Ece 6604 Final Exam
Georgia Institute of Technology
School of Electrical and Computer Engineering
ECE6604 Personal & Mobile Communications
Final Exam
Spring 2010
Tuesday May 6, 11:30am - 2:20pm
• Attempt all questions.
• All questions are of equal value.
• Open book, open notes, exam.
1a) 5 marks: The LCR at the normalized threshold ρ for a 2-D isotropic scattering channel can be expressed as
√
2
LR = 2πfm ρe−ρ , where ρ=
Δ
and Rrms =
R
Ωp
=
R
Rrms
E[α2 ] is the rms envelope level.
i) Find the normalized threshold level ρo at which the LCR reaches its maximum value. ii) Explain why the LCR at ρ decreases as ρ deviates from ρo .
1b) 5 marks: Consider a cellular system with a carrier frequency of 2 GHz. Suppose that the user is in a vehicle travelling at 60 km/h. Assuming that the channel is characterized by 2D isotropic scattering, find
i) the LCR at the normalized level ρ = −3 dB. ii) the AFD at the normalized level ρ = −3 dB.
2) The power delay profile for a WSSUS channel is given by φgg (τ ) =
0.5[1 + cos(2πτ /T )] ,
0,
0 ≤ τ ≤ T /2 otherwise a) 3 marks: Find the channel frequency correlation function.
b) 4 marks: Calculate the mean delay and rms delay spread.
c) 3 marks: If T = 0.1 ms, determine whether the channel exhibits frequencyselective fading to the GSM system.
3) Cellular CDMA systems use soft handoff, where the transmissions to/from multiple base stations are combined to give a macro-diversity.
Here we consider the effects of path loss and shadowing and ignore multipathfading. Suppose that the received signal power corresponding to the link with the ith base-station, Ωpi , has the probability density function pΩpi (x) = √
(dBm)
(x − μΩpi (dBm) )
1
exp −
2
2σΩ
2πσΩ
2
.
where μΩ pi
(dBm)
= E[Ωpi
(dBm) ]
The Ωpi are assumed to be statistically independent.
a) 5 marks: The reverse link uses selection combining such that the best basestation is always selected. In this case,
School of Electrical and Computer Engineering
ECE6604 Personal & Mobile Communications
Final Exam
Spring 2010
Tuesday May 6, 11:30am - 2:20pm
• Attempt all questions.
• All questions are of equal value.
• Open book, open notes, exam.
1a) 5 marks: The LCR at the normalized threshold ρ for a 2-D isotropic scattering channel can be expressed as
√
2
LR = 2πfm ρe−ρ , where ρ=
Δ
and Rrms =
R
Ωp
=
R
Rrms
E[α2 ] is the rms envelope level.
i) Find the normalized threshold level ρo at which the LCR reaches its maximum value. ii) Explain why the LCR at ρ decreases as ρ deviates from ρo .
1b) 5 marks: Consider a cellular system with a carrier frequency of 2 GHz. Suppose that the user is in a vehicle travelling at 60 km/h. Assuming that the channel is characterized by 2D isotropic scattering, find
i) the LCR at the normalized level ρ = −3 dB. ii) the AFD at the normalized level ρ = −3 dB.
2) The power delay profile for a WSSUS channel is given by φgg (τ ) =
0.5[1 + cos(2πτ /T )] ,
0,
0 ≤ τ ≤ T /2 otherwise a) 3 marks: Find the channel frequency correlation function.
b) 4 marks: Calculate the mean delay and rms delay spread.
c) 3 marks: If T = 0.1 ms, determine whether the channel exhibits frequencyselective fading to the GSM system.
3) Cellular CDMA systems use soft handoff, where the transmissions to/from multiple base stations are combined to give a macro-diversity.
Here we consider the effects of path loss and shadowing and ignore multipathfading. Suppose that the received signal power corresponding to the link with the ith base-station, Ωpi , has the probability density function pΩpi (x) = √
(dBm)
(x − μΩpi (dBm) )
1
exp −
2
2σΩ
2πσΩ
2
.
where μΩ pi
(dBm)
= E[Ωpi
(dBm) ]
The Ωpi are assumed to be statistically independent.
a) 5 marks: The reverse link uses selection combining such that the best basestation is always selected. In this case,