rf power control ho parameters

Contents 3 List of tables 5 List of figures 6 Summary of changes 7 1 Overview to RF Power Control and Handover Algorithm 11 2 RF power control and handovers in BSC 15 3 RF Power Control

RF Power Control and Handover Algorithm

2003219 S10.5 ETSI documentation set

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Contents 3 List of tables 5 List of figures 6 Summary of changes 7

1 Overview to RF Power Control and Handover Algorithm 11

2 RF power control and handovers in BSC 15

3 RF Power Control and Handover Algorithm: radio link measurement

processing in BTS and BSC 19

4 RF Power Control and Handover Algorithm: averaging of MSBS

distance 27

5 Bookkeeping and averaging of the RXLEV of the adjacent cell 29

6 RF Power Control and Handover Algorithm: MS speed averaging 33

7 RF Power Control and Handover Algorithm: variable averaging

window size 37

8 RF Power Control and Handover Algorithm: averaging of rapidly

changing signal level 39

9 RF Power Control and Handover Algorithm: FER 41

signal quality 69

11 RF Power Control and Handover Algorithm: BSC handovers 75

11.1 RF Power Control and Handover Algorithm: handover due to uplink/

11.4 RF Power Control and Handover Algorithm: target cell evaluation

according to radio criteria 84

11.5 RF Power Control and Handover Algorithm: handover due to MS-BS

11.8 RF Power Control and Handover Algorithm: power budget handover 100

11.9 RF Power Control and Handover Algorithm: umbrella handover 103

11.10 RF Power Control and Handover Algorithm: handover due to

turn-around-corner MS 108

11.11 RF Power Control and Handover Algorithm: traffic reason handover 112

11.12 RF Power Control and Handover Algorithm: forced handover 113

11.13 RF Power Control and Handover Algorithm: BSC Initiated Traffic Reason

Handover 114

11.13.1 BSC Initiated Traffic Reason Handover with GSM-WCDMA Inter-System

Handover 117

11.14 RF Power Control and Handover Algorithm: Directed Retry Procedure 117

11.15 RF Power Control and Handover Algorithm: order of preference of target

cells 120

11.16 RF Power Control and Handover Algorithm: interval between handovers

and handover attempts 121

11.17 RF Power Control and Handover Algorithm: channel allocation criteria

based on the minimum acceptable C/N ratio 124

11.18 RF Power Control and Handover Algorithm: optimisation of the MS power

level in handover and in call set-up 128

12 RF Power Control and Handover Algorithm parameters 133

List of tables

List of tables

List of figures

Figure 1 Implementation of Power Control and Handover 11

Figure 2 Example of correlation table of one codec, hopping or non-hopping 42

Figure 3 Example of calculated FEP values of one codec derived from the

correlation table, hopping or non-hopping 42

Figure 4 Correction values for updating the correlation table 43

Figure 5 Inversed correction values for using the correlation table 45

Figure 6 MS power increase due to signal level 49

Figure 7 MS power decrease due to signal level 51

Figure 8 MS power increase due to signal quality 53

Figure 9 MS power decrease due to signal quality 57

Figure 10 BTS power increase due to signal level 61

Figure 11 BTS power decrease due to signal level 64

Figure 12 BTS power increase due to signal quality 66

Figure 13 BTS power decrease due to signal quality 70

Figure 14 Handover due to uplink/downlink interference 77

Figure 15 Handover due to uplink/downlink quality 80

Figure 16 Handover due the uplink/downlink level 83

Figure 17 Handover due to MS-BS distance 87

Figure 18 Handover due to rapid field drop 92

Figure 19 Handover due to fast/slow-moving MS 95

Figure 20 Power budget handover 101

Figure 21 Umbrella handover 104

Figure 22 Handover due to turn-around-corner MS 109

Figure 23 Traffic reason handover 112

Figure 24 BSC Initiated Traffic Reason Handover 115

Figure 25 Directed Retry Procedure 118

Summary of changes

Summary of changes

Changes between document issues are cumulative Therefore, the latest documentissue contains all changes made to previous issues

Changes made between issues 11 and 10

The document has been revised throughout to comply with the latestdocumentation standards

Chapter Processing of radio link measurements

Section FER added

Chapter RF Power control, section PC threshold comparison and PC command

The mention of maximum MS transmission power parameters updated and GSM

850 information added

Chapter RF Power control, section MS power increase due to signal quality

Note of AMR PC Rx Quality thresholds added in subsection Thresholdcomparison

Chapter RF Power control, section MS power decrease due to signal quality

Note of AMR PC Rx Quality thresholds added in subsection Thresholdcomparison

Chapter RF Power control, section BTS power increase due to signal quality

Note of AMR PC Rx Quality thresholds added in subsection Thresholdcomparison

Chapter RF Power control, section BTS power decrease due to signal quality

Note of AMR PC Rx Quality thresholds added in subsection Thresholdcomparison

Chapter Handover and Chapter Parameters, section Figures

Equations of Pa, PBGT(n), MAX_INTF_LEV, MS_TXPWR_OPT, pwr(n) andtheir explanations updated Also GSM 850 information added

Summary of changes

Chapter Handover, section Handover due to uplink/downlink interference

In subsection Threshold comparison, uplink quality corrected to downlink quality

in the mention of handover cause downlink interference

Chapter Handover, section Handover due to uplink/downlink quality

Note of new AMR HO Rx Quality thresholds added in subsection Thresholdcomparison

Chapter Handover, section Handover due to fast/slow-moving MS

In figureHandover due to fast/slow-moving MS the equationFastMovingThreshold(n)=0 corrected to FastMovingThreshold(n)>0

Chapter Handover, section BSC initiated traffic reason handover

Note of parameterTrhoGuardTime applying added

Chapter Handover, section Optimisation of the MS power level in handover and in call set-up

The mention of maximum MS transmission power parameters updated and GSM

850 information added

Chapter Parameters

Parameter AmhTrafficControlMCN added

GSM 850 information added to parameters gsmMacrocellThreshold ,gsmMicrocellThreshold and MsTxPwrMin

New parameters AmrHandoverFr.ThresholdDLRXQual , AmrHandoverFr.ThresholdULRXQual , AmrHandoverHr.ThresholdDLRXQual ,

Chapter Parameters, section Figures

In figureHandover due to fast/slow-moving MS the equationFastMovingThreshold(n)=0 corrected to FastMovingThreshold(n)>0

Changes made between issues 10 and 9

Chapter RF power control, section BTS power decrease due to signal level

Description of variable downlink power step size added Figure BTS powerdecrease due to signal level and its caption updated

Chapter RF power control, section BTS power decrease due to signal level

In section Threshold comparison the sentence The BTS power is alwaysdecreased by fixed step removed due to the addition of the description ofvariable downlink power step size

Chapter RF power control, section BTS power decrease due to signal quality

Description of variable downlink power step size added to figure BTS powerdecrease due to signal quality

Chapter RF power control, section BTS power decrease due to signal quality

In section Threshold comparison the sentence The BTS power is alwaysdecreased by fixed step removed

Chapter RF power control, section BTS power decrese due to signal quality

Description of variable downlink power step size added to its own subsectionPower change step size

Chapter Handover, section Handover due to fast/slow moving MS

Description of the definition of the maximum power capability of the MScorrected in subsectionTarget cell evaluation

Chapter Handover, section Umbrella handover

Figure Umbrella handover modified

Chapter Handover, section BSC initiated traffic reason handover

Figure BSC initiated traffic reason handover updated

Summary of changes

Description of the use of parameterCause Field in Handover Request Supportedcorrected.

Chapter Parameters

New parameters OptimumRxLevDL and VariableDLStepUse added

Changes made between issues 9 and 8

Chapter Handover, section BSC initiated traffic reason handover

A new section

Chapter Parameters

New parameters:AmhMaxLoadOfTgtCell, AmhTrhoPbgtMargin,AmhUpperLoadThreshold, TrhoGuardTime, UpperLimitCellLoadHSCSD

1 Overview to RF Power Control and

Handover Algorithm

The Radio Frequency (RF) Power Control and Handover Algorithm isresponsible for processing radio link measurements and for the thresholdcomparison and decision of Power Control (PC) and Handover (HO) Thefollowing figure shows how the different functions involved in the preparationand decision of Power Control and Handover are physically implemented

Figure 1 Implementation of Power Control and Handover

The Base Station Controller (BSC) supports plain measurement preprocessing inthe Base Transceiver Station (BTS); the BTS can calculate an average from two,three or the maximum of four measurement results and send the averaged results

to the BSC in the same form as the raw measurement results The purpose of thepreprocessing in the BTS is to cut down the load of the LAPD-link whennecessary by reducing the number of measurement results that the BTS sends tothe BSC

B S C

- measurementaveraging

- HO thresholdcomparison

- HO target cellevaluation

- HO decision

& command

- PC thresholdcomparison

- PC command

Radiolinkmeasurements

The BSC executes the final processing of the measurement samples:

bookkeeping of the last received samples and averaging procedure After theaveraging procedure the BSC performs both the PC threshold comparison and the

HO threshold comparison The BSC determines the Radio Frequency (RF) outputpower of the Mobile Station (MS) and the BTS by comparing the processedmeasurement results with the PC thresholds If the HO threshold comparisonindicates that a handover might be required, the BSC examines the potentialtarget cells for the handover The BSC performs intra-BSC handoversautonomously If there is an inter-BSC handover to be performed, the BSC sends

a list of the preferred cells to the MSC and the MSC performs the handoveraccording to the list

The software of the BSC is divided into program blocks according to differentfunctions The main functions of the handover and power control are divided intotwo program blocks One is responsible for the actual performance of thehandover, and the other for processing the radio link measurements, the thresholdcomparison and the decision algorithms of the handover and power control

The required parameters are stored in the BSS Radio Network ConfigurationDatabase All parameters controlling the handover and power control areadministered either on a cell-by-cell basis or on a transceiver-by-transceiver basis

by O & M; that is, by using the local MMI in the BSC site or the Nokia NetAct

By changing the values of the parameters it is possible to affect the RF powercontrol and handover decisions at all stages of the procedure, that is duringmeasurement preprocessing, threshold comparison, and the decision algorithm

Related topics

RF power control and handovers in BSC Radio link measurement processing in BTS and BSC Averaging of MS-BS distance

Bookkeeping and averaging of the RXLEV of the adjacent cell

MS speed averaging Variable averaging window size Averaging of rapidly changing signal level FER

RF power control

BSC handovers Parameters

Overview to RF Power Control and Handover Algorithm

2 RF power control and handovers in BSC

The Radio Frequency (RF) power control strategy employed by the BSC definesthe RF power command that is signalled to the MS, and the RF power level that isused by the BTS The RF power control optimises the RF output power of the MSand the BTS and simultaneously ensures that the signal level required at the BTS/

MS is sufficient to maintain adequate speech/data quality

The RF power level to be employed in each case is based on the measurementresults reported by the MS /BTS and on the various parameters set for each cell

. The radio network recovery management initiates a forced handover

(intra-cell or inter-(intra-cell) in order to empty a (intra-cell or a TRX (see Radio Network

Recovery and State Management ).

. The radio resource management initiates a forced inter-cell handover inorder to make room for a high priority call in situations of congestion, that

is, Pre-emption Procedure (see Radio Resource Pre-emption and Queueing

in BSC ).

. Due to congestion in the call set-up phase, a handover from a Stand AloneDedicated Control Channel (SDCCH) of the serving cell to a TrafficChannel (TCH) of an adjacent cell, that is, Directed Retry Procedure (see

Directed Retry Procedure in BSC ).

. The MSC requests the BSC to perform a specified number of handoversfrom one specified cell to other specified cells, that is, Traffic Reason

Handover (see Traffic Reason Handover Procedure in BSC ).

RF power control and handovers in BSC

. A handover from an extended range cell to an inner cell and vice versa

when the site type is Nokia 2nd generation (see Extended Cell ), or when

the site type is Nokia Talk-family, a handover between normal and

extended coverage areas within an extended range cell (see Extended Cell

If other reasons than radio criteria cause the handover, it is not necessary for thetarget cell to be better than the serving cell It suffices that the target cell servesthe call well enough; for example, a handover from an umbrella cell to amicrocell is performed whenever the call can be maintained on the neighbouringmicrocell

Target cell evaluation

The evaluation on the preferred list of the target cells is based on:

1 radio link measurements

2 priority levels of the neighbouring cells

3 load of the neighbouring cells which belong to the local BSS

First the BSC defines and selects those cells which meet the requirements for theradio link properties Then it ranks the cells according to the priority levels andthe load of the neighbouring cells, with the exceptions of the forced handoverprocedure, the directed retry procedure and the traffic reason handover procedurewhen the BSC ranks the cells only according to radio link properties

Handover types

The possible types of handover are the following:

. intra-BTS handover (interference problems)

. intra-BSC handover

. inter-BSC handover (that is, MSC performs the handover)

The handover may take place during a call from a TCH to a TCH (see Handover

Signalling in BSC ) An intra-BTS handover can take place either to a radio time

slot on a new carrier or to a different time slot on the same carrier

A handover may also take place from an SDCCH to a stand alone dedicated

control channel during the initial signalling period of call set-up (see Handover

Signalling in BSC ) The parameter EnableSdcchHO indicates whether the

handover from SDCCH to SDCCH is enabled As far as the algorithm isconcerned, the handover from SDCCH to SDCCH does not differ from thehandover from a TCH to a TCH However, umbrella handover is not performedfrom SDCCH to SDCCH

During the call setup phase in situations of congestion (see Directed Retry

Procedure in BSC ) a handover can take place from the SDCCH of the serving

cell to a traffic channel of an adjacent cell (the parameter EnableSdcchHO has

no effect on the directed retry procedure)

The handover is synchronised or non-synchronised, depending on whether thecells are synchronised or not This information is administered on an adjacentcell-by-cell basis by means of the O & M with the parameter Synchronised ,which indicates whether the adjacent cell is synchronised with the serving cell.The value 'yes' indicates that the cells are synchronised

Interdependence of handover and power control

The Power Control (PC), for both the BTS and the MS, runs independently inparallel with the handover (HO) With a proper choice of the PC and HOthresholds, the BSC maintains call quality by means of power control andproposes handover only when the MS actually reaches the border of the servingcell If both the HO and PC threshold conditions are fulfilled, the handover hasgreater priority than the power control If the handover cannot be performed atthat very moment, power increase may be used as first aid

The BSC determines which RF power level the MS that has been handed overwill use as the initial RF power in the target cell The default initial RF powerlevel is the maximum RF power that an MS is permitted to use on a trafficchannel in the target cell However, in the case of an intra-BSC handover, the PC/

HO algorithm is also able to optimise the initial RF power level so that the RFpower level is lower if the radio link properties of the target cell are good.Optimisation of the MS power level in a handover cuts down the probability of

RF power control and handovers in BSC

high RF power peaks in the uplink after HOs This way it reduces the uplinkinterference in the radio network This property is controlled by the parametersMsPwrOptLevel(n) (inter-cell handover) and the parameter

OptimumRxLevUL (intra-cell handover)

Note

Optimisation of the MS power level in a handover is an optional feature

Back to Overview to RF Power Control and Handover Algorithm.

3 RF Power Control and Handover

Algorithm: radio link measurement processing in BTS and BSC

Measurement preprocessing in BTS

The measurement preprocessing in the BTS comprises of plain averaging of thefollowing measurement results:

. uplink signal level

. uplink signal quality

. downlink signal level (serving cell)

. downlink signal quality

. MS-BS distance

. MS speed

. signal level of the adjacent cells

The averaging procedure is controlled by the parameter BTSMeasAver Theparameter indicates whether the BTS can calculate the average over 1, 2, 3 or 4SACCH multiframes (value 1 actually means that the BTS will not performaveraging) The parameter is controlled on a cell-by-cell basis

When averaging is not active in the BTS, the BTS sends the raw measurementresults it has received from the MS (downlink) and the results of its ownmeasurements (uplink) to the BSC in every SACCH multiframe period Ifaveraging is used in the BTS, the BSC does not receive measurement results fromthe BTS in every SACCH multiframe period, but the BTS sends the averagedresults in every second, third or fourth SACCH multiframe period The BTSsends the averaged results to the BSC in the same form as the raw measurementresults The BSC executes the final averaging of the measurement samples

RF Power Control and Handover Algorithm: radio link measurement processing in BTS

and BSC

When the other averaging parameters are being selected, the factor to be takeninto consideration is whether averaging will be performed already in the BTS,otherwise it is possible that the averaging window sizes accidentally becomemuch longer than expected

Weighted averaging of quality and level

The following measurement results are averaged according to the weightedaveraging technique to produce a reliable quality and level estimate:

. uplink signal level

. uplink signal quality

. downlink signal level (serving cell)

. downlink signal quality

The measurement results are averaged separately for both handover and powercontrol

The weighting takes the reliability of each measurement sample intoconsideration in the averaging procedure The reliability of the measurementsamples varies in consequence of discontinuous transmission (DTX)

Power control and handover parameters for weighted averaging

The averaging procedure is controlled by parameters Power control andhandover have averaging parameters of their own The BSC uses separateparameters for quality and level measurements as well as for uplink and downlinkmeasurements All averaging parameters are administered on a cell-by-cell basis

by Nokia NetAct The averaging parameters are the following:

1 PcAveragingLevDL is used for calculating averaged values fromdownlink signal level measurements for PC threshold comparison

2 PcAveragingLevUL is used for calculating averaged values fromuplink signal level measurements for PC threshold comparison

3 PcAveragingQualDL is used for calculating averaged values fromdownlink signal quality measurements for PC threshold comparison

4 PcAveragingQualUL is used for calculating averaged values fromuplink signal quality measurements for PC threshold comparison

5 HoAveragingLevDL is used for calculating averaged values fromdownlink signal level measurements for HO threshold comparison.

6 HoAveragingLevUL is used for calculating averaged values fromuplink signal level measurements for HO threshold comparison

7 HoAveragingQualDL is used for calculating averaged values fromdownlink signal quality measurements for HO threshold comparison

8 HoAveragingQualUL is used for calculating averaged values fromuplink signal quality measurements for HO threshold comparison

Each averaging parameter is composed of two parts: the size of the averagingwindow (Window size ) and the weighting factor (Weighting ) The range ofthe averaging window size is from 1 to 32 SACCH multiframe periods, where thevalue 1 means that there is basically no averaging at all The range of theweighting factor is from 1 to 3 These values are the same for all the parameterslisted above

Averaging methods for quality and level

The BSC calculates new averaged values in every SACCH multiframe period (ifpreprocessing is used in the BTS, in every second, third or fourth SACCHmultiframe, in other words whenever the BSC receives measurement results fromthe BTS) The averaging procedure is able to take into account the maximum of

32 most recent measurement samples

The basic averaging procedure does not start until the required number ofmeasurement samples is available After the averaging procedure has started, theBSC calculates a new averaged value from the most recent measurement samples

in every SACCH multiframe period (sliding window technique)

For example, if the value of the parameter PcAveragingLevUL/Windowsize is 8, the averaging of uplink level for power control can start as soon asthe BSC has received 8 measurement results

Fast averaging methodThe BSC is also able to start the averaging of level and quality from the firstmeasurement sample In this case the BSC calculates averaged values from thosemeasurement samples which are available until the number of measurementsamples is adequate to calculate averaged values over the intervals determined bythe parameters (Window size ) For example, if the value of the parameterPcAveragingLevUL/Window size is 8 but the number of availablemeasurement samples is 5, the BSC calculates the average from those 5 availablemeasurement samples This property is known as the fast averaging method and it

is controlled by the following parameters:

RF Power Control and Handover Algorithm: radio link measurement processing in BTS

and BSC

1 EnaFastAveCallSetup parameter indicates whether the fastaveraging method is enabled at the beginning of a SDCCH seizure (either

in a call or in a SDCCH handover) The fast averaging method is enabledwhen the value is 'yes'

2 EnaFastAveHO parameter indicates whether the fast averaging method

is enabled at the beginning of a TCH seizure (either in a call or in ahandover) The fast averaging method is enabled when the value is 'yes'

3 EnaFastAvePC parameter indicates whether the fast averaging of signalquality measurements and the scaling of signal level measurements areenabled just after the increase/decrease of the MS/BTS transmission power.The fast averaging method and the scaling of measurement results areenabled when the value is 'yes'

The advantage of the fast averaging method is that handover and power controlthreshold comparisons can start as soon as the BSC has received the firstmeasurement sample The fast averaging method does not, however, effect in anyway the threshold comparison The BSC performs the threshold comparison inthe same way whether the fast averaging method is used or not The parameterslisted above need to be on when using the fast averaging method, if not then theBSC functions as normally However, they do not all have to be on at the sametime, because each parameter affects a different stage

Note

The fast averaging method concerns only the measurement results of the serving

cell not the measurement results of the adjacent cell (see Bookkeeping and

averaging of the RXLEV of the adjacent cell ).

Weighted averaging methodBesides the measurement results, the MS/BTS indicates to the BSC whetherDiscontinuous Transmission (DTX) was used during the previous SACCHmultiframe period (uplink/downlink) DTX NOT USED indicates that the MS/BTS has transmitted all TDMA frames during the previous SACCH multiframeperiod DTX USED indicates that the MS/BTS did not transmit all TDMA framesduring the previous SACCH multiframe period For speech communication DTX

is randomly distributed over the SACCH multiframe periods If the DTX valuecannot be determined, the BSC assumes that DTX was used

If the MS/BTS did not transmit all TDMA frames, the reliability of quality andlevel estimation is not as good as it would be if all TDMA frames weretransmitted Because of this, during the averaging procedure, the samplesaccessed over all TDMA frames are given more weight than the samples accessedover a subset of TDMA frames For example, when uplink signal quality for the

PC is being averaged, the weighting factor has the value of the parameterPcAveragingQualUL/Weighting (range from 1 to 3) if DTX was notused, whereas the weighting factor is 1 for the measurement results when DTXwas used.

The corresponding weighted averaging technique which takes into accountwhether the MS/BTS has used Discontinous Transmission (DTX) during theprevious SACCH multiframe period is described below by averaging the uplinksignal level for the PC

DTX is not allowed on the SDCCH

Examples

The example below indicates the averaging procedure where the samplesavailable include indication on either DTX not used (0) or DTX used (1) In theexample, the parameters (PcAveragingLevUL ) are Weighting , which hasthe value 2, and Window size , which has the value 8

>time

uplink level: 35 42 33 36 39 40 39 35

(2*35)+ (1*42)+ + (2*35) AV_RXLEV_UL_PC = - = 36

2+1+2+2+1+1+1+2

The example below indicates the averaging procedure where the samplesavailable include indication on either DTX not used (0) or DTX used (1) In theexample, the parameters (PcAveragingQualUL) are Weighting , whichhas the value 2, and Window size , which has the value 6

2+1+2+2+1+1

RF Power Control and Handover Algorithm: radio link measurement processing in BTS

and BSC

Note that the BSC uses Bit Error Rate (BER) values defined for each quality bandwhen it averages the signal quality measurements (this also concerns thresholdcomparison) (seeGSM Recommendation 05.08 ).

Averaged results of quality and level

The following correspondence is found between the measurement results,averaging parameters and the averaged results These averaged results are used inthe equations for handover and power control threshold comparison

AVERAGING PARAMETERS

AVERAGED RESULT downlink

level

uplink level

downlink quality

uplink quality

downlink level

uplink level

downlink quality

uplink quality

PcAveragingLevDL

- Window size

- Weighting PcAveragingLevUL

- Window size

- Weighting PcAveragingQualDL

- Window size

- Weighting PcAveragingQualUL

- Window size

- Weighting HoAveragingLevDL

- Window size

- Weighting HoAveragingLevUL

- Window size

- Weighting HoAveragingQualDL

- Window size

- Weighting HoAveragingQualUL

- Window size

- Weighting

Case of a missing downlink measurement report

If, for any multiframe, the downlink measurement report which is normallyreceived from the MS is missing or the report includes an indication thatdownlink measurement results are not valid, the basic procedure is that the BSCexecutes merely the processing for the uplink measurement results (uplink signallevel and uplink signal quality) and both the PC threshold comparison and the

HO threshold comparison for these averages

In this case no new averaged values are calculated from downlink measurements

As a result, no threshold comparison based on those particular averages is started(for example BTS power control) Similarly, the bookkeeping of the downlinkmeasurement results is frozen

As long as downlink measurement reports are missing (or they are not valid), theBSC is only able to control the power of the MS and perform handovers (intra-cell or inter-cell) whose cause is either uplink quality or uplink interference.Normal actions will be resumed when the next valid downlink measurementreport arrives

If the optional feature "Chained cells in rapid field drop" is employed, the BSC isalso able to perform an imperative handover caused by a rapid field drop to anadjacent cell, despite the missing (or non-valid) downlink measurement report.The principle and the function of the feature "Chained cells in rapid field drop"

will be explained in detail in RF Power Control and Handover Algorithm: BSC

handovers

Initialisation of the old measurement results

The measurement results (uplink or downlink) preceding an MS/BTS powerchange are not valid after the power change If the scaling of measurement results

is disabled (selected with the parameter EnaFastAvePC ), the averaging andthreshold comparison based on those measurement results (uplink/downlink)must start from the beginning after the power change (this concerns bothhandover and power control) In this case the BSC initialises the measurementresults preceding the power change as follows:

1 MS power increase/decrease:

. The BSC initialises uplink measurement results

2 BTS power increase/decrease:

. The BSC initialises downlink measurement results (serving cell)

RF Power Control and Handover Algorithm: radio link measurement processing in BTS

and BSC

Scaling of the old measurement results

When the scaling of signal level measurements is enabled (selected with theparameter EnaFastAvePC ), the BSC scales the signal level measurementresults preceding the power change so that they correspond to the newtransmission power level of the MS/BTS For example, the BSC scales the olduplink signal level measurement results 4 dB up when the transmission powerlevel of the MS is increased by 4 dB

The scaling of the old measurement results after the power change affects theaveraging and threshold comparison in the following way:

1 Averaging of signal level

It is not necessary for the BSC to start the averaging of signal levelmeasurement results (uplink/downlink) from the beginning after the MS/BTS power change but the BSC can continue the procedure withoutinterruption

2 Averaging of signal quality

The BSC initialises the signal quality measurement results (uplink/downlink) preceding the MS/BTS power change and starts the averaging

of signal quality from the beginning by using the fast averaging methoduntil the number of measurement samples is adequate to calculate averagedvalues over the intervals determined by the averaging window sizes

3 HO threshold comparison

It is not necessary for the BSC to start the HO threshold comparison fromthe beginning after the MS/BTS power change but the BSC can continuethe procedure without interruption

4 RF Power Control and Handover

Algorithm: averaging of MSBS distance

The absolute MS-BS distance (timing advance) can be used to prevent the mobilestations from grossly exceeding the planned cell boundaries The MS-BS distance

is used as a criterion (selected with the parameter MsDistanceBehaviour )for handover or for call release alternatively

The MS-BS distance is used also as a criterion for a handover from an extendedrange cell to an inner cell and vice versa when the site type is Nokia 2nd

generation (see Extended Cell ), and when the site type is Nokia Talk-family, for a

handover between normal and extended coverage areas within an extended range

cell (see Extended Cell Range ).

Averaging procedure of MS-BS distance

The averaging procedure is controlled by the parameterMSDistanceAveragingParam The parameter determines the averagingwindow size (Window size ) which is used for calculating averaged valuesfrom MS-BS distance (timing advance) for HO threshold comparison The range

of the averaging window size is from 1 to 32 SACCH multiframe periods, wherethe value 1 means that there is basically no averaging at all The parameter iscontrolled on a cell-by-cell basis

The BSC calculates a new averaged timing advance value in every SACCHmultiframe period (if preprocessing is used in the BTS, in every second, third orfourth SACCH multiframe) The averaging procedure is able to take into accountthe maximum of 32 most recent measurement samples

The averaging procedure does not start until the required number of measurementsamples is available After the averaging procedure has started, the BSCcalculates a new averaged value from the most recent measurement sampleswhenever it receives measurement results from the BTS (sliding windowtechnique)

For example, if the value of the parameter MSDistanceAveragingParam/Window size is 6, the averaging of MS-BS distance can start as soon as theBSC has received 6 measurement results

RF Power Control and Handover Algorithm: averaging of MSBS distance

The example below indicates the averaging procedure when Window size hasthe value 8, at SACCH multiframe n:

AV_RANGE_HO = 1/8 (TOA (n)+TOA (n-1)+ +TOA (n-7))

Averaged result of MS-BS distance

The following correspondence is found between the measured timing advance,averaging parameters and the averaged result This averaged result is used in theequations for handover threshold comparison

Back to Overview to RF Power Control and Handover Algorithm.

AV_RANGE_HO

MEASUREMENT RESULT

AVERAGING PARAMETER

AVERAGED RESULT

timing advance (TOA)

MSDistance AveragingParam

- Window size

5 Bookkeeping and averaging of the

RXLEV of the adjacent cell

The BSC averages the signal level of the adjacent cells (RXLEV_NCELL(n))only at the time when the averaged results are needed for the decision procedure.The averaging procedure is able to take into account the maximum of 32 mostrecent measurement samples per adjacent cell and maintain the last 32

measurement samples of up to 32 adjacent cells per BTS

Averaging procedure of the RXLEV of the adjacent cell

The averaging procedure is controlled by the following parameters:

1 AveragingWindowSizeAdjCell determines the averaging windowsize which is used for calculating averaged values from downlink (adjacentcell) signal level measurements for HO threshold comparison and decision.The range of the averaging window size is from 1 to 32 SACCH

multiframe periods, where the value 1 means that there is basically noaveraging at all

2 NumberOfZeroResults indicates the maximum number of zeroresults that can be omitted when the measurement results of the adjacentcells are averaged The range of the parameter is from 0 to 7 zero results

If the zero results are not omitted, they may distort the results of theaveraging procedure A zero result is entered as the measurement result forthose adjacent cells that are missing from the measurement sample.Because the MS is able to report the measurement results of the six cells itreceives best, the adjacent cells that the MS reports can change This leads

to a situation where a relatively good cell can sometimes be left out fromthe six best cells measured by the MS Accordingly, the cell has zeroresults among the good measurement results

3 AllAdjacentCellsAveraged indicates whether measurementresults are averaged for every adjacent cell (value is 'yes') or only for thosesix cells which are the best according to the last measurement sample(value is 'no')

Bookkeeping and averaging of the RXLEV of the adjacent cell

The averaging parameters are controlled on a cell-by-cell basis The BSC mayaverage the signal level of the adjacent cells already after the first receivedmeasurement sample The following examples show how the BSC calculates theaverage.

Examples

1 The parameter AveragingWindowSizeAdjCell has the value 8 andthe parameter NumberOfZeroResults has the value 2, and the BSChas received eight measurement results from the neighbouring cell atSACCH multiframe k:

AV_RXLEV_NCELL (n) = 1/8 (RXLEV_NCELL (n) (k) + RXLEV_NCELL (n) (k-1) + + RXLEV_NCELL (n) (k-7))

If the result k-1 was zero, the effective averaging window size would be 7:

AV_RXLEV_NCELL (n) = 1/7 (RXLEV_NCELL (n) (k) + 0 + RXLEV_NCELL (n) (k-2) + + RXLEV_NCELL (n) (k-7))

2 AveragingWindowSizeAdjCell is 8 andNumberOfZeroResults is 7, and the BSC has received onemeasurement result (RxLev 40) from the neighbouring cell

In this case the average is40/(AveragingWindowSizeAdjCell - NumberOfZeroResults)= 40/(8-7)= 40

3 AveragingWindowSizeAdjCell is 8 andNumberOfZeroResults is 7, and the BSC has received fivemeasurement results (RxLev 40, 42, 39, 40 and 43) from the neighbouringcell (thus there are 3 measurement results missing, and they are fewer thanthe NumberOfZeroResults ; the number of missing results issubtrackted from the AveragingWindowSizeAdjCell )

In this case the average is (40 + 42 + 39 + 40 + 43)/(8-3)= 41

4 AveragingWindowSizeAdjCell is 12 andNumberOfZeroResults is 5, and the BSC has received threemeasurement results (RxLev 40, 42 and 43) from the neighbouring cell(thus there are 9 measurement results missing, and that is more than theNumberOfZeroResults ; the NumberOfZeroResults value issubtrackted from the AveragingWindowSizeAdjCell )

In this case the average is (40 + 42 + 43)/(12-5) = 17

Averaged result of the RXLEV of the adjacent cell

The following correspondence is found between the measurement results (signallevel of the adjacent cell: RXLEV_NCELL(n)), the averaging parameters and theaveraged result This averaged result is used in the equations for handoverthreshold comparison and decision

Back to Overview to RF Power Control and Handover Algorithm

RXLEV_NCELL(n) AV_RXLEV_NCELL(n)

MEASUREMENT RESULT

AVERAGING PARAMETERS

AVERAGED RESULT

AveragingWindow SizeAdjCell NumberOfZero Results AllAdjacent CellsAveraged

Bookkeeping and averaging of the RXLEV of the adjacent cell

6 RF Power Control and Handover

Algorithm: MS speed averaging

Traffic Control Based on the MS Speed is an optional feature in the BSC.Detection of the MS speed makes it possible for the BSC to control trafficbetween the separate layers of the multi-layered cellular network on the basis ofthe speed of the mobile station

When a BTS is able to measure the speed of the MS, the BSC receives MS speedindications from the BTS in every SACCH multiframe period (if preprocessing isused in the BTS, in every second, third or fourth SACCH multiframe) in the sameway as the other measurement results

The BTS is not able to measure the speed of the MS in the following six cases:

1 The BTS does not support the measurement of MS speed

2 The call is on an SDCCH

3 Frequency hopping (base band or RF hopping) is being used in the BTS

(see Frequency Hopping ), with the exception of RF hopping when the call

is on the non-hopping BCCH transceiver

4 Uplink DTX was used during the SACCH multiframe period

5 The MS was changing its output power during the SACCH multiframeperiod

6 Uplink signal levels in two most recent measurement samples differ morethan 3 dB from each other

The BSC also rejects the MS speed indication which is in the first measurementsample after call set-up or handover because it is unreliable

If the BSC does not receive any MS speed indications from the BTS (cases 1 and

2 above), or if all measurement reports include non-valid MS speed indications(case 3 above), the traffic control which is based on the MS speed measured bythe BTS cannot be done For speech communication DTX is randomly distributedover the SACCH multiframe periods, thus uplink DTX does not block the trafficcontrol in question

RF Power Control and Handover Algorithm: MS speed averaging

Averaging of MS speed procedure

The averaging procedure is controlled by the parameter MsSpeedAveraging The parameter determines the averaging window size which is used for

calculating averaged results from the measured MS speed for HO thresholdcomparison The range of the averaging window size is from 1 to 32 SACCHmultiframe periods, where the value 1 means that there is basically no averaging

at all The parameter is controlled on a cell-by-cell basis The averagingprocedure does not start until the required number of measurement samples isavailable For example, if the value of the parameter MsSpeedAveraging is

6, the averaging of MS speed can start as soon as the BSC has received 6measurement results After the averaging procedure has started, the BSCcalculates a new averaged value from the most recent measurement sampleswhenever it receives measurement results from the BTS (sliding windowtechnique)

If, for any multiframe, the MS speed indication is missing from the measurementsample or the indicated speed value is not valid, the BSC ignores the samplewhen it calculates the averaged MS speed The BSC is able to calculate theaveraged MS speed if it has at least one valid measurement sample within theaveraging window

If the averaging window is full of non-valid samples, the traffic control which isbased on the MS speed measured by the BTS is frozen As long as indicated MSspeed values are not valid, the BSC is not able to execute the traffic control inquestion Normal actions will be resumed when the next valid MS speedindication arrives

ExampleThe example below indicates the averaging procedure where the samplesavailable are either valid (0) or non-valid (1) The averaging window size(parameter MsSpeedAveraging ) is 6

4

Averaged result of MS speed

The following correspondence is found between the measured MS speed, theaveraging parameter and the averaged result This averaged result is used in theequations for handover threshold comparison and decision

Back to Overview to RF Power Control and Handover Algorithm.

AVERAGING PARAMETERS

MS speed MsSpeedAveraging AV_MS_SPEED

MEASUREMENT RESULT

AVERAGED RESULT

RF Power Control and Handover Algorithm: MS speed averaging

7 RF Power Control and Handover

Algorithm: variable averaging window size

The variable averaging window size is related to the traffic control based on the

MS speed which is an optional feature in the BSC The BSC may use theinformation on the speed of the mobile station either:

. to control traffic between the separate layers of the multi-layered cellularnetwork on the basis of the speed of the mobile station (parameterMsSpeedDetectionState has the value zero), or

. to scale the values of the averaging parameters on the basis of the speed ofthe mobile station (parameter MsSpeedDetectionState has thevalue 1% - 100%) Here the value means that if, for example, it is 80% itmeans that the averaging window is 80% of the normal window size

Variable averaging window size procedure

The variable averaging window size procedure consists of the following threestages:

1 The BTS measures the speed of the mobile station (see MS speed

averaging ).

2 The handover threshold comparison determines the mobile station either as

a slow-moving MS or as a fast-moving MS (see Handover due to fast/

slow-moving MS ).

3 The scaling of the averaging parameters

The scaling of the averaging parameters is controlled by the parameterMsSpeedDetectionState The parameter indicates how much the values ofthe averaging parameters will be decreased if the mobile station is considered as afast-moving MS The range is from 1% to 100%, the scaling of the averagingparameters is disabled when the value is zero

RF Power Control and Handover Algorithm: variable averaging window size

When the scaling of the averaging parameters is enabled, the speed of the mobilestation affects the averaging parameters in the following way:

1 If the mobile station is considered as a slow-moving MS or the MS speedcannot be determined, the BSC uses the normal values of the averagingparameters

2 If the mobile station is considered as a fast-moving MS, the BSC usesscaled values in the averaging procedure for the following averagingparameters:

Back to Overview to RF Power Control and Handover Algorithm

8 RF Power Control and Handover

Algorithm: averaging of rapidly changing signal level

The averaging procedure is related to the enhanced rapid field drop detectionprocedure which is an optional feature in the BSC The principle and the function

of the enhanced rapid field drop detection procedure will be explained in detail in

chapter BSC handovers

When the handover threshold comparison detects a rapid and deep field drop, forexample when an MS turns around a corner at street junction, the BSC speeds upthe averaging of signal level measurement results by reducing temporarily thesize of the relevant averaging windows The purpose of the reduced the averagingwindow sizes is to enable fast and right handover decisions even in situationswhen the signal levels of the serving cell and the adjacent cells change dozens ofdecibels (for example 20-30 dB) during a few SACCH multiframes

Averaging procedure parameters

The averaging procedure is controlled by the following parameters:

1 ModifiedAveWinNcell determines the averaging window size which

is used after the detection of the rapid field drop for calculating averagedvalues from the signal level measurements for HO threshold comparisonand decision The range of the averaging window size is from 1 to 32SACCH multiframe periods, where the value 1 means that there isbasically no averaging at all

2 ModifiedNOZ indicates the maximum number of zero results that can beomitted when the measurement results of the adjacent cells are averagedafter the detection of the rapid field drop The range of the parameter isfrom 0 to 31 zero results

3 ErfdOver determines the maximum time period starting from thedetection of the rapid field drop during which the averaging of signal levelmeasurements is controlled by the averaging parameters

ModifiedAveWinNcell and ModifiedNOZ The range varies fromzero to 64 seconds

RF Power Control and Handover Algorithm: averaging of rapidly changing signal level

When the handover threshold comparison detects a rapid and deep field drop (see

Handover due to turn-around-corner MS ), the BSC modifies the averaging of

signal level measurements in the following way:

. ModifiedAveWinNcell is used instead of HoAveragingLevDLfor calculating averaged values from downlink signal level measurements

(serving cell) for HO threshold comparison (see Weighted averaging of

quality and level );

. ModifiedAveWinNcell is used instead of HoAveragingLevULfor calculating averaged values from uplink signal level measurements for

HO threshold comparison (see Weighted averaging of quality and level );

. ModifiedAveWinNcell is used instead ofAveragingWindowSizeAdjCell for calculating averaged valuesfrom downlink (adjacent cell) signal level measurements for HO threshold

comparison and decision (see Bookkeeping and averaging of the RXLEV of

the adjacent cell );

. ModifiedNOZ is used instead of NumberOfZeroResults toindicate the maximum number of zero results that can be omitted when the

measurement results of the adjacent cells are averaged (see Bookkeeping

and averaging of the RXLEV of the adjacent cell ).

Normal averaging of signal level measurements will be resumed after the period(parameter ErfdOver ) allowed for the averaging procedure has expired orwhen the MS is handed over from the serving cell to an adjacent cell