GSM Measurements for Inter-RAT Cell Reselection & Handover
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GSM Measurementsfor Inter-RAT
Cell Reselection & Handover
Cell Reselection and Handover
Cell Reselection HandoverDone by MS in the• (circuit switched) idle
mode, and• packet idle and packet
transfer modeGSM cell re-selection to
WCDMA may differ between
• non-GPRS capable mobiles,
• GPRS capable mobiles, and
• GPRS capable mobile with Packet BCCH
Cell reselection to weaker WCDMA cells is possible
Handover from GSM is supported if the load of the serving GSM cell is above certain threshold and the measured quality (CPICH Ec/No) from adjacent WCDMA cell is above a minimum value.Different load threshold for speech calls and Non-Transparent (CS) Data can be set.
Load Reason Algorithm in RAN 1.5Speech calls can be served adequately both in GSM and UMTS. Consequently,
only in a high load situations, multiple RAT phones are handed over from GSM to UMTS. The number of occupied traffic channels on the available transmission resources triggers the handover decision in the BSC.
Circuit switched data calls may not surpass a capacity threshold before the BSC imitates the HO procedure.
GPRS MS can be directly pushed to 3GPP cell reselection.
Load Reason Algorithm in RAN 1.5
100%
80%
0%
Service based handovers for non-transparentdata to provide maximumuser bit rates
Load reason handoversfor speech
Load of GSM cell (Occupation of TCHs in TRXes)
Data to WCDMAregardless of GSM load
Data to WCDMAregardless of GSM load
Speech to WCDMAonly with high GSM load
Speech to WCDMAonly with high GSM load
Higher bit ratesfor data users
Higher bit ratesfor data users
More capacity for
speech
More capacity for
speech
Packet BCCH parameters can be usedto push GPRS mobiles to WCDMA
Packet BCCH parameters can be usedto push GPRS mobiles to WCDMA
Cell Reselection Algorithm from GSM to FDD-WCDMA (cs)Cell Reselection List
WCDMA measurements, when:RLA_C Qsearch_I (Non GPRS)
If, for suitable UMTS cell & for a period of 5 s:
CPICH RSCP > RLA_C + FDD_Qoffset
CPICH Ec/No FDD_Qmin
no prioritiesbetween WCDMA
neighbours
Measurement Updates:• RLC_C value of the serving cell• at least 6 strongest non serving GSM cells
at least every 5 s
check
and
WCDMA cellreselection
BCCH: FDD_Qmin, FDD_Qoffset
Example: cs Cell-Reselection to a Stronger WCDMA Cell
Qsearch_I (e.g. –98 dBm)
5 seconds
Cellreselec
tion
time
FDD_Qoffset(e.g. 8 dB)
Start WCDMA
measurements
ServingGSM cell
Non serving neighbour GSM cell
Suitable neighbourWCDMA cell
CPICH Ec/No
FDD_Qmin
Example: ps Cell-Reselection to a Weaker WCDMA Cell
time
Qsearch_P (e.g. –70 dBm)
Start WCDMA
measurements
FDD_GPRS_Qoffset(e.g. -8 dB)
Cellreselec
tionCPICH
Ec/No FDD_Qmin
5 seconds
ServingGSM cell
Non serving neighbour
GSM cell
Suitable neighbourWCDMA cell
Cell Reselection Parameters
ParameterParameter for NON GPRS
Qsearch_X Qsearch_IFDD_QoffsetFDD_Qoffset
RLA_X RLA_C
Parameter for GPRS
Parameter forPBCCH GPRS
Qsearch_P Qsearch_PFDD_QoffsetFDD_GPRS_Qoffset
RLA_P RLA_P
0-988
-78
1 2-94 -90
9 10-74 -70
3-8611-66
4-8212-62
5-7813-58
6 7-74 Always14 15-54 Never
R_BelowdBm
R_UpperdBm
0Always
80
1 2-28 -24
9 104 8
3-201112
4-161216
5-121320
6 7-8 -414 1524 28
RangedB
RangedB
0-20
1 2-19 -18
3-17
4-16
5-15
6 7-14 -13
RangedB
Parameter
Name for Sys Info (SI)
Qsearch_I
2quater
Qsearch_PQsearch_P
2quater 3quater
FDD_QMin
2ter
FDD_(GPRS)Qoffset
2quater
FDD_REP_QUANT
2ter
3G_search_PRIO
2(3)quarter(PBCCH)
FDD_Qmin
Qsearch_I & Qsearch_P
FDD_Qoffset & FDD_GPRS_Offset
Handover Process incl. RAN 1.5
Handover Triggering Thresholds set in BSCHandover Triggering Thresholds set in BSC
Inter-RAT measurements when: The RXLEV of the serving cell is above or
below the given threshold Qsearch_C
Inter-RAT measurements when: The RXLEV of the serving cell is above or
below the given threshold Qsearch_C
Handover Decision is done in case of• Load of the serving cell > Load_Threshold• and CPICH Ec/No> min Ec/No Threshold
Handover Decision is done in case of• Load of the serving cell > Load_Threshold• and CPICH Ec/No> min Ec/No Threshold
MS reports best UTRAN cell based on measurement results
MS reports best UTRAN cell based on measurement results
Handover command is send to MSCHandover command is send to MSC
Latest after 5 s(one WCDMA band)
However in S10.5 MS is measuring the UTRAN cells continuously if they are defined as a neighbour, measurements are done during idle periods
Example: Handover to a Weaker WCDMA Cell
Qsearch_C
Serving GSM cell
Non serving neighbour GSM cell
Suitable neighbourWCDMA cell
FDD_Qoffset(< 0)
5 seconds
Cellreselec
tion
CPICH Ec/No
FDD_Qmin
GSM ISHO in RAN1.5: Example
• Load Threshold for Speech Calls inter-RAT Handover• LOAD_THRESHOLD_FOR_SC_IS_HO= 80%
• Min Ec/No threshold for a handover to the UTRAN adjacent cell• MIN_ECNO_THRSHOLD = -15 dB
• Qsearch_c = 15 (if Qsearch_c = 15, the mobile is not allowed to measure UTRAN adjacent cells and therefore the BSS does not send the Measurement Information message to the mobile at all)
1 Load of the serving cell = 45% and the measured Ec/No = - 20 dB
--> Handover to the UTRAN not possible due to low load and low Ec/No
2 Load of the serving cell = 45% and the measured Ec/No = - 10 dB
--> Handover to the UTRAN not possible due to low load
3 Load of the serving cell = 95% and the measured Ec/No = -10 dB
--> Handover to the UTRAN possible
Handover example (speech/Transparent data)-
GSM ISHO in RAN1.5: Example
Handover example (Non Transparent data)-
Load Threshold for Non-Transparent Data inter-RAT Handover LOAD_THRESHOLD_FOR_NON_TPC_IS_HO =0% (default)
Min Ec/No threshold for a handover to the UTRAN adjacent cell
MIN_ECNO_THRSHOLD= -15 dB Qsearch_c = 15 (if Qsearch_c = 15, the mobile is not allowed
to measure UTRAN adjacent cells and therefore the BSS does not send the Measurement Information message to the mobile at all)
1 Load of the serving cell = 0% and the measured Ec/No = - 20 dB
--> Handover to the UTRAN not possible due to low Ec/No
2 Load of the serving cell =0% and the measured Ec/No = - 10 dB
--> Handover to the UTRAN possible
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