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Wireless Networks

Wireless Networks. Walid Abu-Sufah University of Jordan Spring 2007. Course Information. Instructor: Walid Abu-Sufah, abusufah@ju.edu.jo Office: 10 Computer Engineering Lecture: Mon. & Wed. 12:30 – 1:45 pm Office hour: Su, Tu, Th 3-4 pm or by appt.

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Wireless Networks

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  1. Wireless Networks Walid Abu-Sufah University of Jordan Spring 2007

  2. Course Information • Instructor: Walid Abu-Sufah, abusufah@ju.edu.jo • Office: 10 Computer Engineering • Lecture: Mon. & Wed. 12:30 – 1:45 pm • Office hour: Su, Tu, Th 3-4 pm or by appt. • Course homepage: http://www.ju.edu.jo/ecourse/cpestcourse/cpestindex.html user/password: cpestudent

  3. Class Goals • Learn wireless networking fundamentals • Discuss challenges and opportunities in wireless networking research

  4. Course Material • Textbook • Mobile Communications by Jochen Schiller • Suggested references • 802.11 Wireless Networks: The Definitive Guide by Matthew S. Gast • Wireless Communications Principles and Practice by Ted Rappaport • Ad Hoc Networking by Charles E. Perkins, Addison Wesley

  5. Course Workload • Grading • Homework/Quizes: 10% • Project: 10 % • Mid-term: 30% • Final : 50% • 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 • Monday, April 2 in class • Final • Sunday, May 27; 2007; 12– 2 PM (might move to 5-7 PM); Rooms to be announced.

  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 (Time Allowing) : Some types of wireless networks • Wireless mesh networks • Sensor networks • Cellular networks • WiMax

  9. Introduction to Wireless Networks

  10. 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

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

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

  13. 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)

  14. 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

  15. 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

  16. Challenges in Wireless Networking

  17. Challenge 1: Unreliable andUnpredictable Wireless Links • Wireless links are less reliable • They may vary over time and space

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

  19. Challenge 2: Open Wireless Medium • Wireless interference • Hidden terminals S1 R1 S2 R1 S1 R S2

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

  21. 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

  22. 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

  23. 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

  24. Introduction to Wireless Networking

  25. 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

  26. Physical Layer

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

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

  29. Signals • Physical representation of data • Wireless signal is a 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

  30. 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

  31. 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.

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

  33. 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

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

  35. 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

  36. 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)

  37. dB and Power conversion • dB • Denote the difference between two power levels P2 & P1 • (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[dBW] = 10*log10(P/1W) • Example: P = 0.001 mW, P = 100 W

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

  39. 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

  40. 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

  41. 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?

  42. Radio Propagation Models • Visit http://people.deas.harvard.edu/~jones/es151/prop_models/propagation.html

  43. 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

  44. Fading • Channel characteristics change over time and location (caused by changes in transmission medium or path) • 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

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

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

  47. Space Multiplexing • Assign each region a channel • Pros • no dynamic coordination necessary • works also for analog signals • Cons • Inefficient resourceutilization channels ki k1 k2 k3 k4 k5 k6 c t c s1 t s2 f f c t s3 f

  48. Frequency Multiplexing • Separation of the whole spectrum into smaller frequency bands • A channel gets a certain band of the spectrum for the whole time • Pros: • no dynamic coordination necessary • works also for analog signals • Cons: • waste of bandwidth if the traffic is distributed unevenly • Inflexible • guard spaces k1 k2 k3 k4 k5 k6 c f t

  49. Time Multiplex • A channel gets the whole spectrum for a certain amount of time • Pros: • only one carrier in themedium at any time • throughput high even for many users • Cons: • precise synchronization necessary k1 k2 k3 k4 k5 k6 c f t

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