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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

background
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

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

WGM/9

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?

WGM/9

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

WGM/9

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%)

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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)

SHORT

Demand (kbps)

WGM/9

wp1 preliminary results 2
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)

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

WGM/9

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

WGM/9

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

WGM/9

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

WGM/9

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