SCIENTIFIC AND TECHNICAL AEROSPACE REPORTS
A Biweekly Publication of the National Aeronautics and Space Administration
VOLUME 44, ISSUE 8 - April 21, 2006
32 COMMUNICATIONS AND RADAR
Includes radar; radio, wire, and optical communications; land and global communications; communications theory.
For related information see also 04 Aircraft Communications and Navigation; and 17 Space Communications, Spacecraft Communications, Command and Tracking; for search and rescue, see 03 Air Transportation and Safety; and 16 Space Transportation and Safety.
20060010231 Michigan Univ., MI, USA
Dual-Band Deramp Radar Design for Ocean Current Measurements
Haynes, Mark S.; Summer Student Research Presentations; August 2005, pp. 35; In English; See also 20060010186; No Copyright; Available from CASI only as part of the entire parent document
A mission has been proposed to remotely measure ocean surface currents and surface wind velocities. It will provide the highest resolution and repeat time of these measurements to date for ocean current models with scientific and societal applications. A ground-based experimental radar unit is needed for proof of concept. The proposed experiment set up is to mount the radar on an oil rig to imitate satellite data acquisition. This summer, I completed the radar design. The design employs chirp/deramp topology with simultaneous transmit/receive channels. These two properties allow large system bandwidth, extended sample time, close range imaging, and low sampling rate. The radar operates in the Ku and Ka microwave bands, at 13.5 and 35.5 GHz, respectively, with a system bandwidth of 300 MHz. I completed the radar frequency analysis and research on potential components and antenna configurations. Subsequent work is needed to procure components, as well as to build, test, and deploy the radar. Author
Ocean Surface; Ocean Currents; Wind Velocity; Data Acquisition; Chirp; Microwave Frequencies; Bandwidth; Signal Reception
20060010265 Iowa State Univ. of Science and Technology, Ames, IA, USA
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An Advanced Orbiting Systems Approach to Quality of Service in Space-Based Intelligent Communication Networks
Riha, Andrew P.; Summer Student Research Presentations; August 2005, pp. 44; In English; See also 20060010186; No Copyright; Available from CASI only as part of the entire parent document
As humans and robotic technologies are deployed in future constellation systems, differing traffic services will arise, e.g., realtime and non-realtime. In order to provide a quality of service framework that would allow humans and robotic technologies to interoperate over a wide and dynamic range of interactions, a method of classifying data as realtime or non-realtime is needed. In our paper, we present an approach that leverages the Consultative Committee for Space Data Systems (CCSDS) Advanced Orbiting Systems (AOS) data link protocol. Specifically, we redefine the AOS Transfer Frame Replay Flag in order to provide an automated store-and-forward approach on a per-service basis for use in the next-generation Interplanetary Network. In addition to addressing the problem of intermittent connectivity and associated services, we propose a follow-on methodology for prioritizing data through further modification of the AOS Transfer Frame. Author
Communication Networks; Robotics
20060010892 Government Accountability Office, Washington, DC, USA
Telecommunications: Challenges to Assessing and Improving Telecommunications for Native Americans on Tribal Lands
Jan. 2006; 92 pp.; In English Report No.(s): PB2006-105584; GAO-06-189; No Copyright; Avail.: CASI: A05, Hardcopy
An important goal of the Communications Act of 1934, as amended, is to ensure access to telecommunications services for all Americans. The Federal Communications Commission has made efforts to improve the historically low subscribership rates of Native Americans on tribal lands. In addition, Congress is considering legislation to establish a grant program to help tribes improve telecommunications services on their lands. This report discusses (1) the status of telecommunications subscribership for Native Americans living on tribal lands; (2) federal programs available for improving telecommunications on these lands; (3) barriers to improvements; and (4) how some tribes are addressing these barriers. NTIS
American Indians; Telecommunication; Law (Jurisprudence)
20060011078 New Mexico Univ., Albuquerque, NM, USA
A Maximum Entropy Encoder for Speech
Angel, Edward; Daigle, L. Don; Rodriquez, Michael; IEEE International Conference on Acoustics, Speech, and Signal Processing, (ICASSP '83), Volume 3; [1983], pp. 1292-1295; In English; See also 20060011043; Copyright; Avail.: Other Sources
A new approach to the encoding of speech signals is proposed based on directly maximizing the first order entropy of the data sent down the channel.
It is formulated recursively and can be implemented via lookup tables.
A corresponding decoder is also derived and can be implemented in a similar manner.
The performance of the system is competitive with other methods but differs qualitatively as the design is based on entropy considerations rather than minimizing mean square error as is done is most other methods. Author
Coders; Maximum Entropy Method; Speech Recognition
20060011079 Texas A&M Univ., College Station, TX, USA
On the Tandem Connection of Differential Encoding Systems: The Case of Cascaded Quantizers
Fischer, Thomas R.; IEEE International Conference on Acoustics, Speech, and Signal Processing, (ICASSP '83), Volume 3; [1983], pp. 1300-1303; In English; See also 20060011043; Copyright; Avail.: Other Sources
A tandem differential pulse code modulation (DPCM) system structure is developed and the design problem formulated. In the simplified case of cascaded quantizers, the low-to-high and high-to-low bit rate tandems are examined and the performance limitations discussed. Finally the performance of tandem DPCM systems operating at various bit rates is evaluated by simulation. Author
Coding; Differential Pulse Code Modulation; Counters
20060011092 Rensselaer Polytechnic Inst., Troy, NY, USA
Signal Restoration from Phase by Projection onto Convex Sets
Levi, Aharon; Stark, Henry; IEEE International Conference on Acoustics, Speech, and Signal Processing, (ICASSP '83), Volume 3; [1983], pp. 1458-1460; In English; See also 20060011043 Contract(s)/Grant(s): F30602-82-K-0151; NSF ECS-81-11265; Copyright; Avail.: Other Sources
We apply the method of alternating projections onto convex sets to the problem of restoring a signal from the phase of its Fourier transform. A method of improving convergence by adaptively varying a set relaxation parameters in the restoration algorithm is described. The advantages of using the method of convex projections are discussed. Author
Convexity; Set Theory; Signal Processing; Optimization; Restoration; Algorithms
20060011103 Naval Research Lab., Washington, DC, USA
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A Generalization of Isolated Word Recognition Using Vector Quantization
Burton, D. K.; Shore, J. E.; Buck, J. T.; IEEE International Conference on Acoustics, Speech, and Signal Processing, (ICASSP '83), Volume 3; [1983], pp. 1021-1024; In English; See also 20060011043; Copyright; Avail.: Other Sources
The use of vector quantization (VQ) for isolated-word speech recognition of a 20-word vocabulary was shown in previous work to achieve more than 99% accuracy for speaker-dependent recognition and 87% accuracy for speaker-independent recognition. Separate VQ codebooks were designed for each word in the recognition vocabulary, and input words were classified by performing VQ and finding the codebook that achieves the smallest average distortion. The method obviates time normalization and makes no use of time-sequence information. This paper presents results for a generalization that incorporates time-sequence information. The generalization, which was motivated by work of Martinez, Riveria, and Buzo, is more accurate and faster than the previous method. Words in the training and input sequences are normalized linearly to the same length and then divided into sections. Separate VQ codebooks are designed for each section of each vocabulary word. Each vocabulary word is then represented by a 'multisection' codebook - a time-dependent sequence of section-codebooks. New words are classified by performing VQ and finding the multi-section codebook that achieves the smallest average distortion. Initial tests on a twenty-word vocabulary resulted in accuracies greater than 97% for speaker-independent recognition. Author
Speech Recognition; Vector Quantization; Words (Language)
20060011105 Royal Signals and Radar Establishment, Malvern, UK
The Discriminative Network: A Mechanism for Focusing Recognition in Whole Word Pattern Matching
Moore, R. K.; Russell, M. J.; Tomlinson, M. J.; IEEE International Conference on Acoustics, Speech, and Signal Processing, (ICASSP '83), Volume 3; [1983], pp. 1041-1044; In English; See also 20060011043; Copyright; Avail.: Other Sources
Whole-word pattern matching using dynamic time-warping (DTW) has achieved considerable success as an algorithm for automatic speech recognition. However, the performance of such an algorithm is ultimately limited by its inability to discriminate between similar sounding words. The problem arises because all differences between speech patterns are treated as being equally important, hence the algorithm is particularly susceptible to confusions caused by irrelevant differences. This paper presents an alternative DTW approach which is able to focus its attention on those parts of a speech pattern which serve to distinguish it from similar patterns.Anetwork-type data structure is derived from reference speech patterns, and the separate paths through the network determine the regions where recognition takes place. Results indicate that discrimination between similar sounding words can be greatly improved. Author
Pattern Recognition; Speech Recognition; Words (Language); Algorithms
Source: NASA
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