Ericsson Locating Hand Over)

Locating• • • • Introduction Ericsson 1 Ericsson 3 Urgency conditions – Quality – Timing Advance • Auxiliary functions – Intra-cell handover – Hierarchical cell structures © TNC Ltd 2002 Page 110 GSM Radio Network Optimisation v1.3 © Childerley Solutions 2002 110 Locating • 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 © TNC Ltd 2002 Page 111 GSM Radio Network Optimisation v1.3 © Childerley Solutions 2002 111 . making it look worse than it really is.3 What happened to Ericsson 2 ??? Algorithms aim to let TCH carriers control cell borders. This is done by subtracting a signal value from the signal strength estimate for the unwanted cell. SS_ULn = min(P. A penalty is removed after the penalty duration has expired. BSRXMIN) • Application of signal strength penalties © TNC Ltd 2002 Page 112 GSM Radio Network Optimisation v1. © Childerley Solutions 2002 112 . 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 >= MSRXMINn SS_ULn >= BSRXMINn Where SS_DL is estimated by calculating DL path loss and subtracting from maximum MS output power. Penalties are applied for handover failure.Locating • 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. bad quality urgency handover and excessive timing advance.MSTXPWRn) – (BSTXPWRn – SS_DLn) Penalties are added to make it more difficult to handover to unsuitable cells. It would be different for BS pair A.s + TRHYSTn.3 Cells satisfying minimum condition are processed for sufficient condition.C.s SS_ULn >= BSRXSUFFn – TROFFSETn. Sufficient level for a serving cell may be different in relation to each different neighbour cell. Calculation of sufficient level: s=serving cell.B.Locating • Sufficient Level Condition • Threshold separating low signal strength cells from high signal strength cells DL min level UL min level B DL effective sufficient level UL effective sufficient level A high signal strength low signal strength © TNC Ltd 2002 Page 113 GSM Radio Network Optimisation v1. Setup shown in diagram is valid only for BS pair A.s + TRHYSTn.s Solid lines in diagram represent final combined UL and DL condition. n=neighbour cell SS_DLn >= MSRXSUFFn – TROFFSETn. © Childerley Solutions 2002 113 . KHYST is used to decrease ranking values to underrate neighbour cells – to prevent ping pong handovers. The cell border is displaced AWAY from cell with positive value.b = -KOFFSETb. Otherwise. K_ULn) – KOFFSETn. If K-cell.Locating • Ranking – signal strength (K) criterion – Signal strength relative to sufficient level • K-cells = Low signal strength cells.a KOFFSET if positive decreases ranking value and if negative increases ranking value.s = SS_ULn.s KHYSTn. It is defined antisymmetrical for a pair of cells: KOFFSETa. – K values are – K_DLn.s = SS_DLn.s – MSRXSUFFn.3 To rank the serving cell as K or L.a © Childerley Solutions 2002 114 . Defined for a pair of cells and is always symmetrical KHYSTa.s • Cells are ranked with the highest K_RANK first © TNC Ltd 2002 Page 114 GSM Radio Network Optimisation v1. then it is ranked with the other Kcells.s – K_Uln. it is ranked with the L-cells.b = KHYSTb. the sufficient level is evaluated with respect to the best neighbour n1.s • Effective K value is minimum of UL and DL K values modified by KHYST and KOFFSET – K ranking • K_RANKn= min(K_DLn.s – BSRXSUFFn. and moved TOWARD the cell with a negative value. s – SS_DLn. Path Loss criterion is independent of BS and MS power ratings.s + LHYSTn. It facilitates transfer of calls from big cell (strong interference) to small cells (less interference).s = BSTXPWRn.Locating • Ranking – path loss (L) criterion – Path loss is assumed symmetrical • Applied to high signal strength cells – Path Loss values • p_Ln. L-criterion should lower overall statistical interference in network © Childerley Solutions 2002 115 .3 LHYST and LOFFSET have the same properties as the K counterparts.s – L ranking values • L_RANKs = p_Ls • L_RANKn = p_Ln + LOFFSETn.s • Cells are ranked with the lowest L_RANK first © TNC Ltd 2002 Page 115 GSM Radio Network Optimisation v1. Locating • Basic Ranking Candidate List Best cell Highest L-Rank (lowest path loss) L-cells list Lowest L-Rank Highest K-Rank (highest signal level) K-cells list Worst cell Lowest K-Rank © TNC Ltd 2002 Page 116 GSM Radio Network Optimisation v1.3 © Childerley Solutions 2002 116 . © Childerley Solutions 2002 117 . a larger hysteresis value can be allowed than when it is low. When high.s – HYSTn.3 The effects of OFFSET and HYST are similar to those described for Ericsson1.Locating • Ericsson 3 – Considers only signal strength – Ranking values • RANKs = SS_DLs • RANKn = SS_DLn – OFFSETn. LOHYST and HIHYST are symmetrical and OFFSET is anti-symmetrical. HYSTEP specifies when signal strength is high or low for serving cell. defined for a pair of cells. in order to reduce the number of handovers. HYSTEP is a cell parameter.s where • HYST = LOHYST if rxlevDLS < HYSTEP • HYST = HIHYST if rxlevDLS ≥ HYSTEP • HYSTEP indicates Low or High signal strength for serving cell © TNC Ltd 2002 Page 117 GSM Radio Network Optimisation v1. unsuitable neighbours are removed from candidate list. a penalty value PSSBQ and penalty duration PTIMBQ are applied to prevent immediate handover back to the old cell.s – BQOFFSETn. even if the level is good • rxqualUL > QLIMUL or • rxqualDL > QLIMDL – Handover is allowed to cell of lower ranking.a A BQ urgency HO prohibited If BQ urgency handover performed. defines how far from nominal border MS can be to qualify for the quality handover.s remove n. Signal strength of serving cell is compared with signal strength of candidates. applied to K-rank and L-rank values.3 When BQ urgency exists.s – BQOFFSETn.s remove n. If L_RANKn – L_RANKs > LHYSTn. © Childerley Solutions 2002 118 .s remove n. but not to cell with worse quality.Locating • Urgency Condition: Bad Quality – Handover is initiated when rxqual exceeds specified thresholds. Nominal cell border B Hysteresis corridor BQ urgency region BQOFFSETb. Ericsson1 If K_RANKn – K_RANKs < -KHYSTn. and those cells with large differences are removed from the list. Ericsson3 If RANKn – RANKs < -HYSTn. • BQOFFSET.s – BQOFFSETn. © TNC Ltd 2002 Page 118 GSM Radio Network Optimisation v1. a penalty value PSSTA and penalty duration PTIMTA is applied to prevent immediate handover back to the old cell. – TA urgency occurs if TAs ≥ TALIM – Urgent handover is performed to neighbour cells where TAn < TALIMs – If no suitable candidate found. call remains on serving cell © TNC Ltd 2002 Page 119 GSM Radio Network Optimisation v1. maximum (63 bits or 35 km).3 If TA urgency handover performed. to force small cells – TALIM is the defined cell limit. © Childerley Solutions 2002 119 .Locating • Urgency Condition: Timing Advance – Timing advance (TA) can be used as a soft cell limiter. Overlaid/Underlaid: for increasing traffic capacity. The ranking values for candidate neighbour cells are recalculated using reduced hysteresis values. used for directing traffic from higher to lower layers. All calls close to border to cells with low load (below defined threshold) become load sharing candidates. Higher layers to pick up traffic when congestion or coverage problems occur. Cell Load Sharing: enables traffic load sharing during peak traffic when traffic load exceeds a defined threshold. smaller re-use distance possible. and setup is “assignment to better cell”. © Childerley Solutions 2002 120 . Hierachical cells: Up to three layers. Overlaid cell serves smaller area. where a better cell other than the serving cell is found. Extended Range: allows cells with radius up to 72 km.3 Assignment to another cell: performed only a certain period after immediate assignment. where congestion exists on serving or better cell.Locating • Auxiliary network functions – – – – – – Assignment to another cell Hierarchical cell structures Dynamic overlaid/underlaid subcells Intra-cell handover Extended range Cell load sharing © TNC Ltd 2002 Page 120 GSM Radio Network Optimisation v1. this cell is first in the locating candidate list. “assignment to worse cell” can be made. 3 QOFFSETUL/DL: quality offset parameters uplink/downlink SSOFSETUL/DL: signal strength offset parameters uplink/downlink FQSS table RXLEV <=30 31 32-35 36-38 39-41 42-45 46-48 49-52 53-55 56-58 59-62 >=63 rxqual infinity 60 59 58 57 56 55 54 53 52 51 50 © Childerley Solutions 2002 121 .Locating • 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. no pc compensation – FQSS = quality vs signal strength function – Does not work for: • BCCH downlink • Random frequency hopping © TNC Ltd 2002 Page 121 GSM Radio Network Optimisation v1. – Handover to a higher layer if lower layer congested or coverage problems exist – Cells in different layers ranked separately © TNC Ltd 2002 Page 122 GSM Radio Network Optimisation v1.Locating • Hierarchical cell structures – Up to three cell layers • Can be configured as an umbrella layer over a microcell layer • Dual band network can be configured as different layers – Aim to carry most traffic on the smaller/lower layer cells.3 © Childerley Solutions 2002 122 .