Mobile Computing and Wireless Networking Lec 01 01/03/2010 ECOM 6320

2 Outline r Introduction to wireless networks and mobile computing r Challenges facing wireless networks and mobile computing r Introduction to wireless physical layer

3 Goal of Wireless Networking and Mobile Computing “People and their machines should be able to access information and communicate with each other easily and securely, in any medium or combination of media – voice, data, image, video, or multimedia – any time, anywhere, in a timely, cost-effective way.” Dr. G. H. Heilmeier, Oct 1992

4 Enabling Technologies r Development and deployment of wireless/mobile technology and infrastructure m in-room, in-building, on-campus, in-the-field, MAN, WAN r Miniaturization of computing machinery... -> PCs -> laptop -> PDAs/smart phones -> embedded computers/sensors r Improving device capabilities/software development environments, e.g., m andriod: m iphone: m windows mobile

Pervasive Use of Mobile Wireless Devices r There are ~4 billion mobile phones m Over 50 countries have mobile phone subscription penetration rates higher than that of the population (Infoma 2007) m etration_rate r The mobile device will be the primary connection tool to the Internet for most people in the world in PEW Internet and American Life Project, Dec

6 At Home WiFi cellular bluetooth UWB satellite WiFi g/n

7 At Home Source:

8 At Home: Last-Mile r Many users still don’t have broadband m reasons: out of service area; some consider expensive r Broadband speed is still limited m DSL: 1-6 Mbps download, and Kbps upload m Cable modem: depends on your neighbors m Insufficient for several applications (e.g., high- quality video streaming)

9 On the Move Source:

10 On the Move: Context-Aware Source:

11 ad hoc GSM/UMTS, cdmaOne/cdma2000, WLAN, GPS DAB, TETRA,... road condition, weather, location-based services, emergency On the Road

12 Example: IntelliDrive (Vehicle Infrastructure Integration) r Traffic crashes resulted in more than 41,000 lives lost in 2007 r Establishing vehicle-to- vehicle (V2V), vehicle-to- infrastructure (V2I) and vehicle-to-hand-held- devices (V2D) communications m safety: e.g., intersection collision avoidance/violation warning/turn conflict warning, curve warning m mobility: e.g., crash data, weather/road surface data, construction zones, emergency vehicle signal pre-emption More info:

13 Collision Avoidance : V2V Networks r stalled vehicle warning r bland spots

14 Collision Avoidance at Intersections r Two million accidents at intersections per year in US Source:

15 Wireless and Mobile Computing r Driven by technology and vision m wireless communication technology m global infrastructure m device miniaturization m mobile computing platforms r The field is moving fast

Why is the Field Challenging? Challenge 1: Unreliable and Unpredictable Wireless Coverage Wireless links are not reliable: they may vary over time and space Challenge 2: Open Wireless Medium Wireless interference Hidden terminals Wireless security eavesdropping, denial of service, …

17 Challenge 3: Mobility r Mobility causes poor-quality wireless links r Mobility causes intermittent connection m under intermittent connected networks, traditional routing, TCP, applications all break r Mobility changes context, e.g., location

18 Challenge 4: Portability r Limited battery power r Limited processing, display and storage Sensors, embedded controllers Mobile phones voice, data simple graphical displays GSM/3G PDA phone data simpler graphical displays /3G Laptop fully functional standard applications battery; Performance/Weight/Power Consumption

19 Challenge 5: Changing Regulation and Multiple Communication Standards cellular phonessatellites wireless LAN cordless phones 1992: GSM 1994: DCS : IMT : CT : Inmarsat- A 1992: Inmarsat-B Inmarsat-M 1998: Iridium 1989: CT : DECT 199x: proprietary 1997: IEEE : b, Bluetooth 1988: Inmarsat- C analogue digital 1991: D-AMPS 1991: CDMA 1981: NMT : NMT : CT0 1984: CT1 1983: AMPS 1993: PDC 2000: GPRS 2000: IEEE a Fourth Generation (Internet based)

20 3G Networks

21 Application Transport Network Data Link Physical Medium Data Link Physical Application Transport Network Data Link Physical Data Link Physical Network Radio Often we need to implement a function across multiple layers. The Layered Reference Model

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

23 Signal r Signal are generated as physical representations of data r A signal is a function of time and location t 1 0 t a special type of signal, sine waves, also called harmonics: s(t) = A t sin(2  f t t +  t ) with frequency f, period T=1/f, amplitude A, phase shift  1 0 ideal digital signal t

24 Fundamental Question: Why Not Send Digital Signal in Wireless Communications? 1 0 ideal digital signal t

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.

26 Fundamental Question: Why Not Send Digital Signal in Wireless Communications? r May cause interference m suppose digital frame length T, then signal decomposes into frequencies at 1/T, 2/T, 3/T, … m let T = 1 ms, generates radio waves at frequencies of 1 KHz, 2 KHz, 3 KHz, …

27 Frequencies for Communications 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

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

29 Spectrum and Bandwidth: Shannon Channel Capacity r The maximum number of bits that can be transmitted per second by a physical channel is: where W is the frequency range of the channel, and S/N is the signal noise ratio, assuming Gaussian noise

30 r Objective m encode digital data into analog signals at the right frequency range with limited usage of spectrum Modulation r Basic schemes m Amplitude Modulation (AM) m Frequency Modulation (FM) m Phase Modulation (PM)

31 r Modulation of digital signals known as Shift Keying r Amplitude Shift Keying (ASK): r Frequency Shift Keying (FSK): r Phase Shift Keying (PSK): 101 t 101 t 101 t Modulation