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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

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

Montreal, 26 October 2004


  • 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


Recap on phase 1 development and validation
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


Phase 2 scope
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?


Phase 2 work plan
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


Wp1 description
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%)


Wp1 preliminary results 1
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)


Demand (kbps)


Wp1 preliminary results 2
WP1: Preliminary Results (2)

  • Demand vs. Throughput

    • Lower persistence ensure capacity is matched for higher demand



Throughput (kbps)

Demand (kbps)

  • Throughput vs. Retransmissions

    • The unicast/info transfer protocols can be tuned to reduce retransmissions

No. Retransmissions


Throughput (kbps)

Wp1 summary of results
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


Wp2 description
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


Wp2 current status
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

    Wp3 realistic scenarios
    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


    Next steps
    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