1. CS434/534: Mobile Computing and Wireless Networks http://zoo.cs.yale.edu/classes/cs434/ Y. Richard Yang 08/30/2012

2. 2 Outline r Pervasive wireless networks and mobile applications r Challenges facing wireless networks and mobile computing r Course information r Introduction to wireless physical layer

3. 3 Overview of Wireless Transmissions source decoding bit stream channel decoding receiver demodulation source coding bit stream channel coding analog signal sender modulation

4. 4 Signal r Signal are generated as physical representations of data r A signal is a function of time and location 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

5. 5 Basic Question: Why Not Send Digital Signal in Wireless Communications? 1 0 ideal digital signal t source coding bit stream channel coding analog signal sender modulation

6. 6 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.

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8. Time vs Frequency 8 - Two representations: time domain; frequency domain - Knowing one can recover the other

9. 9 Basic Question: Why Not Send Digital Signal in Wireless Communications? 1 0 digital signal t

10. Backup 10