Selasa, 01 Desember 2009

Handover Analysis

Handover is an important function, which shows the integrity of the GSM network. If the handover performance is poor, the subscriber will perceive the quality of the network as bad.

Probable Reason of Bad Handover Performance

Bad locating parameter settings

Bad setting might cause the locating will not rank the best cell as a candidate

Uplink interference

Incoming handover failed as the target cell could not decode the handover burst message from the mobile

Missing measurement frequency in BA-list

Prevent any handover to affected neighbor cells

Extra measurement frequency

Can provide inaccuracy of measurement for handover decisions

Co-Channel and Co-BSIC

Measurement result from neighbors can not be distinguished and MS may perform a handover to the wrong cell.

Unnecessary neighbor relation

None or few handover might indicate a unsuitable neighbor relation.

HW faults

Can cause bad neighbor relation.

Permitted NCC (network color code)

Missing NCC of the neighbors will not allow any handover.

Wrong use of HCS parameters

Cause unnecessary handover

Congestion

High congestion might lead to dragged calls (handover performed at a not intended location) a lot of unsuccessful handover.

ho1
Handover Analysis Flowchart.


The following procedure should be performed for handover analysis:

- Check the successful handover per cell

- Check for the handover success rate below certain criteria for example X%. If it doesn’t meet the criteria and change the X% to a higher value and check for the next cell.

- Check the handover activity from the number of handover performed. If the number is above certain value for example Y and then take into consideration.

- Check the site location, whether the site to site distance or co-sited. (Good map is needed here).

- Check whether the cell is isolated or not, if already known problem of no dominant serving cell and take other cell.

- Check the handover flow whether is balance between incoming and outgoing.

- Check the difference performance of incoming and outgoing handover. This is to ensure the priority for more problem direction.

- Focus on the bad direction.

- Check the worst relation and pick one cell.

- Check the cell whether it is external or internal. If external, start inter-BSC analysis.

- If the cell is internal, check the high ratio of lost handover, urgency handover and reversion.

- If one of them is yes, check the uplink & downlink interference problem.

- Check the frequency plan. There might be problem on co-channel or adjacent channel.

- Check the handover related parameters such as relation, BA-list, BSIC, hysteresis, offsets etc.

- Check if many Ping-Pong handover.

- Check if assignment handover are used.

- Check if cell has HW problem. If problem found, swap or repair hardware.

- Check if congested target cell. If the target cell is congested and then solve the congestion by adding TRU.

- Perform measures to improve HO performance. This is the assumption comes from the above analysis.

No or Few Handover Attempts

ho2
No or Few Handover Attempt Flowchart.


The following procedure should be performed for no or few handover attempts:

- Check the neighbor relation with low traffics (less than 10% of average number of handover per relation) and unbalance relations.

- Check from the unbalance relation whether the target cell is congested, if congested, solves the congestion problem.

- Check the missing measurement frequency (MBCCHNO) in Double BA-list in active list (if yes, add the measurement frequency in the BA-list.

- Check unnecessary neighbor cell relations and if found, remove unnecessary relations.

- Check NCCPERM, if NCC of the neighbor is missing, add the NCC of the neighbor list into the NCCPERM list.

- Check the setting of the cells whether they are set in different layer of HCS. (Layer 1 is the highest priority)

- Check if the cell is at the inter BSC border, if so , check the inter BSC HO performance (SIEMENS System).

- Check locating parameters and list out.

- Check the poor setting of parameter and if so, correct the parameter setting

- Check BTS definition (RX commands especially RXMOP).

- Check if BTS is defined but might not be in service. If yes, correct parameter setting or deblock it.

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