adaptive configuration of logical channelsw
TRANSCRIPT
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.