CN115550127A - Carrier index multi-system chaotic modulation and demodulation method based on code shift and modem - Google Patents
Carrier index multi-system chaotic modulation and demodulation method based on code shift and modem Download PDFInfo
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- H04L27/00—Modulated-carrier systems
- H04L27/26—Systems using multi-frequency codes
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- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
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- H04L27/18—Phase-modulated carrier systems, i.e. using phase-shift keying
- H04L27/20—Modulator circuits; Transmitter circuits
- H04L27/2032—Modulator circuits; Transmitter circuits for discrete phase modulation, e.g. in which the phase of the carrier is modulated in a nominally instantaneous manner
- H04L27/2053—Modulator circuits; Transmitter circuits for discrete phase modulation, e.g. in which the phase of the carrier is modulated in a nominally instantaneous manner using more than one carrier, e.g. carriers with different phases
- H04L27/206—Modulator circuits; Transmitter circuits for discrete phase modulation, e.g. in which the phase of the carrier is modulated in a nominally instantaneous manner using more than one carrier, e.g. carriers with different phases using a pair of orthogonal carriers, e.g. quadrature carriers
- H04L27/2067—Modulator circuits; Transmitter circuits for discrete phase modulation, e.g. in which the phase of the carrier is modulated in a nominally instantaneous manner using more than one carrier, e.g. carriers with different phases using a pair of orthogonal carriers, e.g. quadrature carriers with more than two phase states
- H04L27/2071—Modulator circuits; Transmitter circuits for discrete phase modulation, e.g. in which the phase of the carrier is modulated in a nominally instantaneous manner using more than one carrier, e.g. carriers with different phases using a pair of orthogonal carriers, e.g. quadrature carriers with more than two phase states in which the data are represented by the carrier phase, e.g. systems with differential coding
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- H04L27/26—Systems using multi-frequency codes
- H04L27/2601—Multicarrier modulation systems
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- H04L27/00—Modulated-carrier systems
- H04L27/26—Systems using multi-frequency codes
- H04L27/2601—Multicarrier modulation systems
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- H04L27/2649—Demodulators
Abstract
A carrier index multi-system chaotic modulation and demodulation method based on code shift and a modem relate to the technical field of communication signal processing. In addition, the system adopts a repeating circuit at a sending end and an average processing at a receiving end, thereby greatly reducing the noise component in a decision variable and further improving the bit error code performance of the system. Meanwhile, the invention can avoid using time delay units in the receiving end and the transmitting end, effectively reduce the noise component in the decision variable of the receiving end, improve the bit error code performance of the system and obtain lower bit error code rate.
Description
Technical Field
The invention relates to the technical field of communication signal processing, in particular to a carrier index multi-system chaotic modulation and demodulation method based on code shift and a modem.
Background
Most of the existing chaotic digital modulation and demodulation methods are based on a transmission reference method, namely, a carrier signal and a signal carrying information are sent to a receiving end. The Differential Chaos Shift Keying (DCSK) modulation and demodulation method does not need to complete channel estimation, can obtain better error code performance, and shows strong competitiveness in many practical application occasions (namely, wireless personal area networks, wireless sensor networks and the like). However, to ensure orthogonality between the reference signal and the information signal, the DCSK transmits the two signals in different time periods, and thus both the transmitting end and the receiving end must use a delay unit. In ultra-wideband transmission, it is almost impossible to integrate an analog delay unit by using the existing process, and a delay unit implemented in a digital manner consumes huge power.
The Multi-Carrier Differential Shift Keying (MC-DCSK) modulation and demodulation method uses a plurality of subcarriers to simultaneously transmit a reference signal and a plurality of paths of information signals, and distinguishes the reference signal and each path of information signals through different subcarriers. Of all the subcarriers, only 1 subcarrier is allocated to the reference signal, and the remaining subcarriers are allocated to the information signal, and 1 subcarrier is occupied per 1-way information signal. Although the MC-DCSK eliminates the delay unit in the transceiver, the bit error rate of the MC-DCSK is still higher and the bit error performance is not ideal compared with the traditional Binary Phase Shift Keying (BPSK).
Disclosure of Invention
One of the purposes of the present invention is to provide a code shift-based high data rate carrier index multilevel differential chaos keying modulation and demodulation method, so as to solve the problems of high bit error rate, poor bit error performance and low data rate of the existing MC-DCSK modulation and demodulation method.
In order to achieve the purpose, the invention adopts the following technical scheme: a carrier index multilevel chaotic modulation and demodulation method based on code shift comprises the following steps:
converting information to be transmitted into N groups of parallel information in a serial-parallel mode, dividing each group of information into P index bits and 1 modulation bit, wherein each group of index bits is selected by an index selector to be 2 P 1 carrier wave in the carrier waves carries out information bit transmission; after N modulation bits pass through a bit symbol converter, multi-system differential chaos keying modulation is carried out: generating a chaotic signal by a chaotic generator, repeating the chaotic signal for T times, selecting a signal obtained by multiplying 1 Walsh sequence by the chaotic signal as a reference signal, multiplying another 2N different Walsh sequences by the chaotic signal, and inputting the multiplied signal into a multilevel DCSK modulator, wherein in the multilevel DCSK modulator, an odd number of Walsh sequences are multiplied by the chaotic signal and then multiplied by a real part in a multilevel constellation symbol, and an even number of Walsh sequences are multiplied by the chaotic signal and then multiplied by an imaginary part in the multilevel constellation symbol to respectively obtain N paths of multilevel DCSK modulated signals; multiplying the N paths of multi-system DCSK modulation signals by the mapped index bits, adding the N paths of multi-system DCSK modulation signals to the reference signals, and sending the N paths of multi-system DCSK modulation signals to a channel;
at the receiving end:
recovering the reference signal and the 2N paths of information signals respectively through multi-carrier demodulation; and obtaining the averaged reference signal sequence, performing correlation demodulation with the 2N information signal sequences respectively, recovering an index bit and a modulation bit through the energy comparator and the multi-system DCSK demodulation, and finally outputting original information through parallel-serial conversion.
Specifically, at the transmitting end, the signal modulation includes the steps of:
1) Carrying out serial-parallel conversion on an input information signal, and dividing the input information signal into N groups of information, wherein each group of information comprises two parts, namely a P-bit index bit and a 1-bit modulation bit;
2) Passing N groups of index bits through a mapping selector from 2 P Selecting one carrier from the carriers for transmission;
3) The N groups of modulation bits are processed by a bit symbol converter to obtain a constellation symbol s of each group of modulation bits m,i ＝a m,i +ib m,i ；
4) Generating a Logistic chaotic signal with the length of theta, and repeating for T times;
5) Generating 512 by 512 Hadamard matrices from which each row is selected as a Walsh code;
6) Mixing the chaotic signal x with the 1 st Walsh sequence W r Performing a kronecker product multiplication to obtain a reference signal
And is connected with the carrier f 0 Multiplying;
7) Mixing the chaotic signal x with the 2m-1 Walsh sequence W 2m-1 Multiplying by a kronecker product to obtain
Chaotic signal x and 2m Walsh sequence W 2m Multiplying by a kronecker product to obtain
8) The mth constellation symbol s m,i ＝a m,i +ib m,i Real and imaginary parts of (1) and
and
multiplying to realize code shift multi-system DCSK signals;
9) Multiplying the N groups of code shift multi-system DCSK signals by the result of the step 2, and adding the multiplied result to the reference signal of the step 6 to obtain a sending signal of a sending end:
further, at the receiving end, the signal demodulation comprises the following steps:
10 Receiving the signal transmitted in step 9), and comparing it with 2 P Multiplying the +1 synchronous carriers respectively to obtain n paths of product signals;
11 ) 2 obtained in step 10) P The +1 paths of product signals are respectively carried outMatched filtering, of filtered 2 P Time domain sampling is carried out on the +1 path of product signals, and each path of sampled signals respectively passes through a matrix B and a matrix A to obtain 1 path of reference signals and 2N paths of information signals;
12 2N +1 paths of signals obtained in step 11) are multiplied by corresponding Walsh sequences respectively, and obtained results are averaged;
13 Respectively correlating the averaged reference signal sequence obtained in the step 12) with the 2N paths of information signal sequences obtained in the step 11) to obtain 2N correlation values;
14 Respectively combining the real part and the imaginary part of the 2N correlation values obtained in the step 13), and respectively obtaining an element with the maximum absolute value through N energy comparators, so that index bits can be demodulated;
15 Respectively combining the real part and the imaginary part of the 2N correlation values obtained in the step 15), respectively passing through N energy comparators, then passing through a code shift multi-system DCSK demodulator, and then performing symbol bit conversion to recover modulation bits;
16 ) combining the index bit obtained in step 14) and the modulation bit obtained in step 15), and then performing parallel-to-serial conversion to recover the original information signal.
In addition, the invention also provides a carrier index multilevel chaotic modem based on code shift, which comprises a modulator and a demodulator, and the information is modulated and demodulated by adopting the method.
In an embodiment of the present invention, the modulator modulates the input information signal according to the method of the above steps 1) to 9).
Further, the demodulator demodulates the received signal according to the method of the above step 10) to step 16).
In an embodiment of the invention, the modulator includes a chaotic signal generator, a pulse shaping filter, a serial-to-parallel conversion circuit, a repeating circuit, N index selectors, N × 2 P A plurality of carrier multipliers, a plurality of N carrier adders, a plurality of N +1 modulation multipliers, a plurality of 2N +1 Walsh sequence multipliers and a plurality of N code shift multi-system modulators;
the chaotic signal generator is used for generating dispersionThe chaotic signal sequence is subjected to pulse shaping filtering through a pulse shaping filter to obtain a DCSK reference signal in the current symbol period; the pulse shaping filter is used for filtering pulse shaping to obtain a reference signal in the current symbol period; the serial-to-parallel conversion circuit is used for converting serial data bits to be transmitted in the current symbol time into parallel data bits; the repeating circuit is used for repeating the chaotic signal so as to reduce noise interference; the N index selectors are used for selecting one carrier wave to transmit signals according to index bits; the N is 2 P The carrier multiplier is used for multiplying the carrier modulation coefficient with the carrier to realize carrier index modulation; the N carrier adders are used for adding signals multiplied by carriers; the N +1 modulation multipliers are used for multiplying the carrier index modulation signal with a code shift multi-system DCSK signal; the 2N +1 Walsh sequence multipliers are used for multiplying the chaotic signals by the 2N +1 Walsh sequences; the N code-shift multi-system modulators are used for realizing code-shift multi-system DCSK modulation.
Wherein the demodulator comprises 2 P +1 carrier multipliers, 2 P +1 matched filters, 2 P +1 sampling switches, 2N +1 decoding shift circuits, 2N correlators, N energy comparators, N multi-system threshold decision devices, N sign bit conversion circuits and a parallel-serial conversion circuit;
2 is described P +1 carrier multiplier utilization 2 P The +1 synchronized subcarriers are multiplied by the received signals, respectively, to obtain 2 P +1 product signals; 2 is described P +1 matched filter pairs 2 P The +1 product signals are respectively subjected to matched filtering; 2 is described P +1 sampling switch pairs match filtered 2 P The +1 product signals are respectively subjected to time domain sampling to recover 1 path of discrete reference signal sequence and 2 paths of discrete reference signal sequence P A channel discrete information signal sequence; the 2N +1 decoding shift circuits multiply and add sampling results with Walsh codes; the 2N correlators respectively correlate the recovered reference signals with output signals of the decoding shift circuit; the N energy comparators compare the energy of the N paths of signals respectively so as to demodulate index bits; the N multi-system threshold decisionsThe element with the largest absolute value is output by the machine; the N symbol bit conversion circuits convert the symbols into modulation bits and output the modulation bits; and the parallel-serial conversion circuit combines the obtained N paths of index bits and modulation bits into 1 path of serial demodulation data bit respectively and outputs the data bit.
In the code shift-based carrier index multilevel chaotic modulation and demodulation method and the modulator-demodulator, information transmission is carried out through an MDSK constellation and a carrier label, so that the data transmission rate and the energy efficiency of the system are greatly increased. Meanwhile, the invention can avoid using time delay units in the receiving end and the transmitting end, effectively reduce the noise component in the decision variable of the receiving end, improve the bit error code performance of the system and obtain lower bit error code rate.
Drawings
Fig. 1 is a flowchart illustrating a modulation and demodulation method according to an embodiment.
Fig. 2 is a schematic structural diagram of a modulator in an embodiment.
Fig. 3 is a schematic structural diagram of a demodulator in the embodiment.
Fig. 4 is a graph comparing the error performance of the modulation and demodulation method according to the embodiment and the existing MCS-MDCSK method in an additive white gaussian noise channel.
Detailed Description
In order to facilitate understanding of those skilled in the art, the present invention will be further described with reference to the following embodiments and accompanying drawings.
In summary, the present invention converts the information to be transmitted into N sets of parallel information by serial-parallel conversion, and divides each set of information into P index bits and 1 modulation bit, wherein each set of index bits is selected by an index selector to be 2 P 1 carrier wave in the carrier waves carries out information bit transmission; the N modulation bits pass through a bit symbol converter and then are subjected to multilevel differential chaotic keying modulation, and the multilevel differential chaotic keying modulation is realized by using a code shift technology: chaotic signal generated by chaotic generatorRepeating the process for T times, selecting a signal obtained by multiplying 1 Walsh sequence by the chaotic signal as a reference signal, multiplying another 2N different Walsh sequences by the chaotic signal and inputting the multiplied signal to a multilevel DCSK modulator, wherein in the multilevel DCSK modulator, the odd numbered Walsh sequences are multiplied by the chaotic signal and then multiplied by a real part in multilevel constellation symbols, and the even numbered Walsh sequences are multiplied by the chaotic signal and then multiplied by an imaginary part in the multilevel constellation symbols to respectively obtain N paths of multilevel DCSK modulation signals; and multiplying the N paths of multi-system DCSK modulation signals by the mapped index bits, adding the N paths of multi-system DCSK modulation signals to the reference signals, and sending the signals to a channel. At a receiving end, respectively recovering a reference signal and 2N paths of information signals through multi-carrier demodulation; and obtaining an averaged reference signal sequence, performing correlation demodulation on the averaged reference signal sequence and 2N paths of information signal sequences respectively, performing demodulation through an energy comparator and a multi-system DCSK (data rate shift keying) to recover index bits and modulation bits, and finally performing parallel-serial conversion to output original information.
Fig. 1 shows a specific process of code shift-based high data rate carrier index multi-system differential chaos keying modulation and demodulation, which includes the following steps:
at a sending end:
step 1: carrying out serial-parallel conversion on an input information signal, and dividing the input information signal into N groups of information, wherein each group of information comprises two parts, namely a P-bit index bit and a 1-bit modulation bit;
step 2: passing N groups of index bits through a mapping selector from 2 P Selecting one carrier from the carriers for transmission;
and step 3: the N groups of modulation bits are processed by a bit symbol converter to obtain a constellation symbol s of each group of modulation bits m,i ＝a m,i +ib m,i ；
And 4, step 4: generating a Logistic chaotic signal with the length of theta, and repeating the cycle for T times;
and 5: generating 512 by 512 Hadamard matrices from which each row is selected as a Walsh code;
step 6: chaotic signal x and 1 st Walsh sequence W r Performing a kronecker product multiplication to obtain a reference signal
And is connected with the carrier f 0 Multiplying;
and 7: chaotic signal x and 2m-1 Walsh sequence W 2m-1 Multiplying by a kronecker product to obtain
Chaotic signal x and 2m Walsh sequence W 2m Multiplying by a kronecker product to obtain
And 8: mth constellation symbol s m,i ＝a m,i +ib m,i The real part and the imaginary part of
And
multiplying to realize code shift multi-system DCSK signals;
and step 9: multiplying the N groups of code shift multi-system DCSK signals by the result of the step 2, and adding the multiplied result to the reference signal of the step 6 to obtain a sending signal of a sending end:
at the receiving end:
step 10: receiving the signal sent in step 9, and comparing it with 2 P Multiplying +1 synchronous carriers respectively to obtain n paths of product signals;
step 11: 2 obtained in the step 10 P The +1 paths of product signals are respectively subjected to matched filtering, and the 2 paths of product signals after filtering are subjected to matched filtering P Time domain sampling is carried out on the +1 paths of product signals, and each path of sampled signals respectively passes through a matrix B and a matrix A to obtain 1 path of reference signals and 2N paths of information signals;
step 12: multiplying the paths of signals 2N +1 obtained in the step 11 by the corresponding Walsh sequences respectively, and averaging the obtained results;
step 13: respectively correlating the averaged reference signal sequence obtained in the step 12 with the 2N paths of information signal sequences obtained in the step 12 to obtain 2N correlation values;
step 14: respectively combining the real part and the imaginary part of the 2N correlation values obtained in the step 13, and then respectively obtaining an element with the maximum absolute value through N energy comparators, so that index bits can be demodulated;
step 15: respectively combining the real part and the imaginary part of the 2N correlation values obtained in the step 13, respectively passing through N energy comparators, then passing through a code shift multi-system DCSK demodulator, and then performing symbol bit conversion to recover modulation bits;
step 16: and combining the index bits obtained in the step 14 and the modulation bits obtained in the step 15, and then performing parallel-serial conversion to recover the original information signal.
Based on the same technical concept as the modulation and demodulation method, the invention also provides a code shift-based high-data-rate carrier index multi-system differential chaos keying modem, and the modem can modulate and demodulate signals by using the method. Specifically, a certain number of subcarriers are allocated to the transmission of the index bit signals through a modulator, and modulated bits are multiplied by the modulated index bits after being subjected to the multi-input system code shift modulation. The demodulator utilizes an energy comparator, a threshold decision device and the like to realize demodulation.
Fig. 2 shows a specific structure of a modulator in a modem, which mainly includes, in overview: chaotic signal generator, pulse shaping filter, serial-parallel conversion circuit, repeating circuit, N index selectors, N x 2 P A plurality of carrier multipliers, N carrier adders, N +1 modulation multipliers, 2N +1 Walsh sequence multipliers, and N code shift multi-system modulators. Secondly, the chaotic signal generator generates a discrete chaotic signal sequence, and pulse shaping filtering is carried out through a pulse shaping filter to obtain a DCSK reference signal in the current symbol period; the pulse shaping filter is used for filtering pulse shaping to obtain a reference signal in the current symbol period; serial-to-parallel conversion circuit converts serial data bits to be transmitted in current symbol time into parallelA data bit; the repeating circuit repeats the chaotic signal to reduce noise interference; n index selectors are used for selecting one carrier wave to transmit signals according to index bits; n2 P The carrier multiplier multiplies the carrier modulation coefficient by the carrier to realize the carrier index modulation; the N carrier adders add the signals multiplied by the carriers; the N +1 modulation multipliers are used for multiplying a carrier index modulation signal and a code shift multi-system DCSK signal; 2N +1 Walsh sequence multipliers multiply the chaotic signal with 2N +1 Walsh sequences; the N code shift multi-system modulators realize code shift multi-system DCSK modulation.
Fig. 3 shows the structure of a demodulator in a modem, which comprises in particular 2 P +1 carrier multiplier, 2 P +1 matched filters, 2 P +1 sampling switches, 2N +1 decoding shift circuits, 2N correlators, N energy comparators, N multi-system threshold decision devices, N sign bit conversion circuits and a parallel-serial conversion circuit; 2 is described P +1 carrier multiplier utilization 2 P The +1 synchronized subcarriers are multiplied by the received signals, respectively, to obtain 2 P +1 product signals. 2 above P +1 matched filter pairs 2 P The +1 product signals are respectively subjected to matched filtering; 2 P +1 sampling switch pairs matched filtered 2 P The +1 product signals are respectively subjected to time domain sampling to recover 1 path of discrete reference signal sequence and 2 paths of discrete reference signal sequence P A sequence of road discrete information signals; 2N +1 decoding shift circuits multiply and add sampling results and Walsh codes; 2N correlators respectively correlate the recovered reference signals with output signals of the decoding shift circuit; the N energy comparators compare the energy of the N paths of signals respectively, so that index bits can be demodulated; the N multi-ary threshold deciders output the element having the largest absolute value; the N symbol bit conversion circuits convert the symbols into modulation bit outputs; and combining the obtained N paths of index bits and modulation bits by the parallel-serial conversion circuit into 1 path of serial demodulation data bits and outputting the data bits.
In order to verify the specific performance of the code shift-based high data rate carrier index multilevel differential chaos keying modulation and demodulation method for reducing the bit error rate, a specific example is used for verification and description.
At a transmitting end, carrying out code shift-based high-data-rate carrier index multi-system differential chaos keying modulation on a signal, wherein the specific process comprises the following steps:
step 1: selecting the bit signal-to-noise ratio E in the channel b /N 0 When the signal length is 10dB, the length theta of a discrete chaotic signal sequence in one symbol time is 10, and the number of available carriers is 2 P Conditions of +1=9, n =800, p = 3.
Step 2: in 1 symbol period [0, tb ]]In the interior, the chaotic signal generator outputs 1 discrete chaotic signal sequence { x with the length of 10 1 ,x 2 ,...,x 16 And repeated 5 times.
And step 3: and (3) enabling the discrete chaotic signal sequence generated in the step (2) to pass through a 1-path square raised cosine roll-off filter, wherein the time domain impulse response is h (t), completing pulse shaping filtering, and obtaining a reference signal in the current symbol period:
wherein t represents time; t is c Representing the chip time.
And 4, step 4: serial data bits with length of 3200 is transmitted by 1 path in current symbol period and converted into parallel low-speed data bits by 800 paths by using serial-to-parallel conversion circuit. Each group of information comprises two parts of 3-bit index bits and 1-bit modulation bits;
and 5: simultaneously passing 800 groups of index bits through a mapping selector, and selecting one carrier from 8 carriers for transmission;
step 6: the 800 groups of modulation bits are processed by a bit symbol converter to obtain a constellation symbol s of each group of modulation bits m,i ＝a m,i +ib m,i ；
And 7: generating 512 by 512 Hadamard matrices from which each row is selected as a Walsh code;
and 8: chaotic signal x and 1 st Walsh sequence W r Performing a kronecker product multiplicationTo obtain a reference signal
And is connected with the carrier f 0 Multiplying;
and step 9: chaotic signal x and 2m-1 Walsh sequence W 2m-1 Multiplying by a kronecker product to obtain
Chaotic signal x and 2m Walsh sequence W 2m Multiplying by a kronecker product to obtain
Step 10: mth constellation symbol s m,i ＝a m,i +ib m,i The real part and the imaginary part of
And
multiplying to realize code shift multi-system DCSK signals;
step 11: and multiplying the 800 groups of code-shift multi-system DCSK signals by the result of the step 5, adding the multiplied result to the reference signal of the step 8 to obtain a sending signal of a sending end, and sending the sending signal to a demodulator:
at the receiving end, the specific process of signal demodulation is as follows:
step 12: receiving the signal sent in the step 11, and multiplying the signal by 9 synchronous carriers respectively to obtain n paths of product signals;
step 13: respectively performing matched filtering on the 9 paths of product signals obtained in the step 10, performing time domain sampling on the 9 paths of product signals after filtering, and respectively obtaining 1 path of reference signals and 1600 paths of information signals through a matrix B and a matrix A of each path of signals after sampling;
step 14: multiplying 1600+1 paths of signals obtained in step 13 by the corresponding Walsh sequences respectively, and averaging the obtained results;
step 15: respectively correlating the averaged reference signal sequence obtained in the step 14 with the 1600 paths of information signal sequences obtained in the step 12 to obtain 1600 correlation values;
step 16: respectively combining the real part and the imaginary part of the 1600 correlation values obtained in the step 15, and then respectively obtaining the element with the maximum absolute value through 800 energy comparators, thereby demodulating the index bit;
and step 17: respectively combining the real part and the imaginary part of the 1600 correlation values obtained in the step 16, respectively passing through 800 energy comparators, then passing through a code shift multi-system DCSK demodulator, and then performing symbol bit conversion to recover modulation bits;
step 18: combining the index bit obtained in the step 17 and the modulation bit obtained in the step 16, and then performing parallel-serial conversion to recover the original information signal.
The invention adopts computer simulation to test the code shift-based high data rate carrier index multi-system differential chaos keying modulation and demodulation method. In the test, the number of transmitted data bits is 3200, and a discrete chaotic signal sequence is mapped by Logistic
The chaotic signal sampling frequency is 1MHz, the symbol duration T =16 mus, the equivalent signal sampling point number in each symbol time is 16, the roll-off coefficient alpha =0.25 of the square raised cosine roll-off filter, and the central frequency interval of all subcarriers satisfies delta f =1.25MHz.
Fig. 4 shows the simulated bit error rate of the verification example in an additive white gaussian noise channel. For comparison, the bit error rate of the existing MCS-MDCSK method obtained by simulation under the same conditions is also shown in the figure. As can be seen from the figure, compared with the existing MCS-MDSK method, the method of the invention greatly reduces the bit error rate and shows better bit error performance.
In conclusion, the invention can greatly reduce the noise component in the decision variable, thereby obviously improving the bit error performance of the system. Meanwhile, the method can avoid using time delay units in the receiving end and the transmitting end, effectively reduce the noise component in the decision variable of the receiving end, improve the bit error code performance of the system and obtain lower bit error code rate.
The above embodiments are preferred implementations of the present invention, and the present invention can be implemented in other ways without departing from the spirit of the present invention.
Some of the figures and descriptions of the present invention have been simplified to provide a convenient understanding of the modifications of the invention relative to the prior art, and to omit elements for clarity, as those skilled in the art will recognize may also constitute the subject matter of the present invention.
Claims (8)
1. The code shift-based carrier index multilevel chaotic modulation and demodulation method is characterized in that:
at a sending end:
converting information to be transmitted into N groups of parallel information in a serial-parallel mode, dividing each group of information into P index bits and 1 modulation bit, wherein each group of index bits is selected by an index selector to be 2 P 1 carrier in the carrier carries out information bit transmission; after N modulation bits pass through a bit symbol converter, multi-system differential chaos keying modulation is carried out: generating a chaotic signal by a chaotic generator, repeating the chaotic signal for T times, selecting a signal obtained by multiplying 1 Walsh sequence by the chaotic signal as a reference signal, multiplying another 2N different Walsh sequences by the chaotic signal, inputting the multiplied signal into a multilevel DCSK modulator, multiplying an odd number of Walsh sequences by the chaotic signal in the multilevel DCSK modulator by a real part in a multilevel constellation symbol, multiplying an even number of Walsh sequences by the chaotic signal and then by an imaginary part in the multilevel constellation symbol to respectively obtain N paths of multilevel DCSK modulated signals; n-path multi-system DCSK modulation signalMultiplying the number by the mapped index bit, adding the number to a reference signal, and sending the signal to a channel;
at the receiving end:
recovering the reference signal and the 2N paths of information signals respectively through multi-carrier demodulation; and obtaining the averaged reference signal sequence, performing correlation demodulation with the 2N information signal sequences respectively, recovering an index bit and a modulation bit through the energy comparator and the multi-system DCSK demodulation, and finally outputting original information through parallel-serial conversion.
2. The code shift-based carrier index multilevel chaotic modem method according to claim 1, wherein at a transmitting end, the signal modulation comprises the steps of:
1) Performing serial-parallel conversion on an input information signal, and dividing the input information signal into N groups of information, wherein each group of information comprises two parts, namely a P-bit index bit and a 1-bit modulation bit;
2) N groups of index bits are passed through a mapping selector from 2 P Selecting one carrier from the carriers for transmission;
3) The N groups of modulation bits pass through a bit symbol converter to obtain a constellation symbol s of each group of modulation bits m,i ＝a m,i +ib m,i ；
4) Generating a Logistic chaotic signal with the length of theta, and repeating the cycle for T times;
5) Generating 512 by 512 Hadamard matrices from which each row is selected as a Walsh code;
6) Mixing the chaotic signal x with the 1 st Walsh sequence W r Performing a kronecker product multiplication to obtain a reference signal
And is connected with the carrier f 0 Multiplying;
7) Mixing the chaotic signal x with the 2m-1 Walsh sequence W 2m-1 Multiplying by a kronecker product to obtain
Chaotic signal x and 2m Walsh sequence W 2m Performing Crohn's patchesMultiplying by the product to obtain
8) The mth constellation symbol s m,i ＝a m,i +ib m,i The real part and the imaginary part of
And
multiplying to realize code shift multi-system DCSK signals;
9) Multiplying the result of step 2 by N groups of code shift multi-system DCSK signals, and adding the result to the reference signal of step 6 to obtain the sending signal of the sending end:
3. the code shift-based carrier index multilevel chaotic modem method according to claim 1 or 2, wherein at a receiving end, the signal demodulation comprises the steps of:
10 Receiving the signal transmitted in step 9), and comparing it with 2 P Multiplying the +1 synchronous carriers respectively to obtain n paths of product signals;
11 ) 2 obtained in step 10) P The +1 paths of product signals are respectively subjected to matched filtering, and the 2 paths of product signals after filtering are subjected to matched filtering P Time domain sampling is carried out on the +1 paths of product signals, and each path of sampled signals respectively passes through a matrix B and a matrix A to obtain 1 path of reference signals and 2N paths of information signals;
12 Respectively multiplying the 2N +1 path signals obtained in the step 11) by corresponding Walsh sequences, and averaging the obtained results;
13 Respectively correlating the averaged reference signal sequence obtained in the step 12) with the 2N paths of information signal sequences obtained in the step 11) to obtain 2N correlation values;
14 Respectively combining the real part and the imaginary part of the 2N correlation values obtained in the step 13), and then respectively obtaining an element with the maximum absolute value through N energy comparators, so that the index bit can be demodulated;
15 Respectively combining the real part and the imaginary part of the 2N correlation values obtained in the step 15), respectively passing through N energy comparators, then passing through a code shift multi-system DCSK demodulator, and then performing symbol bit conversion to recover modulation bits;
16 ) combining the index bit obtained in step 14) and the modulation bit obtained in step 15), and then performing parallel-to-serial conversion to recover the original information signal.
4. The carrier index multi-system chaotic modem based on the code shift comprises a modulator and a demodulator, and is characterized in that: a method for modulating and demodulating a signal according to claim 1.
5. The code shift-based carrier index multilevel chaotic modem according to claim 4, wherein: the modulator modulates the input information signal according to the method of steps 1) to 9) of claim 2.
6. The code shift-based carrier index multilevel chaotic modem according to claim 4 or 5, wherein: the demodulator demodulates the received signal in accordance with the method of steps 10) to 16) of claim 3.
7. The code shift-based carrier index multilevel chaotic modem according to claim 4 or 5, wherein: the modulator comprises a chaotic signal generator, a pulse shaping filter, a serial-parallel conversion circuit, a repeating circuit, N index selectors, and N x 2 P A plurality of carrier multipliers, a plurality of N carrier adders, a plurality of N +1 modulation multipliers, a plurality of 2N +1 Walsh sequence multipliers and a plurality of N code shift multi-system modulators;
the chaotic signal generator is used for generating a discrete chaotic signal sequence, and pulse shaping filtering is carried out through a pulse shaping filterObtaining a DCSK reference signal in the current symbol period; the pulse shaping filter is used for filtering pulse shaping to obtain a reference signal in the current symbol period; the serial-to-parallel conversion circuit is used for converting serial data bits to be transmitted in the current symbol time into parallel data bits; the repeating circuit is used for repeating the chaotic signal so as to reduce noise interference; the N index selectors are used for selecting one carrier wave to transmit signals according to index bits; the N is 2 P The carrier multiplier is used for multiplying the carrier modulation coefficient by a carrier to realize carrier index modulation; the N carrier adders are used for adding signals multiplied by carriers; the N +1 modulation multipliers are used for multiplying a carrier index modulation signal and a code shift multi-system DCSK signal; the 2N +1 Walsh sequence multipliers are used for multiplying the chaotic signals by the 2N +1 Walsh sequences; the N code-shift multi-system modulators are used for realizing code-shift multi-system DCSK modulation.
8. The code shift-based carrier index multilevel chaotic modem according to claim 7, wherein: the demodulator comprises 2 P +1 carrier multiplier, 2 P +1 matched filters, 2 P +1 sampling switches, 2N +1 decoding shift circuits, 2N correlators, N energy comparators, N multi-system threshold decision devices, N sign bit conversion circuits and a parallel-serial conversion circuit;
2 is described P +1 carrier multiplier utilization 2 P The +1 synchronized subcarriers are multiplied by the received signals, respectively, to obtain 2 P +1 product signals; 2 is described P +1 matched filter pairs 2 P The +1 product signals are respectively subjected to matched filtering; 2 mentioned P +1 sampling switch pairs matched filtered 2 P The +1 product signals are respectively subjected to time domain sampling to recover 1 path of discrete reference signal sequence and 2 paths of discrete reference signal sequence P A channel discrete information signal sequence; the 2N +1 decoding shift circuits multiply and add sampling results with Walsh codes; the 2N correlators respectively correlate the recovered reference signals with output signals of the decoding shift circuit; the N energy comparators input the energy of the N signals respectivelyRow comparison to demodulate index bits; the N multi-ary threshold deciders output an element having a maximum absolute value; the N symbol bit conversion circuits convert the symbols into modulation bit outputs; and the parallel-serial conversion circuit combines the obtained N paths of index bits and modulation bits into 1 path of serial demodulation data bit respectively and outputs the data bit.
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| CN117240673A (en) * | 2023-11-16 | 2023-12-15 | 南京邮电大学 | Multi-carrier index differential chaos shift keying modem and method |
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| CN115801524A (en) * | 2023-01-30 | 2023-03-14 | 中国电子科技集团公司第五十四研究所 | Low signal-to-noise ratio carrier recovery method based on multi-symbol correlation and maximum likelihood selection |
| CN117240673A (en) * | 2023-11-16 | 2023-12-15 | 南京邮电大学 | Multi-carrier index differential chaos shift keying modem and method |
| CN117240673B (en) * | 2023-11-16 | 2024-03-15 | 南京邮电大学 | Multi-carrier index differential chaos shift keying modem and method |
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