FP7 ICT-SOCRATES Controllability for Self-Optimisation of Home eNodeBs Kristina Zetterberg, Ericsson AB Neil Scully, John Turk, Vodafone Ljupco Jorguseski, Adrian Pais, TNO
Outline � Introduction to Home eNodeBs (HeNBs) � Related Work and Scope � Controllability for Self-Optimisation of HeNB Interference and Coverage – Use Case Introduction – Simulation Setup – Control Parameters – Results – Conclusions and Further Work � Controllability for Self-Optimisation of HeNB Handover – Use Case Introduction – Simulation Setup – Control Parameters – Results – Conclusions and Further Work � Summary and Questions WWW.FP7-SOCRATES.EU Kristina Zetterberg, Ericsson AB
Introduction to Home eNodeBs � LTE home base stations � Create or extend coverage � Improve capacity � Typically within buildings, such as an office, a mall or a home � Installed by customer � Potentially large number � Low transmit power � Small coverage area � Open or closed access WWW.FP7-SOCRATES.EU Kristina Zetterberg, Ericsson AB
Related Work and Scope � Feasability of HeNBs investigated in 3GPP and Femto Forum � NGMN recognises the need of self-optimisation for HeNBs � Self-optimisation discussed by H. Claussen et. al. – Focus on open access HeNB power settings to optimise coverage to minimise mobility signalling increase � SOCRATES project Develops self-organisation methods to enhance the operations of LTE networks � Two HeNB use cases considered – Self-Optimisation of HeNB Interference and Coverage – Self-Optimisation of HeNB Handover � Controllability analysis – How and to which extent different parameter settings affect performance – Evaluated using simulations of an LTE network with HeNBs deployed WWW.FP7-SOCRATES.EU Kristina Zetterberg, Ericsson AB
Self-Optimisation of HeNB Interference and Coverage � Optimise coverage area � Minimise interference in the network � Closed access HeNBs – open only for CSG users � Same frequency as macro eNodeBs � Main problem is dead zones � Uplink and downlink HeNB power varied to control trade-off Only HeNB coverage (dead-zone) Only macro coverage Both macro and HeNB coverage WWW.FP7-SOCRATES.EU Kristina Zetterberg, Ericsson AB
Simulation Setup � Static Monte-Carlo simulator � Hexagonal Layout, 7 sites with 21 cells – Coverage Driven Scenario – 1732 meters s2s distance – Capacity Driven Scenario – 500 meters s2s distance � Femto area with grid of houses – 10 x 10 houses – HeNB density 10% – HeNB placement within house varies Femto � One CSG user per HeNB house area � On average one non-CSG user per HeNB house � Requested bitrate 0.25 Mbps UL, 1 Mbps DL � Results collected from users within the HeNB houses WWW.FP7-SOCRATES.EU Kristina Zetterberg, Ericsson AB
Controllability Study � Considered control parameters: – Maximum DL Transmit Power Varied from 0.2 mW to 20 mW in steps of 1 dB Reference signal power follows DL transmit power – Maximum UL Transmit Power Varied from 20 mW to 316 mW in steps of 1 dB � Considered macro – HeNB distances; Coverage Driven Coverage Driven Capacity Driven Scenario A Scenario B Scenario A Site-to-site distance (m) 1732 1732 500 Macro-to-HeNB distance (m) 285 705 64 � A CSG user is connected to the HeNB only if RSRP HeNB > RSRP macro WWW.FP7-SOCRATES.EU Kristina Zetterberg, Ericsson AB
Result Plots � X - axis show power difference in dB, compared to maximum setting � Y - axis show ratio of users that can detect the reference signal, and have non-zero uplink and downlink throughput, in the HeNB houses � The three different plots show the ratio of – CSG users with RS, UL & DL coverage (from macro or HeNB) in the HeNB houses – CSG users with RS, UL & DL coverage from HeNB in the HeNB houses – Non-CSG users with RS, UL & DL coverage (from macro) in the HeNB houses WWW.FP7-SOCRATES.EU Kristina Zetterberg, Ericsson AB
Varying Downlink Power Cov A: s2s 1732 m m2h 285 m Cov B: s2s 1732 m m2h 705 m Cap A: s2s 500 m m2h 64 m WWW.FP7-SOCRATES.EU Kristina Zetterberg, Ericsson AB
Varying Uplink Power Cov A: s2s 1732 m m2h 285 m Cov B: s2s 1732 m m2h 705 m DL power 3.2 mW Cap A: s2s 500 m m2h 64 m WWW.FP7-SOCRATES.EU Kristina Zetterberg, Ericsson AB
Throughput � For the given scenarios, throughput for non-CSG users is not highly affected � Seen effects are probably due to changed macro load Cov A: s2s 1732 m m2h 285 m � For the given scenarios (with a maximum of one CSG user per home eNodeB) throughput for HeNB connected UEs is equal to the requested throughput both in uplink and downlink WWW.FP7-SOCRATES.EU Kristina Zetterberg, Ericsson AB
Conclusions and Further Work � Conclusions – Dead-zones are the major problem when introducing closed access home eNodeBs – HeNB Maximum Transmit Power is a suitable parameter for controlling the trade-off between HeNB coverage and the size of the dead-zone � Possible Further Work – Evaluate effects of adjusting the CSG user RSRP connect margin; CSG user is connected to the HeNB only if RSRP HeNB > RSRP macro – margin – Evaluate effects of using parts of the macro frequency band for the HeNB – Evaluate effects of adjusting the transmit power on parts of the frequency band – Algorithm development WWW.FP7-SOCRATES.EU Kristina Zetterberg, Ericsson AB
Self-Optimisation of HeNB Handover � Minimise dropped calls � Maximise user throughput � Open access HeNBs � Indoor HeNBs, providing coverage also outdoor � Macro – HeNB Handover � HeNB – HeNB Handover WWW.FP7-SOCRATES.EU Kristina Zetterberg, Ericsson AB
Simulation Setup � Dynamic simulator � Single 3-sector macro eNB – Wrap-around – Site-to-site distance 500 meters � Row of houses with HeNBs 165 meters from macro eNB � 15 meters between each HeNB � User experience of a UE moving down a street is modelled 165 m � Full buffer traffic � Study considers – Impact of UE speed – Impact of relative signal strengths between eNB and HeNB – Impact of macro network load WWW.FP7-SOCRATES.EU Kristina Zetterberg, Ericsson AB
Controllability Study � Considered control parameters: – Hysteresis (HYST) Set to the values 0, 3, 6, 9 and 12 dB – Time to trigger (TTT) Set to the values 0, 100, 320, 640 and 1280 ms � Considered scenarios; UE speed (km/h) 3 30 100 Macro-to-HeNB distance (m) 50 165 280 Macro cell load (UEs/sector) 0 1 5 WWW.FP7-SOCRATES.EU Kristina Zetterberg, Ericsson AB
SINR and Serving Cell Low hysteresis and TTT High hysteresis and TTT – Many handovers to HeNBs – UE stays on macro eNB most of the time Hysteresis = 0 dB TTT = 0 ms Hysteresis = 12 dB TTT = 640 ms UE speed = 30 km/h Separation distance = 165 m Load = 5 UEs/sector UE speed = 30 km/h Separation distance = 165 m Load = 5 UEs/sector UE speed = 30 km/h Separation distance = 165 m Load = 5 UEs/sector 40 40 35 Hysteresis = 12 dB TTT = 640 ms UE speed = 30 km/h Separation distance = 165 m Load = 5 UEs/sector 30 30 30 Blue: Data SINR (dB) / Red: Serving cell 25 ed: Serving cell 20 20 15 10 10 (dB) / R 5 R 0 0 ata SIN -5 Blue: D -10 -10 -15 -20 -20 0 2 4 6 8 10 12 14 0 2 4 6 8 10 12 14 Time (s) Time (s) WWW.FP7-SOCRATES.EU Kristina Zetterberg, Ericsson AB
Throughput � Low TTT and small hysteresis gives higher throughput � More pronounced at higher UE speed � Same trends in throughput are seen for higher HeNB-to-macro eNB distance � At a lower distance the impact is not as large, as the UE stays connected to the macro eNB UE speed = 3 km/h Separation distance = 165 m Load = 5 UEs/sector UE speed = 30 km/h Separation distance = 165 m Load = 5 UEs/sector UE speed = 100 km/h Separation distance = 165 m Load = 5 UEs/sector 15 5 15 4 Throughput (Mbps) Throughput (Mbps) Throughput (Mbps) 10 10 3 2 5 5 1 0 0 0 0 0 0 100 100 100 0 320 0 0 3 320 320 3 640 3 6 640 640 6 6 1280 9 1280 9 1280 9 12 TTT (ms) 12 TTT (ms) Hysteresis (dB) TTT (ms) 12 Hysteresis (dB) Hysteresis (dB) 3 km/h 30 km/h 100 km/h WWW.FP7-SOCRATES.EU Kristina Zetterberg, Ericsson AB
Ping-pong Handover Ratio � Low hysteresis and TTT values gives high throughput, but could also lead to ping-pong UE speed = 30 km/h Separation distance = 165 m Load = 5 UEs/sector UE speed = 3 km/h Separation distance = 165 m Load = 5 UEs/sector 0.4 0.8 Ping-pong handover ratio Ping-pong handover ratio 0.3 0.6 0.4 0.2 0.2 0.1 0 0 0 0 100 100 0 0 320 320 3 3 640 640 6 6 1280 9 1280 9 12 TTT (ms) 12 TTT (ms) Hysteresis (dB) Hysteresis (dB) 3 km/h 30 km/h WWW.FP7-SOCRATES.EU Kristina Zetterberg, Ericsson AB
Improving Throughput by Avoiding Handover � Throughput does not always decrease as handover parameter values are increased � Gain is only achieved for low macro cell load Throughput Ratio of time connected to HeNB UE speed = 100 km/h Separation distance = 165 m Load = 0 UEs/sector UE speed = 100 km/h Separation distance = 165 m Load = 0 UEs/sector 6 1 0.8 Throughput (Mbps) 4 Femto ratio 0.6 0.4 2 0.2 0 0 0 0 100 100 0 0 320 320 3 3 640 640 6 6 1280 9 1280 9 12 TTT (ms) 12 TTT (ms) Hysteresis (dB) Hysteresis (dB) WWW.FP7-SOCRATES.EU Kristina Zetterberg, Ericsson AB
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