Digital scrambling for shuttle communication links: Do drawbacks outweigh advantages?

Digital data scrambling has been considered for communication systems using NRZ (non-return to zero) symbol formats. The purpose is to increase the number of transitions in the data to improve the performance of the symbol synchronizer. This is accomplished without expanding the bandwidth but at the expense of increasing the data bit error rate (BER). Models for the scramblers/descramblers of practical interest are presented together with the appropriate link model. The effects of scrambling on the performance of coded and uncoded links are studied. The results are illustrated by application to the Tracking and Data Relay Satellite System links. Conclusions regarding the usefulness of scrambling are also given

Field measurements in MSAT-X

Results from the most recent MSAT-X field experiments, the Tower-3 Experiment and the JPL/FAA/INMARSAT MARECS-B2 Satellite Experiment, are presented. Results that distinguish the propagation environment of the tower set-up are given and explained. The configuration and flight variables of the aeronautical experiment which used an FAA aircraft and an INMARSAT satellite are described. Results that highlight the disturbances on the aeronautical satellite channel are presented. The roles of satellite-induced signal variations and of multipatch are identified and their impact on the link is discussed

Multiple access capacity trade-offs for a Ka-band personal access satellite system

System capability is critical to the economic viability of a personal satellite communication system. Ka band has significant potential to support a high capacity multiple access system because of the availability of bandwidth. System design tradeoffs are performed and multiple access schemes are compared with the design goal of achieving the highest capacity and efficiency. Conclusions regarding the efficiency of the different schemes and the achievable capacities are given

MSAT-X: A technical introduction and status report

A technical introduction and status report for the Mobile Satellite Experiment (MSAT-X) program is presented. The concepts of a Mobile Satellite System (MSS) and its unique challenges are introduced. MSAT-X's role and objectives are delineated with focus on its achievements. An outline of MSS design philosophy is followed by a presentation and analysis of the MSAT-X results, which are cast in a broader context of an MSS. The current phase of MSAT-X has focused notably on the ground segment of MSS. The accomplishments in the four critical technology areas of vehicle antennas, modem and mobile terminal design, speech coding, and networking are presented. A concise evolutionary trace is incorporated in each area to elucidate the rationale leading to the current design choices. The findings in the area of propagation channel modeling are also summarized and their impact on system design discussed. To facilitate the assessment of the MSAT-X results, technology and subsystem recommendations are also included and integrated with a quantitative first-generation MSS design

Experiments for Ka-band mobile applications: The ACTS mobile terminal

To explore the potential of Ka-band to support mobile satellite services, the Jet Propulsion Laboratory (JPL) has initiated the design and development of a Ka-band land-mobile terminal to be used with the Advanced Communications Technology Satellite (ACTS). The planned experimental setup with ACTS is described. Brief functional descriptions of the mobile and fixed terminals are provided. The inputs required from the propagation community to support the design activities and the planned experiments are also discussed

Land-mobile field experiments in Australia

The Mobile Satellite Experiment/Australia Mobile Satellite Experiment (MSAT-X/AUSSAT) experiment offered the first true land-mobile satellite configuration to evaluate the MSAT-X technologies and equipment. Both quantitative data tests and qualitative voice link demonstrations were successfully conducted. From the collected data, system performance in typical land-mobile conditions was extracted. A set of propagation characteristics corresponding to the wide range of environments encountered was also obtained. A brief description is given of the MSAT-X/AUSSAT experiment and a summary of its results analyzed to date

NASA's mobile satellite development program

A Mobile Satellite System (MSS) will provide data and voice communications over a vast geographical area to a large population of mobile users. A technical overview is given of the extensive research and development studies and development performed under NASA's mobile satellite program (MSAT-X) in support of the introduction of a U.S. MSS. The critical technologies necessary to enable such a system are emphasized: vehicle antennas, modulation and coding, speech coders, networking and propagation characterization. Also proposed is a first, and future generation MSS architecture based upon realized ground segment equipment and advanced space segment studies

Performance of DA/FDMA architecture proposed for MSS

The system architecture proposed for the Mobile Satellite Service (MSS) by the National Aeronautics and Space Administration (NASA)/JPL is presented. The demand assigned Frequency Division Multiple Access (FDMA) scheme is described, and results for the associated network access protocol developed by JPL are presented. Both the total number of users that the system can support and the system spectral efficiency are given for a variety of traffic conditions, including those postulated for the Mobile Satellite System Architectures and Multiple Access Techniques Workshop. The results are given for both first- and second-generation one- and two-satellite systems

Rethinking Cairo’s elevated urban highways: Scoping impacts and potentials

Urban policies of the last 50 years in Egypt focused on extending and developing road networks to the extent that Egyptians used to describe it as the era of roads and bridges. From such policy came an introduction of a big number of elevated urban highways that cuts through Cairo’s urban fabric to ensure the flow of the city. Elevated urban highways are often perceived as a tool for mobility, but it introduces much more complicated impacts on the urban fabric and the communities that they pass through. While the international literature has long pointed out such impacts there is a gap in the local Egyptian literature that discusses the notion of elevated urban highways and its various impacts. It is argued that highways introduce a set of social, environmental and economic impacts, but most importantly some of those impacts are actual potentials that can be utilized to serve the needs of the community. This research aims at scoping the impacts and potentials of Cairo’s elevated urban highways. Understanding the impacts and potentials will provide better information for decision-making leading to better urban management of affected areas. This is achieved through studying three independent cases of elevated urban highways in Cairo: Al Azhar bridge, 15th of May bridge, and Saft El-Laban corridor. Through site visits and in-depth interviews with local stakeholders, the research provides an understanding of how the presence of elevated structure impacted each community, analyzes its spatial elements and scopes its potential uses. Based on the observations and investigations, many findings were revealed, like how communities perceive elevated highways differently, and how a negative impact in one case can actually be perceived as a positive impact in another case. Empirical findings presented interesting observations that sometimes contradict with the international literature and theories. The field work lead to realizing how new structures can lead to the formation of different power dynamics related to claiming ownership in each case. Observations and research reflected how the laws and regulations in regards to spaces under the elevated highways are vague, leading to misunderstandings and conflicts in regards to ownership and uses. Most importantly discussions reveal that Cairo’s elevated urban highway holds much more spatial potentials than the common belief of being just a tool for mobility

LEGAL CONSDERATION ON TEXT MESSAGES SENT VIA SOCIAL MEDIA

Digital text messages are of great importance considering the technological progress ofthe majority of dealing with individuals, companies, and banks, which prompted them to usemessages. These text messages have imposed themselves as electronic documents in manyareas of our daily electronic dealings. These text messages became a means of expressing willin an electronic form.This paper deals with some legal issues related to text messages sent through socialmedia, including the controls for presenting them as evidence before the courts and theirpower in proof, how to find a balance between the plaintiff’s right to proof and the sender’sright to privacy. This paper also deals with the legal consequences of disclosing it to a thirdparty without the sender’s permission