Quasi-static crushing behaviour of hybrid and non-hybrid natural fibre composite solid cones

A comprehensive experimental investigation of the quasi-static axial crushing of hybrid and non-hybrid natural fibre/polyester composite solid cones between flat platens has been carried out. The composite solid cones were fabricated from two types of natural fibres namely oil palm fibre and coir fibre and different vertex angles varied from 0° to 60°. Typical load-deformation histories are presented and discussed. Crashworthiness parameters such as load carrying capacity; energy absorption capability and failure mechanism have been discussed. The results presented in this study will help us to understand the behaviour and characteristics of natural fibre composite as a filler material.     

Experimental optimization of composite collapsible tubular energy absorber device

A four-phase program to improve the specific energy absorbed by axially crushed composite collapsible tubular energy absorber devices was undertaken. In the first phase, examining of the crushing behaviour of non-triggered tubes was carried out. The second phase is aimed at obtaining the best position for the triggered wall. The third phase focuses on the effects of material sizing in order to understand the influence of triggered wall length on the responses of composite circular tubes to the axial crushing load. The results of these three phases of the study contribute to the fourth whose objective is to optimize the shape geometry of the cross-section area to further improving in tube energy absorption capability. The experimental results demonstrated the strong potential benefits of optimizing the material distribution. The sizing and shape optimization of composite collapsible tubes exhibited a pronounced effect on their capability to absorb high specific energy under axial compressive load.     

Cross-layer based transmit antenna selection for decision-feedback detection in correlated Ricean MIMO channels

In this paper, we investigate a cross-layer transmit antenna selection (AS) approach for the decision-feedback detector (DFD) over spatially correlated flat Ricean fading multiple-input multiple-output (MIMO) channels. Closed-form expressions for the system throughput with both perfect and imperfect channel estimation are derived. Considering a training-based channel estimation technique, we show that the capacity-based AS is more robust to imperfect channel estimation. However, in all cases, the cross-layer AS delivers higher throughput gains than the capacity-based AS.     

Quasi-static axial and lateral crushing of radial corrugated composite tubes

This paper presents the effect of corrugation geometry on the crushing behavior, energy absorption, failure mechanism, and failure mode of woven roving glass fibre/epoxy laminated composite tube. Experimental investigations were carried out on three geometrical different types of composite tubes subjected to axial and lateral compressive loadings. On the addition to a radial corrugated composite tube, cylindrical composite tube, and corrugated surrounded by cylindrical tube were fabricated and tested under the same condition in order to know the effect of corrugation geometry. The results showed that the loading carrying capability is significantly influenced by corrugation geometry in axial crushing. However, no affect of corrugation geometry was observed for lateral crushing. Load–displacement curve was plotted for all conducted tests, thus clear comparison between different specimen's geometry was achieved. It is also found that radial corrugation could significantly applicable as a stable and effective energy absorber.     

Limitation of the frequency stability by local oscillator phase noise: new investigations and natural improvements

In frequency standards in which the atoms have a continuous interaction with the probe signal, local oscillator phase noise may limit medium term frequency stability. This spurious effect cannot be suppressed whenever there Is any truncation in the spectrum of the resonator response. Nevertheless, a simultaneous processing of the probe signal, similar to that of the NIST, and of the resonator response (by means of an appropriate demodulation) makes it possible to reduce this limiting effect. Previously achieved with a square wave frequency modulation, this result is now extended to various frequency modulations. An uncontrolled distortion in the demodulation waveform may significantly degrade the performance. For the case of a square wave phase modulation, the limiting effect also exists, but it is smaller than for a frequency modulation. When the phase noise of the local oscillator is naturally "not flat", it is possible to easily reduce the spurious effect: using the quasi-static approximation, one can calculate various optimized demodulation waveforms and the corresponding improvements. For the simplest optimized demodulation (f (M), 3f(M)), theoretical predictions are experimentally confirmed for flicker phase noise and flicker frequency noise.     

Code detection in turbo source coding

We consider the lossless compression of binary memoryless sources using a library of turbo codes. The message is compressed by each code and the best result along with the index of the applied code is sent to the decoder. Instead of transmitting the code index, we find a criterion to detect the code index using the transmitted parities. Our method helps to reduce the compression rate of short block length turbo source coders.     

Modified genetic algorithms for manufacturing process planning in multiple parts manufacturing lines

Manufacturing process planning for multiple parts manufacturing is cast as a hard optimization problem for which a modified genetic algorithm is proposed in this paper. A cyclic crossover operation for an integer-based representation is implemented to ensure that recombination will not result in any violation of processing constraints. Unlike classical approaches, in which the mutation operator alone is used to foil the tendency towards premature convergence, a combination of a neighborhood search based mutation operator and a threshold operator were implemented. This combined approach was designed to; (a) improve the exploring potential and (b) increase population diversity of neighborhoods, in the genetic search process. Capabilities of a modified genetic algorithm method were tested through an application example of a multiple parts reconfigurable manufacturing line. Simulation results show that the proposed modified genetic algorithm method is more effective in generating manufacturing process plans when compared to; a simple genetic algorithm, and simulated annealing. A computational analysis indicates that improved, near optimal manufacturing process planning solutions for multiple parts manufacturing lines can be obtained by using a modified genetic algorithm method.     

A green scheduling with adaptive spatial division multiple access grouping for multi‐user coordinated multi‐point networks

Multi‐User Coordinated Multi‐Point (MU‐CoMP), which couples CoMP with Multi User‐Multiple Input Multiple Output (MU‐MIMO), appears as a promising solution to enhance the Long Term Evolution‐Advanced (LTE‐A) system performance. However, some challenging issues in MU‐CoMP networks require more investigation. First, the set of users transmitting under CoMP mode should be properly identified. Secondly, time‐frequency resource should be efficiently partitioned between CoMP and non‐CoMP users in order to improve the system radio capacity. Thirdly, a fair and green scheduler is much needed for a more energy efficient system. This paper deals with these three issues. We propose an adaptive transmission mode selection according to the total load in the cluster and to users' quality of service. The adequate size of the Spatial Division Multiple Access users' groups is also analyzed. We finally propose a new scheduling algorithm to further enhance the radio capacity and the energy consumption in the cluster. Simulations results showed that significant improvements are obtained in terms of total system throughput and outage probability in the cluster with our proposed scheme. Moreover, energy efficiency has increased by four times with our proposed scheduling algorithm as compared to commonly used schedulers. Copyright © 2015 John Wiley & Sons, Ltd.     

A multi‐mode IFFT/FFT processor for IEEE 802.11ac: design and implementation

In this paper, we present 64/128/256/512‐point inverse fast Fourier transform (IFFT)/FFT processor for single‐user and multi‐user multiple‐input multiple‐output orthogonal frequency‐division multiplexing based IEEE 802.11ac wireless local area network transceiver. The multi‐mode processor is developed by an eight‐parallel mixed‐radix architecture to efficiently produce full reconfigurability for all multi‐user combinations. The proposed design not only supports the operation of IFFT/FFT for 1–8 different data streams operated by different users in case of downlink transmission, but also, it provides different throughput rates to meet IEEE 802.11ac requirements at the minimum possible clock frequency. Moreover, less power is needed in our design compared with traditional software approach. The design is carefully optimized to operate by the minimum wordlengths that fulfill the performance and complexity specifications. The processor is designed and implemented on Xilinx Vertix‐5 field programmable gate array technology. Although the maximum clock frequency is 377.84 MHz, the processor is clocked by the operating sampling rate to further reduce the power consumption. At the operation clock rate of 160 MHz, our proposed processor can calculate 512‐point FFT with up to eight independent data sequences within 3.2~μs meeting IEEE 802.11ac standard requirements. Copyright © 2015 John Wiley & Sons, Ltd.     

Distributed opportunistic scheduling for MIMO underlay cognitive radio networks

Cognitive radio networks have emerged to improve the utilization of the scarce spectrum. In this paper, we propose a distributed resource allocation algorithm that allocates resources opportunistically to the secondary users in a multiple‐input multiple‐output environment. In order to reduce the complexity and cost, antenna selection schemes are employed to allow the secondary communication using a single radio frequency chain. The proposed algorithm is proved theoretically and using simulations, to give a performance very close to that of a centralized one with lower delay and overhead. Furthermore, we introduce two techniques for the proposed algorithm based on the allowable data rates referred to as limited and maximum rates. We derive closed‐form expression for the consumed power and tight upper bounds for the average throughput achieved by each technique. A comparison between the proposed techniques is also provided. Both simulations and analytical results show that the proposed algorithm achieves high throughput with low complexity. Moreover, the results show that the tightness of the bounds improves with the diversity order. Finally, the proposed techniques are compared with two suggested random schemes to investigate their effectiveness. Copyright © 2016 John Wiley & Sons, Ltd.