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In this paper, we study the performance of the training based two-step channel estimation in two-way multiple-input multiple-output relay systems over Rayleigh channels. We first estimate the forward channel during the first phase. During the second phase for the composite channel estimation, singular value decomposition based maximum likelihood method is applied in two way relay systems, which is extended from one way relay systems. Hence, the backward channel is estimated with the given forward channel and composite channel. In general, the proposed estimation scheme can also be extended from the system with a single relay antenna to multiple relay antennas. Moreover, we derive the proposed training sequences and relay gain that aim to minimizes the trace of the approximate Bayesian Cramér–Rao lower bound with respect to the individual channels. The numerical results are shown that although the training sequence is designed to improve individual channel mean square error performance, it can also improve composite channel estimator performance. [ABSTRACT FROM AUTHOR]

The Doppler shift of fast-fading channels will generate intercarrier interference (ICI) and, hence, degrade the performance of orthogonal frequency-division multiplexing (OFDM) systems. In this paper, a novel channel-estimation and datadetection method for OFDM systems over the fast-fading dispersive channels has been proposed and investigated. A new pilot pattern is also proposed, and it is composed of a comb-type pilot pattern and a grouped pilot pattern. The required number of pilot subcarriers is, therefore, significantly reduced compared with that of using the grouped pilot pattern only. We present the MSE analysis of the proposed channel estimation based on the proposed pilot pattern and thoroughly investigate the MSE performance of channel estimation by a numerical method. A closed-form mathematical expression has been derived to express the MSE of the proposed channel estimation as a function of the Doppler shift, the number of resolvable paths of the channel, the polynomial order, and so on. Both computer simulation and numerical results show that the proposed channel estimation and data detection based on the proposed pilot pattern have effectively eliminated the ICI in terms of the MSE of the channel estimation and biterror-rate (BER) performance, whereas the required pilot number per OFDM symbol is reduced by about 92.3% in comparison with that of using the grouped and equispaced pilot pattern. [ABSTRACT FROM AUTHOR]

This paper proposes a new hybrid-excited machine, termed parallel-hybrid-excited machine (PHEM) with harmonic-shift (HS) structure, or HS-PHEM. The key is to alternately place the dc-field pole pair and permanent magnet (PM) pole pair in the stator, thereby achieving the dc-field HS from the PM-field harmonics. Consequently, the dc-field harmonics interact with the PM harmonics to regulate the resultant effective harmonics in the airgap while the parallel flux paths of PM flux and dc-field flux can also be obtained, leading to more effective flux regulation ability. The operation principle and harmonics analysis are discussed, with emphasis on the validity of HS concept. Moreover, the electromagnetic performances of the proposed machine are evaluated by finite-element analysis and compared with other existing topologies in terms of torque, core loss, and efficiency. Finally, the experimental prototype is manufactured and tested for verifications. [ABSTRACT FROM AUTHOR]

This paper proposes and implements an all-in-one induction heating system, which can accommodate both pan-shaped and wok-shaped utensils. Traditionally, the pan is heated by a planar induction cooktop while the wok is heated by a curved induction cooktop. In this paper, both magnetic inductive coupling and magnetic resonant coupling are utilized to achieve excellent heating performance of the wok based on a planar primary coil. The key is to flexibly employ a detachable frustum coil for heating the wok. Specifically, the theoretical models of the proposed induction heating system with and without using the frustum coil are derived to analyze the proposed system. Computational simulation results of the magnetic and thermal fields of the proposed system are provided to elaborate the heating performance of the wok. A 1500 W prototype is designed and built. The calculated, simulated and experimental results are all in good agreement, which validate the feasibility of the proposed induction heating system well. [ABSTRACT FROM AUTHOR]