The intelligent vehicle terminal combined with gpsOne positioning technology, CDMA communication technology and GIS technology can cooperate with the control center to realize various applications such as navigation, alarm and monitoring of the vehicle. gpsOne is a hybrid positioning technology that combines the advantages of GPS and wireless networks with wide applicability, high precision, short positioning time and low cost.
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This paper proposes an optimized design scheme for 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 platform.
1 Overview
1î€1 positioning business background
With the development of mobile communications, in addition to voice transmission, telecom service providers and manufacturers have launched various value-added data services and devices to find new sources of revenue. Consumers also hope that mobile phones can have other functions besides calling, sending and receiving emails, and surfing the Internet. The statistics of the National Basic Geographic Information Center also show that 80% of people's daily life information is related to spatial location, and 59% of the information used by enterprises is related to spatial location. Therefore, as one of the most promising value-added application platforms, the mobile location service, Location Based Services (LBS), is receiving unprecedented attention. It can provide applications such as navigation, location-based payment, location information services, network planning and management, property tracking, personal location services, entertainment and emergency services.
1î€2 car navigation device development prospects
In order to alleviate the pressure of modern urban traffic, ITS (Intelligent Transport Systems), which combines the latest communication network technology, satellite positioning technology and geographic information technology, has emerged in recent years. ITS can implement various functions such as positioning, alarming, monitoring, dispatching, rescue or anti-theft of motor vehicles, and greatly improve the quality of traffic management. It can not only rationally utilize and fully utilize the traffic potential of existing roads, but also effectively solve the traffic congestion phenomenon; Moreover, it can improve the operational 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 traffic management accounts for the largest proportion, accounting for about 40% of the total market.
At present and in the future, most GPS applications are mainly 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 the dominant products for land navigation products by 2006. China's existing 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 have an urgent need for navigation terminal products and services.
Based on the above analysis, the development of vehicle-mounted mobile positioning terminal, relying on CDMA (Code Division Multiple Access) network transmission platform, cooperate with the control center to realize vehicle positioning, navigation, alarm, monitoring, scheduling and other location-based Various value-added services can be widely used in the taxi industry, logistics enterprises, official vehicle management of large enterprises and institutions, and private cars and small company vehicles. The market potential is huge.
2 System principle and characteristics of intelligent navigation terminal
2î€1gpsOne system introduction
Obtaining location information using appropriate positioning techniques is a necessary prerequisite for achieving location services such as navigation and scheduling of vehicles. The mobile positioning solution of this system adopts the patented gpsOne technology developed by QUALCOMM.
Overall structure By 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, making it the most widely used mobile positioning system in the world. Traditional wireless positioning technologies can be basically divided into two categories according to the location of the leading entities: network-based solutions and mobile-based solutions. The network-based scheme requires the mobile station to send a signal and is received by a plurality of fixed-location base stations. By measuring the characteristic parameters of the signal 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 AOA (Angle Of Arrival) and arrival time 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 wave diffraction, multipath effect, and the like. In addition, this solution requires the transformation of the base station, adding additional upgrade costs. Mobile-based solutions, most typically using a global satellite positioning (GPS) system, consist of 24 satellites and associated ground stations. The receiver (mobile station) only needs to receive the signals of the three satellites and measure the distance to them to calculate their position.
In addition to the high price of the receiver, this solution has a longer "first capture time" or "first time to TT" (Time To First Fix), especially when the receiver is cold start, it takes more than ten minutes to complete. Satellite search. Moreover, if the mobile station is in a place where indoor, tall plants, buildings, or satellite signals cannot be covered, the number of visible GPS satellites is small, the positioning effect is poor, and the positioning cannot be completed.
Although neither the network nor the GPS is suitable for a single set of commercially valuable positioning solutions, they can complement each other. For example, in rural and suburban areas where base stations are not fully covered, GPS receivers can search for four or more satellites. In contrast, in dense urban areas and tall buildings, although the GPS receiver does not detect enough satellites, the mobile stations have two or more base stations visible. Qualcomm's gpsOne positioning solution, developed with CDMA network, is a hybrid wireless-assisted global positioning system (Hybrid AGPS) that is not only highly accurate, but also suitable for a variety of terrain, including indoor, dense urban areas and rural areas with limited network coverage. . It takes advantage of both the wireless cellular network and the GPS satellite, greatly improving the availability, sensitivity and accuracy of the positioning solution, and even requires only one satellite and one base station to complete the positioning.
The gpsOne feature has been integrated into some of Qualcomm's CDMA chipsets. This not only reduces the manufacturing cost of mobile stations that support gpsOne, but also makes the entire solution quick and easy to deploy, without the need for expensive and complex modifications to existing network equipment, and without the 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 transformation overhead.
2î€2gpsOne system positioning principle analysis
The positioning process of gpsOne mainly involves two activities: signal measurement and position calculation. The signal to be tested that needs to be collected includes not only the positioning information transmitted by the GPS satellite group but also the positioning information from the wireless network. The gpsOne system itself is flexible, allowing different mature radio positioning methods to be used in various network configurations, such as Cell ID Of Origin technology or Advanced Forward Link Trilateration (AFLT) technology. . This is exactly what "wireless assistance" and "mixing" mean. In addition, the system requires two additional components: the GPS Satellite Wide Area Reference Network (WARN) and the Base Station Location Information Database (BSA).
The specific working principle of AGPS is as follows:
1 The user (the mobile station itself or the monitoring center) issues a positioning request, and then the mobile station transmits its base station ID information to the location server (also called Position Determining Entity) located in the network through the wireless network.
2 The location server informs the mobile station of the location information (including the ephemeris and azimuth elevation angle of the GPS, etc.) of the GPS satellites associated with its location based on the approximate location of the mobile station.
3 The mobile station receives the original signal of the visible GPS satellite group based on the auxiliary information provided by the location server (mainly used to boost the TTFF capability of the GPS signal).
4 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, the signals of multiple adjacent base stations are collected by using the above various radio positioning techniques and measured to The distance of each base station and the relevant information is transmitted to the location server.
5 The location server calculates the precise location (including longitude, latitude and altitude) of the mobile station through a series of error correction algorithms based on the transmitted GPS pseudorange and other auxiliary information of the positioning device (such as differential GPS reference station). .
6 The location server sends the location information to the mobile station, a third party service provider SP (Service Provider), a location gateway or other location service (LBS) application platform.
In the above process, when the positioning request short message is sent, the mobile station actively establishes a TCP connection to the PDE, and completes the positioning process conforming to the IS-801 (industrial positioning standard) through the end-to-end IP session with the PDE, and finally The PDE returns the latitude and longitude information to the SP. Signal measurement and position calculation activities can be placed on the mobile station or on the network side, or both.
2î€3 intelligent embedded navigation terminal features
The design of the intelligent embedded navigation terminal is proposed in comparison with the current research of similar products. The program not only draws on the strengths of the family, but also proposes some new and higher requirements for the function of the in-vehicle system based on future development. Embedded intelligent navigation terminals have more advantages than other existing in-vehicle systems. The main features are:
1 The positioning scheme adopts the Qualcomm gpsOne solution based on A-GPS technology.
2 The wireless communication network adopts CDMA network, including the current Unicom CDMA 1X network and the future third generation CDMA2000 network.
3 Using a variety of communication methods, in the communication mode of the vehicle terminal and the control center, providing short messages, voice, data channels and video and other means.
4 Providing richer value-added services, in addition to basic positioning, navigation, monitoring and scheduling functions, it can also add location-based value-added information services such as stolen goods in life, transportation, entertainment, services, public facilities, etc. Tracking, restaurant and park guides, train schedules, weather forecasts, interactive entertainment games and more.
5 Convenient human-computer interface. The in-vehicle system features a 17.8 cm (7 in) TFT color touch LCD display, microphone and speakers.
6 Adopt ARM core-based MCU and embedded Linux operating system.
7 Support for electronic maps.
8 multiple alarm functions. The vehicle system has various alarm functions such as anti-theft alarm, anti-robbery alarm, distress alarm, and damage alarm.
9 Group call function in broadcast mode. The monitoring center can perform group call and group call to the vehicle, which can not only realize the broadcast downlink of traffic, news, stocks, weather and other information, but also real-time statistics on the distribution of taxis in a certain area.
10 Easy to configure and extend. The embedded in-vehicle system consists of a variety of relatively independent modules with basic functions, leaving a variety of common control interfaces.
3 Optimized design and implementation of embedded terminal
The car navigation terminal belongs to a typical embedded system. For embedded systems, a reasonable definition is: application-centric, computer-based, software hardware can be tailored, adapt to the application system for functional, reliability, cost, size, power requirements of the special computer system .
(1) Choice of embedded microprocessor
Because embedded systems are vastly different from general-purpose computer systems in terms of system characteristics, development cycles, 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 inception in 1990, ARM has made breakthroughs in the development of 32-bit RISC CPUs, and its 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 designed core has the significant advantages of low power consumption and low cost. Therefore, it has won the support of many semiconductor manufacturers and complete machine manufacturers, and has achieved great success in the field of embedded applications. By 2004, it has occupied 79% of the embedded processor market, and its ARM9 series core has become the mainstream of product applications.
1 performance. The processor must have sufficient performance to perform tasks and support the product lifecycle. Considering the complexity of intelligent navigation terminal applications (electronic map, color LCD, touch input, gpsOne navigation, voice interaction, etc.), the selection processor needs to be from the memory management unit (MMU), clock frequency, internal memory capacity, general programmable I/O (GPIO) number, terminal controller, LCD controller, ADC/DAC, UART interface, DMA controller and other performance indicators are considered.
2 Is it easy to implement?
3 tool support. Support software creation and debugging system integration code adjustment and optimization tools are critical to the success of the overall project.
4 Operating system support. Embedded system applications need to use helpful abstractions to reduce their complexity. Commercial operating systems (OS) optimized for processor families can reduce equipment development cycles and time to market. ARM has gained support for many well-known embedded (real-time) operating systems such as VxWorks, Windows Mobile (WinCE), and Linux.
(2) Choice of embedded operating system
8-bit microcontrollers only need to write a single control program to work, but with the complexity of the application, 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 of tasks. Information transfer, the original programming method can not meet the system requirements at all, so the embedded system of the post-PC era needs 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 Linux performance, reliability, open source, low cost and technical support, more and more commercial products will Embedded Linux is used as a development platform. Figure 4 illustrates the evolution of Linux in embedded OS.
Trends in embedded OS The solution we chose was to download the standard source code for GNU/Linux and make appropriate cuts and modifications to customize it to the operating system that meets the needs of the navigation terminal. According to Linux Devices, this so-called "Home grown" has become the most popular version of embedded Linux, and its share far exceeds the version of commercial embedded Linux. This is actually an inevitable reaction to the diversity of embedded systems.
(3) System development based on ARM and embedded Linux platform
Porting Linux to an ARM processor and developing applications on this platform involves four levels: boot loader, Linux OS porting (including setting up toolchains, kernels, drivers, file systems, etc.), graphical user interface (or Called GUI) and applications.
1 The boot loader is usually the first piece of code that executes on any hardware. Some popular and freely available Linux boot loaders based on ARM devices are Blob, Redboot, and Bootldr.
2 The purpose of setting up the toolchain is to create a build environment on the host machine (X86-based PC) for compiling the kernel and applications that will run on the target (the ARM-based embedded system). It consists of a set of components for compiling, assembling, and linking kernels and applications.
3 Although Ext2fs is the de facto standard file system for Linux, using JFFS2 in an embedded environment is a better choice. It is a log-based flash chip file system designed for micro-embedded devices.
4 From a user's point of view, a graphical user interface (GUI) is a critical aspect of the system: the user interacts with the system through the GUI. Qt/Embedded is a new graphical user interface system developed by Trolltech for embedded Linux.
Conclusion
Integrated ARM processor, embedded Linux and gpsOne positioning technology, based on the CDMA network transmission platform designed and developed into an intelligent vehicle positioning service system has a wide range of applicability. The 2008 Beijing Olympic Games will bring broader prospects for the application of intelligent vehicle navigation and dispatching systems.
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