Thesis. 1976. M.S.--Massachusetts Institute of Technology. Dept. of Aeronautics and Astronautics. / Microfiche copy available in Archives and Aero. / Bibliograpy: leaf 154. / by Peeter A. Kivestu. / M.S.

Thesis. 1975. M.S.--Massachusetts Institute of Technology. Dept. of Electrical Engineering and Computer Science. / Includes bibliographical references. / M.S.

Rapid technological change and increasing traffic volumes worldwide are adding to the safety challenges for air traffic control. The night shift has traditionally been a period of low workload and work practices have evolved to reflect this. Thus, despite the exemplary safety record, there is a need to consider further systemic defences for maintaining performance and safety on the night shift. One possible strategy is the provision of a scheduled nap at work. In order to investigate the consequences of a scheduled nap on the night shift, 28 operational air traffic controllers were monitored across four roster cycles. Each roster cycle included one of two night shifts. Air traffic controllers were given a nap opportunity on one night shift of each type, and did not nap on the other. Information on the timing, quantity, and quality of sleep during the work week and days off was collected using actigraphy, and supported with logbook data. Sleep during the nap was measured using polysomnography, and the EEG and EOG were further utilised to determine neurophysiological alertness over the latter part of the night shift. Reaction time performance was measured three times across the night shift (beginning, middle, and end) with the psychomotor vigilance test.Actigraphy data indicated that the backward, rapidly-rotating work schedule of air traffic controllers resulted in a progressive loss of sleep across the work week. The reduction in sleep lead to an increasing cumulative sleep debt that was at a maximum prior to the night shift. This sleep debt was not related to reaction time performance at the end of the night shift, but was found to influence neurophysiological alertness.It was determined that the large majority of air traffic controllers were able to sleep during the scheduled 40 minute nap opportunity. However, the latency to sleep onset was long, the sleep short, and of relatively poor quality. Circadian and homeostatic factors increased the likelihood of entry into, and waking from, slow wave sleep (SWS). They were also found to influence reaction time performance and neurophysiological alertness. More variable performance and lowered alertness were seen at the end of the later starting (and finishing) night shift, possibly due to the combined influence of circadian and time-on-task factors. Homeostatic variables had less influence on performance at the end of the night shift, but greater acute sleep loss and higher cumulative sleep debts were related to increased neurophysiological sleepiness.performance and greater neurophysiological alertness in a dose-dependent manner, with even small amounts of stage 1 sleep effecting a performance improvement. Performance improvement was consistent across a range of reaction time measures and consistent improvements were also evident in the neurophysiological data, with the occurrence of SEMs declining, and lower spectral power evident in all frequency bands and single frequencies.These findings clearly demonstrate that a minimal quantity of sleep benefits the performance and alertness of air traffic controllers despite the "noise" of a field setting, thus providing a link between laboratory studies of napping and the actual work environment. The findings also fully support management endorsing a 40 minute napping opportunity for air traffic controllers working the night shift.The short nap sleep had no measurable effect on sleep subsequent to the night shift. However, the amount of sleep obtained in the nap was related to improved reaction time.

The Internet has rapidly evolved from being a scientific experiment to a commercial network connecting millions of hosts that carries traffic generated by a large amount of applications with diverse requirements. Its architecture was however designed to enable efficient point-to-point delivery of bulk data, and can not provide statistical guarantees on the timely delivery of delay sensitive data such as streaming and real-time multimedia. Thus, applications that require low loss probabilities in today's Internet have to use some end-to-end error recovery mechanism. For delay sensitive applications the introduced latency by the applied schemes has to be low as well. Traffic control functions such as delay limited shaping and forward error correction (FEC), and multiple description coding (MDC) have been proposed for variable bitrate video. Their major drawback is, however, that it is difficult to predict their efficiency, as it depends on many factors like the characteristics of the stream itself, the characteristics of the traffic in the network and the network parameters. Consequently, it is difficult to decide which control mechanisms to employ, how to combine them and to choose the right parameters (e.g. block length, code rate) for optimal performance. In this thesis we present results on the efficiency of traffic control functions and MDC for video transmission based on mathematical models and simulations. We investigate the efficiency of delay limited traffic shaping and the trade-offs in the joint use of traffic shaping and forward error correction. We identify the packet size distribution of the traffic in the network as an additional factor that may influence the efficiency of FEC, and present a thorough analysis of its possible effects. We present an analytical comparison of MDC versus media-dependent FEC and media-independent FEC, and based on the results we conclude that MDC is a promising error control solution for multimedia communications with very strict delay bounds in an environment with bursty losses. We combine the analytical results with traces from measurements performed on the Internet to evaluate how efficient these error control schemes are under real loss patterns. We compare the efficiency of MDC and media-dependent FEC in the presence of channel estimation errors; we propose a new rate allocation method, which is robust to mis-estimations of the channel state and which improves error resilience on non-stationary channels. Finally we present an analytical model of the performance of an end-point-based multimedia streaming architecture based on multiple distribution trees and forward error correction, and analyze the behavior of the architecture for a large number of nodes. / QC 20101115

Background: In Sweden, air traffic control is currently performed in a mo-nopoly with the state owned Luftfartsverket as the only sup-plier. A deregulation process has been initiated with the ration-ale of cost reductions, both for airports and airline passengers. Problem and purpose: Economic arguments have been predominant for this potential deregulation and the underlying assumptions are that private al-ternatives would improve efficiency and reduce costs. This has lead the authors to identify what private alternatives would do differently than the current public operator in order to offer these benefits. Method: To fulfill the purpose the authors have used a qualitative ap-proach based on interviews with the current public operator as well as a new potential private alternative. In addition to this, interest organizations and regulative agencies have been con-tacted and secondary data incorporated to provide a holistic perspective. Conclusion: The authors have identified differences in activities between a public and private alternative that would create an advantageous effect on the market. They are: a different management of re-tirement funds, prolonged retirement age, new compensation system, altered recruitment policy, a full utilization of staff and a seizing of non-value adding activities.

Radiotelephony between air traffic controllers and pilots utilises standard phraseology as the medium of communications. Standard phraseology employs specific structure, terminology and pronunciation to ensure effectiveness and accuracy. On occasions when standard phraseology is found insufficient, plain language is used to efficiently relay vital information. By default, English is the designated language of communication between controllers and pilots of international flights. Deviations from the usage of standard phraseology and lack of language proficiency had been identified as one of the causal factors in safety occurrences. Language deficiencies, specifically of the non-native speakers of the English language, had raised much concern but there is limited information in the area. This research attempted to fill a small segment of this knowledge gap. It was focussed on the usage of standard phraseology and English language in an air traffic control environment involving English Second Language users. Audio data was sourced from routine radiotelephony recordings of ‘live’ air traffic control facilities in Malaysia to capture realistic communications between controllers and pilots in the Terminal Approach Radar, Area Radar and Aerodrome Control environments. A detailed cross sectional investigation of the radiotelephony characteristics, deficiencies and errors of transmitted messages revealed the radiotelephony performances of controllers and pilots in the environments. The recurrence of deviations from standards and occurrence of errors implied the likelihood of such deficiencies taking place. Demographic groups’ descriptions complemented the radiotelephony analyses as background information on language related training. The results were comparative to other similar studies and offered new information on English Second Language speakers in the Air Traffic Control environment.

Communication applications have diverse network service requirements. For instance, <em>Voice over IP</em> (VoIP) demands short end-to-end delay, whereas <em>File Transfer Protocol</em> (FTP) benefits more from high throughput than short delay. However, the Internet delivers a uniform best-effort service. As a result, much research has been conducted to enhance the Internet to provide service differentiation. Most of the existing proposals require additional access-control mechanisms, such as admission control and pricing, which are complicated to implement and render these proposals not incrementally deployable. <em>Incentive-compatible Differentiated Scheduling</em> (ICDS) provides incentives for applications to choose a service class according to their burst characteristics without additional access-control mechanisms. <br /><br /> This thesis investigates the behaviour of ICDS with different types of traffic by analysis and extensive simulations. The results show some evidences that ICDS can achieve its design goal. In addition, this thesis revises the initial ICDS algorithm to provide fast convergence for TCP traffic.

<p>Background:</p><p>In Sweden, air traffic control is currently performed in a mo-nopoly with the state owned Luftfartsverket as the only sup-plier. A deregulation process has been initiated with the ration-ale of cost reductions, both for airports and airline passengers.</p><p>Problem and purpose:</p><p>Economic arguments have been predominant for this potential deregulation and the underlying assumptions are that private al-ternatives would improve efficiency and reduce costs. This has lead the authors to identify what private alternatives would do differently than the current public operator in order to offer these benefits.</p><p>Method:</p><p>To fulfill the purpose the authors have used a qualitative ap-proach based on interviews with the current public operator as well as a new potential private alternative. In addition to this, interest organizations and regulative agencies have been con-tacted and secondary data incorporated to provide a holistic perspective.</p><p>Conclusion:</p><p>The authors have identified differences in activities between a public and private alternative that would create an advantageous effect on the market. They are: a different management of re-tirement funds, prolonged retirement age, new compensation system, altered recruitment policy, a full utilization of staff and a seizing of non-value adding activities.</p>

<p>The Internet has rapidly evolved from being a scientific experiment to a commercial network connecting millions of hosts that carries traffic generated by a large amount of applications with diverse requirements. Its architecture was however designed to enable efficient point-to-point delivery of bulk data, and can not provide statistical guarantees on the timely delivery of delay sensitive data such as streaming and real-time multimedia. Thus, applications that require low loss probabilities in today's Internet have to use some end-to-end error recovery mechanism. For delay sensitive applications the introduced latency by the applied schemes has to be low as well. Traffic control functions such as delay limited shaping and forward error correction (FEC), and multiple description coding (MDC) have been proposed for variable bitrate video. Their major drawback is, however, that it is difficult to predict their efficiency, as it depends on many factors like the characteristics of the stream itself, the characteristics of the traffic in the network and the network parameters. Consequently, it is difficult to decide which control mechanisms to employ, how to combine them and to choose the right parameters (e.g. block length, code rate) for optimal performance.</p><p>In this thesis we present results on the efficiency of traffic control functions and MDC for video transmission based on mathematical models and simulations. We investigate the efficiency of delay limited traffic shaping and the trade-offs in the joint use of traffic shaping and forward error correction. We identify the packet size distribution of the traffic in the network as an additional factor that may influence the efficiency of FEC, and present a thorough analysis of its possible effects. We present an analytical comparison of MDC versus media-dependent FEC and media-independent FEC, and based on the results we conclude that MDC is a promising error control solution for multimedia communications with very strict delay bounds in an environment with bursty losses. We combine the analytical results with traces from measurements performed on the Internet to evaluate how efficient these error control schemes are under real loss patterns. We compare the efficiency of MDC and media-dependent FEC in the presence of channel estimation errors; we propose a new rate allocation method, which is robust to mis-estimations of the channel state and which improves error resilience on non-stationary channels. Finally we present an analytical model of the performance of an end-point-based multimedia streaming architecture based on multiple distribution trees and forward error correction, and analyze the behavior of the architecture for a large number of nodes.</p>

Runway incursions (RWYI) are a daily phenomenon in the world and is a threat to safety. The severity of a RWYI can be high and it is a problem that is subject to improvements. The purpose of this report is to present the findings after an investigation of RWYI in general and what is being done to prevent it in Sweden. The main focus is to present the problem from an air traffic controller (ATCO) and pilot perspective. However, we are also presenting all the different stakeholders involved in the problem followed with associated risks and means to prevent a RWYI from happening. We also present technical aids and working methodology used today in air traffic control towers in Sweden and in addition some technology implemented abroad. Some suggested improvements that the stakeholders can take into consideration when developing their work to reduce the risk for a RWYI is also presented. The method used during the investigation has mainly been literature studies, interviews with different stakeholders and study visits to Bromma tower, Arlanda tower and SAAB/Linköping tower. We have found that the pilots and vehicle drivers are the most contributing stakeholders to a RWYI in Sweden. The investigation also shows that ATCOs and pilots share some opinions regarding risks but also improvements. Both ATCOs and pilots agree that weather with bad visibility, as well as darkness, is increasing the risk for an incident or accident to happen. Furthermore, complacency, fatigue and tiredness are also risks that are shared between ATCOs and pilots. We have also found that airports have different means to prevent a RWYI. At Arlanda, the ATC system is well developed with electronic equipment and stop bars at the taxiways, which is not the case for either Bromma or SAAB/Linköping airport. Even pilots in different airlines operate differently when about to enter a runway and there is no standard operating procedure (SOP) developed in all companies. Some of the suggested improvements are to implement stop-bars on every airport and that it should be mandatory to equip vehicles operating on the maneuvering area with maps.