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Abstract This paper presents a comprehensive and accurate algorithm based on circuit model to design reflect-array antennas (RAAs). The proposed algorithm can extract geometry of RAA structure corresponding to radiation parameters without employing any approximation or optimization intervention into the algorithm. Simulation results for some comprehensive examples, verify the validity of the proposed algorithm. This method is simple, fast, accurate, and can be expanded to all species of RAAs with arbitrary geometries. One of the main problems confronted in RAAs is low bandwidth characteristics. To attain wide bandwidth, we exploited the proposed algorithm with combination of multi-layer design of RAAs and subwavelength element. Convergence is observed between simulation and fabrication results, asserting good accuracy in method. In 10–15 GHz band, the maximum gain and -1dB bandwidth of two-layer antenna is 31.4 dB and 18.5%, respectively. [ABSTRACT FROM AUTHOR]

In this paper, we discuss four different optimization problems for distributed antenna systems (DAS) with and without D2D communication, respectively. The first and the third problems are maximizing spectral efficiency (SE) and energy efficiency (EE) of the DAS with D2D communication on the conditions of the minimum SE of DAS as well as D2D pair, the maximum transmit power of each remote access unit (RAU) and maximum transmit power of D2D transmitter. The second and the forth problems are maximizing SE of the DAS on the conditions of the minimum SE as well as the maximum transmit power of RAUs. We exploit the sub-gradient iteration method to obtain the optimal power allocation and summarize optimal power allocation algorithms for the first and second problems. We exploit fractional programming method to investigate the third and fourth problems and develop corresponding optimal power allocation algorithms. Simulation results demonstrate the effectiveness of the proposed power allocation algorithms and show the SE and EE of the DAS by using D2D communication are much better than DAS without D2D communication. [ABSTRACT FROM AUTHOR]

Proximity user equipments (UEs) in mobile networks may be communicated directly without passing their traffic through the base station by using device-to-device (D2D) communications. This can be done using the underlaying approach in which the D2D-UEs (DEs) are allowed to use the same resources allocated for cellular UEs (CEs), which can enhance the spectral efficiency. However, if the resource allocation for DEs is not designed appropriately, it would generate harmful interference on CEs communications. Therefore, this paper addresses a resource allocation and power control problems for D2D communications underlaying multi-cell mobile networks with the consideration of the inter-cell and intra-cell interferences. The problem is formulated to maximise the network performance in terms of achieved throughput while ensuring the quality-of-service (QoS) constraints for CEs and DEs. A two-step algorithm is proposed in which the admission control is performed firstly to determine the set of possible D2D connections and their CE partners that achieve the minimum QoS demands. Then, the optimal power for each permissible DE and its possible partners in different cells are allocated to maximise the network throughput. Simulation results illustrate that the suggested algorithm can remarkably enhance the performance of the network in terms of throughput gain and access rate. [ABSTRACT FROM AUTHOR]

With a small number of elements in uniform circular arrays (UCAs), the performance of beamspace transformation (BT) based methods for 2D direction-of-arrival (DOA) estimation in the presence of mutual coupling suffers serious degradation. The performance breakdown is associated with the residual term which is introduced by the BT. To solve this problem, a novel algorithm which modifies the beamspace data is proposed in this paper. Based on the estimated azimuth angles obtained by a UCA-RARE-like method and the estimated elevation angles obtained by a new searching method, the beamspace data is iteratively revised by removing its residual component. Thus, unbiased 2D DOA estimates can be obtained depending on the revised beamspace data. Simulation results are given to verify the effectiveness of the proposed algorithm and a comparison is made with results from existed methods. [ABSTRACT FROM AUTHOR]

In this paper, we present novel strategies for generating rate-compatible (RC) irregular low-density parity-check (LDPC) codes with short/moderate block lengths. We propose three puncturing and two extension schemes, which are designed to determine the puncturing positions that minimize the performance degradation and the extension that maximizes the performance. The first puncturing scheme employs a counting cycle algorithm and a grouping strategy for variable nodes having short cycles of equal length in the Tanner graph (TG). The second scheme relies on a metric called extrinsic message degree (EMD) and the third scheme is a simulation-based exhaustive search to find the best puncturing pattern among several random ones. In addition, we devise two layer-structured extension schemes based on a counting cycle algorithm and an EMD metric which are applied to design RC-LDPC codes. Simulation results show that the proposed extension and puncturing techniques achieve greater rate flexibility and good performance over the additive white Gaussian noise channel, outperforming existing techniques. [ABSTRACT FROM AUTHOR]

A systematic approach to I / Q mismatch calibration in image-reject receivers is presented in this paper. A new error detection algorithm is proposed, which automatically calibrates for phase and gain mismatches limiting the performance of image-reject receivers. A dual-loop feedback is employed which looks for the minimum phase/gain error using a 2-dimensional analog-based search algorithm and then finds the minimum value for the error. An experimental CMOS prototype RF front-end for cognitive radio applications operating at 400–800 MHz is proposed and simulated in the 0.18 μm CMOS technology, achieving an image rejection ratio (IRR) better than 55-dB in post-layout simulation. The comprehensive mathematical model of this analog algorithm is thoroughly studied in the appendix and the convergence is verified theoretically. [ABSTRACT FROM AUTHOR]

The greatest threat to the OFDM system is the loss of orthogonality between subcarriers due to the carrier frequency offset (CFO) which results in significant performance degradation. In addition to this last problem was the effect of propagation over multipath fading channel. Hence, both the channel and the CFO need to be estimated and corrected at the receiver for subsequent symbol detection. A new joint semi-blind CFO and channel estimation method for OFDM systems operating in multipath fading channels is investigated in this paper. The proposed algorithms are based on virtual subcarriers (VSC) in one hand and on a new design of pilot patterns in OFDM blocks in other hand. We propose to use Newton – Raphson algorithm for the estimation of CFO that has a faster convergence and a lower complexity compared to similar estimators that not employed this algorithm. Finally, we derive the Modified Cramer–Rao bounds (MCRB) for semi-blind CFO and channel estimation to evaluate the performance bounds of the proposed methods for commonly encountered scenarios. The simulation results are given to verify the validity of the proposed methods. [ABSTRACT FROM AUTHOR]

In this paper, an effective switching morphology-mean filter is proposed to remove impulse noise from digital images. The proposed method consists of two stages. The first stage is to detect the impulse noise in an image. The second stage is to construct adaptive structuring elements and remove the impulse noise. In this stage, the “noise-pixels” are filtered out by using the morphology-mean filter, and the “noise-free pixels” are copied directly to the output image. The proposed filter uses the window of size 3 × 3 pixels. Simulation results show that the proposed method outperforms some existing algorithms for high-density impulse noise, both in vision and quantitative measurements. Moreover, our method can preserve effectively the details in an image, and has less processing time. [ABSTRACT FROM AUTHOR]

Wireless devices integrating more and more features in ever-smaller packages have become integral part of everyone's daily life. These systems have seen a continuous push to profit from digital signal processing techniques, in which signals are no longer traditional continuous amplitude and/or phase-modulated carriers, but became pulsed waveforms where the amplitude and/or phase are coded in some on–off digital scheme. This on–off scenario has been addressing new challenges to the circuit-level simulation of such systems. Having this in mind this paper aims to propose an innovative time–frequency simulation technique based on a switch mode algorithm, which is specially conceived for the efficient numerical simulation of RF circuits whose stimuli are intermittently turned on and off for unknown periods of time. At present, to simulate this category of circuits commercial tools have no choice than to make use of full conventional SPICE algorithms. This paper suggests an alternative way, which can result in significant speedups, without perceptible loss in accuracy. [ABSTRACT FROM AUTHOR]

Abstract: Techniques employed in the synthesis of antenna arrays vary from complex analytical methods to iterative numerical methods based on optimisation algorithms. The drawback of these techniques is that they usually consider the array factor but not the interaction between array elements and real-time problems. This omission induces an error in the resultant radiation pattern; therefore, the physical relations between the array feeding details and the corresponding radiation patterns are taken into account to improve the accuracy. The behaviour of an antenna array is nonlinear in nature, resulting in an extremely high complexity using this approach, and it is usually disregarded. A neural-network-based solution can avoid complexity by establishing a relation between the desired radiation patterns and feeding details such as voltage and spacing in the real antenna array and can help convert the real array into a smart array. Several neural network applications in smart antenna array synthesis are reviewed in this paper. [Copyright &y& Elsevier]

Abstract: Based on higher-order statistics and synchronization code, we propose a new digital audio watermarking algorithm with good auditory quality and reasonable resistance toward desynchronization attacks in this paper. Firstly, the wavelet de-noising is performed on the original host audio, the de-noised digital audio is segmented, and then each segment is cut into two parts. Secondly, with the spatial watermarking technique, synchronization code is embedded into the statistics average value of audio samples in the first part. And then, the higher-order statistics are obtained by using the Hausdorff distance. Finally, the digital watermark is embedded into the original audio signal in wavelet domain by using the higher-order statistics. Simulation results show that the proposed watermarking scheme is not only inaudible and robust against common signal processing such as MP3 compression, noise addition, resampling, re-quantization, etc., but also robust against the desynchronization attacks such as random cropping, amplitude variation, pitch shifting, jittering, etc. [Copyright &y& Elsevier]

Abstract: In this paper, we present a modification on delay estimation and tracking using the unscented filter for an asynchronous CDMA system. The algorithm is based on utilizing the minimum excess mean square error criteria (MEMSEC) in deriving the filter update equation. Computer simulations are presented to illustrate the new filter''s performance. More specifically, the delay estimation errors for multipath multiuser CDMA systems are evaluated using the unscented and the proposed modified unscented filters. The results show that the modified unscented filter tracks the delay variations with less errors than the unscented filter. [Copyright &y& Elsevier]

Abstract: In wireless networks, end-to-end communication depends on link capacities which, in turn, are determined by transmit powers of interfering links. Optimal network performance and energy efficiency can be achieved by jointly optimizing congestion control and power control. In this paper, we study this joint optimization problem by formulating it into convex programming, i.e., we maximize a compound function which is a network utility function minus a factor, named tradeoff factor, of the associated power cost. We prove that this tradeoff factor is essential for good energy efficiency while maintaining the network throughput at a satisfactory level. The problem is solved by a distributed dual-decomposition based algorithm energy efficient jointly optimal congestion and power control (EJOC). EJOC tackles the power control problem in a recursive manner, operating as easily as the steepest descent method but converging much faster. This optimization framework is further extended to networks where each data source may have multiple alternative paths to its destination. Simulation results show that the proposed algorithm converges faster than other algorithm and is capable of significantly improving the energy efficiency of the network. [Copyright &y& Elsevier]

Abstract: This paper proposes and compares four block joint detection algorithms for the orthogonal frequency division multiplexing (OFDM)-code division multiple access (CDMA) communication systems. The performance of the proposed OFDM-CDMA joint detectors with orthogonal and non-orthogonal spreading sequences are investigated in mobile radio channels. The proposed OFDM-CDMA detectors are zero forcing (ZF) and minimum mean square error (MMSE) detectors with decision feedback (DF) structures. The proposed joint detectors do not require discrete Fourier transform (DFT) or fast Fourier transform (FFT) operations and can be used to compensate the channel distortion. Hence for hardware implementation, the proposed detectors are more efficient than the conventional methods. The channel sorting method offers approximately 2dB gain for the DF joint detectors and reduces the impairing effect of error propagation. The bit error rate (BER) performance of orthogonal codes is better than that of non-orthogonal ones in time varying channels. Simulation examples are given to demonstrate the effectiveness of the proposed detectors. [Copyright &y& Elsevier]

Abstract: A rule-based segmentation algorithm for color images has been presented in this paper. The proposed strategy is similar to region growing algorithm where the seed points are automatically selected and grown. The similarity percents of neighboring pixels are calculated by means of fuzzy reasoning rules, and the merging of the pixels with regions is performed by comparing the similarity percent with the similarity threshold value. The algorithm does not require any prior knowledge of the number of regions existing in the image and decreases the computational load required for the fuzzy c-means (FCM). Several computer simulations have been performed and the results have been discussed. The simulation results indicate that the proposed algorithm yields segmented color image of perfect accuracy. [Copyright &y& Elsevier]

Abstract: In this paper, a novel solution to bit-loading algorithm for Discrete MultiTone modulation (DMT) systems is proposed. Simulation results, using the carrier serving area (CSA) loops in an ADSL environment impaired by crosstalk, show that the proposed algorithm converges more rapidly than the Campello algorithm, which is the fast algorithm that can be efficiently implemented in practice among those proposed in the past. [Copyright &y& Elsevier]

In this paper, an optimum sequence estimation algorithm for wireless systems with Alamouti's two transmitter diversity in the presence of multipath fading is proposed. The algorithm is based on a jointly iterative channel and sequence estimation according to the maximum likelihood (ML) criterion, using the Expectation-Maximization (EM) algorithm employing an M-level phase-shift keying (M-PSK) modulation scheme with additive Gaussian noise. The discrete multipath channel is represented in terms of the channel gains from each transmit antenna to the receive antenna. EM algorithm estimates jointly the complex channel parameters of each channel and the data sequence transmitted iteratively, which converges to the true ML solution. The channel estimation is achieved in a simple way through the iterative equations by decoupling of the signals transmitted from different antennas. The algorithm is applied to the trellis coded modulation systems and the efficiency of the algorithm proposed has been shown with computer simulations. The simulation results show that the EM algorithm converges quickly for fast fading channels. The performance of the EM-based decoder approaches that of the ML receiver which has perfect knowledge of the channel. [ABSTRACT FROM AUTHOR]