Questions
Introduction
1) Write down the evolution of wireless mobile communication systems.
2) Draw a block diagram of cellular radio network.
3) Draw a timing diagram illustrating how a call to a mobile user is initiated by a landline
subscriber.
4) Show the various upgrade paths for 3G technologies with a neat figure.
5) What is a cellular concept? How did it solve the problem of spectral congestion?
Illustrate.
6) What is frequency reuse? Discuss the relationship between system capacity C and
cluster size N with suitable derivation.
7) What is cell dragging? Illustrate umbrella cell approach.
8) Discuss co-channel and adjacent channel interferences?
Point to Multipoint System(PMP)
9) What is multiple access Method? Why is it necessary?
10) Discuss the multiple access techniques: TDMA, FDMA and CDMA in brief.
11) What is TDD and FDD? Illustrate.
Propagation Theory
12) What do you mean by multi-path propagation? Discuss a RAKE receiver with suitable
diagram.
13) What is fading? Draw a tree diagram and discuss different types of fading in brief.
14) Discuss Hata Model and Okumura model.
15) Discuss space diversity considerations.
16) Differentiate between Equalization and Diversity technique.
Modulation Technique
17) Describe BPSK transmitter and receiver with the help of suitable block diagram.
18) What is coherent and non-coherent detection? List the advantage of DPSK over PSK.
19) Discuss QPSK with its constellation diagram.
GSM technology
20) Why and When GSM technology was introduced?
21) Discuss the services and features of GSM.
22) Explain GSM architecture in detail with diagram.
23) Discuss the various interfaces used in GSM with a diagram.
24) What is the modulation technique used in GSM? Discuss technical aspects of GSM radio
subsystem.
25) Discuss frame and multiframe structure of GSM.
26) Present GSM air interface specifications summary with required parameters.
27) Differentiate between Full rate and Half rate traffic control channel.
28) Draw a tree diagram showing diffrernt channel types in GSM.
29) Discuss hands-off stragegy in cellular system.
30) Prove that for a hexagonal geometry, the co-channel reuse ratio is given by Q = √(3N),
where N = i2+ij+j2. (Hint: Use cosing law and hexagonal cell geometry)
31) Draw the block diagram of Wireless Communication System and explain each block in
detail.
32) Explain how frequency reusing is achieved in cellular systems and also explain the
various methods for improving the capacity of a cellular system.
33) Discribe briefly the network architecture of a cellular mobile communication system.
34) Show that the frequency reuse factor for a cellular system is given by K/S, where K is
average number of channels availabe to the cellulare service provider.
35) Briefly explain the channel assignment strategies in cellular communication.
36) Define traffic and Grade of Service(GOS). What are the assumptions based to derive
Erlang B formula. State the Formula as well.
37) Explain the role of BTS and MSC.
38) Why adjacent channel interference is caused, what are the sources?
39) What are the factors affecting in the choice of digital modulation?
40) Explain the performance advantages of digital modulation over analog?
41) What is duplexing? What are the types of duplexing used in mobile communication
system?
42) What is the advantage of multiple access schemes?
43) Derive path loss equation using free space propagation model.
44) Explain in brief about the hand-off strategies used in cellular communication system.
45) Why is hexagonal cell geometry chosen in cellular design?
46) Differentiate between TDMA,FDMA and CDMA.
47) List out the services that are provided in GSM.
48) Enumerate the latest advancement in mobile communication.
49) What is trunking theory? Why is the cell splitting and sectoring used?
Numericals
1. A Base Station antenna is installed at the height of 25 meters in Nepal Engineering
College area and radiates the signal at the carrier frequency 1800 MHz. A mobile station
is 2 km away from BS and its height is 3 meters. If the receiver sensitivity is ‐60 dB, the
link between the MS and BS will be established or not. If the link is not working, how
can you establish the link? Explain in details. Note that the transmit power is 2 watts
(maximum).
2. If the received power at the reference distance d0=2 km is equal to 1 microwatt, find the
received powers at distances of 5km and 10 km from the same transmitter for the
following path loss models: a) n=3 b) n=4 c) Hata model for a large city environment.
Assume f= 1800 MHz, ht=50m, hr=2m, Gt=Gr=0dB.
3. a)If the transmitter produces 50 watts of power, express the transmit power in terms of (a)
dBW (b) dBm. If 50 watts is applied to a unity gain antenna with a 900 MHz carrier
frequency, find the received power in dBm at free space distance of 100m from the
antenna. What is Pr (10 km)? Assume unity gain for receiver antenna.
4. a)Draw hexagonal coverage area for k=3, 4 and 7 with proper co-channel positions for
channel group 1, 2… 7. Derive the expression for the distance between co-channel cells
for the above given reuse factor. Consider the radius and sides of the hexagon are equal
and is given by R.
b) Calculate the path loss for a case defined by the following parameters by using Hata
model
City zone = suburban
Frequency = 900 MHz
Transmitter height = 47 m
Mobile height = 1.7 m
Distance = 3 km. Assume other parameters.
5. Given a cellular system in which tere are a total of 1000 radio channels available for
handling traffic. It is also given that the area of a cell is 7 Km2 and the area of the entire
system is 2200 Km2.i) Calculate the system capacity if the cluster size is 7.
ii) How many times would the cluster of size of 4 have to be replicated in order to cover
the entire cellular area?
iii) Calculate the system capacity if the cluster size of 4
iv) Does the decreasing the cluster size increase the system capacity? Explain.
6. Given a cellular system in which there are a total of 1000 radio channels available for
handling traffic. It is also given that the area of a cell is 7 Km2 and the area of the entire
system is 2200 Km2.
i) Calculate the system capacity if the cluster size is 7.
ii) How many times would the cluster of size of 4 have to be replicated in order
to approximately cover the entire cellular area?
iii) Calculate the system capacity if the cluster size of 4
iv) Does the decreasing the cluster size increase the system capacity? Explain
7. Prove that for a hexagonal geometry, the co-channel reuse ratio is given by Q = √(3N),
where N = i2+ij+j2.
8. Find the median path loss under the Hata model assuming fc = 900 MHz, ht = 20m, hr =
5 m and d = 100m for a large urban city, a small urban city, a suburb, and a rural area.
9. A cellular service provider decides to use a digital TDMA scheme which can tolerate a
signal-to-interference ratio of 15 dB in the worst case. Find the optimal value of N for (a)
omnidirectional antennas, (b) 120o sectoring, and (c) 60o sectoring. Should sectoring be
used? If so, which case (120o or 60o) should be used? (Assume a path loss exponent of
n=4 and consider trunking efficiency).
10. A receiver in an urban cellular radio system detects a 1 mW signal at d=d0=1meter from
the transmitter. In order to mitigate co-channel interference effects, it is required that the
signal received at any base station receiver from another base station transmitter which
operates with the same channel must be below -120 dB. A measurement team has
determined that the average path loss exponent in the system is n=3. Determine the major
radius of each cell if a seven-cell reuse pattern is used. What is the major radius if a fourcell reuse pattern is used?
11. The U.S. AMPS system is allocated 50 MHz of spectrum in the 800MHz range and
provides 832 channels. 42 of those channels are control channels. The forward channel
frequency is exactly 45 MHz greater than the reverse channel frequency. (a) Is the AMPS
simplex, half-duplex, of duplex? What is the bandwidth for each channel? (b) Assume a
base station transmits control information on channel 352, operating at 880.56 MHz.
What is the transmission frequency of a subscriber unit transmitting on channel 352.(c)
The A-side and B-side cellular carriers evenly split the AMPS channels. Find the number
if voice channels and number of control channels for each carrier. (d) For an ideal
hexagonal cellular layout which has identical cell coverage, what is the distance between
the centers of two nearest co-channel cells for seven-cell reuse? For four-cell reuse?
12. Assume a receiver is located 10km from a 50 W transmitter. The carrier frequency is 6
GHz and free space propagation is assumed, 1 t G = and 1 r G = . (a) Find the power at
the receiver. (b) Find the magnitude of the E-field at the receiver antenna. (c) Find the
rms voltage applied to the receiver input, assuming that the receiver antenna has a purely
real impedance of 50Ω and is matched to the receiver.
13. Free space propagation: Assume the transmitter power is 1W at 60 GHz fed into the
transmitter antenna (AssumeGt = Gr = 29 dB and 30 t P = dBm). (a) Calculate the free
space path loss at 1m, 100m, 1000m. (b) Calculate the received signal power at these
distances. (c) What is the rms voltage received at the antenna if the receiver antenna has
purely real impedance of 50Ω and is matched to the receiver?
14. If the received power at a reference distance d0 =1km is equal to 1 microwatt, find the
received power at distance of 2km, 5km, 10km, and 20km from the same transmitter for
the following path loss models: (a) Free space; (b)n=3; (c)n=4; (d)two-ray ground
reflection using the exact expression. Assume f=1800MHz, ht=40m, hr=3m, Gt = Gr = 0
dB.
15. Assume a SNR of 25dB is desired at the receiver. If a 900MHz cellular
transmitter has an EIRP of 100W, and the AMPS receiver uses a 0dB gain
antenna and has a 10dB noise figure, find the percentage of time that the desired
SNR is achieved at distance of 10km from the transmitter. Assume n=4, σ =8dB,
and d0 =1km.