A waveform compliant with the Software Communications Architecture (SCA) has been developed at the NASA Glenn Research Center. This development is part of the larger Space Telecommunications Radio System project currently underway to define a communications system architecture for future space-based reconfigurable transceivers and software-defined radios. Software-defined radios are becoming more common because of the capabilities of reconfigurable digital signal-processing technologies, such as field-programmable gate arrays (FPGA) and digital processors, placing radio functions in firmware and software that were traditionally performed with analog hardware components. The entire set of these radio functions running in software comprise the waveform, which is run as a software application by the radio processing elements.
The waveform was developed using the SCA framework of rules and requirements that the Department of Defense uses as the standard for the Joint Tactical Radio System. The Department of Defense envisions that their future radios will be SCA compliant. Although the use of the current SCA as a reference has increased our understanding of the architecture, the approach may be impractical for today’s space applications because of its high consumption of processing resources. However, by developing an SCA-compliant waveform, one has direct insight into the resources required to support the reconfigurability offered by this architecture approach. The evolution of NASA’s architecture will continue to identify areas where the SCA should be adapted, with the goal of converging to a common architecture. This will leverage the Department of Defense’s significant investment in software-defined radio technology and software communications architectures.
The waveform was defined using existing telemetry link characteristics and space exploration initiative scenarios. The basic parameters defined were data rate, modulation, coding scheme, symbol rate, baseband data interface, intermediate frequency interface, scrambling scheme, and bandwidth. The waveform was designed from both signal-processing and software component perspectives. Running the waveform at a data rate of 1 megabit per second (Mbps) allowed the majority of signal-processing functions to be implemented in software. In addition, most functions could be implemented in the general-purpose processor, making the waveform ideal for portability and SCA implementation. However, since most applications require higher data rates, several higher rate signal-processing functions were targeted for FPGA implementation. This approach provides options for future waveform scalability.
The final step of the waveform development was integrating the waveform with the SCA infrastructure. The figure illustrates the complexity of waveform transmit functions (e.g., data generator, encoder, modulation, filtering and digital upconversion, and digital-to-analog converter) mapped across the software elements or components (logging function, logical connection ports, and interprocess communication transport mechanisms) of the SCA architecture.
Waveform transmit functions and top-level SCA components and interfaces. IESS, Intelsat Earth Station Standards; CCSDS, Consultative Committee for Space Data Systems; GPP, generic packetized protocol; QPSK, quaternary phase shift keying; BPSK, binary phase shift keying.
Long description of figure.
The completed waveform will serve as a tool in the software-defined radio testbed to support further architecture tradeoffs for the space environment. The waveform routines can be scaled for data rates, frequencies, and alternative architectures to examine the range of communications commonly employed by NASA for space.
Reinhart, Richard C.; Kacpura, Thomas J.; and Johnson, Sandra K.: Software-Defined Radio Architecture Framework Developed for Space-Based Radios. Research & Technology 2005, NASA/TM--2006-214016, 2006, p. 18. http://www.grc.nasa.gov/WWW/RT/2005/RC/RCD-reinhart1.html
Johnson, Sandra K.; Kacpura, Thomas J.; and Reinhart, Richard C.: Software-Defined Radio Technology Analyzed for Space Exploration Scenario. Research & Technology 2005, NASA/TM--2006-214016, 2006, p. 19. http://www.grc.nasa.gov/WWW/RT/2005/RC/RCD-reinhart2.html
Glenn contacts: Richard C. Reinhart, 216-433-6588, Richard.C.Reinhart@nasa.gov; and Sandra K. Johnson, 216-433-8016, Sandra.K.Johnson@nasa.govLast updated: October 12, 2006
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