KPIs
to
be
monitored:
·
SD Blocking
·
SD Drop
SDCCH
Channel:
·
SDCCH channel is a dedicated channel which is using for LAC updation, Call Setup, SMS in Ideal mode. It works in UL & DL
SD
Blocking:
·
SD Blocking means that you are not getting SD resource for the call origination. When MS connects with Network then RACH and AGCH are provided. After AGCH, SDCCH is provided but if SDCCH is not provided at this time due to some problem or due to unavailable of SD by BSC.
KPI
Formula
in
Ericsson:
·
SDCCH CONGESTION = (CCONGS / CCALLS) * 100
·
CCONGS - Congestion counter.
·
CCALLS - Channel allocation attempt counter (on SDCCH).
Reason
for
SD
Blocking:
·
LAC Boundary
·
High Volume of SMS
·
SD utilization is high
·
Time Slot faulty
·
Adaptive configuration of logical channel switch off
·
Wrong SD Dimension
·
Incorrect CHAP Settings
·
Hardware Issue
Solution
for
Removal
of
SD
Blocking:
·
Check the no of SD channels available, if less, then increase SD channel while TCH Blocking should be taken care.
·
Check LAC boundary, if location update is more, then change the LAC of that site and set C2 and HYS.
·
Use of dynamic SDCCH (it is a BSC parameter)
·
Shift SD to new time slot
·
Adaptive configuration of logical channel switch ON
·
Check for T3212 value
Need
to
check
which
parameter:
1. CHAP (Channel
Allocation
Profile): Its Immediate Assignment Process on TCH, It provides different channel allocation strategies,
CHAP
0: Immediate assignment on
TCH is
not permitted,
CHAP
1: Immediate assignment on
TCH is
last preference, where
in TCH
is allocated at immediate assignment only
when there
is no
Idle SDCCH
is available
CHAP2: Immediate assignment on
TCH is
first preference where in
SDCCH may
only be
allocated when
there are
no idle
TCH is
available.
2. Adaptive configuration of logical channel (ACLP):
The purpose of this
features dynamic reconfiguration of
Idle TCH
Channel to
SDCCH Channel, when there
is SDCCH
High load
S LEVEL
Defines: Reconfigure of
an Idle
TCH to
an SDCCH
will take
place; Default 0 Congested rate for
a cell
is increase S LEVEL
2
S TIME
Define Minimum Time Interval between SDCCH, Can be
reconfigured back
to TCH,
Default value
20s, Range
15s to
3600s
3.
T3212:
Periodic update timer value: High volume of LAC
Border can
cause SD
Congestion so
optimize the
periodic registration timer. Irrespective of
the location, coverage, activity, the mobile has to
update its
location to
the MSC
after a
defined time/period.
4. CRH (Cell Reselection
Hysteresis)
:Receiving Signal strength hysteresis for
required cell
reselection over
location area
border, In
order to
overcome the
Ping-Pong effects in cell
reselection across location area
borders, CRO
and PT
can also
used to
delay reselection in
LAC Borders.(Location area
code is
an identity number given
to the
site of
a base
station)
SD DROP:
When SD
is assigned for a
mobile during call connection process and
during this
time due
to any
problem or
any mismatch occurs by
which SD
loss occurs, It is
between allocation of SD
and before TCH allocation.
KPI Formula in Ericsson:
·
SDCCH Drop Rate = (CNDROP-CNRELCONG/CMSESTAB)*100
·
CNDROP- Total number of dropped SDCCH channels in a cell (for the measurement Period).
·
CNRELCONG- Total number dropped (released) connections on SDCCH due to TCH or Tran-coder congestion.
·
CMSESTAB - Total number of successful MS channel establishment on SDCCH.
Reason for SD Drop:
·
Overshooting
·
Shift the SD time slot
·
Interference
·
It may be uplink or downlink issue in which cells foe UL put TMA in that cell and DL provide tilt
·
HW Issue
·
Wrong parameter planning
·
Bad coverage
·
MAIO mismatch
·
High Pathless
·
High LAPD utilization
·
Wrong Power control settings
·
Check the Timer T 3101
·
Check the Timer T 200(20ms)
Solution for Removal of SD Drop:
Interference:
·
Check the BCCH Plan(C/I or C/A)
·
Co-BSIC & Co- BCCH
·
To find out proper frequency to reduce interference
Overshooting:
·
LAC Planning
·
If a cell is picking call from long distance, check the sample log according to TA
·
Cell orientation need to defined according to clutter
Bad Coverage:
·
If the drop call is due to low signal strength uplink, check the receive path of this particular TRX. Check receiver sensitivity, VSWR, feeder connection and etc. Drops due to Low Signal Strength.
·
If the drop call reason is due to low signal strength downlink, then, check the transmit path. Check cards, feeder and etc.
Hardware Fault:
·
Check Alarms.
·
TRX condition.
·
Check Path Imbalance.
·
VSWR of the Cell.
·
Connector Connection.
·
Sometimes you will find issues on BCCH TRX. In this case BCCH shift from one to other TRX will reduce SD drop
Need to
check Which Parameter:
Drop Reason mainly Low
signal strength (UL &
DL), Bad
Quality (UL
& DL)
and Excess Timing Advance
And High
Interference (Co-BCCH & Co-BSIC), Wrong Power
control Settings and Too
High of
CRH Can
result in
SDCCH drops
Power control settings: Lack
of good
power control settings for
SDCCH can
lead to
excess drop.
Two types
of power
control 1.MS
Power control 2.BTS Power
Control
SDCCHREG:
Function of
this parameter Enable (1)/Disable (0),
Enable the
power control to minimize the drops
INIDES (Initial desires signal strength): For
the SDCCH
UL and
DL, Default value -70dbm, especially UL
impact of
drop rate,
because extremely sensitive to
interference, for
INDIES from
-70 dbm
to -85dbm this will
reduce the
cumulative power
emitted by
mobile closer to base
station (which need not
transmit at
very high
power to
communicate with
the BS)
and this
will reduce the interference
Due to ICM Band (CDMA):
·
Some time SD drops takes place due to near sites of CDMA.
·
Check the ICM band value of that site.
·
Use BPF (Band pass filter).
