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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS1995

Adaptive data rate SSMA system for personal and mobile satellite communications

An adaptive data rate SSMA (spread spectrum multiple access) system is proposed for mobile and personal multimedia satellite communications without the aid of system control earth stations. This system has a constant occupied bandwidth and has variable data rates and processing gains to mitigate communication link impairments such as fading, rain attenuation and interference as well as to handle variable data rate on demand. Proof of concept hardware for 6MHz bandwidth transponder is developed, that uses offset-QPSK (quadrature phase shift keying) and MSK (minimum shift keying) for direct sequence spread spectrum modulation and handle data rates of 4k to 64kbps. The RS422 data interface, low rate voice and H.261 video codecs are installed. The receiver is designed with coherent matched filter technique to achieve fast code acquisition, AFC (automatic frequency control) and coherent detection with minimum hardware losses in a single matched filter circuit. This receiver structure facilitates variable data rate on demand during a call. This paper shows the outline of the proposed system and the performance of the prototype equipment.

Ikegami, Tetsushi↗
NASA NTRS2018

Exploration of Backscatter Methods for Wireless Avionics

This report describes and characterizes the low-power Jeeva Passive Radio systems, including Wanscatter (passive Chirp Spread Spectrum) and Passive Wi-Fi, with respect to their applicability to wireless avionics. The Wireless Avionics Intra-Communications (WAIC) objectives document, ITU-R M.2197, describes a number of applications of wireless avionics, and lists requirements specifications for each. Additionally, it describes models for compartments and areas of aircraft or vehicles in which wireless avionics would be applied. This exploratory study attempts to map Jeeva's Passive Radio technology to those scenarios outlined in the ITU-R M.2197 operational objectives document, and determine the areas and applications for which it is most suitable. Jeeva Passive Radio operates differently than conventional radios. In a conventional radio, a sensor-connected radio node must actively emit a signal in order to communicate. In a Jeeva Passive Radio system, that node instead simply reflects radio frequency energy which is emitted by another nearby device (called the Companion), which can be "plugged in" or otherwise has access to more power. Using reflections, a data packet can be generated and interpreted by a standard receiver. This method of communication inherently uses less energy, resulting in the potential for far lower power consumption and thus far longer battery life. Overall, 68.4% of use cases described by the ITU-R M.2197 operational objectives document were found to be addressable by Jeeva's Passive Radio systems (26 addressable of 38 total), with 26 of those best addressable by Wanscatter and three found to be best addressable with passive Wi-Fi. See Section 4.2 for a detailed breakdown of application suitability. The most fitting types of applications were in the LI (Low-rate Indoors) and LO (Low-rate Outdoors) categories, where lower rates were acceptable and thus Wanscatter could be applied and its much better uplink sensitivity leveraged. Jeeva has identified the Wanscatter (Chirp Spread Spectrum) system as likely holding the most promise for applications such as those outlined in the ITU-R M.2197 operational objectives document. We recommend that Wanscatter be a technology considered for adoption in wireless avionics.

Backscatter↗
DOE OSTI2021

Examining the Performance of Walsh-DSSS Against FBMC-SS in HF Channels

Abstract—Filter bank multicarrier spread spectrum (FBMCSS) has proven to be a robust and reliable waveform choice for communication over high frequency (HF) skywave links. However, the performance of this waveform has yet to be contextualized against typical robust HF waveforms, such as the Walsh-encoded waveform detailed in the MIL-STD-188-110D, Appendix D document. In this paper, we first outline the advantages of both the Walsh and FBMC-SS waveforms as well as present their developments. Simulation results are then presented for ideal, simulated HF, and HF with interference channel conditions. Lastly, skywave-HF results are presented for these two waveforms both with and without interference.

99 GENERAL AND MISCELLANEOUS↗
DOE OSTI2020

CP-DSSS: A Novel Waveform for Multiple Access in IoT

Cyclic prefix direct sequence spread spectrum (CPDSSS) is a novel waveform with versatile characteristics that positions itself well as a secondary network to relieve the congested wireless spectrum. The underlying structure of CPDSSS allows for efficient and effective multi-access capabilites through frequency and time division schemes in a given system. The sum-rate capacity of the system is maximized when the spectrum is divided and allocated to users with the best signal-to-noise (SNR) ratio for the given channel slice. We propose an algorithm for dividing and allocating portions of the spectrum to multiple users with the final goal of maximizing the sumrate capacity of the network. We also propose and develop a precoding/equalization technique that reduces the length of the channel impulse response. This, when used along with a matched filter detector, leads to some improvement in the sum-rate capacity of the network

5G and Beyond Communications↗
DOE OSTI2021

A SSTDR Methodology, Implementations, and Challenges

Sequence time-domain reflectometry (STDR) and spread spectrum time-domain reflectometry (SSTDR) detect, locate, and diagnose faults in live (energized) electrical systems. In this paper, we survey the present SSTDR literature for discussions on theory, algorithms used in its analysis, and its more prominent implementations and applications. Our review includes both scientific litera-ture and selected patents. We also discuss future applications of SSTDR.

14 SOLAR ENERGY↗
DOE OSTI2020

CP-DSSS: An OFDM Compatible Variable Rate Modulation for 5G and Beyond

Cyclic prefix direct sequence spread spectrum (CPDSSS) is a recently proposed waveform that has been designed for coexistence with OFDM (orthogonal frequency division multiplexing) in the same or a pair of parallel networks. The first contribution of this paper is to present equations that reveal similarities and differences of CP-DSSS and OFDM. Furthermore, we show that the channel model of CP-DSSS reduces to that of a cyclic prefixed block-wise single carrier modulation (CP-SCM). However, unlike CP-SCM whose symbol rate is always equal to the transmission bandwidth, CP-DSSS can be adopted to any symbol rate equal to or smaller than the transmission bandwidth. This reduction in symbol rate allows CP-DSSS power spectral density to drop to an arbitrarily low level, hence, facilitates it coexistence as a secondary waveform in a network of primary users. The peak-to-average power ratio (PAPR) of CP-DSSS is also explored and a method for reducing it is proposed.

5G↗
NASA NTRS1997

Parallel interference cancellation for CDMA applications

The present invention provides a method of decoding a spread spectrum composite signal, the composite signal comprising plural user signals that have been spread with plural respective codes, wherein each coded signal is despread, averaged to produce a signal value, analyzed to produce a tentative decision, respread, summed with other respread signals to produce combined interference signals, the method comprising scaling the combined interference signals with a weighting factor to produce a scaled combined interference signal, scaling the composite signal with the weighting factor to produce a scaled composite signal, scaling the signal value by the complement of the weighting factor to produce a leakage signal, combining the scaled composite signal, the scaled combined interference signal and the leakage signal to produce an estimate of a respective user signal.

Divsalar, Dariush↗
NASA NTRS1999

Carrier Estimation Using Classic Spectral Estimation Techniques for the Proposed Demand Assignment Multiple Access Service

In any satellite communication, the Doppler shift associated with the satellite's position and velocity must be calculated in order to determine the carrier frequency. If the satellite state vector is unknown then some estimate must be formed of the Doppler-shifted carrier frequency. One elementary technique is to examine the signal spectrum and base the estimate on the dominant spectral component. If, however, the carrier is spread (as in most satellite communications) this technique may fail unless the chip rate-to-data rate ratio (processing gain) associated with the carrier is small. In this case, there may be enough spectral energy to allow peak detection against a noise background. In this thesis, we present a method to estimate the frequency (without knowledge of the Doppler shift) of a spread-spectrum carrier assuming a small processing gain and binary-phase shift keying (BPSK) modulation. Our method relies on an averaged discrete Fourier transform along with peak detection on spectral match filtered data. We provide theory and simulation results indicating the accuracy of this method. In addition, we will describe an all-digital hardware design based around a Motorola DSP56303 and high-speed A/D which implements this technique in real-time. The hardware design is to be used in NMSU's implementation of NASA's demand assignment, multiple access (DAMA) service.

Scaife, Bradley James↗
DOE OSTI2023

Optimal Modulation and DM Filter Design for a High Switching Frequency Single-Stage Microinverter

This paper presents an optimal modulation and systematic filter design approach for a single-stage dual-active-bridge (DAB) based dc-ac microinverter to achieve improved differential-mode (DM) noise performance for electromagnetic interference (EMI) tests. As DM filters contribute significantly to the overall converter volume, the main objective of this work is to leverage the degrees of freedom in the DAB converters to effectively attenuate the EMI noise. In addition, the DM filter design method needs to ensure near unity power factor converter operation. To achieve these targets, this paper analyzes three modulation strategies based on fixed or variable switching frequency operation where the different control modulation variables are varied to find the simulated DM noise spectrum. Based on the required DM attenuation, a constrained optimization problem is formulated to determine minimal DM filter parameters. Simulation results show that a spread spectrum approach with variable switching frequency is shown to minimize the DM EMI attenuation effort by spreading the noise profile. A fully GaN 400 W hardware prototype demonstrated the spread-sprectrum approach.

14 SOLAR ENERGY↗
NASA NTRS1970

Simulation of the TDRS multipath environment

Design principles and implementation methods are discussed for simulating the propagation path between a tracking and data relay satellite and a mission spacecraft. The emphasis is on multipath and Doppler simulation but additive disturbances are also considered. The recommended form of the simulator is fed separately with the unmodulated carrier, the unmodulated subcarriers (or spread-spectrum components) and the data signals. The perturbations are also introduced separately; then successive modulation operations are performed. The simulator is segmented into elements that perform the various functions of direct and specular multipath, diffuse fading, Doppler shift and delay spread. Delay spreads are realized by discrete delays operating on baseband signals. Doppler simulation and ionospheric or diffuse multipath fading are applied to individual paths before or after modulation of the carrier by delayed baseband signals. Block diagrams are presented on how the different elements are combined to create a complete channel simulator.

Baghdady, E. J.↗
NASA NTRS1990

Topology-selective jamming of fully-connected, code-division random-access networks

The purpose is to introduce certain models of topology selective stochastic jamming and examine its impact on a class of fully-connected, spread-spectrum, slotted ALOHA-type random access networks. The theory covers dedicated as well as half-duplex units. The dominant role of the spatial duty factor is established, and connections with the dual concept of time selective jamming are discussed. The optimal choices of coding rate and link access parameters (from the users' side) and the jamming spatial fraction are numerically established for DS and FH spreading.

Polydoros, Andreas↗
DOE OSTI2023

An improved synthetic signal injection routine for the Haloscope At Yale Sensitive To Axion Cold dark matter (HAYSTAC)

Microwave cavity haloscopes are among the most sensitive direct detection experiments searching for dark matter axions via their coupling to photons. When the power of the expected microwave signal due to axion–photon conversion is on the order of 10 −24 W, having the ability to validate the detector response and analysis procedure by injecting realistic synthetic axion signals becomes helpful. Here, we present a method based on frequency hopping spread spectrum for synthesizing axion signals in a microwave cavity haloscope experiment. It allows us to generate a narrow and asymmetric shape in frequency space that mimics an axion’s spectral distribution, which is derived from a Maxwell–Boltzmann distribution. In addition, we show that the synthetic axion’s power can be calibrated with reference to the system noise. Further, compared to the synthetic axion injection in the Haloscope At Yale Sensitive to Axion Cold dark matter (HAYSTAC) Phase I, we demonstrated synthetic signal injection with a more realistic line shape and calibrated power.

47 OTHER INSTRUMENTATION↗