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Explain about parameter GSM that can be optimized. Like handover parameter, access parameter, etc
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GSM-GPRS Operation
BSS Parameter
Module 5
2
Outline BSS Parameters Structure BTS Parameters
MS Mode Idle Mode
Cell Selection Cell Reselection
Dedicated Mode Handover Power Control
BSC parameters
GSM-GPRS Operation
BSS Parameters
BTS Parameters
BSC Parameters
5
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
BTS.
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.
6
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
BTS.
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
slot.
Frequency Hopping System (FHS) The frequency hopping system object contains hopping parameters for the
BTS.
GSM-GPRS Operation
BTS Parameters
GSM-GPRS Operation
Parameter Related To Idle Mode
10
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
FCCH
SCH
BCCH
PCH
RACH
AGCH
SDCCH
FACCH
TCH
FACCH
idle mode
“off” state
dedicated mode
idle mode
11
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.
12
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
13
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.
15
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
16
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
17
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
18
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
20
Idle Mode – Cell Reselection With C2 (2)
For penaltyTime = 640 seconds, C2 = C1 – cellReselectOffset
For penaltyTime < 640 seconds, C2 = C1 + cellReselectOffset – temporaryOffset for T <=
penaltyTime C2 = C1 + cellReselectOffset for T > penaltyTime
23
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
24
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
25
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
26
Cell Selection Case Study (4)
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
27
Cell Selection Case Study (5)
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
28
Cell Selection Case Study (6)
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
29
Cell Selection Case Study (7)
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
30
Cell Selection Case Study (8)
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
34
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
35
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:
36
Idle Mode – Cell Reselection Hysteresis(3)
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
37
Idle Mode – Cell Reselection Hysteresis(4)
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
38
Idle Mode – Cell Reselection Hysteresis(5)
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
GSM-GPRS Operation
Handover Parameters
44
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
45
Handover Design (2)
Network resource: Minimising number of HO minimising switching
load
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
46
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
50
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
51
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
53
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
54
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
55
Handover Design (12)
HO initiation criteria based on 4 variables: Averaging window size Measurement value weighting Threshold level Margin
57
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
64
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
66
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
67
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
72
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
73
Handover – Interference Limited Scenario (2)
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
74
Handover – Interference Limited Scenario (3)
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
77
Handover – Interference Limited Scenario (6)
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
80
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
81
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
84
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)
85
Umbrella Handover (5)
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
86
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
89
Handover Due To Fast/Slow MS Speed (3)
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
90
Handover Due To Fast/Slow MS Speed (4)
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)
91
Handover Due To Fast/Slow MS Speed (5)
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
93
Handover Due To Fast/Slow MS Speed (7)
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
2km/h
94
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
95
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
96
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
99
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
101
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
105
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
107
Queuing
Queuing Parameters :
If both queuePriorityUsed and msPriorityUsedInQueueing are used, queuePriorityUsed will be dominant factor
TimeLimitCall should be shorter than (maxTimeLimitDirectedRetry + minTimeLimitDirectedRetry)
108
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
110
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
113
Power Control (2)
Objective: To adapt the transmit power of MS & BTS to
reception conditions
114
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
118
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
123
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
125
Power Control (14) - 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
av_rxLev_UL = -88 dBm and av_rxQual_UL = 0 Power reduction is MS is 4 dB
127
Power Control (16) - 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 = 1 Power reduction is MS is 8 dB
av_rxLev_UL = -88 dBm and av_rxQual_UL = 1 Power reduction is MS is 2 dB
128
Power Control (17) - Power Decrement Band Setting
Averaging
Weighting is used when DTX is activated in the network
129
Power Control (18) - Power Decrement Band Setting
Weighting: Window size = 8, weighting = 2
130
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)
132
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
135
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
136
Power Control (24) - MS Power Optimization
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
137
Power Control (25) - MS Power Optimization
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
138
Power Control (26) - MS Power Optimization
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
139
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)
141
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?
142
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
GSM-GPRS Operation
TRX parameters
152
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.
153
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
156
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
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Adjacency Parameters (4)
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.
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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
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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
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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
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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)
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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
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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
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MM (10)
A dual-band multi-layer network design…continue Network topology consideration
Neighbour relationships Adjacency parameters set
GSM-GPRS Operation
BSC Parameters
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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
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BSC Parameters (4) – Cell Definition
What these values mean? (MsTxPwrMax(n) = 33dBm) <= (gsmMicrocellThreshold
= 33dBm) the adjacent cell type is microcell
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BSC Parameters (6) – 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
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BSC Parameters (7) – MSC HO
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
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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
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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
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BSC Parameters (10) – Handover Type
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
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BSC Parameters (11) – Handover Type
How to set rxLevBalance? This parameter is used for the purpose of
uplink interference level calculation Typical value = 6 dB
184
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
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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
187
BSC Parameters (15) Advanced Multilayer Handling
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
188
BSC Parameters (16) Advanced Multilayer Handling
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
189
BSC Parameters (17) Advanced Multilayer Handling
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
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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.
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BSC Parameters (19) – Dynamic Hotspot
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<[email protected]
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BSC Parameters (20) – Dynamic Hotspot
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.
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BSC Parameters (21) – Dynamic Hotspot
Operator defined probability table The probability is set by operator
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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
