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

2. 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/cpes tindex.html http://www.ju.edu.jo/ecourse/cpestcourse/cpes tindex.html user/password: cpestudent

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

4. 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. 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. 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. 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. 8 Course Overview (Cont.) Part II (Time Allowing) : Some types of wireless networks –Wireless mesh networks –Sensor networks –Cellular networks –WiMax

9. 9 Introduction to Wireless Networks

10. 10 UMTS, DECT 2 Mbit/s UMTS, GSM 384 kbit/s LAN 100 Mbit/s, WLAN 54 Mbit/s UMTS, GSM 115 kbit/s GSM 115 kbit/s, WLAN 11 Mbit/s GSM 53 kbit/s Bluetooth 500 kbit/s GSM/EDGE 384 kbit/s, WLAN 780 kbit/s LAN, WLAN 780 kbit/s Mobile and Wireless Services – Always Best Connected

11. 11 ad hoc UMTSUMTS, WLAN, DABDAB, GSM,GSM cdma2000cdma2000, TETRA,... Personal Travel Assistant, DAB, PDA, laptop, GSM, UMTS, WLAN, BluetoothBluetooth,... On the Road On the Road

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

13. 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. 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. 15 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 Contaminant TransportEcosystems, Biocomplexity Marine Microorganisms Seismic Structure Response Environmental Monitoring

16. 16 Challenges in Wireless Networking

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

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

19. 19 Challenge 2: Open Wireless Medium Wireless interference Hidden terminals S1 S2 R1 S1R S2

20. 20 Challenge 2: Open Wireless Medium Wireless interference Hidden terminals Exposed terminal S1 S2 R1 S1R S2 R1S1S2R2

21. 21 Challenge 2: Open Wireless Medium Wireless interference Hidden terminals and Exposed terminal Wireless security –Eavesdropping, Denial of service, … S1 S2 R1 S1R1 R2 R1S1S2R2

22. 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. 23 Challenge 4: Limited Resources Limited battery power Limited bandwidth Limited processing and storage power Sensors, embedded controllers Mobile phones voice, data simple graphical displays GSM PDA data simpler graphical displays 802.11 Laptop fully functional standard applications battery; 802.11

24. 24 Introduction to Wireless Networking

25. 25 Internet Protocol Stack 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

26. 26 Physical Layer

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

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

29. 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. 30 Signals (Cont.) Signal parameters of periodic signals: –period T, frequency f=1/T –amplitude A –phase shift phase shift –sine wave as special periodic signal for a carrier: s(t) = A t sin(2  f t t +  t ) 1 0 t

31. 31 1 0 1 0 tt ideal periodical digital signal decomposition Fourier Transform: Every Signal Can be Decomposed as a Collection of Harmonics The more harmonics used, the smaller the approximation error.

32. 32

33. 33 Why Not Send Digital Signal in Wireless Communications? Digital signals need –infinite frequencies for perfect transmission –however, we have limited frequencies in wireless communications

34. 34 Frequencies for Communication Frequencies for Communication VLF = Very Low FrequencyUHF = 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  3x10 8 m/s, frequency f 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 VLFLFMFHFVHFUHFSHFEHFinfraredUV optical transmission coax cabletwisted pair

35. 35 ITU-R holds auctions for new frequencies, manages frequency bands worldwide (WRC, World Radio Conferences)ITU-RWRC Frequencies and Regulations

36. 36 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

37. 37 Signal, Noise, and Interference Signal (S) Noise (N) –Includes thermal noise and background radiationthermal noise –Often modeled as additive white Gaussian noisewhite Gaussian noise Interference (I) –Signals from other transmitting sources SINR = S/(N+I) (sometimes also denoted as SNR)

38. 38 dB and Power conversion dB –Denote the difference between two power levels P2 & P1 –(P2/P1)[dB] = 10 * log 10 (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*log 10 (P/1mW) –P[dBW] = 10*log 10 (P/1W) –Example: P = 0.001 mW, P = 100 W

39. 39 Outline Signal Frequency allocation Signal propagation Multiplexing Modulation Spread Spectrum

40. 40 distance sender transmission detection interference 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 Signal Propagation Ranges

41. 41 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 byReceiving power –shadowing –reflection at large obstacles –refraction depending on the density of a medium –scattering at small obstacles –diffraction at edges –fading (frequency dependent) reflectionscatteringdiffractionshadowing refraction Signal Propagation

42. 42 Path Loss 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?

43. 43 Radio Propagation Models Visit http://people.deas.harvard.edu/~jones/es15 1/prop_models/propagation.html

44. 44 Signal can take many different paths between sender and receiver due to reflection, scattering, diffraction Time dispersion: signal is dispersed over timeTime dispersion  interference with “neighbor” symbols, Inter Symbol Interference (ISI)Inter Symbol Interference (ISI) The signal reaches a receiver directly and phase shifted  distorted signal based on the phases of different parts signal at sender Multipath Propagation signal at receiver LOS pulses multipath pulses LOS: Line Of Sight

45. 45 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) short term fading long term fading t power Fading

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

47. 47 Multiplexing in 4 dimensions –space (s i ) –time (t) –frequency (f) –code (c) Goal: multiple use of a shared medium Important: guard spaces needed! Multiplexing

48. 48 Space Multiplexing Assign each region a channel Pros –no dynamic coordination necessary –works also for analog signals Cons –Inefficient resource utilization s2s2 s3s3 s1s1 f t c k2k2 k3k3 k4k4 k5k5 k6k6 k1k1 f t c f t c channels k i

49. 49 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 k2k2 k3k3 k4k4 k5k5 k6k6 k1k1 f t c

50. 50 f t c k2k2 k3k3 k4k4 k5k5 k6k6 k1k1 Time Multiplex A channel gets the whole spectrum for a certain amount of time Pros: –only one carrier in the medium at any time –throughput high even for many users Cons: –precise synchronization necessary

51. 51 f Time and Frequency Multiplexing Combination of both methods A channel gets a certain frequency band for a certain amount of time (e.g., GSM) Pros: –better protection against tapping –protection against frequency selective interference –higher data rates compared to code multiplex Cons: –precise coordination required t c k2k2 k3k3 k4k4 k5k5 k6k6 k1k1

52. 52 Code Multiplexing Code Multiplexing Each channel has a unique code (i.e.language) All channels use the same spectrum simultaneously Pros: –bandwidth efficient –no coordination and synchronization necessary –good protection against interference and tapping Cons: –lower user data rates –more complex signal regeneration Implemented using spread spectrum technologyspread spectrum technology k2k2 k3k3 k4k4 k5k5 k6k6 k1k1 f t c

53. 53 Outline Signal Frequency allocation Signal propagation Multiplexing Modulation Spread Spectrum

54. 54 Modulation I Digital modulation –digital data is translated into an analog signal (baseband); (e.g. modem translates digital date into analog signals & vice versa) –differences in spectral efficiency, power efficiency, robustnessspectral efficiency Digital wireless transmission requires additional modulation: Analog modulation –shifts center frequency of baseband signal up to the radio carrier –Reasons Antenna size is on the order of signal’s wavelength More bandwidth available at higher carrier frequency Medium characteristics: path loss, shadowing, reflection, scattering, diffraction depend on the signal’s wavelength

55. 55 Modulation and Demodulation digital modulation digital data analog modulation radio carrier analog baseband signal 101101001 radio transmitter synchronization decision digital data analog demodulation radio carrier analog baseband signal 101101001 radio receiver Receiver must synchronize with sender This depends on how digital modulation is done.

56. 56 Digital Modulation Schemes Amplitude Modulation (AM) Frequency Modulation (FM) Phase Modulation (PM)

57. 57 Modulation of digital signals known as Shift Keying Amplitude Shift Keying (ASK): –Pros: simple –Cons: susceptible to noise –Example: optical system, IFR Digital Modulation 01 t Time domain

58. 58 Digital Modulation II Frequency Shift Keying (FSK): –Pros: less susceptible to noise –Cons: requires larger bandwidth 101 t 101 Time domain f1f1 f2f2

59. 59 Digital Modulation III Phase Shift Keying (PSK): shifts in phase of signal represents data –Pros: Less susceptible to noise Bandwidth efficient –Cons: Require synchronization in frequency and phase  complicates receivers and transmitter t Time domain 1 0

60. 60 BPSK (Binary Phase Shift Keying): –bit value 0: sine wave –bit value 1: inverted sine wave (shift phase by 180 o ) –very simple PSK –low spectral efficiency –robust, used in satellite systems Q I 01 Phase Shift Keying Phase Domain Time domain

61. 61 Phase Shift Keying (cont.) 111000 01 Q I 11 01 10 00 A t QPSK (Quadrature Phase Shift Keying): –2 bits coded as one symbol –needs less bandwidth compared to BPSK –symbol determines shift of sine wave –Often also transmission of relative, not absolute phase shift: DQPSK - Differential QPSK shift is not relative to a reference signal but to the phase of the previous two bits Phase Domain Time domain 45 o 135 o 225 o 315 o

62. 62 Quadrature Amplitude Modulation (QAM): combines amplitude and phase modulation It is possible to code n bits using one symbol –2 n discrete levels bit error rate increases with n 0000 0001 0011 1000 Q I 0010 φ a Quadrature Amplitude Modulation Quadrature Amplitude Modulation Example: 16-QAM (4 bits = 1 symbol) Symbols 0011 and 0001 have the same phase φ, but different amplitude a. 0000 and 1000 have same amplitude but different phase Used in standard 9,600 bits/sec modems

63. 63 Spread spectrum technology * * Problem of radio transmission: frequency dependent fading can wipe out narrow band signals for duration of the interference Solution: spread the narrow band signal into a broad band signal using a special code Two Alternatives for Spread Spectrum: –Direct Sequence Spread Spectrum (DSSS) –Frequency Hopping Spread Spectrum (FHSS) detection at receiver interferencespread signal signal spread interference ff power sender spreads narrowband signal receiver converts user signal into narrowband signal & spreads narrow band interference

64. 64 DSSS (Direct Sequence Spread Spectrum) XOR of the signal with pseudo- random number (chipping sequence: 0110101 in figure) –generate a signal with a wider range of frequency: spread spectrum user data chipping sequence resulting signal 01 01101010100111 XOR 01100101101001 = tbtb tctc t b : bit period t c : chip period Spreading factor = t b / t c ; 7 in figure, military applications use s up to 10, 000 If original signal need a bandwidth w, spread signal needs s.w bandwidth user bit 0 > resulting signal 0110101 user bit 1 > resulting signal 1001010

65. 65 Discrete changes of carrier frequency –Available bandwidth is split into many channels of smaller bandwidth plus guard spaces between channels –Transmitter and receiver stay on one of these channels for a certain time and then hop to another channel –sequence of frequency changes determined via pseudo random number sequence –dwell time : time spent on a channel with a certain frequency Two versions –Fast Hopping: several frequencies per user bit –Slow Hopping: several user bits per frequency FHSS (Frequency Hopping Spread Spectrum)

66. 66 Advantages –frequency selective fading and interference limited to short period –simple implementation –uses only small portion of spectrum at any time FHSS (continued)

67. 67 FHSS: Example user data slow hopping (3 bits/hop) fast hopping (3 hops/bit) 01 tbtb 011t f f1f1 f2f2 f3f3 t tdtd f f1f1 f2f2 f3f3 t tdtd t b : bit periodt d : dwell time

68. 68 Comparison between Slow Hopping and Fast Hopping Slow hopping –Pros: cheaper –Cons: less immune to narrowband interference Fast hopping –Pros: more immune to narrowband interference –Cons: tight synchronization transmitter and receiver have to stay synchronized within smaller tolerances to perform hopping at same points in time –  increased complexity