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VDL Mode 4 Performance Simulator (DLS enhancements) presented by EUROCONTROL

VDL Mode 4 Performance Simulator (DLS enhancements) presented by EUROCONTROL. Montreal, 26 October 2004. Background. VDL Mode 4 Performance Simulator (VPS) Developed under contract to Helios Technology Initially developed to investigate broadcast scenarios

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VDL Mode 4 Performance Simulator (DLS enhancements) presented by EUROCONTROL

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  1. VDL Mode 4 Performance Simulator(DLS enhancements)presented by EUROCONTROL Montreal, 26 October 2004

  2. Background • VDL Mode 4 Performance Simulator (VPS) • Developed under contract to Helios Technology • Initially developed to investigate broadcast scenarios • DLS protocol reviewed and updated in 2003 • DLS Simulations activities organized in two phases: • Phase 1: Implementation and validation of point to point protocols in VPS • Phase 2: Investigations and optimisation of point to point protocols performance using VPS WGM/9

  3. Recap on Phase 1: Development and validation • DLS implementation completed • ICAO Manual (Doc 9816) compliant • Validated with testing and comparison against simple quantitative models • Capable of handling static and dynamic scenarios • Demonstrates the key DLS features • Duplicate suppression • Fragmentation of long packets • Priority management • Deterministic re-transmission when ACK not received • Link establishment (ground-air and air-air) • Short and long transmission protocols • Combination of DLPDUs WGM/9

  4. Phase 2: Scope • This study targets to answer the following questions • How can the system be optimised for latency and capacity? • What is optimum burst size for throughput? • What impact for multiple ground stations? • What are the benefits of ground coordination? • How many aircraft can be supported on a single channel? • What is the impact of a dynamic scenario? WGM/9

  5. Phase 2: Work plan • WP1 • relationship between latency and capacity as a function of quality of service parameters • WP2 • Investigate a means of coordinating ground station transmissions will be designed and tested • WP3 • develop a realistic traffic and data scenario • WP4 • validate the results for a dynamic aircraft scenario • WP5 • enhance VPS to include a more automated LME WGM/9

  6. WP1: Description • Simulations designed on following principles • Technical Manual uses default Quality of Service parameters • Average exchange time is currently 6.5 seconds • Can this latency be improved? • What is the impact on capacity? • Scenario description • A single ground station with 641 static aircraft • All aircraft log on within the first 10 minutes • A range of channel loading considered (12% - 130%) WGM/9

  7. WP1: Preliminary Results (1) • Results in terms of • Delay • Throughput • Retransmissions • Average Delay • Demonstrates ability to exercise control on transaction time P = 0.1 Average delay (sec) SHORT Demand (kbps) WGM/9

  8. WP1: Preliminary Results (2) • Demand vs. Throughput • Lower persistence ensure capacity is matched for higher demand P=0.1 P=0.25 Throughput (kbps) Demand (kbps) • Throughput vs. Retransmissions • The unicast/info transfer protocols can be tuned to reduce retransmissions No. Retransmissions WGM/9 Throughput (kbps)

  9. WP1: Summary of results • Two main results • Reducing p-persistence to 0.1 adds to stability of performance • Reducing minimum and maximum range can produce greatly reduced latencies • Can define multiple QoS sets to carry out an automatic trade off of capacity and latency • Thus VDL Mode 4 can support a number of streams with different QOS • Limiting factor is the number of retransmissions • WP2 will focus on reducing the retransmissions through efficient use of ground reserved slots WGM/9

  10. WP2: Description • Use of ground reserved slots is expected to produce increase in capacity • WP1 scenarios use random access to initiate each transaction • WP2 considers placing some of these transactions into ground reserved blocks • Focus of WP2 • Use of ground reserved slots allows coordination of transmissions to avoid garbling • Design of an efficient ground coordination algorithm WGM/9

  11. WP2: Current status • Simulation experiments ongoing • The results likely to show that VDL Mode 4 protocols support good organisation of the slot resource • High success factor for receipt of bursts • Slot sharing • Maintenance of capacity per ground station over wide area • Wide ranging ability to tune QOS • Potential issues to be addressed • There is a poor use of the burst payload capacity (match of data to message length) • Loss in throughput through RTS, CTS, ACK WGM/9

  12. WP3: Realistic scenarios • Builds on the previous work by simulating realistic scenarios • Traffic based on Core European scenario • Data link traffic developed from Link2000 environment • Both single and multiple ground station scenarios considered WGM/9

  13. Next Steps • Finish Core European scenario simulations • Produce definitive results on ground coordination • Look at other optimisation possibilities • Optimization of Burst formats • Encouraging greater combination of messages WGM/9

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