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Cellular Networks and Mobile Computing COMS 6998-10, Spring 2013

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

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Cellular Networks and Mobile Computing COMS 6998-10, Spring 2013

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  1. Cellular Networks and Mobile ComputingCOMS 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

  2. Announcements • Programming assignment 2 will be due tomorrow • Programming assignment 3 will be due March 13. Please start early! • Two lab sessions will be scheduled • Please email me the presentation slides the day before!

  3. Review of Previous Lecture What are the different approaches of virtualization?

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

  5. OS Kernel OS Kernel OS Kernel Hypervisor / VMM Hardware Bare-Metal Hypervisor poor device support / sharing Courtesy: Jason Nieh et al.

  6. OS OS OS kernel module emulated devices Hypervisor / VMM Hardware Host OS Kernel Hosted Hypervisor poor device performance Courtesy: Jason Nieh et al.

  7. Review of Previous Lecture (Cont’d) What approach does Cell use? What are the key design choices for Cell’s extremely low overhead?

  8. Review of Previous Lecture (Cont’d) • Device namespace • It 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.

  9. device namespaces VP 2 VP 1 VP 3 Linux Kernel GPU Input Power Android... Sensors Audio/Video RTC / Alarms Framebuffer WiFi Cell Radio ••• Device Namespaces safely, correctly multiplex access to devices ••• Courtesy: Jason Nieh et al.

  10. Review of Previous Lecture (Cont’d) • What are the most expensive flash memory operations? • Random read • Random write • Sequential write • Sequential read

  11. Random versus Sequential Disparity Performance MB/s Consumer-grade SD performance For several popular apps, substantial fraction of I/O is random writes (including web browsing!) • Performance for random I/O significantly worse than seq; inherent with flash storage • Mobile flash storage classified into speed classes based on sequential throughput • Random write performance is orders of magnitude worse Courtesy: Nitin Agrawal et al.

  12. Should OS Manage Context? Logical Location home, office, mall Motion State sitting, walking, running Interruptible yes, no • export Context Data Units (CDUs) rather than raw sensor data • higher-level abstraction than bytes • apps query or subscribe to CDUs • each CDU is defined by a CDU Generator: a graph of processing components • combine Generators into composite context dataflow • provide a base CDU vocabulary (that is extensible)

  13. CondOS Design app A app G app Z … User space Kernel space other OS services CDU1 CDU2 CDU3 Scheduling Memory Management I/O Interruptible yes, no Logical Location home, office, mall Motion State sitting, walking, running Security Energy Management Audio Features Context Data Generators Location DB Motion Features context dataflow example Silence Filter Geolocation GPS, Cell, WiFi IMU accel, gyro, mag Audio

  14. Syllabus • Mobile App Development (lecture 1,2,3) • Mobile operating systems: iOS and Android • Development environments: Xcode, Eclipse with Android SDK • Programming: Objective-C and android programming • System Support for Mobile App Optimization (lecture 4,5) • Mobile device power models, energy profiling and ebug debugging • Core OS topics: virtualization, storage and OS support for power and context management • Interaction with Cellular Networks (lecture 6,7,8) • Basics of 3G/LTE cellular networks • Mobile application cellular radio resource usage profiling • Measurement-based cellular network and traffic characterization • Interaction with the Cloud (lecture 9,10) • Mobile cloud computing platform services: push notification, iCloud and Google Cloud Messaging • Mobile cloud computing architecture and programming models • Mobile Platform Security and Privacy (lecture 11,12,13) • Mobile platform security: malware detection and characterization, attacks and defenses • Mobile data and location privacy: attacks, monitoring tools and defenses

  15. Outline Goal of this lecture: understand the basics of current networks and future directions • Current Cellular Networks • Introduction • Radio Aspects • Architecture • Power Management • Security • QoS • What Is Next? • A Clean-Slate Design: Software-Defined Cellular Networks • Conclusion and Future Work

  16. Cellular Networks Impact our Lives More Infrastructure Deployment More Mobile Connection 1010100100001011001 0101010101001010100 1010101010101011010 1010010101010101010 0101010101001010101 More Mobile Users More Mobile Information Sharing

  17. Mobile Data Tsunami Challenges Current Cellular Technologies Source: CISCO Visual Networking Index (VNI) Global Mobil Data Traffic Forecast 2011 to 2016 • 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 inadequate • Fundamental redesign of cellular networks is needed

  18. Global Convergence IS-95 cdma2000 EV-DO D-AMPS D-AMPS PDC PDC ? WiMAX • LTE is the major technology for future mobile broadband • Convergence of 3GPP and 3GPP2 technology tracks • Convergence of FDD and TDD into a single technology track 3GPP GSM WCDMA HSPA LTEFDD and TDD TD-SCDMA HSPA/TDD 3GPP2 IEEE

  19. LTE deployments89 commercial networks launched Courtesy: Zoltán Turányi

  20. Mobile subscriptions by technology2008-2017 (estimate) Courtesy: Zoltán Turányi

  21. 3GPP introduction • 3rd Generation Partnership Program • Established in 1998 to define UMTS • Today also works on LTE and access-independent IMS • Still maintains GSM • 3GPP standardizes systems • Architecture, protocols • Works in releases • All specifications are consistent within a release

  22. 3GPP way of working E.g., 22-series specs • Stage 1 • Requirements • “It shall be possible to...” • “It shall support…” • Stage 2 • Architecture • Nodes, functions • Reference points • Procedures (no errors) • Stage 3 • Protocols • Message formats • Error cases E.g., 23-series specs E.g., 29-series specs Specification numbering example: 3GPP TS 23.401 V11.2.0 Updated after a meeting TS=Technical Specification (normative) TR=Technical Report (info only) • Release • Consistent set of specs per release • New release every 1-2 years Spec. number Courtesy: Zoltán Turányi

  23. 3GPP specification groups Protocols 3G/LTE System 2G

  24. Starting points on 3GPP specifications • http://www.3gpp.org/specification-numbering • Pointers to the series of specifications • Architecture documents in 23-series • Main architecture references • 23.002 – Overall architecture reference • 23.401 – Evolved Packet Core with LTE access, GTP-based core • 23.060 – 2G/3G access, and integration to Evolved Packet Core • 23.402 – Non-3GPP access, and PMIP-based core Courtesy: Zoltán Turányi

  25. Example A base stationwith 3 sectors (3 cells) Courtesy: Zoltán Turányi

  26. Key challenges • Large distances • Terminals do not see each other • Tight control of power and timing needed • Highly variable radio channel – quick adaptation needed • Many users in a cell • A UMTS cell can carry roughly 100 voice calls on 5 MHz • Resource sharing must be fine grained – but also flexible • Quality of Service with resource management • Voice – low delay, glitch-free handovers • Internet traffic – more, more, more • Battery consumption critical • Low energy states, wake-up procedures • Parsimonious signaling Courtesy: Zoltán Turányi

  27. Radio basics

  28. Physical Layer: UMTS Simultaneous 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

  29. Physical Layer: UMTS (Cont’d) Code Division Multiple Access (CDMA) • Use of orthogonal codes to separate different transmissions • Each symbol or bit is transmitted as a larger number of bits using the user specific code – Spreading • Spread spectrum technology • The bandwidth occupied by the signal is much larger than the information transmission rate • Example: 9.6 Kbps voice is transmitted over 1.25 MHz of bandwidth, a bandwidth expansion of ~100 Courtesy: Harish Vishwanath

  30. Physical Layer: UMTS (Cont’d) RNC RNC RNC UMTS – Universal Mobile Telecommunication System CDMA – Code Division Multiple Access UE – User Equipment RNC – Radio Network Controller • Uses spread-spectrum to separate users • Common 5 MHz channels • Supports soft-handover • Multiple base stations send/receive same data to the user • Recombining the two paths result in better channel • Requires real-time network between base station and RNC

  31. Resource control HSPA channel (packet-oriented high data rate) HSPA Dedicated channels (64, 128, 384 kbits/s, 2 Mbit/s) DCH DCH Cost: RNC processing power when switching between states Cost: More radio resources More battery need Common channel (low data rate, random access) FACH Battery saving(connected) URA Battery saving(disconnected) IDLE Courtesy: Zoltán Turányi

  32. HSPA • High Speed Packet Access • Packet oriented extension to WCDMA • Time Division Multiplexing within a common channel • Opportunistic scheduling • Users with currently good reception receive more resources • Higher overall capacity than equal share • Hybrid ARQ with soft combining • Only additional redundancy is transmitted on a frame error, not the full frame • Most radio functions moved to NodeB • No soft handover in downlink

  33. LTE air interface One resource block 12 subcarriers during one slot (180 kHz × 0.5 ms) One resource element 12 subcarriers One OFDM symbol One slot frequency Time domain structure Frame (10 ms) • The key improvement in LTE radio is the use of OFDM • Orthogonal Frequency Division Multiplexing • 2D frame: frequency and time • Narrowband channels: equal fading in a channel • Allows simpler signal processing implementations • Sub-carriers remain orthogonal under multipath propagation time Slot (0.5 ms) Subframe (1 ms)

  34. LTE air interface: Downlink • 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 across sub-carriers • Dynamic power allocation across sub-carriers allows for interference mitigation across cells • Orthogonal multiple access T large compared to channel delay spread 1 T Frequency Narrow Band (~10 Khz) Wide Band (~ Mhz) Sub-carriers remain orthogonal under multipath propagation Courtesy: Harish Vishwanath

  35. LTE air interface: Uplink • Users are carrier synchronized to the base • Differential delay between users’ signals at the base need to be small compared to symbol duration User 1 W • Efficient use of spectrum by multiple users • Sub-carriers transmitted by different users are orthogonal at the receiver • - No intra-cell interference • CDMA uplink is non-orthogonal since synchronization requirement is ~ 1/W and so difficult to achieve User 2 User 3 Courtesy: Harish Vishwanath

  36. LTE air interface: Multiplexing • Each color represents a user • Each user is assigned a frequency-time tile which consists of pilot sub-carriers and data sub-carriers • Block hopping of each user’s tile for frequency diversity Frequency Typical pilot ratio: 4.8 % (1/21) for LTE for 1 Tx antenna and 9.5% for 2 Tx antennas Time • Pilot sub-carriers Courtesy: Harish Vishwanath

  37. LTE vs UMTS (3G): Physical Layer • UMTS has CELL_FACH • Uplink un-synchronized • Base station separates random access transmissions and scheduled transmissions using CDMA codes • LTE does not have CELL_FACH • Uplink needs synchronization • Random access transmissions will interfere with scheduled transmissions

  38. LTE Scheduling • Assign each Resource Block to one of the terminals • LTE – channel-dependent scheduling in time and frequency domain • HSPA – scheduling in time-domain only Time-frequency fading, user #2 Time-frequency fading, user #1 User #1 scheduled User #2 scheduled 1 ms Time 180 kHz Frequency Courtesy: Zoltán Turányi

  39. LTE vs. WCDMA 1.4 MHz 3 MHz 5 MHz 10 MHz 15 MHz 20 MHz 6 RB (1.4 MHz) 100 RB (20 MHz) • No Soft handover in OFDM • All real-time functions can be done in the base station • No need for a central RNC • No need for a real-time network between the RNC and base station • Packet oriented • Supports bursty traffic and statistical multiplexing by default • No specific support for circuit switched traffic • Much more flexible spectrum use Courtesy: Zoltán Turányi

  40. Architecture

  41. Pre-rel.8 Architecture PS Core Network • Why separate RAN and CN? • Two CNs with same RAN • Multiple RANs with same CN • Modularization • Independent scaling, deployment and vendor selection • Why two GSNs? • Roaming: traffic usually taken home • Independent scaling, deployment and vendor selection • User can connect to multiple PDNs CSCN Gi • First-hop router • GW towards external PDNs • VPN support over Gi • IP address management • Policy Control GGSN Gn/Gp MSC • Manage CN procedures • HSS connection (authenticator) • Idle mode state • Lawful Intercept • Bearer management SGSN IuCS IuPS 3G Radio Access Network • Real-time radio control • Radio Resource Management • Soft handover • UP Ciphering • Header Compression RNC Iub GPRS – Generic Packet Radio Service GGSN – Gateway GPRS Support Node SGSN – Serving GPRS Support Node RNC – Radio Network Controller PDN – Packet Data Network CN – Core Network PS – Packet Switched CS – Circuit Switched MSC – Mobile Switching Center HSS – Home Subscriber Server NodeB • L1 • HSPA scheduling

  42. Drivers for change Overhead of separate CS core when bulk of traffic is PS PS Core Network CSCN Gi • First-hop router • GW towards external PDNs • VPN support over Gi • IP address management • Policy Control GGSN Too many specialized user plane nodes Gn/Gp MSC • Manage CN procedures • HSS connection (authenticator) • Idle mode state • Lawful Intercept • Bearer management SGSN IuCS IuPS Complex, real-time RAN 3G Radio Access Network • Real-time radio control • Radio Resource Management • Soft handover • UP Ciphering • Header Compression RNC Iub NodeB • L1 • HSPA scheduling Vendor lock-in due to proprietary Iub features Courtesy: Zoltán Turányi

  43. From 3G to EPC/LTE architecture Only two user plane nodes in the typical case. Evolved Packet Core (EPC) SGi PDN GWSGW Packet Data Network GW Serving GW user plane S11 control plane Mobility Management Entity MME User plane/control plane split for better scalability. S1-UP S1-CP LTE Radio Access Network eNodeB eNodeB – Evolved Node B RNC functions moved down to base station PS Core Network CSCN Gi GGSN Gn/Gp MSC SGSN IuCS IuPS PS only RAN and CN 3G Radio Access Network RNC Iub NodeB Courtesy: Zoltán Turányi

  44. Why separate SGW and PDN GW? Evolved Packet Core (EPC) SGi PDN GW Packet Data Network GW S5/S8 SGW Serving GW S11 • SGW and PDN GW separate in some special cases: • Roaming: • PDN GW in home network, • SGW in visited network • Mobility to another region in a large network • Corporate connectivity Mobility Management Entity MME S1-UP S1-CP LTE Radio Access Network eNodeB eNodeB – Evolved Node B Courtesy: Zoltán Turányi

  45. Debate of 2005: “B1 vs B2” Internet/Op.nw. Internet/Op.nw. B1*: All accesses connected to EPC B2*: Inter-AS MM on top of GPRS Core GERAN GERAN GPRS Core SGSN SGSN GGSN UTRAN UTRAN Evolved Access LTE Evolved Packet Core LTE Evolved Packet Core Inter-ASMM Non-3GPP access Non-3GPP access • Conclusion: B1. • Better integration between 3GPP accesses • Fewer user plane entities *Note: Simplified view Courtesy: Zoltán Turányi

  46. Interworking with 3G SGi HSS PDN GW S5 Gn SGW MME SGSN MSC S11 IuCS IuPS RNC S1-U S1-CP Iub eNodeB NodeB UE MSC – Mobile Switching Center Courtesy: Zoltán Turányi

  47. Interworking with non-3GPP accesses SGi HSS PDN GW S5 Gn S2 SGW MME SGSN MSC S11 IuCS IuPS Non-3GPP Access (cdma2000, WiMax, WiFi) RNC S1-U S1-CP Iub eNodeB NodeB UE PMIP – Proxy Mobile IP Courtesy: Zoltán Turányi

  48. Debate of 2006: GTP vs. PMIP SGi HSS PDN GW GTP GTP? GTP S5 Gn PMIP PMIP? S2 SGW MME SGSN MSC PMIP S11 IuCS IuPS Non-3GPP Access (cdma2000, WiMax, WiFi) RNC S1-U S1-CP GTP Iub eNodeB NodeB UE • Conclusion: Specify both Courtesy: Zoltán Turányi

  49. EPC + LTE: 23.401EPC + 2G/3G: 23.060 SGi HSS PDN GW GTP S5 Gn GTP SGW MME SGSN MSC S11 IuCS IuPS RNC S1-U S1-CP GTP Iub eNodeB NodeB UE Courtesy: Zoltán Turányi

  50. EPC + non-3GPP: 23.402 SGi HSS PDN GW S5 PMIP S2 SGW MME PMIP S11 Non-3GPP Access (cdma2000, WiMax, WiFi) S1-U S1-CP GTP eNodeB UE EPC – Evolved Packet Core Courtesy: Zoltán Turányi

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