CN111970045A - Space-based Internet of things signal processing solution with variable message rate - Google Patents
Space-based Internet of things signal processing solution with variable message rate Download PDFInfo
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Abstract
The invention provides a space-based Internet of things signal processing solution with variable message rate, which is characterized by comprising the following steps: step 1, an antenna receives a signal transmitted by a satellite terminal of a space-based Internet of things system, a ground terminal down-converts a radio frequency signal into an intermediate frequency signal, and step 2, the intermediate frequency signal in the step 1 is sampled to obtain a signal s (n); step 3, capturing the sampled signal s (n) to obtain the code phase, code Doppler and carrier Doppler of the m1 guide section; step 4, tracking the m1 guide segment, deframing and finding out the ending mark telegraph text of the m1 guide segment; step 5, continuing to track and analyze the m2 boot segment, finding out an end mark telegraph text of the m2 boot segment, and immediately switching the local pseudo code into a GOLD sequence segment after the m2 boot segment is ended; and 6, continuously tracking and analyzing the GOLD sequence segment, and solving the required data packet text and the like. The invention can greatly reduce the capture time by the capture method of the hierarchical parallel search, further can greatly reduce the duration of the m1 guide segment, thereby increasing the access number of the terminals.
Description
Technical Field
The invention belongs to the field of communication, and particularly relates to a space-based Internet of things signal processing solution with a variable message rate.
Background
In recent years, the technology of internet of things has been rapidly developed, and the technology has been widely applied in the fields of smart home, industrial automation and the like, and is regarded as the third wave of development of the world information industry after computers and the internet. With the development of mobile communication technology, global telecom operators have constructed mobile cellular networks covering the world. However, if the mobile cellular communication technology is directly applied to the internet of things, the problems of large power consumption, high cost and the like of equipment exist. In order to adapt to the development trend of internet of everything, a Low Power Wide Area Network (LPWAN), which is a Low Power Wide Area Network (LPWAN) connection technology with Low Power consumption, long distance, Low cost and large capacity, is produced.
Currently, representative LPWAN technologies mainly include a private network access technology represented by LoRa operating in an unlicensed spectrum and a public network access technology represented by NB-IoT operating in a licensed spectrum. The 2 technologies of LoRa and NBIoT realize low power consumption (the working time of a terminal battery is about 10 years), strong coverage (the communication distance is long, the communication range is 10-20 km) and large connection (the number of nodes reaches ten thousand or even million). However, both NB-IoT technology and LoRa technology require base stations to be constructed on the ground.
Due to the limitation of geographical conditions and construction cost, the base station of the internet of things cannot be constructed in certain areas (such as oceans, deserts and mountains). The space-based Internet of things system has wide coverage range, is not influenced by geographic factors, and can economically realize broadcast and multiple access communication. Particularly, the low-orbit satellite internet of things has the characteristics of small transmission loss, short propagation delay, realization of global seamless coverage by a constellation consisting of a plurality of satellites and miniaturization of ground terminal design, so that the low-orbit satellite internet of things becomes one of the best choices for assisting a ground network in realizing the interconnection of everything.
However, the space-based internet of things technology which can be applied in a large scale is not mature at present, and in a burst access communication mode, the ground terminal access time is too long, so that the number of terminals accessed in unit time is too low.
Disclosure of the invention
The invention aims to solve the problems of long satellite access time and small access number in unit time of a terminal in an antenna-based Internet of things system, provides an antenna-based Internet of things signal system based on code division multiple access, space division multiple access, frequency division multiple access and time division multiple access, has the characteristic of variable message rate, and provides a signal processing solution for the signal system.
The technical scheme of the invention provides a space-based Internet of things signal processing solution with variable message rate, which is characterized by comprising the following steps:
step 1, an antenna receives a signal transmitted by a satellite terminal of a space-based Internet of things system, and a ground terminal down-converts a radio frequency signal into an intermediate frequency signal;
step 2, sampling the intermediate frequency signal in the step 1 to obtain a signal s (n);
step 3, capturing the sampled signal s (n) to obtain the code phase, code Doppler and carrier Doppler of the m1 guide section;
step 4, tracking the m1 boot segment, deframing and finding out the end mark telegraph text of the m1 boot segment, and immediately switching the local pseudo code into the pseudo code corresponding to the m2 boot segment after the m1 boot segment is ended;
step 5, continuing to track and analyze the m2 boot segment, finding out an end mark telegraph text of the m2 boot segment, and immediately switching the local pseudo code into a GOLD sequence segment after the m2 boot segment is ended;
step 6, continuing to track and analyze the GOLD sequence segment, and solving a required data packet telegraph text;
step 7, setting an end mark message at the position where each segment does not end, finding a bit edge after finding the end mark message, and switching to the corresponding pseudo code rate and phase of the next segment;
when finding the GOLD sequence segment end mark telegraph text, quitting the tracking of the current frame, namely judging that the current frame is unlocked, and returning to the step 3 again;
if no ending mark message is found all the time after a certain time, the lock is judged to be lost, and the step 3 is returned again.
Further, step 3 comprises:
step 3.1, acquiring a section of intermediate frequency data, and performing down sampling again by using 2 times of the pseudo code rate; the length of the intermediate frequency data of each section is equal, and at least one message bit duration is provided;
step 3.2, entering a first-stage search, wherein the carrier frequency and the pseudo code frequency in the first-stage search are stepped greatly, so that one carrier Doppler and pseudo code Doppler value and one pseudo code phase are obtained through quick search;
3.3, in order to reduce the time of each stage of search, the intermediate frequency data of the section is cached from the second section of intermediate frequency data, and meanwhile, the previous section of intermediate frequency data is processed; the M carrier stepping values are searched simultaneously and parallelly, and after N sections of intermediate frequency data pass, N × M stepping values can be searched totally, so that all stepping values are searched quickly;
and 3.4, further reducing the search step according to the carrier Doppler, the pseudo code Doppler and the pseudo code phase obtained by the first-stage search, and entering a second-stage search.
Step 3.5, opening a third level and more searches as required;
and 3.6, capturing and outputting the finally obtained carrier Doppler value, pseudo code Doppler value and pseudo code phase for initializing the tracking channel.
Further, step 6 is implemented by:
the actual signal received is modeled as follows:
s(t)＝acos(wit+φi)c(t)d(t) (1)
in the above formula, a is signal amplitude, cos (.) is carrier, c (t) is pseudo code, d (t) is text;
initializing tracking related parameters according to the acquired carrier Doppler value, pseudo code Doppler value and pseudo code phase;
demodulating received signalsObtaining coherent integral value I after modulation and de-spreadingP(n)、QP(n)；
IP(n)＝aD(n)R(τP)sinc(feTcoh)cosφe (2)
QP(n)＝aD(n)R(τP)sinc(feTcoh)sinφe (3)
In the above formula, R (τ)P) For the value of the autocorrelation function, τpAs pseudo code phase error, feIs the carrier frequency difference, phieFor carrier phase difference, TcohIs the coherent integration time length;
wherein, IPThe sign of (n) is determined by the text bits D (n) and can therefore be according to IPAnd (n) is positive and negative to obtain the message.
The invention has the beneficial effects that:
(1) the acquisition method of the hierarchical parallel search can greatly reduce the acquisition time, further greatly shorten the duration of the m1 boot segment, and further increase the number of terminal accesses.
(2) The symbol rate of the m2 guide segment is improved, and the time length of the guide segment can be further reduced on the premise of ensuring carrying necessary information.
(3) By reasonably designing a signal system, the problems of long satellite access time and small access quantity in unit time of a terminal in a space-based Internet of things system are solved, and a corresponding signal processing solution is provided.
Drawings
FIG. 1 is a block diagram of a space-based Internet of things system;
FIG. 2 is a signal scheme between a terminal unit and a satellite unit;
fig. 3 is a signal processing flow diagram.
Detailed Description
The technical scheme of the invention will be described in detail with reference to the accompanying drawings 1-3.
As shown in fig. 1, the space-based internet of things is composed of a satellite terminal and a ground terminal, and a communication system of the satellite and the terminal is code division multiple access + frequency division multiple access + space division multiple access + time division multiple access. The signal system between the terminal single machine and the satellite single machine is a direct spread spectrum signal.
In order to increase the number of terminals accessed per unit time as much as possible, the signals between the terminal unit and the satellite unit are as follows as shown in fig. 2.
The signal between the terminal and the satellite is composed of an m1 guide segment, an m2 guide segment and a GOLD sequence segment.
The m1 leading segment, the m2 leading segment and the GOLD sequence segment are all BPSK + spread spectrum modulation.
The message rate of the m1 guide segment is 200bps, the spreading code rate is 51kcps, the shorter the time of the m1 guide segment is, the better the aim is to enable the satellite terminal to capture the terminal signal as soon as possible;
the m2 guide segment carries necessary message information for initializing GOLD sequence, the message rate is set to 800bps, the spreading code rate is set to 50.4kcps, compared with the m1 guide segment, the m2 guide segment has higher symbol rate, thereby further reducing the synchronization time of the terminal accessing the satellite, and at this time, the switching of spreading codes, the switching of spreading code rate and the switching of message rate exist from the m1 guide segment to the m2 guide segment;
the GOLD sequence segment carries data packets, the telegraph rate is set to be three grades of 200bps, 800bps and 3200bps, the spreading code rate is set to be 51kcps, 50.4kcps and 48kcps, and similarly, when the GOLD sequence segment is guided by m2, spreading code switching, spreading code rate switching and telegraph rate switching exist.
The present invention is directed to the signal system, and as shown in fig. 3, the embodiment provides a solution for processing space-based internet of things signals with variable telegraph text rate, which mainly includes the following steps:
step 1, an antenna receives a signal transmitted by a satellite terminal of a space-based Internet of things system, and a ground terminal down-converts a radio frequency signal into an intermediate frequency signal;
step 2, sampling the intermediate frequency signal in the step 1 to obtain a signal s (n);
step 3, capturing the sampled signal s (n) to obtain the code phase, code Doppler and carrier Doppler of the m1 guide section;
step 3.1, acquiring a section of intermediate frequency data, and performing down sampling again by using 2 times of the pseudo code rate; number of intermediate frequencies per stage
The length is equal, and at least one message bit duration is provided;
and 3.2, entering a first-stage search, wherein the carrier frequency and the pseudo code frequency are greatly stepped in the first-stage search, so that a rough carrier Doppler and pseudo code Doppler value and a pseudo code phase are quickly searched and obtained.
3.3, in order to reduce the time of each stage of search, the intermediate frequency data of the section is cached from the second section of intermediate frequency data, and meanwhile, the previous section of intermediate frequency data is processed; the M carrier stepping values can be searched simultaneously and parallelly, and after N sections of intermediate frequency data pass, N × M stepping values can be searched totally, so that all stepping values are searched quickly;
and 3.4, further reducing the search step according to the carrier Doppler, the pseudo code Doppler and the pseudo code phase obtained by the first-stage search, and entering a second-stage search.
Step 3.5, opening a third level and more searches as required;
the acquisition method of the hierarchical parallel search can greatly reduce the acquisition time, further greatly shorten the duration of the m1 boot segment, and further increase the number of terminal accesses.
And 3.6, capturing and outputting the finally obtained carrier Doppler value, pseudo code Doppler value and pseudo code phase for initializing the tracking channel.
Step 4, tracking the m1 boot segment, deframing and finding out the end mark telegraph text of the m1 boot segment, and immediately switching the local pseudo code into the pseudo code corresponding to the m2 boot segment after the m1 boot segment is ended;
step 5, continuing to track and analyze the m2 boot segment, finding out an end mark telegraph text of the m2 boot segment, and immediately switching the local pseudo code into a GOLD sequence segment after the m2 boot segment is ended;
step 6, continuously tracking and analyzing the GOLD sequence segment, and solving a required data packet telegraph text;
step 6 in the signal processing flow is further described below:
the actual signal received is modeled as follows:
s(t)＝acos(wit+φi)c(t)d(t) (1)
in the above formula, a is the signal amplitude, cos (.) is the carrier, c (t) is the pseudo code, d (t) is the text.
And initializing tracking related parameters according to the acquired carrier Doppler value, pseudo code Doppler value and pseudo code phase. Demodulating and de-spreading the received signal to obtain coherent integral value IP(n)、QP(n)；
IP(n)＝aD(n)R(τP)sinc(feTcoh)cosφe (2)
QP(n)＝aD(n)R(τP)sinc(feTcoh)sinφe (3)
In the above formula, R (τ)P) For the value of the autocorrelation function, τpAs pseudo code phase error, feIs the carrier frequency difference, phieFor carrier phase difference, TcohIs the coherent integration duration.
When the formula (2) is observed, IPThe sign of (n) is determined by the text bits D (n). Thus can be according to IPThe positive and negative of (n) are used to obtain the text, which is coherent demodulation.
Step 7, setting an end mark message at the position where each segment does not end, finding a bit edge after finding the end mark message, and switching to the corresponding pseudo code rate and phase of the next segment;
when finding the GOLD sequence segment end mark telegraph text, quitting the tracking of the current frame, namely judging that the current frame is unlocked, and returning to the step 3 again;
if no ending mark message is found all the time after a certain time, the lock is judged to be lost, and the step 3 is returned again.
While the principles of the invention have been described in detail in connection with the preferred embodiments thereof, it will be understood by those skilled in the art that the foregoing embodiments are merely illustrative of exemplary implementations of the invention and are not limiting of the scope of the invention. The details of the embodiments are not to be interpreted as limiting the scope of the invention, and any obvious changes, such as equivalent alterations, simple substitutions and the like, based on the technical solution of the invention, can be made without departing from the spirit and scope of the invention.
Claims (3)
1. A space-based Internet of things signal processing solution with variable message rate is characterized in that: the method comprises the following steps:
step 1, an antenna receives a signal transmitted by a satellite terminal of a space-based Internet of things system, and a ground terminal down-converts a radio frequency signal into an intermediate frequency signal;
step 2, sampling the intermediate frequency signal in the step 1 to obtain a signal s (n);
step 3, capturing the sampled signal s (n) to obtain the code phase, code Doppler and carrier Doppler of the m1 guide section;
step 4, tracking the m1 boot segment, deframing and finding out the end mark telegraph text of the m1 boot segment, and immediately switching the local pseudo code into the pseudo code corresponding to the m2 boot segment after the m1 boot segment is ended;
step 5, continuing to track and analyze the m2 boot segment, finding out an end mark telegraph text of the m2 boot segment, and immediately switching the local pseudo code into a GOLD sequence segment after the m2 boot segment is ended;
step 6, continuing to track and analyze the GOLD sequence segment, and solving a required data packet telegraph text;
step 7, setting an end mark message at the position where each segment does not end, finding a bit edge after finding the end mark message, and switching to the corresponding pseudo code rate and phase of the next segment;
when finding the GOLD sequence segment end mark telegraph text, quitting the tracking of the current frame, namely judging that the current frame is unlocked, and returning to the step 3 again;
if no ending mark message is found all the time after a certain time, the lock is judged to be lost, and the step 3 is returned again.
2. The space-based internet of things signal processing solution with variable telegraph text rate according to claim 1, characterized in that: the step 3 comprises the following steps:
step 3.1, acquiring a section of intermediate frequency data, and performing down sampling again by using 2 times of the pseudo code rate; the length of the intermediate frequency data of each section is equal, and at least one message bit duration is provided;
step 3.2, entering a first-stage search, wherein the carrier frequency and the pseudo code frequency in the first-stage search are stepped greatly, so that one carrier Doppler and pseudo code Doppler value and one pseudo code phase are obtained through quick search;
3.3, in order to reduce the time of each stage of search, the intermediate frequency data of the section is cached from the second section of intermediate frequency data, and meanwhile, the previous section of intermediate frequency data is processed; the M carrier stepping values are searched simultaneously and parallelly, and after N sections of intermediate frequency data pass, N × M stepping values can be searched totally, so that all stepping values are searched quickly;
step 3.4, according to the carrier Doppler, the pseudo code Doppler and the pseudo code phase obtained by the first-stage search, further reducing the search step and entering a second-stage search;
step 3.5, opening a third level and more searches as required;
and 3.6, capturing and outputting the finally obtained carrier Doppler value, pseudo code Doppler value and pseudo code phase for initializing the tracking channel.
3. The space-based internet of things signal processing solution with variable telegraph text rate according to claim 1, characterized in that: step 6 is realized by the following steps:
the actual signal received is modeled as follows:
s(t)＝acos(wit+φi)c(t)d(t) (1)
in the above formula, a is signal amplitude, cos (.) is carrier, c (t) is pseudo code, d (t) is text;
initializing tracking related parameters according to the acquired carrier Doppler value, pseudo code Doppler value and pseudo code phase;
demodulating and de-spreading the received signal to obtain coherent integral value IP(n)、QP(n)；
IP(n)＝aD(n)R(τP)sinc(feTcoh)cosφe (2)
QP(n)＝aD(n)R(τP)sinc(feTcoh)sinφe (3)
In the above formula, R (τ)P) For the value of the autocorrelation function, τpAs pseudo code phase error, feIs the carrier frequency difference, phieFor carrier phase difference, TcohIs the coherent integration time length;
wherein, IPThe sign of (n) is determined by the text bits D (n) and can therefore be according to IPAnd (n) is positive and negative to obtain the message.
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