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COMM.SYS.300 Communication theory - 24.01.2023

Exam text content

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Original exam
ee a

No materials, no calculator. Prepared by and return to: Mikko Valkama

NB I: Please pay special attention to clear handwriting. If ] cannot read your text with reasonable effort,
your paper cannot be unfortunately graded. So, please, try to write in a clear manner. Thank you.

NB 2: A maximum of two full response sheets is allowed.

1. Explain shortly the following concepts in the context of electrical or electromagnetic
communications: a) spectrum, b) nonlinear distortion, c) correlation function, d) spectral density,
e) white noise, f) signal-to-noise ratio (SNR). No need to dwell on finest details, rough explanations



which show your understanding are enough

Explain the basic principles of Nyquist pulsc-shape filtering based baseband pulse amplitude
modulation (PAM) and I/Q modulated single-carrier PAM/QAM/PSK techniques, in the context of
digital communication. How are the bandwidth and bit-rate calculated in the two techniques
(baseband system and I/Q modulated system) ? Give also a feasible numerical example. What does


intersymbol interference (ISI) mean ?

3. Explain the basic principle of frequency shift keying (FSK). How is the physical-layer bit-rate
calculated for FSK-based systems? What are the most fundamental aspects in designing an FSK-
based system and the associated frequencies ? Finally, explain shortly the concept of minimum shift
keying (MSK).

4. Explain briefly the basic ideas of multicarrier modulation / OFDM and multi-antenna / MIMO
communications. Discuss also shortly the benefits of OFDM compared to  single-carrier
PAM/QAM/PSK and the corresponding benefits of multi-antenna/MIMO compared to single-

antenna systems.

5: Explain shortly what is meant by (i) information, (i) entropy and (iii) mutual information, in the
context of electrical or electromagnetic communications. Explain also what is meant in this context
by channel capacity. Assuming a bandlimited additive white Gaussian noise (AWGN) channel, what

factors are determining the channel capacity ? Give also a numerical example.

Maximum points: 5 x 6 = 30p

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