Orthogonal frequency division multiplexing (OFDM) systems can avoid the eãect of multipath fading by absorbing delayed waves into guard interval. But as the eãect of delayed waves over guard interval becomes stronger, it causes the bit error rate (BER) performance in OFDM systems to be more degraded. This paper proposes the approximate derivation method of the BER in DQPSK/OFDM systems over frequency selective fading channels. In this study, we will derive the approximate equation of the BER with diãerential coding/diãerential detection in the time domain. We conårm that the BER derived from the proposed approximate equation coincides with that by computer simulation even when such parameters as the Doppler frequency shift, the delay spread, the Rician factor and so on are varied. I. INTRODUCTIONOrthogonal frequency division multiplexing (OFDM) systems have attracted considerable attention in the recent past because of its robustness against multipath fading (frequency-selective fading) and high spectrum eé-ciency. The futures have warranted the designation of OFDM as a standard transmission technique for various services, for example, forth generation mobile communications systems, digital terrestrial TV broadcasting and high speed wireless LAN.Besides the above appealing properties, however, OFDM systems suãer severe performance degradation from the impacts of Doppler frequency shift and delayed waves caused by multipath transmission because of the co-channel interference and the inter-carrier interference (ICI) in OFDM systems [1]- [3].We have already derived the approximate equation of the bit error rate (BER) in DQPSK/OFDM systems over frequency non-selective Nakagami-Rice and Rayleigh fading channels in [4]. We evaluated the performance degradation caused by the impact of Doppler frequency shift f D T s , where f D is the maximum Doppler frequency and T s is a symbol duration. OFDM systems can avoid the interference caused by multipath fading by absorbing delayed
Background: Few studies have reported the measurement of anatomical dead space (V d,an) and alveolar tidal volume (V A) in ventilated neonates with respiratory distress. Objective: The aim of this study was to determine the differences in V d,an and V A in ventilated infants between the early and recovery phases of respiratory distress using volumetric capnography (V cap) based on ventilator graphics and capnograms. Methods: This study enrolled twenty-five ventilated infants (mean birth weight, 2,220 ± 635 g; mean gestational age, 34.7 ± 3.3 weeks). We adjusted respiratory settings to maintain appropriate oxygenation and tidal volume (V T), and performed V cap based on waveforms of ventilator graphics and capnograms. V d,an and V A were measured in infants with respiratory disorders, immediately after intubation (early phase) and subsequently when they were clinically stable (recovery phase). Results: The early phase, with lower dynamic lung compliance, required a higher level of ventilator support, not positive end-expiratory pressure, than the recovery phase. There were significant differences between the early and recovery phases for V d,an
The "Flutter-mill" is a power generation device that can be parallelized and downsized more easily than conventional wind-power generators with the added advantage of lower manufacturing costs. Flutter-mills comprise a flexible sheet with an electric power generator at its leading edge. Flutter-mills exhibit complex power generation performance characteristics that are highly dependent on the specifications of the flexible sheet and the inlet flow velocity. In particular, the span width of the sheet affects the stability and flapping behavior significantly. Using the numerical analysis model, these complex flutter-mill characteristics can be estimated without experiments, and thereby numerical model inform the choice of the sheet dimensions, which are critical for designing an effective flutter-mill. Here, we present a numerical model that can provide a preliminary survey of the power generation performance and attempt to clarify the relationship between the aspect ratio of the sheet and the harvested power. The equation of motion for a flexible sheet includes rotational damping at the leading edge of the sheet to emulate the coupling effect between the sheet and the energy harvesting circuit. We verified the validity of our numerical model by evaluating its performance against previously published experimental results, and thus established the relationship between the aspect ratio of the sheet and the harvested power. We found that the local minimum value of the harvested power of the flutter-mill may be caused by the vibration amplitude at the leading edge of the sheet decreasing in the transition domain of the flapping vibration mode if the aspect ratio is large.
Authors developed the flexible biomimetic fish-like robot for usage in narrow passage flow. The robot mainly consists of three sections: a control section, actuator section and flexible fin section. By using the shape memory alloy (SMA) actuators, downsizing and lightening has been achieved. At first, we constructed the fluid-body coupled model of robot fish for consideration of undulatory swimming and nonlinearity of SMA characteristics. We also constructed experimental model to confirm the validity of analytical model. It is known that dynamics of SMA actuator depends on ambient temperature. Therefore over-heating of SMA actuator may cause accumulation of heat in actuator section of the moving body, and decrease of the amplitude of the caudal fin and the thrust force. Thus, in this study, to improve the driving characteristics of actuator, we identified the relation between temperature and moment of SMA actuator. Next, we constructed the fluid-moving body interaction model which is considering the dynamics of actuator. We searched the local optimal input for SMA actuator based on optimization theory. As a result, it was found that for maintaining high thrust force SMA actuator needs to be driven keeping the temperature around 340 [K].
Some organisms using undulatory locomotion show the transition of the swimming frequency and the wavelength of the undulation. This transition of swimming behavior is achieved by sensory feedback, and may have the role to cope with the environmental change. Especially, one of the nematode: Caenorhabditis elegans can modulate its frequency from approximately 0.3 to 2 Hz, and vary the wavelength of undulating body from less than a single body length to almost twice the body length. With this modulation, C. elegans achieves the movement under the conditions from in water to on the surface of an agar. Inspired by this finding, we propose the adaptive control for the multilink swimming robot because the environmental change demands a mobile robot the change of the pattern of the locomotion. Proposed adaptive control employs the sensory feedback from joint angles to inputs of actuators at joints to generate the self-excited oscillation. At first, we construct the multilink model in fluid with sensory feedback. After that, we construct the linearized model to obtain the relationship among the external resistive force, parameters of the multilink model and the swimming frequency by using the eigenvalue analysis. We confirm whether the proposed adaptive control simulates the modulation of undulation like C. elegans. Moreover, we specify parameters of the multilink model which are related to the frequency and wavelength of undulation significantly.
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