Cellular Radio Communications Engineering Education through
Laboratory Experimentation
G. LIODAKIS(1), E. KOKKINOS(1), I.O. VARDIAMBASIS(2),
D. PATERAKIS(2), and M. MAVREDAKIS(2)
(1)
(2)
Laboratory of Telecommunication Systems, Networks and Applications
Microwave Communications and Electromagnetic Applications Laboratory
Telecommunications Division, Department of Electronics,
Technological Educational Institute (T.E.I.) of Crete - Chania Branch,
Romanou 3, Chalepa, 73133 Chania, Crete,
GREECE
Abstract: - This paper presents the issues related to the establishment of a series of laboratory experiments in the
area of cellular radio communications at the Technological Educational Institute of Crete/ Department of
Electronics (TEIoC/DoE), Greece. The experiments described here consist of hands-on experimentation,
simulation work and small project-based activities, and complements the telecommunications engineering
students’ theoretical knowledge in an effective manner. The overall laboratory course illustrates the complex
tasks related to cellular radio engineering, can be regarded as a paradigm for an integrated approach for students’
experimentation in this area and as a case study for development of such a laboratory course with limited
financial resources. The paper concludes with comments about the students’ attitude and experiences as well as
with further directions for enhancing the laboratory curriculum, in line with the evolution of cellular
communications area.
Keywords: - Cellular communications, Hands-on experimentation, Simulation.
1 Introduction
During the last decades, the telecommunications field
experienced extraordinary development. The need to
exchange information with a user, anywhere and
anytime, led to cellular mobile networks, which are
wireless networks integrating several services. The
success of second generation (2G) mobile systems
prompted the development of third-generation (3G)
mobile systems for the provision of high data-rate
services. Furthermore, research efforts are currently
developing frameworks for future 4G networks. The
aforementioned
evolutions
pose
challenging
problems in issues such as, performance modeling,
teletraffic analysis, mobility, radio propagation and
fading in reduced cell sizes, interference
environment,
dynamic
resource
assignment,
modulation and multiple access schemes, multiple
antenna techniques, etc. Therefore, as the landscape
of the profession is continuously changing, third
level educational institutes are realigning what they
teach in telecommunications engineering.
The electronics engineering programs at the
Technological Educational Institutes in Greece are,
after the reform of 2001, organized as a 4-year
program, including the conduction of a student thesis
and incorporating half a year of industrial placement
for workplace learning. As it concerns the
TEIoC/DoE, Greece, in particular, a new curriculum
is under implementation from the academic year
2002-3. The curriculum consists of a number of
courses organized according to the European Credit
Transfer System – ECTS (most of them taught in
combination with laboratory exercises) which leads
to a specialization in the areas of automation and
telecommunications (during the 6th and 7th
semesters). The laboratory experiments presented in
this paper are part of the whole series of experiments
carried out in the framework of the elective senior
course “Mobile and Satellite Communication
Systems” (7th semester). For successful students’
understanding and treatment of cellular mobile
communication
systems’
problems
during
experimentation, some theoretical knowledge is
presumed. Students can obtain these theoretical
knowledge in other courses (Telecommunication
Systems, Digital Tele-communication Systems,
Theoretical and Computational Electromagnetics,
Antenna Analysis and Design, Microwave Theory
and Applications), and the course under
consideration. It should be noted that the
development of the experiments was from nearscratch with limited financial resources. Furthermore,
the overall design process of the experiments focused
on the integration of circuits and systems aspects of
current cellular technology.
A high percentage of papers in proceedings and
journals on education deal with laboratory
implementation in various disciplines related to
electronics engineering: Electronics, Electric Power
Systems, Signal Theory, Wireless Communications,
Computer Networks, Information Technologies, and
so on. These laboratory implementations rely either
on project-based experimentation [1], on hands-on
experimentation [2], on simulation [3]-[4], or on
virtual laboratory implementations [5]. However, to
the extent of the authors’ knowledge, an integrated
approach (relying on projects, hands-on, emulation
and simulation) to cover the practical issues of the
whole “Mobile and Satellite Communication
Systems” course (and of cellular communications
engineering, in particular) with an academic and
research-oriented content, has not been achieved so
far.
The organization of the paper is as follows: In
Section 2, background information about the
laboratory experimentation activities and equipment
used, is presented. In Section 3, a detailed description
of four laboratory experiments in cellular radio
communications engineering, is given. Finally, in
Section 4, further development plans under
examination and/or implementation for this part of
the overall lab course as well as some concluding
remarks are presented.
2 Background
Cellular radio communication engineering is a rather
complex task in which a large number of concepts
must be mastered, in order to be able to optimize this
type of systems. The overall optimization process
should guarantee that an inadequate coverage, a high
probability of blocked or dropped-out calls, low
transmission quality, etc., are to be avoided. In
particular, cellular radio planning involves a
thorough knowledge of propagation effects in various
environments (indoor, urban, suburban, open areas,
etc.). As propagation effects are extremely variable
along the Mobile Subscriber’s (MS) route, the use of
statistical definitions for both coverage quality and
interference levels, is necessary. Furthermore, traffic
planning must be performed in order to allocate to
each Base Station (BS) the sufficient radio resources
and cope with the traffic demand in the cell under
consideration. The traffic-handling capacity of a BS,
when expressed in statistical terms, is by defining an
acceptable Grade of Service (GOS) or probability of
blocked calls. Another aspect that requires attention
is adequate selection of carrier frequencies used in
every BS in order to keep interference below
acceptable limits. Finally, transceiver design issues
should be regarded when considering the integration
of circuits and systems aspects in a cellular
communications environment.
Taking into account all the aforementioned issues,
the laboratory experiments implemented so far and
presented here (as well as for the other parts of the
whole course) are carried out through:
 Hands-on experimentation and emulation for
understanding basic principles, propagation
effects and sources of interference in a cellular
system architecture, as well as for transmitter
design and performance evaluation.
 Simulation study of radio and traffic planning
aspects of a cellular system.
Figure 1. Laboratory Equipment: Spectrum Analyzer
and Educational Kits.
The overall educational process is complemented
by a small project-based laboratory-related activity
and is supported by the e-learning platform of
TEIoC/DoE (for student reports submission, for
provision of additional educational material related to
the laboratory experiments, for the communication
between students and the instructors, etc.). Also, a
lab manual containing description of the
experimental procedures and selected theoretical
issues related to each experiment, is available. The
equipment and tools used during the laboratory
experimentation include (see Fig. 1): Oscilloscope,
Spectrum analyzer (HP 8594E), RF signal generator,
two kits for Gaussian Minimum Shift Keying
(GMSK) and Direct Sequence (DS) spread spectrum
transmitters, walkie-talkies (operating at the 155MHz
frequency of range) for emulating a cellular system, a
software tool developed at TEIoC/DoE for traffic
calculations as well as simulation software (the EDX
SignalPro planning tool which is operational over a
specific geographical area under study).Taking into
account that the oscilloscope, the spectrum analyzer,
and the RF generator were available at the
Telecommunications Sector Labs of TEIoC/DoE and
that the kits were implemented free of charge by
contacting chip manufacturers, we had to purchase
only the set of walkie-talkies.
One of the difficulties of carrying out the
laboratory experiments (from both the students’ and
instructors’ point of view), is the need to cover a
variety of topics about which most of the students
have had little exposure. For example, although
probability theory is known to the students, there
exists some uniqueness to the application of the
concepts to issues concerning cellular radio
communications (outage probabilities, queuing
theory as related to trunking, the statistical nature of
fading, etc.). Therefore, as a prerequisite for the
whole course, knowledge and skills acquired at
previous courses (see Section 1), is presumed. In
addition, although the whole “Mobile and Satellite
Communications” course is offered as an elective to
senior students, the enrollments are high and
increased since the introduction of lab
experimentation in the course (September 2003). It is
felt that these high enrollments are a result of the
strength and visibility of the telecommunications
specialization in our Department as well as the strong
job market in Greece for radio engineers. Such a
positive students’ feedback is also expressed in their
lab reports and by the motivation they apply the
theoretical concepts to a cellular communications
environment. Finally, as it concerns the grading
policy, is as follows: lab reports (20%), small
project-based laboratory-related activity (20%), and
final examination (60%).
3 Lab Experiments Details
The six laboratory experimentation activities for
cellular radio communications engineering are as
depicted in Fig. 2 and described as follows:
3.1 Experiment 1: Traffic planning and
Resource allocation
Figure 2. Organisation of the cellular communications laboratory experimentation activities.
The primary objective of any mobile communication
system is to provide coverage for a large number of
users scattered over a wide geographic area, using
the limited resources (like spectrum, transmitted
power) available. Furthermore, cellular radio systems
rely on trunking which, in turn, exploits the statistical
behavior of the users. Thus, we developed a software
tool using the Visual Basic programming language
and modeling the fundamentals of trunking theory, as
expressed by Erlang B formula which calculates the
GOS = Probability of Blocking.
It should be noted that the Erlang B formula is
used when the lost calls are cleared due to
unavailability of radio channels; in such a case the
system does not have a mechanism to queue the call
request, and the user must retry initiating the call
later. Other assumptions when using the Erlang B
formula include that there exists an infinite number
of users requesting the radio resources, calls arrive as
determined by a Poisson distribution, and that the
call holding time (in general it takes into account the
call length, the call overhead time, plus queueing
time, if any) is exponentially distributed. The
software tool models, also, the case of a cellular
system where the lost calls are queued. Then, as
determined by the Erlang C formula, the likelihood
of a call not having immediate access to a radio
channel depends on the Probability [delay>0].
In such case, the GOS of the cellular system
under study, where blocked calls are delayed more
than t seconds, is given by, [6]:
Probability [delay>t] =
Probability [delay>0] * exp(-(C-A)t/H)
(C: number of trunked channels, A: total traffic load
(in Erlang), H: the holding time of a typical call in
seconds). The assumptions when using the Erlang C
delay formula include a Poisson arrival process, an
infinite number of traffic sources, exponential service
times, and a First-in-First-out (FIFO) server queue
where no calls leave the queue and the waiting area
(queue) is as large as necessary (i.e. infinite).
Therefore, during laboratory experimentation, we
assume that our cellular system is a circuit switched
system following either Erlang B or Erlang C
models. Thus, the student is faced with various
scenarios regarding the callers’ density (in
callers/Km2), the average activity factor per user (in
Erlang), etc. for proper system design. Other cellular
concepts and design approaches (cell splitting,
sectorization, densification of BSs, multilayer cell
architecture, effect of channel bandwidth on the
traffic carried by the system) related to traffic
planning are also examined by the use of the
software tool.
Another set of issues that belong to radio resource
allocation in cellular systems (spectrum efficiency,
multiple access schemes, fixed and dynamic channel
assignment algorithms), is also covered. Finally, the
student is asked to carry out a cellular system design
from scratch with specified capacity, taking into
account both performance and cost criteria.
3.2 Experiment 2: Hands-on experimentation
on Interference and Indoor propagation
Reliability and performance in cellular radio systems
depend on proper deployment, which includes
careful site survey and design, in order to provide
adequate coverage and capacity. However, both
coherent and adjacent channel interference, are major
limiting factors in the performance of cellular radio
systems. As implied by the frequency reuse concept,
in order to reduce cochannel interference, cochannel
cells must be physically separated by a minimum
distance to provide sufficient isolation. Also, as
adjacent channel interference results from imperfect
receiver filters which allow nearby frequencies to
leak into the passband, it can be minimized through
careful channel assignments. Furthermore, when
considering
radio
propagation,
propagation
measurements in a mobile radio channel show that
the average received signal strength at any point
decays as a power law of the distance between the
BS and the MS. In addition, when considering indoor
radio propagation, the indoor radio channel is
different from the traditional mobile radio channel. In
fact, it is influenced by local features, such as the
layout of the building, the construction materials, and
the building type.
During this laboratory experiment, students have
a hands-on experience on interference and indoor
radio propagation issues by means of walkie-talkies
which emulate a cellular system architecture and are
used as a MS, respectively. The RF signal generator
represents an adjacent channel interference source,
while the spectrum analyzer is used for power
measurements. Following the guidelines in the lab
manual, the students have the opportunity to:
a) Understand basic cellular concepts (the cell radio
coverage, the frequency reuse distance and the
power control mechanism)
b) Carry out the Carrier-to-Interference (C/I)
measurements, when cochannel and adjacent
channel interference sources are present.
c) Consider parameters (building penetration, floor
attenuation, working frequency) that affects
pathloss, by taking the associated measurements.
d) Be familiar with methods used by cellular radio
engineers (when conducting site surveys, for
characterization
of
indoor
radio
wave
propagation, etc.)
During experimentation for (a) and (b), students
have to adjust the frequency and power transmitted
by the walkie-talkies for emulating the operation of
BSs. Furthermore, the position of the “BSs” is
changing by students’ movements. In such a way,
various C/I measurements are achieved, the power
collected by the spectrum analyzer is varied, the
quality of voice communication is affected, the cell
radius can be redefined, etc. Considering
experimentation for (c) and (b), students are guided
by the lab manual to follow the required practical
steps and compare their measurements with other
experimental results (in other testbed scenarios, for
other than the 155 MHz frequency range of the
walkie-talkie frequencies, etc.), as derived from
research papers. Thus, the aforementioned real
measurements on real-world signals allow the student
to address practical issues and phenomena often not
observed otherwise.
3.3 Experiment 3: Radio planning
In this laboratory experiment, the student is
confronted with radio planning issues on a specific
region through simulation. Actually, by changing
various parameters and design assumptions, the
student is involved in a trial and error procedure. The
issues covered here include:
a) path loss calculations by employing different
propagation models (Okumura, Hata, COST 231,
ITU-R, etc.),
b) statistical variables, such as the percentage of time
and locations, where a prespecified received
power is exceeded,
c) environmental issues (atmospheric absorption,
climate type, etc.),
d) terrain topography that affects the existence of a
line-of-sight (LOS) or non line-of-sight (NLOS)
communication path,
e) antenna design issues (employment of an
omnidirectional or a directional antenna,
exploitation of space or polarization diversity),
f) the locations where a handover occurs,
g) general cellular system’s design issues
(frequency, the height of the BSs and MSs, the
transmitted power, etc.).
3.4 Experiment 4: Cellular network quality
assessment
The versatility and efficiency of simulation for
performance evaluation and tradeoff analysis is
exploited for the study of various cellular network
architectures in this experiment. By the use of the
same simulation software (as in Experiment 3.3) and
the specific region under consideration, the student
makes assessment of the following aspects of cellular
network quality:
a) Bit Error Rate (BER) predictions for various
modulation schemes, receiver implementations,
data rates, levels of cochannel interference and
Additive White Gaussian Noise (AWGN) and
speeds of the MSs. Thus, for example, the student
can get BER patterns for the area, where a GSM
system will be potentially deployed for coherent
and differential detection receivers.
b) C/(I+N) predictions as well as the effect of fading,
for a MS moving in the area under study.
Therefore, the student, by getting a quantified
picture of the perceived QoS a user is
experiencing, can identify problematic parts of the
simulated region, investigate ways of quality
improvement and seek for the cellular network
quality optimization.
3.5 Experiment 5: GMSK and DS-spread
spectrum transmitter issues
In this experiment two kits developed at TEIoC/DoE
are used for educational purposes and laboratory
experimentation. They include a GMSK transmitter
with a carrier frequency of 125MHz as well as a DS
spread spectrum transmitter operating in the 450MHz
frequency region. As it concerns the implementation
of the DS spread spectrum transmitter, it is based on
two PCBs in order to achieve a higher degree of
modularity. The first PCB includes the Motorola
microcontroller MC68HC12 for controlling the
generation of the spreading code through a 15-bit
shift register and the modulation circuit at the base
band. The chip rate can be chosen from 0.1536
Mchips/sec to 1.2288 Mchips/sec, while the data rate
is 9600 baud. The second PCB contains a synthesizer
for the carrier generation of the overall transmitter
and the frequency for the up-converter, the upconverter itself, as well as the band pass filter (BPF)
and the high frequency amplifier.
The spectrum display is the most common method
for viewing RF modulation. The major benefits of
this technique are the ability to view and measure the
overall channel bandwidth, center frequency and
sidebands and gross out-of-band anomalies.
Therefore, the student by the use of the spectrum
analyzer can get the GMSK modulation output signal
spectrum, to observe the spread spectrum signal
spectrum by altering the chip rate, to measure the
power at the up-converter /BPF/RF amplifier outputs
of the DS spread spectrum transmitter etc.
Furthermore measurements at specific test points (at
the output of the Gaussian low-pass filter of the
GMSK modulator, at the output of the spreading
code generator of the DS spread spectrum
transmitter, etc.) of both kits in the time domain are
taken by the students, letting them understand and
study the architecture and design of both transmitters.
3.6
Experiment 6: Small project-based
laboratory-related activity
In this experimentation activity, students are
encouraged to try their own variations of the
prescribed experiments or to deal with other issues
that are related to one or more of the former five
experiments. Such issues include the experimentation
of various resource allocation algorithms for cellular
communication systems, the role of cellular radio
planning tools when engineering a mobile system,
the comparison of radiowave propagation
measurement results for various wireless channels
and cellular systems, the implementation issues of
transceiver designs for mobile communications, etc.
This experimentation activity takes place during the
whole semester under the instructors’ guidance,
followed by a presentation to all students at the end
of the semester.
4 Further Directions and Conclusions
The evolution and deployment of mobile cellular
systems is characterized by the dominant role of IP
series of protocols and the necessity for a cross-layer
design approach in order to let the mobile user access
a broad range of services in a transparent way. Also,
in alignment with research carried out at the
Telecommunications Division of TEIoC/DoE, and at
the Communication Network and Telematics
Applications (COMNETTA) Group in particular, the
“cell layout” organization of the laboratory
experiments described in this paper could be
enhanced by:
 Traffic planning experimentation in a packetswitched environment
 Simulation study for the provision of various
services. As an example, we are now considering
the Push-to-talk service over cellular networks, by
means of RPT/UDP/IP packet structures.
 Treatment of mobility management issues. As 3G
and 4G mobile networks are characterized by high
user density and high mobility as well as smaller
cell sizes, the number of location updates and
handovers is increasing. Therefore, simulation of
such issues should be useful for students’
understanding of cellular systems operation.
Other
enhancements
of
the
laboratory
experiments of Fig. 2, that are already under
implementation, include:
 Hands-on experimentation for the cellular system
architectures of Digital Audio Broadcasting
(DAB) and Digital Video Broadcasting (DVB)
systems, [7].
 Hands-on experimentation with the GMSK and
DS-Spread Spectrum receivers, that are under
implementation by students of TEIoC/DoE in the
framework of their thesis.
 Study of fading effects by means of simulation in
an RF environment as well as by hands-on
experimentation in the baseband. In such a way,
students will be able to characterize the
propagation effects of a naturally occurring
environment and assess cellular network quality
issues.
 Simulation of a cellular system using the
COMNET software package in order to let the
student examine the role and effects of signaling
traffic between key components of the system,
such as the Mobile Switching Centre (MSC), the
Home Location Register (HLR), the Visitor
Location Register (VLR), etc.
Concluding, the series of experiments developed
on the basis of our findings in [8] and presented here
, has a positive effect on student motivation, learning,
and academic success, since its introduction to the
whole course. The students gain experience,
confidence and thorough understanding of concepts
and design issues in cellular radio communication
systems.
Finally, as the purchase of professional tools used
by mobile operators (such as Erricsson’s TEMS
Cellplanner Universal, Nokia’s TOTEM Vantage or
AirCom’s ASSET radio network planning and
optimization software) could not be afforded by
TEIoC/DoE, the overall laboratory course
development may be regarded as a case study when
limited financial resources are available.
Acknowledgment
This work was supported by the Greek Ministry of
National Education and Religious Affairs and the
European Union under the ΕΠΕΑΕΚ ΙΙ projects:
“Archimedes – Support of Research Groups in TEI
of Crete – Smart antenna study & design using
techniques of computational electromagnetics and
pilot development & operation of a digital audio
broadcasting station at Chania (SMART-DAB)” and
“Reformation of the Electronics Dept’s syllabus”.
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