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FP7 ICT-SOCRATES
Presented by Mehdi Amirijoo
Ericsson Research, Ericsson AB
FP7 SOCRATES final workshop
Karlsruhe, Germany
22 February 2011
Cell Outage Compensation
in LTE
Contributors: Remco Litjens (TNO ICT), Ljupco Jorguseski (TNO ICT), Lars Christoph Schmelz (NSN)
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Mehdi Amirijoo, Ericsson
Outline
� Introduction
� Solution
� Simulation assumptions
� Simulation results
� Conclusion
� For more information refer to D5.9 Section 8.6
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Introduction
� A cell/site does not transmit any radio signal
� Reasons for outages:
– software and hardware failures (radio unit, antenna etc),
– external failures such as power supply or network connectivity
� Outages result in loss of coverage
– customer complaints and dissatisfaction
– loss of potential revenues
� Automatic mitigation of coverage loss
� Challenges:
– Timely response
– Handling tradeoffs between coverage and quality
– Observing coverage
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Solution
Measurements
CompensationOperator policy
Control parameters
Detection
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Solution – Operator Policy
� Manage tradeoff between coverage and quality
� Quality Q: Xth-percentile of UE throughput
– e.g., 10th-percentile UE throughput
� Network is dimensioned according to a cell-specific nominal target
quality QT
� Nominal target quality may not be satisfied during an outage
� Compensating cells have a cell-specific outage target quality Q’T
Example: maximize coverage subject to Q ≥ Q’T
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Solution – Controllability & Observability Study
� Control parameters: – Reference signal power, tilt, UL power control parameters
� Scenarios– Site density and load– Operator policy
� Performance metrics– Coverage probability (SINR)– Quality (uplink/downlink user throughput)
� Controllability result:– UL coverage is the limiting factor in the studied scenarios (and simulation
assumptions)– Tilt and UL target received power are most effective in improving coverage
� Coverage observability is one of the main challenges– Coverage probability estimation– Timely estimation– Use X-maps
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Mehdi Amirijoo, Ericsson
Solution – Algorithms
� Algorithm tunes
– target received power spectral density (PSD) in UL denoted P0
– antenna tilt
� UL transmit PSD T is defined as
where
– P0 = SNRtarget × N0
– N0 is the noise PSD
– PL is the path loss, including shadowing and antenna gains
– α is the path loss compensation fraction
� Decreasing P0 will decrease the spectral efficiency leading to
– more resource consumption per user
– more contention among the users and lower quality
αPLPT ×=
0
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Mehdi Amirijoo, Ericsson
Solution – Algorithms
� By decreasing P0 in the cells around the outage site we
– decrease the UL power by users in these cells
– thereby decrease the UL inter-cell interference
– thereby extend UL coverage
� If Q > Q’T (DL & UL)
P0(k) = max(P0_MIN,P0(k-1) - δ)
else
P0(k) = min(P0_MAX,P0(k-1) + δ)
Received signal power
Distance from base station
High P0
Medium P0
Low P0
Power-limited UEs
Reduction of UL inter-cell interference
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Mehdi Amirijoo, Ericsson
Simulation Assumptions
� Static snapshot simulator
� Network with 57 cells (wrap-around)
� Propagation:
– Okumura-Hata (urban)
– Shadow fading
� UEs distributed uniformly
� Truncated Shannon model
� 3D antenna pattern (3GPP)
� SISO system
� User requested data rate
– DL = 1 Mbps
– UL = 250 kbps-1000 -500 0 500 1000
-1000
-800
-600
-400
-200
0
200
400
600
800
1000
-140
-130
-120
-110
-100
-90
-80
-70
Pathgain [dB]
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PRE-OUTAGE SITUATION POST-OUTAGE SITUATIONWITHOUT COMPENSATION
UP
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POST-OUTAGE SITUATIONWITH OPTIMISED P0
PRE-OUTAGE SITUATION POST-OUTAGE SITUATIONWITHOUT COMPENSATION
UP
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POST-OUTAGE SITUATIONWITH OPTIMISED P0
PRE-OUTAGE SITUATION POST-OUTAGE SITUATIONWITHOUT COMPENSATION
UP
LIN
K U
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R
TH
RO
UG
HP
UT
CO
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PR
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POST-OUTAGE SITUATIONWITH OPTIMISED P0
Simulation Results – Controllability Result (P0,High Load)
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Simulation Results – Algorithm (P0,High Load)
Outage
Start of compensation
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Mehdi Amirijoo, Ericsson
Simulation Results – Algorithm (P0,High Load)
Outage target quality
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Conclusion
� Outages result in customer dissatisfaction & loss of potential revenues
� Solution that alleviates negative impact of outages considering practical limitation(coverage observability)
� Antenna tilt and UL power control parameters have shown to be most effective
� Operator specifies tradeoff between quality and coverage
� Solution adjusts tilt and UL power control parameters in order to balance coverage and quality
� Solution shows that a large portion of the users can be recovered
� Future work:– Develop solutions that can translate a variety of operator policies into algorithms
– Combination of several control parameters
– Observability of coverage using X-maps
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Mehdi Amirijoo, Ericsson
Contact
Mehdi Amirijoo, Ericsson Research, Ericsson AB
E-mail: [email protected]
Phone: +46107115290