Jumat, 05 April 2013

TCH Congestion Analysis

TCH Congestion Analysis


 TCH Availibility

What should I check?
  • Check TCH Availibility and TCH Blocking

Where do I look for it?
  • Use STS counters for TCH performance. The formulas are :

AVAILABLE TCH OF TOTAL NUMBER OF DEFINED TCH

DROPPED TCH CONNECTIONS OF TOTAL NUMBERS OF CALLS TERMINATED IN THE CELL


Why do I need to check this ?
  • Faulty equipment will lead to that all time slots could not be used for handling traffic causing congestion. Low availability can happen if the channels have been manually or automatically blocked and taken out of service. Check the downtime of the cell based on object type ‘DOWNTIME’ is also recommended.


Increasing Traffic Demand

What should I check ?
  • Check if it’s only short-term traffic growth.

Where do I look for ?
Compare traffic trend performance from STS.

Why do I need to check this ?
The high traffic could either be related to an occasional event or due to a long-term growth. Note that by increasing the number of tranceivers may lead to problems with floor space, antenna installations, CDU type, Expansion cabinets and Combiner type.

Load Mean Holding Time

What should I check ?
  • Check Mean Holding Time and Handover Performance.

Where do I look for it ?
  • Look in TCH Mean Holding Time and Handover statistics from STS (refer to next section) :

TCH MEAN HOLDING TIME







Why do I need to check this ?
Too low handover activity might lead to a long mean holding time. A long mean holding time is not a problem, but if there is congestion, new capacity is needed. Increase the number of TCH if no faults.


Low Handover Activity

What should I check ?
  • Check if there is few handover performance and congestion in neighboring cell.

Where do I look for it ?
  • Handover statistic from STS. Check handover parameters such as too high or too low hysteresis values, missing neighbour relations, one-way handover. In addition, review neighboring cell definitions as missing relations could cause handover problems.

Why do I need to check this ?
  • A low handover activity may lead to congestion if the MS is forced to stay on a cell longer than necessary.

Congestion in Surrounding Cells

What should I check ?
  • Check congestion in neighboring cells.s

Where do I need to check this ?
  • Look into STS congestion performance for neighboring cells.
  • Check if Assignments to worse cell is used. If assignment handover to worse cell is used (directed retry). Check the setting of the parameter AWOFFSET.

Why do I need to check this ?
  • Congestion in surrounding cells will push traffic load to the problem cell and preventing traffic from it to be shifted to it’s neighbor cell list. By reviewing the neighbor list, you might find additional neighbors that might not to be so congested. NCS (Neighboring Cell Support) is useful tool in OSS that can help identify the right neighbors based on signal strength.


Features

What should I check ?
  • Check the use of congestion relieving features such as Assignments to Worse cell, Cell Load Sharing and HCS ( Hierarchy Cells Structured ).

Where do I look for it ?
  • Run these BSC command RLLOP (Assignments to Worse), RLLCP (CLS) and RLHBP (HCS band) to see the status of the features. Refer to CAN on how these features parameters are used.

Why do I need to check this ?
  • If the cell is incorrectly defined as higher priority level of Hierarchical Cell Strcture or HCS parameters are not being used properly, it will draw in more traffic than other cells.
  • The interference levels will increase if assignment to Worse cell is used, as some mobiles will be closer to a co-channel cell than was intended in the frequency plan. The feature will be more effective if the neighbors are not congested. In a tight network with a high reuse and congestion in a larger area, the feature might only make the situation worse.
  • The number of idle TCH allowed in both the serving and target cell before CLS is evaluated (CLSEVEL and CLSACC) should be based on the number of transceivers in that cell. This is so that cell resources are utilized to its maximum potential before traffic is pushed out of neighboring cells, this can be achieved by doing trials in this feature.





TCH Dimensioning

What should I check ?
  • Check TCH traffic and congestion.

Where do I look for it ?
  • Identify cells that are heavily congested from the STS statistics during busy hours. Review the TCH dimensioning plan and strategy.

Why do I need to check this ?
  • Bad allocation of TCH in a system may cause unnecessary congestion. Investigate if possible to move transceivers from non-congested areas. Of course, the base station type, CDU-type, current number of transceivers, floor space, Combiner type, etc., should be considered before a recommendation to move transceivers could be made.


High Antenna Position

What should I check ?
  • Check antenna height, antenna type and antenna tilt.

Where do I look for it ?
  • Refer to site data and drive test results. If necessary make a site visit.

Why do I need to check this ?
  • A high antenna position could mean a too large service area. Also antennas placed on hilltops will cover large areas. A large coverage area might mean that the cell takes a lot of traffic. Lower antenna if there is no risk for loss of coverage (no coverage at all). Tilting of the antenna or changing antenna type may also decrease the coverage area.



The flowchart above, explains a general approach to investigate TCH Congestion. The next section describe the action points in this flowchart. The reference to each action point is indicated on the flow chart as well.



TCH Availibility

What should I check?
  • Check TCH Availibility and TCH Blocking

Where do I look for it?
  • Use STS counters for TCH performance. The formulas are :

AVAILABLE TCH OF TOTAL NUMBER OF DEFINED TCH

DROPPED TCH CONNECTIONS OF TOTAL NUMBERS OF CALLS TERMINATED IN THE CELL


Why do I need to check this ?
  • Faulty equipment will lead to that all time slots could not be used for handling traffic causing congestion. Low availability can happen if the channels have been manually or automatically blocked and taken out of service. Check the downtime of the cell based on object type ‘DOWNTIME’ is also recommended.


Increasing Traffic Demand

What should I check ?
  • Check if it’s only short-term traffic growth.

Where do I look for ?
Compare traffic trend performance from STS.

Why do I need to check this ?
The high traffic could either be related to an occasional event or due to a long-term growth. Note that by increasing the number of tranceivers may lead to problems with floor space, antenna installations, CDU type, Expansion cabinets and Combiner type.

Load Mean Holding Time

What should I check ?
  • Check Mean Holding Time and Handover Performance.

Where do I look for it ?
  • Look in TCH Mean Holding Time and Handover statistics from STS (refer to next section) :

TCH MEAN HOLDING TIME







Why do I need to check this ?
Too low handover activity might lead to a long mean holding time. A long mean holding time is not a problem, but if there is congestion, new capacity is needed. Increase the number of TCH if no faults.


Low Handover Activity

What should I check ?
  • Check if there is few handover performance and congestion in neighboring cell.

Where do I look for it ?
  • Handover statistic from STS. Check handover parameters such as too high or too low hysteresis values, missing neighbour relations, one-way handover. In addition, review neighboring cell definitions as missing relations could cause handover problems.

Why do I need to check this ?
  • A low handover activity may lead to congestion if the MS is forced to stay on a cell longer than necessary.

Congestion in Surrounding Cells

What should I check ?
  • Check congestion in neighboring cells.s

Where do I need to check this ?
  • Look into STS congestion performance for neighboring cells.
  • Check if Assignments to worse cell is used. If assignment handover to worse cell is used (directed retry). Check the setting of the parameter AWOFFSET.

Why do I need to check this ?
  • Congestion in surrounding cells will push traffic load to the problem cell and preventing traffic from it to be shifted to it’s neighbor cell list. By reviewing the neighbor list, you might find additional neighbors that might not to be so congested. NCS (Neighboring Cell Support) is useful tool in OSS that can help identify the right neighbors based on signal strength.


Features

What should I check ?
  • Check the use of congestion relieving features such as Assignments to Worse cell, Cell Load Sharing and HCS ( Hierarchy Cells Structured ).

Where do I look for it ?
  • Run these BSC command RLLOP (Assignments to Worse), RLLCP (CLS) and RLHBP (HCS band) to see the status of the features. Refer to CAN on how these features parameters are used.

Why do I need to check this ?
  • If the cell is incorrectly defined as higher priority level of Hierarchical Cell Strcture or HCS parameters are not being used properly, it will draw in more traffic than other cells.
  • The interference levels will increase if assignment to Worse cell is used, as some mobiles will be closer to a co-channel cell than was intended in the frequency plan. The feature will be more effective if the neighbors are not congested. In a tight network with a high reuse and congestion in a larger area, the feature might only make the situation worse.
  • The number of idle TCH allowed in both the serving and target cell before CLS is evaluated (CLSEVEL and CLSACC) should be based on the number of transceivers in that cell. This is so that cell resources are utilized to its maximum potential before traffic is pushed out of neighboring cells, this can be achieved by doing trials in this feature.





TCH Dimensioning

What should I check ?
  • Check TCH traffic and congestion.

Where do I look for it ?
  • Identify cells that are heavily congested from the STS statistics during busy hours. Review the TCH dimensioning plan and strategy.

Why do I need to check this ?
  • Bad allocation of TCH in a system may cause unnecessary congestion. Investigate if possible to move transceivers from non-congested areas. Of course, the base station type, CDU-type, current number of transceivers, floor space, Combiner type, etc., should be considered before a recommendation to move transceivers could be made.


High Antenna Position

What should I check ?
  • Check antenna height, antenna type and antenna tilt.

Where do I look for it ?
  • Refer to site data and drive test results. If necessary make a site visit.

Why do I need to check this ?
  • A high antenna position could mean a too large service area. Also antennas placed on hilltops will cover large areas. A large coverage area might mean that the cell takes a lot of traffic. Lower antenna if there is no risk for loss of coverage (no coverage at all). Tilting of the antenna or changing antenna type may also decrease the coverage area.
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