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ELEC/XJEL3430

Digital Communications

Additional Practice Questions for Unit 2

Problem 1: Baseband Binary Communication

a)    Repeat Problems 1 and 2 in PSet 4 for different input signals. You can pick any shape for s0 (t) and s 1 (t) and go through the same steps again.

b)    In Problem 1 of Pset 4, choose some specific values for A, T, and N0 / 2 , and calculate the BER for that case. If you fancy, you can fix two parameters and change the other one, and calculate the BER in MATLAB. Plot the BER versus your free parameter to see how the amplitude, bit rate and noise power spectral density would affect the BER.

Problem 2: BER vs T

A polar binary signal is given by a fixed amplitude +1 V for bit 1, and -1 V for bit 0, for the bit duration. Bits 0 and 1 happen with equal probability. Additive white Gaussian noise having two-sided power spectral density of 10一3 W/Hz is added to the signal at the receiver. If the received signal is detected with a matched filter receiver, determine the maximum bit rate that can be sent to satisfy a BER < 10-3.

Problem 3: BER for a Non-Gaussian channel

In a binary communication system, the decision variable R is given by si  + ni, for i = 0,1, where si  = (一1)i, and ni is a random variable with uniform distribution between -1.5 and 1.5. Assuming that bits 0 and 1 are equally likely, what is the optimum threshold for decision making? Find the BER at this optimum threshold.