Broad-band fading channels: signal burstiness and capacity

Medard and Gallager (2002) showed that very large bandwidths on certain fading channels cannot be effectively used by direct sequence or related spread-spectrum systems. This paper complements the work of Medard and Gallager. First, it is shown that a key information-theoretic inequality of Medard and Gallager can be directly derived using the theory of capacity per unit cost, for a certain fourth-order cost function, called fourthegy. This provides insight into the tightness of the bound. Secondly, the bound is explored for a wide-sense-stationary uncorrelated scattering (WSSUS) fading channel, which entails mathematically defining such a channel. In this context, the fourthegy can be expressed using the ambiguity function of the input signal. Finally, numerical data and conclusions are presented for direct-sequence type input signals     

Broad-band HBT BPSK and IQ modulator MMICs and millimeter-wave vector signal characterization

Reflection-type binary phase-shift keying and in-phase and quadrature modulator monolithic microwave integrated circuits (MMICs) are reported in this paper. These MMICs are fabricated by 1-/spl mu/m HBT process and evaluated successfully under vector signal characterization. A cold-mode HBT device model with varying bias conditions is proposed, which is suitable for millimeter-wave circuit design and simulation. The analysis and design equations of imbalance effects for the reflection-type modulators are also presented. These MMICs demonstrate measured error vector magnitude of less than 12%, a carrier rejection of better than 15 dB, and an adjacent channel power ratio of better than -21 dBc from 50 to 110 GHz.     

Pseudorandom signal sampler for relaxed design of multistandard radio receiver

This paper proposes a novel software defined radio (SDR) receiver design using non-uniform sampling (NUS) technique implemented by original design of a pseudorandom signal sampler (PSS) circuit for controlling data conversion to relax multistandard receiver circuit constraints. The proposed and designed NUS-based SDR receiver allows spectral alias suppression at integer multiples of sampling frequency offering the advantages of relaxing anti-aliasing filter (AAF), reducing the analog-to-digital converter (ADC) dynamic power consumption and the automatic gain control (AGC) range as well. The PSS circuit, generating pseudorandom clock signal, with enough time-quantization accuracy, was designed. The PSS is implemented in 65-nm digital CMOS technology and occupies 470 (μm)². It features up to 200 MHz “mean clock” for 3.2 GHz main clock while drawing 242 μA for 1.2 V supply. Mixed experimental/simulation tests, of designed NUS-based SDR receiver, revealed a confirmation of alias-free performances and the achievement of a 72 dB (12-bit ADC) dynamic range after signal reconstruction.     

发展宽带网络构筑宽带服务的生态系统

宽带IP网络的发展趋势是端到端的以太网，采用波长路由器和DWDM系统的成智能光网核心网（采用以太网帧传输），由设置在边缘的以太网路由器构成宽带城域网，接入网采用以太网结构。宽带IP网的发展促进了三网融合，而三网融合产生的新业务将形成宽带服务新市场。宽带业务要贯彻有偿服务、按质按量收费的原则，这样才能步入健康发展的轨道。     

ADSP-BF549在高速信号采集回放系统中的应用

在高速信号采集回放系统中，数据量非常庞大，传统的数据采集方式不能胜任。给出了一种基于ADSP—BF549的数据采集回放实现方案，结构简单、完全适合大存储量、高实时性的要求，并且成本较低。同时还对关键模块DDRSDRAM的地址和片选信号扩展进行阐述。     

Board-level optical interconnection and signal distribution using embedded thin-film optoelectronic devices

Optical interconnection and signal distribution at the backplane, board, and substrate level can be implemented using thin-film active optoelectronic devices embedded in polymer waveguide structures. These active embedded devices eliminate the need for optical beam turning to and from photodetectors and emitters, respectively, for inputs and outputs to the substrate waveguides. In this paper, optical interconnections using fully embedded thin-film metal-semiconductor-metal (MSM) photodetectors in polymer optical waveguides are demonstrated, and the experimental characterization of these thin-film MSMs embedded in polymer waveguides is reported. To illustrate the potential for high-level signal distribution at the backplane, board, and substrate levels, a 1/spl times/4 balanced multimode interference (MMI) coupler has also been demonstrated in a photoimageable polymer for the first time. Finally, a 1/spl times/4 thin-film MSM photodetector array has been embedded in the output arms of the a photoimageable polymer MMI for the first time, and the MSM array photocurrent outputs from the 4 arms show that highly balanced optical signal distribution has been achieved.     

Broad-band half-wave dipole

An ultrahigh frequency (UHF) fan-dipole is optimized for wide-band operation near the first resonance in order that the antenna could be used in a planar array of half-wavelength spaced elements operating over a conducting ground plane. The resultant voltage standing-wave ratio (VSWR) of the optimized dipole (with a50 Omegacoax input) is less than 2:1 over a 37 percent bandwidth.     

xDSL宽带接入技术

介绍了几种不同的xDSL技术,并对其传输容量和技术特点进行了比较。ADSL可充分利用现有的铜缆网络,技术成熟且标准化程度较高。HDSL也可利用现有电缆实现扩容,但速率恒定,不能根据应用改变而调整速率。各种DSL技术各有优缺点,今后还会有新DSL技术出现。     

基于以太网的宽带接入技术

作为局域网技术的以太网如果应用到公共的接入网中，需要解决安全性、启用管理、带宽管理、计费、网络维护管理以及供电等问题。2001年7月，信息产业部电信传输所接入网标准研究组讨论通过了《接入网技术要求－基于以太网的宽带接入网》，该标准对用户侧设备和局侧设备的基本功能作了描述。     

Broad-band guided-wave electrooptic modulators

Lumped-element Mach-Zehnder interferometric modulators have been designed, fabricated in LiNbO3, tested and analyzed. These modulators had 3 dB bandwidths from 280 MHz to 2.75 GHz and Vπ's from 1 V to 4 V, respectively. A simpleRLCequivalent circuit is utilized to model the packaged modulator performance and results are compared with those measured using a swept-frequency technique. The model is seen to break down at the higher frequencies due to a frequency-dependent resistance and the electrode and parasitic inductances are seen to limit the overall modulator performance. The effects of varying the electrode capacitance, resistance, or inductance on modulator performance are demonstrated.     

Broad-band multisection electrooptic modulators

A general solution has been derived for expressing the conversion of power from a base frequency to a modulation sideband using a multisection electrooptic modulator. The objective is to obtain broadband frequency modulation of a laser by the use of multiple collinear electrooptic crystals with microwave power levels well below the breakdown threshold. It is found that segmented structures lead to greater bandwidths, which increase with the number of modular sections. This is achieved by adjusting the phases of microwaves between sections to maximize the single-sideband conversion efficiency. It is shown that a 10.6-μm CO₂ laser modulator with six geometrically identical CdTe sections can potentially achieve a 3-dB bandwidth of nearly 6 GHz using a 10-kW traveling-wave tube operating at 16-GHz center frequency     

Broad-band injected-beam crossed-field amplifiers

The design and operation of injected-beam-crossed-field amplifiers, which provide efficient amplification over octave frequency bands with grid control in compact PM Focused format, are described. Dielectric supported meander lines, which are used to provide the low-dispersion and high-interaction impedance required to achieve octave bandwidth, are detailed. Relationships between space charge, gain factor, beam impedance, circuit loss, and circuit dimensions are derived for design optimization. An electron gun with a negative grid, which provides noise suppression, as well as a nonintercepting current control electrode, is shown to be effective in controlling the beam current continuously from zero to full operating value. Operating characteristics of production CFA's, providing 1 kW of average power in pulsed and CW operation and up to 5-kW peak pulsed power, are presented to illustrate the inherent multimode performance which can be achieved with low-voltage grid control.     

宽带雷达RID成像

介绍了雷达成像基本原理,分析了目标自身转动的分量及其转动的主要来源,针对非匀速转动目标,提出了成像补偿的两步法,并探讨了距离瞬时多普勒（RID）成像的可行方法。     

混合拉曼光纤放大器的实现

在拉曼光纤放大器(FRA)和掺铒光纤放大器(EDFA)理论建模的基础上,设计并制作了双波长泵浦的FRA和EDFA相结合的混合光纤放大器,获得了较为平坦的(±1dB),80nm(1533～1613nm)的增益带宽,峰值增益达到了近16.5dB,带内平均增益为15.5dB.     

Broad-band gap coupled microstrip antenna

A microstrip antenna with large bandwidth is developed using a parasitic technique. Compared to the available wideband antennas, the proposed antenna structure is very compact and gives a less distorted radiation pattern with frequency. An impedance bandwidth eight times that of a conventional patch antenna of the same size is achieved. The concept of coupled microstrip line model is extended for theoretical interpretation of the impedance loci. The experimental procedure and results are described, and a theoretical analysis is presented     

Broad-band distributed amplifier impedance-matching techniques

A circuit concept is developed which allows impedance transformations to be performed over extremely broad bandwidths. The transformation is obtained by coupling one or more input or output lines of a distributed amplifier into several output or input lines, respectively. The circuit technique is demonstrated by results for an amplifier for a 1:2 impedance transformation over a 2-20-GHz bandwidth. The amplifier yields a voltage standing wave ratio (VSWR) of better than 1.7:1 into 25 Ω at the input and better than 1.5:1 into 50 Ω at the output while maintaining a gain of 9±1 dB. An application of the technique to the broadband impedance-matching problem of a laser diode driver is discussed. The circuit has a gain of 8.5±1 dB from 0.5 to 12.5 GHz and better than 10 dB return loss at both the input and output     

Broad-band uniplanar hybrid-ring and branch-line couplers

Novel uniplanar 180° and 190° hybrids suitable for MIC and MMIC applications are described. The uniplanar crossover hybrid-ring coupler using a coplanar waveguide (CPW) and slotline provides substantially improved amplitude and phase characteristics over a broad bandwidth compared to conventional microstrip hybrid-ring couplers. Experimental results show that the new coupler has a bandwidth of more than one octave from 2 GHz to 4 GHz with a ±0.4-dB power dividing balance and a ±1° phase balance. A uniplanar two-branch directional coupler using a coupled rectangular slotline ring has also been developed. CPW-to-slotline transitions using uniform and nonuniform CPWs or slotlines are also discussed. These transitions are uniplanar and simple to fabricate. No via-holes are needed for ground connections, and integration with solid-state devices is easy. A pair of broadband transitions using CPW shorts and slotline radial stubs is demonstrated with a 1-dB bandwidth of more than 5.2:1     

Broad-band continuously tunable all-fiber DFB lasers

Up to 27-nm continuous tuning is demonstrated from Er/Yb all-fiber distributed-feedback (DFB) lasers using a simple tuning technique for axial extension and compression. The demonstrated devices operate with powers up to 10 dBm and remain operating in single mode over the full tuning range. Our results represents the broadest tuning-range previously reported in any DFB laser configuration and demonstrate that uniform compression tuning of long Bragg gratings is possible with high reliability