Richard C. Reinhart

Advanced Communications Technology Satellite (ACTS): four-year system performance

The Advanced Communications Technology Satellite (ACTS) was conceived at the National Aeronautics and Space Administration (NASA) in the late 1970s as a follow-on program to ATS and CTS to continue NASAs long history of satellite communications projects. The ACTS project set the stage for the C-band satellites that started the industry, and later the ACTS project established the use of Ku-band for video distribution and direct-to-home broadcasting. ACTS, launched in September 1993 from the Space Shuttle, created a revolution in satellite system architecture by using digital communications techniques employing key technologies such as a fast hopping multibeam antenna, an on-board baseband processor, a wide-band microwave switch matrix, adaptive rain fade compensation, and the use of 900 MHz transponders operating at Ka-band frequencies. This paper describes the lessons learned in each of the key ACTS technology areas, as well as in propagation investigations.

Open Architecture Standard for NASA's Software-Defined Space Telecommunications Radio Systems

NASA is developing an architecture standard for software-defined radios used in space- and ground-based platforms to enable commonality among radio developments to enhance capability and services while reducing mission and programmatic risk. Transceivers (or transponders) with functionality primarily defined in software (e.g., firmware) have the ability to change their functional behavior through software alone. This radio architecture standard offers value by employing common waveform software interfaces, method of instantiation, operation, and testing among different compliant hardware and software products. These common interfaces within the architecture abstract application software from the underlying hardware to enable technology insertion independently at either the software or hardware layer. This paper presents the initial Space Telecommunications Radio System architecture for NASA missions to provide the desired software abstraction and flexibility while minimizing the resources necessary to support the architecture.

CoNNeCT's approach for the development of three Software Defined Radios for space application

National Aeronautics and Space Administration (NASA) is developing an on-orbit, adaptable, Software Defined Radios (SDR)/Space Telecommunications Radio System (STRS)-based testbed facility to conduct a suite of experiments to advance technologies, reduce risk, and enable future mission capabilities. The flight system, referred to as the “SCAN Testbed” will be launched on an HTV-3 no earlier than May of 2012 and will operate on an external pallet on the truss of the International Space Station (ISS) for up to five years. The Communications, Navigation, and Networking reConfigurable Testbed (CoNNeCT) Project, developing the SCAN Testbed, will provide NASA, industry, other Government agencies, and academic partners the opportunity to develop and field communications, navigation, and networking applications in the laboratory and space environment based on reconfigurable, software defined radio platforms and the Space Telecommunications Radio System (STRS) Architecture. Three flight qualified SDRs platforms were developed, each with verified waveforms that are compatible with NASAs Tracking and Data Relay Satellite System (TDRSS). The waveforms and the Operating Environment are compliant with NASAs software defined radio standard architecture, STRS. Each of the three flight model (FM) SDRs has a corresponding breadboard and engineering model (EM) with lower fidelity than the corresponding flight unit. Procuring, developing, and testing SDRs differs from the traditional hardware-based radio approach. Methods to develop hardware platforms need to be tailored to accommodate a “software” application that provides functions traditionally performed in hardware. To accommodate upgrades, the platform must be specified with assumptions for broader application but still be testable and not exceed Size, Weight, and Power (SWaP) expectations. Ideally, the applications (waveforms) operating on the platform should be specified separately to accommodate portability to other platforms and support multiple entities developing the platform from the application. To support future flight upgrades to the flight SDRs, development and verification platforms are necessary in addition to the flight system. This paper provides details on the approach used to procure and develop the SDR systems for CoNNeCT and provide suggestions for similar developments. Unique development approaches for each SDR were used which provides a rare opportunity to compare approaches and provide recommendations for future space missions considering the use of an SDR. Three case studies were examined. In two cases, the SDR vendor (General Dynamics and Harris) was the integrated platform and waveform provider. In these cases, the platform and waveform requirements were considered together by the vendor using high level analysis to support the division of the requirements. In the Harris SDR case, the platform and waveform specification was then integrated into a single document. This case study was for a first generation platform, which offers significant processing and reconfigurablility, but is not optimized for SWaP. This provides a test bed platform for many investigations of future capabilities, but requires additional SWaP than optimized flight radios. In the GD case, the specifications were provided separately. The GD SDR leverages existing platforms with minor changes to the Radio Frequency (RF) portions. The most significant change to the CoNNeCT GD SDR from previous platforms was the addition of a reconfigurable processor. The capability tests the next generation SDR, but offers limited capacity and reconfigurability. In the case of the JPL SDR, the platform was developed by JPL and Cincinnati Electronics. Goddard Space Flight Center (GSFC) provided a waveform that was developed on a ground-based development platform, and Glenn Research Center (GRC) ported the waveform to the flight platform and performed the integrated test and acceptance of the subsystem. This last case also leverages an existing platform development, and offers more capacity for reconfigurability than the second case.

Hardware Architecture Study for NASA's Space Software Defined Radios

This study defines a hardware architecture approach for software defined radios to enable commonality among NASA space missions. The architecture accommodates a range of reconfigurable processing technologies including general purpose processors, digital signal processors, field programmable date arrays (FPGAs), and application specific integrated circuits (ASICs) in addition to flexible and tunable radio frequency (RF) front ends to satisfy varying mission requirements. The hardware architecture consists of modules, radio functions, and interfaces. The modules are a logical division of common radio functions that comprise a typical communication radio. This paper describes the architecture details, module definitions, the typical functions on each module and the module interfaces. Trade-offs between component-based, custom architecture and a functional-based, open architecture are described. The architecture does not specify a physical implementation internally on each module, nor does the architecture mandate the standards or ratings of the hardware used to construct the radios

Pre-Flight Testing and Performance of a Ka-Band Software Defined Radio

National Aeronautics and Space Administration (NASA) has developed a space-qualified, reprogrammable, Ka-band Software Defined Radio (SDR) to be utilized as part of an on-orbit, reconfigurable testbed. The testbed will operate on the truss of the International Space Station beginning in late 2012. Three unique SDRs comprise the testbed, and each radio is compliant to the Space Telecommunications Radio System (STRS) Architecture Standard. The testbed provides NASA, industry, other Government agencies, and academic partners the opportunity to develop communications, navigation, and networking applications in the laboratory and space environment, while at the same time advancing SDR technology, reducing risk, and enabling future mission capability. Designed and built by Harris Corporation, the Ka-band SDR is NASAs first space-qualified Ka-band SDR transceiver. The Harris SDR will also mark the first NASA user of the Ka-band capabilities of the Tracking Data and Relay Satellite System (TDRSS) for on-orbit operations. This paper describes the testbeds Ka-band System, including the SDR, travelling wave tube amplifier (TWTA), and antenna system. The reconfigurable aspects of the system enabled by SDR technology are discussed and the Ka-band system performance is presented as measured during extensive pre-flight testing.

NASA's space communications and navigation test bed aboard the international space station

The NASA SCaN Test Bed flight experiment payload aboard ISS will enable experimenters the unique opportunity to investigate SDRs, navigation, and networking in the space environment. Comprised of three SDRs from industry partners, CoNNeCT allows experimenters to develop and verify new waveforms compliant with the STRS SDR architecture standard, using verified ground systems and then have those waveforms uploaded to the flight SDRs to assess in situ performance and to better understand operational concepts for SDRs in space. In addition to the SDRs, the reprogrammable avionics software allows application software for on-board networking and routing experiments. The flight system communicates with TDRSS at both S-band and Ka-band and can receive within the GPS L-band for navigation waveform development and experiments.

Multi-objective reinforcement learning-based deep neural networks for cognitive space communications

Future communication subsystems of space exploration missions can potentially benefit from software-defined radios (SDRs) controlled by machine learning algorithms. In this paper, we propose a novel hybrid radio resource allocation management control algorithm that integrates multi-objective reinforcement learning and deep artificial neural networks. The objective is to efficiently manage communications system resources by monitoring performance functions with common dependent variables that result in conflicting goals. The uncertainty in the performance of thousands of different possible combinations of radio parameters makes the trade-off between exploration and exploitation in reinforcement learning (RL) much more challenging for future critical space-based missions. Thus, the system should spend as little time as possible on exploring actions, and whenever it explores an action, it should perform at acceptable levels most of the time. The proposed approach enables on-line learning by interactions with the environment and restricts poor resource allocation performance through ‘virtual environment exploration’. Improvements in the multi-objective performance can be achieved via transmitter parameter adaptation on a packet-basis, with poorly predicted performance promptly resulting in rejected decisions. Simulations presented in this work considered the DVB-S2 standard adaptive transmitter parameters and additional ones expected to be present in future adaptive radio systems. Performance results are provided by analysis of the proposed hybrid algorithm when operating across a satellite communication channel from Earth to GEO orbit during clear sky conditions. The proposed approach constitutes part of the core cognitive engine proof-of-concept to be delivered to the NASA Glenn Research Center SCaN Testbed located on-board the International Space Station.

Bandwidth-Efficient Communication through 225 MHz Ka-band Relay Satellite Channel

The communications and navigation space infrastructure of the National Aeronautics and Space Administration (NASA) consists of a constellation of relay satellites (called Tracking and Data Relay Satellites (TDRS)) and a global set of ground stations to receive and deliver data to researchers around the world from mission spacecraft throughout the solar system. Planning is underway to enhance and transform the infrastructure over the coming decade. Key to the upgrade will be the simultaneous and efficient use of relay transponders to minimize cost and operations while supporting science and exploration spacecraft. Efficient use of transponders necessitates bandwidth efficient communications to best use and maximize data throughput within the allocated spectrum. Experiments conducted with NASAs Space Communication and Navigation (SCaN) Testbed on the International Space Station provides a unique opportunity to evaluate advanced communication techniques, such as bandwidth-efficient modulations, in an operational flight system. Demonstrations of these new techniques in realistic flight conditions provides critical experience and reduces the risk of using these techniques in future missions. Efficient use of spectrum is enabled by using high-order modulations coupled with efficient forward error correction codes. This paper presents a high-rate, bandwidth-efficient waveform operating over the 225 MHz Ka-band service of the TDRS System (TDRSS). The testing explores the application of Gaussian Minimum Shift Keying (GMSK), 2/4/8-phase shift keying (PSK) and 16/32- amplitude PSK (APSK) providing over three bits-per-second-per-Hertz (3 b/s/Hz) modulation combined with various LDPC encoding rates to maximize through- put. With a symbol rate of 200 M-band, coded data rates of 1000 Mbps were tested in the laboratory and up to 800 Mbps over the TDRS 225 MHz channel. This paper will present on the high-rate waveform design, channel characteristics, performance results, compensation techniques for filtering and equalization, and architecture considerations going forward for efficient use of NASAs infrastructure.

Multi-Objective Reinforcement Learning for Cognitive Radio-Based Satellite Communications

Previous research on cognitive radios has addressed the performance of various machinelearning and optimization techniques for decision making of terrestrial link properties. In this paper, we present our recent investigations with respect to reinforcement learning that potentially can be employed by future cognitive radios installed onboard satellite communications systems specifically tasked with radio resource management. This work analyzes the performance of learning, reasoning, and decision making while considering multiple objectives for time-varying communications channels, as well as different crosslayer requirements. Based on the urgent demand for increased bandwidth, which is being addressed by the next generation of high-throughput satellites, the performance of cognitive radio is assessed considering links between a geostationary satellite and a fixed ground station operating at Ka-band (26 GHz). Simulation results show multiple objective performance improvements of more than 3.5 times for clear sky conditions and 6.8 times for rain conditions.

Link adaptation for mitigating Earth-to-Space propagation effects on the NASA SCaN testbed

In Earth-to-Space communications, well-known propagation effects such as path loss and atmospheric loss can lead to fluctuations in the strength of the communications link between a satellite and its ground station. Additionally, the typically unconsidered effect of shadowing due to the geometry of the satellite and its solar panels can also lead to link degradation. As a result of these anticipated channel impairments, NASAs communication links have been traditionally designed to handle the worst-case impact of these effects through high link margins and static, lower rate, modulation formats. The work presented in this paper aims to relax these constraints by providing an improved trade-off between data rate and link margin through utilizing link adaptation. More specifically, this work provides a simulation study on the propagation effects impacting NASAs SCaN Testbed flight software-defined radio (SDR) as well as proposes a link adaptation algorithm that varies the modulation format of a communications link as its signal-to-noise ratio fluctuates. Ultimately, the models developed in this work will be utilized to conduct real-time flight experiments on-board the NASA SCaN Testbed.