CN115037330B - Doppler-resistant transmitting method, transmitting device and terminal - Google Patents
Doppler-resistant transmitting method, transmitting device and terminal Download PDFInfo
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
- H04B1/69—Spread spectrum techniques
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/0014—Carrier regulation
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
- H04B1/69—Spread spectrum techniques
- H04B2001/6912—Spread spectrum techniques using chirp
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/0014—Carrier regulation
- H04L2027/0024—Carrier regulation at the receiver end
- H04L2027/0026—Correction of carrier offset
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Abstract
The invention discloses a Doppler-resistant sending method, a sending device and a terminal, wherein the Doppler-resistant sending method comprises the following steps: setting an initial frequency set of the linear frequency modulation signal; coding and converting data to be transmitted into a bit sequence; grouping bit sequences according to the size of the initial frequency set to obtain one or more bit sequence groups, wherein the length of each bit sequence group is the same; mapping each bit sequence group into a chirp signal corresponding to a different initial frequency in the initial frequency set; the chirp signal is transmitted via radio frequency. According to the scheme of the invention, when the linear frequency modulation signal is used for transmitting bit data, the initial frequency set is set, and the interval of initial frequencies among different signals is increased, so that the frequency interval among effective frequency points is increased, the influence caused by Doppler drift is reduced, and the Doppler drift resistance is improved.
Description
Technical Field
The present invention relates to the field of communications, and in particular, to a method, a device, and a terminal for transmitting doppler resistance.
Background
Chirp (LFM) is a spread spectrum modulation technique that does not require a pseudo-random code sequence. Chirped signals are also known as avionic (Chirp) signals, which are also known as Chirp Spread Spectrum (CSS) techniques because their spectral bandwidth falls within the audible range, hearing an avian sound. LFM technology is widely used in radar and sonar technologies, for example, in radar positioning technology, it can be used to increase the radio frequency pulse width, increase the communication distance, increase the average transmit power, and at the same time, maintain sufficient signal spectrum width without reducing the range resolution of the radar.
With the rapid development of space technology, space communication carriers (rockets, satellites, spacecraft, etc.) have been expanded from near-earth space to deep space. Their flight distance is getting longer and longer, and the flight speed is also getting faster and faster. In addition, when the communication carrier moves at a high speed, particularly under the condition of high acceleration, the carrier frequency of the signal generates high dynamic Doppler frequency offset, so that the received signal is asynchronous, and the error rate is generated.
Disclosure of Invention
The invention provides an anti-Doppler transmission method, a transmission device and a terminal, which aim to solve the problem of Doppler frequency offset generated between a sender and a receiver which are mutually communicated under the high dynamic condition. The technical scheme is as follows:
in one aspect, the present invention provides a method for transmitting doppler resistance, including the steps of:
s101: setting an initial frequency set of the linear frequency modulation signal;
S102: coding and converting data to be transmitted into a bit sequence;
s103: grouping bit sequences according to the size of the initial frequency set to obtain one or more bit sequence groups, wherein the length of each bit sequence group is the same;
S104: mapping each bit sequence group into a different linear frequency modulation signal, wherein the initial frequencies corresponding to the linear frequency modulation signals are different;
S105: the chirp signal is transmitted via radio frequency.
Further, step S101 includes the steps of:
S1011: setting a linear frequency modulation signal;
s1012: calculating an initial frequency set of the linear frequency modulation signal;
The chirp signal is as follows:
where B is the signal bandwidth, T s is the single chirp duration, For the frequency turnover time, f 0 epsilon [ -B/2, B/2] is the initial frequency of the linear frequency modulation signal, and the time bandwidth product of the linear frequency modulation signal is BT s =N;
The initial frequency set in step S1012 is calculated in the following manner:
Wherein the method comprises the steps of As a settable variable, the number of elements in the initial frequency set F t is/>The chirp signal represents at most/>A bit sequence packet.
Further, step S103 includes:
The length p of the bit sequence packet is acknowledged by:
wherein/> To an integer power of 2.
Further, step S103 further includes:
For a bit sequence B t＝[d1 d2...dk to be transmitted with length k (k > 0), when k+.p, bit padding is performed at the last bit of the bit sequence B t, the number of bits padded is:
the bit value of the padding is all 0 or all 1, the length of the bit sequence B ' t after padding is changed to k ' =k+delta k, and the bit sequence B ' t after padding is divided into Individual bit sequence grouping/>Each bit sequence packet/>Containing p bits.
Further, step S104 includes:
determining bit sequence groupings by mapping Relationship with parameter K i, wherein parameter K i is corresponding parameter K i in initial frequency set F t, and the mapping relationship is/>
Further, step S105 includes: the chirp signals corresponding to the g bit sequence groups are sequentially used as transmitting signals, and the set of the chirp signals is
Wherein,Representing an initial frequency of/>Is used for the signal processing of the (c) chirp signal,I=1, 2,3, …, g, t=n/B is a digital sample, n is an integer, and n > =0.
Further, step S105 includes:
Before transmitting the set of chirp signals x t (n), the set of chirp signals x t (n) is DA converted or up converted and finally transmitted through an antenna.
On the other hand, the invention provides a Doppler-resistant transmitting device, comprising: the device comprises a frequency generation module, a grouping mapping module and a sending module;
The frequency generation module calculates according to the available linear frequency modulation signals to obtain an initial frequency set of the linear frequency modulation signals;
The grouping module encodes communication data to be transmitted, converts the communication data into bit sequences, groups the bit sequences according to the size of an initial frequency set, and obtains one or more bit sequence groups, wherein the length of each bit sequence group is the same;
the grouping mapping module groups and maps each bit sequence into a linear frequency modulation signal corresponding to a different initial frequency in the initial frequency set;
And the transmitting module transmits the linear frequency modulation signal processed by the packet mapping module through radio frequency.
Further, the initial frequency set is calculated by the following steps:
Wherein the method comprises the steps of As a settable variable, the number of elements in the initial frequency set F t is/>The chirp signal can represent/>, at mostA bit sequence packet.
In still another aspect, the present invention provides a doppler-resistant terminal, which is characterized by comprising the above doppler-resistant transmitting device.
The beneficial effects of the invention are as follows: by using the scheme of the invention, before the bit data is transmitted by using the linear frequency modulation signals, the initial frequency set of the linear frequency modulation signals is set, and the interval of the initial frequencies among different signals is increased, so that the frequency interval among effective frequency points is increased, the influence caused by Doppler drift is reduced, and the Doppler drift resistance is improved.
Drawings
Fig. 1 is a flowchart of an embodiment of a method for doppler resistant transmission according to the present invention;
FIG. 2 is a sub-flowchart of the Doppler-resistant transmission method of FIG. 1;
FIG. 3 is a graph of a real waveform of an embodiment of a chirp signal of the present invention;
FIG. 4 is a graph of an imaginary waveform of an embodiment of a chirp signal according to the present invention;
FIG. 5 is a flow chart of an embodiment of a receiving method according to the present invention;
fig. 6 is a schematic structural diagram of an embodiment of a doppler-resistant transmitting device according to the present invention;
Fig. 7 is a schematic structural diagram of an embodiment of a receiving device according to the present invention;
FIG. 8 is a schematic diagram illustrating an embodiment of the frequency detection module shown in FIG. 7;
fig. 9 is a graph showing the anti-doppler improvement performance according to an embodiment of the present invention.
Detailed Description
In order that the invention may be readily understood, a more particular description thereof will be rendered by reference to specific embodiments that are illustrated in the appended drawings. Preferred embodiments of the present invention are shown in the drawings. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.
Example 1
As shown in fig. 1, in one aspect, the present invention provides a method for anti-doppler transmission, which can modulate communication data to be transmitted with a chirp signal corresponding to a selected initial frequency f 0, and transmit the modulated communication data. The calculation of the initial frequency set is the key point of the invention, when the corresponding initial frequency is selected, the performance of Doppler frequency offset resistance is improved by setting the interval between the initial frequencies, so that the reliability of communication of high dynamic Doppler frequency offset resistance can be effectively improved by using the initial frequency set setting of the invention.
The Doppler resistance sending method comprises the following steps:
s101: setting an initial frequency set of the linear frequency modulation signal;
S102: coding and converting data to be transmitted into a bit sequence;
S103: grouping the bit sequences according to the size of the initial frequency set to obtain one or more bit sequence groups, wherein the length of each bit sequence group is the same;
S104: mapping each bit sequence group into a linear frequency modulation signal corresponding to a different initial frequency in the initial frequency set;
S105: and transmitting the linear frequency modulation signal through radio frequency.
Further, for step S101, the following steps are further included:
S1011: setting a linear frequency modulation signal;
S1012: calculating an initial frequency set of the linear frequency modulation signal;
Specifically, for step S1011, at the transmitting end, since the modulation method is to use different offset sequences of the chirp signal to represent the bit sequence packet to be modulated, an available chirp signal may be set as follows:
Where B denotes the signal bandwidth, T s denotes the single chirp duration, For the frequency turnover time, f 0 E [ -B/2, B/2] is the initial frequency of the chirp signal, and different information bit sequence packets correspond to different f 0. The time-bandwidth product of the chirp signal is BT s =n.
Fig. 3 is a real waveform diagram of an embodiment of the above-mentioned chirp signal, and fig. 4 is an imaginary waveform diagram of an embodiment of the above-mentioned chirp signal. As can be seen from the figure, when the time of 0.125ms is reached, frequency folding is performed, and t f =0.125 in this embodiment.
Specifically, for example, for the above-mentioned chirp signal, the values of the parameters may be: b=1 mhz, ts=0.512 ms, then n=512 can be calculated by BT s =n, the initial frequency f 0 e [ -0.5,0.5];
If the initial frequency f 0 =0.5 MHz is selected, the corresponding frequency turnover time t f =0.5×0.512 ms=0.256 ms;
If the initial frequency f 0 =0.25 MHz is selected, the corresponding frequency turnover time t f =0.75×0.512 ms=0.384 ms.
Specifically, for step S1012, when a corresponding initial frequency is selected, the performance of resisting doppler frequency offset can be improved by setting the size of the interval between the initial frequencies, and the method for calculating the initial frequency set F t of the chirp signal according to the present invention is as follows:
Wherein the method comprises the steps of As a settable variable, it is usually set to 0, and the number of the initial frequencies in the initial frequency set F t is/>And thus can represent/>, at mostA bit sequence packet.
Specifically, for each parameter of the chirp signal in the above embodiment, each parameter in the initial frequency set F t of the available chirp signal may be set to: s=4, n=512, b=1 mhz, f r =0, so that it is possible to obtain
The initial frequency set F t has a size ofSo a maximum of 128 bit sequence packets can be represented.
With the initial frequency f 0 set in this way, the physical meaning is to increase the interval of the initial frequency f 0 between different signals, and set S > =2, which reduces the partial data transmission rate and increases the resistance to doppler shift.
Further, for step S102, the following steps are included:
Firstly, whether communication data need to be transmitted or not is judged, if so, the communication data to be transmitted is converted into a bit sequence through coding, and the bit sequence comprises different information bits, and the mode is specifically expressed as 1001. The coding process may include adding scrambling, coding, etc., and preferably using scrambling, coding with lower algorithm complexity.
Further, for step S103, the following steps are included:
in order to achieve maximum spectral efficiency, the frequency resources in the initial set of frequencies need to be maximally utilized. Specifically, the bit sequences to be transmitted are grouped to obtain one or more bit sequence groups, and the bit sequence groups are modulated into corresponding chirp signals for transmission. Wherein the length of each bit sequence packet is set by calculation so that the length of each bit sequence packet is equal and the initial frequencies in one initial frequency set can be used up completely.
Specifically, it is assumed that one bit sequence packet of length p is transmitted as:
Wherein c j is any one of the representative c 1-cp, and the value is 0 or 1;
Further, the size of p is set as:
Further, to achieve maximum spectral efficiency, it is generally possible to make To an integer power of 2. For example, in the above embodiment, the initial frequency set size is 128, then p=log 2 128=7.
This is because the integer power of 2 is a discrete number of data, while the length p of the bit sequence packet is an integer, and cannot be a fraction, so when the initial frequency set size can represent the maximum number of bit sequence packetsWhen the power is not the integral power of 2, the frequency resource waste is caused. And correspondingly, the pitch at the time of detection becomes smaller, and the performance becomes worse.
Specifically, for a value of 0 or 1 of any one of bit sequences B t＝[d1 d2…dk],d1-dk to be transmitted, which has a length of k (k > 0), B t is to be grouped into a group of g (g is a positive integer) bit sequences of equal length and pBit stuffing problems are involved. This is because the length k of the bit sequence B t cannot be exactly equal to the bit sequence packet/>, each timeWhen k is not an integer multiple of p, bit padding is performed at the last bit of the bit sequence B t, the number of bits padded is/>
In particular, since the bit value of the last bit padding of the bit sequence B t does not affect the data transfer, all 0 s or all 1 s, for example 0..0 or 1..1, can be arbitrarily padded. Assuming that the length of the padded bit sequence B ' t becomes k ' =k+Δk, the padded bit sequence B ' t may be divided intoIndividual bit sequence grouping/>Each bit sequence packetComprising p bits, as/>cj＝0，1。
The following takes the example of a bit sequence packet length p=7, providing three padding bit embodiments:
for example, for a bit sequence 101001 of k=6, the number of bits filled in at its end is A filling value of 0 or 1, thereby obtaining/>The groups of bit sequences. The bit sequence group is 1010010 when the padding value is 0, and 1010011 when the padding value is 1.
As another example, for a bit sequence 10100101 with k=8, the number of bits filled in at its last bit is The filling value is 000000 or 111111, thereby obtaining/> The groups of bit sequences. The resulting bit sequence groupings are 1010010, 1000000 when the padding value is 000000, 1010010, 1111111 when the padding value is 111111.
As another example, for a bit sequence 101..10 of k=800, the number of bits filled in at its last bit isThe filling value is 00000 or 11111, thus obtaining/>The groups of bit sequences. Specifically, 101..1000000 or 101..1011111 is divided into 115 groups of bit sequences of length 7 in order, and when the padding value is 00000, the 115 th bit sequence group is 1000000, and when the padding value is 11111, the 115 th bit sequence group is 1011111.
Further, for step S104, the following steps are further included:
at the transmitting end, the bit sequence packet to be modulated is determined by a given mapping relation A A one-to-one correspondence with parameter K i, where K i is a different value of the corresponding parameter K in the initial set of frequencies of the transmitted chirp signal, as follows:
Correspondingly, there is an inverse function of the mapping relation A, and there is a method for solving the bit sequence group according to the inverse function at the receiving end Is a process of (2). Wherein, in order to increase reliability, coding and scrambling can also be performed during mapping, and correspondingly, decoding and descrambling processes are performed at the receiving end.
Further, according to the foregoing calculation method of the initial frequency set, once the parameter K is uniquely determined, since each initial frequency f 0 corresponds to a determined parameter K value, the corresponding initial frequency f 0 will also be uniquely determined.
Specifically, after grouping the bit sequences, g bit sequence groups are obtainedEach bit sequence packet/>The number of the groups is p, and is: /(I)cj＝0，1。
Correspondingly, the calculation mode of K i can be as follows:
Ki＝20c1+21c2+…+2p-1cp，
In this way, the bit sequences can be uniquely grouped Mapped to an initial frequency f i corresponding to the value of K i, thereby using the chirp signal corresponding to f i as a transmit signal for modulating the bit sequence packet/>The calculation method of K i is not limited to the above method, and may be, for example, to establish a unique correspondence: k i＝20cp+21cp-1+…+2p-1c1.
Repeating the mapping process, and finally sequentially taking the chirp signals corresponding to the g bit sequence groups as transmitting signals, wherein the transmitting signals are as follows:
Wherein, Representing an initial frequency of/>K i＝A(bi), i=1, 2,3, …, g, t=n/B is a digital sample, n is an integer, and n > =0.
Further, for step S105, further comprising:
the set x t (n) of chirped signals obtained by mapping the g bit sequence packets is finally transmitted through an antenna by necessary operations such as DA conversion, up-conversion, etc. The DA conversion means digital-to-analog conversion for converting a digital signal into an analog signal. In high frequency electronic circuits, it is often necessary to linearly shift the spectrum of a signal, i.e., the spectrum structure is unchanged, the relative amplitude of each frequency component is unchanged, the frequency component is not increased or decreased, and only the frequency component is shifted in parallel on the frequency axis. Up-conversion is the conversion of the frequency of an input signal to a higher frequency shift, which is not only advantageous for improving the performance of the device, but also for adapting to many application systems, such as broadcast systems, television systems, mobile communication systems, etc.
Example two
On the other hand, the invention provides a Doppler-resistant receiving method, which can receive and acquire the linear frequency modulation signal, acquire the initial frequency corresponding to the linear frequency modulation signal through iterative frequency compensation, acquire the bit sequence packet carried by the linear frequency modulation signal through demodulation and decoding, and finally acquire accurate communication data. The Doppler receiving method can effectively improve the high-dynamic Doppler frequency offset resistance, thereby improving the communication reliability.
Referring to fig. 5, the above-mentioned anti-doppler receiving method includes the following steps:
s201: receiving a signal, and sampling the signal to obtain a linear frequency modulation signal;
s202: finishing initial frequency offset estimation and initial timing of the linear frequency modulation signal through a preamble sequence, and setting an initial value of a frequency compensation factor;
s203: performing frequency compensation on the linear frequency modulation signal according to the frequency compensation factor;
s204: detecting the initial frequency of the linear frequency modulation signal;
s205: demodulating a bit sequence packet corresponding to the linear frequency modulation signal according to the initial frequency;
s206: adjusting the frequency compensation factor according to the initial frequency;
s207: judging whether a linear frequency modulation signal to be demodulated exists, if so, executing the steps S203 to S206 again, and if not, executing the next step S208;
s208: and decoding the bit sequence packet.
Specifically, for steps S203 to S207, the detection frequency and the frequency compensation are performed on the chirp signal according to the duration Ts of a single chirp signal, each Ts time only includes one chirp signal, and the initial frequency is compensated and then the frequency compensation factor for the next Ts time is correspondingly adjusted, so that all the chirp signals are traversed in a circulating manner.
Further, for step S201, at the receiving end, a signal is received and sampled, and a chirp signal is obtained after the received signal is subjected to nyquist sampling, where the chirp signal is as follows:
where h (n) is the channel gain, f d (n) represents the Doppler frequency offset, Representing the phase change during transmission, w (n) represents the receiver noise, x t (n) is the original chirp signal, and B represents the signal bandwidth.
Further, for step S202, at the receiving end, there are various ways to obtain the initial frequency offset, for example, the initial frequency offset estimation and the initial timing may be completed through the preamble sequence, the sampling start time is considered to be equal to the initial arrival time, and the duration T s is taken as the sampling interval of the nyquist sampling, so that the signal received in the ith T s period is as follows:
Where f d' (n) denotes the residual frequency offset corrected by the initial frequency offset estimate, w i (n) denotes the receiver noise, Representing the phase.
Further, an initial value of the frequency compensation factor may be set according to circumstances, so as to perform frequency compensation on the chirp signal sampled in the next sampling interval. The initial value may be set to 0 or may be adjusted according to a specific communication environment, for example, according to a traveling rate or acceleration of the communication terminal.
Further, in step S203, since the doppler f d' (n) is time-varying, the received signal needs to be doppler tracked to cope with the false detection caused by the doppler shift, so the present invention uses a tracking loop to perform the doppler tracking. During the detection, a single chirp signal duration T s is used as the minimum unit for detection. First, the received ith signal of duration T s is frequency compensated, denoted as
Wherein,For the frequency compensation factor, for a signal within the first single chirp signal duration T s, the frequency compensation factor/>, of that signalSet as the initial value of the frequency compensation factor set in step S202, e.g./>For a signal within the subsequent i (i > 1) th single chirp duration T s, the frequency compensation factor/>, of the signalThe value of (2) will be set in a subsequent step.
Further, for step S204, detecting the initial frequency of the chirp signal at intervals of a single chirp signal duration T s includes the following steps:
the calculation expression of the initial frequency specifically refers to the initial frequency set in the first embodiment, and will not be described herein.
Further, the detection of the initial frequency is obtained by estimating the value of the parameter K in the calculation expression of the initial frequency and the initial frequency set, because according to the scheme described in the first embodiment, the initial frequency can be uniquely determined by the parameter K, so that obtaining the value of the parameter K is equivalent to obtaining the initial frequency of the above-mentioned chirp signal, and the relation expression of the parameter K and the initial frequency is referred to the first embodiment, and will not be repeated herein.
Specifically, the estimated value K i * of the parameter K is as follows:
Wherein for n i * there are the following calculations:
Wherein the physical meaning of the estimated expression of n i * is the sequence number that maximizes the FFT point;
the physical meaning of the estimated expression of K i * is the result of rounding the sequence number with the maximum FFT point;
x l (n) is the local sequence, as follows:
The parameters in the above expression may refer to the detailed description of the chirp signal and the initial frequency set in the first embodiment, and will not be described herein.
Further, for step S205, the following are included:
Due to The initial frequency can be uniquely determined, and the bit sequence packet is correspondingly mapped into the relation/>, of the parameter K i at the transmitting endThus, according to the/>, described aboveThe unique corresponding bit sequence packet for the signal of duration T s can be reverse mapped as follows:
Wherein A -1 is the inverse of A. Thus according to A complete bit sequence packet/>, after frequency compensation, is obtained
Further, for step S206, the following are included:
Due to n i * and Is also one-to-one corresponding, and can update the next frequency compensation factor according to the value of n i * The values of (2) are as follows:
specifically, G is an adjustment strategy function with an argument of n i * and The obtained result is used for updating the next frequency compensation factor/>And the updated frequency compensation factor/>For frequency compensation of the next signal of duration T s.
Specifically, the adjustment policy function G may be as follows:
wherein 0 < Δf', As an adjustable parameter,% represents a remainder operation.
Note that this is only one embodiment, and the present invention is not limited to a specific implementation of the adjustment policy function G.
In addition, the parameter S/2 is also an adjustable parameter.
Further, for step S207, the following are included:
At the receiving end, each duration is T s, and after the signal is received, whether the signal needs to be demodulated or not is judged; when there are more signals to demodulate, steps S203 to S206 are repeated continuously, thereby ensuring that all signals can be frequency compensated and demodulated into bit sequence packets. After confirming that all signals are received, the next step S208 may be performed, and the obtained bit sequence packet is decoded, to finally obtain communication data.
Example III
In order to more intuitively describe the anti-doppler transmission method and the anti-doppler reception method of the present invention, the following is a practical example:
When the system bandwidth is b=1 MHz and the duration of a single chirp signal is T s =0.512 ms, the time bandwidth product is n=512. When s=4, the initial frequency set size of the available chirp signal is 512/4=128. Assuming f r =0, the initial set of frequencies is as follows:
Thus p=7. Assuming 800 bits are to be transmitted, the 800 bits may be generated by encoding, scrambling and interleaving the original communication data, then 5 bits are to be padded, and the padded information bit sequence is divided into g=805/7=115 packets, each packet containing 7 bits. Meanwhile, the function a is a value of converting every 7 bits into a 10-ary number as K, that is, k=2 0b1+21b2+…+2p-1b7. The chirp signals corresponding to the g bit sequence packets are sequentially used as transmission signals, as follows:
At the receiving end, the signal is sampled, the compensated signal is detected, and the estimated value of K i can be expressed as:
Wherein, n i * has the following calculation modes:
Wherein the local sequence x l (n) is expressed as
The inverse of function a is:
thus it can be estimated that
Wherein/>
The frequency compensation factor is then updated, denoted as
Namely:
Further, referring to fig. 9, a packet loss rate curve of the present embodiment in a large doppler scene is shown, where the packet length is 100 bytes. As can be seen from the figure, the anti-doppler performance is excellent and substantially coincides with the case without doppler frequency offset.
Example IV
In still another aspect, referring to fig. 6, the present invention provides a device for transmitting doppler resistance, including: a frequency generation module 301, a grouping module 302, a grouping mapping module 303, and a transmission module 304.
The anti-doppler transmitting device can implement the anti-doppler transmitting method of the first embodiment, modulate the communication data to be transmitted with a chirp signal corresponding to the selected initial frequency, and transmit the modulated communication data to the anti-doppler receiving device for communication, and the specific implementation of the anti-doppler receiving device can refer to the fifth embodiment.
When transmitting bit data using a chirp signal, the initial frequency set is set by the frequency generation module 301, increasing the interval of the initial frequencies between different signals, thereby increasing the resistance to doppler shift.
Specifically, the frequency generation module 301 performs calculation according to the available chirp signals, and obtains an initial frequency set of the chirp signals.
The grouping module 302 encodes communication data to be transmitted, converts the communication data into bit sequences, groups the bit sequences according to the size of an initial frequency set, and obtains one or more bit sequence groups, so that the length of each bit sequence group is the same, and the number of the bit sequence groups can just run out of the initial frequency set when the subsequent groups are mapped.
The packet mapping module 303 maps each bit sequence packet into a chirp signal corresponding to a different one of the set of initial frequencies.
The transmitting module 304 transmits the chirp signal processed by the packet mapping module 303 through radio frequency.
For the specific flow of the anti-doppler transmitting method related to the above modules, please refer to the previous anti-doppler transmitting method embodiment, and the description thereof is omitted.
Example five
In still another aspect, referring to fig. 7 and 8, the present invention provides a doppler-resistant receiving device, which can implement the doppler-resistant receiving method of the second embodiment, receive and acquire a chirp signal, acquire an initial frequency corresponding to the chirp signal through frequency compensation, and then acquire a bit sequence packet carried by the chirp signal through demodulation and decoding, so as to finally acquire accurate communication data.
Preferably, the doppler-resistant receiving device includes: the device comprises a receiving module 401, a frequency detecting module 402, a grouping reflection module 403 and a decoding module 404.
The receiving module 401 receives a signal, and samples the signal to obtain a chirp signal.
The frequency detection module 402 performs initial frequency detection of the linear fm signal, which further includes frequency compensation of the initial frequency.
Packet demapping module 403 demaps the chirp signal to obtain a packet of bit sequences carried by the chirp signal.
The decoding module 404 performs unified decoding on all the obtained bit sequence packets in sequence to obtain final communication data.
Each chirp signal has a duration Ts, and during this period of time, the frequency detection module 402 and the packet demapping module 403 cooperate with each other to determine whether there is a next chirp signal to demodulate each time a chirp signal is received; when there are more chirps to demodulate, the frequency detection module 402 and the packet demapping module 403 may continue to operate, for example, detect the initial frequency corresponding to the current chirps, and perform packet demapping to obtain a bit sequence packet, so as to ensure that all signals can be frequency compensated and demodulated into the bit sequence packet.
Preferably, the frequency detection module 402 includes: an initial frequency offset estimation unit 4021, a frequency compensation unit 4022, an initial frequency calculation unit 4023, and a frequency compensation factor generation unit 4024.
The initial frequency offset estimation unit 4021 completes the initial frequency offset estimation and the initial timing of the above-mentioned chirp signal through the preamble sequence, and sets an initial value of the frequency compensation factor.
The frequency compensation unit 4022 performs frequency compensation on the chirp signal according to the frequency compensation factor.
The initial frequency calculation unit 4023 detects the initial frequency of the above-described chirp signal.
The frequency compensation factor generation unit 4024 adjusts the frequency compensation factor described above according to the initial frequency described above.
For the specific flow of the anti-doppler receiving method related to the above modules, please refer to the previous anti-doppler receiving method embodiment, and the description thereof is omitted herein.
Example six
In still another aspect, the present invention provides a doppler-resistant terminal, including a doppler-resistant transmitting device of the fourth embodiment and/or a doppler-resistant receiving device of the fifth embodiment, where doppler-resistant mobile communications can be performed between two doppler-resistant terminals by using the doppler-resistant transmitting method of the first embodiment and the doppler-resistant receiving method of the second embodiment.
The foregoing is merely illustrative of the present invention, and the present invention is not limited thereto, and any person skilled in the art will readily recognize that variations or substitutions are within the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.
According to the embodiment of the invention, doppler shift can be obviously improved, and communication reliability in a high dynamic Doppler scene is improved, and the specific reference is made to the performance change graph of the drawing.
Claims (7)
1. The Doppler resistance transmitting method is characterized by comprising the following steps:
S101: setting an initial frequency set of the linear frequency modulation signal and the size of an interval between the initial frequencies;
S102: coding and converting data to be transmitted into a bit sequence;
s103: grouping the bit sequences according to the size of the initial frequency set to obtain one or more bit sequence groups, wherein the length of each bit sequence group is the same;
s104: mapping each bit sequence group into a different linear frequency modulation signal, wherein the initial frequencies corresponding to the linear frequency modulation signals are different; determining the bit sequence packet by a mapping relationship A relation with parameter K i, wherein parameter K i is a corresponding parameter K i in the initial frequency set F t, the mapping relation is/>
S105: transmitting the linear frequency modulation signal through radio frequency;
step S101 includes the steps of:
S1011: setting the linear frequency modulation signal;
s1012: calculating an initial frequency set of the linear frequency modulation signal;
the chirp signal is as follows:
where B is the signal bandwidth, T s is the single chirp duration, For the frequency turnover time, f 0 epsilon [ -B/2, B/2] is the initial frequency of the linear frequency modulation signal, the time bandwidth product of the linear frequency modulation signal is BT s =N, t=n/B is a digital sampling point, N is an integer, and N > =0;
the initial frequency set in step S1012 is calculated in the following manner:
Wherein the method comprises the steps of The number of elements in the initial frequency set F t is/>, which is a settable variableThe chirp signal represents at most/>The bit sequence packet is of the type S is an adjustable parameter.
2. The doppler-resistant transmission method according to claim 1, wherein step S103 includes:
The length p of the bit sequence packet is acknowledged by:
wherein/> To an integer power of 2.
3. The method of anti-doppler transmission according to claim 2, wherein step S103 further comprises:
for a bit sequence B t＝[d1 d2 … dk to be transmitted with length k (k > 0), when k+.p, bit padding is performed at the last bit of the bit sequence B t, the number of bits padded is:
The bit value of the padding is all 0 or all 1, the length of the bit sequence B ' t after padding is changed to k ' =k+Δk, and the bit sequence B ' t after padding is divided into Individual bit sequence grouping/>(I=1, 2, …, g), each of said bit sequence packets/>Containing p bits.
4. The method for doppler-resistant transmission according to claim 3, wherein step S105 comprises: sequentially taking the chirp signals corresponding to the g bit sequence groups as transmitting signals, wherein the set of the chirp signals is
Wherein,Representing an initial frequency of/>Is a chirp signal of/>T=n/B is a digital sample point, n is an integer, and n > =0.
5. The method for doppler-resistant transmission according to claim 4, wherein step S105 includes:
Before transmitting the set of chirp signals x t (n), the set of chirp signals x t (n) is DA converted or up converted and finally transmitted through an antenna.
6. A doppler-resistant transmitting device comprising: the device comprises a frequency generation module, a grouping mapping module and a sending module;
The frequency generation module calculates according to the available linear frequency modulation signals to obtain an initial frequency set of the linear frequency modulation signals; wherein the chirp signal is as follows:
where B is the signal bandwidth, T s is the single chirp duration, For the frequency turnover time, f 0 epsilon [ -B/2, B/2] is the initial frequency of the linear frequency modulation signal, the time bandwidth product of the linear frequency modulation signal is BT s =N, t=n/B is a digital sampling point, N is an integer, and N > =0;
the calculation mode of the initial frequency set is as follows:
Wherein the method comprises the steps of The number of elements in the initial frequency set F t is/>, which is a settable variableThe chirp signal may represent/>, at mostThe seed bit sequence groups, S is an adjustable parameter;
the grouping module encodes communication data to be transmitted, converts the communication data into bit sequences, groups the bit sequences according to the size of the initial frequency set, and obtains one or more bit sequence groups, wherein the length of each bit sequence group is the same;
The grouping mapping module groups and maps each bit sequence into the linear frequency modulation signal corresponding to a different initial frequency in the initial frequency set; determining the bit sequence packet by a mapping relationship A relation with parameter K i, wherein parameter K i is a corresponding parameter K i in the initial frequency set F t, the mapping relation is/>
And the transmitting module transmits the linear frequency modulation signal processed by the grouping mapping module through radio frequency.
7. A doppler-resistant terminal comprising the doppler-resistant transmitting device of claim 6.
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