移动WiMAX的发展现状

基于IEEE 802.16-2004及ETSI HiperMAN空中接口标准的WiMAX,正在被证明是一个高性价比的替代有线和DSL服务的固定无线技术.150多次的WiMAX试验及在五大洲的部署,清楚地证明了世界范围内对WiMAX作为固定无线服务技术的接受程度.     

Weighted universal image compression

We describe a general coding strategy leading to a family of universal image compression systems designed to give good performance in applications where the statistics of the source to be compressed are not available at design time or vary over time or space. The basic approach considered uses a two-stage structure in which the single source code of traditional image compression systems is replaced with a family of codes designed to cover a large class of possible sources. To illustrate this approach, we consider the optimal design and use of two-stage codes containing collections of vector quantizers (weighted universal vector quantization), bit allocations for JPEG-style coding (weighted universal bit allocation), and transform codes (weighted universal transform coding). Further, we demonstrate the benefits to be gained from the inclusion of perceptual distortion measures and optimal parsing. The strategy yields two-stage codes that significantly outperform their single-stage predecessors. On a sequence of medical images, weighted universal vector quantization outperforms entropy coded vector quantization by over 9 dB. On the same data sequence, weighted universal bit allocation outperforms a JPEG-style code by over 2.5 dB. On a collection of mixed test and image data, weighted universal transform coding outperforms a single, data-optimized transform code (which gives performance almost identical to that of JPEG) by over 6 dB.     

Filtering of colored noise for speech enhancement and coding

Scalar and vector Kalman filters are implemented for filtering speech contaminated by additive white noise or colored noise, and an iterative signal and parameter estimator which can be used for both noise types is presented. Particular emphasis is placed on the removal of colored noise, such as helicopter noise, by using state-of-the-art colored-noise-assumption Kalman filters. The results indicate that the colored noise Kalman filters provide a significant gain in signal-to-noise ratio (SNR), a visible improvement in the sound spectrogram, and an audible improvement in output speech quality, none of which are available with white-noise-assumption Kalman and Wiener filters. When the filter is used as a prefilter for linear predictive coding, the coded output speech quality and intelligibility are enhanced in comparison to direct coding of the noisy speech     

Deposition of Carotenoids in Eggs from Hens Fed Diets Containing Saponified and Unsaponified Oleoresin Paprika

Deposition of carotenoids in saponified paprika (SP) and unsaponified oleoresin paprika (OP) in egg yolks as well as the dietary level for desired pigmentation were evaluated. Sixty-four hens on a carotenoid-depletion diet were divided into two replicated groups of each of eight dietary treatments containing from 0 to 16 mg paprika carotenoids per kg feed. Colour and the carotenoid content of egg yolk increased linearly ( P< 0·01) with the amounts of paprika carotenoids in the diets. The colours of egg yolks from hens fed similar concentra-tions of OP or SP were not significantly different ( P< 0·01). A low dose (4 mg kg⁻¹) of OP or SP provided yolk colour equivalent to the colour of eggs in supermarkets. High-performance liquid chromatographic analyses showed that carotenoids deposited in the yolk are in the free alcohol form, regardless of the form of carotenoids in the diet. Capsanthin, the predominant carotenoid in paprika, was deposited in egg yolk less efficiently than zeaxanthin and lutein.     

Creating an effective security risk model for outsourcing decisions

Globalisation has had a fundamental impact on the way that business is conducted and approaches to sourcing work have evolved. Outsourcing is here to stay and the proportion of worldwide spend in this market-place will continue to rise. BT’s security community has successfully introduced a new risk model and supporting process to identify the key risk factors applicable to outsourcing, namely, specific environmental conditions, the number of third party personnel involved in the contract and the level of ‘trust’ given to these personnel. The importance of protective monitoring and audit regimes is highlighted from both a compliance and assurance perspective — and is being used to create effective engagement with outsourcing partners to raise security thresholds and discuss security issues. Globalisation, coupled with the requirement for more open networks, will continue to increase in the future and result in corporate infrastructure fragmentation and the breaking down of traditional boundaries. At the same time, approaches to security must also evolve — moving the focus from the infrastructure to the client, application and eventually the data level.     

Mediated Electrochemistry to Mimic Biology's Oxidative Assembly of Functional Matrices

Biology uses diffusible oxidants to perform functions that range from signaling to matrix assembly, and these oxidation chemistries offer surprising selectivities. Here, it is reported that mediated electrochemistry can access the richness of such oxidation chemistries. Specifically, electrode‐imposed voltage inputs are used to locally generate oxidized mediators that can diffuse into polymer solutions and induce the formation of covalent bonds for the deposition and functionalization of hydrogels at the electrode surface. Depending on the mediator's redox potential (E⁰), it is possible to “gate” the voltage inputs to target specific residues (e.g., thiols or amines) and oxidation chemistries. Further, mediators of varying E⁰ offer different reactivities and thus allow control of reaction‐diffusion rates to modulate the hydrogel's crosslink density and mechanical properties. Importantly, this mediated oxidation can be performed under physiologically relevant conditions to preserve labile biological functionalities (e.g., cell viability and protein function). Finally, it is demonstrated that protein fusion tags can be engineered to have “targetable” amino acid residues that enable protein function to be oxidatively conjugated to electrodeposited hydrogels. In summary, mediated electrochemistry can engage orthogonal oxidation chemistries to create functionalized matrices and thus mediated electrochemistry should add important capabilities to the electrofabrication toolbox.     

交错操作模数转换器,实现更高的采样率

设计人员经常试图组合多个模数转换器（ADC),以尽量提高有效采样率。尽管快闪转换器(仍然是最快的ADC体系结构)在高速制造工艺诞生之前就已经问世了,但工艺技术的种种限制使早期的快闪转换器速度局限于10～20Msps(Megosamples per second)的范围内。现在,我们拥有了一些允许以千兆赫兹速率采样的工艺速度和体系结构。     

Three orthogonal polarisation DRA-monopole ensemble

A dual feed HE/sub 11/spl delta// mode dielectric resonator antenna (DRA) loaded monopole antenna ensemble is described. The two antennas were unaffected by co-location, having coupling less than -25 dB at 2.33 GHz, making the ensemble capable of radiating all three orthogonal linear polarisations. The dielectric resonator antenna had an input impedance bandwidth of 1.9%, while the monopole gave 56%. This small volume ensemble antenna is suitable for mobile communications terminals.     

Dithering and its effects on sigma-delta and multistage sigma-delta modulation

The spectrum of the quantization error in a dithered sigma-delta modulator is derived under the constraint that the dithering signal does not cause overload. The results apply to DC, sinusoidal, and more general quasi-stationary signals. It is shown in the case of a simple sigma-delta modulation that no-overload dithering can smooth the error spectrum and can make the quantization error asymptotically uncorrelated with the input. It does not, however, make the quantization error white. In the case of multistage sigma-delta modulation with the appropriate dithering, the quantization error becomes white, even for a system with only two stages. The signal-to-quantization-noise ratio (SQNR) is derived for sigma-delta and multistage sigma-delta oversampled analog-to-digital conversion with additive dithering. Simulation results, are presented to support the theoretical analysis.<>     

Receiver array calibration using disparate sources

We present a new array calibration procedure for over-the-horizon (OTH) radar, using disparate sources. Unlike previous array calibration methods, which require a specific type or class of sources for calibrating the array, the method we propose can use combinations of single-mode, multimode, and near-field sources; each source with either known or unknown DOAs (directions-of-arrival). Multidimensional MUSIC is exploited for time-invariant DOA sources, while single-snapshot techniques are used for sources that have time-varying DOAs. A nonlinear separable least-squares solution to the array calibration problem is used to estimate the array coupling matrix and sensor positions. Simulation results indicate that good estimates are obtained for the unknown parameters and further the array sidelobe levels and bearing errors are significantly reduced when these estimated parameters are used in array processing. The algorithm performance was also compared with the Cramer-Rao lower bound and found to be statistically efficient