NORTHUMBRIA UNIVERSITY
SCHOOL OF CEIS
Mobile Communications
Tutorial: MC3
1 A cellular system operating at a signal power of -90 dBm, observes CCI of 115 dBm. If a total SIR OF 22 dB is required, how much ACI can the system
tolerate?
2 A GSM system has the following specifications:
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One way system bandwidth = 12 MHz
The channel spacing = 180 kHz
Each channel is allocated for 9 users
Three channels per cell are allocated for control channels
Omidirectional receiver
Cell radius = 1.7 km, and the total coverage area is 4000 km2.
Average number of calls /user = 1.2, and the average holding time of a call
is 100s.
Call blocking probability is 3%.
Frequency reuse factor = 0.25.
Calculate the spectral efficiency.
3 In cellular mobile communications identify what contributes to the power
attenuation.
4 Discuss what is meant by the term FADING, and its impact on voice and data
communications. In mobile communication in what conditions the frequencyselective fading may occurs and how it can be quantitatively described?
5 A data signal (pulse) is transmitted over a mobile communication media. If the
bandwidth of the channel is larger than the bandwidth of the message, does
the received pulse experiences pulse distortion. Explain.
6 What happens at the mobile unit if there is a relative motion between the
transmitter base station and the mobile unit?
7 Consider a cellular system with the following data:
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Average call duration: 2.5 mins.,
Probability of blocking: 1%,
Average number of call per subscriber: 1 call/hour
No of traffic channel: 400 for a 7-cell reuse system
Calculate the number of calls per hour, If 120 degree sectoring per cell has
been adopted, then determine the total calls per hour.
8 A mobile base station antenna is transmitting at 1.2 GHz. The mobile unit
travelling at the speed of 50 km/hour is receiving/transmitting data at 180
kbps. Examine whether the channel fading is slow or fast.
9 For a mobile unit is operating in a multipath environment. The measured
coherence bandwidth and time are 10 kHz and 100 μS, respectively. The
transmission data rate is 5 kb/s. Examine whether the channel fading is slow,
fast, frequency-selective, or flat fading.
10 Consider a 7-cell pattern that uses an omidirectional antenna with 144
channels/sector. For GOS of 2%, calculate the trunking efficiency if
i. A 60o sector antenna is used,
ii. A 120o sector antenna is used.
11 A cellular mobile radio system has the following characteristics:
o Transmitted signal power at a base station = -90 dBm
o Cluster size = 7 cells
o The loss exponent factor = 4
o The signal-to-(noise + the total interference ratio) = 16 dB.
Assuming that all the interfering base stations are at equidistant from the
desired base station, and thermal and amplifier noise at the mobile unit are
negligible, determine:
(i) The co-channel interference (CCI) in W and dBm,
(ii) The adjacent channel interference (ACI) in W and dBm.
12 Describe briefly the fast (short term) fading in the context of data and voice
transmission.
13 (a) Using illustrations etc. describe the following multiplexing schemes
commenting on their advantages and disadvantages (two of each):
(i)
(ii)
(iii)
Frequency Division Multiple Access (FDMA)
Time Division Multiple Access
Code Division Multiple Access - Direct Sequence
(b) In GSM cellular mobile radio, access to the RF air interface is based on the
FDMA/TDMA. If 60 radio frequency bands, each of 200 kHz bandwidth, are
divided into 8 time slots, determine
(i) The total bandwidth requirement
(ii) The total number of channels
14 A service provider has adopted an FDMA scheme that uses single-side band
suppressed carrier modulation to provide voice services. If the voice message
is assumed to have a 4 kHz bandwidth and the guard band between channels
is 1 kHz, sketch the followings:
(i)
(ii)
A system block diagram for depicting n channels
The spectrum of the FDMA signal
If the carrier frequency range is to be from 100 to 500 KHz, how many signals
can be multiplexed?
15 A service provider has been allocated 50 MHz of bandwidth at a carrier
frequency of 1 GHz to provide cellular services to an urban area. It uses 20
cells to cover the whole area, and allocates 35 kHz of channel bandwidth for
two-way communications. 4% of the allocated spectrum is dedicated for the
control channels. Assuming that omnidirectional antenna will be used, and
each user will make an average of 4 calls per hour, each lasting an average of
3.5 minutes. For the Grade-of-Services (GOS) of 2% determine:
(i)
(ii)
(iii)
The number user channels per cell
Total traffic carried
The number of user that can be supported
16 The received carrier power C by the mobile unit at the distance d from the
base station is given by C α d-n, where n is a exponent factor related to the
propagation medium.
Discuss briefly slow and fast fading and illustrate how the received carrier
power level varies with time.
(i)
Name two techniques for combating fading
(ii)
A mobile unit move from a range of 2 km to a 9 km away from the base
station. Given that the propagation exponent factor is 4, determine the
changes in the received power (expressed in dB).
Prof. Z. Ghassemlooy