NASA Scientific and Technical Aerospace Reports

20040120946 Cleveland State Univ., Cleveland, OH, USA
Robust Timing Synchronization in Aeronautical Mobile Communication Systems
Xiong, Fu-Qin; Pinchak, Stanley; September 16, 2004; 56 pp.; In English
Contract(s)/Grant(s): NAG3-2619; No Copyright; Avail: CASI; C01, CD-ROM; A04, Hardcopy
This work details a study of robust synchronization schemes suitable for satellite to mobile aeronautical applications. A
new scheme, the Modified Sliding Window Synchronizer (MSWS), is devised and compared with existing schemes, including
the traditional Early-Late Gate Synchronizer (ELGS), the Gardner Zero-Crossing Detector (GZCD), and the Sliding Window
Synchronizer (SWS). Performance of the synchronization schemes is evaluated by a set of metrics that indicate performance
in digital communications systems. The metrics are convergence time, mean square phase error (or root mean-square phase
error), lowest SNR for locking, initial frequency offset performance, midstream frequency offset performance, and system
complexity. The performance of the synchronizers is evaluated by means of Matlab simulation models. A simulation platform
is devised to model the satellite to mobile aeronautical channel, consisting of a Quadrature Phase Shift Keying modulator, an
additive white Gaussian noise channel, and a demodulator front end. Simulation results show that the MSWS provides the
most robust performance at the cost of system complexity. The GZCD provides a good tradeoff between robustness and system
complexity for communication systems that require high symbol rates or low overall system costs. The ELGS has a high
system complexity despite its average performance. Overall, the SWS, originally designed for multi-carrier systems, performs
very poorly in single-carrier communications systems. Table 5.1 in Section 5 provides a ranking of each of the synchronization
schemes in terms of the metrics set forth in Section 4.1. Details of comparison are given in Section 5. Based on the results
presented in Table 5, it is safe to say that the most robust synchronization scheme examined in this work is the
high-sample-rate Modified Sliding Window Synchronizer. A close second is its low-sample-rate cousin. The tradeoff between
complexity and lowest mean-square phase error determines the rankings of the Gardner Zero-Crossing Detector and both
versions of the Early-Late Gate Synchronizer. The least robust models are the high and low-sample-rate Sliding Window
Synchronizers. Consequently, the recommended replacement synchronizer for NASA’s Advanced Air Transportation
Technologies mobile aeronautical communications system is the high-sample-rate Modified Sliding Window Synchronizer. By
incorporating this synchronizer into their system, NASA can be assured that their system will be operational in extremely
adverse conditions. The quick convergence time of the MSWS should allow the use of high-level protocols. However, if
NASA feels that reduced system complexity is the most important aspect of their replacement synchronizer, the Gardner
Zero-Crossing Detector would be the best choice.
Author
Time Measurement; Mobile Communication Systems; Aircraft Communication; Synchronizers; Phase Detectors;
Telecommunication
20040121012 Defence Science and Technology Organisation, Edinburgh, Australia
Range Extension Techniques Available to the Army Tactical Communications System
Blair, W. D.; Dickinson, R. E.; August 2004; 31 pp.; In English; Original contains color illustrations
Report No.(s): DSTO-TN-0573; DODA-AR-013-157; Copyright; Avail: Other Sources
The adoption of the Network Centric Warfare (NCW) philosophy for Land Force operations means that connectivity
through networked communications, typically wireless for mobile operations, is of critical importance. The communications
range of the radio equipment becomes a constraint in operational concepts and the degree of implementation of NCW. To
overcome this range limitation a series of communications techniques covered by the broad title of range extension techniques
enable nodes to communicate within the battlespace through intermediary devices or phenomena. This paper seeks to identify
and discuss the broad spectrum of tactical communications network range extension approaches and technologies available.
As a result Army will be better informed in the development of communications architectures for deployed Land Force
communications.
Author
Communication Networks; Radio Equipment; Warfare
20040121071 NASA Langley Research Center, Hampton, VA, USA
Signal Processing Schemes for Doppler Global Velocimetry
Meyers, James F.; Lee, Joseph W.; Cavone, Angelo A.; [1991]; 20 pp.; In English; 14th International Congress on
Instrumentation in Aerospace Simulation Facilities, 27-31 Oct. 1991, Rockville, MD, USA; Original contains color
illustrations; Copyright; Avail: CASI; A03, Hardcopy
Two schemes for processing signals obtained from the Doppler global velocimeter are described. The analog approach
is a simple, real time method for obtaining an RS-170 video signal containing the normalized intensity image. Pseudo colors
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