ECE4331_class3

ECE4331_class3 - ECE4331, Fall, 2009 Zhu Han Department of...

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Unformatted text preview: ECE4331, Fall, 2009 Zhu Han Department of Electrical and Computer Engineering Class 3 Sep. 1 st , 2009 ECE4331 Review of last class Review of last class Random Process Stationary, Ergodic Mean, correlation, covariance, power spectrum density Gaussian Process Noise Central limit theorem Narrowband Noise In-phase and Quadrature phase N0/2 power each Gaussian Envelope (Rayleigh distribution) and phase (uniform) Ricean distribution Might not cover everything in the textbook ECE4331 Baseband and Carrier Communication Baseband and Carrier Communication Baseband: - Describes signals and systems whose range of frequencies is measured from 0 to a maximum bandwidth or highest signal frequency - Voice: Telephone 0-3.5KHz; CD 0-22.05KHz http://www.youtube.com/watch?v=YjO_VXHxsRw&mode=related&search=- Video: Analog TV 4.5MHz, TV channel is 0-6MHz. Digital, depending on the size, movement, frames per second, - Example: wire, coaxial cable, optical fiber, PCM phone Carrier Communication: - Carrier : a waveform (usually sinusoidal ) that is modulated to represent the information to be transmitted . This carrier wave is usually of much higher frequency than the modulating (baseband) signal. - Modulation: is the process of varying a carrier signal in order to use that signal to convey information . ECE4331 Modulation Modulation Modulation- A process that causes a shift in the range of frequencies of a signal. Gain advantages- Antenna size: half of the antenna size. Thousands of miles for baseband- Better usage of limited bandwidth: less side lopes- Trade bandwidth for SNR: CDMA- Robust to inter-symbol-interference (multipath delay)- Robust to errors and distortions Types- Analog: AM (DSB, SSB, VSB), FM, Delta modulation- Digital: ASK, FSK, PSK, QAM, - Pulse modulation: PCM, PDM, Fiber, phone Advanced: CDMA (3G), OFDM (WLAN, WMAN), . ECE4331 Double Sideband Double Sideband Modulation: time: m(t)cos(w c t), freq: 0.5[M(w-w c )+M(w+w c )] Figure 2.4: LSB, USB, DSB DSB-SC: suppressed carrier, no carrier frequency Wc >= bandwidth of the signal to avoid aliasing. Demodulation: e(t)=m(t)(cos(w c t))^2=0.5(m(t)+m(t)cos(2w c t)) E(w)=0.5M(w)+0.25(M(w+2w c )+M(w-2w c )) Low pass filter to remove the higher frequency ECE4331 DSB-SC DSB-SC Example t t t ) t ( m ) t ( ) ( M ) ( c c - Upper sideband (USB) Lower sideband (LSB) ) t ( ) t cos( c )} t cos( c F{ c ECE4331 Frequency Conversion Frequency Conversion Move the signals to other frequency Multiplying two sinusoids results in two frequencies which are the sum and difference of the frequencies of the sinusoids multiplied....
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ECE4331_class3 - ECE4331, Fall, 2009 Zhu Han Department of...

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