2022年嵌入式GPS导航技术英文文献翻译 .pdf

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1、Research on key technologies of embedded GPS navigation Embedded GPS navigation, based on embedded platform technology, through GPS and GIS and combined with handheld devices, achieves target location, path calculation, route guidance and surrounding search functions of mobile users. This paper, Sym

2、bian OS mobile phones as the terminal, background Linux servers providing the mapping service, path calculation, route guidance, networking search, location query and other functions, using GPRS, WIFI and other wireless communication modes, achieves navigation services provided by professional navig

3、ation mobile phones on light weight thin-client, and, at the same time, takes advantage of mobile phone communication to achieve a certain degree of user interaction. Thus, based on the user interface on Symbian platform, GPS, data persistence layer, audio and network programming, an overall solutio

4、n is proposed and the corresponding key technologies involved are discussed. With the development of 3G technology, the improvement of wireless network coverage, the embedded navigation of mobile phones, because of its good portability, low price, always online and more flexible ways to obtain such

5、services, is more and more concerned about. However, due to wide sorts of mobile phones for different platforms, corresponding software needs to be developed, and therefore a suitable embedded operating system needs to be selected. Currently on the market there are more than 40 common embedded opera

6、ting systems, including Linux, Windows CE, Symbian, etc. These embedded systems have different characteristics, and there into Symbian system, developed by Nokia, because of its large user base and good network functions is a successful one. This paper realizes the Symbian-based GPS navigation syste

7、m. It involves techniques which can be divided into: server-side technology and client-side technology. Client-side technology is mainly related to Symbian programming, GPS module processing, network communication etc; server technology mainly involves Web server technology, database access, and geo

8、graphic information system technology. After server technology roughly introduced, this paper, mainly aiming at client-side technologies, discusses various technologies involved when building mobile phone GPS navigation software with the C/S structure. In order to improve the user experience, it is

9、necessary to convert the operations of high-latency and high memory requirements to the service side. Due to Linuxs open 名师资料总结 - - -精品资料欢迎下载 - - - - - - - - - - - - - - - - - - 名师精心整理 - - - - - - - 第 1 页，共 8 页 - - - - - - - - - source and stability, this paper adopts Linux as the terminal server, u

10、ses Apache to build web services, and makes modular map services, POI queries, path calculationguidance services, and built-in sub-services for the Apache. It shows the General framework of the embedded GPS navigation. Taking into account the mass characteristics of map data, tore duce real-time map

11、 data downloads when browsing the map, hierarchical block strategy about map data will be introduced in detail hereafter. Path calculation, as the core of GPS navigation services, supported by navigation data, adopts a dual-side A-Star algorithm to realize optimal path supporting the three kinds of

12、calculation methods of the least time, the shortest distance and less fee. Route guidance, based on path calculation module, analyzes the best sections of the calculated path and the node attributes, dynamically calculates the junction point in need of guidance information, loads on the display poin

13、ts of path calculation by index technology of matching, transfers to the client through the appropriate protocols, and consequently achieve navigation guidance. POI query service is based on full-text retrieval technology. A key technology of full-text Retrieval System to establish the inverted file

14、 of location index for each word in the article. Inverted index approach can not solve the problem about space search. So the approach of inverted index combined with spatial segmentation is introduced. Firstly, using a grid method segments all POI information according to the relationship of spatia

15、l location. And then inverted index is built for the POI in the space after segmentation. Open extensible multi-tier architecture, combined with search, index, cache and other key technologies for search services, greatly improve service stability and search efficiency Symbian OS, as a set of 32-bit

16、 operating system, with multi-tasking, multi-threaded, low-power, low occupation of memory, etc. is very suitable for mobile communication equipment. It is not difficult to arrive at the following conclusion: In the Symbian client, there are map data mapping, GPS data reception and encryption, path

17、computation and guidance analysis, voice broadcast and other modules. This test system is based on C/S mode, so the network communication module is the core module. Due to the transmission delay of network and unknown transmission errors, etc, multi-threaded scheduling download mechanism is used. An

18、d GPS, voice broadcast and some other modules also need an asynchronous implementation, while, other than Windows programs, they use active objects to realize the asynchronous operation instead of the multithreaded model. HTTP is a basic protocol in Web technologies, which is an application layer pr

19、otocol, directly using TCP layer to transfer information. The server only needs to accept a request and, according to the users requests, to send the appropriate file. It is not necessary for the server to record retrieval track so that the number of users supported by a server can 名师资料总结 - - -精品资料欢

20、迎下载 - - - - - - - - - - - - - - - - - - 名师精心整理 - - - - - - - 第 2 页，共 8 页 - - - - - - - - - greatly increase. However, there are many shortcomings of HTTP: because of its simplification, a TCP connection needs to be built and at the same time a TCP connection needs to be removed each time a file is p

21、assed. Therefore, when you want to send a very small file, it is very uneconomical. In addition , as the server cant reserve retrieval tracks, the password memory, etc. is a big trouble, resulting in decreased efficiency of the system. Thus, this test system needs to maintain a long connection, to a

22、void overhead brought by short Http connection. In the WIFI or mobile CMNET mode, Socket mode is used to realize Http download requests. That is to say, the system will establish a connection with the server, format and send the request header, receive the data returned from the server, split and an

23、alyze the response header and receive data. Afterwards through the establishment of a Socket connection pool, after the work thread activated, the system gets the network connections from Socket Connection Pool and then makes network requests. Meanwhile the network connection object will be re-used,

24、 that is, it will not to be destroyed after download, but to be used continuously until the connection fails. The re-used Socket connection will be put into Socket connection pool to be managed. For Wap of China Unicom or China Mobile, due to its agents through the gateway, the Socket method cant be

25、 used directly to download, so the Socket analog of Http requests or the simple download, directly using the Http protocol interface are necessary. From multi-task download process, it can be seen that, in the main UI process, when the user operates a request, such as POI search, location queries or

26、 path calculation, the UI main thread launches the network request, encapsulate the network task and submit it to the Task Manager. As for the tasks in the queue, the Task Manager requests for idle threads to process from the initialized download thread pool, and at the same time marks the task as b

27、eing processed, making the main UI in a wait state. If there is an idle thread, the system will activate it and initiate a network connection request. If the data download is complete or the connection is timed out, the system notifies the Task Manager, clears the task from the download queue, and u

28、pdates the state of the UI main thread. At the same time, the user can manually terminate current download tasks. The test system shows that this process can realize quick downloads and a good user experience. As for navigation through mobile communication, realtime navigation-related data need to b

29、e downloaded to the local. Because wireless communication network bandwidth is limited, in order to improve the response speed of the software to improve the user experience, the local cache technology of communication navigation is produced. Its basic principle is by sacrificing some storage space

30、to maintain a certain priority level of data or information, when the data request is received, firstly check whether the cache can provide 名师资料总结 - - -精品资料欢迎下载 - - - - - - - - - - - - - - - - - - 名师精心整理 - - - - - - - 第 3 页，共 8 页 - - - - - - - - - the requested data or information, and if it exists,

31、 then it can be fleetly extracted from the cache. In this way, the data need not to be 385 downloaded later so as to improve the speed and to reduce network traffic. When the client requests for services, the requested data will be organized in the local memory in a certain way, which is actually a

32、policy using storage space to exchange the rate. In the local cache, an index mechanism needs to be established, and then in the next request, starting with query in the local cache, if the requested data can not be found in the local cache, the server will be submitted a request to in succession. C

33、ache is the core of the flow chart, and the manipulation on the cached data must be efficient, so cached data must be effectively organized to be managed. As for GIS web service clients, the most data involved in its request are spatial data, so the data management in the cache can adopts the data o

34、rganization model consistent with spatial data organization model in the server. That is to say, hierarchical management model is a choice. For different data types different directories can be used. A data type corresponds to a directory, as for the same directory data, and a logical layer in the s

35、patial database is expressed as a logical layer in the cache directory. The cache does not cache all of the layers in the database, but only stores specific areas of data in those layers selected by the user. Management and organization chart of cache data All of the work of cache module is carried

36、out around the cache index, and all cache operations such as query, add, delete, update, etc, are realized through the cache index. In order to query quickly, Index data in the cache are generally built in the form of hash table. Each data object in the cache corresponds to a node in the hash table.

37、 Data updates in the cache are generally because the updates of server-side data cause the original cache data not available. When data are cached in the local, the data version needs to be recorded. But after updates of service-side data, during the cache operation the validity of the data in the c

38、ache can be determined, and as to invalid data, they will be removed from the cache and then re-downloaded. It is a flow chart of file data update. When the user requests for data update detection the client sends a request to the server. The Server-side will read and returns the latest timestamp of

39、 all files in the cache. The client will determine whether the time stamp of the local file and the returned timestamp is the same, and if they are different the update bit of the file will be modified in the index file. When the file needs to be accessed again, the client will firstly check whether

40、 the file exists in the index file and whether the file needs to be updated. And if updates are necessary the server will be requested to download the data once again. Active object and an event scheduler together provide the non-preemptive 名师资料总结 - - -精品资料欢迎下载 - - - - - - - - - - - - - - - - - - 名师

41、精心整理 - - - - - - - 第 4 页，共 8 页 - - - - - - - - - multitasking, which can be used to replace the multi-threading in Symbian OS. Principle and flow of the local cache 386 active object is: compared with the use of threads, it is programming-simple and CPU-efficient. As the GPS navigation and voice bro

42、adcast both need to obtain information in real time and can not affect the operation of UI, the system will respectively establish an activity object for them, bind the object with a certain asynchronous function in the system, and register the activity object in event scheduler, and then the event

43、scheduler will wait for the completion message returned from the asynchronous function. On receipt of the completion message, the scheduler traverses registered activity objects, and if status!= KRequestPending is found, it will find the activity object corresponding to the status the object, call R

44、un function of it and to tell us asynchronous function has been performed in the way of events. The test proves that asynchronous operations are well realized in this way, and better system performance can be achieved. In this paper, according to the above C/S architecture, through various navigatio

45、n services deployed in the background Linux servers and combined with the three strategies of the client, a test system is established in Nokia 5800 mobile phone, and through GPRS/WIFI and server 6, the information returned from the server is parsed as the appropriate customer requested information.

46、 The test shows that the average delay of path calculation is about 3-10s, and as for POI queries, etc, due to the optimized number of results, the transmission delay is roughly 1-3s. According to the number of blocks in a screen, a map is downloaded with an average size of no more than 10k after Gz

47、ip compression. Through the pre-download mechanism, real-time download of lots of data is well avoided, and smoothly dragging and download and display of map data are realized. Running effect of the test system is shown in Figure 6. Navigation, as a major hot spot application in the IT industry, due

48、 to the rapid development of hardware and software technology in recent years, has been remarkably progressing and gradually transiting from the traditional local car navigation to the handheld communication navigation and three-dimensional navigation. Especially with the maturity of SOA technology,

49、 services as one of the major trends in IT industry, various industries are making traditional applications service-oriented, thereby providing more comprehensive and personalized user experience. In this paper, through a preliminary overview of key technologies of the embedded GPS navigation, on th

50、is basis, a prototype system is developed and tested to verify the correctness and feasibility of the idea. 名师资料总结 - - -精品资料欢迎下载 - - - - - - - - - - - - - - - - - - 名师精心整理 - - - - - - - 第 5 页，共 8 页 - - - - - - - - - 研究嵌入式 GPS 导航的关键技术嵌入式 GPS导航,基于嵌入式平台技术 ,通过 GPS和 GIS 相结合，与手持设备 ,达到目标位置、路径计算、路径引导和周围环境的搜