37630776
SAGE-based estimation of doubly selective channel with an orthogonal polynomial model
A space alternating generalized expectation-maximization (SAGE)-based estimation algorithm for doubly selective channel is proposed, which has very similar performance to the rectangular-windowed least squares methods introduced by Borah and Hart while providing large savings in computational complexity. Theoretical analysis shows that the proposed algorithm is always globally convergent. The convergence rate is also investigated through simulations.
1781908
An EM-Based Time-Domain Channel Estimation Algorithm Using a priori Information
Based on the expectation-maximization (EM) algorithm, an iterative time-domain channel estimation approach capable of using a priori information is proposed for orthogonal frequency division multiplexing (OFDM) systems in this letter: it outperforms its noniterative counterpart in terms of estimation accuracy as well as bit error rate (BER) performance. Numerical simulations demonstrate that an SNR gain of 1 dB at BER = 10 -4 with only one iteration and estimation mean square error (MSE) which nearly coincides with the Cramer-Rao bound (CRB) in the low SNR region can be obtained, thanks to the efficient use of a priori information.
44610157
A New Robust Bandpass Sampling Scheme for Multiple RF Signals in SDR System
Software defined radio (SDR) technology has been widely applied for its powerful universality and flexibility in the past decade. To address the issue of bandpass sampling of multiband signals, a novel and efficient method of finding the minimum valid sampling frequency is proposed. Since there are frequency deviations due to the channel effect and hardware instability in actual systems, we also consider the guard-bands between downconverted signal spectra in determining the minimum sampling frequency. In addition, the case that the spectra within the sampled bandwidth are located in inverse placement can be avoided by our proposed method, which will reduce the complexity of the succeeding digital signal process significantly. Simulation results illustrate that the proper minimum sampling frequency can be determined rapidly and accurately.
12120268
Performance of Coded pi/2 NS-8QAM Modulation
Spectrum and Bit Error Rate (BER) performance of a coded π/2 phase shift Non-Square (NS) 8 Quadrature Amplitude Modulation (QAM) system are studied in this letter. The modulation process of this scheme removes all 180° phase shift between adjacent constellation points and contains inherent memory which can be treated as a type of inner coding in coded system. Simulation results show that this modulation scheme has much lower spectrum regrowth and better BER performance when passing through nonlinear channel compared with conventional mode.
20317272
Burst receiver for upstream communications over twisted pair lines
This paper presents algorithms and implementations of a burst receiver chip for upstream communications over twisted pair lines. The receiver is an all-digital chip, which receives digitized IF QAM signal, and demodulate QPSK, 16-QAM or 64-QAM burst data at 312.5 kbauds. The receiver structure consists of direct digital frequency synthesizer (DDFS), several stages of filtering, burst detection, fast acquiring timing/phase/gain recovery, and adaptive equalizer with fast convergence rate. The receiver is prototyped using programmable FPGA.
5397904
Modeling and Throughput Analysis for Wireless Ad Hoc Networks
This paper presents a novel analytical model for wireless ad hoc networks. Based on the strong points in the literature, an accurate performance model for IEEE 802.11 MAC protocol is proposed. Moreover, by introducing the properties of spatial reuse, we extend the proposed model to support the throughput analysis of wireless ad hoc networks with directional antenna. An extensive set of simulations and numerical calculations validate our model by showing high accurate results.
39739560
Optimal Motion Generation of Flexible Macro-micro Manipulator Systems Using Estimation of Distribution Algorithm
In this paper, a new approach for motion generation and optimization of the flexible macro-micro manipulator system is proposed based on Estimation of Distribution Algorithm (EDA). The macro-micro manipulator system is a redundant system, of which inverse kinematics remains challenging, with no generic solution to date. Here, the manipulator system configurations, or the optimal joint motions, are generated using the EDA algorithm base on Gaussian probability model. Compared with simple genetic algorithms (SGA), this approach uses fewer parameters and the time for motion optimization is remarkably reduced. The proposed approach shows excellent performance on motion generation and optimization of a flexible macro-micro manipulator system, as demonstrated by the simulation results.
40155382
Efficient Solution of Bidomain Equations in Simulation of Cardiac Excitation Anisotropic Propagation
Bidomain equations are used to characterize myocardial physiological activation and propagation. Their numerical solution is costly computation because of the higher temporal and spatial discretization requirements, especially in three dimensions. In most previous studies, the heart was supposed to be homogeneous isotropic medium, and thus can use the mondomain equation in stead of the bidomain equations to simulate the heart excitation propagation. Simulation of heart excitation anisotropic propagation in three-dimensional large tissue size by solving bidomain equations has not been implemented yet. In this paper, we present an efficient solution of bidomain equations in simulation of heart excitation anisotropic propagation by combining some numerical techniques such as non-standard finite difference (NSFD), domain decomposition and multigrid methods. The results show that the proposed method can successfully be used to simulate heart excitation anisotropic propagation in three-dimensional large tissue size, and it suggests that such method may provide a good basis for heart simulation research in a more physiologically way.
17572677
Decision-Feedback Receiver for Quasi-Orthogonal Space-Time Coded OFDM Using Correlative Coding Over Fast Fading Channels
Orthogonal frequency division multiplexing (OFDM) is robust against frequency selective fading, but it is very vulnerable to time selective fading. In quasi-orthogonal space-time coded OFDM (ST-OFDM) systems, channel variations cause not only inter-carrier interference among different subcarriers in one OFDM block, but also inter-transmit-antenna interference (ITAI). When applied in fast fading channels, common ST-ODFM receivers usually suffer from an irreducible error floor. In this letter, we apply frequency-domain correlative coding combined with a modified decision-feedback detection scheme to effectively suppress the error floor of quasi-orthogonal ST-OFDM over fast fading channels. The effectiveness of the proposed scheme in mitigating the effects of channel time selectivity is demonstrated through comparison with existing schemes such as zero-forcing, two-stage zero-forcing, and sequential decision feedback estimation