FP7 ICT-SOCRATES Handover parameter optimization in LTE self- organizing networks 72nd Vehicular Technology Conference 6 – 9 September 2010 Ottawa, Canada T. Jansen, I. Balan, J. Turk I. Moerman, T. Kürner
Outline 1. Introduction 2. Simulation environment and metrics 3. Initial performance studies 4. Handover optimisation SON algorithm 5. Simulation results 6. Conclusion WWW.FP7-SOCRATES.EU Dipl.-Ing. Thomas Jansen, TU Braunschweig, Institut für Nachrichtentechnik 2/17
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 3/17
MATLAB LTE system-level simulator Input data – Realistic SOCRATES scenario Start – 1.5 km * 1.5 km area – Up to 78 cells Read scenario – Microscopic traffic simulator data – Mobile users (cars) with different speed (up to 50 km/h) End of Yes – Ray-Tracer No End Simulation? – Pathloss information to best 30 cells – User position updates every 100 ms Update Save results RSRP/SINR Next step Update RSRP/SINR – 3dB shadow fading map HO procedure HO algorithm Handover procedure / algorithm WWW.FP7-SOCRATES.EU Dipl.-Ing. Thomas Jansen, TU Braunschweig, Institut für Nachrichtentechnik 4/17
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 5/17
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 6/17
Initial performance 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 7/17
Call dropping behaviour 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 8/17
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 w 1 1.0 w 2 0.5 w 3 2.0 WWW.FP7-SOCRATES.EU Dipl.-Ing. Thomas Jansen, TU Braunschweig, Institut für Nachrichtentechnik 9/17
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 10/17
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 11/17
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 12/17
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 13/17
Handover optimisation SON algorithm Optimisation criteria for HPIs HO SON algortihm Handover Time- 1) Performance Hysteresis to- Optimisation Next cell Indicator Trigger ↑ TTT 2) < 5 dB Update HPIs Handover ↑ TTT & ↑ HYS 5 dB – 7 dB failure ratio ↑ HYS > 7 dB 3) Yes No ↑ TTT HPIs < < 2.5 dB Ping-Pong threshold? ↑ TTT & ↑ HYS 2.5 dB – 5.5 dB handover 4) 6) Increase good Increase bad ↑ HYS performance time performance time ratio > 5.5 dB ↓ TTT & ↓ HYS > 0.6 s > 6 dB 5) 7) Reset bad Reset good ↓ TTT performance time performance time > 0.6 s <= 6 dB ↓ TTT & ↓ HYS Call dropping <= 0.6 s > 7.5 dB ratio 3.5 dB – 6.5 ↑ HYS <= 0.6 s 8) Yes No Good dB perform- ance? ↑ TTT & ↑ HYS <= 0.6 s < 3.5 dB 9) 11) Decrease HPI No Bad thresholds Optimisation actions are added up perform- ance? 10) Hys and TTT are only changed by one Yes Reset good performance time 12) step at a time Change handover operating point The new operating point has to belong to 13) the set of “meaningful operating points” Reset bad performance time WWW.FP7-SOCRATES.EU Dipl.-Ing. Thomas Jansen, TU Braunschweig, Institut für Nachrichtentechnik 14/17
Handover optimisation simulation results Handover performance for the operating point (6, 0.32) 10 Handover failure 9 Ping-Pong handover Call dropping 8 7 6 Ratio [%] 5 4 3 2 1 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 15/17
Handover optimisation simulation results Handover performance (Optimisation) 8 Handover failure Ping-Pong handover 7 Call dropping 6 5 Ratio [%] 4 3 2 1 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 16/17
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