Exam text content

Konstantin, rykovObtut. F

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TLT-6106 Basic Course on Wireless Communications, Exam 16 January.2012, Please
give the answers in English. Students' own calculators or faculty's calculators are allowed.
The attached 2-page formulas are allowed. Exam's compiler: Simona Lohan, TG116.

1. (6p) Describe the basic principles of FDMA and CDMA multiple access schemes. Use
illustrative block diagrams to explain these concepts. Compare FDMA with CDMA: basic
principle, advantages, and disadvantages. Give examples of systems which employ FDMA
and CDMA technologies.

2. (6p) A commercial mobile receiver for data transmission is specified with a sensitivity of -
100 dBm (dBm=power in dB per mW). Assuming a 1 mW transmit power, a transmission
freguency of 2.1 GHz, transmitter (or base station) antenna height of 10 m, and receiver
antenna height of 0.01 m, what would be the radius of service area under the following path
loss models?

A) Lg 120+40108,5 dy, 201080 pytyn 700 ray- mode)
OL 3 232.44+ 201080 dn + 2010810 Sis hu spau [01> most
OL p =46.3+33.9108 9 (11) 13.82 108,0 (fy 1) +(47—6.55 10810 (17) 10810 (Ap)

Empelitai JoU loss mot

Ny p 15 the transmit antenna height in meters and hp m 5 the receive antenna height in
meters.
To which path loss model each of the formulas above corresponds?
At egual cell radius, for which of the 3 models above do you get the minimum path loss and
why?
How is the path loss varying with the distance (in linear scale) for these models?

3. a) (3p) Describe briefly the following concepts: i) Soft handover, ii) Isotropic antenna, iii)

Multipath propagation, iv) Fading, v) Inter-symbol interference (ISI) , vi) Antenna gain.
b) (3p) What is the cluster size (N) in the figure below? If the cell range is R=300 m, what is
the value of the re-use distance? What is the value of the Signal to Interference ratio (SIR) in

decibels for this cluster size, in an environment with the path loss factor n=4? What about

SIR in an environment with path loss factor n=2. Discuss the differences.
poster!" Wy Clas]

0 | Cluster 2
A Cluster 3
ikCtuster 4
€) Clusters
Cluster 6

+ Cluster 7

  

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4. (6p) The following block diagram shows the simplified GSM+UMTS network architecture.

Explain the name and functionality of each of the blocks from 1 till 15. Hint: some blocks
have the same functionality/name. Based on this block diagram, compare GSM system
architecture with UMTS system architecture, by emphasizing the similarities and differences.
Gives some examples of data rates typical for GSM and for UMTS based connections.

N

 

5

a) (3p) Two DS-CDMA spreading codes in vector form are s1=[-1 1 1-1 -1] and s2=[1-11-
1 +1]. Calculate the cross correlation values between the spreading code s1 and signal s11
which is defined as a bit seguence b1=[1 1] spread by s1. What is the spreading factor? What
is the processing gain in dB?

b) (3p) Make a judgment on the evolution and challenges on the future wireless networks
(write down your ideas what on what will be next and what are the challenges we have to
cope with). Think about the physical layer and Medium Access Control (MAC) layer
reguirements and how to achieve them.