1,898 research outputs found
Lunar contour mapping system /lucom/ final report, 5 aug. 1964 - 18 mar. 1965
Radar sensor system for acquisition of lunar surface data - Lunar contour mapping syste
On-board processing concepts for future satellite communications systems
The initial definition of on-board processing for an advanced satellite communications system to service domestic markets in the 1990's is discussed. An exemplar system with both RF on-board switching and demodulation/remodulation baseband processing is used to identify important issues related to system implementation, cost, and technology development. Analyses of spectrum-efficient modulation, coding, and system control techniques are summarized. Implementations for an RF switch and baseband processor are described. Among the major conclusions listed is the need for high gain satellites capable of handling tens of simultaneous beams for the efficient reuse of the 2.5 GHz 30/20 frequency band. Several scanning beams are recommended in addition to the fixed beams. Low power solid state 20 GHz GaAs FET power amplifiers in the 5W range and a general purpose digital baseband processor with gigahertz logic speeds and megabits of memory are also recommended
Report on the development of the Manned Orbital Research Laboratory /MORL/ system utilization potential. Task area IV - MORL SYSTEM improvement study, book 4
Communications and telemetry subsystem analyses for Manned Orbital Research Laboratory system improvement stud
WHOI acoustic telemetry project interim report 12/1/88 - 6/1/89
This interim report covers the progress of the acoustic telemetry project
during the period 12/1/88 to 5/15/89. In general, the work followed the
format specified in WHOI proposal No. 5674.1. The major exception was
the deletion of the transmitter array development task and a corresponding
funding decrease from 170,000. In addition, the period for the
funding was extended to June 30, partly due to a two month delay in project
startup.
The telemetry project was centered around the construction, programming
and testing of a digital receiver prototype capable of supporting future
signal processing algorithms in real-time over ocean acoustic channels. The
baseline receiver consists of a two-channel analog quadrature demodulator,
and interface to a multiprocessor receiver for digital signal processing.
The software developed includes routines for command and control of the
analog demodulator, data handling and formatting, and minimal software
to digitally implement an incoherent MFSK demodulator, synchronizer and
data decoder. Data storage and display programs were also completed to
facilitate the performance analysis of the unit during testing.
The system was tested in Woods Hole harbor at data rates up to 4800
bits/sec. The acoustic channel was time-dispersive Rayleigh fading, and
performance close to theoretical expectations was achieved. We are confident
that the system error behavior is arising from channel-caused effects and
known deficiencies in system performance, such as excessive synchronizer
steady-state jitter.Funding was provided by the Office of Naval Research
under contract Number N00014-86-K-0751, and
by the Charles Stark Draper Laboratory Inc
NASA Tech Briefs Index, 1977, volume 2, numbers 1-4
Announcements of new technology derived from the research and development activities of NASA are presented. Abstracts, and indexes for subject, personal author, originating center, and Tech Brief number are presented for 1977
Engineering evaluations and studies. Volume 3: Exhibit C
High rate multiplexes asymmetry and jitter, data-dependent amplitude variations, and transition density are discussed
Underwater acoustic communications and adaptive signal processing
This dissertation proposes three new algorithms for underwater acoustic wireless communications. One is a new tail-biting circular MAP decoder for full tail-biting convolution (FTBC) codes for very short data blocks intended for Internet of Underwater Things (IoUT). The proposed algorithm was evaluated by ocean experiments and computer simulations on both Physical (PHY) and Media access control (MAC) layers. The ocean experimental results show that without channel equalization, the full tail-biting convolution (FTBC) codes with short packet lengths not only can perform similarly to zero-tailing convolution (ZTC) codes in terms of bit error rate (BER) in the PHY layer. Computer simulation results show that the FTBC codes outperform the ZTC codes in terms of MAC layer metrics, such as collision rate and bandwidth utilization, in a massive network of battery powered IoUT devices.
Second, this dissertation also proposes a new approach to utilizing the underwater acoustic (UWA) wireless communication signals acquired in a real-world experiment as a tool for evaluating new coding and modulation schemes in realistic doubly spread UWA channels. This new approach, called passband data reuse, provides detailed procedures for testing the signals under test (SUT) that change or add error correction coding, change bit to symbol mapping (baseband modulation) schemes from a set of original experimental data --Abstract, page iv
PCM telemetry data compression study, phase II Quarterly report, 25 Nov. 1965 - 25 Feb. 1966
Model analyses and computer simulations used in data compression study for improved pulse code modulation telemetry link
Spectrum Sensing Techniqes in Cognitive Radio: Cyclostationary Method
Cognitive Radios promise to be a major shift in wireless communications based on developing a novel approach which attempt to reduce spectrum scarcity that growing up in the past and waited to increase in the future. Since formulating stages for increasing interest in wireless application proves to be
extremely challenging, it is growing rapidly. Initially this growth leads to huge demand for the radio spectrum. The novelty of this approach needs to optimize the spectrum utilization and find the efficient way for sharing the radio frequencies through spectrum sensing process. Spectrum sensing is one of the most significant
tasks that allow cognitive radio functionality to implement and one of the most challenging tasks. A main challenge in sensing process arises from the fact that, detecting signals with a very low SNR in back ground of noise or severely masked by interference in specific time based on high reliability. This thesis describes the fundamental cognitive radio system aspect based on design and implementation by connecting between the theoretical and practical issue. Efficient method for
sensing and detecting are studied and discussed through two fast methods of computing the spectral correlation density function, the FFT Accumulation Method and the Strip Spectral Correlation Algorithm. Several simulations have been performed to show the ability and performance of studied algorithms.fi=Opinnäytetyö kokotekstinä PDF-muodossa.|en=Thesis fulltext in PDF format.|sv=Lärdomsprov tillgängligt som fulltext i PDF-format
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