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COMM.SYS.450 Multicarrier and Multiantenna Techniques, 5 cr
Exam on Wednesday 11.05.2022 / Prepared by Taneli Riihonen

Calculator or any material is not allowed.
You may answer in English or in Finnish.

1. [6p] Explain briefly (2-3 sentences) what the concepts mean.
a) [1p] in-band distortion d) [1p] diversity gain
b) [1 p] out-of-band emission e) (1 p] multiplexing gain
c) [1p] discrete multitone (DMT) f) [1p] Alamouti scheme

2. [6p] (Essay) Explain the principles of common multicarrier techniques and
compare their advantages and disadvantages to single-carrier transmission.

3. [6p] Consider CP-OFDM transmission over a time- and frequency-selective channel.

a) [3 p] Assume bandwidth is 20 MHz, channel delay spread is 3 us at maximum, timing
error is less than 1 us, and the design target is to have about 10% overhead due to the
cyclic prefix. How would you choose the basic physical-layer OFDM parameters? Why?

b) [1 p] What prevents one from making the overhead due to the cyclic prefix
vanishing by choosing the subcarrier spacing to be very narrow?

c) [2p] Assume subcarrier spacing is 10 kHz and the cyclic prefix adds 10% overhead. How
would you choose the time-frequency reference symbol grid efficiently if channel
coherence time is 1 ms and coherence bandwidth is 200 kHz? Why?

4. [6 p] The signals, 7a and 7p, received through two antennas can be expressed for
a certain multiantenna technique that transmits a single symbol, Sa, as follows:
Ta= hy Wi Sa + Ma
rp = hz w2 Sat My

a) [2 p] What kind of a multiantenna technique is this? What is its purpose?
b) [2 p] How Wy and W2 are chosen to benefit from multiantenna operation?
c) [2 p] What is the corresponding signal model for closed-loop transmit diversity?

5. [6p] Mention two different modern standardized communication systems and
explain in detail what/how multiantenna techniques are implemented therein.

Total maximum: 30 points.