Robert J. Kerczewski

Technology Assessment Results of the Eurocontrol/FAA Future Communications Study

The US Federal Aviation Administration (FAA) and Eurocontrol jointly initiated the future communications study (FCS) to develop a common approach for a globally harmonized air traffic management (ATM) communications system. The FCS includes operational concepts and communications requirements development, analysis of business and institutional elements, and identification and assessment of technology alternatives. The FCS technology assessment determined the best set of available technologies for aviation safety communications for ATM given key constraints such as cost, transition feasibility, technical requirements, and spectrum availability. From 2004 to 2007, the assessment progressed in three phases, yielding technical results and recommendations for development and phased implementation of a future aviation communications infrastructure.

Interference analysis for an Aeronautical Mobile Airport Communications System

The next generation of aeronautical communications for airport surface applications has been identified through a NASA research program and an international collaborative future communications study. The result, endorsed by both the United States and European regulatory agencies is called AeroMACS (Aeronautical Mobile Airport Communications System) and is based upon the IEEE 802.16e mobile wireless standard. Coordinated efforts to develop appropriate aviation standards for the AeroMACS system are now underway within RTCA (United States) and Eurocae (Europe). AeroMACS will be implemented in a recently allocated frequency band, 5091–5150 MHz. As this band is also occupied by fixed satellite service uplinks, AeroMACS must be designed to avoid interference with this incumbent service. The aspects of AeroMACS operation that present potential interference to the fixed satellite service are under analysis in order to enable the definition of standards that assure that such interference will be avoided. The NASA Glenn Research Center has been involved in this analysis, and the first results of modeling and simulation efforts directed at this analysis are the subject of this paper.12

Clinical evaluation of wavelet-compressed digitized screen-film mammography

RATIONALE AND OBJECTIVES The authors compared diagnostic accuracy and callback rates with conventional screen-film mammograms and wavelet-compressed digitized images. MATERIALS AND METHODS Sixty sets of mammograms (four views per case) were digitized at a spatial resolution of 100 microm. The images were wavelet compressed to a mean compression ratio of 8:1 and reviewed by three mammographers. Five regions were evaluated in each breast. Suspicion of malignancy was graded on a scale of 0% to 100%, and receiver operating characteristic (ROC) analysis was performed. Callback rates were calculated by using the American College of Radiologys Breast Imaging Reporting and Data System lexicon scale. RESULTS The mean diagnostic accuracy with compressed and conventional images was 0.832 and 0.860, respectively. The upper 95% confidence bound for the difference in ROC areas was 0.061. The mean false-positive rate at a fixed sensitivity of 0.90 was 0.041 for compressed images and 0.059 for conventional images. The mean callback rates for normal, benign, and malignant regions were 0.023, 0.305, and 0.677, respectively, for compressed images and 0.036, 0.447, and 0.750, respectively, for conventional images. The upper 95% confidence bound for the (absolute) differences in callback rates was 0.012 for normal regions, 0.163 for benign regions, and 0.138 for malignant regions. CONCLUSION Diagnostic accuracies were equivalent for both compressed and conventional images. The mean false-positive rate at fixed sensitivity was much better with the compressed images. However, the callback rates for malignant lesions were lower when the compressed images were used.

A Hybrid Satellite-Terrestrial Approach to Aeronautical Communication Networks

Rapid growth in air travel has been projected to continue for the foreseeable future. To maintain a safe and efficient national and global aviation system, significant advances in communications systems supporting aviation are required. Satellites will increasingly play a critical role in the aeronautical communications network. At the same time, current ground-based communications links, primarily very high frequency (VHF), will continue to be employed due to cost advantages and legacy issues. Hence a hybrid satellite-terrestrial network, or group of networks, will emerge. The increased complexity of future aeronautical communications networks dictates that system-level modeling be employed to obtain an optimal system fulfilling a majority of user needs. The NASA Glenn Research Center is investigating the current and potential future state of aeronautical communications, and is developing a simulation and modeling program to research future communications architectures for national and global aeronautical needs. This paper describes the primary requirements, the current infrastructure, and emerging trends of aeronautical communications, including a growing role for satellite communications. The need for a hybrid communications system architecture approach including both satellite and ground-based communications links is explained. Future aeronautical communication network topologies and key issues in simulation and modeling of future aeronautical communications systems are described.

Automated Measurement of the Bit-Error Rate as a Function of Signal-to-Noise Ratio for Microwave Communications Systems

The performance of microwave systems and components for digital data transmission can be characterized by a plot of the bit-error rate as a function of the signal-to-noise ratio (or Eb/No). Methods for the efficient automated measurement of bit-error rates and signal-to-noise ratios, developed at NASA Lewis Research Center, are described. Noise measurement considerations and time requirements for measurement accuracy, as well as computer control and data processing methods, are discussed.

Secure Wireless Multicast for Delay-Sensitive Data via Network Coding

Wireless multicast for delay-sensitive data is challenging because of the heterogeneity effect where each receiver may experience different packet losses. Fortunately, network coding, a new advanced routing protocol, offers significant advantages over the traditional Automatic Repeat reQuest (ARQ) protocols in that it mitigates the need for retransmission and has the potential to approach the min-cut capacity. Network-coded multicast would be, however, vulnerable to false packet injection attacks, in which the adversary injects bogus packets to prevent receivers from correctly decoding the original data. Without a right defense in place, even a single bogus packet can completely change the decoding outcome. Existing solutions either incur high computation cost or cannot withstand high packet loss. In this paper, we propose a novel scheme to defend against false packet injection attacks on network-coded multicast for delay-sensitive data. Specifically, we propose an efficient authentication mechanism based on null space properties of coded packets, aiming to enable receivers to detect any bogus packets with high probability. We further design an adaptive scheduling algorithm based on the Markov Decision Processes (MDP) to maximize the number of authenticated packets received within a given time constraint. Both analytical and simulation results have been provided to demonstrate the efficacy and efficiency of our proposed scheme.

Communications, navigation and surveillance for improved oceanic air traffic operations

Air traffic management around the world is implemented using ground-based communications, navigation and surveillance systems. For obvious reasons, such systems are not available in oceanic airspace, nor are they available in remote land regions. In general, aircraft operating in these regions maintain safe separations by relying on procedural separation methods. Such methods require separations of 50 nautical miles (nm) or more to be maintained. As air traffic across the oceans increases, the procedural separations are leading to increased inefficiencies in oceanic and remote operations. These inefficiencies result from schedule delays, inability to fly preferred routes (for best wind advantages), and the inability to use the most efficient altitudes, leading to higher fuel burn rates. New methods of operating in oceanic and remote airspace are needed, and indeed they are being developed and implemented, but they depend on an improved communications, navigation and surveillance (CNS) systems, which of necessity must be primarily supplied by satellite-based systems. This paper summarizes current and future air traffic management operations, the CNS requirements for future operations and satellite-based systems which have the potential for fulfilling these requirements, and what is needed to bring such system to implementation

Comparison of VDL modes in the aeronautical telecommunications network

VHF digital link (VDL) has been identified as a method of communication between aircraft and ground stations in the aeronautical telecommunications network (ATN). Three different modes of VDL have been suggested for implementation. Simulations were conducted to compare the data transfer capabilities of VDL modes 2, 3, and 4. These simulations focus on up to 50 aircraft communicating with a single VDL ground station. The data traffic is generated by the standard file transfer protocol (FTP) and hyper text transfer protocol (HTTP) applications in the aircraft. Comparisons of the modes are based on the number of files and pages transferred and the response time.

UAS CNPC satellite link performance — Sharing spectrum with terrestrial systems

In order to provide for the safe integration of unmanned aircraft systems into the National Airspace System, the control and non-payload communications (CNPC) link connecting the ground-based pilot with the unmanned aircraft must be highly reliable. A specific requirement is that it must operate using aviation safety radiofrequency spectrum. The 2012 World Radiocommunication Conference (WRC-12) provided a potentially suitable allocation for radio line-of-sight (LOS), terrestrial based CNPC link at 5030-5091 MHz. For a beyond radio line-of-sight (BLOS), satellite-based CNPC link, aviation safety spectrum allocations are currently inadequate. Therefore, the 2015 WRC will consider the use of Fixed Satellite Service (FSS) bands to provide BLOS CNPC under Agenda Item 1.5. This agenda item requires studies to be conducted to allow for the consideration of how unmanned aircraft can employ FSS for BLOS CNPC while maintaining existing systems. Since there are terrestrial Fixed Service systems also using the same frequency bands under consideration in Agenda Item 1.5 one of the studies required considered spectrum sharing between earth stations on-board unmanned aircraft and Fixed Service station receivers. Studies carried out by NASA have concluded that such sharing is possible under parameters previously established by the International Telecommunications Union. As the preparation for WRC-15 has progressed, additional study parameters Agenda Item 1.5 have been proposed, and some studies using these parameters have been added. This paper examines the study results for the original parameters as well as results considering some of the more recently proposed parameters to provide insight into the complicated process of resolving WRC-15 Agenda Item 1.5 and achieving a solution for BLOS CNPC for unmanned aircraft.

On selection of proper IEEE 802.16-based standard for Aeronautical Mobile Airport surface Communications (AeroMACS) application

A new aviation-specific transmission technology based on the WiMAX (Worldwide Interoperability for Microwave Access) IEEE 802.16e-based standard; over a newly available C-band allocation (5091–5150 MHz), has been recently recommended for the airport surface wireless communications network now known as Aeronautical Mobile Airport Communications System (AeroMACS). The proposed standards will be used to support fixed and mobile ground to ground applications and services. It has been established that no technical obstacle exists that would prevent the application of WiMAX networks to AeroMACS. In this article WiMAX networks and some of their salient features are briefly reviewed. The challenges of broadband radio communications through airport surface channels are discussed. A major concern about deployment of AeroMACS over the 5091–5150 MHz band is interference to co-allocated applications such as the Mobile Satellite Service (MSS) feeder link. This limits the power levels that are allowed for AeroMACS networks. We propose an investigation into the feasibility of the application of IEEE 802.16j Amendment (relay-based multi-hop network) to AeroMACS. The potential benefits of multihop relay configuration for AeroMACS networks are identified. Perhaps the most relevant benefit of the multihop relay configuration to AeroMACS is the flexible and cost effective radio range extension that it provides for airport areas shadowed by large constructions and natural obstacles without raising the required network power levels.