Engineering Instructions on RF

8/10/2019 Engineering Instructions on RF

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ENGINEERING INSTRUCTION

BENCHMARKING OF RF NETWORK, PROCEDURE AND FIELD SURVEY: / / & 075(No.: GSM/RF/O&M-075)

,

()

,(... 9001:2008 )

,

,

,

482001

BHARAT SANCHAR NIGAM

LIMITED

(A Govt. of India Enterprise)

INSPECTION CIRCLE,

(ISO 9001:2008 Certified)

SANCHAR VIKAS BHAWAN,

RESIDENCY ROAD,

JABALPUR,

MP-482001

(No of Pages) : 16

(Issue Number) : 01

(Issued By) : Inspection Circle

(Approved By) : CGM Inspection Circle

(Date of Issue) : Draft

( )(Amendment No. If Any): Nil

(Page Nos. Amended) :

(Issued By) :

(Approved By) :

(Date of Issue) :

All efforts have been made to incorporate all relevant up to date information available, any discrepancies or

need for addition or deletion is felt necessarily may please be intimated to this office for further improvement,

on E-Mail Id [email protected].

(Restricted use by BSNL Employees only)


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ENGINEERING INSTRUCTIONS GSM

RF

O&M - 075

INDEX

BENCHMARKING OF RF NETWORK PROCEDURE AND FIELD SURVEY

Sl. TOPIC PAGE

1 Scope 3

2 Introduction 3

3 Channels in GSM 3

4 Call Origination process 5

5 Call Scenario MS To Landline 56 Network Performance and Quality of Service (QOS) 9

7 DRIVE TEST 12

7.1 Types of Drive Tests 13

7.2 Equipments used in Drive Test 14

7.3 Calling methods used in drive tests 14

8 Defining the routes 15

9 Analysis of Data 15

10 Procedure 15

11 Conclusion 16

Reference 16

Abbreviation 16

BHARAT SANCHAR NIGAM LIMITED

(A Govt. Of India Enterprise)

Restricted to BSNL Staff only

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Types of Logical Channel:

SN Typeof Logical

channel

Subtype Use

1 Traffic Channel

TCH,

i)TCH/H

ii)TCH/F

Carry voice and data

These are used for sending

information.

2 Broadcast

Channel

Carry Signalling information

i)BCCH Broadcast Control

Channle

Used in D/L and MS is informed

about LAI, CI etc.

ii)FCCH FrequencyCorrection Channel

Used to tune MS with BTS inU/Ll,D/L direction.

iii)SCH Synchronisation

Channel

Used for time synchronization

of MS and BTS in D/L Direction.

iv)CBCH Cell Broadcast

Channel

Used in D/L Direction.

3 Common

control Channel

Used for control information

i)PCH Paging Channel Used for paging to MS in D/L

Direction.

ii)RACH Random Access

Channel

MS sends channel requests on

this in D/L direction.iii) AGCH Access Grant

Channel

In response to RACH , channel

id is send on AGCH.

4 Dedicated

Control Channel

Point to Point full duplex

channels used for signaling.

i)SACCHSlow Associated Chl Always associated with TCH or

SDCCH and is used in non

urgent procedures.

ii)FACCH Fast Associated

Channel

It is a main signalingchl used in

call setup and release phase.

iii)SDCCH StandaloneDedicated Channel

Carries all signaling inf betweenMS and BTS when no TCH chl is

allocated.Sigannling inf carried

is like location

update,subscriber

authentication,ciphering &

assignment of TCH




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4. Call Origination process:

1) MS sends channel request or demands to BTS, BTS forwards this request to BSC, BSC

activates a counter upon receiving channel request from MS in cell/BTS

2) BTS sends channel activation and to MS through BTS and another CT is activated inorder to count channel allocation in cell/BTS

3) Authentication is done by MSC and a call is initiated, after call connection another

counter is started to watch and count abnormal call failure or drop due to BSS or radio

link problem

5. CALL Scenario MS to Landline:

STEPS IN REQUEST FOR SERVICE PHASE:

The following is an example of a scenario of a mobile-to-land call. It is assumed that the MS

is already registered with the system and has been allocated a Temporary Mobile subscriberIdentity Number (TMSI).

MS BSSMSC/

Channel Request

SDCCH Assignment

Service Request Authentication Ciphering

Equipment Validation Call

set up

Handover(s)

Um A

RACH

AGCH

SDCCH




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Request for service

Authentication

Ciphering

MS BSSMSC/

IME I Request

Um A

SDCCH

SDCCH

IMEI Response (IMEI)

EIR

F

IMEI Check Results

Check IMEI

Call setup

Handover(s)

7




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MS BSSMSC/

Call Setu Re uest

Request for service

Authentication Ciphering

Equipment Validation

Um A

SDCCH

SDCCH

Call Proceeding

Request for Service

Authentication

Ciphering

M

BSSMSC

PST

Um A

Network

Network

Connect

Start Billin

Alertin

FACCH

Connect

FACCH

Connect

10

1

10

1

FACCHHandover(s)

Call releae

10

11

12

13

14

14

15




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1 MS transmits a channel request message over the Random Access Channel (RACH)

2 Once the BSS receives the Channel Request message, it allocated a Stand-alone

Dedicated Control Channel (SDCCH) and forwards this channel assignment information

to the MS over the Access Grant channel (AGCH). It is over the SDCCH that the MS willcommunicate with the BSS and MSC until a traffic channel is assigned.

3 The MS transmits a service request message to the BSS over the SDCCH. Included in this

message are the MS TMSI and Location Area Identification (LAI). The BSS forwards the

service request message to the MSC/ VLR.

4 The MSC transmits a request to the MS requesting it to respond with its International

Mobile Equipment Identity (IMEI)

5 The MS upon receiving this request, reads its equipment serial number and returns this

value to the MSC

MS BSSMSC/ PSTN

Um A

Disconnect

Network Release

Stop Billing

Release

Release complete

Clear Complete

FACCH

FACCH

Channel Release

FACCH

16

17

18

19

20

21

FACCH

22




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6 The MSC then requests the EIR to check the IMEI for validity. The EIR will first check to

see if the IMEI value is within a valid range. If, so it then checks to see if the IMEI is on a

suspect or know list of invalid equipment.

7 The EIR returns to the MSC the results of the IMEI validation. If the results are negative,

the MSC might abort the call or possibly let the call continue but inform the network

service provider of the event. In this scenario, well assume that the IMEI is valid.

8 The MS transmits a call setup request message to the MSC/ VLR after it has ciphered the

radio channel. Included in this request message are the dialed digits. The MSC, upon

receiving the call setup request message, will request the VLR to supply subscriber

parameters necessary for handling the call. The VLR will check for call barring conditions,

such as the MS being barred from making specific outgoing call (e.g. international calls),

or possibly if some supplementary services are active which prevent the call from being

granted. If the VLR determines that the call cannot be processed, the VLR will provide

the reason to the MSC. In this scenario, well assume that his procedure is successful.The VLR returns a message to the MSC containing the service parameters for the

particular subscriber.

9 The MSC allocates a trunk to the BSS currently serving the MS. The MSC sends a

message to the BSS supplying it with the trunk number allocated (TN), and requests the

BSS to allocate a radio traffic channel (TCH) for the MS

The BSS allocates a radio traffic channel and transmits this assignments to the MS over

the SDCCH

The MS tunes to the assigned radio traffic channel and transmits an acknowledgment to

the BSS.The BSS connects the radio traffic channel to the assigned trunk of the MSC. Since a

small portion of a radio traffic channel is available for out-of-band signaling, the SDCCH

is no longer used for signaling between the BSS and MS. The BSS de-allocates the SDCCH.

The BSS then transmits a trunk and radio assignment complete message to the MSC.

10 The MSC sends a network setup message to the PSTN requesting that a call be setup.

Included in the message are the MS dialed digits (DD) and details specifying which trunk

should be used for the call.

6. Network Performance and Quality of Service (QOS):

Network performance and Quality of service (QOS) decide the customer satisfaction

and so are of commercial importance for every operator. Network performance evaluation

is done by deciding certain Key performance Indicators KPIs. Every network event Call

initiator, Traffic channel demand, Channel assignment etc are reported by BTS to BSC and

these events trigger different counters (CT). These counters are either incremented or

decremented by and are measured over a period of time generally one hour and are stored

in Operation and Maintenance Center (OMC), the OMC is used to configure and control BTS.

These counters are used to different KPI, The KPIs and counters are used to represent QOS

of network. QOS reports are generated by OMC on daily, weekly and monthly basis. KPIs are

generally prepared by considering traffic events of normal day but network performance is




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generally evaluated by considering typical congestion situation, The important KPIs used to

evaluate n/w performance and benchmarking of RF n/w against to competitors.

1) Call Set up Success Rate ( CSSR)

2) Call Drop Rate (CDR)

3) Handover Success Rate (HSR)4) Traffic Channel Congestion Rate (TCHCR)

During congestion traffic channel (TCH) and control channel (SDCCH) get blocked and so this

blocking is analysed to improve n/w performance.

A) Call Set up Success Rate (CSSR) :

It is defined as rate of Call attempts until successful assignment of TCH

CSSR = No. of successful regime of SD chl_____

Total no. of request for regime of SD chl

= [ CTO 1 + CTO 2 ]* 100

CTO 3

Let SD denotes Stand alone dedicated control chl

TCH denotes Traffic chl

Where :

1) CTO1 = Counter for SD chl successfully sized for call termination

2) CTO 2 = Counter showing SD chl successfully sized for call origination

3) CTO 3 = It counts SD chl sized request

Reasons for degradation:

1) Faulty BSS Hardware

2) Increase in Inbound traffic,

3) Lack of radio resource allocation.

4) Congestion in radio interface

Remedies:

1) Replace faulty hardware like TRX.

2) Expansion of Transmission network and end hardware.

3) Redefining OMCR parameters like half rate, traffic load sharing etc.

Blocked call complaints from customer is a common flag of CSSR.

B) Call Drop Rate (CDR) :

It is defined as rate of call snot completed successfully.

CDR = Number of TCH Drops after assignment

Total number of TCH Assignment.

CDR= { (CT04+CT05)/ CT06 }*100BHARAT SANCHAR NIGAM LIMITED



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WHERE:

1) CT04 = Counter value indicating TCH drops due to radio interface problems.

2) CT05= Counter value indicating TCH drops due to BSS Problems.

3) CT06= Counter value indicating number of TCH successfully seized/assigned.

Causes of CDR Degradation:

1) Hardware faults in BSS/BTS.

2) Coverage Limitations.

3) Improper definition of certain parameters defining adjencies.

4) Internal and external interference over Air Interface, Internal interference is due

to in band (900MHZ,1800 MHZ) problems. External Interference is due to other

wireless networks.

Ways of detection of CDR:

1) Customers complaints of blocked calls in a particular area./sector.2) Adulterated carrier frequencies causing interference can be detected by using

Spectrum Scanners.

3) OMCR Alarms: OMCR Monitors certain counters and does some defined

calculation including uplink interface and raises alarms of CDR.

4) Average of Effective Radiated Power over downlink and Received power over

uplink is used to carry out Path Balance Statistics which helps in finding CDR.

Methods to improve CDR:

1) Antenna Orientation ( Azimuth) tilts, change in some parameters at OMCR

like Radiated power level improve CDR2) Timely rectification of hardware faults in BTB/BSC

3) Frequency hopping techniques to reduce interference and use of RF

repeaters also help in reducing CDR

4) Introducing new sites at proper location reduce CDR

5) CDR can also be improved by coverage optimization

C) Handover Success Rate (HSR) :

It is defined as rate of successful handover, It include both inter cell and intracell handover mathematically

HSR = { (CTO7 + CTO8)/(CTO9 + CTO10)} * 100

Where

CTO7 = Counter indicating incoming successful handover

CTO8 = Counter indicating no. of successful Outgoing handover

CTO9 = Indicates no. of Outgoing handover requests

CTO10 = Counter value indicating no. of Incoming handover requests

Reasons for HSR degradation :

1) Hardware faults in BTS/BSS

2) Improper planning/definition of Location area code (LAC)BHARAT SANCHAR NIGAM LIMITED



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3) Coverage limitation and air interface interferences

4) Wrong definition at OMCR for adjencies parameters

Methods to improve HSR :

1) Parameter modification in OMCR such as handover margin, traffic handover, powerbudget parameters

2) BSS recourse augmentation such as TRX

3) Coverage improvement and adjacencies audits

D) TCH Congestion rate (TCHCR) :

It is defined as rate of blocked calls due to unavailability of radio resources

TCHCR = No. of calls blocked due to unavailable radio resources

Total no. of requests= ( CTI 1/CTI 2) * 100

Where :

CTI 1 = Counters indicating no. of assignment failure when TCH is available

CTI 2 = Counter indicating no. of normal assignment request for TCH establishment

Reasons for TCHCR degradation :

1) Media unavailability, Hardware unavailability

2) Increased subscriber density in a particular area

3) TRX hardware fault

Flags pointing TCHCR :

1) Locolised customer complaints

2) OMCR carriers out radio counters mentioned above and raised alarms

Worst cell ratio WCR and CSSR also points to TCH congestion

7. Drive Test:

Drive Test is another tool used by the operator to optimize the mobile radio network

and solve the network- coverage related problems , such as congestion ,limited coverage,

QOS issues. This tool helps in comparing own RF Network with that of other Operators

which helps in subscriber retention and also providing minimum Quality Of Service made

mandatory by Regulatory Authorities of the country.

The RF Drive tool is comprised of Test Mobile Handsets, motor vehicle and a mobile

radio network air interface measurement equipment with software that detects and record

variety of the physical and virtual parameters of the RF network while moving in the field.




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Data collected by this tool is in the form of log files. These files get stored and are

then assessed to evaluate the important Key Performance Indicators of the network under

study. Following data is collected by the Drive Test Tool:

1) Receive Signal level.

2) Signal Quality Level.

3) Call setup RATES.

4) Service level statics.

5) Interference of signals.

6) Dropped Calls.

7) Handover Information.

8) Neighboring call information.

9) GPS Coordinates.

10)Service Quality.

7.1 Types of Drive Tests:

There are two types of drive tests. They are:

I) Pre swap drive tests:

These are carried out to set reference levels for verification of the Post Swap RF

Network performance .The result of this test are called Network Quality Index

(NQI). NQI s are generally consists of:

a) Received Downlink signal strength.b) Received Quality

c) Call Setup success rate

d) Handover Success Rate

e) Call Drop Rate.

These tests are carried out in predefined cities on predefined routes.

II) Post Swap DRIVE Tests:

These Drive test is carried out on routes/cities used in Pre swap Tests after Swap

Activity is completed and the result obtained is compared with NQI of pre swap

tests.The objective of this Radio Network Benchmarking is to compare the actually

achieved radio network performanance parameters with the NQI target from the

Pre Swap Drive Test.

Post Swap drive tests are further classified into :

A) Network Benchmarking Tests:

In this sophisticated multichannel tools are used to measure several network

technologies and service types simultaneously to high degree of accuracy to

provide directly comparable information in respect of signal strength and

weakness. Commonly obtained data from this benchmarking is Comparative




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Coverage Analysis and Comparative network speed analysis and is generally

used in marketing campaigns. This test is the only way by which the operator

can acquire accurate competitive true level data of its own and competitors

network.

B) Optimization and trouble shooting :These drive tests are used to solve area specific problems such as call drop in

roll out phases of new network and to solve the area specific problems

reported by customers during Operational Phase.

C) Service Quality Monitoring :

In this, automated test calls are made across the network to access the

relative quality of various services using Mean Opinion Score (MOS).It is

focused in finding out the end user experience and helps the operator in

providing technical solutions to problems observed and in maintaining the

QOS standards set by Regulatory Authority of the country.

7.2 Equipments used in Drive Test:

Drive test system consist of

1. Mobile Handset with charger, headset data cable and USB

2. Laptop and adapter

3. GPS

4. Inverter and Terminal

5. Scanner for GSM

7.3 Calling methods used in drive tests: Calling methods used in drive tests are-

i) Idle Mode The MS is on but the call is not in progress.ii) Dedicated Mode: The MS is ON and call is in progress.

The call made is either a short call or long call.Generally a

combination of calling methods is adopted i.e. Idle+short call,

Idle+Long call etc.

The use of calling methods is as under:

Test Methods Purpose

Idle It is used to record the network condition at idle

state and the level of CI on BCCH

Dedicated- Short Call Used for testing the accessibility and mobility of

network.

Dedicated-Long Call It is used to test retain-ability and sustain-ability.

e.g CDR,HOS




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8. Defining the routes:

Mainly there are two type of routes depending upon the distribution density of sites and

the surrounding radio environment. They are

1. Urban Area

Here the test route covers the cells are around the BTS and care is taken that the

actual coverage area is covered and handovers can be verified.

Test routes should be so designed that the local customs of traffic are properly

followed so that waiting in traffic is reduced.

2. Suburban area:

The main features of these routes are

i)Route should cover the roads which are covered by different sectors of the site to

be tested.ii) The overlapping area of surrounding neighbor cells should be covered so that the

handover functions can be verified.

iii) For isolated sites normal coverage area should be covered.

9. Analysis of Data:

The data collecting software like TEMS is used for analysis of data.The data collected

by this software consist of:

1. GSM Radio parameters2. Current channel

3. Serving +Neighbor Window

4. The data like site name Lat Long Building Height Tower Height, Tower Type, Average

Clutter height, Indoor Rx Level, Seving Cells Max AGL Availability, Azimuth for Max

AGL Availability. LOS Clear, Deviation Of Lat/ Long etc is taken .After collecting this

information the drive test is started. The equipment is set up in a vehicle and long as

well as short calls are generated. A long call is used to measure the handover success

rate and Rx quality while short call is used for CSSR and Rx level.

10. Procedure:

Tool can accommodate two mobiles one for long call and another for short call.

Following parameters are enabled in Route Map

i) Rx Level

ii) Rx Quality

iii) Survey Markers (like CSSR,DCR)

iv) Cell site database.




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v) Call Statistics.

The drive test is conducted covering all sectors observing Rx Level, Rx Quality,

Interference on BCCH& Hopping Frequencies, Call setup failure reasons etc.

11. Conclusion:

Analysis and performance evaluation of GSM network can be done by drive tests and

by using KPIs .This can also be used for Benchmarking of network of different cellular

operators. It also helps in ensuring a better QOS which satisfies the threshold levels set by

regulatory authorities. Benchmarking activity helps in keeping tight control on Opex

(Operating Expenses), Network parameter setting and stringent QOS desired by customers.

Reference:

1) ITU-T recommendations G.1000, Communication Quality of service : A framework

and definition

2) Halonen T. Romero J. : GSM, GPRS, EDGE performance John Wiley and sons

Abbreviations:

1) WCR : Worst Cell Ratio

2) CSSR : Call Setup Success Rate3) KPI : Key Performance Indicator

4) TRX : Trans Receiver

5) LAI: Location Area Identity

6) CI: Cell Identity

7) U/L:Uplink

8) D/L: Down link

9) BCCH: Broadcast control channel

10)FCCH: Frequency allocation Channel

11)SCH:Synchronisation Channel

12)CBCH: Cell Broadcast channel

13)PCH: Paging channel

14)RACH: Random access channel

15)AGCH: Access grant channel

16)SACCH:Slow associated control channels

17)FACCH:Fast associated control channels

18)SDCCH:Stand alone dedicated control channel

19)LOS: Line of site




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Engineering Instructions on RF

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