modul 5 bss parameter

GSM-GPRS Operation

BSS Parameter

Module 5

Outline BSS Parameters Structure BTS Parameters

MS Mode Idle Mode

Cell Selection Cell Reselection

Dedicated Mode Handover Power Control

BSC parameters

kris.sujatmoko@gmail.com

GSM-GPRS Operation

BSS Parameters

BTS Parameters

BSC Parameters

BSS Parameters Structure

BSS Parameters Structure (2) Base Station Controller (BSC)

The BSC object contains BSC-specific radio network data.

BCCH Allocation Frequency List (BA) The BA object contains data for building the BCCH allocation.

Mobile Allocation Frequency List (MA) The MA object contains data for building the mobile allocation for RF

hopping.

Base Control Function (BCF) The BCF object contains data that is specific for the O&M functions of the

Base Transceiver Station (BTS) The BTS object contains BTS-specific radio network data.

Handover Control (HOC) The handover control object contains parameters which control the handover

procedure.

BSS Parameters Structure (3) Power Control (POC)

The power control object contains parameters which control the power control procedure.

Adjacent Cell (ADJC) The adjacent cell object contains a description of the adjacent cell of the

Transceiver (TRX) The TRX object contains TRX-specific data.

Radio Time Slot (RTSL) The radio time slot object contains parameters for the physical radio time

Frequency Hopping System (FHS) The frequency hopping system object contains hopping parameters for the

GSM-GPRS Operation

BTS Parameters

BTS - Parameter

GSM-GPRS Operation

Parameter Related To Idle Mode

MS Mode

Search for Frequency Correction Burst

Search for Synchronisation sequence

Read System Informations

listen for Paging

send Access burst

wait for signalling channel allocation

Call setup

traffic channel is assigned

Conversation

Call release

idle mode

“off” state

dedicated mode

idle mode

Idle Mode – Cell Selection

Radio constraints: The MS uses a "path loss criterion" parameter C1 to

determine whether a cell is suitable to camp on [GSM 03.22]

C1 depends on 4 parameters: Received signal level (suitably averaged) The parameter rxLevAccessMin, which is broadcast on the

BCCH, and is related to the minimum signal that the operator wants the network to receive when being initially accessed by an MS

The parameter msTxPwrMaxCCH, which is also broadcast on the BCCH, and is the maximum power that an MS may use when initially accessing the network

The maximum power of the MS.

Idle Mode – Cell Selection (2)

Path loss criterion parameter C1 used for cell selection and reselection is defined by : C1 = (A - Max(B,0))

where A = Received Level Average - rxLevAccessMin B = msTxPwrMaxCCH – P Except for the class 3 (4 watts) DCS 1 800 MS

where : B = msTxPwrMaxCCH + POWER OFFSET - P

Idle Mode – Cell Selection (3) rxLevAccessMin = Minimum received level at the

MS required for access to the system.

msTxPwrMaxCCH = Maximum TX power level an MS may use when accessing the system until otherwise commanded.

POWER OFFSET = The power offset to be used in conjunction with the MS TXPWR MAX CCH parameter by the class 3 DCS 1 800 MS.

P = Maximum RF output power of the MS.

Idle Mode – Cell Selection (4) Procedure

Idle Mode – Cell Selection (5) Example

C1(cell_A) = AV_RXLEV - rxLevAccessMin - Max(0, msTxPwrMaxCCH – max output power of MS)

C1(cell_A) = -80dBm – (-100dBm) – max(0, 36dBm – 33dBm) C1(cell_A) = 17 > 0 C1(cell_B) = -82dBm – (-105dBm) – max(0, 33dBm – 33dBm) C1(cell_B) = 23 > C1(cell_A) Thus MS camps on cell_B

Idle Mode – Cell Reselection

Why C2 ? Cell Prioritisation

As a means of encouraging MSs to select some suitable cells in preference to others

Example: In dualband network--to give different priorities for

different band In multilayer--to give priority to microcell for slow

moving traffic Any other special case where specific cell

required higher priority than the rest

Idle Mode – Cell Reselection (2)

How the MS knows? cellReselectOffset, penaltyTime,

temporaryOffset are cell reselection parameters These parameters are broadcast on the cell

BCCH when cellReselectparamInd is set to yes

Cell Reselection Strategy: Positive offset--encourage MSs to select that cell Negative offset--discourage MSs to select that

cell for the duration penaltyTime period

Idle Mode – Cell Reselection (3)

MS will calculate the C1 and C2 for the serving cell, every 5 s

MS will calculate the C1 and C2 for the neighbour cells, every 5 s

Cell re-selection is needed if : Path Loss criterion C1 < 0 for cell camped on, for

more than 5 sec There is DL signaling failure The cell camped on has been barred The is a better cell in terms of C2 criterion

Idle Mode – Cell Reselection With C2 (1)

For penaltyTime = 640 seconds, C2 = C1 – cellReselectOffset

For penaltyTime < 640 seconds, C2 = C1 + cellReselectOffset – temporaryOffset for T <=

penaltyTime C2 = C1 + cellReselectOffset for T > penaltyTime

Cell Selection Case Study A dualband network, 1800 layer is preferred during

call setup Why?

To relieve blocking in 900 layer To absorb traffic from 900 layer

Strategy? Use C2 parameters

How? Minimising massive BSS parameters change in the existing

900 layer Traffic is increase in a control manner Only 1800 layer required BSS parameter change

Cell Selection Case Study (2)

How to set? Cell Reselection Parameters activated in 1800

layer 900 layer remain unchanged--operation as normal

What value?

reselectOffset is initial set at low value during initial stage and further optimised in later stage

Cell Selection Case Study (3) The Rationale?

cellReselectParamInd--YES No C2 parameters will be broadcast on cell BCCH if this

parameter is not turned on cellReselectOffset = 8 dB

The 1800 layer having a C2 of 8 dB higher than C1 of 900 after the penaltyTime expires

PenaltyTime = 20 seconds Assume 1800 cell radius 400 meters Fast moving traffic speed 80 km/h A MS takes approximately 20 seconds to cross a cell 1800

cell Because the initial coverage for 1800 is not contiguous, the

fast moving traffic is not allowed to move to 1800 layer

The Rationale? PenaltyTime = 20 seconds

During the penaltyTime period, the fast moving MS will set up call on 900 layer

Slow moving traffic will set up call on 1800 layer temporaryOffset = 10 dB

This value should be set higher than cellReselectOffset value

In order to have a negative offset (with reference to 1800 C1 value) during the penaltyTime period

The Rationale? cellBarQualify = NO

Cell selection priority is normal status If set to YES, cellBarred parameter can be overwrite

and cell selection priority will become low

The Scenario: GSM900: rxLevAvg = -75dBm; rxLevAccessMin = -

97dBm DCS1800: rxLevAvg = -80dBm; rxLevAccessMin = -

95dBm For serving GSM900 cell,

C2 = C1 = rxLev – rxLevAccessMin – max ([msTxPowerMaxCCH - max RF output of MS], 0)

C1 = -75dBm – (-97dBm) – max([33 – 33], 0) C1 = 22 dB

The Scenario: For non-serving DCS1800 cell,

C1 = rxLev – rxLevAccessMin – max ([msTxPowerMaxCCH – maxRF output of MS], 0)

C1 = -80dBm – (-95dBm) – max([30 – 30], 0) C1 = 15 dB

During the penalty time period of 20 seconds; before the penalty time expires C2 = C1 + cellReselectOffset – temporaryOffset = 15 + 8 –10

= 13dB < C2 for GSM900 cell (= 22dB)

MS stays in GSM900 layer during this period

The Scenario: After the penalty time period of 20 seconds

expires C2 = C1 + cellReselectOffset = 15 + 8 = 23dB > C2

for GSM900 cell (= 22dB) MS reselects DCS1800 layer after penalty time

expires

Idle Mode – Cell Reselection Hysteresis

Cell Reselection Hysteresis MS is moving in a border area between location areas MS might repeatedly change between cell of different location

areas Each change of location area requires a location update LU causes

Causes heavy signalling load Increases risk of paging message being lost

To prevent this, cell reselect hysteresis is used How this parameter works?

A cell in a different location area is only selected if it is “better” than all the cell in the current LA by at least the value of cellReselectHysteresis

In term of path loss criterion

Idle Mode – Cell Reselection Hysteresis(2)

Cell Reselection Hysteresis What value to set? Typical value is 6~8 dB Example:

A static class 4 MS camping on cell 1 in idle mode.

The MS monitor the BCCH of cell 1 and cell 2 and measures the following levels rxLevAvg = -80dBm in cell 1 rxLevAvg = -86dBm from neighbour cell 2

The following parameters are set:

Does the MS perform cell reselect? If cell 1 and cell 2 belong to the same LA If the cell 1 and cell 2 belong to different LAs

What are the conditions? For the same LA:

C1 (cell 2) > C1 (cell 1)

For the different LA: C1 (cell 2) > C1 (cell 1) + cellReselectHysteresis

C1 (cell 1) = rxLevAvg – rxLevAccessMin – max ([msTxPowerMaxCCH – max RF output of MS], 0) C1 (cell 1) = -80dBm – (-100dBm) – max([36 – 33], 0) C1 (cell 1) = 17 dB

C1 (cell 2) = rxLevAvg – rxLevAccessMin – max ([msTxPowerMaxCCH – max RF output of MS], 0) C1 (cell 2) = -84dBm – (-104dBm) – max([33 – 33], 0) C1 (cell 2) = 20 dB

C1 (cell 2) = 20 dB > C1 (cell 1) = 17 dB For the same LA:

C1 (cell 2) > C1 (cell 1) cell reselection

For the different LA: C1 (cell 2) < C1 (cell 1) + cellReselectHysteresis No cell reselection

GSM-GPRS Operation

Parameter Related To Dedicated Mode

Dedicated Mode

Handover Power Control

GSM-GPRS Operation

Handover Parameters

Handover Parameter

Handover Design (1)

Handover definition: A mechanism that transfers an ongoing call from

one cell to another as a user moves through a coverage area of a GSM system

Trends: Smaller cells to meet the demands for increased

capacity number of cell boundary crossing increase

Impact: Network Resource: switching load Delay Quality of Service

Handover Design (2)

Network resource: Minimising number of HO minimising switching

QoS : Minimising delay minimises co-channel

interference

Challenge optimium HO parameters settings using the existing HO algorithm so that the perceived QoS does not degrade

Handover Design (3) – Guidelines

General HO Design Guidelines HO design involves setting of:

HO parameters GenHandoverRequestMessage in BSC parameter MsTxPwrMax in BTS parameter PcLowerThresholdLevDL/UL in power control parameter hoMargin in adjacency parameter

HO objectives: maintenance of connection in case of cell change

(movement) channel change in case of severe disturbance

(interference) design of cell borders and radio network structure

Handover Design (4)

HO is divided into several sub processes

Handover Design (5)

Handover Design (6)

HO Sub Processes Flow

Handover Design (7) Handover performance metrics used to evaluate HO

performance: Call blocking probability -the probability that a new call

attempt is blocked Handover blocking probability - the probability that a

handover attempt is blocked Handover probability - the probability that, while

communicating with a particular cell, an ongoing call requires a handover before the call terminates. This metric translates into the average number of handovers per call

Call dropping probability - the probability that a call terminates due to a handover failure. This metric can be derived directly from the handover blocking probability and the handover probability

Handover Design (8) Probability of an unnecessary handover - the probability

that a handover is stimulated by a particular handover algorithm when the existing radio link is still adequate

Rate of handover - the number of handovers per unit time. Combined with the average call duration, it is possible to determine the average number of handovers per call, and thus the handover probability.

Duration of interruption - the length of time during a handover for which the mobile terminal is in communication with neither base station. This metric is heavily dependent on the particular network topology and the scope of the handover

Delay -the distance thc mobile moves from the point at which the handover should occur to the point at which it does

Handover Design (9)

Handover Design (10)

Relative signal strength: HO triggered at point A Unnecessary HO when the serving cell signal is

still adequate

Relative signal strength with threshold: If threshold set at T1, same as relative signal

strength trigger point A If threshold set at T2, HO is delayed, occurs at

point B If threshold set at T3, delay too long# may result

in dropped call and suffers co-channel interference

Handover Design (11) Relative signal strength with margin:

Triggered only when the target cell signal strength is stronger than the serving cell by a margin h, point C

Prevent “ping-pong” effect repeated HO between two cells due to rapid fluctuations in received signal from both cells

Unnecessary HO may occur if the serving cell is sufficiently strong

Relative signal strength with margin and threshold Triggered when the serving cell signal drop below

threshold and the target cell signal is stronger by a margin Occurs at point C if the threshold is set at T1 and T2 Occurs at point D if threshold is set at T3

HO initiation criteria based on 4 variables: Averaging window size Measurement value weighting Threshold level Margin

Parameter to enable different type Of HO :

Handover Design (14) – HO Priority

RR-radio resource: target cells are ranked according to radio link

properties and priority levels

Imperative: target cells are ranked according to radio link

properties priority levels are not used

Handover Design (15) – HO Priority

Handover Causes And Decisions (1)

Handover Causes And Decisions (2)

Handover Regions (1) – Threshold Setting

Handover Regions (2) – Handover Level Threshold

Handover Flow

Handover Scenario (1)

HO Thresholds: Set to meet the optimum HO performance

2 Scenarios to be considered: Noise Limited Interference Limited

MS behaves differently in the above 2 scenarios

Handover Scenario (2)

HO Thresholds parameters and values

Handover – Noise Limited Scenario

Noise Limited Scenario Large cell with low traffic load, specially in rural area rxLev at cell border is just a few dB higher than receiver

reference sensitivity Main Handover criteria is level criteria

Receiver Reference Sensitivity according to GSM 05.05

Handover – Noise Limited Scenario (2)

Noise Limited Scenario Imperative to set the optimum values to avoid

“forward-back” HO General guideline:

rxLevMinCell – hoThresholdsLevDL = level hysteresis > 0 (+4dB..10dB)

rxLevMinCell > hoThresholdsLevDL + level hysteresis and

hoThresholdsLev > MS sensitivity + 3 dB

only DL is mentioned for illustration; in actual parameters planning, both UL/DL

Handover – Interference Limited Scenario (1)

Interference Limited Scenario Small cell with high traffic load, especially in urban area rxLev at cell border is significant higher than the receiver

sensitivity C/I is not much higher than the reference interference level Main Handover criteria is power budget criteria

Receiver Reference Interference Level according to GSM 05.05

Interference Limited Scenario Better cell criteria should be the main HO criteria Power budget HO guarantee that the MS is

served by the cell with lowest path loss Thus, higher chance for power control to reduce

interference

General guideline: hoMarginPBGT (cell1 cell2) + hoMarginPBGT (cell2 cell1) =

PBGT hysteresis > 0 (+6dB..12dB) Normally hoMarginPBGT is set symmetrically Low hoMarginPBGT values high “forward-backward” HO rate High hoMarginPBGT values low “forward-backward” HO rate Unsymmetrical hoMarginPBGT value is set to adapt cell service

area to traffic load Increases one cell service area and at the same time reducing its

corresponding neighbour cell service area

Power Budget Hysteresis

General guideline: Symmetrical hoMarginPBGT = 6dB: point x and a Unsymmetrical hoMarginPBGT (cell1 cell2) = 9dB

and hoMarginPBGT (cell2 cell1) = 3dB PBGT hysteresis = 12dB Point y and b Cell2 service area reduced from point x to y Cell1 service area increased from point a to b

Other HO Types And Features

Umbrella Handover

The Objective: To serve the target traffic more efficiently

Umbrella HO has priority over power budget HO The mapping table for gsmMacrocellThreshold

and gsmMicrocellThreshold

Umbrella Handover (2)

What does the table mean? Example:

If you set the gsmMocrocellThreshold** smaller than the MS class maximum output power, the MS is only allowed to HO to macrocell

At the same cell, its adjacency parameter msTxPwrMaxCell(n) should be set smaller than gsmMacrocellThreshold

Note ** gsmMacrocellThreshold is a BSC parameter, it need additional adjacency parameter to control per adjacency basis

Umbrella HO Algorithm

Umbrella Handover (4) When AV_RXLEV_NCELL(n) = -75dBm A MS class 4 in dedicated mode is in macrocell 1’ AV_RXLEV_NCELL(n) > hoLevUmbrella(n) (MS class 4 = 33dBm) <= (gsmMicrocellThrsehold =

33dBm) and (MsTxPwrMaxCell(n) = 33dBm) <=

(gsmMicrocellThreshold = 33dBm) Umbrella HO to microcell occurs When MS is at microcell border, av_rxLev = -98dBm and

av_rxLev_cell(n) = - 82dBm 1. av_RxLevUL/DL < hoThresholdsLevUL/DL 2. AV_RXLEV_NCELL(n) – av_RxLevDL –

(btsTxPwrMax – BTS_TXPWR) > hoMarginLev(n)

When MS is at microcell border, av_rxLev = -98dBm and AV_RXLEV_NCELL(n) = -82dBm

1. av_RxLevDL < hoThresholdsLevDL -98 dBm < -95 dBm

2. AV_RXLEV_NCELL(n) – av_RxLevDL – (btsTxPwrMax – BTS_TXPWR) > hoMarginLev(n) -82 – (-98) – (0 – 0) = 16 dB > 3 dB

HO due to level

Handover Due To Fast/Slow MS Speed

2 possibilities: MS speed in relation to cell size Measured MS speed

Both need AdjCellLayer(n) and hoLevelUmbrella(n) parameters **

Note ** see detail HO due to fast/slow moving MS algorithm

Handover Due To Fast/Slow MS Speed Algorithm

Handover Due To Fast/Slow MS Speed (2)

MS speed in relation to cell size Parameters are set per adjacency basis From Macro to micro Counter for each adjacent microcell +2 for each measurement >= rxLevMinCell(n) –1 for each measurement < rxLevMinCell(n) or no measurement

How to set fastMovingThreshold?

if microcell radius is about 200 meters, taking 2.5 m/s as slow moving limit; thus

total time to cross the microcell is 200/2.5 = 80 seconds if averaingWindowSizeAdjCell is set to 6 SACCH, this equal to

about 3 seconds for each measurement it take 5 seconds to decode an adjacent cell BSIC, thus total

measurements is (5 + 3* measurements) = 80 seconds thus total measurements are (80-5)/3 = 25 number of

measurements the fastMovingThreshold = 25*2 = 50 (because counter

increases by 2 for each measurement)

When the counter > fastMovingThreshold = 50; and

AV_RXLEV_NCELL(n) > hoLevUmbrella (n) = -80dBm

Umbrella HO due to slow moving MS ? what is the speed limit if

fastMovingThreshold = 24 for a cell radius of 205 meters ? 24 = 12 measurements; 12*3 + 5 = 41 seconds;

200 meters/ 41 = 4.8 m/s

Measured MS speed Related parameters:

Slow moving MS to lower layer adjacent cells (lowerSpeedLimit) Fast moving MS to upper layer adjacent cells (upperSpeedLimit) One unit value of lowerSpeedLimit upperSpeedLimit equal to

Handover – MS-BTS Distance To prevent MS from exceeding cell boundary Related Parameters:

msDistanceBehaviour 0 : Release immediately 1 - 60 : Release after certain time 1 - 60 s, try imperative

handover during that time 255 : No release, only imperative handover attempt

Handover – MS-BTS Distance (2)

msDistanceHoThresholdParam 1 step size correlates to 550 meters this parameter value depends on the designed

cell radius if the value is set to 2, the maximum cell radius for

the MS is 2*550 = 1100meters before the imperative HO is attempted in the 30 seconds period set in the parameter msDistanceBehaviour; if HO execution fails; the call will be terminated

enableMSDistanceProcess Set to yes to activate this feature

Traffic Reason Handover

TRHO effectively reduces the service area of a congested cell and Increases the service area of the under-utilised

target cells HO is triggered with amhTrhopPbgtMargin

instead of hoMarginPBGT General guideline:

Target cell minimum access level should be set higher to avoid bad DL rxQual after HO

amhTrhoPbgtMargin should be much lower than hoMarginPBGT

TRHO Algorithm

Traffic Reason Handover (2) – TRHO Parameter

BSC Parameter

BTS Parameter

Traffic Reason Handover (3) – TRHO Parameter

Adjacency Parameters

amhTrhoPbgtMargin(n) should be set lower than hoMarginPBGT

trhoTargetLevel(n) should be set higher than rxLevMinCell(n) to ensure only good adjacent cell is used

Traffic Reason Handover (4)

Directed Retry (DR)

A transition (handover) from a SDCCH in one cell to a TCH in another cell during call setup due to unavailability of an empty TCH within the first cell

To control traffic distribution between cells to avoid a call rejection

Can be used for both MOC and MTC Setting guidelines:

drThreshold should be higher than rxLevMinCell; else the improved target cell selection criteria will be ignored even drMethod = 1

Directed Retry (2) – Parameter Related

Directed Retry (2) - Algorithm

Directed Retry (3)

Example

Directed Retry (4)

the BSC cannot start the target cell evaluation within 2 seconds period from the start of directed retry procedure is triggered

after 2 seconds, the BSC continues to evaluate the target cell until 6 seconds period expires and if no suitable target cells are available, directed retry will be aborted **

** MS need at least 5 seconds to decode the neighbouring BSIC. Thus minimum maxTimeLimitDirectedRetry should be 5 seconds

cellType will be set based on the macro or micro cell in the network

Intelligent Directed Retry (IDR)

Queuing

Queuing Parameters :

If both queuePriorityUsed and msPriorityUsedInQueueing are used, queuePriorityUsed will be dominant factor

TimeLimitCall should be shorter than (maxTimeLimitDirectedRetry + minTimeLimitDirectedRetry)

Queuing (2) MaxQueueLength: The parameter specifies the number of call

attempts and handover attempts that can wait for a TCH release in a BTS. The value is the percentage of TRXs times 8

For a 4 TRXs cell, maxQueueLength = 50%, 50%*4*8 = 16 call attempts and HO attempts can wait for a TCH release in a cell

queuingPriorityHandover should be set higher than queuingPriorityCall

queuingPriorityCall should be set higher than queuePriorityNonUrgentHo

Non urgent HO: power budget HO, umbrella HO, slow moving MS HO and traffic reason HO

Urgent HO: quality and level reason HO

Queuing And Directed Retry

Queuing And Directed Retry (2)

Reference to Figure in previous slide, Timing Diagram for Queuing and Directed

Retry the call setup will not be able to handover to

directed retry if the timeLimitCall is longer than maxTimeDirectedRetry and the call will be terminated when the timeLimitCall expires

GSM-GPRS Operation

Power Control parameters

Power Control (1)

Power Control (2)

Objective: To adapt the transmit power of MS & BTS to

reception conditions

Power Control (3)

Power control advantages: reduction in MS average power consumption reduction in overall network interference level

Power control is applied separately: for uplink and downlink each logical channel

Power control is not applied to: downlink burst using the BCCH frequency

Power Control (4) - Algorithm

Power Control (5) - Regions

Power Control (6) - Implementation

Power Control (7) Measurement preprocessing for power control:

for each call UL and DL received signal level UL and DL received signal quality

The measurements are made over each SACCH multiframe 104 TDMA frames (480 ms) for a TCH 102 TDMA frames (470,8 ms) for an SDCCH

every SACCH multiframe, MS sends in the next SDCCH message block the DL measurement on dedicated channel via the Measurement report message to the serving TRX of the BTS

serving TRX performs UL measurements on the dedicated channel

Power Control (8) – General POC Parameters

Power Control (9) – Step Size

Power Control (10) – Step Size Or Variable

Power Control (11) – POC Range

Power Control (12) – POC Range

If optimumRxLevUL feature is activated; i.e. set to –85 dBm;

alternative power control algorithm for MS will be used

pwrDecrLimitBand0 pwrDecrLimitBand1 pwrDecrLimitBand2 pwrdecrQualFactor

Power Control (13) - Power Decrement Band Setting

TRX parameter: optimumRxLevUL = -85 dBm POC parameter:

pcUpperThresholdQualUL = 1 pwrDecrLimitBand0 = 10 dB pwrDecrLimitBand1 = 8 dB pwrDecrLimitBand2 = 6 dB

av_rxLev_UL = -80 dBm and av_rxQual_UL = 0 Power reduction is MS is 10 dB

TRX parameter: optimumRxLevUL = -85 dBm POC parameter:

pcUpperThresholdQualUL = 1 pwrDecrLimitBand0 = 10 dB pwrDecrLimitBand1 = 8 dB pwrDecrLimitBand2 = 6 dB

Averaging

Weighting is used when DTX is activated in the network

Weighting: Window size = 8, weighting = 2

Power Control (19) - Power Control Averaging

PC Priority: PC due to Lower quality thresholds (UL and DL) PC due to Lower level thresholds (UL and DL) PC due to Upper quality thresholds (UL and DL) PC due to Upper level thresholds (UL and DL)

Power Control (19) - Threshold

Power Control (20) - Threshold

Guideline: thresholds setting is imperative to avoid

undesirable ping pong effect of power control if the pcUpperThresholdsLev is set too low, power

down due to level at low rxlev will casue rxqual to deteriorate and subsequently power up occurs due to rxqual

rxqual improvement will lead to power down due to level again and the loop recurs

Power Control (21) - Regions

Power Control (22) - POC Threshold Values Example

Power Control (23) - MS Power Optimization

MS Power Optimisation 2 scenario:

During call setup During handover

Use the optimized MS output power to reduce the uplink interference

MS Power Optimisation Without MS Power Optimisation, MS access the cell with maximum Tx

power as specified by msTxPwrMaxCCH During Call Setup:

Related Parameters: per TRX

Example: MS_TXPWR_ OPT = MsTxPwrMax - MAX ( 0, (RXLEV_UL

- OptimumRxLevUL) ) When RXLEV_UL = -80dBm MS-TXPWR_OPT = 33 – max(0, (-80 + 85) = 28dBm compare to maximum power 33 dBm

MS Power Optimisation During Handover:

Related Parameters: per Adjacency

Indicates the optimum UL RF signal level after Handover

Only for intra-BSC HO When BSC calculates the optimized MS output

power, it presumes that the UL signal level is equal to downlink signal level measured by MS

If the DL is stronger than UL by 6 dB, msPwrOPtLevel should be set 6 dB than the desired UL signal level

MS Power Optimisation During Handover:

If AV_RXLEV_NCELL(n) = -75dBm, and Set msPwrOptLevel = -80dBm

MS_TXPWR_ OPT(n) = msTxPwrMax(n) - MAX ( 0, (AV_RXLEV_NCELL(n) - msPwrOptLevel) )

MS_TXPWR_ OPT(n) = 33 – max ( 0, (-75 + 80) = 28 dBm

Thus MS uses 28 dBm output power instead of 33 dBm

Power Control And Handover Control

Rule of thumb: POC should happen before HOC

2 ways to make this happens Thresholds Averaging windows size

RxLev Thresholds for POC > RxLev Thresholds for HOC

RxQual Thresholds for POC >= RxQual Thresholds for HOC

Window size (POC) <= window size (HOC)

Power Control And Handover Control (2)

Rxlev timing diagram

Power Control And Handover Control (3) - Example

RxLev Thresholds and window size: For UL (refer to the figure in previous slide)

POC: pcUpperThresholdsLevDL = -75 dBm, px = 2, nx

= 3 pcLowerThresholdsLevDL = -89 dBm , px = 2, nx

= 3 HOC:

hoThresholdsLevDL = -95 dBm, px = 3, nx = 4 What these setting mean?

Power Control And Handover Control (4) - Example

MS will power down if the 2 out of 3 av_RxLev_UL measurement samples is better than –75dBm

MS will power up if the 2 out of 3 av_RxLev_UL measurement samples is worse than –89dBm

If after powering up, the av_RxLev_UL is still lower than –95dBm with measurement sample 3 out of 4, HO will take place**

**Note: this happen when the MS is at the cell border and is transmitting at the maximum power

RxQual timing diagram

POC And HO relationships

Power Control And Handover UL

Power Control And Handover UL (2)

Power Control And Handover DL

Power Control And Handover DL (2)

GSM-GPRS Operation

TRX parameters

TRX Parameter

TRX Parameters

TRX parameters (2) preferredBCCHMark:

BCCH is automatically configure to its original state after the TRX fault has been eliminated

Benefit of using TRX output power within a common cell

optimumRxLevUL: Used in conjunction with POC –MS power optimisation

ETRX: Extended TRX A cell radius of an ordinary cell is 35 km. Extended TRX can serve up to about 70 km The implementation is based on one-BCCH (broadcast control

channel) and two-TRX (transceiver) solution. The normal coverage area is served with different TRXs than the

extended coverage area.

TRX Parameters (3)

ETRX: Timing of the TRXs which serve the extended

coverage area is delayed so that they can serve the area beyond 35 km

Effectively 2 cell radius for a single cell

floatingMode: TRX can be dynamically switched to operate in

any of the sectors within a BTS Automatically replaces a faulty BCCH TRX

GSM-GPRS Operation

Adjacency Parameters

Adjacency Parameters (2)

Used to control dedicated mode MS for HO purpose These parameters play only the support role to HO or

any other optional features

hoTargetArea: indicates whether the adjacent cell is an extended range

cell or a normal cell If the adjacent cell is an extended cell, it determines which

TRX (extended or normal) of the adjacent cell from where the BSC will allocates a TCH during an intra-BSC HO attempt

0 = Normal cell 1 = Extended range cell, a TCH is allocated from a normal

TRX 2 = Extended range cell, a TCH is allocated from an

extended range TRX. 3 = Extended range cell, a TCH is allocated from a TRX

whose type (extended range or normal range) is the same as the type of the serving TRX.

Dualband Parameters multibandCell

define whether adjacent cells with a BCCH allocated from a different frequency band than the serving cell BCCH are taken into account in handovers and in idle mode cell selection or reselection

earlySendingIndication accept or forbid the early sending of the MS Classmark 3

message in call setup phase to the network

multiBandCellReporting define the number of adjacent cells from the other

frequency band that the MS will report in the RX level report

GSM-GPRS Operation

MS Mobility Management

Mobility Management Dual-band MS:

Idle mode Dedicated mode

Objectives: To manage traffic more efficiently To increase call setup success rate

Strategies: Accommodate both single and dualband MS in both dedicated

and idle mode with existing network configuration and traffic volume

How to design? Using existing BSS parameters Dualband parameters

MM (2) – Idle Mode

MM (3) – Case Study Case study as follows: Network access preference:

GSM900 layer DCS1800 layer

Justification? GSM900 is a contiguous coverage layer DCS1800 is a capacity relief layer

How to design? Idle Mode:

Make DCS1800 layer less attractive by setting negative offset to C2

Only singleband (1800) MS is allowed to access the DCS1800 layer

Dualband and singleband(900) access GSM900 layer

MM (4) – Dedicated Mode

MM (5) – Case Study

Case study as follows:…continue Dedicated Mode: Depending on the cell traffic and cell

configuration HO preference:

G900 to D1800 (negative power budget margin) D1800 to D1800 (normal power budget with

higher priority) G900 to G900 (normal power budget with lower

priority) D1800 to G900 (large positive power budget

margin)

MM (6) Case study as follows:…continue The good and the bad of this strategy Advantage:

Simple parameter modification (only C2 required change for idle mode MM)

DCS1800 traffic load can be managed based on cell-by-cell basis

Disadvantage: GSM900 may suffer call setup blocking (both dualband and

G900 MS access network directly) High HO rate

MM (7) – Idle Mode

MM (8) – Dedicated Mode

Dual Band Network Operation

Idle Mode For Dualband Mobile Management

MM (9)

A dual-band multi-layer network design Design criteria:

GSM band layer consideration Macro-micro layer consideration

Idle mode preference: GSM900->DCS900 Micro followed by macro for slow moving Macro followed by micro for fast moving

Dedicated mode preference: DCS1800->GSM900

MM (10)

A dual-band multi-layer network design…continue Network topology consideration

Neighbour relationships Adjacency parameters set

GSM-GPRS Operation

BSC Parameters

BSC Parameters (2)

Cell Definition For Multilayer Network

BSC Parameters (3) – Cell Definition

How to set? MsTxPwrMaxCell(n) >= gsmMacrocellThreshold–

adjacent cell type is macrocell MsTxPwrMaxCell(n) <= gsmMicrocellThreshold–

adjacent cell type is microcell BSC Parameters:

gsmMicrocellThreshold = 33 dBm gsmMacrocellThreshold = 35 dBm

Cell Parameter: msTxPwrMax(n) = 33 dBm

BSC Parameters (4) – Cell Definition

What these values mean? (MsTxPwrMax(n) = 33dBm) <= (gsmMicrocellThreshold

= 33dBm) the adjacent cell type is microcell

BSC Parameters (5) – MSC HO

How to set disableIntHo? Set to YES – not all HO is controlled by MSC

Only inter-BSC HO requires MSC Intra-BSC HO will not require MSC To reduce MSC load

Set to NO - all HO is controlled by MSC

How to set genHandoverRequestMessage? Typical values is 3

3 preferred cells are included in the HANDOVER REQUIRED message

The message is sent from BSC to MSC Only for inter-BSC HO scenario

BSC Parameters (8) – Directed Retry

How to set disableExtDr? Set to YES – external directed retry HO will not be

allowed Set to NO – external directed retry HO will be

allowed when it is necessary Inter-BSC directed retry HO will take place for cells at

the BSC boundary

BSC Parameters (9) – Handover Type

How to set hoPreferenceOrderInterfDL? Set to inter – intercell HO is preferred when

HO is due to DL interference Set to intra - intracell HO is preferred when

HO is due to DL interference

How to set msDistanceBehaviour? Action taken after timing advance has exceeded the

threshold Value = 255 – no channel release, only HO attempts Value = 0 – release channel immediately, no HO

attempts Value = 10

HO attempt within 10 seconds after the timing advance has been exceeded

Channel will be released if HO does not succeed during the 10 seconds window period

How to set rxLevBalance? This parameter is used for the purpose of

uplink interference level calculation Typical value = 6 dB

BSC Parameters (12) – MS Speed Detection

How to set msSpeedC11? This parameter for MS speed related HO If you decide maximum MS speed for slow moving traffic is 20

km/h The value should be set to 10 Any MS speed exceeds the 20 km/h threshold will be considered

fast moving traffic

BSC Parameters (13) – Advanced Multilayer Handling

BSC Parameters (14) Advanced Multilayer Handling

How to set amhUpperLoadThreshold? This parameter defines the maximum cell

traffic load When the the cell traffic load exceeds the

threshold, intra-BSC traffic reason HO will occur

Example: amhUpperLoadThreshold = 70% If the cell traffic load is 75%, Traffic Reason HO

will be initiated

How to set amhLowerLoadThreshold? This parameter defines the minimum cell

traffic load If the traffic load of the serving cell does not

exceed the amhLowerLoadThreshold, the IUO handover or the Direct Access to super-reuse TRX are not allowed

How to set amhMaxLoadOfTargetCell? This parameter defines the maximum

adjacent cell traffic load If the adjacent cell traffic load is below this

threshold, the cell can be the target for Traffic Reason HO

Example: amhMaxLoadOfTargetCell = 80% If the adjacent cell traffic load is 60%, this cell can

be the target cell for Traffic Reason HO

How to set amhTrhoGuardTime? This parameter defines the guard time before

Handover back to original cell is allowed If set to 10 seconds

BSC-controlled or MSC-controlled Traffic Reason HO occurs

During this 10 seconds period, HO back to the original cell is NOT allowed

Handover back to original cell can only be allowed after the 10 seconds period expires

BSC Parameters (18) – Dynamic Hotspot

What these parameters mean? badQualLimit:

define the limit for bad signal quality in term of proportion of bad samples in all samples in signal quality measurement.

goodQualLimit: define the limit for good signal quality. The value of the parameter has to be equal to or smaller than the

value of the signal quality limit 2 (SQL2) parameter.

sigQualLimit1: define the lower limit for adequate signal quality in adjacent

cells. the value of the parameter has to be equal to or smaller

than the value of the bad quality limit (BQL) parameter.

sigQualLimit2: define the upper limit for adequate signal quality in

adjacent cells. The value of the parameter has to be equal to or smaller

than the value of the signal quality limit 1 (SQL1) parameter.

GQL<=SQL2<=SQL1<=BQLkris.sujatmoko@gmail.com

tchProbability1: define the probability of TCH allocation when signal quality in the adjacent cell, x signal quality limit 1 (SQL1) <= x < bad quality limit (BQL) .

tchProbability2: define the probability of TCH allocation when signal quality in the adjacent cell, y signal quality limit 2 (SQL2) <= y < signal quality limit 1 (SQL1) >= TCH probability 1 (TCP1) parameter.

tchProbability3: define the probability of TCH allocation when signal quality in the adjacent cell, z good quality limit (GQL) <= z < signal quality limit 2 (SQL2). >= TCH probability 2 (TCP2) parameter.

Operator defined probability table The probability is set by operator

BSC Parameters (22) – Dynamic Hotspot Example

BSC Parameters (23) – Dynamic Hotspot Example

The probability to allocate TCH in cell A is 51% The probability to allocate TCH in cell B is 80% The average probability is 51%*80% = 40% < fixed reference = 50% Reject resource request

GSM-GPRS Operation

End of Section 5

BSS Parameter

modul 5 bss parameter

cell reselection parameters

cell bcch

idle mode cell reselection

specific cell

s cell

serving cell

cell prioritisation

better cell

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