CN109164468B - Integrated measurement communication method suitable for microsatellite multi-satellite formation - Google Patents
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Abstract
本发明公开了一种适用于微小卫星多卫编队的一体化测量通信方法，协议的物理层采用扩频体制，在两个正交的载波上分别建立PDCH和PMCH通道，并且定义了物理层传输帧，传输帧的长度固定、连续发送，并以传输帧的帧头作为特征信号，从而完成星间测距和时差测量。本发明确定了通信体制，对测距和时差测量方案做了兼容性改进，解决了卫星编队内部的相对测量、测控数据通信及其标准化问题；本发明不仅改进了时差测量方法，而且标准化了一种兼容时差测量、相对测距、数据通信的协议，该协议不仅可以满足星间测控的基本需求，而且还能拓展到卫星编队中使用，对于微小卫星多星编队有着巨大的应用价值。
The invention discloses an integrated measurement and communication method suitable for multi-satellite formations of microsatellites. The physical layer of the protocol adopts the spread spectrum system, respectively establishes PDCH and PMCH channels on two orthogonal carriers, and defines the transmission of the physical layer. The length of the transmission frame is fixed and continuously sent, and the frame header of the transmission frame is used as the characteristic signal, so as to complete the inter-satellite ranging and time difference measurement. The invention determines the communication system, improves the compatibility of ranging and time difference measurement schemes, and solves the problems of relative measurement, measurement and control data communication and standardization within the satellite formation; the invention not only improves the time difference measurement method, but also standardizes a It is a protocol compatible with time difference measurement, relative ranging, and data communication. This protocol can not only meet the basic needs of inter-satellite measurement and control, but also be extended to satellite formations. It has huge application value for multi-satellite formations of microsatellites.
Description
Technical Field
The invention belongs to the technical field of satellite communication and measurement and control, and particularly relates to an integrated measurement communication method suitable for microsatellite multi-satellite formation.
Background
The development of the formation of the satellite is in the transition period from double stars to multiple stars, and meanwhile, with the progress of the microminiature aerospace technology, the formation of the microminiature multiple stars is coming. The premise and the basis of cooperative work of satellite formation are that inter-satellite relative position sensing and formation time standards are unified, although a Global Positioning System (GPS) can provide positioning and timing services for satellite formation, compared with an inter-satellite RF link measurement method, the relative positioning and timing method based on the GPS has the disadvantages of low precision, complex measurement data processing, and the need of inter-satellite links to transmit resolving information, and therefore, in order to not be limited by the limitations of navigation systems such as the GPS and the like to adapt to the deep space exploration task of future satellite formation, the satellite formation must have two basic functions of autonomous relative position sensing based on the inter-satellite links and on-orbit real-time difference measurement.
However, at the present stage, although inter-satellite ranging and time difference measurement are already studied, because each research and development mechanism independently develops each inter-satellite measurement and control system, a set of complete protocol and technical standard is not formed, which results in poor generality among the systems and incapability of mutual compatibility, and restricts further development of micro-satellite formation to some extent. In addition, the current inter-satellite measurement and control system is almost based on a one-to-one topological structure, although time division multiplexing or frequency division multiplexing can enable the system to be directly transplanted to multi-satellite formation application, due to the fact that the satellite distance is long, the propagation delay is large, the time division multiplexing scheme is low in efficiency, and the real-time performance of measurement cannot be guaranteed; the frequency division multiplexing scheme puts high requirements on satellite resources and space frequency band resources, which is an unbearable overhead for microminiaturized satellites.
The current ranging scheme based on the inter-satellite link mainly has two modes of ranging signal forwarding and ranging signal opposite transmission, and although the mode of the ranging signal forwarding can avoid introducing reference frequency source noise of a forwarding satellite (Wang C, Zhou M C. novel Approach to inter-satellite Distance Measurement with High access [ J ]. Journal of guiding Control & Dynamics 2014,38(5):944 949.), the possibility of measuring the time difference of two satellites is lost; the ranging accuracy of the ranging signal transmission mode is relatively low, but the inter-satellite time difference measurement can be supported theoretically.
TWSTFT (Two-WaySatellite Time and Frequency Transfer) is a Time difference measurement method based on inter-satellite links (Li Y G, Li H X, Zhang H.reduction for the Two-way satellite Time and Frequency Transfer [ J ]. Acta Astronomica Sinica,2002,43(4):422 and 431.), and the method requires that each satellite is provided with a high-precision atomic clock, a 1pps pulse generator and a high-precision Time interval timer, and the three devices are not only expensive and violate the original purpose of low-cost microsatellites, but also have high energy consumption and cannot be used on microsatellites.
Disclosure of Invention
In view of the above, the invention provides an integrated measurement communication method suitable for microsatellite multi-satellite formation, the protocol determines a communication system, compatibility improvement is carried out on a distance measurement and time difference measurement scheme, and the problems of relative measurement, measurement and control data communication and standardization in the satellite formation are solved.
An integrated measurement communication method suitable for microsatellite multi-satellite formation simultaneously realizes multi-satellite relative ranging and multi-satellite in-orbit autonomous time difference measurement on a spread spectrum transponder, and comprises the following specific steps:
the transponders of the master satellite and the slave satellites both adopt a spread spectrum system, the distance measurement between the master satellite and the slave satellite adopts a two-way transmission ranging principle, and the measurement of propagation delay is realized by comparing the phase difference of a pseudo code ranging signal at the transmission and receiving moments of a characteristic signal, so that the inter-satellite distance is calculated; the precondition for measuring the time difference between the master satellite and the slave satellite is that the spread spectrum transponders and the clocks of the two satellites are driven by the same frequency source, the pseudo code phase of the transponder transmitter at the moment is generated by comparing the characteristic signals of the two parties, the transmitter pseudo code phase difference of the two satellite transmitters at the respective characteristic moment is obtained, and the calculation of the time difference of the two satellites is completed by using the precondition of the same frequency source.
The invention supports a one-to-many topological structure, namely, the topological structure comprises a master satellite and a plurality of slave satellites, multiple access is realized between the master satellite and the slave satellites through the orthogonality of spread spectrum pseudo codes, a link from the master satellite to the slave satellites is called a downlink, a reverse link is called an uplink, and the uplink and the downlink are subjected to frequency division.
Furthermore, the communication between the master satellite and the slave satellite relates to a physical layer and a data link layer, wherein the physical layer adopts a spread spectrum modulation mode, a pseudo code and a modulation data code element are coherent during modulation, namely the hopping time of the data code element is the starting time of a spread spectrum pseudo code sequence and satisfies Tb＝K×TPN，TbIs the duration of a data symbol, TPNIs the duration of one period of the pseudo code sequence, K being a positive integer.
Further, the physical layer involves two transmission channels: the device comprises a physical layer measuring channel and a physical layer data channel, wherein original code streams of the two channels are respectively modulated by orthogonal carrier waves after scrambling and spreading.
Further, the transmission frame length of the physical layer is fixed and continuously transmitted without interval, and the transmission frame is composed of the following parts:
the length of the head of the transmission frame is 1 byte, the code word is 8Bh, the code word is a delimiter of each transmission frame, and the starting moment of the head of the frame is a characteristic signal of distance measurement and time difference measurement;
a transmission frame information area with the length of 1 byte, wherein the high four bits are marked with the version of the transmission frame, and the low four bits are the source address;
a transmission frame counting area with the length of 1 byte and the cycle of 0-255, wherein 1 is added to each transmission frame;
a transmission frame loading region for loading several data packets (including pseudo code phase and satellite measurement and control data), the length of the loading region is LLOADByte:
wherein: l isTOTIs the total length of the transmission frame, in bits,
represents rounding down;
a transmission frame check area is filled with 8-bit CRC check codes and occupies 1 byte;
a transmission frame filling region of a length L of a consecutive 1 sequenceGP＝LTOT-8×(LLOAD+4) in bits for adjusting the transmission frame length.
Furthermore, the data link layer adopts short and fixed-length data packets, and each data packet consists of a data packet header and a data packet content area; the length of the data packet content area is 4 bytes, and the data packet content area bears the content to be transmitted; the length of the data packet head is 1 byte, the high four bits are destination addresses, and the low four bits are packet types, wherein the packet types are divided into the following types:
the time difference measurement data packet is loaded with a time difference measurement code;
the ranging data packet is loaded with ranging codes;
signaling data packet, loading signaling;
a user data packet 1 for loading a first data packet of user data;
a user data packet 2 for loading an intermediate data packet of user data;
the user data packet 3 is a last data packet of user data.
Further, the distance measurement and time difference measurement between the master satellite and the slave satellite are carried out as follows:
(1) sampling the pseudo code phase of a downlink transmission frame from the head moment of the satellite uplink transmission frame, and filling the pseudo code phase into an uplink transmission frame load area;
(2) the main satellite samples the pseudo code phase of the uplink transmission frame at the head moment of the downlink transmission frame and fills the pseudo code phase into a load area of the downlink transmission frame;
(3) the main satellite samples the pseudo code phase of the downlink transmission frame at the head moment of the uplink transmission frame, and obtains the pseudo code phase from the load area of the uplink transmission frame, thereby solving the space between the two satellites;
(4) the slave satellite analyzes the packet head of the data packet in the load area of the downlink transmission frame, and if the address is matched with the slave satellite, the pseudo code phase of the master satellite is obtained from the load area of the downlink transmission frame, so that the time difference between the two satellites is calculated;
the distance between two satellites is K (pseudo code phase obtained by sampling of the main satellite-pseudo code phase obtained by the main satellite from an uplink transmission frame load area)/2, K is LC, and C is the speed of light in vacuum;
the difference between two stars is L (pseudo code phase obtained from star sampling-pseudo code phase obtained from star from load region of downlink transmission frame)/2, L is 1/(2 pi f)1)，f1The frequency of the pseudo code phase.
The integrated measurement communication protocol not only improves the time difference measurement method, but also standardizes a protocol compatible with time difference measurement, relative distance measurement and data communication, can meet the basic requirements of inter-satellite measurement and control, can be expanded to be used in satellite formation, and has great application value for multi-satellite formation of microsatellites.
Drawings
Fig. 1 is a schematic diagram of a topology of satellite multi-satellite formation.
Fig. 2 is a diagram illustrating physical layer modulation of a communication protocol according to the present invention.
Fig. 3 is a diagram illustrating a format of a transmission frame in a communication protocol according to the present invention.
Fig. 4 is a schematic diagram of a communication protocol layer model according to the present invention.
Fig. 5 is a schematic diagram illustrating the ranging principle of the communication protocol of the present invention.
Fig. 6 is a schematic diagram illustrating the time difference measurement principle of the communication protocol of the present invention.
FIG. 7 is a data transmission flow diagram of the communication protocol of the present invention.
Fig. 8 is a diagram illustrating DCP retransmission state transition in a communication protocol according to the present invention.
Detailed Description
In order to more specifically describe the present invention, the following detailed description is provided for the technical solution of the present invention with reference to the accompanying drawings and the specific embodiments.
In the multi-satellite measurement and communication integrated protocol, transponders of a master satellite and a slave satellite both adopt a spread spectrum system; the distance measurement adopts a two-way opposite-transmitting distance measurement principle, and the measurement of the propagation delay is realized by comparing the phase difference of the pseudo code distance measurement signal at the transmitting and receiving moments of the characteristic signal, so that the inter-satellite distance is calculated; the precondition of time difference measurement is that the spread spectrum transponder of the satellite and the clock of the satellite are both driven by the same frequency source, the pseudo code phase of the transponder transmitter at the moment is generated by comparing the characteristic signals of the two parties, the transmitter pseudo code phase difference of the two satellite transmitters at the respective characteristic moment is obtained, and the solution of the two-satellite time difference is completed by using the precondition of the same frequency source.
The communication protocol supports a one-to-many topology structure which comprises a master satellite and a plurality of slave satellites, as shown in figure 1, the protocol realizes multiple access through orthogonality of spread spectrum pseudo codes, a link from the master satellite to the slave satellites is called as a downlink, a reverse link is called as an uplink, and the uplink and the downlink are subjected to frequency division.
The communication protocol of the invention relates to a physical layer and a data link layer, wherein the physical layer adopts a spread spectrum modulation mode, and a pseudo code and a modulation data code element are coherent during modulation, namely the hopping time of the data code element is the starting time of a spread spectrum pseudo code sequence and satisfies the relation Tb＝K·TPN，TbIs a data symbolDuration of (D), TPNIs the duration of one period of the pseudo code sequence, K being a positive integer.
The physical layer of the communication protocol of the present invention involves two transmission channels: a physical layer measurement channel (PMCH) and a physical layer data channel (PDCH), where original code streams of the two channels are modulated by orthogonal carriers after scrambling and spreading, respectively, as shown in fig. 2.
The transmission frame length of the physical layer of the communication protocol of the invention is fixed and continuously sent without interval, fig. 3 shows a format schematic that the transmission frame length is 400 bits, and the transmission frame is composed of the following parts:
(1) the length of a transmission frame header (DELI) is 1 byte, the code word is 8Bh, the transmission frame header is a delimiter of each frame, and the starting time of the frame header is a characteristic signal for distance measurement and time difference measurement;
(2) a transmission frame information area (INFO) with the length of 1 byte, wherein the upper four bits are marked with the version of the transmission frame, and the lower four bits represent the original address;
(3) a transmission frame counting area (CNT) with the length of 1 byte and the cycle of 0-255, wherein one is added to each transmission frame;
(4) a LOAD area (LOAD) for carrying several data packets, the length of the LOAD area is LLOADByte:
in the formula: l isTOTThe total length of the transmission frame, in bits,
represents a maximum integer no greater than α;
(5) a transmission frame Check Region (CRC) which adopts 8-bit CRC check and occupies one byte;
(6) a transmission frame padding (GP) of a consecutive 1 sequence of length LGP＝LTOT-8×(LLOAD+4), unit bit, for adjusting the transmission frame length.
The data link layer of the communication protocol of the invention adopts short and fixed-length data Packets (PACK), and the data packets are composed of the following parts:
(1) the length of the data packet header is 1 byte, the high four bits represent a destination address, and the low four bits represent a packet type, wherein the packet types are divided into the following types:
a. time difference measurement data packet: loading time difference measuring codes;
b. a ranging data packet: loading a ranging code;
c. signaling data packet: loading signaling;
d. user data packet 1: loading a first data packet of user data;
e. user data packet 2: loading an intermediate data packet of user data;
f. user data packet 3: loading a tail data packet of the user data;
wherein a and b are collectively called as a measurement data packet (MCP), d-f are collectively called as a user data packet (DCP), and a signaling data packet (SCP) is self-classified; the data type is represented by 4 bits, there are 16 combinations, the above only relates to 6 types, and the remaining types are defined as reserved types.
(2) The data packet content area is 4 bytes in length and bears the content to be transmitted; the length of the data packet is determined by the resolution of the pseudo-code based ranging system if the pseudo-code chip rate is fCP5.115MCPS, one Gold code period contains NGEach pseudo code chip, the length of the chip counter y being log2NGIn-chip phase is represented by x-bit binary number, symbol counter in transmission frame is represented by z-bit binary number, and ranging code minimum resolution dminComprises the following steps:
in the formula: c represents the speed of light, the maximum unambiguous distance d of the range findingmaxComprises the following steps:
range finder based on spread spectrum pseudo codeThe degree is typically in centimeters, so when x is 14, the ranging resolution d isminCan reach 0.0036 m; if N is presentG1023, K1, the packet content area length is 4 bytes, i.e. x + y + z + log2K is 32, the maximum unambiguous distance is 7680 km, and most distance measurement requirements can be met. Under the above conditions, the minimum resolution t of the time difference measurementminAnd maximum unambiguous time difference tmaxRespectively as follows:
the time difference measurement accuracy is generally several tens of picoseconds, so when x is 22, the time difference measurement resolution tmaxThe time difference can reach 0.046 picosecond, and the maximum unambiguous time difference is 100 microseconds; increasing the length of the z field can increase the unambiguous distance or the unambiguous time difference, but the minimum ranging resolution and the time difference resolution will increase, in practical application, the protocol can increase a plurality of packet types to be compatible with different values of x, y, z and K, thereby meeting the requirements of various application scenarios.
The PMCH in the communication protocol of the invention preferentially bears MCP and SCP, if bandwidth is vacant, DCP can be transmitted simultaneously, if the current DCP transmitting capacity is larger, the PDCH is opened temporarily for DCP data transmission; generally speaking, in order to ensure the measurement accuracy, only one path of PMCH is activated from the satellite transmitter, and the SCP and the DCP are multiplexed in the PMCH.
The layered model of the communication protocol of the invention is shown in fig. 4, and the data link layer is respectively composed of an MAC sublayer, an RTM sublayer, an MSC sublayer and a DPM sublayer. The MAC sublayer is responsible for power control and generating and processing signaling; the RTM layer resolves the satellite time difference and the inter-satellite distance through the pseudo code phase information of the physical layer and the information contained in the MCP; the role of the MSC sublayer is to check the correctness of the transmission frame and add necessary information of the transmission frame except the PACK; the DPM sublayer distributes PACK to different sublayers and provides reliability guarantees for DCP, and in addition, this layer is responsible for PACK to PMCH and PDCH mapping work. In fig. 4, arrow A, B is a serial data flow, arrows C, D, E, F represent various types of PACKs, arrow I represents a control and feedback interface of physical layer work, arrow H represents a physical layer measurement phase acquisition interface, and arrow G represents an interface of a multi-satellite measurement and communication integration protocol and an upper layer system.
The communication protocol defines the starting time of the frame head of the transmission frame as the characteristic time, the relative distance measurement principle is shown in figure 5, and the characteristic time (t) of the slave satellite at the transmitter is measured during the distance measurement1) The pseudo code phase of the receiver is sampled and defined as the ranging code, which is recorded as
Characteristic time (t) of the main satellite at the receiver2) The pseudo code phase of the transmitter is sampled and defined as the ranging code, denoted as phiA(t2) T is the propagation delay of Δ t from the satellite transmission frame to the master satellite2＝t1+ Δ t, then φA(t2)＝φA(t1+ Δ t). Because the propagation delay of delta t is also passed by the transmission frame of the slave satellite to the master satellite, the ranging code phase sampled by the slave satellite receiver can be replaced by the ranging code phase before delta t of the master satellite, and then
Will phiA(t2) And
and performing difference and dividing the difference by the frequency f of the ranging code to obtain:
therefore, only by measuring from stars
Then, the mixture is mixed with
And the propagation delay can be obtained by the main satellite after the main satellite sends the propagation delay back, and the inter-satellite distance is calculated according to the light speed.
The time difference measurement principle of the communication protocol of the present invention is shown in fig. 6, and the preconditions of the time difference measurement are as follows: the pseudo code of the spread spectrum transponder is coherent with the modulated data symbols and the transponder is co-located with the satellite clock. The time difference measurement comprises the following steps:
(1) characteristic time t of main satellite at transmitter1The pseudo code phase of the receiver is sampled and defined as the time difference measurement code, recorded as
Where the superscript Rx represents the receiver and the subscript 1 represents the primary star. Because the code element is coherent with the pseudo code sequence, the time difference measuring code phase of the transmitter of the characteristic time method is zero; at the same time, the slave satellite is also at the characteristic time t of the transmitter2Sampling the pseudo-code phase of the receiver to obtain a time difference measurement code from the satellite
(2) Master satellite will time difference measuring code
And sending to the slave star.
(3) Obtained from demodulation of stars
Because the uplink and downlink are symmetrical, the propagation delay of signals in uplink and downlink is equal, the delay is marked as delta t, and then the time difference measuring code of the receiving time of the master satellite can be replaced by the sending time of the slave satellite:
the time difference measurement code of the time of reception from the star can be replaced by the time of transmission from the master star similarly:
and (3) subtracting the time difference measuring code, recording the time difference as delta phi, and simplifying to obtain:
in the formula: f. of1For the frequency of the time difference measurement code, Δ Φ actually represents the phase difference between the characteristic time of the respective transmitter of the two satellites and the time difference measurement code of the opposite transmitter, and the satellite transmitter and the satellite clock are driven by the same crystal oscillator, so that the satellite clock and the time difference measurement code of the transmitter are correlated, then Δ Φ can also be used to represent the clock face time difference Δ T of the respective characteristic time of the two satellites, that is:
the data transmission flow of the communication protocol of the present invention is shown in fig. 7, in which the dotted line boxes represent four sublayers in the data link layer, the RTM sublayer and the MAC sublayer generate and process corresponding PACKs, while the processing flows of the DPM sublayer and the MSC sublayer at the time of transmission and reception need to be described specifically, the left half is the processing flow of the transmitting end, and the right half is the processing flow of the receiving end.
The sending end processing flow is as follows:
t1: the user data packet (DCP) is stored in the buffer memory in the DPM sublayer and is sent according to the first-in first-out sequence.
T2: and when the LOAD has a vacancy, extracting a corresponding amount of DCP from the buffer to LOAD the DCP into the LOAD.
T3: the DPM sublayer sends the LOAD to the MSC sublayer, the MSC sublayer calculates CRC check information of the transmission frame at first, and then adds a frame header, frame information, frame counting, CRC, filling data and the like before and after the LOAD according to a frame format, so that the frame and the LOAD form a complete transmission frame.
T4: the MSC sublayer then maps the transmission frames carrying the measurement information into the PMCH in the form of a bitstream, and maps the transmission frames carrying only user data into the PDCH in the form of a bitstream.
T5: the physical layer then scrambles, spread-spectrum modulates, and then mixes the PDCH and PMCH bit streams for transmission.
The receiving end processing flow is as follows:
r1: the physical layer despreads the signal and extracts the original received data stream.
R2: and the MSC sublayer searches the head of the transmission frame to complete the frame synchronization of the data stream, performs CRC (cyclic redundancy check) on the transmission data, continues the R3 step if the CRC is successful, and discards the transmission frame if the CRC is not successful.
R3: the MSC sublayer extracts the frame information, frame count and data packets and submits them to the DPM sublayer.
R4: and the DPM sublayer distributes data packets of corresponding types to the RTM sublayer, the MAC sublayer and the DCP guarantee module according to the types of the PACKs.
R5: the reliability guarantee module takes the continuity of transmission frames as a standard, if the received CNTs are continuous, the DCP transmission is reliable, otherwise, the DCP reliability guarantee module informs the MAC sublayer to generate a corresponding signaling request for retransmission.
The DCP reliability guarantee state transition process is as shown in fig. 8, and is similar to a backoff N-ARQ mechanism, where a sending end firstly sends all DCPs at one time, and then listens to the feedback result of the other party, and if the feedback result is not received within a specified time, the DCP is completely retransmitted; if the received feedback result is x, retransmitting from the xth transmission frame, if x is the total number of DCP transmission, indicating that the DCP transmission is correct, returning to the idle state again, and waiting for the next DCP transmission task.
The embodiments described above are presented to enable a person having ordinary skill in the art to make and use the invention. It will be readily apparent to those skilled in the art that various modifications to the above-described embodiments may be made, and the generic principles defined herein may be applied to other embodiments without the use of inventive faculty. Therefore, the present invention is not limited to the above embodiments, and those skilled in the art should make improvements and modifications to the present invention based on the disclosure of the present invention within the protection scope of the present invention.
Claims (6)
1. An integrated measurement communication method suitable for microsatellite multi-satellite formation realizes multi-satellite relative ranging and multi-satellite in-orbit autonomous time difference measurement on a spread spectrum transponder simultaneously, and is characterized in that:
the transponders of the master satellite and the slave satellites both adopt a spread spectrum system, the distance measurement between the master satellite and the slave satellite adopts a two-way transmission ranging principle, and the measurement of propagation delay is realized by comparing the phase difference of a pseudo code ranging signal at the transmission and receiving moments of a characteristic signal, so that the inter-satellite distance is calculated; the precondition for measuring the time difference between the master satellite and the slave satellite is that the spread spectrum transponders and the clocks of the two satellites are both driven by the same frequency source, the pseudo code phase of the transponder transmitter at the moment is generated by comparing the characteristic signals of the two parties, the transmitter pseudo code phase difference of the two satellite transmitters at the respective characteristic moment is obtained, and the calculation of the two-satellite time difference is completed by using the precondition of the same frequency source;
the distance measurement and time difference measurement between the master satellite and the slave satellite are carried out as follows:
(1) sampling the pseudo code phase of a downlink transmission frame from the head moment of the satellite uplink transmission frame, and filling the pseudo code phase into an uplink transmission frame load area;
(2) the main satellite samples the pseudo code phase of the uplink transmission frame at the head moment of the downlink transmission frame and fills the pseudo code phase into a load area of the downlink transmission frame;
(3) the main satellite samples the pseudo code phase of the downlink transmission frame at the head moment of the uplink transmission frame, and obtains the pseudo code phase from the load area of the uplink transmission frame, thereby solving the space between the two satellites;
(4) the slave satellite analyzes the packet head of the data packet in the load area of the downlink transmission frame, and if the address is matched with the slave satellite, the pseudo code phase of the master satellite is obtained from the load area of the downlink transmission frame, so that the time difference between the two satellites is calculated;
the distance between two satellites is K (pseudo code phase obtained by sampling of the main satellite-pseudo code phase obtained by the main satellite from an uplink transmission frame load area)/2, K is LC, and C is the speed of light in vacuum;
the difference between two stars is L (pseudo code phase obtained from star sampling-pseudo code phase obtained from star from load region of downlink transmission frame)/2, L is 1/(2 pi f)1)，f1The frequency of the pseudo code phase.
2. The integrated measurement communication method according to claim 1, characterized in that: the system supports a one-to-many topological structure, namely, the system comprises a master satellite and a plurality of slave satellites, multiple access is realized between the master satellite and the slave satellites through orthogonality of spread spectrum pseudo codes, a link from the master satellite to the slave satellites is called a downlink, a reverse link is called an uplink, and the uplink and the downlink are subjected to frequency division.
3. The integrated measurement communication method according to claim 1, characterized in that: the communication between the master satellite and the slave satellite relates to a physical layer and a data link layer, wherein the physical layer adopts a spread spectrum modulation mode, a pseudo code and a modulation data code element are coherent during modulation, namely the hopping time of the data code element is the starting time of a spread spectrum pseudo code sequence and satisfies Tb＝K×TPN，TbIs the duration of a data symbol, TPNIs the duration of one period of the pseudo code sequence, K being a positive integer.
4. The integrated measurement communication method according to claim 3, characterized in that: the physical layer involves two transmission channels: the device comprises a physical layer measuring channel and a physical layer data channel, wherein original code streams of the two channels are respectively modulated by orthogonal carrier waves after scrambling and spreading.
5. The integrated measurement communication method according to claim 3, characterized in that: the transmission frame length of the physical layer is fixed and continuously sent without interval, and the transmission frame consists of the following parts:
the length of the head of the transmission frame is 1 byte, the code word is 8Bh, the code word is a delimiter of each transmission frame, and the starting moment of the head of the frame is a characteristic signal of distance measurement and time difference measurement;
a transmission frame information area with the length of 1 byte, wherein the high four bits are marked with the version of the transmission frame, and the low four bits are the source address;
a transmission frame counting area with the length of 1 byte and the cycle of 0-255, wherein 1 is added to each transmission frame;
a transmission frame loading region for loading several data packets, the length of the loading region is LLOADByte:
wherein: l isTOTIs the total length of the transmission frame, in bits,
represents rounding down;
a transmission frame check area is filled with 8-bit CRC check codes and occupies 1 byte;
a transmission frame filling region of a length L of a consecutive 1 sequenceGP＝LTOT-8×(LLOAD+4) in bits for adjusting the transmission frame length.
6. The integrated measurement communication method according to claim 3, characterized in that: the data link layer adopts short and fixed-length data packets, and each data packet consists of a data packet header and a data packet content area; the length of the data packet content area is 4 bytes, and the data packet content area bears the content to be transmitted; the length of the data packet head is 1 byte, the high four bits are destination addresses, and the low four bits are packet types, wherein the packet types are divided into the following types:
the time difference measurement data packet is loaded with a time difference measurement code;
the ranging data packet is loaded with ranging codes;
signaling data packet, loading signaling;
a user data packet 1 for loading a first data packet of user data;
a user data packet 2 for loading an intermediate data packet of user data;
the user data packet 3 is a last data packet of user data.
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