CN117040605A - Ground terminal satellite searching method for low-orbit satellite communication - Google Patents
Ground terminal satellite searching method for low-orbit satellite communication Download PDFInfo
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Abstract
The application relates to a ground terminal satellite searching method for low-orbit satellite communication, belongs to the field of satellite communication, and solves the problems of long satellite searching time, difficult satellite dynamic tracking and other industry pain points and difficulties of a low-orbit satellite communication system in the prior art. The technical scheme of the application is that a low orbit satellite acquires position information in real time to modulate and generate a position broadcasting signal, and then the position broadcasting signal and a communication broadcasting signal are transmitted in a time-sharing way by utilizing a single narrow beam antenna which is equipped with the low orbit satellite; the ground terminal is provided with double antennas, the wide beam antenna is used for receiving position broadcast signals, the position information of the low-orbit satellite is obtained through demodulation and analysis, and after the satellite-ground alignment angle is calculated, the narrow beam antenna of the ground terminal is guided to be aligned with the low-orbit satellite, and communication broadcast signals are received and analyzed, so that the satellite searching process is completed. Compared with the prior art, the method and the device do not need to predict the ephemeris data of the low-orbit satellite, and realize that the ground terminal can quickly and accurately finish searching and tracking the low-orbit satellite.
Description
Technical Field
The application relates to the technical field of satellite communication, in particular to a ground terminal satellite searching method for low-orbit satellite communication.
Background
Compared with medium-high orbit satellite communication, low orbit satellite communication has the characteristics of low communication time delay, large communication capacity and the like, and related technologies are rapidly developed in recent years. Meanwhile, the low orbit brings high-speed motion of the satellite, so that quick search and reliable tracking of the ground terminal on the low orbit satellite become industry pain and difficulty.
The existing ground terminal satellite searching method for low-orbit satellite communication mainly comprises a method based on ephemeris data, a method based on satellite wide-narrow beam combination and combined use of the two methods.
The method based on the ephemeris data requires a third party platform to provide the ephemeris data, and the ephemeris data of the low orbit satellite is generally low in precision, so that high-precision timing and orientation application is difficult to meet. The method based on the combination of the satellite wide and narrow beam antennas is to configure a narrow beam antenna and a wide beam antenna on a satellite, and the ground terminal only has the narrow beam antenna. The ground terminal searches the wide beam antenna signal on the satellite, reduces the searching range, and then searches the narrow beam signal of the satellite in a small range, thereby completing the satellite searching. According to the scheme, two types of antennas on the satellite respectively transmit different types of signals at different frequencies, so that additional occupied antenna resources are needed, the low-orbit satellite is high in motion speed, and the ground terminal is low in satellite-ground alignment angle adjustment efficiency, so that the improvement of the satellite searching speed of the ground terminal is limited; the combined use of the two methods can improve the satellite searching speed of the ground terminal to a certain extent, but cannot get rid of the dependence on ephemeris data and the extra occupation of satellite antenna resources.
Disclosure of Invention
In view of the above analysis, the embodiment of the application aims to provide a ground terminal satellite searching method for low-orbit satellite communication, which is used for solving the problems of low satellite searching efficiency and extra occupation of satellite antenna resources due to dependence on ephemeris data in the prior art.
The application aims to overcome the defects of the prior art and provides a ground terminal satellite searching method for low-orbit satellite communication, which comprises the following steps:
step 101, the low-orbit satellite acquires the position information of the low-orbit satellite in real time, generates a position broadcasting signal modulated, generates and modulates communication information into a communication broadcasting signal, and uses a single narrow-beam antenna to transmit two types of signals at maximum power in a time sharing manner;
102, the ground terminal is provided with two types of antennas, namely a wide-beam antenna and a narrow-beam antenna, wherein the ground terminal wide-beam antenna receives the position broadcast signal;
step 103, the ground terminal demodulates and analyzes the received position broadcast signals to obtain the low-orbit satellite position information;
104, the ground terminal calculates a satellite-ground alignment angle according to the self position information and the low-orbit satellite position information;
step 105, the ground terminal directs the ground terminal narrow beam antenna to aim at the low orbit satellite according to the satellite-ground aiming angle;
step 106, the ground terminal receives the communication broadcast signal through the ground terminal narrow beam antenna;
and 107, demodulating and analyzing the communication broadcast signal by the ground terminal to obtain system information required by the random access initiated by the ground terminal, and completing the star searching process.
Based on a further improvement of the above method, the position broadcast signal is a narrowband signal with a higher power spectral density carrying the low-orbit satellite position information; the communication broadcast signal is a wideband signal with a lower power spectral density that includes system information required for the ground terminal to initiate random access and does not include the low-orbit satellite position information.
In the above technical solution, the process of generating and modulating the position broadcast signal by the low-orbit satellite includes:
step 201, adding cyclic redundancy check to the low-orbit satellite position information to obtain a checked information sequence;
based on further improvement of the method, cyclic redundancy check is added to the low-orbit satellite position information, and the obtained checked sequence is realized through the following processes:
converting the low-orbit satellite position information into an information sequence a 0 ,a 1 ,a 2 ,a 3 ,…,a A-1 Inputting and calculating to obtain a check bit p 0 ,p 1 ,p 2 ,p 3 ,…,p L-1 Wherein A is the input sequence length, L is the check bit length, and the output sequence with added cyclic redundancy check is denoted b 0 ,b 1 ,b 2 ,b 3 ,…,b B-1 Wherein b=a+l, satisfies the relationship,
b k ＝a k ,k＝0,1,2,…,A-1
b k ＝p k-A ,k＝A,A+1,A+2,…,A+L-1
the addition of the check bits is required to satisfy the following polynomial integer division by the generator polynomial over GF (2) domain,
a 0 D A+L-1 +a 1 D A+L-2 +…+a A-1 D L +p 0 D L-1 +p 1 D L-2 +…+p L-2 D 1 +p L-1 D 0 ；
wherein GF (2) domain is a Gal Luo Huayou finite domain containing only 0 and 1 elements, D is a delay operator, A>L, the highest order term D of the generator polynomial L The coefficients and constant terms of (2) are 1, and the coefficients of the remaining terms may take different values with different generator polynomials.
Step 202, performing channel coding on the checked sequence to obtain a coded information sequence;
step 203, scrambling the coded sequence to obtain a scrambled information sequence;
step 204, adding a single-tone pilot frequency information sequence and a synchronous information sequence to the scrambled sequence to obtain a framed information sequence;
based on further improvement of the method, a single-tone pilot sequence and a synchronization sequence are added to the scrambled sequence to obtain a framing sequence, wherein the single-tone pilot sequence, the synchronization sequence and the scrambled sequence are arranged in sequence in time, the single-tone pilot sequence provides frequency information for a receiving end, the synchronization sequence provides timing information for the receiving end, and the scrambled sequence carries low-orbit satellite position information;
step 205, modulating the sequence after framing to obtain a modulated signal sequence;
and 206, performing shaping filtering on the modulated sequence to obtain the position broadcast signal.
In the above technical solution, the demodulation and analysis process of the received position broadcast signal by the ground terminal includes:
step 301, performing matched filtering on the position broadcast signal to obtain a complex baseband signal sequence after filtering;
step 302, capturing a single-tone pilot frequency complex baseband sequence of the filtered complex baseband signal sequence, and completing frequency offset estimation and compensation to obtain a complex baseband sequence after frequency offset compensation;
based on a further improvement of the above method, the single tone pilot complex baseband sequence acquisition is realized by the following ways:
for the received complex baseband signal r i Capturing the complex baseband sequence of the single-tone pilot frequency by taking N as a signal sampling interval and taking the length 2N as a signal processing length, and processing r for the first time 0 ,r 1 ,r 2 ,…,r 2N-1 Second treatment r N ,r N-1 ,r N-2 ,…,r 3N-1 By analogy in turn,
a Fourier transform acquisition function is performed each time on the 2N point signal complex baseband sample values,
wherein the method comprises the steps ofIn imaginary units, e is a natural constant, m is the number of times the current acquisition process is performed (m takes on values from 0, m=0, 1, 2, 3, 4, …), n is the number of input complex baseband signals, R k To do soThe fourier transformed output frequency domain signal, k being the number of the output frequency domain signal,
the signal processing is continued until R is obtained k And if the maximum amplitude exceeds the threshold value, completing the capture of the single-tone pilot complex baseband sequence.
Based on the further improvement of the method, the single-tone pilot complex baseband sequence is captured in a complex baseband signal range with the length of 2N, according to the fixed position relation between the single-tone pilot complex baseband sequence and the synchronous complex baseband sequence, namely, the synchronous complex baseband sequence is captured in the complex baseband signal range with the length of 2N, the complex baseband signal and the local synchronous complex baseband sequence are further subjected to point-by-point sliding conjugate multiplication accumulation in the 2N range, when the accumulated value amplitude is maximum, the corresponding conjugate multiplication accumulation initial position is the accurate time domain position of the synchronous complex baseband sequence, wherein the local synchronous complex baseband sequence is known by the low-orbit satellite and the ground terminal, the maximum value of the conjugate multiplication accumulation amplitude is obtained by the following functions,
m is the length of the synchronous complex baseband sequence, l n Synchronous complex baseband sequence locally generated for ground terminal, i is pair l n Taking the conjugate complex number i as the initial position for conjugate multiplication accumulation operation.
Step 303, synchronous complex baseband sequence detection is carried out on the frequency offset compensated sequence, timing synchronization is completed, and a synchronous complex baseband sequence is obtained;
step 304, demodulating the synchronous complex baseband sequence to obtain a demodulated information sequence;
step 305, descrambling the demodulated information sequence to obtain a descrambled information sequence;
step 306, performing channel decoding on the descrambled information sequence to obtain a decoded information sequence;
step 307, performing cyclic redundancy check on the decoded information sequence to obtain a checked information sequence;
and 308, performing sequence analysis on the checked information sequence to obtain the low-orbit satellite position information.
In another aspect, the present application provides a ground terminal satellite search system for low-orbit satellite communications, comprising a low-orbit satellite, a ground terminal, wherein,
the low-orbit satellite generates two types of signals, namely a position broadcast signal generated by acquiring the position information of the low-orbit satellite in real time and a communication broadcast signal, and the two signals are transmitted in a time-sharing way through the same narrow-wave-speed antenna;
the ground terminal is provided with two types of antennas, namely a wide beam antenna and a narrow beam antenna, the position broadcast signals are received through the wide beam antenna, the position information of the low-orbit satellite is obtained through analysis, the satellite-ground angle is obtained through calculation, the narrow beam antenna is controlled to be aligned with the low-orbit satellite, the communication broadcast signals are received through the narrow beam antenna, the system information required by the ground terminal to initiate random access is obtained through analysis, and the satellite searching is completed.
Compared with the prior art, the application has the following beneficial effects:
1. according to the application, the ephemeris data are not dependent, and the ground terminal does not need to acquire the ephemeris data provided by a third party by accessing other networks;
2. the application is based on the real-time position of low orbit satellite broadcasting, greatly improves the alignment speed and precision of the receiving and transmitting antenna wave beam;
3. the application simplifies the design of the low-orbit satellite antenna and improves the operation reliability of the low-orbit satellite.
In the application, the technical schemes can be mutually combined to realize more preferable combination schemes. Additional features and advantages of the application will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the application. The objectives and other advantages of the application may be realized and attained by the structure particularly pointed out in the written description and drawings.
Drawings
The drawings are only for purposes of illustrating particular embodiments and are not to be construed as limiting the application, like reference numerals being used to designate like parts throughout the drawings;
FIG. 1 is a flow diagram of a fast search for low-orbit satellites for a ground terminal in one embodiment;
FIG. 2 is a diagram illustrating a position broadcast signal generation process according to an embodiment of the present application;
fig. 3 is a schematic diagram of a demodulation and parsing process of a position broadcast signal according to an embodiment of the present application.
Detailed Description
The present application will be further described with reference to the accompanying drawings, which form a part hereof, and in conjunction with the examples of the present application, illustrate the principles of the present application, and not by way of limitation.
For the convenience of understanding, the related concepts related to the present application will be described first.
Wide beam antenna: an antenna for transmitting and receiving electromagnetic waves using a wide beam angle and a relatively low antenna gain can realize wide-range, low-precision transmission and reception of electromagnetic waves, and is used for broadcasting communication and mobile communication.
Narrow beam antenna: the antenna for receiving and transmitting electromagnetic waves by using a narrower beam angle and a relatively higher gain has the characteristics of high precision, high quality, long distance and narrow communication range, and is widely used for radar and satellite communication.
Narrowband signal: the application refers to a broadcast signal with high power spectrum density carrying low-orbit satellite position information, and the requirement on communication speed is low because the carrying information quantity is small, so that a narrow band is adopted.
Broadband signal: the application refers to a communication signal carrying low-orbit satellite communication information and having lower power spectral density.
As shown in fig. 1, in one embodiment of the present application, a method for searching satellites by a ground terminal for low-orbit satellite communication is disclosed, including:
step 101, the low-orbit satellite acquires the position information of the low-orbit satellite in real time, modulates and generates a position broadcasting signal, modulates and generates communication information into a communication broadcasting signal, and uses a single narrow-beam antenna to transmit two types of signals in a time-sharing manner;
preferably, the location information may be orbital 6 root coordinate data based on SGP4 model, satellite location coordinate data based on ECEF coordinate system, etc.;
preferably, the two types of signals can be sent through the maximum power, so that the wide beam antenna with lower gain of the ground terminal can still complete the signal receiving and processing;
102, the ground terminal is provided with two types of antennas, namely a wide-beam antenna and a narrow-beam antenna, wherein the ground terminal wide-beam antenna receives the position broadcast signal;
preferably, the wide beam antenna may be a hemispherical antenna, so as to receive satellite broadcast signals in the space as much as possible;
step 103, the ground terminal demodulates and analyzes the received position broadcast signals to obtain the low-orbit satellite position information;
104, the ground terminal calculates a satellite-ground alignment angle according to the self position information and the low-orbit satellite position information;
preferably, the calculated satellite-ground alignment angle is calculated by unifying the position information of the low-orbit satellite and the information of the ground terminal to the same coordinate system;
step 105, the ground terminal directs the ground terminal narrow beam antenna to aim at the low orbit satellite according to the satellite-ground aiming angle;
preferably, said alignment is accomplished by servo rotation means controlling said ground terminal antenna;
step 106, the ground terminal receives the communication broadcast signal through the ground terminal narrow beam antenna;
and 107, demodulating and analyzing the communication broadcast signal by the ground terminal to obtain system information required by the random access initiated by the ground terminal, and completing the star searching process.
Compared with the prior art, the technical scheme provided by the embodiment is different in that:
the method for acquiring the position information by the low-orbit satellite is changed, the low-orbit satellite is provided with a navigation receiver, and the navigation receiver can output the position information after receiving the navigation satellite signal, namely the current position of the low-orbit satellite. Compared with the prior art, the method needs to send the position information at the beginning, the position information is very accurate, the method based on ephemeris data does not need to send the position information of the satellite in real time, the position (namely ephemeris) of the satellite can be obtained through the Internet, but the position information is usually only of a forecasting property and is inaccurate, moreover, the low-orbit satellite has a fast motion speed, the valid time of the ephemeris is usually only a few hours, and the support of a third-party network (Internet) is needed, so that for the low-orbit satellite running at a high speed, the method for directly sending the position information is more reliable than the method for predicting the motion trail through the ephemeris data.
The method comprises the steps of respectively generating two types of signals, namely a modulation position broadcast signal and a communication broadcast signal, by using a single narrow-beam antenna to transmit the two types of signals, wherein the ground terminal is provided with a wide-beam antenna and a narrow-beam antenna to receive the two types of signals respectively, so that on one hand, the antenna design and the resource use on the low-orbit satellite are simplified, and on the other hand, the ground terminal obtains satellite position information in an optimized and simplified mode and speed by means of the arrangement of the antennas at the two ends of the satellite and the communication mechanism and the change of signal generation modulation and demodulation analysis.
Based on a further improvement of the above method, the position broadcast signal is a narrowband signal with a higher power spectral density carrying the low-orbit satellite position information; the communication broadcast signal is a wideband signal with a lower power spectral density that includes system information required for the ground terminal to initiate random access and does not include the low-orbit satellite position information. The low-orbit satellite position broadcast signals are transmitted through narrow-band signals with higher power spectral density, on one hand, the carried satellite position information data volume is small, the bandwidth requirement is not high, and the requirements can be completely met by adopting narrow-band and low-speed communication; on the other hand, the narrow-band and low-speed signals with high power spectral density can ensure that the ground terminal wide-beam antenna can still effectively analyze signals under the condition of lower gain.
As shown in fig. 2, the process of modulating the position broadcast signal generated by the low-orbit satellite includes:
step 201, adding cyclic redundancy check to the position information of the low orbit satellite to obtain a checked sequence;
converting the low-orbit satellite position information into a binary information sequence a 0 ,a 1 ,a 2 ,a 3 ,…,a A-1 Calculating to obtain a binary check bit p 0 ,p 1 ,p 2 ,p 3 ,…,p L-1 Where A is the input sequence length and L is the check bit length. A variety of generator polynomials may be supported, including, but not limited to, the following generator polynomials:
-g CRC24A (D)＝[D 24 +D 23 +D 18 +D 17 +D 14 +D 11 +D 10 +D 7 +D 6 +D 5 +D 4 +D 3 +D+1]
-g CRC24B (D)＝[D 24 +D 23 +D 6 +D 5 +D+1]
-g CRC24C (D)＝[D 24 +D 23 +D 21 +D 20 +D 17 +D 15 +D 13 +D 12 +D 8 +D 4 +D 2 +D+1]
-g CRC16 (D)＝[D 16 +D 12 +D 5 +1]
-g CRC11 (D)＝[D 11 +D 10 +D 9 +D 5 +1]
-g CRC6 (D)＝[D 6 +D 5 +1]
the addition of check bits will enable the following polynomial to be divided by the generator polynomial over the GF (2) domain:
a 0 D A+L-1 +a 1 D A+L-2 +…+a A-1 D L +p 0 D L-1 +p 1 D L-2 +…+p L-2 D+p L-1
outputting the additional cyclic redundancy check-back binaryThe sequence is denoted b 0 ,b 1 ,b 2 ,b 3 ,…,b B-1 Wherein b=a+l, satisfies the relationship:
b k ＝a k ,k＝0,1,2,…,A-1
b k ＝p k-A ,k＝A,A+1,A+2,…,A+L-1
wherein GF (2) domain is a gamma Luo Huayou finite domain containing only two elements of 0 and 1, D is a delay operator. To ensure information transmission efficiency, should A>L, at the same time, generating the highest order term D of the polynomial L The coefficients and constant terms of (2) are 1, and the coefficients of the remaining terms may take different values with different generator polynomials.
Step 202, performing channel coding on the checked sequence to obtain a coded sequence;
inputting the binary sequence b after verification 0 ,b 1 ,b 2 ,b 3 ,…,b B-1 Adding redundant information to obtain output coded binary sequence c 0 ,c 1 ,c 2 ,c 3 ,…,c C-1 Wherein B is<And C, the channel coding output sequence added with the redundant information has forward error correction capability.
Preferably, the channel coding may employ convolutional codes, turbo codes, polar codes, etc.
Step 203, scrambling the coded sequence to obtain a scrambled sequence;
from the coded binary sequence c 0 ,c 1 ,c 2 ,c 3 ,…,c C-1 Generating binary scrambling sequences s of equal length 0 ,s 1 ,s 2 ,s 3 ,…,s C-1 Performing binary addition operation on the two sequences to obtain a scrambled binary sequence d 0 ,d 1 ,d 2 ,d 3 ,…,d C-1 Wherein
d i ＝(c i +s i )mod 2,i＝0,1,2,…,C-1
Step 204, adding a single-tone pilot frequency sequence and a synchronization sequence to the scrambled sequence to obtain a framing sequence;
the single-tone sequence, the synchronous sequence and the scrambled sequence are arranged in sequence in time, wherein the single-tone sequence is usually a full 0 or a full 1 binary sequence, frequency information is provided for a receiving end, the synchronous sequence is a binary sequence known by a transmitting and receiving end, timing information is provided for the receiving end, and the scrambled sequence carries satellite position information.
Step 205, modulating the framing sequence to obtain a modulated sequence;
modulation converts the three binary sequences of the single-tone sequence, the synchronization sequence and the scrambled sequence into a complex baseband sequence which characterizes the amplitude/phase of the radio signal, so that the complex baseband sequence can be transmitted through the radio signal.
Preferably, the modulation may employ Minimum Shift Keying (MSK) modulation, gaussian Minimum Shift Keying (GMSK) modulation, or the like.
Step 206 performs shaping filtering on the modulated sequence to obtain the position broadcast signal.
As shown in fig. 3, the demodulation and parsing process of the received position broadcast signal by the ground terminal includes:
step 301, performing matched filtering on the position broadcast signal to obtain a filtered signal sequence.
Step 302, capturing the single-tone pilot complex baseband sequence of the filtered sequence, wherein the process is as follows:
for a single-tone pilot complex baseband sequence f of length N 0 ,f 1 ,f 2 ,f 3 ,…,f N-1 N is taken as a signal sampling interval when the signal is captured, and the length 2N is taken as a signal processing length. I.e. for the received complex baseband signal r i First process r 0 ,r 1 ,r 2 ,…,r 2N-1 Second treatment r N ,r N-1 ,r N-2 ,…,r 3N-1 And so on, performing Fourier transform on the complex baseband sampling value of the 2N-point signal each time, taking the first processing signal as an example, the Fourier transform is as follows:
wherein the method comprises the steps ofIn imaginary units, e is a natural constant, m is the number of times the current acquisition process is performed (m takes on values from 0, m=0, 1, 2, 3, 4, …), n is the number of input complex baseband signals, R k K is the number of the output frequency domain signal in order to output the frequency domain signal after fourier transform. If R is obtained by one treatment k The maximum amplitude exceeds a threshold value, so that the capture of the single-tone pilot complex baseband sequence is realized;
completing frequency offset estimation and compensation based on the single-tone pilot frequency complex baseband sequence to obtain a complex baseband sequence after frequency offset compensation;
step 303, synchronous complex baseband sequence detection is carried out on the complex baseband sequence after frequency offset compensation, timing synchronization is completed, and a complex baseband sequence after synchronization is obtained;
besides frequency synchronization, the single-tone pilot complex baseband sequence can realize timing coarse synchronization, namely, the time domain range of the single-tone pilot complex baseband sequence is obtained, and further, the time domain range of the synchronous complex baseband sequence can be obtained according to the fixed relative relation between the single-tone pilot complex baseband sequence and the synchronous complex baseband sequence. In order to achieve correct demodulation of the signal, it is necessary to achieve timing fine synchronization by means of the synchronous complex baseband sequence, i.e. to know the exact time domain position where the synchronous complex baseband sequence is located. The synchronous complex baseband sequence is known by convention for both low-orbit satellites and ground terminals, and the ground terminal can locally generate the synchronous complex baseband sequence given that the length of the synchronous complex baseband sequence is M 0 ,l 1 ,l 2 ,…,l M-1 Performing conjugate multiplication accumulation with the local synchronous complex baseband sequence within a 2N signal processing length range after shifting the captured single-tone pilot complex baseband sequence in step 302 by itself length N, and then obtaining the corresponding receiving sequence starting position when the accumulated value amplitude is maximum as the accurate time domain position of the synchronous complex baseband sequence, as shown in the following formula:
wherein M is the length of the synchronous complex baseband sequence, l n Synchronous complex baseband sequence locally generated for ground terminal, i is pair l n Taking the conjugate complex number i as the initial position for conjugate multiplication accumulation operation.
After the synchronous complex baseband sequence is obtained, timing synchronization is carried out based on the synchronous complex baseband sequence, and a complex baseband sequence after synchronization is obtained;
step 304, demodulating the synchronous complex baseband sequence to obtain a demodulated complex baseband sequence;
the complex baseband sequence is converted into soft information, i.e. a real sequence, which characterizes the binary bit value probabilities of 0 and 1.
Step 305, descrambling the demodulated sequence to obtain a descrambled information sequence;
according to the demodulated real number sequence f 0 ,f 1 ,f 2 ,f 3 ,…,f C-1 Generating binary scrambling sequences g of equal length 0 ,g 1 ,g 2 ,g 3 ,…,g C-1 The binary scrambling sequence g i Generating a real scrambling sequence h as follows i ：
h i ＝1-2g i
Further let f i And h i The two sequences are subjected to bit-by-bit multiplication operation to obtain a real number sequence k after descrambling 0 ,k 1 ,k 2 ,k 3 ,…,k C-1 Wherein
k i ＝f i ·h i ,i＝0,1,2,…,C-1
Step 306, performing channel decoding on the descrambled information sequence to obtain a decoded information sequence;
and the channel decoding utilizes redundant information in the input real number sequence to automatically correct errors in the transmission process and outputs a decoded binary sequence.
Step 307, performing cyclic redundancy check on the decoded sequence to obtain a checked information sequence;
based on the first A bit a of the input binary information sequence 0 ,a 1 ,a 2 ,a 3 ,…,a A-1 Calculating to obtain a binary check bit p 0 ,p 1 ,p 2 ,p 3 ,…,p L-1 Where a is the input information sequence length and L is the check bit length. A variety of generator polynomials can be supported, and the addition of check bits will enable the following polynomials to be divided over GF (2) domain by generator polynomials:
a 0 D A+L-1 +a 1 D A+L-2 +…+a A-1 D L +p 0 D L-1 +p 1 D L-2 +…+p L-2 D 1 +p L-1 D 0
if binary check bit p 0 ,p 1 ,p 2 ,p 3 ,…,p L-1 Identical to the last L bits of the input binary information sequence, then indicates that the check passes, a 0 ,a 1 ,a 2 ,a 3 ,…,a A-1 Outputting an information sequence after verification; if the sequences are different, the transmission errors are indicated, and the sequence discarding is not used.
And 308, performing sequence analysis on the checked sequence to obtain the low-orbit satellite position information.
Those skilled in the art will appreciate that all or part of the flow of the methods of the embodiments described above may be accomplished by way of a computer program to instruct associated hardware, where the program may be stored on a computer readable storage medium. Wherein the computer readable storage medium is a magnetic disk, an optical disk, a read-only memory or a random access memory, etc.
The present application is not limited to the above-mentioned embodiments, and any changes or substitutions that can be easily understood by those skilled in the art within the technical scope of the present application are intended to be included in the scope of the present application.
Claims (10)
1. A method for a ground terminal to quickly search for low-orbit satellites, comprising:
the method comprises the steps that a low-orbit satellite acquires the position information of the low-orbit satellite in real time, modulates the position information of the low-orbit satellite to generate a position broadcast signal, modulates communication information to generate a communication broadcast signal, and uses a single narrow-beam antenna to transmit two types of signals in a time sharing mode;
the ground terminal is provided with two types of antennas, namely a wide beam antenna and a narrow beam antenna, wherein the ground terminal wide beam antenna receives the position broadcast signal, and the ground terminal analyzes the position broadcast signal to obtain low-orbit satellite position information;
the ground terminal calculates a satellite-ground alignment angle according to the self position information and the low-orbit satellite position information;
the ground terminal directs the ground terminal narrow beam antenna to aim at the low orbit satellite according to the satellite-ground aiming angle;
the ground terminal receives the communication broadcast signals through the ground terminal narrow beam antenna; and analyzing the communication broadcast signals to obtain system information required by the ground terminal to initiate random access, and completing the star searching process.
2. A method for a ground terminal to quickly search for low-orbit satellites according to claim 1 wherein the location broadcast signal is a narrowband signal with a higher power spectral density carrying the low-orbit satellite location information.
3. A method for a ground terminal to quickly search for low-orbit satellites according to claim 1 wherein the communication broadcast signal is a wideband signal with a lower power spectral density that contains system information required for the ground terminal to initiate random access and does not contain the low-orbit satellite position information.
4. The method for a ground terminal to quickly search for low-orbit satellites according to claim 1 wherein modulating the low-orbit satellite position information to generate a position broadcast signal comprises:
adding cyclic redundancy check to the low-orbit satellite position information to obtain a checked information sequence;
performing channel coding on the checked sequence to obtain a coded information sequence;
scrambling the coded sequence to obtain a scrambled information sequence;
adding a single-tone pilot frequency information sequence and a synchronous information sequence to the scrambled sequence to obtain a framed information sequence;
modulating the framing sequence to obtain a modulated signal sequence;
and performing shaping filtering on the modulated sequence to obtain the position broadcast signal.
5. The method for quickly searching for a low-orbit satellite by a ground terminal according to claim 4, wherein the cyclic redundancy check is added to the position information of the low-orbit satellite, and the obtained checked sequence is realized by the following steps:
converting the low-orbit satellite position information into an information sequence a 0 ,a 1 ,a 2 ,a 3 ,…,a A-1 Inputting and calculating to obtain a check bit p 0 ,p 1 ,p 2 ,p 3 ,…,p L-1 Wherein A is the input sequence length, L is the check bit length, and the output sequence with added cyclic redundancy check is denoted b 0 ,b 1 ,b 2 ,b 3 ,…,b B-1 Wherein b=a+l, satisfies the relationship,
b k ＝a k ,k＝0,1,2,…,A-1
b k ＝p k-A ,k＝A,A+1,A+2,…,A+L-1
the addition of the check bits is required to satisfy the following polynomial integer division by the generator polynomial over GF (2) domain,
a 0 D A+L-1 +a 1 D A+L-2 +…+a A-1 D L +p 0 D L-1 +p 1 D L-2 +…+p L-2 D 1 +p L-1 D 0 ；
wherein GF (2) domain is a gamma Luo Huayou finite domain containing only two elements of 0 and 1, D is a delay operator, a > L.
6. The method for quickly searching for low-orbit satellites on ground according to claim 4 wherein a single-tone pilot sequence and a synchronization sequence are added to the scrambled sequence to obtain a framed sequence, wherein the single-tone pilot sequence, the synchronization sequence and the scrambled sequence are arranged in sequence in time, the single-tone pilot sequence provides frequency information for a receiving end, the synchronization sequence provides timing information for the receiving end, and the scrambled sequence carries low-orbit satellite position information.
7. The method for a ground terminal to quickly search for low-orbit satellites according to claim 1 wherein demodulating the resolved position broadcast signal comprises:
performing matched filtering on the position broadcast signals to obtain a complex baseband signal sequence after filtering;
capturing the single-tone pilot frequency complex baseband sequence of the filtered complex baseband signal sequence to finish frequency offset estimation and compensation, and obtaining a complex baseband sequence after frequency offset compensation;
synchronous complex baseband sequence detection is carried out on the complex baseband sequence after frequency offset compensation, timing synchronization is completed, and a complex baseband sequence after synchronization is obtained;
demodulating the synchronous complex baseband sequence to obtain a demodulated information sequence;
descrambling the demodulated information sequence to obtain a descrambled information sequence;
channel decoding is carried out on the descrambled information sequence to obtain a decoded information sequence;
performing cyclic redundancy check on the decoded information sequence to obtain a checked information sequence;
and carrying out sequence analysis on the checked information sequence to obtain the low-orbit satellite position information.
8. The method for a ground terminal to quickly search for low-orbit satellites according to claim 7 wherein the single-tone pilot complex baseband sequence acquisition is accomplished by:
for the received complex baseband signal r i Capturing the complex baseband sequence of the single-tone pilot frequency by taking N as a signal sampling interval and taking the length 2N as a signal processing length, and processing r for the first time 0 ,r 1 ,r 2 ,…,r 2N-1 Second treatment r N ,r N-1 ,r N-2 ,…,r 3N-1 By analogy in turn,
a fourier transform acquisition function is performed each time for a 2N point signal complex baseband sample value,
wherein the method comprises the steps ofIn imaginary units, e is a natural constant, m is the number of times the current acquisition process is performed (m takes on values from 0, m=0, 1, 2, 3, 4, …), n is the number of input complex baseband signals, R k For the fourier transformed output frequency domain signal, k is the number of the output frequency domain signal,
the signal processing is continued until R is obtained k And if the maximum amplitude exceeds the threshold value, completing the capture of the single-tone pilot complex baseband sequence.
9. The method of claim 8, wherein the capturing of the synchronous complex baseband sequence is started after the signal length of the subsequent signal offset length is N, that is, the complex baseband signal and the local synchronous complex baseband sequence are further subjected to point-by-point sliding conjugate multiplication accumulation within the range of 2N, when the accumulated value amplitude is maximum, the corresponding conjugate multiplication accumulation starting position is the accurate time domain position of the synchronous complex baseband sequence, wherein the maximum value of the conjugate multiplication accumulation amplitude is obtained by the following functions,
m is the length of the synchronous complex baseband sequence, l n Synchronous complex baseband sequence locally generated for ground terminal, i is pair l n Taking the conjugate complex number i as the initial position for conjugate multiplication accumulation operation.
10. A ground terminal satellite searching system for low-orbit satellite communication is characterized by comprising a low-orbit satellite and a ground terminal, wherein,
the low-orbit satellite generates two types of signals, namely a position broadcast signal generated by acquiring the position information of the low-orbit satellite in real time and a communication broadcast signal, and the two signals are transmitted in a time-sharing way through the same narrow-wave-speed antenna;
the ground terminal is provided with two types of antennas, namely a wide beam antenna and a narrow beam antenna, the position broadcast signals are received through the wide beam antenna, the position information of the low-orbit satellite is obtained through analysis, the satellite-ground angle is obtained through calculation, the narrow beam antenna is controlled to be aligned with the low-orbit satellite, the communication broadcast signals are received through the narrow beam antenna, the system information required by the ground terminal to initiate random access is obtained through analysis, and the satellite searching is completed.
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