cellular networks and mobile computing coms 6998-10, spring 2013

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Cellular Networks and Mobile Computing COMS 6998-10, Spring 2013. Instructor: Li Erran Li ( lierranli@cs.columbia.edu ) http://www.cs.columbia.edu/~lierranli/coms6998-10Spring2013/ 2/26/2013: Introduction to Cellular Networks. Announcements. Programming assignment 2 will be due tomorrow - PowerPoint PPT Presentation


  • Cellular Networks and Mobile ComputingCOMS 6998-10, Spring 2013Instructor: Li Erran Li (lierranli@cs.columbia.edu)http://www.cs.columbia.edu/~lierranli/coms6998-10Spring2013/2/26/2013: Introduction to Cellular Networks

  • AnnouncementsProgramming assignment 2 will be due tomorrowProgramming assignment 3 will be due March 13. Please start early!Two lab sessions will be scheduledPlease email me the presentation slides the day before!*

  • Review of Previous LectureWhat are the different approaches of virtualization?

  • Review of Previous LectureWhat are the different approaches of virtualization?Bear-metal hypervisor, hosted hypervisor, container (Linux LXC, Samsung Knox)

  • Bare-Metal Hypervisorpoor device support / sharingCourtesy: Jason Nieh et al.

  • Hosted Hypervisorpoor device performanceCourtesy: Jason Nieh et al.

  • Review of Previous Lecture (Contd)What approach does Cell use?What are the key design choices for Cells extremely low overhead?

  • Review of Previous Lecture (Contd)Device namespaceIt is designed to be used by individual device drivers or kernel subsystems to tag data structures and to register callback functions. Callback functions are called when a device namespace changes state. Each VP uses a unique device namespace for device interaction. Cells leverages its foreground-background VP usage model to register callback functions that are called when the VP changes between foreground and background state.

  • Device Namespacessafely, correctly multiplex access to devicesCourtesy: Jason Nieh et al.

  • Review of Previous Lecture (Contd)What are the most expensive flash memory operations?Random readRandom writeSequential writeSequential read

  • Random versus Sequential DisparityPerformance for random I/O significantly worse than seq; inherent with flash storageMobile flash storage classified into speed classes based on sequential throughputRandom write performance is orders of magnitude worseConsumer-grade SD performancePerformance MB/s

    For several popular apps, substantialfraction of I/O is random writes (including web browsing!)Courtesy: Nitin Agrawal et al.

    Vendor(16GB)Speed ClassCost US $Seq WriteRand WriteTranscend2264.21.18RiData2277.90.02Sandisk4235.50.70Kingston4254.90.01Wintec62515.00.01A-Data63010.80.01Patriot102910.50.01PNY102915.30.01

  • Motion Statesitting, walking, runningInterruptibleyes, noLogical Locationhome, office, mallShould OS Manage Context?export Context Data Units (CDUs) rather than raw sensor datahigher-level abstraction than bytesapps query or subscribe to CDUseach CDU is defined by a CDU Generator: a graph of processing componentscombine Generators into composite context dataflowprovide a base CDU vocabulary (that is extensible)

  • Motion FeaturesMotion Statesitting, walking, runningAudioAudio FeaturesInterruptibleyes, noCDU2CDU3IMUaccel, gyro, magSilence FilterLogical Locationhome, office, mallCDU1GeolocationGPS, Cell, WiFiLocation DBapp Aapp Gapp ZUser space

    Kernel spaceContext Data GeneratorsCondOS Designother OS servicesScheduling SecurityI/OMemoryManagementEnergyManagementcontextdataflowexample

  • SyllabusMobile App Development (lecture 1,2,3)Mobile operating systems: iOS and Android Development environments: Xcode, Eclipse with Android SDKProgramming: Objective-C and android programmingSystem Support for Mobile App Optimization (lecture 4,5)Mobile device power models, energy profiling and ebug debuggingCore OS topics: virtualization, storage and OS support for power and context managementInteraction with Cellular Networks (lecture 6,7,8) Basics of 3G/LTE cellular networksMobile application cellular radio resource usage profilingMeasurement-based cellular network and traffic characterizationInteraction with the Cloud (lecture 9,10)Mobile cloud computing platform services: push notification, iCloud and Google Cloud MessagingMobile cloud computing architecture and programming modelsMobile Platform Security and Privacy (lecture 11,12,13)Mobile platform security: malware detection and characterization, attacks and defensesMobile data and location privacy: attacks, monitoring tools and defenses*

  • OutlineGoal of this lecture: understand the basics of current networks and future directions

    Current Cellular NetworksIntroductionRadio AspectsArchitecturePower ManagementSecurityQoSWhat Is Next?A Clean-Slate Design: Software-Defined Cellular NetworksConclusion and Future Work


  • Cellular Networks Impact our Lives*

  • Mobile Data Tsunami Challenges Current Cellular Technologies Global growth 18 times from 2011 to 2016

    AT&T network:Over the past five years, wireless data traffic has grown 20,000%At least doubling every year since 2007

    Existing cellular technologies are inadequateFundamental redesign of cellular networks is neededSource: CISCO Visual Networking Index (VNI) Global Mobil Data Traffic Forecast 2011 to 2016*

  • Global ConvergenceLTE is the major technology for future mobile broadbandConvergence of 3GPP and 3GPP2 technology tracksConvergence of FDD and TDD into a single technology track


  • LTE deployments89 commercial networks launchedCourtesy: Zoltn Turnyi

  • Mobile subscriptions by technology2008-2017 (estimate)Courtesy: Zoltn Turnyi

  • 3GPP introduction3rd Generation Partnership ProgramEstablished in 1998 to define UMTSToday also works on LTE and access-independent IMSStill maintains GSM3GPP standardizes systemsArchitecture, protocolsWorks in releasesAll specifications are consistent within a release

  • 3GPP TS 23.401 V11.2.0 Stage 1Requirements It shall be possible to... It shall support3GPP way of workingE.g., 22-series specsStage 2Architecture Nodes, functions Reference points Procedures (no errors)Stage 3Protocols Message formats Error casesE.g., 23-series specsE.g., 29-series specsSpecification numbering example: Spec. numberTS=Technical Specification (normative)TR=Technical Report (info only)Release Consistent set of specs per release New release every 1-2 yearsUpdated after a meetingCourtesy: Zoltn Turnyi

  • 3GPP specification groups2G3G/LTESystemProtocols

  • Starting points on 3GPP specificationshttp://www.3gpp.org/specification-numbering Pointers to the series of specificationsArchitecture documents in 23-seriesMain architecture references23.002 Overall architecture reference23.401 Evolved Packet Core with LTE access, GTP-based core23.060 2G/3G access, and integration to Evolved Packet Core23.402 Non-3GPP access, and PMIP-based core

    Courtesy: Zoltn Turnyi

  • ExampleA base station with 3 sectors (3 cells)Courtesy: Zoltn Turnyi

  • Large distancesTerminals do not see each otherTight control of power and timing neededHighly variable radio channel quick adaptation neededMany users in a cell A UMTS cell can carry roughly 100 voice calls on 5 MHz Resource sharing must be fine grained but also flexibleQuality of Service with resource managementVoice low delay, glitch-free handoversInternet traffic more, more, moreBattery consumption criticalLow energy states, wake-up procedures Parsimonious signalingKey challengesCourtesy: Zoltn Turnyi

  • Radio basics

  • Physical Layer: UMTSSimultaneous meetings in different rooms (FDMA)Simultaneous meetings in the same room at different times (TDMA) Multiple meetings in the same room at the same time (CDMA)*Courtesy: Harish Vishwanath

  • Code Division Multiple Access (CDMA) Use of orthogonal codes to separate different transmissionsEach symbol or bit is transmitted as a larger number of bits using the user specific code SpreadingSpread spectrum technologyThe bandwidth occupied by the signal is much larger than the information transmission rateExample: 9.6 Kbps voice is transmitted over 1.25 MHz of bandwidth, a bandwidth expansion of ~100*Courtesy: Harish VishwanathPhysical Layer: UMTS (Contd)

  • Physical Layer: UMTS (Contd)Uses spread-spectrum to separate usersCommon 5 MHz channelsSupports soft-handoverMultiple base stations send/receive same data to the userRecombining the two paths result in better channelRequires real-time network between base station and RNC

    UMTS Universal Mobile Telecommunication SystemCDMA Code Division Multiple AccessUE User EquipmentRNC Radio Network Controller

  • Resource controlCost:More radio resourcesMore battery needHSPA channel(packet-oriented high data rate)HSPACommon channel(low data rate, random access)FACHBattery saving (connected)Battery saving (disconnected)IDLECost:RNC processing power when switching between statesDedicated channels(64, 128, 384 kbits/s, 2 Mbit/s)DCHDCHURACourtesy: Zoltn Turnyi

  • HSPAHigh Speed Packet AccessPacket oriented extension to WCDMATime Division Multiplexing within a common channelOpportunistic schedulingUsers with currently good reception receive more resourcesHigher overall capacity than equal shareHybrid ARQ with soft combiningOnly additional redundancy is transmitted on a frame error, not the full frameMost radio functions moved to NodeBNo soft handover in downlink

  • LTE air interfaceThe key improvement in LTE radio is the use of OFDMOrthogonal Frequency Division Multiplexing2D frame: frequency and timeNarrowband channels: equal fading in a channelAllows simpler signal processing implementationsSub-carriers remain orthogonal under multipath propagation


  • Orthogonal Frequency Division Multiple Access (OFDM)Closely spaced sub-carriers without guard band Each sub-carrier undergoes (narrow band) flat fading- Simplified receiver processing Frequency or multi-user diversity through coding or scheduling acr


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