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Unformatted text preview: ECE 146A: Communications I Lab 2: Introduction to Complex Baseband Models Carrier Phase Uncertainty and Wireless Multipath Channels Lab Report: Due at the beginning of lab Thursday Jan 27 1 Objective The goal of this lab is to explore modeling and receiver operations in complex baseband, and to practice writing Matlab code from scratch (i.e., without using prepackaged routines or Simulink) for simple computations. We consider two experiments: (1) modeling and undoing the effect of carrier phase mismatch between the receiver LO and the incoming carrier, (2) modeling the effect of a wireless multipath channel. 2 Equipment Matlab is available in the workstations in the software lab. 3 Experiment 1: Modeling Carrier Phase Uncertainty Consider a pair of independently modulated signals, u c ( t ) = ∑ N n =1 b c [ n ] p ( t − n ) and u s ( t ) = ∑ N n =1 b s [ n ] p ( t − n ), where the symbols b c [ n ] , b s [ n ] are chosen with equal probability to be +1 and 1, and p ( t ) = I [0 , 1] ( t ) is a rectangular pulse. Let N = 100. (1.1) Use Matlab to plot a typical realization of u c ( t ) and u s ( t ) over 10 symbols. Make sure you sample fast enough for the plot to look reasonably “nice.” (1.2) Upconvert the baseband waveform u c ( t ) to get u p, 1 ( t ) = u c ( t )cos 40 πt This is a socalled binary phase shift keyed (BPSK) signal, since the changes in phase due to the changes in the signs of the transmitted symbols. Plot the passband signal u p, 1 ( t ) over four symbols. (1.3) Now, add in the Q component to obtain the passband signal u p ( t ) = u c ( t )cos 40 πt − u s ( t )sin40 πt Plot the resulting Quaternary Phase Shift Keyed (QPSK) signal u p ( t ) over four symbols. (1.4) Downconvert u p ( t ) by passing 2 u p ( t )cos(40 πt + θ ) and 2 u p ( t )sin(40 πt + θ ) through crude lowpass filters with impulse response h ( t ) = I [0 , . 25] ( t ). Denote the resulting I and Q components 1 by v c ( t ) and v s ( t ), respectively. Plot v c and v s for θ = 0 over 10 symbols. How do they compare to u c and u s ? Can you read off the corresponding bits b c [ n ] and b s [ n ] from eyeballing the plots for v c and v s ? (1.5) Plot v c and v s for θ = π/ 4. How do they compare to u c and u s ? Can you read off the corresponding bits b c [ n ] and b s [ n ] from eyeballing the plots for v c and v s ?...
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This note was uploaded on 12/28/2011 for the course ECE 146A taught by Professor Madhow during the Fall '09 term at UCSB.
 Fall '09
 MADHOW

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