General computation method of outage time for digital radio links

A method to compute outage time during clear air conditions on any radio path for various types of digital modulation is proposed. The performance of digital systems depends on combined effects of in-band amplitude dispersion (IBAD) in the channel bandwidth, and of carrier to noise ratio (CNR). Outage time is then computed for a given period using the statistical dependence of IBAD and CNR in the propagation mechanisms occurring on the path and using the formal relation of IBAD with CNR characterising the digital equipment in service.<>     

Bandwidth and threshold calculations for angle-tuned parametric oscillators

The bandwidth of angle-tuned optical parametric oscillators, in some cases, is limited by the noncolinear interaction of the pump, signal, and idler beams, which results when the non-linear material is rotated relative to the pump beam. The decreased beam overlap reduces the parametric gain and increases the pump power threshold. To determine this bandwidth, a theoretical expression for the threshold is derived in the near field limit taking into account double refraction for a noncolinear interaction. Angle tuning can be done by 1) rotating the crystal and mirrors as a unit, or by 2) rotating the crystal only. Expressions for determining the tuning rate and threshold increase for both tuning methods are derived. Angle tuning about the 90° phase-matching axis in LiNbO3(the low-threshold design) is shown to be not practical. A combination of step temperature tuning and voltage fine tuning is found to be most practical in this case. A wide-band oscillator with a small threshold increase is shown to be possible by angle tuning about an axis not parallel to a crystal axis. The threshold increases very little if the oscillator is tuned by rotating only the crystal inside an optical cavity made of one curved and one flat mirror.     

Combined channel estimation and data detection using softstatistics for frequency-selective fast-fading digital links

A novel adaptive nonlinear equalizer for fast time-varying multipath channels that combines the channel estimation and data detection tasks is presented. The a posteriori probabilities (APPs) of the states of the intersymbol interference (ISI) channel are recursively computed from the received data by a symbol-by-symbol (SbS) detector and are then employed by a Kalman-type nonlinear channel estimator. Robust channel tracking and good data-detection performance are obtained, with a reasonable receiver complexity     

Si-based receivers for optical data links

We present results for Ge_xSi_1-x waveguide pin detectors grown by rapid thermal chemical vapor deposition (RTCVD). Detectors with multiple Ge_0.29Si_0.71 absorption layers show an internal quantum efficiency of 33% at λ=1.3 μm with a dark current of 27 pA/μm². The external quantum efficiency is limited to 7% by the fiber-to-waveguide coupling efficiency. The output eye diagram for a hybrid λ=1.3 μm silicon receiver at 500 Mb/s is demonstrated. Prospects of a silicon-based optoelectronic receiver array technology are discussed     

Giga-bit CMOS equalizers for high-speed data links

Consumer electronics are experiencing an explosive growth in bandwidth requirements. This growth is driven by demand for fiber-to-the-home Internet connections, the increasing capabilities of in-home consumer devices as well as the demands of multimedia recording and playback in mobile devices. However, traditional copper channels and previous generations of optical fiber experience dispersive effects at data rates above 1 Gbps, leading to inter-symbol interference (ISI). This paper presents a finite impulse response filter-based feed forward equalizer (FFE) to reduce the effect of ISI on these channels. The efficacy is of the FFE is demonstrated by measuring the eye diagrams of a 10 Gbps signal transmitted through an optical fiber as well as a copper backplane with and without FFE compensation. The proposed FFEs successfully compensate ISI for both the optical and copper backplane links. All circuits are fabricated using a 0.18 μm CMOS process.     

Pulsed frequency-response calculations for a digital control system

A method for digital-computer calculation of the pulsed real frequency-response function of a continuous system is presented. The approach, via the discrete transition matrix, provides programming generality and avoids the algebraic manipulation inherent in the direct transformation approach. An application of the technique is to the design of digital and sampled-data control systems by frequency-domain methods.     

Bandwidth efficient constant-envelope digital signalling with phase-tree demodulation

A method is given for analysing constant-envelope signalling schemes with partial-response baseband pulses. We consider coherent phase-tree demodulation for the Gaussian channel. The results show that very good spectral properties can be obtained for systems with error probabilities equal to or better than for binary phase-shift keying.     

The capacity of digital links in tandem

Suppose we haveLdigital links in tandem. Between successive links we have a repeater. The links are each white Gaussian channels with no bandwidth constraint. The repeater may either be a {em binary repeater}, which sends on each bit separately having made a binary decision on each, or a {em Shannon repeater}, which perfectly reproduces at one end the bits that were transmitted at the other end of the link. What is the loss in capacity if we use only binary repeaters and code for the entire L links at the transmit end? For largeL, the capacity drops by a factor asymptotic to InL, and the normalized optimum timeTper symbolT_{opt}^{L}is also asymptotic toln L. Arbitrarily shortLgives0capacity forL > 1. More precise asymptotic results are obtained and compared with computed numerical values. These results show when it pays to code each link separately in digital data transmission.     

A codec for HDTV signal transmission through terrestrial and satellite digital links

A codec for digital transmission of HDTV is described. The bit-rate compression algorithm is based on advanced techniques such as spatial discrete cosine transform (DCT), temporal differential PCM (DPCM), variable length coding. The codec is designed to operate with both the interlaced studio systems 1125/60 and 1250/50, and, thanks to the inherent flexibility of the packet structure, a wide range of line bit-rates can be used as a compromise between video quality and bit-rate constraints of the digital transmission link. The flexibility of the HDTV codec is highlightened through examples of applications over satellite digital links in practical situations.     

Real time digital thresholding of data from continuous scanning linear arrays

Some consequences of utilising the potential for real time digital thresholding on a line basis in an implemented system for fast image acquisition and analysis, the Edinburgh FIP-system, are discussed.The line by line approach may give rise to directionally dependent shape distortions of detected objects. The types of distortions encountered depend on the thresholding algorithm and the types of objects in question. The importance of the distortions is determined by the application for which the system is used.For application to metaphase finding the implemented dynamic thresholding scheme provides satisfactory results, which could not in any obvious way be improved by a corresponding two-dimensional alternative.For application to cervical smear screening an initial implementation of a local thresholding scheme is found inadequate. A straightforward software compensation is inhibited by the system's ‘interval-coding’, which on the other hand seems to provide a basis for alternative ways of surmounting the problem.The line by line approach imposes limitations on the applicability of the system, but many problems can be reformulated so as to allow solution in a fast line-scanning environment.     

Copyright protection for digital data

If Γ_p is a p-ary code of length n, and a and b are two codewords, then c is called a descendant of a and b if c_i ∈{a_i, b_i} for i=1,…,n. We are interested in codes Γ_p with the property that for any two codewords a and b their only descendant codewords are a and b themselves. This way a coalition of two users who are given codewords a and b cannot frame a third user who is given the codeword c. Intersecting codes over primary field GF(p) with the above mentioned property are found     

Collusion-secure fingerprinting for digital data

This paper discusses methods for assigning code-words for the purpose of fingerprinting digital data, e.g., software, documents, music, and video. Fingerprinting consists of uniquely marking and registering each copy of the data. This marking allows a distributor to detect any unauthorized copy and trace it back to the user. This threat of detection will deter users from releasing unauthorized copies. A problem arises when users collude: for digital data, two different fingerprinted objects can be compared and the differences between them detected. Hence, a set of users can collude to detect the location of the fingerprint. They can then alter the fingerprint to mask their identities. We present a general fingerprinting solution which is secure in the context of collusion. In addition, we discuss methods for distributing fingerprinted data     

基于粒子群优化的多数据链任务分配模型及方法

数据链作为"战斗力的倍增器"受到各国军方的重视,多种数据链被开发出来以应对不同的场景,然而不同的数据链有不同的特性,难以实现多数据链间的互联互通。针对此问题,提出了一种通过多数据链平台分发任务的模式,给出了多数据链任务分配的数学模型,应用基于粒子群的算法对该问题进行了求解。模拟计算结果表明,该任务分配算法可以在不违反任何约束的情况下有效地实现多数据链间的互联互通。     

基于LabVIEW的变压器温升数据采集系统

变压器产品出厂前,为了验证变压器性能好坏,需要对其进行温升试验。温升即变压器油、绕组、铁心等位置的温度与环境温度之差。在此以Lab VIEW作为软件开发平台,开发一款软件,该软件主要通过取几个环境温度点的平均值,然后每个通道的温度与平均值做差,得到温升曲线。最终得到一款包括温度、温升实时显示,通道配置以及数据、图像保存等功能的软件。     

Demonstration of photonically controlled GaAs digital/MMIC for RFoptical links

We report design, fabrication, and test of a monolithic GaAs optoelectronic integrated circuit (OEIC) implementing a broad-band optically driven digital/analog radio frequency (RF) interface. The integrated circuit (IC) was fabricated using a foundry-compatible enhancement/depletion metal-semiconductor field-effect transistor (MESFET) process with no added lithography steps. A single optical fiber carries externally amplitude modulated 0.85-μm light to the on-chip GaAs metal-semiconductor-metal interdigitated photodetector. RF as well as simultaneous digital information encoded at up to 10 Mb/s using a novel waveform set is transmitted over the fiber. The serial digital data is self-clocked into on-chip registers to control the RF signal chain, which includes a three-bit digital attenuator. The circuit operates in an asynchronous mode to detect digital and RF on the single optical-fiber input, control RF level, and transmit the 2-8-GHz RF to the IC's electrical output. Measurements characterizing the RF and digital performance of the IC as well as a demonstration of the full optoelectronic mixed-mode functioning of the IC are presented     

星间激光链路数据中继技术研究进展

基于高性能激光链路构建高速安全的数据中继卫星系统可为不同轨道、不同功能的对地观测卫星和用户航天器提供大容量、无缝隙的数据中继服务,在军事和民用领域均具有广泛的应用前景。以欧洲为代表的发达国家相继开展了星间激光链路数据中继技术的理论研究和星上演示验证,并启动了相应的工程验证计划。综述了国内外星间激光链路数据中继技术的研究现状,对几种典型激光链路数据中继卫星系统,着重研究了系统结构、激光终端及模拟验证实验。最后,分析了数据中继卫星激光链路组网中着重关注的几个方向。     

A retransmission scheme for circuit-mode data on wireless links

The cellular radio link is characterized by deep fades leading to long error bursts (lasting hundreds of milliseconds). Data transmission over such links results in large packet error rates (in the range 10^-3 to 10^-1). We have designed a radio link protocol (RLP) to achieve high throughput on such links. The RLP is based on frequent, complete or partial feedback of the receiver state. Performance results for the US digital cellular TDMA standard show that the scheme can provide the equivalent of 9.6 kb/s service per full-rate TDMA channel above a carrier to interference ratio of 18 dB     

高带宽数据中心网络的动态光链接结构

信息传输对带宽的要求越来越高,采用密集波分复用等常规方法来提高系统容量会大大增加数据中心成本,针对这一问题提出了一种低成本、高带宽具有动态结构的光网络。分析结果表明,这种光网络可以适应未来通信模式的发展要求。