LiTH, Linköpings tekniska högskola
IDA, Institutionen för datavetenskap
Juha Takkinen
2007-03-19
1(4)
Written examination in the course
TDDC22 Mobile wireless networks:
systems and applications
2007-03-15 at 8–12
Hall
TER2.
Helping materials
A simple calculator with memory erased and an English dictionary (not electronical) are allowed.
Results
The results are published at latest twelve working days after the exam.
Points
Maximum is 40 points. For a pass, 20 points are needed in total.
Teachers on duty
Juha Takkinen, 0731-50 03 93, who will visit the hall at 8.45 and 10.15.
Instructions
Read the questions carefully. Justify your answers, if not told otherwise, and
state explicitly your assumptions. The use of figures is encouraged, except
where other instructions apply. Answers that are not legible will not be graded. You can use either English or Swedish.
Put only one problem on each sheet of paper, with the exception of subproblems a, b, etc., which can be on the same sheet.
Make sure that you keep the same order of each alternative and table entry
when you copy answers from the examination paper to your sheet.
”They have computers, and they may have other weapons
of mass destruction.” —Janet Reno
Good luck!
2(4)
Wireless networks
1.
The following are true or false about wireless networks (check True or False,
or none of the two. Do not motivate your answer. Copy the answer to your
answer sheet in the same order.):
(3 p.)
True False
a. ❏ ❏
The different planes of orbit of communications satellites can be
categorized as either LEO, NEO, or GEO
b. ❏ ❏
The ad hoc mode of IEEE 802.11 requires an access point but not
a distribution system.
c. ❏ ❏
The distribution system in the IEEE 802.11 standard can be
another wireless system.
d. ❏ ❏
The basic unit of networking in Bluetooth is the piconet, which
can consist of up to 8 active master devices.
e. ❏ ❏
A Bluetooth usage model is a set of protocols that implement a
particular Bluetooth-based application, for example “file
transfer“.
f. ❏ ❏
A hand-off (handover) occurs in a wireless network, for example,
when the mobile stations moves out of range of an access point
(base station) and into the range of another access point.
(0.5 points for a correct answer; – 0.5 points for wrong; 0 points for no answer;
minimum 0 points on the whole questions or a maximum 3 points.)
2.
Define the following concepts:
(3 p.)
a. Interframe spacing
b. Basic Service Set.
c. CRC.
3.
Explain how the hidden-terminal problem is solved in IEEE 802.11b.
4.
Under what circumstances would you use a GEO satellite and a LEO
satellite, respectively?
(2 p.)
5.
List and explain two ways of increasing the capacity of a cellular
system.
6.
(2 p.)
(2 p.)
Name the main elements of the GSM system architecture and describe
their functions.
(2 p.)
3(4)
Telecommunication
7.
The following are true or false about telecommunication (see question 1
above for instructions):
(3 p.)
True False
8.
a. ❏ ❏
Frequency hopping spread spectrum can be used to compress
signals with varying spectrum.
b. ❏ ❏
A non-zero syndrom block indicates transmission without errors.
c. ❏ ❏
The Huffman code is used to make a spread spectrum signal.
d. ❏ ❏
The entropy of a source is always smaller than log2(M), where M
is the number of symbols.
e. ❏ ❏
The Hamming code can correct two errors or detect one errors.
f. ❏ ❏
Delta modulation approximates an analog signal with a staircase
signal.
Explain the following concepts with two sentences:
(3 p.)
a. Amplitude modulation
a. Frequency multiple access (FDMA)
a. Nyquist bandwidth.
9.
For each statement below, explain if it is true or false. Motivate your answer.
a. The rate of an error correcting code is always chosen to be smaller than
the channel capacity.
(2 p.)
b. Code division multiplex can only be used on channels with a single
transmitter and a single receiver because the signal will use all available
spectrum.
(2 p.)
10. A stochastic source generates symbols from the set {a, b, c, d, e} with
probabilities 0.7, 0.1, 0,1, 0.05, and 0.05. Compute the entropy of the source
and construct a code to compress the data. Explain the code construction
and compute the average code-words length.
(3 p.)
4(4)
GIS
11. Describe the difference between traditional systems such as CAD, business
planning tools, and economic information systems versus GIS.
(2 p.)
12. Vector and raster are two methods to represent geographical data. Describe
these two methods and mention some factors influencing the choice between
the methods with regard to analysis.
(3 p.)
13. Data capture are all the methods to get data into a database. Mention at
least five methods to capture geographical (spatial) data.
(2 p.)
14. What problems could you possibly face when integrating data from various
sources? Mention at least three problems.
(3 p.)
15. Data capture, storage, and retrieval will all effect the choice of GIS
solutions. Discuss this—maybe with examples from your own work—
and argue for your choice.
(3 p.)