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AUTOMATIC DETERMINATION OF CALL SETUP TIME AND RING TONE QUALITY IN GSM NETWORK 1
O. A. Ayo-Bello 1*, A. M. Aibinu 2, A. J. Onumanyi3
Department of Telecommunication Engineering Federal University of Technology, Minna Niger State, Nigeria *
[email protected],
[email protected],
[email protected] ABSTRACT One essential Key Performance Indicator (KPI) for mobile network performance assessment is Call setup time (CST). However, there is no standard measurement possible for this parameter, therefore the different operators can measure it differently. In this paper, the possibility of implementing an algorithm for CST measurement using citizen sensing techniques where individual GSM users’ can quantify CST from their cell telephone without the utilization of Drive Test is been proposed. Consequently, examination of GSM ringing tone, call time and the sound nature of the ringing tone is analyzed using a Labview and Matlab. The proposed procedure enables the discovery of the territories with unacceptable estimations of Call setup time and relates these to an overview of the Quality of Service of the network. Keywords: Call Set-up Time, Independent Measurement, Key Performance Indicator, Mobile Network. 1.
These made external measurement of QoS status to remain
INTRODUCTION
a challenge. System execution and Quality of Service (QoS) appraisal of a Global System for Mobile Communication (GSM) is a
In view of this, new methods to independently measure
critical operational prerequisite for Mobile Network
QoS of the MNP data are being developed. These have
Providers (MNP), as it specifically influences the income
formed a recent area of research interest as it has been used
era and client happiness (Sireesha, Varadarajan, Vivek and
in different reports. The Key Performance Indicators (KPIs)
Naresh). An MNP has a higher business sector advantage
used for QoS estimation include Call Setup Time (CST),
when its QoS is better, this makes the MNPs to put
Call Completion Rate (CCR), Call Drop Rate (CDR), Call
immense effort in monitoring their respective networks and
Handover Success Rate (CHSR) and Standalone Dedicated
maintain broad and accurate prominence of its quality.
Control Channel (SDCCH), but focus here will be on the use of the Call Setup Time (CST) parameter for QoS
There has been a decrease in the QoS experienced by most end users due to the high demand for GSM services. (Amaldi, Capone, and Malucelli 2008) which has resulted in monitoring the level of QoS maintained by most MNPs (Carvalho de Gouveia, Magedanz 2008). It has been the custom of depending solely on statistics provided by the MNPs in measuring the network QoS. Dependability and reliability of such statistics remain uncertain as the public
characterization. Therefore, it is the goal of this paper to provide an overview of high-tech methods used in this regards. As part of an on-going research work, this assessment will provide the different methods in use, the tools being employed, including soft and hardware; their strengths and limitations, and the future direction in this area. In addition, an overview into the development of a comprehensive system for CST measurement is introduced.
unfortunately has no access to these data except through legal permission or some cooperation from the vendors.
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Subsequently, the rest of the paper is organized as follows:
leads to instability and congestion on the links. If the
the details on the process involved in setting up a call in a
preceding problem occurs during call setup, the call setup
GSM network and drive test tools used for conducting
time increases (Yang, C. 2008).
drive test experiments are given in Section 2, Section 3
The CST can be obtained through traffic measurement and
describes the working principle of the proposed system for
Drive Test (DT). However, based on the need for
CST measurement and conclusion is drawn in Section 4.
independent measurement, we discuss the DT approach, which guarantees independence in the next section.
2.
METHODOLOGY
The Call Setup Time (CST) is the mean time of the establishment of a call from a subscriber. It is the average setup time of several successful calls. A long call setup time affects the user experience and perception about QoS for the MNPs. Thus, call setup time is one of the KPIs that is of greater concern for Mobile Network Providers (MNP) as it provides a measure to control and assure the Quality of Service (QoS) requirements. Hence, CST is an important key
Performance
Indicator
(KPI)
to
evaluate
the
2.1
Drive Test
Coverage, capacity and Quality of Service (QoS) of a mobile radio network can be evaluated with Drive Testing method. It is carried out to check the coverage criteria of the cell site with the RF drive test tool. The procedure involves using a car containing mobile radio network air interface measurement equipment that can detect and keep a wide variety of the physical and virtual parameters of mobile cellular service in a given geographical area. Drive test equipment typically gathers information and services
performance of a network (Carvalho de Gouveia 2000).
running on the network such as voice or data, radio CST can be calculated from L3 messages and estimated by drive test. For GSM network, CST is the period from Requesting a Channel until Alerting, it is usually 7-8 s for Mobile to Mobile Calls.
CST is the duration from
Requesting RRC Connection until Alerting for WCDMA,
frequency scanner and GPS information to provide location logging (Amaldi et. al 2008). There are different types of tools to carry out a DT among which are: JDSU E6474A v15.2, TEMS Investigation, Nemo Outdoor. However, in this research work an algorithm was developed using Matlab and LabView to
usually 6-7 s for MMC. Call setup time increases as a result of problem in hardware, transmission, coverage, or interference. A faulty TRX or combiner or an incorrectly connected RF cable makes seizing of the SDCCH or TCH difficult, and thus resulted in call setup time been increased (Yang, C. 2008).
analyze the ring tone from mobile network providers for their call time characteristics. The result gotten will then be used in the CST Analyzer to predict QoS as explain in the next section. 2.2
Poor transmission quality, instability of transport links, insufficiency of resources, or bit errors on the Abis and A interfaces may lead to an increase in the error rate on the links, which results in more message retransmissions between switches. Thus, the message transfer delay
Proposed CST Analyzer to Predict QoS of a
GSM Network using a Citizen Sensing Approach Ringtone and CST analyzer to predict QoS of a GSM network is being proposed as part of on going research using a citizen sensing approach. This section only focuses on the discussion of the proposed CST estimation algorithm
increases and congestion may occur on the links which in severe cases causes routes to change frequently, which
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which consists of a four distinct stages as shown in Figure
The sound quality analysis involve three processes namely
2.
Signal Quality to Noise Ratio (SQNR) measurement,
Call tone recording software will be installed on a test
Amplitude measurement and Frequency measurement.
phone for acquisition of the required ringing tone. The
The analysis of the input signal consist of four distinct
software will be activated during a call dialing process and
stages
when answering a call. The software works in the
1. Compression/Collapsing
background or transparently without affecting any call in
2. Flattening of near zero components
progress. The recorded data will then be stored in the phone memory for the Format converter to converts the saved file into the right format and checks if it is well converted and save it into the appropriate location. The output of the format converter will be fed into the Call Timer Analyzer to measure the Call Time characteristics such as Silent mode time also known as call setup time, Intra-Burst Time Inter-Burst Time, Number of Burst and Ringing Duration as shown in Figure 2. Figure 2 shows the flow chart for the ringing tone acquisition and Figure 4 and Figure 5 shows the flow chart for the Call timer Analyzer and Labview design of Sound Quality Analyzer respectively. From Figure 3, the Silent Mode Time (SMT) can be calculated mathematically, by subtracting the time the counter start from the time the counter stopped
4. Extraction of relevant parameters
It was discovered that most of the signals have sudden and sporadic zero values occurring. The presence of these zero values is due to high sampling frequency which in this case is 8000Hz per samples. These values however, affect the computational procedure. Hence averaging technique was used to nullify sporadic zero values occurring in the signal i.e. 8000 samples in a second was effectively compressed to 8 samples in the same second. Using thresholding, we reduced the values less than 0.01 that are discovered to be noise to zero. The signal is then differentiated so as to enable the effective tracking of gradients. A positive gradient would indicate the start of a burst and the return of the gradient to zero signifies the end of burst and the start
SMT = tstop − t0 -------------------------------------------(1) Where t stop is the silence mode end time and
3. Differentiating the signal
of an inter burst time.
t0 is the
beginning of the silence mode period. Also, Intra Burst
In the Matlab command window, enter these command: y = gsm_voice(#, ′all′ );
Time (IntraBT) can be calculated by subtracting the time the first peak is detected from the time the end of a burst is
Where # = 0, 1, 2,3. These values represent each Mobile
detected
network operator. The two command gives the call
IntraBT= t2 − t1 ----------------------------------------(2) Where
GetParameters(y);
characteristics of the mobile nework operator in question as
t1 and t2 is the start and end of burst respectively
shown in Figure1
Inter Burst Time (InterBT) can be calculated by subtracting the time the end of the first burst is detected from the time the next burst started
InterBT= t2 − t0 ----------------------------------------(3)
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Figure 3: Flow chart for the ringing tone acquisition Figure 1: command Window of Matlab
Intra-Burst Time Inter-Burst Time
SMT
Ring Duration
Figure 2: Typical GSM ring pattern
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3.
PRELIMINARY RESULTS AND DISCUSSIONS
Start
The result gotten from the analysis is shown in Table 1. A Initialize a call
problem
in
hardware,
transmission,
coverage,
or
interference may result in an increase in the call setup time Initiate burst counter, bn
and also the longer the SMT the less likely a successful call setup.
Start Time counter, Time=t0
Table 1: Call Time characteristics for various Mobile Network Providers. Detect the first peak, Time= t1 Mobile Operator
Call Setup
No of
Average
Average
Time (SMT)
Burst
Intraburst
Interbrust
5
9
1.388
1.458
Glo - Etisalat
6.625
6
1.375
3.604
Glo - A switched
3.625
1
5.375
NaN
6.25
1
25
1.25
(s)
Stop Time counter, Time= tstop Glo - MTN
SMT
Time (s)
Time (s)
OFF phone Glo - Glo 121 Detect end of burst, Time= t2
IntraBT
10
11
1.261
1.6
Glo - Glo
5.25
11
1.318
3.137
Glo - Busy
0.5
1
11.375
NaN
5.125
9
1.375
1.5
Glo - Airtel
Destination Etisalat - MTN
InterBT
Etisalat - Glo Etisalat - Airtel Etisalat
Ringing duration
Etisalat
No of burst
End
Figure 4: Flow chart for the Call timer Analyzer
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-
9.5
7
1.5
3.25
6.375
11
1.397
1.625
4.875
6
1.354
3.645
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Figure 5: Labview design of Sound Quality Analyzer
CONCLUSION
4.
30
Call Setup Time (SMT) (s)
25
This paper provides a tutorial on the process involved in measuring the Call Setup Time (CST) in a GSM network. A practical approach to the CST analyzer to predict QoS
No of Burst
Amplitude
20
and citizen sensing approach have also been presented. It should be noted that this paper forms part of an on-going
15
research effort geared towards developing an analyser to predict QoS through CST measurement using citizen
Average Intrabur st Time (s)
10
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