FP7 ICT-SOCRATES Self-Optimising Call Admission Control for LTE Downlink Joint COST 2100 / SOCRATES workshop February 5, 2010 Work performed within the context of the SOCRATES project ~ www.fp7-socrates.eu K. Spaey, B. Sas, C. Blondia IBBT / University of Antwerp
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FP7 ICT-SOCRATES
Self-Optimising Call Admission Control for LTE
Downlink
Joint COST 2100 / SOCRATES workshop February 5, 2010
Work performed within the context of the SOCRATES project ~ www.fp7-socrates.eu
K. Spaey, B. Sas, C. Blondia IBBT / University of Antwerp
WWW.FP7-SOCRATES.EU
(Self-optimising) call admission control
Reference admission control algorithm
Metrics
Self-optimising algorithm for ThHO
Evaluation methodology
Simulation results
Conclusions and future work
Outline
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Kathleen Spaey, IBBT / University of Antwerp
WWW.FP7-SOCRATES.EU
Call admission control (AC) algorithm – Decides if a call request will be admitted or rejected – Bases its decisions on:
• Enough resources available to guarantee QoS new call? • If call is accepted, QoS of already accepted calls will be
maintained?
Self-optimising call admission control – Self-optimise / auto-tune parameters of the AC algorithm – In response to changes
(Self-optimising) call admission control
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Kathleen Spaey, IBBT / University of Antwerp
WWW.FP7-SOCRATES.EU
Development of a simple self-optimising AC algorithm Evaluation under sudden overload
Reference AC algorithm (static algorithm) needed – AC algorithms are vendor specific – Literature:
• Prioritisation of acceptance of handover over fresh calls • Recognise diverse QoS requirements for delay-sensitive (RT) and
Cell capacity depends on → packet scheduler decisions → channel conditions users → location users → varies over time → estimate of time-varying cell
capacity needed *
€
c* (t) + creq ≤ margin × C(k)
* Based on “Adaptive connection admission control scheme for high data rate mobile networks”, S.S. Jeong, J.A. Han, W.S. Jeon, VTC Fall 2005
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Reference admission control algorithm
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Kathleen Spaey, IBBT / University of Antwerp
t: time of call arrival C(k): most recent estimate of
cell capacity creq: required capacity of arriving call c*(t): required capacity of already
accepted active calls c*
RT(t): required capacity of already accepted active RT calls
fresh calls are blocked
priority is given to HO calls
avoid that cell capacity is entirely filled with RT calls
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GoS measurements
– HO failure ratio = (# HO calls rejected by the AC algorithm) / (# generated HO calls)
– Call blocking ratio = (# fresh calls rejected by the AC algorithm) / (# generated fresh calls)
QoS measurements (only for admitted traffic)
– Traffic loss ratio = (# lost traffic) / (# generated traffic) • measured for RT traffic (voice / video)
– Call throughput = (# bits of call) / (call transfer time) • measured for NRT traffic (web) • we focus on the fraction of web calls with a call throughput smaller
than the minimum call throughput requested to the packet scheduler
Metrics to assess performance
7
Kathleen Spaey, IBBT / University of Antwerp
WWW.FP7-SOCRATES.EU
Simulations in which the 4 performance metrics are obtained – for various ThHO values – in scenarios with varying call arrival rate or varying %HO calls
Changes in the measured performance might require opposite adaptations of ThHO, depending on which performance measure is considered
– QoS degradation of ongoing calls – Increasing HO failure ratio – Increasing call blocking ratio → increase of ThHO
Operator policy to decide on this trade-off
SON algorithm which auto-tunes ThHO should take the chosen policy into account
Sensitivity analysis on ThHO
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Kathleen Spaey, IBBT / University of Antwerp
decrease of ThHO
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Desired properties – ThHO should be adapted based on GoS / QoS measurements, rather
than on measurements on the system conditions – Measurements should be smoothed – Follow policy to handle contradictions in required adaptations of ThHO
Policy considered In order of priority: – Aim to guarantee QoS of the accepted calls – Accept HO calls with priority over fresh calls – Aim to reduce call blocking ratio
Self-optimising algorithm for ThHO
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Kathleen Spaey, IBBT / University of Antwerp
WWW.FP7-SOCRATES.EU
At regular time instants t = kΔ, measurements are collected
Measurements in [ kΔ ; (k+1) Δ [ , smoothed with parameter αSON – QoS_RT(k): trafic loss ratio real-time traffic – QoS_NRT(k): fraction of non-real-time calls with call throughput smaller
than amount requested to scheduler – GoS_HO(k): HO failure ratio – GoS_fresh(k): call blocking ratio
Self-optimising algorithm for ThHO
10
Kathleen Spaey, IBBT / University of Antwerp
WWW.FP7-SOCRATES.EU
Self-optimising algorithm for ThHO
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Kathleen Spaey, IBBT / University of Antwerp
bad QoS or bad HO failure ratio
good QoS and good HO failure ratio and bad call blocking ratio
decrease ThHO
increase ThHO
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Evaluation of SON algorithm under sudden overload (unpredictable event)
– Scenarios where there is a sudden increase in call arrival rate or/and %HO calls
Comparison of performance obtained with – Self-optimising AC algorithm (reference algorithm + auto-tuning of ThHO) – Static AC algorithm (reference algorithm, fixed ThHO)
Evaluation methodology
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Kathleen Spaey, IBBT / University of Antwerp
WWW.FP7-SOCRATES.EU
Simulator for downlink direction developed using OPNET Modeler
Call generation: – fresh / HO calls – VoIP (RT) / video streaming (RT) / web browsing (NRT)