Turbo-BLAST for wireless communications: theory and experiments

Turbo-BLAST is a novel multitransmit multireceive (MTMR) antenna scheme for high-throughput wireless communications. It exploits the following ideas: the Bell Labs layered space time (BLAST) architecture; random layered space-time (RLST) coding scheme by using independent block codes and random space-time interleaving; sub-optimal turbo-like receiver that performs iterative decoding of the RLST codes and estimation of the channel matrix in an iterative and, most important, simple fashion. The net result is a new transceiver that is not only computationally efficient compared with the optimal maximum likelihood decoder, but it also yields a probability of error performance that is orders of magnitude smaller than traditional BLAST schemes for the same operating conditions. This paper also presents experimental results using real-life indoor channel measurements demonstrating the high-spectral efficiency of turbo-BLAST.     

移动通信中的开放性

技术创新的层出不穷,使得关于开放体系和专有体系之间的争论愈演愈烈。历史经验证明,开放体系带来长期的令人瞩目的商业价值。如开放标准通过漫游呼叫和不断增长的短信互通流量,大大提高了运营商的收入。汲取早期的成功经验,移动通信产业正在选择开放?体系,以期在多媒体信息及更先进的第三代移动服务方面取得进一步的成功。移动产业中的有关各方均从开放性中获益:消费者在终端、服务方面有更多选择,成本也更低廉;运营商能够以更低廉的成本快速部署新服务;设备制造商可以从更大的规模效益和由此带来的低成本中获益;应用开发商、供应商和转包…     

Chaotic communications with correlator receivers: theory and performance limits

This paper provides a review of the principles of chaotic digital communications using correlator receivers. Modulation schemes using one and two chaotic basis functions, as well as coherent and noncoherent correlation receivers, are discussed. The performance of differential chaos shift keying (DCSK) in multipath channels is characterized. Results are presented for DCSK with multiuser capability and multiple bits per symbol.     

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.     

Grey systems theory applications to wireless communications

This paper discusses grey systems theory (GST) applications in wireless communications and highlights its potential to cognitive radio. GST consists of information theory concepts and practical algorithms developed to address situations where information is incomplete and affected by random uncertainties. Two GST concepts, grey relational analysis (GRA) and grey model (GM) prediction theory are discussed. GRA provides a method to quantify the similarity between a reference data series and set of data while GM is used for modeling time series data and enables prediction of future values with limited data points and unknown probability distributions. These two techniques are surveyed with respect to their applications to wireless communications. Their application to predictive Cognitive Radio and as a similarity measure for case based reasoning cognitive engines is highlighted. A GRA based Automatic Modulation Classification (AMC) algorithm is applied to digital communications signals with preliminary results shown in simulation.     

The design of a QoS-controlled ATM-based communications system inChorus

We describe the design of an application platform able to run distributed real-time and multimedia applications alongside conventional UNIX programs. The platform is embedded in a microkernel/PC environment and supported by an ATM-based, QoS-driven communications stack. In particular, we focus on resource-management aspects of the design and deal with CPU scheduling, network resource-management and memory-management issues. An architecture is presented that guarantees QoS levels of both communications and processing with varying degrees of commitment as specified by user-level QoS parameters. The architecture uses admission tests to determine whether or not new activities can be accepted and includes modules to translate user-level QoS parameters into representations usable by the scheduling, network, and memory-management subsystems     

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     

Improving bit-error-rate performance of the free-space optical communications system with channel estimation based on radiative transfer theory

In order to improve the performance of terrestrial free-space optical communication systems in adverse visibility conditions, we present a method for estimation of the atmospheric channel impulse response function which governs the optical intensity propagation. This method reduces run-time computational demands and system complexity in comparison to our previously proposed dual-wavelength channel estimation technique. We consider propagation of optical wavelengths in fog, where the droplet diameters are close to the wavelength and thus scattering and absorption effects are significant. A method for rapid calculation of a channel response function based on estimating the effective optical depth of the channel and curve-fitting is described. The channel response estimate can then be used to design a receiver-side equalizer (minimum meansquared error linear equalizer) to correct the signal distortion due to propagation through the dispersive channel. The channel estimates are based on parametric curve-fitting functions which have been developed using the modified-vector radiative transfer theory to model the channel response. The optimal fit parameters are found using particle-swarm optimization to minimize the simulated bit-error rate of the received signal.     

扩频通信系统干扰及其仿真技术

扩展频谱技术有多种基本实现方式,本文主要介绍的是直接序列扩频技术,特别针对二进制的PSK调制解调技术,直接序列扩频系统的抗干扰能力分析与直接序列扩频系统的同步方法,并进行了相关仿真分析。     

利用高空无人机实现区域通信的系统设计方法

提出了利用高空无人机实现军用(或应急民用)无线数字移动通信系统的一种设计方法;描述了该通信系统的概念框架、机载通讯设备的组成方式和系统的工作原理;给出了无线链路的分析方法和计算公式,并列出了对上下行链路的计算结果。     

通信供电系统中的"瓶颈"

通信电源配电系统容量，受制于所有因素中容量最小的因素的影响，系统容量是变化的、逐渐下降的，温度是重要的变化参数，配电器件使用中注意安全等级的排列，保安器动作额定容量关系到电源系统的安全性。     

Software bugs and communications system performance

Software bugs and their manifestations are of concern in real-time systems such as communications systems. The reliability modeling of these systems has generally defined hardware performance models in great detail but only specified an estimate for the software performance. Software reliability modeling is usually based on the number of software bugs and not based on bug manifestations. The ultimate service provided by communications systems is dependent upon the level of criticality of bug manifestations and the frequency of occurrence of these manifestations. This paper discusses the current trend for the qualification and quantification of communications systems performance with emphasis on software bug manifestations.     

ATC ground communications system optimization techniques

The authors address the optimization of three major components of the US Federal Aviation Administration's (FAA's) hybrid leased/owned ground communications system supporting air traffic control (ATC). The optimizations are performed with respect to cost, performance, and reliability. First, optimization of the radio communications link (RCL) backbone microwave transmission system is discussed. A heuristic optimization procedure that minimizes cost subject to capital cost and availability constraints is presented. Second, two levels of user access network (UAN) optimization are discussed. The first level is optimization of the selection of RCL sites to open as drop-and-insert points for access by private leased-line UANs. The second level is optimization of the selection of transmission media used for implementing UANs. A dynamic programming method is presented for identifying FAA facilities where low-density microwave UANs are cost-effective. Third, optimization of the National Airspace Data Interchange Network (NADIN) II packet data switching system is discussed. Because this network will use the FAA-owned RCL transmission resources, the primary measures for optimization are performance and reliability instead of cost. Two methods are presented for this problem: an analytic method and a simulation method     

Carrier-density modulation effects in a traveling-wavesemiconductor optical amplifier: communications theory analysis andexperiment

A communications theory equivalent model suitable for analyzing carrier-density modulation effects within a traveling-wave semiconductor optical amplifier is derived by linearizing the amplifier rate equation. This model is used to analyze dual-channel amplification, and it is shown to give results which are in good agreement with those given by nonlinear polarization theory and experimental measurements. The effect of four-wave mixing on the amplification of many optical channels for worst-case operating conditions is studied, and it is shown that the individual channels experience different gains. It is also shown that if the individual channel gains are to be confined to lie within a ±1-dB band when operating the amplifier at high values of unsaturated power gain