Analysis of link-layer backoff schemes on point-to-point Markov fading links

Backoff algorithms are typically employed in multiple-access networks (e.g., Ethernet) to recover from packet collisions. We propose and carry out the analysis for three types of link-layer backoff schemes, namely linear backoff, exponential backoff, and geometric backoff, on point-to-point wireless fading links where packet errors occur non-independently. In such a scenario, the backoff schemes are shown to achieve better energy efficiency without compromising much on the link layer throughput performance.     

Transmit diversity for combined 2G and 3G CDMA systems

In this letter, we propose modifications to existing transmit-diversity techniques to provide transmit diversity in code-division multiple-access cellular systems which must support both second-generation and third-generation mobiles on a common carrier. The proposed method, which we call symmetric-sweep transmit diversity, combines phase-sweep transmit diversity (PSTD) and space-time spreading (STS) in a way that allows second-generation and non-STS-capable mobiles to obtain the full advantage of PSTD, while third-generation mobiles obtain the full advantage of STS.     

Adaptive estimation of hidden nearly completely decomposable Markov chains with applications in blind equalization

This paper proposes maximum likelihood (ML) estimation schemes for nearly completely decomposable Markov chains (NCDMCs) in white Gaussian Noise. Aggregation techniques based on stochastic complementation are applied to significantly reduce the dimension of the resulting hidden Markov model (HMM) and hence substantially reduce the computational requirements of the estimation algorithms. Stochastic complementation results in exact aggregation in that no approximations are involved in the steady state probability distribution of the Markov chain. We then present an off-line estimation algorithm for the parameters and states of the HMM based on the estimation of the aggregated HMM. This off-line algorithm is an ML estimation scheme and is based on the expectation maximization (EM) algorithm. It has a significantly reduced computational complexity compared with the standard (full-order) EM-based HMM estimation scheme. Finally we present an application of our techniques. We show that hidden NCDMCs can be used to formulate the blind equalization problem for noisy FIR channels with Markov inputs, e.g. phase-shiftkeyed (PSK) signals. We then propose recursive EM and gradient estimation techniques for the aggregated HMM resulting in on-line estimates of the channel coefficients and signal estimate. For an N_a-state Markov chain our aggregate-based estimation scheme has a computational complexity O(N^?2_a), whereas standard algorithms have a complexity O(N_a^{?L + 1}) at each time instant, where L is the length of the FIR channel.     

Functionalized Cellulose for Water Purification,Antimicrobial Applications,and Sensors

As the most abundant natural polymer, cellulose presents a unique advantage for large‐scale applications. To fully unlock its potential, the introduction of desired functional groups onto the cellulose backbone is required, which can be realized by either chemical bonding or physical surface interactions. This review gives an overview of the chemistry behind the state‐of‐the‐art functionalization methods (e.g., oxidation, esterification, grafting) for cellulose in its various forms, from nanocrystals to bacterial cellulose. The existing and foreseeable applications of the obtained products are presented in detail, spanning from water purification and antibacterial action, to sensing, energy harvesting, and catalysis. A special emphasis is put on the interactions of functionalized cellulose with heavy metals, focusing on copper as a prime example. For the latter, its toxicity can either have a harmful influence on aquatic life, or it can be conveniently employed for microbial disinfection. The reader is further introduced to recent sensing technologies based on functionalized cellulose, which are becoming crucial for the near future especially with the emergence of the internet of things. By revealing the potential of water filters and conductive clothing for mass implementation, the near future of cellulose‐based technologies is also discussed.     

Electro-Discharge Machining of Inconel 825 Super alloy: Effects of Tool Material and Dielectric Flushing

Aspects of machinability of Inconel 825 super alloy during electro-discharge machining was attempted in this work. The extent of machinability was investigated in purview of process performance (i.e. material removal rate), surface integrity (morphology as well as topography) of the EDMed work surface including surface roughness, surface crack density, white layer thickness, and micro-indentation hardness. Effects of variation of tool material (graphite, tungsten, brass and copper) were analyzed in this work. Metallurgical characteristics of the EDMed work surface were studied in view of phase information (matrix and precipitates), grain refinement (crystallite size, micro-strain and dislocation density) etc. Results were further interpreted in support of EDS, and micro-hardness test data. Additionally, effects of flushing condition (with and without flushing) of the dielectric medium were examined on influencing EDM performance on Inconel 825 work material. Moreover, effects of peak discharge current on EDM responses were discussed.

     

Functional modelling,validation and testing of analog to digital converters (ADC) from system design perspective

In this paper a methodology to develop PSpice (SPICE) model for flash type analog to digital converters and its validation is presented. With the onset of the Internet of Things and ongoing digitization of electronic devices around us, almost every device needs an interface or controlling unit as a digital computing device. As more and more products perform calculations in the digital or discrete time domain, more sophisticated data converters must translate the digital data to and from our inherent analog world. This varied nature of interfaces necessitates simulation of ADC along with a functional simulation of the system to optimize the performance of design and improve reliability. The paper focuses on the development of a functional model for ADC which can expedite system development. The design philosophy was at the block level and the development was conducted for commercially available ADC, AD7828. The complete model has been simulated using PSpice and results were compared with laboratory test measurements using AD7828.     

New Analytical Expressions for ASEP of Modulation Techniques with Diversity Over Lognormal Fading Channels with Application to Interference-Limited Environment

In this paper, the analytical expressions of the average symbol error probability (ASEP) for both coherent and non-coherent modulation formats with diversity schemes such as maximal ratio combining (MRC), equal-gain combining (EGC), and selection combining (SC) over the lognormal (LN) distribution assuming independent and identically distributed (i.i.d.) channels have been derived. The functions involving LN distribution are simplified using the Gauss–Hermit and Gaussian Quadrature integration. Furthermore, the effect of the diversity order and constellation size on the error probability has been examined extensively under various shadowing conditions such as infrequent light, average, and frequent heavy shadowing. As an application, the derived results are used to analyze the performance of the communication systems over the interference-limited environment. The impact of the number of interferers on important performance metrics such as the outage probability, the ASEP, and the channel capacity has been examined. The accuracy of the analytical results are validated by comparing them with the exact numerical results and Monte Carlo simulations. The analytical expressions are simple and easily implementable in software package such as MATLAB. The proposed analytical expressions are supposed to be a vital tool in areas such as IEEE 802.15.3a wireless communication system, indoor environment, radio channel effect by body worn devices, ultra-wideband indoor channel.     

Image formation in detuned interference-filter-aided in-line Fraunhofer holography

Detuned interference filters as Fourier processors can be used to enhance the poor fringe contrast often encountered with in-line Fraunhofer holography of small or many far-fields-away micro-objects. The subsequent effect on the reconstructed-image irradiance distribution is described. The modified aperture-limited image shape and size, and the possible consequences on the quantitative analysis are discussed.