FP7 ICT-SOCRATES Sensitivity Analysis of the Optimal Parameter Settings of an LTE Packet Scheduler I. Fernandez Diaz (TNO) R. Litjens (TNO) J.L van den Berg (TNO) K. Spaey (IBBT) D. Dimitrova (UT) May 18, 2010, VTC ’10 Spring, Taipei, Taiwan
CONTEXT � Driven by … – technological complexities – market-oriented perspectives � … there is an on-going trend towards self-organisation of future mobile networks – Self-configuration – ‘Plug and play’ installation of new base stations and features continuous loop – Self-healing – Cell outage detection – Cell outage compensation: automatic minimisation of coverage/capacity loss – Self-optimisation – Power/tilt optimisation – Load balancing – Self-optimisation of packet scheduling parameters – Automatic turning off/on sites triggered by – … incidental events WWW.FP7-SOCRATES.EU 2/ ∞
CONTEXT � Driven by … – technological complexities – market-oriented perspectives � … there is an on-going trend towards self-organisation of future mobile networks – Self-configuration – ‘Plug and play’ installation of new base stations and features continuous loop – Self-healing – Cell outage detection – Cell outage compensation: automatic minimisation of coverage/capacity loss – Self-optimisation – Power/tilt optimisation – Load balancing – Self-optimisation of packet scheduling parameters – Automatic turning off/on sites triggered by – … incidental events WWW.FP7-SOCRATES.EU 3/ ∞
OUTLINE � Context � Objective � Packet scheduling in LTE networks � Reference packet scheduler � Approach sensitivity analysis � Numerical results � Concluding remarks WWW.FP7-SOCRATES.EU 4/ ∞
OBJECTIVE THIS PAPER: Assessment of the sensitivity of optimal downlink LTE packet scheduling parameters with respect to a variety of traffic and environment aspects FOLLOW-UP (IF SIGNIFICANT SENSITIVITY IS FOUND): Develop self-optimisation algorithms to observe traffic/environment changes and adapt scheduling parameters WWW.FP7-SOCRATES.EU 5/ ∞
PACKET SCHEDULING IN LTE NETWORKS � Task of the packet scheduling algorithm – On a TTI timescale, assign cell’s radio resources to active sessions – Resource granularity in time domain � 1 TTI = 1 ms – Resource granularity in frequency domain � 1 ‘subchannel’ = 180 kHz WWW.FP7-SOCRATES.EU 6/ ∞
REFERENCE PACKET SCHEDULING ALGORITHM � Supports RT and NRT sessions – With a tuneable degree of session-based differentiation – (As opposed to class-based differentiation) � Comprises three key principles – Proportional fairness → Tuneable channel-adaptivity: efficiency vs fairness → RT packets are characterised by limited delay budgets – Packet urgency → Aim to utilise all resources – Work-conserving WWW.FP7-SOCRATES.EU 7/ ∞
REFERENCE PACKET SCHEDULING ALGORITHM � For each session i and subchannel c, calculate the priority level ( ) • = potential bit rate at which session R c t i, ( ) ( ) ξ i can be served on subchannel c ⎛ ⎞ R t ( ) W t ⎜ ⎟ = ρ ⋅ + at TTI t i , c i P t 1 ⎜ ⎟ ( ) ( ) − i , c service ˆ ( ) ⎝ ⎠ T W t R t ˆ • = filtered average bit rate at which R t i i i i session i has been served up to TTI t channel packet ( ) • = aggregate bit rate at which R i t - 1 adaptivity urgency session i was served in TTI t-1 factor factor ( ) • = delay of HOL packet of session i W i t experienced up to TTI t with for each session i • = maximum allowed packet delay T ( ) ( ) ( ) ( ) = − α − + α i ˆ ˆ R t 1 R t 1 R t - 1 for session i i i i ρ • = minimum desired bit rate service � Assign subchannels to sessions ξ • = parameter which sets the relative based on above priorities importance of the packet urgency � Select uniform MCS per session factor α • = filtering parameter WWW.FP7-SOCRATES.EU 8/ ∞
APPROACH SENSITIVITY ANALYSIS � Sensitivity analysis of the optimum packet scheduling parameter settings with respect to – Service mix – Average file size (data service) – Coefficient of variation of the file size (data service) – Multipath fading environment – Variability of avg signal strengths between sessions � Reference scenario – Service mix � file downloads only – Average file size (data service) � 500 kbit – Coefficient of variation of the file size (data service) � 1 – Multipath fading environment � PedestrianA, 3 km/h – Variability of avg signal strengths between sessions � spatially uniform user distribution, σ shadowing = 9.4 dB WWW.FP7-SOCRATES.EU 9/ ∞
NUMERICAL RESULTS � Reference scenario Reference scenario Reference scenario Reference scenario Reference scenario Reference scenario 4000 4000 1400 1400 10% Percentile of throughput (kbit/s) 10% Percentile of throughput (kbit/s) 3500 3500 1200 1200 Average throughput (kbit/s) Average throughput (kbit/s) 3000 3000 1000 1000 Max SINR Max SINR Max SINR Max SINR 2500 2500 alpha=0.001 alpha=0.001 alpha=0.001 alpha=0.001 800 800 2000 2000 2000 alpha=0.01 alpha=0.01 alpha=0.01 alpha=0.01 600 600 alpha=0.1 alpha=0.1 alpha=0.1 alpha=0.1 1500 1500 1500 RR RR RR RR 400 400 1000 1000 1000 200 200 500 500 500 0 0 0 0 0 0 0 200 200 400 400 600 600 800 800 1000 1000 0 0 200 200 400 400 600 600 800 800 1000 1000 Cell load (kbit/s) Cell load (kbit/s) Cell load (kbit/s) Cell load (kbit/s) Reference scenario Reference scenario Reference scenario Reference scenario Reference scenario 1400 1400 1400 1400 1400 10% Percentile of throughput at cell 10% Percentile of throughput at cell 10% Percentile of throughput at cell Maximum supported cell load (kbit/s) Maximum supported cell load (kbit/s) 1200 1200 1200 1200 1200 1000 1000 1000 1000 1000 Max SINR Max SINR Max SINR edge (kbit/s) edge (kbit/s) edge (kbit/s) Max SINR Max SINR alpha=0.001 alpha=0.001 alpha=0.001 800 800 800 alpha=0.001 alpha=0.001 800 800 alpha=0.01 alpha=0.01 alpha=0.01 500 kb/s alpha=0.01 alpha=0.01 600 600 600 alpha=0.1 alpha=0.1 alpha=0.1 600 600 alpha=0.1 alpha=0.1 RR RR RR target 400 400 400 RR RR 400 400 (FAIRNESS) 200 200 200 200 200 0 0 0 0 0 0 200 200 200 400 400 400 600 600 600 800 800 800 1000 1000 1000 0 0 Cell load (kbit/s) Cell load (kbit/s) Cell load (kbit/s) Alpha Alpha WWW.FP7-SOCRATES.EU 10/ ∞
NUMERICAL RESULTS � Reference scenario Reference scenario Reference scenario Reference scenario Reference scenario Reference scenario 4000 4000 1400 1400 10% Percentile of throughput (kbit/s) 10% Percentile of throughput (kbit/s) 3500 3500 1200 1200 Average throughput (kbit/s) Average throughput (kbit/s) 3000 3000 1000 1000 Max SINR Max SINR Max SINR Max SINR 2500 2500 alpha=0.001 alpha=0.001 alpha=0.001 alpha=0.001 800 800 2000 2000 2000 alpha=0.01 alpha=0.01 alpha=0.01 alpha=0.01 600 600 alpha=0.1 alpha=0.1 alpha=0.1 alpha=0.1 1500 1500 1500 RR RR RR RR 400 400 1000 1000 1000 200 200 500 500 500 0 0 0 0 0 0 0 200 200 400 400 600 600 800 800 1000 1000 0 0 200 200 400 400 600 600 800 800 1000 1000 Cell load (kbit/s) Cell load (kbit/s) Cell load (kbit/s) Cell load (kbit/s) Reference scenario Reference scenario Reference scenario Reference scenario Reference scenario 1400 1400 1400 1400 1400 10% Percentile of throughput at cell 10% Percentile of throughput at cell 10% Percentile of throughput at cell Maximum supported cell load (kbit/s) Maximum supported cell load (kbit/s) 1200 1200 1200 1200 1200 1000 1000 1000 1000 1000 Max SINR Max SINR Max SINR edge (kbit/s) edge (kbit/s) edge (kbit/s) Max SINR Max SINR alpha=0.001 alpha=0.001 alpha=0.001 800 800 800 alpha=0.001 alpha=0.001 800 800 alpha=0.01 alpha=0.01 alpha=0.01 500 kb/s alpha=0.01 alpha=0.01 600 600 600 alpha=0.1 alpha=0.1 alpha=0.1 600 600 alpha=0.1 alpha=0.1 RR RR RR Target 400 400 400 RR RR 400 400 (FAIRNESS) 200 200 200 200 200 0 0 0 0 0 0 200 200 200 400 400 400 600 600 600 800 800 800 1000 1000 1000 0 0 Cell load (kbit/s) Cell load (kbit/s) Cell load (kbit/s) Alpha Alpha WWW.FP7-SOCRATES.EU 11/ ∞
NUMERICAL RESULTS � Sensitivity w.r.t. average file size Larger files allow a lower α (higher spectrum efficiency; larger ‘fairness window’) WWW.FP7-SOCRATES.EU 12/ ∞
NUMERICAL RESULTS � Sensitivity w.r.t. coefficient of variation of file size A larger CoV means more small files for which a higher α is optimal (see previous slide) WWW.FP7-SOCRATES.EU 13/ ∞
NUMERICAL RESULTS � Sensitivity w.r.t. multipath fading environment WWW.FP7-SOCRATES.EU 14/ ∞
NUMERICAL RESULTS � Sensitivity w.r.t. variability of avg signal strengths between sessions low = dense hot spot, no shadowing medium = reference scenario high = uniform spatial user distribution, σ shadowing = 14 dB Under very low variability, fairness is established even with a pure channel-aware scheduler. The higher the variability, a high α is needed to lift up the cell edge sessions. WWW.FP7-SOCRATES.EU 15/ ∞
Recommend
More recommend
