KPIs for InterRAT MRO - itg.lkn.ei.tum.de strength (RSRP in case of LTE) • RLF is triggered by...
Transcript of KPIs for InterRAT MRO - itg.lkn.ei.tum.de strength (RSRP in case of LTE) • RLF is triggered by...
1 © Nokia Siemens Networks
Inter-RAT MROWhat are the important KPIs?
B. Wegmann
Nokia Siemens Networks - ResearchMunich, Germany
Workshop ITG FG 5.2.4 on"Consistent system optimization in 3G/4G wireless networks“Stuttgart, October 6, 2010
Workshop ITG FG 5.2.4 / 06.10.20102 © Nokia Siemens Networks
Outline
• Inter-RAT mobility scenario
• MRO objectives
• Motivation for inter-RAT MRO
• Inter-RAT mobility problems and KPIs
• Inter-RAT vs. Intra-RAT & intra-frequency
• Conclusion
Abbreviations:
RAT: Radio Access Technology
MRO: Mobility Robustness Optimization
KPI: Key Performance Indicator
Workshop ITG FG 5.2.4 / 06.10.20103 © Nokia Siemens Networks
Inter-RAT mobility scenario
3G (or 2G)cell deployment
LTE cell deployment(limited coverage)
Intra-RAT mobility
Inter-RAT HO
triggered exemplarily by limited coverage of LTE
Inter-RAT HO / Cell reselection
triggered exemplarily by traffic management policies
Workshop ITG FG 5.2.4 / 06.10.20104 © Nokia Siemens Networks
MRO objectives
• Generic MRO aspects
– Replacing or minimizing the human intervention of mobility optimization tasks
– Automatically adapting of the mobility-related cell parameters based on evaluation of performance counters
– Dynamically improving the network performance in terms of mobility in order to provide improved end-user experience as well as increased network capacity
• Inter-RAT MRO aspects
– Automated alignment of thresholds and trigger event between different RATs
– Automated adapting of inter-RAT mobility parameters acc. to changing traffic steering policies
Workshop ITG FG 5.2.4 / 06.10.20105 © Nokia Siemens Networks
Motivation for inter-RAT MRO
• Deployment of 1st LTE roll-out phase will be concentrated on relevant traffic hotspot areas
• Full coverage provided by overlaying 2G/3G network
• Consequently, the limited LTE coverage will result in many inter-RAT handovers
• Trouble-free operation of the inter-RAT handovers is very important for operators from day one on
• Consistent joint parameter optimization among different RATsis difficult with traditional optimization means� An autonomous approach is required
Inter-RAT MRO is highly demanded SON featureInter-RAT MRO is highly demanded SON feature
Workshop ITG FG 5.2.4 / 06.10.20106 © Nokia Siemens Networks
Inter-RAT mobility problems
Failure events (RLF / drop)during inter-RAT HO
Unwantedinter-RAT HO events
Too late
Inte
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AT
HO
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Workshop ITG FG 5.2.4 / 06.10.20107 © Nokia Siemens Networks
Problem case: Too late inter-RAT HO (exemplarily)
• HO is triggered by signal strength (RSRP in case of LTE)
• RLF is triggered by SINR(below Qout)
• LTE end-of-coverage� no interference� bad S(I)NR due to weak signal
• RLF happens in RAT 1 before inter-RAT HO has been triggered
• After a certain time interval (t_recovery) UE reconnects to another RAT (RAT 2)
time
B2-1
LTE
B2-2
(-INF)
3G
RSRP
RSCP
time
Qout
LTE
B2-2
(-INF)
3G
SINR
t_QoutRLF
Trigger for HO� too late
Re-connectionto 3G
RAT 1
RAT 2 time
t_recovery
RLF
Workshop ITG FG 5.2.4 / 06.10.20108 © Nokia Siemens Networks
Impact of interference during HO
f1 f1
S I
Intra-RAT & intra-frequency
f1
f2
Signalstrength
Signalstrength
RAT A
RAT B
Frequency
f2
f1
Range
No interference(different frequency bands)
Inter-RAT / inter-frequency
SINR > 0 SINR < 0
Target cell = Interferer
Workshop ITG FG 5.2.4 / 06.10.20109 © Nokia Siemens Networks
Inter-RAT vs. Intra-LTE / intra-frequency mobility
Inter-RAT mobility …
• does not suffer from interference between source and target cell
– No “cell edge problem” (neighbor cell interference from reuse N=1)
– Large area where UEs can be connected either to source or targetcell with good signal quality (could be whole cell area in case of co-sited cells)
– Conservative thresholds avoid RLF-affected HO problems as “too late inter-RAT HO” on expense of coverage of one RAT and number of inter-RAT HOs (eventually even unnecessary HOs)
• is quite often policy-driven (traffic steering) and not dominately caused by radio condition (e.g. end-of-coverage)
Workshop ITG FG 5.2.4 / 06.10.201010 © Nokia Siemens Networks
Inter-RAT vs. Intra-LTE / intra-frequency mobility
Inter-RAT mobility …
• is missing X2-interface between source and target cell
• cannot utilize regular UE measurements
– Inter-RAT UE measurements have to be triggered (measurement event reporting)
– Measurement gaps required � additional costs
Workshop ITG FG 5.2.4 / 06.10.201011 © Nokia Siemens Networks
Critical use case:Mismatch of mobility parameters among RATs
LTE
3G
Traffic steering policy in 3G:
Handover to LTE whenever LTE
coverage is there, e.g.
3A-2 = RSRP > -125dBm
independent from the 3G signal quality
Traffic steering policy in LTE:
Handover to 3G, if LTE coverage gets
bad:
B2-1 = RSRP < -123dBm
and 3G coverage is sufficient, i.e.
B2-2 = RSCP > -108dBm
1
2
3
RSRP=-124dBm
RSCP=
-95dBm
time
RSRP = -123 dBm
LTE
3G
RSRP
RSCP
RSRP = -125 dBm
RSCP = -108 dBm B2-2
B2-1
1UE is setup in 3G and realizes that the measured LTE signal strength is> -125 dBm
2Handover to LTE and realizing inter-RAT trigger events B2 are fulfilled
3
3A-2
1
2
3 Handover back to 3G � Pingpong
3A-1
Workshop ITG FG 5.2.4 / 06.10.201012 © Nokia Siemens Networks
Conclusion
• RLF affected mobility issues can be accomplished easier than in intra-LTE case due to missing interference between source and target cell
• Unnecessary HOs (e.g. pingpongs) due inconsistent thresholds among RATs are quite likely, due to
– uncoordinated parameter configuration
– changing traffic steering policy
• Pingpongs are critical in inter-RAT case, since
– inter-RAT measurements yield connection interruptions
� danger of packet loss
� danger of missed paging attempts
� capacity reduction
Unnecessary HOs as Pingpongmust get higher significance in inter-RAT MRO
13 © Nokia Siemens Networks
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Research
Radio Systems
Phone: +49 89 5159-31560Fax: +49 89 5159-4431560
Dr.-Ing. Mobile: +49 173 3507281
Bernhard Wegmann Email: [email protected]
Research
Radio Systems
Phone: +49 89 5159-31560Fax: +49 89 5159-4431560
Dr.-Ing. Mobile: +49 173 3507281
Bernhard Wegmann Email: [email protected]