CS395T: Wireless Networking

1. CS395T: Wireless Networking Lili Qiu UT Austin Aug. 30, 2006

2. Course Information • Instructor: Lili Qiu, lili@cs.utexas.edu • Office: ACES 6.242 • Lecture: Mon. & Wed. 3 – 4:30 pm • Office hour: Mon. & Wed. 4:30 – 5:30 pm or by appt. • TA’s office hour: Tue. 1-2pm & Thur. 2-3pm, ESB 229, Desk 1 • Course homepage: http://www.cs.utexas.edu/users/lili/classes/F06/index.html • Mailing list: cs395t-wireless2006@lists.cc.utexas.edu • Subscribe mailing list: email listproc@lists.cc.utexas.edu subscribe cs395t-wireless2006 YourFirstName YourLastName

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 • 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% • Mid-term: 25% • Course project: 40% • Classroom participation: • Actively participate in class discussions • Make insightful comments and/or initiate interesting discussions • Homework • Assignment • Paper review: submit a review for one paper of your choice at the beginning of each class (1-2 pages) • Review form • Mid-term • Oct. 16 in class, open books/open notes • Does Anyone have class after 4:30pm?

6. Course Workload (Cont.) • Course project • Goal: obtain hands-on experience in wireless networking research • Work in a group of 2-3 • I’ll hand out a list of project topics next week • You may also choose your own topic approved by me • Initial report + Mid-point report + final report + presentation • Vote for best project

7. Course Overview • Part I: Introduction to wireless networks • Physical layer • MAC • Introduction to MAC and IEEE 802.11 • Channel assignment and channel hopping • Power control • Rate control • Multi-radio • Routing • Mobile IP • DSR and AODV • TCP over wireless • Problems with TCP over wireless • Other proposals

8. Course Overview (Cont.) • Part II: Different types of wireless networks • Wireless mesh networks • Sensor networks • Cellular networks • Delay tolerant networks • RFID • WiMax

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

10. Class Time • Due to conference travel, I have to reschedule classes on Sept. 13, 25, 27 • Will Sept. 8, 22, 29 (Friday) work for you? • What time?

11. Introduction to Wireless Networks

12. Mobile and Wireless Services – Always Best Connected UMTS, GSM 115 kbit/s LAN 100 Mbit/s, WLAN 54 Mbit/s GSM 53 kbit/s Bluetooth 500 kbit/s LAN, WLAN 780 kbit/s 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

13. On the Road UMTS, WLAN, DAB, GSM, cdma2000, TETRA, ... ad hoc Personal Travel Assistant, DAB, PDA, laptop, GSM, UMTS, WLAN, Bluetooth, ...

14. Home Networking iPod Game WiFi WiFi Surveillance UWB WiFi HDTV Camcorder High-quality speaker WiFi WiFi Surveillance Game Surveillance

15. Last-Mile • Many users still don’t have broadband • End of 2002 • Worldwide: 46 million broadband subscribers • US: 17% household have broadband • Reasons: out of service area; some consider expensive • Broadband speed is still limited • DSL: 1-3 Mbps download, and 100-400Kbps upload • Cable modem: depends on your neighbors • Insufficient for several applications (e.g., high-quality video streaming)

16. Disaster Recovery Network • 9/11, Tsunami, Hurricane Katrina, South Asian earthquake … • 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

17. 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

18. Challenges in Wireless Networking Research

19. 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”

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

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

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

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

24. 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 in-network storage to support communication under such environments

25. 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

26. Introduction to Wireless Networking

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

28. Physical Layer

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

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

31. 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

32. 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

33. 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.

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

36. 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

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

38. 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, S/N is the signal noise ratio

39. 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)

40. 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 • dBm and dBW • Denote the power level relative to 1 mW or 1 W • P[dBm] = 10*log10(P/1mW) • P[dB] = 10*log10(P/1W) • Example: P = 0.001 mW, P = 100 W

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

42. 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

43. 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

44. Path Loss • Free space model • Two-ray ground reflection model • Log-normal shadowing • Indoor model • P = 1 mW at d0=1m, what’s Pr at d=2m?

45. Multipath Propagation • Signal can take many different paths between sender and receiver due to reflection, scattering, diffraction • Time dispersion: signal is dispersed over time interference with “neighbor” symbols, Inter Symbol Interference (ISI) • The signal reaches a receiver directly and phase shifted  distorted signal based on the phases of different parts LOS pulses multipath pulses LOS: Line Of Sight signal at sender signal at receiver

46. Fading • Channel characteristics change over time and location • e.g., movement of sender, receiver and/or scatters •  quick changes in the power received (short term/fast fading) • Additional changes in • distance to sender • obstacles further away •  slow changes in the average power received (long term/slow fading) long term fading power t short term fading

47. Received Signal Power (dB) path loss shadow fading Rayleigh fading log (distance) Typical Picture

48. Real world example

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

50. Multiplexing • Multiplexing in 4 dimensions • space (si) • time (t) • frequency (f) • code (c) • Goal: multiple use of a shared medium • Important: guard spaces needed!