What is Mobile Computing Wireless Communication Systems Mobile

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 TECHNOLOGIES Concepts of positioning Satellite-based solutions Network-based solutions IMU-based solutions

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: Wi. Fi, PHS, GSM

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

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

GPS distance is measured by time of arrival (To. A) [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 300 m distance error GPS systems USA: GPS Russia: GLONASS Europe: Galileo China: Beidou

DATA TRANSFERRED FROM SATELLITES Constellation [星曆，星座區域，衛星的位置] of 24 satellites L 1 frequency for civilian use L 2 frequency for military and government use 1500 bits/frame, 50 bps (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

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]

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 E 911 operators: no need to change telecommunication infrastructure

AGPS CONCEPT

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 150 m 西元2000年後，移除SA干擾，定位誤差可到 25 m，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: 100 m vertical accuracy: 156 m commercial use

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

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 (< 5 m) [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]

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

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

NETWORK-BASED POSTIONING Properties need communication infrastructure more suitable in indoor environments example: Wi. Fi, PHS, GSM Site survey deployment radio of base stations map Categories cell-ID triangulation / trilateration fingerprinting

CELL-ID LOCALIZATION Error = 200 m~1 km 1. User找最近的BS 2. 管理者需經過site survey知道BS座標 3. Cell-ID localization最易實作， 但誤差大(約數百公尺到一公里)

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)

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

SMS FORLOCATION 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: 業技術研究院GPS位置資訊簡訊共通標準座談會

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 Geo. SMS/2; 2502. 01, N; 12133. 851, E; P; 101/02 -81018898/台北市 信義路五段七號 Source: 業技術研究院GPS位置資訊簡訊共通標準座談會

APPLICATION: CAR ACCIDENT INSURANCE PROCESS

KEY TECHNOLOGIES OF MOBILE COMPUTING Positioning Mobility management Routing Mobile agent

MOBILE MANAGEMENT – CELLULAR SYSTEM

GSM SYSTEM ARCHITECTURE

GSM LOCATION AREA HIERARCHY

HANDOFF

INTER-LA REGISTRATION

INTER-MSC REGISTRATION

INTER-VLR REGISTRATION Successful registration Location update into HLR Deregistration Delete VLR data TMSI MS IMSI & other data for authentication TMSI, old LAI, MSC, VLR new TMSI

CALL ORIGINATION PROCEDURE

CALL TERMINATION PROCEDURE

MOBILE MANAGEMENT – MOBILE IPV 4 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

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

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

NOTE: NETWORK PREFIX 7 A: 0 24 Network Host 14 B: C: 1 1 0 1 16 Network 0 Host 21 8 Network Host Class A Network (/8 Prefixes) Class B Networks (/16 Prefixes) Class C Networks (/24 Prefixes)

IP addresses are divided into three different classes each of the following figure defines different-sized network and host parts there 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 A: 0 24 Network Host 14 B: 1 0 16 Network Host 21 C: 1 1 0 Network 8 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 (= 22 l) 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 (Co. A) assigned to the mobile by the foreign network a mobile uses its Co. A to receive IP packets in the foreign network

Foreign agent (FA) provides Co. As 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

TWO TYPES OF COAS IN MIPV 4 Foreign Agent Co. A an IP address of a FA each FA is responsible for providing FA Co. As to visiting mobiles when FA Co. A is used, the mobile’s HA tunnels the packets to the mobile’s current FA that addressed to the mobile’s home address the FA will then de-tunnel the packets and deliver them to the mobile

Co-located Co. A acquired by a mobile terminal through any method external to Mobile IP example, a mobile may use the Dynamic Host Configuration Protocol (DHCP) to obtain a temporary address dynamically the mobile terminal’s HA tunnels the packets addressed to the mobile’s home address directly to the mobile itself; these packets do not have to go through any FA

KEY TECHNOLOGIES OF MOBILE COMPUTING Positioning Mobility management Routing Mobile agent

AD HOC ROUTING PROTOCOLS Ad hoc routing protocols must deal with high power consumption low bandwidth high error rates Ad hoc routing protocols category table-driven source-initiated (demand-driven)

Ad hoc routing protocols Table-driven DSDV CGSR WRP Source-initiated on-demand AODV DSR LMR ABR TORA SSR

TABLE-DRIVEN ROUTING PROTOCOLS Table-driven routing protocols maintain consistent, up-to-date routing information require each node to maintain one or more tables to store routing information Protocols Destination-Sequenced Distance-Vector Routing (DSDV) Clusterhead Gateway Switch Routing (CGSR) Wireless Routing Protocol (WRP)

SOURCE-INITIATED ON-DEMAND ROUTING PROTOCOLS Source-initiated on-demand routing protocols creates routes only when desired by the source node Some routing scheme Ad Hoc On-Demand Distance Vector Routing (AODV) Dynamic Source Routing (DSR) Temporally Ordered Routing Algorithm (TORA) Associativity-Based Routing (ABR) Signal Stability Routing (SSR)

AD HOC ON-DEMAND DISTANCE VECTOR ROUTING (AODV) A source node initiates a path discovery process when desires to send a message does not already have a valid route Path discovery broadcasts a route request (RREQ) packet to its neighbors then forward the request to their neighbors until either the destination or an intermediate node with a "fresh enough" route to the destination is located

PROPAGATION OF THE PREQ

RREQ & RREP intermediate nodes record the address of the neighbor from which the first copy of the broadcast packet is received if additional copies of the same RREQ are later received, these packets are discarded once the RREQ reaches the destination, the destination node responds by unicasting a route reply (RREP) packet back if a route entry is not used within the specified lifetime, the route will be deleted

PATH OF THE RREP TO THESOURCE

KEY TECHNOLOGIES OF MOBILE COMPUTING Positioning Mobility management Routing Mobile agent

WHAT IS A MOBILE AGENT? Mobile Agent (Intelligent Message) an electronic message carries a computer program either procedural or declarative it can be executed by the receiving servers on behalf of the originating client the program in the message can instruct a receiving server to forward the message to another server continuously in a pipeline fashion

MOBILE AGENT MODEL

The agent model is based on the concepts of places and agents places provide the environment for executing mobile agents a place is entirely located on a single node of the underlying network an agent system consists of a number of these places

agents mobile agents are active entities, which may move from place to meet other agents and to access the places' services an agent can be identified by a globally unique agent identifier, which is generated at the agent's creation time and is not changed throughout its life communication between agents may be local or global

MOBILE AGENT ITINERY

CLASSIFICATION OF AGENTS IN A MOBILE AGENT SYSTEM Mobile agents Service agents system services application-level services

TYPES OF AGENTS COMMUNICATION Agent / service agent interaction [client/server] Mobile agent / mobile agent interaction [peer-topeer] Anonymous agent group interaction User / agent interaction

AGENT / SERVICE AGENT INTERACTION Service agents are the representatives of services in the agent world, the style of interaction is typically client/server Services are requested by issuing requests, results are reported by responses An RPC-like communication mechanism should be provided

CLIENT SERVER PARADIGM

MOBILE AGENT / MOBILE AGENT INTERACTION The rule of the communication partners in this type are peer-to-peer rather than client/server Each mobile agent has its own agenda and hence initiates and controls its interactions according to its needs and goals

MOBILE AGENT PARADIGM

WHY MOBILE AGENTS FOR MOBILE COMPUTING? Resolve the problems with wireless communications noisy expensive low bandwidth unreliable (intermittent connection) limited battery life Scalable clients

Resource optimization if an agent's goals require extensive communication with a particular resource on the network, moving closer to the resource can reduce or eliminate network traffic, allowing the agent to perform its duties more quickly Distributed parallel processing agents can move to lightly loaded machines when necessary and delegate subtasks to other mobile agents, allowing true parallel processing

Reliability mobility and autonomy allow an agent to move from its point of origin into a network and continue to operate, even if the originating device is temporarily or permanently disconnected from the network by doing so, the agent can provide services and satisfy predefined goals without user intervention

MOBILE AGENT SYSTEMS