The aerospace industry has been adopting avionics architectures to take advantage of advances in computer engineering. Integrated Modular Avionics (IMA), as described in ARINC 653, distributes functional modules into a robust configuration interconnected with a "virtual backplane" data communications network. Each avionics module's function is defined in software compliant with the APEX Application Program Interface. The Avionics Full-Duplex Ethernet (AFDX) network replaces the point-topoint connections used in previous distributed systems with "virtual links". This network creates a command and data path between avionics modules with the software and network defining the active virtual links over an integrated physical network. In the event of failures, the software and network can perform complex reconfigurations very quickly, resulting in a very robust system.In this paper, suitable architectures, standards and conceptual designs for IMA computational modules and the virtual backplane are defined and analyzed for applicability to spacecraft. The AFDX network standard is examined in detail and compared with IEEE 802.3 Ethernet. A reference design for the "Ancillary Sensor Network" (ASN) is outlined based on the IEEE 1451 "Standard for a Smart Transducer Interface for Sensors and Actuators" using realtime operating systems, time deterministic AFDX and wireless LAN technology. Strategies for flight test and operational data collection related to Systems Health Management are developed, facilitating vehicle ground processing. Finally, a laboratory evaluation defines performance metrics and test protocols and summarizes the results of AFDX network tests, allowing identification of design issues and determination of ASN subsystem scalability, from a few to potentially thousands of smart and legacy sensors. 12
Abstract-Wireless sensor networks (WSN) based on the IEEE 802.15.4 Personal Area Network standard are finding increasing use in the home automation and emerging smart energy markets. The network and application layers, based on the ZigBee 2007 PRO Standard, provide a convenient framework for component-based software that supports customer solutions from multiple vendors. This technology is supported by System-on-a-Chip solutions, resulting in extremely small and low-power nodes. The Wireless Connections in Space Project addresses the aerospace flight domain for both flight-critical and non-critical avionics. WSNs provide the inherent fault tolerance required for aerospace applications utilizing such technology. The team from Ames Research Center has developed techniques for assessing the fault tolerance of ZigBee WSNs challenged by radio frequency (RF) interference or WSN node failure. 1The ZigBee Network layer forms a mesh network capable of routing data around failed nodes. A two-tier ZigBee network is tested in the lab and various failures induced in sensor and router nodes, simulating realistic fault conditions. A ZigBee network analyzer is used to view the packet traffic and measure the response to these induced faults at the Network layer. Certain faults are induced using Radio Frequency (RF) interference or disruption of the Physical layer, so RF signal levels are monitored during the experiments. The speed at which an orphaned sensor node is detected and an alternative route formed is an important characteristic for fault-tolerant sensor networks. Our working definitions of metrics describing WSN fault tolerance are presented along with a summary of on-going test results from our development lab.A brief overview of ZigBee technology is presented along with RF measurement techniques designed to gauge susceptibility to interference caused by other transmitters such as wireless networks. Since 802.11 and 802.15.4 technology share the 2.4 GHz ISM band, spectrum management is used to ensure every network has a reasonably clear channel for communications. Quantitative RF characterization of the WSN is performed under varying duty cycle conditions to understand the effect of wireless networks and other interference sources on its performance. Furthermore, multipath interference caused by delayed reflections of RF signals is a significant issue, given that the WSN must run in confined metallic spaces, which produce 1 U.S. Government work not protected by U.S. copyright. IEEEAC Paper #1480, Version I, Updated December 9, 2010 high levels of reflected multipath RF energy. The results of RF characterization and interference testing of our prototype WSN in the lab are presented and summarized. The architecture and technical feasibility of creating a single fault-tolerant WSN for aerospace applications is introduced, based on our experimental findings.
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