Unequal Error Protection Using Partially Regular LDPC Codes

In this paper, we propose a scheme to construct low-density parity-check (LDPC) codes that are suitable for unequal error protection (UEP). We derive density evolution (DE) formulas for the proposed unequal error protecting LDPC ensembles over the binary erasure channel (BEC). Using the DE formulas, we optimize the codes. For the finite-length cases, we compare our codes with some other LDPC codes, the time-sharing method, and a previous work on UEP using LDPC codes. Simulation results indicate the superiority of the proposed design methodology for UEP     

A translation matrix formulation for an arbitrarily interconnected stack of piezoelectric transducers

A new method of formulating the core matrix of a transducer model, which is in the form of a translation matrix, is presented. This method of formulation enables easy analysis of any arbitrary connection of a group of transducers and/or acoustic and electrical loads.     

New results on unequal error protection using LDPC codes

In this letter, we propose a new scheme to construct low-density parity-check (LDPC) codes that are suitable for unequal error protection (UEP). We derive UEP density evolution (UDE) formulas for the proposed ensemble over the binary erasure channel (BEC). Using the UDE formulas, high performance UEP codes can be found. Simulation results depict an improvement in the bit error rate of more important bits in comparison with previous results on UEP-LDPC codes.     

Low-density parity-check codes for volume holographic memory systems

We investigate the application of low-density parity-check (LDPC) codes in volume holographic memory (VHM) systems. We show that a carefully designed irregular LDPC code has a very good performance in VHM systems. We optimize high-rate LDPC codes for the nonuniform error pattern in holographic memories to reduce the bit error rate extensively. The prior knowledge of noise distribution is used for designing as well as decoding the LDPC codes. We show that these codes have a superior performance to that of Reed-Solomon (RS) codes and regular LDPC counterparts. Our simulation shows that we can increase the maximum storage capacity of holographic memories by more than 50 percent if we use irregular LDPC codes with soft-decision decoding instead of conventionally employed RS codes with hard-decision decoding. The performance of these LDPC codes is close to the information theoretic capacity.     

Terminal sliding mode observers for uncertain linear systems with matched disturbance

In this paper, a terminal sliding mode observer (TSMO) for systems with general state‐space representation is proposed. The effects of uncertainties and matched disturbances are incorporated in the system dynamics. Compared to conventional sliding mode observers, which are capable of finite time convergence of the measured states’ (outputs) errors and asymptotic convergence of unmeasured states’ errors, the proposed TSMO guarantees finite time convergence of all states. Three appropriate Lyapunov functions are defined for proving robust and finite time convergence of all state estimation errors of the TSMO. In addition, to highlight the effectiveness of the methodology, the developed TSMO is applied to a well‐known realistic wind turbine model. Results confirm that the proposed TSMO estimates all the states in finite time with good accuracy.     

Designing a hand rest tremor dynamic vibration absorber using H 2 optimization method

An optimal single DOF dynamic absorber is presented. A tremor has a random nature and then the system is subjected to a random excitation instead of a sinusoidal one; so the H ₂ optimization criterion is probably more desirable than the popular H _∞ optimization method and was implemented in this research. The objective of H ₂ optimization criterion is to reduce the total vibration energy of the system for overall frequencies. An objective function, considering the elbow joint angle, θ ₂, tremor suppression as the main goal, was selected. The optimization was done by minimization of this objective function. The optimal system, including the absorber, performance was analyzed in both time and frequency domains. Implementing the optimal absorber, the frequency response amplitude of θ ₂ was reduced by more than 98% and 80% at the first and second natural frequencies of the primary system, respectively. A reduction of more than 94% and 78%, was observed for the shoulder joint angle, θ ₁. The objective function also decreased by more than 46%. Then, two types of random inputs were considered. For the first type, θ ₁ and θ ₂ revealed 60% and 39% reduction in their rms values, whereas for the second type, 33% and 50% decrease was observed.     

Effects of incorporation of micro and nano Al2O3 layers on thermal shock behaviour of YSZ thermal barrier coatings

In the present paper, thermal shock behaviour of usual YSZ and layered composite TBCs was evaluated. The layered composite TBCs used in this study were YSZ/micro Al₂O₃ and YSZ/nano Al₂O₃ in which Al₂O₃ was as a topcoat on the YSZ layer. In addition, coating microstructures were investigated using scanning electron microscope; EDS and X-ray diffraction techniques before and after thermal shock test. The results showed that incorporation of a nano Al₂O₃ oxygen barrier layer caused better thermal shock resistance, while micro Al₂O₃ layer on the top of YSZ sample resulted in sooner coating failure, compared to the usual TBC coating. Also, the thermal shock behaviour and failure mechanism of mentioned coatings were investigated.     

Optimum bandpass optical filter synthesis using periodic corrugatedwaveguides with π/2 phase shifts

A graphical method is proposed for the synthesis of optical bandpass filters, using π/2-phase shift sections. Bandpass filters with the desired characteristics, such as central wavelength, bandwidth, ripple factor, selectivity, minimum attenuation etc., can be synthesized by proper choice of corrugation pitch, coupling coefficient, filter length, and the location of π/2-phase shift sections. This method is relatively simple as compared to the previous works. Besides, it allows to optimize certain criteria     

Rateless Codes With Unequal Error Protection Property

In this correspondence, a generalization of rateless codes is proposed. The proposed codes provide unequal error protection (UEP). The asymptotic properties of these codes under the iterative decoding are investigated. Moreover, upper and lower bounds on maximum-likelihood (ML) decoding error probabilities of finite-length LT and Raptor codes for both equal and unequal error protection schemes are derived. Further, our work is verified with simulations. Simulation results indicate that the proposed codes provide desirable UEP. We also note that the UEP property does not impose a considerable drawback on the overall performance of the codes. Moreover, we discuss that the proposed codes can provide unequal recovery time (URT). This means that given a target bit error rate, different parts of information bits can be decoded after receiving different amounts of encoded bits. This implies that the information bits can be recovered in a progressive manner. This URT property may be used for sequential data recovery in video/audio streaming     

Initial vertex partitioning and testing isomorphism of graphs and digraphs

In this paper, we present a new method for initial vertex partitioning of graphs (digraphs) using the notion of a vertex label that includes several parameters of the graph for each vertex of the graph (digraph). Our method provides a more refined initial vertex partitioning for graphs (digraphs) than any of the known methods in O(nE) time for a graph with n vertices and E edges. Several examples are given as illustrations of the method. A computational comparison of our method with the Schmidt-Druffel algorithm is presented. The method can be coupled with any existing good back-tracking method for testing isomorphism of graphs and digraphs.