Radio access Network Audit and optimization

1. International Journal of Engineering & Technology IJET-IJENS Vol:10 No:01 55
108401-2727 IJET-IJENS © February 2010 IJENS
I J E N S
Abstract— Network audit is necessary to judge the network
performance and maintain QOS standards. The network audit
identifies inconsistencies or limitations in current overall
network design, helps to improve processes resulting in
optimized network and improved quality of service. Radio Access
Network audit includes many aspects of network like
performance, neighbor, parameter, frequency, competitive
benchmark audits. In this paper, real GSM Radio Access
network evaluated, and different issues, findings, trials and
improvements have been summarized and
observations/recommendations have been listed to correlate the
practical aspects of RF optimization, which affect the
performance, and QoS of an operational cellular network.
Index term— RAN, BSC, MSC, BTS, CSSR, CDR, HSR, TCH,
COVERAGE, QUALITY, KPI, DT and QoS.
I. INTRODUCTION
The mobile communication aims to offer anytime and
anywhere communications between any objects. GSM , One
of the fastest growing and most demanding of all
telecommunications technologies .
GSM Network usually called as „cellular network‟ (as the
whole coverage area is divided into different cells and sectors)
is comprised of a mobile Station (MS) which is connected to
the Base Transceiver Station (BTS) via air interface. In
addition to other hardware, BTS contains the equipment called
Transceiver (TRX), which is responsible for the transmission
and reception of several radio frequency (RF) signals to/from
the end user .BTS is then connected to the base station
controller (BSC) via abis interface. BSC usually handles radio
resource management and handovers of the calls from one
BTS (or cell/sector) to the other BTS (or cell/sector) equipped
in it. BSC is then connected to Mobile Switching Centre
(MSC).
This paper focuses on audit of radio access part of GSM
network, suggestions to optimize the network and post
optimization benchmarks. Following is sequence of
Objectives.
1. Network Audit and Recommendations
2. Optimization Plan and Cluster optimization
3. Post Optimization Evaluations (Benchmark
Improvements)
II. RADIO ACCESS NETWORK AUDIT
The ultimate purpose of the audit is to establish a baseline that
measures overall network design, quality, performance and
process, and to identify and characterize the areas where
improvement can be achieved. The audit is usually a
comparative process and requires an initial baseline of KPI‟s
and/or objectives. These can be derived from the design
guidelines, service requirements, customer expectation,
market benchmarks and others. The comparative baseline
and/or the KPI‟s can be re-adjusted during the audit itself to
improve its diagnostic capabilities.
Benefits of Network Audit.
Key benefits of network audit are:
 Identify actions to improve network quality in problem
areas.
 Discover inconsistencies or limitations in current overall
network design.
 Discover practices or processes that can be improved or
optimized
 Results in improved Network quality , thereby reduced
churn
 Optimize overall network design:
 Reduction of excess network elements
 Postponement future CAPEX, leading to CAPEX
savings
 It takes only a delay in the CAPEX for few BTS‟s to
justify the network audit investment
 Streamline processes:
 OPEX savings
Network Audit Steps
The audit has 3 distinct steps:
1. Information gathering (The Diagnosis)
2. Information analysis and results (The Prognosis)
3. Recommendations (The Cure)
III. INFORMATION GATHERING (DATA COLLECTION)
Following data will be collected for radio network audit
1. BSS Network Design and Performance Data.
 All Site Data : sites position, antenna types,
height, tilt electric and Mechanical) and azimuth,
sector power, number of sectors, Number of
TRXs per sector
 Macro Site data and Micro Layer data
 BSC and transcoder designs
 Coverage data
 Neighbor List
 Handover Parameter
 Frequency Plan and Interference Analysis
 OMC Statistics.
 Drive Test Statistics.
2. Major Complaints from Customer Care.
Radio Access Network Audit & Optimization in
GSM (Radio Access Network Quality
Improvement Techniques)
Mudassar Ali, Asim Shehzad, Dr. M.Adeel Akram.

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I J E N S
3. Revenue Churn report from Revenue assurance
department
IV. INFORMATION ANALYSIS-RADIO NETWORK AUDIT FLOW
CHART
Algorithm for audit methodology used for test case of
network of city K is given in Fig.1
Fig. 1. Radio Network Audit Flow Chart
V. RADIO NETWORK PERFORMANCE AUDIT
All the events being occurred over air interface are
triggering different counters in the Base Station
Controller (BSC). The KPIs are derived with the help of
these counters using different formulations.
A. Accessibility
Service accessibility is : “The ability of a service to be
obtained, within specified tolerances and other given
conditions, when requested by the user.” In other words:
NetworktoAccessesCallsTotal
SetupCallslSuccessfulofNOTotal
tyAcessibili
____
_____

Listed below are the KPIs connected to accessibility.
1. Paging Success Rate
The paging success rate measures the percentage of how many
paging attempts that have been answered, either as a result of
the first or the second repeated page.
PagingofTime
sponsesPagingofTime
PSR
__
Re___

Possible reasons for poor Paging Performance could be:
 Paging congestion in MSC
 Paging congestion in BSC
 Paging congestion in Base Transceiver Station (BTS)
 Poor paging strategy
 Poor parameter setting
 Poor coverage
 High interference
2. SDCCH Access Success Rate.
SDCCH access success rate is a percentage of all SDCCH
accesses received in the BSC.
Possible reasons for poor SDCCH Access Performance could
be:
 Too High Timing Advance (MHT)
 Access Burst from another Co-channel, Co-BSIC
Cell
 Congestion
 False Accesses due to High Noise Floor
 Unknown Access Cause Code
3. SDCCH Drop Rate
The SDCCH DROP RATE statistic compares the total number
of RF losses (while using an SDCCH), as a percentage of the
total number of call attempts for SDCCH channels. This
statistic is intended to give an indication of how good the
cell/system is at preserving calls.
SeizuresSDCCH
DropsSDCCH
RateDropSDCCH
_
_
__ 
Possible reasons for SDCCH RF Loss Rate could be:
 Low Signal Strength on Down or Uplink
 Poor Quality on Down or Uplink
 Too High Timing Advance
 Congestion on TCH
4. Call Setup Success Rate
The Call Setup success rate measures successful
TCH Assignments of total number of TCH
assignment attempts.
  RateSuccessAssignmentTCHRateCongestionSDCCHCSSR ___*__1 
    100*reRatement_failuTCH_Assign1*tion_RateTCH_Conges1*
_AttemptsSDCCH_Call
flowsSDCCH_Over
1CSSR  





Reasons for low call setup success rate could be:
 TCH congestion
 Interference

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 Poor coverage
 Faulty HW units
5. Call Setup TCH Congestion Rate
The Call Setup TCH Congestion Rate statistic provides the
percentage of attempts to allocate a TCH call setup that were
blocked in a cell.
AttemptsTCHofNo
HOExcludingBlocksTCHofNo
RateCongestionTCHSetupCall
___
)_(___
____ 
Possible reasons for call setup block could be:
 Increasing Traffic Demand
 Bad Dimensioning
 HW Fault & Installation Fault
 High Antenna Position
 High Mean Holding Time (MHT)
 Low Handover Activity
 Congestion in Surrounding Cells
B. Retain ability
Service retain ability is “The ability of a service, once
obtained, to continue to be provided under given conditions
for a requested duration.” In other words:
setupcallsSuccessfulTotal
CompletedCallsTotal
ytainabilit
___
__
Re 
Listed below are the KPIs connected to retain ability.
1. Call Drop Rate
This KPI gives rate of drop call. Percent of TCH dropped after
TCH assignment complete.
successesHOOutgoingSuccessesHOgIncoDRgincosuccessesAssignmentNormalTCH
DropsTCHTotal
CDR
____min_min___
__


*DR is directed retry
Possible reasons for TCH Drop Call Rate could be:
 Low Signal Strength on Down or Uplink
 Lack of Best Server
 Congestion in neighboring cells
 Battery Flaw
 Poor Quality on Down or Uplink
 Too High Timing Advance
 Antenna problems
 Low BTS Output Power
 Missing Neighboring Cell Definitions
 Unsuccessful Outgoing Handover
 Unsuccessful Incoming Handover
2. Handover Success Rate
The handover success rate shows the percentage of successful
handovers of all handover attempts. A handover attempt is
when a handover command is sent to the mobile.
HOSR
Possible reasons for poor handover success rate could be:
 Congestion
 Link Connection or HW Failure
 Bad Antenna Installation
 The MS Measures Signal Strength of another Co-or-
Adjacent Cell than Presumed
 Incorrect Handover Relations
 Incorrect Locating Parameter Setting
 Bad Radio Coverage
 High Interference, Co-channel or Adjacent
VI. NEIGHBOR, PARAMETERS AND FREQUENCY AUDIT.
It is important for the neighbor list to be updated and
optimized as it directly affects handover decisions in a
mobile network. Wrong or missing neighbor relations may
cause an on-going connection to drop or be handed over to the
wrong neighbor cell. Excessive neighbor relations in a cell, on
the other hand, may cause wrong handover decision on the
part of the BSS because of inaccurate measurements.
Neighbor relations and parameters are cross checked to
identify and remove
 One way neighbors
 Illogical neighbor Relations
Methods used to assign frequencies in the network are
reviewed and the steps are taken to control interference and
maximize network capacity through frequency planning.
BCCH/BSIC reuse is crosschecked. MA (Moblile Allocation)
List is cross verified.
VII. COMPETITIVE BENCHMARK AUDIT
In competitive benchmarking, coverage and quality
comparison of network is performed with competitors.
Below is coverage and quality comparison for two operators
for a city, Results are taken Drive test tool, TEMS.
Coverage Comparison :
As visible from Plots mentioned in Fig.2 and Fig .3 operator 1
have better coverage than operator 2. which is also visible in
KPIs.
Fig. 2 . Coverage Plot for Operator 1 For City K :

4. International Journal of Engineering & Technology IJET-IJENS Vol:10 No:01 58
108401-2727 IJET-IJENS © February 2010 IJENS
I J E N S
Fig. 3. Coverage Plot for Operator 2 for City K
Legend For Coverage is given below .
Formula For Coverage Rate:
100*
_
90_____
_
SamplesTotal
dbmstrengthSignalhavingsamplesofNo
RateCovergae


Results for Coverage rate for operator 1 and operator 2 taken
for city K are given below
KPI Operator 1 Operator 2
COVERAGE
RATE 94.64% 72.77%
Quality Comparison:
As visible from plots mentioned in Fig 4 and Fig 5 , Operator
1 has better quality than operator 1 , which is also visible in
KPIs
Fig. 4. Quality Plots for Operator 1 For City K.
Fig. 5. Quality Plots for Operator 2 for city K
Legend For Quality Plots is as follows :
Formula for Quality:
SamplesTotal
QualRXQualRXQualRXQualRXQualRXQualRXQualRX
Qualityceive
_
07.)6_5_4_()3_2_1_0_(
_Re


Results for receive quality for operator 1 and operator 2 taken
for city K.
KPI Operator 1 Operator 2
Rx QUALITY 88.19% 87.18%
VIII. REFERENCES
[1] Halonen T., Romero J., Melero J.: GSM, GPRS and EDGE
Performance. John Wiley & Sons Ltd, 2003.
[2] ITU-T recommendation G.1000 (2001), Communication quality of
Service: A framework and definition.
[3] Jens Zander. „Radio Resource Management for Wireless
Networks‟. Artech House Inc., 2001
[4] [4] Bilal Haider,M.Zafarrullah Khan, M.K.Islam: Radio Frequency
Optimization and QOS in operational GSM network.