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What is Mobile Computing? Wireless Communication Systems Mobile Communication Systems Architecture Key Technologies of Mobile Computing Applications. Key Technologies of Mobile Computing. Positioning Mobility management Routing Mobile agent. Positioning – Needs of Pedestrains.

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What is Mobile Computing? Wireless Communication Systems Mobile Communication Systems Architecture


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    Presentation Transcript
    1. What is Mobile Computing? • Wireless Communication Systems • Mobile Communication Systems Architecture • Key Technologies of Mobile Computing • Applications

    2. Key Technologies of Mobile Computing • Positioning • Mobility management • Routing • Mobile agent

    3. Positioning – Needs of Pedestrains 汽車導航:靠GPS,精準度容忍較高 行人導航:可能在indoor或地下室,精準度容忍較低

    4. Positioning Technologies • Concepts of positioning • Satellite-based solutions • Network-based solutions • IMU-based solutions

    5. Concepts of Positioning 測量使用者與衛星距離 系統管理者survey network infrastructure, BS如何佈置,訊號特徵 慣性導航,感測手機加速度及方向(角度)改變以進行導航

    6. Comparisons of Positioning Technologies • Satellite-based solutions • higher hardware cost (terminal-based positioning) • function well in outdoor environments[高樓大廈密集會有問題] • example: GPS, A-GPS, D-GPS • Network-based solutions • need communication infrastructure[e.g. base station] • more suitable in indoor environments[有infrastructure訊號覆蓋就可以] • example: WiFi, PHS, GSM

    7. IMU (Inertial Measurement Unit)-based solutions • extra hardware cost[G-sensor (重力感應器) 和M-sensor (電子羅盤)] • without any infrastructure support • inherently accumulated errors[同時需要依賴其他技術及參考座標,會有累積誤差問題] • usually operate as auxiliary component

    8. Satellite-Based Solutions • Triangulation (Trilateration) • triangulation:利用GPS或BS訊號,透過TOA (Time of Arrival)技術,量測自己跟三個點的距離跟角度 • trilateration: a method for determining the intersections of three sphere surfaces given the centers and radii of the three spheres. • measure distances or angles of at least three reference points • usually need specific hardware supports • widely used in many positioning systems, such as GPS

    9. GPS • GPS • distance is measured by time of arrival (ToA)[根據打下來的訊號傳送到參考點的時間,再乘以光速當做距離的判斷] • need very precise time synchronization • 1μs time shift will result in 300m distance error • GPS systems • USA: GPS • Russia: GLONASS • Europe: Galileo • China: Beidou

    10. Data Transferred from Satellites • Constellation [星曆,星座區域,衛星的位置] of 24 satellites • L1 frequency for civilian use • L2 frequency for military and government use • 1500 bits/frame, 50bps (pretty low)[星曆資訊包在一個frame的內容中傳送,手機透過GPS設備接受此星曆資訊] • Time of week, TOW

    11. Data Transferred from Satellites • Broadcast Ephemeris [【天】星曆表;(帶星曆表的)曆書] (accurate position) • Almanac [曆書;年曆] • At least 30 sec. for first fix[開機後需30 sec設定時間,對汽車導航算是可接受,對手機使用者LBS服務30 sec時間太長]

    12. AGPS (Assisted GPS) • GPS’s weaknesses • TTFF (Time To First Fix) of GPS > 30 seconds (average case: 2~3 min) • signal cannot be correctly received in buildings or sheltered areas • Possible solutions • A-GPS • 透過BS接收星曆資訊,透過網路傳給手機 • FCC: a preferred solution for E911 • operators: no need to change telecommunication infrastructure

    13. AGPS Concept

    14. Positioning Errors of GPS • Standard Positioning Service (SPS) • C/A-Code (Coarse/Acquisition Code) • SA (Selective Availability) • 西元2000年前US Army在衛星加入SA干擾,定位誤差達150m • 西元2000年後,移除SA干擾,定位誤差可到25m,汽車導航才能精準使用,但需求精準度更高的LBS服務仍無法使用 • horizontal accuracy: 100m • vertical accuracy: 156m • commercial use

    15. Deviation is more than 5 meters • weather error • multipath error • GDOP (Geometric Dilution of Precision) • receiver error • Ephemeris error • SA (Selective Availability) • cycle slips

    16. DGPS (Differential GPS) • Goal: increase the accuracy of positions derived from GPS receivers • Use base receivers with known locations nearby the GPS receivers to achieve high positioning accuracy (< 5m)[根據自己的經緯度座標,再與收到的衛星訊號做計算,最後把校正碼(corrections)送給附近的使用者]

    17. The cost of build-in GPS chip is more than 10% of the material cost of mobile phones • The number of mobile phones equipped with GPS

    18. OBSERVATION • Americans time spent • indoors: 89% • transport: 6% • outdoors: 5%

    19. Network-Based Postioning • Properties • need communication infrastructure • more suitable in indoor environments • example: WiFi, PHS, GSM • Site survey • deployment of base stations • radio map • Categories • cell-ID • triangulation / trilateration • fingerprinting

    20. Cell-ID Localization Error = 200m~1km User找最近的BS 管理者需經過site survey知道BS座標 Cell-ID localization最易實作,但誤差大(約數百公尺到一公里)

    21. Problems: propagation attenuation, multipath Triangulation Localization 利用訊號衰減做為距離量測方式 根據收到三個BS訊號強度,換算距離,可定自己的位置 缺點:訊號強度不穩定,會有multipath的問題

    22. Fingerprinting Localization Indoor is better, error = 3m 1. 西元2000年,Microsoft Lab提出,透過特徵比對做定位 2. 管理者先做site survey,在固定點收訊號,用特徵值表示在該位置附近的BS所收訊號 (Radio Pattern) 3. 將這些特徵值存在DB (包括經緯座標及訊號特徵) 4. 商業化系統:Skyhook Wireless Technology Used in Revolutionary iPhone and iPod touch (蒐集上億802.11訊號) 5. 此方法適用在indoor (精準度可達3m),其位置與訊號特徵值差異不會太大

    23. IMU-Based Positioning • Properties • without any infrastructure support • inherently accumulated errors • usually operate as auxiliary component • Extra hardware cost • inertia reference • relative acceleration (G-Sensor [重力感應器], Pedometer [步數計;步程計] Function) • relative angle (M-Sensor [電子羅盤], Compass Function)

    24. Summary of Positioning Technologies • A reliable and ubiquitous positioning technology is the key factor of LBS • There is no dominating positioning technology • Hybrid positioning may be the answer

    25. SMS for Location • Simple format for mobile phones’short message service [描述定位結果] • Google Maps and Google Latitude support announce location via SMS (proprietary format). Source: 工業技術研究院GPS位置資訊簡訊共通標準座談會

    26. OPEN GeoSMS • Examples • OMIA,1;2504.8015,N;12133.9766,E;1;101,02-81018898,台北市信義路五段七號 • GeoSMS/2;2502.01,N;12133.851,E;P;101/02-81018898/台北市信義路五段七號 Source: 工業技術研究院GPS位置資訊簡訊共通標準座談會

    27. Application: Car Accident Insurance Process

    28. Key Technologies of Mobile Computing • Positioning • Mobility management • Routing • Mobile agent

    29. Mobile Management – Cellular System

    30. GSM System Architecture

    31. GSM Location Area Hierarchy

    32. Handoff

    33. Inter-LA Registration

    34. Inter-MSC Registration

    35. Inter-VLR Registration Successful registration Location update into HLR Deregistration Delete VLR data TMSI MS IMSI & other data for authentication new TMSI TMSI, old LAI, MSC, VLR

    36. Call Origination Procedure

    37. Call Termination Procedure

    38. Mobile Management –Mobile IPv4 • Mobility issues in IP Networks • once a mobile terminal moves to a new subnet, a correspondent node needs to use the mobile’s new IP address • it is difficult to force every possible correspondent node to keep track when a mobile terminal may change its IP address and what the mobile’s new address will be • changing IP address will cause on-going TCP sessions to break

    39. Mobility management should • ensure on-going TCP connection does not break • restore quickly if TCP connection breaks

    40. Home Network • Home address • a globally unique and routable IP address • preconfigured or dynamically assigned • Home network • the network whose network address prefix matches that of the mobile terminal’s home address • Home agent (HA) • maintain up-to-date location information for the mobile • intercept packets addressed to the mobile’s home address • tunnel packets to the mobile’s current location

    41. 7 24 A: 0 Network Host 14 16 B: 1 0 Network Host 21 8 C: 1 1 0 Network Host Note: Network Prefix Class A Network (/8 Prefixes) Class B Networks (/16 Prefixes) Class C Networks (/24 Prefixes)

    42. IP addresses are divided into three different classes • each of the following figure defines different-sized network and host parts • there are also class D addresses specify a multicast group, and class E addresses that are currently unused • in all cases, the address is 32 bits long

    43. 7 24 A: 0 Network Host 14 16 B: 1 0 Network Host 21 8 C: 1 1 0 Network Host IP addresses: (a) class A; (b) class B; (c) class C

    44. the class of an IP address is identified in the most significant few bits • if the first bit is 0, it is a class A address • if the first bit is 1 and the second is 0, it is a class B • if the first two bits are 1 and the third is 0, it is a class C address • of the approximately 4 billion (= 232)possible IP addresses • one-half are class A • one-quarter are class B • one-eighth are class C

    45. Class A addresses • 7 bits for the network part and 24 bits for the host part • 126 (= 27-2) class A networks (0 and 127 are reserved) • each network can accommodate up to 224-2 (about 16 million) hosts (again, two are reserved values) • Class B addresses • 14 bits for the network part and 16 bits for the host part • 65,534 (= 216-2) hosts

    46. Class C addresses • 21 bits for the network part and 8 bits for the host part • 2,097,152 (= 22l) class C networks • 254 hosts (host identifier 255 is reserved for broadcast, and 0 is not a valid host number)

    47. IP addresses are written as four decimal integers separated by dots • each integer represents the decimal value contained in 1 byte (= 0~255) of the address, starting at the most significant • eg., 171.69.210.245 • Internet domain names (DNS) • also hierarchical • domain names tend to be ASCII strings separated by dots, e.g., cs.nccu.edu.tw

    48. Foreign Network • Care-of Address (CoA) • assigned to the mobile by the foreign network • a mobile uses its CoA to receive IP packets in the foreign network

    49. Foreign agent (FA) • provides CoAs and other necessary configuration information (e.g., address of default IP router) to visiting mobiles • de-tunnels packets from the tunnel sent from a visiting mobile’s HA and then delivers the packets to the visiting mobile • acts as the IP default router for packets sent by visiting mobile terminals • helps visiting mobiles to determine whether they have moved into a different network