A theoretical framework for soft-information-based synchronization in iterative (Turbo) receivers

This contribution considers turbo synchronization, that is to say, the use of soft data information to estimate parameters like carrier phase, frequency, or timing offsets of a modulated signal within an iterative data demodulator. In turbo synchronization, the receiver exploits the soft decisions computed at each turbo decoding iteration to provide a reliable estimate of some signal parameters. The aim of our paper is to show that such “turbo-estimation” approach can be regarded as a special case of the expectation-maximization (EM) algorithm. This leads to a general theoretical framework for turbo synchronization that allows to derive parameter estimation procedures for carrier phase and frequency offset, as well as for timing offset and signal amplitude. The proposed mathematical framework is illustrated by simulation results reported for the particular case of carrier phase and frequency offsets estimation of a turbo-coded 16-QAM signal

Development of an acoustic communication link for micro underwater vehicles

PhD ThesisIn recent years there has been an increasing trend towards the use of Micro Remotely Operated Vehicles (μROVs), such as the Videoray and Seabotix LBV products, for a range of subsea applications, including environmental monitoring, harbour security, military surveillance and offshore inspection. A major operational limitation is the umbilical cable, which is traditionally used to supply power and communications to the vehicle. This tether has often been found to significantly restrict the agility of the vehicle or in extreme cases, result in entanglement with subsea structures. This thesis addresses the challenges associated with developing a reliable full-duplex wireless communications link aimed at tetherless operation of a μROV. Previous research has demonstrated the ability to support highly compressed video transmissions over several kilometres through shallow water channels with large range-depth ratios. However, the physical constraints of these platforms paired with the system cost requirements pose significant additional challenges. Firstly, the physical size/weight of transducers for the LF (8-16kHz) and MF (16-32kHz) bands would significantly affect the dynamics of the vehicle measuring less than 0.5m long. Therefore, this thesis explores the challenges associated with moving the operating frequency up to around 50kHz centre, along with the opportunities for increased data rate and tracking due to higher bandwidth. The typical operating radius of μROVs is less than 200m, in water < 100m deep, which gives rise to multipath channels characterised by long timespread and relatively sparse arrivals. Hence, the system must be optimised for performance in these conditions. The hardware costs of large multi-element receiver arrays are prohibitive when compared to the cost of the μROV platform. Additionally, the physical size of such arrays complicates deployment from small surface vessels. Although some recent developments in iterative equalisation and decoding structures have enhanced the performance of single element receivers, they are not found to be adequate in such channels. This work explores the optimum cost/performance trade-off in a combination of a micro beamforming array using a Bit Interleaved Coded Modulation with Iterative Decoding (BICM-ID) receiver structure. The highly dynamic nature of μROVs, with rapid acceleration/deceleration and complex thruster/wake effects, are also a significant challenge to reliable continuous communications. The thesis also explores how these effects can best be mitigated via advanced Doppler correction techniques, and adaptive coding and modulation via a simultaneous frequency multiplexed down link. In order to fully explore continuous adaptation of the transmitted signals, a real-time full-duplex communication system was constructed in hardware, utilising low cost components and a highly optimised PC based receiver structure. Rigorous testing, both in laboratory conditions and through extensive field trials, have enabled the author to explore the performance of the communication link on a vehicle carrying out typical operations and presenting a wide range of channel, noise, Doppler and transmission latency conditions. This has led to a comprehensive set of design recommendations for a reliable and cost effective link capable of continuous throughputs of >30 kbits/s

Third International Symposium on Space Mission Operations and Ground Data Systems, part 1

Under the theme of 'Opportunities in Ground Data Systems for High Efficiency Operations of Space Missions,' the SpaceOps '94 symposium included presentations of more than 150 technical papers spanning five topic areas: Mission Management, Operations, Data Management, System Development, and Systems Engineering. The papers focus on improvements in the efficiency, effectiveness, productivity, and quality of data acquisition, ground systems, and mission operations. New technology, techniques, methods, and human systems are discussed. Accomplishments are also reported in the application of information systems to improve data retrieval, reporting, and archiving; the management of human factors; the use of telescience and teleoperations; and the design and implementation of logistics support for mission operations

Earth Resources: A continuing bibliography with indexes, issue 1

This bibliography lists 616 reports, articles, and other documents introduced into the NASA scientific and technical information system between January 1974 and March 1974. Emphasis is placed on the use of remote sensing and geophysical instrumentation in spacecraft and aircraft to survey and inventory, natural resources and urban areas. Subject matter is grouped according to agriculture and forestry, environmental changes and cultural resources, geodesy and cartography, geology and mineral resources, oceanography and marine resources, hydrology and water management, data processing and distribution systems, instrumentation and sensors, and economic analysis

Earth Resources: A continuing bibliography with indexes (Issue 37)

This bibliography lists 512 reports, articles, and other documents introduced into the NASA scientific and technical information system between January 1 and March 31, 1983. Emphasis is placed on the use of remote sensing and geophysical instrumentation in spacecraft and aircraft to survey and inventory natural resources and urban areas. Subject matter is grouped according to agriculture and forestry, environmental changes and cultural resources, geodesy and cartography, geology and mineral resources, hydrology and water management, data processing and distribution systems, instrumentation and sensors, and economic analysis

Life Sciences Program Tasks and Bibliography for FY 1996

This document includes information on all peer reviewed projects funded by the Office of Life and Microgravity Sciences and Applications, Life Sciences Division during fiscal year 1996. This document will be published annually and made available to scientists in the space life sciences field both as a hard copy and as an interactive Internet web page

Design Development Test and Evaluation (DDT and E) Considerations for Safe and Reliable Human Rated Spacecraft Systems

A team directed by the NASA Engineering and Safety Center (NESC) collected methodologies for how best to develop safe and reliable human rated systems and how to identify the drivers that provide the basis for assessing safety and reliability. The team also identified techniques, methodologies, and best practices to assure that NASA can develop safe and reliable human rated systems. The results are drawn from a wide variety of resources, from experts involved with the space program since its inception to the best-practices espoused in contemporary engineering doctrine. This report focuses on safety and reliability considerations and does not duplicate or update any existing references. Neither does it intend to replace existing standards and policy

Life Sciences Program Tasks and Bibliography for FY 1997

This document includes information on all peer reviewed projects funded by the Office of Life and Microgravity Sciences and Applications, Life Sciences Division during fiscal year 1997. This document will be published annually and made available to scientists in the space life sciences field both as a hard copy and as an interactive internet web page

NASA/ASEE Summer Faculty Fellowship Program. 1994 research reports

This document is a collection of technical reports on research conducted by the participants in the 1994 NASA/ASEE Summer Faculty Fellowship Program at Kennedy Space Center (KSC). This was the tenth year that a NASA/ASEE program has been conducted at KSC. The 1994 program was administered by the University of Central Florida in cooperation with KSC. The program was operated under the auspices of the American Society for Engineering Education (ASEE) with sponsorship and funding from the Office of Educational Affairs, NASA Headquarters, Washington, D.C. The KSC Program was one of nine such Aeronautics and Space Research Programs funded by NASA Headquarters in 1994. The NASA/ASEE program is intended to be a two-year program to allow in-depth research by the University faculty member. The editors of this document were responsible for selecting appropriately qualified faculty to address some of the many problems of current interest to NASA/KSC

Earth Resources: A continuing bibliography with indexes, issue 13

This bibliography lists 524 reports, articles, and other documents introduced into the NASA scientific and technical information system between January 1977 and March 1977. Emphasis is placed on the use of remote sensing and geophysical instrumentation in spacecraft and aircraft to survey and inventory natural resources and urban areas. Subject matter is grouped according to agriculture and forestry, environmental changes and cultural resources, geodesy and cartography, geology and mineral resources, hydrology and water management, data processing and distribution systems, instrumentation and sensors, and economic analysis