ADAPTIVE CONFIGURATION OF LOGICAL CHANNELS

Purpose of the Feature• The purpose of the feature is to minimize the

risk of SDCCH congestion by automatically adapting the number of SDCCHs in a cell to the demand for such channels.

• As a result, the network will have higher capacity.

SDCCH Usage

• Notify the network about its location and status

• Send or receive a Short Message Services

• Call setup

Which cells need more SDCCH usage?

• Cells at the border of a Location Area (LA) need more SDCCHs than other cells.

• Cells with a high amount of SMSp-p traffic also need more SDCCHs.

Intra-Cell Handover

• Number of intra-cell handovers might increase slightly. The reason is that when a timeslot is to be reconfigured, any ongoing traffic on that timeslot is handed over to other idle channels.

• Algorithm is valid only for SDCCH/8s. An SDCCH/4 can not be dynamically configured by means of this feature.

Per Cell

• Adaptive Configuration of Logical Channels is activated and deactivated on a per cell basis.

• The feature can add and remove SDCCH/8 both in the underlaid (UL) and overlaid (OL) subcells if a subcell structure is defined.

Is it Fast ???

• The feature has a very fast reaction to change a TCH to an SDCCH/8 but much slower to change back.

• The SDCCH/8s are added and removed one at a time according to the different criteria.

Parameters• SLEVEL ->defines the number of remaining idle

subchannels when an attempt to reconfigure a TCH to an SDCCH/8 is initiated.

• Default value=0 Value range= 0-2 ,CONG

• STIME defines the minimum time it will take before a reconfiguration of an SDCCH/8 to a TCH is started.

• Default value=20 Recomemded value=40• Value range = 15-360

The Increase Criterion

1-# of idle SDCCH subchannels <= SLEVEL

2-# of idle TCHs > 4, Or

# of idle TCHs > #of TRXs in the cell.

3-#of already defined SDCCH/8s must be less than the max # of SDCCH/8s.

The Decrease Criterion

• A counter is initiated with a value equal to the value of parameter STIME.

• A check is made every third second to see how many idle SDCCH subchannels that are left in the cell.

The Decrease Criterion

• # of idle SDCCH subchannels > 8+SLEVEL-> the counter is decreased with 3

• # of idle SDCCH < 8+SLEVEL-> counter = STIME

• # of idle SDCCH subchannels = 8+SLEVEL ->the counter is not stepped at all.

** When the counter reaches zero, a reconfiguration of an SDCCH/8 to a TCH starts.

Example

** A-S represents new adaptive SDCCH/8.

Example

**When an SDCCH/8 is to be removed, the feature will remove an SDCCH/8 from the channel group where the latest added SDCCH/8 were configured.

Increasing Time

• Number of configurations can be decreased by increasing STIME or decreasing SLEVEL.

**Increased STIME will lower the SDCCH congestion while decreased SLEVEL will raise it.

System Load

• In best case -> (3+4)/40 = 0.175 Erlang

• In worst case (10+10)/40 = 0.5 Erlang

Immediate Assignment on TCH

• The Immediate Assignment on TCH feature can enable the TCHs to be used also for signalling. This means that the connections experiencing congestion on SDCCH, before another SDCCH/8 have successfully been added to the cell, may use an idle TCH for the call setup signalling.

• The Immediate assignment on TCH feature may also be useful if there is congestion on SDCCH and no new SDCCH/8 is allowed to be configured.