The Design and Application of C-band Base Station Based Multi-target Telemetry Network System
Authors Shiwei, Guo; Zhongjie, Wang; Xin, Zhang; Zhaohui, Huo
Publisher International Foundation for Telemetering
Journal International Telemetering Conference Proceedings
Rights Copyright © held by the author; distribution rights International Foundation for Telemetering
Download date 03/10/2021 09:16:44
Link to Item http://hdl.handle.net/10150/631707 The Design and Application of C-band Base Station Based Multi-target Telemetry Network System
Guo Shiwei, Wang zhongjie, Zhang Xin, Huo Zhaohui, Chinese Flight Test Establishment Xi’an, Shaanxi Province, China, [email protected]
ABSTRACT
A C-band base station based multi-target telemetry network system for flight test is designed in this paper. The requirements of multi-target transmission are realized by TDMA and TDD technology. And the transmission rate of up to 50 Mbps is provided by the high efficient modulation method. An integrated air-to-ground telemetry network is built with C-band wireless two-way link. The telemetry signals of super large airspace are covered seamlessly through multiple base stations, therefore the shortage of current telemetry is solved, and the demand of multi-target and mass date transmission for flight test is satisfied. The development of the system provides technical support for the high speed data transmission of the flight test, which will lay a foundation for the construction of integrated air-to-ground test and the test network system.
INTRODUCTION
At present, the S-band and one-way point to point of PCM data stream transmission mode is adopted in the aviation flight test system. Limited by equipments and technologies, the maximum transmission rate of point to point mode is 20 Mbps. However, when the transmission rate exceeds 10 Mbps, there will be high bit error rate and poor demodulation performance in practice. The technology can only adapt to the test of single flight target, and cannot meet the requirements of new technology, new test demand and new test subject for data transmission, such as multi-machine cooperative test flight, large space area, super long distance, ultra low altitude and other subjects.
In view of the above problems, a C-band [1] base station based multi-target telemetry network system is designed in this paper. Many advanced technologies are used to solve the shortcomings of the current telemetry, improve the data transmission rate, realize the seamless coverage of the telemetry signal in the super large space, and meet the needs of the flight test telemetry for multi-target and mass data transmission.
OVERALL DESIGN OF THE MULTI-TARGET TELEMETRY NETWORK SYSTEM
At present, the single plane flight test is mainly carried out, and the airborne to the ground point to point transmission mode is adopted. In this paper the bidirectional C-band wireless network link is studied, which increases the transmission bandwidth while increasing the uplink transmission capacity. It can connect the test aircrafts, C-band ground base stations and the test area network to realize the information sharing. Based on this, we can also achieve multi-points to the one point, multi-points to multi-points networking modes. This way of transmission forms a telemetry network system of air-to-ground integration. As long as the bandwidth of the telemetry network system is allowed, it can easily increase the experimental objects.
The flight test is combined with the commercial communication base station technology, and the C-band base station network terminal is used as the carrier of the air and ground data transmission. Through the C-band base station network on the ground, the data of all the test machines can be imported into the ground data processing center. Fig.1 is an interactive diagram of the C-band base station telemetry network system.
Airborne Testing System
Airborne Network Terminal Bi-directional Transceiver C-band Airborne Antenna
Ground Base Station Network Base Station Network Terminal Bi-directional Transceiver C-band Ground Antenna
C-band Base Station Network
Figure 1 C-band base station telemetry network system
The airborne network terminal, two-way power amplifier and C-band airborne antenna are modified to the test aircraft. The C-band multi-planar array antenna, bidirectional power amplifier and base station network terminal are installed on the C-band broadband network base station. The switch is connected to the base station, so that all base stations can converge to the test data processing center through the ground optical fiber network. The network transmission links in the air and the ground are opened up, and the C-band base station deployment method is studied to carry out the comprehensive coverage test area and to construct the test network system of the air and ground integrated cross test area. In view of the compatibility with existing systems, agNET interface devices can be installed in airborne test systems, and then the PCM data stream of the airborne acquisition system is converted to the network output.
The network based distributed architecture has clear layers, reasonable topology and is easy extended, which can be compatible with the existing flight test system, as shown in Fig.2. Among them, the airborne test network system (aNET) includes data acquisition network, switch control network and data application network. The telemetry network system (TmNS) includes test objects, base station network management system, network transmission link and telemetry terminals. The ground data processing network (gNET) includes integrated network management system and data processing system. Data acquisition network Airborne test Switch control network network system Data application network
Airborne telemetry network terminal
Architecture of the Ground telemetry Base station network link network system network system Ground telemetry network terminal
Base station network management system
Ground data Integrated network management system processing network Data processing system
Figure 2 the architecture of the network system
CORE TECHNOLOGIES
The C-band base station based multi-target telemetry network system adopts high precision clock synchronization technology, telemetry network security authentication technology, data transmission encryption technology and space soft switching technology based on access terminal.
[1] The clock synchronization technology
Because the network system adopts TDMA [2] access mode, it is necessary to achieve high precision time synchronization when the test aircraft needs to enter the network and transmit data. Figure 3 is the time synchronization schematic. The ground time server calibrates its own time standard by receiving the time calibration information from the Beidou/GPS antenna. The server periodically sends the IEEE 1588 protocol packets to the aircraft in the network through the ground base station network, so as to realize the time unification of the entire telemetry network. At the same time, the aircrafts which are not in the network could calibrate airborne system time through the connection between its own Beidou/GPS antenna with the satellite. When the aircraft needs to enter the network, only time accuracy is unified so that it will not interfere with the normal network connection of the aircrafts which are in the network.
In the telemetry network system, the network precise clock synchronization protocol (IEEE 1588) is used to replace the traditional network time protocol (NTP), and the time synchronization of the telemetry network system is raised from millisecond to 100 microseconds to meet the high precision time synchronization requirements of the telemetry network in the simultaneous test flight of multiple aircrafts.
Beidou/GPS satellite
Wireless IEEE1588 network protocol link packet
Beidou antenna
Timer server Figure 3 time synchronization schematic
[2] The security authentication technology of the telemetry network system and the data transmission encryption technology
The telemetry network system is connected by base station telemetry network and ground telemetry data processing system. It has the characteristics of high openness, wide space, far distance and high power, so that the transmission information is easily stolen, tampered and inserted. Thus, the safety and authentication of telemetry network system is particularly important. The security authentication of telemetry network includes the identity authentication system and the data security.
The identity authentication system consists of three parts: the authentication server, the base station authentication terminal and the test aircraft authentication terminal, as shown in Figure 4. The authentication terminal of the test aircraft connects the application of authentication request to the device. The access request is sent through the request port of the authentication end of the aircraft. Authenticate the access request by using the authentication PAE of the base station authentication terminal. The authentication server is an entity that provides certification services for the authentication system, authenticates the requesting party, and then tells the authenticator whether the request is authorized or not.
The system uses link encryption and end-to-end encryption to ensure the security of the data. Link encryption uses high efficiency and high strength cryptographic algorithm specified by WLAN standard. After user access authentication is successful, it can be used for secure data transmission. End-to-end encryption is one way of encrypting data from one end to the other. The input and output terminals of the network terminal in the test machine and the base station each add a data encryption machine that is authenticated by secrecy to achieve high-level data encryption and decryption.
Wireless network link Test aircraft 2 authentication Test aircraft 1 terminal authentication terminal
Base station authentication terminal
Authentication server
Figure 4 Telemetry network security authentication systems
[3] The space soft switching technology
The C-band base station based multi-target telemetry network system uses the soft switching way. The process takes the access terminal as the leading factor and switches over the coverage edge area of two or more space base stations. Before interrupting the communication with the old base station, the connection is established with the new base station at which the access terminal receives the signal with the measurement information returned by the multiple space base stations. When the result satisfies certain conditions, the connection with the old base station is cut off, as shown in Figure 5. C-band base station Before
Switching
After
Figure 5 Schematic diagram of base station switching
The space soft switching technology is one of the key technologies of the space base station system. Its algorithms and the settings of the parameters directly affect the quality of service in the space information network.
TESTS AND RESULTS
[1] Single aircraft (transport plane / unmanned aerial vehicle) flight test
It mainly carries out functional verification of the C-band base station antenna system with single point to ground multi-points as well as the demonstration and verification of point to point transmission and network flight test. The function of automatic switching of the antenna, the long-distance transmission and networking function of network data link in real environment and its main technical indicators (the maximum distance, the uplink and downlink rate, the transmission delay, etc.) will also be verified.
[2] Simulation tests of two test aircrafts and a ground moving vehicle.
It mainly carries on the transmission and the networking test between three air points and one ground point. Their transmission function, dynamic switching and transmission performance of base station system are verified.
The results of the experiment are shown in Table 1.
Table 1 The results of the C-band base station basedmulti-target telemetry network system
Test contents Performance Test contents Performance Range 100km Synchronization <100 us (single station) precision Working band C band Downlink rate >50 Mbps Delay <200ms Uplink rate >3 Mbps
The test results show that the system can connect multi-point devices and communicate normally. The transmission range of a single base station is 100 km, the downlink transmission rate is greater than 50 Mbps, and the uplink transmission rate is greater than 3 Mbps. The average transmission delay of the network data is less than 200 ms, and the accuracy of time synchronization is less than 100 us.
CONCLUSIONS
In this paper, a C-band base station multi-target telemetry network system for flight test is designed, which can achieve high speed and safe transmission of flight test data, solve the contradiction between the current monitoring requirements and telemetry resources, and meet the mass transmission requirements of flight test.
TDMA and TDD [3] are used to achieve multi-target data transmission demand; OFDM [4] and QPSK [5] are adopted to improve spectrum utilization and expand transmission bandwidth; Security authentication technology is used to transfer the data safely; The C-band wireless two-way link is used to build an integrated air-to-ground telemetry network; and the seamless coverage of telemetry signals in super large airspace can be achieved through multiple base stations. The development of the system has laid the foundation for the construction of integrated test network system.
REFERENCES
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