A Novel 3D Analytical Scattering Model for Air-to-Ground Fading Channels

A geometry-based three-dimensional (3D) novel stochastic channel model for air-to-ground (A2G) and ground-to-air (G2A) radio propagation environments is proposed. The vicinity of a ground station (GS) is modelled as surrounded by effective scattering points; whereas the elevated air station’s (AS) vicinity is modelled as a scattering-free region. Characterization of the Doppler spectrum, dispersion in the angular domain and second order fading statistics of the A2G/G2A radio communication channels is presented. Closed-form analytical expressions for joint and marginal probability density functions (PDFs) of Doppler shift, power and angle of arrival (AoA) are derived. Next, the paper presents a comprehensive analysis on the characteristics of angular spread on the basis of shape factors (SFs) for A2G/G2A radio propagation environments independently in both the azimuth and elevation planes. The analysis is further extended to second order statistics of the fading channel; where the behaviour of the level crossing rate (LCR), average fade duration (AFD), auto-covariance and coherence distance for the A2G/G2A radio propagation environment is studied. Finally, the impact of physical channel parameters, such as the mobility of AS, the height of AS, the height of GS and the delay of the longest propagation path, on the distribution characteristics of Doppler shift, angular spread and second order statistics is thoroughly studied

Efficient Measurement System to Investigate Micro-Doppler Signature of Ballistic Missile

Micro-Doppler (MD) shift caused by the micro-motion of a ballistic missile (BM) can be very useful to identify it. In this paper, the MD signatures of three scale-model BMs are investigated using a portable measurement system. The measurement system consists of an X-band 2-by-2 phase comparison mono-pulse radar, and a mechanical device that can impart controlled spinning and coning motions simultaneously to a model to yield the MD signature that replicates the characteristic of each target and the corresponding micro-motion. The coning motion determined the overall period of MD, and the spinning motion increased its amplitude. MD was also dependent on aspect angle. The designed system is portable, and can implement many micro-motions; it will contribute to analysis of MD in various situations.110Ysciescopuskc

Proceedings of the Second International Mobile Satellite Conference (IMSC 1990)

Presented here are the proceedings of the Second International Mobile Satellite Conference (IMSC), held June 17-20, 1990 in Ottawa, Canada. Topics covered include future mobile satellite communications concepts, aeronautical applications, modulation and coding, propagation and experimental systems, mobile terminal equipment, network architecture and control, regulatory and policy considerations, vehicle antennas, and speech compression

The Use of a Laser Doppler Velocimeter in a Standard Flammability Tube

The use of the Laser Doppler Velocimeter, (LDV), to measure the flow associated with the passage of a flame through a standard flammability limit tube (SFLT) was studied. Four major results are presented: (1) it is shown that by using standard ray tracing calculations, the displacement of the LDV volume and the fringe rotation within the experimental error of measurement can be predicted; (2) the flow velocity vector field associated with passage of an upward propagating flame in an SFLT is determined; (3) it is determined that the use of a light interruption technique to track particles is not feasible; and (4) it is shown that a 25 mW laser is adequate for LDV measurements in the Shuttle or Spacelab

Airborne forward pointing UV Rayleigh lidar for remote clear air turbulence (CAT) detection: system design and performance

A high-performance airborne UV Rayleigh lidar system was developed within the European project DELICAT. With its forward-pointing architecture it aims at demonstrating a novel detection scheme for clear air turbulence (CAT) for an aeronautics safety application. Due to its occurrence in clear and clean air at high altitudes (aviation cruise flight level), this type of turbulence evades microwave radar techniques and in most cases coherent Doppler lidar techniques. The present lidar detection technique relies on air density fluctuations measurement and is thus independent of backscatter from hydrometeors and aerosol particles. The subtle air density fluctuations caused by the turbulent air flow demand exceptionally high stability of the setup and in particular of the detection system. This paper describes an airborne test system for the purpose of demonstrating this technology and turbulence detection method: a high-power UV Rayleigh lidar system is installed on a research aircraft in a forward-looking configuration for use in cruise flight altitudes. Flight test measurements demonstrate this unique lidar system being able to resolve air density fluctuations occurring in light-to-moderate CAT at 5 km or moderate CAT at 10 km distance. A scaling of the determined stability and noise characteristics shows that such performance is adequate for an application in commercial air transport.Comment: 17 pages, 19 figures. Pre-publish to Applied Optics (OSA

Proceedings of the Mobile Satellite Conference

A satellite-based mobile communications system provides voice and data communications to mobile users over a vast geographic area. The technical and service characteristics of mobile satellite systems (MSSs) are presented and form an in-depth view of the current MSS status at the system and subsystem levels. Major emphasis is placed on developments, current and future, in the following critical MSS technology areas: vehicle antennas, networking, modulation and coding, speech compression, channel characterization, space segment technology and MSS experiments. Also, the mobile satellite communications needs of government agencies are addressed, as is the MSS potential to fulfill them

A Wideband Adaptive Communication System

The concept of an open loop Adaptive Communication link is established as one which is capable of monitoring the medium through which it must perform while simultaneously transmitting information and continuously adjusting its modes of operation so as to optimize its performance with respect to a performance criterion chosen a priori. Statistical methods are applied to the adaptive communication problem. Communicating through a random multipath channel with additive noise is considered. The transmitter is specified as one which transmits one of two possible noise-like waveforms which are assumed to be known at the receiver. At any time, it is postulated that the receiver is to make its decision in accordance with the Bayes Rules which appropriately fits the amount of channel knowledge stored at the receiver. The knowledge concerning the channel state is derived a posteriori at the receiver from the information bearing signal. Consequently, as the a posteriori information changes (corresponding to changing propagation medium characteristics) the receiver’s decision circuitry also changes. Hence, the receiver is one which continuously adapts itself to yield optimum performance under the measured channel parameters. These random parameters are taken to be: channel gain, channel multipath structure, and the channel phase characteristic. Probability of error is evaluated in closed form for three different modes of operation. A major conclusion taken from these expressions is that the probability of error in no ease depends directly on the channel gain, but lather is a function of the total average energy received from all propagation modes, numerical evaluation of the error expressions enables comparisons to be made among the various systems modes of operation. These results show that measurement of the channel gain is the least important of these quantities. Given the multipath structure, the channel phase characteristic is the most important, In the optimum case a gain of about 6 db to 8 db (depending on the signal-to-noise ratio) is accomplished over the Receiver mode which performs only the multipath measurement. It is shown that the information gain concerning the multipath structure increases rapidly for a few bauds of identification time after which information build up begins to saturate. This is important because there will be available at the receiver only a finite time for which to identify this channel condition. The variance of the channel estimates are computed for maximum and minimum identification time. It is shown that the bandwidth of the transmitted waveform is the important parameter for accurate measurement of the multipath structure, while a sinusoid is sufficient for measuring the channel gain. By combining the channel measurement techniques and signal detection results, two Adaptive Receiver structures are formulated and their operation discussed. Finally, commentaries on future research are made and conclusions given about the above work

Non-Stationary 3D M2M Channel Modeling and Verification with Aircraft-to-Aircraft, Drone-to-Drone, Vehicle-to-Vehicle, and Ship-to-Ship Measurements

Mobile-to-mobile (M2M) propagation channels have gained significant attention over the last years with the development of advanced communication systems for all kind of mobile stations such as aircraft, drones, cars, and ships. However, most available channel models do not account for the environment where the stations are located, but are defined for either average or worst-case conditions, not being able to predict the channel behaviour in specific scenarios. This is especially true for the scattering components of the channel, which are generally either ignored or defined as a rough extrapolation of the scattering components observed in other scenarios. In this work, we propose a geometry-based channel modeling technique that can be applied to any M2M scenario and that can calculate the channel accurately based on the environment around the stations. We first use finite and infinite planes to model the environment. Then, we use the proposed channel modeling technique to obtain analytically the contributions of each plane to the delay-dependent and joint delay Doppler probability density functions of the channel, as well as its squared delay/Doppler-spread function. Our technique focuses mainly on the scattering components but it also addresses the line-of-sight and specular reflection components. We apply the proposed channel modeling technique to different aircraft-to-aircraft, drone-to-drone, carto-car, and ship-to-ship scenarios where channel measurements are available. In all scenarios, the channel estimated using the proposed channel modeling technique matches the channel measurements very accurately. Specifically, we observe that the scattering components are recreated very faithfully, and that we can even estimate how the channel evolves over time as the stations move and are affected differently by the environment

Assessing the performance of ultrafast vector flow imaging in the neonatal heart via multiphysics modeling and In vitro experiments

Ultrafast vector flow imaging would benefit newborn patients with congenital heart disorders, but still requires thorough validation before translation to clinical practice. This paper investigates 2-D speckle tracking (ST) of intraventricular blood flow in neonates when transmitting diverging waves at ultrafast frame rate. Computational and in vitro studies enabled us to quantify the performance and identify artifacts related to the flow and the imaging sequence. First, synthetic ultrasound images of a neonate's left ventricular flow pattern were obtained with the ultrasound simulator Field II by propagating point scatterers according to 3-D intraventricular flow fields obtained with computational fluid dynamics (CFD). Noncompounded diverging waves (opening angle of 60 degrees) were transmitted at a pulse repetition frequency of 9 kHz. ST of the B-mode data provided 2-D flow estimates at 180 Hz, which were compared with the CFD flow field. We demonstrated that the diastolic inflow jet showed a strong bias in the lateral velocity estimates at the edges of the jet, as confirmed by additional in vitro tests on a jet flow phantom. Furthermore, ST performance was highly dependent on the cardiac phase with low flows (< 5 cm/s), high spatial flow gradients, and out-of-plane flow as deteriorating factors. Despite the observed artifacts, a good overall performance of 2-D ST was obtained with a median magnitude underestimation and angular deviation of, respectively, 28% and 13.5 degrees during systole and 16% and 10.5 degrees during diastole