This paper puts forward the optimized design scheme of intelligent car navigation system, analyzes the positioning principle of gpsOne, discusses several key technologies in system development, and gives an engineering example based on ARM and Linux platforms.
1? 1 background of the location business
With the development of mobile communications, in addition to voice transmission, telecommunication service providers and manufacturers have launched various value-added data services and devices in order to find new sources of income. Consumers also hope that mobile phones can have other functions besides calling, sending and receiving emails, and surfing the Internet. Statistics of the National Basic Geographic Information Center also show that 80% of people's daily life information is related to spatial location, while 59% of information used by enterprises is related to spatial location. Therefore, as one of the most potential value-added application platforms, mobile location services, that is, location-based services LBS (LocaTIon Based Services), are receiving unprecedented attention. It can provide many applications such as navigation, location-based payment, location information services, network planning and management, property tracking, personal location services, entertainment and emergency rescue.
1 2 Development prospects of car navigation
In order to alleviate the pressure of modern urban transportation, in recent years, ITS (Intelligent Transport Systems), which combines the latest communication network technology, satellite positioning technology and geographic information technology, has emerged. ITS can implement various functions such as positioning, alarming, monitoring, dispatching, rescue or anti-theft for motor vehicles, greatly improving the quality of traffic management.It can not only reasonably use and fully exploit the traffic potential of existing roads, and effectively solve the phenomenon of traffic congestion; And it can improve the operating efficiency of vehicles and reduce operating costs.
ABI and IEK's October 2002 research report pointed out that the global GPS market conservatively estimates that the compound annual growth rate (CAGR) from 2000 to 2006 is about 24%, and the 2006 output value is about 34 billion US dollars. In the current satellite navigation application field, intelligent transportation management accounts for the largest proportion, accounting for about 40% of the total market.
At present and in the future, the vast majority of GPS application products are mainly based on land navigation and positioning systems, accounting for more than 70%, and the proportion is increasing year by year. Car navigation, communication applications, and fleet tracking management will become dominant in land navigation products by 2006. China currently has 4.3 million freight cars, 1.7 million passenger cars, 4.5 million cars and more than 900,000 ships of various types. Such a large number of cars and ships has an urgent need for navigation terminal products and services.
Based on the above analysis, research and development of vehicle-mounted mobile positioning terminals, relying on the CDMA (Code Division MulTIple Access, code division multiple access) network transmission platform, in cooperation with the control center, to achieve vehicle positioning, navigation, alarm, monitoring, scheduling and other location-based Various value-added services can be widely used in the rental car industry, logistics companies, large-scale enterprises and institutions for official vehicle management and private cars and small company vehicles, the market potential is huge.
2 System principle and characteristics of intelligent navigation terminal
2? 1gpsOne System Introduction
Using appropriate positioning technology to obtain location information is a necessary prerequisite for implementing location services such as vehicle navigation and dispatch. The mobile positioning solution of this system adopts the gpsOne patented technology developed by QUALCOMM.
Overall structure As of February 2003, more than 10 million gpsOne terminals have been put into commercial use in Japan, South Korea, and the United States, surpassing the total sales of commercial GPS terminals of all manufacturers worldwide, and becoming the most widely used mobile positioning system in the world. The traditional wireless positioning technology can be basically divided into two categories according to the position of the dominant entity: network-based solutions and mobile station-based solutions. The network-based solution requires the mobile station to send out signals and be received by multiple fixed-position base stations. By measuring the characteristic parameters of the signals from the mobile station to the base station, the location of the measured object (mobile station) is determined according to a specific algorithm.
Commonly used angle of arrival AOA (Angle Of Arrival) and time of arrival TOA (TIme Of Arrival) and other technologies. When the signal is weak, the positioning accuracy of this scheme will decrease, and it will also be affected by the coverage of the base station, radio diffraction, and multipath effects. In addition, this kind of scheme also needs to transform the base station, adding additional upgrade costs. Based on mobile station solutions, the most typical is the use of a global satellite positioning (GPS) system, consisting of 24 artificial satellites and supporting ground stations. The receiver (mobile station) only needs to receive the signals from the three satellites, measure the distance to them, and then calculate its own position.
In addition to the high cost of the receiver, this solution also has a long "first acquisition time" or "first fix time" TTFF (TIme To First Fix), especially when the receiver is cold-started, it takes more than ten minutes to complete the Satellite search. Moreover, if the mobile station is located indoors, in a place where tall plants, buildings, or satellite signals cannot be covered, due to the small number of visible GPS satellites, the positioning effect is poor, and even positioning cannot be completed. Although neither the network nor the GPS is suitable as a set of positioning solutions with commercial value, they can learn from each other. For example, in rural and suburban areas where the base station coverage is incomplete, the GPS receiver can search for four or more satellites. In contrast, in dense urban areas and tall buildings, although GPS receivers cannot detect enough satellites, there are two or more base stations visible to mobile stations. The gpsOne positioning solution developed by Qualcomm with the help of CDMA network is a hybrid wireless assisted global positioning system (Hybrid AGPS), which is not only highly accurate, but also suitable for various terrains, including indoor, dense urban areas and rural areas with limited network coverage . It makes full use of the advantages of both wireless cellular networks and GPS satellites, greatly improving the availability, sensitivity and accuracy of positioning solutions, and even only requires one satellite and one base station to complete positioning.
Some Qualcomm CDMA chipsets have integrated the gpsOne function. This not only reduces the manufacturing cost of mobile stations that support the gpsOne function, but also makes the entire solution quick and easy to deploy. There is no need for expensive and complicated transformation of existing network equipment, and there is no need to add new base stations. In addition, it complies with industrial positioning standards, supports roaming, and is compatible with existing GSM networks, minimizing network reconstruction costs.
2? 2gpsOne system positioning principle analysis
The positioning process of gpsOne mainly involves two activities: signal measurement and position calculation. The signals to be measured include not only the positioning information sent by the GPS satellite group, but also the positioning information from the wireless network. The gpsOne system itself is very flexible, allowing different mature radio positioning methods to be used in various network configurations, such as source cell COO (CellID Of Origin) technology or advanced forward link triangle positioning AFLT (Advanced Forward Link Trilateration) technology, etc. . This is precisely the meaning of "wireless assist" and "hybrid". In addition, the system also needs two other components: GPS satellite wide area reference network (WARN) and base station location information database (BSA).
The specific working principle of AGPS is as follows:
â‘ The user (mobile station or monitoring center) issues a positioning request, and then the mobile station transmits the ID information of the base station where it is located to the location server (also called positioning entity, PDE, Position Determining Entity) located in the network through the wireless network.
â‘¡ Based on the approximate location of the mobile station, the location server informs the mobile station which GPS satellite positioning information (including GPS ephemeris and azimuth elevation angle, etc.) related to its location should be monitored.
â‘¢ The mobile station receives the original signal of the visible GPS satellite group according to the auxiliary information provided by the location server (mainly used to improve the TTFF capability of the GPS signal).
â‘£ The mobile station demodulates the signal and calculates its pseudorange to all visible satellites (pseudorange is the distance affected by various GPS errors); at the same time, it uses the above various radiolocation techniques to collect signals from multiple neighboring base stations and measure it to The distance of each base station and transfer the relevant information to the location server.
â‘¤ The location server calculates the precise position of the mobile station (including longitude, latitude and altitude) through a series of error correction algorithms based on the transmitted GPS pseudorange and auxiliary information of other positioning devices (such as differential GPS reference stations, etc.) .
â‘¥ The location server sends the location information to the mobile station, third-party service provider SP (Service Provider), positioning gateway or other location service (LBS) application platform.
In the above process, when the positioning request short message is sent, the mobile station will actively establish a TCP connection to the PDE and complete the positioning process in compliance with IS-801 (industrial positioning standard) through the end-to-end IP session with the PDE. PDE returns the latitude and longitude information to the SP. The activities of signal measurement and position calculation can be carried out on the mobile station or the network side, or both.
2? 3 Features of Intelligent Embedded Navigation Terminal
The design of the intelligent embedded navigation terminal is put forward under the research and comparison of the current similar products. This solution not only draws on the strengths of the public, but also puts forward some new and higher requirements on the functions of the vehicle-mounted system according to future development. Compared with other existing vehicle-mounted systems, the embedded intelligent navigation terminal has more advantages, and the main features are:
â‘ The positioning solution adopts Qualcomm gpsOne solution based on A? GPS technology.
â‘¡ The wireless communication network adopts CDMA network, including the current Unicom CDMA 1X network and the future third-generation CDMA2000 network.
â‘¢ A variety of communication methods are adopted. In the communication method between the vehicle-mounted terminal and the control center, various means such as short message, voice, data channel and video are provided.
â‘£ Provide richer value-added services, in addition to basic positioning, navigation, monitoring and scheduling functions, you can also add various value-added information services based on location in life, transportation, entertainment, services, public facilities, such as stolen goods Tracking, restaurant and park guides, train schedules, weather forecasts, interactive entertainment games and more.
â‘¤ Convenient human-computer interaction interface. The in-vehicle system is equipped with a 17.8 cm (7 in) TFT color touch LCD display, microphone and speaker.
â‘¥ Adopt MCU based on ARM core and embedded Linux operating system.
â‘¦ Support electronic map.
â‘§ Various alarm functions. The vehicle-mounted system has multiple alarm functions such as anti-theft alarm, anti-robbery alarm, distress alarm, and damage alarm.
â‘¨ Group call function in broadcast mode. The monitoring center can make group calls and group calls to vehicles, which can not only broadcast and download traffic, news, stocks, weather and other information, but also real-time statistics on the distribution of taxis in a certain area.
â‘© Convenient configuration and expansion. The embedded vehicle-mounted system is composed of relatively independent modules with basic functions, and common control interfaces remain.
3 Optimized design and implementation of embedded terminal Car navigation terminal belongs to a typical embedded system. For embedded systems, a more reasonable definition is: application-centric, computer technology-based, software and hardware can be tailored, special computer systems that meet the strict requirements of application systems for function, reliability, cost, volume, and power consumption .
(1) Selection of embedded microprocessor
Because embedded systems are so different from general-purpose computer systems in terms of system characteristics, development cycle, and design requirements, the choice of embedded processors is affected by many unique factors. This terminal selects a 32-bit RISC processor based on ARM core. Since its establishment in 1990, ARM has continuously made breakthroughs in the field of 32-bit RISC CPU development, and its system architecture has evolved from V3 to V6. It has been selling intellectual property to major semiconductor manufacturers as an IP (Intelligence Property) provider, without interfering with the production and sales of chips. The core of its design has obvious advantages such as low power consumption and low cost. Therefore, it has obtained strong support from many semiconductor manufacturers and machine manufacturers, and has achieved great success in the field of embedded applications. By 2004, it had occupied 79% of the embedded processor market, and its ARM9 series core has become the mainstream of product applications.
â‘ Performance. The processor must have sufficient performance to perform tasks and support the product life cycle. Considering the complexity of smart navigation terminal applications (electronic maps, color LCD, touch input, gpsOne navigation, voice interaction, etc.), the selection of the processor requires a memory management unit (MMU), clock frequency, internal memory capacity, general programmable I / O (GPIO) quantity, terminal controller, LCD controller, ADC / DAC, UART interface, DMA controller and other performance indicators are considered comprehensively.
â‘¡ Whether it is easy to realize.
â‘¢ Tool support. Supporting software creation and debugging system integrated code adjustment and optimization tools is critical to the success of the overall project.
â‘£ Operating system support. Embedded system applications need to use helpful abstractions to reduce their complexity. A commercial operating system (OS) optimized for processor series products can shorten the device development cycle and time to market. ARM has received support from many well-known embedded (real-time) operating systems, such as VxWorks, Windows Mobile (WinCE), and Linux.
(2) Selection of embedded operating system
8-bit microcontrollers only need to directly write a single control program to work, but with the complexity of applications, an embedded controller may have to control and monitor many peripherals at the same time; there are many processing tasks, and there are many kinds For information transmission, the original programming method cannot meet the system requirements at all. Therefore, the embedded systems in the post-PC era all need an operating system running on the embedded processor. There are four major operating systems in the field of smart terminals, namely Symbian, Windows Mobile, Palm OS and Linux; but due to the performance, reliability, open source code, low cost and technical support of Linux, more and more commercial products will Use embedded Linux as a development platform. Figure 4 illustrates the development trend of Linux in embedded OS.
In the development trend of embedded OS, the program we chose is: download the standard source code of GNU / Linux and make appropriate cuts and modifications, and customize it to meet the needs of navigation terminals. According to Linux Devices statistics, this so-called "Home grown" has become the most popular version of embedded Linux, and its share far exceeds the commercial embedded Linux version. This is actually an inevitable response to the diversity of embedded systems.
(3) System development based on ARM and embedded Linux platform
Porting Linux to the ARM processor and performing application development on this platform generally involves four levels: bootloader, Linux OS porting (including setting tool chain, kernel, driver, file system, etc.), graphical user interface (or Called GUI) and applications.
â‘ The bootloader is usually the first piece of code executed on any hardware. Some popular and free Linux boot loaders based on ARM devices are Blob, Redboot and Bootldr.
â‘¡ The purpose of setting up the tool chain is to create a build environment on the host machine (PC with X86 architecture) for compiling the kernel and applications that will run on the target (embedded system with ARM architecture). It consists of a set of components used to compile, assemble and link the kernel and application programs.
â‘¢ Although Ext2fs is the de facto standard file system for Linux, it is a better choice to use JFFS2 in an embedded environment. It is a log-type flash memory chip file system designed for micro-embedded devices.
â‘£ From the user's point of view, the graphical user interface (GUI) is a crucial aspect of the system: the user interacts with the system through the GUI. Qt / Embedded is a graphical user interface system newly developed by Trolltech for embedded Linux.
The intelligent vehicle positioning service system designed and developed by integrating the ARM processor, embedded Linux and gpsOne positioning technology and relying on the CDMA network transmission platform has wide applicability. The 2008 Beijing Olympics will bring broader prospects for the application of intelligent vehicle navigation and dispatch systems.
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