Ericsson Locating Hand Over)

8/2/2019 Ericsson Locating Hand Over)

1/13 Childerley Solutions 2002 110

GSM Radio Network Optimisation v1.3Page 110 TNC Ltd 2002

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Introduction Ericsson 1 Ericsson 3 Urgency conditions

Quality Timing Advance

Auxiliary functions

Intra-cell handover Hierarchical cell structures




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Locating Algorithm Works out conditions for handover decisions

for MS in active mode Inputs to algorithm are

Signal strength measurements Quality measurements

Output is list of candidate cells for handover Cells are ranked and sorted in descending order of

preference for handover




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Basic Cell Ranking Two algorithms

Ericsson 1: signal strength & path loss Ericsson 3: signal strength only

Common process stages Correction of base station output power

different levels possible on BCCH/TCH carriers

Calculation of minimum signal strength Thresholds MSRXMIN (DL) and BSRXMIN (UL)

SSmin = min (MSRXMIN, BSRXMIN) Application of signal strength penalties

What happened to Ericsson 2 ???Algorithms aim to let TCH carriers control cell borders.

Corrected signal strength SS_DLn in neighbour cell n: for different output powers

between BCCH (BSPWR) and other carriers BSTXPWR:SS_DLn = rxlevn + BSTXPWRn BSPWRn

Minimum signal strength conditions:SS_DLn >= MSRXMINnSS_ULn >= BSRXMINn

Where SS_DL is estimated by calculating DL path loss and subtracting frommaximum MS output power.

SS_ULn = min(P,MSTXPWRn) (BSTXPWRn SS_DLn)Penalties are added to make it more difficult to handover to unsuitable cells. This isdone by subtracting a signal value from the signal strength estimate for the unwantedcell, making it look worse than it really is. Penalties are applied for handover failure,bad quality urgency handover and excessive timing advance. A penalty is removedafter the penalty duration has expired.




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Sufficient Level Condition Threshold separating low signal strength cells from

high signal strength cells

high signalstrength

low signal strength

DL min levelUL min level

DL effective sufficient level

UL effective sufficient level

B

A

Cells satisfying minimum condition are processed for sufficient condition.

Calculation of sufficient level: s=serving cell, n=neighbour cellSS_DLn >= MSRXSUFFn TROFFSETn,s + TRHYSTn,sSS_ULn >= BSRXSUFFn TROFFSETn,s + TRHYSTn,s

Solid lines in diagram represent final combined UL and DL condition.Sufficient level for a serving cell may be different in relation to each differentneighbour cell. Setup shown in diagram is valid only for BS pair A,B. It wouldbe different for BS pair A,C.




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Ranking signal strength (K) criterion Signal strength relative to sufficient level

K-cells = Low signal strength cells, K values are

K_DLn,s = SS_DLn,s MSRXSUFFn ,s K_Uln,s = SS_ULn,s BSRXSUFFn ,s

Effective K value is minimum of UL and DL K valuesmodified by KHYST and KOFFSET

K ranking K_RANKn= min(K_DLn, K_ULn) KOFFSET n,s -

KHYST n,s Cells are ranked with the highest K_RANK first

To rank the serving cell as K or L, the sufficient level is evaluated withrespect to the best neighbour n1. If K-cell, then it is ranked with the other K-cells. Otherwise, it is ranked with the L-cells.

KHYST is used to decrease ranking values to underrate neighbour cells toprevent ping pong handovers. Defined for a pair of cells and is alwayssymmetrical KHYSTa,b = KHYSTb,aKOFFSET if positive decreases ranking value and if negative increasesranking value. The cell border is displaced AWAY from cell with positivevalue, and moved TOWARD the cell with a negative value. It is defined anti-symmetrical for a pair of cells: KOFFSETa,b = -KOFFSETb,a




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Ranking path loss (L) criterion Path loss is assumed symmetrical

Applied to high signal strength cells

Path Loss values p_Ln,s = BSTXPWRn,s SS_DLn,s

L ranking values L_RANKs = p_Ls L_RANKn = p_Ln + LOFFSET n,s + LHYST n,s Cells are ranked with the lowest L_RANK first

LHYST and LOFFSET have the same properties as the K counterparts.

Path Loss criterion is independent of BS and MS power ratings. It facilitatestransfer of calls from big cell (strong interference) to small cells (lessinterference). L-criterion should lower overall statistical interference innetwork




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Basic Ranking Candidate List

L-cells list

K-cells list

Best cell

Worst cell

Highest L-Rank(lowest path loss)

Lowest L-Rank

Highest K-Rank(highest signal level)

Lowest K-Rank




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Ericsson 3 Considers only signal strength Ranking values

RANKs = SS_DLs RANKn = SS_DLn OFFSET n,s HYST n,swhere HYST = LOHYST if rxlevDL S < HYSTEP HYST = HIHYST if rxlevDL S HYSTEP

HYSTEP indicates Low or High signal strength forserving cell

The effects of OFFSET and HYST are similar to those described forEricsson1.HYSTEP specifies when signal strength is high or low for serving cell. When

high, a larger hysteresis value can be allowed than when it is low, in order toreduce the number of handovers.LOHYST and HIHYST are symmetrical and OFFSET is anti-symmetrical,defined for a pair of cells. HYSTEP is a cell parameter.




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Urgency Condition: Bad Quality Handover is initiated when rxqual exceeds

specified thresholds, even if the level is good rxqualUL > QLIMUL or rxqualDL > QLIMDL

Handover is allowed to cell of lower ranking,but not to cell with worse quality.

BQOFFSET , applied to K-rank and L-rank values,defines how far from nominal border MS can be to

qualify for the quality handover.

When BQ urgency exists, unsuitable neighbours are removed from candidate list.Signal strength of serving cell is compared with signal strength of candidates, andthose cells with large differences are removed from the list.

Ericsson1If K_RANKn K_RANKs < -KHYSTn,s BQOFFSETn,s remove n.If L_RANKn L_RANKs > LHYSTn,s BQOFFSETn,s remove n.

Ericsson3If RANKn RANKs < -HYSTn,s BQOFFSETn,s remove n.

If BQ urgency handover performed, a penalty value PSSBQ and penalty durationPTIMBQ are applied to prevent immediate handover back to the old cell.

ABHysteresis corridor BQ urgency HO

prohibited

BQ urgency region

BQOFFSETb,aNominal cell border




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Urgency Condition: Timing Advance Timing advance (TA) can be used as a soft cell

limiter, to force small cells TALIM is the defined cell limit, maximum (63

bits or 35 km). TA urgency occurs if TAs TALIM Urgent handover is performed to neighbour

cells where TAn < TALIMs

If no suitable candidate found, call remains onserving cell

If TA urgency handover performed, a penalty value PSSTA and penaltyduration PTIMTA is applied to prevent immediate handover back to the oldcell.




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Auxiliary network functions Assignment to another cell Hierarchical cell structures Dynamic overlaid/underlaid subcells Intra-cell handover Extended range Cell load sharing

Assignment to another cell: performed only a certain period after immediateassignment.where a better cell other than the serving cell is found, this cell is first in the

locating candidate list, and setup is assignment to better cell.where congestion exists on serving or better cell, assignment to worse cell

can be made.Hierachical cells: Up to three layers, used for directing traffic from higher tolower layers. Higher layers to pick up traffic when congestion or coverageproblems occur.Overlaid/Underlaid: for increasing traffic capacity. Overlaid cell servessmaller area, smaller re-use distance possible.Extended Range: allows cells with radius up to 72 km.

Cell Load Sharing: enables traffic load sharing during peak traffic whentraffic load exceeds a defined threshold. All calls close to border to cells withlow load (below defined threshold) become load sharing candidates. Theranking values for candidate neighbour cells are recalculated using reducedhysteresis values.




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Intra-cell handover Try to find another frequency and/or timeslot

in the same cell with better quality Only if RxQual is bad AND RxLev is good

RxQual_UL/DL > QOFFSETUL/DL +FQSS (RXLEV_UL/DL +SSOFSETUL/DL)

RxLev_DL/UL = actual measured signal strengths, nopc compensation

FQSS = quality vs signal strength function

Does not work for:

BCCH downlink Random frequency hopping

QOFFSETUL/DL: quality offset parameters uplink/downlinkSSOFSETUL/DL: signal strength offset parameters uplink/downlink

FQSS tableRXLEV rxqual

=63 50


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Hierarchical cell structures Up to three cell layers

Can be configured as an umbrella layer over amicrocell layer

Dual band network can be configured as differentlayers

Aim to carry most traffic on the smaller/lowerlayer cells.

Handover to a higher layer if lower layer

congested or coverage problems exist Cells in different layers ranked separately

Ericsson Locating Hand Over)

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