Lectures 1 & 2
Text: "Wireless Communications," by Andreas F. Molisch, John Wiley & Sons
1.
a.) Let the symbol duration T be 0.1msec and the number of subca
ier is 3. What is the third symbol of the baseband OFDM signal for the following data sequence?
1
1
-1
1
-1
1
-1
1
-1
1
-1
1
.) What are the three main advantages of using an OFDM system?
2.
Determine the symbol duration T and guard time duration Tg of an OFDM system with cyclic prefix to achieve
1.) highest spectral efficiency
2.) highest power efficiency
3.) highest data rate
Express these three parameters in terms of the following parameters
TD: Maximum Delay Spread
B: Bandwidth
M - ary symbol constellation
Rc = Code Rate<1 (e
or detection and co
ection code)
Fo = Fractional overhead for channel estimation (e.g. pilot symbols).
Fr = Frequency re-use factor (in cellular systems)
tc=coherent time. (Note that we require T<=0.2tc)
3.
Spectrum of an OFDM sub-ca
ier:
a) Derive the spectrum of the truncated (k+1)th sub-ca
ier
2
1
(()())
jktT
eututT
T
p
--
) Where is the global maximum of the spectrum?
c) What is the global maximum value?
d) Where are the local maximum of the spectrum?
e) What are local maximum values?
f) Where are the zeros of the spectrum?
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