Proposed by: RFO Central. LIAO QI LIANG.

2010-4-4
Main Parameter Summary for Concentric Cell
There are two types of concentric cells. The first one is single band S6 cell in which concentric
attribute is caused by different combination loss among TRXs. Combination loss difference is
around 3-4 dB between under-laid and over-laid TRX (due to additional loss in DCOM or SCU)
assuming all TRX having same output power.
The second type of concentric cell is Co-BCCH cell in which concentric attribute is caused by
different propagation loss between GSM and DCS sectors. The propagation loss difference is
around 8dB in average assuming ANT parameters (Height/Tilt/Azimuth) are same between both
bands.
The main issue in these 2 types of concentric is different and thus need to be analyzed
separately. For S6 cell, main issue lays in insufficient resource in UL. High congestion rate is
common and we need to adjust parameters to push traffic to OL. For Co-BCCH cell, UL resource
is enough (4TRX) and we will not face congestion as it is in S6 cells. The main issue lays in weak
coverage of DCS-OL (around 8 dB poorer than GSM-UL). We need to be careful to maintain a
good TCH assignment success rate when pushing traffic to DCS.
Below are main parameters explanations as well as suggested settings. Also included are some
cases obtained during daily optimization activities.

For Single band Concentric Cell Parameters
1. Cell Type Attributes (Concentric/Normal)
Normally speaking, we set cell type to concentric for S6 cells. But if a cell is located in
urban and coverage is good, we can remove concentric via decreasing TRXPWR by 4
dB in UL TRXs. The advantage is we can avoid TCH congestion when allocating UL
channels but we might face risk of losing coverage. So just make it sure that we dont
have any coverage risk before PWR reduction in UL TRXs.
Proposed by: RFO Central. LIAO QI LIANG.2010-4-4
Parameter involved is Power Level. TRXPWR is reduced by 2dB when increasing
Power Level by one step. Below is detail description.
Power Level
This parameter specifies the transmit power level of the TRX. The greater this parameter is, the
smaller the transmit power is. When this parameter is set to 0, the transmit power level of the TRX is
the greatest. Each time this parameter increases by one level, the transmit power reduces by 2 dB.
Besides, if we are using 2 antennas for S6 cell instead of one dual polarized antenna, we can
remove SCU/DCOM and thus all TRXs have same EIRP. In this case, we should set cell type
to Normal Cell

On the other hand, for S8 cells in which EIRP is same among all TRXs, we should configure
cell type as Normal cell instead of Concentric.



Proposed by: RFO Central. LIAO QI LIANG.2010-4-4
Case Study
8TRX cells 3830-1 & 3830-3 are set as concentric cell. It is observed huge number of congestion in UL
since then. After remove the concentric attributes, KPI returns to normal


2. Concentric Attributes in TRX and DDPU Settings

The criteria in configuring TRX concentric attributes is that, TRXs connected to SCU or
DCOM should be configured as UL while others are configured as OL.

Proposed by: RFO Central. LIAO QI LIANG.2010-4-4


Besides, we should also pay attention to the DDPU settings of BTS3012. TRXs connected
to DCOM should be under same downlink tributary group. There is no solid evidence to
prove that TRXPWR will be bypassed or KPI affected under second kind of setting but it
is suggest follow the first one according to Huawei BSS.



Proposed by: RFO Central. LIAO QI LIANG.2010-4-4


Case Study
22 cells in BSC02 have been wrongly set TRX UL/OL attributes after expansion. Only 1 TRX is set as UL for
each cell and huge number of congestion is observed since then. After changing UL/OL attributes
according to the criteria, TCH congestion returns to normal


Proposed by: RFO Central. LIAO QI LIANG.2010-4-4
3. Enhanced Concentric cell allowed (YES/NO)

Suggest set to YES to avoid blind assignment in overlaid and underlaid. When it is
enabled, uplink measurement report is taken into account during immediate assignment
and incoming HO process. Channels in OL and UL are assigned accordingly, thus TCH
assignment successful rate can be guarantee. Besides, BCCH of serving cell is reported
in MS measurement report as well as that of TCH, which can improve the intra-cell HO.


Below parameters are invalid if we enable the enhanced concentric cell function.
RX_LEV Threshol/ RX_LEV Hysteresis
RX_QUAL Threshold
TA Threshold/TA Hysteresis
UO Signal Intensity Difference

4. Assign Optimum Layer/Pref. Subcell in Intra-BSC HO/ Incoming-to-BSC HO Optimum
Layer
Suggest setting as System optimization for S6 cells in Assign Optimum Layer/Pref. Subcell in
Intra-BSC HO.
Proposed by: RFO Central. LIAO QI LIANG.2010-4-4
Suggest setting as Underlaid Subcell for Incoming-to-BSC HO Optimum Layer. The purpose
in doing this is do reduce the congestion without degrading the KPI
Case Study
Assignment optimum layer and Pref. Subcell in Intra-BSC HO are set to over-laid in 2061-2. Congestion is
greatly reduced but call drop rate is degraded after that.



5. Concentric Cell HO Allowed (YES/NO)
This parameter specifies whether the concentric cell handover is enabled. We should set
it to YES to enable the HO from UL->OL and vice visa. Otherwise UL channels are very
easy to be fully occupied.
Case Study
Concentric Cell HO Allowed is set to NO in 3894-2 after expansion. Huge number of congestion is
observed and no OL/UL HOs take place. After we enable this parameter, congestion reduced a lot.
Proposed by: RFO Central. LIAO QI LIANG.2010-4-4




6. Assignment optimum Level Threshold
If the Assign Optimum Layer parameter is set to System Optimization, current received level on the
SDCCH can be estimated based on the uplink measurement value in the measurement reports sent on
the SDCCH. Then, the BSC determines whether a TCH in the UL subcell or in the OL subcell should be
Proposed by: RFO Central. LIAO QI LIANG.2010-4-4
assigned based on result of comparing the uplink receive level on the SDCCH and Assign-optimum-level
Threshold.
The default value is 35, which means -75 dBm in uplink SDCCH. According to path balance statistics, we
have around 6dB difference between downlink and uplink in under-laid. So when it is -75dBm in uplink,
it is -69dBm in underlaid downlink. Thus in overlaid downlink, it is -72 dBm(3dB difference). If we are
going to push traffic to OL to reduce congestion, we can reduce this value. For example, we can set it to
20 which correspondent to -87dBm in overlaid downlink (It means if overlaid downlink is better than
-87dBm, the call and incoming HO will be assigned to OL)
Case Study
We have one cell 3830-2 which is covering remote area near Fallujah. After reducing assignment
optimum level threshold to 20, congestion reduces and traffic is pushed more to OL without KPI
degradation (call drop/Assignment rate/OL quality)



Proposed by: RFO Central. LIAO QI LIANG.2010-4-4




Case Study
We have one cell 2321-2 which is covering urban area in Baghdad. After reducing assignment optimum
level threshold to 20, congestion reduces and traffic is pushed more to OL without KPI degradation (call
drop/Assignment rate/OL quality
Proposed by: RFO Central. LIAO QI LIANG.2010-4-4



Proposed by: RFO Central. LIAO QI LIANG.2010-4-4


7. TA Threshold of Assignment Pref.
Suggest setting it to 63. Otherwise, TA is going to be considered in assigning OL channels and
this is not preferred if we are going to push more traffic to OL to release congestion

8. UtoO (OtoU) HO Received Level Threshold
If downlink Rxlev of Underlay is GREATER than the UtoO Received Level Threshold, calls can HO
to overlay. This parameter should be set close to the Assignment optimum level threshold.
On the other hand, if downlink Rxlev of overlaid is LESS than the OtoU Received Level Threshold,
calls can HO to underlay.
We have to pay attention to the settings and make sure that UtoO Received Level Threshold is
GREATER than OtoU Received Level Threshold at least 3 dB. Otherwise, ping pong HO between
layers will occur.
If we are going to push the traffic to OL, suggest setting the OtoU HO Received Level Threshold =
20 and UtoO HO Received Level Threshold = 25

Proposed by: RFO Central. LIAO QI LIANG.2010-4-4

Case Study
We have one cell 2007-1 which is covering urban area in Baghdad. Congestion is high with the default
settings in OU HO level threshold. After setting the OtoU HO Received Level Threshold = 20 and UtoO HO
Received Level Threshold = 25, congestion is reduced.



9. UtoO Traffic HO Allowed (YES/NO)
This parameter determines whether traffic load in UL subcell determines the UL to OL
handover or the OL to UL handover in an enhanced concentric cell. If the cell is
congested, we can set it to Yes to release congestion

Case Study
After enable UtoO traffic HO allowed, congestion reduced in cell TazzaSilo-3 (East Region)
Proposed by: RFO Central. LIAO QI LIANG.2010-4-4

10. EDGE HO Threshold
If we reduce OtoU Received Level Threshold, it is likely that we need to change the
EDGE HO correspondingly. (Because we want EDGE HO takes place later than the OtoU
HO)
Below is one example, if we set OtoU HO to 20 (-90dBm), we can revise the DL EDGE HO
threshold to 17(-93dBm). Below chart shows the boundary of each threshold.
Assignment optimum level threshold=20;
UtoO HO Level Threshold=25
OtoU HO Level Threshold=20;
DL EDGE HO Thrshold=17

Proposed by: RFO Central. LIAO QI LIANG.2010-4-4
For Co-BCCH Concentric Cell Parameters
For Co-BCCH Cells, main concern is not UL congestion but the weak coverage of OL.So we are
following different strategy in setting the IUO parameters
In common Co-site dual band cells, we are using Interlayer HO threshold/EDGE HO threshold in
dedicated mode to shift traffic to DCS.
Below are the matching parameters in Co-BCCH if we consider 8dB in band propagation loss
difference.
Considering we set interlayer HO threshold =25 (-85dBm) and DL EDGE HO threshold=-90dBm
in common Dual band (means if the DCS Rxlev is better than -85dBm, calls will HO to DCS layer.
If Rxlev of DCS is less than -90dBm, it will HO out to GSM), below are the mapping
Assignment optimum level threshold=27
UtoO HO Level Thrshold=33
OtoU HO Level Threshold=20
DL EDGE HO Threshold=17

Besides, for other parameters, below is the suggestion.
Enhanced concentric cell Allowed=Yes
Concentric Circle HO Allowed=Yes
Assignment optimum layer=system optimization
Pref. Subcell in intra-BSC HO= system optimization (or underlaid)
Incoming-to-BSC HO Optimum Layer = underlaid
UtoO traffic HO allowed= No