0008] Step 1: Set the communication system parameters, set the sending information rate to , unit is , corresponding to a bit symbol duration , is the base frequency of the chaotic shaping filter.

[0009] Step 2: Generate bit index bits and bit modulation bits that need to be sent in the current symbol period, where .

[0010] Step 3: Perform bit symbol conversion on the bit index bits generated in step 2 to generate a ary position index symbol.

[0011] Step 4: Perform polarity transformation on the bit modulation bits generated in step 2 to generate bit serial bipolar bits.

[0012] Step 5: According to the ary position index symbol generated in step 3, insert bit 0 into a specific one of interval positions, and sequentially insert the remaining bipolar bits generated in step 4 into the interval positions to generate a sending symbol sequence , is a positive integer.

[0013] Step 6: Generate a sending chaotic signal . Send the sending symbol sequence generated in step 5 into the chaotic shaping filter for pulse shaping to generate a sending chaotic signal , and the expression of the output signal of the chaotic shaping filter is as follows:

[0014] , where is the bit in the sending symbol sequence , is the base frequency of the chaotic shaping filter, and is the basis function of the chaotic shaping filter, and its expression is:

[0015]

[0016] where This is the fundamental frequency of the chaotic shaping filter.

[0017] This invention also discloses a time-indexed chaotic communication modulator based on a chaotic shaping filter, comprising a bit symbol converter, a polarity converter, a PPM modulator, and a chaotic shaping filter, wherein:

[0018] The bit sign converter is used to change index bits into index signs.

[0019] The polarity converter is used to convert the original bit stream into polarity modulated bits.

[0020] The PPM modulator is used to generate Each interval position, and then based on the generated The base position index sign inserts bit 0 into One of the interval positions, and the remaining interval positions are inserted sequentially. One bipolar modulation bit, thereby generating the transmission sequence. .

[0021] The chaos shaping filter is used to generate chaotic signals. .

[0022] On the other hand, the present invention also discloses a time-indexed chaotic communication demodulation method based on a chaotic shaping filter, comprising the following steps:

[0023] Step S1: Receive the signal Perform chaotic matched filtering. Receive the received signal from the transmitter. The signal is then fed into a chaotic matched filter for chaotic matched filtering to obtain the demodulated signal. The expression for the output signal of the matched filter is as follows:

[0024] ,

[0025] in The output signal of the chaotic matched filter. The input signal for the chaotic matched filter. Represents the integral variable. Describing the basis functions of a chaotic matched filter Delay time Chaotic matched filter basis function is a basis function The reverse of time, that is .

[0026] Step S2: Extract the optimal signal-to-noise ratio point by sampling the matched filter output signal generated in step S1. According to sampling interval Perform maximum signal-to-noise ratio (MSNR) point sampling to obtain the maximum MSNR point sampling sequence. Its expression is:

[0027] ,

[0028] in, It is a positive integer. The duration of a bit symbol.

[0029] Step S3: Sample the maximum signal-to-noise ratio point sequence generated in step S2. The data is fed into the minimum absolute value detector, which takes the absolute value of each element and finds the index of the element with the smallest absolute value. .

[0030] Step S4: Find the index of the element with the smallest absolute value found in Step S3. The data is fed into the index bit demodulator, which then converts the index value into a digital input. Convert to binary and demodulate the index bits .

[0031] Step S5: Sample the maximum signal-to-noise ratio point sequence generated in step S2. and the index of the smallest absolute value element found in step S3 The data is fed into the modulation bit demodulator, which then converts the index generated in step S3 into a digit. The corresponding sampling points are sampled from the maximum signal-to-noise ratio point sampling sequence generated in step S2. Remove from the middle to obtain the sampling sequence with the smallest absolute value removed. .

[0032] Step S6: Remove the element with the smallest absolute value from the sampling sequence generated in step S5. Threshold decision is performed in the modulation bit demodulator to demodulate the modulation bits. The decision rule is as follows: when the sampled sequence value is greater than the threshold value 0, the demodulated data bits are "1"; otherwise, the demodulated data bits are "0".

[0033] Furthermore, this invention also discloses a demodulator for a time-indexed chaotic communication demodulation method based on a chaotic shaping filter, comprising a chaotic matched filter, a sampling switch, an absolute minimum detector, an index bit demodulator, and a modulation bit demodulator, wherein:

[0034] The chaotic matched filter is used to process the received signal. Perform chaotic matched filtering.

[0035] The sampling switch is used to process the chaotic matched-filtered output signal. The sampling interval is Time-domain sampling yields the point sampling sequence with the highest signal-to-noise ratio. .

[0036] The single absolute minimum detector is used to find the sampling sequence with the maximum signal-to-noise ratio. The index of the element with the smallest absolute value .

[0037] The single index bit demodulator is used to convert the input index value Convert to binary and demodulate the index bits .

[0038] The one modulation bit demodulator is used to convert the index The sampling sequence corresponding to the sampling point with the smallest absolute value is sampled from the point with the largest signal-to-noise ratio. Removing from the middle yields a new sampling sequence. At the same time, Each sample value is used for threshold decision demodulation with a threshold of zero to obtain the modulation bits. .

[0039] As can be seen from the above technical solution, this invention discloses a time-indexed chaotic communication modulation and demodulation method and system based on a chaotic shaping filter. This invention employs a Pulse Position Modulation (PPM) modulator, which uses a dual information encoding mechanism. Bit index bits are mapped to One of the time slot positions is used, and a bit 0 is inserted in this specific time slot. The remaining time slot positions transmit bipolar modulation bits to achieve hybrid modulation. Therefore, with the same transmission energy, a certain number of bits can be transmitted within one symbol. This invention achieves better bit error rate performance by reducing the number of bits. It employs a chaotic shaping filter to directly transmit the symbol sequence generated by the PPM modulator through the channel after pulse shaping, eliminating the need for a reference signal. This allows for the transmission of more data with the same transmission energy, improving transmission efficiency. At the receiving end, chaotic matched filtering is applied to the received signal, and sampling is performed at the optimal signal-to-noise ratio point to maximize signal detection performance and enhance the system's noise and interference resistance. Compared to existing second-order hybrid differential chaotic shift keying systems, this invention reduces the bit error rate of the system without transmitting a reference signal.

[0040] This invention optimizes the spectrum and improves the practicality and compatibility of chaotic signals through a chaotic shaping filter, while PPM modulation enhances the concealment and energy efficiency of chaotic communication from a time-domain coding perspective. The combination of these two methods demonstrates unique advantages in scenarios requiring strong anti-interference capabilities, low power consumption, and high security.

[0041] The application directly transmits the symbol sequence generated by the PPM modulator through the channel after pulse shaping, does not need to transmit a reference signal, can transmit more data under the same transmission energy, improves the transmission efficiency, performs chaotic matching filtering on the received signal at the receiving end, samples and extracts at the best signal-to-noise ratio point, maximizes the signal detection performance, and enhances the anti-noise and anti-interference capability. Compared with SOHS-DCSK, the bit error rate performance is improved. BRIEF DESCRIPTION OF DRAWINGS

[0042] Figure 1 The overall flowchart of the embodiment of the application is shown in the figure;

[0043] Figure 2 The structural diagram of the time-indexed chaotic communication modulator based on the chaotic shaping filter according to the embodiment of the application is shown in the figure;

[0044] Figure 3 The chaotic signal output by the chaotic matching filter and the corresponding discrete symbol according to the embodiment of the application are shown in the figure;

[0045] Figure 4 The structural diagram of the time-indexed chaotic communication demodulator based on the chaotic shaping filter according to the embodiment of the application is shown in the figure;

[0046] Figure 5 The chaotic matching filter output signal and the best sampling point according to the embodiment of the application are shown in the figure;

[0047] Figure 6 The bit error rate performance comparison diagram of the modulation and demodulation method of the application and the existing SOHS-DCSK method in an additive white Gaussian noise channel under the condition of the same transmission rate is shown in the figure. DETAILED DESCRIPTION

[0048] To make the purpose, technical scheme and advantages of the embodiments of the application clearer, the technical scheme in the embodiments of the application will be described clearly and completely below with reference to the drawings in the embodiments of the application. Obviously, the described embodiments are some embodiments of the application, but not all the embodiments of the application.

[0049] REFERENCE Figures 1-5 For one embodiment of the application, the embodiment provides a time-indexed chaotic communication modulation and demodulation method based on a chaotic shaping filter, including a modulation method and a demodulation method.

[0050] The modulation system of the time-indexed chaotic communication modulation method based on the chaotic shaping filter according to the embodiment of the application is shown in the figure, including a bit symbol converter, a polarity converter, a PPM modulator and a chaotic shaping filter. Figure 2

[0051] ​The bit sign converter is used to change index bits into index signs.

[0052] The polarity converter is used to convert the original bit stream into polarity modulated bits.

[0053] The PPM modulator is used to generate Each interval position, and then based on the generated The base position index sign inserts bit 0 into One of the interval positions, and the remaining interval positions are inserted sequentially. One bipolar modulation bit, thereby generating the transmission sequence. .

[0054] The chaos shaping filter is used to generate chaotic signals. .

[0055] At the transmitting end, the signal is subjected to time-indexed chaotic communication modulation based on a chaotic shaping filter, specifically including:

[0056] Step 1: Set communication system parameters. In this example, the information transmission rate is set to [value missing]. The duration of a corresponding bit symbol The fundamental frequency of the chaotic shaping filter is .

[0057] Step 2: Prepare the binary information to be sent, and pre-generate the 2 index bits to be sent within the current symbol period. and 3-bit modulation bits .

[0058] Step 3: Convert the 2-bit index bit generated in Step 2 to generate a 4-ary position index symbol (symbol 1).

[0059] Step 4: Perform a polarity transformation on the 3-bit modulation bits generated in Step 2 to generate 3-bit serial bipolar bits. .

[0060] Step 5: The PPM modulator inserts bit 0 into a specific position 1 in one of the four interval positions according to the 4-ary index symbol generated in step 3, and then inserts the bipolar modulation bits generated in step 4 into the remaining interval positions in sequence. This generates a sequence of transmitted symbols. .

[0061] Step 6: Generate and transmit chaotic signals The transmitted symbol sequence generated in step 5 The signal is fed into a chaotic shaping filter for pulse shaping to generate the transmitted chaotic signal. Among them, the base frequency Be configured as As shown in Figure 3 the chaotic signal output by the chaotic matched filter and the corresponding transmitted symbol sequence , wherein the solid line is a continuous chaotic signal , and the dashed line is a discrete symbol sequence embedded therein , because the base frequency of the configured chaotic shaping filter , four discrete symbols are generated within 1S.

[0062] In another aspect, the present application also discloses a demodulation system of a chaotic communication demodulation method based on a chaotic shaping filter, as shown in Figure 4 , comprising a chaotic matched filter, one sampling switch, one absolute minimum value detector, one index bit demodulator, and one modulation bit demodulator, wherein:

[0063] The chaotic matched filter is used to perform chaotic matched filtering on the received signal .

[0064] The one sampling switch is used to perform time domain sampling with a sampling interval of on the output signal of the chaotic matched filtering to obtain a maximum signal-to-noise ratio point sampling sequence .

[0065] The one absolute minimum value detector is used to find the index value of the element with the minimum absolute value in the maximum signal-to-noise ratio point sampling sequence .

[0066] The one index bit demodulator is used to convert the input index value into a binary number and demodulate the index bit .

[0067] The one modulation bit demodulator is used to remove the sampling point corresponding to the absolute minimum value of the index from the maximum signal-to-noise ratio point sampling sequence to obtain a new sampling sequence , and simultaneously perform threshold decision demodulation on the sampling values with a threshold of zero to demodulate the modulation bit .

[0068] At the receiving end, the signal is received and demodulated, specifically including:

[0069] Step S1: Chaotic matched filtering is performed on the received signal . The received signal from the sending end is received ​​The signal is then fed into a chaotic matched filter for chaotic matched filtering to obtain the demodulated signal. ,like Figure 5 The chaotic matched filter output signal shown As can be seen, the chaotic matched filter effectively reduces the impact of noise.

[0070] Step S2: Extract the optimal signal-to-noise ratio point by sampling the matched filter output signal generated in step S1. according to Periodically perform maximum signal-to-noise ratio (MSNR) point sampling to obtain the maximum MSNR point sampling sequence. Its expression is:

[0071] ,

[0072] in, It is a positive integer. The duration of a bit symbol.

[0073] In the embodiments, according to The expression calculates the sampling time sequence with the maximum signal-to-noise ratio for the matched-filtered signal. For the first symbol, the calculated sampling time is 0.125s. For the second symbol, the sampling time is 0.375s. For the third symbol, the sampling time is 0.625s. For the fourth symbol, the calculated sampling time is 0.875s. Figure 5 The circular markers represent the optimal sampling points of the chaotic matched filter output signal in this embodiment of the invention, and the corresponding sampling sequences. .

[0074] Step S3: Sample the maximum signal-to-noise ratio point sequence generated in step S2. The data is fed into the minimum absolute value detector, which takes the absolute value of each element and finds the index of the element with the smallest absolute value. .

[0075] Step S4: Find the index of the element with the smallest absolute value found in Step S3. The data is fed into the index bit demodulator, which will... Convert to binary number And demodulate the index bits .

[0076] Step S5: Sample the maximum signal-to-noise ratio point sequence generated in step S2. and the index of the smallest absolute value element found in step S3 The sample is fed into the modulation bit demodulator. The modulation bit demodulator takes the sampling point with the smallest absolute value found in step S3, index 1, corresponding to the sampling point -0.0509, from the maximum signal-to-noise ratio point sample sequence generated in step S2. The sample sequence with the smallest removed absolute value is obtained .

[0077] Step S6: obtaining the sample sequence with the smallest removed absolute value from the sample sequence generated in step S5 Threshold decision is made in the modulation bit demodulator, and the decision rule is: if the sample sequence value> threshold value 0, then the demodulated data bit is "1", otherwise, the demodulated data bit is "0". In the embodiment, the demodulated modulation bit is , and thus the communication is completed.

[0078] In the embodiment, 2-bit index bits and 3-bit modulation bits are transmitted, and the base frequency of the chaotic shaping filter is set to .

[0079] Figure 6 The bit error rate performance of the method of the application obtained by simulation in an additive white Gaussian noise channel is shown in the figure. As a comparison, the bit error rate performance of the existing SOHS-DCSK method obtained by simulation under the same conditions is also shown in the figure. It can be seen from the figure that the application has better bit error rate performance compared with the existing SOHS-DCSK method.

[0080] In summary, the embodiments of the application improve the energy efficiency and the bit error rate performance of the system without the need to transmit reference signals.

[0081] The above embodiments are only used to illustrate the technical solutions of the application, rather than limit them; although the application has been described in detail with reference to the foregoing embodiments, it should be understood by those skilled in the art that the technical solutions recorded in the foregoing embodiments can be modified, or some technical features can be replaced by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the application.

Claims

1. A chaotic filter based time-index communication modulation method, characterized by, comprising the steps of Step 1: Set the communication system parameters, and set the information transmission rate to [value missing]. The unit is The duration of a corresponding bit symbol , This is the fundamental frequency of the chaotic shaping filter; Step 2: generate the bits to be transmitted in the current symbol period bit index bits and bit modulation bits where ; Step 3: Bit sign conversion is performed on the bit index to generate a quaternary position index symbol ; Step 4: Perform a polarity transform on the bit modulated bits generated in Step 2 to generate bit string bipolar bits; and bit string bipolar bits; and Step 5: Based on the results generated in Step 3 The base position index sign inserts bit 0 into Select one of the interval positions, and insert the remaining interval positions sequentially into the positions generated in step 4. One bipolar bit is used to generate the transmitted symbol sequence. , It is a positive integer; Step 6: The sequence of transmit symbols generated in Step 5 is fed into a chaotic shaping filter for pulse-shaping filtering to generate a transmitted chaotic signal Step 7: The transmitted chaotic signal is transmitted over the channel ; comprising comprising the steps of The expression of the chaotic shaping filter output signal is as follows: wherein is the kth symbol of the transmitted symbol sequence bit, is the base frequency of the chaotic shaping filter, is the basis function of the chaotic shaping filter, which is expressed as wherein is the fundamental frequency of the chaotic shaper.

2. A chaotic filter based time-index communication modulator for implementing the time-index communication modulation method of claim 1, characterized by: comprising a bit-to-symbol converter, a polarity converter, a PPM modulator, a chaotic shaping filter, wherein: the bit-to-symbol converter is used to change the index bits into index symbols; the polarity converter is used to convert the original bit stream into polarity modulation bits; The PPM modulator is used to generate one of the interval positions, and the rest of the interval positions are sequentially inserted with binary modulation bits, thereby generating a transmission sequence ;​​ The chaotic shaping filter is used to generate a chaotic signal .

3. A chaotic filter based time index communication modulator according to claim 2, wherein, Chaotic signal The expression of the chaotic signal is as follows: wherein is the kth symbol of the transmitted symbol sequence bit, is the base frequency of the chaotic shaping filter, is the basis function of the chaotic shaping filter, which is expressed as wherein is the fundamental frequency of the chaotic shaper.

4. A method of demodulating a time-indexed communication based on a chaotic filter, characterized in that, comprising the steps of Step S1: receiving signal The received signal from the transmitting end is subjected to chaotic matched filtering The received signal from the transmitting end is subjected to chaotic matched filtering The expression of the output signal of the chaotic matched filter is as follows: ， wherein is the chaotic matched filter output signal, is the chaotic matched filter input signal, denotes the integration variable, denotes the chaotic matched filter basis function delay time , chaotic matched filter basis function basis function the inverse of the time of ; Step S2: optimum SNR point sampling extraction, the matched filter output signal generated in step S1 is sampled at the optimum SNR point at a sampling interval to obtain a maximum SNR point sampling sequence whose expression is: ， wherein is a positive integer, is the duration of one bit symbol; Step S3: sampling the maximum signal-to-noise ratio point generated in step S2 into an absolute value minimum detector, which takes the absolute value of each element and finds the index of the element with the minimum absolute value ; Step S4: finding the index of the element with the smallest absolute value in step S3 into an index bit demodulator, which converts the index value into a binary number and demodulates the index bit ; Step S5: Sample the maximum signal-to-noise ratio point sequence generated in step S2. and the index of the smallest absolute value element found in step S3 The data is fed into the modulation bit demodulator, which then converts the index generated in step S3 into a digit. The corresponding sampling points are sampled from the maximum signal-to-noise ratio point sampling sequence generated in step S2. By removing the sampled points, we obtain the sampling sequence with the smallest absolute value after removing the sampled points. ; Step S6: removing the minimum element of the absolute value from the sampling sequence generated in step S5 Threshold decision is made in the modulated bit demodulator to demodulate the modulated bit The decision rule is: if the sampling sequence value is greater than the threshold value 0, then the demodulated data bit is "1", otherwise, the demodulated data bit is "0".

5. A chaotic filter based time-indexed communication demodulator for implementing the time-indexed communication demodulation method of claim 4, characterized by: comprising a chaotic matched filter, 1 sample switch, 1 absolute value minimum detector, 1 index bit demodulator, 1 modulation bit demodulator, wherein: The chaotic matched filter is used to chaotically matched filter the received signal ; The 1 sampling switch is used for sampling the output signal filtered by the chaotic matched filter The sampling interval is The time domain sampling is performed to obtain a maximum signal-to-noise ratio point sampling sequence ; The 1 absolute value minimum detector is used to find the maximum signal to noise ratio point sample sequence The index value of the element with the smallest absolute value ; The 1 index bit demodulator is used to demodulate the input index value into a binary number and demodulate the index bits ; The one modulation bit demodulator is used to convert the index The sampling sequence corresponding to the sampling point with the smallest absolute value is sampled from the point with the largest signal-to-noise ratio. Removing from the middle yields a new sampling sequence. At the same time, Each sample value is used for threshold decision demodulation with a threshold of zero to obtain the modulation bits. .

6. A chaotic filter based time index communication demodulator according to claim 5, characterized by: Chaotic matched filter output signal The expression is as follows: ， wherein is the chaotic matched filter output signal, is the chaotic matched filter input signal, denotes the integration variable, denotes the chaotic matched filter basis function delay time , chaotic matched filter basis function basis function the inverse of the time of the basis function, i.e. .

7. A chaotic filter based time index communication demodulator according to claim 5, characterized by: Obtaining maximum signal-to-noise ratio point sample sequences , the expression is: ， wherein is a positive integer, is the duration of one bit symbol.

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