Beidou navigation system is a satellite navigation system independently developed by China, featuring precise timing, short message communication and fast positioning. Aiming at the problems of large size of Beidou antenna and RF signal processing module, a portable terminal that communicates with Beidou module by using Bluetooth module is proposed. The system uses STM32F103RBT single-chip microcomputer as the core, and adds Bluetooth communication module between Beidou RF signal processing module and Beidou information processing module to realize the wireless interconnection of these two parts, thus solving the problem of inconvenience of Beidou terminal system.
0 Preface
Beidou Satellite Navigation System (BDS) is a self-developed, independent global satellite navigation system being implemented in China. It is committed to providing high-quality positioning, navigation and timing services to users around the world, and can provide it to authorized users with higher requirements. Further service, both military and civilian purposes.
China completed the Beidou satellite navigation test system with regional navigation function in 2003, and then began to build the Beidou satellite navigation system serving the whole world. Since 2012, it has officially provided services to most parts of Asia-Pacific, and plans to complete the global system by 2020. Construct.
In addition to acquiring time information and location information, the Beidou satellite navigation system is characterized by short message communication functions, enabling end users in the system coverage area to perform two-way communication, which is an innovation not found in other satellite navigation systems. Sexual function, featuring a combination of communication and navigation. At present, there are not many products on the market with Beidou satellite as the navigation system. Especially the civilian products are still in their infancy, so the huge potential market of Beidou related applications has yet to be explored and developed. The Beidou communication portable terminal based on the Bluetooth module proposed in this paper is also a positive attempt in the Beidou application market.
1 Introduction to Beidou Terminal System
Beidou navigation and positioning system is the same as other navigation and positioning systems. User application terminal equipment is always an important part of it. It is mainly responsible for completing Beidou information reception and realizing user-specific application requirements. Divided from the application objects of the satellite navigation terminal, the user application terminal usually includes a plurality of types, such as a handheld terminal, a vehicle-mounted terminal, a ship-mounted terminal, and an embedded terminal, and provides real-time navigation and positioning, message communication, and timing service. The main components are Beidou receiving antenna, Beidou RF signal processing module and Beidou baseband information analysis processing module, which complete the function of receiving, demodulating and data parsing of Beidou RF signal.
Beidou satellite communication uses BCD encoding long messages, and the length of each frame message is greater than 200 B/time. There are two main types of communication: one is the control command issued by the user terminal equipment to the Beidou space terminal; the other is the Beidou information data information sent back by the Beidou space terminal. The format of these communication data frames is as follows:
Frame header: The header of the control instruction contains the synchronization header and the instruction type, and the frame header of the received information data frame contains the synchronization header and the received information type; the frame length: indicates the data frame length; the source address: indicates the control instruction transmission address or Is the receiving information receiving address; the data frame content: including the control command communication application information or the information content of the received information frame; the check code: the control command data frame and the received information frame are verified by the checksum method, The XOR sum of the data before the check code is compared with the check code to check the correctness of the data frame.
2 system hardware module design
2.1 overall system design
The Beidou terminal system can be divided into Beidou RF signal processing module and Beidou user information analysis processing module. At present, the two parts on the market are mostly connected by wire, and the antenna and RF baseband part of the Beidou RF signal processing module are relatively large. If this part is combined with the Beidou user information analysis and processing module, there will be a practical application. A lot of inconvenience. In view of the current situation of this application, the Beidou terminal of this subject has added the Bluetooth communication function module in the RF signal processing part and the Beidou user information analysis processing part, and connected by Bluetooth wireless transmission mode, which greatly reduces the volume of the Beidou user information analysis processing module. It is easy for users to carry. Therefore, the Beidou terminal system designed in this thesis consists of Beidou RF signal processing module, Beidou user information analysis processing module and Bluetooth communication module. The overall structure of the system design The overall structure of the Beidou terminal is shown in Figure 1.
2.2 Beidou terminal RF signal processing module
The Beidou terminal RF signal demodulation receiver module is mainly responsible for receiving the Beidou RF information, conditioning and demodulation output from the Beidou space station.
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