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Unformatted text preview: ECE-501 Introduction to Analog and Digital Communications Au2011 Homework #4 Oct. 21, 2011 HOMEWORK ASSIGNMENT #4 Due Fri. Oct. 29, 2011 (in class) Reading: Online lecture notes, pages 38-54; text, chapter 7; text chapter 8 (8.1, 8.2, 8.6-8.8, 8.10) Problems: 1. Towards building an acoustic modem : Reconsider the simple modulation exercise from homework #1 (code repeated below). (a) Modify the symbol sequence to be taken from a QPSK constellation, rather than a BPSK constellation. (b) Use the wavplay and wavrecord commands (or similar) in Matlab to transmit and receive using a carrier frequency of 15kHz i. change f c to achieve the 15kHz carrier frequency. ii. change f s = 1 /Ts to an appropriate value to avoid aliasing (see help wavplay for list of sampling rates) iii. Set the oversampling factor, N , so that the symbol rate is approximately 200 per second iv. Open two Matlab command windows. From one, use wavrecord to begin recording r ( t ). Then, quickly switch to the second command window and execute wavplay to send s ( t ). Be sure to record for a sufficiently long duration to capture the transmitted waveform. (c) Use plotttf and the zoom option to explore s ( t ) and r ( t ). Write down your observations. %set parameters fs = 22050; %22.05k samples per second for DAC and ADC fc = 7000;%carrier frequency at 7000 Hz N = 21; %oversampling factor (samples per symbol interval) pulse = srrc(3, 0.5, N);%pulse waveform; see srrc.m from course webpage %define symbols symbols = [1, -1, -1, 1, 1, 1]; %simple example with six symbols...
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This note was uploaded on 11/11/2011 for the course ECE 501 taught by Professor Schniter,p during the Fall '08 term at Ohio State.
- Fall '08