Lecture_6b

# Lecture_6b - Signal Transmission Lecture 6b(advanced...

This preview shows pages 1–5. Sign up to view the full content.

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: Signal Transmission Lecture 6b (advanced concepts/issues) • how to relate the basic concepts to Fourier Transform • more picture analysis in the frequency domain • what can go wrong with coherent (synchronous) modulation • concepts on I/Q modulation (quadrature multiplexing) Some content taken with permission from material developed for the course EECS6.02 by C. Sodini, M. Perrot and H. Balakrishnan The Concept of Modulation Why Modulation? • Easier to transmit electro-magnetic waves at higher frequencies • Transmitting multiple signals through the same medium using different carriers - multiplexing • Fitting signals to “channels” with limited passbands • Others... • Many methods (amplitude, frequency, phase) • Focus here for the most part on A mplitude M odulation ( AM ) How? Transmitted Signal x(t) Carrier Signal Modulation Consider a message signal x(t) has frequency spectrum X(f) In modulation, the message is multiplied (mixed) by a carrier cos (2 π f c t) [ ] ) ( ) ( 2 1 ) 2 cos( ) ( c c c f f X f f X t f t x − + + ↔ π Baseband signal Frequency translated (modulated) signal Modulation Modulation W 2W ) ( ) ( f X t x ↔ (Fourier transform pair) Recovery of Baseband Signal Recovery of Baseband Signal To recover the baseband signal, we can simply multiply the translated signal with cos (2 π f c t) . [ ] ) 4 cos( 2 ) ( 2 ) ( ) 2 ( cos ) ( ) 2 cos( ) 2 cos( ) ( 2 t f t x t x t f t x t f t f t x c c c c π π π π + = = We obtain the baseband signal x(t) and a signal whose spectral range extends from ( 2f c-W ) to ( 2f c +W ). As f c >> W , the extra signal is removed by a low-pass filter ....
View Full Document

{[ snackBarMessage ]}

### Page1 / 27

Lecture_6b - Signal Transmission Lecture 6b(advanced...

This preview shows document pages 1 - 5. Sign up to view the full document.

View Full Document
Ask a homework question - tutors are online