A Beidou/GPS positioning module solution with independent intellectual property rights chips as the core is proposed. It uses a highly integrated radio frequency chip and a low-power navigation baseband processor. It can receive Beidou and GPS signals at the same time to achieve high -precision positioning, speed measurement and timing, fully compatible with GPS modules, very suitable for civil navigation application environments.
On December 27, 2021, the Chinese government announced to the world that the Beidou Navigation Satellite System (BDS) will officially provide high-quality all-weather navigation, positioning, timing and speed measurement services to the Asia-Pacific region for free from now on [1]. The Beidou system is an independently developed and independently operated global satellite navigation system that is being implemented in my country. It is planned to be fully completed in 2020. It will cooperate with the United States’ Global Positioning System (GPS ), Russia’s GLONASS, and Europe’s Galileo satellite navigation system. (Gali-leo) has been identified as the world’s four major satellite navigation systems by the International Committee on Global Navigation Satellite Systems (ICG).
Our country is accelerating the construction of the Beidou satellite navigation system, and is gradually transitioning to a service system in which Beidou satellite navigation is compatible with other satellite navigation systems for important industries and fields involving the national economy and public security. Foreign companies use their Accumulated advantages in technology, products and brands in the field of GPS to compete for the Chinese market [2]. To complete the promotion and application of Beidou in the field of national economic security and the rapid promotion in the mass market in a relatively short period of time, the first step is to design a receiver chip with core independent intellectual property rights [3]; the second step is to quickly launch pin size compatible, The Beidou module with compatible interface protocol, comparable power consumption and affordable price can replace the GPS module in situ.
1. Overview of the development of foreign GPS chips
GPS modules have grown with the development of GPS chips. The chip is one of the key parts of the GPS module. The quality of the chip determines the performance of the GPS product to a large extent. The block diagram of a typical GPS module [ 4] is shown in Figure 1.
LNA detects and processes GPS radio frequency signals, and the RF front-end downconverts the GHz satellite signal to an intermediate frequency that can be processed by digital circuits; the GPS engine is used to process GPS intermediate frequency signals, and ROM and Flash store the embedded GPS. Software code, cooperates with GPS engine to search and Tracking the GPS satellite signal, the CPU solves the user coordinates and speed.
The GPS module can be divided into three parts: RF unit, engine unit and CPU processing unit. The development of GPS chips is the process of integrating these three units.
First generation: 1990s, 3-stage design, low integration, the three parts of the circuit are discrete chips, as shown in each module in Figure 1;
Second generation: late 20th century, 2-stage design, LNA, filter, mixer, frequency synthesizer and oscillator are integrated into one RF chip; baseband processing integrates engine, CPU, memory, power management and clock, etc. [5]; shown as the dotted line in Figure 1.Third generation: In the early 21st century, SOC design, from RF to digital baseband processing, is integrated into a single chip [6], requiring only simple peripherals
The GPS module design can be completed using software and more functions are integrated, as shown in Figure 1.
At present, the fourth generation of GPS chips is being developed abroad, which are developing in the direction of small size, high sensitivity, low power consumption, multi-mode (compatible with navigation systems such as Galileo), and A-GPS, and are highly integrated with a variety of applications, as shown in the outer frame of Figure 1 It shows that software processing is developing in the direction of weak signal capture, high dynamics, indoor positioning, etc., and the size of terminal products is becoming increasingly lighter, thinner and smaller. The Beidou module dedicated chip mainly includes radio frequency and baseband signal processing chips, which constitute the core component of the Beidou module. Currently, about 10 companies in mainland China have Beidou chip and module design and R&D capabilities.
Domestic positioning modules have gone through three main stages of development: all imported, gradually achieving partial independent design, and finally achieving independent integrated design of the entire machine. The domestic Beidou chip architecture has also experienced these three main development stages:
The first stage: foreign commercial RF chip FPGA general processor; the chip design is in the prototype stage. The Beidou module has extremely high volume, power consumption and cost, and can only be used for specific industry users and cannot be commercialized on a large scale[7];
The second stage: domestic radio frequency chip domestic engine general processor; similar to the second generation GPS chip [8];
The third stage: domestic radio frequency chip domestic baseband processor; similar to the third generation GPS chip.
Beidou’s biggest advantage lies in its independent property rights. Foreign companies are unable to obtain the key algorithms and technical parameters of Beidou navigation and positioning, which objectively constitutes a technical barrier to foreign-invested companies. It is unrealistic and equivalent to giving up core technology dominance to expect foreign countries to provide relevant core chips. Therefore, Beidou’s core technologies such as chips and core algorithms can only be developed independently.
At present, several domestic companies have been involved in the research and development of Beidou RF chips, such as Guangzhou Runxin, Xi’an Huaxun, Beijing Guangjia, etc. Guangzhou Runxin, Xi’an Huaxun and Southwest Integration have done well in commercial- scale applications. The main manufacturers of Beidou baseband chips include Higer Communications, Hexinxingtong, Xi’an Huaxun, Dongguan Taidou, Dongguan United Star and other companies. The technical level of my country’s Beidou components has achieved independent integrated design. At present, domestic Beidou multi-mode solutions are still mainly based on radio frequency baseband application processor solutions, and ASIC solutions with integrated processors in the baseband have emerged. As the Beidou system gradually improves, the performance gap between chips produced by domestic enterprises and research institutions and foreign products is gradually narrowing. Although HeZhongStrong’s UGB-2PT module is less sensitive, its price of 199 yuan is already comparable to that of a GPS module; Taiwanese companies have also designed Beidou/GPS modules using MediaTek’s MT3332/3333 chips.
2. Design and implementation of Beidou/GPS positioning module
If Beidou wants to expand into the civilian field and fully compete with GPS, it will inevitably be compatible with GPS. The use of the Beidou module to replace the original GPS module must not affect the user experience or change the original usage habits, that is , the upgrade and replacement of the positioning module must be transparent to users. This requires that the Beidou module must be compatible with the GPS module in terms of physical size, interface protocol, etc., and its power consumption and cost must be comparable to the GPS module to be competitive. After inspecting the technical level and supply situation of the main suppliers of Beidou chips, it was determined that the Beidou module adopts a two-stage architecture. The detailed design is as follows.
1) Beidou module block diagram
The Beidou module is mainly composed of Beidou (B1)/GPS (L1) radio frequency front-end chip and baseband processing chip. The satellite signal is amplified by the LNA inside the B1L1 active antenna, and the satellite signal is converted into an intermediate frequency signal suitable for AD sampling through the B1L1 radio frequency front end; The internal AD sampling unit of the RF front-end digitally outputs the analog intermediate frequency signal to the baseband chip. The baseband chip completes satellite signal acquisition, loop tracking, bit synchronization , frame synchronization, measurement, message extraction, positioning calculation, etc., and finally outputs positioning information. The Beidou module selects highly integrated, fully SMD components with a very small number of chips, which reduces hardware design requirements.
2) RF front-end design B1L1 The RF front-end chip selected is the RF front-end chip RX3007 of Runxin Company that integrates the B1L1 frequency point [9]. RX3007 adopts 0.13μm RFCMOS technology, one-time conversion low-IF receiving architecture, parallel dual-channel frequency conversion processing, high integration, and few peripheral circuit components. The RF front-end of many Beidou modules is designed using two max2769 chips. Each max2769 consumes 20mA of current and power, and the two chips total 40mA. However, the RX3007 consumes only 28mA, which greatly saves power consumption and significantly reduces power consumption. significantly reduce module size, and Can greatly reduce costs.
3) Baseband processing design. The baseband chip uses Haiger’s Beidou/GPS digital baseband system.
System-level chip HGBD102. HBD102 adopts 0.13μm CMOS process, built-in Beidou/GPS dual-mode capture engine and tracking channel, 2-digit digital IF interface, seamlessly matches mainstream RF front-end chips; the capture and tracking sensitivities are -143dBm and -157dBm respectively, and the performance reaches GPS No. Third-generation chip level; the output data is compatible with the NMEA0183 protocol. The embedded processor can complete system status management, channel and related resource management and control, received signal processing and measurement calculation. The standardized navigation calculation software is used to search and track satellite signals. , and solve for the user coordinates and velocity. The software has been solidified on the Flash chip and does not require secondary development and debugging. The module reserves a software upgrade interface to facilitate program updates.
4) Integrated navigation software design
The integrated navigation software completes the control and data fusion calculation of the Beidou module software system. Figure 3 shows the data processing flow.
After the module is powered on, the initialization unit will
condition, determine whether to enter the hot start, warm start or cold start star selection mode; the satellite signal acquisition unit simultaneously performs loss-of-lock reacquisition or reacquisition of the Beidou/GPS satellites according to the set parameters; after the acquisition is successfully, it enters the signal tracking process, in which The main tasks include loop control, bit synchronization, frame synchronization and message reception; GPS and Beidou are two independent global navigation satellite and positioning systems. There are differences between the systems in coordinates, time , ephemeris, pseudo-range observation, etc. Therefore, the data fusion unit completes time conversion, format conversion, coordinate conversion, pseudo-range combination, autonomous integrity monitoring (RAIM) and other processing; finally, the navigation calculation unit completes the calculation and output of position, speed, time and other information.
Each unit module of the integrated navigation software is a sub-task of the real-time operating system (RTOS) and is uniformly managed by RTOS.
5) Clock management
The clock selects a 16.368 MHz temperature compensated crystal oscillator (TCXO), which is provided to the RF front-end and baseband chips. HG-BD102 itself integrates the 32.678 kHz crystal required by the real-time clock (RTC), so an external supercapacitor is used as a backup power supply to save key data and realize the hot start function.
6) Performance comparison test, static test and sports car test graphical data are shown in Figure 4 and Figure 5
Under the same conditions, using the GPS module as a reference, the Beidou module was tested in terms of positioning accuracy, speed measurement accuracy, capture and tracking sensitivity, hot start time, cold start time and power consumption. As can be seen from the figure, the error between the elevation accuracy and GPS is negligible, and the error between the horizontal accuracy and GPS is within the range of 8 m. At present, the Beidou system is still in the stage of gradual construction and improvement. The number of Beidou satellites is less than that of GPS. The single Beidou positioning mode has slightly worse performance than the GPS module under certain conditions, but in the combined positioning mode, the performance is equivalent to the GPS module.
3 Conclusion The Beidou module designed in this design is compatible with mainstream GPS modules in terms of physical size, pin packaging and interface protocol. Its key indicators such as function, positioning accuracy and speed measurement accuracy are close to the level of mainstream GPS modules. It has been successfully applied in a transportation project. [10].
Author of this article: Pan Weizhuang Keywords of this article: positioning module
Dutch 
English 
Russian 
German 
Spanish 
Italian 
Portuguese 
French