7CCSMCTH Communication Theory Homework#2
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7CCSMCTH
Communication Theory
Homework#2
1. A multi-path fading channel has one reflecting path with voltage gain 0 共 议 想 1 ofthe main path. The relative delay on this path is T seconds and the carrier sees a phase shift of arg(a) which is constant on the second path. The pulse response of such a strictly band-limited channel is modelled as
P(O) =〈|((1 + ae_jOT ), _ 共 O 共
|l0, elsewhere
where 0 共 a 想 1 is a complex constant, i.e., 议 = 议ejarg (议) .
a) Using Matlab, plot the magnitude of the Fourier transform of sampled pulse response, i.e., 20log10 P(e_jOT ) , with T = 1and a = 0.9.
b) Show that p(t) 2 = 1 + aa * .
c) Find the Fourier transform of the sampled channel deterministic autocorrelation function, Q(e_jOT ).
d) By substituting D = e_jOT , show that
Q(D) = a *D _ 1 + p(t) 2 + aD
p(t) 2 .
By substituting D = e_jOT , with T = 1 , use MATLAB to plot Q(e_jOT ) for a = 0.5and
a = 0.9
e) Find the zero forcing and the minimum mean square error linear equalisers WZFE (D) and WMMSE -LE (D).
f) By substituting D = e_jOT , with T = 1and assuming SNR MFB = 10 p(t) 2 , use Matlab to plot WZFE (e_jO ) and WMMSE -LE (e_jO ) for a = 0.5and a = 0.9 .
Hint: Try to plot the corresponding curves in parts (d) and (f) for each value of a on the same axis and discuss.
g) Assuming a = 0.5 , E x = 1andC2 = 0. 1 , find the time-zero coefficient w0 for the MMSE-LE and the ZFE and compute CM(2)MSE -LE , CZ(2)FE ,yMMSE -LE and yZFE .
h) Repeat part (g) for a = 0.9 and discuss the results, comparing parts (g) and (h).
2) The channel given in homework#1, i.e.,
p(t) = - sin c + 1 + sin c - sin c ,
is used for QAM transmission with Ex = 1 and SNR MFB = 10dB .
Find WMMSE -LE (D), oM(2)MSE -LE , and SNR MMSE -LE .
(Hint: Follow the same steps as you did in homework#1 for ZFE.)
2023-04-14