CN115378494B - OTFS-based low-orbit satellite navigation integrated transmission method and system - Google Patents
OTFS-based low-orbit satellite navigation integrated transmission method and system Download PDFInfo
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Abstract
The invention discloses an OTFS-based low-orbit satellite lead integrated transmission method and system, which modulate a lead fusion signal from a time delay-Doppler domain to a time domain to obtain a time domain signal; before transmitting a time domain signal, adding a pseudo-random sequence code according to the channel condition, inserting the pseudo-random sequence code at intervals in the time domain signal, and transmitting a time domain continuous channel fusion signal in the time domain; the receiving end generates a pseudo-random sequence identical to that of the transmitting end, and the propagation distance of the signal is obtained by multiplying the propagation time of the signal by the speed of light and is used as the distance between a positioning satellite and a target receiver; solving a navigation signal by repeatedly using a small mean square error algorithm, and obtaining satellite running condition and satellite coordinate information according to the obtained navigation message information; and determining at least four groups of navigation message information, and combining the pseudo-range information to obtain the position of the receiver, so as to realize OTFS-based low-orbit satellite navigation integrated transmission. The invention realizes reliable and efficient communication and positioning functions at the signal level.
Description
Technical Field
The invention belongs to the technical field of wireless satellite communication and satellite navigation, and particularly relates to an OTFS-based low-orbit satellite navigation integrated transmission method and system.
Background
As is well known, the aspects of modern society are not separated from communication and navigation. The actions of the spacecraft, whether it be people's daily life or the spacecraft travel to space, are highly dependent on communication services and positioning services. As Information Communication Technology (ICT) is further popularized and applied in the future, these two types of services will face a wider and more complex demand.
With the maturity of artificial intelligence and 5G technology, more and more intelligent scenes, such as unmanned driving, internet of vehicles, internet of things, smart cities and the like, are attracting attention, and have become a hot spot for academic research. The high-speed growth of the novel intelligent industry brings up new development opportunities for communication and positioning technologies, particularly brings forward new requirements of high performance and generalization for location services, and is particularly embodied in the aspects of positioning accuracy, reliability, service range and the like. Therefore, the situation of the isolated development of the current communication system and the navigation system is gradually not suitable for the requirement of high performance of the future intelligent scene, and the fusion of communication and navigation is sought to develop into a new hot spot.
After the communication and guide integration of the relay base mobile communication positioning network, the satellite base communication and guide integration is paid great attention, and the technology can be used as a supplement for realizing high-precision positioning service in a mobile communication-free area, which is important for the construction of projects such as unmanned and smart cities in the future. In the early Iridium age, students have studied the positioning by utilizing an Iridium system; the united states national aviation and aerospace agency proposes space conduction integrated engineering and provides a system architecture of a network thereof; the Beidou navigation system in China has short message communication capability, and realizes the function of communication and guide integration to a certain extent. The satellite-based communication integration can be used as a supplement for realizing high-precision positioning service in a mobile communication-free area, and is important for the construction of projects such as unmanned and smart cities in the future. Because the low orbit satellite constellation has the advantages of large satellite quantity and high signal intensity, the satellite group cooperation can be carried out, and the service availability and reliability can be comprehensively improved both for communication and positioning. The communication navigation integrated system based on the low orbit satellite becomes an important development direction of a future satellite-based communication navigation integrated technology, related technical research is developed, and a communication navigation fusion signal adaptive to the system is designed.
The frequency spectrum of current satellite communication systems and satellite navigation systems increasingly tends to saturate, while the upper limit on the number of satellites that can be accommodated by the orbit also prevents further development. The novel communication navigation integrated signal system is designed, so that one-star multi-purpose is realized, the satellite spectrum utilization rate and the space utilization rate are improved, and the method has great practical significance. At the same time, low orbit satellites operate at fast speeds, up to several kilometers per second, and this high mobility poses a dual challenge of time-varying and high doppler shift to their channels. The existing Orthogonal Frequency Division Multiplexing (OFDM) is very sensitive to carrier frequency offset, and reliable transmission of signals cannot be realized under the channel condition, so that the problem of how to realize reliable and efficient communication and positioning is also considered in the scene of realizing communication and guide integration by using a low-orbit satellite.
Disclosure of Invention
The technical problem to be solved by the invention is to provide the OTFS-based low-orbit satellite navigation integrated transmission method and system for solving the defects of resource waste, poor collaboration and the like caused by the development of traditional satellite communication and satellite navigation isolation, and simultaneously solving the technical problems of sensitivity to carrier frequency deviation and inapplicability to satellite-to-ground systems with high maneuverability in the classical OFDM technology.
The invention adopts the following technical scheme:
an OTFS-based low-orbit satellite navigation integrated transmission method comprises the following steps:
s1, leading the navigation signal S nav [n]And communication signal S com [n]Multiplying and adding different power distribution factors to form a conductive fusion signal s [ n ]]The orthogonal time-frequency air conditioning technology is utilized to conduct and fuse the signal s [ n ]]Obtaining a time domain signal s (t) from the delay-Doppler domain modulation to the time domain;
s2, before the time domain signal S (t) obtained in the step S1 is sent, adding a pseudo-random sequence code according to channel conditions, inserting the pseudo-random sequence code at intervals in the time domain signal S (t) obtained in the step S1, estimating delay Doppler channel impulse response of a double-selected channel, and finally sending a time domain continuous channel fusion signal z (t) in the time domain;
s3, the receiving end generates a pseudo-random sequence identical to the transmitting end in the step S2, continuously calculates with the time domain continuous conduction fusion signal z (t) generated in the step S2, searches the position with the maximum correlation value to capture and synchronize data so as to determine the frame head of the data code and the starting time of signal transmission, reads the local signal receiving time, subtracts the local signal receiving time to obtain the propagation time of the signal, and multiplies the propagation time of the signal by the light velocity to obtain the propagation distance of the signal as the distance between the positioning satellite and the target receiver;
S4, the receiving end carries out channel estimation on a time delay-Doppler domain on a star-earth double-selection channel which is experienced by a time domain continuous conduction fusion signal z (t), after finishing data acquisition and synchronization in the step S3, a pseudo-random sequence in an acquisition signal is used as a training symbol to carry out two-dimensional matched filtering of time and frequency, channel impulse response on the time delay-Doppler domain is restored, a pseudo-random sequence added in a time domain signal is removed, a data part is extracted, and an obtained receiving signal is converted from the time domain to the time delay-Doppler domain through an orthogonal time frequency space demodulation technology, so that the channel impulse response of the time delay-Doppler domain is obtained;
s5, utilizing the time delay-Doppler domain channel impulse response obtained in the step S4, and adopting a minimum mean square error algorithm to solve the communication signal S sent in the step S1 com [n]And subtracting the decoded communication signal S from the received signal obtained in step S4 com [n]Obtaining a residual signal, wherein the residual signal comprises a useful navigation signal, interference which is not completely counteracted by a communication signal and a noise item, and the navigation signal is solved by repeatedly using a small mean square error algorithm in the residual signal;
s6, carrying out double-code AltBOC demodulation and despreading on the navigation signal obtained in the step S5, separating out two paths of different navigation data, restoring the obtained navigation data into the original data in the step S1, obtaining satellite running conditions and satellite coordinate information according to the obtained navigation message information, determining at least four groups of navigation message information, and obtaining a receiver position by combining the pseudo-range information obtained in the step S3, thereby realizing OTFS-based low-orbit satellite navigation integrated transmission.
Specifically, step S1 specifically includes:
s101, dividing a time-frequency domain and a time delay-Doppler domain into grids, and mutually converting the time-frequency domain and the time delay-Doppler domain through an octave Fourier transform and an anti-octave Fourier transform to obtain a time-frequency domain grid Λ as follows:
Λ＝{(nT,mΔf),n,m∈Z}
wherein T is a time interval, and Δf is a frequency interval;
s102, representing the lead fusion signal S [ n ] in the delay-Doppler domain of the step S101, and converting the lead fusion signal S [ n ] into a time-frequency domain through inverse octyl Fourier transform;
s103, converting the conducting fusion signal S [ n ] in the step S102 from a time-frequency domain to a time domain for transmission through the Haisnberg transformation.
Further, in step S102, the conducting fusion signal S [ n ] is:
wherein p is 1 Power allocation factor for navigation signal, p 2 Allocating factors, s, for communication signal power nav [n]And the navigation message is modulated.
Further, navigation message signal s nav [n]The method comprises the following steps:
wherein D is 1 [n]And D 2 [n]Respectively represent two paths of different navigation message data codes, χ AltBOC [n]Representing a dual code alternating binary offset carrier modulated square wave subcarrier,represents conjugation, PN [ n ]]Is a locally generated pseudo-random sequence.
Further, in step S103, the time domain signal S (t) of the fusion signal is:
Wherein g tx (t) represents a transmission pulse, M is the number of frequency domain lattices, m=0,..m-1, N is the number of time domain lattices, n=0,..n-1, s [ N, M)]Is a signal on a time-frequency grid;
the inner product of the transmit pulse and the receive pulse satisfies the biorthogonal relationship of time delay and frequency
Wherein,to accept the displacement conjugate of the pulse, δ (m) and δ (n) are unit impulse functions.
Specifically, in step S4, the delay-doppler domain channel impulse response is obtained specifically as follows:
s401, the received signal r (t) is represented by using a time domain continuous form as:
r(t)＝∫∫f(τ,ν)g tx (t-τ)e j2πν(t-τ) dνdτ+N 0 (t)
wherein τ represents time delay, ν represents frequency, N 0 (t) represents additive white gaussian noise, and f (τ, ν) represents a transmission signal affected by a channel;
s402, converting the received signal obtained in the step S801 into a time-frequency domain by adopting Wiggner transformation;
s403, converting the received signal obtained in step S802 from the time-frequency domain to the delay-doppler domain by SFFT conversion.
Further, the pseudo random sequence in the captured signal is used as a training symbol to perform two-dimensional matched filtering of time and frequency, and the channel impulse response on the delay-Doppler domain is restored as follows:
r[n]＝e(ω 0 n)s[n-δ 0 ]+N 0 [n]
wherein r (n) is the time domain received signal, M (r, PN) [ delta, omega ]Correlation values obtained for correlation of the received signal with the delay-doppler-shifted signal of the local pseudorandom sequence,<·>representing the correlation operation, N 0 (t) represents additive Gaussian white noise, PN [ n ]]Representing locally generated pseudo-randomThe sequence of the sequences is set up,and->Respectively representing the errors between the correlation value and the ideal value 1 under different conditions, delta is the estimated time delay, omega is the estimated Doppler frequency, delta 0 Omega is the actual time delay 0 Is the actual doppler frequency.
Specifically, in step S6, the separation of two paths of different navigation data is specifically:
s601, determining navigation signals after serial interference elimination of a receiving end;
s602, multiplying the navigation signal obtained in the step S601 by the AltBOC square wave subcarrier which is the same as the transmitting end;
s603, respectively taking a real part and an imaginary part of the result obtained in the step S602, and separating two paths of different navigation signals;
s604, performing coherent integration, decomposition and expansion on the two paths of different navigation signals obtained in the step S603 respectively, and restoring the original data codes before source coding.
Further, in step S601, a navigation signal r nav [n]The method comprises the following steps:
wherein s is nav [n]For the navigation signal sent by the sender, P 2 For the navigation power allocation factor, h is the channel gain, ηn]As a residual of the communication signal after the serial interference cancellation, N 0 Is additive white gaussian noise.
In a second aspect, an embodiment of the present invention provides an OTFS-based integrated transmission system for low-orbit satellite navigation, including:
a time domain module for generating a navigation signal s nav [n]And communication signal S com [n]Multiplying and adding different power distribution factors to form a conductive fusion signal s [ n ]]By positive use ofThe cross-time-frequency air conditioning technology leads the fusion signal s [ n ]]Obtaining a time domain signal s (t) from the delay-Doppler domain modulation to the time domain;
the estimation module is used for adding a pseudo-random sequence code according to the channel condition before transmitting the time domain signal s (t) obtained by the time domain module, inserting the pseudo-random sequence code at intervals in the time domain signal s (t) obtained by the time domain module, estimating the delay Doppler channel impulse response of the double-selected channel, and finally transmitting a time domain continuous channel fusion signal z (t) in the time domain;
the distance module is used for generating a pseudo-random sequence identical to the transmitting end of the estimation module by the receiving end, continuously carrying out operation on the pseudo-random sequence and a time domain continuous conduction fusion signal z (t) generated by the estimation module, searching a position with the maximum correlation value for data capture and synchronization so as to determine a data code frame head and the starting time of signal transmission, then reading the local signal receiving time, subtracting the local signal receiving time to obtain the propagation time of the signal, and multiplying the propagation time of the signal by the light velocity to obtain the propagation distance of the signal as the distance between a positioning satellite and a target receiver;
The conversion module is used for carrying out channel estimation on a time delay-Doppler domain on a star-earth double-selection channel which is experienced by a time domain continuous channel fusion signal z (t) by a receiving end, carrying out two-dimensional matched filtering on time and frequency by taking a pseudo-random sequence in a captured signal as a training symbol after the distance module finishes data capturing and synchronization, restoring channel impulse response on the time delay-Doppler domain, eliminating the pseudo-random sequence added in a time domain signal, extracting a data part, and converting the obtained received signal from the time domain to the time delay-Doppler domain by an orthogonal time frequency space demodulation technology to obtain the channel impulse response of the time delay-Doppler domain;
the calculation module is used for solving the communication signal S sent by the time domain module by adopting the minimum mean square error algorithm by utilizing the delay-Doppler domain channel impulse response obtained by the conversion module com [n]And subtracting the communication signal S from the received signal obtained by the conversion module com [n]Obtaining a residual signal, wherein the residual signal comprises a useful navigation signal plus interference and noise items which are not completely counteracted by a communication signal, and the navigation signal is solved by repeatedly using a small mean square error algorithm in the residual signalA number;
the transmission module is used for carrying out double-code AltBOC demodulation and despreading on the navigation signal obtained by the calculation module, and separating out two paths of different navigation data; restoring the navigation data obtained by the demodulation module into the original data of the time domain module, and obtaining satellite running conditions and satellite coordinate information according to the obtained navigation message information; and determining at least four groups of navigation message information, and calculating the position of a receiver by combining the pseudo-range information obtained by the distance module to realize OTFS-based low-orbit satellite navigation integrated transmission.
Compared with the prior art, the invention has at least the following beneficial effects:
the OTFS-based integrated transmission method for low orbit satellite navigation is characterized in that after a navigation signal and a communication signal are respectively subjected to double-code AltBOC modulation and QPSK modulation, the navigation signal and the communication signal are multiplied by different power distribution coefficients and added to form a fusion signal, and superposition of the two signals in a power domain is completed. The receiving end uses a serial interference elimination technology to separate and demodulate, so that multiplexing of time-frequency resources is realized, and the transmission efficiency of the integrated fusion system of the communication and the guide is improved; the fusion signal is modulated in an OTFS modulation mode and then is sent, and the OTFS can characterize the signal and the channel on a time delay-Doppler domain, so that compared with a traditional time-frequency domain, the time-varying Doppler shift double-selection channel impulse response is changed into a distinguishable state, and the influence of the double-selection channel on signal transmission is reduced to the greatest extent; the satellite communication signals and the satellite navigation signals are superimposed in the power domain, and meanwhile, the commonality of the pseudo random code applied in the satellite navigation system and the satellite communication system is utilized, so that the proposed time domain data frame format can simultaneously complete the functions of signal capturing, data synchronization, pseudo range measurement and channel estimation; meanwhile, the time-varying and Doppler frequency shift characteristics of the satellite-to-ground channel are considered, the double-code alternating binary offset carrier modulation is combined, the adverse effect can be well eliminated by the introduced orthogonal time-frequency space OTFS modulation, the deep integration of navigation and communication is realized from the aspect of a signal system, and a navigation and communication solution which is high in reliability, good in compatibility, low in cost and available is provided for users.
Further, the orthogonal time-frequency space modulation is used for representing the signals and the channels in the time delay-Doppler domain, so that the impulse response of the satellite-to-ground time-varying Doppler shift double-selected channel is changed from indistinguishable to resolvable compared with the traditional time-to-frequency domain, and the influence of the double-selected channel on signal transmission is reduced to the greatest extent.
Further, the navigation signal and the communication signal are respectively multiplied by different power distribution coefficients and added to form a communication fusion signal, so that superposition of the two signals in a power domain is completed. The multiplexing of time-frequency resources is realized, and the transmission efficiency of the communication and conduction integrated fusion system is improved.
Furthermore, the dual-code alternating binary offset carrier (AltBOC) modulation is used, so that channel resources are effectively utilized, two paths of navigation signals are transmitted simultaneously, and the AltBOC modulation can enable the spectrum of the modulated signal to shift to two sides so as to reduce interference to the main peak of the spectrum of the communication signal.
Furthermore, the frame head ranging code and the intra-frame training sequence which exist in the form of pseudo random sequence are inserted in the time domain, so that the aims of ranging and channel estimation can be fulfilled simultaneously. The frame head ranging code is used for realizing the synchronization of the received signal, ranging and primary channel estimation, and other training sequences in the frame can continuously perform channel estimation and timely master the change of the channel.
Furthermore, the dual-code alternating binary offset carrier (AltBOC) modulation can offset the spectrum of the modulated signal to two sides, so that the interference to the main peak of the spectrum is reduced as much as possible, two paths of signals can be multiplexed in an I path and a Q path, and the two paths of signals can be separated in an imaginary part and a real part only by multiplying the same AltBOC subcarrier at a receiving end.
Furthermore, the pseudo-random sequence has good autocorrelation and sharp autocorrelation function, in the satellite navigation system, different pseudo-random sequences are often used for distinguishing different satellites, a receiving end generates specific pseudo-random sequence codes to perform correlation operation with a received signal, the magnitude of a correlation value is judged to judge whether the received signal is a useful signal, and meanwhile, due to the autocorrelation characteristic, the time-frequency characteristic of the received signal can be matched by properly adjusting the local input signal of the correlation operation, so that the signal is reflected by the influence of a channel.
Further, to understand the original transmitted signal, it is necessary to convert the time domain signal directly received by the receiving end back into the original delay-doppler domain, because the signal is largely dispersed and aliased in other domains due to various conversions, and cannot be directly restored.
Furthermore, the serial interference elimination technology is aimed at the most common demodulation mode of the power multiplexing signal, the signal with larger power is first resolved, and then the signal with smaller power is resolved.
It will be appreciated that the advantages of the second aspect may be found in the relevant description of the first aspect, and will not be described in detail herein.
In summary, the invention designs the OTFS-based low-orbit satellite navigation integrated transmission method by considering the complex situation of satellite-ground scene channels, and realizes reliable and efficient communication and positioning functions at the signal level.
The technical scheme of the invention is further described in detail through the drawings and the embodiments.
Drawings
FIG. 1 is a flow chart of a conductance integrated system implementation;
FIG. 2 is a communication navigation signal superposition constellation;
FIG. 3 is a diagram of an orthogonal time-frequency air conditioning process;
FIG. 4 is a diagram of the representation format of the superimposed signal in different domains;
FIG. 5 is a graph of receiver position solution error as a function of signal to noise ratio;
FIG. 6 is a graph of bit error rate versus signal-to-noise ratio for a communication signal;
fig. 7 is a graph of the error rate of a navigation signal as a function of signal to noise ratio.
Detailed Description
The following description of the embodiments of the present invention will be made clearly and fully with reference to the accompanying drawings, in which it is evident that the embodiments described are some, but not all embodiments of the invention. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
In the description of the present invention, it will be understood that the terms "comprises" and "comprising," when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.
It is also to be understood that the terminology used in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used in this specification and the appended claims, the singular forms "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.
It should be further understood that the term "and/or" as used in the present specification and the appended claims refers to any and all possible combinations of one or more of the associated listed items, and includes such combinations, e.g., a and/or B, may represent: a exists alone, A and B exist together, and B exists alone. In addition, the character "/" herein generally indicates that the front and rear associated objects are an "or" relationship.
It should be understood that although the terms first, second, third, etc. may be used to describe the preset ranges, etc. in the embodiments of the present invention, these preset ranges should not be limited to these terms. These terms are only used to distinguish one preset range from another. For example, a first preset range may also be referred to as a second preset range, and similarly, a second preset range may also be referred to as a first preset range without departing from the scope of embodiments of the present invention.
Depending on the context, the word "if" as used herein may be interpreted as "at … …" or "at … …" or "in response to a determination" or "in response to detection". Similarly, the phrase "if determined" or "if detected (stated condition or event)" may be interpreted as "when determined" or "in response to determination" or "when detected (stated condition or event)" or "in response to detection (stated condition or event), depending on the context.
Various structural schematic diagrams according to the disclosed embodiments of the present invention are shown in the accompanying drawings. The figures are not drawn to scale, wherein certain details are exaggerated for clarity of presentation and may have been omitted. The shapes of the various regions, layers and their relative sizes, positional relationships shown in the drawings are merely exemplary, may in practice deviate due to manufacturing tolerances or technical limitations, and one skilled in the art may additionally design regions/layers having different shapes, sizes, relative positions as actually required.
The invention provides an OTFS-based integrated transmission method for low-orbit satellite navigation, which starts from the signal system level, realizes deep integration of navigation and communication, and provides a navigation and communication solution with high reliability, good compatibility, low cost and availability for users. On the other hand, the low orbit satellite constellation has high running speed, the mobility increase causes the system to have great Doppler frequency shift and expansion, the channel of the system faces the problem of fast time-varying fading, and meanwhile, the change of the terminal speed can cause the change of the attenuation coefficient and the time-varying Doppler expansion, and the problem causes the communication performance to be seriously degraded. In order to solve the defect that the classical OFDM technology is not suitable for a high-speed satellite communication system due to the fact that the classical OFDM technology is sensitive to carrier frequency offset, the method combines double-code alternating binary offset carrier (AltBOC) modulation, and uses an orthogonal time-frequency air conditioner (Orthogonal Time Frequency Space, OTFS) to send communication navigation fusion signals in a time delay domain and a Doppler domain.
Referring to fig. 1, the invention relates to an OTFS-based low-orbit satellite navigation integrated transmission method, which includes the following steps:
s1, leading the navigation signal S nav [n]And communication signal S com [n]Multiplying and adding different power distribution factors to form a conductive fusion signal s [ n ] ]The orthogonal time-frequency air conditioning technology is utilized to conduct and fuse the signal s [ n ]]Obtaining a time domain signal s (t) from the delay-Doppler domain modulation to the time domain;
generating navigation electricity at satellite transmitting endThe text data, the content of which comprises satellite category, satellite orbit related information and ephemeris parameters, converts the original data into hexadecimal, converts the hexadecimal into binary, then carries out source coding, spreads the spectrum after the coding, then carries out double-code alternate binary offset carrier (AltBOC) modulation, and generates a navigation signal s nav [n]；
Generating a navigation signal s nav [n]The specific steps of (a) are as follows:
the transmitting end generates pseudo-random code and codes the pseudo-code spread spectrum of the navigation message signal by compiling the navigation message information into data code, and the data code is coded by adopting a BCH (15, 11) error correction code;
double-code alternating binary offset carrier (AltBOC) modulation is carried out on the navigation spread spectrum signal, and in order to ensure that the signal amplitude is 1, two superimposed signals are needed to be halved in amplitude, and the modulated signal s nav [n]Expressed as:
wherein D is 1 [n]And D 2 [n]Respectively represent two paths of different navigation message data codes, χ AltBOC [n]Representing a double code alternating binary offset carrier (AltBOC) modulated square wave subcarrier,represents conjugation in the form of
χ AltBOC [n]＝χ cos [n]+j·χ sin [n]
Wherein χ is cos [n]And χ (x) sin [n]Respectively representing a cosine square wave carrier wave and a sine square wave subcarrier wave, specifically:
χ cos [n]＝sgn(cos(2πf s n))
χ sin [n]＝sgn(sin(2πf s n))
wherein f s Representing subcarrier frequency, modulating and mapping the navigation signal by the steps, and changing the value into +/-1, +/-i, which is equivalent to a rotary QPSK signal;
the lead fusion signal s [ n ] is:
here, the sum of the power division factors is required to be 1, i.e., p 1 +p 2 ＝1，
The constellation mapping relation of the channel fusion signal is represented by fig. 2, the single communication signal can be represented by x in the figure through QPSK modulation, and the channel fusion signal is based on the communication signal, and a part of energy is separated for transmitting the navigation signal, so that the representation of the channel fusion signal on the constellation is shifted by a certain distance around taking x as the center, namely, the position of the channel fusion signal is located;
referring to fig. 3, the pilot fusion signal is modulated to a corresponding carrier wave by using an orthogonal time-frequency air conditioning (OTFS) technique and transmitted; the orthogonal time-frequency-space modulation (OTFS) modulation procedure is as follows:
s101, dividing a time-frequency domain and a time delay-Doppler domain into grids, wherein the dimensions of the two grids have a one-to-one correspondence, and can be mutually converted, and the time-frequency domain grids are expressed as follows:
Λ＝{(nT,mΔf),n,m∈Z}
where T and Δf represent the time interval and the frequency interval, respectively, and the lead fusion signal is then represented on a time-frequency grid as:
S[n,m],n＝0,...N-1,m＝0,...M-1
The system duration is NT seconds and the total bandwidth is mΔfhz.
Accordingly, the guided fusion signal is represented on the delay-doppler grid as:
s[k,l],k＝0,...N-1,l＝0,...M-1
the two are mutually converted by the octave fourier transform (SFFT) and the inverse octave fourier transform (ISFFT), namely:
wherein s is p [k,l]And S is p [n,m]A cycle extension representing a signal time-frequency domain representation and a delay-doppler domain representation, respectively;
s102, representing the guided fusion signal in the delay-doppler domain, i.e. S [ k, l ], k=0, & gt, N-1, l=0, & gt, M-1, and then converting to the time-frequency domain by an inverse octyl fourier transform (ISFFT)
Wherein W is tx [n,m]Representing a square integrable window function of a transmitting end, and shortening a periodic expression form of a guided fusion signal;
s103, converting the lead fusion signal from a time-frequency domain to a time domain for transmission through a Haisnberg transformation (Heisenberg transform).
The conducting fusion signal time domain signal s (t) is:
wherein g tx And (t) represents a transmission pulse.
Correspondingly, the receiving end has receiving pulse, and the inner product of the sending pulse and the receiving pulse satisfies the double orthogonal relation of time delay and frequency as follows:
s2, before the time domain signal S (t) obtained in the step S1 is sent, adding a pseudo-random sequence code according to channel conditions, inserting the pseudo-random sequence code at intervals in the time domain signal S (t) obtained in the step S1, estimating delay Doppler channel impulse response of a double-selected channel, and finally sending a time domain continuous channel fusion signal z (t) in the time domain;
In order to realize the positioning function, a pseudorandom sequence code with the duration longer than the signal propagation time is required to be continuously transmitted before a data code is transmitted so as to be convenient for a receiving end to carry out ranging, and meanwhile, in order to overcome the influence of a double-selection channel, the delay Doppler channel impulse response of the double-selection channel is required to be estimated;
referring to fig. 4, the transmission format of the signals in each domain is specifically implemented by transmitting pseudo-random codes in a data frame gap, wherein the communication navigation signals are respectively multiplied by different power distribution factors to be superimposed on a power domain, and are arranged on a delay-doppler grid, and are denoted as S [ k, l ], k=0,..n-1, l=0,..m-1, and then transformed onto a time-frequency domain, and at this time, the communication navigation signals are dispersed into the whole time-frequency domain, denoted as S [ N, M ], n=0,..n-1, m=0, and then transformed into a time domain S (t), and at this time, the preamble pseudo-random sequence codes and the intra-pseudo-random code training sequence are added according to the above steps.
S3, the receiving end locally generates a pseudo-random sequence identical to the transmitting end, continuously carries out correlation operation with the received signal until a position of a maximum value of correlation values of the local pseudo-random sequence and the received channel fusion signal is found, so that a data code frame head is found, the starting time of signal transmission is determined, then the local signal receiving time is read, the signal receiving time minus the signal transmission starting time is the propagation time of the channel fusion signal, and the propagation distance d of the signal is obtained by multiplying the propagation time of the channel fusion signal by the speed of light;
d＝c*(t arrival -t send )
Wherein c represents the speed of light, t arrival And t send Respectively representing the arrival time and the transmission time;
s4, carrying out channel estimation on a time delay-Doppler domain on a star-earth double-selection channel which is experienced by a time continuous channel fusion signal z (t) at a receiving end, after finishing data acquisition and synchronization in step S3, carrying out two-dimensional matched filtering of time and frequency by using a pseudo-random sequence in an acquisition signal as a training symbol, restoring channel impulse response on the time delay-Doppler domain, eliminating a pseudo-random sequence added in a time domain signal, extracting a data part, and converting the obtained receiving signal from the time domain to the time delay-Doppler domain by an orthogonal time frequency space demodulation technology to obtain the channel impulse response of the time delay-Doppler domain;
the pseudo-random sequence is used as training symbol to perform two-dimensional matched filtering of time and frequency, and the channel impulse response on the delay-Doppler domain is restored so as to perform equalization and offset the influence of the double selected channels, and the specific process is as follows:
r[n]＝e(ω 0 n)s[n-δ 0 ]+N 0 [n]
to facilitate a clear explanation of the two-dimensional matched filtering process, the received signal in the time domain is denoted herein as r (n) in discrete form, which simply illustrates that the transmitted signal is subject to doppler frequency shift and delay through the channel, <·>Representing the correlation operation, N 0 (t) represents additive Gaussian white noise, PN [ n ]]Representing a locally generated pseudo-random sequence, M (r, PN) [ delta, omega ]]Representing correlation values obtained by correlating the received signal with a delay-doppler-shifted signal of the local pseudorandom sequence,and->Representing the error between the correlation value and the ideal value 1 in different cases, respectively, the above procedure is described as successively changing the locally generated pseudo-random sequence by a certain delay delta or Doppler frequency omegaWhile ensuring that delta and omega are a point on the delay-doppler grid, if one attempts, the estimated delay delta and doppler frequency omega and the actual delay delta 0 Or Doppler frequency omega 0 Matching, when the correlation value reaches a maximum, the estimated value may be approximated as the actual delay and doppler shift values of the channel for subsequent decoding, and then the pseudo-random sequence is stripped from the received signal obtained in step S6.
Converting the received signal of the obtained stripped pseudo-random sequence from the time domain to the time-frequency domain, which is called Wigner transform (Wigner transform);
s401, a time domain continuous form of the received signal is expressed as:
r(t)＝∫∫f(τ,ν)g tx (t-τ)e j2πν(t-τ) dνdτ+N 0 (t)
wherein τ represents time delay, ν represents frequency, N 0 (t) represents additive white gaussian noise, and f (τ, ν) represents a transmission signal affected by a channel.
The transmission signal f (τ, ν) affected by the channel is:
where h (τ, ν) is the channel impulse response represented by the delay-doppler domain σ For the defined deconvolution operation, the received signal is processed using the received pulses, as follows:
s402, converting a time domain received signal into a time-frequency domain by using Wigner transform (Wigner transform);
Y[n,m]＝A grx,r (τ,ν)|τ＝nT,ν＝mΔf
s403, converting the received signal from the time-frequency domain to the delay-doppler domain by SFFT conversion.
S5, obtaining by utilizing the step S4The communication signal S transmitted in the step S1 is solved by adopting a minimum mean square error algorithm according to the time delay-Doppler domain channel impulse response of (1) com [n]And subtracting the decoded communication signal S from the received signal obtained in step S4 com [n]Obtaining a residual signal, wherein the residual signal comprises a useful navigation signal, interference which is not completely counteracted by a communication signal and a noise item, and the navigation signal is solved by repeatedly using a small mean square error algorithm in the residual signal;
s6, carrying out double-code AltBOC demodulation and despreading on the navigation signal obtained in the step S5, separating out two paths of different navigation data, converting binary data codes into hexadecimal, restoring the obtained hexadecimal navigation data into the original data of the step S1, obtaining satellite running conditions and satellite coordinate information according to the obtained navigation message information, determining at least four groups of navigation message information aiming at different satellites, and calculating to obtain the position of a receiver by combining the pseudo-range information obtained in the step S3 so as to realize OTFS-based low-orbit satellite navigation integrated transmission; in addition, the communication data solved in step S6 can also complete the corresponding communication function at the same time; therefore, navigation and communication are realized at the same time, and the integration of navigation and communication is completed.
The demodulation process is as follows:
s601, determining the expression form of a navigation signal after serial interference elimination by a receiving end:
wherein ηn represents a residual term in which the communication signal is not completely cancelled after the serial interference cancellation;
s602, multiplying the navigation signal by the same AltBOC square wave subcarrier as the transmitting end after the serial interference elimination is carried out on the receiving end obtained in the step S601;
the expression is as follows:
/>
wherein r is nav [n]Indicating receipt ofNavigation signal after serial interference elimination, PN [ n ] at receiving end of (a)]Representing a locally generated pseudo-random sequence χ AltBOC [n]Representing a double-code alternating binary offset carrier (AltBOC) modulated square wave subcarrier, χ cos [n]And χ (x) sin [n]Respectively representing a cosine square wave carrier wave and a sine square wave subcarrier wave, D 1 [n]And D 2 [n]Respectively representing two different navigation message data codes.
S603, respectively taking a real part and an imaginary part of the result obtained in the step S602, and separating two paths of different navigation signals;
s604, performing coherent integration, decomposition and expansion on the two paths of different navigation signals obtained in the step S603 respectively, and restoring the original data codes before source coding.
In still another embodiment of the present invention, an OTFS-based integrated transmission system for low-orbit satellite navigation is provided, where the system can be used to implement the OTFS-based integrated transmission method for low-orbit satellite navigation, and specifically, the OTFS-based integrated transmission system for low-orbit satellite navigation includes a time domain module, an estimation module, a distance module, a conversion module, a calculation module, and a transmission module.
Wherein, the time domain module is used for transmitting the navigation signal s nav [n]And communication signal S com [n]Multiplying and adding different power distribution factors to form a conductive fusion signal s [ n ]]The orthogonal time-frequency air conditioning technology is utilized to conduct and fuse the signal s [ n ]]Obtaining a time domain signal s (t) from the delay-Doppler domain modulation to the time domain;
the estimation module is used for adding a pseudo-random sequence code according to the channel condition before transmitting the time domain signal s (t) obtained by the time domain module, inserting the pseudo-random sequence code at intervals in the time domain signal s (t) obtained by the time domain module, estimating the delay Doppler channel impulse response of the double-selected channel, and finally transmitting a time domain continuous channel fusion signal z (t) in the time domain;
the distance module is used for generating a pseudo-random sequence identical to the transmitting end of the estimation module by the receiving end, continuously carrying out operation on the pseudo-random sequence and a time domain continuous conduction fusion signal z (t) generated by the estimation module, searching a position with the maximum correlation value for data capture and synchronization so as to determine a data code frame head and the starting time of signal transmission, then reading the local signal receiving time, subtracting the local signal receiving time to obtain the propagation time of the signal, and multiplying the propagation time of the signal by the light velocity to obtain the propagation distance of the signal as the distance between a positioning satellite and a target receiver;
The conversion module is used for carrying out channel estimation on a time delay-Doppler domain on a star-earth double-selection channel which is experienced by a time domain continuous channel fusion signal z (t) by a receiving end, carrying out two-dimensional matched filtering on time and frequency by taking a pseudo-random sequence in a captured signal as a training symbol after the distance module finishes data capturing and synchronization, restoring channel impulse response on the time delay-Doppler domain, eliminating the pseudo-random sequence added in a time domain signal, extracting a data part, and converting the obtained received signal from the time domain to the time delay-Doppler domain by an orthogonal time frequency space demodulation technology to obtain the channel impulse response of the time delay-Doppler domain;
the calculation module is used for solving the communication signal S sent by the time domain module by adopting the minimum mean square error algorithm by utilizing the delay-Doppler domain channel impulse response obtained by the conversion module com [n]And subtracting the communication signal S from the received signal obtained by the conversion module com [n]Obtaining a residual signal, wherein the residual signal comprises a useful navigation signal, interference which is not completely counteracted by a communication signal and a noise item, and the navigation signal is solved by repeatedly using a small mean square error algorithm in the residual signal;
the transmission module is used for carrying out double-code AltBOC demodulation and despreading on the navigation signal obtained by the calculation module, and separating out two paths of different navigation data; restoring the navigation data obtained by the demodulation module into the original data of the time domain module, and obtaining satellite running conditions and satellite coordinate information according to the obtained navigation message information; and determining at least four groups of navigation message information, and calculating the position of a receiver by combining the pseudo-range information obtained by the distance module to realize OTFS-based low-orbit satellite navigation integrated transmission.
For the purpose of making the objects, technical solutions and advantages of the embodiments of the present invention more apparent, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention, and it is apparent that the described embodiments are some embodiments of the present invention, but not all embodiments of the present invention. The components of the embodiments of the present invention generally described and illustrated in the figures herein may be arranged and designed in a wide variety of different configurations. Thus, the following detailed description of the embodiments of the invention, as presented in the figures, is not intended to limit the scope of the invention, as claimed, but is merely representative of selected embodiments of the invention. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
Four real satellites are selected and navigation text information is acquired, and the real satellite navigation text information is derived from a real observation station. By applying the OTFS-based integrated fusion signal design scheme, the communication signal and the navigation message signal are transmitted at the signal level, separated and decoded at the receiving end and the position of the receiver is calculated, and the change of the positioning error of the receiver along with the signal-to-noise ratio is shown in figure 5.
In this experiment, too large positioning deviation was regarded as positioning failure, and the value was uniformly assigned to 9999m. The satellite channel is set as a rice channel, and in order to verify the feasibility of the scheme, only the transmission and reception process of the whole transmission and reception process under the condition of line-of-sight (LOS) is considered, and in the scene, the delay estimation result of the main path can be directly used as the basis of ranging to help positioning, and also can be used as the channel estimation result to help decoding.
The signal-to-noise ratio is defined as snr=10log (P 0 /P N ) Wherein P is 0 To the power of the useful signal, P N For the power of the noise, the range is set to be [6, 30]dB, setting the dimension of time delay-frequency domain as 256×15, the central frequency as 2GHz, the total bandwidth as 3.84MHz, the power of communication signal as P 1 The navigation signal power is denoted as P 2 . Each satellite independently generates a channel according to the propagation time, and each satellite needs to transmit 44 OTFS frames to transmit all information required by positioning calculation, and noise and channel fading coefficients of each OTFS frame in an experiment are independently generated.
The comparison scheme is as follows:
an Orthogonal Frequency Division Multiplexing (OFDM) technology which is widely applied in 5G at present is used as a basis for transmitting a communication navigation fusion signal, namely, the communication signal and a navigation signal are modulated to a carrier wave through OFDM after being overlapped in power domain, the relative motion speed of a transmitting end and a receiving end is set to be 500km/h, the power ratio of the communication signal is set to be 85%, the navigation power ratio is set to be 15%, and simulation result diagrams are shown in fig. 5, 6 and 7.
As seen from the three figures, this comparison scheme compares with the OTFS-based transmission scheme under the same configuration:
in terms of the communication signal error rate, when the relative motion speed of the transmitting end and the receiving end is 500km/h under the same power configuration, the communication signal error rate of the OTFS-based communication signal integrated scheme is lower than that of the communication signal error rate of the OFDM-based communication signal integrated scheme, the OTFS-based communication and conduction integrated signal system can overcome the influence of double selection channels caused by movement in a high-mobility environment, so that better transmission reliability is realized.
In the aspect of the error rate of the navigation signal, the navigation signal adopts a spread spectrum communication mode, so that the influence of too little power distribution is reduced, the noise immunity is improved, and even if the distributed power is less than the communication signal, the lower error rate can be realized. It can also be seen from the error rate curve of the navigation signal that the transmission effect of the OTFS-based integrated signal transmission scheme on the pilot signal is better than that of the OFDM-based integrated signal transmission scheme.
In the aspect of receiver positioning calculation, the error rate of the navigation signal can be obviously reduced by adopting the OTFS-based communication and guide integrated signal transmission scheme, so that accurate positioning can be realized under the condition of poor signal-to-noise ratio by adopting the scheme.
In order to explore the influence of power distribution on communication signals and navigation signals, the communication power is respectively set to be 85 percent of the total power, and the navigation signals are set to be 15 percent of the total power; communication power accounts for 75% of the total power, and navigation signals account for 25% of the total power; the communication power accounts for 65% of the total power, the navigation signal accounts for 35% of the total power, and simulation results are shown in fig. 5, 6 and 7. As can be seen from the figure, two signals are distributed in the power domain, and a competition relationship is presented between the two signals, and the more power is distributed, the better the effect of the corresponding function is achieved.
In summary, the OTFS-based low-orbit satellite navigation integrated transmission method and system have the following advantages:
the invention completes the integration of the communication and navigation functions on the signal system level, is beneficial to improving the satellite navigation and the frequency spectrum utilization rate of the satellite communication, and reduces the design and use cost of the integration system.
The double-code AltBOC modulation mode is used for the navigation signals on the basis of spread spectrum, so that channel resources can be efficiently utilized, and two paths of navigation signals can be transmitted simultaneously. AltBOC modulation can shift the modulated signal spectrum to both sides to reduce interference to the main peaks of the communication signal spectrum.
After the navigation signal and the communication signal are respectively subjected to double-code AltBOC modulation and QPSK modulation, the navigation signal and the communication signal are multiplied by different power distribution coefficients and added to form a fusion signal, and superposition of the two signals in a power domain is completed. The receiving end uses serial interference cancellation technique to separate demodulation. The multiplexing of time-frequency resources is realized, and the transmission efficiency of the communication and conduction integrated fusion system is improved.
The fusion signal is modulated in an OTFS modulation mode and then transmitted, and the OTFS can characterize the signal and the channel on a time delay-Doppler domain, so that compared with a traditional time-frequency domain, the time-varying Doppler shift dual-selection channel impulse response becomes distinguishable, and the influence of the dual-selection channel on signal transmission is reduced to the greatest extent.
The purposes of ranging and channel estimation can be accomplished simultaneously by inserting the frame header ranging code and the intra-frame training sequence in the form of pseudo-random sequences in the time domain. The frame head ranging code is used for realizing the synchronization of the received signal, ranging and primary channel estimation, and other training sequences in the frame can continuously perform channel estimation and timely master the change of the channel.
It will be appreciated by those skilled in the art that embodiments of the present application may be provided as a method, system, or computer program product. Accordingly, the present application may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, the present application may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, and the like) having computer-usable program code embodied therein.
The present application is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems) and computer program products according to embodiments of the application. It will be understood that each flow and/or block of the flowchart illustrations and/or block diagrams, and combinations of flows and/or blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
The above is only for illustrating the technical idea of the present invention, and the protection scope of the present invention is not limited by this, and any modification made on the basis of the technical scheme according to the technical idea of the present invention falls within the protection scope of the claims of the present invention.
Claims (10)
1. The OTFS-based low-orbit satellite navigation integrated transmission method is characterized by comprising the following steps of:
s1, leading the navigation signal S nav [n]And communication signal S com [n]Multiplying and adding different power distribution factors to form a conductive fusion signal s [ n ]]The orthogonal time-frequency air conditioning technology is utilized to conduct and fuse the signal s [ n ]]Obtaining a time domain signal s (t) from the delay-Doppler domain modulation to the time domain;
s2, before the time domain signal S (t) obtained in the step S1 is sent, adding a pseudo-random sequence code according to channel conditions, inserting the pseudo-random sequence code at intervals in the time domain signal S (t) obtained in the step S1, estimating delay Doppler channel impulse response of a double-selected channel, and finally sending a time domain continuous channel fusion signal z (t) in the time domain;
S3, the receiving end generates a pseudo-random sequence identical to the transmitting end in the step S2, continuously calculates with the time domain continuous conduction fusion signal z (t) generated in the step S2, searches the position with the maximum correlation value to capture and synchronize data so as to determine the frame head of the data code and the starting time of signal transmission, reads the local signal receiving time, subtracts the local signal receiving time to obtain the propagation time of the signal, and multiplies the propagation time of the signal by the light velocity to obtain the propagation distance of the signal as the distance between the positioning satellite and the target receiver;
s4, the receiving end carries out channel estimation on a time delay-Doppler domain on a star-earth double-selection channel which is experienced by a time domain continuous conduction fusion signal z (t), after finishing data acquisition and synchronization in the step S3, a pseudo-random sequence in an acquisition signal is used as a training symbol to carry out two-dimensional matched filtering of time and frequency, channel impulse response on the time delay-Doppler domain is restored, a pseudo-random sequence added in a time domain signal is removed, a data part is extracted, and an obtained receiving signal is converted from the time domain to the time delay-Doppler domain through an orthogonal time frequency space demodulation technology, so that the channel impulse response of the time delay-Doppler domain is obtained;
s5, utilizing step S4The obtained time delay-Doppler domain channel impulse response adopts a minimum mean square error algorithm to solve the communication signal S transmitted in the step S1 com [n]And subtracting the decoded communication signal S from the received signal obtained in step S4 com [n]Obtaining a residual signal, wherein the residual signal comprises a useful navigation signal, interference which is not completely counteracted by a communication signal and a noise item, and the navigation signal is solved by repeatedly using a small mean square error algorithm in the residual signal;
s6, carrying out double-code AltBOC demodulation and despreading on the navigation signal obtained in the step S5, separating out two paths of different navigation data, restoring the obtained navigation data into the original data in the step S1, obtaining satellite running conditions and satellite coordinate information according to the obtained navigation message information, determining at least four groups of navigation message information, and obtaining a receiver position by combining the pseudo-range information obtained in the step S3, thereby realizing OTFS-based low-orbit satellite navigation integrated transmission.
2. The OTFS-based low-orbit satellite navigation integrated transmission method according to claim 1, wherein step S1 specifically comprises:
s101, dividing a time-frequency domain and a time delay-Doppler domain into grids, and mutually converting the time-frequency domain and the time delay-Doppler domain through an octave Fourier transform and an anti-octave Fourier transform to obtain a time-frequency domain grid Λ as follows:
Λ＝{(nT,mΔf),n,m∈Z}
wherein T is a time interval, and Δf is a frequency interval;
S102, representing the lead fusion signal S [ n ] in the delay-Doppler domain of the step S101, and converting the lead fusion signal S [ n ] into a time-frequency domain through inverse octyl Fourier transform;
s103, converting the conducting fusion signal S [ n ] in the step S102 from a time-frequency domain to a time domain for transmission through the Haisnberg transformation.
3. The OTFS-based low-orbit satellite navigation integrated transmission method according to claim 2, wherein in step S102, the navigation fusion signal S [ n ] is:
wherein p is 1 Power allocation factor for navigation signal, p 2 Allocating factors, s, for communication signal power nav [n]And the navigation message is modulated.
4. The OTFS-based low orbit satellite navigation integrated transmission method according to claim 3, wherein the navigation message signal s nav [n]The method comprises the following steps:
wherein D is 1 [n]And D 2 [n]Respectively represent two paths of different navigation message data codes, χ AltBOC [n]Representing a dual code alternating binary offset carrier modulated square wave subcarrier,represents conjugation, PN [ n ]]Is a locally generated pseudo-random sequence.
5. The OTFS-based low-orbit satellite navigation integrated transmission method according to claim 2, wherein in step S103, the time domain signal S (t) of the navigation fusion signal is:
wherein g tx (t) represents a transmission pulse, M is the number of frequency domain lattices, m=0,..m-1, N is the number of time domain lattices, n=0,..n-1, s [ N, M) ]Is a signal on a time-frequency grid;
the inner product of the transmit pulse and the receive pulse satisfies the biorthogonal relationship of time delay and frequency
Wherein,to accept the displacement conjugate of the pulse, δ (m) and δ (n) are unit impulse functions.
6. The OTFS-based low-orbit satellite navigation integrated transmission method according to claim 1, wherein in step S4, the delay-doppler domain channel impulse response is obtained specifically as follows:
s401, the received signal r (t) is represented by using a time domain continuous form as:
wherein τ represents time delay, ν represents frequency, N 0 (t) represents additive white gaussian noise, and f (τ, ν) represents a transmission signal affected by a channel;
s402, converting the received signal obtained in the step S801 into a time-frequency domain by adopting Wiggner transformation;
s403, converting the received signal obtained in step S802 from the time-frequency domain to the delay-doppler domain by SFFT conversion.
7. The OTFS-based low orbit satellite navigation integrated transmission method according to claim 6, wherein the two-dimensional matched filtering of time and frequency is performed using a pseudo-random sequence in the acquisition signal as a training symbol, and the channel impulse response on the delay-doppler domain is restored as follows:
r[n]＝e(ω 0 n)s[n-δ 0 ]+N 0 [n]
Wherein r (n) is the time domain received signal, M (r, PN) [ delta, omega]Correlation values obtained for correlation of the received signal with the delay-doppler-shifted signal of the local pseudorandom sequence,<·>representing the correlation operation, N 0 (t) represents additive Gaussian white noise, PN [ n ]]Representing a locally generated pseudo-random sequence,and->Respectively representing the errors between the correlation value and the ideal value 1 under different conditions, delta is the estimated time delay, omega is the estimated Doppler frequency, delta 0 Omega is the actual time delay 0 Is the actual doppler frequency.
8. The OTFS-based low-orbit satellite navigation integrated transmission method according to claim 1, wherein in step S6, the separation of two different navigation data is specifically:
s601, determining navigation signals after serial interference elimination of a receiving end;
s602, multiplying the navigation signal obtained in the step S601 by the AltBOC square wave subcarrier which is the same as the transmitting end;
s603, respectively taking a real part and an imaginary part of the result obtained in the step S602, and separating two paths of different navigation signals;
s604, performing coherent integration, decomposition and expansion on the two paths of different navigation signals obtained in the step S603 respectively, and restoring the original data codes before source coding.
9. The OTFS-based low orbit satellite navigation integrated transmission method according to claim 8, wherein in step S601, the navigation signal r is nav [n]The method comprises the following steps:
wherein s is nav [n]For the navigation signal sent by the sender, P 2 For the navigation power allocation factor, h is the channel gain, ηn]As a residual of the communication signal after the serial interference cancellation, N 0 Is additive white gaussian noise.
10. An OTFS-based low-orbit satellite navigation integrated transmission system, comprising:
a time domain module for generating a navigation signal s nav [n]And communication signal S com [n]Multiplying and adding different power distribution factors to form a conductive fusion signal s [ n ]]The orthogonal time-frequency air conditioning technology is utilized to conduct and fuse the signal s [ n ]]Obtaining a time domain signal s (t) from the delay-Doppler domain modulation to the time domain;
the estimation module is used for adding a pseudo-random sequence code according to the channel condition before transmitting the time domain signal s (t) obtained by the time domain module, inserting the pseudo-random sequence code at intervals in the time domain signal s (t) obtained by the time domain module, estimating the delay Doppler channel impulse response of the double-selected channel, and finally transmitting a time domain continuous channel fusion signal z (t) in the time domain;
the distance module is used for generating a pseudo-random sequence identical to the transmitting end of the estimation module by the receiving end, continuously carrying out operation on the pseudo-random sequence and a time domain continuous conduction fusion signal z (t) generated by the estimation module, searching a position with the maximum correlation value for data capture and synchronization so as to determine a data code frame head and the starting time of signal transmission, then reading the local signal receiving time, subtracting the local signal receiving time to obtain the propagation time of the signal, and multiplying the propagation time of the signal by the light velocity to obtain the propagation distance of the signal as the distance between a positioning satellite and a target receiver;
The conversion module is used for carrying out channel estimation on a time delay-Doppler domain on a star-earth double-selection channel which is experienced by a time domain continuous channel fusion signal z (t) by a receiving end, carrying out two-dimensional matched filtering on time and frequency by taking a pseudo-random sequence in a captured signal as a training symbol after the distance module finishes data capturing and synchronization, restoring channel impulse response on the time delay-Doppler domain, eliminating the pseudo-random sequence added in a time domain signal, extracting a data part, and converting the obtained received signal from the time domain to the time delay-Doppler domain by an orthogonal time frequency space demodulation technology to obtain the channel impulse response of the time delay-Doppler domain;
the calculation module is used for solving the communication signal S sent by the time domain module by adopting the minimum mean square error algorithm by utilizing the delay-Doppler domain channel impulse response obtained by the conversion module com [n]And subtracting the communication signal S from the received signal obtained by the conversion module com [n]Obtaining a residual signal, wherein the residual signal comprises a useful navigation signal, interference which is not completely counteracted by a communication signal and a noise item, and the navigation signal is solved by repeatedly using a small mean square error algorithm in the residual signal;
the transmission module is used for carrying out double-code AltBOC demodulation and despreading on the navigation signal obtained by the calculation module, and separating out two paths of different navigation data; restoring the navigation data obtained by the demodulation module into the original data of the time domain module, and obtaining satellite running conditions and satellite coordinate information according to the obtained navigation message information; and determining at least four groups of navigation message information, and calculating the position of a receiver by combining the pseudo-range information obtained by the distance module to realize OTFS-based low-orbit satellite navigation integrated transmission.
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