Joint Synchronization and Channel Estimation for OFDM Systems

1Introduction Orthogonal Frequency Division Multiplexing(OFDM) has become a popular technique for transmis-sion of signals over wireless channels . OFDMhas beenadoptedinseveral wireless standards such as Digital Au-dio Broadcasting ( DAB) , Digital Video Broadcasting(DVB-T) ,the IEEE 802 .11a[1]Local Area Network(LAN) standard and high performance LAN type 2(HIPERLAN/2)[2]standard. OFDMis also being pur-sued for Dedicated Short-Range Communications(DSRC) for road side to …     

Joint Frequency Offset and Channel Estimation for MIMO Systems in the Presence of Timing Error

This paper deals with the problem of joint frequency offset (FO) and channel estimation for multi-input multi-output (MIMO) systems in the presence of a timing error. Two equivalent signal models with FO and a timing error are given, and then a joint estimation method is derived. The proposed estimation method consists of two steps. Firstly, a maximum likelihood (ML) FO estimator is proposed based on the second signal model. Secondly, based on the FO estimate, we formulate the timing error and channel estimation as a problem of composite hypothesis testing according to the first signal model, and then solve the problem using a composite hypothesis testing approach. Simulation results are performed to show the effectiveness of the proposed method.     

Robust Channel Estimation and Multiuser Detection for MC–CDMA Systems Under Narrowband Interference

In this paper, we present a robust adaptive channel estimator and a robust multiuser detector for wireless multicarrier code-division multiple access (MC–CDMA) systems under narrowband interference (NBI). The conventional least-squares (LS) channel estimator performs poorly when narrowband interfering signals contaminate the multicarrier systems. A new weighted recursive least M-estimate (WRLM) channel estimator is hence developed to estimate multipath fading channels in the presence of NBI. The new robust channel estimator resorts to M-estimate and weighted least-squares (WLS) techniques. Simulations show that the WRLM channel estimator offers substantial performance gain over conventional recursive least-squares (RLS), recursive least M-estimate (RLM) and weighted RLS (WRLS) channel estimators under NBI. With the estimated channel coefficients, a robust multiuser detector is proposed to jointly suppress multiple access interference (MAI) and NBI. The performance of the linear decorrelator will degrade substantially in the presence of NBI. A weighted least M-estimate (WLM) algorithm is therefore developed to combat the NBI. The WLM multiuser detector is also based on the weighted M-estimate concept. Numerical results show that the proposed WLM multiuser detector significantly outperforms over the conventional linear decorrelator, the robust decorrelator with M-estimate and the WLS detector under NBI.

Low-Complexity Joint Weighted Neumann Series and Gauss–Seidel Soft-Output Detection for Massive MIMO Systems

We introduce a joint weighted Neumann series (WNS) and Gauss–Seidel (GS) approach to implement an approximated linear minimum mean-squared error (LMMSE) detector for uplink massive multiple-input multiple-output (M-MIMO) systems. We first propose to initialize the GS iteration by a WNS method, which produces a closer-to-LMMSE initial solution than the conventional zero vector and diagonal-matrix based scheme. Then the GS algorithm is applied to implement an approximated LMMSE detection iteratively. Furthermore, based on the WNS, we devise a low-complexity approximate log-likelihood ratios (LLRs) computation method whose performance loss is negligible compared with the exact method. Numerical results illustrate that the proposed joint WNS-GS approach outperforms the conventional method and achieves near-LMMSE performance with significantly lower computational complexity.

     

Innovator: what does it take to be one?

Innovation continues to be an ever-more-critical issue as the global economy expands: it determines organizational sustainability. This paper addresses the issues of whether you want to become an innovator and how to become an innovator, from the innovator's perspective. Research on innovation has not provided a theory of innovation. The process of innovation continues to depend on the individual and the environment in which the innovator functions. This paper characterizes the scope and complexity of being the innovator, presents a set of concepts that can be applied in formulating, evaluating, and implementing innovation, considers the skills for dealing with technological uncertainty, and defines the issues that determine success or failure. There are no recipes for becoming the innovator, but there are basics that must be followed. This paper presents an overview of innovation, discusses types of innovation, provides insight to the innovation process, describes what it takes to be an innovator, considers the issues in overcoming resistance to innovation, and explains why innovators fail     

Robust Stochastic Stabilization and H �� Control for?Neutral Stochastic Systems with Distributed Delays

This paper considers the problem of robust stabilization and H _∞ control for a class of uncertain neutral stochastic systems, in which delay is distributed and the parametric uncertainties are norm-bounded. By designing a state feedback controller, we obtain a delay-dependent criterion such that the resulting closed-loop system is robustly stochastically asymptotically stable in the mean square and the effect of the disturbance input on the controlled output is less than a prescribed level for all admissible parameter uncertainties. New sufficient conditions are presented based on the linear matrix inequality approach. Finally, numerical examples are used to illustrate the effectiveness and feasibility of the approaches proposed in this paper.     

Tomlinson-Harashima Precoded MIMO in wireless networks: to THP or not to THP?

We investigate a wireless network architecture that utilizes Tomlinson Harashima Precoded Multiple Input Multiple Output (THP MIMO) technique for improved system capacity. We consider THP MIMO in a multi user scenario, together with a proposed smart scheduling technique and we explore the capacity performance through extensive capacity analysis considering varying SNR levels, varying number of users and number of transmit/receive antennas, under fading and shadowing, also considering errors in channel state information (CSI). We also evaluate the complexity of THP MIMO and present a low-complexity scheduling algorithm that employs Gram-Schmidt algorithm for incremental implementation of THP’s QR factorization. In the end, we identify the network and channel conditions under which THP MIMO can be preferred over classical conventional MIMO, and we conclude that for practical transceivers with up to four antennas, THP MIMO can provide significant capacity enhancement over conventional MIMO at lower complexity, performing slightly below the sum rate capacity bound. Another important advantage that is observed in this study is better immunity of THP MIMO to CSI errors, as compared to conventional MIMO.     

A Delay-Dependent Approach to Robust H ∞ Control for Uncertain Stochastic Systems with State and Input Delays

In this paper, the problem of delay-dependent robust H _∞ control for uncertain stochastic systems with state and input delays is investigated. The time delays are assumed to be bounded and time varying and the uncertainties are assumed to be norm bounded. By using the Lyapunov functional method, a new delay-dependent robust H _∞ control scheme is presented in terms of linear matrix inequalities (LMIs). Some numerical examples are given to illustrate the effectiveness of the proposed approach. This work is partially supported by the Natural Science Foundation of China (60674055, 60774047), and the Taishan Scholar Programme of Shandong Province. An erratum to this article can be found at     

The diffusivity of the vacancy in silicon: Is it fast or slow?

Vacancies in silicon are known to be highly mobile both at high temperatures (just below the melting point) and at cryogenic temperatures. Contrary to this, however, vacancy diffusivity near 800 °C — as deduced from the radiation-enhanced self-diffusion coefficient D_sd — was reported to be surprisingly low. An apparent explanation of this contradiction is that the defect concentrations (and accordingly D_sd) are reduced by an impurity-mediated recombination of vacancies and self-interstitials. This effect however is shown to be insufficient to account for such a low D_sd. A suggested solution to the puzzle is that self-interstitials (and vacancies as well) exist in two structural forms, a localized one and an extended one, of strongly differing diffusivities. A low diffusivity manifested in radiation-enhanced self-diffusion is likely to correspond to a low apparent diffusivity of self-interstitials (averaged over the two forms) rather than that of vacancies. The fast and slow forms of vacancies are concluded to be both of a high diffusivity at elevated temperatures while it is most likely that one of them (the extended one) becomes practically immobile at low temperatures.     

The Internet: Is it a replicable technological and social phenomenon for central Europe and the Commonwealth of Independent States?

The Internet is more than just inter-connectivity between computers across geo-political boundaries. The Internet is also a means of exchanging ideas to augment human endeavor. This paper explores conditions for, and possible benefits of, the evolution of the Internet in Central and Eastern Europe and the Commonwealth of Independent States.     

Is it feasible to reconstruct body segment 3-D position and orientation using accelerometric data?

The analysis of the mechanics of the musculo-skeletal system during the execution of a motor task requires the determination of the instantaneous position and orientation of the body segments involved in relation to an inertial system of reference. By using adequately assembled uniaxial accelerometric sensors, an easy-to-manage measurement system can be obtained that estimates the three-dimensional position and orientation (P&O) of a body segment through an appropriate analytical model. However, the extent to which experimental errors, in particular accelerometers (ACs) assembly inaccuracies, affect such estimation has never been systematically investigated. This paper systematically analyzes the sensitivity of analytical models of body segment P&O reconstruction through a six-AC system and a nine-AC system to different sources of experimental error. We simulated and statistically assessed the performance of these models in the case of body segment motions typical of movements under muscular control. The results obtained indicated that the inaccuracy in the orientation of the individual AC's active axes and the offset error in the AC responses were the major sources of P&O estimation errors. In particular, no accurate estimation of position was possible with the analytical models analyzed. Under the motion conditions simulated in this study, no substantial advantages were found in using a nine-AC system rather than a six-AC system. Considering that the magnitudes of the simulated experimental errors were quite low (< or = 0.1 deg: AC's orientation; < or = 10(-4) m: uncertainty of the distance between two ACs; < or = 10(-2) ms(-2): random error; 0.5 x 10(-2) ms(-2): offset error), the results indicate that none of the two ACs systems analyzed is suitable for body segment P&O estimation in routine biomechanical applications.     

How to reduce the impedance for pHRI: Admittance control or underactuation?

Many applications of physical human–robot interaction (pHRI) seek to minimize the impedance felt by the operator. For large-scale operations, such as industrial material handling, two architectures have been proposed. The first uses a rigid robotic manipulator with force sensing and an admittance controller, such as the class of Intelligent Assist Devices (IADs). The second utilizes an underactuated macro-mini manipulator system, such as the uMan Assist Device. Given an application with a large payload, which of these two systems can offer the lowest inertia interaction? This work analyzes the effective inertia experienced by the operator in each of the systems. It compares the conditions under which each provides the lightest manipulation, conditions that depend on the payload as well as the frequency of manipulation. The results are validated on a large overhead robotic system configured alternatively in each of the configurations.     

Codebook Design and Beam Training for Extremely Large-Scale RIS: Far-Field or Near-Field?

Reconfigurable intelligent surface(RIS) is more likely to develop into extremely large-scale RIS(XL-RIS) to efficiently boost the system capacity for future 6 G communications. Beam training is an effective way to acquire channel state information(CSI) for XL-RIS. Existing beam training schemes rely on the far-field codebook. However, due to the large aperture of XL-RIS, the scatters are more likely to be in the near-field region of XL-RIS. The far-field codebook mismatches the near-field channe...     

Melatonin for the treatment of disorders in circadian rhythm and sleep: could it form a basis for medication?

The various aspects of the existing knowledge on the physiological role of melatonin and its mode of action in circadian rhythms and sleep are presented. Furthermore, the possibility of its clinical application in maintenance of sleep under regular and environmental changes is discussed.     

Cooperative Transmissions in 5G Large-scale Relay Systems: How to Keep a Balance Between Performance and Complexity?

This paper presents a generalized i-vector representation framework with phonetic tokenization and tandem features for text independent as well as text dependent speaker verification. In the conventional i-vector framework, the tokens for calculating the zero-order and first-order Baum-Welch statistics are Gaussian Mixture Model (GMM) components trained from acoustic level MFCC features. Yet besides MFCC, we believe that phonetic information makes another direction that can benefit the system performance. Our contribution in this paper lies in integrating phonetic information into the i-vector representation by several extensions, forming a more generalized i-vector framework. First, the tokens for calculating the zero-order statistics is extended from the MFCC trained GMM components to phonetic phonemes, trigrams and tandem feature trained GMM components, using phoneme posterior probabilities. Second, given the zero-order statistics (posterior probabilities on tokens), the feature used to calculate the first-order statistics is also extended from MFCC to tandem feature, and is not necessarily the same feature employed by the tokenizer. Third, the zero-order and first-order statistics vectors are then concatenated and represented by the simplified supervised i-vector approach followed by the standard Probabilistic Linear Discriminant Analysis (PLDA) back-end. We study different token and feature combinations, and we show that the feature level fusion of acoustic level MFCC features and phonetic level tandem features with GMM based i-vector representation achieves the best performance for text independent speaker verification. Furthermore, we demonstrate that the phonetic level phoneme constraints introduced by the tandem features help the text dependent speaker verification system to reject wrong password trials and improve the performance dramatically. Experimental results are reported on the NIST SRE 2010 common condition 5 female part task and the RSR 2015 part 1 female part task for text independent and text dependent speaker verification, respectively. For the text independent speaker verification task, the proposed generalized i-vector representation outperforms the i-vector baseline by relatively 53 % in terms of equal error rate (EER) and norm minDCF values. For the text dependent speaker verification task, our proposed approach also reduced the EER significantly from 23 % to 90 % relatively for different types of trials.     

Customization,information provision and choice: what are we willing to give up for personal service?

Consumers are being increasingly asked to provide personal information in exchange for individually tailored product/service offerings. If there are discrepancies between the personal information disclosed (quality and completeness) and the actual profile of the individual, the resulting customized offer will not match the expected offer. The paper uses several theories to develop a framework to understand the disclosure/customization process and the valuation of information. Self-concept theory suggests that an individual’s self-perception influences his/her behavior and attitudes regarding a variety of issues including how and what personal information is provided. Attribution theory can be used to explain how customization successes and failures may be perceived by the consumer, in light of information incompleteness and/or inaccuracy of disclosure. An application of the framework is illustrated with an example of an online dating service.     

Digital technology and innovation trajectories in the Mediterranean region: A casualty of or an antidote to the economic crisis?

Weak macroeconomic conditions mean admittedly that government spending on Information and Communication Technologies (ICTs) is reduced and consequently that ICT-related policies are scrutinized for their necessity, efficiency and impact on growth. At the same time, such conditions bring into the spotlight and set priority to measures targeting the ICT sector and promoting ICT-based innovation as a means of pursuing economic recovery. The 2008 financial crisis affected severely several parts of the world and particularly the Mediterranean region, where, even today, several years after the start of this economic turmoil in Europe, finding an effective response to mitigating the consequences of recession is still pertinent. Building on previous literature that recognizes ICT-based innovation as a crisis mitigation enabler, this paper propels discussion on the association among ICT- and innovation-oriented indicators and the economic crisis context in four Mediterranean countries, namely Spain, Greece, Italy and Cyprus. In this respect, it leverages a set of open and credible indicators of both technological and economic character and attempts to reflect on the effects of the crisis on ICT or conversely seen the potential of the latter to enable the affected countries to come out of the crisis.