1. CS 414 Indian Institute of Technology, Bombay CS 414 Wireless Propagation Basics

2. CS 414 Indian Institute of Technology, Bombay Last Lecture ● Radio waves – 3KHz to 300 Ghz ● Analog and Digita data and signals – Bandwidth and Data Rate

3. CS 414 Indian Institute of Technology, Bombay Last Lecture ● db – relative measure – db = 10 log 10 (ratio) ● if Ps = 10 mW and Pr = – 10mW ~ 0 db – 1 mW ~ -10 db – 100 mW ~ 10 db – 1000 mW ~ 20 db ● dbm, dbv, dbi, dbW... – absolute measure

4. CS 414 Indian Institute of Technology, Bombay dbW, dbm, dbi, dbv... ● db = relative maginutes ● Fix reference for to initial signal for absolute compariton ● dbm = 10 log (Power mW / 1mW) – 1 mW = 0 dbm – 10 mW = 10 dbm – 30 dbm = ? ● If P1 – P2 = 10 dbm then, absolute difference is ? ● 1 dbW = ? dbm

5. CS 414 Indian Institute of Technology, Bombay Antennas ● Essential wireless propogation component ● Entry and end-points of RF signals ● Two funtions – Transmission ● Converts electric energy to electro-magnetic – Receiver ● Converts received electro-magnetic energy to electric signal ● Passive element

6. CS 414 Indian Institute of Technology, Bombay Antenna Types ● Omni-directional – radiation in all directions ● Directional – Focuses (more) power in certain direction – Does not amplify

7. CS 414 Indian Institute of Technology, Bombay Types of Antennas λ/4 Quarter-wave Antenna λ/4 λ/2 Half-wave Dipole www.cellamericas.com Parabolic Antenna

8. CS 414 Indian Institute of Technology, Bombay Antenna Gain ● Isotropic Antenna – Idealized omni-directional antenna – Tranmits power in all directions uniformly ● Antenna Gain (G) – ratio of transmit/receive power in a particular direction w.r.t to an isotropic antenna – G = P direction /P isotropic – Measure of reception/tranmission strength of antenna – Transmit Gain = Receive Gain – Typical units: dBi (dB gain w.r.t to isotropic)

9. CS 414 Indian Institute of Technology, Bombay Antenna Gain ● Isotropic – G = 1 in all directions ● Non-uniform/Directional – G a = ? – G b = ? – G c = ? A B C

10. CS 414 Indian Institute of Technology, Bombay Antenna Parameters ● Radiation Pattern – Spread of transmitter power ● (Half-power) Beam width – Angle between half power point (direction) and the point (direction) of maximum power – Assumption: Reception beyond beam width is poor and unreliable

11. CS 414 Indian Institute of Technology, Bombay Antenna Parameters ● Antenna Polarization – Orientation/plane of the electric field (E-plane) ● w.r.t earth's surface Horizontally polarized Vertically polarized image source: wikipedia

12. CS 414 Indian Institute of Technology, Bombay RF Propagation – Questions: Relation between RF propogation & ● distance ● different environments ● quantification metrics – Goals: Provide connectivity, Estimate link quality (Is this link good?) – Solution Design: ● Antenna placement ● Link quality mapping and monitoring ● Tranmist power, antenna height

13. CS 414 Indian Institute of Technology, Bombay Propagation Phenomena

14. CS 414 Indian Institute of Technology, Bombay

16. Path Loss Example ● P t = 50 mW, f = 2.4 Ghz, d = 2Km, P r = ? ● G t = 24 dBi, G r = 24 dBi, Pr = ?

17. CS 414 Indian Institute of Technology, Bombay Next Class ● Loss proportional to d 2... in reality ? ● Reading “The Mistaken axioms of wireless-network research”, D. Kotz, C. Newport, C. Elliott http://pdos.csail.mit.edu/decouto/papers/kotz03.pdf “ Most research on ad-hoc wireless networks makes simplifyingassumptions about radio propagation. The “Flat Earth” model of the world is surprisingly popular: all radioshave circular range, have perfect coverage in thatrange, and travel on a two-dimensional plane.... We then present a set of 802.11 measurements that clearly demonstrate that these “axioms” are contrary to fact.” http://pdos.csail.mit.edu/decouto/papers/kotz03.pdf