A high-reliability multi-target real-time telemetry system

Abstract

The application relates to a high-reliability multi-target real-time telemetry system and belongs to the field of communication. Each target telemetry unit takes a data integration device as a core, is additionally provided with a spread spectrum telemetry unit or a frequency modulation telemetry unit according to respective working task requirements, selects different frequency points and pseudo code combinations, and forms respective communication links; the data integration device is provided with a data link port and can realize self-organizing networking between different target telemetry units; the spread spectrum telemetry unit adopts a PCM-CDMA-BPSK spread spectrum telemetry system, distinguishes target addresses through code types, and allows signals to be sent to use the same frequency band at the same time. The frequency modulation telemetry unit adopts a PCM-FM system and TPC coding, and the frequency points and the frequency points selected by the spread spectrum telemetry unit keep a reliable interval. The application solves the problems of single telemetry system, limited communication unit quantity, large link interference and limited space environment of a traditional spacecraft.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of communication and relates to a high-reliability multi-target real-time telemetry system. BACKGROUND

[0002] In a conventional space communication system, a specific communication system is mainly used to realize single-target tracking telemetry. In recent years, multi-target real-time telemetry technology has attracted widespread attention. Each target unit can work in parallel and interact with the ground platform in real time. Meanwhile, each target unit has networking capability, and data backup telemetry is realized through data sharing in the region. In the face of a new working scenario, the limitations of the traditional telemetry communication mode are highlighted:

[0003] a) The communication system is single and cannot adapt to multiple application scenarios;

[0004] b) Poor scalability, limited number of target units;

[0005] c) Serious electromagnetic interference, limited spectrum resources, and when multiple units work at the same time, the communication links interfere with each other, reducing signal transmission quality;

[0006] d) Affected by the space environment, when interference is introduced on the communication link or the arrow-ground antenna cannot be directly opposite, the communication will be temporarily interrupted, and the reliability is difficult to guarantee in a complex environment. SUMMARY

[0007] The technical problem solved by the application is: to solve the problems of single telemetry system of traditional spacecraft, limited number of communication units, large link interference, and limited space environment, a high-reliability multi-target real-time telemetry system is proposed.

[0008] The technical solution of the application is:

[0009] A high-reliability multi-target real-time telemetry system, each target telemetry unit takes a data integration device as the core, selects different frequency points and pseudo code combinations according to the respective work task requirements, and forms respective communication links;

[0010] The data integration device: has a data link port and can realize self-networking between different target telemetry units; is additionally provided with a spread spectrum telemetry unit or a frequency modulation telemetry unit to realize two kinds of telemetry systems; is responsible for collecting and summarizing the data of each target telemetry unit, and integrates and frames according to the frame format requirements, and after being modulated and amplified by the frequency modulation telemetry unit and the spread spectrum telemetry unit, is sent to the ground platform through the antenna feeder;

[0011] Spread spectrum telemetry unit: PCM-CDMA-BPSK spread spectrum telemetry system is adopted, the target address is distinguished by code type, and the signals allowed to be sent use the same frequency band at the same time; M typical frequency points are selected in the available frequency band, N groups of orthogonal pseudo-codes are selected for each frequency point, and at most MxN communication links are divided;

[0012] Frequency modulation telemetry unit: PCM-FM system is adopted, and TPC coding is adopted; the frequency points selected by the spread spectrum telemetry unit maintain reliable interval to avoid signal crosstalk; the reliable interval between frequency modulation signals is set to not less than 1+a times the signal bandwidth, and the reliable interval between spread spectrum signal frequency points is set to not less than 2 times the pseudo-code rate, wherein a is the modulation degree of the frequency modulation telemetry unit.

[0013] Preferably, the redundant transmission between each target telemetry unit is realized through the backup link.

[0014] Preferably, multiple target telemetry units are grouped according to the spatial distribution during design, internal information multicast communication is realized through short-distance networking in the group by data link, and the communication bandwidth is effectively utilized through TDMA; a network time reference is formed in the group, and time slot division is performed;

[0015] An external interaction node is periodically elected in each group to realize data communication between groups; based on the data link network, when a communication link is interfered or fails to be captured by the ground platform, the data of the target telemetry unit is broadcasted to the external interaction node in the group, and is transmitted to other groups with good communication through the external interaction node, and is further transmitted to the ground platform to realize data backup link transmission.

[0016] Preferably, the end-to-end mode is adopted for inter-group communication.

[0017] Preferably, the time slot includes a synchronization section, an information section and a protection section;

[0018] The synchronization section is used for frequency hopping synchronization search, the information section is used for sending telemetry data, and the protection section is used for data encryption field to realize protection transmission.

[0019] Preferably, the ground receiving station adopts a cross-correlation interference suppression algorithm, and first removes strong signals from strong signals, and then removes medium-strong signals from weak signals, and receives strong signals, medium-strong signals and weak signals in turn through three-stage demodulation.

[0020] Preferably, the inter-group node adopts a Doppler frequency offset compensation algorithm to ensure reliable synchronization between the data receiving end and the sending end in link communication, and the Doppler frequency offset compensation algorithm is as follows:

[0021] The data receiving end calculates the frequency offset of the received signal and the set frequency point:

[0022] f mS =f r -f0

[0023] Wherein, f mS is the frequency offset of the received signal, f r is the carrier frequency of the received signal, f0 is the set carrier frequency of the received signal;

[0024] According to the calculated frequency offset, the self-transmission frequency is adjusted, and the adjustment method is: the current carrier Doppler value is obtained from the receiving channel, and the compensation is calculated according to the set center frequency of the receiving and transmitting channels:

[0025]

[0026] Wherein, f mL is the compensation frequency offset of the return signal, f1 is the static carrier frequency of the return signal;

[0027] f out =f1-f mL

[0028] Wherein, f out is the actual transmission carrier frequency of the return signal.

[0029] Preferably, for the nodes in the group, on the one hand, a dynamic networking mode is designed at the network layer and the data link layer, so as to ensure the ordered transmission of information of each node and have corresponding network access and network exit strategies; on the other hand, a coherent frequency hopping technology is used at the physical layer to realize interference avoidance of high-rate signals, and has lower signal combination loss.

[0030] The beneficial effects of the present application compared with the prior art are:

[0031] The present application realizes code division multiple access by using CDMA, and can support real-time telemetry of data of multiple target telemetry units at the same time. Two communication systems of spread spectrum and frequency modulation are supported, each unit can adapt to high-speed communication demand and adapt to multiple application scenarios by adding a frequency modulation telemetry unit, and can improve anti-interference ability and realize high-reliability communication by adding a spread spectrum telemetry unit. When receiving multiple target data on the ground, a cross-correlation interference suppression algorithm is used to isolate strong interference signals and analyze target signals. Self-networking can be realized between target telemetry units, each target telemetry unit can transmit data to adjacent units to realize backup telemetry of key data, and the high reliability of data transmission in complex environments is ensured. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 Schematic diagram of multi-target telemetry system architecture;

[0033] Figure 2 Cross-correlation interference mitigation principle block diagram;

[0034] Figure 3 Time division multiple access (TDMA) structure;

[0035] Figure 4 Data telemetry schematic diagram. DETAILED DESCRIPTION

[0036] The application will be further described in conjunction with the embodiments.

[0037] To solve the above problems, the application provides a multi-target real-time telemetry system with high reliability. With the continuous increase in the number of communication targets, code division multiple access (CDMA) gradually becomes the research focus in the field of wireless communication. CDMA can realize multi-target simultaneous response under limited frequency band resources, effectively reduce link interference, and greatly increase the number of communication units. At the same time, by using direct sequence spread spectrum (DSSS), the processing gain is improved, and the anti-interference ability of communication is enhanced. In order to adapt to multi-scene application, combined with frequency modulation communication system, short distance high speed data transmission is realized. The units disturbed by the communication link can complete information forwarding through adjacent units to realize real-time communication with the outside, and have link backup capability.

[0038] Figure 1 The figure is a schematic diagram of a multi-target telemetry system architecture. In the multi-target real-time telemetry system, each target telemetry unit takes a data integration device as the core, selects different frequency points and pseudo code combinations according to the respective work task requirements, and forms its own communication link. The data integration device has a data link port, which can realize self-organizing network between different telemetry units for key data transmission. The spread spectrum telemetry unit or the frequency modulation telemetry unit is added to realize two kinds of telemetry systems. The data integration device is responsible for data collection and summarization, and integrates and frames according to the frame format requirements, and then sends the data to the ground platform through the antenna feeder.

[0039] The spread spectrum telemetry unit adopts PCM-CDMA-BPSK spread spectrum telemetry system. The target address is distinguished by code type, the signals allowed to be sent use the same frequency band at the same time, and the synchronization requirement is low. At the same time, the spread spectrum system has strong anti-interference and anti-fading ability, which can improve the communication reliability of the system. In the available frequency band, M typical frequency points are selected, N groups of orthogonal pseudo codes are selected for each frequency point, and at most MxN communication links are divided. By dividing in the frequency domain and code domain, the interference between links is reduced, which provides the possibility for reliable multi-unit real-time communication.

[0040] The frequency modulation telemetry unit adopts PCM-FM system, the modulation degree is a, and TPC coding is used to realize high-speed communication. The frequency points are selected to maintain a reliable interval with the spread spectrum link frequency points to avoid signal crosstalk. The reliable interval between frequency modulation signals is set to not less than 1+a times the signal bandwidth, and the reliable interval between spread spectrum signal frequency points is set to not less than 2 times the pseudo code rate.

[0041] Multiple telemetry signals exist in space at the same time. Due to the spatial distribution, the intensity of the signals transmitted to the same ground receiving station is different. The out-of-band interference of the strong signal has a certain impact on the reception of the weak signal. In order to further enhance the anti-interference of signal reception, the ground receiving station uses a cross-correlation interference suppression algorithm. The principle of the algorithm is: first, the strong signal is stripped from the medium-strong signal, and then the medium-strong signal is stripped from the weak signal, so that the strong signal, the medium-strong signal and the weak signal can be demodulated through three levels. The principle diagram of cross-correlation interference mitigation is shown in Figure 2 .

[0042] In order to improve the reliability of data transmission, the target telemetry unit can realize redundant transmission through the backup link to enhance the reliability of data transmission. The implementation of the backup link is based on ad hoc network technology.

[0043] A large number of communication units are divided into multiple groups according to the spatial distribution during design. The internal information multicast communication is realized through the data link short-distance networking in the group, and the communication bandwidth is effectively utilized through TDMA (Time Division Multiplexing). A network time reference is formed in the network, and time slots are divided. The time slot includes a synchronization section, an information section and a protection section. The synchronization section is used for frequency hopping synchronization search, the information section is used for sending telemetry data, and the protection section is used for data encryption field to realize protection transmission. As shown in Figure 3 .

[0044] Each group periodically elects an external interaction node to realize data communication between groups. The end-to-end mode is adopted for inter-group communication. Based on the data link network, when a communication link is disturbed or the ground platform fails to capture, the data of the communication unit can still be transmitted to the ground platform through the backup link. Taking Figure 4 for example, the wireless link between the A1 communication unit of group A and the ground platform is disturbed, and the data cannot be telemetered. However, the communication unit will broadcast the key data in the group, and further transmit it to group C through the external interaction node. Group C transmits the data to the ground platform through the normally working C6 node to realize data backup transmission.

[0045] For the nodes in the group, the number is large and the functions are different, and high-speed networking and reliable communication need to be realized at a high information rate. On the one hand, intelligent communication protocols and dynamic networking methods need to be designed in the network layer and the data link layer to ensure that the information of each node is transmitted in order and has the corresponding network entry and network exit strategy. On the other hand, the coherent frequency hopping technology is used in the physical layer to realize the interference avoidance of high-rate signals, and the signal combination loss is lower.

[0046] The dynamic networking method is as follows:

[0047] After each node enters the network, it periodically inquires the communication state of the surrounding nodes and elects an external interactive node. According to the information interaction between the nodes, each node calculates the shortest communication link to other nodes in the group, and realizes the data communication in the network. Time division multiplexing algorithm is used for communication scheduling, and the external interactive node can automatically adjust the time slot occupancy state of each node according to the traffic, thereby improving the time slot utilization rate of the whole system. With the change of space link, the external interactive node in the group can be dynamically replaced, and the communication link between each node in the group is updated, so as to ensure the reliability of data interaction.

[0048] For the nodes between groups, the signal transmission will produce dynamic Doppler frequency offset due to long transmission distance and large speed deviation, which will affect the synchronization of signal reception. The nodes between groups need to use Doppler frequency offset compensation algorithm to calculate the frequency difference between the received signal and the set frequency point, and adjust the transmission frequency according to the calculated frequency deviation, so as to ensure the reliable synchronization of the data receiving end and the sending end in the return link communication. The adjustment method is as follows:

[0049] When the nodes between groups communicate, the receiving end obtains the current carrier frequency from the receiving channel when receiving the signal; and determines the carrier frequency set in advance for the signal by analyzing the signal to obtain the station information of the current signal. The Doppler frequency offset value is calculated. Then, the receiving signal carrier frequency and the carrier frequency of the transmitted return signal are converted and compensated according to the pre-set, that is, the transmitted signal is compensated according to the specified multiple of the Doppler frequency offset of the received signal, so as to ensure that the return signal can be reliably synchronized and received.

[0050] Specifically, the Doppler frequency offset compensation algorithm is as follows:

[0051] The data receiving end calculates the frequency offset between the received signal and the set frequency point:

[0052] f mS =f r -f0

[0053] Wherein, f mS is the frequency offset of the received signal, f r is the carrier frequency of the received signal, and f0 is the set carrier frequency of the received signal;

[0054] Adjust the transmission frequency according to the calculated frequency offset, and the adjustment method is as follows: obtain the current carrier Doppler value from the receiving channel, and convert and compensate according to the center frequency of the set receiving and transmitting channel:

[0055]

[0056] Wherein, f mL is the compensation frequency offset of the return signal, and f1 is the static carrier frequency of the return signal;

[0057] f out= f1 - f mL

[0058] wherein f out is the actual transmitted carrier frequency of the return signal.

[0059] The data integration device comprises a data link interface, a spread spectrum telemetry unit, a frequency modulation telemetry unit, a waveguide, a baseband processing module, a data integration module and a power module. The data link interface can realize networking between target telemetry units and data sharing. The data integration module receives data of each target telemetry unit and other systems and performs summarization, and sends the data to the baseband processing module. The baseband processing module compiles the received telemetry data into frequency modulation telemetry frames and spread spectrum telemetry frames, sends the frequency modulation telemetry frames to the frequency modulation telemetry unit, and sends the spread spectrum telemetry frames to the spread spectrum telemetry unit. The frequency modulation telemetry unit and the spread spectrum telemetry unit modulate and amplify the frequency modulation telemetry frames and the spread spectrum telemetry frames, and transmit the telemetry data through the waveguide connected to the antenna. The device adopts integrated power distribution design, and the power module supplies power to the above-mentioned modules.

[0060] The contents not described in detail in the specification of the present application are known to those skilled in the art.

Claims

1. A high-reliability multi-target real-time telemetry system, characterized by: Each target telemetry unit takes the data integration device as the core, selects different frequency points and pseudo code combinations according to respective working task requirements, and forms respective communication links; The data integration device has a data link port and can realize self-organizing network between different target telemetry units; the spread spectrum telemetry unit and the frequency modulation telemetry unit are added, so that two kinds of telemetry systems are realized; the data integration device is responsible for collecting and summarizing data of each target telemetry unit, and performs integrated framing according to frame format requirements, and then transmits the data to the ground platform through the antenna feeder after modulation and amplification by the frequency modulation telemetry unit and the spread spectrum telemetry unit; The spread spectrum telemetry unit adopts PCM-CDMA-BPSK spread spectrum telemetry system, distinguishes target addresses through code types, and allows signals to be transmitted to use the same frequency band at the same time; M typical frequency points are selected in the available frequency band, and N groups of orthogonal pseudo codes are selected for each frequency point, so as to divide at most MxN communication links; The frequency modulation telemetry unit adopts PCM-FM system and adopts TPC coding; The frequency points selected by the spread spectrum telemetry unit and the frequency points maintain reliable intervals to avoid signal crosstalk; the reliable intervals between frequency modulation signals are set to be not less than 1+a times the signal bandwidth, and the reliable intervals between spread spectrum signal frequency points are set to be not less than 2 times the pseudo code rate, wherein a is the modulation degree of the frequency modulation telemetry unit.

2. The high-reliability multi-target real-time telemetry system according to claim 1, characterized in that: Redundant transmission is realized between each target telemetry unit through the backup link.

3. The high-reliability multi-target real-time telemetry system according to claim 1, wherein: When designing, multiple target telemetry units are grouped according to spatial distribution, internal information multicast communication is realized through data link short-distance networking in the group, and communication bandwidth is effectively utilized through TDMA; A network time reference is formed in the group, and time slots are divided; An external interaction node is periodically elected in each group to realize data communication between groups; When a communication link is interfered or fails to be captured by the ground platform, the data of the target telemetry unit corresponding to the communication link is broadcast to the external interaction node in the group, and then transmitted to other groups with good communication through the external interaction node, and then transmitted to the ground platform to realize data backup link transmission.

4. The high-reliability multi-target real-time telemetry system of claim 3, wherein: End-to-end mode is adopted for inter-group communication.

5. The high-reliability multi-target real-time telemetry system of claim 3, wherein: The time slot includes a synchronization section, an information section and a protection section; The synchronization section is used for frequency hopping synchronization search, the information section is used for transmitting telemetry data, and the protection section is used for data encryption field to realize protection transmission.

6. The high-reliability multi-target real-time telemetry system of claim 1, wherein: The ground receiving station adopts a cross-correlation interference suppression algorithm, first removes strong signals from strong signals, and then removes medium-strong signals from weak signals, and receives strong signals, medium-strong signals and weak signals in turn through three-level demodulation.

7. The high-reliability multi-target real-time telemetry system of claim 1, wherein: The inter-group node adopts a Doppler frequency offset compensation algorithm to ensure reliable synchronization between the data receiving end and the transmitting end in link communication, and the Doppler frequency offset compensation algorithm is as follows: The data receiving end calculates the frequency offset of the received signal and the set frequency point: f mS = f r -f0 wherein f mS is the frequency offset of the received signal, f r is the carrier frequency of the received signal, and f0is the set carrier frequency of the received signal. According to the calculated frequency offset, the transmitting frequency is adjusted, and the adjustment method is as follows: the current carrier Doppler value is obtained from the receiving channel, and the center frequency of the set receiving and transmitting channel is converted and compensated: wherein f mL is the frequency offset of the return signal, and f1is the static carrier frequency of the return signal. f out = f1 - f mL where f out is the actual transmitted carrier frequency of the return signal.

8. The high-reliability multi-target real-time telemetry system of claim 1, wherein: For the nodes in the group, on the one hand, the dynamic networking mode is designed at the network layer and the data link layer to ensure the ordered transmission of information of each node and the corresponding network access and network exit strategies; on the other hand, the coherent frequency hopping technology is adopted at the physical layer to realize the interference avoidance of high-rate signals and has lower signal combination loss.

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