Satellite communication networks with on-board processing (OBP) satellites can provide high-speed da-ta transmission rates and global service coverage with reduced propagation delays. In addition, a use of soft-ware defined radio (SDR) in a small satellite can support flexible small satellite communications and offer flexible and adaptive communication protocols. OBP and SDR systems are implemented in static random-access memory (SRAM)-based field-programmable gate arrays (FPGAs) that are the most representative devices for reprogrammable platforms. However, the SRAM, a volatile memory, is very vulnerable to the space radiation environments and the most common damages are single event upsets (SEUs) that generate the OBP and SDR system malfunctions or system failures. In communication channels, high frequency carri-ers in the channel between satellites and terrestrial gateways are extremely susceptible to weather attenuation and other atmospheric turbulences, which induce unavoidably high bit error rates (BERs) in each communi-cation channel. Besides, with growing demands of wireless network service, bursty traffic in packet transmis-sions will increase, which lead high packet loss ratio (PLR). Such factors have degraded the reliability of satel-lite communications networks over time. This thesis suggests a prediction model for OBP and SDR system failure rates, and a means of analyzing the quantitative reliability of the satellite communication network systems. The first subject presents an OBP system adopting Triple Modular Redundancy with the concept of mitigation windows and external scrubber, and then suggests a mathematical model that predicts the OBP system failure rate by only using the information of system configuration resources. Our mathematical deri-vation can estimate on-board processor system reliability as a function of the SEU rate, the number of miti-gation windows, and on-board processor shield thickness. The second subject proposes a means of analyzing the quantitative reliability of the satellite communi-cation network systems. We identify the four major factors that affect the quality of network services: the OBP states, uplink channels, downlink channels, and uplink packet collision losses. Based on these four fac-tors, a Markov model is derived to analyze the probability distributions of various network states. Based on the developed model, a method is suggested for iteratively updating the reliability distribution of network sys-tems affected by changes in the four factors as well as network access time changes. Finally, the third subject contains a derivation of a Markov model presenting reliability of the small satellite network with respect to SDR structures, transmitted signal powers on uplink/downlink channels, code rates, and packet collisions through an enhanced random access (RA) protocol. Our model provides the quantitative network reliability in terms of SDR structures with bad space radiation environments, signal-to-noise ratios (SNRs) on uplink and downlink channels, and PLRs through an enhanced RA protocol.
Table Of Contents
Abstract i List of contents ii List of figures v List of tables viii
1. Introduction 1 1.1 Motivation 1 1.2 Research Scope and Objectives 2 1.3 Overview of Thesis 3
2. Predicting System Failure Rates of SRAM-Based FPGA On-Board Processors in Space Radiation Environments 4 2.1 Introduction 4 2.2 Related Work 11 2.3 SEU Rate Prediction 15 2.4 Estimation of Accumulation Error Rate 21 2.4.1 SEU Mitigation and Correction Strategies 21 2.4.2 Accumulation Error Rate 22 2.4.3 Mitigation of Accumulation Error Rate 26 2.5 Estimation of OBP System Failure Rates 28 2.5.1 Advantages of Mathematical SEU Error Model 28 2.5.2 SEU Error Model in Combinatorial Logic 29 2.5.3 SEU Error Model in Routing Network 31 2.5.4 System Failure Rate due to SEU 32 2.6 Assessment of System Reliability by OBP Shield Thickness 34 2.7 Conclusions 42
3. End-To-End Reliability of Satellite Communication Network Systems 45 3.1 Introduction 45 3.2 Modeling of Major Factors for Network Reliability 54 3.2.1 OBP System Errors 54 3.2.2 Bit Error Rates in Uplink and Downlink Satellite Channels 56 3.2.3 Uplink Packet Collisions 56 3.3 Multi-State Markov Model of A Network System Reliability 59 3.3.1 Failure and Repair Rates 59 3.3.2 Markov Model 61 3.3.3 Derivation of State Probabilities 62 3.4 Analysis of The System Reliability with A Space Environment and Network Through-put 66 3.4.1 Network Reliability in Space Environments 66 3.4.2 Network Reliability and Throughput with ACRDA 68 3.5 Update of Reliability Functions 71 3.6 Conclusion 77 Appendix A 77 Appendix B 78
4. Reliability of Small Satellite Networks with Software-Defined Radio and Enhanced Mul-tiple Access Protocol 79 4.1 Introduction 79 4.2 SDR Reliability and Asynchronous Random Access Protocol 85 4.3 Modeling of Link Reliability 88 4.3.1 SDR Failure Rate and Repair Rate 89 4.3.2 Small Satellite Communication Links 91 4.3.3 Packet Loss Ratio Approximation 94 4.4 Modeling of Link Reliability 97 4.5 Analysis of Reliability with The Changes of Communication Parameters 99 4.6 Conclusion 103 Appendix 104