CN115001917A - Modulation signal generation method for radar communication integration - Google Patents
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Abstract
The invention discloses a modulation signal generation method for radar communication integration, and relates to the field of communication modulation methods. In the method, user data is subjected to spread spectrum modulation and chip interleaving and then is grouped, wherein the grouping comprisespBit map set sumqA bit modulation group; based on long spherical wave function generationNA transmission waveform for loading data; mapping each data combination of the mapping group into the slave data combination according to a one-to-one mapping relationNSelecting from the transmission waveformqA waveform combination consisting of a plurality of transmission waveforms; using waveform amplitude modulation, modulating saidqEach bit of the bit modulation group is loaded to the bit modulation groupqOn a transmission waveform, formed by superposition of time-domain waveformsA time domain waveform and its integrated version is used as an additional phase of the non-chirped signal to form the modulated signal. The technical scheme disclosed by the invention improves the anti-interference capability of the modulation signal, improves the information transmission rate and the power utilization efficiency of the system, and has multi-user communication capability.
Description
Technical Field
The invention relates to the field of communication modulation methods, in particular to a modulation signal generation method for radar communication integration.
Background
The radar communication integrated design solves the problems of mutual interference, poor electromagnetic compatibility, large occupied space and high energy consumption of various electronic devices on the platform, and greatly improves the comprehensive application capability of the platform. In addition, the integrated waveform design can also fully utilize the large bandwidth characteristic of the radar frequency band, the communication rate is improved, and the narrow beam characteristic of the radar signal is also beneficial to improving the working distance and the hiding capability of the communication signal.
In the prior art, the core of the radar communication integrated design is the generation of a modulation signal, namely, user data is carried on the premise of meeting the detection target of a radar. Compared with the traditional pulse radar signal, the linear frequency modulation signal has the characteristic of large bandwidth, so that the resolution of target detection can be improved when the linear frequency modulation signal is used for detecting a target. Therefore, in the prior art, the radar communication integrated design method generally applies BPSK modulation or MSK modulation to the user data and then loads the user data into the chirp signal. This method is only applicable to low-speed systems because of its low bandwidth utilization. The OFDM modulation has the characteristic of high-frequency spectrum utilization rate, so that the OFDM modulation is popularized and applied in the field of mobile communication, and an OFDM modulation signal is a large-time wide-bandwidth product signal and can meet the requirements of high distance resolution and high speed resolution of a radar detection target when being used in a radar system. Therefore, in the prior art, designing a radar communication integrated waveform based on OFDM to meet the requirement of a high-speed communication system is a hot research problem of designing a radar communication integrated modulation signal. However, the OFDM modulation signal has a high peak-to-average ratio characteristic due to its multi-carrier characteristic, and the range of a linear working area of the radar power amplifier system is limited, and the high peak-to-average ratio greatly reduces the power utilization rate of the power amplifier system, thereby reducing the distance of the radar system to target detection and seriously affecting the working performance of the radar system. In the prior art, although the peak-to-average ratio of the modulation signal can be relieved to a certain extent by adopting a method for reducing the peak-to-average ratio, the peak-to-average ratio of the modulation signal still fluctuates in a large range, and the problem is difficult to fundamentally solve.
Therefore, how to improve the frequency band utilization rate of the integrated modulation signal and reduce the peak-to-average power ratio on the premise of keeping the detection performance of the radar system is a difficult problem to be solved by the existing radar communication integrated design.
Disclosure of Invention
The invention aims to disclose a technical scheme, which reduces the peak-to-average ratio of a modulation signal and improves the frequency band utilization rate of a system on the premise of keeping the detection performance of a radar system so as to realize the integrated design of radar communication.
In order to achieve the purpose of the invention, the invention provides a modulation signal generation method for radar communication integration. In the method, in the first stepkThe modulation signal in each data symbol period is:
wherein,f c in order to modulate the carrier frequency of the signal,Bfor the purpose of a signal bandwidth factor,Tis a factor of the time of the signal,Mis a number of terms of a fourier series,F i are the coefficients of a Fourier series and are,Nto generate the number of transmission waveforms for loading information based on the long spherical wave function,a j (t) Is as followsjThe bits are used for waveform amplitude modulated data to be transmitted,ω j (c,t) Is as followsjA transmission waveform for waveform amplitude modulation,cthe time bandwidth product factor of the long spherical wave function satisfies the relational expression
；
The method for generating the transmission waveform for loading information based on the long spherical wave function comprises the following steps: according to the sequence of the energy accumulation of the frequency domain from big to smallNEven order or odd order long spherical wave function; according to the long spherical surfaceSpectral symmetry of wave function, respectively interceptingNA half frequency spectrum of the wavelength function of the long spherical surface is converted into time domain waveforms according to the conversion relation from the frequency domain to the time domainω j (c,t)，j=1，2，…，NForming means for loading dataNA transmit waveform.
Further, in the technical solution disclosed in the present invention, generating the modulation signal includes the steps of:
the method comprises the following steps: data to be transmitted by a userD(t) Direct sequence spread spectrum modulation with a spread spectrum sequence to produce a spread spectrum modulated signalK(t)；
Step two: the spread spectrum modulation signalK(t) Interleaving the chips by an interleaving method to generate an interleaved signalZ(t)；
Step three: interleaving the signalZ(t) Performing a grouping, the grouping comprisingpBit map setY(t)=
Andqbit modulation setA(t)=
；
Based on long spherical wave function generationNA transmission waveform for loading dataω 1 (c,t)、ω 2 (c,t)、…、ω N (c,t)；
The above-mentionedNAndqsatisfy the relationq=N-1；
Step four: according to a one-to-one mapping relation, the method comprises the following steps ofpEach data combination of the bitmap group is mapped to be respectively mapped from the bit map groupNA transmission waveform selected fromqA waveform combination of transmitted waveforms, saidpEach data combination in the bit mapping group can only correspond to one waveform combination, and the waveform combinations corresponding to any two data combinations are different;
step five: using waveform amplitude modulation, modulating saidqEach of the bit modulation groupsBit data are loaded to theqOn the transmission waveform, a time domain waveform is formed by superposing the time domain waveforms, and the integral form of the time domain waveform is used as an additional phase of the non-linear frequency modulation signal to form a modulation signal, and the second step is thatkThe non-chirp signal for each data symbol period is:
furthermore, in the technical solution disclosed in the present invention, the number of data bits of the mapping grouppAnd the number of the generated transmission waveformsNSatisfies the relation:
。
further, in the technical solution disclosed in the present invention, when performing direct sequence spread spectrum modulation, users are different, and the selected spreading sequences are different; the method for generating the spread spectrum sequence comprises the following steps:
the 32-bit sequence: 01111100111010010000101011101100, the sequences are cyclically shifted one bit at a time to the left by means of a cyclic left shift to form new sequences.
Further, in the technical solution disclosed in the present invention, the interleaving method is implemented by using a convolutional interleaver, and different users and different convolutional interleavers for implementing the interleaving method are used.
Preferably, in the technical solution disclosed in the present invention, the number of terms M =7 in the fourier series, and the coefficients of the fourier series are F respectively 1 =-0.1145，F 2 =0.0396，F 3 =-0.0202，F 4 =0.0118，F 5 =-0.0082，F 6 =0.0055，F 7 =-0.004。
Further, in the technical solution disclosed in the present invention, the modulation signal is transmitted in a pulse form, the pulse period includes a pulse transmission period and a pulse stop period, the time length of the pulse transmission period is 6.6 microseconds, and the time length of the pulse stop period is 6.6 microseconds.
Preferably, in the technical solution disclosed in the present invention, the transmission waveform is a transmission waveform designed by taking 0 th order, 2 nd order, 4 th order and 6 th order prolate spheroidal wave function respectively in the order from large to small according to the frequency domain energy aggregation based on the prolate spheroidal wave function, and the number of waveforms in the transmission waveform combination participating in the waveform amplitude modulation is 3.
Preferably, in the technical solution disclosed in the present invention, the interleaving signals are grouped according to a size of 5 bits, and the grouping includes a 2-bit mapping group and a 3-bit modulation group.
Compared with the prior art, the invention has the following beneficial effects:
(1) the anti-interference capability of the modulation signal is improved.
In the prior art, when designing a radar communication integrated signal, a chirp signal is often used for design, and the signal has a large side lobe, and when the side lobe is suppressed by a matched filter or a window function, the modulated signal generates a serious waveform distortion, so that the anti-interference capability of the signal in a channel transmission process is reduced, and the application environment of the signal is limited. In the technical scheme disclosed by the invention, a frequency domain nonlinear weighting mode is adopted, and a weighting window is approximated through a polynomial Fourier series expansion to construct a nonlinear frequency modulation signal, so that the frequency domain change of the radar modulation signal presents nonlinear characteristics, the purpose of reducing the sidelobe amplitude of the radar modulation signal is achieved, and the signal distortion generated when the radar signal is radiated through antenna filtering is reduced, thereby improving the SNR (signal to noise ratio) of the radar modulation signal, enabling the radar modulation signal to have stronger anti-electromagnetic interference capability in the channel transmission process, and further expanding the applicable application environment.
(2) The information transmission rate is improved.
In the technical scheme disclosed by the invention, the traditional mode of only adopting amplitude parameters to load information is abandoned, the way of transmitting waveform loading information is expanded, and two modes of waveform mapping and waveform amplitude modulation are adopted to load information at the same time; furthermore, the transmission waveform for loading information only uses half of the frequency spectrum based on the symmetrical characteristic of the frequency spectrum, thereby effectively improving the utilization rate of the frequency spectrum and further improving the information transmission rate of the system.
(3) The peak-to-average ratio is reduced, and the power utilization efficiency is improved.
In the technical scheme disclosed by the invention, the transmission waveform for completing data loading adopts an integral form as an additional phase of a nonlinear frequency modulation signal, and the integrated waveform design of radar communication is realized, so that the integrated modulation signal has a constant envelope characteristic. Therefore, compared with the prior art, the power utilization efficiency of the radar system can be effectively improved, the action distance of target detection is enhanced, and meanwhile, higher information transmission rate can be achieved.
(4) Having multi-user communication capabilities.
In the technical scheme disclosed by the invention, direct sequence spread spectrum modulation and chip level interleaving are adopted to realize user identification, and the number of network users is increased. When the user data is subjected to spread spectrum modulation, users are different, the selected spread spectrum sequences are different, namely, the spread spectrum sequences are adopted to distinguish different users; in order to further meet the requirement of the number of large-scale network communication users, in the technical scheme disclosed by the invention, interleaving is arranged after direct sequence spread spectrum, namely, an interleaved object is converted into chip-level interleaving of spread spectrum signals by traditional bit-level data interleaving; and users are different, the adopted interleaving scheme or the interleaver for realizing the interleaving method is different, so that the interleaving also becomes an identifier for identifying the user address, namely, two modes of a spread spectrum code and the interleaver are adopted for further expanding the number of users in network communication. In the prior art, the modulated signal for radar communication integrated design is generally only suitable for point-to-point communication.
Additional advantages and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention.
Drawings
Fig. 1 is a schematic diagram of spectrum clipping disclosed by the embodiment of the invention.
Fig. 2 is a schematic diagram of the modulation signal generation disclosed in the embodiment of the present invention.
Detailed Description
In the prior art, radar communication integrated waveform designs have two types. Firstly, the information to be transmitted is loaded by adopting conventional digital modulation, such as BPSK modulation or MSK modulation, and then is combined with a radar signal to form an integrated signal. If the integrated modulation signal based on the combination of the MSK modulation and the chirp signal is as follows:
wherein,
is the carrier frequency and is,μin order to be a linear frequency modulation parameter,a k is the user data. The integrated modulation signal has the advantages of constant modulation signal envelope, high power utilization rate of a radar system and long target detection distance, but the method has poor information carrying capacity and low frequency band utilization rate and can only be suitable for low-speed systems.
The other type is that radar communication integrated waveform is designed based on OFDM, the transmission rate of the system is improved by using the high-frequency spectrum utilization rate of an OFDM modulation signal, and meanwhile, the OFDM modulation signal is also a large time-bandwidth product signal, and when the OFDM modulation signal is used in a radar system, the requirements of high distance resolution and high speed resolution of a radar detection target can be met, and generally, the type of integrated modulation signal can be expressed as:
wherein,Nthe number of sub-carriers is represented,C k which is indicative of the information to be transmitted,
which represents the bandwidth of the sub-carriers,f c representing the carrier frequency. The integrated modulation signal has the characteristics that the orthogonal multi-carrier signal simultaneously carries information, the frequency band utilization is high, and the integrated modulation signal is suitable for a high-speed system. But do notThe OFDM modulation signal has the characteristic of high peak-to-average ratio due to the multi-carrier characteristic, the range of a linear working area of the radar power amplification system is limited, and the power utilization rate of the power amplification system is greatly reduced due to the high peak-to-average ratio, so that the distance of the radar system to target detection is reduced, and the working performance of the radar system is seriously influenced. Although the peak-to-average ratio of the modulation signal can be relieved to a certain extent by adopting the method for reducing the peak-to-average ratio, the peak-to-average ratio of the modulation signal still fluctuates in a large range, so that the problem cannot be fundamentally solved.
Therefore, in the prior art, the radar communication integrated modulation signal design method is difficult to achieve simultaneously in the aspects of high spectrum utilization rate and low peak-to-average ratio, and generally only performance in one aspect can be sacrificed to obtain performance in the other aspect, but not both aspects can be achieved.
In the prior art, compared with a pulse modulation signal, a chirp signal has a wider spectrum bandwidth, so that the resolution can be improved when the chirp signal is used for detecting a target. Therefore, when designing the radar communication integrated signal, a chirp signal is often used. However, the chirp signal has a large spectrum side lobe, and when the side lobe is suppressed by a matched filter or a window function, the modulation signal generates a serious waveform distortion, so that the SNR (signal to noise ratio) of the signal is reduced, the anti-interference capability of the signal in the channel transmission process is reduced, and the application environment is limited.
In order to solve the problem, in the technical solution disclosed in the embodiment of the present invention, a frequency domain nonlinear weighting mode is adopted for the modulation signal, and a weighting window is approximated by a polynomial fourier series expansion to construct a nonlinear frequency modulation radar modulation signal, that is, the nonlinear frequency modulation radar modulation signal is constructed
The frequency domain change of the radar modulation signal presents a nonlinear characteristic so as to achieve the purpose of reducing the sidelobe amplitude of the radar modulation signal, and the signal distortion generated when the radar signal is radiated by antenna filtering is reduced, so that the SNR (signal to noise ratio) of the radar modulation signal is improved, the radar modulation signal has stronger anti-electromagnetic interference capability in the channel transmission process, and the applicable application environment of the radar modulation signal is expanded.
Preferably, in the technical solution disclosed in the embodiment of the present invention, the number of terms M =7 in the fourier series, and the coefficients of the fourier series are F respectively 1 =-0.1145，F 2 =0.0396，F 3 =-0.0202，F 4 =0.0118，F 5 =-0.0082，F 6 =0.0055，F 7 =-0.004。
Therefore, the embodiment of the invention adopts the nonlinear frequency modulation signal as the radar signal to improve the transmission reliability of the radar signal, and on the basis, the radar signal and the communication modulation signal are integrally designed to achieve better radar detection performance and data transmission performance.
In order to solve the problem that the prior art cannot give consideration to both high-frequency spectrum utilization rate and low peak-to-average power ratio, the embodiment of the invention discloses a modulation signal generation method for radar communication integration. In the method, in the first stepkThe modulation signal in each data symbol period is:
wherein,f c in order to modulate the carrier frequency of the signal,Bfor the purpose of a signal bandwidth factor,Tis a factor of the time of the signal,Mis a term number of a fourier series,F i are the coefficients of a Fourier series and are,Nto generate the number of transmission waveforms for loading information based on the long spherical wave function,a j (t) Is as followsjThe bits are used for waveform amplitude modulated data to be transmitted,ω j (c,t) Is as followsjA transmission waveform for waveform amplitude modulation,cis a time-bandwidth product factor of a long spherical wave function and satisfies a relation
。
Further, in the technical scheme disclosed by the embodiment of the invention, the transmission waveform of the loaded information is combined with the nonlinear frequency modulation radar signal in a phase-adding mode, so that the nonlinear frequency modulation signal has a constant envelope characteristic, when the signal is sent to a channel for transmission, the power utilization rate of a radar system is high, the distance of a detected target is long, and the problem that the performance of the radar is reduced by a high peak ratio in the prior art is solved.
In the prior art, the long spherical Wave function (PSWFs) is determined in a given time interval [ -T s /2，T s /2]And, the following integral equation is satisfied:
wherein,
is composed ofnThe characteristic value corresponding to the order spherical wave function is used for representing the energy concentration factor,nin order of the steps,
in order to be the angular frequency of the frequency,cis a time bandwidth product factor. The energy gathering device has the characteristics of optimal energy gathering property and the like, so that the energy gathering device can be widely applied to the field of communication. Under the condition of a certain time bandwidth product factor, a plurality of orders of long spherical wave functions which are orthogonal in pairs and mutually overlapped in frequency spectrum can also exist at the same time. The inventor designs a transmission waveform by taking the orthogonality and the frequency spectrum overlapping of the function as starting points, and adopts a plurality of long spherical wave functions with mutually overlapped frequency spectrums as information carriers to modulate information so as to achieve the purpose of improving the frequency spectrum utilization rate. The orthogonality can be used for separation at the receiving end to eliminate the intersymbol interference. Although the OFDM modulation method has a wide application prospect in the field of mobile communication because of its high frequency band utilization ratio, the essence of the OFDM modulation method is to use a sine and cosine function in which a plurality of frequency spectrums are overlapped by 50% each other as an information carrier to perform information modulation, so as to achieve the purpose of improving the frequency spectrum utilization ratio. However, the long spherical wave function relative to the sine-cosine functionThe number has more advantages in the aspect of energy aggregation, the side lobe of the signal is small, and the anti-interference capacity is strong when the method is used for channel transmission. Furthermore, the function also has the characteristic of large time bandwidth and high energy aggregation, so that when the function is used in the field of radar, the resolution of a detected target is favorably improved. Therefore, compared with sine and cosine functions, the radar communication integrated waveform is designed by the long spherical wave function, and better performance is brought.
The inventor can find out by analyzing the spectrum characteristics of the long spherical wave function that the spectrum of the even-order or odd-order long spherical wave function has the following characteristics:
therefore, the odd-order long spherical wave function has the frequency spectrum odd symmetry characteristic in the frequency domain, and the even-order long spherical wave function has the frequency spectrum even symmetry characteristic in the frequency domain. Based on the characteristics, when the transmission waveform is designed by adopting an odd-order or even-order prolate spheroidal wave function, the transmission waveform can be designed by utilizing the symmetrical characteristic of the frequency spectrum, the frequency spectrum is intercepted, half of the frequency spectrum is intercepted, the conversion relation from the frequency domain to the time domain is utilized, the time domain waveform is converted, and then information loading is carried out, so that the frequency spectrum utilization rate can be greatly improved, and the information transmission rate is improved. The method comprises the steps of carrying out frequency domain transformation on an odd-order or even-order long spherical wave function, intercepting a half frequency spectrum of the long spherical wave function according to the symmetrical characteristic of the frequency spectrum, and respectively converting the long spherical wave function into time domain waveforms according to the transformation relation from the frequency domain to the time domain to form transmission waveforms for loading data. As shown in the left side of fig. 1, the spectrums of the long spherical wave functions with odd symmetry characteristics and even symmetry characteristics are respectively, and the spectrums after being cut by half are shown in the right side of fig. 1 according to the spectrum symmetry characteristics. When the receiving end demodulates the information, firstly, according to the time period length of the data code element, the received signal is subjected to spectrum symmetry copying according to the spectrum symmetry, the whole spectrum of the transmission waveform is recovered, then, the time domain orthogonality is utilized to carry out signal separation, and the information extraction is completed.
Therefore, in the technical scheme disclosed by the embodiment of the invention, the transmission waveform is designed based on the prolate spheroidal wave function, only the spectrum signal within a half spectrum range is transmitted, the spectrum is copied at the receiving end according to the spectrum symmetry, the full spectrum signal is recovered, and the information is demodulated, so that the spectrum utilization efficiency is greatly improved. Moreover, at the receiving end, the spectrum is copied according to the spectrum symmetry, so that the symmetric distortion of the modulation signal caused by interference in the transmission process can be further corrected, and the anti-interference capability of signal transmission can be improved. Therefore, according to the technical scheme disclosed by the embodiment of the invention, the information-loaded transmission waveform is designed by adopting the half-spectrum prolate spheroidal wave function, so that the frequency band utilization rate of the system is improved.
In the prior art, when a long spherical wave function is used for information transmission in the communication field, information is only loaded through amplitude parameters, and although the long spherical wave function has certain advantages compared with an OFDM modulation mode, the improved space is greatly restricted by the information loading mode.
In order to further improve the frequency band utilization rate of the system, the inventor abandons the traditional mode of only adopting amplitude parameters to load information and expands the way of transmitting waveform loading information. And information is loaded simultaneously by adopting two modes of waveform mapping and amplitude modulation so as to further improve the frequency band utilization rate of the system.
Further, in the technical solution disclosed in the embodiment of the present invention, the waveform mapping is to select a part of transmission waveforms from a plurality of transmission waveforms to form a waveform combination, and the selected waveform combination is unknown and has a certain probability, so that information can be carried. For example, 3 kinds of transmission waveforms are selected from 4 kinds of transmission waveforms to constitute a waveform combination, and the probability of occurrence of any one group of waveform combinations consisting of 3 kinds of transmission waveforms is one fourth, and as can be seen from the information theory, two bits of information can be carried, that is, information of two bits can be carried
bit; then each waveform in the selected 3 waveforms adopts amplitude parameter loading information, namely the forward amplitude and the reverse amplitude of the transmission waveform are utilized to represent two states of 1-bit binary digital information, so that the amplitude parameter of each waveform can load 1-bit information, and 3 waveforms can load 3-bit information. Therefore, the two modes of waveform mapping and amplitude parameter can load 2bit +3bit =5bit information in total; however, if the traditional method of loading information by using a single amplitude parameter is adopted, only 4 bits of information can be loaded by 4 transmission waveforms. Therefore, compared with the prior art, the method and the device adopt two modes of waveform mapping and amplitude parameter loading to load information, and can effectively improve the information transmission capability. When loading information, the information to be transmitted by the user is processed according to the following formulap+q) The bit size is grouped, the grouping comprisingpBit map set sumqA bit modulation group, saidpThe data combination of the bit mapping group is mapped into a waveform combination according to a one-to-one mapping relation by adopting a waveform mapping mode, so that information loading is realized; the above-mentionedqAnd the data in the bit modulation group is loaded by adopting waveform amplitude modulation. At a receiving end, a received signal is extracted according to the mapping relation between the waveform combination and the data combinationpMapping the data of the group, and then demodulating the data according to the corresponding relation between the amplitude of the waveform amplitude modulation signal and the informationqThe bits modulate the block data. Therefore, according to the technical scheme disclosed by the embodiment of the invention, the waveform mapping and the amplitude parameter are adopted to carry information at the same time, and compared with the traditional mode of loading information by using a single amplitude parameter, the information transmission capability is improved.
Further, in the technical solution disclosed in the embodiment of the present invention, in order to improve the reliability of information transmission, data to be transmitted by a user and a spread spectrum sequence are subjected to direct sequence spread spectrum modulation to generate a spread spectrum signal, so as to improve the concealment capability and the anti-interception capability of the signal; the spread spectrum signal is interleaved at a chip level by adopting an interleaving method to generate an interleaved signal so as to resist the capability of burst interference and scatter the burst interference to be converted into random interference so as to improve the reliability of information transmission.
Further, in the technical solution disclosed in the embodiment of the present invention, in order to maintain the high frequency band utilization rate of the radar communication integrated signal and simultaneously implement the low peak-to-average ratio design, the transmission waveform for completing data loading adopts an integral form as the additional phase of the non-linear frequency modulation signal, so that the integrated modulation signal has a constant envelope characteristic. Therefore, compared with the prior art, the power utilization efficiency of the radar system can be effectively improved, the action distance of target detection is enhanced, and meanwhile, higher information transmission rate can be achieved.
Further, in the technical solution disclosed in the embodiment of the present invention, as shown in fig. 2, generating the modulation signal includes the following steps:
the method comprises the following steps: data to be transmitted by a userD(t) Direct sequence spread spectrum modulation with a spread spectrum sequence to produce a spread spectrum modulated signalK(t)；
Step two: the spread spectrum modulation signalK(t) Interleaving the chips by an interleaving method to generate an interleaved signalZ(t)；
Step three: interleaving the signalZ(t) Performing a grouping, the grouping comprisingpBit map setY(t)=
Andqbit modulation setA(t)=
；
Based on long spherical wave function generationNA transmission waveform for loading dataω 1 (c,t)、ω 2 (c,t)、…、ω N (c,t) (ii) a The above-mentionedNAndqsatisfy the relationq=N-1；
The method for generating the transmission waveform for loading data based on the long spherical wave function comprises the following steps: according to the sequence of the energy accumulation of the frequency domain from large to smallNEven order or odd order long spherical wave function; respectively intercepting the long spherical surface wave function according to the frequency spectrum symmetry of the long spherical surface wave functionNAfter half the frequency spectrum of the long spherical wave function, according to the frequency domain to the time domainTransforming the relation and converting into time-domain waveformsω j (c,t)，j=1，2，…，NForming means for loading dataNA transmission waveform;
step four: according to a one-to-one mapping relation, the method comprises the following steps ofpEach data combination of the bitmap group is mapped to be respectively mapped from the bit map groupNA transmission waveform selected fromqA waveform combination of transmitted waveforms, saidpEach data combination in the bit mapping group can only correspond to one waveform combination, and the waveform combinations corresponding to any two data combinations are different;
step five: using amplitude modulation of the waveformqEach bit of the bit modulation group is loaded to the bit modulation groupqOn the transmission waveform, a time domain waveform is formed by superposing the time domain waveforms, and the integral form of the time domain waveform is used as an additional phase of the non-linear frequency modulation signal to form a modulation signal, and thenkThe non-chirp signal for each data symbol period is:
preferably, in the technical solution disclosed in the embodiment of the present invention, the first 4 even-order prolate spheroidal wave functions are taken in the order of the frequency domain energy aggregation from large to small
、
、
And
designing a transmission waveform, intercepting a frequency spectrum in a half frequency spectrum range according to even symmetry characteristics of an even-order long spherical wave function in a frequency domain frequency spectrum, and then respectively converting the frequency spectrum into a time domain waveform according to a conversion relation from the frequency domain to the time domain
、
、
And
4 transmission waveforms are formed. The information to be transmitted by a user is subjected to direct sequence spread spectrum modulation and chip level interleaving, and then is grouped according to the size of 5 bits, wherein the grouping comprises a 2-bit mapping group and a 3-bit modulation group. And the 2-bit mapping group respectively maps each data combination of the 2-bit mapping group into a waveform combination consisting of 3 transmission waveforms selected from the 4 transmission waveforms according to a one-to-one mapping relation, and the corresponding relation between the data combination of the mapping group and the transmission waveform combination is shown in table 1.
TABLE 1 one-to-one correspondence of mapping group data combinations to waveform combinations
In the technical solution disclosed in the embodiment of the present invention, the one-to-one mapping relationship between the data combinations and the waveform combinations in the mapping group is not limited to table 1, as long as it can be satisfied that each data combination in the mapping group has only one waveform combination corresponding to it, and the waveform combinations corresponding to any two data combinations are different.
Preferably, in the technical solution disclosed in the embodiment of the present invention, the number of data bits of the mapping grouppAnd the number of transmission waveforms generatedNSatisfies the relation:
in the embodiment of the present invention, the first and second substrates,p=2，N= 4. After the mapping between the data combination and the waveform combination is completed, the mapped waveformAnd each waveform in the combination is subjected to waveform amplitude modulation to complete second information loading. For example, the waveform combination mapped by data combination 00 described in Table 1 is
、
And
and each waveform in the waveform combination is subjected to waveform amplitude modulation respectively, namely the forward amplitude and the reverse amplitude of the waveform are used for representing two states of 1-bit binary information respectively, so that the loading of 3-bit data in the modulation group is completed. And after the information loading is finished, a time domain waveform is formed by superposing the time domain waveforms, and the integral form of the time domain waveform is used as an additional phase of the non-linear frequency modulation signal, so that the radar communication integrated waveform design is realized, and the modulation signal is formed. The formed modulation signal has a constant envelope characteristic, the power utilization rate of a power amplification system is improved, the detection performance of a target is ensured, and the problem of low power utilization rate caused by a high peak ratio in the prior art is solved.
As can be seen from the above analysis, in the technical solution disclosed in the embodiment of the present invention, information is loaded simultaneously in two ways, i.e., waveform mapping and amplitude modulation, and the designed 4 transmission waveforms can transmit 5bit (2 bit +3 bit) information, whereas in the prior art, if only waveform amplitude modulation is adopted, 4 transmission waveforms can only transmit 4bit information. Therefore, the technical scheme disclosed by the embodiment of the invention improves the information transmission rate. Furthermore, in the technical scheme disclosed by the embodiment of the invention, the transmission waveform sent to the channel is only a half frequency spectrum, so that the frequency spectrum resource is saved, and the frequency spectrum utilization rate is improved; and the formed modulation signal has a constant envelope characteristic, so that the power utilization efficiency is improved, the high-frequency spectrum utilization rate and the low peak-to-average ratio design are realized, and the aim of taking both the high-frequency spectrum utilization rate and the low peak-to-average ratio into consideration is fulfilled.
In the prior art, radar communication integrated waveform design is generally designed for data transmission between point-to-point users. With the rapid development and wide application of data link technology, information interaction and sharing among multiple platforms have become a development trend. Therefore, the radar communication integrated waveform design needs to meet the network communication requirement among multiple platforms.
In order to solve the problems in the prior art, in the technical solution disclosed in the embodiment of the present invention, when the user data is subjected to spread spectrum modulation, users are different, and the selected spreading sequences are different, that is, spreading sequences are used to distinguish different users; the method for generating the spread spectrum sequence comprises the following steps:
the 32-bit sequence: 01111100111010010000101011101100, 32 spreading sequences can be formed by circularly shifting left one bit at a time to form a new sequence. The 32-bit spreading sequence formed has cyclic autocorrelation, which can be used at the receiving end to distinguish user data. In order to further meet the requirement of the number of large-scale network communication users, in the technical scheme disclosed by the embodiment of the invention, interleaving is arranged after direct sequence spread spectrum, namely, an interleaved object is converted into chip-level interleaving of spread spectrum signals by the traditional bit-level data interleaving; and the users are different, the adopted interleaving scheme or the interleaver realizing the interleaving method is different, so that the interleaving also becomes an identifier for identifying the user address, namely, two modes of a spread spectrum code and the interleaver are adopted to further expand the number of the users in the network communication. Because of the adoption of a chip-level interleaving mode, the correlation among users is effectively inhibited. At a receiving end, the characteristic can be utilized to realize user identification by adopting a multi-user iterative detection algorithm. The algorithm mainly realizes user identification through an Elementary Signal Estimator (ESE) and an a posteriori probability decoder (APP DECs). With respect to the multi-user iterative detection algorithm, those skilled in the art can implement the multi-user iterative detection algorithm based on the prior knowledge and conventional means, and the detailed description is omitted here.
Preferably, in the technical solution disclosed in the embodiment of the present invention, the interleaving method is implemented by using convolutional interleavers, and different users have different convolutional interleavers for implementing the interleaving method, that is, different interleaving depths of the convolutional interleavers; scrambling the chip sequence through a convolutional interleaver to enable spreading codes to have non-correlation; and realizing user identification at a receiving end by adopting a multi-user iterative algorithm based on the characteristics.
In the prior art, the modulated signal is typically transmitted continuously. However, the continuously transmitted signals are susceptible to being intercepted by electronic spying equipment and to interference. In order to solve the problem, in the technical solution disclosed in the embodiment of the present invention, the radar communication integrated modulation signal is transmitted in a pulse form. Compared with continuous transmission, the pulse form transmission can further expand the frequency spectrum bandwidth of the modulation signal, reduce the power spectrum density of the signal and improve the concealment capability of the signal; further, the modulation signal is transmitted in a pulse form, the pulse period comprises a pulse transmission period and a pulse stop period, the time length of the pulse transmission period is 6.6 microseconds, and the time length of the pulse stop period is 6.6 microseconds, so that the capability of the modulation signal for resisting forwarding interference is further enhanced.
While embodiments of the invention have been disclosed above, it is not intended to be limited to the uses set forth in the specification and examples. It can be applied to all kinds of fields suitable for the present invention. Additional modifications will readily occur to those skilled in the art. Therefore, the invention is not to be limited to the specific details and illustrations shown and described herein, without departing from the general concept as defined by the claims and their equivalents.
Claims (9)
1. A method for generating a modulation signal for radar communication integration, characterized in thatkThe modulation signal in each data symbol period is:
wherein,f c in order to modulate the carrier frequency of the signal,Bfor the purpose of a signal bandwidth factor,Tis a factor of the time of the signal,Mare a FuThe number of terms in the number of the leaf levels,F i are the coefficients of a Fourier series and are,Nto generate the number of transmission waveforms for loading information based on the long spherical wave function,a j (t) Is as followsjThe bits are used for waveform amplitude modulated data to be transmitted,ω j (c,t) Is as followsjA transmission waveform for waveform amplitude modulation,cis a time-bandwidth product factor of a long spherical wave function and satisfies a relation
；
The method for generating the transmission waveform for loading information based on the long spherical wave function comprises the following steps: according to the sequence of the energy accumulation of the frequency domain from big to smallNEven order or odd order long spherical wave function; respectively intercepting according to the frequency spectrum symmetry of the long spherical wave functionNA half frequency spectrum of the wavelength function of the long spherical surface is converted into time domain waveforms according to the conversion relation from the frequency domain to the time domainω j (c,t)，j=1，2，…，NForming means for loading dataNA transmit waveform.
2. The method of claim 1, wherein generating the modulation signal comprises:
the method comprises the following steps: data to be transmitted by a userD(t) Direct sequence spread spectrum modulation with a spread spectrum sequence to produce a spread spectrum modulated signalK(t)；
Step two: the spread spectrum modulation signalK(t) Interleaving the chips by an interleaving method to generate an interleaved signalZ(t)；
Step three: interleaving the signalZ(t) Performing a grouping, the grouping comprisingpBit map setY(t)= 
Andqbit modulation setA(t)= 
；
Based on long spherical wave function generationNA transmission waveform for loading dataω 1 (c,t)、ω 2 (c,t)、…、ω N (c,t)；
The above-mentionedNAndqsatisfy the relationq=N-1；
Step four: according to a one-to-one mapping relation, the method comprises the following steps ofpEach data combination of the bitmap group is mapped to be respectively mapped from the bit map groupNA transmission waveform is selected fromqA waveform combination of transmitted waveforms, saidpEach data combination in the bit mapping group can only correspond to one waveform combination, and the waveform combinations corresponding to any two data combinations are different;
step five: using waveform amplitude modulation, modulating saidqEach bit of the bit modulation group is loaded to the bit modulation groupqOn the transmission waveform, a time domain waveform is formed by superposing the time domain waveforms, and the integral form of the time domain waveform is used as an additional phase of the non-linear frequency modulation signal to form a modulation signal, and the second step is thatkThe non-chirp signal for each data symbol period is:
3. the method of claim 2, wherein the number of data bits in the mapping group is greater than the number of data bits in the mapping grouppAnd the number of the generated transmission waveformsNSatisfies the relation:
。
4. the method according to claim 3, wherein the spreading sequence is selected differently depending on the user when the direct sequence spread spectrum modulation is performed; the method for generating the spread spectrum sequence comprises the following steps:
the 32-bit sequence: 01111100111010010000101011101100, the sequences are cyclically shifted one bit at a time to the left by means of a cyclic left shift to form new sequences.
5. The method according to claim 3, wherein the interleaving method is implemented by a convolutional interleaver, and the convolutional interleaver for implementing the interleaving method is different from user to user.
6. The method according to claim 3, wherein the number of terms of the Fourier series is M =7, and the coefficients of the Fourier series are F 1 =-0.1145，F 2 =0.0396，F 3 =-0.0202，F 4 =0.0118，F 5 =-0.0082，F 6 =0.0055，F 7 =-0.004。
7. The method according to claim 3, wherein the modulated signal is transmitted in a form of a pulse, a period of the pulse includes a pulse transmission period and a pulse stop period, the pulse transmission period is 6.6 microseconds in length, and the pulse stop period is 6.6 microseconds in length.
8. The method according to claim 3, wherein the transmission waveforms are designed based on prolate spheroidal wave functions, in which 0, 2, 4 and 6 orders of prolate spheroidal wave functions are respectively selected in the order of frequency domain energy aggregation from large to small, and the number of waveforms in the combination of the transmission waveforms participating in waveform amplitude modulation is 3.
9. The method of claim 8, wherein the interleaved signals are grouped into 5-bit size, and the grouping comprises 2-bit mapping groups and 3-bit modulation groups.
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