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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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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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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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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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

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POST-OUTAGE SITUATIONWITH OPTIMISED P0

PRE-OUTAGE SITUATION POST-OUTAGE SITUATIONWITHOUT COMPENSATION

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POST-OUTAGE SITUATIONWITH OPTIMISED P0

PRE-OUTAGE SITUATION POST-OUTAGE SITUATIONWITHOUT COMPENSATION

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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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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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Contact

Mehdi Amirijoo, Ericsson Research, Ericsson AB

E-mail: mehdi.amirijoo@ericsson.com

Phone: +46107115290