What is Mobile Computing?

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• What is Mobile Computing?
• Wireless Communication Systems
• Mobile Communication Systems Architecture
• Key Technologies of Mobile Computing
• Applications

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Key Technologies of Mobile Computing

• Positioning
• Mobility management
• Routing
• Mobile agent

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Positioning Needs of Pedestrains
?????GPS,??????? ???????indoor????,???????
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Positioning Technologies

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

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Concepts of Positioning
??????????
?????survey network infrastructure, BS????,????
????,??????????(??)???????
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Comparisons of Positioning Technologies

• Satellite-based solutions
• higher hardware cost (terminal-based positioning)
• function well in outdoor environments??????????
  
• example GPS, A-GPS, D-GPS
• Network-based solutions
• need communication infrastructure e.g. base
  station
• more suitable in indoor environments?infrastruct
  ure???????
• example WiFi, PHS, GSM

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• IMU (Inertial Measurement Unit)-based solutions
• extra hardware costG-sensor (?????) ?M-sensor
  (????)
• without any infrastructure support
• inherently accumulated errors???????????????,???
  ?????
• usually operate as auxiliary component

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Satellite-Based Solutions

• Triangulation (Trilateration)
• triangulation??GPS?BS??,??TOA (Time of
  Arrival)??,??????????????
• 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

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GPS

• GPS
• distance is measured by time of arrival
  (ToA)?????????????????,????????????
• need very precise time synchronization
• 1µs time shift will result in 300m distance error
• GPS systems
• USA GPS
• Russia GLONASS
• Europe Galileo
• China Beidou

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Data Transferred from Satellites

• Constellation ??,????,????? of 24 satellites
• L1 frequency for civilian use
• L2 frequency for military and government use
• 1500 bits/frame, 50bps (pretty low)????????frame
  ??????,????GPS?????????
• Time of week, TOW

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Data Transferred from Satellites

• Broadcast Ephemeris ??????(?????)?? (accurate
  position)
• Almanac ????
• At least 30 sec. for first fix????30
  sec????,??????????,??????LBS??30 sec????

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AGPS (Assisted GPS)

• GPSs weaknesses
• TTFF (Time To First Fix) of GPS gt 30 seconds
  (average case 23 min)
• signal cannot be correctly received in buildings
  or sheltered areas
• Possible solutions
• A-GPS
• ??BS??????,????????
• FCC a preferred solution for E911
• operators no need to change telecommunication
  infrastructure

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AGPS Concept
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Positioning Errors of GPS

• Standard Positioning Service (SPS)
• C/A-Code (Coarse/Acquisition Code)
• SA (Selective Availability)
• ??2000??US Army?????SA??,?????150m
• ??2000??,??SA??,??????25m,??????????,?????????LBS?
  ??????
• horizontal accuracy 100m
• vertical accuracy 156m
• commercial use

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

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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 (lt 5m)??????????,????????????,??????(co
  rrections)????????

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• 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

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OBSERVATION

• Americans time spent
• indoors 89
• transport 6
• outdoors 5

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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

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Cell-ID Localization
Error 200m1km

1. User????BS
2. ??????site survey??BS??
3. Cell-ID localization????,????(?????????)

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Triangulation Localization
Problems propagation attenuation, multipath

1. ??????????????
2. ??????BS????,????,???????
3. ?????????,??multipath???

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Fingerprinting Localization
Indoor is better, error 3m
1. ??2000?,Microsoft Lab??, ????????? 2.
?????site survey,???????, ?????????????BS????
(Radio Pattern) 3. ????????DB (??????
?????) 4. ?????Skyhook Wireless Technology
Used in Revolutionary iPhone and iPod touch
(????802.11??) 5. ??????indoor (?????3m),
???????????????
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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 ?????,
  Pedometer ?????? Function)
• relative angle (M-Sensor ????, Compass Function)

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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

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SMS for Location

• Simple format for mobile phones short message
  service ??????
• Google Maps and Google Latitude support announce
  location via SMS (proprietary format).
• Source ???????GPS?????????????

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OPEN GeoSMS

• Examples
• OMIA,12504.8015,N12133.9766,E1101,02-81018898,
  ??????????
• GeoSMS/22502.01,N12133.851,EP101/02-81018898/?
  ?????????
• Source ???????GPS?????????????

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Application Car Accident Insurance Process
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Key Technologies of Mobile Computing

• Positioning
• Mobility management
• Routing
• Mobile agent

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Mobile Management Cellular System
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GSM System Architecture
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GSM Location Area Hierarchy
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Handoff
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Inter-LA Registration
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Inter-MSC Registration
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Inter-VLR Registration
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Call Origination Procedure
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Call Termination Procedure
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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 mobiles 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
  mobiles new address will be
• changing IP address will cause on-going TCP
  sessions to break

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

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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 terminals home address
• Home agent (HA)
• maintain up-to-date location information for the
  mobile
• intercept packets addressed to the mobiles home
  address
• tunnel packets to the mobiles current location

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Note Network Prefix
Class A Network (/8 Prefixes) Class B Networks
(/16 Prefixes) Class C Networks (/24 Prefixes)
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• 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

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IP addresses (a) class A (b) class B (c) class
C
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• 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

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• 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

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• 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)

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• IP addresses are written as four decimal integers
  separated by dots
• each integer represents the decimal value
  contained in 1 byte ( 0255) 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

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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

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• 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 mobiles 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

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Two Types of COAs in MIPv4

• Foreign Agent CoA
• an IP address of a FA
• each FA is responsible for providing FA CoAs to
  visiting mobiles
• when FA CoA is used, the mobiles HA tunnels the
  packets to the mobiles current FA that addressed
  to the mobiles home address
• the FA will then de-tunnel the packets and
  deliver them to the mobile

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• Co-located CoA
• a CoA 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 terminals HA tunnels the packets
  addressed to the mobiles home address directly
  to the mobile itself these packets do not have
  to go through any FA

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Key Technologies of Mobile Computing

• Positioning
• Mobility management
• Routing
• Mobile agent

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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)

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

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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)

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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
• 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

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Propagation of the PREQ
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• 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

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Path of the RREP to the Source
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Key Technologies of Mobile Computing

• Positioning
• Mobility management
• Routing
• Mobile agent

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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

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Mobile Agent Model
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• The agent model is based on the concepts of
  places and agents
• places
• 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

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• agents
• mobile agents are active entities, which may move
  from place to 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

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Example of a Mobile Agent

• ??l ??????
• ??2 ?????????(airline A)?????
• ??3 ????????????????????????
• ??4 ????AVIS?????????
• ??5 ?????????,?????????????,?????
• ??6 ?????????????????
• ??7 ???????????,?????????????
• ??8 ??????????(PC?smart phone?)
• ??9 ???????
• ??10 ??????

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Mobile Agent Itinery
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Classification of Agents in a Mobile Agent System

• Mobile agents
• Service agents
• system services
• application-level services

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Types of Agents Communication

• Agent / service agent interaction client/server
• Mobile agent / mobile agent interaction
  peer-to-peer
• Anonymous agent group interaction
• User / agent interaction

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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

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Client Server Paradigm
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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

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Mobile Agent Paradigm
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Why Mobile Agents for Mobile Computing?

• Resolve the problems with wireless communications
  
• noisy
• expensive
• low bandwidth
• unreliable (intermittent connection)
• limited battery life
• Scalable clients

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• 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

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• 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

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Mobile Agent Systems