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CS386W: Wireless Networking

CS386W: Wireless Networking. Lili Qiu UT Austin Sept. 9, 2013. Course Information. Instructor: Lili Qiu, lili@cs.utexas.edu Office: GDC 6.806 Office hour: Mon. 2 – 4 pm or by appt. Lecture: Mon. 9 am – noon TA: Apurv Bhartia apurvb@cs.utexa.edu TA office hour: Wed. 10-11:30am

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CS386W: Wireless Networking

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  1. CS386W: Wireless Networking Lili Qiu UT Austin Sept. 9, 2013

  2. Course Information • Instructor: Lili Qiu, lili@cs.utexas.edu • Office: GDC 6.806 • Office hour: Mon. 2 – 4 pm or by appt. • Lecture: Mon. 9 am – noon • TA: Apurv Bhartia apurvb@cs.utexa.edu • TA office hour: Wed. 10-11:30am • Course homepage: http://www.cs.utexas.edu/~lili/classes/F13 • Mailing list: • cs386w-fall2013@utlists.utexas.edu

  3. Class Goals • Learn wireless networking fundamentals • Discuss challenges and opportunities in wireless networking research • Obtain hands-on wireless research experience

  4. Course Material • Suggested references (2-hour library loan) • Mobile Communications by Jochen Schiller • 802.11 Wireless Networks: The Definitive Guide by Matthew S. Gast • Wireless Communications Principles and Practice by Ted Rappaport • Selected conference and journal papers • Other resources • MOBICOM, SIGCOMM, INFOCOM proceedings

  5. Course Workload • Grading • Classroom participation: 5% • Homework: 30% • Exam: 25% • Course project: 40% • Classroom participation • Actively participate in class discussion • Make insightful comments and/or initiate interesting discussions • Homework • Assignment • Paper review • Review form online • Starting next class, submit a review for one paper in each session of your choice at the beginning of each class (2 pages) • Your grade is determined by the highest 12 reviews • Project peer review • Next class: HW 1 + up to 2 paper reviews

  6. Course Workload (Cont.) • In class exam: 11/18 • 11/4 class  11/1 (Friday) class? • Course project • Goal: obtain hands-on experience in wireless networking research • Work by yourself or with another student • I’ll hand out a list of project topics next class • You may also choose your own topic approved by me • Project components • Initial report • Mid-point report • Final report (peer reviewed) • Presentation: 12/2 • Vote for best project • We will strictly enforce UTCS code of conduct

  7. How to read a paper? • Three-pass approach • 1st pass • Read title, abstract, intro, conclusion, section title • Identify category, context, correctness, contributions • 2nd pass • Read the paper carefully but ignore proofs • Grasp the content of the paper • 3rd pass • Virtually re-implement the paper • Identify innovations, limitations, and future work http://blizzard.cs.uwaterloo.ca/keshav/home/Papers/data/07/paper-reading.pdf

  8. Paper Review Form • http://www.cs.utexas.edu/~lili/classes/F11/review-form.htm • Submit paper reviews in hardcopies at the beginning of every class • Summarize the paper in a few sentences. • What are the major strengths of the paper? • What are the major weaknesses of the paper? • What do you learn from the paper? It can be either a new research area, or a new problem, or the approach itself, or evaluation methodology, or the results. • What are the avenues for future work that you think are important? If you are asked to work on the problem studied in this paper, what will you do differently? • Detailed comments.

  9. Course Overview • Part I: Introduction to wireless networks • Physical layer • MAC • Introduction to MAC and IEEE 802.11 • Rate control • Packet recovery • Routing • Mobile IP • DSR, AODV, DSDV • Transport protocols in wireless networks • Problems with TCP over wireless • Other proposals

  10. Course Overview (Cont.) • Part II: Different types of wireless networks • Wireless LANs • Wireless mesh networks • Sensor networks • Vehicular networks • Cellular networks • Delay tolerant networks • Cognitive networks • Emergent networks

  11. Course Overview (Cont.) • Part III: Wireless network management and security • Localization • Wireless network diagnosis • Wireless network security

  12. Introduction to Wireless Networks

  13. Can you live without your cell phone?

  14. Mobile and Wireless Services – Always Best Connected UMTS, GSM 115 kbit/s GSM 53 kbit/s Bluetooth 500 kbit/s LAN, WLAN 600 Mbps 100kps UMTS, DECT 2 Mbit/s GSM/EDGE 384 kbit/s, WLAN 780 kbit/s UMTS, GSM 384 kbit/s GSM 115 kbit/s, WLAN 11 Mbit/s

  15. On the road

  16. On the Road UMTS, WLAN, DAB, GSM, WiMAX, LTE cdma2000, TETRA, ... ad hoc GPS, GSM, WLAN, Bluetooth, Ad hoc networks

  17. Home Networking iPod Game Bluetooth WiFi Surveillance UWB WiFi HDTV Camcorder High-quality speaker WiFi WiFi Game Surveillance Surveillance GSM, LTE,WiMAX

  18. Last-Mile

  19. Last-Mile • Many users still don’t have broadband • Reasons: out of service area; some consider expensive • Broadband speed is still limited • DSL: 300Kbps – 6Mbps • Cable modem: depends on your neighbors • Insufficient for several applications (e.g., high-quality video streaming)

  20. Disaster Recovery Network • 9/11, Tsunami, Irene, Hurricane Katrina, China, South Asian, Haidi earthquakes … • Wireless communication capability can make a difference between life and death! • How to enable efficient, flexible, and resilient communication? • Rapid deployment • Efficient resource and energy usage • Flexible: unicast, broadcast, multicast, anycast • Resilient: survive in unfavorable and untrusted environment

  21. Environmental Monitoring • Micro-sensors, on-board processing, wireless interfaces feasible at very small scale--can monitor phenomena “up close” • Enables spatially and temporally dense environmental monitoring • Embedded Networked Sensing will reveal previously unobservable phenomena Ecosystems, Biocomplexity Contaminant Transport Marine Microorganisms Seismic Structure Response

  22. Wearable Computing

  23. Challenges in Wireless Networking Research

  24. Challenge 1: Unreliable and Unpredictable Wireless Links • Wireless links are less reliable • They may vary over time and space Standard Deviation v. Reception rate Reception v. Distance Asymmetry vs. Power *Cerpa, Busek et. al What Robert Poor (Ember) calls “The good, the bad and the ugly”

  25. Challenge 2: Open Wireless Medium • Wireless interference S1 R1 S2 R2

  26. Challenge 2: Open Wireless Medium • Wireless interference • Hidden terminals S1 R1 S2 R2 S1 R1 R2 S2

  27. Challenge 2: Open Wireless Medium • Wireless interference • Hidden terminals • Exposed terminal S1 R1 S2 R1 S1 R1 R2 R1 S1 S2 R2

  28. Challenge 2: Open Wireless Medium • Wireless interference • Hidden terminals • Exposed terminal • Wireless security • Eavesdropping, Denial of service, … R1 S1 S2 R1 S2 S1 R1 R1 S1 S2 R2

  29. Challenge 3: Intermittent Connectivity • Reasons for intermittent connectivity • Mobility • Environmental changes • Existing networking protocols assume always-on networks • Under intermittent connected networks • Routing, TCP, and applications all break • Need a new paradigm to support communication under such environments

  30. Laptop • fully functional • standard applications • battery; 802.11 • PDA • data • simpler graphical displays • 802.11 Sensors, embedded controllers • Mobile phones • voice, data • simple graphical displays • GSM Challenge 4: Limited Resources • Limited battery power • Limited bandwidth • Limited processing and storage power

  31. Introduction to Wireless Networking

  32. Application: supporting network applications FTP, SMTP, HTTP Transport: data transfer between processes TCP, UDP Network: routing of datagrams from source to destination IP, routing protocols Link: data transfer between neighboring network elements Ethernet, WiFi Physical: bits “on the wire” Coaxial cable, optical fibers, radios application transport network link physical Internet Protocol Stack

  33. Physical Layer

  34. Outline • Signal • Frequency allocation • Signal propagation • Multiplexing • Modulation • Spread Spectrum

  35. source decoding channel coding channel decoding source coding demodulation modulation Overview of Wireless Transmissions sender analog signal bit stream receiver bit stream

  36. Signals • Physical representation of data • Function of time and location • Classification • continuous time/discrete time • continuous values/discrete values • analog signal = continuous time and continuous values • digital signal = discrete time and discrete values

  37. Signals (Cont.) • Signal parameters of periodic signals: • period T, frequency f=1/T • amplitude A • phase shift  • sine wave as special periodic signal for a carrier: s(t) = At sin(2  ft t + t) 1 0 t

  38. Fourier Transform: Every Signal Can be Decomposed as a Collection of Harmonics 1 1 0 0 t t ideal periodicaldigital signal decomposition The more harmonics used, the smaller the approximation error.

  39. Why Not Send Digital Signal in Wireless Communications? • Digital signals need • infinite frequencies for perfect transmission • however, we have limited frequencies in wireless communications

  40. Frequencies for Communication twisted pair coax cable optical transmission 1 Mm 300 Hz 10 km 30 kHz 100 m 3 MHz 1 m 300 MHz 10 mm 30 GHz 100 m 3 THz 1 m 300 THz visible light VLF LF MF HF VHF UHF SHF EHF infrared UV VLF = Very Low Frequency UHF = Ultra High Frequency LF = Low Frequency SHF = Super High Frequency MF = Medium Frequency EHF = Extra High Frequency HF = High Frequency UV = Ultraviolet Light VHF = Very High Frequency Frequency and wave length:  = c/f , wave length , speed of light c  3x108m/s, frequency f

  41. Frequencies and Regulations • ITU-R holds auctions for new frequencies, manages frequency bands worldwide (WRC, World Radio Conferences)

  42. Why Need A Wide Spectrum

  43. Why Need A Wide Spectrum: Shannon Channel Capacity • The maximum number of bits that can be transmitted per second by a physical channel is: • where W is the frequency range that the media allows to pass through, SINR is the signal noise ratio

  44. Signal, Noise, and Interference • Signal (S) • Noise (N) • Includes thermal noise and background radiation • Often modeled as additive white Gaussian noise • Interference (I) • Signals from other transmitting sources • SINR = S/(N+I) (sometimes also denoted as SNR)

  45. dB and Power conversion • dB • Denote the difference between two power levels • (P2/P1)[dB] = 10 * log10 (P2/P1) • P2/P1 = 10^(A/10) • Example: P2 = 100 P1, P2/P1=10 dB • dBm and dBW • Denote the power level relative to 1 mW or 1 W • P[dBm] = 10*log10(P/1mW) • P[dBW] = 10*log10(P/1W) • Example: P = 0.001 mW, P = 100 W

  46. Outline • Signal • Frequency allocation • Signal propagation • Multiplexing • Modulation • Spread Spectrum

  47. Signal Propagation Ranges • Transmission range • communication possible • low error rate • Detection range • detection of the signal possible • no communication possible • Interference range • signal may not be detected • signal adds to the background noise sender transmission distance detection interference

  48. Signal Propagation • Does signal propagation via a straight line?

  49. Signal Propagation • Propagation in free space always like light (straight line) • Receiving power proportional to 1/d² (d = distance between sender and receiver) • Receiving power additionally influenced by • shadowing • reflection at large obstacles • refraction depending on the density of a medium • scattering at small obstacles • diffraction at edges • fading (frequency dependent) refraction shadowing reflection scattering diffraction

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