1,721,853 research outputs found
Iterative Carrier Phase Synchronization in the Presence of Residual Frequency Offset
No full textIn this paper we propose an iterative carrier phase recovery method to be used in conjunction with a turbo-decoder based on the BCJR (Bahl-Cocke-JeIinek-Raviv) algorithm. The basic idea consists in: i) exploiting the forward recursion of only one SISIO decoder in order to calculate a sort of expectation of the transmitted symbols; ii) using such soft decision symbols in a modified Costas loop to update the (time-variant) carrier phase offset. The simulation results show that the proposed estimation scheme shows itself quite robust even with a severe frequency offset
A Fast Timing Recovery Algorithm for Turbo-coded System
No full textWe proposed a new type of timing recovery scheme to work with a system that uses BCJR (Bahl-Cocke-Jelinek-Raviv) decoding algorithm and BPSK modulation. The unknown timing offset is estimated by the modified Mueller and Müller estimator with the aid of the decoder. Timing offset can be acquired as soon as the symbols are received and be updated symbol by symbol. The simulation results for turbo codes whose decoder uses BCJR algorithm show a satisfactory performance even in case of severe timing jitter
Joint Fine Time Synchronization and Channel Estimation for MIMO-OFDM WLAN
No full textThe fine time syncllronization for OFDM (ortllogonal frequency division multiplexing) system is carried out by taking cor·relation between the received sequence and reference sequence. This conventional method sllows unsatisfactory performllnce in WLAN (wireless local area network) environment due to large value of rms delay spread. This paper proposes an algorithm to improve the performance of the estimator by exploiting the characteristics of the channel. We also present a channel estimation algoritltm in time domain for MIMO-OFDM (multiple-input multiple-output OFDM) with tile same complexity as that in single antenna sy stem. The simulation results show that (1) For symbol time synchronization, the probability of incorrect timing in proposed aIgorithm is hundreds times lower than that in conventional algorithm. (2) For channel estimation, witb the use of two consecutive training sequences as in standard IEEE 802.11a, there is JdB decrease in SNR to acbieve the same MSE as in case of one training sequence only
낮은 복잡도를 갖는 위성 통신용 위상 동기 알고리즘
No full text본 논문에서는 고속 TDMA (Time Division Multiple Access) 위성 통신 시스템에 적합한 위상 동기 방식을 제시하고 성능을 평가하였다. 낮은 SNR 에서 작동하고 초기 포착 특성이 우수한 방식을 사용해야 하는 위성 통신 시스템에 있어 채널 코딩은 필수적이기 때문에 이에 맞는 위상 동기 방식이 필요하다. 그러나 기존의 DD (Decision Directed)나 NDA (Non Data Aided) 방식은 낮은 SNR 에서 Cycle slipping 과 Hangup 현상에 민감하기 때문에 코딩 이득을 제대로 얻을 수 없다. 이러한 현상을 보완 하기 위해 TD (Tentative Decision) 방식과 PSP (Per Survivor Processing) 방식이 제안 되었다. PSP 방식은 TD 방식에 비해 성능이 뛰어나기는 하지만 복잡도가 크다는 단점을 가지고 있다. 따라서 본 논문에서는 채널 상태에 따라 적응적으로 PSP 방식과 TD 방식을 결합하여, 복잡도 문제를 해결하고 PSP 방식의 성능에 근접하는 ARSE (Adaptive Reduced State Estimator) 방식을 제안 하였다
Joint Channel Estimation and Synchronization for OFDM System in Multipath Fading
No full text본 논문에서는 채널 추정 및 DFT의 시점을 결정하는 시간 동기의 결과를 상호 참조하여 채널 추정 및 시간 동기의 정확도를 높일 수 있는 방법을 제안하였다. 제안한 시간 동기 방법의 경우, 기존의 상호상관 (Cross-correlation) 방법을 기반으로 하면서 제안한 DFT기반의 채널 추정 방법에서 잔존 시간 동기 옵셋을 계산하여 상호 상관법의 결과를 보정 하여 좀 더 정확한 시간 동기를 구할 수 있다. 제안한 DFT기반 채널 추정 방법은 유효 채널 구간을 추정하는 방법을 이용하여 성능을 개선하였으며 제안된 시간 동기 방법에서 추정된 정확한 DFT시점을 이용하여 잔존 옵셋이 없는 좀 더 정확한 채널 추정을 할 수 있다. 유효 채널 구간은 특정 문턱 값을 이용해 결정 할 수 있는데, 이 문턱 값은 채널의 MSE를 최소화시키기 위해 채널의 전력과 잡음 전력의 관계에서 구할 수 있다. 제안한 채널 추정 방법은 채널의 통계적 특성에 대하여 강인한 특성을 가진다
Existence, blow-up and exponential decay of solutions for a porous-elastic system with damping and source terms
No full textIn this paper we consider a porous-elastic system consisting of nonlinear boundary/interior damping and nonlinear boundary/interior sources. Our interest lies in the theoretical understanding of the existence, finite time blow-up of solutions and their exponential decay using non-trivial adaptations of well-known techniques. First, we apply the conventional Faedo-Galerkin method with standard arguments of density on the regularity of initial conditions to establish two local existence theorems of weak solutions. Moreover, we detail the uniqueness result in some specific cases. In the second theme, we prove that any weak solution possessing negative initial energy has the latent blow-up in finite time. Finally, we obtain the so-called exponential decay estimates for the global solution under the construction of a suitable Lyapunov functional. In order to corroborate our theoretical decay, a numerical example is provided.This research is funded by Vietnam National University Ho Chi Minh City (VNU-HCM) under Grant no. B2017-18-04. The work of the first author was partly supported by a postdoctoral fellowship of the Research Foundation-Flanders (FWO)
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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