concentric cell main parameter

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.


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.


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.


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.


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


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.


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.


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


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)


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


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


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)


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


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

concentric cell main parameter

Documents

type of concentric cell

normal cell

trx concentric attributes

types of concentric

ul trxs

power level

cobcch cell

trx cells