CN110208822B - Communication method based on low-orbit mobile communication satellite - Google Patents

Communication method based on low-orbit mobile communication satellite Download PDF

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CN110208822B
CN110208822B CN201910452270.9A CN201910452270A CN110208822B CN 110208822 B CN110208822 B CN 110208822B CN 201910452270 A CN201910452270 A CN 201910452270A CN 110208822 B CN110208822 B CN 110208822B
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spt
pch
time
communication satellite
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CN110208822A (en
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蒙艳松
严涛
周昀
王瑛
雷文英
王国永
边朗
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Xian Institute of Space Radio Technology
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S19/00—Satellite radio beacon positioning systems; Determining position, velocity or attitude using signals transmitted by such systems
    • G01S19/01—Satellite radio beacon positioning systems transmitting time-stamped messages, e.g. GPS [Global Positioning System], GLONASS [Global Orbiting Navigation Satellite System] or GALILEO
    • G01S19/03—Cooperating elements; Interaction or communication between different cooperating elements or between cooperating elements and receivers
    • G01S19/05—Cooperating elements; Interaction or communication between different cooperating elements or between cooperating elements and receivers providing aiding data
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S19/00—Satellite radio beacon positioning systems; Determining position, velocity or attitude using signals transmitted by such systems
    • G01S19/01—Satellite radio beacon positioning systems transmitting time-stamped messages, e.g. GPS [Global Positioning System], GLONASS [Global Orbiting Navigation Satellite System] or GALILEO
    • G01S19/03—Cooperating elements; Interaction or communication between different cooperating elements or between cooperating elements and receivers
    • G01S19/10—Cooperating elements; Interaction or communication between different cooperating elements or between cooperating elements and receivers providing dedicated supplementary positioning signals
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S19/00—Satellite radio beacon positioning systems; Determining position, velocity or attitude using signals transmitted by such systems
    • G01S19/01—Satellite radio beacon positioning systems transmitting time-stamped messages, e.g. GPS [Global Positioning System], GLONASS [Global Orbiting Navigation Satellite System] or GALILEO
    • G01S19/13—Receivers
    • G01S19/24—Acquisition or tracking or demodulation of signals transmitted by the system
    • G01S19/25—Acquisition or tracking or demodulation of signals transmitted by the system involving aiding data received from a cooperating element, e.g. assisted GPS
    • G01S19/256—Acquisition or tracking or demodulation of signals transmitted by the system involving aiding data received from a cooperating element, e.g. assisted GPS relating to timing, e.g. time of week, code phase, timing offset
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S19/00—Satellite radio beacon positioning systems; Determining position, velocity or attitude using signals transmitted by such systems
    • G01S19/01—Satellite radio beacon positioning systems transmitting time-stamped messages, e.g. GPS [Global Positioning System], GLONASS [Global Orbiting Navigation Satellite System] or GALILEO
    • G01S19/13—Receivers
    • G01S19/24—Acquisition or tracking or demodulation of signals transmitted by the system
    • G01S19/29—Acquisition or tracking or demodulation of signals transmitted by the system carrier including Doppler, related
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S19/00—Satellite radio beacon positioning systems; Determining position, velocity or attitude using signals transmitted by such systems
    • G01S19/01—Satellite radio beacon positioning systems transmitting time-stamped messages, e.g. GPS [Global Positioning System], GLONASS [Global Orbiting Navigation Satellite System] or GALILEO
    • G01S19/13—Receivers
    • G01S19/24—Acquisition or tracking or demodulation of signals transmitted by the system
    • G01S19/30—Acquisition or tracking or demodulation of signals transmitted by the system code related

Abstract

A communication method based on a low-orbit mobile communication satellite generates a low-orbit mobile communication satellite signal for safe positioning time service and carries out communication; the signal has the following characteristics: time domain structure: the communication satellite signal adopts a time division multiplexing system in a time domain; and (3) frequency domain structure: the communication satellite signal adopts a frequency division multiplexing system in a frequency domain; the communication satellite signal is a multi-beam multi-color multiplexing system, each beam uses one or more sub-frequency bands according to requirements, and simultaneously multi-color multiplexing of adjacent beams is met so as to reduce interference among the beams; the communication satellite signal has at least one sub-band for broadcasting paging channel signal, i.e. PCH signal; the sub-band of the communication satellite signal is removed from the PCH signal, the rest SPT signal which can be used for safe positioning time service of broadband spread spectrum is left, and the SPT signal is in the N of the PCH signalPCHBroadcast in one time slot. The invention designs a communication navigation fusion SPT signal system, and realizes positioning time service and improvement of anti-interference capability.

Description

Communication method based on low-orbit mobile communication satellite
Technical Field
The invention belongs to the field of satellite navigation, and mainly relates to a low-orbit mobile communication satellite signal communication method based on anti-interference safe positioning time service.
Background
With the development of Global Navigation Satellite System (GNSS), the basic structure of four large GNSS has been formed, and the application based on GNSS gradually permeates the aspects of national economic life and becomes an indispensable national infrastructure. Meanwhile, the inherent vulnerability of the GNSS signal, such as low signal landing power, easy interference, deception and the like, attracts people's extensive attention.
At present, low orbit satellite constellations are developing vigorously at home and abroad. The low-orbit satellite has the natural advantage of low orbit, the limitation of the signal landing power is higher than that of a GNSS signal, and the 'vulnerability' of a satellite navigation signal can be compensated. Broadcasting the communication and guidance fusion signal by using the low-orbit mobile communication satellite is an effective means, the communication signal has the advantages of high power and deception resistance, the ranging and Timing capability of the navigation signal is fused, the secure Positioning Timing and Timing (SPT) can be provided, the GNSS can be assisted to promote the indoor availability, the GNSS capability can be assisted to promote, and the GNSS can also be used as a low-precision backup system when the GNSS is unavailable.
The first plan is a high integrity GPS project (or called iGPS project) based on a low-orbit mobile communication satellite to provide positioning time signals, and the iGPS plan utilizes a Next generation Iridium (Iridium Next) low earth orbit communication satellite system to broadcast GPS signals and GPS auxiliary enhancement information, so that the first positioning time is accelerated, military code signals are directly acquired, and the positioning accuracy and the anti-interference capability are improved. The iGPS carries out adaptive transformation on the original iridium satellite signal, and utilizes an idle communication channel resource to broadcast a navigation ranging signal (patent number: US 7579987B2), but an uplink signal and a downlink signal adopt a same-frequency time division structure, the navigation signal is discontinuously broadcast, and when the communication service is busy, the positioning and time service function can be interrupted.
The final iGPS project is not implemented on the next generation of iridium stars, but instead a Satellite positioning Time and Location (STL) signal is broadcast. STL is a 25kHz symbol rate, which is redesigned for the paging channel of Iridium signals, and QPSK is used. The paging channel frequency may be 1626.104MHz, which is an improvement over the unidirectional time slot of 20.32 ms. The proprietary STL burst includes a CW, a PRN code sequence, and modulated data. The STL burst is broadcast once every 1.4s on average, and is broadcast in a time-division polling mode in a plurality of beams of the Iridium satellite.
The STL signal system design is limited by the original iridium communication system, and in order to reduce the influence on the signal system, only small improvements are made on the basis of the original iridium communication signal system. Thus, the STL signal is a high power signal with a pulse regime, low duty cycle, narrow band (25 kcps). The STL signal grounding power is 30dB higher than that of the GPS signal, the STL signal grounding power can be used indoors, and compared with a GNSS signal, the signal usability is improved. However, since STL is a narrowband spread pulse signal and GNSS is a wideband spread signal, the enhancement of interference rejection capability of the STL signal itself is limited.
The domestic research on the aspect of the communication and navigation fusion system based on the low-orbit mobile communication satellite is still in the initial stage, but the communication and navigation fusion signal system has some achievements. The patent "a method for realizing global navigation positioning by using iHCO communication satellite" (patent number: CN 201310325604.9) realizes the positioning function by using iHCO communication satellite to forward the navigation signal uploaded on the ground. The patent 'navigation signal communication method based on digital watermarking and compressed sensing' (patent number: CN 201410119558.1) obtains a small amount of data by compressed measurement of a watermark image hidden with a navigation signal through a compressed sensing technology, and the small amount of data replaces the watermark image to be transmitted, thereby realizing the safe communication of the navigation signal. The patent "integrated method and system of satellite navigation communication" (patent number: CN 201410514108.2) provides an integrated method of satellite navigation communication, which performs multi-carrier modulation on navigation signals and communication signals, obtains modulated signals and then sends the modulated signals. In the patent "broadcast positioning signal generation method, positioning method and apparatus" (patent No. CN 201010517356.4), the ranging spreading code is hidden in the OFDM modulated communication signal to realize the positioning function.
It can be seen that the above patent usually adds a navigation signal similar to GNSS signal to the communication signal, and is not designed for the characteristics of the communication signal. The iGPS patent broadcasts a narrow-band PRN by using an idle communication service channel, and the positioning and time service functions are not guaranteed; the STL signal is an improvement on the original unidirectional time slot of the iridium satellite, is a narrowband pulse spread spectrum signal and has limited self anti-interference capability.
Disclosure of Invention
The invention aims to: the method overcomes the defects of the prior art, provides a low-orbit mobile communication satellite signal communication method based on anti-interference safe positioning time service for a low-orbit mobile communication satellite, designs a communication navigation fusion SPT signal system, and realizes positioning time service and interference resistance improvement.
The technical solution of the invention is as follows:
a communication method based on a low-orbit mobile communication satellite generates a low-orbit mobile communication satellite signal for safe positioning time service, and uses the low-orbit mobile communication satellite signal for safe positioning time service to carry out communication; the communication satellite signal has the following characteristics:
time domain structure: the communication satellite signal adopts a time division multiplexing system in a time domain, and carries out communication service by using a basic frame and a time slot; signal with TFIs a basic frame length, each basic frame is divided into NslotA time slot, each time slot having a length of Tslot＝TF/Nslot；
And (3) frequency domain structure: the communication satellite signal adopts a frequency division multiplexing system in a frequency domain, and the whole downlink frequency band occupies a bandwidth BW which is divided into NsubbandBW (blast furnace dust)subband＝BW/NsubbandEach sub-band is divided into a plurality of carrier intervals according to the requirement;
the communication satellite signal is a multi-beam multi-color multiplexing system, each beam uses one or more sub-frequency bands according to requirements, and simultaneously multi-color multiplexing of adjacent beams is met so as to reduce interference among the beams;
the communication satellite signal has at least one sub-band for broadcasting paging channel signal, i.e. PCH signal; the PCH signal is a unidirectional downlink signal, is used for downlink synchronization, called paging and broadcast information, and is fixed on a sub-band for broadcasting; the PCH signal uses N of a basic framePCHOne time slot, frame length of PCH signal is TPCH＝NPCH·Tslot；
The sub-band of the communication satellite signal is removed from the PCH signal, the rest SPT signal which can be used for safe positioning time service of broadband spread spectrum is left, and the SPT signal is in the N of the PCH signalPCHBroadcast in one time slot.
PCH signals between different beams under the same communication satellite are broadcast in a time division polling mode so as to avoid same frequency interference between the beams. The SPT signals are also time division polling broadcast between beams to avoid co-channel interference between beams.
The SPT signal is obtained by the following method:
(1) designing an SPT signal frame structure: n on broadcasting PCH signalPCHIn each time slot, other control information and service information are not broadcast, the frame length of the SPT signal is limited by the frame length of the PCH signal, and the functions of distance measurement, positioning and time service are realized by introducing a broadband spread spectrum pseudo-random code (PRN);
(2) SPT signal broadband spread spectrum generation: generating a spread spectrum code according to a designed SPT signal frame structure, and carrying out broadband spread spectrum modulation and SPT signal framing;
(3) designing a beam polling pattern: the SPT signal is subjected to time division polling and broadcast in a plurality of wave beams, and the polling mode is determined by a wave beam polling pattern;
(4) beam selection and SPT signaling: the generated SPT signal frames are broadcast on the corresponding beams by digital beamforming.
The SPT signal frame structure specifically includes:
(1.1) the PCH signal uses the lowest frequency or the highest frequency sub-band, i.e. the PCH signal is located on the edge of the whole BW bandwidth, the SPT signal uses the remaining BW-BWsubbandA frequency band; each basic frame length TFPCH signal occupies TPCHUsing N per basic framePCHSpread out in one time slot, the SPT signal is also in this NPCHBroadcasting in a time slot;
(1.2) SPT Signal frame Length is TSPT，TSPT≤TPCHThe system consists of a continuous wave CW part and a broadband spread spectrum PRN part, wherein the continuous wave CW is used for signal capture, and the broadband spread spectrum PRN code part is used for measurement and message broadcasting of SPT signals;
(1.3) the length of the continuous wave CW is TCW，0≤TCW≤1/2TSPTWhen T isCWWhen 0, the SPT signal does not contain CW;
(1.4) wideband spreading PRN code partial duration TPRN＝TSPT-TCW。
The SPT signal broadband spread spectrum is generated and obtained by the following method:
(2.1) generating a spread PRN code for the SPT signal, including a pilot PRN code and a data PRN code;
PRN code rate of RcChip width of Tc＝1/RcThe bandwidth of the PRN code signal is not greater than BW-BWsubbandI.e. 2Rc≤BW-BWsubbandPilot PRN code sequence { cp,iLength is NpChip, data PRN code sequence { c) after SPT signal message modulationd,iLength is NdOne chip.
(2.2) generating all 1 or all-1 sequences of the CW baseband signals;
the length of CW is equal to NCWOne chip wide, baseband equivalent to a sequence of all 1's or all-1's cCW,iCan choose cCW,i＝1，i＝0，…，NCW-1；
(2.3) the CW, pilot PRN code, and data PRN code of the SPT signal are time-divided by (N)CW+Np+Nd)Tc＝TSPTBase band representation s of SPT signalSPT(t) is:
Figure BDA0002075511180000051
wherein p (T) is a width TcP (t) is defined as:
Figure BDA0002075511180000052
(2.4) Baseband representation s of SPT SignalSPT(t) filtering through a symmetrical FIR low-pass filter, sSPT(t) low pass filtering is denoted as
Figure BDA0002075511180000053
The SPT signal broadband spread spectrum is generated and obtained by the following method:
(2.1) generating a spread PRN code for the SPT signal, including a pilot PRN code and a data PRN code;
PRN code rate of RcChip width of Tc＝1/Rc(ii) a The bandwidth of the PRN code signal is not greater than BW-BWsubbandI.e. 2Rc≤BW-BWsubband(ii) a Pilot PRN code sequence { cp,iLength is Np,dChip, data PRN code sequence { c) after modulating SPT messaged,iLength is Np,dA chip number;
(2.2) generating all 1 or all-1 sequences of the CW baseband signals;
the length of CW is equal to NCWOne chip wide, baseband equivalent to a sequence of all 1's or all-1's cCW,i}，cCW,i＝1，i＝0，…，NCW-1；
(2.3) the pilot PRN code and data PRN code of the SPT signal are located on orthogonal branches, time-divided with CW, by (N)CW+Np,d)Tc＝TSPTBase band representation s of SPT signalSPT(t) is:
sSPT(t)＝sSPT,I(t)+jsSPT,Q(t)
in the formula, sSPT,I(t) is the I branch signal, sSPT,Q(t) is the Q branch signal, respectively expressed as:
Figure BDA0002075511180000061
Figure BDA0002075511180000062
(2.4) branch I Signal sSPT,I(t) and Q branch signal sSPT,Q(t) filtering with the same FIR low-pass filter, respectively
Figure BDA0002075511180000063
And
Figure BDA0002075511180000064
after low pass filtering is recorded as
Figure BDA0002075511180000065
The designed beam polling pattern is obtained by the following method:
(3.1) Low-orbit Mobile communication satellite sharing NbeamA beam of NGroupGroups of N beams, N ═ Nbeam/NGroup(ii) a To shorten the polling interval of SPT signals, N is broadcast simultaneouslyGroupSPT signals, each SPT signal time-division polled in N beams;
(3.2) sequentially polling among the N wave beams by the SPT signal according to a preset mode, wherein the wave beam polling pattern is as follows: beam 1, beam 2, …, beam N, beam 1, beam 2, …, beam N, …;
(3.3) every Nt.T. from one beamFTime, broadcast a length of TSPTSPT signal frame of time domain duty cycle TSPT/(N·TF)。
The designed beam polling pattern is obtained by the following method:
(3.1) Low-orbit Mobile communication satellite sharing NbeamA beam of NGroupGroups of N beams, N ═ Nbeam/NGroup(ii) a To shorten the polling interval of SPT signals, N is broadcast simultaneouslyGroupSPT signals, each SPT signal time-division polled in N beams;
(3.2) randomly time-division polling the SPT signal among the N wave beams in a random mode; the beam polling pattern is controlled by a pseudo-random number generator which outputs a number N from 1 to N for each SPT signalbeam；
(3.3) from a beam perspective, the intervals at which the SPT signals appear are random and unequal, which is equivalent to introducing time-hopping characteristics.
The beam selection and the SPT signal broadcasting are obtained by the following method:
(4.1) selecting the beam on which the SPT signal is broadcast as a beam n according to the beam polling patternbeam；
(4.2) adjusting the digital beam forming DBF coefficient, modulating the SPT signal to the beam nbeam；
And (4.3) broadcasting through a multi-beam antenna after DAC, up-conversion and amplification.
The invention discloses an anti-interference navigation signal system based on a low-orbit mobile communication satellite, which realizes safe positioning time service, can be deeply fused with a low-orbit mobile communication signal, and has the following advantages compared with the prior art:
(1) the SPT signal provided by the invention is broadcasted in the time slot of the PCH signal according to the characteristics of a low-orbit mobile communication signal system, the power, the frequency and the time slot resource of a satellite can be fully utilized, and the communication service is not influenced.
(2) The SPT signal provided by the invention adopts a broadband spread spectrum system, and compared with a narrow-band spread spectrum system, the anti-interference capability is obviously improved.
(3) The SPT signal of the invention adopts broadband spread spectrum, has high code rate, and improves the ranging performance and the time service precision compared with a narrowband spread spectrum system.
(4) According to the invention, by designing the SPT signal time-division polling pattern, the combination of time hopping and broadband spread spectrum is realized, and the anti-interference performance of the signal is further improved.
Drawings
FIG. 1 illustrates an anti-interference SPT signaling scheme disclosed herein;
FIG. 2 is a time division structure of a low earth orbit mobile communication satellite signal
FIG. 3 is a frequency division structure of a low-earth-orbit mobile communication satellite signal
FIG. 4 is a schematic diagram of the relationship between the time domain and the frequency domain of the SPT signal and the PCH signal
FIG. 5 is a schematic diagram of the frame structure of SPT signal
FIG. 6 is a schematic diagram of an equally spaced time division polling pattern
FIG. 7 is a diagram of a random time-division polling pattern
Fig. 8 is a schematic diagram of SPT signal generation and dissemination.
Detailed Description
The invention is described in detail below with reference to the figures and specific embodiments.
The invention belongs to the field of satellite navigation, and particularly relates to a Secure Positioning Timing (SPT) signal modulation method and a generation method based on a low-orbit mobile communication satellite.
The low-orbit mobile communication satellite signal based on the invention adopts a time division/frequency division/space division mixed system, namely, a downlink service signal adopts a TDMA + FDMA + multi-beam system, and an uplink and a downlink are also frequency-divided.
In order to achieve the above purpose, the present invention discloses a communication method based on low-orbit mobile communication satellite signals with anti-interference safe positioning and time service performance, as shown in fig. 1.
Generating a low-orbit mobile communication satellite signal for safe positioning time service, and communicating by using the low-orbit mobile communication satellite signal for safe positioning time service; the communication satellite signal has the following characteristics:
time domain structure: the communication satellite signal adopts a time division multiplexing system in a time domain, and carries out communication service by using a basic frame and a time slot; signal with TFIs a basic frame length, each basic frame is divided into NslotA time slot, each time slot having a length of Tslot＝TF/Nslot(ii) a As shown in fig. 2.
And (3) frequency domain structure: the communication satellite signal adopts a frequency division multiplexing system in a frequency domain, and the whole downlink frequency band occupies a bandwidth BW which is divided into NsubbandBW (blast furnace dust)subband＝BW/NsubbandEach sub-band is divided into a plurality of carrier intervals according to the requirement; as shown in fig. 3.
The communication satellite signal is a multi-beam multi-color multiplexing system, each beam uses one or more sub-frequency bands according to requirements, and simultaneously multi-color multiplexing of adjacent beams is met so as to reduce interference among the beams;
the communication satellite signal has at least one sub-band for broadcasting paging channel signal, i.e. PCH signal; the PCH signal is a unidirectional downlink signal, is used for downlink synchronization, called paging and broadcast information, and is fixed on a sub-band for broadcasting; the PCH signal uses N of a basic framePCHOne time slot, frame length of PCH signal is TPCH＝NPCH·Tslot(ii) a In order to avoid the same frequency interference between beams, the PCH signals between different beams under the same satellite are broadcast in a time division polling mode.
The sub-band of the communication satellite signal is removed from the PCH signal, the rest SPT signal which can be used for safe positioning time service of broadband spread spectrum is left, and the SPT signal is in the N of the PCH signalPCHBroadcast in one time slot. The SPT signal is a wideband spread spectrum, the wideband spread spectrum SPT signal uses sub-bands other than the sub-band of the PCH signal, has positioning and timing capabilities, and is also broadcast in time-division polling between beams, and the broadcast relationship between the SPT signal and the PCH signal is shown in fig. 4.
The SPT signal, as shown in fig. 5, is composed of two parts, namely, a continuous wave CW and a PRN code, and can be obtained in two ways:
the first mode is as follows:
(1) designing an SPT signal frame structure: n on broadcasting PCH signalPCHIn each time slot, other control information and service information are not broadcast, the frame length of the SPT signal is limited by the frame length of the PCH signal, and the functions of distance measurement, positioning and time service are realized by introducing a broadband spread spectrum pseudo-random code (PRN);
the SPT signal frame structure specifically includes:
(1.1) the PCH signal uses the lowest frequency or the highest frequency sub-band, i.e. the PCH signal is located on the edge of the whole BW bandwidth, the SPT signal uses the remaining BW-BWsubbandA frequency band; each basic frame length TFPCH signal occupies TPCHUsing N per basic framePCHSpread out in one time slot, the SPT signal is also in this NPCHBroadcasting in a time slot;
(1.2) SPT Signal frame Length is TSPT，TSPT≤TPCHThe system consists of a continuous wave CW part and a broadband spread spectrum PRN part, wherein the continuous wave CW is used for signal capture, and the broadband spread spectrum PRN code part is used for measurement and message broadcasting of SPT signals;
(1.3) the length of the continuous wave CW is TCW，0≤TCW≤1/2TSPTWhen T isCWWhen 0, the SPT signal does not contain CW;
(1.4) wideband spreading PRN code partial duration TPRN＝TSPT-TCW。
(2) SPT signal broadband spread spectrum generation: generating a spread spectrum code according to a designed SPT signal frame structure, and carrying out broadband spread spectrum modulation and SPT signal framing;
SPT signal broadband spread spectrum generation is carried out, and the SPT signal broadband spread spectrum generation method is obtained through the following steps:
(2.1) generating a spread PRN code for the SPT signal, including a pilot PRN code and a data PRN code;
PRN code rate of RcChip width of Tc＝1/RcThe bandwidth of the PRN code signal is not greater than BW-BWsubbandI.e. 2Rc≤BW-BWsubbandPilot PRN code sequence { cp,iLength is NpChip, data PRN code sequence { c) after SPT signal message modulationd,iLength is NdOne chip.
(2.2) generating all 1 or all-1 sequences of the CW baseband signals;
the length of CW is equal to NCWOne chip wide, baseband equivalent to a sequence of all 1's or all-1's cCW,iCan choose cCW,i＝1，i＝0，…，NCW-1；
(2.3) the CW, pilot PRN code, and data PRN code of the SPT signal are time-divided by (N)CW+Np+Nd)Tc＝TSPTBase band representation s of SPT signalSPT(t) is:
Figure BDA0002075511180000101
wherein p (T) is a width TcP (t) is defined as:
Figure BDA0002075511180000102
(2.4) Baseband representation s of SPT SignalSPT(t) filtering through a symmetrical FIR low-pass filter, sSPT(t) low pass filtering is denoted as
Figure BDA0002075511180000103
The second mode is as follows:
SPT signal broadband spread spectrum generation is carried out, and the SPT signal broadband spread spectrum generation method is obtained through the following steps:
(2.1) generating a spread PRN code for the SPT signal, including a pilot PRN code and a data PRN code;
PRN code rate of RcChip width of Tc＝1/Rc(ii) a The bandwidth of the PRN code signal is not greater than BW-BWsubbandI.e. 2Rc≤BW-BWsubband(ii) a Pilot PRN code sequence { cp,iLength is Np,dChip, data PRN code sequence { c) after modulating SPT messaged,iLength is Np,dA chip number;
(2.2) generating all 1 or all-1 sequences of the CW baseband signals;
the length of CW is equal to NCWOne chip wide, baseband equivalent to a sequence of all 1's or all-1's cCW,i}，cCW,i＝1，i＝0，…，NCW-1；
(2.3) the pilot PRN code and data PRN code of the SPT signal are located on orthogonal branches, time-divided with CW, by (N)CW+Np,d)Tc＝TSPTBase band representation s of SPT signalSPT(t) is:
sSPT(t)＝sSPT,I(t)+jsSPT,Q(t)
in the formula, sSPT,I(t) is the I branch signal, sSPT,Q(t) is the Q branch signal, respectively expressed as:
Figure BDA0002075511180000111
Figure BDA0002075511180000112
(2.4) branch I Signal sSPT,I(t) and Q branch signal sSPT,Q(t) filtering with the same FIR low-pass filter, respectively
Figure BDA0002075511180000113
And
Figure BDA0002075511180000114
after low pass filtering is recorded as
Figure BDA0002075511180000115
(3) Designing a beam polling pattern: the SPT signal is subjected to time division polling and broadcast in a plurality of wave beams, and the polling mode is determined by a wave beam polling pattern;
there are also two implementations of beam polling patterns:
the first solution, as shown in fig. 6:
designing a beam polling pattern, and obtaining the beam polling pattern by the following method:
(3.1) Low-orbit Mobile communication satellite sharing NbeamA beam of NGroupGroups of N beams, N ═ Nbeam/NGroup(ii) a To shorten the polling interval of SPT signals, N is broadcast simultaneouslyGroupSPT signals, each SPT signal time-division polled in N beams;
(3.2) sequentially polling among the N wave beams by the SPT signal according to a preset mode, wherein the wave beam polling pattern is as follows: beam 1, beam 2, …, beam N, beam 1, beam 2, …, beam N, …;
(3.3) every Nt.T. from one beamFTime, broadcast a length of TSPTSPT signal frame of time domain duty cycle TSPT/(N·TF)。
The second scheme, as shown in fig. 7:
designing a beam polling pattern, and obtaining the beam polling pattern by the following method:
(3.1) Low-orbit Mobile communication satellite sharing NbeamA beam of NGroupGroups of N beams, N ═ Nbeam/NGroup(ii) a To shorten the polling interval of SPT signals, simulcastNGroupSPT signals, each SPT signal time-division polled in N beams;
(3.2) randomly time-division polling the SPT signal among the N wave beams in a random mode; the beam polling pattern is controlled by a pseudo-random number generator which outputs a number N from 1 to N for each SPT signalbeam；
(3.3) from a beam perspective, the intervals at which the SPT signals appear are random and unequal, which is equivalent to introducing time-hopping characteristics.
(4) Beam selection and SPT signaling: the generated SPT signal frames are broadcast on the corresponding beams by digital beamforming.
The beam selection and the SPT signal broadcasting are obtained by the following method:
(4.1) selecting the beam on which the SPT signal is broadcast as a beam n according to the beam polling patternbeam；
(4.2) adjusting the digital beam forming DBF coefficient, modulating the SPT signal to the beam nbeam；
And (4.3) broadcasting through a multi-beam antenna after DAC, up-conversion and amplification.
The two parts of signal generation and broadcasting are combined, and the schematic diagram of SPT signal generation and broadcasting is shown in FIG. 8.
The SPT signal provided by the scheme of the invention has the following characteristics:
(1) aiming at the characteristics of a low-orbit mobile communication signal system, the PCH signal is broadcasted in the time slot, the power, the frequency and the time slot resource of the satellite can be fully utilized, and the communication service is not influenced.
(2) The SPT signal provided by the invention adopts a broadband spread spectrum system, and compared with a narrow-band spread spectrum system, the anti-interference capability is obviously improved.
(3) The SPT signal provided by the invention adopts broadband spread spectrum, has high code rate, and improves the ranging performance and the time service precision compared with a narrowband spread spectrum system.
According to the invention, by designing the SPT signal time-division polling pattern, the combination of time hopping and broadband spread spectrum is realized, and the anti-interference performance of the signal is further improved.
The examples given in the present invention are as follows:
the invention discloses an anti-interference safe positioning time service low-orbit mobile communication satellite signal system which comprises the following operation steps:
(1) a time domain structure.
The signal is in frame unit, and a basic frame length is TF40ms, one frame is equally divided into Nslot20 time slots, one time slot of length Tslot＝2ms。
(2) And (4) frequency domain structure.
The communication signal adopts frequency division multiplexing system in frequency domain, the whole downlink frequency band occupies bandwidth BW equal to 6MHz, and is divided into Nsubband40 BWsubbandEach subband may be divided into a number of smaller carrier spacings, e.g., into 5 carrier spacings of 30kHz, as desired for a 150kHz subband.
(3) Multi-beam antenna multi-color multiplexing system
Low earth orbit mobile communication satellite has NbeamThe method adopts a multicolor multiplexing system, each beam uses one or more 150kHz sub-bands according to requirements, and simultaneously satisfies multicolor multiplexing of adjacent beams, thereby reducing interference between the beams.
(4) A Paging Channel (PCH) signal.
The PCH signal uses N of a basic framePCHLength T of 8 time slotsPCHBroadcast 16ms first of each basic frame. In order to avoid the same frequency interference between beams, the PCH signals between different beams under the same satellite are broadcast in a time division polling mode. The PCH signal is broadcast on the 30kHz carrier among the 5 carriers using the lowest frequency sub-band of 150 kHz.
(5) A secure positioning time Service (SPT) signal.
The SPT signal is broadcast in 8 time slots for broadcasting PCH signal, the SPT signal is a broadband spread spectrum, the broadband spread spectrum SPT signal uses 5.85MHz sub-band except PCH sub-band, has positioning time service capability, and the SPT signal is also broadcast in time-division polling among wave beams, the method is as follows:
1) SPT signal frame structure.
The SPT signal is consistent with the PCH signal, and is broadcast in the first 8 time slots of each basic frame, the SPT signal frame is long TSPT16 ms. Consists of two parts, a Continuous Wave (CW) for fast acquisition of the signal and a wideband spread PRN code part for accurate measurement and teletext of the SPT signal. CW has a length TCW＝4ms。
2) And generating the SPT signal by broadband spread spectrum.
The wideband spreading PRN code portion is 12ms in length and is divided into a pilot PRN code and a data PRN code, with the pilot and data being located on two orthogonal branches. PRN code rate of Rc2.046Mcps, pilot PRN code sequence { cp,iThe length of the primary code is Np,d2046 chips, modulating the textual data PRN code sequence { c) of the SPT signald,iThe length of the primary code is also 2046 chips, one primary code period is 1ms, and 12ms is 12 primary code periods.
An all-1 or all-1 sequence of CW baseband signals is generated. The length of CW is equal to NCW8184 chip widths, baseband is equivalent to a sequence c of all 1's or all-1' sCW,i}，cCW,i＝1，i＝0，…，NCW-1；
The pilot PRN code and data PRN code of the SPT signal are time-divided with the CW, and the base band of the SPT signal represents sSPT(t) is:
sSPT(t)＝sSPT,I(t)+jsSPT,Q(t)
in the formula, sSPT,I(t) is the I branch signal, sSPT,Q(t) is the Q branch signal, respectively expressed as:
Figure BDA0002075511180000141
Figure BDA0002075511180000142
sSPT,I(t) and sSPT,Q(t) filtering with the same FIR low-pass filter, respectively
Figure BDA0002075511180000143
And
Figure BDA0002075511180000144
after low pass filtering is recorded as
Figure BDA0002075511180000145
3) And (4) designing a beam polling pattern.
N of low-orbit mobile communication satellitebeamAn average of N for 50 beamsGroupEach group has 25 beams, and simultaneously broadcasts 2 SPT signals, and each SPT signal is time-division polled in 25 beams; the beam polling pattern is controlled by a pseudo-random number generator which outputs a number n in the range 1 to 25 per SPT signalbeamThe SPT signal is polled between 25 beams in a random manner; from one beam, the SPT signals appear at random unequal intervals, equivalent to introducing time-hopping characteristics, with the average SPT signal received at intervals of 25 × 40ms — 1 s.
4) Beam selection is broadcast with the SPT signal.
Selecting the beam for broadcasting the SPT signal as a beam n according to the beam polling patternbeam(ii) a Adjusting Digital Beamforming (DBF) coefficients to modulate SPT signals to beam nbeam(ii) a After DAC, up-conversion and amplification, the signals are broadcast by a multi-beam antenna.
Those skilled in the art will appreciate that those matters not described in detail in the present specification are well known in the art.

Claims (6)

1. A communication method based on a low-orbit mobile communication satellite is characterized in that: generating a low-orbit mobile communication satellite signal for safe positioning time service, and communicating by using the low-orbit mobile communication satellite signal for safe positioning time service; the communication satellite signal has the following characteristics:
time domain structure: the communication satellite signal adopts a time division multiplexing system in a time domain, and carries out communication service by using a basic frame and a time slot; signal with TFIs a basic frame lengthEach basic frame is divided into NslotA time slot, each time slot having a length of Tslot＝TF/Nslot；
And (3) frequency domain structure: the communication satellite signal adopts a frequency division multiplexing system in a frequency domain, and the whole downlink frequency band occupies a bandwidth BW which is divided into NsubbandBW (blast furnace dust)subband＝BW/NsubbandEach sub-band is divided into a plurality of carrier intervals according to the requirement;
the communication satellite signal is a multi-beam multi-color multiplexing system, each beam uses one or more sub-frequency bands according to requirements, and simultaneously multi-color multiplexing of adjacent beams is met so as to reduce interference among the beams;
the communication satellite signal has at least one sub-band for broadcasting paging channel signal, i.e. PCH signal; the PCH signal is a unidirectional downlink signal, is used for downlink synchronization, called paging and broadcast information, and is fixed on a sub-band for broadcasting; the PCH signal uses N of a basic framePCHOne time slot, frame length of PCH signal is TPCH＝NPCH·Tslot；
The sub-band of the communication satellite signal is removed from the PCH signal, the rest SPT signal which can be used for safe positioning time service of broadband spread spectrum is left, and the SPT signal is in the N of the PCH signalPCHBroadcasting in each time slot;
the SPT signal is obtained by the following method:
(1) designing an SPT signal frame structure: n on broadcasting PCH signalPCHIn each time slot, other control information and service information are not broadcast, the frame length of the SPT signal is limited by the frame length of the PCH signal, and the functions of distance measurement, positioning and time service are realized by introducing a broadband spread spectrum pseudo-random code (PRN);
the SPT signal frame structure specifically includes:
(1.1) the PCH signal uses the lowest frequency or the highest frequency sub-band, i.e. the PCH signal is located on the edge of the whole BW bandwidth, the SPT signal uses the remaining BW-BWsubbandA frequency band; each basic frame length TFPCH signal occupies TPCHUsing N per basic framePCHSpread out in one time slot, the SPT signal is also in this NPCHBroadcasting in a time slot;
(1.2) SPT Signal frame Length is TSPT，TSPT≤TPCHThe system consists of a continuous wave CW part and a broadband spread spectrum PRN part, wherein the continuous wave CW is used for signal capture, and the broadband spread spectrum PRN code part is used for measurement and message broadcasting of SPT signals;
(1.3) the length of the continuous wave CW is TCW，0≤TCW≤1/2TSPTWhen T isCWWhen 0, the SPT signal does not contain CW;
(1.4) wideband spreading PRN code partial duration TPRN＝TSPT-TCW；
(2) SPT signal broadband spread spectrum generation: generating a spread spectrum code according to a designed SPT signal frame structure, and carrying out broadband spread spectrum modulation and SPT signal framing;
the SPT signal broadband spread spectrum is generated and obtained by the following method:
(2.1) generating a spread PRN code for the SPT signal, including a pilot PRN code and a data PRN code;
PRN code rate of RcChip width of Tc＝1/RcThe bandwidth of the PRN code signal is not greater than BW-BWsubbandI.e. 2Rc≤BW-BWsubbandPilot PRN code sequence { cp,iLength is NpChip, data PRN code sequence { c) after SPT signal message modulationd,iLength is NdA chip number;
(2.2) generating all 1 or all-1 sequences of the CW baseband signals;
the length of CW is equal to NCWOne chip wide, baseband equivalent to a sequence of all 1's or all-1's cCW,iCan choose cCW,i＝1，i＝0，…，NCW-1；
(2.3) the CW, pilot PRN code, and data PRN code of the SPT signal are time-divided by (N)CW+Np+Nd)Tc＝TSPTBase band representation s of SPT signalSPT(t) is:
Figure FDA0002854398620000021
wherein p (T) is a width TcP (t) is defined as:
Figure FDA0002854398620000022
(2.4) Baseband representation s of SPT SignalSPT(t) filtering through a symmetrical FIR low-pass filter, sSPT(t) low pass filtering is denoted as
Figure FDA0002854398620000031
(3) Designing a beam polling pattern: the SPT signal is subjected to time division polling and broadcast in a plurality of wave beams, and the polling mode is determined by a wave beam polling pattern;
(4) beam selection and SPT signaling: the generated SPT signal frames are broadcast on the corresponding beams by digital beamforming.
2. The method of claim 1, wherein the method comprises: PCH signals between different beams under the same communication satellite are broadcast in a time division polling mode so as to avoid same frequency interference between the beams; the SPT signals are also time division polling broadcast between beams to avoid co-channel interference between beams.
3. The method of claim 1, wherein the method comprises: the SPT signal broadband spread spectrum generation can be further obtained by the following method:
(2.1) generating a spread PRN code for the SPT signal, including a pilot PRN code and a data PRN code;
PRN code rate of RcChip width of Tc＝1/Rc(ii) a The bandwidth of the PRN code signal is not greater than BW-BWsubbandI.e. 2Rc≤BW-BWsubband(ii) a Pilot PRN code sequence { cp,iLength is Np,dOne chip, modulating the data PR after SPT telegraph textN code sequence { cd,iLength is Np,dA chip number;
(2.2) generating all 1 or all-1 sequences of the CW baseband signals;
the length of CW is equal to NCWOne chip wide, baseband equivalent to a sequence of all 1's or all-1's cCW,i}，cCW,i＝1，i＝0，…，NCW-1；
(2.3) the pilot PRN code and data PRN code of the SPT signal are located on orthogonal branches, time-divided with CW, by (N)CW+Np,d)Tc＝TSPTBase band representation s of SPT signalSPT(t) is:
sSPT(t)＝sSPT,I(t)+jsSPT,Q(t)
in the formula, sSPT,I(t) is the I branch signal, sSPT,Q(t) is the Q branch signal, respectively expressed as:
Figure FDA0002854398620000041
Figure FDA0002854398620000042
(2.4) branch I Signal sSPT,I(t) and Q branch signal sSPT,Q(t) filtering with the same FIR low-pass filter, respectively
Figure FDA0002854398620000043
And
Figure FDA0002854398620000044
after low pass filtering is recorded as
Figure FDA0002854398620000045
4. The method of claim 1, wherein the method comprises: the designed beam polling pattern is obtained by the following method:
(3.1) Low-orbit Mobile communication satellite sharing NbeamA beam of NGroupGroups of N beams, N ═ Nbeam/NGroup(ii) a To shorten the polling interval of SPT signals, N is broadcast simultaneouslyGroupSPT signals, each SPT signal time-division polled in N beams;
(3.2) sequentially polling among the N wave beams by the SPT signal according to a preset mode, wherein the wave beam polling pattern is as follows: beam 1, beam 2, …, beam N, beam 1, beam 2, …, beam N, …;
(3.3) every Nt.T. from one beamFTime, broadcast a length of TSPTSPT signal frame of time domain duty cycle TSPT/(N·TF)。
5. The method of claim 1, wherein the method comprises: the designed beam polling pattern is obtained by the following method:
(3.1) Low-orbit Mobile communication satellite sharing NbeamA beam of NGroupGroups of N beams, N ═ Nbeam/NGroup(ii) a To shorten the polling interval of SPT signals, N is broadcast simultaneouslyGroupSPT signals, each SPT signal time-division polled in N beams;
(3.2) randomly time-division polling the SPT signal among the N wave beams in a random mode; the beam polling pattern is controlled by a pseudo-random number generator which outputs a number N from 1 to N for each SPT signalbeam；
(3.3) from a beam perspective, the intervals at which the SPT signals appear are random and unequal, which is equivalent to introducing time-hopping characteristics.
6. The method of claim 1, wherein the method comprises: the beam selection and the SPT signal broadcasting are obtained by the following method:
(4.1) selecting the beam on which the SPT signal is broadcast as a beam n according to the beam polling patternbeam；
(4.2) adjusting the digital beam forming DBF coefficient, modulating the SPT signal to the beam nbeam；
And (4.3) broadcasting through a multi-beam antenna after DAC, up-conversion and amplification.
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