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Analysis of Two-Layer Performance Models by Using Generalized Approaches from Teletraffic Theory

Analysis of Two-Layer Performance Models by Using Generalized Approaches from Teletraffic Theory. L. N. Popova Institute for Mobile Communications, University of Erlangen-Nürnberg, Germany . V. B. Iversen COM - DTU , Technical University of Denmark, Lyngby, Denmark .

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Analysis of Two-Layer Performance Models by Using Generalized Approaches from Teletraffic Theory

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  1. Analysis of Two-Layer Performance Models by Using Generalized Approaches from Teletraffic Theory L. N. Popova Institute for Mobile Communications, University of Erlangen-Nürnberg, Germany V. B. Iversen COM - DTU, Technical University of Denmark, Lyngby, Denmark

  2. Motivation Multi-Service UMTS Network: • Simultaneous support for a wide range of services with different characteristics on a common carrier • Universal frequency reuse High spectrum efficiency • Flexible service bit rate • Statistical Multiplexing among services Higher resource utilization Problem: • Diversity of service requirements difficult to ensure sufficient QoS for all services

  3. Capacity of UMTS • UMTC cell capacity is power based capacity • Each new user increases the total power level in the frequency channel • Capacity is limited by the amount of interference in the air interface • Packet user doesn’t occupy a channel continuously (on-off source ) produce interference only when it is actually transmitting Inherent but uncontrolled Statistical Multiplexing no fixed value of the maximal cell capacity

  4. Conventional Traffic Models • Classical traffic models from fixed networks only deal with the system behavior at connection level (call arrival process)

  5. Conventional Traffic Models

  6. Conventional Traffic Models

  7. Conventional Traffic Models

  8. Conventional Traffic Models Aggregated Traffic

  9. Conventional Traffic Models Adjusted according to the measured quality Overbooking

  10. Conventional Traffic Models

  11. Conventional Traffic Models

  12. Conventional Traffic Models

  13. Connection Level Call Admission Control Blocked-Call-Cleared: • If not enough capacity block call completely • Erlang BCC model • Hard blocking only too pessimistic performance results

  14. Problem Definition • Classical traffic models don’t take into account diversity of service requirements on packet-oriented wireless networks • Just a rough approximation for network performance • Don’ t ensure sufficient QoS for all services • Important features of WCDMA radio interface are neglected: • Variable on –off user transmission rate • Packet buffering/delay • Dynamic cell capacity (wireless interference) • Handover strategies are not included

  15. Contribution • Proposal of a new unified analytical traffic model for a system with mixed services: • Analysis of interaction between the two performance levels: • Connection level call admission procedure • Packet level call handling process • Individual performance assessment for each service class • Proposal of an extended call handling policy buffer scheme • Analysis of impact of buffer on: • The average system performance • Individual users’ throughput

  16. Multi-Layer Traffic Model (recap)

  17. Multi-Layer Traffic Model (recap)

  18. Multi-Layer Traffic Model (recap)

  19. Multi-Layer Traffic Model (recap)

  20. Multi-Layer Traffic Model (recap) Aggregated Traffic

  21. Multi-Layer Traffic Model (recap) Adjusted according to the measured quality Overbooking

  22. Multi-Layer Traffic Model (recap) Blocked-Call-Held: • In case of overbooking, there is loss for the period of congestion • Fry-Molina BCH model • Loss sharing between simultaneously transmitted blocks of distinct users • Soft Capacity The same TTI during decoding: all blocks are affected

  23. Modified Multi-Layer Traffic Model Blocked-Call-Buffered

  24. Modified Multi-Layer Traffic Model Blocked-Call-Buffered

  25. Modified Multi-Layer Traffic Model Blocked-Call-Buffered Congested Traffic

  26. Modified Multi-Layer Traffic Model Buffered Traffic Carried Delayed Traffic

  27. Advantages of Suggested Approach (1) Blocked-Call-Held: Blocked-Call-Buffered: Main difference between two models is the system throughput utilization

  28. Advantages of Suggested Approach (2) Key aspects of the algorithm: • Fast and stable algorithm • Supports the coupling between connection and packet-level QoS characteristics. • Individual performance measure for each traffic stream • More realistic model for analysing behaviour of multiple traffic flows • Supports all classical loss/delay models. • Applicable to performance prediction and the optimum design of virtually arbitrary networks

  29. Traffic Model and Assumptions • Radio interface of W-CDMA, Perfect Power control, Uplink • Multiple service classes with different QoS-parameters: Binomial – Poisson – Pascal (BPP) multi-rate traffic • Connection - Level: Blocked-Call-Cleared (Erlang) model: • Each traffic stream is characterized by: • Mean offered traffic • Peakedness • Data rate required by stream • Packet – Level: Blocked–Call–Buffered model • On-off traffic with activity factor • State-dependent loss probability • Neighbor cell interference (log normal)

  30. Numerical results (1) Packet Handling Policy: • Blocked-Call-Held model • Setup: • mixed services: Radio stream (Poisson); = 4(8)128 (Erl.) Web browsing (Engset); = 40 (Erl.) Email (Pascal); = 37(Erl.) • Activity factor: 0.5; 0.3; 0.7 • FIFO-principle • No trunk reservation • Total cell capacity N=128 channels

  31. Numerical results (1) Packet Handling Policy: • Blocked-Call-Held model • Blocked-Call-Buffered model • Setup: • mixed services: Radio stream (Poisson); = 4(8)128 (Erl.) Web browsing (Engset); = 40 (Erl.) Email (Pascal); = 37(Erl.) • Activity factor: 0.5; 0.3; 0.7 • FIFO-principle • No trunk reservation • Total cell capacity N=128 channels

  32. Modified Call Handling Policy Packet Handling Policy: • Blocked-Call-Held model • Blocked-Call-Buffered model • Blocked-Call-Buffered model with wireless interference • Setup: • mixed services: Radio stream (Poisson); = 4(8)128 (Erl.) Web browsing (Engset); = 40 (Erl.) Email (Pascal); = 37(Erl.) • Activity factor: 0.5; 0.3; 0.7 • Other cell-interference factor=0.55 • Total cell capacity N=128 channels

  33. Conclusions • Goal: Analysis of resource allocation scheme for large-scale queuing networks with WCDMA radio interface • Proposal of an extended call handling policy (introducing of buffer scheme) • How: by using a novel generalized algorithm from extended teletraffic theory: • Combines properties of both loss and queuing systems • Addresses connection and packet-level QoS metrics simultaneously. • Allows explicit theoretical analysis of complex multimedia traffic behavior • Generalizes scheduling policy and service priority discipline for performance evaluation of traffic streams with different QoS provisioning problems. • Findings: Comparison of Blocked-Call-Held scheme with Blocked-Call-Buffered traffic model: • Blocked-Call-Buffered traffic model is a more realistic approach for modelling system processes on the complex network packet-level • Applicable to performance prediction and the optimum design of virtually arbitrary networks

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