2G Handover Details (Huawei)

2G Handover Details
Md. Mustafizur Rahman
RNPO Engineer

2
Objectives
Upon completion this course, you will
be able to:
– Understand the type of handover.
– Master handover judgment flow
– Configure handover data
– Master handover signaling flow

3
Chapter 1 Introduction of Handover
Chapter 2 HO Algorithm process
Chapter 3 HO Data Configuration
Chapter 4 HO Signaling process

8
Chapter 1 Introduction of Handover
Chapter 3 HO Data Configuration
Chapter 4 HO Signaling process

9
Section 1 General HO process
Section 2 Measurement report preprocessing
Section 3 Penalty processing
Section 4 Basic ranking and Secondary ranking
Section 5 Condition of handover

10
General HO Algorithm Process
M.R.
preprocessing
Penalty
processing
Basic ranking
Secondary
ranking
HO judgment
TA emergency HO
BQ emergency HO
RSD emergency
HO
Interf. emergency HO
Load Sharing HO
Edge HO
Layer HO
PBGT HO
Processing
program
OM forced HO
Directed retry
Overlaid/underlaid HO
Fast moving MS
HO
1
1

11

12
Measurement Report
• Uplink MR includes uplink receiving level and quality.
• Downlink MR includes downlink receiving level, downlink
receiving quality of the serving cell and other downlink
receiving levels from the neighbor cells.
Serving cell Neighbour cell
The downlink
measurement report
of the serving cell
The uplink measurement
report of MS
The downlink measurement report
of the neighbour cell (BCCH)

13
Measurement Report
• In the MR, the TCH measurement of the serving cell is classified into FULLSET and
SUBSET. The FULLSET measures the TCH channels (signal receive level and
quality), whereas the SUBSET measures the channels in DTX mode (signal receive
level and quality). The MRs provided by the MS and BTS indicate whether the DTX
scheme is adopted.
• If DtxMeasUsed is set to TRUE, then the FULLSET or SUBSET values should be
taken according to the DTX indication bit in the MR. That is, if the MR indicates
that DTX is used, then the SUBSET values should be selected; otherwise, the
FULLSET values should be selected. Especially, if no DL measurement reports
sending to BSS, the FULLSET values will be selected.
• If DtxMeasUsed is set to FALSE and the MR indicates that DTX is not used, the
FULLSET values should be taken; if the MR indicates that DTX is used, then the
SUBSET values should be taken. In the latter case, the SUBSET values should be
used irrespective how DTX is indicated in the MR.

15
Period of measurement report
• The downlink MR is sent to BTS in SACCH uplink
– The interval is 480ms/per time when MS is on TCH
– The interval is 470ms/per time when MS is on SDCCH
12TCH 12TCH1SACCH 1 Idle
480ms 4 TCH multi-frames

16
MR interpolation
– Every time BSC receives a measurement report, there will be an
update to the basic rank of the cells.
– BTS may fail to receive the measurement report from MS. Before
the rank-update, BSC needs to recover the lost measurement
reports according to Filter Table. If the lost MR amount is within the
allowed range, then recovers the lost MR according to the algorithm.

17
MR interpolation
– If the latest two received MR are not continuous, that is, their serial numbers are
not consecutive, then apply the interpolation as follows:
– For the serving cell, when the number of lost MRs is less than the value of
Allowed MR Number Lost, then the linear interpolation of the MRs must be
performed.
– If the number of lost MRs is greater than the value of Allowed MR Number
Lost, then the previous measurement values should be discarded and the
recalculation should be performed on receipt of the MRs.

19
Filter length Parameters:
 Filter Length for TCH Level ( Recommended Value = 4)
 Filter Length for TCH Qual ( Recommended Value = 4)
 Filter Length for TA ( Recommended Value = 4)
Straight average filtering is used in all HO algorithm except fast moving HO.

20
Filtering: rxlevn =à* rxlev (n-1) + ß *(signal strength )n
ß=1-à
Filtering: Exponential filter
 Exponential filter is used in Fast moving HO decision algorithm.
 Exponential filter has faster response time.
MR
MR
Continuous MR
flow

22

30
BTS
HO failure
BSC
Cell A
Cell B
Penalty on the Target Cell
Punish the target cell when a HO fails.
This is to avoid the MS to select this
cell again in next HO judgment.

31
BTS
BQ& TA HO
BSC
Cell A
Cell B
Penalty on the Source Cell
Punish the original serving cell
when an emergency HO ( due to
BQ and TA) occurs.

32
Penalty on Non-umbrella Layer
• Giving penalty on the other three layers after MS handovers to Umbrella cell by
fast-moving-HO. This is to keep MS staying in the umbrella cell and avoid
frequent HO.

33
Penalty on Overlaid/Underlaid Cell
• A new Overlaid/Underlaid HO is
prohibited within a penalty time
after an Overlaid/Underlaid HO
failure.

35

39
• After the M rule , the serving cell and candidate neighbor cells are ranked in descending
order according to the receiving level only
• Both the serving cell and the neighbor cells have their own 16bits value. The smaller the
value, the higher the priority and position of the cell is in the cell list.
K rule Criterion

50
The 15th bit: determined by Cell Type
• The 15th bit: Bit value is decided by cell type
– Serving cell or Neighbor cells:
– When cell type is extension cell 1.
– When cell type is normal cell 0.
• The 16th bit: Reserved bit
16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1

52

Condition:
If the MR used for handover decision is a pre-processed MR, then the flag bit in the MR is used for
handover decision directly and if the MR is not pre-processed, then
Where,
SS_ULs_interp_1 indicates the receive level on the latest uplink TCH of the serving cell.
Tborder_ul indicates Edge HO UL RX_LEV Threshold.
B indicates Filter Parameter B.
SS_ULs_fm_f is equal to original uplink receive level x Filter Parameter A1-A8.

66
Summary Emergency HO Parameters

68

69
Types of Handover Condition
• Emergency HO
– Timing Advance HO
– Bad Quality HO
– Interference HO (off)
– Rx_Level_Drop HO (off)
• Load HO (off)
• Normal HO
– Edge HO, Layer cell HO and PBGT HO
• Fast moving HO (off)
• Overlaid/Underlaid HO

73
Cell Load HO
• Cell Load HO Criterions :
– System load of BSC < System Flux Threshold for
Load HO
– Load of serving cell > Load HO threshold
• Requirements for the target cell
– Load of target cell < Load HO threshold

76
Normal HO
EDGE Handover
Condition: Neighbor RxLev> Serving Rxlev + Inter-Cell HO Hysteresis

77
Normal HO…
EDGE HO Parameters

79
Normal HO…
• When the serving cell is micro cell :
– When the MS has traveled through P numbers of cell, and there are Q (=<P)
numbers of cell that the MS has traveled in high speed, the criteria is satisfied.
MS will be handed over to umbrella cell.
• When the serving cell is umbrella cell :
– When the MS is traveling high speed in umbrella cell, a greater penalty can be
given to the micro cell for a duration of time (penalty time). In this way, the
MS will not use the micro cell. Note :In this case, the micro cell is only used
under urgency conditions( Poor TA and BQ ).
This parameter indicates whether an MS that moves fast in a micro cell can be
handed over to a macro cell. MS that moves fast in a micro cell can be handed
over to a macro cell, thus reducing handovers.
Fast Moving Handover

80
Normal HO…
If the duration for an MS to stay in the serving cell is less than the value of MS Fast-
moving Time Threshold (s) the number of fast-moving cells for the MS is calculated.
• Criteria
– The MS travels across a number of cells (the number is specified by MS Fast-
moving Watch Cells) in sequence. Among these cells, a small number of
cells (the number is specified by MS Fast-moving Valid Cells) are of fast
movement
– The target cell is a macro cell having the higher level of the cell layer.
– The candidate neighbor cells must meet the following:
– The neighbor cells have the smallest 16-bit sequence number

82
Normal HO…
Fast Moving Handover Parameter

84
Normal HO
• Layer HO criterions: follow 16-Bit rule
– Serving cell :
– No requirement
– Target cell :
– Layer of the Target cell is lower than the serving cell.
– Receive level of the Target cell > Inter -layer cell threshold + Inter-layer cell
hysteresis.
– Target cell should be ranked higher than the serving cell.
– If all these conditions are met during the period specified by Layer HO Valid Time(s) within
the latest Layer HO Watch Time(s), that is, if the P/N criterion is met, then the hierarchical
handover is triggered.
Layer Handover

85
Normal HO…
Layer HO Parameters

87
Normal HO…
• PBGT HO Criterions : follow 16-Bit rule
– Target cell’s path loss is smaller than the serving cell’s path loss by the PBGT
threshold value.
– {Rxlev (n) – Rxlev (s)} > PBGT HO Threshold
– Satisfying the P/N rule.
– Target cell should be ranked higher than the serving cell.
• Note :
– PBGT HO can only occur between same-priority cell. If the system permits
PBGT HO for the cell, PBGT HO can occur in either inter-BSC or inter-MSC.
– The lower the PBGT HO Threshold the easier to handed over the call to a
lower level neighboring cell.
Power Budget Handover

88
Normal HO…
Power Budget Handover Parameter

92
Underlaid/Overlaid Handover
• Enhanced Underlaid/Overlaid Subcell will be based in the following factors:
– Received Signal level
– Timing Advance
– Quality
– Traffic Load of the Underlaid
 Settings of Assign Optimum Layer will be followed during TCH Assignment in a Concentric cell whether
to Underlaid/Overlaid/No preference or by System Optimization.
System Optimization: Assignment according to the MR provided through the SDCCH.

93
 Handover on the Subcell TCH can be classify into the following:
 Handover from Underlaid Subcell to Overlaid Subcell due to moving
MS
 Handover from Overlaid subcell to Underlaid subcell due to Traffic
Load Condition
 Handover from Overlaid Subcell to Underlaid subcell due to moving
MS
Note: Provided that None of the emergency handover, enhanced dual-band network handover,
load handover, edge handover, better cell handover, and PBGT handover is triggered.

94
Handover from Underlaid Subcell to Overlaid Subcell due to moving MS
 Handover Criteria:
 The penalty timer with duration of Penalty Time of UL to OL HO already expired
 Number of Failed Handovers from Underlaid Subcell to Overlaid Subcell < value of MaxRetry Time after UtoO Fail
 If RX_LEV for UO HO Allowed is set to Yes, the downlink receive level after power control compensation is greater
than the value of UL to OL HO Received Level Thrsh.
 If ATCBHoSwitch is set to Yes, then (downlink receive level of the primary BCCH in the underlaid subcell - downlink
receive level of the neighbor cell whose level is the highest) > value of Distance Between Out And Inn Cell
boundary. (Set to Closed in GP Network)
 If RX_QUAL for UO HO Allowed is set to Yes, the downlink receive quality of underlaid subcell after filtering < value
of RX_QUAL Thrsh
 If TA for UO HO Allowed is set to Yes, the TA of underlaid subcell after filtering < (TA Thrsh.- TA Hysteresis)

95
UL to OL Handover due to moving MS Parameter

96
Overlaid/Underlaid Handover
Handover from Overlaid Subcell to Underlaid Subcell due to Traffic Load Condition
UL to OL HO due to Traffic Load criteria
 UtoO Traffic HO Allowed should be set to YES
 If TCH usage of the underlaid subcell > En Iuo Out Cell General OverLoad Thred, and the MSs that meet the handover
conditions are within the handover margin. The handover margin is stepped from the maximum level (-47 dBm) to the
boundary of the overlaid and underlaid subcells level by level.
 If the TCH usage of the underlaid subcell > En Iuo Out Cell Serious OverLoad Thred, the period specified by En Iuo In
Cell Load classification HO Period should be shortened to enable the faster handover of the MSs in the underlaid subcell
to the overlaid subcell.
OL to UL HO due to Traffic Load criteria
 UtoO Traffic HO Allowed should be set to YES
 If the load of the underlaid subcell < En Iuo Out Cell Low Load Thred and if the MS is within the handover margin, the
handover from the overlaid subcell to the underlaid subcell is triggered. The maximum range of the handover margin is from
OL to UL HO Received Level Thrsh. to the maximum level (-47 dbm).
 If En Iuo In Cell Load classification HO Period of the handover margin is stepped to the BTS from OL to UL HO
Received Level Thrsh. for En Iuo In Cell Load classification HO Step, the MSs on the overlaid subcell boundary are
preferentially handed over to the underlaid subcell.

97
OL to UL Handover due to moving Traffic Load Condition Parameter

98
Handover from Overlaid Subcell to Underlaid Subcell due to moving MS
 Handover Criteria:
 If RX_LEV for UO HO Allowed is set to Yes, the downlink receive level after power control
compensation < value of OL to UL HO Received Level Thrsh.
 If ATCBHoSwitch is set to Yes, (downlink receive level of the primary BCCH in the underlaid subcell –
downlink receive level of the neighbor cell whose level is the highest) < (Distance Between Out And
Inn Cell boundary - Distance Hyst Between Out And Inn Cell Boundary) (Set to Closed in GP
Network)
 If RX_QUAL for UO HO Allowed is set to Yes, the downlink receive quality of the underlaid
subcell after filtering > RX_QUAL Thrsh.
 If TA for UO HO Allowed is set to Yes, the TA of the underlaid subcell after filtering > (TA Thrsh. + TA
Hysteresis)

99
OL to UL Handover due to moving MS Parameter

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GSM1800
GSM900

2G Handover Details (Huawei)

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