Mobile Computing

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					                  Chapter ONE

    Introduction to Mobile Computing

 What is Mobile Computing?
 Motivations for Going Mobile
 Growth of Computing Technologies
 Mobile Computing Vs. Pervasive Computing
 Current Status and the Future
 Example Applications
 Basic Components of a Mobile Computing System
 Mobile Computing Technologies and Research
                What is Mobile Computing?
   What is Mobile Computing?
     A simple answer =>
      • Performing computation in mobile units (i.e., mobile games)
      • Supporting computation to mobile users (i.e., browsing)
     MORE than that …, everything could be mobile …
   Mobile
     Able to move freely. How to support mobility? Connected & communicate
     Through a long wired/wireless. Wireless normally
     Need to consider the scope of mobility and movement speed
   Computing
     The activity of performing computations. What is computation?
     Define the logics (i.e., steps of completing a job and data structures to
      model the information) in a program based on application requirements
     Execute a program to simulate the application (virtual environment) to
      follow the logics to generate (virtual) outputs

   Mobile Computing = Mobile + (Communications) + Computation
                 What is Mobile? Examples
   Mobile clients
       Browsing web in train
       Reading emails
       Playing mobile games on the way to a country park

   Mobile servers
       Mobile server/hosts
       Connecting to a mobile game server

   Mobile data and applications, i.e.,
       Cross harbour tunnel payment system using RFID
       Tracking location information of goods in inventory control
       Finding the nearest restaurants for dinner
                      What are Mobile Units?
   Here we concentrate on mobility, i.e., able to move around (still connected,

   Mobility
       No cable restricts the movement of users and entities in the system
        •   Different surrounding environment and locations
       They can roam/move among different wireless networks and occasionally
        may enter into a wired network (a heterogeneous networking system)

   What are the mobile entities?
       Supporting mobile users (i.e., submitting requests)
       Supporting mobile hosts (i.e., providing services)
       Supporting mobile applications (i.e., systems)
       Supporting applications in mobile devices (i.e., interface for mobile users)
             What is Mobile Computing?
      Note: mobile computing is NOT just mobile communication
Users prefer to have accesses to information/applications anytime, and
  anywhere  SHARE the wired and wireless networks (everywhere)
   to access to APPLICATIONS (Mobile Services)
                   Network/applications everywhere
        This description is similar to Pervasive Computing (PC)

  Portable                                               Data Server,
                                  Network                Other People,
                      Mobile Components
   Mobile communication just provides an architecture/system for
    connecting the entities (mobile units)

   In addition to connections, we also need to support mobile applications
    and manage them. What? How?

   Three basic components
       Networks: mobile/wireless networks + wired networks (how to
        maintain the network quality and guaranteed services, …)
       Devices and computing units (normally limited resources, i.e.,
        processing power, memory, energy, devices)
       Applications (distributed applications with mobile users and mobile
        data, …)
               Mobile Computing Problems
   What are the problems in mobile computing systems?
       Networks: everywhere but without wire => Wireless WAN, Wireless
        LAN, …, poor and unpredictable performance
       Devices: small or even tiny, limited resources, power and energy, …
       Applications: real-time requirements and proactive services (pushing
        of interested information and alerts), …

   Then, we can design solutions for solving the problems based on the
    identified characteristics (tradeoffs) => mobile ≠mobile

   In general, mobile computing is closely related to pervasive computing
    and distributed computing (similar problems and solution approaches,
    but not exactly the same …)
       I.e., communication problems, data management problem and
        mobility management problems
                  Mobile Communications

   The demand for mobile communication creates the needs for
    integration of wireless networks into existing fixed networks:
      local area networks: standardization of IEEE 802.11
      Internet: Mobile IP extension of the internet protocol IP
      Wide area networks: e.g., internetworking of GSM and ISDN, VoIP
        over WLAN
      …
          What is Mobile Computing?
   Summary

… More than mobile communication
… More than just providing computations to mobile users/in mobile units
… Belongs to distributed computing and related to pervasive computing
    but the focus is different
… Information and applications may be mobile
… Computing and system environment can be highly dynamic
… Need to consider the characteristics of mobile applications,
    limitations of mobile devices, and mobile networks
... Mobility in applications creates new challenges
… Need to minimize the impacts of mobile communication on
    application performance
   What are the Motivations for
         Going Mobile?

  Application Needs from End-Users


Growth of Computing (and other related)
          Growth of Computing Technology
   Standalone computers Vs. Networked computers (connected and can

   Standalone computers: for computation only (like a calculator)
       Limitations …

   Distributed Computing (starting from about 30 years ago)
       A computing job may be divided into sub-tasks to be performed by
        different processing units (in parallel or sequential)
       Middleware provides distribution transparency (distributed
        components but logically centralized interfaces to applications)
       Better performance (concurrency), higher degrees in resources
        sharing, and more reliable and scalable systems, … (adv. of DC)
                     The Middleware

Middleware: hiding the heterogeneity of underlying platform from
          Growth of Computing Technology
   Mobile computing (starting from about 15 years ago)
       Because of the development of wireless communication and mobile
        devices/computing units
       The users may move around with computing units (notebooks,
        laptop, etc.) while connections are still maintained
       The system supports computing tasks/requests from moving users
        through a wireless network (i.e., download files and browsing)

   Note: wireless ≠mobile (cordless phone ≠ mobile phone)
       Wireless: no wire (may be stationary). The mobility may be quite
        limited in scope (stationary is only a relative concept), i.e. download
        files from a notebook through infra red
       Mobile: able to move such that the connectivity is still maintained
        while you are moving or stationary
           Pervasive Vs. Mobile Computing
   Initial definitions (not formal definitions)
   Ubiquitous/Pervasive computing systems
     Providing computing services everywhere and anytime
     It is invisible, and you do not notice it (minimal intervention)
     It is inside things/objects (embedded) and within the living infrastructure
     It is integrated in your everyday life (i.e., in school, in office, at home)
     The objects are mobile so it needs to support mobile computing
   Every ware: exists everywhere (what? Computing units and services)
   Mobile computing systems
     Some of the system components are mobile and applications/services are
   Distributed computing systems
     May be static (fixed locations and wired connection)
     Why wired connections? Better performance
     A task is divided into sub-tasks for parallel/sequential execution
     What are the benefits and costs for distributed computing?
         Pervasive Vs. Mobile Computing
   Mobile computing Vs Pervasive computing
   Structurally are similar (i.e., mobile devices and mobile networks) but
    functional and operation requirements are different
   Mobile computing
     Support mobile applications
     Mobile networks so that users, objects and computing units can be
     Applications are mobile and access to mobile data (sources)
   Pervasive computing
     Also are mobile applications (networks) but MORE than that
     Providing applications everywhere at anytime
     Main requirements are in how to use the applications and how the
       applications fit into our living.
     Requirements: smart spaces/services, invisible, proactive
       localization, etc., and applications become part of our life. They
       become our assistants and secretaries
                  Pervasive Computing Vs.
                     Mobile Computing

PC: smart and fit into our       Distributed Systems
living naturally
What is the meaning of
Do you think that the                        Pervasive
computer systems are easy                    Computing
to use? Input, display,       Mobile         Systems
location, appearances, etc.   Computing
MC: just concentrate on
supporting mobile units
Growth of Computing Technology
            Standalone computers

      Networked computers (connected)

Distributed Computing (sharing and cooperative)

          Mobile computing (Current)

 Pervasive Computing (Moving into the Future)
            Growth of Computing Technology
   Why do we have such a computing trend?
       Distributed: performance reasons
        •   What are the performance requirements?
        •   Throughput, response time, quality, reliability, etc.
        •   Sharing of resources and cooperation in completing a task
       DC and PC:
        •   Our life and living, thus our needs (follow us) are mobile
        •   Nothing is static (absolutely) in our world, i.e., always changing including
            locations and our needs
        •   Our world is distributed (centralized is again a relative concept)
        Note: computing systems simulate our world and perform logic
        operations similar to the way that are happened in our world
     Improvements in hardware/electronic technologies and operation
      environment (i.e., OS, networks and tools for operations/development)
      • More powerful and smaller devices, higher bandwidth networks, more
        network connection points for mobile users
        Mobile Phones per 100 People (1999)
    Great Britain
                    0   10       20          30   40          50      60

2005: 70-90% penetration in Western Europe
                                                       Fr. Schiller
    Worldwide cellular subscriber growth

      Subscribers [million]





                                     1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002

Note that the curve starts to flatten in 2000 – 2008: over 3.3 billion subscribers

                                                                            Fr. Schiller
                     The Current Status
   Build on top of existing computing trends
     Driven by our needs and new technologies (needs <=> products)
     New needs create new products (both hardware and software)
       • Any suggestions of new products?
     New products create new needs

   Nowadays, many electronic devices are equipped with a processor
    (intelligence & computation) and memory for performing computing jobs,
    i.e., mobile phone, camera and MP3 players. Mobile phones do not just
    mobile phones

   Are they computers? Yes? Perform computing jobs = “Computers”
     Remember what is the Chinese meaning of “computing”
     Each one simulates a “part” of our daily life
                       The Current Status
   Currently, most of these devices/systems are embedded and semi-
    closed systems (mobile computing)
       Embedded system: predefined functions to be completely
        performed by the device itself
       Closed system: standalone system, and no direct connection (I/O)
        with other devices (separated)
       Semi-closed system: limited connections

   The future could be very different => all connected computing units
                          The Current Status
   Network everywhere
       Fixed networks, mobile networks, ad hoc networks are building to
        connect the devices together and to other parts of the systems
       I.e., bluetooth devices, your video camera, HiFi and TV sets are
        connected to your computers

   Current limitations
       The connections are still not reliable and have limitations in
       Energy and computation power are still problems
       Reliability and stability is another important concern
       Any more …
       These are the problems that we need to resolve
                      The Current Trends
   Solving the problems needs to identify the characteristics of the new
    (mobile and pervasive) applications

   What are the differences between traditional and mobile computing
       Further decentralization of devices and getting smaller in size
       Localization in processing
       Functions: Diversification Vs Integration
       Connectivity (everywhere)
       Real-time tasks (getting real-time information and responses)
       Proactive Requirements (pushing of information)
       Any more?
                      The Current Trends

   Further decentralization and getting smaller in size
     Continue to shift from a centralized computing to a decentralized
       computing (benefits of DC)
     Many small computing units are connected by wired and wireless
       • Price/performance and reliable distributed computing services
       • Different computing units for different purposes/functions and may
         work together (collaborative)
       • Connections can be ad hoc or pre-defined and more long lasting
                       The Current Trends
   Localization: Computation (performed by multiple computing units) is
    performed close to the place where the event is detected (real-time
     Computation is performed at device level if possible (what are the
     From Client/Server to Peer-to-peer (same level)
     Advantages of distributed computing => reliability, scalability, etc..
     Faster in response (localized processing)
     Minimize data transmission workload
     If you have a problem and want someone to help you, will you ask
       someone next to you or far away from you?
                        The Current Trends
   Diversification Vs. Integration
       Different types of embedded devices for their own functions (mobile
        phone, MP3 player, camera and TV) and operation environment
       Diversification: mobile phone, MP3 player, camera…
       Integration: one device contains all
       Integration in the future??? Benefits?
       Do you prefer to have a single devices to do all the jobs?
                         The Current Trends

   Connectivity (both fixed and mobile)
       The computing units are connected if necessary (even moving)
       The computing units work together cooperatively to complete a task
       Heterogeneous networks with different QoS of services
        •   QoS: Quality of services (a measure of how good the service is)
        •   Normally, we require a guarantee of QoS and not just a claim of a
            function. I.e., you may use your mobile phone for watching TV
       Is it better to have a single high performance global network instead
        of multiple networks? Yes, no handoffs and easier to manage but it
        may not be adaptive (Technologies advance gradually)
                     The Current Trends

   Real-time jobs
     Our world is changing => mostly we need to respond to our event
      immediately => use computers to assist us to deal with the “real-
      time” events occurring in our world
     I.e., Booking, car park status, navigation, on-line games
     Real-time: current state => then, computation, if action needed
      (actuation) => generate a response immediately (within a pre-
      defined time frame)
     Real-time: tasks have deadlines on completion times
     Multiple tasks => multiple deadline constraints need to be met =>
      scheduling problem
                      The Current Trends
   Proactive requirements
     Event monitoring/surveillance: want to get the latest status of the
       world, then react to it immediately, i.e., latest stock prices, sport
       results, ticketing and transportation information
     Define monitoring rules
     Once a new data item is received, check the new system status
     If the conditions are met, trigger an action (actuator
     If not ignore (filter out) the received data items
     A lot of data values are pushing in front of you and require
       attention for processing
       • Prioritizing, filtering and consolidation (summary)
     Filtering and pushing interested values => You can concentrate
       on those interested tasks
                    Example Applications
   Vehicles
      Transmission of news, road condition, weather, music, etc.
      Personal communication using GSM
      Positioning via GPS
      Local ad-hoc network with vehicles close-by to prevent accidents,
       guidance system, redundancy
      Vehicle data (e.g., from busses, high-speed trains) can be
       transmitted in advance for maintenance

   Emergencies
      Early transmission of patient data to the hospital, current status,
       first diagnosis
      Replacement of a fixed infrastructure in case of earthquakes,
       hurricanes, fire etc.
      Crisis, war, ...
                    Example Applications
   Traveling salesmen
      Direct access to customer files stored in a central location
      Consistent databases for all agents
      Mobile office

   Replacement of fixed networks
      Remote sensors, e.g., weather, earth activities
      Flexibility for trade shows
      LANs in historic buildings

   Entertainment, education, ...
      Outdoor Internet access
      Intelligent travel guide with up-to-date
       location dependent information
      Ad-hoc networks for multi user games
                     The Next Computers
   Computers are integrated
      Small, cheap, portable, replaceable - no more separate devices

   Technology is in the background
      Computer are aware of their environment and adaptive (“location
      Computer recognize the location of the user and react appropriately
       (e.g., call forwarding, fax forwarding, “context awareness”))

   Advances in technology
      More computing power in smaller devices
      Flat, lightweight displays with low power consumption
      New user interfaces due to small dimensions
      More bandwidth per cubic meter
      Multiple wireless interfaces: wireless LANs, wireless WANs, regional
       wireless telecommunication networks etc. (“overlay networks”)
              Location Dependent Services
   LDS: different locations providing different services
   Location aware services
      What services, e.g., printer, fax, phone, server etc. exist in the local
   Follow-on services
      Automatic call-forwarding, transmission of the actual workspace to
        the current location
   Information services
      “Push”: e.g., current special offers in the supermarket
      “Pull”: e.g., where is the Black Forrest Cheese Cake?
   Support services
      Caches, intermediate results, state information etc. “follow” the
        mobile device through the fixed network
   Privacy, security and reliability
      Who should gain knowledge about the location
                 Basic Components of
              a Mobile Computing System
   Front end devices, networks, backend server, operating systems, tools
    and development, and applications
     Could be very different in the future

   FE devices: for capturing the system status (generating updates) and for
     User devices: PDA, notebook computers, mobile phones, wearable
       computers, etc..
     Sensors and mobile units

   Work stations: for integration of data from various sources and devices

   Backend servers: for processing the updates and responding to the
    events occurred in the environment
                  Basic Components of
               a Mobile Computing System
   Networks: connecting front-end devices to the workstations and servers
     Satellite communication, GSM, 3G, wireless LAN, personal area
      network (PAN), ad hoc network and sensor network

   Operating systems: build on top of the networks for connection, i.e.,
    Palm OS, WinCE, EPOC, etc.

   Tools and standards: for development, i.e., J2ME, Jini, Bluetooth, WAP,
    GSM, ..

   Mobile applications (entertainment and services): MP3 players, game
    console, digital camera, intelligent toys, etc. (cooperative and work
                                     Mobile Devices
              Pager                        PDA                                      Laptop/Notebook
              • receive only               • graphical displays                     • fully functional
              • tiny displays              • character recognition                  • standard applications
              • simple text                • simplified WWW


                          Mobile phones                      Palmtop (wearable computer)
                          • voice, data                      • tiny keyboard
                          • simple graphical displays        • simple versions
                                                               of standard applications

              How do you feel about the performance and the uses of your
              mobile devices?
                                                                     Fr. Schiller
                  Wearable Computers
 Wearable computers: the computers
  that you can wear
    Simplified I/O (reduced display) and
      voice input together with simple
      panel to make it more easy to use
    Compact design to make it easy to
      carry (reduce unnecessary

 What can you do with this device?

 Easy to operate and fit into your
  working/living environment

 What will be the future wearable
  computers? Tiny, easier to operate, …
                       Wireless Sensors
   What is a sensor?
      Sensing the environment (i.e., temperature, pressure, presence
        of unknown objects, etc.)
      Sensors continuously (periodically) capture the current status of
        their operation environment
   MICA Motes, sensors, and TinyOS => go further small and tiny and
    large in number
   Why sensors? Work like our sensors. Small and can distributed in
    large number

               Effects of Device Portability
   Power consumption
      Limited computing power, low quality displays, small disks due to
       limited battery capacity
      CPU: power consumption ~ CV2f
         • C: internal capacity, reduced by integration
         • V: supply voltage, can be reduced to a certain limit
         • f: clock frequency, can be reduced temporally
   Loss of data
      Higher probability, has to be included in advance into the design
       (e.g., defects, theft)
   Limited user interfaces
      Compromise between size of fingers and portability
      Integration of character/voice recognition, abstract symbols
   Limited memory limited usage of mass memories with moving parts
      Flash-memory or as alternative
           Networks for Mobile Computing
   Integration of heterogeneous networks
     Network at everywhere enabling anytime-anywhere connectivity
     An integrated network of fixed and mobile networks
     Tremendous improvements in fixed network bandwidth
     Broadband connectivity to the home and office (i.e., the “last mile”
       has been solved)
     Variation in wireless connection quality and reliability
     How to switch from one network into another (vertical handoff)

   Examples of mobile communications
     Satellites communications
     WWAN (cellular digital packet data: uses satellite, 19.2kps)
     Cellular networks: GSM, GPRS, TDMA, CDMA
     Wireless LAN (IEEE 802.11a, IEEE 802.11b) (11-25Mps)
     Ad hoc networks (networks with dynamic configuration)
       Networks in
Mobile Computing Systems

                                             Fr. Schiller
Note the variation in connection qualities
 Integration of heterogeneous fixed and
 mobile networks with varying
 transmission characteristics

         Vertical Handoff                                         regional
         From network system to
         another one

                                                  metropolitan area

                                                   Handoff from one base
                               campus-based        station to another one

                      personal area    Detection and
                                       performance of
Why do we need handoff?                                     Fr. Schiller
                                       handoff operations
Signaling problem
Typical Application: Road Traffic

   cdma2000, TETRA, ...

                          Personal Travel Assistant,
                          PDA, Laptop,
                          GSM, UMTS, WLAN,
                          Bluetooth, ...

                             Fr. Schiller
            Mobile and Wireless Services
              Always Best Connected
                                    UMTS, GSM       LAN
DSL/ WLAN    GSM/GPRS 53 kbit/s     115 kbit/s      100 Mbit/s,
3 Mbit/s     Bluetooth 500 kbit/s                   WLAN
                                                    54 Mbit/s

                                                                  2 Mbit/s

    GSM/EDGE 384 kbit/s,
    DSL/WLAN 3 Mbit/s
                                                 UMTS, GSM
                           GSM 115 kbit/s,       384 kbit/s
                           WLAN 11 Mbit/s
                                             Fr. Schiller
              Simple Reference Model

Application                                            Application

Transport                                              Transport

 Network              Network      Network              Network

Data Link             Data Link   Data Link            Data Link

 Physical             Physical    Physical              Physical

              Radio                           Medium

                                                   Fr. Schiller
       Influence of mobile communication to
                  the layer model
Application layer        service location
                         new/adaptive applications
Transport layer          congestion/flow control
                         quality of service
Network layer            addressing, routing
                         device location
Data link layer          authentication
                         media access/control
Physical layer           modulation

                                      Fr. Schiller
                       Ad hoc Network
   Communication by radio frequency (limited range)
   Provide point-to-point, multicast and broadcast
   A large number of mobile (fixed) nodes
   No fixed configuration (moving, mobile ad hoc network (MANET))
   They communicate with their neighboring nodes using radio signals
       Limited bandwidth and may have collision if no coordination
        (medium access control protocol)
   The neighboring nodes should not be far from it
   If a node (source node) wants to communicate with another node
    (destination node), it may rely on relay nodes to forward the message
    to the destination node
           Mobile Network Characteristics
   Variant connectivity (unstable)
      Low bandwidth and low reliability (obstacles)
   Frequent disconnection
      Predictable or unpredictable
      Location dependent
   High error rate (signaling problems)
      Error corrected coding for transmission
      Increase the message size (message overhead)
   Asymmetric communication
      Downlink bandwidth >> uplink bandwidth
      Downlink: from base station to mobile unit
      Uplink: from mobile unit to base station
   Monetarily expensive
      Charges per connection or message/packet
      What are the consequences? => connect only if necessary
   Connectivity is weak and intermittent
      Pre-fetching of data under good connection
     Wireless Networks Vs. Fixed Networks
   Higher loss-rates due to interference
      Emissions of, e.g., engines, lightning
   Restrictive regulations of frequencies
      Frequencies have to be coordinated, useful frequencies are almost
       all occupied
   Low transmission rates
      Local some Mbit/s, regional currently, e.g., 53kbit/s with
   Higher delays, higher jitter
      Connection setup time with GSM in the second range, several
       hundred milliseconds for other wireless systems
   Lower security, simpler active attacking
      radio interface accessible for everyone, base station can be
       simulated, thus attracting calls from mobile phones
   Always shared medium
      Secure access mechanisms important
               Integrations of Technologies

 Applications:                                 Protocols:
                        Infrastructure:         IP,B3G              Performance:
  Video call,          Wireless Networks                             Quality of
     Conf,                                     Multimedia
                           & Internet            Flows                 Service
On-demand etc.


  High Performance                  Advanced                        Multimedia/Smart
 & Client on Demands             Wireless/Mobile                         Phones
                                                     Fr. Schiller
      Areas of Research in Mobile Computing
   Wireless communication and mobile networks
      Transmission quality (bandwidth, error rate, delay)
      Modulation, coding, interference
      Media access control, routing and connections, …

   Supporting mobility Services
      Location dependent services, location transparency
      Quality of service support (delay, jitter, security)
      Mobile data management, mobility management
      Supporting disconnected operations and caching of data, …

   Portability and adaptability
      Power consumption
      Limited computing power, sizes of display
      Usability, adaptation and trans-coding, security and authentication, …
   …
   Schiller (ch 1)
   M. Satyanarayanan, “Pervasive Computing Vision and Challenges”
    IEEE Personal Communications, Aug 2001

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