The Experts below are selected from a list of 243 Experts worldwide ranked by ideXlab platform

Ifiok Otung - One of the best experts on this subject based on the ideXlab platform.

  • Scintillation Fade and Enhancement Duration Statistics at 20, 40 and 50GHz
    20th AIAA International Communication Satellite Systems Conference and Exhibit, 2002
    Co-Authors: Ali Savvaris, C.n. Kassianides, Ifiok Otung
    Abstract:

    Statistics of observed durations of scintillation fades and enhancements of the ITALSAT satellites at 20, 40 and 50GHz are presented for various threshold signal levels, and their use in fade countermeasures is examined. The analysis shows that most signal amplitude deviations from the mean level are of short duration and do not depend on the threshold level. Distribution of fade durations at thresholds 0.1 and 0.5dB were reasonably well approximated by the lognormal function. Introduction The saturation of C-band and the ever-increasing demand for new services that require greater bandwidth has led to the exploitation of higher frequencies. The higher frequencies offer various advantages such as, increased bandwidth, smaller Antennas, and smaller satellite footprint that give higher EIRP and permit frequency reuse. The main obstacle however is that they are subject to stronger propagation degradation. The small size Antennas employed in VSAT and USAT systems significantly reduce the cost of earth station terminals and also eliminate tracking requirements, but they lose the mitigating effect of aperture averaging and hence experience stronger scintillation [1]. Scintillations are rapid fluctuations in amplitude and phase of the received signal arising from fluctuations in the atmospheric refractive index due to turbulence. Increasing the transmitted power or the receiving Antenna Diameter to provide an adequate fade margin is often not feasible in VSAT systems. An alternative scintillation countermeasure, which is being investigated, is the use of Forward Error Correction (FEC) codes and adaptive modulation schemes. Link budget engineers use annual and worst month cumulative distribution functions to calculate the link budget for a new satellite communication system. The use of digital signal processing however requires the knowledge of the dynamics of tropospheric scintillation, including the distribution of scintillation fade duration and inter-fade interval. Fade duration statistics are particularly important for the design of high frequency satellite systems. In such high frequency systems, operating at a fixed small fade margin, the best way to mitigate propagation impairments is by introducing adaptive techniques, adaptive fade countermeasure strategies. Fade and interfade duration statistics provide the system designer with useful information for evaluating various mitigation techniques that will be employed to ensure a given system availability and quality of service. In this paper attention is focused on the analysis of scintillation fades and enhancements at 18.7, 39.6 and 49.5 GHz, which will be hereafter referred to as the 20, 40 and 50GHz, respectively, using propagation data from the ITALSAT F1 and ITALSAT F2 satellites. Experiment and Analysis ITALSAT was Italy's first operational communication satellite launched on the 16 of January 1991 by an Ariane booster and stationed in geostationary orbit at 13.2 degrees east. The design life for the ITALSAT vehicle originally was only five years, but ITALSAT F1 operated beyond its expected life, facilitated by the adoption of a propellant saving option in which the North/South station keeping was abandoned. As a consequence it became necessary for the beacon receivers to track the satellite position. Towards the end of 1997 the 50 GHz beacon receiver at Sparsholt was equipped with a tracking unit to counter the problem. The same goal was attained for the 40 GHz receiver in August 1998 [2]. The data examined can be divided into two sets: a) Data set 1: This contains data measurement from the ITALSAT F2 satellite, operating at 20 GHz and covering a 1-year period from September 99 to August 2000. b) Data set 2: This contains data measurement from the ITALSAT F1 satellite, operating at 40 and 50 GHz and covering a 1-year period from September 96 to August 97. 20th AIAA International Communication Satellite Systems Conference and Exhibit 12-15 May 2002, Montreal, Quebec, Canada AIAA 2002-1906 Copyright © 2002 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved. 2 American Institute of Aeronautics and Astronautics Both data sets were recorded at Sparsholt (51.0814°N, 1.3947°W), UK at a path elevation of 30° and at a sampling rate of 1 Hz. Cassegrain Antennas of Diameters 1.22m for the 20 GHz and 0.61m for both the 40 GHz and 50 GHz beacons were employed. The propagation data together with a range of meteorological measurements recorded at the same sampling rate were archived to a compact disk once a month. Pre-processing of the raw propagation data was carried out. This involved visual inspection of graphs of the data to identify gaps and spurious samples, and high-pass filtering using a 6 order Butterworth filter with a cut-off frequency of 0.04 Hz to extract scintillation [3]. Distribution of Scintillation Fade & Enhancement In Figure 1, the observed annual cumulative distributions of scintillation fades and enhancements at 20, 40 and 50GHz are presented. It can be seen from this figure, that for 0.01% of the time the fade levels at 20 and 50GHz are 0.8 dB and 1.5 dB, respectively. This represents an increase in the scintillation signal amplitude by a factor of 1.88.

  • Prediction of tropospheric amplitude scintillation on a satellite link
    IEEE Transactions on Antennas and Propagation, 1996
    Co-Authors: Ifiok Otung
    Abstract:

    Semi-empirical models are presented for annual and worst-month distributions of scintillation fades, enhancements, peak-to-peak amplitude excursions, and intensity. The models utilize the well-known theoretical scaling of scintillation with signal frequency, Antenna Diameter, and path-elevation angle, and its empirical dependence on the wet term of atmospheric refractivity. Dependence on time percentage is obtained by detailed regression analysis of experimental scintillation data obtained at Sparsholt, UK (51.5850/spl deg/ N, 1.5033/spl deg/ W) over a one-year period using the Olympus satellite 19.7704 GHz beacon viewed at a nominal elevation of 28.74/spl deg/. Results are compared where possible with the ITU-R and Moulsley-Vilar scintillation models and with Olympus measurements in Germany.

W. Wiesbeck - One of the best experts on this subject based on the ideXlab platform.

  • Compact, Dual-Polarized UWB-Antenna, Embedded in a Dielectric
    IEEE Transactions on Antennas and Propagation, 2010
    Co-Authors: Grzegorz Adamiuk, Thomas Zwick, W. Wiesbeck
    Abstract:

    A compact dual-polarized Antenna is described for ultrawideband (UWB) applications. The main features of the Antenna, besides an ultrawidebandwidth are low cross-polarization and small dimensions. The feed of the Antenna is based on the tapered slot Antennas, enclosed in a dielectric. The new Antenna concept, including the feed of the Antenna for dual-polarization and its integration, is described in detail. Prototypes are shown and their performances are demonstrated, based on simulation and measurement results in frequency and time domain. The Antenna prototype input match is better than -10 dB, a maximal gain of 10.5 dBi and a mean polarization decoupling of approximately 17 dB in the main beam direction in the 3.1-10.6 GHz UWB band are achieved. In the time domain a peak value of 0.4 m/ns, a full width at half maximum of 100 ps and a ringing of 145 ps are measured. With a maximum Antenna Diameter of 35 mm and 53 mm length this new Antenna is also suited for UWB Antenna arrays.

  • Compact, Dual-Polarized UWB-Antenna, Embedded
    2010
    Co-Authors: Grzegorz Adamiuk, Thomas Zwick, W. Wiesbeck
    Abstract:

    A compact dual-polarized Antenna is described for ul- trawideband (UWB) applications. The main features of the an- tenna, besides an ultrawidebandwidth are low cross-polarization and small dimensions. The feed of the Antenna is based on the ta- pered slot Antennas, enclosed in a dielectric. The new Antenna con- cept, including the feed of the Antenna for dual-polarization and its integration, is described in detail. Prototypes are shown and their performances are demonstrated, based on simulation and mea- surement results in frequency and time domain. The Antenna pro- totype input match is better than , a maximal gain of 10.5 dBi and a mean polarization decoupling of approximately 17 dB in the main beam direction in the 3.1-10.6 GHz UWB band are achieved. In the time domain a peak value of 0.4 m/ns, a full width at half maximum of 100 ps and a ringing of 145 ps are measured. With a maximum Antenna Diameter of 35 mm and 53 mm length this new Antenna is also suited for UWB Antenna arrays.

Qiang Zhang - One of the best experts on this subject based on the ideXlab platform.

  • Long-range micro-pulse aerosol lidar at 1.5 μm with an upconversion single-photon detector.
    Optics letters, 2015
    Co-Authors: Haiyun Xia, Guo-liang Shentu, Shangguan Mingjia, Xiu-xiu Xia, Jia Xiaodong, Chong Wang, Jun Zhang, Jason S. Pelc, Martin M. Fejer, Qiang Zhang
    Abstract:

    A micro-pulse lidar at eye-safe wavelength is constructed based on an upconversion single-photon detector. The ultralow-noise detector enables using integration technique to improve the signal-to-noise ratio of the atmospheric backscattering even at daytime. With pulse energy of 110 μJ, pulse repetition rate of 15 kHz, optical Antenna Diameter of 100 mm and integration time of 5 min, a horizontal detection range of 7 km is realized. In the demonstration experiment, atmospheric visibility over 24 h is monitored continuously, with results in accordance with the weather forecasts.

  • Long-range micro-pulse aerosol lidar at 1.5 um with an up-conversion single-photon detector
    arXiv: Optics, 2014
    Co-Authors: Haiyun Xia, Guo-liang Shentu, Shangguan Mingjia, Xiu-xiu Xia, Jia Xiaodong, Chong Wang, Jun Zhang, Qiang Zhang, Xiankang Dou, Jian-wei Pan
    Abstract:

    A micro-pulse lidar at eye-safe wavelength is constructed based on an up-conversion single-photon detector. The ultralow noise detector enables using integration technique to improve the signal-to-noise ratio of the atmospheric backscattering even at daytime. With the pulse energy of 110uJ, the pulse repetition rate of 15 kHz, the optical Antenna Diameter of 100 mm and integration time of 5 minutes, a horizontal detection range of 7 km is realized. In the demonstration experiment, atmospheric visibility over 24 hours is monitored continuously, with results in accordance with the weather forecasts.

S.i.s. Hassan - One of the best experts on this subject based on the ideXlab platform.

  • Investigation of a rural telecommunication system using VSAT technology in Malaysia
    9th Asia-Pacific Conference on Communications (IEEE Cat. No.03EX732), 1
    Co-Authors: Emir Husni, M.a. Abdullah, S.i.s. Hassan
    Abstract:

    This study investigates the VSAT network that is applied to rural telecommunication network. The VSAT network is planned based on telecommunication demand as obtained from the survey. The network uses Measat-1 satellite and existing hub of Maxis located at Shah Alani. Selangor. The network is also based on a star network using access of FDMA-MCPC inbound and a TDM outbound channels. To decide Antenna Diameter and HPA power of Antenna, the satellite link budget is calculated based on the service requirement of BER at 10/sup -7/, 64 kbps inbound information bit rate and BPSK modulation techniques. Rain attenuation is calculated by using the local measured rain rate with 0.01% time of the year that is exceeding 129 mm/h [Hassan, 2002].

Haiyun Xia - One of the best experts on this subject based on the ideXlab platform.

  • Long-range micro-pulse aerosol lidar at 1.5 μm with an upconversion single-photon detector.
    Optics letters, 2015
    Co-Authors: Haiyun Xia, Guo-liang Shentu, Shangguan Mingjia, Xiu-xiu Xia, Jia Xiaodong, Chong Wang, Jun Zhang, Jason S. Pelc, Martin M. Fejer, Qiang Zhang
    Abstract:

    A micro-pulse lidar at eye-safe wavelength is constructed based on an upconversion single-photon detector. The ultralow-noise detector enables using integration technique to improve the signal-to-noise ratio of the atmospheric backscattering even at daytime. With pulse energy of 110 μJ, pulse repetition rate of 15 kHz, optical Antenna Diameter of 100 mm and integration time of 5 min, a horizontal detection range of 7 km is realized. In the demonstration experiment, atmospheric visibility over 24 h is monitored continuously, with results in accordance with the weather forecasts.

  • Long-range micro-pulse aerosol lidar at 1.5 um with an up-conversion single-photon detector
    arXiv: Optics, 2014
    Co-Authors: Haiyun Xia, Guo-liang Shentu, Shangguan Mingjia, Xiu-xiu Xia, Jia Xiaodong, Chong Wang, Jun Zhang, Qiang Zhang, Xiankang Dou, Jian-wei Pan
    Abstract:

    A micro-pulse lidar at eye-safe wavelength is constructed based on an up-conversion single-photon detector. The ultralow noise detector enables using integration technique to improve the signal-to-noise ratio of the atmospheric backscattering even at daytime. With the pulse energy of 110uJ, the pulse repetition rate of 15 kHz, the optical Antenna Diameter of 100 mm and integration time of 5 minutes, a horizontal detection range of 7 km is realized. In the demonstration experiment, atmospheric visibility over 24 hours is monitored continuously, with results in accordance with the weather forecasts.