1,720,976 research outputs found
Interference in intradiscal pressure measurement using a needle-type pressure transducer.
No full textCross-layer design for block subchannel allocation and admission control in the IEEE 802.16 OFDMA networks
No full text[[abstract]]The flexibility of orthogonal frequency-division multiple access (OFDMA) technology necessitates a compromise between spectrum efficiency and quality of service (QoS) in IEEE 802.16 broadband wireless networks. This article proposes a complete solution with the nice feature of adaptive modulation and a coding scheme to provide both delay and loss rate guarantees for real-time services. The proposed method first determines the subframe boundary according to the current downlink and uplink backlogs. To comply with the IEEE 802.16 standard, the proposed method then groups contiguous subchannels and allocates them to proper connections based on the current loss rate and available modulation and coding schemes for each connection. By modeling the aggregated required subchannels as a Gaussian distribution, this study develops a simple admission control algorithm by checking if there are enough resources for a new connection. Simulation results show that the proposed solution can provide QoS guarantee with high spectrum efficiency.[[note]]SC
Generalised proportional fairness scheduler for broadband orthogonal frequency-division multiple access systems with heterogeneous traffics
No full text[[abstract]]The popular proportional fairness (PF) scheduler is very suitable for achieving a trade-off between system throughput and fairness, but the authors observed two issues while applying it to broadband networks with heterogeneous traffics. As the PF scheduler only considers average throughput and channel quality, it favours users with low-data rates. In addition, the credits of idle users accumulate because their average throughputs decrease with time during their idle periods. This study proposes a generalised PF scheduler that considers profit instead of average throughput, and it integrates a new mechanism for updating the utility functions to mitigate the issue of credit accumulation. Simulation results show that the proposed PF scheduler outperforms the traditional algorithms in terms of fairness and transient behaviour.[[note]]SC
Energy-Efficient Multi-Polling Scheme for Wireless LANs
No full text[[abstract]]In the past few years, IEEE 802.11 wireless LANs (WLANs) has rapidly gained large popularity for broadband wireless access. With the growing of various applications, users are demanding features such as higher throughput white keeping respectable operation time for their devices. To provide higher system bandwidth utilization, multi-polling mechanisms are often employed to reduce protocol overhead. However, they require wireless stations (STAs) to spend much time in overhearing which tends to waste energy and reduce battery lifetime. In this paper, we propose an energy-efficient multi-polling mechanism which combines power management strategy with a low overhead Medium Access Control (MAC) protocol. The main idea is to put STAs into the Doze state and determine a suitable wake-up time schedule to statistically achieve desirable guarantee of bandwidth utilization. From both analysis and simulation results, we found that, compared with the original ordered-contention multi-polling scheme, our proposed mechanism saves up to 80% of energy for a network consisting of 20 polled STAs with 5% loss of system bandwidth utilization as tradeoff. The significant saving of energy is a consequence of alleviating the overhearing problem with well scheduled wake-up times for STAs.[[note]]SC
Joint bit loading and power allocation for downlink minimum mean square error combining based multi-carrier code division multiple access systems
No full text[[abstract]]The performance of a downlink multi-carrier code-division multiple-access (MC-CDMA) system heavily depends on the receiver type at the user side. The minimum mean square error-combining scheme possesses the finest performance. However, the resource allocation problem becomes a highly complex task because of multiple access interference. This study investigates a realistic scenario, where the base station determines the bit loading and power for all downlink users with both the power and bit error rate (BER) constraints to maximise the overall system throughput. The authors first derive the instantaneous signal to interference and noise ratio (SINR) and then approximate data transmission as an equivalent M-QAM system with a signal-to-noise ratio (SNR) equal to the instantaneous SINR of that user. Combined with accurate BER formulas of M-QAM system, the authors estimate the BER for each user given a set of power and bit loading configuration. Finally, the authors develop an iterative joint bit loading and power allocation algorithm to maximise the system throughput. The simulation results show that the proposed solution achieves performance close to the optimal one and maintains the BER close to the desired target.[[note]]SC
Adaptive resource allocation for downlink grouped MC-CDMA systems with power and BER constraints
No full text[[abstract]]This paper proposes a complete solution to adaptively allocate resource for downlink Multi-Carrier Code Division Multiple Access (MC-CDMA) systems with the power and bit error rate (BER) constraints. Under frequency-selective fading channels, the whole spectrum is divided into several groups and each user is allocated to a group based on its channel state information (CSI). After grouping, the adaptive modulation algorithm assigns the bit loading and allocates the transmission power for each user according to its effective channel response. Simulation results show that the proposed solution can achieve high throughput, guarantee the required BER, and reduce the blocking probability. (C) 2013 Elsevier GmbH. All rights reserved.[[note]]SC
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
SiO2 passivation effect on the hydrogen adsorption performance of a Pd/AlGaN-based Schottky diode
No full text[[abstract]]in this work, the comprehensive study of the hydrogen adsorption effects on the Pd/AlGaN-based MOS Schottky diode with SiO(2) passivation is demonstrated. Hydrogen sensing performance of the proposed device is significantly enhanced with the insertion of SiO2 layer. The MOS diode exhibits a maximum sensing response value of 3.3 x 10(5) at 70 degrees C under a 1% H(2)/air gas. Additionally, the operating temperature for the maximum sensing response is decreased from 150 degrees C to 70 degrees C with the insertion Of SiO(2) layer. Moreover, the lowering of Schottky barrier height is 230 (200)meV for the MOS (MS) diode at room temperature. The hydrogen adsorption effect also largely influence the effective Richardson's constant. Furthermore, the transient-state experiments reveal that the MOS Schottky diode exhibits an activation energy of 14.1 kJ/mol which is lower than the MS Schottky diode (25 kJ/mol). Therefore, hydrogen sensing performance of the AlGaN-based Schottky diode can be significantly enhanced with the SiO(2) passivation on the AlGaN surface. (c) 2008 Elsevier B.V. All rights reserved.[[note]]SC
On a Pd/InAlAs metamorphic high electron mobility transistor (MHEMT)-based hydrogen sensor
No full text[[abstract]]The hydrogen sensing properties of a Pd/InAlAs metamorphic high electron mobility transistor (MHEMT) are investigated. Experimentally, a threshold voltage shift (Delta V(th)) of 260 mV is observed upon exposing to a 1% H(2)/air gas. The drain current sensing response (S(R)) shows the strong dependence on the gate bias voltage V(GS). A maximum S(R) of 107% is found at the applied voltage of V(GS) = -0.5 V. In addition. the temperature behavior of S(R) is predominantly determined by the hydrogen sticking coefficient and the exothermic reaction of hydrogen adsorption. It is also found that rectification ratio R can be changed with different hydrogen concentrations Furthermore, the response rate analyses reveal that the initial response rate is increased with the hydrogen concentration and temperature. The activation energy E(a) of 2.88 kJ mol(-1) suggests that the studied Pd/InAlAs MHEMT hydrogen sensor has a low barrier for the adsorption of hydrogen. (C) 2009 Elsevier B.V. All rights reserved.[[note]]SC
- …
