A backbone highway communications system using coaxial cable

The problem of providing the communication link for modern highway management and control is analyzed. A 100- mile span of highway is analyzed for typical voice and control function requirements plus closed circuit television monitoring capability. Based on this analysis, the number of channels and hence the bandwidth required to meet typical requirements is developed. It is proposed that a coaxial cable system can best provide the bandwidth and access flexibility that will be necessary for the many links required for effective highway management. A coaxial cable system as a transmission path is shown to be two dimensional in that it involves absolute signal levels as well as spectrum considerations. An analysis of distortion characteristics of state of the art coaxial cable systems is included to arrive at signal to noise plus distortion ratios versus cable length and amplifier gains. Typical cable costs, burial and tunneling labor costs are discussed to show economic practicality. Finally, two high-capacity cable systems are discussed to illustrate the communications capacity of coaxial cable systems.     

XeF laser performance for F2and NF3fuels

XeF laser performance has been investigated for F2versus NF3as the halogen donor (fuel). The experiments were all performed in 3 AMAGAT Ne/Xe/fuel mixtures at ambient temperature and a pump rate of 132 KW/cm³on a 1 me-beam pumped laser. The F2-based laser mixture has been shown to be recyclable, with no loss in laser output, while laser performance steadily degrades for NF2-fueled mixtures under repetitively pulsed conditions. Despite the fact that F3absorbs at the XeF wavelength, it has been demonstrated that under appropriately chosen conditions the XeF intrinsic efficiency is essentially the same (2.2 percent) for both F2and NF3fuels for deposited energy loadings up to at least 150 j/l. Absorption, gain, fuel burn-up, and fluorescence were also measured in order to better characterize the laser medium and to determine the major factors contributing to the efficiency.     

Small-signal gain and time-resolved spectroscopy of the D2-F2/CO2pulsed chemical transfer laser system

Measurements made of the small-signal gain and time-resolved spectral output of a flash-initiated D2-F2/CO2chemical transfer laser system are reported. Small-signal gain measurements indicate a possible lack of rotational equilibration among the rotational levels of the CO2during the DF-CO2V-V energy transfer process. Time-resolved spectral output of this system, operated as a laser oscillator, is presented as verification of the small-signal gain results.     

Laser actinometry of flash-photolyzed H2/F2/He mixtures

Actinometric and time-to-threshold experiments with flash-initiated H2/F2/He mixtures have been modeled with the RESALE chemical laser code. Comparison of the salient features of both experiments with those predicted by the code determines the efficiency of our xenon flashlamp in dissociating F2. The results indicate that our 1000-J 20-μs full width at half maximum (FWHM) lamp is capable of dissociating 1.2 percent of the F2initially present in dilute F2/He mixtures.     

Laser action from atmospheric-pressure H2-F2mixtures made at 300K

Thirty-five photons (lambda = 3 mum) per photolytic F atom have been obtained from a 40-cm³photochemical laser filled with 400 torr of F2, 100 torr of H2, and minor amounts of Ar and O2mixed at 300 K. With 0.035-percent dissociation of the F2, 0.83-J 250-ns full width at half maximum (FWHM) pulses were observed.     

A personal communications network using a Ka-bandsatellite

The feasibility of a personal communications network using portable terminals that can provide 4.8 kb/s voice communications to a hub station via Ka-band geosynchronous satellite has been investigated. Tradeoffs are examined so that the combined system of hub and gateway earth stations, the satellite, and the personal terminals can provide a competitive service in terms of cost, availability, and quality. A baseline system that uses a spacecraft with approximately 140 spot beams to cover the contiguous US (CONUS) and 5 W power amplifiers in each beam is described. Satellite access in both the forward and return directions uses frequency-division multiple-access/code-division multiple-access (FDMA/CDMA) with a chip rate of 2.5 Mchip/s     

A theoretical study of the atmospheric pulsed H2+ F2chemical laser including rotational nonequilibrium effects

An atmospheric pulsed F2/H2/He chemical laser is studied numerically by a model which incorporates rotational nonequilibrium effects. The results are compared with experimental results of Chen et al. The fit between the experimental and theoretical results was found to be reasonably good. The results were also compared with those obtained from a model with an equilibrated rotational distribution. It is found that inclusion of a rotational nonequilibrated distribution which decreases the output energy by 25 percent has a certain effect on the output energy distribution among the various vibrational states but is of little importance for the lasing duration.     

Theoretical analysis of electron-beam-excited KrF laser performance: New F2concentration optimization

For an electron-beam-excited KrF laser, we analyzed theoretically the dependence of the performance characteristics on the excitation rate and initial F2concentration. According to the analysis of KrF* formation processes, KrF* relaxation processes, 248 nm absorption processes, and their individual efficiencies, a novel optimization method for initial F2concentrations is necessary instead of a conventional method of a "constant" F2burn-up rate. Then, we determined optimum F2concentration as a function of the excitation rate for excitation pulses of 20-500 ns FWHM. Finally, we obtained the scaling law for the intrinsic KrF laser efficiency.     

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.     

LOCNET-an experimental communications system using optical routing

Experiences gained with the installation and operation of an experimental communication system are reported. The system uses distributed switching in its narrow-band part, integrating ISDN services and high-speed data communication, and a star coupler as a central device. LiNbO₃ optical switches behind the star coupler prevent line tapping. In the wideband subsystem, optical routing is used for videophone. The central device is a space-division-switching unit consisting of cascaded 4×4 LiNbO₃ switching matrices. Both the narrowband and wideband parts of the system have been operated with bit error rates less than 10^-9     

A multimedia medical communications system

The problem of communicating the radiologist's findings to the attending physician is introduced, and it is shown why it is essentially a multimedia communication problem. A multimedia communications system that was designed with a focus on database and medical reports organization and architecture is described. A report is presented of some of the key results of an in-house trial linking the Department of Radiological Sciences and the Emergency Department at the Ottawa Civic Hospital, Canada, a 950-bed tertiary-care teaching hospital     

A future satellite communications system using millimetre-wave bands and an on-board processor

This paper proposes the system concept of a personal satellite communications system that will be available in the first decade of the 21st century. Technologies of millimetre-wave bands and an onboard processor with baseband switching promise to meet the requirements of a personal communications system: portability, low-cost, and large capacity. Based on the prospects of these technologies, the most likely parameters for the future personal satellite communications system and the configuration of a suitable on-board processor are proposed. A trial model of such an on-board processor has been made. In this paper, details of the trial model on-board processor and its future developments are described.     

A go-back-N protocol for mobile communications

The author describes a go-back-N (GBN) protocol, which is a type of automatic repeat request (ARQ) technique. The protocol has a buffer and memory at the receiver side and offers low implementation complexity and a structure especially suited to mobile communications. The optimization of the protocol parameters is determined through numerical analysis. Performance is evaluated by computer simulation using a channel model suitable for mobile communications. The results show that the proposed ARQ scheme achieves a higher performance than that of other ARQ protocols and that at high error rates its efficiency compares favorably with selective repeat protocols having an infinite buffer     

Satellite communications relay system using a retrodirective space antenna

A system has been developed for relaying messages via a satellite between earth points. In this system, messages transmitted to a satellite modulate a retrodirective antenna. Earth stations receive messages by irradiating the satellite antenna. Methods of modulating the retrodirective array are discussed with emphasis on methods to facilitate communications among several ground stations. There are advantages in spectrum usage and sharing with surface facilities. System design parameters are presented. Minimal power is required in the satellite as compared to the active communications satellites. Extremely high reliability is inherent in the design of the satellite electronic system, which can be made entirely from solid-state components.     

一种基于L_1范数的非局部变分图像复原模型

针对L_2范数的非局部变分模型在迭代过程中未考虑图像局部梯度信息,模糊图像细节信息的缺点,提出了一种基于L_1范数的非局部变分模型。首先,对基于L_1范数的非局部变分模型的扩散性能进行了详细的分析。接着,将该模型应用于退化图像的复原中,并推导出该模型的Bregman交替迭代求解过程。最后,通过对比实验,证明本文提出的L_1范数的非局部变分复原模型能更好地重构图像的细节信息,相对于L_2范数的非局部变分模型峰值信噪比提高大于1dB,图像复原性能更优。     

A multimedia interhospital communications system for medicalconsultations

The authors present a study whose main objective has been to explore the use of high-bandwidth multimedia communications technology for medical applications physically distributed among hospitals, that is to say an interhospital multimedia communications system. The design and development issues of a prototype are described, as well as the results of an in-field trial. From the results of this trial, a performance study has been developed for evaluating the expected communications requirements of a large-scale configuration of the system     

A self-steered array system for microwave communications

The paper presents a self-steered algorithm that can be used to correct pointing errors in microwave communications. The algorithm is based on the fact that the output power of an optimized beamformer achieves a local maximum if the steering vector coincides with that of the desired signal, as long as the interferences are outside the mainbeam. By approximating the steering vector by its first-order Taylor series expansion in terms of the steering angles, the maximization process reduces to a two-dimensional optimization problem. Numerical results are presented to illustrate the performance achievable     

Blind quality assessment system for multimedia communications using tracing watermarking

This paper presents a novel method to blindly estimate the quality of a multimedia communication link by means of an unconventional use of digital fragile watermarking. Data hiding by digital watermarking is usually employed for multimedia copyright protection, authenticity verification, or similar purposes. However, watermarking is here adopted as a technique to provide a blind measure of the quality of service in multimedia communications. Specifically, a fragile watermark is hidden in an MPEG-like host data video transport stream using a spread-spectrum approach. Like a tracing signal, the watermark tracks the data, where it is embedded, since both the watermark and the host data follow the same communication link. The estimation of the tracing watermark allows dynamically evaluating the effective quality of the provided video services. This depends on the whole physical layer, including the employed video co/decoder. The performed method is based on the evaluation of the mean-square-error between the estimated and the actual watermarks. The proposed technique has been designed for application to wireless multimedia communication systems. According to the results obtained, the sensitivity of the detected tracing watermark on the quality of service (QoS) indices provides for some useful capabilities for analyzing future mobile Universal Mobile Telecommunications System (UMTS) services.     

用复合正交换频码进行调制的M—ary MC—CDMA方法

本文提出了一种用复合正交扩频码进行调制的M－ary MC-CDMA方法,在频率选择性慢衰落信道,用等增益合成和最大化率合成分析了系统下行链的性能,并与单扩频码系统进行了比较,最后给出了保护时隙对系统的影响。