On numerical optimization of communications system design

The limiting factor in the use of computer tools for the design of communications systems is often the amount of human intervention needed, rather than the actual computation time. A technique is presented by which a large proportion of the low-level decision making is delegated to the computer, thereby allowing the designer to concentrate on the engineering aspects and higher-level tradeoffs. The implementation described can be used with existing design programs (e.g., transmission simulators). The possibilities and limitations of the technique are discussed, and several examples of its application are given     

IP communications in air traffic control (ATC)

Although established some 60 years ago voice communications is still the sole means to separate and guide aircrafts. Voice communication systems are therefore amongst the most critical installations in air traffic control (ATC). Frequentis was the first to introduce PCM (pulse code modulated) based equipment for ATC worldwide and is on the leading edge of steering into the world of packetized voice communications. VoIP is the emerging voice communication technology which has already proven to provide satisfactory service for commercial applications. However, in ATC a number of requirements exceeding commercial applications have to be met. The voice communication system for ATC integrates radio communication as a prime service. Delays generated by the system therefore directly affect the performance on the radio channel and need to be extremly low. Both the radio control (push-to-talk, PTT) and the voice content need to be processed and delivered in a timely manner. SIP (session initiated protocol) based signalling represents a promising approach to tackle the delay problem. In addition, voice communication systems are required to provide high availability figures. VoIP based systems strongly rely on the communications infrastructure as they are distributed by nature. Resilient packet ring structures allow for these high availablity figures for the communications infrastructure.     

Modem techniques in satellite communications

Since the mid 1980s, research and development in satellite modem techniques has been very active and has yielded promising results. In the article the author presents a summary of the current status of work in this area, and discusses the directions this work is taking     

Effects of the ground on power-line communications

In this paper, a radiated-emission model of broad-band power-line communications (PLCs) in the frequency range from 1 to 30 MHz is presented. The model is based on the full-wave approach with the formulations of the extracted Maxwell equations. The transmission characteristic of the power line is obtained with the boundary conditions. The effects of the ground on the transmission characteristic and radiation are emphasized. Experiments were made to check the validity and accuracy of our model. It shows that the model is useful in predicting the effect of the ground on the radiation of straight PLCs.     

Blockage mitigation techniques in satellite communications

This article proposes systematic approaches to minimize severe channel degradation. Detection of channel condition is performed by means of two continuous ARQ NAK counting schemes. Stop-and-wait ARQ non-NAK counting is used for timed complete blockage. A single (31,21,5) code is designed for all the ARQ systems proposed. After the blockage state of a transmission channel is determined, satellite link parameter trade-offs and other specific remedy alternatives are recommended to enhance channel performance. System performance criteria are derived with different Earth station capabilities.     

Synchronization techniques for underwater acoustic communications

Underwater acoustic channel is a challenging medium for communication due to the presence of significant multipath, high noise, frequency-dependent propagation loss, and high and non-uniform Doppler spread. Doppler shift is non-negligible in underwater communication due to the low velocity of underwater signals. Synchronization and Doppler estimation are important requirements for achieving good performance in this channel. Synchronization algorithms that give good performance in radio communication do not work well in underwater communication. Hence, this area has received a lot of attention from researchers. This paper surveys important works in the area. The techniques proposed in the literature for frame synchronization, frequency and phase synchronization, and timing synchronization in single carrier communications are reviewed here. The synchronization techniques proposed for OFDM, MIMO OFDM, and spread spectrum communication are also surveyed. Doppler estimation methods proposed in the literature are also reviewed. It is found that most of the recent works in underwater acoustic communication focus on OFDM synchronization. Deep learning-based methods proposed in the literature are also reviewed. Key open problems and areas that require future research attention in the field of synchronization and Doppler estimation in underwater communications are highlighted in this paper. The area needing most attention of underwater communication researchers was found to be MIMO OFDM due to the difficulty in synchronization in such systems while used in underwater communication. Reducing the computational complexity of the algorithms used is also important for future work. Schemes that work with Doppler due to relative velocity over 10 m/s also need to be developed.     

An improved ATC radar beacon system

This paper summarizes the work of the Beacon Systems Panel of the Air Traffic Control Advisory Committee.     

机动多功能航管雷达系统研究

机动多功能航管雷达系统是在传统固定站式航路监视雷达研究基础上,具有高机动、高可靠、多功能、智能化、高数据率的新雷达技术系统,以满足在特定环境下对中低空和机场空域航路监视的要求。该雷达系统按照功能划分为雷达子系统、ATC子系统、应急通信子系统。叙述了机动多功能航管雷达系统的设计原理和技术特点。     

Aircraft interface with the future ATC system

The authors outline how the advantages of improved navigational accuracy can benefit both the individual aircraft and the air transportation system despite a mixed environment. The development of advanced navigation, flight planning, performance optimization, automatic guidance, and other capabilities in current and future flight management systems, together with the availability of digital communications between the airplane and ATC, suggests the need to review the potential airplane contributions to the ATC system of the future. A number of application areas utilizing current airborne flight management technology have been proposed for use with ATC that could provide significant operational benefits. These include: time-navigation applications in traffic management; multisensor navigation to provide automatic dependent surveillance; improved precision for approach, missed approach, and departure procedures; and improved navigational accuracy supporting reduced airway widths, holding pattern airspace, and aircraft separation standards. Several examples of operational benefits for operators and ATC during the transition period are identified, and the need for integrating these features into future ATC capabilities and procedures is stressed     

Multiring techniques for scalable battlespace group communications

Network-centric warfare must leverage off a common network to support different purposes. While group communications based on a single virtual ring overlay may satisfy the most important requirements for survivability and security, scalability may for cc redesign because a single ring generally has higher delay and delay jitter. In order to provide scalability as the number of group members grows, large single rings may be broken into, smaller multirings interconnected together. Thus, comparing the characteristics of different multiring techniques provides insight into which battlespace applications may be supported via virtual rings. In this article we consider different approaches to providing scalable battlespace group communications using multi-ring techniques, classifying the techniques according to the primary military requirements of QoS, security, and survivability. Some important design issues of multiring techniques, such as the number of ring levels and number of rings per level, are dependent on, application QoS requirements and the underlying network infrastructure in terms of topology (dense vs. sparse) and link bandwidths (bottleneck capacities). Through our survey, we conclude that while no existing multiring scheme provides the single solution to battlespace group communications, some aspects of existing multiring schemes do match specific scenarios and provide us useful insights for designing new schemes for battlespace group communication. To our knowledge, this is the first article to survey and categorize multiring algorithms.     

Some cryptographic techniques for machine-to-machine data communications

Some of the threats to the integrity of multiuser teleprocessing systems and to the data they contain can be countered by the use of cryptography. Stream-generator ciphers are not ideally suited for such an application, thus the use of block ciphers, which have the beneficial property of a strong nonlinear intersymbol dependence, is suggested. This property provides the means for automatic error detection for verifying the authenticity of terminal operators, and for ensuring messase integrity. An experimental demonstration system has been constructed to illustrate protection features that can be provided for real applications.     

Interference rejection techniques in spread spectrum communications

It is argued that the ability of a spread-spectrum system to withstand interference, both intentional and unintentional, is probably its greatest asset. Any spread spectrum receiver can only suppress a given amount of interference; if the level of interference becomes too great, the system will not function properly. Even under these latter circumstances, however, other techniques, which enhance the performance of the system over and above the performance improvement that comes automatically to systems from using spread spectrum, are available for use. These techniques typically involve some type of additional signal processing and are examined here. Two general types of narrowband interference suppression schemes are discussed and an overview is presented for several other techniques. The two classes of rejection schemes emphasized are (1) those based on least-mean-square estimation techniques, and (2) those based on transform-domain processing structures     

An optimization model of communications satellite planning

A mathematical planning model is developed to help make cost effective decisions on key physical and operational parameters, for a satellite intended to provide customer premises services. The major characteristics of the model are: (1) interactions and tradeoffs among technical variables are formally captured; (2) values for capacity and operational parameters are obtained through optimization; (3) effects of physical and regulatory constraints are included; and (4) the effects of market prices for transmission capacity on planning variables are explicitly captured. The model is solved optimally using geometric programming methods. Sensitivity analysis yields coefficients, analogous to shadow prices, that quantitatively indicate the change in objective function value resulting from variations in input parameter values. This helps in determining the robustness of planning decisions and in coping with some of the uncertainty that exists at the planning stage. The model can therefore be useful in making economically viable planning decisions for communications satellites     

A single-frequency communications system

In those radio communications applications where area coverage is not desired, a series of repeaters, each operating at low power, can be used to extend the radio over long distances. Microwave relay systems operate on this principle with each node representing a point of potential local distribution. Where it is desirable to have the nodes closely spaced, such as along a highway, it becomes desirable to utilize a single frequency for all transmissions in one direction in the interest of conserving spectrum. This paper covers such a system operating in the 935-MHz band. The system described provides both the "backbone" communications system which employs single-frequency repeaters and the "roadside" communications from the repeater node points to users in their vehicles. The functioning of the repeaters is described, and the relationship between signal levels, isolation, external noise levels, and thresholds is presented. Both analog and digital modulations are employed, and it is shown how each repeater is remotely switched between "backbone" and "roadside" communications modes. Extensions from current single-channel to multiple-channel operation is described in terms of the application to a variety of highway-related uses. The results of propagation experiments both along the "backbone" and on the "roadside" are described and related to theoretical models. From these data, conclusions can be drawn about the relationship between repeater spacing, height, and power level, as well as their relationship to user antenna height, output power, and receiver sensitivity.