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A polymer electrolyte membrane is a core component of proton exchange membrane fuel cell. Since the ionic conductivity of polymer electrolyte membrane depends on water content, it is necessary to understand the water transport mechanism in the polymer electrolyte membrane. When the electric current demand is varied rapidly, the transient water transport results in the shortage or flooding in the polymer electrolyte membrane. The transient behavior of water transport in the polymer electrolyte membrane is nonlinear due to the water sorption/desorption mechanism. In this study, the nonlinear water transport mechanism of polymer electrolyte membrane is established to understand the transient behavior of water transport over the rapid change of electric current. Since the nonlinear dynamics delay the response of water transport under rapid change of electric current, system-level simulation is conducted to evaluate the system response by delayed water transport. Results show that the rapid change of electric current dramatically affects the water transport dynamics. As a result, this study confirms that water transport in the electrode is delayed depending on the polymer electrolyte membrane (PEM) thickness and that flooding occurs in the cathode depending on the relative humidity at the anode inlet. [ABSTRACT FROM AUTHOR]

The 3rd Generation Partnership Project (3GPP) has recently developed device-to-device (D2D) communication to cope with the explosively increasing mobile data traffic. The D2D communication uses sidelink that is based on the single-carrier frequency-division multiple access scheme because of its low peak-to-average power ratio. In addition, the demodulation reference signal is designed to support multiple input multiple output. In this paper, we propose a DFT-based channel estimation scheme for sidelink in D2D communication. The proposed scheme uses the two-dimensional minimum mean square error interpolation scheme for a user moving at a high speed. We performed a system level simulation based on 20-MHz bandwidth of the 3GPP LTE-Advanced system. Simulation results show that the proposed channel estimation scheme has improved signal-to-interference-plus-noise ratio, throughput, and spectral efficiency as compared with a conventional scheme. [ABSTRACT FROM AUTHOR]

In this paper, we propose a channel estimation scheme for a long term evolution-advanced (LTE-A) downlink system. The proposed scheme uses the fast Fourier transform (FFT) interpolation scheme for the user moving at a high speed. The FFT interpolation scheme converts the channel frequency response obtained from the least square or minimum mean square error channel estimation scheme to a time-domain channel impulse response by using the inverse FFT (IFFT). After windowing the channel response in the time domain, the channel frequency response can be obtained using the FFT. We performed a system-level simulation based on the 20 MHz bandwidth of the 3rd Generation Partnership Project LTE-A downlink system. Simulation results show that the proposed channel estimation scheme can improve the signal-to-noise-plus-interference ratio, as well as the throughput and spectral efficiency, of a conventional system. [ABSTRACT FROM AUTHOR]

The third Generation Partnership Project (3GPP) Long-Term Evolution (LTE) is becoming the first truly global wireless communication standard. LTE system is expected to have an ability to sense the wireless environment. To evaluate the performance of cognitive LTE network, the design of system level simulation platform is proposed. This platform realizes relevant spectrum sensing algorithm and dynamic spectrum allocation strategy. The architecture of this simulation platform is introduced. Based on LTE system level simulator, cognitive radio function is implemented and five modules are developed, including spectrum sensing module, spectrum allocation module, spectrum switching module, link adaptation module, link-system interface module. Class diagram of the simulation platform is also given in this paper. Simulation flow chart introduces the working mechanism in detail. Finally network performance of cognitive LTE system, including average throughput, average spectral efficiency, detection probability, false alarm probability, miss alarm probability, is evaluated using this platform. [ABSTRACT FROM AUTHOR]

In this paper, we evaluate the performance of OFDMA/TDD-based broadband mobile internet access system with the features of adaptive modulation & coding (AMC) and hybrid ARQ. We present a framework of system-level simulation and furthermore, intend to derive the insightful results towards understanding the performance of broadband mobile internet access system. The average system throughput as well as delay performance is evaluated for the different channel characteristics and system parameters, which allows for predicting the system capacity in the varying cellular network environment. [ABSTRACT FROM AUTHOR]