Satellite communication and navigation integrated processing system and method
阅读说明：本技术 卫星通信与导航一体化处理系统及方法 (Satellite communication and navigation integrated processing system and method ) 是由 曹璐 王建 范广腾 李献斌 覃江毅 郭鹏宇 于 2020-04-17 设计创作，主要内容包括：本发明公开了一种卫星通信与导航一体化处理系统及方法,该系统中低轨微纳卫星内设置有通信导航一体化收发机。通信基带信号产生单元发出的通信信号顺次经数模转换模块、正交上变频模块、功率放大模块和发射天线发送至地面通信设备。接收天线接收GPS卫星的导航信号、北斗卫星的导航信号和地面通信设备的通信信号,接收到的信号顺次经低噪声放大模块、正交下变频模块、数模转换模块进入通信导航信号分离模块进行信号分离,然后经数字频谱搬移模块消除频偏后,分别发送到GPS信号处理模块、北斗信号处理模块或通信基带信号处理模块进行处理。本发明的卫星通信与导航一体化处理系统及方法,具有高集成度和轻量化和小型化的显著优势。(The invention discloses a satellite communication and navigation integrated processing system and a method. The communication signal sent by the communication baseband signal generating unit is sent to the ground communication equipment through the digital-to-analog conversion module, the orthogonal up-conversion module, the power amplification module and the transmitting antenna in sequence. The receiving antenna receives a navigation signal of a GPS satellite, a navigation signal of a Beidou satellite and a communication signal of ground communication equipment, the received signals enter the communication navigation signal separation module for signal separation through the low-noise amplification module, the quadrature down-conversion module and the digital-to-analog conversion module in sequence, and then are respectively sent to the GPS signal processing module, the Beidou signal processing module or the communication baseband signal processing module for processing after frequency deviation is eliminated through the digital frequency spectrum moving module. The satellite communication and navigation integrated processing system and method have the remarkable advantages of high integration level, light weight and miniaturization.)
1. A satellite communication and navigation integrated processing system, the system comprising: the system comprises a GPS satellite, a Beidou satellite, a low-orbit micro-nano satellite and ground communication equipment;
the low-orbit micro-nano satellite is internally provided with a communication and navigation integrated transceiver, and the transceiver comprises a communication baseband signal generating unit, a digital-to-analog conversion module, an orthogonal up-conversion module, a power amplification module, a transmitting antenna, a receiving antenna, a low-noise amplification module, an orthogonal down-conversion module, an analog-to-digital conversion module, a communication and navigation signal separation module, a digital frequency spectrum shifting module, a communication baseband signal processing module, a GPS signal processing module and a Beidou signal processing module;
the communication signal sent by the communication baseband signal generating unit is sequentially sent to the ground communication equipment through the digital-to-analog conversion module, the orthogonal up-conversion module, the power amplification module and the transmitting antenna;
the receiving antenna receives the navigation signal of the GPS satellite, the navigation signal of the Beidou satellite and the communication signal of the ground communication equipment, the received signals enter the communication navigation signal separation module for signal separation through the low-noise amplification module, the orthogonal down-conversion module and the digital-to-analog conversion module in sequence, and then are respectively sent to the GPS signal processing module, the Beidou signal processing module or the communication baseband signal processing module for processing after frequency deviation is eliminated through the digital frequency spectrum shifting module.
2. The integrated satellite communication and navigation processing system according to claim 1, wherein the communication baseband signal generating unit, the communication navigation signal separating module, the digital spectrum moving module, the communication baseband signal processing module, the GPS signal processing module, and the beidou signal processing module are implemented in a programmable processing chip;
the digital-to-analog conversion module, the orthogonal up-conversion module, the power amplification module, the low-noise amplification module, the orthogonal down-conversion module and the analog-to-digital conversion module are realized by high-integration transceiver chips.
3. A satellite communication and navigation integrated processing method is characterized by comprising the following steps:
the communication baseband signal generating unit sends out a communication signal, the communication signal is subjected to digital-to-analog conversion through the digital-to-analog conversion module, modulated to a preset frequency band chopping wave through the orthogonal up-conversion module, subjected to power amplification through the power amplification module and then sent to the ground communication equipment through the transmitting antenna;
the receiving antenna obtains signals within a preset frequency range, the signals within the preset frequency range comprise Beidou navigation signals, GPS navigation signals and communication signals sent by ground communication equipment, the received signals are subjected to low-noise amplification through a low-noise amplification module, a preset carrier frequency is selected through an orthogonal down-conversion module to be subjected to orthogonal down-conversion, analog-to-digital conversion is carried out through an analog-to-digital conversion module to obtain I/Q baseband digital signals, the Beidou navigation signals located in adjacent frequency bands are separated from the communication signals through a communication navigation signal separation module, the digital spectrum moving module eliminates frequency deviation of the signals, and the Beidou navigation signals, the GPS navigation signals and the communication signals are respectively sent to a Beidou signal processing module, the GPS signal processing module or the communication baseband signal processing module to be processed.
4. The integrated processing method for satellite communication and navigation according to claim 3, wherein the navigation receiving frequency band is 1555MHz to 1580MHz, L1 frequency point signal 1575.42MHz +/-1.023 MHz covering GPS system and B1 frequency point signal 1561.098MHz +/-2.046 MHz covering Beidou system;
the frequency band of an uplink communication link from the ground communication equipment to the satellite is an L frequency band from 1530MHz to 1555MHz, and the carrier frequency of the signal is fc。
5. The integrated processing method for satellite communication and navigation according to claim 4,
the orthogonal up-conversion module modulates the communication signal to an S frequency band carrier; a downlink communication link between the low-orbit micro-nano satellite and the ground communication equipment works in an S frequency band;
the receiving antenna receives signals in a band range of 1530-1580 MHz, and selects a 1555MHz carrier frequency to perform orthogonal down-conversion after low-noise amplification.
6. The integrated processing method for satellite communication and navigation according to claim 5, wherein the received signal frequency bandwidth is BW, and the distribution range is [ -BW/2, BW/2 [ -BW/2 ]]The analog-to-digital conversion module is used for sampling frequency fsOversampling the signal by a factor of U, i.e. fsThe bandwidth of the communication signal is BW within the signal band with the width BW1The frequency range occupied in the signal band is [ -BW [ - ]1-Δ1,-Δ1](ii) a Bandwidth of B1 frequency point Beidou navigation signal is BW2The frequency range occupied within the signal band is [ Delta ]2,Δ2+BW2](ii) a Designing a digital low-pass filter h (N) with the order of N-1 and meeting the following requirements, wherein N is 0,1, …, N-1:
a. passband cut-off frequency omegacSatisfy the requirement of
b. The width of the transition belt is not more than
7. The integrated satellite communication and navigation processing method according to claim 6, wherein ω is represented by the following formula0-pi/2, separate communication signal:
where x (n) denotes a received baseband signal, y0(n) represents the communication signal separated from x (n), and "+" represents the convolution operation;
for y0(n) 1/2 extraction yields:
wherein x isp(m)＝x(2m-p)，hp(m)＝h(2m+p)；
Let ω be1Pi/2, separating the navigation signal y1(n)：
1/2 extraction of the navigation signal results in:
by usingIs shown in
wherein z (l) ═ xp(m)·(-1)m*hp(m))|m＝UlCan be further expressed as:
wherein x isp,d(i)＝xp(Ui-d)，hp,d(i)＝hp(Ui+d)。
8. The integrated satellite communication and navigation processing method according to claim 7, wherein the signal separation process includes input weighting, filtering and post-processing;
input weighting: directly inputting data x (4n), x (4n +1), n is 0,1,2, … into the filter, and inputting data x (4n +2), x (4n +3), n is 0,1,2, … multiplied by-1 into the filter;
recombining h (N), N ═ 0,1, …, N-1 into the following 2U lines:
the row order is further adjusted as follows:
2U-1→2U→2U-3→2U-2→2U-5→2U-4→…→3→4→1→2
after the line order is adjusted, respectively storing N/(2U) column coefficients into tap coefficient register groups corresponding to N/(2U) multipliers of the filter; in addition, a data register group with the length of 2U is also respectively configured at the input end of each adder and used for storing an intermediate calculation result; in the working process of the filter, when one effective data is input, the cyclic shift is carried out on the tap coefficient register group and the data register group once;
and (3) post-treatment: the odd serial number values (1 st, 3 rd, … …) output by the filter are sent to the lower branch of the post-processing unit, and the even serial number values (2 nd, 4 th, … …) are sent to the upper branch; each branch utilizes U input data to calculate an accumulation result, then the accumulation results of the two branches are weighted in parallel and then the radix-2 butterfly operation is executed to obtainAnd
9. The integrated satellite communication and navigation processing method of claim 8, wherein the communication signal and the navigation signal are separated and calculated
respectively calculate
10. The integrated processing method for satellite communication and navigation according to claim 9, wherein the ground communication device controls the transmission power of the communication signal according to the communication elevation angle of the low-orbit micro-nano satellite relative to the ground communication device.
Technical Field
The invention relates to the technical field of satellite communication, in particular to a satellite communication and navigation integrated processing system and method.
Background
With the development of satellite communication and satellite navigation technologies, it has become an important trend to implement satellite navigation functions while performing satellite communication, which requires the design of an integrated communication and navigation system. At present, the integration of communication and navigation mainly includes the following several implementation approaches:
(1) the mechanism structure is integrated: the method mainly comprises the steps of designing a unified chassis structure and board card sizes, packaging all board cards of a communication transceiver and a navigation receiver in the same structure, uniformly providing power distribution of the board cards by a power distribution management unit, and designing a broadband antenna at an antenna end to receive communication and navigation signals at the same time.
(2) Digital processing integration: the functions of the communication transceiver and the digital processing board card of the navigation receiver are fused, the received communication signal navigation signal is processed by the same signal processing board card, and a unified external information interaction and control interface is provided.
(3) Integration of a signal system: the method mainly breaks through the existing navigation signal form, and designs a signal system with both communication function and navigation function. For example, in a Multi-Carrier communication system such as Orthogonal Frequency Division Multiplexing (OFDM) modulation or Universal Filtered Multi-Carrier (UFMC), a pilot symbol or a timing synchronization training symbol is used to carry a navigation message, and a navigation function such as ranging is completed while communication is performed. The other solution is to add a communication message into the navigation message to realize the transmission of the communication data in the navigation signal.
The inventor finds that the prior art has at least the following problems:
(1) the multiplexing of the communication function and the navigation function to partial hardware resources is realized on a hardware level no matter the mechanism structure integration and the digital processing integration are realized. In these schemes, independent signal transceiving channels are still used for communication and navigation, and it is difficult to meet the application requirement of high integration degree miniaturization.
(2) The signal system integration breaks through the existing navigation signal system, cannot be compatible with a mature and widely applied satellite navigation system such as Beidou or GPS and the like, and has great limitation in the aspect of application scenes. Meanwhile, the communication and navigation integrated signal system based on multiple carriers requires that communication signals can only be transmitted in a multi-carrier mode, and the application flexibility needs to be improved; the integrated signal system of communication and navigation message fusion can only support low-speed communication tasks, and can reduce navigation performance and precision.
Disclosure of Invention
In order to solve the technical problems in the prior art, the invention provides a satellite communication and navigation integrated processing system and a method. The specific technical scheme is as follows:
in a first aspect, a satellite communication and navigation integrated processing system is provided, the system includes: the system comprises a GPS satellite, a Beidou satellite, a low-orbit micro-nano satellite and ground communication equipment;
the low-orbit micro-nano satellite is internally provided with a communication and navigation integrated transceiver, and the transceiver comprises a communication baseband signal generating unit, a digital-to-analog conversion module, an orthogonal up-conversion module, a power amplification module, a transmitting antenna, a receiving antenna, a low-noise amplification module, an orthogonal down-conversion module, an analog-to-digital conversion module, a communication and navigation signal separation module, a digital frequency spectrum shifting module, a communication baseband signal processing module, a GPS signal processing module and a Beidou signal processing module;
the communication signal sent by the communication baseband signal generating unit is sequentially sent to the ground communication equipment through the digital-to-analog conversion module, the orthogonal up-conversion module, the power amplification module and the transmitting antenna;
the receiving antenna receives the navigation signal of the GPS satellite, the navigation signal of the Beidou satellite and the communication signal of the ground communication equipment, the received signals enter the communication navigation signal separation module for signal separation through the low-noise amplification module, the orthogonal down-conversion module and the digital-to-analog conversion module in sequence, and then are respectively sent to the GPS signal processing module, the Beidou signal processing module or the communication baseband signal processing module for processing after frequency deviation is eliminated through the digital frequency spectrum shifting module.
In one possible design, the communication baseband signal generating unit, the communication navigation signal separating module, the digital spectrum moving module, the communication baseband signal processing module, the GPS signal processing module, and the beidou signal processing module are implemented in a programmable processing chip; the digital-to-analog conversion module, the orthogonal up-conversion module, the power amplification module, the low-noise amplification module, the orthogonal down-conversion module and the analog-to-digital conversion module are realized by high-integration transceiver chips.
In a second aspect, a satellite communication and navigation integrated processing method is provided, where the method includes:
the communication baseband signal generating unit sends out a communication signal, the communication signal is subjected to digital-to-analog conversion through the digital-to-analog conversion module, modulated to a preset frequency band chopping wave through the orthogonal up-conversion module, subjected to power amplification through the power amplification module and then sent to the ground communication equipment through the transmitting antenna;
the receiving antenna obtains signals within a preset frequency range, the signals within the preset frequency range comprise Beidou navigation signals, GPS navigation signals and communication signals sent by ground communication equipment, the received signals are subjected to low-noise amplification through a low-noise amplification module, a preset carrier frequency is selected through an orthogonal down-conversion module to be subjected to orthogonal down-conversion, analog-to-digital conversion is carried out through an analog-to-digital conversion module to obtain I/Q baseband digital signals, the Beidou navigation signals located in adjacent frequency bands are separated from the communication signals through a communication navigation signal separation module, the digital spectrum moving module eliminates frequency deviation of the signals, and the Beidou navigation signals, the GPS navigation signals and the communication signals are respectively sent to a Beidou signal processing module, the GPS signal processing module or the communication baseband signal processing module to be processed.
In one possible design, the navigation receiving frequency range is selected from 1555MHz to 1580MHz, L1 frequency point signals covering a GPS system are 1575.42MHz +/-1.023 MHz, and Beidou system B1 frequency point signals are 1561.098MHz +/-2.046 MHz; the frequency band of an uplink communication link from the ground communication equipment to the satellite is an L frequency band from 1530MHz to 1555MHz, and the carrier frequency of the signal is fc。
In one possible design, the quadrature upconversion module modulates the communication signal onto an S-band carrier; a downlink communication link between the low-orbit micro-nano satellite and the ground communication equipment works in an S frequency band; the receiving antenna receives signals in a band range of 1530-1580 MHz, and selects a 1555MHz carrier frequency to perform orthogonal down-conversion after low-noise amplification.
In one possible design, the received signal bandwidth is BW, and the distribution range is [ -BW/2, BW/2 [ -BW [ -2 ]]The analog-to-digital conversion module is used for sampling frequency fsOversampling the signal by a factor of U, i.e. fsThe bandwidth of the communication signal is BW within the signal band with the width BW1The frequency range occupied in the signal band is [ -BW [ - ]1-Δ1,-Δ1](ii) a Bandwidth of B1 frequency point Beidou navigation signal is BW2The frequency range occupied within the signal band is [ Delta ]2,Δ2+BW2](ii) a Designing a digital low-pass filter h (N) with the order of N-1 and meeting the following requirements, wherein N is 0,1, …, N-1:
a. passband cut-off frequency omegacSatisfy the requirement of
b. The width of the transition belt is not more than
In one possible design, let ω be0-pi/2, separate communication signal:
where x (n) denotes a received baseband signal, y0(n) represents the communication signal separated from x (n), and "+" represents the convolution operation;
for y0(n) 1/2 extraction yields:
wherein x isp(m)＝x(2m-p)，hp(m)＝h(2m+p)；
Let ω be1Pi/2, separating the navigation signal y1(n)：
1/2 extraction of the navigation signal results in:
and
by usingIs shown inAnd on the basis of signals obtained by further 1/U extraction, the following signals are obtained:
wherein z (l) ═ xp(m)·(-1)m*hp(m))m＝UlCan be further expressed as:
wherein x isp,d(i)＝xp(Ui-d)，hp,d(i)＝hp(Ui+d)。
In one possible design, the signal separation process includes input weighting, filtering, and post-processing;
input weighting: directly inputting data x (4n), x (4n +1), n is 0,1,2, … into the filter, and inputting data x (4n +2), x (4n +3), n is 0,1,2, … multiplied by-1 into the filter;
recombining h (N), N ═ 0,1, …, N-1 into the following 2U lines:
the row order is further adjusted as follows:
2U-1→2U→2U-3→2U-2→2U-5→2U-4→…→3→4→1→2
after the line order is adjusted, respectively storing N/(2U) column coefficients into tap coefficient register groups corresponding to N/(2U) multipliers of the filter; in addition, a data register group with the length of 2U is also respectively configured at the input end of each adder and used for storing an intermediate calculation result; in the working process of the filter, when one effective data is input, the cyclic shift is carried out on the tap coefficient register group and the data register group once;
and (3) post-treatment: the odd serial number values (1 st, 3 rd, … …) output by the filter are sent to the lower branch of the post-processing unit, and the even serial number values (2 nd, 4 th, … …) are sent to the upper branch; each branch utilizes U input data to calculate an accumulation result, then the accumulation results of the two branches are weighted in parallel and then the radix-2 butterfly operation is executed to obtainAnd
In one possible design, the communication signal and the navigation signal are separated and then calculated
respectively calculate
In one possible design, the ground communication device controls the transmission power of the communication signal according to the communication elevation angle of the low-orbit micro-nano satellite relative to the ground communication device.
The technical scheme of the invention has the following main advantages:
according to the satellite communication and navigation integrated processing system and method, the communication and navigation integrated transceiver is carried in the low-orbit micro-nano satellite, the receiving and processing capabilities of GPS and Beidou dual-mode navigation signals are improved through a signal processing technology, the integrated multiplexing of the communication and navigation functions of receiving baseband processing from an antenna and a radio frequency is realized, the satellite communication and navigation integrated processing system has the remarkable advantages of high integration level, light weight and miniaturization, and is particularly suitable for a satellite platform with the same volume and limited weight of the micro-nano satellite. The system is compatible with the existing signal systems of satellite navigation systems such as Beidou, GPS and the like, has no constraint on communication signal systems, supports various systems such as multi-carrier, single carrier, spread spectrum and the like, and has wide application range and stronger flexibility.
Drawings
The accompanying drawings, which are included to provide a further understanding of embodiments of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the invention and not to limit the invention. In the drawings:
fig. 1 is an architecture diagram of an integrated processing system for satellite communication and navigation according to an embodiment of the present invention;
fig. 2 is a schematic structural diagram of a transceiver in an integrated processing system for satellite communication and navigation according to an embodiment of the present invention;
fig. 3 is a schematic frequency spectrum diagram of a signal received by a receiving antenna in the integrated processing method for satellite communication and navigation according to an embodiment of the present invention;
fig. 4 is a schematic diagram illustrating separation of communication and navigation signals in an integrated processing method for satellite communication and navigation according to an embodiment of the present invention;
fig. 5-1 is a schematic diagram of design parameters of a frequency response of a low-pass filter for filtering a navigation signal in an integrated processing method for satellite communication and navigation according to an embodiment of the present invention;
fig. 5-2 is a schematic diagram of design parameters of an impulse response amplitude value of a low-pass filter for filtering a navigation signal in the integrated satellite communication and navigation processing method according to an embodiment of the present invention;
fig. 6 is a schematic view illustrating an internal working principle of a digital spectrum shifting device in the satellite communication and navigation integrated processing method according to an embodiment of the present invention;
fig. 7 is a schematic diagram illustrating a relationship between the change of the ERIP emitted by the ground communication device with the communication elevation angle in the satellite communication and navigation integrated processing method according to an embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the technical solutions of the present invention will be clearly and completely described below with reference to the specific embodiments of the present invention and the accompanying drawings. It is to be understood that the described embodiments are merely a few embodiments of the invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments of the present invention without making any creative effort, shall fall within the protection scope of the present invention.
The technical scheme provided by the embodiment of the invention is described in detail below with reference to the accompanying drawings.
In a first aspect, an embodiment of the present invention provides an integrated processing system for satellite communication and navigation, as shown in fig. 1, the system includes: the system comprises a GPS satellite, a Beidou satellite, a low-orbit micro-nano satellite and ground communication equipment. The low-orbit micro-nano satellite is internally provided with a communication and navigation integrated transceiver, and the transceiver comprises a communication baseband signal generating unit, a digital-to-analog conversion module, an orthogonal up-conversion module, a power amplification module, a transmitting antenna, a receiving antenna, a low-noise amplification module, an orthogonal down-conversion module, an analog-to-digital conversion module, a communication and navigation signal separation module, a digital spectrum moving module, a communication baseband signal processing module, a GPS signal processing module and a Beidou signal processing module; the communication signal sent by the communication baseband signal generating unit is sent to the ground communication equipment through the digital-to-analog conversion module, the orthogonal up-conversion module, the power amplification module and the transmitting antenna in sequence. The receiving antenna receives a navigation signal of a GPS satellite, a navigation signal of a Beidou satellite and a communication signal of ground communication equipment, the received signals enter the communication navigation signal separation module for signal separation through the low-noise amplification module, the quadrature down-conversion module and the digital-to-analog conversion module in sequence, and then are respectively sent to the GPS signal processing module, the Beidou signal processing module or the communication baseband signal processing module for processing after frequency deviation is eliminated through the digital frequency spectrum moving module.
According to the satellite communication and navigation integrated processing system provided by the embodiment of the invention, the communication and navigation integrated transceiver carried in the low-orbit micro-nano satellite increases the receiving and processing capabilities of GPS and Beidou dual-mode navigation signals through a signal processing technology, realizes the integrated multiplexing of the communication and navigation functions of receiving baseband processing from an antenna and a radio frequency, has the remarkable advantages of high integration level, light weight and miniaturization, and is particularly suitable for a satellite platform with the volume of the micro-nano satellite and limited weight. The system is compatible with the existing signal systems of satellite navigation systems such as Beidou, GPS and the like, has no constraint on communication signal systems, supports various systems such as multi-carrier, single carrier, spread spectrum and the like, and has wide application range and stronger flexibility.
As shown in fig. 2, in the communication and navigation integrated transceiver, the communication baseband signal generation unit, the communication and navigation signal separation module, the digital spectrum shift module, the communication baseband signal processing module, the GPS signal processing module, and the beidou signal processing module may be classified into digital parts, and may be implemented in a programmable processing chip (e.g., FPGA, DSP, etc.). The digital-to-analog conversion module, the quadrature up-conversion module, the power amplification module, the low noise amplification module, the quadrature down-conversion module, and the analog-to-digital conversion module may be classified as a radio frequency/analog part, and may be implemented by using a highly integrated transceiver chip (e.g., AD9361, AD9371, etc.). Therefore, the embodiment of the invention can realize the integrated communication and navigation function without changing the hardware of the transceiver.
In a second aspect, an embodiment of the present invention provides a satellite communication and navigation integrated processing method, where the method includes:
the communication baseband signal generating unit sends out a communication signal, the communication signal is subjected to digital-to-analog conversion through the digital-to-analog conversion module, modulated to a preset frequency band chopping wave through the orthogonal up-conversion module, subjected to power amplification through the power amplification module and then sent to the ground communication equipment through the transmitting antenna;
the receiving antenna obtains signals within a preset frequency range, the signals within the preset frequency range comprise Beidou navigation signals, GPS navigation signals and communication signals sent by ground communication equipment, the received signals are subjected to low-noise amplification through a low-noise amplification module, a preset carrier frequency is selected through an orthogonal down-conversion module to be subjected to orthogonal down-conversion, analog-to-digital conversion is carried out through an analog-to-digital conversion module to obtain I/Q baseband digital signals, the Beidou navigation signals located in adjacent frequency bands are separated from the communication signals through a communication navigation signal separation module, the digital spectrum moving module eliminates frequency deviation of the signals, and the Beidou navigation signals, the GPS navigation signals and the communication signals are respectively sent to a Beidou signal processing module, the GPS signal processing module or the communication baseband signal processing module to be processed.
According to the satellite communication and navigation integrated processing method provided by the embodiment of the invention, the receiving and processing capabilities of GPS and Beidou dual-mode navigation signals are increased through a signal processing technology, the integrated multiplexing of the communication and navigation functions from antenna and radio frequency receiving to baseband processing is realized, the obvious advantages of high integration level and light weight and miniaturization are achieved, and the satellite communication and navigation integrated processing method is particularly suitable for a satellite platform with the same volume and limited weight of a micro-nano satellite. The system is compatible with the existing signal systems of satellite navigation systems such as Beidou, GPS and the like, has no constraint on communication signal systems, supports various systems such as multi-carrier, single carrier, spread spectrum and the like, and has wide application range and stronger flexibility.
Specifically, for a specific working principle of a communication and navigation integrated transceiver in a low-orbit micro/nano satellite, the following description is given with reference to an example:
first, system frequency division is performed:
(1) the navigation receiving frequency range is selected from 1555MHz to 1580MHz, and L1 frequency point signals 1575.42MHz +/-1.023 MHz of a GPS system and B1 frequency point signals 1561.098MHz +/-2.046 MHz of a Beidou system are covered;
(2) the frequency band of an uplink communication link from the ground communication equipment to the satellite is an L frequency band from 1530MHz to 1555MHz, the L frequency band is adjacent to a navigation receiving frequency band, and the carrier frequency of a signal is fc；
(3) The downlink communication link from the satellite to the ground communication equipment works in an S frequency band, and is determined according to the receiving and transmitting isolation index in practical application.
Based on the frequency division, when the low-orbit micro-nano satellite sends a communication signal to the ground communication equipment, the orthogonal up-conversion module modulates the signal to an S-frequency-band carrier wave. The receiving antenna acquires signals in a band range of 1530-1580 MHz, and selects a 1555MHz carrier frequency to perform orthogonal down-conversion after low-noise amplification.
In the embodiment of the invention, the generation and processing of the communication baseband signal and the processing of the GPS and Beidou navigation signals are all based on the existing mature scheme, and the communication navigation signal separation module and the digital spectrum moving module are new modules designed for realizing the integrated processing of communication and navigation. The two modules are described in detail below:
the frequency spectrum of the resulting IQ baseband digital signal for the receive path is shown in fig. 3. According to the frequency division scheme, the frequency bandwidth of the received signal is BW 50MHz, and the distribution range is [ -BW/2, BW/2]. The analog-to-digital conversion module takes the sampling frequency as fsOversampling the signal by a factor of U, i.e. fsU · BW. Having a bandwidth BW for communication signals within a BW-wide signal band1The frequency range occupied in the signal band is [ -BW [ - ]1-Δ1,-Δ1](ii) a Bandwidth of B1 frequency point Beidou navigation signal is BW22.046MHz, the occupied frequency range within the signal band is Δ2,Δ2+BW2]. Designing a digital low-pass filter h (N) with the order of N-1 and meeting the following requirements, wherein N is 0,1, …, N-1:
a. passband cut-off frequency omegacSatisfy the requirement of
b. The width of the transition belt is not more than
The received baseband signal, y, being represented by x (n)0(n) denotes the communication signal separated from x (n), let ω be0-pi/2, then:
wherein ". sup" denotes a volumeAnd (4) performing product operation. After filtering the navigation signal, at [ -fs/2,fs/2]Only communication signals are within the frequency band of (a), and thus can be used for y0(n) 1/2 extraction yields:
wherein xp(m)＝x(2m-p)，hp(m) ═ h (2m + p). Will omega0Replacement by-pi/2 to omega1Pi/2, and the rest is kept unchanged, and the navigation signals separated in x (n) can be obtained by following the above process:
also 1/2 extraction is performed on the navigation signal, and the following can be obtained:
andcan be uniformly expressed in the following form:
due to the sampling frequency fsIs 2U times of communication or navigation frequency bandwidth BW/2, which is illustrated in
wherein z (l) ═ xp(m)·(-1)m*hp(m))|m＝UlCan be further expressed as:
where x isp,d(i)＝xp(Ui-d)，hp,d(i)＝hp(Ui+d)。
Based on the communication navigation signal separation method, the proposed signal separation process is shown in fig. 4, and the working process of the communication navigation signal separation module is divided into three steps: input weighting, filtering and post-processing, the workflow is introduced as follows:
a. input weighting: directly inputting data x (4n), x (4n +1), n is 0,1,2, … into the filter, and inputting data x (4n +2), x (4n +3), n is 0,1,2, … multiplied by-1 into the filter;
b. filtering: recombining h (N), N ═ 0,1, …, N-1 into the following 2U lines:
the row order is further adjusted as follows:
2U-1→2U→2U-3→2U-2→2U-5→2U-4→…→3→4→1→2
after the line order is adjusted, the N/(2U) column coefficients are respectively stored in the tap coefficient register groups corresponding to the N/(2U) multipliers of the filter. In addition, a data register group with the length of 2U is also respectively configured at the input end of each adder and used for storing intermediate calculation results. During the operation of the filter, the tap coefficient register set and the data register set are cyclically shifted once every time effective data is input.
c. And (3) post-treatment: the odd numbered values (1 st, 3 rd, … …) output by the filter are sent to the lower branch of the post-processing unit, and the even numbered values (2 nd, 4 th, … …) are sent to the upper branch. Each branch utilizes U input data to calculate an accumulation result, then the accumulation results of the two branches are weighted in parallel and then the radix-2 butterfly operation is executed to obtainAnd
Therefore, the separation process of the communication navigation signal is completed, and as the weighting of the input data and the data weighting in the post-processing unit can be realized by the subtracter and logic judgment, the main resource overhead of the communication and navigation signal separation device provided by the invention is as follows: the filtering module occupies N/(2U) multipliers and N/(2U) -1 adders, the post-processing module occupies 4 adders, and the total overhead is N/(2U) multipliers and N/(2U) +3 adders. And if h (n) pairs are directly utilizedAndfor parallel filtering, 2N multipliers and 2N-2 adders are required, and the resource overhead is about 4U times that of the scheme provided by the invention.
The working principle of the digital spectrum shifting module is explained in detail as follows:
the output communication of the signal separation module and the sampling frequency of the navigation signal are all changed into BW/2 which is 25MHz, however, residual frequency offset exists, the frequency offset of the communication and navigation signals needs to be eliminated through a digital frequency spectrum moving device, and then the signals are sent to corresponding modules for processing. The frequency offset analysis of the different signals is as follows:
carrier frequency of communication signal fcAfter the processing of the down-sampling and signal separation module, the residual frequency deviation of the signal is delta f0＝fc-1555+BW/2＝fc1542.5 MHz. Thus by calculationThe residual frequency offset in the communication signal may be eliminated.
The navigation signals comprise signals of two systems of a GPS system L1 frequency point and a Beidou system B1 frequency point, wherein the residual frequency offset of the GPS signals is delta f11575.42-1555-BW/2 7.92MHz, the residual frequency offset of the Beidou signal is delta f21561.098-1555-BW/2-6.402 MHz. Respectively calculate
min{1575.42-1.023-1561.098-2.046,1561.098-2.046-1555+1580-1575.42-1.023}＝7.609MHz
therefore, the pass band width of the low-pass filter can be set to 0.2 pi, and the width of the transition band does not exceed 0.5 pi. Note that the low pass filter transitions with large margins and therefore the filter order requirements are not high. As shown in fig. 5-1 and fig. 5-2, the 19 th order low pass filter based on the Kaiser window function can meet the design requirement, and the stop band attenuation capability reaches 80 dB.
Based on the above knowledge, the schematic diagram of the internal working principle of the digital spectrum moving module provided by the embodiment of the invention is shown in fig. 6, and is mainly used for calculation
In the embodiment of the invention, a radio frequency channel is used for simultaneously receiving communication and navigation signals, and in order to simultaneously ensure high-sensitivity reception of the communication and navigation signals, the transmitting power of the communication signals needs to be controlled, so that the power reaching the low-orbit micro-nano satellite receiving antenna is close to the power of the navigation signals, and the problem of inhibition of the communication signals on the amplification factor of the navigation signals can not occur when the communication signals and the navigation signals pass through a low-noise amplification module. Since the ground transmitting device knows the satellite ephemeris, the communication elevation angle α of the satellite relative to the ground device can be calculated in real time when the satellite passes the top, and in the embodiment of the present invention, the communication elevation angle is used to control the equivalent omnidirectional Radiated Power (ERIP) of the communication signal. First, when the satellite orbit height is h (in Km) and the elevation angle is α (in degrees), the communication distance between the satellite and the ground equipment can be expressed as:
where R ise6371Km denotes the earth radius. According to the free space propagation loss model, the signal propagation attenuation corresponding to the distance d is as follows:
Ls＝32.45+20lg(fc)+20lg(d)dB
wherein f isc(in MHz) represents the signal carrier frequency. With Er(in dBm) represents the signal strength, G, of the satellite receptionrDenotes the receive antenna gain, LrainRepresenting the extra link loss due to rainfall, moisture, etc., and representing the link margin, then sending the ERIP may be expressed as:
ERIP＝Er+Ls+Lrain-Gr+dBm
in this expression, ErSelecting signal intensity similar to navigation signal, and removing space propagation loss LsAll other variables are constant values. Due to LsDirectly affected by the transmission distance d, which is related to the communication elevation α, a correspondence between the transmission ERIP and the communication elevation α is established, the dashed line in FIG. 7 is denoted by Er＝-120dBm，Lrain＝0dB，Gr-5dB, 3dB, carrier frequency fc1540MHz, 500Km as an example, describes the relationship between the transmission ERIP and the elevation angle of the communication. To reduce the control complexity, in practical applications, the ERIP may be adjusted in steps when the elevation angle changes beyond a certain range, as shown by the step-like solid line in fig. 7.
It is noted that, in this document, relational terms such as "first" and "second," and the like, may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Also, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. In addition, "front", "rear", "left", "right", "upper" and "lower" in this document are referred to the placement states shown in the drawings.
Finally, it should be noted that: the above examples are only for illustrating the technical solutions of the present invention, and not for limiting the same; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.