An Analysis of GSM Handover based On Real Data

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(IJCSIS) International Journal of Computer Science and Information Security,
Vol. 9, No. 7, 2011

An Analysis of GSM Handover based On Real Data

Isha Thakur Bhavana Jharia Gopal Chandra Manna
ME Student, Communication System Associate Professor, Depptt. Of EC Sr. General Manager
Engineering Branch Jabalpur Engineering College BSNL, Jabalpur
Jabalpur Engineering College, M.P., India M.P, India M.P, India
ishathakur_4@yahoo.com dr.bhavana.jharia@jec-jabalpur.org gcmanna@gmail.com

the RxLev and RxQual ,alone, is not sufficient to provide the
Abstract—Handover decisions in GSM networks are based on the accurate result for optimum handover solution .So, there is a
difference in received signal strength, between the serving cell need of a new handover scheme which not only consider
and the neighboring cells. But in a practical scenario, RxQual and RxLev ,but also some other important parameters,
particularly in city area ,considering difference in signal level for a better handover process .
strength alone , is an inferior criteria to decide handover issue
,because the towers are in close proximity & the absolute signal
strength is quite good to continue the communication ,without In the present work ,we focus our attention on
much difficulty .Also, in these environments, multipath incorporating some more decision criterion in the handover
reflections, scattering due to moving vehicles & diffraction from algorithm .After an extensive study of the GSM measurement
multiple building edges ,contributes to poor signal quality, hence reports obtained from a telecom company, it has been
forcing the mobile to transmit more power to continue the validated that the transmit power (TxPower) ,aggregate C/I &
communication. the FER ,should be given due importance in the handover
decision ,along with RxLev and RxQual. The reason behind
Continuation of an active call is one of the most incorporating these parameters is explained ahead.
important quality measures in the cellular systems. Handover
process enables a cellular system to provide such a facility by In the dedicated mode, TxPower consumes the battery
transferring an active call from one cell to another. Different
power of the mobile handset .Normally the acceptable range
approaches have been proposed and applied in order to achieve
better handover service, by various researchers. The principal of the TxPower is between 5 and 15, where 5 is the desired
parameters considered in the present work, which are used to value. .Hence, TxPower has been proposed to be an important
evaluate handover techniques are: Received signal quality parameter in the handover decision process. The FER may
(RxQual), FER, Received signal level, MS-BS distance, transmit increase in two cases (1) If the complete frame is lost or
power (TxPower) & aggregate C/I. destroyed in transmission and (2) Frame could not be obtained
because error correcting code is destroyed .Hence, FER is a
In the present work, thorough analysis has been done for considerable parameter in handover decision. Similarly the
the received signal strength difference threshold, along with interference level received from all the interference sources in
other RF quality parameters. To ensure best performance to all the system should be given due importance in the criterion list
mobile users at all times and all locations an active set of
for the handover decision .The desired carrier level and the
parameters has been calculated for critical values along with
signal strength difference threshold. interfering carrier level are calculated and measured in
dBm.For convenience, we normally use the C/I ratio to
Keywords: Received signal quality (RxQual), FER, Received determine whether an interference case is acceptable or not.
signal level (RxLev on uplink and downlink), MS-BS distance,
transmit power (TxPower) & aggregate C/I. Since in the real time cellular systems, handover failure
may occur due to a number of practical issues, by introducing
additional criteria for handover decision making, spurious
handover can be avoided to a large extent. Conventional
I. INTRODUCTION techniques suffer from inefficiencies caused by the fact that in
Traditional handover algorithms are based on relative the practical scenario, particularly in city area, difference in
signal strength, relative signal strength with threshold, relative signal level strength has proved to be an inferior criteria to
signal strength with hysteresis, relative signal strength with decide handover issue .To overcome these limitations, the
hysteresis and threshold [1] [2]. Handover analysis uses fuzzy authors has proposed an active set of parameters along with
logic based prediction techniques also [3] [4].Later an their optimum values which can be used to provide better
extensive study found that the received signal strength handover decision efficiency.
(RxLev) & the received signal quality (RxQual), are the prime
parameters in the handover decision. However ,considering

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The rest of the article is organized as follows. Section II III. HANDOVER ANALYSIS
reviews related works. Section III gives analysis of the
handover algorithm. In Section IV, results are discussed, as Handover initiation criteria analyzed in the present
obtained from the model. Finally, conclusions and future paper is based essentially on five variables: the received signal
perspectives are discussed in Section V. level (RxLev), received signal quality (RxQual), FER,
transmit power (Txpower) & aggregate C/I value. In order to
study the effect of the above mentioned variables on the
II. LITERATURE REVIEW handover decision, extensive analysis of the GSM
measurement data has been carried out .Out of total 21
Several aspects of the analytical handover model have been handovers, few handovers were like transit entry into cell, few
investigated in the previous works. An analytic model of were false handover triggers and only in 10 cases, the call
handover algorithm has been presented in [5, 6, 7] based on continued for appreciable time i.e. the handover was stable
the level crossings of the difference between the signal .The data collected before and after handover were reliable
strengths received from two base stations in a log normal and taken into consideration for detailed study.
fading environment. The basic model has the route of the
mobile chosen to be the straight line between two BSs. Two A. Parameter Evaluation
important performance indicators of a handover algorithm are
the mean number of handoffs for this route and the delay in We start the analysis by studying the behavior of
handing off, both of which need to be minimized. The tradeoff various performance metrics with respect to the distance
curve between these two conflicting indicators was drawn in between serving base station & the mobile unit. The line of
order to determine the amount of hysteresis and averaging to sight distance is calculated for a number of cells using the
be used in the algorithm. distance Haversine formula as under

In [5], the validity of the Poisson model has been Dist_Los= SQRT (POWER (F, 2) +POWER (K, 2)
demonstrated for the specific case where the signal strength is Where,
stationary. The handover process was studied in terms of F=height of the BTS antenna in meter
certain level crossings of the difference between the received K=non-line of sight distance in meter
signal strength from two BSs; the model works well where it
is most needed, in the range of optimal parameters. This work Where,
has been extended in [6, 7] for the no stationary case, in which K= (ACOS (SIN(C)*SIN (H) +COS(C)*COS (H)*COS (J-
the level crossings are modeled as Poisson process with time- E)))*6371*1000
varying rate functions. Further, theoretical analysis using level
crossings is given in [8]. In [9], the model was applied to Where,
obtain certain criteria for designing practical handoff C=latitude of BTS antenna
algorithm, especially for designing algorithms that are robust E=longitude of BTS antenna
with respect to variations in the radio propagation H=latitude of mobile station
environment. This includes extensions of the model to take J=longitude of mobile station
into account the absolute value of the signal strength from the Radius of earth 6371 Km
current BS to avoid handoffs when the weaker signal is strong Once the distance values are obtained, the plots between
enough, has been shown in [10]. this distance & the respective parameter is plotted.

It has been observed that the analysis done in the previous 1) RxLev vs. Distance
work on handover ,has been validated by simulation results
only .None of the work has been done on the practical data to Ideal plot of the RxLevel verses distance ,will be the one
validate their findings .However in the present paper ,the in which the RxLevel value should exhibit a downtrend with
effect of several performance metrics (RxLev,RxQual,FER, an increasing distance .One of the plots shown in figure.1
Aggregate C/I &TxPower ) on the handover decision has been ,exhibits this behavior .As the distance between the mobile
validated by analyzing the measurement data ,as obtained station & the serving base station increases ,the received
from the drive test results in GSM network, from Katni town signal level decreases .The entry to this cell occurred at a
of Madhya Pradesh state ,India. distance about 320m, from 320 m to ~340m, the signal
strength varies heavily from -60 dam to -77dbm which
indicates that the recording are done at shade coupled with
heavy transient reflections form neighboring moving vehicles .
As the distance is increased, line of sight is available, signal
strength was stable and there were gradual fall with distance
.The points where the handover situation occurs, are identified
by observing the sudden downtrend in the RxLev .Once these

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points are known, the behavior of the RxLevel over these
points is recorded for observation.
3) FER vs. Distance

In the cellular communication, not only the continuation of
the call is necessary but also quality of speech is an essential
parameter in analyzing the performance of handover
algorithms. The Frame Error Rate (FER) measurement is used
by the mobile to detect bad frames. The mobile starts the
substitution and muting process, and within 300 ms of bad
frame reception it completely mutes the speech. Out of 104,
FER measurements are done over 100 frames, which
correspond to ~2 s of speech. The variation of %FER with the
distance between the serving BTS & the MS is as shown in
figure 3.In contrast to observations in case of RxLevel and
RxQual ,FER shows better performance at the near region and
even at the far region with exception in the middle. This
shows strong immunity of GSM system from frame errors.
But, the overall trend was in upward direction indicating
contribution of this parameter for handover decision.
Figure 1. RxLev vs. Distance

2) RxQual vs. Distance

RxQual is a value between 0 and 7, where each value
corresponds to an estimated number of bit errors in a number
of bursts. Each RxQual value corresponds to the estimated bit-
error rate according, which varies from BER <0.2% for
RxQual 0, 0.8 %< BER<1.6% for RxQual 3 and BER >12.8%
for RxQual 7.
The RxQual value showing an increase contributes to the
handover decision making .The variation of this parameter
with the distance ,one of which is shown as under in Figure.2
.At the entry into the cell, RxQual had wide variation which
shows presence of strong interference .Slowly this situation
improves as the vehicle goes slightly away where a dominant
part in line of sight signal .At the end ,few observations show Figure 3. FER vs. Distance
RxQual>4 which indicated requirement of handover .Overall
positive slope indicated healthy situation for handover
prediction . 4) Aggregate C/I vs. Distance
The aggregate carrier-to-Interference (C/I) ratio is the ratio,
expressed in dB, between a desired carrier (C) and an
interfering carrier (I) received by the same receiver. The
variation of the aggregate C/I with the distance (Figure
.4),better than 15dBm in most cases shows that it has only a
minor effect on the handover decision, but considered here as it
has positive slope.

Figure 2. RxQual vs. Distance

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value – initial value) are taken into account . The distance of
the mobile unit from the serving station & the target station is
also examined .This approach is adopted to identify the role of
each parameter in the handover, more clearly & accurately.
The handover cases which exhibit the near ideal situation are
identified & are taken into consideration for deriving the
optimized handover situation.

Calculations:

The handover position is identified in the excel sheet of the
drive test report ,by looking at the „event type‟ column .After
selecting the location ,a set of about 50 observations ,before &
after the handover event are considered for evaluating the
average values of the before & after values of each parameter
.A sample sheet is shown in APPENDIX to demonstrate method
Figure 4. Aggregate C/I vs. Distance of calculation has been done (sheet 1).The transition
(handover) had taken place from cell id 509 to 619 at the
position highlighted in the sheet .Before values pertains to
5) TxPower vs. Distance values (and average thereafter) before transition in old cell and
after values after transition to new cell .This method is carried
Transmit power plays a very important role in sustaining out for each parameter. The calculations & the respective
higher battery life of the mobile handset .In the dedicated sheets are obtained by performing the calculations in the
mode, TxPower is monitored constantly by the serving station similar manner .The delta (∆) values of the five parameters are
.Normally the acceptable range of the TxPower is between 5 obtained by performing the subtraction of the final & initial
& 15, where 5 is the desired value..Higher TxPower is values respectively. The two other distance calculations (from
unacceptable not only because it consumes the battery power serving cell to target cell & from serving cell to mobile
of the mobile, but also because it may adversely affect the station) is performed by the distance haversine formula as
mobile user‟s health. The variation of the TxPower with the mentioned in previous section.
distance is given in figure 5.
C. Optimization

The optimum situation for handover is identified by
comparative analysis. The comparison of the parameter values
at the time of handover is done with respect to the
recommended range of values & the ideal values respectively
.The tabulated form of the values obtained is given in sheet2.
It has been found that the handover situation in the 5, 8 & 9 th
cell case is exhibiting „near ideal‟ situation. These 3 cases are
then scrutinized to obtain the optimum condition for handover.

Comparisons:

(a)RxLev and ∆RxLev: The 4.3dbm increase in the RxLev
after the handover has taken place, averaged for all 3 cells,
is a sure sign of a successful handover.
Figure 5. Txpower vs. Distance (b)RxQual and ∆RxLev: The performance of the RxQual
value ~=1.46 is most appropriate in the cell after
averaging.
(c)FER & ∆FER: The optimum performance of the FER is
B. Handover Cell Analysis fulfilled by the cell of the serial number 8.

Once the relationship between the distance & the respective (d)TxPower: The cell of the serial number 5 is exhibiting the
parameters is drawn, the analysis of handover cells is studied best case of the TxPower based decision criteria.
exclusively. The cells in which the handover has occurred are
first identified & then the parameter values are studied for (e)Aggregate C/I: The aggregate C/I criteria is fulfilled by the
each cell separately .Not only the absolute values of the cell of the serial number 5.
various parameters is studied but also the relative values (final

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IV. RESULT & DISCUSSION
REFERENCES
We have validated the role of various parameters on the
handover decision making in this paper. It has been found that [1] Gregory P. Pollioni, “Trends in Handover Design”, IEEE
the behavior of the respective parameters & the role of each Communications Magazine, vol. 34, March 1996, pp. 82-90
chosen parameter on the handover decision making, is
satisfying the ideal cases to a close extent .Also the [2] P. Marichamy, S. Chakrabati and S. L. Maskara,
optimization has contributed to obtain a set of values of the “Overview of handoff schemes in cellular mobile networks
respective parameters, which serve as the best case to decide and their comparative performance evaluation”, IEEE
the handover ,as given table1 . VTC‟99, vol. 3, 1999, pp. 1486-1490

TABLE I RESULT [3] M. Chiu, M. Bassiouni, “Predictive Schemes for HandoN
Prioritization in Cellular Networks Based an Mobile
Positioning”, EEE Joumal on selected amas in
RxLev
RxQual FER Tx Power(dBm) communications, Vol. 18, No. 3, March 2000
(dBm) Aggregate C/I
2
-72 5 15 15.82 [4] M.S.Dang, A Prakash, D.K. Anvekar, D. Kapoor,
∆RxLev ∆Tx ∆Aggregate R.Shorey, "Fuzzy Logic Based Handoff in Wireless
∆RxQual ∆FER Networks", in Proceedings of the 51st Vehicular Technology
(dBm) Power(dBm) C/I
-0.3794 Conference (VTC 2000 Spring), Tokyo,
4.3 -1.5 -6.537 1.1066
15-18 May 2000, pp.2375-2379

[5] R. Vijayan and J. M. Holtzman, “The dynamic behavior of
V. CONCLUSION handoff algorithms,” in Proc. Ist Internat. Con$ UniversG 1
Personal Commun., Dallas, TX, Sept. 1992.
The aim of this investigation was first to define some
appropriate performance measures for inter-cell handovers. [6] “Analysis of handoff algorithm using nonstationary signal
The obtained results showed the outperformance of handover strength measurements,” in Proc. GLOBECOM ‟92, Orlando,
algorithm based on multiple parameters (i.e. RSS, BER etc). In FL., Dec. 1992.
this paper, we have extended the model for analyzing the
performance of the handoff algorithm based on signal strength [7] “A model for analyzing handoff algorithms,” IEEE
measurements. This model enables us to achieve good Trans. Veh. Technol., vol. 42, no. 3, Aug. 1993.
analytical approximations easily and fast. Therefore, this
model can be used by the network designer to help optimize [8] R. Vijayan and J. M. Holtzman, “Foundations for level
the behavior of the handover strategy by setting appropriate crossing analysis of handoff algorithm,” in Proc. ICC ‟93,
hysteresis, absolute threshold, and other parameters such as Geneia, Switzerland, May 1993.
the averaging length for different propagation environments.
Handover condition for at least 3 of the 5 parameters should [9] R. Vijayan and J. M. Holtzman, “Sensitivity of handoff
be met to take handover decision while 4 conditions meeting algorithms to variations in the Drooagation environment.” in
will be sufficient. Prcc 2nd Internat. Conf I s -Universal Personal Commun.,
As a future course of work, more importance can be Ottawa, Canada, Oct. 1993.
given to the QoS issues where in more number of radio and
network parameters are taken into consideration for averaging [10] R. Beck, F. W. Ho, “Evaluation and performance of field
the threshold values. This ensures that a handover can be strength relatedhandover strategies for micro-cellular systems,”
hastened or delayed as the situation requires and also prevent in Proc. 3rd Nordic Sem. Digital Land Mobile Radio Commun.,
unnecessary handover that may take place due to momentary Copenhagen, Denmark, 1988.
fading of any one of the parameter. Hastening the handover
ensures that a call is not dropped due to non availability of
resources. Handover delayed ensures that unnecessary
handover does not take place leading to loading of the base
station.

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AUTHORS PROFILE

Isha Thakur received her B.E. (Hons.) From 1997 to 2002, Dr. Manna has worked as Deputy General
degree in Electronics and Manager in a Telecommunication Training Centre of DoT. He was
Telecommunication Engineering from first to install live training node for Internet Service Provider (ISP),
Takshshila Institute of Engineering and designed training schedules and prepared handbook and lab practice
Technology Jabalpur (M. P.) in 2008. schedules. He had conducted training programs for 5 batches of
Currently, she is pursuing her M. E. participants deputed by Asia Pacific Telecomm unity (APT) and 3
from the Department of Electronics and more exclusive batches for Sri Lankan Telecom. He had also
Telecommunication Engineering, conducted several seminars with international experts through
Government Engineering College UNDP/ITU projects. In 2000, he had delivered distinguished speech
Jabalpur. Her research interest includes on ADSL in a seminar organized by ITU. During 1995 and 1996, Dr.
Computer networks and Future Manna was posted in Telecommunication Engineering Centre (TEC)
generation in mobile communication System. and developed Artificial Intelligence (AI) based software for E10B
telephone exchanges named E10B Maintenance Advisor
(E10BMAD).
Dr. Manna had worked as Development Officer in WEBEL
Bhavana Jharia received her B.E. (erstwhile PHILLIPS) Telecommunication Industries during 1983-
degree in Electronics and 1984 after which he joined DoT and worked in different executive
Telecommunication Engineering from capacities up to 1994.He was awarded National Scholarship in 1973
Govt. Engineering College Jabalpur (M. based on school level examination and silver medal for performance
P.) in 1987. She did her M.E. (Solid in college. He had both graduated and post graduated in Radio
State Electronics) from University of Physics and Electronics Engineering from University of Calcutta and
Roorkee, Roorkee in 1998 and Ph.D. undergone trainings at Beijing University of Post and Telecom China
(VLSI Technology) from I.I.T. Roorkee in 1990 and DARTEC, Montreal, Canada in 1999.
in 2005. She joined the Department of
Electronics and Telecommunication
Engineering, Govt. Engineering College
Jabalpur (M. P.) as faculty in 1990, where at present she is working
as an Associate Professor. She has 25 publications in National,
International referred Journals and Conferences. Her research
interests are in Electronics Design and Simulation and Low Power
VLSI Technology. She is a member of IE (I), CSI, VLSI Society of
India, senior member of IACSIT and Life Member of ISTE.

Dr. Gopal Chandra Manna is
working as Senior General Manager
(Head Quarters), Inspection Circle,
BSNL, a wholly owned Company
under Department of
Telecommunications (DoT), Govt. of
India. Dr. Manna has carried out
extensive research on coverage issues
of GSM, CDMA, WCDMA and
WiMAX radio access. Study of
Wireless Traffic and QoS estimation of
Cognitive Radio are his current areas of
research. In Addition, he has written several articles on advanced
telecommunications which has been published in national and
international journals and symposiums. Dr. Manna is regularly
invited as a panel expert, invited speaker, session chair etc. in
seminars and conferences.
Dr. Manna has developed and conducted one week course on Quality
of Service Monitoring at Information and Communication
Technologies Authority, Mauritius as International Expert through
Commonwealth Telecom Organisation London during August 2010.
He had also delivered a speech on WiMAX coverage Evaluation at
International Conference on Advanced Communications Technology
2011 at Seoul, Korea and chaired a session on Network Management.
He had also delivered speech on ADSL at International
Telecommunication Union seminar in 2000 at Bangalore, India.

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APPENDIX
[1] SHEET 1

[2]SHEET2

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