gsm parameters

8/12/2019 GSM Parameters

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CELLULAR NETWORK

The geographical area to be covered by the Radio Network is divided into cells. A cell is the area cover

1. Type of Cells

There are two main types of cells: omni-cell and sector-cell

An omni cell is served by a BTS placed in its center. The antenna system transmits equally in all dire

A sector cell is served by a BTS placed on its edge and uses a sector antenna (e.g. 120 or 180). On

Typically, omni directional cells are used to gain coverage, whereas sector cells are used to gain ca

Example of a 32 sector site RBS2000 CDU A

BTS Configuration


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Antenna Configuration top view (with duplex filter)

2. Frequency Allocation

Since an operator only has access to a limited number of frequency carriers, the frequencies have t

Example: a reuse-factor 3.

The distance D between two cells using the same frequencies must be long enough to ensure that


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Ericsson recommends (C/I)min = 18 dB for analog systems (NMT, TACS) and 12 dB for GSM. But

Example MRP :

The operator has 37 frequencies. BCCH carriers have a frequency reuse factor 12. The second TR

3. Cell Capacity

Cell planning begins with traffic and coverage analysis. The analysis should produce information ab

Cost

Capacity

Coverage

Grade of Service (GoS)

Available frequencies

Speech quality

System growth capability

The basis for all cell planning is the traffic channel demand, i.e. how many subscribers use the net

A = n x T/3600 Erlang

Where,

A = offered traffic from one or more users in the system

n = numbers of calls per hour

T = average call time in seconds

The geographical distribution of traffic demand can be calculated by the use of demographic data s

Population distribution

Car usage distribution

Income level distribution

Land usage data

Telephone usage statistics


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Other factors like subscription/call charge and price of MSs.

Calculation of required number of BTSs.

To determine the number and layout of BTSs the number of subscribers and the Grade of Service (

If n = 1 and T = 90 seconds the traffic per subscriber is:A = 1 x 90/3600 = 25 mE

If the following data exist for a network:

Number of subscribers = 10000

Available frequencies = 24

Cell pattern = 4/12

Gos = 2%

Traffic per subscriber 25 mE

This lead to the following calculations:

Frequencies per cell = 24/12 = 2

Traffic channels per cell = 2 x 8 2 (control ch.) = 14 TCH

Traffic per cell = 14 TCH with a 2% GoS implies 8.2 Erlangs per cell (use erlang table)

The number of subscribers per cell = 8.2 E / 25 mE = 328 subscribers per cell

If there are 10000 subscribers then the number of cells needed is 10000 / 328 = 30 cells

Therefore the number of three sector sites needed is 30 / 3 = 10


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d by a set of frequencies (transceivers). Each cell has at least one control channel (for BCCH, PCH, S

tions (360) and can be constituted of an omni-antenna or an array of sector antennas.

e BTS site can serve one, two or three sector cells.

pacity. Each cell requires two RX antennas (for RX diversity) and a number of TX antennas (depending


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o be reused in the network. In order to prevent co-channel interference (C/I), the frequencies are reused

/I is superior to a certain threshold. With a reuse factor 9, C/I will be superior to 9 dB; with reuse factor


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dB is acceptable if interference-reducing features are used (such as frequency hopping, DTX, MS/BT

in each cell have a frequency reuse-factor 8, the third have a reuse-factor 6 and the fourth have a reu

out the geographical area and the expected capacity (traffic load). The types of data collected are:

ork and how much traffic they generate. The Erlang (E) is a unit of measurement of traffic intensity. It c

ch as:


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GoS)have to be known. The GoS is the percentage of allowed congested calls and defines the quality o


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CCH, etc)

on the type of TX combiner). It is possible to reduce the number of antennas by using duplex filters and


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in an organised way, according to certain re-use pattern.

12, C/I > 12 dB and with reuse factor 21, C/I > 18 dB. If we use 3-sector sites, the corresponding cell pa


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power control). This means that a 4/12 pattern must be used for BCCH carriers (which cannot use fea

e-factor 4.

n be calculated with the following formula.


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the service.


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X-polarised antennas, see below.


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tterns are called 3/9 (3 sites/9 cells), 4/12 and 7/21. The figure below shows 4/12 and 3/9.


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ures such as fhop, DTX, pwr ctrl). However, the other carriers can have tighter reuse factor such as 9 o


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r less. This is called Multiple Reuse Pattern (MRP).


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Handover Analysis

Handover is an important function, which shows the

integrity of the GSM network. If the handover

performance is poor, the subscriber will perceive the

quality of the network as bad.

Bad locating parameter settings

Uplink interference

Missing measurement frequency in BA-list

Extra measurement frequency

Co-Channel and Co-BSIC

Unnecessary neighbor relation

HW faults

Permitted NCC (network color code)

Wrong use of HCS parameters

Congestion

Probable Reason of Bad Handover Performance


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Handover Analysis Flowchart.

The following procedure should be performed for

handover analysis:

- Check the successful handover per cell

- Check for the handover success rate below certain cr

- Check the handover activity from the number of han

- Check the site location, whether the site to site

distance or co-sited. (Good map is needed here).

- Check whether the cell is isolated or not, if already k

- Check the handover flow whether is balance between

- Check the difference performance of incoming and o

- Focus on the bad direction.

- Check the worst relation and pick one cell.

- Check the cell whether it is external or internal. If

external, start inter-BSC analysis.

- If the cell is internal, check the high ratio of lost han

- If one of them is yes, check the uplink & downlink in


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- Check the frequency plan. There might be problem o

- Check the handover related parameters such as

relation, BA-list, BSIC, hysteresis, offsets etc.

- Check if many Ping-Pong handover.

- Check if assignment handover are used.

- Check if cell has HW problem. If problem found, swa

- Check if congested target cell. If the target cell is

congested and then solve the congestion by adding

TRU.

- Perform measures to improve HO performance. This

No or Few Handover Attempts


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No or Few Handover Attempt Flowchart.

The following procedure should be performed for no

or few handover attempts:

- Check the neighbor relation with low traffics (less th

- Check from the unbalance relation whether the targe

- Check the missing measurement frequency (MBCCH

- Check unnecessary neighbor cell relations and if

found, remove unnecessary relations.

- Check NCCPERM, if NCC of the neighbor is missing,

- Check the setting of the cells whether they are set

in different layer of HCS. (Layer 1 is the highest

priority)

- Check if the cell is at the inter BSC border, if so , ch

- Check locating parameters and list out.

- Check the poor setting of parameter and if so, corre

- Check BTS definition (RX commands especially

RXMOP).

- Check if BTS is defined but might not be in service. I


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Bad setting might cause the locating will not rank the

best cell as a candidateIncoming handover failed as the target cell could not

decode the handover burst messa e from the mobilePrevent any handover to affected neighbor cells

Can provide inaccuracy of measurement for handover

decisionsMeasurement result from neighbors can not be

distinguished and MS may perform a handover to the

wron cell.

None or few handover might indicate a unsuitablenei hbor relation.Can cause bad neighbor relation.

Missing NCC of the neighbors will not allow any

handover.Cause unnecessary handover

High congestion might lead to dragged calls (handover

performed at a not intended location) a lot of

unsuccessful handover.


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iteria for example X%. If it doesnt meet the criteria and change the X% to a higher val

over performed. If the number is above certain value for example Y and then take into

nown problem of no dominant serving cell and take other cell.

incoming and outgoing.

tgoing handover. This is to ensure the priority for more problem direction.

over, urgency handover and reversion.

erference problem.


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n co-channel or adjacent channel.

or repair hardware.

is the assumption comes from the above analysis.


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n 10% of average number of handover per relation) and unbalance relations.

t cell is congested, if congested, solves the congestion problem.

O) in Double BA-list in active list (if yes, add the measurement frequency in the BA-list

dd the NCC of the neighbor list into the NCCPERM list.

ck the inter BSC HO performance (SIEMENS System).

t the parameter setting

f yes, correct parameter setting or deblock it.


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ue and check for the next cell.

consideration.


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.


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TCH Assignment analysis

Successful assignments show the number

At unsuccessful assignment, the Assignme

The formula is defined as:

No dominant serving cell

Severe congestion on TCH

Low signal strength for call access

InterferenceFaulty transceiver

The following procedure should be perform

For TCH assignment success rate, the first

If there is congestion on TCH, it is recomm

If there is no congestion on TCH, check the

If the output power is ok, check the faulty

If hardware fault found, swap or repair HW.

Perform drivetests to check the coverage a

If no dominant cell or similar signal strengt

If there is no problem on the dominant cell,

Check the disturbance whether it is on SDC

Mostly, the problems of low TCH assignme

Traffic congestion is one of the major netw

Short term growth

If the high traffic related to an occasional e

Long term growth

% TCH ASSIGNMENT SUCCESS RATE

Probable Reason


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If there is a long-term growth the network

Type of Congestion

The congestion analysis begins by identifyi

Consider how many channels that are alloc

SDCCH Congestion

In R8, the time congestion should be used i

Ericsson recommends using the SDCCH Ti

where PERLEN is the measurement period i

SDCCH Congestion Analysis

The flowchart below, Figure 51, explains a

SDCCH TIME CONGESTION OF TOTAL

MEASUREMENT INTERVAL


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Diposkan oleh waveice di 00:20 0 komentar

Low Availability

What should I check?

SDCCH Availability.

Where do I look for it?

STS Counters on SDCCH availability. Th

Run BSC commands to see if the chann

Why do I need to check this?

Available SDCCHs of Total Number of Defined

SDCCHs
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We need to check this area to make sur

Location Area Border Cell &


Check site position and location area bo


Refer to site database for site info.

Location Update performance should coYou can run BSC command RLSSPto ch


If the cell is situated on a misplaced Loc

The CRH is the hysteresis value used w

TCH Congestion


Check if TCH congestion exists and if th


Use STS Counters and look into time co

Note that if the feature Adaptive configuration of l


Check if TCH congestion exists and if th


Use STS Counters and look into time co
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If activated, check CLS and Assignment


TCH congestion causes the mobiles to s

SMS Usage


Check SMS activity.


Check STS counters for SMS on SDCCH.


Extensive SMS usage increases the SDC

Too Frequent Periodic Regis


Check Random Access Distribution. Che


STS Object Type RANDOMACCfor Rand


To prevent intervals of Location Updatin

Increasing Traffic Demand


Check if its short-term traffic growth an


TCH TIME CONGESTION OF TOTAL

MEASUREMENT INTERVAL


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Compare the traffic trends and refer to


The high traffic could be related to an o

Cell Broadcast Used


Check if Cell Broadcast is active.


Run BSC command RLCCP.


CBCHis the cell broadcast channel and i

Long Mean Holding time


Check SDCCH Mean Holding Time.


STS counter for SDCCH Mean Holding ti


If the mean holding time is too long, thi

SDCCH Dimensioning


Check how SDCCH is dimensioned.


Check the SDCCH settings from CNA pa

SDCCH MEAN HOLDING TIME


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As no of subscribers steadily increase, p

Bad use of Adaptive Configu


Check if ACSTATE is on or off. If its on,


Run RLACPin BSC for ACSTATE status


By using the Adaptive Configuration of


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f successful TCH allocations at call setup.

t Complete message, sent by the MS, was never received by the BTS.

= TCASSAL

L

X 100 %

TASSALL

The serving cell cannot cope with the TCH traffic.

Failing TCH allocation for assignment or handover due to

con estionThe signal strength might be higher on the BCCH than on the

TCH.

Disturbance on SDCCH or target TCHFaulty equipment

d for TCH Assignment analysis:

hing, check the TCH Time Congestion.

nd doing the dimensioning and adding TRU based on carried TCH traffic demand.

output power of the BTS. If the output power is low, increase the output power.

TS by extracting BTS error log.

d received RxLEV.

hs of a few cells found during drivetests, it is recommended to add BTS.

check the interference whether co-channel or adjacent channel.

CH or target TCH. If disturbance found, improve the frequency plan.

t are TCH availability and interference.

rk problems in a mobile system. A high congestion deteriorates the overall performance of the

vent, like sports event, fairs, conference, a temporary solution might be considered.


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capacity has to grow according to the demand.

g if there is only SDCCH or TCH congestion or both. Congestion on both SDCCH and TCH may

ted in the cell. If possible, expand the capacity with new transceivers, otherwise a new site m

nstead of congestion based on access attempts as there is no way to estimate the number of a

e congestion as a KPI in R8. The formula is defined as:

= CTCONG

S

X 100 %

PERLEN

* 60

n minutes.

lowchart

eneral approach to investigate SDCCH Congestion. The next section describes the action point


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e formula is:

= CAVAAC

C

X 100 %

CAVASC

AN *

CNUCHC

NT

ls are manual, control or automatic blocked.


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that there is no hardware problem as faulty equipment can affect SDCCH availability. If need

RH

rder, Location Update Performance and parameter CRH.

e from the MSC. eck CRH value.

ation Area border, this means that unnecessary many normal Location Updating are performed

en the MS in idle mode crosses a LA border. The default value for this parameter is 4. If a high

SDCCH mean holding time is high. Check CLS and Assignment to Worse cell parameter settin

gestion to see how severe is the TCH Congestion. The formula is:

ogical channels is active the formulahave no meaning. Then S_AV_NR is recommended to be used instead.

SDCCH mean holding time is high. Check CLS and Assignment to Worse cell parameter settin

gestion to see how severe is the TCH Congestion. The formula is:


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= TFTCON

GS

X 100 %

PERLEN

* 60

to worse cells parameters from CNA.

ay extra long time on the SDCCH. Increase TCH capacity if required. Utilize the features for tra

Counters are CSMSDWNand CSMSUP.

CH traffic and could cause congestion if badly dimensioned SDCCH channels. Re-dimension the

ration

k the timer T3212 in the BSC.

om Access and look into CNA for T3212 setting.

g which is too short that it affects Random Access Performance to deteriorate.

d whether combined SDCCH is used.


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lanning on how SDCCH is dimensioned.

casional event or due to a long-term growth. If its a special one-time event of surge in traffic,

ndicates whether or not a CBCH shall be included in one of the SDCCH/8 sub-channels for the

e. The formula is:

= CTRALAC

C*PERLE

N*60

X 100 %

CNSCAN

*CMSES

TAB

s can possibly generates a higher traffic load.

ameters.


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revious SDCCH dimensioning plan might be insufficient. Review SDCCH dimensioning requirem

ation of Logical Channels

check the parameter settings.

nd use CNA to check these feature parameter settings.

ogical Channels feature, the basic SDCCH configuration in a cell will be under-dimensioned. If


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network and should be minimized.


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mean that the only way to get rid of the congestion is to add more physical capacity in ter

st be implemented. Frequency planning schemes such as MRP and FLP could be used to r

cess attempts a single mobile does.

in this flowchart. The reference to each action point is indicated on the flow chart as well


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d, the O&M procedures need to be reviewed.

. If the site is located close to major road or railway, consider moving the Location Area b

number of Location Updating occurs in a Location Area border cell, a higher CRH can be s

s.

s.


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ffic distribution such as CLS and Assignment to Worse Cell.

SDCCH channels with consideration taken to SMS usage.


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then it shouldnt cause too much concerned. But if the trends continue, then SDCCH migh

ell or channel group. It is defined per cell or per channel group. If it is active, check if the


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ent to existing demands.

his feature is not used correctly, it will cause SDCCH congestion.


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ms of transceivers or sites.

lieve congestion. Microcells cou

.


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rder.

t in order to reduce the numbe


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t need to be re-dimensioned

network uses it. If it is


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Frequency Planning (GSM)

CELL

Definition: Area Coverage of Radio Base of Station.

Type :

Sectored Cell, Omni Cell, etc

Coverage measure:

MacroCell (>5 km), MicroCell (3


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Reuse factor

Tighter Reuse : + higher capacity ; Interference between cells.

Design Frequency Reuse:

Basic Parameters:

C/I = Measure of signal quality

* FDMA (AMPS) : C/I > 18 dB ===>

====>

* TDMA (GSM) : C/I > 12 dB ===>

====>

* CDMA : Quality evaluated from Eb/Io

Cluster (K) = Frequency grouping

*Measure of Cluster depended from C/I system condition.

N ( Total Frequency Spare)

Example : Frequency Reuse pattern with N = 6so that: K = 4

SIGNAL TO INTERFERENCE RATIO :

1. Consider closest co-channel cells (SIRmin)
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2. Measure of Cluster (N)

3. Co-Channel reuse distance ratio

CELL SPILTTING

Is needed at the time of :

1. Overload traffic on cell mount.

2. TCH Congestion

To increase the capacity, the operator performs cell splittings:
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Strategy Frequency Reuse pattern for cell splitting

Type of Interference :

Co Channel Interference

Adjacent Channel Interference

Reasons is:

Poor frequency plan

No dominant cell > low C/I > increased Rxqual

Frequency Hopping is off

External interference e.g. jammer

Analysis :
http://goengineer.files.wordpress.com/2009/10/cell-splitting.jpg


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Identify areaswith Rxqual > 5

=>> Identify source using Map and STS

=>> New drive test around problem area?

Solution:

Enable Frequency Hopping or add frequencies to Hopping group.

Enable BTS Power Control, MS power control and make it less aggressive.

Change frequency of interferer or interfered cell (Possible to find new frequency by using TEMS Scan

Down tilt or change antenna of interferer.

Redo frequency plan.


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wer, etc.


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ning).


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Interference

Type of Interference :

Co Channel Interference

Adjacent Channel Interference

Reasons is:

Poor frequency plan

No dominant cell > low C/I > increased Rxqual

Frequency Hopping is off

External interference e.g. jammer

Analysis :

Identify areaswith Rxqual > 5

=>> Identify source using Map and STS

=>> New drive test around problem area?

Solution:

Enable Frequency Hopping or add frequencies to Hopping group.

Enable BTS Power Control, MS power control and make it less aggressive.

Change frequency of interferer or interfered cell (Possible to find new frequency by using TEMS Scan

Down tilt or change antenna of interferer.

Redo frequency plan.

Add new site.


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ning).


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Handover Ping Pong (Repeated)

Handover case :

1. Repeated handover (Ping Pong)

2. Repeated Intra-cell handover

3. Handover failure4. Unrealistic handover

Reasons :

1. Repeated HandOver (Ping pong)

No dominant server

Locating penalty settings e.g. PSSBQ, PTIMBQ

Too small hysterisis setting

Solution :

a. Change physical Antenna

Antenna direction

Antenna Tilts

Plan for new site Change

Locating Parameter e.g. KHYST or LHYST

b. Change Parameter, KHYST or LHYST


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2. Repeated Intra-Cell HandOver

Repeated Intra-Cell HandOver the following reasons is:

Wrong intra-cell handover settings

External Uplink Interference

Solution :

Consider to change parameters:

SSOFFSETUL, SSOFFSETDL

QOFFSETUL, QOFFSETDL

A wrong setting of parameters will cause unnecessary IHO

Turn off Intra-cell Handover?

3. HandOver Reversion

Check layer 3 message

Handover command BSC correct?

Check reason for handover SS, RXQUAL

Target cell?

Handover Reversion the following reasons is :

Duplicates of BSIC BCCH combinations in neighboring list

Solution:

Change one of the BSIC between BTS with same BSIC or Rotation Cell Parameters.


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Other Reasons:

Uplink interference in target cell

Downlink interference at MS

Solution:

Interference Investigation

Statistics

Scaning

4. Unrealistic HandOver

Reasons :


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Wrong locating settings, in Serving or Target cell

Note : Could be on purpose e.g. Dual Band network with HCS

Solution:

Fix locating settings e.g. MSRXSUFF, BSRXSUFF


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Call Setup Failure Analysis

Call Setup Failure the following reasons is :

1. Low Signal Strength

2. Interference3. High Congestion on SDCCH

4. High Congestion on TCH

5. Transmission Fault

6. Faulty TRU/Hardware

7. Central Processor Overload

8. Software File Congestion

9. Cell is not defined in MSC

Possible Solutions:

Low signal strength=> Signal strength analysis.

Interference => Interference analysis.High Congestion on SDCCH:

==> Define more SDCCHs.

==> Activate adaptive configuration of logical channel feature and immediate assignment to T

High Congestion on TCH:

==> Add capacity/Tune coverage array.

==> Activate assignment to worse cell.

Analysis :

SDCCH Blocking

Multiple Channel Requests.

Successful Random Access after the third try.

==> Congestion in SDCCH.


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From plot, identify which & where in logfile the dropped call occurs.

In the log file, Jump the drop call event.

Check if there is a disrupt in the recording. If yes ==> could be a false drop due to TEMS mobile disc

Check the Radio environment just before drop:

If High Rxqual for a longer period of time and RLINKTexpire ==> Interference problem.

If Low SS DL, SSDL < MS SENS ( -104dBm) ==> low signal strength problem.

If TA> 63 ==> too far from the cell.

If DL radio is good, check the TX power. If there is MS power down regulation when the MS is close t

Verify or isolate the problem using STS (Drop call and reasons).


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H.


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nnection during recording!!!

the cell. If full power ==> suspect uplink interference or antenna, TMA problem.


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Signalling protocols are decomposed into layers, each layer having a specific function.

Example :

The protocols used in BSS are :

On Layer 1 :

G.703. This protocol is used in the Transmission Network ( A, A-bis)

Signalling processing and Radio. This used in the Radio Network ( Um)

On Layer 2 :

LAPD (Link Access Procedure on D-Channel). This protocol is used on A-bis, for safe transport of BT

LAPDm. This protocol is use on Um, for safe transport of Traffic management messages between M

On layer 3 :

BTS O&M. This protocol is only used on A-bis (between BTS and BSC), for operation and maintenan

Traffic Management. This protocol is used on all interfaces ( between Mobile, BTS, BSC and MSC) to

Signalling used layer 1, 2 and 3 while speech and data only layer 1.


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S O&M and Traffic Management messages. BTS O&M use the OML Link, Traffic Management use the

bile and BTS.

e of the BTSs.

handle the phone calls.


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RSL Link.


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TCH Blocking maybe due to the following reasons

1. Handover and Power budget margins

2. Cells too large

3. Capacity Limitations (Congestion)

4. Incorrect or Inapproriate Timer

Optimization for tips :

1. Handover and Power budget Margins

Handover Margins should be properly optimised to move the traffic to neighbouring cell. Strict hand

TIPS :

6 dB handover margin is considered to be an approriate margin for handover. A strict handover mar

2. Cells too Large

If cell are too large meaning antenna too high or antenna too shallow, it will pull in out of area traffic

TIPS :

Consider reducing antenna height to reduce the footprint of the site. Also increase the antenna tilt (t


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ver margins can results in lower handovers and ultimatelly congestion in cell.

gin results in the strict criteria for Power Budget Handovers also. Setting a lower value of handover mar

again causing congestion in the cell.

he max tilt is 12)


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in will initiate ping pongs handovers, which are not considered good for network health. (handover mar


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in have already been discussed).


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SDCCH Blocking

SDCCH Blocking is probably due to one or more reasons

1. No Access to SDCCH

2. Failure before Assignment of TCH.

3. High Paging Load

4. Incorrect or Inapproriate timer values


1. No Access to SDCCH

This cases before has already been discussed

2. Failure before Assignment of TCH

This cases before has already been discussed

3. High Paging Load

Irreguler paging distribution in location areas results in SDCCH Blocking. Higher paging load in cert

TIPS :

A location area with a high paging load needs to be reduced in size to relieve SDCCH Blocking. A l

4. Incorrect or Inapproriate timer values

Timer rr_t3 111 sets the amount of time allowed to delay the deactivation of a traffic channel (TCH)

TIPS :

The suitable value for this timer is 1200 ms (max being 1500 ms). The timer will cause the BSS to


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in location area mean higher location updates on SDCCH resulting in SDCCH Blocking.

cation area with low paging load need to be enlarged in size to reduced the overal number of location a

after the disconnection of the main signaling link.

ait before the channel in question is allocated another connection. A lower value of timer will result in hi


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res.

gher capacity since the channel is held for less time before being released.


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High Handover Failure Rate

High handover failures rate will probably be due to one or more of the following reason.

1. High Neighbour Interference

2. No Dominant Server

3. Database Parameters


1. High Neighbour Interference

While handling off to the best neighbour the interference on the target cell frequency may result in t

TIPS:

When designing the cell frequencies care should be taken that there is proper frequency spacing b

2. No Dominant Server

If cell sites are designed poorly there might be areas where neighbour being received at the same l

TIPS :

Antenna tilts provide the good way to reduce the footprint of the sites. Efforts should be made that a

3. Database Parameters

Received level, receive quality and power budget algorithm are set in the system information to defi

TIPS:

Enable the per neighbour feature which dispalys the successful and unsuccessful handovers on a

All those cells can be identified which are problematics in terms of hand off so one can focus only s

a. Defines the lower threshold for uplink quality handovers.

ex : Range 0 to 1800

Step size = 0.01

a value of 500 defines the lower threshold value of 5 (BER) for a quality handover to be trigge

b. Defines the lower threshold for downlink quality handovers.

c. Defines the lower threshold for received level uplink handovers.


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Ex : A value of 20 defines the threshold value of -90 dBm for a level handover to be triggered

Range 0 to 63

Where 0 = -110 dBm

1 = -109 dBm

63 = -47 dBm

The optimum value for this threshold is 15 ( 95 dBm). If the signal level goes below that,

d. Defines the lower threshold for received level downlink handovers.

e. Defines the upper threshold for uplink interference handovers

f. Defines the upper threshold for downlink interference handovers


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e hand off failure.

tween the cells to avoid neighbour interference. In most of the cases Ping Pong Handover starts i.e the

vel and some neighbour randomly look good for hand off for a certain amount of time. Such situation is

single dominant server should serve the specific area. Timing advance limitation is applied to cell area

e the criteria for handover. Improper values for these criteria may result in poor handoff.

per cell basis. In optimization, monitor the following stats, which comes under cell statistic category.

ecific cell causing the major contribution towards poor HSSR. Ensure that handover margins are optimi

ed for uplink. The optimum for this threshold is 500.


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for uplink.

a level handover is initiated.


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mobile hand off to a cell for better level and due to interference (Quality issues) hand off again to origin

disastrous because handoff decision will be hard and mostly it will end up unsuccessful handovers.

where there is multiple servers.

sed. Rule of thumb is a 4 dB for adjecent frequencies and 6 dB per cell without adjecent frequencies. T


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l cell. A through drive test can determine the interfering frequencies which should be eliminated from t

e following parameters can be played for defining the threshold for imperative and non-imperative han


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he frequencies plan.

overs.


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High Call Drop Rate (HCR) Guidelines

For healthy network the drop call rate should be less than 1%. There are again number of reasons, whi

1. Drop on Handover

2. Low signal Level

3. Adjacent channel Interference

4. Co-channel Interference

5. Extraneous Interference

6. Link Imbalance

Optimization for Tips :

1. Drop on Handover

The call may drop on handover. Its mostly high neighbor interference on the target cell, which caus

TIPS :

Within optima, monitor the following statistic. Theses statistics are defined under the category of BS

a. total and successful handover on UL/DL quality

b. total and successful handover on UL/DL signal strength.

c. total and successful power budget handovers.

From the above statistics, quality or level must be estimated.

2. Low signal Level

Signal level below -95 dBm is considered to be poor. If the mobile is unable to handoff to a better c

TIPS:

First of all path balances should be checked. If path balances are deviating fro the standard value t

a. I_Rx Lev_DL_p

Defined the lower value for receive level for the power control to be triggered.

Range 0 to 63

Where 0 = -110 dBm

1 = -109 dBm


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63 = -47 dBm

Example : If the value of 20 is set it means that the BTS will start transmitting more if it sense

b. U_RxLev_DL_p

Defines the upper threshold value for receive level for the power control to be triggered (Rang

Example : On setting the value of 50 (equivalent to -60 dBm) BTS will lower down the power.

3. Adjacent and Co-channel Interference

Frequency planning plays a major role to combat adjecent channel and Co-channel Interference. C

TIPS :

An Optimization tools like Neptune could be helpful in identifying the interference on the particular a

a. TCH Interference level 1

b TCH Interference level 2

c. TCH Interference level 3

d. TCH Interference level 4

When a TCH timeslot is idle it is constantly monitored for an uplink ambient noise. During a SACCH

4. Extraneous Interference

Extraneous Interference might be from :

a. Others mobile network

b. Military communication

c. Cordless Telephones

d. Illegal radio communition equipment.

TIPS :

External interference is always measured through spectrum analyser which can scan the whole ban

5. Link Imbalance

Sometime the multifunctionality of vendor hardware becomes responsible for high Call Drop Rate.

a. Transmited and receiving antenna facing different direction

b. Transmited and receiving antennas with different tilts.


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c. Antenna feeder demage, crossion or water ingress.

d. Physical obstruction.


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h could contribute towards higher dropped call rate is :

s the main problem. Sometime the mobile is on the wrong source cell (not planed for that area but ser

C level statistics.

ll on level basis, the call will possibly be dropped. Topology or Morpology issues may also be there like i

en check the BTS transmited power with the help of wattmeter. BTS may transmit low power because


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that downlink receive level is below -90 dBm.

is same as described above).

channel is observed mostly when mobile is elevated and receives signals from cell far away but using

ea. Such frequencies can be cleaned from existing frequency plan. The following statistic can also be

Multiframe an idle timeslot is monitered 104 times. These samples are the processed to procedure a n

d. Some spectrum analyser can even decode voice from AMPS circuits or Cordless Phones.

ne of the possible scanarios could be :


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es due to the antenna overshoot) which may the result in the drop call.

f Mobile enters into a tunnel or a building , higher RF losses will be develoved.

f the malfunctioning of radio or higher combiner losses. Also check the feeder losses, antenna connect


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he same frequencies.

onitored to confirm that there interferences issues in the cell. These stats are defined in optima under t

ise level average per 480 ms. An interference band is allocated to an idle slot depending upon the inter


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rs. Enable Downlink power control. Power control is be directional. The lower and Upper recieve level d


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e category of BSC stats.

ference level. The threshold for these levels can be set in the system parameters. Interference level 1 b


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ownlink power control values should be properly defined.


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eing the least ambient and interference level 4 being the most ambient. While planning the Network car


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should be taken that the cell do have the proper frequency spacing.


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SDCCH Success Rate is percentace of MS Call Setup success due to TimeSlot at the first call.

Where :

SDCCH success rate = [(Call Setup Success - Call Setup Failure )/ Call setup success] x 100%

The call setup rate should be above 90% for a healthy network. However a cssr of 85% 90% is satisf

There could be so many reasons for a poor cssr. Some are described as follows :

1. No access to SDCCH

2. CM Service Reject

3. TCH Failure Assignment

4. Hardware Problem

Optimization Tips for :

1. No Access to SDCCH.

BSS detacts channel request (in the form of RACH) from a source, requesting resources for networ

Case :

a. Valid RACH ( SDCCH Congestion)

Due to unavailability of SDCCH, BSS will response to MS with immediate assignment reject, t

Invalid RACH (Invalid established cause detected in the received RACH)

b. Phantom RACHs

The received RACH is in fact genereted from an unknown source, wherby it fails to continue

TIPS:

Within the optima there are certain stats which can be monitored before coming to conclusion that t

a. SDCCH Blocking

b. SDDCH Congestion (Valid RACH)

If the SDCCH blocking greater than 1% or SDCCH Congestion greater than 2% than that mean tha

A TCH can be allocated by passing SDCCH. A parameter namely Immediate Assign Mode when en

2. CM Service Reject

CM Service Request (MOC) or Paging Response (MTC) to BSC/MSC. Inside the CM service requ


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3. TCH Failure Assignment

Upon completion of MS/BSC/MSC link established, MS issues Assignment Request to BSC, Reque

Case :

TCH Congestion

TIPS :

For TCH Congestion certain features can be enabled like TCH queuing , Directed Retry and Conge

Interference analysis on a particular carier can be done through an optimization tools like Neptune.

4. Hardware Problem

Hardware failures also play major role for poor CSSR. Improper functinality of any BTS hardware ca

TIPS :

If there are no capacity or RF issues then equipment needs to be checked. Before starting the drive


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ctory.

s transactions. After validation of the RACH, BSS will attempt to allocate a dedicated channel (SDCCH

rminating the transactions. In which case, call setup is termed as unsuccessful due to SDCCH congesti

the transaction after SDCCH has been allocated by the BSS. For instances, case of channel request de

here is SDDCH problem :

it is a capacity related issue and more slots should be assigned for SDCCH.

abled allocates TCH by passing SDCCH.

st message (MS initiated service request), MS informs the network the types of service it requires (i.e.


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sting TCH Assignment to the dedicated MS. Subsequently, BSS will attempt to allocated free TCH for M

tion Relief. In case of the TCH queuing feature is enable, MS will queue in the Original SDCCH , awaiti

nce interfering frequencies are determind, the frequency plan can be cleaned from such frequencies.

n affect the overall performance of sites.

est make sure that the cell site are free for any hardware alarms. The important parameter to check is t


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for the source. One the availability of SDCCH channel is confirmed, the BSS will send immediate assig

on.

tected by overshooting cells, handover access burst from distanced MS, hardware deficiency, UL/DL im

obile Originationl, Emergency Call, Short Message transfer or Suplementary services activity), wherby


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S voice messaging. Once Assignment Command is received by MS, stating the availability of TCH for t

ing for the next available TCH. It is to be remainded that once Queuing timer expires. BSS will also term

he path balance. If path balances are not fine then start checking the power from radio to connected ant


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nment to MS indicating the dedicated SDCCH sub-channel (via AGCH), wherby subsequent message e

balance path, MS moving out of range would carry the Phantom RACHs symptoms.

Paging response is specific to MTC. Subsequently, BSS embraces the information with its own initiated


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e MS, it will move to the dedicated TCH and responds with Assignment Complete. In turns, BSS will su

inates transactions, in which case, call setup is termed as unsuccessfull due to TCH Congestion. The s

ennas. If we take the examples of GSM 900 scenario, the link budget defines that the radio should trans


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xchange will be preformed over the dedicated SDCCH.

connection request BSSMAP message, send to MSC to approval. MSC will response with either conne


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bmit Assignment Complete to MSC as to complete the signal activity.

me situation also applies in situation where Congestion Relief feature is enabled. In the case of Directe

mit 40 watts power and at the top of the cabinet, 20 watts are recaived ( Considering the 3 dB loss of c


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tion confirmed, confirming the success in link establishment between MS-BSC-MSC, or connection Re


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d Retry feature is enabled, MS will perform Handover to TCH of another cell if a valid handover neighbo

mbiner). While checking the power, if any components seems to procedure more losses than expected


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used, Indicating the termination of the specific network transaction.


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r is detected. The best thing to do is to add more radios in the cell to remove congestion.

, change that component. Similarly check the power at antenna feeder ports. Some time due to the wate


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r ingress, connectors get rusty and needs to be replaced.


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TCH Call drop

Causes of TCH Call Drop:-

Usually, the typical causes for sending the Clear_Request mssg are as follows ;

1. Radio Interface Failure

2. O & M Intervention

3. Equipment Failure

gsm parameters

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