Distributed differential space-time coding for wireless relay networks

Distributed space-time coding is a cooperative transmission scheme for wireless relay networks. With this scheme, antennas of the distributive relays work as transmit antennas of the sender and generate a space-time code at the receiver. It achieves the maximum diversity. Although the scheme needs no channel information at relays, it does require full channel information, both the channels from the transmitter to relays and the channels from relays to the receiver, at the receiver. In this paper, we propose a differential transmission scheme, which requires channel information at neither relays nor the receiver, for wireless relay networks. As distributed space-time coding can be seen as the counterpart of space-time coding in the network setting, this scheme is the counterpart of differential space-time coding. Compared to coherent distributed space-time coding, the differential scheme is 3dB worse. In addition, we show that Alamouti, square real orthogonal, and Sp(2) codes can be used differentially in networks with corresponding numbers of relays. We also propose distributed differential space-time codes that work for networks with any number of relays using circulant matrices.     

Graphene functionalized decellularized scaffold promotes skin cell proliferation

An increasing number of new strategies for skin tissue engineering have been developed with the potential to mimic the biological properties of native tissue with a high degree of complexity, flexibility, and reproducibility. In this study, decellularized tissue (DT) was prepared from the bovine heart by using chemical treatments. However, the mechanical properties of the DT constructs were poorer than the extra cellular matrix of the skin tissue. To overcome this challenge, hybrid scaffolds of DT and graphene oxide (GO) were developed and the effects of the GO concentration on the morphology, pore size, porosity, mechanical strength, and water uptake capacity of the samples were evaluated. Moreover, the biocompatibility of hybrid scaffolds was studied by Live/Dead staining. The results show that a hybrid scaffold incorporating 3 % graphene oxide improved the mechanical strength and cell viability by ~25 % in comparison to the DT scaffolds. Cell viability results confirmed that the porous scaffolds could support cell adhesion, proliferation, and cell activity for 7 days. This study provides new insight into and opportunities for using graphene-based materials to develop biomimetic constructs for clinical applications.     

Combining Beamforming and Space-Time Coding Using Noisy Quantized Feedback

The goal of combining beamforming and spacetime coding is to obtain full-diversity order and to provide additional received power (array gain) compared to conventional space-time codes. In this work, a class of code constellations is proposed, called generalized partly orthogonal designs (PODs) and both high-rate and low-rate feedback information is incorporated with possible feedback errors. A binary symmetric channel (BSC) model characterizes feedback errors. Two cases are studied: first, when the BSC bit error probability is known a priori to the transmission ends, and second, when it is not known exactly. Based on a minimum pairwise error probability (PEP) design criterion, we design a channel optimized vector quantizer (COVQ) for feedback information and a precoder matrix codebook to adjust the transmission codewords. The attractive property of our combining scheme is that it converges to conventional space-time coding with low-rate and erroneous feedback and to directional beamforming with high-rate and error-free feedback. This scheme also shows desirable robustness against feedback channel modeling mismatch.     

Comparison of different methods of classification in subband codingof images

This paper investigates various classification techniques, applied to subband coding of images, as a way of exploiting the nonstationary nature of image subbands. The advantages of subband classification are characterized in a rate-distortion framework in terms of "classification gain" and overall "subband classification gain." Two algorithms, maximum classification gain and equal mean-normalized standard deviation classification, which allow unequal number of blocks in each class, are presented. The dependence between the classification maps from different subbands is exploited either directly while encoding the classification maps or indirectly by constraining the classification maps. The trade-off between the classification gain and the amount of side information is explored. Coding results for a subband image coder based on classification are presented. The simulation results demonstrate the value of classification in subband coding.     

Novel Transmit Beamforming Schemes for Time-Selective Fading Multiantenna Systems

Transmit beamforming has been widely adopted for wireless systems with multiple transmit antennas. For a block fading channel, the Grassmannian beamformer has been shown to provide very good performance for finite rate feedback. However, the original Grassmannian beamformer does not take the time domain correlation of the channel fading into consideration. In this paper, based on a first-order autoregressive (AR1) dynamic fading model, we develop two new classes of beamforming algorithms that exploit the interframe correlations in the channel fading. We first introduce an algorithm based on a standard predictive vector quantization (PVQ) approach, and the resulting PVQ beamformer accomplishes superior power delivery at the receiver. However, the error performance of the PVQ beamformer is not satisfactory at high signal-to-noise ratios, and it also has a high implementation complexity. To resolve these issues, we then develop a novel successive beamforming (SBF) algorithm. The new SBF scheme uses the knowledge of the previous fading blocks to aid the beamforming codebook design of the current fading block. The beamforming codebook is constructed based on the successive partition of the surface of a spherical cap. The new SBF scheme accomplishes nearly the same performance as that of the PVQ beamformer, and it has a much simpler implementation. Through numerical simulations, we demonstrate that the proposed beamformers outperform the other previously proposed beamformers at various fading scenarios     

Space–Time Trellis Codes Based on Channel-Phase Feedback

Space-time coding (STC) has been proposed recently for multiple-antenna wireless communication systems. Most of the proposed STC schemes use the assumption that either no channel-state information, or the channel mean/covariance information, is available at the transmitter. In this paper, we propose a new STC scheme for a closed-loop transmission system, where quantized channel-phase information is available at the transmitter. A new performance criterion is derived for the quasi-static fading channel. This design criterion is then used to construct a new class of space-time trellis codes (STTCs). The proposed code construction is based on the concatenation of a standard multiple trellis-coded modulation outer code with an inner code. The inner code is selected from a series of inner codes using the channel-phase feedback. The series of inner codes are constructed based on the systematic set partitioning of several classes of space-time signal designs. Simulation results show significant performance improvement over the other STTCs in the literature. In addition, the proposed coding scheme enjoys low peak-to-average-power ratio, simple decoding, and power-efficient low-cost implementation     

Fast reconstruction of subband-decomposed progressively transmittedsignals

We propose a fast reconstruction method for a subband-decomposed, progressive signal coding system. We show that unlike the conventional approach which requires a fixed computational complexity, the computational complexity of the proposed approach is proportional to the number of refined coefficients at each level of progression. Therefore, unrefined coefficients do not add to the computational complexity of the proposed scheme. It is shown, through specific examples, that the proposed approach can lead to significant reductions in reconstruction complexity. Furthermore, the proposed approach provides the capability for an online updating of the reconstructed image based on receiving the refinement of each coefficient.     

Finite Element Model Updating Using Evolutionary Strategy for Damage Detection

Abstract: Structural health monitoring through the use of finite element model updating techniques for dispersed civil infrastructures usually deals with minimizing a complex, nonlinear, nonconvex, high‐dimensional cost function with several local minima. Hence, stochastic optimization algorithms with promising performance in solving global optimization problems have received considerable attention for finite element model updating purposes in recent years. In this study, the performance of an evolutionary strategy in the finite element model updating approach was investigated for damage detection in a quarter‐scale two‐span reinforced concrete bridge system which was tested experimentally at the University of Nevada, Reno. The damage sequence in the structure was induced by a range of progressively increasing excitations in the transverse direction of the specimen. Intermediate nondestructive white noise excitations and response measurements were used for system identification and damage detection purposes. It is shown that, when evaluated together with the strain gauge measurements and visual inspection results, the applied finite element model updating algorithm of this article could accurately detect, localize, and quantify the damage in the tested bridge columns throughout the different phases of the experiment.     

An Efficient Progressive Bitstream Transmission System for Hybrid Channels With Memory

We consider progressive transmission over a hybrid channel introducing bit errors and packet erasures. The existing solutions are analyzed and extended to the case of a channel that exhibits memory on both bit errors and packet erasures. We then propose a simple, low-complexity coding scheme that transforms the hybrid channel into a channel with a single impairment for which various optimization techniques exist. Both rate-based and distortion-based optimization problems are investigated. It is shown that our proposed solution has lower channel coding and rate-distortion optimization complexities compared to the known solutions. Simulation results for channels with and without memory show the effectiveness of our proposed solution over a wide range of operating conditions. Numerical results also indicate that the rate-based solution of our proposed algorithm is very close to the corresponding distortion-based solution