1. CS 414 Indian Institute of Technology, Bombay CS 414 Signals & Transmission Wireless Propagation

2. CS 414 Indian Institute of Technology, Bombay Roadmap for CS414 ● Wireless propagation basics – antennas, RF propgation, radiation patterns, multipexing, modulation, interference ● 802.11 (MAC issues and WLANs) – 802.15.4, Bluetooth, GSM, CDMA... ● Mobile IP, Routing Protocols (AODV & DSR) ● TCP and Wireless ● RFID & Sensor Systems

3. CS 414 Indian Institute of Technology, Bombay Data ● Analog Data – Continuously generated data – Examples: ● Digital Data – Data present/generated at discrete instances – Examples:

4. CS 414 Indian Institute of Technology, Bombay Data as Signals ● Analog Signals – Continuously time-varying signal intensity ● Digital Signals – Signal intensity varies periodically

5. CS 414 Indian Institute of Technology, Bombay Analog Signaling ● Analog Data via Analog Signals – Audio (20 Hz to 20 Khz) ● Practical: 300 to 3400 Hz – Telephone ● Translate speech to frequency and amplitude pattern ● Digital data via Analog Signals – Modems ● Modulate carrier frequency according to data ● Demodulate at receiver

6. CS 414 Indian Institute of Technology, Bombay Digital Signaling ● Analog Data via Digital Signals – Coder encodes analog signal ● Period sampling – Decoder decodes ● Digital Data via Digital Signals – Signal levels to represent data bits

7. CS 414 Indian Institute of Technology, Bombay Sine Wave ● Fundamental analog signal ● s(t) = A sin(2πft+ Ø) – A : amplitude, f: frequency, Ø :phase shift ● Any waveform can be appromixated / constructed using a set of sinusoids – Different amplitudes and frequencies – Example (board)

8. CS 414 Indian Institute of Technology, Bombay Bandwidth & Data Rate ● Bandwidth = Range of frequencies in a signal – Spectrum of signal – Overloaded with data rate – Unit: Hertz ● Data rate is bits per second transmitted

9. CS 414 Indian Institute of Technology, Bombay Bandwidth vs Data Rate ● Higher the bandwidth => Higher the data rate ● Examples (board) ● Theortically infinite bandwidth (data rate) – Limited by transmission medium – Cost and Hardware complexity – Higher frequencies have little amplitude ● Higher data rates at lower bandwidths more susceptible to distortions and errors

10. CS 414 Indian Institute of Technology, Bombay Decibels and Signal Strength ● Signal strength: Magnitude of electric field at a location – Changes with distance in wireless – Approximately like a log-function ● Decibel relative measure of signal strength – db = 10 log 10 (P s /P r ) – P s :Sender power – P r :Receiver power

11. CS 414 Indian Institute of Technology, Bombay Decibel Examples ● Let P s = 10mW – P r = 5mW – G = 10 log 10 (0.5) = - 3 db (i.e., 3db loss) – P r = 1mW, G = -10 db – P r = 0.1mW, G = -20 db – P r = 0.01mW, G = -30 db – P r = 0.001mW, G = -40 db ● If P s = P r = 10 mW, G = ? ● If G =1, Pr = ?

12. CS 414 Indian Institute of Technology, Bombay Decibel Math ● Gain is multplicative – Addition in db space – e.g., signal is reduced by half on first hop then amplifed by factor of 2 – P s = 10 mW, P 1 = 5 mW, P 2 = 10 mW – G 1 = -3db – G 2 = +3db – G at P2 = G 1 + G 2 = 0 db =>P s = P 2

13. 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

14. CS 414 Indian Institute of Technology, Bombay Antennas ● Essential wireless propogation components ● 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

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

16. CS 414 Indian Institute of Technology, Bombay Next Class ● Antenna basics – beam width, types, gain, path loss ● 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