Modeling and Evaluation of Aerial Layer Communications System Architectures by Stephen P Ajemian B.S. Electrical Engineering The Johns Hopkins University, 2004 M.S. Electrical Engineering The Johns Hopkins University, 2008 Submitted to the System Design and Management Program in Partial Fulfillment of the Requirements for the Degree of Master of Science in Engineering and Management at the Massachusetts Institute of Technology September 2013 ©2013 Stephen P Ajemian. All rights reserved. The author hereby grants to MIT permission to reproduce and to distribute publicly paper and electronic copies of this thesis document in whole or in part in any medium now known or hereafter created. Signature of Author:_____________________________________________________________ Stephen Ajemian System Design and Management Program Certified by:___________________________________________________________________ Bruce Cameron Lecturer of Engineering Systems Thesis Supervisor Accepted by:___________________________________________________________________ Patrick Hale Director System Design and Management Fellows Program (THIS PAGE INTENTIONALLY LEFT BLANK) 2 Modeling and Evaluation of Aerial Layer Communications System Architectures by Stephen Ajemian Submitted to the System Design and Management Program on 7/12/2013 in Partial Fulfillment of the Requirements for the Degree of Master of Science in Engineering and Management Abstract Airborne networks are being developed to provide communications services in order to augment space-based and terrestrial communications systems. These airborne networks must provide point to point wireless communications capabilities between aircraft and to ground- based users. Architecting airborne networks requires evaluating the capabilities offered by candidate aircraft to operate at the required altitudes to bridge communications among ground users dispersed over large geographic areas. Decision makers are often faced with choices regarding the type and number of aircraft to utilize in an airborne network to meet information exchange requirements. In addition, the type of radio required to meet user needs may also factor into the architecture evaluation for an airborne network. Aircraft and radio design choices must be made under cost constraints in order to deliver capable communications architectures at an acceptable cost. Evaluating communications architectures is often conducted with modeling and simulation. However, evaluations typically focus on specific network configurations and can become intractable when varying design variables such as aircraft and radio types due to the complexity of the trade space being analyzed. Furthermore, the growth in choices for design variables (such as additional aircraft types) can lead to enormous growth in the number of feasible candidate architectures to analyze. The methodology developed and presented herein describes an approach for evaluating a large number of architecture combinations which vary on aircraft type and radio type for representative airborne networks. The methodology utilizes modeling and simulation to generate wireless communications performance data for candidate aircraft and radio types and enumerates a large trade space through a computational tool. The trade space is then evaluated against a multi-objective decision model to rapidly down-select to a handful of candidate architectures for more detailed analysis. The results of this analysis provide effective tools for reducing the complex trade space to a tractable number of architectures to make an informed architectural decision with no prior articulation of preferences for performance measures. For the notional concept of operation analyzed, the number of feasible architectures was approximately 500,000 for each of the two 3 radio types examined. The decision model implemented reduced the feasible architectures to approximately 50 near-optimal architectures for each radio type. From this manageable set of near-optimal architectures, an analysis is conducted to evaluate marginal benefits versus cost to further reduce the candidate architectures to 3 architectures for each radio type. From these remaining architectures, detailed analysis and visualization can be conducted to aid decision makers in articulating preferences and identifying a single “best” architecture based on mission needs. The enumeration of the trade space using the computational tool and multi-objective decision model is highly flexible to incorporating new constraints and generating new candidate architectures as stakeholder preferences become clearer. The trade space enumeration and decision model can be conducted rapidly to down-select large trade spaces to a tractable number of communications architectures to inform an architectural recommendation. Thesis Supervisor: Bruce Cameron Title: Lecturer of Engineering Systems 4 Table of Contents Acknowledgements ....................................................................................................................... 10 1 Introduction .......................................................................................................................... 11 2 Motivation ............................................................................................................................. 14 3 Methodology ......................................................................................................................... 18 3.1 Literature Review ........................................................................................................... 18 3.2 Enumeration and Evaluation of Candidate Architectures ............................................. 19 4 Concept of Operation ........................................................................................................... 21 5 Scenario Development .......................................................................................................... 22 5.1 Radio Systems ................................................................................................................ 22 5.2 Aircraft ............................................................................................................................ 25 5.3 Communications Model ................................................................................................. 27 5.3.1 Systems Tool Kit Overview ...................................................................................... 27 5.3.2 Deployment Scenario .............................................................................................. 29 5.3.3 Aircraft Model ......................................................................................................... 31 5.3.4 Mobile Ground Vehicle Model ................................................................................ 32 6 Architectural Decision Strategy ............................................................................................ 33 6.1 Architecture Cost............................................................................................................ 35 6.2 Ground Coverage ........................................................................................................... 36 6.3 Site-to-Site Connectivity ................................................................................................. 37 7 Enumeration of Trade Space ................................................................................................ 38 7.1 Ground Coverage Computations.................................................................................... 38 7.2 Site-to-Site Connectivity ................................................................................................. 40 8 Multi-Objective Optimization Model .................................................................................... 42 5 8.1 Definitions ...................................................................................................................... 43 8.1.1 Multi-Objective Optimization Problem Definition.................................................. 44 8.2 Objective Function Description ...................................................................................... 44 8.2.1 Cost Objective Function .......................................................................................... 45 8.2.2 Ground Coverage Objective Function ..................................................................... 45 8.2.3 Site-to-Site Connectivity Objective Function .......................................................... 46 8.3 Enumeration of the Pareto Front ................................................................................... 47 8.3.1 Genetic Algorithm Overview ................................................................................... 48 8.4 MATLAB Decision Model Implementation ..................................................................... 51 8.4.1 MATLAB Global Optimization Toolbox ................................................................... 51 9 Architecture Evaluation Results ............................................................................................ 54 9.1 Performance Results ...................................................................................................... 54 9.1.1 Total Coverage Area vs. Cost .................................................................................. 54 9.1.2 Site-to-Site Connectivity vs. Cost ............................................................................ 55 9.1.3 Site-to-Site Connectivity vs Area Covered .............................................................. 56 9.2 Down-Selection from the Pareto Front .......................................................................... 57 9.2.1 Radio A Down-Selection of the Pareto Front .......................................................... 58 9.2.2 Radio B Down-Selection of the Pareto Front .......................................................... 59 9.3 Sensitivity Analysis ......................................................................................................... 61 10 Detailed Analysis of Selected Architectures ......................................................................... 64 10.1 STK Evaluation of Final Candidate Architectures ........................................................... 66 10.1.1 Radio Comparison for Maximum Site-to-Site Connectivity .................................... 66 10.1.2 Radio Comparison for Maximum Area Covered ..................................................... 68 10.1.3 Radio Comparison for Balanced Architecture ........................................................ 69 6 10.2 Suitability of Site-to-Site Connectivity as a Measure of Network Resilience ................ 71 10.2.1 Analysis of Average Crosslinks in the Presence of Node Failures ........................... 72 11 Future Extensions ................................................................................................................. 78 11.1 Dynamic Aircraft ............................................................................................................. 78 11.2 Adaptive Data Rates ....................................................................................................... 79 11.3 Network Topology Optimization .................................................................................... 79 12 Conclusions ........................................................................................................................... 81 Appendix A – MATLAB Source Code ............................................................................................. 83 Glossary ......................................................................................................................................... 89 References .................................................................................................................................... 90 7 List of Tables Table 1. Radio Horizon for Various Altitudes ................................................................................ 15 Table 2. Radio A Tolerable Path Loss ............................................................................................ 24 Table 3. Radio B Tolerable Path Loss ............................................................................................ 25 Table 4. Summary of Candidate Radio Systems ........................................................................... 25 Table 5. Aircraft Assumptions ....................................................................................................... 26 Table 6. Site Locations .................................................................................................................. 30 Table 7. Architectural Decisions ................................................................................................... 33 Table 8. Performance Outputs ...................................................................................................... 34 Table 9. Intermediate Performance Outputs ............................................................................... 35 Table 10. Sample Data for Ground Coverage Computation for Aircraft/Radio Pair .................... 40 Table 11. Sample Radio B Site-to-Site Connectivity Matrix .......................................................... 41 Table 12. Down-Selected Pareto Front for Radio A ...................................................................... 58 Table 13. Radio A Consolidated Architecture Summary ............................................................... 58 Table 14. Down-Selected Pareto Front for Radio B ...................................................................... 60 Table 15. Radio B Consolidated Architecture Summary ............................................................... 60 Table 16. Consolidated Final Candidate Architectures ................................................................. 66 Table 17. Simulated Network Performance Metrics .................................................................... 74 Table 18. Example Adaptive Data Rate RSL Thresholds ............................................................... 79 List of Figures Figure 1. Example Airborne Network Use Case ............................................................................ 12 Figure 2. Communications Architecture Evaluation Methodology .............................................. 20 Figure 3. Sample of STK Graphical Output .................................................................................... 28 Figure 4. Deployment Scenario Modeled in STK .......................................................................... 30 Figure 5. 3-D View of Local Terrain from Site 10 .......................................................................... 31 Figure 6. Aircraft with Dipole Antenna ......................................................................................... 32 Figure 7. Mobile Ground Vehicle with Dipole Antenna ................................................................ 32 Figure 8. Process Flow for Architecture Evaluation ...................................................................... 35 8 Figure 9. Ground Coverage Computation ..................................................................................... 39 Figure 10. Simple GA Flow Chart .................................................................................................. 50 Figure 11. Area Covered vs. Cost .................................................................................................. 55 Figure 12. Average Number of Crosslinks vs. Cost ....................................................................... 56 Figure 13. Average Number of Crosslinks vs. Area Covered ........................................................ 57 Figure 14. Aircraft Composition for Down-Selected Pareto Front Using Radio A ........................ 59 Figure 15. Aircraft Composition for Down-Selected Pareto Front Using Radio B ........................ 61 Figure 16. Comparison of Pareto Front to Initial Population 1 .................................................... 62 Figure 17. Comparison of Pareto Front to Initial Population 2 .................................................... 63 Figure 18. Average Crosslinks vs. Area Covered for Pared Pareto Front ...................................... 64 Figure 19. Final Candidate Architectures for Radio A and Radio B .............................................. 65 Figure 20. Architecture 10 for Radio A (Maximum Site-to-Site Connectivity) ............................. 67 Figure 21. Architecture 11 for Radio B (Maximum Site-to-Site Connectivity).............................. 67 Figure 22. Architecture 13 for Radio A (Maximum Area Covered) ............................................... 68 Figure 23. Architecture 8 for Radio B (Maximum Area Covered) ................................................. 69 Figure 24. Architecture 12 for Radio A (Balanced Architecture) .................................................. 70 Figure 25. Architecture 9 for Radio B (Balanced Architecture) .................................................... 70 Figure 26. Aggregate Air Force Fleet Rates for Mission Capability [21] ....................................... 71 Figure 27. Example Network Generated in MATLAB .................................................................... 73 Figure 28. Example Degraded Network ........................................................................................ 74 Figure 29. Island Nodes for 100 Trials (MC Rate of 60%) ............................................................. 75 Figure 30. Island Nodes for 100 Trials (MC Rate of 70%) ............................................................. 76 Figure 31. Island Nodes for 100 Trials (MC Rate of 80%) ............................................................. 76 9 Acknowledgements Throughout my time in the Systems Design and Management (SDM) program, I have continued to be awed and inspired by the amazing talents of the people within the MIT community. I have been challenged more than I could have ever anticipated and express my gratitude for the knowledge I’ve obtained throughout this program, both personally and professionally. I am honored to have the privilege of experiencing both the intellectual challenges of the MIT experience and my amazing professors and classmates. I would like to express my sincerest thanks to Dr. Bruce Cameron for his constant guidance and support on this thesis. His research in system architecture was the inspiration for this work and his expertise was invaluable in helping me to understand and navigate through a complex problem space. I want to express my appreciation for his time and effort in advising me, reviewing my work and helping me communicate a complex topic clearly. I would also like to thank him for providing me access to the talented people in the System Architecture Lab, Daniel Selva and Marc Sanchez, who were instrumental in steering me in the right direction for this analysis. Daniel and Marc exposed me to a rich set of tools and techniques that I can apply beyond the SDM program to simplify complex systems and impact high technology development efforts for my entire career. I would also like to thank Daniel for reviewing my thesis and providing his expertise in trade space enumeration and multi-objective optimization which not only strengthened this thesis, but also my understanding of these subjects. I would also like to thank my employer, the MITRE Corporation, for providing me with the opportunity to attend the SDM Program. Lastly, I would like to thank my loving wife and lifelong friend, Lyndsay, for her unwavering support throughout this entire program. Yes, I can come on a walk with you and Vinnie now. The views expressed in this thesis are those of the author and do not reflect the views or the positions of the Department of Defense or the MITRE Corporation. 10