FP7 ICT-SOCRATES Handover parameter optimization in LTE self- organizing networks TD (10)10068 COST 2100, 10 th MCM Athens, Greece February 3 rd – 5 th TUBS, Braunschweig, Germany IBBT, Ghent, Belgium VOD, Newbury, England
Outline 1. Introduction 2. Simulation scenario and LTE system-level simulator 3. Simulation metrics 4. Controllability and Observability studies 5. Performance of the non-optimised network 6. Handover optimisation SON algorithm 7. Simulation results 8. Conclusion WWW.FP7-SOCRATES.EU Dipl.-Ing. Thomas Jansen, TU Braunschweig, Institut für Nachrichtentechnik 2/22
Introduction Problem – Handover parameter optimisation is done manually – high OPEX – long optimisation intervals based on error reports – Non-optimal handover performance – handover failures – ping-pong handovers – call dropping Handover parameter optimisation objective – automate the optimisation – adapt the handover parameters on a short-term scale – optimise the handover performance Approach – analyse the system behaviour – develop handover optimisation algorithm WWW.FP7-SOCRATES.EU Dipl.-Ing. Thomas Jansen, TU Braunschweig, Institut für Nachrichtentechnik 3/22
Realistic SOCRATES Scenario Simulations LTE Simulator Assembling Network Decorated User Scenario Data Information Snapshots Correlated User Processing Data Snapshots Network Environment User locations Generating Source Data Braunschweig Traffic Distri- Network data OpenSteetMap Scenario bution WWW.FP7-SOCRATES.EU Dipl.-Ing. Thomas Jansen, TU Braunschweig, Institut für Nachrichtentechnik 4/22
Realistic SOCRATES Scenario Computing the landuse information from openstreetmap.org Landuse classes: Road, Building, Water, Street and Railway WWW.FP7-SOCRATES.EU Dipl.-Ing. Thomas Jansen, TU Braunschweig, Institut für Nachrichtentechnik 5/22
MATLAB LTE system-level simulator Input data Read input Start data – Realistic SOCRATES scenario Build Network Build Users Power mask – Soft frequency reuse End of No Set Power Mask Simulation? Call generation – All users connected Yes Call Generation End Update RSRP/SINR – Shadow fading maps Next step Update RSRP/SINR Handover procedure/algorithm HO algorithm HO procedure WWW.FP7-SOCRATES.EU Dipl.-Ing. Thomas Jansen, TU Braunschweig, Institut für Nachrichtentechnik 6/22
Simulation metrics Control Control parameters Values parameter – Hysteresis (0, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, Hysteresis 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10 ) in [dB] – Time-to-Trigger (0 0.04 0.064 0.08 0.1 0.128 0.16 Time-to-Trigger 0.256 0.32 0.48 0.512 0.64 1.024 1.280 2.56 5.12) in [s] Assessment metrics – Handover failure ratio – Call dropping ratio N N HO _ fail HO _ dropped HPI HPI HOF DC N N N HO _ fail HO _ succ HO _ accepted – Ping-Pong handover ratio N HO _ pp HPI HPP N N N HO _ pp HO _ npp HO _ fail WWW.FP7-SOCRATES.EU Dipl.-Ing. Thomas Jansen, TU Braunschweig, Institut für Nachrichtentechnik 7/22
Simulation metrics System metrics – RSRP (Reference Signal Received Power) – cell transmit power P c – pathloss L to the UE ue L – shadow fading with a standard deviation of 3dB fad RSRP , P L L c ue c ue fad – SINR (Signal to Interference Noise Ratio) – interfering cells N RSRP , ue N n 10 SINR RSRP 10 log 10 c , ue c , ue 10 n 1 WWW.FP7-SOCRATES.EU Dipl.-Ing. Thomas Jansen, TU Braunschweig, Institut für Nachrichtentechnik 8/22
Controllability and Observability studies Objective Simulation parameter Value Analyse the system behaviour Simulation time 200 [s] and sensitivity Simulation step time 0.01 [s] Find handover algorithm Simulation area (mobile users) 1.5 km * 1.5 km approach Number of users 30 eNodeB transmit power 46 [dBm] Simulation assumptions Number of considered cells in the scenario 76 All resources are used in all Measured cells (N) 21 cells (maximum interference) Considered interfering cells for SINR 20 calculations Simulation approach Critical ping-pong handover time (T_crit) 5 [s] Perform system simulations for Handover execution time 0.25 [s] all hysteresis and time-to- trigger value combination SINR averaging window 0.1 [s] (handover operating point) Min. SINR threshold - 6.5 [dB] WWW.FP7-SOCRATES.EU Dipl.-Ing. Thomas Jansen, TU Braunschweig, Institut für Nachrichtentechnik 9/22
C & O: Handover failures Handover Failures Handover failure ratio 0.04 10 0.02 8 0 6 5 2 1 4 0.5 0.25 2 0.1 Hysteresis [dB] 0 Time-to-Trigger [s] 0 WWW.FP7-SOCRATES.EU Dipl.-Ing. Thomas Jansen, TU Braunschweig, Institut für Nachrichtentechnik 10/22
C & O: Ping-Pong handovers Ping-Pong Handovers Ping-Pong handover ratio 0.8 0.6 0.4 0.2 0 10 5 2 8 1 6 0.5 0.25 4 0.1 2 Time-to-Trigger [s] Hysteresis [dB] 0 0 WWW.FP7-SOCRATES.EU Dipl.-Ing. Thomas Jansen, TU Braunschweig, Institut für Nachrichtentechnik 11/22
C & O: Call dropping Call drops 0.8 Call dropping ratio 0.6 0.4 0.2 0 5 10 2 1 8 0.5 6 0.25 4 0.1 2 Time-to-Trigger [s] Hysteresis [dB] 0 0 WWW.FP7-SOCRATES.EU Dipl.-Ing. Thomas Jansen, TU Braunschweig, Institut für Nachrichtentechnik 12/22
Handover performance weighting function HP = w 1 HPI HOF + w 2 HPI HPP + w 3 HPI DC – w x is the weight of the individual HPI – HPI HOF is the handover failure performance indicator – HPI HPP is the ping-pong handover performance indicator – HPI DC is the dropped calls performance indicator Weighting parameter Value 0.5, 0.6, …, 2.0 w 1 0.5, 0.6, …, 2.0 w 2 0.5, 0.6, …, 2.0 w 3 4096 valid weighting parameter combinations have been considered If (HP<0.05) => “meaningful” handover parameter operating point WWW.FP7-SOCRATES.EU Dipl.-Ing. Thomas Jansen, TU Braunschweig, Institut für Nachrichtentechnik 13/22
Handover performance Handover Performance (weights = [1 0.5 2]) Normalised sum of weighted HO failure rate, ping-pong HO rate and call dropping rate 1 0.5 0 10 5 8 2 1 6 0.5 0.25 4 0.1 2 Hysteresis [dB] Time-to-Trigger [s] 0 0 WWW.FP7-SOCRATES.EU Dipl.-Ing. Thomas Jansen, TU Braunschweig, Institut für Nachrichtentechnik 14/22
“meaningful” handover operating points Operating Points (Threshold: 5%) 10 5 9 8 2 7 1 6 0.5 5 0.25 4 3 0.1 2 Hysteresis [dB] 1 Time-to-Trigger [s] 0 0 WWW.FP7-SOCRATES.EU Dipl.-Ing. Thomas Jansen, TU Braunschweig, Institut für Nachrichtentechnik 15/22
Simulation parameters for the performance analysis Simulation parameter Value Simulation time 1000 [s] Simulation step time 0.01 [s] Simulation area (mobile users) 1.5 km * 1.5 km Number of users 50 eNodeB transmit power 46 [dBm] Operating points (4, 0.48), (6, 0.32), (8, 0.1), (9, 0.08) in [dB, s] (Hysteresis, Time-to-Trigger) Number of considered cells in the scenario 78 Measured cells (N) 21 Considered interfering cells for SINR 20 calculations Handover performance averaging window 60 [s] Critical ping-pong handover time (T_crit) 5 [s] Handover execution time 0.25 [s] SINR averaging window 0.1 [s] Min. SINR threshold - 6.5 [dB] WWW.FP7-SOCRATES.EU Dipl.-Ing. Thomas Jansen, TU Braunschweig, Institut für Nachrichtentechnik 16/22
Performance of the non-optimised network Handover Performance for the operating point (4, 0.48) 25 Handover failure Ping-Pong handover Call dropping 20 15 Ratio [%] 10 5 0 100 200 300 400 500 600 700 800 900 1000 Time [s] WWW.FP7-SOCRATES.EU Dipl.-Ing. Thomas Jansen, TU Braunschweig, Institut für Nachrichtentechnik 17/22
Performance of the non-optimised network Ping-Pong handover performance Handover failure performance 25 4 Operating point (4, 0.48) Operating point (4, 0.48) Operating point (6, 0.32) Operating point (6, 0.32) 3.5 Operating point (8, 0.1) Operating point (8, 0.1) Operating point (9, 0.08) 20 Operating point (9, 0.08) 3 Ping-Pong handover ratio [%] Handover failure ratio [%] 2.5 15 2 10 1.5 1 5 0.5 0 0 100 200 300 400 500 600 700 800 900 1000 100 200 300 400 500 600 700 800 900 1000 Time [s] Time [s] Call dropping performance 6 Comparison of the network Operating point (4, 0.48) Operating point (6, 0.32) Operating point (8, 0.1) performance for four different 5 Operating point (9, 0.08) operating points 4 Call dropping ratio [%] (4 dB Hys, 0.48 s TTT) 3 (6 dB Hys, 0.32 s TTT) 2 (8 dB Hys, 0.1 s TTT) 1 (9 dB Hys, 0.08 s TTT) 0 100 200 300 400 500 600 700 800 900 1000 Time [s] WWW.FP7-SOCRATES.EU Dipl.-Ing. Thomas Jansen, TU Braunschweig, Institut für Nachrichtentechnik 18/22
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