2 Locating

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END TECHNOLOGIES www.legend-technologies. Handover (Locating)

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2 Locatingjj

Transcript of 2 Locating

Slide 1

Handover (Locating)LEGEND TECHNOLOGIESwww.legend-technologies.orgHandover (Locating) Algorithm

The Handover (Locating) Algorithm is the basic feature to provide mobility in the Radio Network.

Aims At? i) Keep the continuity of a current call with acceptable quality. ii) Cell size control in-order to decrease total interference in the system.

Implemented where? In the BSC.

Location process initiated when? After Hand Over (HO), Assignment or Immediate Assignment.

Inputs to the Algorithm? Signal Strength & Quality measurements for serving cell and Signal Strength measurements for neighbor cells.

Output from the Algorithm? List of candidates which the algorithm judges to be possible candidates for HO (List of HO candidates are ranked and sorted in descending order)

LEGEND TECHNOLOGIESwww.legend-technologies.orgHandover (Locating) Algorithm

What types of Handover (locating) algorithm we have?

i) SS & Path Loss based Algorithm: Follows the GSM specifications. HO decision is taken based on both Signal Strength (SS) and Path Loss.

ii) SS based Algorithm: HO decision is taken based on Signal Strength only and this leads to better performance. It is less complex, uses less parameters and easy to be maintained in the Radio Network.

LEGEND TECHNOLOGIESwww.legend-technologies.orgHandover (Locating) AlgorithmThe main Flow of the Handover (locating) Algorithm goes as follow:

FilteringBasic RankingUrgency Conditions HandlingInitiationsAuxiliary Radio Network Features EvaluationOrganizing the ListSending the List & Allocation ReplyLEGEND TECHNOLOGIESwww.legend-technologies.orgHandover (Locating) Algorithm

InitiationFiltering.Basic Ranking.Urgency Conditions Handling.Auxiliary Radio Network Features Evaluation.Organizing the List.Sending the List & Allocation Reply

LEGEND TECHNOLOGIESwww.legend-technologies.orgInitiation of the Handover (Locating) Process/AlgorithmThe Locating Process is initiated when one of the following occurs:

Handover: Normal, Intra Cell HO (IHO), Sub-cell change (OLUL or ULOL)

Assignment: You completed call setup on SDCCH and youre assigned a TCH channel to talk on.

Immediate assignment: You are assigned SDCCH to make call setup, or a TCH to make call setup on when no free SDCCH channels exist.

LEGEND TECHNOLOGIESwww.legend-technologies.org6Initiation of the Handover (Locating) Process/Algorithm

Handover on SDCCH can be enabled/disabled based on parameter SCHO

At initiation of Locating after successful HO, Assignment or Immediate assignment a timer TINIT starts which will disable HO for some time until it expires.

The reason is to leave the connection on the current channel for some time until the locating algorithm produces reliable results we can rely on.

TINIT will disable HO only, but Assignment on own or other cell will occur normally and will not wait TINIT till expired.

TINIT is a BSC parameter not a cell parameter and it measured in SACCH periods.

LEGEND TECHNOLOGIESwww.legend-technologies.orgThis is to decrease the call setup time and to free the SDCCH fast.

7Handover (Locating) Algorithm

InitiationFilteringBasic Ranking.Urgency Conditions Handling.Auxiliary Radio Network Features Evaluation.Organizing the List.Sending the List & Allocation Reply

LEGEND TECHNOLOGIESwww.legend-technologies.orgFiltering

Simply it is the process of collecting the required data on Signal Strength (SS), Quality and Time Advance (TA) for serving and neighbor cells and average these consecutive measurements over a specified period to rank these cells.

This is accomplished in two steps:Measurements preparationSS, Quality and TA filtering

LEGEND TECHNOLOGIESwww.legend-technologies.orgFilteringMeasurements preparation

Data that is measured:

The MS can measure the SS of up to 32 neighbors but only the six strongest neighbors (which it succeeded to decode its BSIC over the last 10 seconds) are reported and considered candidates for HO.

Cell on which measurements are reportedMeasured QuantityWho makes the measurements?Serving CellSS DLMSQuality DL (rxqual_DL)MSQuality UL (rxqual_UL)BTSSS UL (only in some special cases)MSTABTS6 Strongest neighbor cellsSS DLMSTABTSSS UL (only in some special cases)MSLEGEND TECHNOLOGIESwww.legend-technologies.orgFilteringMeasurements Preparation

SS measurements are delivered as integer values 0 63 corresponds to real SS from -110 dBm -47 dBm

Quality is measured based on the BER and it may be represented in two forms:Integers 0 (Best) 7 (Worst)Decitransformed Quality units (dtqu) from 0 (Best) 70 (Worst)

Time Advance (TA) is reported as values between 0 63 bitsN.B: If TA=1 then the MS is at nearly 0.5 km from the cell

LEGEND TECHNOLOGIESwww.legend-technologies.orgFiltering

SS, Quality and TA filtering:

The consecutive measurements for SS, Quality and TA are averaged in some way based on the equation of the filter used.

Weve 5 Types of Filters that may be used, each one has its own equation or its way to produce output results from the collected consecutive measurements:General FIR filtersRecursive Straight Average filterRecursive exponential filterRecursive 1st order Butterworth filterMedian filter

LEGEND TECHNOLOGIESwww.legend-technologies.orgFiltering

SS, Quality and TA filtering:

In addition to the way each filter use to produce output results from the consecutive measurements, each filter has what we call filter length which is the period over which measurements are considered.

We have controlling parameters on cell basis to select the type of filter used and the length of the filter.

Also the type of the filter used in signaling (call setup) and dedicated phases may be configured separately as well see.

LEGEND TECHNOLOGIESwww.legend-technologies.orgFiltering

SS, Quality and TA filtering:

2-i) Signal Strength Filters controlling parameters

SSEVALSI Selects the Type of the filter that will be used during Signaling phase.SSEVALSD Selects the Type of the filter that will be used during Connection phase.SSLENSI Selects the Length of the filter that will be used during Signaling phase.SSLENSD Selects the Length of the filter that will be used during Connection phase.

N.B: SSLENSI&SSLENSD are measured in the form of SACCH periods, i.e. if SSLENSD=10, then the length of the filter during the connection phase = 10*0.12 sec = 1.2 seconds

LEGEND TECHNOLOGIESwww.legend-technologies.orgFiltering

SS, Quality and TA filtering:

2-ii) Quality Filters controlling parameters

QEVALSI Selects the Type of the filter that will be used during Signaling phase.QEVALSD Selects the Type of the filter that will be used during Connection phase.QLENSI Selects the Length of the filter that will be used during Signaling phase.QLENSD Selects the Length of the filter that will be used during Connection phase.

N.B: QLENSI&QLENSD are measured in the form of SACCH periods, i.e. if QLENSD=10, then the length of the filter during the connection phase = 10*0.12 sec = 1.2 seconds

LEGEND TECHNOLOGIESwww.legend-technologies.orgFiltering

SS, Quality and TA filtering:

2-iii) Time Advance (TA) controlling parameters

One single type of filters is used which is the Recursive Straight Average Filter and the length of the filter is specified by parameter TAAVELEN which is also measured in SACCH periods.

LEGEND TECHNOLOGIESwww.legend-technologies.orgHandover (Locating) Algorithm

InitiationFilteringBasic RankingUrgency Conditions Handling.Auxiliary Radio Network Features Evaluation.Organizing the List.Sending the List & Allocation Reply

LEGEND TECHNOLOGIESwww.legend-technologies.orgBasic Ranking

It is called Basic coz in this stage ranking is done before handling the urgency conditions and evaluation of the auxiliary radio network features.

As mentioned earlier, two algorithms are available for basic ranking (SS&Path loss based Algorithm and SS based Algorithm) and theyre selected according to the parameter EVALTYPE

EVALTYPE=1, SS & Path loss based Algorithm is used for basic ranking taking into consideration both Signal Strength measurements and the path loss.

EVALTYPE=3, SS based Algorithm is used for basic ranking taking into consideration Signal Strength measurements only.

LEGEND TECHNOLOGIESwww.legend-technologies.orgBasic Ranking

Basic Ranking Algorithm following the SS based Algorithm will be done on four steps:

Correction of Base Station output power. Common for Evaluation of the minimum signal strength condition for neighbors. both AlgorithmsSubtraction of signal strength penalties.Rank the Candidates after applying Offsets and Hysteresis.

LEGEND TECHNOLOGIESwww.legend-technologies.orgBasic Ranking

Basic Ranking Algorithm following the SS based Algorithm

Correction of Base Station output power

The location algorithm aims at making the Pure traffic frequencies to control the cell borders and not the BCCH frequencies, coz most of the time the seized TCH Time slot will be located on a TCH frequency.

BSPWR is a parameter to set the output power of the BCCH carrier and BSTXPWR is a parameter to set the output power of the TCH frequencies.

Correction for the output power will done for both: (A-i) Correction for Neighbor Cells. (A-ii) Correction for Serving Cell.

LEGEND TECHNOLOGIESwww.legend-technologies.orgBasic Ranking

Basic Ranking Algorithm following the SS based Algorithm

Correction of Base Station output power

(A-i) Correction for Neighbor Cells

The MS is informed by the BCCH frequencies of the neighbors cells on which he has to perform his measurements.

SS_corrected_DLneighbor = SS_measured_DLneighbor - ( BSPWR - BSTXPWR )

LEGEND TECHNOLOGIESwww.legend-technologies.orgBasic Ranking

Basic Ranking Algorithm following the SS based Algorithm

Correction of Base Station output power

(A-ii) Correction for Serving Cell

TCH Time Slot (TS) is on the BCCH frequency SS_corrected_DLservingcell = SS_measured_DLservingcell - ( BSPWR - BSTXPWR )

TCH TS is hopping between a BCCH frequency and a TCH frequency:SS_corrected_DLservingcell = SS_measured_DLservingcell - ( BSPWR - BSTXPWR )/N , Where N is the no. of the hopping frequencies

TCH TS is on the OL (Over Laid sub cell)SS_corrected_DLUnderLaid = SS_measured_DLOverLaid+ ( BSPWRUnderLaid - BSTXPWROverLaid )

LEGEND TECHNOLOGIESwww.legend-technologies.orgBasic Ranking

Basic Ranking Algorithm following the SS based Algorithm

Evaluation of the minimum Signal Strength condition for Neighbors

Not all the neighbors are allowed to be ranked!!The neighbor should pass the minimum signal strength condition in order to be ranked.SS_corrected_DLneighbor will be compared with respect to parameter called MSRXMIN, If SS_corrected_DLneighbor MSRXMIN this neighbor will be included in rankingIf SS_corrected_DLneighbor < MSRXMIN this neighbor will be excluded from ranking

If UL measurements are included then SS_corrected_ULneighbor will be compared with respect to parameter called BSRXMIN, If SS_corrected_ULneighbor BSRXMIN this neighbor will be included in rankingIf SS_corrected_ULneighbor < BSRXMIN this neighbor will be excluded from ranking

LEGEND TECHNOLOGIESwww.legend-technologies.orgBasic Ranking

Basic Ranking Algorithm following the SS based Algorithm

Evaluation of the minimum Signal Strength condition for Neighbors

Example: Assume that a MS is connected to cell A that has five neighbors B,C,D,E&F, the MSRXMIN for all the cells is -104 dBm and the SS_corrected_DLneighbor for each cell after correcting the BTS o/p power is given in the below Table

NeighborsSS_corrected_DLneighborB-85 dBmC-110 dBmD-87 dBmE-70 dBmF-100 dBm Cell C will be excluded from ranking and wont be considered in the next stage and the MS will never HO to itLEGEND TECHNOLOGIESwww.legend-technologies.orgBasic Ranking

Basic Ranking Algorithm following the SS based Algorithm

Subtraction of signal strength penalties

Penalties or Punishments will be applied on cells that are for some reasons temporarily undesirable.

A Penalty value will decrease the rank of some cells for certain penalty time.

SS_punished_DL = SS_corrected_DL Locating Penalties HCS Penalties

In the coming slides well talk about the two types of penalties:(C-i) Locating Penalties(C-ii) HCS Penalties

LEGEND TECHNOLOGIESwww.legend-technologies.orgBasic Ranking

Basic Ranking Algorithm following the SS based Algorithm

Subtraction of signal strength penalties

(C-i) Locating Penalties

1) Due to HO failure: If HO to a neighbor cell failed then weve to apply a penalty value for some time on this neighbor so when basic ranking is done again we dont go back to this cell. Penalty value will be configured using parameter PSSHF (default 63 dB) Penalty time will be configured using parameter PTIMHF (default 5 sec)

LEGEND TECHNOLOGIESwww.legend-technologies.orgBasic Ranking

Basic Ranking Algorithm following the SS based Algorithm

Subtraction of signal strength penalties

(C-i) Locating Penalties

2) Due to Bad Quality (BQ) Urgency HO:If a cell was abandon due to BQ, then it should have been the best cell from SS point of view so without penalties using the basic ranking well be back to this cell.Penalty value will be configured using parameter PSSBQ (default 7 dB) Penalty time will be configured using parameter PTIMBQ (default 5 seconds)

3) Due to Excessive TA Urgency HO:Handled in the same manner like the BQ case.Penalty value will be configured using parameter PSSTA (default 63 dB) Penalty time will be configured using parameter PTIMTA (default 30 seconds)

LEGEND TECHNOLOGIESwww.legend-technologies.orgBasic Ranking

Basic Ranking Algorithm following the SS based Algorithm

Subtraction of signal strength penalties

(C-ii) HCS Penalties

It is related to the HCS (Hierarchical Cell Structure) feature when a MS is detected as a fast moving mobile.

A penalty will be applied on lower layer cells so in ranking we will prioritize cells in the same layer of the serving cell and cells in higher layers and in this way unnecessary HOs are prevented ( ex: layer2 cells will be prioritized than layer1 cells)

LEGEND TECHNOLOGIESwww.legend-technologies.orgBasic RankingBasic Ranking Algorithm following the SS based Algorithm

Rank the Candidates after applying Offsets and Hysteresis

Ranking for neighbor cells will be done after applying Offsets and Hysteresis.

Offset: Displace the cell border as compared to The border strictly given by SS.Controlling parameter: OFFSET (default: zero dBm)

Hysteresis: To reduce the risk of ping pong HO a region for Hysteresis is applied around the cell border.

LEGEND TECHNOLOGIESwww.legend-technologies.orgBasic Ranking

Basic Ranking Algorithm following the SS based Algorithm

Rank the Candidates after applying Offsets and Hysteresis

If the Hysteresis value is too high there will be a risk that the MS will be connected to the cell of low SS for long time and if the Hysteresis is too low then there will be a risk that ping pong HOs occur.

So the applied value of Hysteresis will be variable based on the received SS of the serving cell.

SS_corrected_DLservingcell will be compared to value HYSTSEP (default -90 dBm),If SS_corrected_DLservingcell > HYSTSEP, then the serving cell is strong enough and high value of Hysteresis will be applied such that Hysteresis value=HIHYST (default 5 dBm)If SS_corrected_DLservingcell < HYSTSEP, then the serving cell is not strong enough and low value of Hysteresis will be applied such that Hysteresis value=LOHYST (default 3 dBm)

LEGEND TECHNOLOGIESwww.legend-technologies.orgBasic Ranking

Basic Ranking Algorithm following the SS based Algorithm

Rank the Candidates after applying Offsets and Hysteresis

SS_corrected_DLservingcell > HYSTSEP

HYST=HIHYST

Now, Rankservingcell = SS_corrected_DLservingcell Rankneighbor= SS_punished_DLneighbor OFFSETneighbor HYSTneighbor

HYST=LOHYSTOutput from Basic RankingLEGEND TECHNOLOGIESwww.legend-technologies.orgHandover (Locating) Algorithm

InitiationFilteringBasic RankingUrgency Conditions HandlingAuxiliary Radio Network Features Evaluation.Organizing the List.Sending the List & Allocation Reply

LEGEND TECHNOLOGIESwww.legend-technologies.orgUrgency Conditions Handling

After the Basic Ranking stage a check is made on the serving cell to know if Urgency conditions are detected or not.

We have two types of Urgency HO:Bad Quality (BQ) Urgency HOExcessive Time Advance (TA) Urgency HO

If Urgency conditions are detected then the serving cell should be abandon as fast as possible, but some of the neighbors will be removed from the candidate list and the MS will not be able to HO to them as we will see later.

As seen before, cells that were abandon due to Urgency HO will be subjected to punishment/penalty.

LEGEND TECHNOLOGIESwww.legend-technologies.orgUrgency Conditions Handling

Bad Quality (BQ) Urgency HO

The Quality measured at the DL and UL for the serving cell will be compared with two parameters QLIMDL & QLIMUL (default 50 dtqu) and if:rxqual_DL > QLIMDLrxqual_UL > QLIMUL

The Quality may drop like that as a result of Co-Channel Interference or when the SS became very low.

When Urgency condition is detected the MS has to leave the cell and make HO to other cell, but in this case the serving cell is the one that has the highest SS so the MS has to HO to a cell of worse SS, but is the MS allowed to HO to any worse cell?

Or Urgency HO due to BQ should be performedLEGEND TECHNOLOGIESwww.legend-technologies.orgUrgency Conditions Handling

Bad Quality (BQ) Urgency HO

Is the MS allowed to HO to any worse cell? No, this will be based on a parameter called BQOFFSET which will ensure that far neighbors wont be selected.

If Rankservingcell Rankneighbor < BQOFFSET, then this neighbor is near to the serving cell and it is not much worse than the serving cell and it can be candidate for HO.

If Rankservingcell Rankneighbor > BQOFFSET, then this neighbor is far from the serving cell and it will be removed from the candidate list.

Ex: If Urgency condition is detected where Rankservingcell = -75 dBm and the neighbors: RankB = -79 dBm ,RankC = -90 dBm ,RankD = -87 dBm and BQOFFSET=5dBRankservingcell RankB = 4dB < BQOFFSET= 5dB Cell B is kept in the candidate listRankservingcell RankC = 15dB > BQOFFSET= 5dB Cell C is removed from the candidate listRankservingcell Rank = 8dB > BQOFFSET= 5dB Cell D is removed from the candidate list

LEGEND TECHNOLOGIESwww.legend-technologies.orgUrgency Conditions Handling

Excessive Time Advance (TA) Urgency HO

TA can be used as a measure for the distance between the BTS and the MS.

If TA > TALIM (63 bits) Urgency HO due to TA is initiated.

LEGEND TECHNOLOGIESwww.legend-technologies.orgAfter Basic Ranking and Evaluation of the Urgency Conditions, the Serving cell and Neighbor cells will be divided into 3 Groups

Categorization #1

Better CellServing CellWorse CellLEGEND TECHNOLOGIESwww.legend-technologies.orgHandover (Locating) Algorithm

InitiationFilteringBasic RankingUrgency Conditions HandlingAuxiliary Radio Network Features EvaluationOrganizing the List.Sending the List & Allocation Reply

LEGEND TECHNOLOGIESwww.legend-technologies.orgAuxiliary Radio Network Features Evaluation

Assignment to Another Cell EvaluationCell Load Sharing EvaluationOver Laid/Under Laid sub-cell EvaluationIHO EvaluationHCS Evaluation

After these Evaluations, some candidates will be removed from the HO candidate list andCategorization#2 will be performed.

LEGEND TECHNOLOGIESwww.legend-technologies.orgAuxiliary Radio Network Features EvaluationAssignment to Another Cell Evaluation

The Locating Algorithm may be initiated after immediate assignment to know whether it is better for the MS to take a TCH time slot on the current cell or not.

If during the signaling phase a better cell was found after ranking then Assignment to Better Cell will be initiated.

If during the signaling phase no better cell was found, then the MS will normally be assigned a TCH time slot on the current cell.

If the Better/Serving cells were congested then Assignment to Worse Cell will be done.

LEGEND TECHNOLOGIESwww.legend-technologies.orgAuxiliary Radio Network Features EvaluationAssignment to Another Cell Evaluation

Is the MS allowed to take TCH time slot on any worse cell? No, this will be based on a parameter called AWOFFSET which will ensure that far neighbors wont be selected.

Only if Rankservingcell Rankneighbor < AWOFFSET, then this neighbor is near to the serving cell and it is not much worse than the serving cell and assignment to it can be done.

If Rankservingcell Rankneighbor > AWOFFSET, then this neighbor is far from the serving cell and it will be removed from the candidate list.

LEGEND TECHNOLOGIESwww.legend-technologies.orgAuxiliary Radio Network Features EvaluationCell Load Sharing (CLS) Evaluation

This feature is used to reduce congestion on the serving cell.When CLS is activated and the load on the serving cell becomes higher than certain threshold then:Valid CLS HO candidates are definedRe-calculation of their ranking values will be performed.

LEGEND TECHNOLOGIESwww.legend-technologies.orgAuxiliary Radio Network Features EvaluationCell Load Sharing (CLS) Evaluation

Valid CLS HO candidates are defined as follow:Worse cells: Coz if they were better then theyll be chosen at Basic RankingLoad on neighbor cells < CLS load thresholdInternal cells: lies in the same BSCSame Layer

Re-calculation of their ranking values will be performedWere going to recalculate the Ranking values of the valid CLS neighbors with reduced Hysteresis so these worse neighbors will appear with higher SS than they really are and the MS can make HO to them and relief the congestion on the current cell.

LEGEND TECHNOLOGIESwww.legend-technologies.orgAuxiliary Radio Network Features EvaluationOL/UL Sub-Cell Evaluation

The OL/UL feature provides a way of increasing the traffic capacity in a cellular network without building new sites.

Since OL subcell serves smaller area than the corresponding UL subcell a smaller reuse distance can be used in in the OL subcell than in the under laid.

The OL/UL evaluation may result in a recommendation to change the subcell from the one currently in use, this evaluation is based on:DL SS, TA serving Cell, Distance to cell border, Traffic Load in the cell

This feature will be discussed in details afterwards.

LEGEND TECHNOLOGIESwww.legend-technologies.orgAuxiliary Radio Network Features EvaluationIntra Cell HO (IHO) Evaluation

The IHO feature provides a way to improve the speech quality during the conservation when bad quality is detected while the SS is high.

This is can be accomplished by changing the channel the connection is currently using within the same cell.

LEGEND TECHNOLOGIESwww.legend-technologies.orgAuxiliary Radio Network Features EvaluationHierarchical Cell Structure (HCS) Evaluation

The HCS feature provides the possibility to give priority to cells that are not strongest but provide sufficient SS.

The priority of a cell is given by associating a layer to the cell.

We have 8 layers from layer 1 (Highly prioritized) to layer 8 (least prioritized).

Micro cells are prioritized than Macro cells for capacity purposes.

Cells of lower layers will be ranked higher than cells of higher layers in the HO candidate list.

LEGEND TECHNOLOGIESwww.legend-technologies.orgAfter the Auxiliary Radio Network features evaluation some candidates may be prioritized and the order of the candidate list will be modified. The Serving cell and Neighbor cells will be divided into 3 Groups

Categorization #2

Above SServing Cell (SC)Below SLEGEND TECHNOLOGIESwww.legend-technologies.orgHandover (Locating) Algorithm

InitiationFilteringBasic RankingUrgency Conditions HandlingAuxiliary Radio Network Features EvaluationOrganizing the ListSending the List & Allocation Reply

LEGEND TECHNOLOGIESwww.legend-technologies.orgOrganizing the List

The final list will contain maximum up to six neighbors + the serving cell and categorized as follows: Serving Cell (SC), Above S, Below S

To reach the final form before sending the list the following steps will be done:Removal of CandidatesOrdering the Candidate list based on the Current Conditions.

LEGEND TECHNOLOGIESwww.legend-technologies.orgOrganizing the List

Removal of Candidates Some Candidates may be removed coz:

The Frequency band of the Candidate cell is not supported by the MS.

Some Controlling timers are active and preventing HO to certain cell:TALLOC: This timer prevents HO on a target cell for some time after assignment/HO failure due to congestion on target cell. (N.B: No penalties are applied on this cell)

TURGEN: This timer prevents HO on a target cell for some time after urgency HO failure due to congestion on target cell.

LEGEND TECHNOLOGIESwww.legend-technologies.orgWe saw timers to prevent HO after HO success (At initiation) TINITWe saw timers through which the penalties are active PTIMHF(HO Signaling failure), PTIMBQ, PTIMTA50Organizing the List

Ordering the Candidate list based on the Current Conditions

Means what? Means in what order the 3 categories (Above S, S, Below S) will be arranged before sending the candidate list. This will be based on some condition flags.Condition flags: 1 Assignment Request Arrived 2 Assignment to Worst Cell is in use 3 Excessive TA detected 4 BQ Urgency HO 5 OL/UL Subcell load change or IHO

LEGEND TECHNOLOGIESwww.legend-technologies.orgOrganizing the ListOrdering the Candidate list based on the Current ConditionsCondition flags: 1 Assignment Request Arrived 2 Assignment to Worst Cell is in use 3 Excessive TA detected 4 BQ Urgency HO 5 OL/UL Subcell load change or IHO

CaseCondition FlagsOrderingComment1234510x000Above SNormal Case20x010Above S Below SServing Cell has BQ so it should be abandon either to the Above S or Below S cell310000Above S SAn Assignment request came and the AW flag is not raised411000Above S S Below SAn Assignment request came and the AW flag is raised50x011Above S S Below SServing Cell has BQ so it should be abandon but coz the OL/UL subcell change flag is raised, then the serving cell is included coz this subcell change may solve the issue with no need to go for a below worse cellLEGEND TECHNOLOGIESwww.legend-technologies.orgHandover (Locating) Algorithm

InitiationFilteringBasic RankingUrgency Conditions HandlingAuxiliary Radio Network Features EvaluationOrganizing the ListSending the List & Allocation Reply

LEGEND TECHNOLOGIESwww.legend-technologies.orgSending the List & Allocation Reply

The resulting candidate list will form the basis on which HO will be performed.

Empty list means that no options are better than remaining on the current cell and no HO will occur.

The channel allocation reply may be success or failure.

Failure may be due to congestion or signaling failure on the target cell.

Based on the result of allocation either success/failure, some actions will be taken like applying some penalties or enabling of certain timers as we saw previously.

LEGEND TECHNOLOGIESwww.legend-technologies.orgExample:

Assume that the o/p from the Filtering stage for the SS measurements is as below and we want to prepare the Basic Ranking Candidate list for HO:

Where,BSPWR = BSTXPWR, MSRXMIN = -90 dBm, Cell A was abandon due to BQ urgency HO (PSSBQ=7dB)SS based Algorithm is in use where OFFSET=0, HYSTSEP= -90 dBm,HIHYST= 5 dB, LOHYST= 3 dB

CellSS(dBm)A-70B (Serving Cell)-74C-78D-68E-80F-92G-95LEGEND TECHNOLOGIESwww.legend-technologies.orgSolution:

A) Correction of Base Station output power: Since BSPWR = BSTXPWR then the current measurements will be kept as it is.SS_corrected_DLneighbor = SS_measured_DLneighborSS_corrected_DLserving = SS_measured_DLserving

B) Evaluation of the minimum Signal Strength condition for NeighborsThe SS for neighbors will be compared against MSRXMIN = -90 dBm Cell F and Cell G have SS < MSRXMIN then they will be removed from the list and cant be candidates for HO.

CellSS(dBm)A-70B (Serving Cell)-74C-78D-68E-80F-92G-95LEGEND TECHNOLOGIESwww.legend-technologies.orgSolution:

C) Subtraction of signal strength penalties

Since Cell A was abandon due to BQ urgency HO (PSSBQ=7dB) then it will be punished,SS_punished_DL Cell A = SS_corrected_DL PSSBQ = -70 7 = -77 dBm

The candidate list will now be in the following form:

CellSS(dBm)A-77B (Serving Cell)-74C-78D-68E-80LEGEND TECHNOLOGIESwww.legend-technologies.orgSolution:

D) Rank the Candidates after applying Offsets and Hysteresis

Since SSServing cell B = -74 dBm > HYSTSEP= -90 dBm, then it is better to stay on the current cell and high Hysteresis will be applied i.e. HYST = HIHYST = 5 dB

Rankservingcell B = -74 dBm Serving CellRankA= -77 dBm OFFSET HYST = -77 0 5 = -82 dBm Worse CellRankC= -78 dBm OFFSET HYST = -78 0 5 = -83 dBm Worse CellRankD= -68 dBm OFFSET HYST = -68 0 5 = -73 dBm Better CellRankE= -80 dBm OFFSET HYST = -80 0 5 = -85 dBm Worse Cell

CellSS(dBm)A-77B (Serving Cell)-74C-78D-68E-80LEGEND TECHNOLOGIESwww.legend-technologies.orgSolution:

Now the final list according to Categorization#1 will be arranged as follows:

Categorization#1CellSS(dBm)Category D-73Better Cell B -74Serving CellA-82Worse CellC-83Worse CellE-85Worse CellLEGEND TECHNOLOGIESwww.legend-technologies.orgDisconnection Criteria

The Disconnection algorithm is not part of the locating algorithm but for completeness, the topic is treated here.

The Disconnection algorithm manages when the connection between the MS and the Network shall be dropped when signaling failure is detected.

The Disconnection criterion can be made in both the DL and the UL such that:In the DL: managed by the MS and in the UL: managed by the BSC.

LEGEND TECHNOLOGIESwww.legend-technologies.orgDisconnection Criteria

In DL:Controlled by a parameter RLINKT , when the MS couldnt decode a SACCH message (0.48 sec), the RLINKT will be decreased by 1 unit, when the MS successfully decodes a SACCH message, the RLINKT will be increased by 2 units, if RLINKT reached value = Zero then disconnection will occur, recommended value RLINKT=16

In UL: The disconnection algorithm will run in the same way, the BSC will make the evaluation, and the controlling parameter is called RLINKUP, , recommended value RLINKUP=16

LEGEND TECHNOLOGIESwww.legend-technologies.orgParameters SummaryAlgorithm SelectionParameter NameValue RangeRecommended ValueUnitEVALTYPE1 or 33 Flow Control ParametersParameter NameValue RangeRecommended ValueUnitTINIT0 to 12010SACCH period=480 msecTALLOC0 to 1202SACCH period=480 msecTURGEN0 to 1202SACCH period=480 msecLEGEND TECHNOLOGIESwww.legend-technologies.orgParameters Summary

Filtering Control ParametersParameter NameValue RangeRecommended ValueUnitSSEVALSI1 to 96SSEVALSD1 to 96QEVALSI1 to 96QEVALSD1 to 96SSLENSI1 to 204SACCH period=480 msecSSLENSD1 to 2010SACCH period=480 msecQLENSI1 to 204SACCH period=480 msecQLENSD1 to 2010SACCH period=480 msecTAAVELEN1 to 204SACCH period=480 msecLEGEND TECHNOLOGIESwww.legend-technologies.orgParameters SummarySignal Strength based Basic Ranking ParametersParameter NameValue RangeRecommended ValueUnitHYSTSEP150 to 0-90dBmLOHYST0 to633dBHIHYST0 to633dBOFFSET63 to 630dBHandover Failure Parameters (Signaling Failure)Parameter NameValue RangeRecommended ValueUnitPSSHF0 to 6363dBPTIMHF0 to 6005SecondsLEGEND TECHNOLOGIESwww.legend-technologies.orgParameters SummaryUrgency Conditions ParametersParameter NameValue RangeRecommended ValueUnitQLIMUL0 to 10055dtquQLIMDL0 to 10055dtquBQOFFSET0 to 633dBPSSBQ0 to 637dBPTIMBQ0 to 60015SecondsTALIM0 to 6362Bit Period (0.577msec)PSSTA0 to 6363dBPTIMTA0 to 60030SecondsDisconnection Algorithm ParametersParameter NameValue RangeRecommended ValueUnitRLINKT4 to 64 in steps of 416SACCH period=480 msecRLINKUP1 to 6316SACCH period=480 msecLEGEND TECHNOLOGIESwww.legend-technologies.orgThank YouLEGEND TECHNOLOGIESwww.legend-technologies.org