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Search Results: 1 - 10 of 19031 matches for " mobile satellite antennas systems "
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Adaptive robust controller of mobile satellite antenna systems
移动卫星天线的自适应鲁棒控制系统

LI Guo,HU Jian-fei,YU Da-tai,
李果
,胡剑飞,余达太

控制理论与应用 , 2007,
Abstract: The use of the adaptive robust controller for improving control performance and stability of mobile satellite antenna systems is investigated in this paper.An adaptive robust control system of mobile satellite antennas is presented. The adaptive robust controller is designed according to the mobile satellite antenna systems model.The proposed adaptive controller and the corresponding robust adaptive law not only keep the closed-loop system robustly stable,but also provide the expected performance.Finally,the effectiveness of the algorithm is verified by experimental results,demonstrating that the control performance and stability of mobile satellite antenna systems are improved,and the control system maintains satisfactory control performance despite the change of road surface condition.
Sensor Integration in a Low Cost Land Mobile Mapping System
Sergio Madeira,José A. Gon?alves,Luísa Bastos
Sensors , 2012, DOI: 10.3390/s120302935
Abstract: Mobile mapping is a multidisciplinary technique which requires several dedicated equipment, calibration procedures that must be as rigorous as possible, time synchronization of all acquired data and software for data processing and extraction of additional information. To decrease the cost and complexity of Mobile Mapping Systems (MMS), the use of less expensive sensors and the simplification of procedures for calibration and data acquisition are mandatory features. This article refers to the use of MMS technology, focusing on the main aspects that need to be addressed to guarantee proper data acquisition and describing the way those aspects were handled in a terrestrial MMS developed at the University of Porto. In this case the main aim was to implement a low cost system while maintaining good quality standards of the acquired georeferenced information. The results discussed here show that this goal has been achieved.
Torque Free Axi-Symmetric Gyros with Changing Moments of Inertia  [PDF]
A. I. Ismail, Fawaz D. El-Haiby
Applied Mathematics (AM) , 2016, DOI: 10.4236/am.2016.716159
Abstract: The properties and characteristics of torque free gyros with rotational symmetry and changing moments of inertia are the subject of the subsequent discussion. It shall be understood that the symmetry can be expressed by the notation (A=B)?which does not presuppose geometric symmetry, where A and B are the principle moments of inertia about x and y axes respectively. We study the case of a torque free gyro upon which no external torque is acting. The equations of motion are derived when the origin of the xyz-coordinate system coincides with the gyro’s mass center c. This study is useful for the satellites, which have rotational symmetry and changed inertia moments, the antennas and the solar power collector systems.
Multiband LTE-A/WWAN Antenna for a Tablet  [PDF]
Wael S. Elshennawy, E. A. Hashish, A. M. Attiya
Open Journal of Antennas and Propagation (OJAPr) , 2015, DOI: 10.4236/ojapr.2015.33003
Abstract: In this paper, an internal multiband antenna is proposed for LTE-A/WWAN wireless applications in tablet computer. The proposed antenna is configured to have two branch radiators. These two branch radiators are a U-shaped driven monopole and a nonuniform wrapped inverted U-shaped monopole. The impedance bandwidths across dual operating bands are 89.7 MHz and 4185 MHz at the LTE-A/WWAN bands. Various techniques, such as branching and parasitic element are used to enhance the antenna’s bandwidth, the matching, and the size of the proposed antenna. The antenna is presented on an area of 50 × 15 mm2. Experimental results of this antenna show nearly omni-directional coverage and stable gain variation across the LTE-A/WWAN bands.
Influence-Number of Antennas on the Total Sensing Time in Cognitive Radio Systems
Ahmed S. Kadhim,Haider M. AlSabbagh
Journal of Emerging Trends in Computing and Information Sciences , 2011,
Abstract: In the cognitive radio (CR) systems the total scanning time that is the time taken by the receiver to sense the spectrum is one of the issues in perspective of the overall system performance. This paper proposes architecture for a dedicated receiver capable to reduce sensing time with using dual part: the main receiver and a dedicated one, each with multiple antennas (M). The achieved results show that the total sensing time is reduced by approximately 1/M with using the proposed structure.
Blind Identification of Out-of-Cell Users in DS-CDMA
Jiang Tao,Sidiropoulos Nicholas D
EURASIP Journal on Advances in Signal Processing , 2004,
Abstract: In the context of multiuser detection for the DS-CDMA uplink, out-of-cell interference is usually treated as Gaussian noise, possibly mitigated by overlaying a long random cell code on top of symbol spreading. Different cells use statistically independent long codes, thereby providing means for statistical out-of-cell interference suppression. When the total number of (in-cell plus out-of-cell) users is less than the spreading gain, subspace identification techniques are applicable. If the base station is equipped with multiple antennas, then completely blind identification is possible via three-dimensional low-rank decomposition. This works with more users than spreading and antennas, but a purely algebraic solution is missing. In this paper, we develop an algebraic solution under the premise that the codes of the in-cell users are known. The codes of out-of-cell users and all array steering vectors are unknown. In this pragmatic scenario, we show that in addition to algebraic solution, better identifiability is possible. Our approach yields the best known identifiability result for three-dimensional low-rank decomposition when one of the three component matrices is partially known, albeit noninvertible. Simulations show that the proposed identification algorithm remains close to the pertinent asymptotic (symbol-independent) Cramér-Rao bound, which is also derived herein.
A Swarm Intelligence Networking Framework for Small Satellite Systems  [PDF]
Zijing Chen, Yuanyuan Zeng
Communications and Network (CN) , 2013, DOI: 10.4236/cn.2013.53B2033
Abstract: Recent development of technologies and methodologies on distributed spacecraft systems enable the small satellite network systems by supporting integrated navigation, communications and control tasks. The distributed sensing data can be communicated and processed autonomously among the network systems. Due to the size, density and dynamic factors of small satellite networks, the traditional network communication framework is not well suited for distributed small satellites. The paper proposes a novel swarm intelligence based networking framework by using Ant colony optimization. The proposed network framework enables self-adaptive routing, communications and network reconstructions among small satellites. The simulation results show our framework is suitable for dynamic factors in distributed small satellite systems. The proposed schemes are adaptive and scalable to network topology and achieve good performance in different network scenarios.
A Novel Tool for the Determination of Tropopause Heights by Using GNSS Radio Occultation Data  [PDF]
Francesco Vespe, Rosa Pacione, Elisa Rosciano
Atmospheric and Climate Sciences (ACS) , 2017, DOI: 10.4236/acs.2017.73022
Abstract: The tropopause is a transitional layer between the troposphere and the stratosphere. The exchange of chemical constituents of the atmosphere (namely masses of air, water vapor, trace gases etc.) and energy between the troposphere and the stratosphere occurs through this layer. We suppose that just exchanges that are taking place at the tropopause heights are strongly influenced by the Global Change forcing. For this reason it is particularly urgent to accumulate temporal data the most accurate possible and with a certain continuity series to understand comprehensively what is happening to our climate. It is well known that Radio Occultation technique applied using Global Navigations Satellite Systems (GNSS-RO) is a powerful tool to detect the tropopause heights. It can be done working on the level 2 data provided by GNSS-RO payload: i.e. atmospheric profiles of pressure and temperature. We propose to measure tropopause using GNSS-RO level 1 data; i.e. the bending angles (BA) of the GNSS signal through the atmosphere. We fit the BA profiles applying in the integral relationship of BA as refractivity profile of background the Hopfield dry model of atmosphere which depends on the fourth degree of the height above the Earth. Through the layers in which tropopause is contained, the residuals between the background model and the observed BA have an anomalous trend. The residuals in this zone form anomalous non-gaussian bumps that we have exploited just to determine the relevant parameters of the tropopause. Such bumps are due to the wrong theoretical assumption made by Hopfield for the re-construction of the dry refractivity that the temperature lapse rate of the atmosphere is constant. But we know that the definition of tropopause according the World Meteorological Organization (WMO) is just the height where a sudden change of the temperature lapse rate usually occurs. Thus in the present work we have determined tropopause heights with new algorithms which exploit the bumps occurring along the BA profiles achieved by GNSS-RO. We have used the huge amount of data provided by several space missions devoted to GNSS-RO (namely COSMIC, METOP, etc.) for tuning the algorithms, performed a validation and provided a robust statistical soundness. The same GNSS-RO observations are helpful also to reconstruct the Mapping Function commonly applied in geodetic applications. Global mapping functions built with GNSS-RO and their evolution in time can be an interesting parameter helpful for climate investigations as well.
Meandered Monopoles for 700 MHz LTE Handsets and Improved MIMO Channel Capacity Performance
I. Dioum,M. Clemente,A. Diallo,C. Luxey
Radioengineering , 2011,
Abstract: In this paper, we present the design and the measurement of MIMO meandered monopole antennas and the computation of their channel capacity performance. The initial proposed handset-system is composed of a meandered monopole operating in the LTE 700 MHz band, connected to a parasitic radiating element for the upper 2.5 GHz LTE band. Two antennas of the same kind are then closely positioned on the same 120x50 mm2 Printed Circuit Board (PCB). A neutralization line connects the two antennas to enhance their port-to-port isolation in the 700 MHz band. The computation of the channel capacity performance in this band is based on propagation simulations performed with the GRIMM model from the CREMANT. Two system-prototypes are evaluated: one with the neutralization line for enhanced port-to-port isolation and a second without the neutralization exhibiting poor antenna-to-antenna isolation. It is demonstrated that the neutralization technique helps in giving a minimum improvement of 12% of the capacity performance of the handset-system, and a maximum improvement 46%, in the chosen environment.
Two-Element PIFA Array Structure for Polarization Diversity in UMTS Mobile Phones
F. Ferrero,A. Diallo,C. Luxey,B. Derat
Radioengineering , 2009,
Abstract: In this paper, we demonstrate the possibility to strongly modify the radiated fields of a UMTS handset by using a phased two-element PIFA array. The structure is composed of a 100x40 mm2 metallic ground plane acting as the Printed Circuit Board (PCB) of the mobile phone. Two UMTS PIFAs are located at the top edge of this PCB. They are fed by a double Quasi-Lumped Coupler able to provide a 360 phase difference between its two outputs. By properly choosing the DC bias of the double QuasiLumped Coupler, we can set a specific phase difference between the two PIFAs. In this way the two-element array is able to radiate different electromagnetic fields. Simulated and measured radiation patterns in the two main planes of the chassis are presented for different phase differences. It is especially revealed that the novel twoantenna structure is able to radiate vertically-polarized electric fields in the azimuthal plane of the phone and horizontally-polarized electric fields in the same plane when changing the phase shift between the antennas from 0 to 180. Potential applications are polarization-diversity techniques and Specific Absorption Rate reduction for handsets.
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