Data Communication Link Research Articles

DGPS-based aircraft flight guidance/test system

The utilization of the GPS system for Aircraft Flight Guidance/Test (AFGT) is a research project in China. The paper describes the concepts and the technical realization of such a system, including three components: ground subsystem, on-board subsystem and data communication link using TDMA technique. The purpose of the proposed AFGT system is to calibrate and verify performance of an on-board radar. Therefore, it must meet the requirements of evaluation of radar performances in several areas: accuracy, coverage range, and others. The AFGT System's displays are separately: a Moving Colored Digital Map on which flight trajectories, waypoints, and heights of aircrafts are clearly marked; and a Polar Coordinate Figure on which the bearings, headings, and distances of aircrafts relative to the origin of the ground control center are shown. The AFGT may monitor and guide several aircrafts flying in the pointed airspace. It support airport surface surveillance and air traffic control at the terminal area. A real-time software package RTTEST, which includes tracking display software and on-flight test software for radar evaluation, has conducted simulation with satisfactory position accuracy.

PARALLELIZATION OF THE SIMULATION TOOL WING‐SPACE FOR THE ANALYSIS AND DESIGN OF TRANSMISSION SYSTEMS

The growing complexity and performance of modern digital communication links call for enhanced efficiency of the computer simulation software packages that are routinely used as particularly effective and flexible analysis and design tools. The relevant typical computing environment in the telecommunication design laboratories is a cluster of heterogeneous workstations connected by a local area network (LAN). In this paper, we describe how a pre-existing tool for the simulation of transmission systems is parallelized in such a way that the distributed computing power is exploited at its best. The experiment was carried out with the aid of TRACS, a programming environment for networked, heterogeneous machines and led to the development of a ‘parallel execution’ feature of simulation runs. Such a feature is activated by the end-user, with no further modifications to the description of the transmission system under consideration. A few results are reported on the performance boost due to parallelization with respect to the standard serial execution.

Smart antenna arrays for CDMA systems

There are a diverse range of products and services currently on the market, but cellular or personal communications services (PCS) radio networks probably have the highest public profile. These services provide highly mobile, widely accessible two-way voice and data communications links. In general, the most complex and expensive part of the radio path for these systems is the base station. As a result, manufacturers have been designing networks that have high efficiency in terms of the bandwidth occupied and the number of users per base station. Base station antenna arrays are a promising method for providing large capacity increases in cellular mobile radio systems. This article considers channel-modeling issues, receiver structures, and algorithms, and looks at the potential capacity gains that can be achieved. It considers antenna arrays for the mobile-to-base-station or reverse link of a CDMA cellular system. It begins with an introduction to CDMA communications systems and also addresses the general topic of antenna array receivers.

Analysis of level crossing scintillation statisticsfor 0.83 µmpropagation on 4.1 km path across central London

The level crossing statistics for the measured amplitude scintillations of a 0.83 µm laser beam propagating across a 4.1 km path in central London are analysed in terms of the normalised irradiance of the received signal in dB. The level crossing probability density function, the number of times a level was crossed and the mean time duration of events are calculated for different turbulent conditions. The results are similar to ITU predictions for microwave frequencies. This study can help in the evaluation of the performance of a digital free space optical communication link.

A Laboratory Glass-Cockpit Flight Simulator for Automation and Communications Research

A laboratory glass-cockpit flight simulator supporting research on advanced commercial flight deck and Air Traffic Control (ATC) automation and communication interfaces has been developed at the Aviation Operations Branch at the NASA Ames Research Center. This system provides independent and integrated flight and ATC simulator stations, party line voice and datalink communications, along with video and audio monitoring and recording capabilities. Over the last several years, it has been used to support the investigation of flight human factors research issues involving: communication modality; message content and length; graphical versus textual presentation of information, and human accountability for automation. This paper updates the status of this simulator, describing new functionality in the areas of flight management system, EICAS display, and electronic checklist integration. It also provides an overview of several experiments performed using this simulator, including their application areas and results. Finally future enhancements to its ATC (integration of CTAS software) and flight deck (full crew operations) functionality are described.

Intelligent sensors: structure and system

Outlines the current research work on intelligent sensors and intelligent transducers which will be required in complex systems. Discusses the elements of an intelligent sensor and concludes that these require analogue filtering, data conversion and compensation, and a digital communication link to a common signal bus. Explains what is meant by a systems approach to intelligent sensors with layered information processing. Concludes that unless a deeper understanding of the basics of sensor systems is acquired new intelligent sensor design will be very difficult.

Convergence analysis of decision-directed adaptive echo cancellers for baseband data transmission

This article deals with the analysis of a decision-directed echo canceller working in a baseband data communication link. This guided scheme, as known in self-adaptive equalization systems, introduces stable local minima in the error surface thus dissuading any gradient search procedure. Regardless of this drawback, the article studies two stochastic gradient algorithms in a multimodal error surface context. They are based in the minimization of absolute and quadratic norms (L/sub 1/ and L/sub 2/) of an improved error reference signal. The analysis assumes bipolar data contaminated with a residual intersymbol interference plus background white noise. The article introduces a new perspective on the analysis of conditions that guarantees convergence towards any desired steady state even with the existence of local minima. It uses a dynamic bounding function for the adaption step dependent on the residual echo variance that allows tracking of the global convergence-condition in the working range. Furthermore, the analysis makes it also possible to predict whether the algorithm will converge or whether it could be trapped in any stable stationary point. It also shows the risky dependence of the convergence towards an undesired steady state on some internal and working variables, such as initial filter settings, interference level, etc.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Folding and double mapping of the matrix multiplication algorithm

The data dependence method for algorithm implementation on processor arrays is based on linear transformations of the data dependencies and the index set of the algorithm and results in a regular data flow, but the method is still unable to optimize the array size or the implementation. The presented implementations are developed using properties of some special linear transformations, i.e., symmetry interlocking translation and processors working in swapped active and inactive time moments. The 2D hex matrix multiplication systolic algorithm has all these properties. The array implementation from this example is folded and a triangular solution is obtained using a regular translated folding transformation and double mapping technique. A valid folding transformation is chosen to obtain no increase either in the data communication links or in processor operation.

Error probability estimator structures based on analysis of the receiver decision variable

The paper presents schemes for rapid on-line error probability estimation of digital communications links. Several estimator structures are proposed based on the assumption of sample independence, including weighted least squares (WLS) and maximum likelihood (ML) forms. The continuous-form ML estimator is shown to lie on the Rao-Cramer bound, making it a most efficient estimator of probability of error. The design, performance, implementation complexity and behavior of these estimators is described for AWGN. >

A LOW COST SIMULTANEOUS VOICE AND DATA COMMUNICATIONS LINK FOR LOCAL AREA NETWORKS ON A 4 WIRE SYSTEM

This paper provides details concerning the design of an integrated voice and data communications link for a Local Area Network that must utilize residential type 2 pair telephone wiring as its transmission medium. The communications link can provide a worst case total data rate of 80 K bps (full duplex), 80 K analog samples of audio signals total (full duplex), as well as power and ground for remote terminals. In a system design that utilizes the communications link discussed here, the above total values of data and audio information flow can be divided by the number of terminals anticipated in the system in any ratio desired. The intent of the design of the communications link is to provide what is believed to be the most cost effective means of implementing an intelligent network of consumer based products in a residential or small business type of environment. In this document, the original technical problem is discussed along with details concerning the development of the solution presented here. The system design example that is presented is only provided as an aid to understanding how the communications link can be applied and is not the focus of the central concept. In that example, the system is comprised of 8 remote terminals and one central control terminal — all of which are voice and data devices. Therefore, the available continuous data rate per terminal is 10 K bps with 5 Khz full duplex audio.

Blind equalization using decision feedback prediction and tricepstrum principles

Abstract Combined blind decision feedback equalization and blind carrier phase tracking for digital communication links with nonminimum phase channels is examined. An algorithm that employs decision feedback prediction to equalize the amplitude information of the channel and adaptive fourth-order cumulant methods to equalize the phase information of the channel is proposed. It is shown that the proposed method opens the eye pattern of 64-QAM and 256-QAM signal constellations faster than existing decision feedback equalization algorithms that employ explicitly fourth-order cumulants and exhibit similar computational complexity.

Detection for binary transmission in a mixture of Gaussian noise and impulsive noise modeled as an alpha-stable process

The impact of nonGaussian impulsive noise combined with Gaussian noise on the performance of the binary transmission is analyzed. The impulsive noise is modeled as an alpha-stable process. The probability of error for optimum, linear and nonlinear receivers is derived. The proposed nonlinear detectors show substantial improvements in performance compared to linear ones. The obtained results will be useful in performance evaluation of digital communication links subject to Gaussian and impulsive noises.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Electronically enhanced low voltage motor protection and control

The major advances in motor protection and control today and in the future will be based on electronic enhancements. Electromechanical-based systems are limited to simple protection modes and typically have a one-to-one relationship between input (e.g., current) and reaction (e.g., deflection). Microcomputer chips, with their ever increasing processing speeds and program instruction sets, have given designers the tools and the freedom to package multiple protection modes as well as customized protection. This computing power allows designers to develop modern multi-function motor protection systems that include control functions previously achieved only through complex hard-wired control circuits. The designer can now re-examine motor protection requirements and provide unique solutions. It is also possible to replace some high level programmable controller solutions with a dedicated controller built into a more user friendly, individual motor protection package. This same package may provide data communication links for factory-wide management systems. Such a motor protection and control system addresses motor application needs that, in the past, were often beyond the range of practicality.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A framework for the specification of SCADA data links

SCADA system overall performance is dependent on satisfactory performance of the integral data communication links. Therefore a specification of the required data link performance is required as part of the system specification. But what should the data link specification include? The specification of data rate alone is shown to be insufficient to guarantee performance under all operating conditions. To determine the additional attributes that must be specified, the sensitivity of SCADA performance to the set of data link attributes is analysed by computer simulation. From the results of the simulation a subset of significant data link attributes is identified. This is the desired data link specification framework.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Resource Management in the Highly Automated Airspace System

The introduction of highly sophisticated, glass cockpit aircraft has profoundly affected the flightdeck environment, and has changed the nature of crew resource management (CRM). CRM and decision making in advanced aircraft are qualitatively different from the same processes in older fleets. Automation also alters the nature of interaction among crewmembers, and between crewmembers and Air Traffic Control (ATC) These differences would seem to necessitate special training and procedures for CRM in glass cockpits. Moreover, training for managing automation cannot be merely an added module in current CRM programs. The effects of automation pervade throughout all aspects of resource management. Coincidentally, advances in the air traffic control system are altering the modern airspace environment. In the not-too-distant future, it will be possible for ATC computers to generate or amend clearances, which the Air Traffic Manager will send to the aircraft via datalink. The aircraft FMS (flight management system) will determine whether or not the clearance may be accepted, and its effects on fuel consumption, arrival time, etc. The role of the pilot will be to accept or reject the suggested clearance. The effects of automation on operator and team processes in both of these domains, as well as on the interaction between the domains, has only begun to be defined. Some of the issues already raised in the flightdeck realm, such as diffusion of responsibility among crewmembers, the breakdown of traditional roles and responsibilities as a result of familiarity with automation, or the possibility that crewmembers will “communicate” more with the automation than with each other, may only be exacerbated by increased automation in the air-ground communication link. The goal of this panel is to present an overview of some of the issues and questions to be resolved if resource management is to be a vital construct in the highly automated airspace system. To open discussion, the first panel member will present an overview of the general issues involved in the confluence of CRM and automation. Following, an industry representative will discuss one airline's specialized program to introduce crewmembers to the glass cockpit, and guide them in the appropriate use of automation. The measurement of CRM components specifically related to crew interaction with automation will be the focus of the third panelist. The analysis of CRM issues associated with equipment design, and, in particular, with the introduction of datalink communication systems, will be the next panel topic. Lastly, possible implications for human operators of the increasing sophistication and decision-making capabilities of automated systems in the air and on the ground will be introduced. The panel chair will summarize the major points and propose questions for discussion.

Identification of Important “Party Line” Information Elements and Implications for Situational Awareness in the Datalink Environment

The perceived importance and utilization of “party line” information by air carrier flight crews was investigated through a survey and flight simulation study. The Importance, Availability, and Accuracy of party line information elements were explored through a survey of active air carrier pilots. The survey identified numerous party line information elements that were considered important. These elements were scripted into a full-mission flight simulation experiment that examined the utilization of party line information by studying subject responses to specific information element stimuli. Some party line information elements perceived as important were effectively utilized by flight crews. However, other party line elements stimulated little or no increase in situational awareness. The ability to assimilate and use party line information appeared to be greatest when the crew had time to monitor the party line and had clear authority to act on the information. The assimilation of party line information was lowest during high workload periods, such as during takeoff, and pilots were reticent to question air traffic control based on party line information alone. In addition, the results of both the survey and the simulation indicated that the importance of party line information appeared to be greatest for operations near or on the airport. This indicates that caution should be exercised when implementing datalink communications in tower and close-in terminal control sectors. © 1993 John Wiley & Sons, Inc.

Data-link communication between controllers and pilots: a review and synthesis of the simulation literature : Kerns, KInt J Aviat Psychol Vol 1 No 3 (1991) pp 181–204 (24 refs)

Data-link communication between controllers and pilots: a review and synthesis of the simulation literature : Kerns, KInt J Aviat Psychol Vol 1 No 3 (1991) pp 181–204 (24 refs)

Two CMOS gate arrays for the EPACT experiment

Two semicustom CMOS digital gate arrays are described which have been developed for the Energetic Particles: Acceleration, Composition, and Transport (EPACT) experiment. The first device, the event counter is 16*24-bit (EC1624), implements sixteen 24-bit ripple counters, and has flexible counting and readout options. The second device, the serial transmitter/receiver (SXR), is a multipersonality chip that can be used at either end of a serial, synchronous communications data link. It can be configured as a master in a central control unit, or as one of many slaves within remote assemblies. Together, a network of SXRs allows for commanding and verification of distributed control signals. Both gate arrays were radiation hardened and qualified for space flight use. The architecture of each chip is presented, and the benefits to the experiment summarized. >

Influence of Controllability-Type Properties on Reliability and Stability of Desynchronized Systems

Systems with high level of failures are considered that permanently operate due to this reason in a transient dynamical regime. In real systems amplitude restrictions for state variables are inevitable and also the so called overshooting effect is inwardly intrinsic. Therefore the operation in transient regime can lead to a great number of secondary failures. At the same time it is known that some classes of the so called desynchronized systems are insensitive to failures in data communication links. In the paper the notion of quasi-controllability for desynchronized systems is introduced that allow easy and efficient to estimate the overshooting measure. This presents the means to design the variety of highly reliable fault-tolerant control and manufacturing systems.

Manchester encoder–decoder for optical data communication links

A new encoder-decoder (CODEC) design of a Manchester coding scheme suitable for optical data communication links is presented. The design is simple and uses off-the-shelf digital electronic components and subsystems. The CODEC can be used for high data rate transmissions, typical of opticalfiber systems and local area networks. The decoder is insensitive to variations in the clock rates within the range of +/-33%, whereas the encoder, which is a simple XOR logic gate, is not affected by clock variations. During high-frequency operation (e.g., at 100 MHz), the CODEC can be operated at a wide range of frequencies (from 66.6 to 133.3 MHz) without modification to the CODEC circuitry. Furthermore, the CODEC can be made to operate at any data rate by a simple change of a single capacitor or a single resistor in the decoder circuit. The CODEC was built in the laboratory by using transistor-transistor logicintegrated circuits. It was experimentally found that with this decoder the transmitted data, as well as the cloc, can be recovered from the Manchester coded signal without being affected by clock variations within the designed range.